Mineral resource of the month: Pumice and pumicite

USGS Publications Warehouse

Crangle, Robert

2015-01-01

Pumice is an extrusive igneous volcanic rock formed through the rapid cooling of air-pocketed lava, which results in a low-density, high-porosity rock. Fine-grained pumice, or pumicite, is defined as minute grains, flakes, threads or shards of volcanic glass, with a size finer than 4 millimeters. 

Drift pumice in the Central Indian Ocean Basin: Geochemical evidence

NASA Astrophysics Data System (ADS)

Pattan, J. N.; Mudholkar, A. V.; Jai Sankar, S.; Ilangovan, D.

2008-03-01

Abundant white to light grey-coloured pumice without ferromanganese oxide coating occurs within the Quaternary sediments of the Central Indian Ocean Basin (CIOB). Two distinct groups of pumice are identified from their geochemical composition, which allow one to define two different origins linked to two separate eruptions. One group of pumice is a dacitic type characterized by high Fe, Ti, Mg, Al and Ca with comparatively low contents of Si, rare-earth elements (∑REE, 69 ppm), Rb, Sr, U, Th, Ba, V, Nb, Sc, Mo and Co, which strongly suggest an origin from the 1883 Krakatau eruption. The other group is rhyolitic and is characterized by low contents of Fe, Ti, Mg and Ca and high Si, ∑REE content (121 ppm), Rb, Sr, U, Th, Ba, V, Nb, Mo, Co, and Sc and correlates well with the composition of the Youngest Toba Tuff (YTT) eruption of ˜74 ka from Northern Sumatra and is being reported for the first time. Therefore, correlation of the pumice to the 1883 Krakatau and YTT eruptions indicates that the pumice drifted to the CIOB and eventually sank when it became waterlogged. However, physical properties such as density, specific gravity, porosity and degree of saturation required for sinking of pumice for both 1883 Krakatau and YTT are almost similar.

Influence of calcium and silicon supplementation into Pleurotus ostreatus substrates on quality of fresh and canned mushrooms.

PubMed

Thongsook, T; Kongbangkerd, T

2011-08-01

Supplements of gypsum (calcium source), pumice (silicon source) and pumice sulfate (silicon and calcium source) into substrates for oyster mushrooms (Pleurotus ostreatus) were searched for their effects on production as well as qualities of fresh and canned mushrooms. The addition of pumice up to 30% had no effect on total yield, size distribution and cap diameters. The supplementation of gypsum at 10% decreased the total yield; and although gypsum at 5% did not affect total yield, the treatment increased the proportion of large-sized caps. High content (>10%) of pumice sulfate resulted in the lower yield. Calcium and silicon contents in the fruit bodies were not influenced by supplementations. The centrifugal drip loss values and solid content of fresh mushrooms, and the percentage of weight gained and firmness of canned mushrooms, cultivated in substrates supplemented with gypsum, pumice and pumice sulfate were significantly (p≤0.05) higher than those of the control. Scanning electron micrographs revealed the more compacted hyphae of mushroom stalks supplemented with silicon and/or calcium after heat treatment, compared to the control. Supplementation of P. ostreatus substrates with 20% pumice was the most practical treatment because it showed no effect on yield and the most cost-effective.

Textural and geochemical constraints on eruptive style of the 79AD eruption at Vesuvius

NASA Astrophysics Data System (ADS)

Balcone-Boissard, Hélène; Boudon, Georges; Villemant, Benoît.

2010-05-01

The 79AD eruption of Vesuvius, also known as the "Pompeii eruption", is the reference for one of the explosive eruptive styles, the plinian-type eruption. The eruption involved H2O-rich phonolitic magmas and is commonly divided into three phases: an initial phreatomagmatic phase, followed by a plinian event which produced a thick pumice fallout deposit and a final phase that was dominated by numerous column-collapse events. During the plinian phase, a first white pumice fallout was produced from a high steady eruptive column, followed by a grey pumice fallout originated by an oscillatory eruptive column with several partial column collapse events. This study focuses on the pumice fallout deposits, sampled in a proximal thick section, at the Terzigno quarry, 6 km southeast of the present crater. In order to constrain the degassing processes and the eruptive dynamics, major element compositions, residual volatile contents (H2O, Cl) and textural characteristics (vesicularity and microcrystallinity) were studied. A previous study that we performed on the pre-eruptive Cl content has shown that Cl may be used as an indicator of magma saturation with Cl-rich fluids and of pre-eruptive pressures. Cl contents measured in melt inclusions show that only the white pumice and the upper part of the grey pumice magma were H2O saturated prior eruption. Large variations in residual volatile contents exist between the different eruptive units and textural features strongly differ between white and grey pumice clasts but also within the grey pumice clasts. The degassing processes were thus highly heterogeneous: the white pumice eruptive units represent a typical closed-system degassing evolution whereas the first grey pumice one, stored in the same pre-eruptive saturation conditions, follows a particular open-system degassing evolution. Here we propose a new model of the 79AD eruption where pre-eruptive conditions (H2O saturation, magma temperature and viscosity) are the critical parameters which determine the diversity of the syn-eruptive degassing processes and hence the eruptive dynamics. We suggest that the oscillatory regime that dominates the grey pumice eruptive phase is linked to the pre-eruptive water undersaturation of most part of the grey magma and to the time delays necessary for H2O exsolution.

Origin and significance of the 2011 El Hierro xeno-pumice

NASA Astrophysics Data System (ADS)

Zaczek-Pedroza, Kirsten; Troll, Valentin R.; Deegan, Frances M.; Meade, Fiona C.; Burchardt, Steffi; Carracedo, Juan C.; Klügel, Andreas; Harris, Chris; Wiesmaier, Sebastian; Berg, Sylvia E.; Barker, Abigail K.

2014-05-01

During the first week of the 2011/2012 submarine eruption off El Hierro (Canary Islands), peculiar light-coloured pumiceous rocks (xeno-pumice) were found floating on the sea. The appearance of these rocks led to a potentially inappropriate response from the authorities, because the rocks were viewed as likely indicators of high-silica magma and possible explosive eruptive behaviour. However, the eruption remained a relatively minor and dominantly effusive event and the origin and significance of these peculiar xeno-pumice rocks for volcanic monitoring remains unresolved. Three contrasting models have been put forward, describing them as: a) recycled hydrothermally altered felsic magmatic rocks (Meletlidis et al., 2012, Geophys. Res. Lett., 39:L17302), b) sediment-contaminated high-silica magma (Sigmarsson et al., 2013, Contrib. Mineral. Petrol., 165:601-622) or c) frothy xenoliths from pre-island sedimentary strata that were melted while immersed in magma (Troll et al., 2012, Solid Earth, 3:97-110). Here, we combine the three available datasets to assess the origin of El Hierro xeno-pumice in the light of texture, mineralogy, major and trace element composition, and oxygen isotope characteristics in order to discuss their significance. We note that: 1) Sedimentary relicts occur frequently in xeno-pumice samples with occasionally observed relict bedding. 2) Vesicle sizes are extremely variable, which documents multiple degassing events. The vesicles are biggest especially close to sedimentary relicts, likely the result of a complex mix of minerals and porewaters originally present. 3) The mineral assemblage of xeno-pumice includes quartz, smectite, illite, wollastonite, jasper and mica (XRD) and is akin to marine sedimentary rocks in the region (Hoernle, 1998, J. Petrol.,39:859-880; Robertson & Stillman, 1979, J. Geol. Soc., 136:47 -60; Aparicio et al., 2006, Geol. Mag. 143:181 -193). 4) CIPW norms calculated from xeno-pumice major element compositions show the samples to be Si-oversaturated, partly corundum-normative, but with not magmatic mineral components in the norm. 5) Trace element concentrations of xeno-pumice are unlike any magmatic rocks from El Hierro and La Palma, but similar to known sedimentary rocks from the region. 6) A distinct Eu anomaly, typical for continentally derived sediment, is present in xeno-pumice but absent in El Hierro and La Palma magmatic rocks. Lastly, 7) Oxygen isotope values range from 9.1 to 11.6 o (n=6), which are elevated with respect to magmatic rocks from the Canaries (5.2 to ~ 7 o), but are characteristic for sediment derived from a mixture of continental (S- and I-type) granite sources. The combined datasets allow for a more thorough discussion on the origin of El Hierro xeno-pumice and we conclude that xeno-pumice is compositionally akin to sedimentary rocks from the region, but strikingly dissimilar to magmatic rocks from El Hierro and La Palma. We suggest a dominantly sedimentary origin for xeno-pumice. Xeno-pumice is therefore not an indicator for explosive felsic magma within volcanic plumbing systems, but a reflection of magma-crust interaction during ascent and emplacement. The occurrence of similar frothy sedimentary xenoliths in recent and historical eruptions on Lanzarote, Gran Canaria, Tenerife and La Palma make a case for xeno-pumice being a common phenomenon in the region.

Erosion, transport and segregation of pumice and lithic clasts in pyroclastic flows inferred from ignimbrite at Lascar Volcano, Chile

NASA Astrophysics Data System (ADS)

Calder, E. S.; Sparks, R. S. J.; Gardeweg, M. C.

2000-12-01

Investigations have been made on the distribution of pumice and lithic clasts in the lithic rich Soncor ignimbrite (26.5 ka) and the 1993 pumice flow deposits of Lascar Volcano, Chile. The Soncor ignimbrite shows three main lithofacies which grade into one another. Coarse lithic breccias range from matrix poor stratified varieties, irregular shaped sheets and elongate hummocks in proximal environments, to breccia lenses with pumiceous ignimbrite matrix. Massive, lithic rich facies comprise the bulk of the ignimbrite. Pumice rich facies are bimodal with abundant large pumice clasts (often with reverse grading), rare lithic clasts and occur distally and on high ground adjacent to deep proximal valleys. In the 1993 pyroclastic flow deposits lithic rich facies are deposited on slopes up to 14° whereas pumice rich facies are deposited only on slopes <4°. Lithic rich parts show a thin pumice rich corrugated surface which can be traced into the pumice rich facies. The high lithic content in the Soncor ignimbrite is attributed to the destruction of a pre-existing dome complex, deep explosive cratering into the interior of the volcano and erosion during pyroclastic flow emplacement. Lithic clasts incorporated into the flows during erosion of the basement substrate have been distinguished from those derived from the vent. Categorisation of these lithics and knowledge of the local geology allows these clasts to be used as tracers to interpret former flow dynamics. Lithic populations demonstrate local flow paths and show that lithics are picked up preferentially where flows move around or over obstacles, or through constrictions. Eroded lithics can be anomalously large, particularly close to the location of erosion. Observations of both the Soncor ignimbrite and the 1993 deposits show that lithic rich parts of flows were much more erosive than pumice rich parts. Both the Soncor and 1993 deposits are interpreted as resulting from predominantly high concentration granular suspensions where particle-particle interactions played a major role. The concentrated flows segregated from more expanded and turbulent suspension currents within a few kilometres of the source. During emplacement some degree of internal mixing is inferred to have occurred enabling entrained lithics to migrate into flow interiors. The facies variations and distributions and the strong negative correlation between maximum pumice and lithic clast size are interpreted as the consequence of efficient density segregation within the concentrated flows. The frictional resistance of the lithic rich part is greater so that it deposits on steeper slopes and generally closer to the source. The lower density and more mobile pumice rich upper portions continued to flow and sequentially detached from the lithic rich base of the flow. Pumice rich portions moved to the margins and distal parts of the flow so that distal deposits are lithic poor and non-erosive. The flows are therefore envisaged as going though several important transformations. Proximally, dense, granular flow, undercurrents are formed by rapid sedimentation of suspension currents. Medially to distally the undercurrents evolve to flows with significantly different rheology and mobility characteristics as lithic clasts are sedimented out and distal flows become dominated by pumice.

Eruption dynamics and explosive-effusive transitions during the 1400 cal BP eruption of Opala volcano, Kamchatka, Russia

NASA Astrophysics Data System (ADS)

Andrews, Benjamin J.; Dufek, Josef; Ponomareva, Vera

2018-05-01

Deposits and pumice from the 1400 cal BP eruption of Opala volcano record activity that occurred at the explosive-effusive transition, resulting in intermittent, or stop-start, behavior, where explosive activity resumed following a pause. The eruption deposited distinctive, biotite-bearing rhyolite tephra across much of Kamchatka, and its stratigraphy consists of a lithic-rich pumice fall, overlain by pumice falls and pyroclastic density deposits, with the proportion of the latter increasing with height. This sequence repeats such that the middle of the total deposit is marked by a lithic-rich fall with abundant obsidian clasts. Notably, the eruptive pumice are poorly vesiculated, with vesicle textures that record fragmentation of a partially collapsed magmatic foam. The eruption vent, Baranii Amphitheater is filled with obsidian lavas of the same composition as the rhyolite tephra. Based upon the stratigraphic and compositional relations, we divide the eruption into four phases. Phase I initiated with eruption of a lithic-rich pumice fall, followed by eruption of Plinian falls and pyroclastic density currents. During Phase II, the eruption paused for at least 5-6 h; in this time, microlites nucleated and began to grow in the magma. Phase III essentially repeated the Phase I sequence. Obsidian lavas were emplaced during Phase IV. The pumice textures suggest that the magma ascended very near the threshold decompression rate for the transition between explosive (fast) and effusive (slow) behavior. The pause during Phase II likely occurred as decompression slowed enough for the magma to develop sufficient permeability for gas to escape resulting in collapse of the magmatic foam, stopping the eruption and temporarily sealing the conduit. After about 5-6 h, eruption resumed with, once again, magma decompressing very near the explosive-effusive transition. Phase III ended when the decompression rate slowed and lava dome emplacement began. Distributions of pumice and lithic clasts, and inclusion of data from previous workers, indicate minimum deposit volumes of 0.75 and 0.75-1.15 km3 (DRE) and eruption column heights of 18 and 20 km for Phases I and III, respectively. Phases I-III had a likely total duration of 60-80 h, including a pause in activity of 5-6 h during Phase II. This study demonstrates that analysis of vesicle textures from numerous pumice combined with stratigraphic data can reveal syn-eruptive changes in and links between magma permeability, decompression rate, and eruption style. OP-22-Pum is a typical Opala pumice. XRCT scans reveal that vesicles in pumice without obvious banding in hand sample are highly elongate and strongly aligned in different regions. The first half of the animation shows vesicles (white) and the second half shows the solid portions of the pumice (yellow). The field of view is 930 × 930 × 520 μm. OP-22-PumGlass is a pumice with alternating glassy and pumiceous domains. XRCT scans show that the glassy regions contain only small, sparse vesicles, whereas the pumiceous regions comprise elongate, aligned, and interconnected vesicles. The white domains are vesicles. The field of view is 1300 × 1950 × 520 μm.

Effect of Peat Moss and Pumice on Douglas Fir Bark based Soilless Substrate Physical and Hydraulic Properties

USDA-ARS?s Scientific Manuscript database

Douglas fir [Pseudotsuga menziesii Mirb.(Franco)] bark (DFB), sphagnum peat moss, and pumice are the most common substrate components used in the Oregon nursery industry. The objective of this study was to document the effect of peat and pumice addition on the physical and hydrological properties o...

Studies on desorption and regeneration of natural pumice for iron removal from aqueous solution.

PubMed

Indah, S; Helard, D; Binuwara, A

2018-05-01

To make the adsorption process more economic and environmental friendly, it is necessary to study desorption and reutilization of the adsorbents. In the present study, the effectiveness of natural pumice in removal of iron from aqueous solution was investigated in several sorption-desorption cycles. The desorption characteristics of previously adsorbed iron ions on natural pumice were tested by various desorbing agents such as HCl, NaOH and aquadest. Among them, HCl showed the highest desorption efficiency (37.89%) with 0.1 M of concentration and 60 min of contact time. The removal efficiency of iron ions in reused natural pumice could be maintained up to 90% in the third cycle of adsorption. The results indicate that although complete desorption was not achieved, natural pumice from Sungai Pasak, West Sumatra, Indonesia, can be sufficiently reused up to three cycles of adsorption-desorption.

Rapid, Long-Distance Dispersal by Pumice Rafting

PubMed Central

Bryan, Scott E.; Cook, Alex G.; Evans, Jason P.; Hebden, Kerry; Hurrey, Lucy; Colls, Peter; Jell, John S.; Weatherley, Dion; Firn, Jennifer

2012-01-01

Pumice is an extremely effective rafting agent that can dramatically increase the dispersal range of a variety of marine organisms and connect isolated shallow marine and coastal ecosystems. Here we report on a significant recent pumice rafting and long-distance dispersal event that occurred across the southwest Pacific following the 2006 explosive eruption of Home Reef Volcano in Tonga. We have constrained the trajectory, and rate, biomass and biodiversity of transfer, discovering more than 80 species and a substantial biomass underwent a >5000 km journey in 7–8 months. Differing microenvironmental conditions on the pumice, caused by relative stability of clasts at the sea surface, promoted diversity in biotic recruitment. Our findings emphasise pumice rafting as an important process facilitating the distribution of marine life, which have implications for colonisation processes and success, the management of sensitive marine environments, and invasive pest species. PMID:22815770

Voluminous juvenile lithic fragments in the pumice-fall deposit of the 1108 eruption of Asama volcano: Evidence of repeated compaction and fragmentation in the shallow conduit

NASA Astrophysics Data System (ADS)

Nakamura, M.; Kichise, T.; Yasui, M.; Nagahashi, Y.; Yoshida, T.

2010-12-01

The pumice-fall deposit of the 1108 eruption of Asama volcano, central Japan, contains a large amount of lithic fragments (up to 40 wt%) that are angular, dense, and juvenile. The deposit consists of eight sublayers, comprising three thick layers of pumice (1.0-1.4 g/cm3) containing 5-40 wt% lithic fragments (1.4-2.7 g/cm3) interbedded with two thin pumiceous layers, two thin layers of lapilli-sized lithic fragments, and a volcanic ash layer. The average volume of each sublayer is ~0.01 km3. The large volume of lithic fragments and their occurrence throughout the deposit show that their source lava plugs formed and fragmented continuously during the eruption. The lithic fragments are not coated with vesicular matrix, indicating that the fragments were entrained into mist flows of the eruption columns; i.e., after the magma fragmentation that produced the pumice clasts. The plagioclase microlites in the lithic fragments have a range (55-75 mol%) and frequency distribution of anorthite content similar to those in the pumices, indicating that the lithic fragments and pumices have a similar history of decompression from the magma reservoir to the shallow conduit. The groundmass of the pumices has a porosity approximately ranging from 40% to 60% and positive correlation with groundmass crystallinity; this is consistent with an interpretation that magma with higher porosity is more decompressed and thus crystallized in the shallower conduit. The highest crystallinity of the pumice, of which the groundmass porosity is ca. 60%, coincides with the lowest crystallinity of the lithic fragments. In addition, the pore connectivity of the pumice increases (with increasing porosity) steeply at a groundmass porosity of ca. 60%. These petrographical observations strongly suggest that the lithic fragments are the collapsed and compacted products of magma foam (at a groundmass porosity of ca. 60%) just before it fragmented to become pumices. The lithic fragments often have mosaic texture with healed cracks, suggesting that they were formed by repeated shear-induced fragmentation and welding. The average water contents of the glasses in the groundmass of the lithic fragments and pumices are 0.35 and 0.54 wt%, respectively, corresponding to approximate quench depths of 200 and 300 m, respectively. The average volume of the erupted lithic fragments in each sublayer is equivalent to the volume of a magma plug with a diameter of 200 m and depth of 200 m, which is almost equal to the present crater size of Asama. These genetic and occurrence relations between the lithic fragments and pumices indicate that the magma ascent condition of the 1108 eruption was near the bifurcation boundary between the formations of the lava plug via foam compaction and the eruption column via magma fragmentation. Therefore, the magma ascent rate of the 1108 eruption could be used as a rough criterion for predicting the eruption styles in the future volcanic crisis of Asama.

The submarine record of a large-scale explosive eruption in the Vanuatu Arc: ˜1 Ma Efaté Pumice Formation

NASA Astrophysics Data System (ADS)

Raos, Alison M.; McPhie, Jocelyn

The Efaté Pumice Formation (EPF) is the record of a major explosive eruption that occurred in the Vanuatu arc, southwestern Pacific, at about 1 Ma. The EPF is the oldest stratigraphic unit of the Efaté Island Group and consists of a succession of non-welded, trachydacitic pumice breccia and shard-rich sand and silt beds with a minimum thickness of ˜500 m and a minimum bulk volume of approximately 85 km3. The lower part (Efaté Pumice Breccias) of the EPF comprises very thick beds composed almost exclusively of glassy, trachydacitic, pumice fragments with ragged terminations. In contrast, the upper part (Rentabau Tuffs) consists of up to 70 m of well-bedded and well-sorted shard-rich sand and silt. The clast population of this upper part comprises >95% glassy or formerly glassy shards, but fossil foraminifera are a ubiquitous and important non-volcanic component. Some glass shards have blocky, equant shapes and arcuate fracture surfaces, features typically associated with the influence of external water during fragmentation, but most are cuspate and platy bubble-wall shards. Pyroclast morphologies indicate that the Efaté Pumice Breccias were largely generated by magmatic-volatile-driven ("dry"), explosive fragmentation processes, and lithofacies characteristics indicate deposition in below-storm-wave-base environments, from eruption-sourced, water-supported density currents of waterlogged pumice. The Rentabau Tuffs are interpreted to represent a change to hydromagmatic activity in response to waning discharge that allowed ingress of water (presumably seawater) to the vent(s).

Is Efate (Vanuatu, SW Pacific) a result of subaerial or submarine eruption? An alternative model for the 1 Ma Efate Pumice Formation

NASA Astrophysics Data System (ADS)

Stewart, Robert B.; Németh, Karoly; Cronin, Shane J.

2010-09-01

The Efate Pumice Formation (EPF) is a trachydacitic volcaniclastic succession widespread in the central part of Efate Island and also present on Hat and Lelepa islands to the north. The volcanic succession has been inferred to result from a major, entirely subaqueous explosive event north of Efate Island. The accumulated pumice-rich units were previously interpreted to be subaqueous pyroclastic density current deposits on the basis of their bedding, componentry and stratigraphic characteristics. Here we suggest an alternative eruptive scenario for this widespread succession. The major part of the EPF is distributed in central Efate, where pumiceous pyroclastic rock units several hundred meters thick are found within fault scarp cliffs elevated about 800 m above sea level. The basal 200 m of the pumiceous succession is composed of massive to weakly bedded pumiceous lapilli units, each 2-3 m thick. This succession is interbedded with wavy, undulatory and dune bedded pumiceous ash and fine lapilli units with characteristics of co-ignimbrite surges and ground surges. The presence of the surge beds implies that the intervening units comprise a subaerial ignimbrite-dominated succession. There are no sedimentary indicators in the basal units examined that are consistent with water-supported transportation and/or deposition. The subaerial ignimbrite sequence of the EPF is overlain by a shallow marine volcaniclastic Rentanbau Tuffs. The EPF is topped by reef limestone, which presumably preserved the underlying EPF from erosion. We here propose that the EPF was formed by a combination of initial subaerial ignimbrite-forming eruptions, followed by caldera subsidence. The upper volcaniclastic successions in our model represent intra-caldera pumiceous volcaniclastic deposits accumulated in a shallow marine environment in the resultant caldera. The present day elevated position of the succession is a result of a combination of possible caldera resurgence and ongoing arc-related uplift in the region.

Recharge of an Unconfined Pumice Aquifer: Winter Rainfall Versus Snow Pack, South-central Oregon

NASA Astrophysics Data System (ADS)

Cummings, M. L.; Weatherford, J. M.; Eibert, D.

2015-12-01

Walker Rim study area, an uplifted fault block east of the Cascade Range, south-central Oregon, exceeds 1580 m elevation and includes Round Meadow-Sellers Marsh closed basin, and headwaters of Upper Klamath Basin, Deschutes Basin, and Christmas Lake Valley in the Great Basin. The water-bearing unit is 2.8 to 3.0 m thick Plinian pumice fall from the Holocene eruption of Mount Mazama, Cascade Range. The perched pumice aquifer is underlain by low permeability regolith and bedrock. Disruption of the internal continuity of the Plinian pumice fall by fluvial and lacustrine processes resulted in hydrogeologic environments that include fens, wet meadows, and areas of shallow water table. Slopes are low and surface and groundwater pathways follow patterns inherited from the pre-eruption landscape. Discharge for streams and springs and depth to water table measured in open-ended piezometers slotted in the pumice aquifer have been measured between March and October, WY 2011 through WY2015. Yearly occupation on same date has been conducted for middle April, June 1st, and end of October. WY2011 and WY2012 received more precipitation than the 30 year average while WY2014 was the third driest year in 30 years of record. WY2014 and WY2015 provide an interesting contrast. Drought conditions dominated WY2014 while WY2015 was distinct in that the normal cold-season snow pack was replaced by rainfall. Cumulative precipitation exceeded the 30-year average between October and March. The pumice aquifer of wet meadows and areas of shallow water table experienced little recharge in WY2015. Persistence of widespread diffuse discharge from fens declined by middle summer as potentiometric surfaces lowered into confining peat layers or in some settings into the pumice aquifer. Recharge of the perched pumice aquifer in rain-dominated WY2015 was similar to or less than in the snow-dominated drought of WY2014. Rain falling on frozen ground drove runoff rather than aquifer recharge.

Fission-track dating of pumice from the KBS Tuff, East Rudolf, Kenya

USGS Publications Warehouse

Hurford, A.J.; Gleadow, A.J.W.; Naeser, C.W.

1976-01-01

Fission-track dating of zircon separated from two pumice samples from the KBS Tuff in the Koobi Fora Formation, in Area 131, East Rudolf, Kenya, gives an age of 2.44??0.08 Myr for the eruption of the pumice. This result is compatible with the previously published K-Ar and 40Ar/ 39Ar age spectrum estimate of 2.61??0.26 Myr for the KBS Tuff in Area 105, but differs from the more recently published K-Ar date of 1.82??0.04 Myr for the KBS Tuff in Area 131. This study does not support the suggestion that pumice cobbles of different ages occur in the KBS Tuff. ?? 1976 Nature Publishing Group.

25 CFR 225.3 - Definitions.

Code of Federal Regulations, 2013 CFR

2013-04-01

... not limited to sand, gravel, pumice, cinders, granite, building stone, limestone, clay, silt, or any... severance and treatment of minerals; however, when sand, gravel, pumice, cinders, granite, building stone...

25 CFR 225.3 - Definitions.

Code of Federal Regulations, 2014 CFR

2014-04-01

... not limited to sand, gravel, pumice, cinders, granite, building stone, limestone, clay, silt, or any... severance and treatment of minerals; however, when sand, gravel, pumice, cinders, granite, building stone...

25 CFR 225.3 - Definitions.

Code of Federal Regulations, 2012 CFR

2012-04-01

... not limited to sand, gravel, pumice, cinders, granite, building stone, limestone, clay, silt, or any... severance and treatment of minerals; however, when sand, gravel, pumice, cinders, granite, building stone...

Removal of tetracycline from wastewater using pumice stone: equilibrium, kinetic and thermodynamic studies

PubMed Central

2014-01-01

In this study, pumice stone was used for the removal of tetracyline (TC) from aqueous solutions. It was characterized by XRD, FT-IR, SEM and BET analyses. Cation exchange capacity of pumice stone was found to be 9.9 meq/100 g. Effect of various parameters such as solution pH (2–11), adsorbent dosage (0.5-10 g/L), contact time (2.5-120 min), initial TC concentration (5–300 mg/L) and temperature (20–50°C) on TC adsorption onto pumice was investigated. Also the adsorption of TC on pumice stone was studied as a function of Na+ and Cu2+ cations changing pH from 2 to 11 using batch experiments. The best removal efficiency performance was exhibited at adsorbent dosage 10 g/L, pH 3, contact time 120 min. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models were applied to the equilibrium data. The result has shown that the adsorption was favorable, physicochemical in nature and agrees well with Langmuir and Freundlich models. The maximum Langmuir adsorption capacity was found to be 20.02 mg/g. The adsorption behavior of TC on pumices stone was fitted well in the pseudo-second order kinetics model. Thermodynamic parameters calculated from the adsorption data at different temperature showed that the adsorption reaction was feasible, spontaneous and exothermic. PMID:24936305

25 CFR 211.3 - Definitions.

Code of Federal Regulations, 2012 CFR

2012-04-01

... resources; and includes but is not limited to, sand, gravel, pumice, cinders, granite, building stone..., gravel, pumice, cinders, granite, building stone, limestone, clay or silt is the subject mineral, an...

25 CFR 211.3 - Definitions.

Code of Federal Regulations, 2014 CFR

2014-04-01

... resources; and includes but is not limited to, sand, gravel, pumice, cinders, granite, building stone..., gravel, pumice, cinders, granite, building stone, limestone, clay or silt is the subject mineral, an...

How to fragment peralkaline rhyolites: Observations on pumice using combined multi-scale 2D and 3D imaging

NASA Astrophysics Data System (ADS)

Hughes, Ery C.; Neave, David A.; Dobson, Katherine J.; Withers, Philip J.; Edmonds, Marie

2017-04-01

Peralkaline rhyolites are volatile-rich magmas that typically erupt in continental rift settings. The high alkali and halogen content of these magmas results in viscosities two to three orders of magnitude lower than in calc-alkaline rhyolites. Unless extensive microlite crystallisation occurs, the calculated strain rates required for fragmentation are unrealistically high, yet peralkaline pumices from explosive eruptions of varying scales are commonly microlite-free. Here we present a combined 2D scanning electron microscopy and 3D X-ray microtomography study of peralkaline rhyolite vesicle textures designed to investigate fragmentation processes. Microlite-free peralkaline pumice textures from Pantelleria, Italy, strongly resemble those from calc-alkaline rhyolites on both macro and micro scales. These textures imply that the pumices fragmented in a brittle fashion and that their peralkaline chemistry had little direct effect on textural evolution during bubble nucleation and growth. We suggest that the observed pumice textures evolved in response to high decompression rates and that peralkaline rhyolite magmas can fragment when strain localisation and high bubble overpressures develop during rapid ascent.

Highly evolved rhyolitic glass compositions from the Toba Caldera, Sumatra

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chesner, C.A.

1985-01-01

The quartz latite to rhyolitic ash flow tuffs erupted form the Toba Caldera, perhaps the largest caldera on earth (100 by 30 kms), provide the unique opportunity to study a highly differentiated liquid in equilibrium with numerous mineral phases. Not only are the rocks very crystal rich (30-50%), but at present a minimum of 15 co-existing mineral phases have been identified. Both whole-rock and glass analyses were made by XRF techniques providing data on both major and trace elements. Whole rock chemistry of individual pumices from the youngest eruption at Toba (75,000 years ago), are suggestive of the eruption ofmore » two magma compositions across a boundary layer in the magma chamber. Glass chemistry of the pumices also show two distinct liquid compositions. The more silicic pumices, which have the most evolved glass compositions, are similar to the whole rock chemistry of the few aplitic pumices and cognate granitic xenoliths that were collected. This highly evolved composition resulted from the removal of up to 15 mineral phases and may be a fractionation buffered, univariant composition. The glasses from the less silicic pumices are similar to the whole rock chemistry of the more silicic pumice, thus falling nicely on a fractionation trend towards the univariant composition for these rocks. This set of glass compositions allows an independent test for the origin of distal ashes thought to have erupted from Toba and deposited in Malaysia, the Indian Ocean, and as far away as India.« less

Magma degassing and eruption dynamics of the Avellino pumice Plinian eruption of Somma-Vesuvius (Italy). Comparison with the Pompeii eruption

NASA Astrophysics Data System (ADS)

Balcone-Boissard, H.; Boudon, G.; Ucciani, G.; Villemant, B.; Cioni, R.; Civetta, L.; Orsi, G.

2012-05-01

The eruptive history of Mt. Somma-Vesuvius is characterised by large explosive events: Pomici di Base eruption (22,030 ± 175 yr cal BP), Mercato (8890 ± 90 yr cal BP), Avellino (3945 ± 10 yr cal BP) and Pompeii (79 AD). Pre-eruptive conditions and sin-eruptive degassing processes of the Avellino eruption, the highest-magnitude Plinian event, have been investigated, using volatile contents (F, Cl, H2O) in melt inclusions and residual glass, and textural characteristics of pumice clasts of the 9 fallout layers sampled in detail in a representative sequence. The sequence displays an up-section sharp colour change from white to grey, corresponding to variations in both magma composition and textural characteristics. The pre-eruptive conditions have been constrained by systematic measurements of Cl content in both melt inclusions and matrix glass of pumice clasts. The pumice glass composition varies from Na-rich phonolite (white pumice) to K-rich phonolite (grey pumice). The measured Cl values constantly cluster at 5200 ± 400 ppm (buffer value), whatever the composition of the melt, suggesting that the entire magma body was saturated with sub-critical fluids. This Cl saturation constrains the pre-eruptive pressures and maximum H2O contents at 200 ± 10 MPa and 6.3 ± 0.2 wt.% H2O for the white pumice melt and 195 ± 15 MPa and 5.2 ± 0.2 wt.% H2O for the grey pumice melt. The fluid phase, mainly composed of a H2O-rich vapour phase and brine, probably accumulated at the top of the reservoir and generated an overpressure able to trigger the onset of the eruption. Magma degassing was rather homogeneous for the white and grey eruptive units, mostly occurring through closed-system processes, leading to a typical Plinian eruptive style. A steady-state withdrawal of an H2O-saturated magma may explain the establishment of a sustained Plinian column. Variation from white to grey pumice is accompanied by decrease of mean vesicularity and increase of mean microcrystallinity and permeability related to significant vesicle coalescence. Despite this, the ascending magma column still evolves under closed-system degassing, without significant gas loss through conduit walls. The Avellino eruption shows numerous similarities with the 79 AD Pompeii eruption in pre-eruptive conditions, degassing processes and eruptive style which are discussed here.

Pumice in the interglacial Whidbey Formation at Blowers Bluff, central Whidbey Island, WA, USA

USGS Publications Warehouse

Dethier, D.P.; Dragovich, J.D.; Sarna-Wojcicki, A. M.; Fleck, R.J.

2008-01-01

A new 40Ar/39Ar age of 128??9 ka and chemical analyses of pumice layers from interglacial alluvium at Blowers Bluff, Whidbey Island, WA, show that the deposits are part of the Whidbey Formation, a widespread, mainly subsurface unit. Glass chemistry of the dated dacitic pumice does not match any analyzed northern Cascade source, but upper Pleistocene dacites from Glacier Peak and early Pleistocene silicic rocks from the Kulshan caldera are chemically similar. The chemistry of pumiceous dacite in younger units, including the latest Pleistocene Partridge Gravel, is similar to that of the dated material. The deep troughs of the modern northern Puget lowland must have been filled during deposition of the Whidbey Formation, allowing volcanic-rich sediment to reach what is now Whidbey Island. Topographic analysis of LIDAR images demonstrates that extensive erosion occurred during latest Pleistocene ice retreat. The Partridge Gravel likely records subglacial fluvial erosion along an ice tunnel and ice-marginal deposition into adjacent marine waters. Pumice in the Partridge Gravel probably was reworked from stratigraphically and topographically lower deposits, including those at Blowers Bluff. ?? 2007 Elsevier Ltd and INQUA.

Unravelling the magmatic processes behind zoned fall units on Ascension Island, South Atlantic

NASA Astrophysics Data System (ADS)

Chamberlain, K. J.; Barclay, J.; Preece, K.; Brown, R. J.; Davidson, J.

2015-12-01

Ascension Island, an isolated composite volcano in the south Atlantic, has a wide spectrum of explosive and effusive deposits. Eruptions on the island have produced ash and pumice fall deposits, ignimbrites, scoria cones, lava flows and lava domes, which vary in composition from basalt to rhyolite. We report, for the first time, the presence of multiple, zoned pumice fall deposits. These deposits grade upwards (stepwise or gradationally) from pumice to scoria. We present detailed observations of two key deposits which typify the range in zonation observed in the unusual fall units. Forensic examination of these deposits and their petrological and geochemical characteristics provide critical information about the interactions and processes behind the wide spectrum of magma compositions and past eruptive behaviour on Ascension Island. The first deposit changes gradationally from fayalite-bearing trachytic pumice fall (61.1 wt.% SiO2) at the base, to basaltic trachy-andesite scoria fall (54.5 wt.% SiO2) at the top. The second deposit is more complex. It contains mingled pumice-scoria clasts, has a rapid transition from pumice to scoria and no intermediate clasts were observed. New analyses of H2O, CO2 and key trace elements within melt inclusions combined with systematic whole rock and phenocryst analyses enable us to probe the relationship of these co-erupted magmas to other deposits on the island. This has yielded insights into the magma plumbing system; and improved understanding of the roles that fractional crystallisation and magma mixing play in generating the range in compositions observed at this unique ocean island volcano.

Opal-A in Glassy Pumice, Acid Alteration, and the 1817 Phreatomagmatic Eruption at Kawah Ijen (Java), Indonesia

NASA Astrophysics Data System (ADS)

Lowenstern, Jacob B.; van Hinsberg, Vincent; Berlo, Kim; Liesegang, Moritz; Iacovino, Kayla; Bindeman, Ilya N.; Wright, Heather M.

2018-02-01

At Kawah Ijen (Indonesia), vigorous SO2 and HCl degassing sustains a hyperacid lake (pH 0) and intensely alters the subsurface, producing widespread residual silica and advanced argillic alteration products. In 1817, a VEI 2 phreatomagmatic eruption evacuated the lake, depositing a widespread layer of muddy ash fall, and sending lahars down river drainages. We discovered multiple types of opaline silica in juvenile low-silica dacite pumice and in particles within co-erupted laharic sediments. Most spectacular are opal-replaced phenocrysts of plagioclase and pyroxene adjacent to pristine matrix glass and melt inclusions. Opal-bearing pumice has been found at numerous sites, including where post-eruption infiltration of acid water is unlikely. Through detailed analyses of an initial sampling of 1817 eruption products, we find evidence for multiple origins of opaline materials in pumice and laharic sediments. Evidently, magma encountered acid-altered materials in the subsurface and triggered phreatomagmatic eruptions. Syn-eruptive incorporation of opal-alunite clasts, layered opal, and fragment-filled vesicles of opal and glass, all suggest magma-rock interactions in concert with vesiculation, followed by cooling within minutes. Our experiments at magmatic temperature confirm that the opaline materials would show noticeable degradation in time periods longer than a few tens of minutes. Some glassy laharic sedimentary grains are more andesitic than the main pumice type and may represent older volcanic materials that were altered beneath the lake bottom and were forcefully ejected during the 1817 eruption. A post-eruptive origin remains likely for most of the opal-replaced phenocrysts in pumice. Experiments at 25°C and 100°C reveal that when fresh pumice is bathed in Kawah Ijen hyperacid fluid for six weeks, plagioclase is replaced without altering either matrix glass or melt inclusions. Moreover, lack of evidence for high-temperature annealing of the opal suggests that post-eruption alteration of pumice is more likely than pre-eruption envelopment of euhedral opal-replaced phenocrysts in dacitic melt. At Ijen and elsewhere, the ascent of magma into hydrous acid-altered mineral assemblages (e.g., opal, kaolinite, alunite) could induce rapid dehydration of hydrous minerals and amorphous materials, generating considerable steam and contributing to magmatic-hydrothermal and phreatomagmatic explosions.

Opal-A in glassy pumice, acid alteration, and the 1817 phreatomagmatic eruption at Kawah Ijen (Java), Indonesia

USGS Publications Warehouse

Lowenstern, Jacob B.; van Hinsberg, Vincent; Berlo, Kim; Liesegang, Moritz; Iacovino, Kayla D.; Bindeman, Ilya N.; Wright, Heather M.

2018-01-01

At Kawah Ijen (Indonesia), vigorous SO2 and HCl degassing sustains a hyperacid lake (pH ~0) and intensely alters the subsurface, producing widespread residual silica and advanced argillic alteration products. In 1817, a VEI 2 phreatomagmatic eruption evacuated the lake, depositing a widespread layer of muddy ash fall, and sending lahars down river drainages. We discovered multiple types of opaline silica in juvenile low-silica dacite pumice and in particles within co-erupted laharic sediments. Most spectacular are opal-replaced phenocrysts of plagioclase and pyroxene adjacent to pristine matrix glass and melt inclusions. Opal-bearing pumice has been found at numerous sites, including where post-eruption infiltration of acid water is unlikely. Through detailed analyses of an initial sampling of 1817 eruption products, we find evidence for multiple origins of opaline materials in pumice and laharic sediments. Evidently, magma encountered acid-altered materials in the subsurface and triggered phreatomagmatic eruptions. Syn-eruptive incorporation of opal-alunite clasts, layered opal, and fragment-filled vesicles of opal and glass, all suggest magma-rock interactions in concert with vesiculation, followed by cooling within minutes. Our experiments at magmatic temperature confirm that the opaline materials would show noticeable degradation in time periods longer than a few tens of minutes. Some glassy laharic sedimentary grains are more andesitic than the main pumice type and may represent older volcanic materials that were altered beneath the lake bottom and were forcefully ejected during the 1817 eruption. A post-eruptive origin remains likely for most of the opal-replaced phenocrysts in pumice. Experiments at 25°C and 100°C reveal that when fresh pumice is bathed in Kawah Ijen hyperacid fluid for 6 weeks, plagioclase is replaced without altering either matrix glass or melt inclusions. Moreover, lack of evidence for high-temperature annealing of the opal suggests that post-eruption alteration of pumice is more likely than pre-eruption envelopment of euhedral opal-replaced phenocrysts in dacitic melt. At Ijen and elsewhere, the ascent of magma into hydrous acid-altered mineral assemblages (e.g., opal, kaolinite, alunite) could induce rapid dehydration of hydrous minerals and amorphous materials, generating considerable steam and contributing to magmatic-hydrothermal and phreatomagmatic explosions.

Late Holocene Andesitic Eruptions at Mount Rainier

NASA Astrophysics Data System (ADS)

Sisson, T. W.; Vallance, J. W.

2005-12-01

Holocene Mt. Rainier erupted much more frequently than is recorded by its 11 pumiceous tephras. In the 2.6-2.2 ka Summerland eruptive period, 6 groups of thin (1-5 mm) Sparsely Vesicular Glassy (SVG) ashes were deposited (S1-S6), followed by the 0.3 km3 C-tephra. Two groups of andesitic lava flows and one andesitic block-and-ash flow (2.45 ka) also erupted in the Summerland period (ice conceals any other products). Based on glass composition the pyroclastic flow correlates with S4 ashes that also contain pumiceous grains and rare pumice lapilli. The first of the lava groups, exposed in windows through the Emmons and Winthrop glaciers, is Sr-rich for Mt. Rainier eruptives and correlates with S5 & S6 ashes based on similar high-Sr plagioclase. The ensuing C-tephra formed by plinian eruption of mixed and mingled magma comprising 4 juvenile components: mixed porphyritic andesite pumice, crystal-poor andesite scoria, vesicular high-Sr dacite blebs in pumice and scoria, and poorly inflated crystal-rich high-Sr dacite. High-Sr components were probably entrained conduit linings and segregations from the preceding high-Sr eruptions. The youngest lava group, exposed at the summit, is normal-Sr andesite lacking mixing textures of the C-tephra, and represents eruption of another small batch of andesitic magma perhaps just after the C event. SVG ash grains have blocky-to-fluidal shapes, are rich in plagioclase microlites, and their glasses are high-SiO2 (66-78%) and low-Al2O3 (15-11%). Melting experiments yield apparent equilibration pressures <50MPa for SVG liquids. SVG ashes likely result from shallow hydromagmatic explosions as largely degassed magmas transited the upper-edifice hydrothermal system during effusive eruptions. Rare pumice lapilli codeposited with S1, S2, and S4 ashes have microlite-free dacitic glasses, one with nonreacted hbl phenocrysts. These pumice formed from magmas that ascended rapidly from reservoir depths, synchronous with or closely between effusive-hydromagmatic eruptions. Mt. Rainier's late Holocene activity was typified by repeated arrival and eruption of slightly different andesitic magmas. Most eruptions were effusions of largely degassed magma, accompanied by near-surface explosions that blanketed the proximal region with fine-grained glassy ash. Associated rapidly ascended magma led to sparse pumice, pyroclastic flows, or plinian tephra fall, depending on amount.

Predicting the movement of pumice rafts in the South Pacific using GNOME for enhanced navigational warnings and coastal hazard management policies

NASA Astrophysics Data System (ADS)

Kelly, J.; Bender, M.; Kelly, M.; Walters, C.

2013-12-01

Pumice rafts formed from explosive shallow submarine eruptions in the South Pacific pose a significant hazard to local maritime transportation and global coastal communities. Local concerns include the possibility of individual pumice clasts blocking seawater intake valves of ships, damaging the hull of smaller vessels, and inundating harbors bringing fishing and transport to a standstill. Additionally, pumice rafts can introduce harmful invasive species to delicate coastal communities around the world as they dramatically increase dispersal distances for otherwise benthic or relatively sedentary organisms. Two volcanoes in this region have recently formed pumice rafts: Home Reef volcano (Tonga) in 2006 and Havre Seamount (Kermadec Islands) in 2012. These raft events were used as case studies to test a trajectory prediction model since they occurred during times at which high spatial and temporal resolution satellite data were being collected and/or have been described in peer reviewed literature, both of which were necessary for providing model validation. The model was created using the General NOAA Observational Modeling Environment (GNOME), which utilizes sea surface winds and sea surface height (SSH) datasets to predict the possible trajectory a pollutant might follow on a body of water. Wind and ocean current data were acquired from the SeaWinds and Poseidon-3 sensors on board the NASA Earth Observing System (EOS) satellites QuikSCAT and Jason-2. Model outputs showed the 2012 Havre Seamount raft rapidly disperse as it drifted in an ENE direction and the 2006 Home Reef raft drifted quickly in a NW direction towards Papua New Guinea. The 2006 Home Reef prediction model was validated by comparing it to another published model that was based on an integrated surface velocity field in addition to in situ observations. The 2012 Havre Seamount prediction model was validated by spatially and temporally correlating the GNOME trajectory output with moderate-resolution MODIS multispectral data acquired from EOS satellites Aqua and Terra since the raft event has scarcely been studied. Pumice rafts in their early stages are easily observed in MODIS 250 m imagery but after ~5 weeks of exposure to wind shear while drifting, the rafts thinned to <1 km and became extremely difficult to see. Utilization of a higher spatial resolution sensor such as the Operational Land Imager on board LandSat 8 is necessary for imaging and tracking pumice rafts beyond this timeframe, although a significant decrease in temporal resolution is realized. This novel and easily adaptable methodology can be used by island nations and fishery managers to forecast when and where a pumice raft will be, drastically enhancing maritime navigational warnings and response times to eventual pumice landfall.

Are Avellino (4365 cal BP) and Pompeii twin plinian eruptions? Pre-eruptive constraints and degassing history

NASA Astrophysics Data System (ADS)

Boudon, Georges; Balcone-Boissard, Hélène; Villemant, Benoît.; Ucciani, Guillaume; Cioni, Raffaello

2010-05-01

Somma-Vesuvius activity started 35 ky ago and is characterized by numerous eruptions of variable composition and eruptive style, sometimes interrupted by long periods of unrest. The main explosive eruptions are represented by four plinian eruptions: Pomici di Base eruption (22 cal ky), Mercato (~8900 cal BP), Avellino (4365 cal BP) and Pompeii (79 AD). The 79 AD eruption embodies the most famous eruption since it's responsible of the destruction of Pompeii and Herculanum and it's the first described eruption. The Avellino eruption represents the last plinian event that preceded the Pompeii eruption. The eruptive sequence is similar to the 79 AD plinian eruption, with an opening phase preceding a main plinian fallout activity which ended by a phreatomagmatic phase. The fallout deposit displays a sharp colour contrast from white to grey pumice, corresponding to a magma composition evolution. We focus our study on the main fallout deposit that we sampled in detail in the Traianello quarry, 9 km North-North East of the crater, to investigate the degassing processes during the eruption, using volatile content and textural observations. Density and vesicularity measurements were obtained on a minimum of 100 pumice clasts sampled in 10 stratigraphic levels in the fallout deposit. On the basis of the density distribution, bulk geochemical data, point analytical measurements on glasses (melt inclusions and residual glass) and textural observations were obtained simultaneously on a minimum of 5 pumice clasts per eruptive unit. The glass composition, in particular the Na/K ratio, evolves from Na-rich phonolite for white pumices to a more K-rich phonolite for grey pumices. The pre-eruptive conditions are constrained by systematic Cl measurements in melt inclusions and matrix glass of pumice clasts. The entire magma was saturated relative to sub-critical fluids (a Cl-rich H2O vapour phase and a brine), with a Cl melt content buffered at ~6000 ppm, and a mean pre-eruptive H2O content depending of the magma composition. Most of the pumices of the different eruptive units show that H2O degassing during the eruption followed a typical closed-system evolution as expected for plinian eruption. Contrary to H2O, Cl was not efficiently degassed during the plinian phase of the eruption: the matrix glass composition remains close to the pre-eruptive content. Compared to the 79AD eruption the degassing processes showed by the whole Avellino plinian phase is more homogeneous and similar to the white pumice phase of the Pompeii eruption whereas the open-system degassing mode identified from the grey pumices of the 79AD eruption is not represented during the Avellino eruption.

The pumice raft-forming 2012 Havre submarine eruption was effusive

NASA Astrophysics Data System (ADS)

Manga, Michael; Fauria, Kristen E.; Lin, Christina; Mitchell, Samuel J.; Jones, Meghan; Conway, Chris E.; Degruyter, Wim; Hosseini, Behnaz; Carey, Rebecca; Cahalan, Ryan; Houghton, Bruce F.; White, James D. L.; Jutzeler, Martin; Soule, S. Adam; Tani, Kenichiro

2018-05-01

A long-standing conceptual model for deep submarine eruptions is that high hydrostatic pressure hinders degassing and acceleration, and suppresses magma fragmentation. The 2012 submarine rhyolite eruption of Havre volcano in the Kermadec arc provided constraints on critical parameters to quantitatively test these concepts. This eruption produced a >1 km3 raft of floating pumice and a 0.1 km3 field of giant (>1 m) pumice clasts distributed down-current from the vent. We address the mechanism of creating these clasts using a model for magma ascent in a conduit. We use water ingestion experiments to address why some clasts float and others sink. We show that at the eruption depth of 900 m, the melt retained enough dissolved water, and hence had a low enough viscosity, that strain-rates were too low to cause brittle fragmentation in the conduit, despite mass discharge rates similar to Plinian eruptions on land. There was still, however, enough exsolved vapor at the vent depth to make the magma buoyant relative to seawater. Buoyant magma was thus extruded into the ocean where it rose, quenched, and fragmented to produce clasts up to several meters in diameter. We show that these large clasts would have floated to the sea surface within minutes, where air could enter pore space, and the fate of clasts is then controlled by the ability to trap gas within their pore space. We show that clasts from the raft retain enough gas to remain afloat whereas fragments from giant pumice collected from the seafloor ingest more water and sink. The pumice raft and the giant pumice seafloor deposit were thus produced during a clast-generating effusive submarine eruption, where fragmentation occurred above the vent, and the subsequent fate of clasts was controlled by their ability to ingest water.

Tsunami deposits associated with the 7.3 ka caldera-forming eruption of the Kikai Caldera, insights for tsunami generation during submarine caldera-forming eruptions

NASA Astrophysics Data System (ADS)

Geshi, Nobuo; Maeno, Fukashi; Nakagawa, Shojiro; Naruo, Hideto; Kobayashi, Tetsuo

2017-11-01

Timing and mechanism of volcanic tsunamis will be a key to understand the dynamics of large-scale submarine explosive volcanism. Tsunami deposits associated with the VEI 7 eruption of the Kikai Caldera at 7.3 ka are found in the Yakushima and Kuchinoerabujima Islands, 40 km south -southeast of the caldera rim. The tsunami deposits distribute along the rivers in their northern coast up to 4.5 km from the river exit and up to 50 m above the present sea level. The tsunami deposits in the Yakushima area consist of pumice-bearing gravels in the lower part of the section (Unit I) and pumiceous conglomerate in the upper part (Unit II). The presence of rounded pebbles of sedimentary rocks, which characterize the beach deposit, indicates a run-up current from the coastal area. The rip-up clasts of the underlying paleosol in Unit I show strong erosion during the invasion of tsunami. Compositional similarity between the pumices in the tsunami deposit and the juvenile materials erupted in the early phase of the Akahoya eruption indicates the formation of tsunami deposit during the early phase of the eruption, which produced the initial Plinian pumice fall and the lower half of the Koya pyroclastic flow. Presence of the dense volcanic components (obsidians and lava fragments) besides pumices in the tsunami deposit supports that they were carried by the Koya pyroclastic flow, and not the pumices floating on the sea surface. Sequential relationship between the Koya pyroclastic flow and the tsunami suggests that the emplacement of the pyroclastic flow into the sea surrounding the caldera is the most probable mechanism of the tsunami.

76 FR 69700 - Klamath National Forest; California; Pumice Vegetation Management Project

Federal Register 2010, 2011, 2012, 2013, 2014

2011-11-09

... Management Project AGENCY: Forest Service, USDA. ACTION: Notice of intent to prepare an environmental impact.... Grantham, Forest Supervisor, Attn: Ben Haupt, Pumice Vegetation Management Project Team Leader, Goosenest... Management Project will recommend implementation of one of the following: (1) The proposed action; (2) an...

The 0.57 Ma plinian eruption of the Granadilla Member, Tenerife (Canary Islands): an example of complexity in eruption dynamics and evolution

NASA Astrophysics Data System (ADS)

Bryan, S. E.; Cas, R. A. F.; Martí, J.

2000-12-01

The Granadilla Member is one of the most widely dispersed and largest volume pyroclastic units at Tenerife (Canary Islands) and represents the culminating eruption to a second cycle of explosive volcanism of the Las Cañadas edifice. The member, dated at 0.57 Ma, comprises a plinian fall deposit, the Granadilla pumice, which is overlain by ignimbrite up to 30 m thick. The Granadilla pumice is up to 9 m thick approximately 10 km from source (Pyle bt value is 5.35 km), and is subdivided into four fall units. Unit 1 is up to 1.2 m thick and is further divisible into another four pumice fall subunits, based on bedding and grainsize differences. Unit 2 is a thin but distinctive ash layer (˜2 cm thick), and its wide dispersal (>550 km2), constant thickness, planar laminations and ash aggregate textures collectively indicate a phreatoplinian fall origin. The lithic-rich nature and abundance of unaltered lithic fragments reflect magma interaction with aquifer-derived water at depth. Unit 3 (≤1.8 m thick), records a reversal to dry plinian eruptive activity. Unit 4, the thickest of the fall units (up to 6.3 m thick), records the maximum dispersal and intensity of the eruption (Pyle bt and bc values are 5.7 and 6.3 km, respectively), best illustrated by the presence of large pumice bombs up to 30 cm diameter (at distances up to 20 km from vent), and reverse grading of lithic and pumice clasts. The widespread (>500 km2), nonwelded and pumice-rich Granadilla ignimbrite (unit 5) records the collapse of the plinian eruption column. The ignimbrite has a simple sheet-like geometry, but exhibits a complex internal stratigraphy. The base of the ignimbrite locally cuts down through the underlying Granadilla pumice removing it entirely, indicating up to 9 m of erosion by the pyroclastic flows. A coarse, vent-derived lithic breccia horizon towards the top of the ignimbrite is interpreted to record the onset of caldera collapse late in the eruption. Minimum volume estimates for the Granadilla pumice and ignimbrite are 5.2 and 5 km3, respectively. The dispersal area, deposit characteristics, and exponential thickness and clast size decay relationships with (isopach area)1/2 are consistent with dispersal and fallout from the umbrella region of a moderately high (˜17 to ≥25 km) plinian column. We propose that the eruption involved two vents, probably aligned along a NE-SW fissure within the Las Cañadas caldera.

Structure and physical characteristics of pumice from the climactic eruption of Mount Mazama (Crater Lake), Oregon

USGS Publications Warehouse

Klug, C.; Cashman, K.; Bacon, C.

2002-01-01

The vesicularity, permeability, and structure of pumice clasts provide insight into conditions of vesiculation and fragmentation during Plinian fall and pyroclastic flow-producing phases of the ???7,700 cal. year B.P. climactic eruption of Mount Mazama (Crater Lake), Oregon. We show that bulk properties (vesicularity and permeability) can be correlated with internal textures and that the clast structure can be related to inferred changes in eruption conditions. The vesicularity of all pumice clasts is 75-88%, with >90% interconnected pore volume. However, pumice clasts from the Plinian fall deposits exhibit a wider vesicularity range and higher volume percentage of interconnected vesicles than do clasts from pyroclastic-flow deposits. Pumice permeabilities also differ between the two clast types, with pumice from the fall deposit having higher minimum permeabilities (???5??10-13 m2) and a narrower permeability range (5-50??10-13 m2) than clasts from pyroclastic-flow deposits (0.2-330??10-13 m2). The observed permeability can be modeled to estimate average vesicle aperture radii of 1-5 ??m for the fall deposit clasts and 0.25-1 ??m for clasts from the pyroclastic flows. High vesicle number densities (???109 cm-3) in all clasts suggest that bubble nucleation occured rapidly and at high supersaturations. Post-nucleation modifications to bubble populations include both bubble growth and coalescence. A single stage of bubble nucleation and growth can account for 35-60% of the vesicle population in clasts from the fall deposits, and 65-80% in pumice from pyroclastic flows. Large vesicles form a separate population which defines a power law distribution with fractal dimension D=3.3 (range 3.0-3.5). The large D.value, coupled with textural evidence, suggests that the large vesicles formed primarily by coalescence. When viewed together, the bulk properties (vesicularity, permeability) and textural characteristics of all clasts indicate rapid bubble nucleation followed by bubble growth, coalescence and permeability development. This sequence of events is best explained by nucleation in response to a downward-propagating decompression wave, followed by rapid bubble growth and coalescence prior to magma disruption by fragmentation. The heterogeneity of vesicle sizes and shapes, and the absence of differential expansion across individual clasts, suggest that post-fragmentation expansion played a limited role in the development of pumice structure. The higher vesicle number densities and lower permeabilities of pyroclastic-flow clasts indicate limited coalescence and suggest that fragmentation occurred shortly after decompression. Either increased eruption velocities or increased depth of fragmentation accompanying caldera collapse could explain compression of the pre-fragmentation vesiculation interval.

Spectroscopic analysis of Ahlat stone (ignimbrite) and pumice formed by volcanic activity

NASA Astrophysics Data System (ADS)

Aygun, Z.; Aygun, M.

2016-09-01

Natural materials such as ignimbrites are preferred commonly not only in historical places but also in houses or in different kind of buildings all over the world especially around Ahlat in Bitlis-Turkey. Durability, lightness and good-insulation are the significative properties of these stones. Also, pumice is an another preferred material because of its advantages in construction industry. In this paper, four kinds of ignimbrite (light-yellow, yellow, black and white) and pumice from Ahlat region have been investigated by EPR method to determine magnetic properties of them. The results obtained by EPR, EDS and XRD methods are evaluated together. SEM technique is also used to understand the surface morphology of the samples.

Influence of pumice and plant roots on substrate physical properties over time

USDA-ARS?s Scientific Manuscript database

An experiment was conducted to test the hypothesis that either pumice or plant roots maintain air space and porosity over time, or renders substrates more resistant to shrinkage. Treatment design was a 3×2 factorial with three substrate types and either presence or absence of a plant. The three su...

COMPRESSOR BUILDING, TRA626. ELEVATIONS. WINDOWS. WALL SECTIONS. PUMICE BLOCK BUILDING ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

COMPRESSOR BUILDING, TRA-626. ELEVATIONS. WINDOWS. WALL SECTIONS. PUMICE BLOCK BUILDING HOUSED COMPRESSORS FOR AIRCRAFT NUCLEAR PROPULSION EXPERIMENTS. MTR-626-IDO-2S, 3/1952. INL INDEX NO. 531-0626-00-396-110535, REV. 2. - Idaho National Engineering Laboratory, Test Reactor Area, Materials & Engineering Test Reactors, Scoville, Butte County, ID

Effects of Volcanic Pumice Inputs on Microbial Community Composition and Dissolved C/P Ratios in Lake Waters: an Experimental Approach.

PubMed

Modenutti, B E; Balseiro, E G; Bastidas Navarro, M A; Lee, Z M; Souza, M S; Corman, J R; Elser, J J

2016-01-01

Volcanic eruptions discharge massive amounts of ash and pumice that decrease light penetration in lakes and lead to concomitant increases in phosphorus (P) concentrations and shifts in soluble C/P ratios. The consequences of these sudden changes for bacteria community composition, metabolism, and enzymatic activity remain unclear, especially for the dynamic period immediately after pumice deposition. Thus, the main aim of our study was to determine how ambient bacterial communities respond to pumice inputs in lakes that differ in dissolved organic carbon (DOC) and P concentrations and to what extent these responses are moderated by substrate C/P stoichiometry. We performed an outdoor experiment with natural lake water from two lakes that differed in dissolved organic carbon (DOC) concentration. We measured nutrient concentrations, alkaline phosphatase activity (APA), and DOC consumption rates and assessed different components of bacterial community structure using next-generation sequencing of the 16S rRNA gene. Pumice inputs caused a decrease in the C/P ratio of dissolved resources, a decrease in APA, and an increase in DOC consumption, indicating reduced P limitation. These changes in bacteria metabolism were coupled with modifications in the assemblage composition and an increase in diversity, with increases in bacterial taxa associated with biofilm and sediments, in predatory bacteria, and in bacteria with gliding motility. Our results confirm that volcanic eruptions have the potential to alter nutrient partitioning and light penetration in receiving waterways which can have dramatic impacts on microbial community dynamics.

Experimental Determination of One-Atmosphere Phase Relations of Rhyodacite Pumice Erupted from Chaos Crags, Lassen Volcanic Center, California

NASA Astrophysics Data System (ADS)

Quinn, E. T.; Schwab, B. E.

2012-12-01

A series of one-atmosphere high-temperature anhydrous phase equilibrium melting experiments was performed on a natural rhyodacite pumice from the 1103±13 years BP pyroclastic flow from the Chaos Crags, Lassen Volcanic Center, California. The pumice (CCP) is the most silicic product known of the 1103 eruption of Chaos Crags. All experimental runs were performed in a Deltech VT-31 one-atmosphere gas-mixing furnace at the Experimental Petrology Lab, Humboldt State University, Arcata, California. Six ~90-99 hour runs were conducted at 35-55°C intervals, with target temperatures from 1000°C to 1200°C at the Ni-NiO buffer. The nominally anhydrous liquidus of the rhyodacite pumice is >1196°C and solidus is <998°C, outside the investigated temperature range. All experimental run products contain glass, plagioclase, quartz, and Fe-Ti oxides. Amphibole with breakdown textures is observed at temperatures ≤1159°C, and appears more stable in lower temperature runs. At 998°C, amphibole appears most stable, with only minor breakdown texture. Biotite, a major phase in starting material, is not observed in any run products. Based on comparison between experimental and natural phase assemblages and glass, plagioclase, and amphibole compositions, the Chaos Crags rhyodacite pumice erupted at a temperature <998°C, the lowest experimental run temperature investigated. Additional experimental runs at temperatures <998°C are currently being conducted.

Geology and Geochemistry of the 25.0 Ma Underdown Caldera Tuffs and tuff of Clipper Gap, Western Nevada Volcanic Field caldera belt, north-central Nevada

NASA Astrophysics Data System (ADS)

Cousens, B.; Klausen, K. B.; Henry, C.

2016-12-01

The 25.0 Ma Underdown Caldera of the Shoshone Mountains near Austin, Nevada, is part of the Ignimbrite Flare-up suite of calderas in north-central Nevada. Our goal is to characterize the geochemistry and geochronology of the tuffs, determine magma sources, and contrast Underdown with nearby contemporaneous caldera suites. The caldera is contained within a single, mildly west-tilted fault block (Bonham, 1970). The basement rocks are altered intermediate volcanic rocks, rarely intruded by rhyolite veins. The lowermost caldera unit, exposed only on the east side of the fault block, is the sparsely qtz-feld-phyric Underdown Tuff, a high-silica rhyolite (Bonham, 1970) that is columnar-jointed, densely welded, commonly includes aphyric pumice, but locally includes porphyritic pumice. Stretched pumice, flow folds, and foliations that reach nearly vertical demonstrate significant rheomorphism. A densely-welded porphyritic tuff is also present along the southeast side of the exposed caldera, and may be either blocks of an older tuff or a porphyritic phase of the Underdown Tuff. Correlative outflow, the tuff of Clipper Gap, emplaced east of the caldera, is petrographically similar with the same two pumice types. Overlying the Underdown Tuff is the Bonita Canyon Formation, which is moderately welded, commonly lithic- and pumice-rich with minor biotite, quartz and feldspar crystals, and contains reworked lenses; megabreccia of intermediate volcanic rocks and abundantly porphyritic tuff are common. This formation may be an upper part of the Underdown Tuff. On the west side of the Shoshone Mountains, the Bonita Canyon units are overlain by a more porphyritic, variably pumiceous, commonly vitrophyric, and densely welded tuff. At 24.7 Ma, this tuff is petrographically similar to and may be a younger part of the 25.2 Ma tuff of Arc Dome exposed to the east in the Toiyabe Range. Ongoing dating and geochemical analyses will constrain the timing and relationships between the tuffs.

pXRF quantitative analysis of the Otowi Member of the Bandelier Tuff: Generating large, robust data sets to decipher trace element zonation in large silicic magma chambers

NASA Astrophysics Data System (ADS)

Van Hoose, A. E.; Wolff, J.; Conrey, R.

2013-12-01

Advances in portable X-Ray fluorescence (pXRF) analytical technology have made it possible for high-quality, quantitative data to be collected in a fraction of the time required by standard, non-portable analytical techniques. Not only do these advances reduce analysis time, but data may also be collected in the field in conjunction with sampling. Rhyolitic pumice, being primarily glass, is an excellent material to be analyzed with this technology. High-quality, quantitative data for elements that are tracers of magmatic differentiation (e.g. Rb, Sr, Y, Nb) can be collected for whole, individual pumices and subsamples of larger pumices in 4 minutes. We have developed a calibration for powdered rhyolite pumice from the Otowi Member of the Bandelier Tuff analyzed with the Bruker Tracer IV pXRF using Bruker software and influence coefficients for pumice, which measures the following 19 oxides and elements: SiO2, TiO2, Al2O3, FeO*, MnO, CaO, K2O, P2O5, Zn, Ga, Rb, Sr, Y, Zr, Nb, Ba, Ce, Pb, and Th. With this calibration for the pXRF and thousands of individual powdered pumice samples, we have generated an unparalleled data set for any single eruptive unit with known trace element zonation. The Bandelier Tuff of the Valles-Toledo Caldera Complex, Jemez Mountains, New Mexico, is divided into three main eruptive events. For this study, we have chosen the 1.61 Ma, 450 km3 Otowi Member as it is primarily unwelded and pumice samples are easily accessible. The eruption began with a plinian phase from a single source located near center of the current caldera and deposited the Guaje Pumice Bed. The initial Unit A of the Guaje is geochemically monotonous, but Units B through E, co-deposited with ignimbrite show very strong chemical zonation in trace elements, progressing upwards through the deposits from highly differentiated compositions (Rb ~350 ppm, Nb ~200 ppm) to less differentiated (Rb ~100 ppm, Nb ~50 ppm). Co-erupted ignimbrites emplaced during column collapse show similar trace element zonation. The eruption culminated in caldera collapse after transitioning from a single central vent to ring fracture vents. Ignimbrites deposited at this time have lithic breccias and chaotic geochemical profiles. The geochemical discrepancy between early and late deposits warrants detailed, high-resolution sampling and analysis in order to fully understand the dynamics behind zonation processes. Samples were collected from locations that circumvent the caldera and prepared and analyzed in the field and the laboratory with the pXRF. Approximately 2,000 pumice samples will complete this unprecedented data set, allowing detailed reconstruction of trace element zonation around all sides of the Valles Caldera. These data are then used to constrain models of magma chamber processes that produce trace element zonation and how it is preserved in the deposits after a catastrophic, caldera-forming eruption.

Spectroscopic analysis of Ahlat stone (ignimbrite) and pumice formed by volcanic activity.

PubMed

Aygun, Z; Aygun, M

2016-09-05

Natural materials such as ignimbrites are preferred commonly not only in historical places but also in houses or in different kind of buildings all over the world especially around Ahlat in Bitlis-Turkey. Durability, lightness and good-insulation are the significative properties of these stones. Also, pumice is an another preferred material because of its advantages in construction industry. In this paper, four kinds of ignimbrite (light-yellow, yellow, black and white) and pumice from Ahlat region have been investigated by EPR method to determine magnetic properties of them. The results obtained by EPR, EDS and XRD methods are evaluated together. SEM technique is also used to understand the surface morphology of the samples. Copyright © 2016 Elsevier B.V. All rights reserved.

Mixed-severity fire in lodgepole-dominated forests: Are historical regimes sustainable on Oregon's Pumice Plateau, USA?

Treesearch

Emily K. Heyerdahl; Rachel A. Loehman; Donald A. Falk

2014-01-01

In parts of central Oregon, coarse-textured pumice substrates limit forest composition to low-density lodgepole pine (Pinus contorta Douglas ex Loudon var. latifolia Engelm. ex S. Watson) with scattered ponderosa pine (Pinus ponderosa Lawson & C. Lawson) and a shrub understory dominated by antelope bitterbrush (Purshia tridentata (Pursh) DC.). We reconstructed the...

Precipitated Silica from Pumice and Carbon Dioxide Gas (Co2) in Bubble Column Reactor

NASA Astrophysics Data System (ADS)

Dewati, R.; Suprihatin, S.; Sumada, K.; Muljani, S.; Familya, M.; Ariani, S.

2018-01-01

Precipitated silica from silica and carbon dioxide gas has been studied successfully. The source of silica was obtained from pumice stone while precipitation process was carried out with carbon dioxide gas (CO2). The sodium silicate solution was obtained by extracting the silica from pumice stone with sodium hydroxide (NaOH) solution and heated to 100 °C for 1 h. The carbon dioxide gas is injected into the aqueous solution of sodium silicate in a bubble column reactor to form precipitated silica. m2/g. The results indicate that the products obtained are precipitate silica have surface area in the range of 100 - 227 m2/g, silica concentration more than 80%, white in appearance, and silica concentration reached 90% at pH 7.

Stratigraphy, distribution, and evidence for mafic triggering of the ca. 8.5 ka Driftwood Pumice eruption, Makushin Volcano, Alaska, U.S.A

NASA Astrophysics Data System (ADS)

Lerner, Allan H.; Crowley, Peter D.; Nicolaysen, Kirsten P.; Hazlett, Richard W.

2018-05-01

Makushin Volcano on Unalaska Island, Alaska, threatens the Aleutian's largest population centers (Unalaska and Dutch Harbor), yet its eruption mechanisms are poorly known. This study presents a detailed stratigraphic and geochemical investigation of Makushin's most recent highly explosive event: the ca. 8.5 ka Driftwood Pumice eruption. The Driftwood Pumice has measured thicknesses of over 2.5 m, and isopach reconstructions estimate a total deposit volume of 0.3 to 1.6 km3, indicating a VEI 4-5 eruption. Proximal deposits consist of normally-graded, tan, dacitic to andesitic pumice, capped by a thinner dark layer of lower-silica andesitic scoria mixed with abundant lithic fragments. This stratigraphy is interpreted as an initial vent-clearing eruption that strengthened into a climactic ejection of pumice and ash and concluded with vent destabilization and the eruption of somewhat more mafic, gas-poor magma. Within the pumice, geochemical trends, disequilibrium mineral populations, and mineral zonation patterns show evidence of magma mixing between a bulk silicic magma and a mafic melt. Euhedral high-Ca plagioclase (An68-91) and high-Mg olivine (Fo69-77) phenocrysts are in disequilibrium with trachydacitic glass (65-68 wt% SiO2) and more abundant sodic plagioclase (An34-55), indicating the former originally crystallized in a more mafic melt. Tephra whole rock compositions become more mafic upwards through the deposit, ranging from a basal low-silica dacite to an andesite (total range: 60.8-63.3 wt% SiO2). Collectively, these compositional variations suggest magma mixing in the Driftwood Pumice (DWP) magma reservoir, with a systematic increase in the amount of a mafic component (up to 25%) upward through the deposit. Olivine-liquid and liquid-only thermometry indicate the mafic magma intruded at temperatures 140-200 °C hotter than the silicic magma. Diffusion rates calculated for 5-7 μm thick, lower-Mg rims on the olivine phenocrysts (Fo60 rim vs Fo76 bulk) suggest that the eruption occurred several days to weeks following the mafic injection into a dacitic reservoir. Based on this timing, we infer that the mafic intrusion provided a thermal pulse that initiated convection and volatile exsolution, and ultimately resulted in the DWP eruption. Unalaska's Holocene stratigraphy includes multiple light-dark ashfall couplets with physical and geochemical similarities to the DWP, suggesting that magma mixing may be a common eruptive trigger at Makushin Volcano.

Can thinning slash cause a nitrogen deficiency in pumice soils of central Oregon?

Treesearch

P.H. Cochran

1968-01-01

Decomposition of thinning slash deposited on the soil surface should have no direct adverse effect on the soil nitrogen available to higher plants in the pumice soil region. Decomposition of roots of cut trees would immobilize nitrogen in the soil immediately adjacent to the root during the decomposition period, which appears to be short for the smaller roots. However...

Managing ponderosa pine forests in central Oregon: who will speak for the soil?

Treesearch

Matt D. Busse; Gregg M. Riegel

2005-01-01

The soils of the central Oregon pumice plateau are relatively young and infertile, yet support an array of plant diversity and growth in the region's pine forests. Whether these coarse-textured, pumice and ash soils are resilient to forest disturbance is not well understood. We present results from a long-term experiment that examined changes in soil quality in...

Structural and mechanical study of concrete made from cementitious materials of low environmental impact

NASA Astrophysics Data System (ADS)

González, A. K.; Montaño, A. M.; González, C. P.; Santos, A.

2017-12-01

This work shows the results obtained by replacing Type I Portland®, by cementitious geopolymers materials, derived from minerals, in concrete mixtures. Synthesis of both geopolymers through alkaline activation of two alluminosilicates: Bentonite and Pumice with sodium silicate (Na2SiO3). XRD, SEM and XRDE are used to structural study of new geopolymers. Concrete mixtures with replacement of Portland have 10% and 30% of geopolymer. Finally, concrete mortars formed were mechanically analysed according to ICONTEC 220 at 7, 14, 28, 41, 90 and 120 days of cure. Results shows that compressive strength of concrete from Bentonite and Pumice are almost the same for the standard concrete at 28 days of cure. At 90 days of cure, compression resistance of concrete from Pumice at 10% is even higher than those that standard concrete shows.

Anomalously high porosity in subduction inputs to the Nankai Trough (SW Japan) potentially caused by volcanic ash and pumice

NASA Astrophysics Data System (ADS)

Huepers, A.; Ikari, M.; Underwood, M.; Kopf, A.

2013-12-01

At convergent margins, the sedimentary section seaward of the trench on the subducting oceanic lithosphere provides the source material for accretionary prisms and eventually becomes the host rock of the plate boundary megathrust. The mechanical properties of the sediments seaward of the subduction zone have therefore a first order control on subduction zone forearc mechanics and hydrogeology. At the Nankai Trough (SW Japan) the majority of sediment approaching the subduction zone is clay-rich. Scientific drilling expeditions in the framework of the Ocean Drilling Program (ODP) and the Integrated Ocean Drilling Program (IODP) have revealed an anomalous zone of high porosity in a major lithologic unit known as the Upper Shikoku Basin facies (USB), which is associated with elevated volcanic ash content and high amounts of silica in the interstitial water. The existence of the high porosity zone has previously been associated with advanced silica cementation, driven by the dual diagenetic transition of opal-A to opal-CT, and opal-CT to quartz. However, temperature estimates from recent drilling expeditions offshore the Kii peninsula reveal different in situ temperatures at the proposed diagenetic boundary in the Shikoku Basin. Furthermore, laboratory measurements using core samples from the USB show that cohesive strength is not elevated in the high porosity zone, suggesting that a process other than cementation may be responsible. The USB sediment is characterized by abundant volcanic ash and pumice, therefore the high porosity zone in the USB may be closely linked to the mechanical behavior of this phase. We conducted consolidation tests in the range 0.1 to 8 MPa effective vertical stress on artificial ash-smectite and pumice-smectite mixtures, as well as intact and remolded natural samples from the IODP Sites C0011 and C0012 to investigate the role of the volcanic constituent on porosity loss with progressive burial. Our results show that both remolded and intact natural samples have high porosities of up to ~71 to 75% at a vertical effective stress of 0.1 MPa, which decreases to 39 to 49% at 8 MPa vertical effective stress. The behavior of the remolded samples is in good accordance with compiled in-situ porosity vs. depth profiles from the high porosity zone. This suggests that cementation is not the cause for the anomalously high porosity. The consolidation tests on the artificial samples document that pure ash and pumice samples are highly resistant to consolidation. Between 0.1 to 8 MPa vertical effective stress, the porosity decreases from 51 to 47% for the ash sample and 60% to 46% for the pumice sample. The higher initial porosity in the pumice may be explained by a porous internal grain structure that allows storage of additional water. Mixtures with smectite are characterized by higher compressibility and higher porosity. For a mixture of 80% smectite and 20% pumice the porosity decreases from 65% to 39%, similar to that of the natural samples. Our results suggest that the high porosity zone is caused by the bulk mechanical behavior of pumice in the USB.

Production and characterization of a composite insulation material from waste polyethylene teraphtalates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kurtulmus, Erhan; Karaboyacı, Mustafa; Yigitarslan, Sibel

2013-12-16

The pollution of polyethylene teraphtalate (PET) is in huge amounts due to the most widely usage as a packaging material in several industries. Regional pumice has several desirable characteristics such as porous structure, low-cost and light-weight. Considering the requirements approved by the Ministry of Public Works on isolation, composite insulation material consisting of PET and pumice was studied. Sheets of composites differing both in particle size of pumice and composition of polymer were produced by hot-molding technique. Characterization of new composite material was achieved by measuring its weight, density, flammability, endurance against both to common acids and bases, and tomore » a force applied, heat insulation and water adsorption capacity. The results of the study showed that produced composite material is an alternative building material due to its desirable characteristics; low weight, capability of low heat conduction.« less

The largest deep-ocean silicic volcanic eruption of the past century.

PubMed

Carey, Rebecca; Soule, S Adam; Manga, Michael; White, James; McPhie, Jocelyn; Wysoczanski, Richard; Jutzeler, Martin; Tani, Kenichiro; Yoerger, Dana; Fornari, Daniel; Caratori-Tontini, Fabio; Houghton, Bruce; Mitchell, Samuel; Ikegami, Fumihiko; Conway, Chris; Murch, Arran; Fauria, Kristen; Jones, Meghan; Cahalan, Ryan; McKenzie, Warren

2018-01-01

The 2012 submarine eruption of Havre volcano in the Kermadec arc, New Zealand, is the largest deep-ocean eruption in history and one of very few recorded submarine eruptions involving rhyolite magma. It was recognized from a gigantic 400-km 2 pumice raft seen in satellite imagery, but the complexity of this event was concealed beneath the sea surface. Mapping, observations, and sampling by submersibles have provided an exceptionally high fidelity record of the seafloor products, which included lava sourced from 14 vents at water depths of 900 to 1220 m, and fragmental deposits including giant pumice clasts up to 9 m in diameter. Most (>75%) of the total erupted volume was partitioned into the pumice raft and transported far from the volcano. The geological record on submarine volcanic edifices in volcanic arcs does not faithfully archive eruption size or magma production.

The largest deep-ocean silicic volcanic eruption of the past century

PubMed Central

Carey, Rebecca; Soule, S. Adam; Manga, Michael; White, James D. L.; McPhie, Jocelyn; Wysoczanski, Richard; Jutzeler, Martin; Tani, Kenichiro; Yoerger, Dana; Fornari, Daniel; Caratori-Tontini, Fabio; Houghton, Bruce; Mitchell, Samuel; Ikegami, Fumihiko; Conway, Chris; Murch, Arran; Fauria, Kristen; Jones, Meghan; Cahalan, Ryan; McKenzie, Warren

2018-01-01

The 2012 submarine eruption of Havre volcano in the Kermadec arc, New Zealand, is the largest deep-ocean eruption in history and one of very few recorded submarine eruptions involving rhyolite magma. It was recognized from a gigantic 400-km2 pumice raft seen in satellite imagery, but the complexity of this event was concealed beneath the sea surface. Mapping, observations, and sampling by submersibles have provided an exceptionally high fidelity record of the seafloor products, which included lava sourced from 14 vents at water depths of 900 to 1220 m, and fragmental deposits including giant pumice clasts up to 9 m in diameter. Most (>75%) of the total erupted volume was partitioned into the pumice raft and transported far from the volcano. The geological record on submarine volcanic edifices in volcanic arcs does not faithfully archive eruption size or magma production. PMID:29326974

Explosive eruptive history of Pantelleria, Italy: Repeated caldera collapse and ignimbrite emplacement at a peralkaline volcano

NASA Astrophysics Data System (ADS)

Jordan, Nina J.; Rotolo, Silvio G.; Williams, Rebecca; Speranza, Fabio; McIntosh, William C.; Branney, Michael J.; Scaillet, Stéphane

2018-01-01

A new, pre-Green Tuff (46 ka) volcanic stratigraphy is presented for the peralkaline Pantelleria Volcano, Italy. New 40Ar/39Ar and paleomagnetic data are combined with detailed field studies to develop a comprehensive stratigraphic reconstruction of the island. We find that the pre-46 ka succession is characterised by eight silica-rich peralkaline (trachyte to pantellerite) ignimbrites, many of which blanketed the entire island. The ignimbrites are typically welded to rheomorphic, and are commonly associated with lithic breccias and/or pumice deposits. They record sustained radial pyroclastic density currents fed by low pyroclastic fountains. The onset of ignimbrite emplacement is typically preceded (more rarely followed) by pumice fallout with limited dispersal, and some eruptions lack any associated pumice fall deposit, suggesting the absence of tall eruption columns. Particular attention is given to the correlation of well-developed lithic breccias in the ignimbrites, interpreted as probable tracers of caldera collapses. They record as many as five caldera collapse events, in contrast to the two events reported to date. Inter-ignimbrite periods are characterised by explosive and effusive eruptions with limited dispersal, such as small pumice cones, as well as pedogenesis. These periods have similar characteristics as the current post-Green Tuff activity on the island, and, while not imminent, it is reasonable to postulate the occurrence of another ignimbrite-forming eruption sometime in the future.

Effects of pumice mining on soil quality

NASA Astrophysics Data System (ADS)

Cruz-Ruíz, A.; Cruz-Ruíz, E.; Vaca, R.; Del Aguila, P.; Lugo, J.

2016-01-01

Mexico is the world's fourth most important maize producer; hence, there is a need to maintain soil quality for sustainable production in the upcoming years. Pumice mining is a superficial operation that modifies large areas in central Mexico. The main aim was to assess the present state of agricultural soils differing in elapsed time since pumice mining (0-15 years) in a representative area of the Calimaya region in the State of Mexico. The study sites in 0, 1, 4, 10, and 15 year old reclaimed soils were compared with an adjacent undisturbed site. Our results indicate that gravimetric moisture content, water hold capacity, bulk density, available phosphorus, total nitrogen, soil organic carbon, microbial biomass carbon and phosphatase and urease activity were greatly impacted by disturbance. A general trend of recovery towards the undisturbed condition with reclamation age was found after disturbance, the recovery of soil total N being faster than soil organic C. The soil quality indicators were selected using principal component analysis (PCA), correlations and multiple linear regressions. The first three components gathered explain 76.4 % of the total variability. The obtained results revealed that the most appropriate indicators to diagnose the quality of the soils were urease, available phosphorus and bulk density and minor total nitrogen. According to linear score analysis and the additive index, the soils showed a recuperation starting from 4 years of pumice extraction.

Mafic intrusion remobilising silicic magma under El Hierro, Canary Islands

NASA Astrophysics Data System (ADS)

Sigmarsson, O.; Laporte, D.; Marti, J.; Devouard, B.; Cluzel, N.

2012-04-01

The 2011 submarine eruption at El Hierro, Canary Islands, has produced volcanic bombs that degas at sea surface, boil seawater and sink when cooled and degassed. At the beginning of the eruption white coloured pumices enveloped in darker coloured spatters floated on land. These composite pumices show evidence of magma mingling with folds and undulations of the darker coloured magma within the white pumice suggesting magma mingling in a viscous regime. The white pumice is highly vesicular and resembles foam. Most of the vesicular structure is made of tightly packed, polygonal bubbles of uniform size (˜ 100 μm), suggesting a single event of homogeneous bubble nucleation. An earlier event of heterogeneous bubble nucleation is indicated by the presence of a few large bubbles developed around tiny quartz crystals. Both the darker and lighter coloured pumices are almost aphyric. A few olivine crystals with perfect euhedral morphology occur within the darker part. Rare olivines of same composition are also found in the white pumice glass but then display somewhat rounded outlines and hopper-type structure. Melt inclusions in olivines of the darker pumice are of the same composition as the enveloping mafic glass, whereas olivines in the mixing boundary layer have melt inclusions of less mafic composition. The whole-rock composition and slightly more evolved glass composition are of basanitc and alkali rhyolitic composition (at the limit of the trachyte field) according to the TAS classification. Such rhyolitic compositions are rare in the Canaries. Analyses of residual volatile concentration in the glasses show that the silicic glass is highly degassed (F: 511 ±222; Cl: 202 ±58; S: below detection limit; values in ppm,1SD, n=10), whereas the basanitic glass still has very high halogene concentrations (F: 1354 ±151; Cl: 1026 ±47; S: 362 ±29; 1SD, n=10). In-situ analysis of trace element compositions of the dark glasses reveal typical basanitic compositions with elevated incompatible element concentrations and primitive mantle normalised spectra characteristic for the Canary Island basanites (e.g. La is of 100 times higher concentration than primitive mantle with important LREE enrichments). In contrast, the trace element composition of the alkali rhyolite shows surprisingly low concentrations for all elements except the most incompatible ones (such as Rb, Ba, K and Th). All other measured incompatible LILE, HFSE and REE have significantly lower concentration than the basanitic counterpart. This differences increase with the atomic number of the REE reaching maximum for the MREE and thus forming an intriguing U-shaped rhyolite spectra. Furthermore, unusual U-depletion is observed in the rhyolite. Other negative spikes, such as those for Sr and P, are readily accounted for by the removal of plagioclase and apatite during magma evolution from a basanite to a more evolved melt. The results obtained so far suggest an intrusion of gas-rich basanitic melt at the base of an evolved intrusion remobilising a stagnant phonolitic melt present as late differentiate in the crust. Interaction with old oceanic crust and the volcanic edifice can be quantified and shown to have modified the phonolite melt composition and produced the alkali rhyolitic composition of the white floating pumice. Extensive gas exsolution shortly before the melt-glass transition explains the foam texture and the low volatile concentrations in the quenched alkali rhyolite.

Breakin' up is hard to do: Fragmentation mechanisms of the 2012 submarine Havre eruption

NASA Astrophysics Data System (ADS)

Mitchell, S. J.; Manga, M.; Houghton, B. F.; Carey, R.

2017-12-01

The production of clastic or effusive material in volcanic eruptions is primarily controlled by if, when and where magma fragments. Assessing conditions for the fragmentation threshold is essential for eruptions with no direct observations, such as those within the deep submarine environment where hydrostatic pressure is considered to suppress bubble expansion and hence, explosive eruptions. The 2012 deep submarine eruption of Havre produced a series of rhyolitic lava flows and domes from vents between 1220 and 650 mbsl, and >1.3 km3 of pumiceous rhyolite clasts erupted at 900 mbsl. Calculated mass discharge rates (106 kg s-1) for the highest-intensity eruptive phase are comparable to subaerial silicic explosive eruptions. However, giant pumiceous clasts on the seafloor with curviplanar surfaces are more consistent with examples of effusive pumiceous lava-dome carapaces. These contradictory observations lead us to theoretically examine conflicting fragmentation mechanisms for Havre magma. Using equilibrium and disequilibrium degassing models, and Havre pre-eruptive conditions determined from geochemical and microtextural studies, we: 1) determine that an equilibrium degassing assumption is valid, as decompression rates are far below those that lead to disequilibrium degassing; and 2) calculate that Havre magma would not reach the critical strain rates sufficient to induce fragmentation within the conduit under hydrostatic vent pressure of 9 MPa. Equilibrium model results are consistent with measurements of modal vesicle diameters and magma vesicularity made on samples recovered by the 2015 MESH expedition. This further validates the equilibrium degassing assumption, but implies that Havre magma did not undergo magmatic fragmentation prior to eruption. We consider brittle fragmentation and the propagation of cracks through a vesicular pumiceous carapace as the mechanism required to fragment Havre magma. In line with calculated high mass discharge rates, we propose that rapidly-ascending, coherent magma quenched by seawater produced large pumiceous blocks above the eruptive vent, but the event was not, namely, an `explosive' eruption.

The 23,500 y 14C BP White Pumice Plinian eruption and associated debris avalanche and Tochimilco lava flow of Popocatépetl volcano, México

NASA Astrophysics Data System (ADS)

Siebe, Claus; Salinas, Sergio; Arana-Salinas, Lilia; Macías, José Luis; Gardner, James; Bonasia, Rosanna

2017-03-01

The White Pumice (WP) is one of the thickest and most voluminous Plinian fallouts produced by Popocatépetl volcano in central Mexico during the Late Pleistocene-Holocene. Its eruption 23,500 14C y BP (27,800 cal BP) was triggered by the catastrophic failure of the SW flank of the volcano. The resulting debris avalanche was highly mobile reaching 72 km from the cone with an apparent coefficient of friction (L/H) of 0.06. The deposit covers an area of 1200 km2, and has a volume of 10.4 km3. This gigantic landslide, characterized by exceptionally large proximal hummocks (> 400 m) provoked the sudden decompression of the hydrothermal and magmatic systems, which produced an initial blast followed by the rise of a Plinian column that reached an altitude of 33 km. The isopach map allows the recognition of a dispersal axis pointing toward the south, where an area of 2490 km2 was covered by > 10 cm of pumice and ash. The total volume of the pumice fallout was estimated at 1.9 km3 DRE (Dense Rock Equivalent). Pumice clasts are dacitic (62-66 wt.% SiO2, anhydrous basis), highly vesicular (55-88 vol.%) and display a seriate texture with phenocrysts of plagioclase + hornblende + augite + hypersthene + oxides (Ti-magnetite and ilmenite) + apatite. As the eruption advanced, discharge rates became more intermittent and the height of the column fluctuated and finally collapsed, generating pumice-and-ash flows that were emplaced around the volcano. This short but intense activity was followed during subsequent years by rain-induced lahars that reached great distances from the volcano. At the same time, more degassed andesitic-dacitic (61-65 wt.% SiO2) magma was erupted effusively (4.4 km3, DRE) in the new horseshoe-shaped 5 km-wide crater from which the Tochimilco lava flow descended toward the SSE, where it inundated an area of 68 km2 and reached as far as 22 km from its source. Since then, multiple eruptions have reconstructed the summit cone, almost completely obliterating the horseshoe-shaped crater. During the course of this catastrophic eruption (VEI = 5) a total volume of 6.3 km3 (DRE) of juvenile magma (pumice and lava) were emitted and at least an additional 10 km3 of pre-existing rocks (debris avalanche) mobilized. It surpasses in magnitude most other known Plinian eruptions from Popocatépetl and can be envisaged as an example of a worst-case scenario for hazard evaluation purposes. It dramatically changed the morphology of the volcano and had profound and far-reaching effects beyond its immediate vicinity along rivers draining surrounding plains as well as on the lacustrine basins (e.g. Chalco) to the NE. A repeat of such an eruption in this densely populated area would certainly cause a major calamity of unprecedented dimensions.

Crystallisation ages in coeval silicic magma bodies: 238U-230Th disequilibrium evidence from the Rotoiti and earthquake flat eruption deposits, Taupo volcanic zone, New Zealand

USGS Publications Warehouse

Charlier, B.L.A.; Peate, D.W.; Wilson, C.J.N.; Lowenstern, J. B.; Storey, M.; Brown, S.J.A.

2003-01-01

The timescales over which moderate to large bodies of silicic magma are generated and stored are addressed here by studies of two geographically adjacent, successive eruption deposits in the Taupo Volcanic Zone, New Zealand. The earlier, caldera-forming Rotoiti eruption (>100 km3 magma) at Okataina volcano was followed, within months at most, by the Earthquake Flat eruption (??? 10 km3 magma) from nearby Kapenga volcano; both generated nonwelded ignimbrite and coeval widespread fall deposits. The Rotoiti and Earthquake Flat deposits are both crystal-rich high-silica rhyolites, with sparse glass-bearing granitoid fragments also occurring in Rotoiti lag breccias generated during caldera collapse. Here we report 238U-230Th disequilibrium data on whole rocks and mineral separates from representative Rotoiti and Earthquake Flat pumices and the co-eruptive Rotoiti granitoid fragments using TIMS and in situ zircon analyses by SIMS. Multiple-grain zircon-controlled crystallisation ages measured by TIMS from the Rotoiti pumice range from 69??3 ka ( 350 ka, with a pronounced peak at 70-90 ka. The weighted mean of isochrons is 83??14 ka, in accord with the TIMS data. One glass-bearing Rotoiti granitoid clast yielded an age of 57??8 ka by TIMS (controlled by Th-rich phases that, however, are not apparently present in the juvenile pumices). Another glass-bearing Rotoiti granitoid yielded SIMS zircon model ages peaking at 60-90 ka, having a similar age distribution to the pumice. Age data from pumices are consistent with a published 64??4 ka eruptive age (now modified to 62??2 ka), but chemical and/or mineralogical data imply that the granitoid lithics are not largely crystalline Rotoiti rhyolite, but instead represent contemporaneous partly molten intrusions reflecting different sources in their chemistries and mineralogies. Similarly, although the Earthquake Flat eruption immediately followed (and probably was triggered by) the Rotoiti event, age data from juvenile material are significantly different. A multiple-grain zircon-controlled crystallisation age measured by TIMS from a representative pumice is 173??5 ka, while SIMS model ages range from 70-26+34 ka to >350 ka, with a peak at 105 ka. These age data coupled with previously published geochemical and isotopic data show that the Rotoiti and Earthquake Flat deposits were erupted from independent, unconnected magma bodies. Published by Elsevier Science B.V.

Clast comminution during pyroclastic density current transport: Mt St Helens

NASA Astrophysics Data System (ADS)

Dawson, B.; Brand, B. D.; Dufek, J.

2011-12-01

Volcanic clasts within pyroclastic density currents (PDCs) tend to be more rounded than those in fall deposits. This rounding reflects degrees of comminution during transport, which produces an increase in fine-grained ash with distance from source (Manga, M., Patel, A., Dufek., J. 2011. Bull Volcanol 73: 321-333). The amount of ash produced due to comminution can potentially affect runout distance, deposit sorting, the volume of ash lofted into the upper atmosphere, and increase internal pore pressure (e.g., Wohletz, K., Sheridan, M. F., Brown, W.K. 1989. J Geophy Res, 94, 15703-15721). For example, increased pore pressure has been shown to produce longer runout distances than non-comminuted PDC flows (e.g., Dufek, J., and M. Manga, 2008. J. Geophy Res, 113). We build on the work of Manga et al., (2011) by completing a pumice abrasion study for two well-exposed flow units from the May 18th, 1980 eruption of Mt St Helens (MSH). To quantify differences in comminution from source, sampling and the image analysis technique developed in Manga et al., 2010 was completed at distances proximal, medial, and distal from source. Within the units observed, data was taken from the base, middle, and pumice lobes within the outcrops. Our study is unique in that in addition to quantifying the degree of pumice rounding with distance from source, we also determine the possible range of ash sizes produced during comminution by analyzing bubble wall thickness of the pumice through petrographic and SEM analysis. The proportion of this ash size is then measured relative to the grain size of larger ash with distance from source. This allows us to correlate ash production with degree of rounding with distance from source, and determine the fraction of the fine ash produced due to comminution versus vent-fragmentation mechanisms. In addition we test the error in 2D analysis by completing a 3D image analysis of selected pumice samples using a Camsizer. We find that the roundness of PDC pumice at MSH increases with distance from source, as does the quantity of fine-grained ash. In addition, we have made the first steps towards determining the proportion of fine ash produced by comminution with distance from source. These results are being tested by numerical methods to understand the effect of an increase in fine ash on overall flow dynamics of the PDCs in which they were produced.

Holocene tephra succession of Puyehue-Cordón Caulle and Antillanca/Casablanca volcanic complexes, southern Andes (40-41°S)

NASA Astrophysics Data System (ADS)

Naranjo, J. A.; Singer, B. S.; Jicha, B. R.; Moreno, H.; Lara, L. E.

2017-02-01

Puyehue-Cordón Caulle and Antillanca volcanic complexes are two of at least 50 active frontal arc volcanoes that define the 1400 km-long Southern Volcanic Zone of Chile. Holocene tephra deposits in Chile and Argentina (40-41°S) up to 100 km east of these volcanoes comprise at least five voluminous ( 1 to 8 km3) pyroclastic-fall layers that preceded several recently deposited Cordón Caulle pumice fallouts. Field observations of proximal, medium, and distal facies of the deposits, in conjunction with geochronology and geochemistry of the volcanic complexes, indicate that three fall layers are derived from Puyehue volcano (Puyehue 1 and 2, and Mil Hojas), whereas two are sourced from the Antillanca complex (Playas Blanca-Negra, and Nahuel Huapi Tephra), 20 km to the south. The oldest tephra (calibrated 14C age 10.49 ± 0.12 ka, 2σ), found only at medium-distal facies, is deposited directly on granitic moraine boulders and consists of deeply weathered, orange dacitic pumice lapilli. The next prominent tephra at 7 ka comprises dacitic pumice and its age is equivalent to a rhyodacitic dome exposed in the Puyehue summit crater. Above these deposits there are phases of a complex eruption consisting of a conspicuous compositionally-zoned tephra. It also comprises a pyroclastic density current, together with lithic rich and scoriaceous fallout deposits. Mineralogical, geochemical, and Sr isotope evidence, plus the isopach maps, confirm that this sequence of eruptive events is sourced from Antillanca at 1932 ± 68 yrBP. The total volume of this eruptive sequence exceeds 8 km3, making it the largest Holocene eruption from either volcanic complex. This eruption was likely responsible for the destruction of an ancestral Antillanca volcano and the formation of a 4.5 km diameter caldera. A distinctive younger unit in the region is a voluminous rhyodacitic pumice fall (calibrated 14C age 1.11 ± 0.07 ka), above which a series of several alternating dark lithic and pumice lapilli beds accumulated. Correlation with proximal deposits indicates that the 1.11 ka eruption was derived from Puyehue and destroyed 3 km3 of rhyodacitic domes at this volcano summit. Historic explosive activity at the nascent Casablanca volcano and along Cordón Caulle, including the 2011-2012 eruption ( 1 km3 of uncompacted pumice), the largest from this fissural zone, emphasizes an increased risk for volcanic hazards in central Chile and Argentina.

LPT. Elevations of low power test building (TAN640 and 641). ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

LPT. Elevations of low power test building (TAN-640 and -641). West and south elevations show stepped shield wall. South and east elevations show pumice block passageway on south side. Reactor cell walls are concrete. One-story parts are pumice block. Metal rollup doors. Ralph M. Parsons 1229-12 ANP/GE-7-640-A-2. November 1956. Approved by INEEL Classification Office for public release. INEEL index code no. 038-0640-00-693-107275 - Idaho National Engineering Laboratory, Test Area North, Scoville, Butte County, ID

Technology Insertion Engineering Services Masking Process Evaluation Task Order No. 7. (Phase 1). Revision B

DTIC Science & Technology

1989-10-06

spent pumice cleaning. All parts can be pumice cleaned faster by using the method described in Quick Fix Plan paragraph 6.0. Soaking the scrubbed masked...times were run at an unusuall fast pace. For two other days workers were observed masking parts and by excluding the time spent talking and working on...stop-off Lacquer, MICCROSTOP REDUCER is recom. mended. Also, a shot soak in caustic cleaner, both at 212’ F., will break the adhesion and the coating is

Nature and composition of interbedded marine basaltic pumice in the ˜52-50 Ma Vastan lignite sequence, western India: Implication for Early Eocene MORB volcanism offshore Arabian Sea

NASA Astrophysics Data System (ADS)

Sensarma, Sarajit; Singh, Hukam; Rana, R. S.; Paul, Debajyoti; Sahni, Ashok

2017-03-01

The recognition of pyroclasts preserved in sedimentary environments far from its source is uncommon. We here describe occurrences of several centimetres-thick discontinuous basaltic pumice lenses occurring within the Early Eocene Vastan lignite mine sedimentary sequence, western India at two different levels - one at ˜5 m and the other at 10 m above a biostratigraphically constrained 52 Ma old marker level postdating the Deccan Volcanism. These sections have received global attention as they record mammalian and plant radiations. We infer the repetitive occurrence of pumice have been sourced from a ˜52-50 Ma MORB related to sea-floor spreading in the western Arabian Sea, most plausibly along the Carlsberg Ridge. Pyroclasts have skeletal plagioclase with horsetail morphologies ± pyroxene ± Fe-Ti oxide euhedral crystals, and typically comprise of circular polymodal (radii ≤10 to ≥30 μm), non-coalescing microvesicles (>40-60%). The pumice have undergone considerable syngenetic alteration during oceanic transport and post-burial digenesis, and are a composite mixture of Fe-Mn-rich clay and hydrated altered basaltic glass (palagonite). The Fe-Mn-rich clay is extremely low in SiO 2, Al 2 O 3, TiO 2, MgO, alkalies and REE, but very high in Fe 2 O 3, MnO, P, Ba, Sr contents, and palagonitization involved significant loss of SiO 2, Al 2 O 3, MgO and variable gain in Fe 2 O 3, TiO 2, Ni, V, Zr, Zn and REE. Bubble initiation to growth in the ascending basaltic magma (liquidus ˜1200-1250 ∘C) may have occured in ˜3 hr. Short-distance transport, non-connected vesicles, deposition in inner shelf to more confined lagoonal condition in the Early Eocene and quick burial helped preservation of the pumice in Vastan. Early Eocene Arabian Sea volcanism thus might have been an additional source to marginal sediments along the passive margin of western India.

Juvenile pumice and pyroclastic obsidian reveal the eruptive conditions necessary for the stability of Plinian eruption of rhyolitic magma

NASA Astrophysics Data System (ADS)

Giachetti, T.; Shea, T.; Gonnermann, H. M.; McCann, K. A.; Hoxsie, E. C.

2016-12-01

Significant explosive activity generally precedes or coexists with the large effusion of rhyolitic lava (e.g., Mono Craters; Medicine Lake Volcano; Newberry; Chaitén; Cordón Caulle). Such explosive-to-effusive transitions and, ultimately, cessation of activity are commonly explained by the overall waning magma chamber pressure accompanying magma withdrawal, albeit modulated by magma outgassing. The tephra deposits of such explosive-to-effusive eruptions record the character of the transition - abrupt or gradual - as well as potential changes in eruptive conditions, such as magma composition, volatiles content, mass discharge rate, conduit size, magma outgassing. Results will be presented from a detailed study of both the gas-rich (pumice) and gas-poor (obsidian) juvenile pyroclasts produced during the Plinian phase of the 1060 CE Glass Mountain eruption of Medicine Lake Volcano, California. In the proximal deposits, a multitude of pumice-rich sections separated by layers rich in dense clasts suggests a pulsatory behavior of the explosive phase. Density measurements on 2,600 pumices show that the intermediate, most voluminous deposits have a near constant median porosity of 65%. However, rapid increase in porosity to 75-80% is observed at both the bottom and the top of the fallout deposits, suggestive of rapid variations in magma degassing. In contrast, a water content of pyroclastic obsidians of approximately 0.6 wt% does remain constant throughout the eruption, suggesting that the pyroclastic obsidians degassed up to a constant pressure of a few megapascals. Numerical modeling of eruptive magma ascent and degassing is used to provide constraints on eruption conditions.

Swellable clay minerals in weathering products of volcanic sediments related to landslides by 2016 Kumamoto Earthquake

NASA Astrophysics Data System (ADS)

Isobe, H.; Torii, M.

2016-12-01

2016 Kumamoto Earthquake triggered numerous landslides in Aso caldera area, Japan and incurred heavy casualties. Landslides occurred not only on steep slopes at the caldera cliffs or the barranco but also on relatively gradual slopes at the side of the central cones in the Aso caldera. The Aso volcano is a volcanic complex with huge caldera formed by catastrophic eruption at approximately 90ka and central cones formed by subsequent activities to recent years. The central cones are volcanic peaks contain various rocks including basaltic, andesitic and rhoyolitic lavas and pyroclastic materials. In this study, we analyzed the samples collected from the bottom surface of landslides occurred at the gradual hillside on the western flank of the Aso central cones. The subsurface geology of the site is Takanoobane rhyolite lava, 51ka, covered by dark silty or pelitic tuffs and black soil strata including Kusasenri pumice layer, 31ka. The bottom plane of the landslides can be seen as flat surfaces at boundaries between units in the Kusasenri pumice or bottom of the Kusasenri pumice on the pelitic tuff with charcoaled plants. The Kusasenri pumice layer is a coarse grained and highly permeable but poorly continuous. X-ray diffraction analysis revealed that the main component of the samples is halloysite (10Å). Halloysite (10Å) is alteration product of fine grained volcanic ash, and swellable clay with interlayer water molecules which bring sticky and deformable characteristics. The landslides caused by 2016 Kumamoto Earthquake occurred without precipitation within a week. Strong earthquake may fluidize swellable clay layers in gradual slopes and triggered heavy landslides.

Water in melt inclusions from phenocrysts of dacite pumice of the Vetrovoy Isthmus (Iturup Island, Southern Kuriles)

NASA Astrophysics Data System (ADS)

Kotov, A. A.; Smirnov, S. Z.; Maksimovich, I. A.; Plechov, P. Yu; Chertkova, N. V.; Befus, A. I.

2017-12-01

This work is devoted to the study of one of the largest caldera eruptions of the Kurile-Kamchatka island-arc system that occurred on the island of Iturup. The object of investigation of this work are phenocrysts of quartz and plagioclase from dacite pumice of the Isthmus of the Isthmus, which is located on the island of Iturup. The purpose of this work is to determine the water content in the melts that participated in the caldera eruption of the Vetrovoy Isthmus and the patterns of their changes during the crystallization of magma. In the course of the work, the following were carried out: 1) adaptation and calibration of the Raman spectroscopy method for determining water in rhyolite melt’s inclusions glasses in quartz and plagioclase from pumice stone; 2) determination of composition and estimation of water content in melt inclusions in quartz and plagioclase according to x-ray spectral analysis; 3) establishment of the regularities of the change in the water content during the evolution of the magmatic melt; 4) evaluation of fluid pressure by comparison with experimental data

Petrology, sedimentology, and diagenesis of hemipelagic limestone and tuffaceous turbidities in the Aksitero Formation, central Luzon, Philippines

USGS Publications Warehouse

Garrison, Robert E.; Espiritu, E.; Horan, L.J.; Mack, L.E.

1979-01-01

The Aksitero Formation of central Luzon is an upper Eocene and lower Oligocene sequence of evenly bedded hemipelagic limestone with a few thin interlayers of tuffaceous turbidites. The limestone consists chiefly of planktonic foraminifers and calcareous nannofossils, with up to 30 percent of noncarbonate components, chiefly volcaniclastic debris. The tuff layers are graded beds. Composed mainly of glass shards, pumice fragments, crystals, and fine-grained volcanic rock fragments. Hydrocarbons migrated into the pores of the tuffaceous layers early during diagenesis but they were subsequently flushed out and only bitumen remains, chiefly as thin coatings on grains and wthin pumice vesicles. Later during diagenesis, zeolites (mordenite and c1inoptilolite) and secondary calcite preferentially replaced glass shards and pumice fragments. Deposition of the Aksitero Formation probably occurred at depths of at least 1,000 meters within a subsiding basin adjacent to an active island arc system. Submarine ash eruptions of silicic composition caused volcaniclastic turbidity currents that occasionally reached the basin floor. The more proximal facies of these volcaniclastic deposits may be prospective for hydrocarbons.

Mapping the distribution of vesicular textures on silicic lavas using the Thermal Infrared Multispectral Scanner

NASA Technical Reports Server (NTRS)

Ondrusek, Jaime; Christensen, Philip R.; Fink, Jonathan H.

1993-01-01

To investigate the effect of vesicularity on TIMS (Thermal Infrared Multispectral Scanner) imagery independent of chemical variations, we studied a large rhyolitic flow of uniform composition but textural heterogeneity. The imagery was recalibrated so that the digital number values for a lake in the scene matched a calculated ideal spectrum for water. TIMS spectra for the lava show useful differences in coarsely and finely vesicular pumice data, particularly in TIMS bands 3 and 4. Images generated by ratioing these bands accurately map out those areas known from field studies to be coarsely vesicular pumice. These texture-related emissivity variations are probably due to the larger vesicles being relatively deeper and separated by smaller septa leaving less smooth glass available to give the characteristic emission of the lava. In studies of inaccessible lava flows (as on Mars) areas of coarsely vesicular pumice must be identified and avoided before chemical variations can be interpreted. Remotely determined distributions of vesicular and glassy textures can also be related to the volatile contents and potential hazards associated with the emplacement of silicic lava flows on Earth.

Satellite Observations of New Volcanic Island in Tonga

NASA Astrophysics Data System (ADS)

Vaughan, R. Greg; Abrams, Michael J.; Hook, Simon J.; Pieri, David C.

2007-01-01

A rising volcanic plume from an unknown source was observed on 9-11 August 2006 in the Vava'u Island group in the northernmost islands of Tonga [Matangi News Online, 2006]. On 12 August, the crew on board the yacht Maiken, sailing west from Vava'u to Fiji, encountered ``a vast, many miles wide, belt of densely packed pumice'' floating on the water (F. Fransson personal communication, 2006). Later, the crew sailed south and discovered that the source of the pumice was a newly erupting submarine volcano near Home Reef (18.991°S, 174.767°W) (Figure 1a).

Satellite Observations of New Volcanic Island in Tonga

NASA Technical Reports Server (NTRS)

Vaughan, R. Greg; Abrams, Michael J.; Hook, Simon J.; Pieri, David C.

2007-01-01

A rising volcanic plume from an unknown source was observed on 9-11 August 2006 in the Vava'u Island group in the northernmost islands of Tonga [Matangi News Online, 2006]. On 12 August, the crew on board the yacht Maiken, sailing west from Vava'u to Fiji, encountered 'a vast, many miles wide, belt of densely packed pumice' floating on the water (F. Fransson personal communication, 2006). Later, the crew sailed south and discovered that the source of the pumice was a newly erupting submarine volcano near Home Reef (18.991 deg S, 174.767 deg W).

Fine-scale ignimbrite morphology revealed in LiDAR at Crater Lake, OR

NASA Astrophysics Data System (ADS)

Robinson, J. E.; Bacon, C. R.; Wright, H. M.

2011-12-01

Mount Mazama erupted ~7,700 years ago resulting in the collapse of Crater Lake caldera, ash fall across the Pacific Northwest, and emplacement of compositionally zoned ignimbrite. Early climactic ignimbrite contains uniform rhyodacitic pumice and traveled far from the vent, whereas late, less mobile ignimbrite is dominated by crystal-rich andesitic scoria and mafic crystal mush. Funded by the USGS, NPS, and FHWA, the DOGAMI-led Oregon LiDAR Consortium contracted with Watershed Services to collect ~800 km2 of LiDAR over Crater Lake National Park from Aug 2010 to Sept 2010. Ground laser returns have an average density of 1.63 returns/m2 over the heavily forested area of interest. The data have a lateral RMSE and vertical accuracy of 0.05 m. A bare earth terrain model allows a virtual removal of the forest, revealing fine-scale surface morphology, notably in the climactic ignimbrite. Secondary pyroclastic flows, explosion craters, erosion by water, and compaction-related deformation modified the originally smooth ignimbrite surface. Distinct pyroclastic flow fronts are evident in the LiDAR in Annie Creek valley. Leveed flows stand approximately 5 m above the lower ignimbrite surface, and individual toes are about 1-2 m high. Preliminary field checking indicates that rhyodacitic pumice dominates the lower ignimbrite surface, but the leveed flows are a subequal mix of locally oxidized rhyodacitic pumice and andesitic scoria. We hypothesize that these deposits were secondary pyroclastic flows formed by gravitational failure of late ignimbrite. In the Castle Creek valley, is a 2-meter collapse scarp that may have spawned a small secondary pyroclastic flow; several such headwall scarps are present in Sand Creek valley. Differential compaction features are common in many thick ignimbrites. We suggest this caused the deformation of the ignimbrite apparent in the LiDAR. In Annie Creek valley are a series of flow parallel asymmetric ridges, with shallower slopes toward the valley center, in the surface of the rhyodacitic ignimbrite. The ridges are 1-2 m high, and have a variable wavelength averaging 60 m. We hypothesize that this terrain is a series of antithetic faults due to downbending towards the thickest part of the ignimbrite. The ignimbrite near the Pumice Desert is likely over 100 m thick. Here, cracks positioned on topographic highs or at breaks in slope are 50 m to 800 m long and up to 30 m wide. The cracks open towards the thickest part of the ignimbrite in the downslope direction. They appear to be tension fractures that opened because of differential compaction of the ignimbrite. Breakaway fractures mark where ignimbrite thickness abruptly decreases laterally, such as north-northeast of the caldera and at valley margins. Some fractures show evidence of water erosion during formation of fractures. On the lee side of Timber Crater, north of Crater Lake, is a series of N-S trending ribs composed of pumice fall from the climactic eruption deposited on glaciated andesite lava. Timber Crater lies on the main dispersal axis of the pumice fall. We suggest that high-energy pyroclastic flows encountered topographic bumps on the flanks of Timber Crater. This affected flow turbulence causing linear troughs to erode into the fall deposit and leaving pumice-fall ribs.

Recent eruptive history of Mount Hood, Oregon, and potential hazards from future eruptions

USGS Publications Warehouse

Crandell, Dwight Raymond

1980-01-01

Each of three major eruptive periods at Mount Hood (12,000-15,000(?), 1,500-1,800, and 200-300 years ago) produced dacite domes, pyroclastic flows, and mudflows, but virtually no pumice. Most of the fine lithic ash that mantles the slopes of the volcano and the adjacent mountains fell from ash clouds that accompanied the pyroclastic flows. Widely scattered pumice lapilli that are present at the ground surface on the south, east, and north sides of Mount Hood may have been erupted during the mid-1800's, when the last known activity of the volcano occurred. The geologically recent history of Mount Hood suggests that the most likely eruptive event in the future will be the formation of another dome, probably within the present south-facing crater. The principal hazards that could accompany dome formation include pyroclastic flows and mudflows moving from the upper slopes of the volcano down the floors of valleys. Ash clouds which accompany pyroclastic flows may deposit as much as a meter of fine ash close to their source, and as much as 20 centimeters at a distance of 11 kilometers downwind from the pyroclastic flows. Other hazards that could result from such eruptions include laterally directed explosive blasts that could propel rock fragments outward from the sides of a dome at high speed, and toxic volcanic gases. The scarcity of pumiceous ash erupted during the last 15,000 years suggests that explosive pumice eruptions are not a major hazard at Mount Hood; thus, there seems to be little danger that such an eruption will significantly affect the Portland (Oregon) metropolitan area in the near future.

Geology and forestry classification from ERTS-1 digital data

NASA Technical Reports Server (NTRS)

Lawrence, R. D.; Herzog, J. H.

1975-01-01

Computer classifications into seven and ten classes of two areas in central Oregon of interest to geology and forestry demonstrate the extraction of information from ERTS-1 data. The area around Newberry Caldera was classified into basalt, rhyolite obsidian, pumice flats, Newberry pumice, ponderosa pine, lodgepole pine, and water classes. The area around Mt. Washington was classified into two basalts, three forest, two clearcut, burn, snow, and water classes. Both also include an unclassified category. Significant details that cannot be extracted from photographic reconstitutions of the data emerge from these classifications, such as moraine locations and paleowind directions. Spectral signatures for the various rocks are comparable to those published elsewhere.

Ultrafine cementitious grout

DOEpatents

Ahrens, Ernst H.

1999-01-01

An ultrafine cementitious grout in three particle grades containing Portland cement, pumice as a pozzolanic material and superplasticizer in the amounts of about 30 wt. % to about 70 wt. % Portland cement; from about 30 wt. % to about 70 wt. % pumice containing at least 70% amorphous silicon dioxide; and from 1.2 wt. % to about 5.0 wt. % superplasticizer. The superplasticizer is dispersed in the mixing water prior to the addition of dry grout and the W/CM ratio is about 0.4 to 1/1. The grout has very high strength and very low permeability with good workability. The ultrafine particle sizes allow for sealing of microfractures below 10 .mu.m in width.

Removal of Arsenic (V) from Aqueous Solutions Using Chitosan-Red Scoria and Chitosan-Pumice Blends.

PubMed

Asere, Tsegaye Girma; Mincke, Stein; De Clercq, Jeriffa; Verbeken, Kim; Tessema, Dejene A; Fufa, Fekadu; Stevens, Christian V; Du Laing, Gijs

2017-08-09

In different regions across the globe, elevated arsenic contents in the groundwater constitute a major health problem. In this work, a biopolymer chitosan has been blended with volcanic rocks (red scoria and pumice) for arsenic (V) removal. The effect of three blending ratios of chitosan and volcanic rocks (1:2, 1:5 and 1:10) on arsenic removal has been studied. The optimal blending ratio was 1:5 (chitosan: volcanic rocks) with maximum adsorption capacity of 0.72 mg/g and 0.71 mg/g for chitosan: red scoria (Ch-Rs) and chitosan: pumice (Ch-Pu), respectively. The experimental adsorption data fitted well a Langmuir isotherm ( R ² > 0.99) and followed pseudo-second-order kinetics. The high stability of the materials and their high arsenic (V) removal efficiency (~93%) in a wide pH range (4 to 10) are useful for real field applications. Moreover, the blends could be regenerated using 0.05 M NaOH and used for several cycles without losing their original arsenic removal efficiency. The results of the study demonstrate that chitosan-volcanic rock blends should be further explored as a potential sustainable solution for removal of arsenic (V) from water.

Removal of Arsenic (V) from Aqueous Solutions Using Chitosan–Red Scoria and Chitosan–Pumice Blends

PubMed Central

Asere, Tsegaye Girma; Mincke, Stein; De Clercq, Jeriffa; Verbeken, Kim; Tessema, Dejene A.; Fufa, Fekadu; Stevens, Christian V.; Du Laing, Gijs

2017-01-01

In different regions across the globe, elevated arsenic contents in the groundwater constitute a major health problem. In this work, a biopolymer chitosan has been blended with volcanic rocks (red scoria and pumice) for arsenic (V) removal. The effect of three blending ratios of chitosan and volcanic rocks (1:2, 1:5 and 1:10) on arsenic removal has been studied. The optimal blending ratio was 1:5 (chitosan: volcanic rocks) with maximum adsorption capacity of 0.72 mg/g and 0.71 mg/g for chitosan: red scoria (Ch–Rs) and chitosan: pumice (Ch–Pu), respectively. The experimental adsorption data fitted well a Langmuir isotherm (R2 > 0.99) and followed pseudo-second-order kinetics. The high stability of the materials and their high arsenic (V) removal efficiency (~93%) in a wide pH range (4 to 10) are useful for real field applications. Moreover, the blends could be regenerated using 0.05 M NaOH and used for several cycles without losing their original arsenic removal efficiency. The results of the study demonstrate that chitosan-volcanic rock blends should be further explored as a potential sustainable solution for removal of arsenic (V) from water. PMID:28792443

Tube pumices as strain markers of the ductile-brittle transition during magma fragmentation

NASA Astrophysics Data System (ADS)

Martí, J.; Soriano, C.; Dingwell, D. B.

1999-12-01

Magma fragmentation-the process by which relatively slow-moving magma transforms into a violent gas flow carrying fragments of magma-is the defining feature of explosive volcanism. Yet of all the processes involved in explosively erupting systems, fragmentation is possibly the least understood. Several theoretical and laboratory studies on magma degassing and fragmentation have produced a general picture of the sequence of events leading to the fragmentation of silicic magma. But there remains a debate over whether magma fragmentation is a consequence of the textural evolution of magma to a foamed state where disintegration of walls separating bubbles becomes inevitable due to a foam-collapse criterion, or whether magma is fragmented purely by stresses that exceed its tensile strength. Here we show that tube pumice-where extreme bubble elongation is observed-is a well-preserved magmatic `strain marker' of the stress state immediately before and during fragmentation. Structural elements in the pumice record the evolution of the magma's mechanical response from viscous behaviour (foaming and foam elongation) through the plastic or viscoelastic stage, and finally to brittle behaviour. These observations directly support the hypothesis that fragmentation occurs when magma undergoes a ductile-brittle transition and stresses exceed the magma's tensile strength.

Titanium zoning and diffusion chronometry reveal dynamic and late-stage quartz growth in the Youngest Toba Tuff, Indonesia

NASA Astrophysics Data System (ADS)

Tierney, C. R.; Reid, M. R.; Burns, D. H.; Costa Rodriguez, F.; Chesner, C. A.

2017-12-01

The enormous 74 ka Youngest Toba Tuff (YTT) ejected 2800 km3 of compositionally zoned (68-77 wt.% SiO2) ignimbrite and co-ignimbrite ash. Titanium zoning within YTT quartz records a dynamic growth history, and sometimes concludes with a final growth stage under different conditions. We investigated the timescales of quartz growth using diffusion chronometry, and determined whether the last stage of crystallization was the result of a discrete and chamber-wide magmatic event. This work offers insight into the dynamics and timescales of storage and remobilization of voluminous silicic magmas - an important consideration for hazards assessment. High-resolution (1 µm steps) hyperspectral CL was mapped from 5-20 quartz crystals from each of five pumices spanning the YTT compositional spectrum. CL intensity was calibrated to Ti concentration via EPMA, and numerically modeled time-dependent diffusional relaxation curves where fit to concentration profiles across zone boundaries. CL-bright/high-Ti rims are found in quartz from all samples, but become less common and have lower Ti concentrations with increasing host pumice silica content (e.g., 70 ppm vs 50 ppm). Some large crystals contain distinct CL-bright interior zones with similar Ti concentration to the rims. Onset of growth of CL-bright rims commenced between 15 and 100 years before eruption, and interior bands between 30 and 1500 years. Neither rim nor interior ages correlate significantly with host pumice silica. Rim growth on quartz evidently occurred closer to eruption than a previous estimate of several decades to centuries for quartz from a single YTT pumice (Matthews et al., 2012). The similar timing for the onset of high-Ti quartz rim growth across all samples suggests a marked and temporally discrete magmatic event in the years to decades prior to eruption and may be recording the chamber-wide influence of magmatic recharge or remobilization. High-Ti interior zones likely record older recharge events that did not lead to eruption. The lower abundance and lower Ti concentrations of CL-bright rims in high-silica pumices indicates that the agent of recharge/remobilization may not have chemically impacted the more evolved parts of the system appreciably, potentially due to thermal buffering by the near-eutectoid composition of the magmatic system.

Geochemical characterization of mid-distal Nisyros tephra on Datça peninsula (southwestern Anatolia)

NASA Astrophysics Data System (ADS)

Gençalioğlu-Kuşcu, Gonca; Uslular, Göksu

2018-04-01

We present new distal records of tephra deposits that overly the Kos ignimbrite in seven locations of Datça peninsula. Tephra in one of these locations were previously associated with Nisyros Kyra sub-unit based only on the field characteristics. We use different proxies such as field observations, petrography, mineral, glass, and whole-rock chemistry in order to characterize and correlate the previously and recently identified pumice fall deposits on Datça. The total thickness of the fall deposit reaches to 3.5 m. The size of the pumice clasts is generally within the range of lapilli, and they have vitrophyric texture consisting mainly of plagioclase (andesine to labradorite) with scarce clinopyroxene (diopside to augite), olivine (Fo48-50), amphibole (magnesio-hastingsite), and biotite crystals. Amphibole is a ubiquitous phenocryst in all Datça tephra units and used as a criterion for the correlation. Glass major element analyses by EMPA reveal two different groups with andesitic and dacitic compositions. Difference in silica content (up to ca. 4 wt%) detected in the same specimen also designates the heterogeneity in pumice glass. This heterogeneity in glass composition is also supported by the frequent occurrence of banded pumice clasts in Datça tephra. Whole-rock composition of the pumice is mainly andesitic with calc-alkaline affinity. Multi-element patterns on primitive-mantle normalized diagram display typical arc-magmatism signature (i.e. depletion in Nb, Ta, Ti, and P). In order to check and eliminate the potential alternatives, we compared the distal deposits on Datça not only with Kyra, but also with other Nisyros tephra units. Yet, Kyra is the only unit that has comparable depositional characteristics, calcic amphibole crystals, andesitic-dacitic glass and whole-rock chemistry, and distal tephra deposits on neighboring islands (Tilos and Chalki). Therefore, we associate Datça tephra deposits with some proximal Kyra subunits of intermediate composition. However, if further geochemical (especially glass and mineral chemistry) data are provided for the Lakkí and Melisserí tephra units, a more thorough tephra correlation will be possible. Finally, our results may have implications on Nisyros tephra dispersal and geochemical characterization. Table S2 Characteristics of Nisyros proximal tephra units in comparison to Datça tephra. Table S3 Depositional characteristics and nomenclature of proximal and distal Kyra subunits on Tilos.

Stratigraphic, Granulometric and Geochemical Studies of a Major Plinian Eruption on Dominica, Lesser Antilles

NASA Astrophysics Data System (ADS)

Smith, A. L.; Daly, G.; Killingsworth, N.; Deuerling, K.; Schneider, S.; Fryxell, J. E.

2008-12-01

The island of Dominica, located in the center of the Lesser Antilles island arc has witnessed, probably within the last 100,000 years, three large volume Plinian eruptions. One of these, associated with the Morne Diablotins center, forms the Grande Savane pyroclastic flow fan, that extends off shore as a distinctive submarine feature for a distance of at least 14 km. Stratigraphical studies of road cuts and well-exposed sea cliffs indicate the fan is composed of an older unit composed of reworked deposits at the base followed by at least four sequences, based on the presence of paleosols, of block and ash flow deposits. The upper unit of block and ash flows is overlain, with no evidence of an intervening paleosol, by a sequence of ignimbrites and pumiceous surges (representing the Plinian eruption). There is no evidence of an initial Plinian fall deposit, so the lowest bed in the succession is an ignimbrite with a highly irregular base that cuts into the underlying block and ash flow deposits, the upper parts of which are colored red due to thermal effects. This lowest ignimbrite is welded (minimum porosity of 15%) throughout its thickness (maximum thickness of greater than 21 m), although a few outcrops near the margins show a thin (20-30 cm) non-welded but lithified zone beneath the welded zone. The remainder of the sequence is composed of lithified ignimbrite that can be subdivided into three units separated by pumiceous surge layers. The ignimbrite succession is overlain, with no obvious break, by a thin fall deposit containing accretionary lapilli and gas cavities, followed by three pumiceous surge deposits (lower and upper show planar stratification and the middle surge shows massive bedding); towards the north the upper two surge deposits are separated by thin pumiceous lapilli fall and ash fall deposits. This surge sequence extends laterally outside of the main area of ignimbrite deposition. The pumice clasts from the ignimbrites are andesitic in composition and show essentially no variation up stratigraphy. In contrast, the surges are more variable in composition, ranging from andesite to dacite. Modeling of these data will provide information on the dynamics of this major Plinian eruption including the effects of water/magma interaction.

Re-examining Distal Facies of the Grand Bay Ignimbrite at Fond St. Jean, Dominica

NASA Astrophysics Data System (ADS)

Ebner, N.; Frey, H. M.; Wirth, K. R.; Waters, L. E.; Manon, M. R. F.

2017-12-01

The Grand Bay ignimbrite in southern Dominica is a relatively young (43 ± 13 ka by U-Th of zircon), voluminous (0-.5-1 km3 on-land) and laterally extensive pyroclastic flow deposit spanning over 20 km2 that has been associated with the Micotrin volcanic center or Plat Pays complex. The Grand Bay ignimbrite typically occurs as a massive valley fill facies, approximately 9-14 meters thick, exposed on the southern coastal road, rich in white-light gray, relatively crystal rich (25-31%) andesitic (62-63.5 wt% SiO2, 16.7 wt% Al2O3, 6.5 wt % Fe2O3) pumice, whose mineral assemblage is dominated by plagioclase (22-25%), orthopyroxene (3-4%), and clinopyroxene (1-1.5%), in an unconsolidated gray ashy matrix. In the literature, distal facies of the Grand Bay ignimbrite have been proposed at Fond St. Jean (FSJ), but this supposition has recently been called into question. The 9 m thick stratified Fond St. Jean ignimbrite, (38,890 k.a. ± 600 B.P. by14C), is weathered yellow orange and overlies a 4 m thick lithified beach deposit on a sharp contact. Andesitic pumice clasts (60.5-64.5 wt% SiO2, 18 wt% Al2O3, 5.5 wt % Fe2O3) from the base of the FSJ ignimbrite contain similar mineral assemblages to Grand Bay clasts, however, FSJ pumices are relatively less crystal-rich (16-19%), contain significantly less plagioclase (13-16%), opx (1.0-1.5%), cpx (0.1 - 0.6%), and, most strikingly, up to 1% hornblende, which was not present in any Grand Bay samples. The lowermost three meters of the FSJ ignimbrite sequence is composed of meter thick sections of clast (5-7 cm pumice and ≤1 cm lithics) supported beds (70 cm), grading upwards into 30 cm of ash laminations and small pumice clasts (1-3 cm). Following a 40 cm bed of massive ash containing 1-3 cm clasts of pumice, the initial sequence repeats itself for 5 meters, with 30-40 cm lithic blocks in the uppermost unit. In addition to the stark stratigraphic and petrographic differences from the Grand Bay Beach exposure, Fe-Ti oxide geothermometry reveals eruption temperature of 820 + 7°C at Grand Bay Beach (ΔNNO - 0.16) and 864 ± 33 °C (ΔNNO - 0.25) at Fond St. Jean. Plagioclase composition ranges from An51-88 at Grand Bay and An57-75 at Fond St. Jean respectively. Furthermore, plagioclase hygrometry shows a range of 7.8 to 7.3 wt% H2O at Grand Bay, with slightly drier conditions of 7.3 to 7.1 wt% H2O at Fond St. Jean.

Potential hazards from future eruptions of Mount St. Helens Volcano, Washington

USGS Publications Warehouse

Crandell, Dwight Raymond; Mullineaux, Donal Ray

1978-01-01

Mount St. Helens has been more active and more explosive during the last 4,500 years than any other volcano in the conterminous United States. Eruptions of that period repeatedly formed domes, large volumes of pumice, hot pyroclastic flows, and, during the last 2,500 years, lava flows. Some of this activity resulted in mudflows that extended tens of kilometers down the floors of valleys that head at the volcano. This report describes the nature of the phenomena and their threat to people and property; the accompanying maps show areas likely to be affected by future eruptions of Mount St. Helens. Explosive eruptions that produce large volumes of pumice affect large areas because winds can carry the lightweight material hundreds of kilometers from the volcano. Because of prevailing winds, the 180-degree sector east of the volcano will be affected most often and most severely by future eruptions of this kind. However, the pumice from any one eruption will fall in only a small part of that sector. Pyroclastic flows and mudflows also can affect areas far from the volcano, but the areas they affect are smaller because they follow valleys. Mudflows and possibly pyroclastic flows moving rapidly down Swift and Pine Creeks could displace water in Swift Reservoir, which could cause disastrous floods farther downvalley.

Age and whole rock glass compositions of proximal pyroclastics from the major explosive eruptions of Somma-Vesuvius: A review as a tool for distal tephrostratigraphy

NASA Astrophysics Data System (ADS)

Santacroce, Roberto; Cioni, Raffaello; Marianelli, Paola; Sbrana, Alessandro; Sulpizio, Roberto; Zanchetta, Giovanni; Donahue, Douglas J.; Joron, Jean Louis

2008-10-01

A review of compositional data of the major explosive eruptions of Vesuvius is presented, comparing compositions (major elements) of whole rock with glass shards from the proximal deposits, hopefully useful for long-distance correlation. A critical review of published and new geochronological data is also provided. All available 14C ages are calibrated to give calendar ages useful for the reconstruction of the volcanological evolution of the volcanic complex. The pyroclastic deposits of the four major Plinian eruptions (22,000 yr cal BP "Pomici di Base", 8900 yr cal BP "Mercato Pumice", 4300 yr cal BP "Avellino Pumice", and A.D. 79 "Pompeii Pumice") are widely dispersed and allow a four-folded, Plinian to Plinian, stratigraphic division: 1. B-M (between Pomici di Base and Mercato); 2. M-A (between Mercato and Avellino); 3. A-P (between Avellino and Pompeii); 4. P-XX (from the Pompeii Pumice to the last erupted products of the XXth century). Within each interval, the age, lithologic and compositional features of pyroclastic deposits of major eruptions, potentially useful for tephrostratigraphic purposes on distal areas, are briefly discussed. The Vesuvius rocks are mostly high Potassic products, widely variable in terms of their silica saturation. They form three groups, different for both composition and age: 1. slightly undersaturated, older than Mercato eruption; 2. mildly undersaturated, from Mercato to Pompeii eruptions; 3. highly undersaturated, younger than Pompeii eruption. For whole rock analyses, the peculiar variations in contents of some major and trace elements as well as different trends in element/element ratios, allow a clear, unequivocal, easy diagnosis of the group they belong. Glass analyses show large compositional overlap between different groups, but selected element vs. element plots are distinctive for the three groups. The comparative analysis of glass and whole rock major element compositions provides reliable geochemical criteria helping in the recognition, frequently not obvious, of distal products from the different single eruptions.

25 CFR 212.3 - Definitions.

Code of Federal Regulations, 2012 CFR

2012-04-01

..., cinders, granite, building stone, limestone, clay, silt, or any other energy or non-energy mineral... treatment of minerals; Provided, when sand, gravel, pumice, cinders, granite, building stone, limestone...

25 CFR 212.3 - Definitions.

Code of Federal Regulations, 2014 CFR

2014-04-01

..., cinders, granite, building stone, limestone, clay, silt, or any other energy or non-energy mineral... treatment of minerals; Provided, when sand, gravel, pumice, cinders, granite, building stone, limestone...

H2O Contents of Submarine and Subaerial Silicic Pyroclasts from Oomurodashi Volcano, Northern Izu-Bonin Arc

NASA Astrophysics Data System (ADS)

McIntosh, I. M.; Tani, K.; Nichols, A. R.

2014-12-01

Oomurodashi volcano is an active shallow submarine silicic volcano in the northern Izu-Bonin Arc, located ~20 km south of the inhabited active volcanic island of Izu-Oshima. Oomurodashi has a large (~20km diameter) flat-topped summit located at 100 - 150 metres below sea level (mbsl), with a small central crater, Oomuro Hole, located at ~200 mbsl. Surveys conducted during cruise NT12-19 of R/V Natsushima in 2012 using the remotely-operated vehicle (ROV) Hyper-Dolphin revealed that Oomuro Hole contains numerous active hydrothermal vents and that the summit of Oomurodashi is covered by extensive fresh rhyolitic lava and pumice clasts with little biogenetic or manganese cover, suggesting recent eruption(s) from Oomuro Hole. Given the shallow depth of the volcano summit, such eruptions are likely to have generated subaerial eruption columns. A ~10ka pumiceous subaerial tephra layer on the neighbouring island of Izu-Oshima has a similar chemical composition to the submarine Oomurodashi rocks collected during the NT12-19 cruise and is thought to have originated from Oomurodashi. Here we present FTIR measurements of the H2O contents of rhyolitic pumice from both the submarine deposits sampled during ROV dives and the subaerial tephra deposit on Izu-Oshima, in order to assess magma degassing and eruption processes occurring during shallow submarine eruptions.

The Ottaviano eruption of Somma-Vesuvio (8000 y B.P.): a magmatic alternating fall and flow-forming eruption

NASA Astrophysics Data System (ADS)

Rolandi, G.; Maraffi, S.; Petrosino, P.; Lirer, L.

1993-11-01

The Ottaviano eruption occurred in the late neolithic (8000 y B.P.). 2.40 km 3 of phonolitic pyroclastic material (0.61 km 3 DRE) were emplaced as pyroclastic flow, surge and fall deposits. The eruption began with a fall phase, with a model column height of 14 km, producing a pumice fall deposit (LA). This phase ended with short-lived weak explosive activity, giving rise to a fine-grained deposit (L1), passing to pumice fall deposits as the result of an increasing column height and mass discharge rate. The subsequent two fall phases (producing LB and LC deposits), had model column heights of 20 and 22 km with eruption rates of 2.5 × 10 7 and 2.81 × 10 7 kg/s, respectively. These phases ended with the deposition of ash layers (L2 and L3), related to a decreasing, pulsing explosive activity. The values of dynamic parameters calculated for the eruption classify it as a sub-plinian event. Each fall phase was characterized by variations in the eruptive intensity, and several pyroclastic flows were emplaced (F1 to F3). Alternating pumice and ash fall beds record the waning of the eruption. Finally, owing to the collapse of a eruptive column of low gas content, the last pyroclastic flow (F4) was emplaced.

Application of acidic treated pumice as an adsorbent for the removal of azo dye from aqueous solutions: kinetic, equilibrium and thermodynamic studies

PubMed Central

2012-01-01

Colored effluents are one of the important environment pollution sources since they contain unused dye compounds which are toxic and less-biodegradable. In this work removal of Acid Red 14 and Acid Red 18 azo dyes was investigated by acidic treated pumice stone as an efficient adsorbent at various experimental conditions. Removal of dye increased with increase in contact time and initial dye concentration, while decreased for increment in solution temperature and pH. Results of the equilibrium study showed that the removal of AR14 and AR18 followed Freundlich (r2>0.99) and Langmuir (r2>0.99) isotherm models. Maximum sorption capacities were 3.1 and 29.7 mg/g for AR 14 and AR18, namely significantly higher than those reported in the literature, even for activated carbon. Fitting of experimental data onto kinetic models showed the relevance of the pseudo-second order (r2>0.99) and intra-particle diffusion (r2>0.98) models for AR14 and AR18, respectively. For both dyes, the values of external mass transfer coefficient decreased for increasing initial dye concentrations, showing increasing external mass transfer resistance at solid/liquid layer. Desorption experiments confirmed the relevance of pumice stone for dye removal, since the pH regeneration method showed 86% and 89% regeneration for AR14 and AR18, respectively. PMID:23369579

Evaluation of the surface roughness of three heat-cured acrylic denture base resins with different conventional lathe polishing techniques: A comparative study.

PubMed

Rao, Duggineni Chalapathi; Kalavathy, N; Mohammad, H S; Hariprasad, A; Kumar, C Ravi

2015-01-01

Surface roughness promotes adhesion and colonization of denture plaque. Therefore, it is important to know the effects of polishing and finishing on the surface roughness of various acrylic resin materials. To evaluate and compare the effects of different conventional lathe polishing techniques on heat cured acrylic resins in producing surface roughness. Three different commercially available heat-cured acrylic resin materials namely DPI, Meliodent and Trevalon Hi were selected. 30 Specimens of each acrylic material (30 x 3 = 90, 10 x 60 x 2mm) were prepared and divided into 5 groups, each group consisted of 6 Nos. of specimens per material(6x3=18) and were grouped as Group A(unfinished), Group B (finished), Group C (Polishing Paste), Group D (Polishing Cake) and Group E (Pumice and Gold rouge). The resulted surface roughness (μm) was measured using Perthometer and observed under Scanning Electron Microscope. The values obtained were subjected statistical analyses. Among the materials tested, better results were obtained with Trevalon Hi followed by Meliodent and DPI. Among the polishing methods used, superior results were obtained with universal polishing paste followed by polishing cake; Pumice and Gold rouge. Although Pumice and Gold rouge values produced greater roughness value, they were well within the threshold value of 0.2 mm.

Tephrostratigraphy of the late Quaternary record from Lake Chalco, central México

NASA Astrophysics Data System (ADS)

Ortega-Guerrero, Beatriz; Caballero García, Lizeth; Linares-López, Carlos

2018-01-01

Lacustrine sequences in active volcanic settings preserve the record of fall-out products (tephras) from explosive volcanic activity from both proximal and distal sources. Sediments of Lake Chalco, located in the western part of the Trans Mexican Volcanic Belt, offer the opportunity to develop a detailed tephrostratigraphy of proximal and distal sources, and to provide stratigraphic marker horizons for the correlation of paleoclimate records. Here, we present major oxide glass and pumice data from 18 tephra layers interbedded in the lacustrine sediments of Chalco, from 11.5 to 31.3 cal ka BP. Tephra glass compositions range from basaltic trachyandesitic to rhyolitic. Two tephras were successfully correlated with the Tutti Frutti Plinian Eruption of Popocatépetl volcano; and two tephra layers from the Nevado de Toluca Plinian activity: the Upper Toluca Pumice and the Lower Toluca Pumice. Although the source of most of the tephras analyzed is unknown, their geochemical characterization, coupled with a robust chronology, contributes to establish a detailed tephrostratigraphy for the region. This tephra record also contributes to improving the estimated frequency of explosive volcanic activity for future hazards in the Basin of México and surrounding areas, where more than 29 million people live. Our findings estimate a recurrence interval of volcanic activity of ca. 1100 years in the interval between ca. 32 and 11.5 cal ka BP, shorter than previously estimated.

36 CFR 228.42 - Definitions.

Code of Federal Regulations, 2010 CFR

2010-07-01

... and posted on the ground from which nonexclusive disposals of mineral materials may be made to low..., stone, pumice, pumicite, cinders, clay, and other similar materials. Common varieties do not include...

Geochemical homogeneity of a long-lived, large silicic system; evidence from the Cerro Galán caldera, NW Argentina

NASA Astrophysics Data System (ADS)

Folkes, Chris B.; de Silva, Shanaka L.; Wright, Heather M.; Cas, Raymond A. F.

2011-12-01

By applying a number of analytical techniques across a spectrum of spatial scales (centimeter to micrometer) in juvenile components, we show that the Cerro Galán volcanic system has repeatedly erupted magmas with nearly identical geochemistries over >3.5 Myr. The Cerro Galán system produced nine ignimbrites (˜5.6 to 2 Ma) with a cumulative volume of >1,200 km3 (DRE; dense rock equivalent) of calc-alkaline, high-K rhyodacitic magmas (68-71 wt.% SiO2). The mineralogy is broadly constant throughout the eruptive sequence, comprising plagioclase, quartz, biotite, Fe-Ti oxides, apatite, and titanite. Early ignimbrite magmas also contained amphibole, while the final eruption, the most voluminous Cerro Galán ignimbrite (CGI; 2.08 ± 0.02 Ma) erupted a magma containing rare amphibole, but significant sanidine. Each ignimbrite contains two main juvenile clast types; dominant "white" pumice and ubiquitous but subordinate "grey" pumice. Fe-Ti oxide and amphibole-plagioclase thermometry coupled with amphibole barometry suggest that the grey pumice originated from potentially hotter and deeper magmas (800-840°C, 3-5 kbar) than the more voluminous white pumice (770-810°C, 1.5-2.5 kbar). The grey pumice is interpreted to represent the parental magmas to the Galán system emplaced into the upper crust from a deeper storage zone. Most inter-ignimbrite variations can be accounted for by differences in modal mineralogy and crystal contents that vary from 40 to 55 vol.% on a vesicle-free basis. Geochemical modeling shows that subtle bulk-rock variations in Ta, Y, Nb, Dy, and Yb between the Galán ignimbrites can be reconciled with differences in amounts of crystal fractionation from the "grey" parent magma. The amount of fractionation is inversely correlated with volume; the CGI (˜630 km3) and Real Grande Ignimbrite (˜390 km3) return higher F values (proportion of liquid remaining) than the older Toconquis Group ignimbrites (<50 km3), implying less crystal fractionation took place during the upper-crustal evolution of these larger volume magmas. We attribute this relationship to variations in magma chamber geometry; the younger, largest volume ignimbrites came from flat sill-like magma chambers, reducing the relative proportion of sidewall crystallization and fractionation compared to the older, smaller-volume ignimbrite eruptions. The grey pumice clasts also show evidence of silicic recharge throughout the history of the Cerro Galán system, and recharge days prior to eruption has previously been suggested based on reversely zoned (OH and Cl) apatite phenocrysts. A rare population of plagioclase phenocrysts with thin An-rich rims in juvenile clasts in many ignimbrites supports the importance of recharge in the evolution and potential triggering of eruptions. This study extends the notion that large volumes of nearly identical silicic magmas can be generated repeatedly, producing prolonged geochemical homogeneity from a long-lived magma source in a subduction zone volcanic setting. At Cerro Galán, we propose that there is a zone between mantle magma input and upper crustal chambers, where magmas are geochemically "buffered", producing the underlying geochemical and isotopic signatures. This produces the same parental magmas that are delivered repeatedly to the upper crust. A lower-crustal MASH (melting, assimilation, storage, and homogenization) zone is proposed to act as this buffer zone. Subsequent upper crustal magmatic processes serve only to slightly modify the geochemistry of the magmas.

The compositionally zoned eruption of 1912 in the Valley of Ten Thousand Smokes, Katmai National Park, Alaska

USGS Publications Warehouse

Hildreth, W.

1983-01-01

On June 6-8, 1912, ??? 15 km3 of magma erupted from the Novarupta caldera at the head of the Valley of Ten Thousand Smokes (VTTS), producing ??? 20 km3 of air-fall tephra and 11-15 km3 of ash-flow tuff within ??? 60 hours. Three discrete periods of ash-fall at Kodiak correlate, respectively, with Plinian tephra layers designated A, CD, and FG by Curtis (1968) in the VTTS. The ash-flow sequence overlapped with but outlasted pumice fall A, terminating within 20 hours of the initial outbreak and prior to pumice fall C. Layers E and H consist mostly of vitric dust that settled during lulls, and Layer B is the feather edge of the ash flow. The fall units filled and obscured the caldera, but arcuate and radial fissures outline a 6-km2 depression. The Novarupta lava dome and its ejecta ring were emplaced later within the depression. At Mt. Katmai, 10 km east of the 1912 vent, a 600-m-deep caldera of similar area also collapsed at about this time, probably owing to hydraulic connection with the venting magma system; but all known ejecta are thought to have erupted at Novarupta. Mingling of three distinctive magmas during the eruption produced an abundance of banded pumice, and mechanical mixing of chilled ejecta resulted in deposits with a wide range of bulk composition. Pumice in the initial fall unit (A) is 100% rhyolite, but fall units atop the ash flow are > 98% dacite; black andesitic scoria is common only in the ash flows and in near-vent air-fall tephra. Pumice counts show the first half of the ash-flow deposit to be 91-98% rhyolite, but progressive increases of dacite and andesite eventually reduced the rhyolitic component to 20 km to the lowermost VTTS, and deposited 1-8 m of debris there. Rhyolitic ejecta contain only 1-2% phenocrysts but andesite and dacite have 30-45%. Quartz is present and augite absent only in the rhyolite, but all ejecta contain plagioclase, orthopyroxene, titanomagnetite, ilmenite, apatite, and pyrrhotite; rare olivine occurs in the andesite. The zoning ranges of phenocrysts in the rhyolitic and intermediate ejecta do not overlap. New chemical data show the bulk SiO2 range to be: rhyolite 77 ?? 0.6, dacite 66-64.5, and andesite 61.5-58.5%. The dacitic and andesitic ejecta contrast in color and density, and it is not certain whether they form a compositional continuum. Analyses reported by Fenner within the 66-76% SiO2 range were of banded pumice and lava and of bulk tephra that mechanically fractionated and mixed during flight. Despite the gap of 10% SiO2, Fe-Ti-oxide temperatures show a continuous range from rhyolite (805-850??C) through dacite (855-955??C) to andesite (955-990??C). Thermal continuity and isotopic and trace-element data suggest that all were derived from a single magmatic system, whether or not they were physically contiguous before eruption. If the rhyolitic liquid separated from dacitic magma, extraction was so efficient that no dacitic phenocrysts were retained and no bulk compositions in the range 66-76% SiO2 were created; if it were a partial me

Volcanic activity in the Acambay Graben: a < 25 Ka subplinian eruption from the Temascalcingo volcano and implications for volcanic hazard.

NASA Astrophysics Data System (ADS)

Pedrazzi, Dario; Aguirre Díaz, Gerardo; Sunyé Puchol, Ivan; Bartolini, Stefania; Geyer, Adelina

2016-04-01

The Trans-Mexican Volcanic Belt (TMVB) contains a large number of stratovolcanoes, some well-known, as Popocatepetl, Iztaccihuatl, Nevado de Toluca, or Colima and many others of more modest dimensions that are not well known but constitute the majority in the TMVB. Such volcanoes are, for example, Tequila, San Juan, Sangangüey, Cerro Culiacán, Cerro Grande, El Zamorano, La Joya, Palo Huerfano, Jocotitlán, Altamirano and Temascalcingo, among many others. The Temascalcingo volcano (TV) is an andesitic-dacitic stratovolcano located in the Trans-Mexican Volcanic Belt (TMVB) at the eastern part of the Acambay Graben (northwest portion of Estado de México). The TV is composed mainly by dacitic, porphyritic lavas, block and ash deposits and subordinate pumice fall deposits and ignimbrites (Roldán-Quintana et al., 2011). The volcanic structure includes a summit caldera that has a rectangular shape, 2.5×3.5 km, with the largest side oriented E-W, parallel to major normal faults affecting the edifice. The San Mateo Pumice eruption is one of the greatest paroxysmal episodes of this volcano with pumice deposits mainly exposed at the scarp of the Acambay-Tixmadeje fault and at the northern and northeastern flanks of TV. It overlies a paleosol dated at 25 Ka. A NE-trending dispersion was obtained from field data covering an area of at least 80 km2. These deposits overlie older lava flows and mud flows and are discontinuously covered and eroded by younger reworked deposits of Temascalcingo volcano. This event represents a highly explosive phase that generated a relatively thick and widespread pumice fallout deposit that may occur again in future eruptions. A similar eruption today would have a significantly impact in the region, overall due to the fact that there has been no systematic assessment of the volcanic hazard in any of the studies that have been conducted so far in the area. So, this is a pending and urgent subject that must be tackled without delay. Financed by grant DGAPA-PAPIIT IN-104615.

Graphite in the Bishop Tuff and its effect on postcaldera oxygen fugacity

USGS Publications Warehouse

Hildreth, Edward; Ryan-Davis, Juliet; Harlow, Benjamin

2017-01-01

Several cubic kilometers of Paleozoic graphite-bearing argillitic country rocks are present as lithic fragments in Bishop Tuff ignimbrite and fallout. The lithics were entrained by the 650 km3 of rhyolite magma that vented during the 5- to 6-day-long, caldera-forming eruption at Long Valley, California. The caldera is floored by a 350 km2 roof plate that collapsed during the eruption and consists in large part of the Paleozoic strata that provided the abundant hornfelsed metapelitic lithic clasts in the tuff. Graphite has been identified by Raman spectroscopy, electron-dispersive spectroscopy, and X-ray diffraction as an irregularly dispersed component in the small fraction of Bishop Tuff pumice that is dark-colored. Carbon concentration has been determined in pumice, lithics, and wall rocks. Values of δ13C range from –21‰ to –29‰ Vienna Peedee Belemnite (VPDB) for pumice, lithics, and argillitic wall rocks, reflecting the biogenic origin of the reduced carbon in oxygen-limited black Paleozoic marine mudrocks. Carbonate contents, measured separately, are negligible in fresh pumice and lithics. Microprobe analyses of titanomagnetite-ilmenite pairs show that oxygen-fugacity values of numerous batches of postcaldera Early Rhyolite (750–640 ka; ~100 km3) are up to one log unit more reduced than those of the temperature–oxygen fugacity (T-fO2) array of the Bishop Tuff (767 ka), despite similar major-element compositions and Fe-Ti–oxide temperature ranges. All of the many batches of Early Rhyolite, which erupted episodically over an interval of ~125,000 years, yield the reduced fO2 values, indicating that reaction with graphite lowered magmatic fO2 after the caldera-forming eruption but before the first eruption of Early Rhyolite. It is inferred that reaction of postcaldera rhyolite magma with the reduced carbon in a great mass of subsided roof rocks lowered its fO2. It is suggested that comparable effects could have attended caldera collapse of other magma chambers hosted in continental sedimentary rocks.

Vertical Structural Variation and Their Development of the Sanukayama Rhyolite Lava in Kozushima Island, Japan

NASA Astrophysics Data System (ADS)

Furukawa, K.; Uno, K.; Kanamaru, T.; Nakai, K.

2017-12-01

We revealed structural development of the Pleistocene Sanukayama rhyolite lava of Kozushima Island, Japan. The good exposure, with about 130 m thick, provides valuable opportunity to understand the vertical structural variation. This exposure corresponds to the upper half of the lava. The paleomagnetic results show that the lava emplaced in subaerial condition at least in the exposed part. The vertical lithofacies are divided into the pumiceous (25-40 m thick), obsidian (40-60 m), spherulitic (30-50 m) layers from top to base. The pumiceous layer is characterized by massive foliated pumice. The foliation dips are gradually changed from gentle (10-30°) in lower part to steep (around 90°) in upper part. This shows the balloon-like morphology. The massive pumiceous layer would be generated from late stage diapiric inflation of the lava (Fink and Manley, 1987). The obsidian layer is composed of massive and welded-brecciated parts. The ductile-deformed light-colored veins, with a few mm thick, are frequently developed. In the microscopic observation, the veins are composed of broken crystals and obsidian clasts indicating fracturing of the lava followed by ductile deformation such as the RFH process (Tuffen et al., 2003). In this layer, extensive vesiculation and microlite development must have been prevented by higher load pressure and faster cooling, respectively. Consequently, they resulted in formation of the obsidian. The spherulitic layer is characterized by development of the ductile-deformed flow banding. The microscopic observation shows that the bands are formed by the spherulite trail. Furthermore, the microlites are aligned within the spherulites. In the heat-retained inner part of the lava, microlites would be developed around the healed fractures. The microlites acted as nucleation site of spherulite. In transition layer between obsidian and spherulitic layers (<10 m thick), the fragments of spherulitic rhyolite are entrained within the obsidian layer. This would be caused by high flow-induced shear arising from their rheological contrast. We showed the complicated structure of the Sanukayama rhyolite lava, especially for varied crystal occurrences. The variation is considered to be caused by specific phenomena of high-viscous magma such as sluggish atomic mobility and lava fracturing.

'Snake River (SR)-type' volcanism at the Yellowstone hotspot track: Distinctive products from unusual, high-temperature silicic super-eruptions

USGS Publications Warehouse

Branney, M.J.; Bonnichsen, B.; Andrews, G.D.M.; Ellis, B.; Barry, T.L.; McCurry, M.

2008-01-01

A new category of large-scale volcanism, here termed Snake River (SR)-type volcanism, is defined with reference to a distinctive volcanic facies association displayed by Miocene rocks in the central Snake River Plain area of southern Idaho and northern Nevada, USA. The facies association contrasts with those typical of silicic volcanism elsewhere and records unusual, voluminous and particularly environmentally devastating styles of eruption that remain poorly understood. It includes: (1) large-volume, lithic-poor rhyolitic ignimbrites with scarce pumice lapilli; (2) extensive, parallel-laminated, medium to coarse-grained ashfall deposits with large cuspate shards, crystals and a paucity of pumice lapilli; many are fused to black vitrophyre; (3) unusually extensive, large-volume rhyolite lavas; (4) unusually intense welding, rheomorphism, and widespread development of lava-like facies in the ignimbrites; (5) extensive, fines-rich ash deposits with abundant ash aggregates (pellets and accretionary lapilli); (6) the ashfall layers and ignimbrites contain abundant clasts of dense obsidian and vitrophyre; (7) a bimodal association between the rhyolitic rocks and numerous, coalescing low-profile basalt lava shields; and (8) widespread evidence of emplacement in lacustrine-alluvial environments, as revealed by intercalated lake sediments, ignimbrite peperites, rhyolitic and basaltic hyaloclastites, basalt pillow-lava deltas, rhyolitic and basaltic phreatomagmatic tuffs, alluvial sands and palaeosols. Many rhyolitic eruptions were high mass-flux, large volume and explosive (VEI 6-8), and involved H2O-poor, low-??18O, metaluminous rhyolite magmas with unusually low viscosities, partly due to high magmatic temperatures (900-1,050??C). SR-type volcanism contrasts with silicic volcanism at many other volcanic fields, where the fall deposits are typically Plinian with pumice lapilli, the ignimbrites are low to medium grade (non-welded to eutaxitic) with abundant pumice lapilli or fiamme, and the rhyolite extrusions are small volume silicic domes and coule??es. SR-type volcanism seems to have occurred at numerous times in Earth history, because elements of the facies association occur within some other volcanic fields, including Trans-Pecos Texas, Etendeka-Paran, Lebombo, the English Lake District, the Proterozoic Keewanawan volcanics of Minnesota and the Yardea Dacite of Australia. ?? Springer-Verlag 2007.

78 FR 24716 - Information Collection: Disposal of Mineral Materials

Federal Register 2010, 2011, 2012, 2013, 2014

2013-04-26

... petrified wood and common varieties of sand, stone, gravel, pumice, pumicite, cinders, clay, and other... validity of the methodology and assumptions used; (3) ways to enhance the quality, utility, and clarity of...

Vapor-rich Hydrothermal Fluid Migration Within Pumiceous Sediment in the Iheya North Knoll, Okinawa Trough

NASA Astrophysics Data System (ADS)

Ishibashi, J.; Suzuki, R.; Hamasaki, H.; Yamanaka, T.; Chiba, H.; Tsunogai, U.; Ijiri, A.; Nakagawa, S.; Nunoura, T.; Takai, K.; Kinoshita, M.; Ashi, J.

2007-12-01

The newly developed ROV NSS (Navigable Sampling System) enabled pin-point piston core sampling from the active hydrothermal field. In the Iheya North hydrothermal field in the mid-Okinawa Trough (27°47.5'N, 126°53.8'E, depth = 1000m), animal colonies are observed not only around the central mound structure (named as NBC) which discharges vigrously high temperature (T=311°C) clear fluid, but also as Calyptogena colony at 200m east from the NBC mound and as tube-worm colony at 250m southeast from the NBC mound. During Leg 3 of KY05-14 cruise (R/V Kaiyo of JAMSTEC) in Jan. 2005, fourn piston cores were successfully recovered with length from 65cm to 250cm. Surface sediments from the Calyptogena colony and the tube-worm colony were revealed as mainly composed of pumiceous sediment. Pore fluids from the Calyptogena Field showed unusual chemistry characterized as very low salinity (Cl=420mM), low Mg concentration, significantly lower Na/Cl ratio than seawater and high methane concentration, which suggests contribution of a vapor-rich hydrothermal component migrating within the pumice layer from the activity center. Moreover, decrease of SO4 accompanied by increase of alkalinity is notable even less than one meter depth below the seafloor. In situ sulfate reduction in the surface sediment caused by entrainment of the hydrothermal component would be a source of hydrogen sulfide that supports Calyptogena colony.

Magnesium isotopic behavior during the formation of chlorite-rich hydrothermal sediment in the middle Okinawa Trough

NASA Astrophysics Data System (ADS)

Shao, H.; Yang, S.; Teng, F. Z.; Cai, D.; Humphris, S. E.

2016-12-01

Chlorite is a common alteration product during water-rock reactions in seafloor hydrothermal systems. This chlorite is commonly characterized by high concentrations of magnesium. However, the source of the Mg and its behavior during hydrothermal alteration have yet to be clarified. Mg isotopes have been used in recent years to investigate a variety of geological processes, including low temperature weathering and metamorphism processes, and Mg cycling in sediments. In this study, we investigate the source of Mg and its behavior in chlorite-rich sediments collected during IODP Expedition 331 from the active hydrothermal Iheya North Knoll field in the middle Okinawa Trough — an intra-continental rift in continental crust. This area is characterized by hemipelagic muds with interbedded thick layers of felsic pumiceous volcanic material. Based on mineralogical, geochemical, and isotopic data, we have previously suggested that the chlorite-rich sediments resulted from hydrothermal alteration of the pumiceous layers at temperatures of 220-300°C. Prior to Mg isotope analysis, all selected samples were pretreated with 1N HCl in order to remove carbonates and other unstable minerals, and measurements were made on both the residues (mainly chlorite) and leachates, as well as on bulk samples. The residues are expected to show higher δ26Mg than the leachates reflecting the Mg isotopic signature of the pumiceous material precursor and provide insight into the behavior of Mg isotopes during the high-temperature hydrothermal processes.

Natural microbial populations in a water-based biowaste management system for space life support

NASA Astrophysics Data System (ADS)

Bornemann, Gerhild; Waßer, Kai; Tonat, Tim; Moeller, Ralf; Bohmeier, Maria; Hauslage, Jens

2015-11-01

The reutilization of wastewater is a key issue with regard to long-term space missions and planetary habitation. This study reports the design, test runs and microbiological analyses of a fixed bed biofiltration system which applies pumice grain (16-25 mm grain size, 90 m2 /m3 active surface) as matrix and calcium carbonate as buffer. For activation, the pumice was inoculated with garden soil known to contain a diverse community of microorganisms, thus enabling the filtration system to potentially degrade all kinds of organic matter. Current experiments over 194 days with diluted synthetic urine (7% and 20%) showed that the 7% filter units produced nitrate slowly but steadily (max. 2191 mg NO3-N/day). In the 20% units nitrate production was slower and less stable (max. 1411 mg NO3-N/day). 84% and 76% of the contained nitrogen was converted into nitrate. The low conversion rate is assumed to be due to the high flow rate, which keeps the biofilm on the pumice thin. At the same time the thin biofilm seems to prevent the activity of denitrifiers implicating the existence of a trade off between rate and the amount of nitrogen loss. Microbiological analyses identified a comparatively low number of species (26 in the filter material, 12 in the filtrate) indicating that urine serves as a strongly selective medium and filter units for the degradation of mixed feedstock have to be pre-conditioned on the intended substrates from the beginning.

Pyroclastic deposits as a guide for reconstructing the multi-stage evolution of the Somma-Vesuvius Caldera

NASA Astrophysics Data System (ADS)

Cioni, Raffaello; Santacroce, Roberto; Sbrana, Alessandro

The evolution of the Somma-Vesuvius caldera has been reconstructed based on geomorphic observations, detailed stratigraphic studies, and the distribution and facies variations of pyroclastic and epiclastic deposits produced by the past 20,000years of volcanic activity. The present caldera is a multicyclic, nested structure related to the emptying of large, shallow reservoirs during Plinian eruptions. The caldera cuts a stratovolcano whose original summit was at 1600-1900m elevation, approximately 500m north of the present crater. Four caldera-forming events have been recognized, each occurring during major Plinian eruptions (18,300 BP "Pomici di Base", 8000 BP "Mercato Pumice", 3400 BP "Avellino Pumice" and AD 79 "Pompeii Pumice"). The timing of each caldera collapse is defined by peculiar "collapse-marking" deposits, characterized by large amounts of lithic clasts from the outer margins of the magma chamber and its apophysis as well as from the shallow volcanic and sedimentary units. In proximal sites the deposits consist of coarse breccias resulting from emplacement of either dense pyroclastic flows (Pomici di Base and Pompeii eruptions) or fall layers (Avellino eruption). During each caldera collapse, the destabilization of the shallow magmatic system induced decompression of hydrothermal-magmatic and hydrothermal fluids hosted in the wall rocks. This process, and the magma-ground water interaction triggered by the fracturing of the thick Mesozoic carbonate basement hosting the aquifer system, strongly enhanced the explosivity of the eruptions.

Physical and mathematical modeling of transient infiltration through shallow layered pyroclastic deposits

NASA Astrophysics Data System (ADS)

Damiano, Emilia; Greco, Roberto; Guida, Andrea; Olivares, Lucio; Picarelli, Luciano

2017-04-01

Layered pyroclastic deposits covering steep slopes, characteristic of large mountainous areas of Campania (southern Italy), are often affected by shallow landslides triggered by heavy rainfall events. In fact, the equilibrium of such deposits is usually guaranteed by the contribution to soil shear strength offered by soil suction, which decreases during wetting. As the return period of the triggering events has been in many cases not extreme, other factors concur to establish triggering conditions. In this respect, heterogeneities, strongly affecting transient infiltration, may in some cases play a crucial role. In this study, the effect of the presence of soil layers, characterized by markedly different hydraulic properties, on the rainwater infiltration process is investigated. In fact, the pyroclastic covers of Campania, being the result of the deposition of materials originated by several eruptions of the nearby volcanic complexes, usually consist of alternating layers of ashes (silty sands) and pumices (gravel with sand). The presence of coarse-textured pumices between finer ashes strongly affects the infiltration process. In fact, the pumices, which are characterized by saturated hydraulic conductivity larger than ashes, are capable of retaining less water than ashes in unsaturated conditions, so that their unsaturated hydraulic conductivity is usually very small. Hence, depending on the water potential distribution throughout the cover at the onset of rainfall, pumices may act as a barrier to the propagation of the wet front (the so-called capillary barrier effect), or, approaching saturation, let the water pass through them very quickly. Such a complex behavior has been studied by means of a series of infiltration experiments carried out in an instrumented flume in the Geotechnical Laboratory of the University of Campania (http://www.dicdea.unina2.it/it/dipartimento/laboratori/laboratorio-di-geotecnica). Starting from different initial moisture conditions, small scale physical models of layered slopes, with various geometry and inclination, have been subjected to rainfalls of various intensities. During the infiltration processes and the following water redistribution phases, soil moisture and matric potential have been measured at various locations by means of TDR probes and tensiometers, respectively. The interpretation of the experimental results has been aided by a 2D mathematical model based on the integration of Richards' equation with the finite differences method. The obtained results indicate that a layer of dry pumices may induce lateral redistribution of water through the overlying ashes. In steep sloping deposits, this may favor the establishment of downslope directed subsurface runoff, which drains part of the infiltrating water towards the toe of the slope. In real slopes, depending on local morphology, such a downslope flow may have a beneficial effect on slope stability, as some water is drained out of the slope, or may even contribute to the establishment of triggering conditions, as it can result in flow concentration leading to local failure.

The unusual mineralogy of the Hayes River rhyolite, Hayes Volcano, Cook Inlet, Alaska

NASA Astrophysics Data System (ADS)

Hayden, L. A.; Coombs, M. L.; McHugh, K.

2013-12-01

Hayes Volcano is an ice-covered volcanic massif located in the northern Cook Inlet region approximately 135 miles northwest of Anchorage, Alaska. The last major eruptive episode of Hayes, and the only known in any detail, occurred ~3,700 yr B.P. and produced the Hayes Tephra Set H, a series of dacitic fall deposits widespread throughout southcentral Alaska (Riehle et al., 1994, Quat. Res. 33, p. 91-108). An undated, early Holocene pyroclastic-flow deposit exposed beneath Tephra Set H in the Hayes River valley is unusual in the Aleutian-Alaska subduction zone in whole-rock composition and mineralogy. The deposit comprises rhyolite pumice (~75 wt% SiO2) that contain phenocrysts of plagioclase, sanidine, quartz, and biotite in vesicular, clear matrix glass, and <1% dense, white cognate inclusions with the same whole-rock composition and phenocryst assemblage as the pumice, but a crystalline matrix. Holocrystalline inclusions may represent portions of the magma body that rapidly quenched in the shallow subsurface as dikes or chamber rinds and were then excavated during explosive eruption. Rhyolite and inclusions are peraluminous (2-3 % normative corundum), high-K, enriched in incompatible elements, and depleted in Sr and Eu. In accord with its evolved and enriched composition the rhyolite pumice and inclusions contain an abundance of accessory phases, including apatite, monazite, xenotime, and zircon. Monazite are euhedral, as large as 500 um, ThO2-rich (up to 4 wt%) and contain significant amounts of Ag (200-500 ppm). Xenotime are generally smaller than the monazite and occur frequently as small blebs. Rhyolite pumices also contain Fe-sulfides, Cu, Sn, Ni, and barite. Sanidine phenocrysts in the pumice and inclusions are sharply zoned and highly enriched in the celsian component (up to 5 wt% BaO) and also show LREE enrichment. Inclusions contain abundant Mn-rich cordierite (~3 wt% Mn2O3) in the san-plag-qtz matrix, as well as Fe-Ti oxides that are relatively high in Mn2O3 (>1 wt%) and REE-enriched. Zircon saturation temperatures (716° C) and two-feldspar thermometry (630-700° C for phenocryst rims; 660° C for inclusion matrix microphenocrysts) suggest a cool magma that must have been volatile-rich given its relatively low phenocryst content (~25 %). A lack of crustal xenocrysts, and Pb, Sr, and Nd isotopes similar to other Cook Inlet volcanoes (McHugh et al., 2012 Fall AGU, V31A-2760) suggest that the rhyolite is not a crustal melt, and we suggest that it formed by low degrees of melting or high degree of crystallization of mafic arc-related rocks. At Hayes, concentrations of REE and metals resulted from extreme fractionation process(es), which active over extended time period may lead to the formation of mineral deposits.

Late Holocene history of Chaitén Volcano: new evidence for a 17th century eruption

USGS Publications Warehouse

Lara, Luis E.; Moreno, Rodrigo; Amigo, Álvaro; Hoblitt, Richard P.; Pierson, Thomas C.

2013-01-01

Prior to May 2008, it was thought that the last eruption of Chaitén Volcano occurred more than 5,000 years ago, a rather long quiescent period for a volcano in such an active arc segment. However, increasingly more Holocene eruptions are being identified. This article presents both geological and historical evidence for late Holocene eruptive activity in the 17th century (AD 1625-1658), which included an explosive rhyolitic eruption that produced pumice ash fallout east of the volcano and caused channel aggradation in the Chaitén River. The extents of tephra fall and channel aggradation were similar to those of May 2008. Fine ash, pumice and obsidian fragments in the pre-2008 deposits are unequivocally derived from Chaitén Volcano. This finding has important implications for hazards assessment in the area and suggests the eruptive frequency and magnitude should be more thoroughly studied.

Ultrafine cementitious grout

DOEpatents

Ahrens, E.H.

1998-07-07

An ultrafine cementitious grout is described having a particle size 90% of which are less than 6 {micro}m in diameter and an average size of about 2.5 {micro}m or less, and preferably 90% of which are less than 5 {micro}m in diameter and an average size of about 2 {micro}m or less containing Portland cement, pumice as a pozzolanic material and superplasticizer in the amounts of about 40 wt. % to about 50 wt. % Portland cement; from about 50 wt. % to about 60 wt. % pumice containing at least 60% amorphous silicon dioxide; and from 0.1 wt. % to about 1.5 wt. % superplasticizer. The grout is mixed with water in the W/CM ratio of about 0.4--0.6/1. The grout has very high strength and very low permeability with good workability. The ultrafine particle sizes allow for sealing of microfractures below 10 {micro}m in width. 4 figs.

Ultrafine cementitious grout

DOEpatents

Ahrens, Ernst H.

1998-01-01

An ultrafine cementitious grout having a particle size 90% of which are less than 6 .mu.m in diameter and an average size of about 2.5 .mu.m or less, and preferably 90% of which are less than 5 .mu.m in diameter and an average size of about 2 .mu.m or less containing Portland cement, pumice as a pozzolanic material and superplasticizer in the amounts of about 40 wt. % to about 50 wt. % Portland cement; from about 50 wt. % to about 60 wt. % pumice containing at least 60% amorphous silicon dioxide; and from 0.1 wt. % to about 1.5 wt. % superplasticizer. The grout is mixed with water in the W/CM ratio of about 0.4-0.6/1. The grout has very high strength and very low permeability with good workability. The ultrafine particle sizes allow for sealing of microfractures below 10 .mu.m in width.

Experimental analysis of energy absorption behaviour of Al-tube filled with pumice lightweight concrete under axial loading condition

NASA Astrophysics Data System (ADS)

Rajak, D. K.; Deshpande, P. G.; Kumaraswamidhas, L. A.

2017-08-01

This Paper aimed at experimental investigation of compressive behaviour of square tube filled with pumice lightweight concrete (PLC). Square section of 20×20×30 mm is investigated, which is the backbone structure. The compression deformation result shows the better folding mechanism, displacement value, and energy absorption. PLC concrete filled with aluminium thin-wall tubes has been revealed superior energy absorption capacity (EAC) under low strain rate at room temperature. Superior EAC resulted as a result of mutual deformation benefit between aluminium section and PLC is also analysed. PLC was characterised by Fourier Transform Infrared (FTIR) and Field Emission Scanning Electron Microscopy (FESEM), and Energy Dispersive X-ray Spectrometry (EDX) analysis for better understanding of material behaviour. Individual and comparative load bearing graphs is logged for better prospective of analysing. Novel approach aimed at validation of porous lightweight concrete for better lightweight EA filler material.

Nitrogen availability in composted poultry litter using natural amendments.

PubMed

Turan, N Gamze

2009-02-01

Poultry litter compost is used as fertilizer on agricultural land because of its high nutrient content. A major limitation of land application of poultry litter compost is the loss of nitrogen via NH3 volatilization. The present work was conducted to monitor nitrogen availability during composting of poultry litter with natural zeolite, expanded perlite, pumice and expanded vermiculite. Poultry litter was composted for 100 days using five in-vessel composting simulators with a volumetric ratio of natural materials:poultry litter of 1:10. It was found that natural materials significantly reduced NH3 volatilization. At the end of the process, the control treatment without any natural materials had the lowest rate of total N: 72% of the initial total N was lost from the compost made with no amendment, while 53, 42, 26 and 16% of initial total N was lost from compost containing expandable perlite, expandable vermiculite, pumice and natural zeolite, respectively.

EFFECT OF DIFFERENT PROPHYLAXIS METHODS ON SOUND AND DEMINERALIZED ENAMEL

PubMed Central

Honório, Heitor Marques; Rios, Daniela; Abdo, Ruy César Camargo; Machado, Maria Aparecida de Andrade Moreira

2006-01-01

Considering the importance of professional plaque control for caries prevention, this study comprised an in vitro evaluation of wear by two prophylaxis methods (sodium bicarbonate jet – Profident and pumice and brush) on sound bovine enamel and with artificial carious lesions. Sixty enamel fragments were employed (4x4mm), which were divided into 4 groups: GI – 15 sound blocks treated with pumice and brush; GII – 15 sound blocks treated with Profident; GIII – 15 demineralized blocks treated with pumice and brush, and GIV – 15 demineralized blocks treated with Profident. In the fragments of Groups III and IV, artificial carious lesions were simulated by immersion in 0.05M acetic acid solution 50% saturated with bovine enamel powder at 37oC for 16h. The specimens were submitted to the prophylactic treatments for 10 seconds. Wear analysis was performed by profilometer and revealed the following results: 0.91μm – GI; 0.42μm – GII; 1.6μm – GIII, and 0.94μm – GIV. The two-way ANOVA and Tukey's test (p<0.05) revealed significant difference between all groups. Scanning electron microscopy images were employed to illustrate the wear pattern, with observation of larger alteration on the demineralized enamel surface (GIII; GIV), round-shaped wear on GI and GIII and blasted aspect on GII and GIV. The study indicated that the demineralized enamel presented more wear than the sound enamel, and the brush led to larger wear when compared to Profident. PMID:19089042

Early Pleistocene 40Ar/39Ar ages for Bapang Formation hominins, Central Jawa, Indonesia

PubMed Central

Larick, Roy; Ciochon, Russell L.; Zaim, Yahdi; Sudijono; Suminto; Rizal, Yan; Aziz, Fachroel; Reagan, Mark; Heizler, Matthew

2001-01-01

The Sangiran dome is the primary stratigraphic window for the Plio-Pleistocene deposits of the Solo basin of Central Jawa. The dome has yielded nearly 80 Homo erectus fossils, around 50 of which have known findspots. With a hornblende 40Ar/39Ar plateau age of 1.66 ± 0.04 mega-annum (Ma) reportedly associated with two fossils [Swisher, C.C., III, Curtis, G. H., Jacob, T., Getty, A. G., Suprijo, A. & Widiasmoro (1994) Science 263, 1118–1121), the dome offers evidence that early Homo dispersed to East Asia during the earliest Pleistocene. Unfortunately, the hornblende pumice was sampled at Jokotingkir Hill, a central locality with complex lithostratigraphic deformation and dubious specimen provenance. To address the antiquity of Sangiran H. erectus more systematically, we investigate the sedimentary framework and hornblende 40Ar/39Ar age for volcanic deposits in the southeast quadrant of the dome. In this sector, Bapang (Kabuh) sediments have their largest exposure, least deformation, and most complete tephrostratigraphy. At five locations, we identify a sequence of sedimentary cycles in which H. erectus fossils are associated with epiclastic pumice. From sampled pumice, eight hornblende separates produced 40Ar/39Ar plateau ages ranging from 1.51 ± 0.08 Ma at the Bapang/Sangiran Formation contact, to 1.02 ± 0.06 Ma, at a point above the hominin-bearing sequence. The chronological sequence of 40Ar/39Ar ages follows stratigraphic order across the southeast quadrant. An intermediate level yielding four nearly complete crania has an age of about 1.25 Ma. PMID:11309488

Early Pleistocene 40Ar/39Ar ages for Bapang Formation hominins, Central Jawa, Indonesia.

PubMed

Larick, R; Ciochon, R L; Zaim, Y; Sudijono; Suminto; Rizal, Y; Aziz, F; Reagan, M; Heizler, M

2001-04-24

The Sangiran dome is the primary stratigraphic window for the Plio-Pleistocene deposits of the Solo basin of Central Jawa. The dome has yielded nearly 80 Homo erectus fossils, around 50 of which have known findspots. With a hornblende (40)Ar/(39)Ar plateau age of 1.66 +/- 0.04 mega-annum (Ma) reportedly associated with two fossils [Swisher, C.C., III, Curtis, G. H., Jacob, T., Getty, A. G., Suprijo, A. & Widiasmoro (1994) Science 263, 1118-1121), the dome offers evidence that early Homo dispersed to East Asia during the earliest Pleistocene. Unfortunately, the hornblende pumice was sampled at Jokotingkir Hill, a central locality with complex lithostratigraphic deformation and dubious specimen provenance. To address the antiquity of Sangiran H. erectus more systematically, we investigate the sedimentary framework and hornblende (40)Ar/(39)Ar age for volcanic deposits in the southeast quadrant of the dome. In this sector, Bapang (Kabuh) sediments have their largest exposure, least deformation, and most complete tephrostratigraphy. At five locations, we identify a sequence of sedimentary cycles in which H. erectus fossils are associated with epiclastic pumice. From sampled pumice, eight hornblende separates produced (40)Ar/(39)Ar plateau ages ranging from 1.51 +/- 0.08 Ma at the Bapang/Sangiran Formation contact, to 1.02 +/- 0.06 Ma, at a point above the hominin-bearing sequence. The chronological sequence of (40)Ar/(39)Ar ages follows stratigraphic order across the southeast quadrant. An intermediate level yielding four nearly complete crania has an age of about 1.25 Ma.

The transition from explosive to effusive eruptive regime: The example of the 1912 Novarupta eruption, Alaska

USGS Publications Warehouse

Adams, N.K.; Houghton, Bruce F.; Fagents, S.A.; Hildreth, W.

2006-01-01

The shift from explosive to effusive silicic volcanism seen in many historical eruptions reflects a change in the style of degassing of erupted magma. This paper focuses on such a transition during the largest eruption of the twentieth century, the 1912 eruption of Novarupta. The transition is recorded in a dacite block bed, which covers an elliptical area of 4 km2 around the vent. Approximately 700 studied blocks fall into four main lithologic categories: (1) pumiceous, (2) dense, (3) flow-banded dacites, and (4) welded breccias. Textural analyses of the blocks indicate portions of the melt underwent highly variable degrees of outgassing. Vesicle populations show features characteristic of bubble coalescence and collapse. A decrease in measured vesicularity and increased evidence for bubble collapse compared with pumice from earlier Plinian episodes mark the transition from closed- to open-system degassing. Block morphology and textures strongly suggest the magma was first erupted as a relatively gas-rich lava dome/plug, but incomplete out-gassing led to explosive disruption. Heterogeneous degassing of ascending magma began in Plinian Episode III and resulted in instability during Episode IV dome growth and a (series of) Vulcanian explosion(s). Modeling of the dynamics of explosion initiation and ejecta dispersal indicates that a significant concentration in gas is required to produce the explosions responsible for the observed block field dispersal. The amount of gas available in the hot pumiceous dome material appears to have been inadequate to drive the explosion(s); therefore, external water most likely contributed to the destruction. ?? 2006 Geological Society of America.

Natural microbial populations in a water-based biowaste management system for space life support.

PubMed

Bornemann, Gerhild; Waßer, Kai; Tonat, Tim; Moeller, Ralf; Bohmeier, Maria; Hauslage, Jens

2015-11-01

The reutilization of wastewater is a key issue with regard to long-term space missions and planetary habitation. This study reports the design, test runs and microbiological analyses of a fixed bed biofiltration system which applies pumice grain (16-25 mm grain size, 90 m(2)/m(3) active surface) as matrix and calcium carbonate as buffer. For activation, the pumice was inoculated with garden soil known to contain a diverse community of microorganisms, thus enabling the filtration system to potentially degrade all kinds of organic matter. Current experiments over 194 days with diluted synthetic urine (7% and 20%) showed that the 7% filter units produced nitrate slowly but steadily (max. 2191 mg NO3-N/day). In the 20% units nitrate production was slower and less stable (max. 1411 mg NO3-N/day). 84% and 76% of the contained nitrogen was converted into nitrate. The low conversion rate is assumed to be due to the high flow rate, which keeps the biofilm on the pumice thin. At the same time the thin biofilm seems to prevent the activity of denitrifiers implicating the existence of a trade off between rate and the amount of nitrogen loss. Microbiological analyses identified a comparatively low number of species (26 in the filter material, 12 in the filtrate) indicating that urine serves as a strongly selective medium and filter units for the degradation of mixed feedstock have to be pre-conditioned on the intended substrates from the beginning. Copyright © 2015 The Committee on Space Research (COSPAR). Published by Elsevier Ltd. All rights reserved.

Crystal zoning in a large-volume ignimbrite: constraints on the thermal history of a supervolcano magma system

NASA Astrophysics Data System (ADS)

Matthews, N. E.; Pyle, D. M.; Wilson, C. J.

2009-12-01

Chemical zoning of crystals provides an important archive of information that allows for the reconstruction of complex thermal histories and changes in melt composition of the magma reservoir during crystallization. Here we investigate cathodoluminescence (CL) and Ti zonation in quartz crystals extracted from pumices from the Whakamaru and Rangitaiki ignimbrite units (part of the large-volume Whakamaru Group Ignimbrites), New Zealand, to reconstruct the thermal history of the parent magma chamber(s). CL intensity images are taken as a proxy for Ti content and temperature variation during crystal growth, and direct estimates of temperature are made using the TitaniQ geothermometer (Wark & Watson 2006 Cont. Min. Pet.) based on Ti concentration in quartz. These results are reviewed in comparison with temperatures from Fe-Ti oxide geothermometry. Quartz zoning is also compared to zonation in feldspars (using BSE imaging) from the same pumice clasts in order to establish the degree to which different crystal species record similar or contrasting magmatic histories. Quartz crystals in Whakamaru pumice display a variety of CL zoning patterns and resorption boundaries. Overgrowths typically appear to truncate CL growth zoning within the crystal core, indicating periods of resorption and subsequent re-growth - consistent with magma recharge causing a marked change in conditions (temperature and/or volatile saturation) and multi-stage crystallisation. Crystals typically display a dark (lower Ti) resorbed core, with an abrupt change to a CL-bright rim, although irregular textures and complex variations between crystals are observed. Core-to-rim profiles of Ti concentration in analysed quartz crystals show Ti variations within the range 50-225 ppm, corresponding to crystallisation temperatures of 733-935°C (assuming TiO2 activity in the melt of 0.6), with the lowest values recorded in the crystal core, increasing in a step-wise pattern towards the rim. These values are consistent with Fe-Ti oxide temperature data for the same pumice clasts which provide a temperature range of 660-933°C. It is inferred that the major steps in Ti content (and thus CL brightness) represent short-term temperature fluctuations due to magma chamber recharge and rejuvenation of a crystal mush, while rim temperatures are likely to record the magma temperature at the time of eruption.

Floating stones off El Hierro, Canary Islands: xenoliths of pre-island sedimentary origin in the early products of the October 2011 eruption

NASA Astrophysics Data System (ADS)

Troll, V. R.; Klügel, A.; Longpré, M.-A.; Burchardt, S.; Deegan, F. M.; Carracedo, J. C.; Wiesmaier, S.; Kueppers, U.; Dahren, B.; Blythe, L. S.; Hansteen, T. H.; Freda, C.; Budd, D. A.; Jolis, E. M.; Jonsson, E.; Meade, F. C.; Harris, C.; Berg, S. E.; Mancini, L.; Polacci, M.; Pedroza, K.

2012-03-01

A submarine eruption started off the south coast of El Hierro, Canary Islands, on 10 October 2011 and continues at the time of this writing (February 2012). In the first days of the event, peculiar eruption products were found floating on the sea surface, drifting for long distances from the eruption site. These specimens, which have in the meantime been termed "restingolites" (after the close-by village of La Restinga), appeared as black volcanic "bombs" that exhibit cores of white and porous pumice-like material. Since their brief appearance, the nature and origin of these "floating stones" has been vigorously debated among researchers, with important implications for the interpretation of the hazard potential of the ongoing eruption. The "restingolites" have been proposed to be either (i) juvenile high-silica magma (e.g. rhyolite), (ii) remelted magmatic material (trachyte), (iii) altered volcanic rock, or (iv) reheated hyaloclastites or zeolite from the submarine slopes of El Hierro. Here, we provide evidence that supports yet a different conclusion. We have analysed the textures and compositions of representative "restingolites" and compared the results to previous work on similar rocks found in the Canary Islands. Based on their high-silica content, the lack of igneous trace element signatures, the presence of remnant quartz crystals, jasper fragments and carbonate as well as wollastonite (derived from thermal overprint of carbonate) and their relatively high oxygen isotope values, we conclude that "restingolites" are in fact xenoliths from pre-island sedimentary layers that were picked up and heated by the ascending magma, causing them to partially melt and vesiculate. As they are closely resembling pumice in appearance, but are xenolithic in origin, we refer to these rocks as "xeno-pumice". The El Hierro xeno-pumices hence represent messengers from depth that help us to understand the interaction between ascending magma and crustal lithologies beneath the Canary Islands as well as in similar Atlantic islands that rest on sediment-covered ocean crust (e.g. Cape Verdes, Azores). The occurrence of "restingolites" indicates that crustal recycling is a relevant process in ocean islands, too, but does not herald the arrival of potentially explosive high-silica magma in the active plumbing system beneath El Hierro.

The Riscos Bayos Ignimbrites of the Caviahue-Copahue volcanic caldera complex, southern Andes, Argentina

NASA Astrophysics Data System (ADS)

Colvin, A.; Merrill, M.; Demoor, M.; Goss, A.; Varekamp, J. C.

2004-05-01

The Caviahue-Copahue volcanic complex (38 S, 70 W) is located on the eastern margin of the active arc in the southern Andes, Argentina. Volcán Copahue, an active stratovolcano which hosts an active hydrothermal system, sits on the southwestern rim of the elliptical Caviahue megacaldera (17 x 15 km). The caldera wall sequences are up to 0.6 km thick and consist of lavas with 51 -69 percent SiO2 and 0.2 - 5 percent MgO as well as breccias, dikes, sills, domes and minor ignimbrites. Andesitic lava flows also occur within the caldera, and are overlain by a chaotic complex of silicic lava and intracaldera pyroclastic flow deposits. The eastern wall sequence is capped by several extracaldera ignimbrites (Riscos Bayos formation) of about 50 m maximum thickness which extend 30 km east-southeast of the caldera. Young back-arc alkali basalt scoria cones occur east of the Caviahue-Copahue volcanic complex. The eruption of the Riscos Bayos formation at about 1.1 Ma (12 km cubed) may be related to the Caviahue caldera formation, though the Riscos Bayos account for only about 7 percent of the caldera volume. The Riscos Bayos consists of three lithic-bearing flow units: a grey basal flow, a tan middle flow and a bright-white, highly indurated uppermost flow. The basal unit consists of white and grey pumice fragments, black scoria clasts, black obsidian clasts (which give it the grey color), and accidental volcanic lithics set in a matrix of ash and crystals. The middle unit is composed of large mauve pumice fragments and accidental lithics set in a fine tan ash groundmass. The uppermost unit is composed of small pink and white pumice fragments set in a matrix of fine white ash. These pumices carry quartz and biotite crystals, whereas the lower two units are orthopyroxene-bearing trachy-dacites. The Caviahue-Copahue magmas all bear arc signatures, but possibly some magma mixing between the andesitic arc magmas and basaltic back-arc magmas may have occurred. The evolved top layer of the Riscos Bayos ignimbrite may be genetically unrelated to the other magmas, and is possibly a local crustal melt. Trace element and isotope data for the Caviahue-Copahue volcanoes suggest the presence of a subducted sediment component with minor continental crust assimilation.

New stratigraphic, chronologic, and magnetic fabric constraints for Neogene and Quaternary ignimbrites in the Central Andes (South Peru)

NASA Astrophysics Data System (ADS)

De La Rupelle, A.; Thouret, J. C.; Cubukcu, H. E.; Jicha, B.; Bréard, E.; Gerbe, M.-C.; Le Pennec, J.-L.; Diot, H.; Boivin, P.

2012-04-01

Central Andean deformation history in southern Peru is recorded in Neogene volcanic units of Ocoña and Cotahuasi canyons that cut across the western Cordillera. Acceleration (<25 Ma) of uplift in the region is reflected in the Neogene epiclastic deposits with interspersed and subsequent rhyolitic ignimbrites between 24.6 and 1.37 Ma. Large-volume (>100 km3) Nazca (c.24.6 Ma), Alpabamba (19.4-18.0 Ma), and Huaylillas (14.25-12.7 Ma) ignimbrite sheets preceded the canyon incision, whereas sheets of smaller volume (<50 km3), Caraveli (9.5-8.9 Ma), Lower (5.13-3.6 Ma) and Upper Sencca (c.2 Ma) and Las Lomas (c.1.56-1.37 Ma), were deposited during canyon incision and are interspersed with Lower and Upper Barroso lava flows. The Alpabamba compound ignimbrite sheets comprise a vitrophyre at the base, grading into a strongly welded, eutaxitic, crystal-rich facies overlain by a thick, multi-bedded ash-flow tuff and a lithic-rich, indurated flow unit. The Huaylillas ignimbrite sheet comprises a strongly welded, crystal-rich, lithic-poor, columnar lithofacies, with devitrified pumice. The Caraveli ignimbrite sheet has a jointed vitrophyre overlain by a welded, blocky, crystal-rich flow unit. A vacuolar, saccharolytic unit forms the top of the sequence. The Lower Sencca ignimbrite sheet comprises of a basal vitrophyre and a slightly welded, fibrous pumice-rich flow unit, which grades into a welded, vapor-phase unit that contains more crystals than pumice and lithics. The Upper Sencca ignimbrite sheet consists of a black vitrophyre, grading into a strongly welded, crystal-rich, eutaxitic cooling unit. The latter is capped by a slightly welded unit, and an indurated pumice-rich, crystal-poor vapour-phase facies. Quaternary valley-fill termed Las Lomas consists of unwelded, crystal-poor pumice-flow deposits. Eighteen new 40Ar/39Ar analyses have been carried out on feldspar/glass separates from pumice and lavas. Results for the Caraveli ignimbrite (9.35±0.06 Ma), Upper Barroso lavas (2.24±0.45 Ma) and Upper Sencca ignimbrite (2.00-2.06±0.09 Ma) are in good agreement with previous data. New ages for the Lower Barroso lavas (7.32±0.05; 5.36±0.12 Ma) and Lower Sencca ignimbrites (5.13±0.01, 5.09±0.03, 4.65±0.11, 4.36 ± 0.16) extend their temporal history towards older times. Lower Barroso lava flow activity occurred as early as~7.3 and lasted until 5.4 Ma just before the Lower Sencca eruptions. The Lower Sencca ignimbrites spanned at least 1.5 Ma and are larger and more widespread than the Upper Sencca ignimbrites, which may have formed in one pulse around 2 Ma. The Anisotropy of Magnetic Susceptibility (AMS) method and the magnetic fabric at 24 sites have been used to indicate flow directions and to infer the source location of the rhyolitic ignimbrites. Mean directions and confidence cones were calculated using Bingham statistics. Most AMS ellipsoids are oblate with near-vertical, slightly imbricated minimum susceptibility directions. The magnetic signal is dominantly carried by coarse multi-domain and a few fine single-domain grains of titanomagnetite. Inferred transport directions based on AMS results reveal that the source of Huaylillas, Lower Sencca and Upper Sencca units is probably located below the Nevado Coropuna volcano. The source of the Caraveli unit points to a depression W of Nevado Sara Sara. The Alpabamba source could not be clearly determined. Keywords: ignimbrites, Peru, stratigraphy, chronology, AMS, fabric, Neogene, Quaternary.

77 FR 25738 - Notice of Intent To Repatriate Cultural Items: Yale Peabody Museum of Natural History, New Haven, CT

Federal Register 2010, 2011, 2012, 2013, 2014

2012-05-01

...; two broken pumice stones marked with red ochre; six bone arrowheads; four broken stone pipes; sixteen dentalium and other shell beads; and thirteen small items including ochre, bone carving fragments, and bone...

36 CFR 228.41 - Scope.

Code of Federal Regulations, 2010 CFR

2010-07-01

... wood and common varieties of sand, gravel, stone, pumice, pumicite, cinders, clay, and other similar... materials. This category includes, but is not limited to, minerals such as sand, gravel, clay, crushed rock..., granules, sand, pebbles, scoria, cinders, cobbles, boulders, slabs, and other components in retaining walls...

Optimization and evaluation of a bottom substrate denitrification tank for nitrate removal from a recirculating aquaculture system.

PubMed

Pungrasmi, Wiboonluk; Playchoom, Cholticha; Powtongsook, Sorawit

2013-08-01

A bottom substrate denitrification tank for a recirculating aquaculture system was developed. The laboratory scale denitrification tank was an 8 L tank (0.04 m2 tank surface area), packed to a depth of 5 cm with a bottom substrate for natural denitrifying bacteria. An aquarium pump was used for gentle water mixing in the tank; the dissolved oxygen in the water was maintained in aerobic conditions (e.g. > 2 mg/L) while anoxic conditions predominated only at the bottom substrate layer. The results showed that, among the four substrates tested (soil, sand, pumice stone and vermiculite), pumice was the most preferable material. Comparing carbon supplementation using methanol and molasses, methanol was chosen as the carbon source because it provided a higher denitrification rate than molasses. When methanol was applied at the optimal COD:N ratio of 5:1, a nitrate removal rate of 4591 +/- 133 mg-N/m2 tank bottom area/day was achieved. Finally, nitrate removal using an 80 L denitrification tank was evaluated with a 610 L recirculating tilapia culture system. Nitrate treatment was performed by batch transferring high nitrate water from the nitrification tank into the denitrification tank and mixing with methanol at a COD:N ratio of 5:1. The results from five batches of nitrate treatment revealed that nitrate was successfully removed from water without the accumulation of nitrite and ammonia. The average nitrate removal efficiency was 85.17% and the average denitrification rate of the denitrification tank was 6311 +/- 945 mg-N/m2 tank bottom area/day or 126 +/- 18 mg-N/L of pumice packing volume/day.

The unsteady end to a powerful Plinian eruption: insights from a Vulcanian block apron from the 1912 eruption of Novarupta, Alaska

NASA Astrophysics Data System (ADS)

Isgett, S. J.; Houghton, B. F.; Burgisser, A.; Arbaret, L.

2016-12-01

Current models propose a static conduit architecture prior to Vulcanian eruptions where a dense, outgassed dome/plug overlies an orderly, texturally horizontally layered conduit. Blocks from a Vulcanian phase (Episode IV) during the 1912 eruption of Novarupta provide special insight to the state of the magma within a complex shallow conduit prior to fragmentation. Extreme conduit heterogeneity is seen in a diverse range of dacitic block types, including pumiceous, dense, flow-banded, and variably welded breccia clasts, all with a range of surface-breadcrusting. Diverse 2D and 3D textures suggest a variety of degassing states, with ranges of vesicle textures (e.g. bubble number, shape, and size) in each of the block types. The nonbreadcrusted pumice exhibit textures similar to preceding Plinian phases, reflecting bubble nucleation, growth, and coalescence followed by fragmentation. Breadcrusted rind and dense dacite textures are the result of bubble collapse with the dense dacites progressing furthest along the outgassing pathway. Residual water contents within the quenched glass are all less than 0.5 wt% and indicate that the melt came from the upper 100 m of the conduit. There is no correlation between water content and vesicularity. Overall, the evidence indicates 1) the mingling of variably degassed and outgassed melts in varying states of chemical disequilibrium over a narrow depth range close to the surface and 2) fragmentation was probably driven by the melt forming the non-breadcrusted pumices which we consider was probably newly arrived in the shallow conduit at the time of fragmentation. We therefore propose a revised, dynamic model applicable to Vulcanian explosions in the context of downscaling Plinian eruptions that involves vigorous mingling of melts that are all actively degassing and outgassing to varying degrees within the shallow conduit.

Roughness of human enamel surface submitted to different prophylaxis methods.

PubMed

Castanho, Gisela Muassab; Arana-Chavez, Victor E; Fava, Marcelo

2008-01-01

The purpose of this in vitro study was to evaluate alterations in the surface roughness and micromorphology of human enamel submitted to three prophylaxis methods. Sixty-nine caries-free molars with exposed labial surfaces were divided into three groups. Group I was treated with a rotary instrument set at a low speed, rubber cup and a mixture of water and pumice; group II with a rotary instrument set at a low speed, rubber cup and prophylaxis paste Herjos-F (Vigodent S/A Indústria e Comércio, Rio de Janeiro, Brazil); and group III with sodium bicarbonate spray Profi II Ceramic (Dabi Atlante Indústrias Médico Odontológicas Ltda, Ribeirão Preto, Brazil). All procedures were performed by the same operator for 10 s, and samples were rinsed and stored in distilled water Pre and post-treatment surface evaluation was completed using a surface profilometer (Perthometer S8P, Marh, Perthen, Germany) in 54 samples. In addition, the other samples were coated with gold and examined in a scanning electron microscope (SEM). The results of this study were statistically analyzed with the paired t-test (Student), the Kruskal-Wallis test and the Dunn (5%) test. The sodium bicarbonate spray led to significantly rougher surfaces than the pumice paste. The use of prophylaxis paste showed no statistically significant difference when compared with the other methods. Based on SEM analysis, the sodium bicarbonate spray presented an irregular surface with granular material and erosions. Based on this study, it can be concluded that there was an increased enamel surface roughness when teeth were treated with sodium bicarbonate spray when compared with teeth treated with pumice paste.

Mineral and chemical variations within an ash-flow sheet from Aso caldera, Southwestern Japan

USGS Publications Warehouse

Lipman, P.W.

1967-01-01

Although products of individual volcanic eruptions, especially voluminous ash-flow eruptions, have been considered among the best available samples of natural magmas, detailed petrographic and chemical study indicates that bulk compositions of unaltered Pleistocene ash-flow tuffs from Aso caldera, Japan, deviate significantly from original magmatic compositions. The last major ash-flow sheet from Aso caldera is as much as 150 meters thick and shows a general vertical compositional change from phenocryst-poor rhyodacite upward into phenocryst-rich trachyandesite; this change apparently reflects in inverse order a compositionally zoned magma chamber in which more silicic magma overlay more mafic magma. Details of these magmatic variations were obscured, however, by: (1) mixing of compositionally distinct batches of magma during upwelling in the vent, as indicated by layering and other heterogeneities within single pumice lumps; (2) mixing of particulate fragments-pumice lumps, ash, and phenocrysts-of varied compositions during emplacement, with the result that separate pumice lenses from a single small outcrop may have a compositional range nearly as great as the bulk-rook variation of the entire sheet; (3) density sorting of phenocrysts and ash during eruption and emplacement, resulting in systematic modal variations with distance from the caldera; (4) addition of xenocrysts, resulting in significant contamination and modification of proportions of crystals in the tuffs; and (5) ground-water leaching of glassy fractions during hydration after cooling. Similar complexities characterize ash-flow tuffs under study in southwestern Nevada and in the San Juan Mountains, Colorado, and probably are widespread in other ash-flow fields as well. Caution and careful planning are required in study of the magmatic chemistry and phenocryst mineralogy of these rocks. ?? 1967 Springer-Verlag.

Degassing of Cl, F, Li and Be during extrusion and crystallization of the rhyolite dome at Volcán Chaitén, Chile during 2008 and 2009

USGS Publications Warehouse

Lowenstern, Jacob B.; Bleick, Heather; Vazquez, Jorge A.; Castro, Jonathan M.; Larson, Peter B.

2012-01-01

We investigated the distribution of Cl, F, Li, and Be in pumices, obsidians, and crystallized dome rocks at Chaitén volcano in 2008–2009 in order to explore the behavior of these elements during explosive and effusive volcanic activity. Electron and ion microprobe analyses of matrix and inclusion glasses from pumice, obsidian, and microlite-rich dome rock indicate that Cl and other elements were lost primarily during crystallization of the rhyolitic dome after it had approached the surface. Glass in pumice and microlite-free obsidian has 888 ± 121 ppm Cl, whereas residual glass in evolved microlite-rich dome rock generally retains less Cl (as low as 0.7 Mt Cl, with a potential maximum of 1.8 Mt for the entire 0.8-km3 dome. Elemental variations reflect an integrated bulk distribution ratio for Cl > 1.7 (1.7 times more Cl was degassed or incorporated into crystals than remained in the melt). Because Cl is lost dominantly as the very last H2O is degassed, and Cl is minimally (if at all) partitioned into microlites, the integrated vapor/melt distribution ratio for Cl exceeds 200 (200 times more Cl in the evolved vapor than in the melt). Cl is likely lost as HCl, which is readily partitioned into magmatic vapor at low pressure. Cl loss is accelerated by the change in the composition of the residual melt due to microlite growth. Cl loss also may be affected by open-system gas fluxing. Integrated vapor-melt distribution ratios for Li, F, and Be all exceed 1,000. On degassing, an unknown fraction of these volatiles could be immediately dissolved in rainwater.

Effect of basaltic pumice aggregate addition on the material properties of fly ash based lightweight geopolymer concrete

NASA Astrophysics Data System (ADS)

Top, Soner; Vapur, Hüseyin

2018-07-01

In this study, fly ash (FA) based geopolymer (GP) concretes were produced by using a mixture of basaltic pumice (BP) aggregates and a fly ash (Class F) for lightweight concrete production. ANOVA Yates' test technique was applied to find out the effective curing parameters. BP aggregates were ground four different fractions of particle sizes as -12 + 4 mm, -4+0.425 mm, -0.425 + 0 mm and the one containing the size distribution of Turkish Standard 802. Also, effects of the curing time in the oven were investigated. The uniaxial compressive strength (UCS) (20-55 MPa), the point load strength (4-14 kN), the water absorption (1.05%-17%), the Mohs hardness (5.5-3) and the sonic speed values (4.12-2.72 km/sn) were measured. Stress-strain curves were graphed. The density of the concrete ranged from 1700 kg/m3 to 1792 kg/m3 which confirm the lightweight concretes.

The role of mycorrhizal fungi and microsites in primary succession on Mount St. Helens.

PubMed

Titus, J; Del Moral, R

1998-03-01

This study was designed to examine the role of vesicular-arbuscular mycorrhizae (VAM) and microsites on the growth of pioneer species. Flat, rill, near-rock, and dead lupine microsites were created in plots in barren areas of the Pumice Plain of Mount St. Helens. VAM propagules were added to the soil in half of the plots. Six pioneer species were planted into both VAM and non-VAM inoculated microsites. Plants in dead lupine microsites were greater in biomass than those in flat, rill, and near-rock microsites. Significant effects of VAM on plant biomass did not occur. Microsites continue to be important to plant colonization on the Pumice Plain, but VAM do not yet appear to play an important role. This may be due to limited nutrient availability and the facultatively mycotrophic nature of the colonizing plant species. It is unlikely that VAM play an important role in successional processes in newly emplaced nutrient-poor surfaces.

Inclusion of geopolymers derivate from fly ash and pumice in reinforced concrete

NASA Astrophysics Data System (ADS)

Montaño, A. M.; González, C. P.; Castro, D.; Gualdron, G.; Atencio, R.

2017-12-01

This paper presents results of a research project related to the development of alkali-activated geopolymers, synthesized from alumina-silicate minerals (fly ash and pumice) which are added to concrete. Alkali sources used in geopolymer synthesis were sodium hydroxide and sodium silicate solution. New materials were structurally characterized by Infra-Red spectroscopy (IR) and X-Ray Diffraction (XRD). Concretes obtained after geopolymers addition as Portland cement substitutes at 10%, 20% and 30%, were mechanically analysed by compression resistance at 7, 14, 28 and 90 drying days. Results were referred to standard (concrete of Portland cement) allows to know cementitious characteristics of geopolymers are lower than those for standard, but it keeps growing at longer drying time than Portland cement. By Electrochemical Impedance Spectroscopy (EIS) it is found that this new material shows high electrical resistance and have been proved as a protection agent against corrosion in reinforced concrete exhibiting anticorrosive properties higher than those showed by the conventional concrete mixture.

A basalt trigger for the 1991 eruptions of Pinatubo volcano?

USGS Publications Warehouse

Pallister, J.S.; Hoblitt, R.P.; Reyes, A.G.

1992-01-01

THE eruptive products of calc-alkaline volcanos often show evidence for the mixing of basaltic and acid magmas before eruption (see, for example, refs 1, 2). These observations have led to the suggestion3 that the injection of basaltic magma into the base of a magma chamber (or the catastrophic overturn of a stably stratified chamber containing basaltic magma at its base) might trigger an eruption. Here we report evidence for the mixing of basaltic and dacitic magmas shortly before the paroxysmal eruptions of Pinatubo volcano on 15 June 1991. Andesitic scoriae erupted on 12 June contain minerals and glass with disequilibrium compositions, and are considerably more mafic than the dacitic pumices erupted on 15 June. Differences in crystal abundance and glass composition among the pumices may arise from pre-heating of the dacite magma by the underlying basaltic liquid before mixing. Degassing of this basaltic magma may also have contributed to the climatologically important sulphur dioxide emissions that accompanied the Pinatubo eruptions.

Catastrophic debris avalanche deposit of Socompa volcano, northern Chile

NASA Technical Reports Server (NTRS)

Francis, P. W.; Gardeweg, M.; Ramirez, C. F.; Rothery, D. A.

1985-01-01

Between 10,000 and 500 yr ago the Socompa volcano in northern Chile experienced a catastrophic collapse of a 70 deg sector of the original cone, causing a debris avalanche that descended nearly 3000 m vertically and traveled more than 35 km from the volcano. The deposits cover some 490 sq km and have a minimum volume of 15 cu km. Parts of the original cone slumped in a nearly coherent form and are now preserved as large blocks more than 400 m high. The primary avalanche traveled northwestward over sloping ground before coming to rest transiently, forming a prominent marginal ridge, and then slid away northeastward to form a secondary flow, overriding much of the primary avalanche deposit. Abundant, prismatic, jointed dacite blocks within the debris avalanche deposit and a thin, fine-grained pumiceous deposit beneath it suggest that the collapse was triggered by magmatic activity and may have been accompanied by a violent lateral blast. Collapse was followed by eruption of pumiceous pyroclastic flows and extrusion of voluminous dacite domes.

Correlation of ash-flow tuffs.

USGS Publications Warehouse

Hildreth, W.; Mahood, G.

1985-01-01

Discrimination and correlation of ash-flow sheets is important in structurally complex, long-lived volcanic fields where such sheets provide the best keys to the regional stratigraphic framework. Three-dimensional complexities resulting from pulsatory eruptions, sectorial emplacement, mechanical sorting during outflow, thermal and compositional zoning of magmas, the physical zoning of cooling units, and structural and erosional disruption can make such correlation and discrimination difficult. When lithologic, magnetic, petrographic, chemical, and isotopic criteria for correlating ash-flow sheets are critically evaluated, many problems and pitfalls can be identified. Distinctive phenocrysts, pumice clasts, and lithic fragments are among the more reliable criteria, as are high-precision K-Ar ages and thermal remanent magnetization (TRM) directions in unaltered welded tuff. Chemical correlation methods should rely principally upon welded or nonwelded pumice blocks, not upon the ash-flow matrix, which is subject to fractionation, mixing, and contamination during emplacement. Compositional zoning of most large sheets requires that many samples be analyzed before phenocryst, glass or whole-rock chemical trends can be used confidently as correlation criteria.-Authors

46 CFR 164.009-3 - Noncombustible materials not requiring specific approval.

Code of Federal Regulations, 2010 CFR

2010-10-01

... subpart: (a) Sheet glass, block glass, clay, ceramics, and uncoated fibers. (b) All metals, except... only sand, gravel, expanded vermiculite, expanded or vesicular slags, diatomaceous silica, perlite, or pumice. (d) Woven, knitted or needle punched glass fabric containing no additives other than lubricants...

Late Holocene stratigraphy of the Tetimpa archaeological sites, northeast flank of Popocatepetl volcano, central Mexico

USGS Publications Warehouse

Panfil, M.S.; Gardner, T.W.; Hirth, K.G.

1999-01-01

Late Holocene (240 km2 on the east side of the volcano with >25 cm of tephra. Lavas from eruptive sequence I dammed drainage in the lowland area near the town of San Nicolas and caused local upstream deposition of as much as 30 m of lacustrine silts, clays, and sands. These lacustrine deposits record an eruptive hiatus for the Tetimpa area of about 750 14C yr: between ca. 2100 and ca. 1350 yr B.P., no major tephras were deposited in the Tetimpa area. In upland areas, this time period is represented by an unconformity and by Entisols formed in the top of pumice deposits and lavas from eruptive sequence I. Artifacts, agricultural furrows, and dwellings record human reoccupation of this surface. At the end of this hiatus, several lahars were deposited above the lacustrine sequence and locally above the Entisol in upland positions adjacent to streams. Between ca. 1350 and ca. 1200 yr B.P., tephras from eruptive sequence II buried these paleosols, occupation sites, lacustrine sediments, and lahars. Andesitic (~62% SiO2) pumice lapilli deposits in the Tetimpa area record three pumice-fall eruptions directed northeast and east of the crater. The first and smallest of these (maximum Tetimpa area thickness = 12 cm; >52 km2 covered by >25 cm) took place at ca. 1350 yr B.P. and was accompanied by pyroclastic surge events preserved in the Tetimpa area by charcoal, sand waves, and cross-stratified sand-sized tephra. At ca. 1200 yr B.P., the products of two Plinian-style events and additional pyroclastic surges reached the Tetimpa area. The largest of these tephra-fall events covered the Tetimpa area with 0.5-1 m of tephra and blanketed an area of >230 km2 with a thickness of >25 cm. The Tetimpa record confirms two of the four periods of explosive volcanism recognized by studies conducted around Popocatepetl in the past 30 yr. Eruptive sequence I corresponds to the explosive period between 2100 and 2500 yr B.P., and eruptive sequence II corresponds to the period between 900 and 1400 yr B.P. The archaeology and lacustrine stratigraphy of the Tetimpa area help constrain the timing of the Plinian phase of eruptive sequence I to ca. 2100 yr B.P. and suggest that the pumice-fall eruptions of eruptive sequence II took place in at least two intervals between ca. 1350 and ca. 1200 yr B.P.

Pyroclast textural variation as an indicator of eruption column steadiness in andesitic Plinian eruptions at Mt. Ruapehu

USGS Publications Warehouse

Pardo, Natalia; Cronin, Shane J.; Wright, Heather M.N.; Schipper, C. Ian; Smith, Ian; Stewart, Bob

2014-01-01

Between 27 and 11 cal. ka BP, a transition is observed in Plinian eruptions at Mt. Ruapehu, indicating evolution from non-collapsing (steady and oscillatory) eruption columns to partially collapsing columns (both wet and dry). To determine the causes of these variations over this eruptive interval, we examined lapilli fall deposits from four eruptions representing the climactic phases of each column type. All eruptions involve andesite to basaltic andesite magmas containing plagioclase, clinopyroxene, orthopyroxene and magnetite phenocrysts. Differences occur in the dominant pumice texture, the degree of bulk chemistry and textural variability, the average microcrystallinity and the composition of groundmass glass. In order to investigate the role of ascent and degassing processes on column stability, vesicle textures were quantified by gas volume pycnometry (porosity), X-ray synchrotron and computed microtomography (μ-CT) imagery from representative clasts from each eruption. These data were linked to groundmass crystallinity and glass geochemistry. Pumice textures were classified into six types (foamy, sheared, fibrous, microvesicular, microsheared and dense) according to the vesicle content, size and shape and microlite content. Bulk porosities vary from 19 to 95 % among all textural types. Melt-referenced vesicle number density ranges between 1.8 × 102 and 8.9 × 102 mm−3, except in fibrous textures, where it spans from 0.3 × 102 to 53 × 102 mm−3. Vesicle-free magnetite number density varies within an order of magnitude from 0.4 × 102 to 4.5 × 102 mm−3 in samples with dacitic groundmass glass and between 0.0 and 2.3 × 102 mm−3 in samples with rhyolitic groundmass. The data indicate that columns that collapsed to produce pyroclastic flows contained pumice with the greatest variation in bulk composition (which overlaps with but extends to slightly more silicic compositions than other eruptive products); textures indicating heterogeneous bubble nucleation, progressively more complex growth history and shear-localization; and the highest degrees of microlite crystallization, most evolved melt compositions and lowest relative temperatures. These findings suggest that collapsing columns in Ruapehu have been produced when strain localization is prominent, early bubble nucleation occurs and variation in decompression rate across the conduit is greatest. This study shows that examination of pumice from steady phases that precede column collapse may be used to predict subsequent column behaviour.

ETR ELECTRICAL BUILDING, TRA648. EMERGENCY STANDBY GENERATOR AND DIESEL UNIT. ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

ETR ELECTRICAL BUILDING, TRA-648. EMERGENCY STANDBY GENERATOR AND DIESEL UNIT. METAL ROOF AND PUMICE BLOCK WALLS. CAMERA FACING SOUTHWEST. INL NEGATIVE NO. 56-3708. R.G. Larsen, Photographer, 11/13/1956 - Idaho National Engineering Laboratory, Test Reactor Area, Materials & Engineering Test Reactors, Scoville, Butte County, ID

49 CFR 1039.11 - Miscellaneous commodities exemptions.

Code of Federal Regulations, 2010 CFR

2010-10-01

..., etc. 26 214 Wrapping paper, wrappers or coarse paper. 26 218 Sanitary tissue stock. 26 471 Sanitary... 30 111 Rubber pneumatic tires or parts. 31 ......do Leather or leather products. 32 ......do Clay... 32 952 15 Cinders, clay, shale expanded shale), slate or volcanic (not pumice stone), or haydrite. 33...

43 CFR 3832.21 - How do I locate a lode or placer mining claim?

Code of Federal Regulations, 2013 CFR

2013-10-01

... bearing gold or valuable detrital minerals; (ii) Hosted in soils, alluvium (deposited by water), eluvium...) Bedded gypsum, limestone, cinders, pumice, and similar mineral deposits; or (iv) Mineral-bearing brine...) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) LOCATING MINING CLAIMS...

43 CFR 3832.21 - How do I locate a lode or placer mining claim?

Code of Federal Regulations, 2014 CFR

2014-10-01

... bearing gold or valuable detrital minerals; (ii) Hosted in soils, alluvium (deposited by water), eluvium...) Bedded gypsum, limestone, cinders, pumice, and similar mineral deposits; or (iv) Mineral-bearing brine...) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) LOCATING MINING CLAIMS...

43 CFR 3832.21 - How do I locate a lode or placer mining claim?

Code of Federal Regulations, 2011 CFR

2011-10-01

... bearing gold or valuable detrital minerals; (ii) Hosted in soils, alluvium (deposited by water), eluvium...) Bedded gypsum, limestone, cinders, pumice, and similar mineral deposits; or (iv) Mineral-bearing brine...) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) LOCATING MINING CLAIMS...

43 CFR 3832.21 - How do I locate a lode or placer mining claim?

Code of Federal Regulations, 2012 CFR

2012-10-01

... bearing gold or valuable detrital minerals; (ii) Hosted in soils, alluvium (deposited by water), eluvium...) Bedded gypsum, limestone, cinders, pumice, and similar mineral deposits; or (iv) Mineral-bearing brine...) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) LOCATING MINING CLAIMS...

Geology of the region of Guadalajara, Mexico, and its relationships with processes of subsidence

NASA Astrophysics Data System (ADS)

Suarez-Plascencia, C.; Delgado-Argote, L. A.; Nuñez-Cornu, F. J.; Sanchez, J. J.

2008-12-01

The city of Guadalajara, Mexico, began an accelerated urban growth in early 1950. During a span of 25 years a large number of gullies were artificially filled, with the aim of incorporating new areas for urbanization, particularly in the areas north and west of the city. These gullies originally formed a complex dendritic-type system, whose evolution may be associated with faults or fracture zones whose current identification are only possible based on escarpments along the Canyon of the Rio Grande de Santiago (CRGS), north of Guadalajara. Reports of affectations documented in the 80's described subsidence in buildings and infrastructure, a process that has been continued during 2008. We present the results of work done in the CRGS, which is a tectonic erosive-depression with an average depth of 500 m and exhibits a sequence of volcanic and sedimentary deposits with rapid lateral facies changes. The stratigraphic column spans a 15 km-long section along the Matatlán-Arcediano road, and, from top to bottom contains: 1) Unconsolidated pumice and tuffs with an average thickness of 12 m; 2) basaltic lavas with average thickness of 60 m; 3) the San Gaspar ignimbrite; 4) fluvial- sedimentary deposits with a thickness of approximately 20 meters that include both sub-rounded and angular volcanic clasts, with sizes up to 0.15 m; 5) a thick sequence of ignimbrites and dacitic lavas. At a depth of 1200 m.a.s.l. in the town of Arcediano, the basal sequence is composed of dacites and andesites with interbedded pumice-rich ignimbrites with 10-20 m thickness. The Rio Grande de Santiago talweg to 1018 m.a.s.l. (apparently the base of the sequence) is formed by andesite lava. In the area of San Gaspar we identified oblique-normal left-lateral faults in lavas, with a strike 191° and a dip 89°. In the Colimilla dam, 1297 m.a.s.l., we observed normal faulting (strike 267° and dip 81°), with 20-30 m jumps with reference to a unit of tephra of 3-10 m thickness. The lavas in this site present deformation, the main shear being parallel to the Rio Verde. At the site of the San Gaspar river the faults have a strike of 285° and a dip of 83v and affect ignimbrites that overlie dacitic lavas. In the area of the Arcediano bridge the normal faulting has a strike 188v and dip of 75° in andesites, and in the pumice-rich ignimbrites a shear direction with strike of 92° and dip of 84° that is parallel to the Rio Verde. During the past two years we identified approximately 1100 cases of sinking with varying magnitude in the urban area of Guadalajara. Some of these can be grouped to form alignments that are oriented with the faults identified in the CRGS region. The process of subsidence can be controlled by structures that affect the pumice sequence laying under the city of Guadalajara, facilitating the movement of groundwater through areas of weakness, removing tuffs and pumice and creating voids that later collapse, affecting buildings and infrastructure in the city.

Compositional zoning of the bishop tuff

USGS Publications Warehouse

Hildreth, W.; Wilson, C.J.N.

2007-01-01

Compositional data for >400 pumice clasts, organized according to eruptive sequence, crystal content, and texture, provide new perspectives on eruption and pre-eruptive evolution of the >4600 km3 of zoned rhyolitic magma ejected as the BishopTuff during formation of Long Valley caldera. Proportions and compositions of different pumice types are given for each ignimbrite package and for the intercalated plinian pumice-fall layers that erupted synchronously. Although withdrawal of the zoned magma was less systematic than previously realized, the overall sequence displays trends toward greater proportions of less evolved pumice, more crystals (0-5 24 wt %), and higher FeTi-oxide temperatures (714-818??C). No significant hiatus took place during the 6 day eruption of the BishopTuff, nearly all of which issued from an integrated, zoned, unitary reservoir. Shortly before eruption, however, the zoned melt-dominant portion of the chamber was invaded by batches of disparate lower-silica rhyolite magma, poorer in crystals than most of the resident magma but slightly hotter and richer in Ba, Sr, andTi. Interaction with resident magma at the deepest levels tapped promoted growth ofTi-rich rims on quartz, Ba-rich rims on sanidine, and entrapment of near-rim melt inclusions relatively enriched in Ba and CO2.Varied amounts of mingling, even in higher parts of the chamber, led to the dark gray and swirly crystal-poor pumices sparsely present in all ashflow packages. As shown by FeTi-oxide geothermometry, the zoned rhyolitic chamber was hottest where crystal-richest, rendering any model of solidification fronts at the walls or roof unlikely.The main compositional gradient (75-195 ppm Rb; 0.8-2.2 ppm Ta; 71-154 ppm Zr; 0.40-1.73% FeO*) existed in the melt, prior to crystallization of the phenocryst suite observed, which included zircon as much as 100 kyr older than the eruption.The compositions of crystals, though themselves largely unzoned, generally reflect magma temperature and the bulk compositional gradient, implying both that few crystals settled or were transported far and that the observed crystals contributed little to establishing that gradient. Upward increases in aqueous gas and dissolved water, combined with the adiabatic gradient (for the 5 km depth range tapped) and the roofward decline in liquidus temperature of the zoned melt, prevented significant crystallization against the roof, consistent with dominance of crystal-poor magma early in the eruption and lack of any roof-rind fragments among the Bishop ejecta, before or after onset of caldera collapse. A model of secular incremental zoning is advanced wherein numerous batches of crystal-poor melt were released from a mush zone (many kilometers thick) that floored the accumulating rhyolitic melt-rich body. Each batch rose to its own appropriate level in the melt-buoyancy gradient, which was selfsustaining against wholesale convective re-homogenization, while the thick mush zone below buffered it against disruption by the deeper (non-rhyolitic) recharge that augmented the mush zone and thermally sustained the whole magma chamber. Crystal-melt fractionation was the dominant zoning process, but it took place not principally in the shallow melt-rich body but mostly in the pluton-scale mush zone before and during batchwise melt extraction. ?? Published by Oxford University Press (2007).

Momentum Enhancement from Hypervelocity Crater Ejecta: Implications for the AIDA Target

NASA Astrophysics Data System (ADS)

Flynn, G. J.; Durda, D. D.; Patmore, E. B.; Jack, S. J.; Molesky, M. J.; Strait, M. M.; Macke, R. M.

2017-09-01

We performed hypervelocity impact cratering of porous meteorites and terrestrial pumice and found higher values of the momentum enhancement factor due to ejecta than found in hydrocode modeling. This has important implications for kinetic impact deflection of small, hazardous asteroids and on the Asteroid Impact and Deflection Assessment mossion.

Should ponderosa pine be planted on lodgepole pine sites?

Treesearch

P.H. Cochran

1984-01-01

Repeated radiation frosts caused no apparent harm to the majority of lodgepole pine (Pinus contorta Dougl.) seedlings planted on a pumice flat in south-central Oregon. For most but not all of the ponderosa pine (Pinus ponderosa Dougl.) seedlings planted with the lodgepole pine, however, damage from radiation frost resulted in...

Water Use and Growth of Two Woody Taxa Produced in Varying Indigenous Douglas-Fir Based Soilless Substrates

USDA-ARS?s Scientific Manuscript database

In the Pacific Northwest (PNW) container crops are grown in soilless substrates that contain different percentages of Douglas-fir bark (DFB), sphagnum peat moss and pumice. Previous research conducted by Gabriel et al. found varying combinations and ratios of these components result in differing phy...

Distribution of biomass and nutrients in lodgepole pine/bitterbrush ecosystems in central Oregon.

Treesearch

Susan N. Little; Laurl J. Shainsky

1992-01-01

We investigated the distribution of biomass and nutrients in lodgepole pine (Pinus contorta var. murryana Dougl.) ecosystems on pumice soils in south-central Oregon. Sixty-three trees were sampled to develop equations for estimating dry weights of tree crowns, boles, bark, and coarse roots from diameter at breast height and...

Hepatotoxic microcystin removal using pumice embedded monolithic composite cryogel as an alternative water treatment method.

PubMed

Gurbuz, Fatma; Ceylan, Şeyda; Odabaşı, Mehmet; Codd, Geoffrey A

2016-03-01

Microcystins are the most commonly encountered water-borne cyanotoxins which present short- and long-term risks to human health. Guidelines at international and national level, and legislation in some countries, have been introduced for the effective health risk management of these potent hepatotoxic, tumour-promoters. The stable cyclic structure of microcystins and their common production by cyanobacteria in waterbodies at times of high total dissolved organic carbon content presents challenges to drinking water treatment facilities, with conventional, advanced and novel strategies under evaluation. Here, we have studied the removal of microcystins using three different forms of pumice particles (PPs), which are embedded into macroporous cryogel columns. Macroporous composite cryogel columns (MCCs) are a new generation of separation media designed to face this challenging task. Three different MCCs were prepared by adding plain PPs, Cu(2+)-attached PPs and Fe(3+)-attached PPs to reaction media before the cryogelation step. Column studies showed that MCCs could be successfully used as an alternative water treatment method for successful microcystin removal. Copyright © 2016 Elsevier Ltd. All rights reserved.

Surface morphology of caldera-forming eruption deposits revealed by lidar mapping of Crater Lake National Park, Oregon- Implications for emplacement and surface modification

USGS Publications Warehouse

Robinson, Joel E.; Bacon, Charles R.; Major, Jon J.; Wright, Heather M.; Vallance, James W.

2017-01-01

Large explosive eruptions of silicic magma can produce widespread pumice fall, extensive ignimbrite sheets, and collapse calderas. The surfaces of voluminous ignimbrites are rarely preserved or documented because most terrestrial examples are heavily vegetated, or severely modified by post-depositional processes. Much research addresses the internal sedimentary characteristics, flow processes, and depositional mechanisms of ignimbrites, however, surface features of ignimbrites are less well documented and understood, except for comparatively small-volume deposits of historical eruptions. The ~7,700 calendar year B.P. climactic eruption of Mount Mazama, USA vented ~50 km3 of magma, deposited first as rhyodacite pumice fall and then as a zoned rhyodacite-to-andesite ignimbrite as Crater Lake caldera collapsed. Lidar collected during summer 2010 reveals the remarkably well-preserved surface of the Mazama ignimbrite and related deposits surrounding Crater Lake caldera in unprecedented detail despite forest cover. The ±1 m lateral and ±4 cm vertical resolution lidar allows surface morphologies to be classified. Surface morphologies are created by internal depositional processes and can point to the processes at work when pyroclastic flows come to rest. We describe nine surface features including furrow-ridge sets and wedge-shaped mounds in pumice fall eroded by high-energy pyroclastic surges, flow- parallel ridges that record the passage of multiple pyroclastic flows, perched benches of marginal deposits stranded by more-mobile pyroclastic-flow cores, hummocks of dense clasts interpreted as lag deposit, transverse ridges that mark the compression and imbrication of flows as they came to rest, scarps indicating ignimbrite remobilization, fields of pit craters caused by phreatic explosions, fractures and cracks caused by extensional processes resulting from ignimbrite volume loss, and stream channels eroded in the newly formed surface. The nine morphologies presented here illustrate a dynamic depositional environment that varied spatially and with time during the eruption, and show that multiple processes modified the ignimbrite after deposition, both during and after the eruption.

Stratigraphy of Pyroclastic Deposits of EL Aguajito Caldera, Baja California Sur, MÉXICO

NASA Astrophysics Data System (ADS)

Osorio Ocampo, L. S.; Macias, J. L.; García Sánchez, L.; Pola, A.; Saucedo, R.; Sánchez, J. M.; Avellán, D. R.; Cardona, S.; Reyes-Agustín, G.; Arce, J. L.

2015-12-01

El Aguajito caldera is located in the State of Baja California Sur, it comprises an area of 450 km2 and sits within the Santa Rosalía Basin which is controlled by NE-SW extensional structures and the NW-SE Cimarron Fault that transects the caldera structure. The oldest rocks are ~90 Ma granodiorites covered by an Oligocene-Miocene volcano-sedimentary sequence, the Miocene Santa Lucia Formation and La Esperanza basalt. Pliocene volcanism is represented by La Reforma caldera, El Aguajito caldera, and the Tres Vírgenes Volcanic complex. This study focuses on the cartography and stratigraphy of area in order to understand the evolution of the volcanic system. The stratigraphy from base to top consists of a series of shallow marine sediments (fossiliferous sandstones) covered by a thick sequence of ignimbrites and pyroclastic flows interbedded with volcaniclastic deposits (Gloria and El Infierno Formations). On top of these deposits is El Aguajito caldera, it consists of a 2 m thick pumice fallout followed by an ignimbrite with three transitional lithofacies: a ≤30-m thick light-pink pyroclastic flow enriched in pumice at the base that gradually becomes enrich in lithics towards the top with the occurrence of degasing pipes. On top rests a 15 m-thick light-purple ignimbrite slightly welded with fiammes and a sequence of pumiceous pyroclastic flows and fallouts. These deposits have been associate to the caldera formation with a collapse diameter of ~8 km marked by rhyolitic domes exposed along a ring collapse crowned the sequence as well as NW-SE aligned rhyolitic domes parallel to the seashore. This cartography allowed to present a preliminary new geological map with four stratigraphic units recognized so far, that were emplaced under subaerial conditions beginning with a Plinian column followed by the emplacement of El Aguajito ignimbrite with its subsequent caldera collapse and finally the extrusion of resurgent domes.

Surface morphology of caldera-forming eruption deposits revealed by lidar mapping of Crater Lake National Park, Oregon - Implications for deposition and surface modification

NASA Astrophysics Data System (ADS)

Robinson, Joel E.; Bacon, Charles R.; Major, Jon J.; Wright, Heather M.; Vallance, James W.

2017-08-01

Large explosive eruptions of silicic magma can produce widespread pumice fall, extensive ignimbrite sheets, and collapse calderas. The surfaces of voluminous ignimbrites are rarely preserved or documented because most terrestrial examples are heavily vegetated, or severely modified by post-depositional processes. Much research addresses the internal sedimentary characteristics, flow processes, and depositional mechanisms of ignimbrites, however, surface features of ignimbrites are less well documented and understood, except for comparatively small-volume deposits of historical eruptions. The 7700 calendar year B.P. climactic eruption of Mount Manama, USA, vented 50 km3 of magma, deposited first as rhyodacite pumice fall and then as a zoned rhyodacite-to-andesite ignimbrite as Crater Lake caldera collapsed. Lidar collected during summer 2010 reveals the remarkably well-preserved surface of the Manama ignimbrite and related deposits surrounding Crater Lake caldera in unprecedented detail despite forest cover. The ± 1 m lateral and ± 4 cm vertical resolution lidar allows surface morphologies to be classified. Surface morphologies are created by internal depositional processes and can point to the processes at work when pyroclastic flows come to rest. We describe nine surface features including furrow-ridge sets and wedge-shaped mounds in pumice fall eroded by high-energy pyroclastic surges, flow-parallel ridges that record the passage of multiple pyroclastic flows, perched benches of marginal deposits stranded by more-mobile pyroclastic-flow cores, hummocks of dense clasts interpreted as lag deposit, transverse ridges that mark the compression and imbrication of flows as they came to rest, scarps indicating ignimbrite remobilization, fields of closely spaced pits caused by phreatic explosions, fractures and cracks due to extensional processes resulting from ignimbrite volume loss, and stream channels eroded in the newly formed surface. The nine morphologies presented here illustrate a dynamic depositional environment that varied spatially and with time during the eruption, and show that multiple processes modified the ignimbrite after deposition, both during and after the eruption.

Pyroclastic flow hazard assessment at Somma-Vesuvius based on the geological record

NASA Astrophysics Data System (ADS)

Gurioli, L.; Sulpizio, R.; Cioni, R.; Sbrana, A.; Santacroce, R.; Luperini, W.; Andronico, D.

2010-11-01

During the past 22 ka of activity at Somma-Vesuvius, catastrophic pyroclastic density currents (PDCs) have been generated repeatedly. Examples are those that destroyed the towns of Pompeii and Ercolano in AD 79, as well as Torre del Greco and several circum-Vesuvian villages in AD 1631. Using new field data and data available from the literature, we delineate the area impacted by PDCs at Somma-Vesuvius to improve the related hazard assessment. We mainly focus on the dispersal, thickness, and extent of the PDC deposits generated during seven plinian and sub-plinian eruptions, namely, the Pomici di Base, Greenish Pumice, Pomici di Mercato, Pomici di Avellino, Pompeii Pumice, AD 472 Pollena, and AD 1631 eruptions. We present maps of the total thickness of the PDC deposits for each eruption. Five out of seven eruptions dispersed PDCs radially, sometimes showing a preferred direction controlled by the position of the vent and the paleotopography. Only the PDCs from AD 1631 eruption were influenced by the presence of the Mt Somma caldera wall which stopped their advance in a northerly direction. Most PDC deposits are located downslope of the pronounced break-in slope that marks the base of the Somma-Vesuvius cone. PDCs from the Pomici di Avellino and Pompeii Pumice eruptions have the most dispersed deposits (extending more than 20 km from the inferred vent). These deposits are relatively thin, normally graded, and stratified. In contrast, thick, massive, lithic-rich deposits are only dispersed within 7 to 8 km of the vent. Isopach maps and the deposit features reveal that PDC dispersal was strongly controlled by the intensity of the eruption (in terms of magma discharge rate), the position of the vent area with respect to the Mt Somma caldera wall, and the pre-existing topography. Facies characteristics of the PDC deposits appear to correlate with dispersal; the stratified facies are consistently dispersed more widely than the massive facies.

Bulk rock composition and geochemistry of olivine-hosted melt inclusions in the Grey Porri Tuff and selected lavas of the Monte dei Porri volcano, Salina, Aeolian Islands, southern Italy

USGS Publications Warehouse

Doherty, Angela L.; Bodnar, Robert J.; De Vivo, Benedetto; Bohrson, Wendy A.; Belkin, Harvey E.; Messina, Antonia; Tracy, Robert J.

2012-01-01

The Aeolian Islands are an arcuate chain of submarine seamounts and volcanic islands, lying just north of Sicily in southern Italy. The second largest of the islands, Salina, exhibits a wide range of compositional variation in its erupted products, from basaltic lavas to rhyolitic pumice. The Monte dei Porri eruptions occurred between 60 ka and 30 ka, following a period of approximately 60,000 years of repose. The bulk rock composition of the Monte dei Porri products range from basaltic-andesite scoria to andesitic pumice in the Grey Porri Tuff (GPT), with the Monte dei Porri lavas having basaltic-andesite compositions. The typical mineral assemblage of the GPT is calcic plagioclase, clinopyroxene (augite), olivine (Fo72−84) and orthopyroxene (enstatite) ± amphibole and Ti-Fe oxides. The lava units show a similar mineral assemblage, but contain lower Fo olivines (Fo57−78). The lava units also contain numerous glomerocrysts, including an unusual variety that contains quartz, K-feldspar and mica. Melt inclusions (MI) are ubiquitous in all mineral phases from all units of the Monte dei Porri eruptions; however, only data from olivine-hosted MI in the GPT are reported here. Compositions of MI in the GPT are typically basaltic (average SiO2 of 49.8 wt %) in the pumices and basaltic-andesite (average SiO2 of 55.6 wt %) in the scoriae and show a bimodal distribution in most compositional discrimination plots. The compositions of most of the MI in the scoriae overlap with bulk rock compositions of the lavas. Petrological and geochemical evidence suggest that mixing of one or more magmas and/or crustal assimilation played a role in the evolution of the Monte dei Porri magmatic system, especially the GPT. Analyses of the more evolved mineral phases are required to better constrain the evolution of the magma.

210Pb and 210Po Abundances in Dacites Erupted May, 2003 From Anatahan Volcano: Implications for the Time-scales of Magma Generation and Degassing

NASA Astrophysics Data System (ADS)

Reagan, M. K.; Matthew, W.; Brian, H.

2003-12-01

Six samples of dacite pumice and scoria erupted in May, 2003 and collected from a number of sites around Anathan by Tobias Fischer and David Hilton were analyzed for 210Po activities on three occasions between early June and the time of this writing. With two exceptions, all scoria and pumice samples have 210Po activities that plot on a single growth curve indicating initial (210Po)=0.15 +/-0.07 (1σ ) dpm/g and (210Pb)=1.08+/-0.20 dpm/g. More precise values for these initial activities will be presented at the meeting after further analyses are performed in November. Preliminary alpha spectrometry analyses for U and Th, and ICPMS analyses distributed by Terry Plank suggest that the average (238U) is about 0.53 dpm/g. Equilibrium (228Th)/( 232Th) ratios indicate that these samples do not have excess 228Ra. Assuming that (210Pb )< (226Ra) because of minor degassing of 210Pb (see Gauthier and Condomines, 1999, EPSL, v. 172), the degassing efficiency factor for 210Po is greater than or equal to about 0.85, which is identical to the value calculated for a basaltic andesitic lava from Arenal volcano in Costa Rica (Gill et al., 1985, GRL, v. 12). This is surprising, as the May 10 plinian eruption of Anatahan should have resulted in more closed-system degassing than a lava eruption. This and the similar 210Po values for the scoria and pumice samples suggest that the shallow-level degassing history has little impact on the efficiency of polonium degassing. The scoria and pumice samples from sample 8-1e both have significant excesses of 210Po over the calculated initial (210Pb) value for the other samples. These excesses were partially leachable, indicating that 210Po was sublimated onto these samples, and that these ejecta resided in the vent before being ejected and redeposited The high inferred (226Ra)/( 230Th) for the Anatahan dacites despite the nearly equilibrium (238U)/( 230Th) value measured for one sample contrasts with the values for these ratios in more mafic Mariana samples, which are characterized by a direct correlation between radium and uranium excesses (Turner et al., 2001, Science, v. 292). Assuming that these trends hold up after additional analysis, the most straightforward interpretation of our alpha spectrometry data is that the dacite was generated by distillation of more mafic intrusives over a period of time that is significant compared to the half-life of 230Th, and that radium was added to the dacite recently either by inmixing a Ra-enriched basalt or a crust-derived fluid.

Impact of the AD 79 explosive eruption on Pompeii, II. Causes of death of the inhabitants inferred by stratigraphic analysis and areal distribution of the human casualties

NASA Astrophysics Data System (ADS)

Luongo, Giuseppe; Perrotta, Annamaria; Scarpati, Claudio; De Carolis, Ernesto; Patricelli, Giovanni; Ciarallo, Annamaria

2003-08-01

Detailed descriptions of the effects of explosive eruptions on urban settlements available to volcanologists are relatively rare. Apart from disease and starvation, the largest number of human deaths caused by explosive eruptions in the twentieth century are due to pyroclastic flows. The relationship between the number of victims related to a specific hazard and the presence of urban settlements in the area covered by the eruption has been shown. However, pyroclastic falls are also extremely dangerous under certain conditions. These conclusions are based on archaeological and volcanological studies carried out on the victims of the well-known AD 79 eruption of Vesuvius that destroyed and buried the Roman city of Pompeii. The stratigraphic level in the pyroclastic deposit and the location of all the casualties found are described and discussed. The total number of victims recovered during the archaeological excavations amounts to 1150. Of these, 1044 well recognisable bodies plus an additional group of 100 individuals were identified based on the analysis of several groups of scattered bones. Of the former, 394 were found in the lower pumice lapilli fall deposit and 650 in the upper stratified ash and pumice lapilli pyroclastic density currents (PDCs) deposits. In addition, a tentative evaluation suggests that 464 corpses may still be buried in the unexcavated part of the city. According to the reconstruction presented in this paper, during the first phase of the eruption (August 24, AD 79) a huge quantity of pumice lapilli fell on Pompeii burying the city under 3 m of pyroclastic material. During this eruptive phase, most of the inhabitants managed to leave the city. However, 38% of the known victims were killed during this phase mainly as a consequence of roofs and walls collapsing under the increasing weight of the pumice lapilli deposit. During the second phase of the eruption (August 25, AD 79) 49% of the total victims were on the roadways and 51% inside buildings. All of these inhabitants, regardless of their location, were killed by the unanticipated PDCs overrunning the city. New data concerning the stratigraphic level of the victims in the pyroclastic succession allow us to discriminate between the sequential events responsible for their deaths. In fact, casts of some recently excavated corpses lay well above the lower PDCs deposit, testifying that some of the inhabitants survived the first pyroclastic current. Finally, during the PDCs phase the victims died quite rapidly by ash asphyxiation. From the attitude of some casts, it seems that some people survived the initial impact of the second pyroclastic current and tried to support head and bust during the progressive aggradation of the deposit at the base of the current.

Field-trip guide for exploring pyroclastic density current deposits from the May 18, 1980, eruption of Mount St. Helens, Washington

USGS Publications Warehouse

Brand, Brittany D.; Pollock, Nicholas; Sarocchi, Damiano; Dufek, Josef; Clynne, Michael A.

2017-07-05

Pyroclastic density currents (PDCs) are one of the most dangerous phenomena associated with explosive volcanism. To help constrain damage potential, a combination of field studies, laboratory experiments, and numerical modeling are used to establish conditions that influence PDC dynamics and depositional processes, including runout distance. The objective of this field trip is to explore field relations that may constrain PDCs at the time of emplacement.The PDC deposits from the May 18, 1980, eruption of Mount St. Helens are well exposed along the steep flanks (10–30° slopes) and across the pumice plain (5–12° slopes) as far as 8 km north of the volcano. The pumice plain deposits represent deposition from a series of concentrated PDCs and are primarily thick (3–12 m), massive, and poorly sorted. In contrast, the steep east-flank deposits are stratified to cross-stratified, suggesting deposition from PDCs where turbulence strongly influenced transport and depositional processes.The PDCs that descended the west flank were largely nondepositional; they maintained a higher flow energy and carrying capacity than PDCs funneled through the main breach, as evidenced by the higher concentration of large blocks in their deposits. The PDC from the west flank collided with PDCs funneled through the breach at various points along the pumice plain. Evidence for flow collision will be explored and debated throughout the field trip.Evidence for substrate erosion and entrainment is found (1) along the steep eastern flank of the volcano, which has a higher degree of rough, irregular topography relative to the west flanks where PDCs were likely nonerosive, (2) where PDCs encountered debris-avalanche hummocks across the pumice plain, and (3) where PDCs eroded and entrained material deposited by PDCs produced during earlier phases of the eruption. Two features interpreted as large-scale (tens of meters wide) levees and a large (~200 m wide) channel scour-and-fill feature provide the first evidence of self-channelization within PDCs sustained for minutes to tens of minutes (total volume of deposits is ~0.12 km3; area covered is ~15.5 km2; Rowley and others, 1981).Our ability to interpret the deposits of PDCs is critical for understanding transport and depositional processes that control PDC dynamics. The results of extensive work on the May 18, 1980, PDC deposits show that slope and irregular topography strongly influence PDC flow path, dynamics, criticality (for example, supercritical versus subcritical), carrying capacity, and erosive capacity. However, the influence of these conditions on ultimate flow runout and damage potential warrants further exploration through the combination of field, experimental, and numerical approaches.

Ectomycorrhizal communities of ponderosa pine and lodgepole pine in the south-central Oregon pumice zone

Treesearch

Maria O. Garcia; Jane E. Smith; Daniel L. Luoma; Melanie D. Jones

2016-01-01

Forest ecosystems of the Pacific Northwest of the USA are changing as a result of climate change. Specifically, rise of global temperatures, decline of winter precipitation, earlier loss of snowpack, and increased summer drought are altering the range of Pinus contorta. Simultaneously, flux in environmental conditions within the historic ...

Conference wrap-up

Treesearch

Richard E. Miller

2007-01-01

My purpose is twofold: to review key messages from previous speakers and to offer some concepts that may help you link recently acquired information. When Mt. Mazama erupted about 7,000 years ago, its airborne ash and pumice fell on a wide variety of existing soils. This Mazama tephra was a new parent material for soil development (fig. 1). At some locations, the...

Volcanic ash - Terrestrial versus extraterrestrial

NASA Technical Reports Server (NTRS)

Okeefe, J. A.

1976-01-01

A principal difference between terrestrial and extraterrestrial lavas may consist in the greater ability of terrestrial lavas to form thin films (like those of soap bubbles) and hence foams. It would follow that, in place of the pumice and spiny shards found in terrestrial volcanic ash, an extraterrestrial ash should contain minute spherules. This hypothesis may help to explain lunar microspherules.

Natural regeneration of lodgepole pine in south-central Oregon

Treesearch

P.H. Cochran

1973-01-01

A sequence of events is necessary for natural regeneration in the pumice soil region: Adequate seed must be probed and distributed over the area, germination must be favored by warm and moist surface soils, daily surface temperature variation must be moderate, seedlings must survive summer drought, and weather conditions must prevent severe frost heaving the fall after...

25 years of ecological change at Mount St. Helens.

Treesearch

V.H. Dale; C.M. Crisafulli; F.J. Swanson

2005-01-01

18 May 2005 marks the 25th anniversary of the massive eruption of Mount St. Helens. This eruption involved diverse geological processes (1) that disturbed forests, meadows, lakes, an drivers (2) (see the figure). A huge landslide and searing flows of hot gases and pumic framents (pyroclastic flows) inundated 60 km2 of land, obliterating...

LOFT, TAN650. Camera facing southeast. From left to right: stack ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

LOFT, TAN-650. Camera facing southeast. From left to right: stack in distance, pre-amp wing, dome, north side of loft "service building." Note poured concrete wall of pre-amp wing on lower section; pumice block above. Date: May 2004. INEEL negative no. HD-39-19-3 - Idaho National Engineering Laboratory, Test Area North, Scoville, Butte County, ID

Developing resilient ponderosa pine forests with mechanical thinning and prescribed fire in central Oregon's pumice region

Treesearch

Matt D. Busse; P.H. Cochran; William E. Hopkins; William H. Johnson; Gregg M. Riegel; Gary O. Fiddler; Alice W. Ratcliff; Carol J. Shestak

2009-01-01

Thinning and prescribed burning are common management practices for reducing fuel buildup in ponderosa pine forests. However, it is not well understood if their combined use is required to lower wildfire risk and to help restore natural ecological function. We compared 16 treatment combinations of thinning, prescribed fire, and slash retention for two decades...

Chemical complexity and source of the White River Ash, Alaska and Yukon

USGS Publications Warehouse

Preece, S.J.; McGimsey, Robert G.; Westgate, J.A.; Pearce, N.J.G.; Hartmann, W.K.; Perkins, W.T.

2014-01-01

The White River Ash, a prominent stratigraphic marker bed in Alaska (USA) and Yukon (Canada), consists of multiple compositional units belonging to two geochemical groups. The compositional units are characterized using multiple criteria, with combined glass and ilmenite compositions being the best discriminators. Two compositional units compose the northern group (WRA-Na and WRA-Nb), and two units are present in the eastern group (WRA-Ea and the younger, WRA-Eb). In the proximal area, the ca. 1900 yr B.P. (Lerbekmo et al., 1975) WRA-Na displays reverse zoning in the glass phase and systematic changes in ilmenite composition and estimated oxygen fugacity from the base to the top of the unit. The eruption probably tapped different magma batches or bodies within the magma reservoir with limited mixing or mingling between them. The 1147 cal yr B.P. (calibrated years, approximately equivalent to calendric years) (Clague et al., 1995) WRA-Ea eruption is only weakly zoned, but pumices with different glass compositions are present, along with gray and white intermingled glass in individual pumice clasts, indicating the presence of multiple magmatic bodies or layers. All White River Ash products are high-silica adakites and are sourced from the Mount Churchill magmatic system.

Fabrication of naturel pumice/hydroxyapatite composite for biomedical engineering.

PubMed

Komur, Baran; Lohse, Tim; Can, Hatice Merve; Khalilova, Gulnar; Geçimli, Zeynep Nur; Aydoğdu, Mehmet Onur; Kalkandelen, Cevriye; Stan, George E; Sahin, Yesim Muge; Sengil, Ahmed Zeki; Suleymanoglu, Mediha; Kuruca, Serap Erdem; Oktar, Faik Nuzhet; Salman, Serdar; Ekren, Nazmi; Ficai, Anton; Gunduz, Oguzhan

2016-07-07

We evaluated the Bovine hydroxyapatite (BHA) structure. BHA powder was admixed with 5 and 10 wt% natural pumice (NP). Compression strength, Vickers micro hardness, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction studies were performed on the final NP-BHA composite products. The cells proliferation was investigated by MTT assay and SEM. Furthermore, the antimicrobial activity of NP-BHA samples was interrogated. Variances in the sintering temperature (for 5 wt% NP composites) between 1000 and 1300 °C, reveal about 700 % increase in the microhardness (~100 and 775 HV, respectively). Composites prepared at 1300 °C demonstrate the greatest compression strength with comparable result for 5 wt% NP content (87 MPa), which are significantly better than those for 10 wt% and those that do not include any NP (below 60 MPa, respectively). The results suggested the optimal parameters for the preparation of NP-BHA composites with increased mechanical properties and biocompatibility. Changes in micro-hardness and compression strength can be tailored by the tuning the NP concentration and sintering temperature. NP-BHA composites have demonstrated a remarkable potential for biomedical engineering applications such as bone graft and implant.

Assessment of evidence-based dental prophylaxis education in postdoctoral pediatric dentistry programs.

PubMed

Redford-Badwal, Deborah A; Nainar, S M Hashim

2002-09-01

The objective of the study was to investigate various aspects of evidence-based dental prophylaxis education in postdoctoral pediatric dentistry training programs in the United States. An anonymous nationwide postal survey of fifty-two postdoctoral pediatric dentistry program directors was conducted in September 2001. The survey had a response rate of 75 percent with all geographic regions of the nation represented and with a preponderance of university-based programs (62 percent). Most of the training programs (74 percent) routinely recommended dental prophylaxis for all recall patients. The proportion of programs that recommended dental prophylaxis for the following indications were: plaque, stain and/or calculus removal--97 percent; caries prevention--59 percent; prior to topical fluoride application--67 percent; prior to sealant application--62 percent; and for behavioral modification--77 percent. Most training programs (77 percent) defined dental prophylaxis as both rubber cup pumice prophylaxis and toothbrush prophylaxis. However, only one-half of the training programs (51 percent) had modified their teaching to substitute toothbrush prophylaxis in lieu of rubber cup pumice prophylaxis. In conclusion, only one half of postdoctoral pediatric dentistry training programs in the United States teach evidence-based practice of dental prophylaxis for recall patients.

Advanced treatment of biologically pretreated coal chemical industry wastewater using the catalytic ozonation process combined with a gas-liquid-solid internal circulating fluidized bed reactor.

PubMed

Li, Zhipeng; Liu, Feng; You, Hong; Ding, Yi; Yao, Jie; Jin, Chao

2018-04-01

This paper investigated the performance of the combined system of catalytic ozonation and the gas-liquid-solid internal circulating fluidized bed reactor for the advanced treatment of biologically pretreated coal chemical industry wastewater (CCIW). The results indicated that with ozonation alone for 60min, the removal efficiency of chemical oxygen demand (COD) could reach 34%. The introduction of activated carbon, pumice, γ-Al 2 O 3 carriers improved the removal performance of COD, and the removal efficiency was increased by 8.6%, 4.2%, 2%, respectively. Supported with Mn, the catalytic performance of activated carbon and γ-Al 2 O 3 were improved significantly with COD removal efficiencies of 46.5% and 41.3%, respectively; however, the promotion effect of pumice supported with Mn was insignificant. Activated carbon supported with Mn had the best catalytic performance. The catalytic ozonation combined system of MnO X /activated carbon could keep ozone concentration at a lower level in the liquid phase, and promote the transfer of ozone from the gas phase to the liquid phase to improve ozonation efficiency.

LA-ICP-MS Pb-U Dating of Young Zircons from the Kos-Nisyros Volcanic Centre, SE Aegean Arc (Greece)

NASA Astrophysics Data System (ADS)

Guillong, M.; Von Quadt, A.; Peytcheva, I.; Bachmann, O.

2014-12-01

Zircon Pb-U dating has become a key technique for answering many important questions in geosciences. This paper describes a new LA-ICP-MS approach. We show, using previously dated samples of a large quaternary rhyolitic eruption in the Kos-Nisyros volcanic centre (the 161 ka Kos Plateau Tuff), that the precision of our LA-ICP-MS method is as good as via SHRIMP, while ID-TIMS measurements confirm the accuracy. Gradational age distribution over >140 ka of the Kos zircons and the near-absence of inherited cores indicate near-continuous crystallisation in a growing magma reservoir with little input from wall rocks. Previously undated silicic eruptions from Nisyros volcano (Lower Pumice, Nikia Flow, Upper Pumice), which are stratigraphically constrained to have happened after the Kos Plateau Tuff, are dated to be younger than respectively 124 ± 35 ka, 111 ± 42 ka and 70 ± 24 ka. Samples younger than 1 Ma were corrected for initial thorium disequilibrium using a new formula that also accounts for disequilibrium in 230Th decay. Guillong, M. et al., 2014, JAAS, 29, p. 963-967; doi: 10.1039/c4ja00009a.

Paleomagnetic and AMS studies of the El Castillo ignimbrite, central-east Mexico: Source and rock magnetic nature

NASA Astrophysics Data System (ADS)

Alva-Valdivia, L. M.; Agarwal, A.; Caballero-Miranda, C.; García-Amador, B. I.; Morales-Barrera, W.; Rodríguez-Elizarraráz, S.; Rodríguez-Trejo, A.

2017-04-01

Lithological, petromagnetic, paleomagnetic and magnetic fabric studies are employed to determine the flow direction and the location of the source of the, 2.44 to 2.21 Ma, El Castillo ignimbrite in the central-east Mexico. Based on the increasing matrix to pumice ratio and decreasing pumice size, the ignimbrite field is divided into the northwestern, central and south-southeastern sectors. Lithological comparisons among the three sectors reveal that the ignimbrite had flowed from NW to SE, and the source is in the NW part of the study area. Thermomagnetic results concur with the increasing matrix proportions from the proximal to the distal sector. The coercivity and magnetization ratios of the hysteresis parameters are lower in the SE sector than in the NW and central sectors. The dominant flow direction inferred through magnetic fabrics, at most sites, is NW to SE, which coincides with the direction inferred from lithological comparisons. However, at some sites magnetic fabrics demonstrate flow towards ENE or other various directions. The paleomagnetic analysis and field observations reveal that these anomalous directions are a consequence of anticlockwise block rotation and tilting due to normal and lateral faulting in the region.

Suppression of Bacterial Wilt and Fusarium Wilt by a Burkholderia nodosa Strain Isolated from Kalimantan Soils, Indonesia.

PubMed

Nion, Yanetri Asi; Toyota, Koki

2008-01-01

A trial was conducted to suppress bacterial wilt of tomato (BWT) caused by Ralstonia solanacearum using biocontrol agents (BCAs) isolated from soils in Kalimantan, Indonesia. Five isolates were selected from 270 isolates as better performing BCAs through screening four times using a pumice medium. The isolates selected were identified as Burkholderia nodosa, Burkholderia sacchari, Burkholderia pyrrocinia and Burkholderia terricola according to 16S rDNA sequences, fatty acid composition and carbon source utilization patterns. Among them, B. nodosa G5.2.rif1 had significant suppressive effects on Fusarium wilt of tomato (FWT) and spinach (FWS) as well as BWT. When B. nodosa G5.2rif1 was inoculated into a pumice medium in combination with sucrose, it showed even more stable disease suppression for BWT, but not for FWS. This suppression was considered to mainly occur through competition for nutrients. In two times greenhouse experiments for BWT using pots comparable in size to those used commercially, B. nodosa G5.2rif1 significantly suppressed the disease index by 33-79%, with no inhibitory effects on the growth, yield and quality of tomatoes.

78 FR 36241 - Notice of Inventory Completion: University of Oregon Museum of Natural and Cultural History...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-06-17

... 13 points, 9 scrapers, 1 blade, 1 bone awl, 1 pumice block, and 1 lot of pigment samples. In 1946... objects are 1 scraper fragment, 1 copper pendant, 1 pipe in fragments, 2 worked tuff, 1 worked bone, 1 dentalium shell, 1 bird bone, 1 pestle, 1 worked chert, and 2 bone fragments. In 1951, human remains...

LPT. Shield test facility (TAN645 and 646). Elevations show three ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

LPT. Shield test facility (TAN-645 and -646). Elevations show three types of siding: Asbestos cement, pumice block, concrete. Ralph M. Parsons 1229-17 ANP/GE-6-6445-A-3. April 1957. Approved by INEEL Classification Office for public release. INEEL index code no. 037-06445/0646-00-693-107349 - Idaho National Engineering Laboratory, Test Area North, Scoville, Butte County, ID

Mineral Deposits and Mineral Potential of the China Lake Complex of the Naval Weapons Center, China Lake, California

DTIC Science & Technology

1983-12-01

Tucker and R. J. Sampson. 16 A field check of the area confirmed many of the physical aspects of the property as reported, but the tungsten grades...iron, mercury, perlite, pumice, aggregate, evaporites, travertine, and diatomite . Geothermal and water-producing strata were also investigated. The...Prospect ( Diatomite ) (N-1602) ..... ... 436 Evaporites .......... ....................... .436 Bonanza Group (N-1502) ..... ............... ... 436

Soil moisture depletion in three lodgepole pine stands in northeastern Oregon.

Treesearch

Daniel M. Bishop

1961-01-01

A 1-year study in the Blue Mountains of northeastern Oregon indicates that substantial amounts of soil moisture are consumed during the growing season in lodgepole pine stands. Dual purposes of the study were to estimate the quantities of water that can be stored in basalt-pumice soils typical of the Blue Mountains, and to determine the rate and amount of moisture...

Eruption Depths, Magma Storage and Magma Degassing at Sumisu Caldera, Izu-Bonin Arc: Evidence from Glasses and Melt Inclusions

NASA Astrophysics Data System (ADS)

Johnson, E. R.

2015-12-01

Island arc volcanoes can become submarine during cataclysmal caldera collapse. The passage of a volcanic vent from atmospheric to under water environment involves complex modifications of the eruption style and subsequent transport of the pyroclasts. Here, we use FTIR measurements of the volatile contents of glass and melt inclusions in the juvenile pumice clasts in the Sumisu basin and its surroundings (Izu-Bonin arc) to investigate changes in eruption depths, magma storage and degassing over time. This study is based on legacy cores from ODP 126, where numerous unconsolidated (<65 ka), extremely thick (few m to >250 m), massive to normally graded pumice lapilli-tuffs were recovered over four cores (788C, 790A, 790B and 791A). Glass and clast geochemistry indicate the submarine Sumisu caldera as the source of several of these pumice lapilli-tuffs. Glass chips and melt inclusions from these samples were analyzed using FTIR for H2O and CO2 contents. Glass chips record variable H2O contents; most chips contain 0.6-1.6 wt% H2O, corresponding to eruption depths of 320-2100 mbsl. Variations in glass H2O and pressure estimates suggest that edifice collapse occurred prior-to or during eruption of the oldest of these samples, and that the edifice may have subsequently grown over time. Sanidine-hosted melt inclusions from two units record variably degassed but H2O-rich melts (1.1-5.6 wt% H2O). The lowest H2O contents overlap with glass chips, consistent with degassing and crystallization of melts until eruption, and the highest H2O contents suggest that large amounts of degassing accompanied likely explosive eruptions. Most inclusions, from both units, contain 2-4 wt% H2O, which further indicates that the magmas crystallized at pressures of ~50-100 MPa, or depths ~400-2800 m below the seafloor. Further glass and melt inclusion analyses, including major element compositions, will elucidate changes in magma storage, degassing and evolution over time.

Assessment of farm soil, biochar, compost and weathered pine mulch to mitigate methane emissions.

PubMed

Syed, Rashad; Saggar, Surinder; Tate, Kevin; Rehm, Bernd H A

2016-11-01

Previous studies have demonstrated the effective utility of volcanic pumice soil to mitigate both high and low levels of methane (CH 4 ) emissions through the activity of both γ-proteobacterial (type I) and α-proteobacterial (type II) aerobic methanotrophs. However, the limited availability of volcanic pumice soil necessitates the assessment of other farm soils and potentially suitable, economical and widely available biofilter materials. The potential biofilter materials, viz. farm soil (isolated from a dairy farm effluent pond bank area), pine biochar, garden waste compost and weathered pine bark mulch, were inoculated with a small amount of volcanic pumice soil. Simultaneously, a similar set-up of potential biofilter materials without inoculum was studied to understand the effect of the inoculum on the ability of these materials to oxidise CH 4 and their effect on methanotroph growth and activity. These materials were incubated at 25 °C with periodic feeding of CH 4 , and flasks were aerated with air (O 2 ) to support methanotroph growth and activity by maintaining aerobic conditions. The efficiency of CH 4 removal was monitored over 6 months. All materials supported the growth and activity of methanotrophs. However, the efficiency of CH 4 removal by all the materials tested fluctuated between no or low removal (0-40 %) and high removal phases (>90 %), indicating biological disturbances rather than physico-chemical changes. Among all the treatments, CH 4 removal was consistently high (>80 %) in the inoculated farm soil and inoculated biochar, and these were more resilient to changes in the methanotroph community. The CH 4 removal from inoculated farm soil and inoculated biochar was further enhanced (up to 99 %) by the addition of a nutrient solution. Our results showed that (i) farm soil and biochar can be used as a biofilter material by inoculating with an active methanotroph community, (ii) an abundant population of α-proteobacterial methanotrophs is essential for effective and stable CH 4 removal and (iii) addition of nutrients enhances the growth and activity of methanotrophs in the biofilter materials. Further studies are underway to assess the feasibility of these materials at small plot and field scales.

Lichen Persistence and Recovery in Response to Varied Volcanic Disturbances

NASA Astrophysics Data System (ADS)

Nelson, P.; Wheeler, T. B.

2015-12-01

Volcanic eruptions produce many ecological disturbances that structure vegetation. While lichens are sensitive to disturbances, little is known about their responses to volcanic disturbances, except for colonization of lava. We examined lichen community responses through time to different disturbances produced by the May 1, 2008 eruption of Volcan Chaiten in south-central Chile. Pre-eruption vegetation near the volcano was old-growth Valdivian temperate rainforest dominated by closed-canopy Nothofagus sp... In 2012, we installed thirteen 1-acre plots across volcanic disturbance zones on which a time-constrained search was done for all macrolichen species, each of which was assigned an approximate log10 categorical abundance. We also installed a 0.2 m2 quadrat on two representative trees per plot for repeat photography of lichen cover. We remeasured at least one plot per disturbance zone in 2014 and re-photographed tree quadrats in 2013 and 2014. We then analyzed species composition and abundance differences among disturbance zones. In 2012, the blast (pyroclastic density flow), scorch (standing scorched forest at the edge of the blast) and deep tephra (>10 cm) zones had the lowest lichen species richness (5-13 species), followed by reference (unimpacted) and shallow (<10 cm) tephra (17-20 species). Gravel rain (preexisting rock ejected by eruption initiation), gravel rain + pumice and flooded forests (fluvially reworked volcanic material entrained by heavy rains) were species-rich (25-42 species). In 2014, the blast and deep tephra had regained 2-3 times the number of lichen species since 2012 while the light tephra and reference were essentially unchanged. Gravel rain, gravel rain + pumice and flooded forest plots all had about the same number of species in 2014 as 2012. Lichen colonization and growth in tree quadrats varied widely, from very little colonization in the blast to prolific colonization in the gravel rain + pumice zone. Lichen's varied responses to different volcanic disturbances were attributable to varying degrees of mortality and subsequent availability of substrate, quantity of light and removal of competitors. While sensitive to disturbance, lichens are apparently resilient to and can quickly recolonize after a variety of large, violent volcanic disturbances.

Assembling an ignimbrite: Compositionally defined eruptive packages in the 1912 Valley of Ten Thousand Smokes ignimbrite, Alaska

USGS Publications Warehouse

Fierstein, J.; Wilson, C.J.N.

2005-01-01

The 1912 Valley of Ten Thousand Smokes (VTTS) ignimbrite was constructed from 9 compositionally distinct, sequentially emplaced packages, each with distinct proportions of rhyolite (R), dacite (D), and andesite (A) pumices that permit us to map package boundaries and flow paths from vent to distal extents. Changing pumice proportions and interbedding relationships link ignimbrite formation to coeval fall deposition during the first ???16 h (Episode I) of the eruption. Pumice compositional proportions in the ignimbrite were estimated by counts on ???100 lapilli at multiple levels in vertical sections wherever accessible and more widely over most of the ignimbrite surface in the VTTS. The initial, 100% rhyolite ignimbrite package (equivalent to regional fall Layer A and occupying ???3.5 h) was followed by packages with increasing proportions of andesite, then dacite, emplaced over ???12.5 h and equivalent to regional fall Layers B1-B3. Coeval fall deposits are locally intercalated with the ignimbrite and show parallel changes in R:D (rhyolite:dacite) proportions, but lack significant amounts of andesite. Andesite was thus dominantly a low-fountaining component in the eruption column and is preferentially represented in packages filling the VTTS north of the vent. The most extensive packages (3 and 4) occur in B1 and early B2 times where flow mobility and volume were optimized; earlier all-rhyolite flows (Package 1) were highly energetic but less voluminous, while later packages (5-9) were both less voluminous and emplaced at lower velocities. Package boundaries are expressed as one or more of the following: sharp color changes corresponding to compositional variations; persistent finer-grained basal parts of flow units; compaction swales filled by later packages; erosional channels cut by the flows that fill them; lobate accumulations of one package; and (mostly south of the vent) intercalated fall deposit layers. Clear flow-unit boundaries are best developed between ignimbrite of non-successive packages, indicating time breaks of tens of minutes to hours. Less well-defined stratification may represent rapidly emplaced successive flow units but often changes over short distances and indicates variations in localized depositional conditions. ?? 2005 Geological Society of America.

ETR CRITICAL FACILITY, TRA654. SCIENTISTS STAND AT EDGE OF TANK ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

ETR CRITICAL FACILITY, TRA-654. SCIENTISTS STAND AT EDGE OF TANK AND LIFT REMOVABLE BRIDGE ABOVE THE REACTOR. CONTROL RODS AND FUEL RODS ARE BELOW ENOUGH WATER TO SHIELD WORKERS ABOVE. NOTE CRANE RAILS ALONG WALLS, PUMICE BLOCK WALLS. INL NEGATIVE NO. 57-3690. R.G. Larsen, Photographer, 7/29/1957 - Idaho National Engineering Laboratory, Test Reactor Area, Materials & Engineering Test Reactors, Scoville, Butte County, ID

State summaries: Idaho

USGS Publications Warehouse

Gillerman, V.S.; Weaver, M.J.; Bennett, E.H.

2006-01-01

According to the United States Geological Survey (USGS), Idaho's preliminary nonfuel mineral production value jumped to $893 million in 2005. Principal minerals by value included molybdenum concentrates, phosphate rock, sand and gravel, silver and portland cement. The state ranked second in phosphate and garnet production, third in silver and pumice, fourth in molybdenum concentrate production, and 21st overall. Majority of mining increases for the year were spurred by demand for metals by China's growing economy.

Mineral resource of the month: perlite

USGS Publications Warehouse

,

2010-01-01

The article talks about perlite, which is a mineral used as an aggregate for lightweight construction products, filler for paints and horticultural soil blends. Perlite comes from viscous lava, mined and processed to produce lightweight material that competes with pumice, exfoliated vermiculite and expanded clay and shale. It is mined in about 35 countries that include Greece, Japan and the U.S. Other uses include insulation, concrete and plaster aggregate, and stonewashing.

Isogloss: language and legacy on Mount St. Helens

Treesearch

E. Dodd

2012-01-01

Nothing standing aboveground today was here thirty years ago. The ground itself wasn't here. Oh, there was ground, but much of it lay below the surface where my boot soles slip a little in the loose pebbles of pumice. Rolling on loose rock and big ideas, for a moment I lose my sense of balance, glancing first at the sky above, then at the nearby peak of Mount St...

HOT CELL BUILDING, TRA632, INTERIOR. WINDOWED ROOM IS OFFICE; NEXT ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

HOT CELL BUILDING, TRA-632, INTERIOR. WINDOWED ROOM IS OFFICE; NEXT DOOR WAS DARKROOM, AND THIRD DOOR LED TO ANOTHER OFFICE. ALL ARE ALONG NORTH WALL OF BUILDING (ETR EXTENSION OF 1958). CAMERA FACES NORTHEAST. PUMICE BLOCK WALLS. INL NEGATIVE NO. HD46-29-1. Mike Crane, Photographer, 2/2005 - Idaho National Engineering Laboratory, Test Reactor Area, Materials & Engineering Test Reactors, Scoville, Butte County, ID

Microleakage of self-etching sealant on noncontaminated and saliva-contaminated enamel.

PubMed

2011-01-01

The purpose of this study was to compare the microleakage of a self-etching sealant with a traditional phosphoric acid-etched sealant under noncontaminated and saliva-contaminated conditions. Fifty-two sound extracted human molars were randomly divided into 4 groups (N=13). Teeth in Groups 1 and 2 were cleaned with pumice, etched with phosphoric acid, rinsed, coated with a drying agent, placed with sealants (UltraSeal XT Plus), and light cured. Teeth in Groups 3 and 4 were cleaned with a proprietary flour pumice and rinsed prior to being sealed with a self-etching sealant (Enamel Loc). Teeth in Groups 2 and 4 were contaminated with saliva and thoroughly air-dried prior to the sealant placement. All teeth were subjected to a thermocycling process, stained with silver nitrate, and sectioned, and images of the sealant on the occlusal surface were recorded. Microleakage distance was measured in millimeters and subjected to a 2-way analysis of variance. Significantly larger microleakage distances were found for the self-etching sealant vs the traditional sealant (P<.001). Saliva contamination did not significantly affect the microleakage distance (P<.17). Under the conditions used in this in vitro study, the self-etching sealant, regardless of contamination condition, had extensive microleakage distances vs. little microleakage in the traditional phosphoric acid-etched sealant.

Surtsey and Mount St. Helens: a comparison of early succession rates

NASA Astrophysics Data System (ADS)

del Moral, R.; Magnússon, B.

2014-04-01

Surtsey and Mount St. Helens are celebrated but very different volcanoes. Permanent plots allow for comparisons that reveal mechanisms that control succession and its rate and suggest general principles. We estimated rates from structure development, species composition using detrended correspondence analysis (DCA), changes in Euclidean distance (ED) of DCA vectors, and by principal components analysis (PCA) of DCA. On Surtsey, rates determined from DCA trajectory analyses decreased as follows: gull colony on lava with sand > gull colony on lava, no sand ≫ lava with sand > sand spit > block lava > tephra. On Mount St. Helens, plots on lahar deposits near woodlands were best developed. The succession rates of open meadows declined as follows: Lupinus-dominated pumice > protected ridge with Lupinus > other pumice and blasted sites > isolated lahar meadows > barren plain. Despite the prominent contrasts between the volcanoes, we found several common themes. Isolation restricted the number of colonists on Surtsey and to a lesser degree on Mount St. Helens. Nutrient input from outside the system was crucial. On Surtsey, seabirds fashioned very fertile substrates, while on Mount St. Helens wind brought a sparse nutrient rain, then Lupinus enhanced fertility to promote succession. Environmental stress limits succession in both cases. On Surtsey, bare lava, compacted tephra and infertile sands restrict development. On Mount St. Helens, exposure to wind and infertility slow succession.

Surtsey and Mount St. Helens: a comparison of early succession rates

NASA Astrophysics Data System (ADS)

del Moral, R.; Magnússon, B.

2013-12-01

Surtsey and Mount St. Helens are celebrated, but very different volcanoes. Permanent plots allow comparisons that reveal mechanisms that control succession and its rate and suggest general principles. We estimated rates from structure development, species composition using detrended correspondence analysis (DCA), changes in Euclidean distance (ED) of DCA vectors and by principal components analysis (PCA) of DCA. On Surtsey, rates determined from DCA trajectory analyses decreased as follows: gull colony on lava with sand > gull colony on lava, no sand ≫ lava with sand > sand spit > block lava > tephra. On Mount St. Helens, plots on lahar deposits near woodlands were best developed. The succession rates of open meadows declined as follows: Lupinus-dominated pumice > protected ridge with Lupinus > other pumice and blasted sites > isolated lahar meadows > barren plain. Despite the prominent contrasts between the volcanoes, common themes were revealed. Isolation restricted the number of colonists on Surtsey and to a lesser degree on Mount St. Helens. Nutrient input from outside the system was crucial. On Surtsey, seabirds fashioned very fertile substrates, while on Mount St. Helens wind brought a sparse nutrient rain, then Lupinus enhanced fertility to promote succession. Environmental stress limits succession in both cases. On Surtsey, bare lava, compacted tephra and infertile sands restrict development. On Mount St. Helens, exposure to wind and infertility slow succession.

Changes in growth, essential oil yield and composition of geranium (Pelargonium graveolens L.) as affected by growing media.

PubMed

Rezaei Nejad, Abdolhossein; Ismaili, Ahmad

2014-03-30

Using proper growing medium is known to be an effective way to improve crop growth and yield. However, the effects of growing media on geranium essential oil have scarcely ever been examined in detail. In this research, the effects of different growing media (soil, sand, pumice, perlite and perlite + cocopeat) on growth, oil yield and composition of geranium were studied. Growth was significantly improved in soilless-grown plants compared with soil-grown plants. Oil yield of soilless-grown plants (except for pumice) was about threefold higher than that of soil-grown plants. The increase in oil yield was correlated with higher leaf dry weight (r²  = 0.96), as oil content was not affected. The citronellol/geranium ratio of oil was clearly affected by growing media, ranging from 5:1 in soil culture to 3:1 in soilless culture. The latter is acceptable for perfumery. Compared with soil, soilless media could produce higher yields of high-quality geranium oil that fits market requirements. Growth, oil yield and composition of plants grown in sand (a cheap and abundant growing medium) were not significantly different from those of plants grown in perlite and perlite + cocopeat. © 2013 Society of Chemical Industry.

Submarine basalt from the Revillagigedo Islands region, Mexico

USGS Publications Warehouse

Moore, J.G.

1970-01-01

Ocean-floor dredging and submarine photography in the Revillagigedo region off the west coast of Mexico reveal that the dominant exposed rock of the submarine part of the large island-forming volcanoes (Roca Partida and San Benedicto) is a uniform alkali pillow basalt; more siliceous rocks are exposed on the upper, subaerial parts of the volcanoes. Basalts dredged from smaller seamounts along the Clarion fracture zone south of the Revillagigedo Islands are tholeiitic pillow basalts. Pillows of alkali basalts are more vesicular than Hawaiian tholeiitic pillows collected from the same depths. This difference probably reflects a higher original volatile content of the alkali basalts. Manganese-iron oxide nodules common in several dredge hauls generally contain nucleii of rhyolitic pumice or basalt pillow fragments. The pumice floated to its present site from subaerial eruptions, became waterlogged and sank, and was then coated with manganese-iron oxides. The thickness of palagonite rinds on the glassy pillow fragments is proportional to the thickness of manganese-iron oxide layers, and both are a measure of the age of the nodule. Both oldest basalts (10-100 m.y.) and youngest (less than 1 m.y.) are along the Clarion fracture zone, whereas basalts from Roca Partida and San Benedicto volcanoes are of intermediate age. ?? 1970.

Experimental petrology applied in deposits of the 550 yr b.p. eruption at El Chichon volcano, Chiapas.

NASA Astrophysics Data System (ADS)

Mora, J. C.

2002-12-01

The 550 years ago a plinian-type eruption took place at El Chich¢n volcano, this event produced a 1.5 km3 pumice fall deposit. Contrary to the 1982 eruption, this event occurred under open vent conditions similar to the present crater. Comparing the pre-eruptive conditions of these two events would shed new lights on the location of the magma chamber, and the magmatic evolution. In order to determine the pre-eruptive conditions (P and T) of the 550 yr BP magma, laboratory experiments were carried out under fixed pressure and temperature conditions at the University of Alaska at Fairbanks. For this purpose fresh samples of the pumice were crushed, pulverized and saturated with water. The sample was then placed into ~2mg experimental tube charges of Ag70Pd30 of 2mm diameter. Our results indicate that prior to the 550 plinian the magma has a temperature of 825-830°C. and at approximated pressure of 2500 bars. This pressure estimate differs from the 4000 bars estimated with the geobaromether of Al-hornblende. The water contents obtained in the experiments were oversaturated similar to the calculated with the plagioclase-melts equation (5.3-6.1 percent in vol.)

Timescales and conditions of crystallization in the Pokai and Chimpanzee Ignimbrites, Taupo Volcanic Zone, New Zealand

NASA Astrophysics Data System (ADS)

Connor, M.; Gualda, G. A.; Gravley, D. M.

2013-12-01

Silicic magmas give rise to explosive eruptions that are both of scientific and societal interest. The central Taupo Volcanic Zone in New Zealand has been volcanically active for 2 Ma and represents the most active volcanic area in the world today. Particularly intense volcanic activity took place as part of a flare-up event that occurred from ~340 to ~240 ka, when 7 large ignimbrite eruptions took place, as well as many smaller eruptions, which erupted a total of at least 3000 km3 of magma. This project seeks to identify the conditions and timescales over which magma bodies that gave rise to these ignimbrite eruptions evolved. We aim to understand how much of the tens of thousands of years between successive eruptions were characterized by the presence of large bodies of silicic magma within the crust, as well the magma distribution within the crust during those times. We focus on the Chimpanzee and Pokai ignimbrites, which together erupted ~150 km3 of magma. The Pokai ignimbrite erupted at ~275 ka, while the Chimpanzee ignimbrite (undated) erupted between ~320 and 275 ka. Pumice clasts from the Chimpanzee and Pokai ignimbrite were collected in the field. Pumice bulk densities were measured using a submersion technique. Quartz and plagioclase crystals were extracted through a crushing, sieving, and winnowing procedure. Whole crystals were hand-picked under a conventional microscope, mounted on epoxy, and polished to expose grain interiors. Grain mounts were analyzed under an SEM using back-scattered electron, cathodoluminescence (CL), and energy-dispersive x-ray (EDX) imaging. Bulk-densities vary from 0.42 to 0.81 g/cm3 for Pokai and between 0.52 and 0.64 g/cm3 for Chimpanzee pumice clasts. Plagioclase is the dominant crystal phase in both units. Several plagioclase crystals have inclusions of orthopyroxene, ilmenite, magnetite, and zircon, which in some cases form clusters. Quartz is rare but is present in pumice from both deposits. Both plagioclase and quartz have glass inclusions. Quantitative EDX analyses under the SEM reveal high-silica rhyolite compositions (~78 wt. % SiO2), consistent with crystallization at shallow crustal levels (~100 MPa). Rhyolite-MELTS barometry confirms this suggestion, with estimated crystallization pressures of 70-110 MPa. Such crystallization depths are characteristic of magma bodies that give rise to ignimbrites in the Taupo Volcanic Zone. CL images of a small number of quartz crystals reveal zoning that is variable in character, from unzoned to distinctly zoned. Zoned crystals have several discrete zones, each one with its own characteristic homogeneous brightness; bright CL rims are observed in these crystals. Contacts between zones can be used to calculate crystallization times using diffusional relaxation assuming that CL intensity variations are due to Ti zonation. We estimate that quartz crystallization took place over decades to a few centuries, with rims crystallizing over months to years at most. These short timescales suggest that magma bodies with eruptible magma are very short-lived, much shorter-lived than the 10s of ka repose periods between eruptions that make up the flare-up event.

Constructing a reference tephrochronology for Augustine Volcano, Alaska

USGS Publications Warehouse

Wallace, Kristi; Coombs, Michelle L.

2013-01-01

Augustine Volcano is the most historically active volcano in Alaska's populous Cook Inlet region. Past on-island work on pre-historic tephra deposits mainly focused on using tephra layers as markers to help distinguish among prevalent debris-avalanche deposits on the island (Waitt and Beget, 2009, USGS Prof Paper 1762), or as source material for petrogenetic studies. No comprehensive reference study of tephra fall from Augustine Volcano previously existed. Numerous workers have identified Holocene-age tephra layers in the region surrounding Augustine Island, but without well-characterized reference deposits, correlation back to the source volcano is difficult. The purpose of this detailed tephra study is to provide a record of eruption frequency and magnitude, as well as to elucidate physical and chemical characteristics for use as reference standards for comparison with regionally distributed Augustine tephra layers. Whole rock major- and trace-element geochemistry, deposit componentry, and field context are used to correlate tephra units on the island where deposits are coarse grained. Major-element glass geochemistry was collected for use in correlating to unknown regional tephra. Due to the small size of the volcanic island (9 by 11 km in diameter) and frequent eruptive activity, on-island exposures of tephra deposits older than a couple thousand years are sparse, and the lettered Tephras B, M, C, H, I, and G of Waitt and Beget (2009) range in age from 370-2200 yrs B.P. There are, however, a few exposures on the south side of the volcano, within about 2 km of the vent, where stratigraphic sections that extend back to the late Pleistocene glaciation include coarse pumice-fall deposits. We have linked the letter-named tephras from the coast to these higher exposures on the south side using physical and chemical characteristics of the deposits. In addition, these exposures preserve at least 5 older major post-glacial eruptions of Augustine. These ultra-proximal sites, along with an off-island section 20 km to the west, provide the first continuous tephrochronology for Augustine that extends from the earliest to latest Holocene. Because examined pumice-fall exposures are limited to a narrow azimuth on the south side of the volcano, the on-island record is likely an incomplete catalog of major eruptions. It is possible however, that the coarse-grained near vent exposures (within 2 km) represent large eruptions that blanketed the entire island in tephra and are representative of the entire Holocene record. The major Holocene tephra units exposed on-island are composed of coarse-grained (cm-scale) pumice ranging in color from white to cream (variably oxidized), and light to medium gray as well as banded varieties. Accidental lithic assembles are highly variable and often unique for individual eruptions. Pumices range from 60-66 wt % SiO2 in whole-rock composition and are distinguishable using trace and minor element abundances and field context. Glass geochemistry is often distinguishable between tephras, but more overlap exists among deposits and presents challenges for correlating to regional tephras.

Soil heating during the complete combustion of mega-logs and broadcast burning in central Oregon USA pumice soils

Treesearch

Jane E. Smith; Ariel D. Cowan; Stephen A. Fitzgerald

2016-01-01

The environmental effect of extreme soil heating, such as occurs with the complete combustion of large downed wood during wildfires, is a post-fire management concern to forest managers. To address this knowledge gap, we stacked logs to create ‘mega-log’ burning conditions and compared the temperature, duration and penetration of the soil heat pulse in nine high...

Investigation of photon attenuation coefficient of some building materials used in Turkey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dogan, B.; Altinsoy, N.

In this study, some building materials regularly used in Turkey, such as concrete, gas concrete, pumice and brick have been investigated in terms of mass attenuation coefficient at different gamma-ray energies. Measurements were carried out by gamma spectrometry containing NaI(Tl) detector. Narrow beam gamma-ray transmission geometry was used for the attenuation measurements. The results are in good agreement with the theoretical calculation of XCOM code.

[Comparative studies on fissure sealing: composite versus Cermet cement].

PubMed

Hickel, R; Voss, A

1989-06-01

Fifty two molars sealed with either composite or Cermet cement were compared. The composite sealant was applied after enamel etching using a rubber dam. Before sealing with Cermet cement the enamel was only cleaned with pumice powder and sodium hypochlorie and the material was applied without enamel etching. After an average follow-up of 1.6 years composite sealants proved to be significantly more reliable. Cermet cement sealings showed defects more frequently.

Hydrothermal alteration of a rhyolitic hyaloclastite from Ponza Island, Italy

NASA Astrophysics Data System (ADS)

Ylagan, Robert F.; Altaner, Stephen P.; Pozzuoli, Antonio

1996-12-01

A rhyolitic hyaloclastite from Ponza island, Italy, has been hydrothermally altered producing four distinct alteration zones based on XRD and field textures: (1) non-pervasive argillic zone; (2) propylitic zone; (3) silicic zone; and (4) sericitic zone. The unaltered hyaloclastite is a volcanic breccia with clasts of vesiculated obsidian in a matrix of predominantly pumice lapilli. Incomplete alteration of the hyaloclastite resulted in the non pervasive argillic zone, characterized by smectite and disordered opal-CT. Obsidian clasts, some pumice lapilli, and pyrogenic plagioclase and biotite are unaltered. Smectite has an irregular flakey morphology, although euhedral particles are occasionally observed. The propylitic zone is characterized by mixed-layer illite/smectite (I/S) with 10 to 85% illite (I), mordenite, opal-C and authigenic K-feldspar (akspar). The matrix of the hyaloclastite is completely altered and obsidian clasts are silicified; however, plagioclase and biotite phenocrysts remain unaltered. Flakey I/S replaces pumice, and mordenite, akspar and silica line and fill pores. I/S particles are composed predominantly of subequant plates and euhedral laths. The silicic zone is characterized by highly illitic I/S with ≥ 90% I, quartz, akspar and occasional albite. In this zone the matrix and clasts are completely altered, and pyrogenic plagioclase shows significant alteration. Illitic I/S has a euhedral lath-like morphology. In the sericitic zone the hyaloclastite altered primarily to illitic I/S with ≥ 66% I, quartz, and minor akspar and pyrite. Clay minerals completely replace pyrogenic feldspars and little evidence remains of the original hyaloclastite texture. Unlike other zones, illitic I/S is fibrous and pure illite samples are composed of euhedral laths and hexagonal plates. The temperatures of hydrothermal alteration likely ranged from 30 to 90 °C for the argillic zone, from 110 to 160 °C for the propylitic zone, from 160 to 270 °C for the silicic zone, and were possibly as high as 300 °C for the sericitic zone. The four zones occur as linear bands that increase in intensity north of the bentonite mine at Cala dell'Acqua. The alteration zones have two orientations and may be structurally controlled by E-W- and NE-SW-trending faulting which is consistent with the dominant structural trends of the Pontine archipelago. Finally, hydrothermal alteration most likely involved seawater based on the geologic evolution of Ponza.

Primary Igneous Anhydrite: Progress Since the 1982 El Chichón Eruption (Mexico)

NASA Astrophysics Data System (ADS)

Luhr, J. F.

2006-05-01

Anhydrite (CaSO4) was confirmed as a stable primary igneous mineral, capable of precipitating from a silicate melt, through petrographic observations of fresh trachyandesitic pumices erupted in the spring of 1982 from El Chichón, a little known, isolated tuff and lava-dome complex in eastern Mexico. The 1982 eruption was also notable for the associated release of an estimated 5-9 megatons of SO2 to the stratosphere and troposphere, as measured by the Total Ozone Mapping Spectrometer. Subsequent years saw confirmation of primary igneous anhydrite in laboratory phase-equilibrium experiments, and anhydrite was also observed in the products of several subsequent explosive eruptions, most importantly dacitic pumices from the massive 15 June 1991 eruption of Mount Pinatubo, in the Philippines. That eruption involved ~5X the mass of magma and ~3X the mass of SO2 release compared to El Chichón's eruption. For both the Pinatubo and El Chichón eruptions, it has been concluded that the sulfur released to the atmosphere was too great in mass to have been dissolved in the erupted melt volume just prior to eruption. In both cases workers advocated the existence of a separate gas phase prior to eruption, where much of the subsequently released sulfur was present. Thus, primary igneous anhydrite has been linked with another important phenomenon: excess sulfur release during volcanic eruptions. This presentation will review other developments concerning primary igneous anhydrite since 1982. These include: (1) other examples of primary anhydrite from volcanic samples (Nevado del Ruiz, Colombia; Lascar, Chile; Sutter Buttes, USA; Eagle Mountain, USA; Shiveluch, Russia; (2) examples of primary anhydrite from plutonic samples (Julcani, Peru; Santa Rita, USA; Cajon Pass Scientific Drillhole, USA); (3) laboratory experiments that have expanded our understanding of the T-P-fO2 conditions of anhydrite stability, melt/vapor partition coefficients for sulfur as a function of these conditions, and the solubility of anhydrite in NaCl-H2O solutions at high P and T; and (4) ion-microprobe studies of sulfur isotopic compositions for anhydrite crystals in both El Chichón and Pinatubo pumices, which have revealed individually homogeneous crystals, but large inter-crystalline isotopic variations among neighboring grains.

40Ar/(39)Ar dating of the Kapthurin Formation, Baringo, Kenya.

PubMed

Deino, Alan L; McBrearty, Sally

2002-01-01

The(40)Ar/(39)Ar radiometric dating technique has been applied to tuffs and lavas of the Kapthurin Formation in the Tugen Hills, Kenya Rift Valley. Two variants of the(40)Ar/(39)Ar technique, single-crystal total fusion (SCTF) and laser incremental heating (LIH) have been employed to date five marker horizons within the formation: near the base, the Kasurein Basalt at 0.61+/-0.04 Ma; the Pumice Tuff at 0.543+/-0.004 Ma; the Upper Kasurein Basalt at 0.552+/-0.015 Ma; the Grey Tuff at 0.509+/-0.009 Ma; and within the upper part of the formation, the Bedded Tuff at 0.284+/-0.012 Ma. The new, precise radiometric age determination for the Pumice Tuff also provides an age for the widespread Lake Baringo Trachyte, since the Pumice Tuff is the early pyroclastic phase of this voluminous trachyte eruption. These results establish the age of fossil hominids KNM-BK 63-67 and KNM-BK 8518 at approximately 0.510-0.512 Ma, a significant finding given that few Middle Pleistocene hominids are radiometrically dated. The Kapthurin hominids are thus the near contemporaries of those from Bodo, Ethiopia and Tanzania. A flake and core industry from lacustrine sediments in the lower part of the formation is constrained by new dates of 0.55-0.52 Ma, a period during which the Acheulian industry, characterized by handaxes, is known throughout East Africa. Points, typical of the Middle Stone Age (MSA), are found in Kapthurin Formation sediments now shown to date to between 0.509+/-0.009 Ma and 0.284+/-0.012 Ma. This date exceeds previous estimates for the age of the MSA elsewhere in East Africa by 49 ka, and establishes the age of Acheulian to MSA transition for the region. Evidence of the use of the Levallois technique for the manufacture of both small flakes and biface preforms, the systematic production of blades, and the use and processing of red ochre also occurs in this interval. The presence of blades and red ochre at this depth is important as blades signify a high degree of technical competence and red ochre suggests symbolic behavior. Copyright 2002 Academic Press.

Magma batches in the Timber Mountain magmatic system, Southwestern Nevada Volcanic Field, Nevada, USA

NASA Astrophysics Data System (ADS)

Mills, James G.; Saltoun, Benjamin W.; Vogel, Thomas A.

1997-09-01

The common occurrence of compositionally and mineralogically zoned ash flow sheets, such as those of the Timber Mountain Group, provides evidence that the source magma bodies were chemically and thermally zoned. The Rainier Mesa and Ammonia Tanks tuffs of the Timber Mountain Group are both large volume (1200 and 900 km 3, respectively) chemically zoned (57-78 wt.% SiO 2) ash flow sheets. Evidence of distinct magma batches in the Timber Mountain system are based on: (1) major- and trace-element variations of whole pumice fragments; (2) major-element variations in phenocrysts; (3) major-element variations in glass matrix; and (4) emplacement temperatures calculated from Fe-Ti oxides and feldspars. There are three distinct groups of pumice fragments in the Rainier Mesa Tuff: a low-silica group and two high-silica groups (a low-Th and a high-Th group). These groups cannot be related by crystal fractionation. The low-silica portion of the Rainier Mesa Tuff is distinct from the low-silica portion of the overlying Ammonia Tanks Tuff, even though the age difference is less than 200,000 years. Three distinct groups occur in the Ammonia Tanks Tuff: a low-silica, intermediate-silica and a high-silica group. Part of the high-silica group may be due to mixing of the two high-silica Rainier Mesa groups. The intermediate-silica group may be due to mixing of the low- and high-silica Ammonia Tanks groups. Three distinct emplacement temperatures occur in the Rainier Mesa Tuff (869, 804, 723 °C) that correspond to the low-silica, high-Th and low-Th magma batches, respectively. These temperature differences could not have been maintained for any length of time in the magma chamber (cf. Turner, J.S., Campbell, I.H., 1986. Convection and mixing in magma chambers. Earth-Sci. Rev. 23, 255-352; Martin, D., Griffiths, R.W., Campbell, I.H., 1987. Compositional and thermal convection in magma chambers. Contrib. Mineral. Petrol. 96, 465-475) and therefore eruption must have occurred soon after emplacement of the magma batches into the chamber. Emplacement temperatures of the pumice fragments from the Ammonia Tanks Tuff show a continuous gradient of temperatures with composition. This continuous temperature gradient is consistent with the model of storage of magma batches in the Ammonia Tanks group that have undergone both thermal and chemical diffusion.

Equilibrium and Disequilibrium of 230Th-238U in Zircon from the Minoan Eruption, Santorini, Aegean Sea, Greece

NASA Astrophysics Data System (ADS)

Schmitt, A. K.; Stockli, D. F.; Song, E. J.; Storm, S.

2016-12-01

The Minoan eruption (ca. 1600 BCE; 40-80 km3 dense rock equivalent) occurred after a ca. 18 ka period of dormancy followed by rapid reinvigoration through arrival of new magma from deep reservoirs colliding with evolved magmas in shallow storage. Although zoned phenocrysts indicate brief timescales ranging between years to decades for final pre-eruptive magma recharge and mixing, it remains unclear how magma accumulation vs. crystallization were balanced in the subvolcanic reservoir during the preceding inter-eruptive cycle. To directly probe magma presence over the repose interval prior to the Minoan eruption and further back in time, we reconnoitered the potential of U-Th zircon geochronology to date the crystallization of individual zircon crystals from pumice from the Minoan eruption. Zircon crystals were extracted from composite pumice samples (several kg each) from basal fall out deposits using gravity and magnetic separation. Etching in cold HF removed adherent glass and revealed the shape of crystals, which were pressed into indium metal to expose unpolished rims to the ion beam of a CAMECA IMS 1270 secondary ionization mass spectrometer. Adherent glass was ubiquitous, indicating that crystals were in contact with melt at the time of eruption. Six of 18 crystals were in 230Th/238U secular equilibrium, two crystals yielded ages of ca. 160 ka, and the remaining rims dated between eruption age and ca. 20 ka. Low Th/U of some secular equilibrium zircon suggests recycling of metamorphic basement zircon, which is also indicated by the presence of rutile in heavy mineral separates. U-Th dates also reveal recycling of zircon from Pleistocene intrusions that likely represent left-over magma from antecedent eruption cycles. We tentatively interpret the dominant zircon population with near-eruption to ca. 20 ka ages to indicate continuous melt presence underneath Santorini during the last repose interval. Distinguishing a hiatus in zircon crystallization between 20 ka and 160 ka from continuous presence of a crystal mush capable of crystallizing zircon throughout the late Pleistocene requires further analyses. A corollary of mixed zircon populations of heterogeneous provenance in Minoan pumice is that the age significance of U-series data for major phases analyzed in bulk is suspect.

MX Siting Investigation. Geotechnical Evaluation. Verification Study - Pahroc Valley, Nevada. Volume I. Synthesis.

DTIC Science & Technology

1981-06-30

Range both consist of Paleozoic limestone and dolomite overlain by Tertiary ash-flow tuffs and undiffer- entiated volcanic rocks. The central portion...andesite, detrital material, volcanic tuff, pumice). FAULT - A plane or zone of fracture along which there has been * I displacement. FAULT BLOCK...D2850-70). To conduct the test, a cylindrical specimen of soil is surrounded by a fluid in a pressure chamber and subjected to an isotropic pressure . An

ETR BUILDING, TRA642. SOUTH SIDE VIEW INCLUDES SOUTH SIDES OF ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

ETR BUILDING, TRA-642. SOUTH SIDE VIEW INCLUDES SOUTH SIDES OF ETR BUILDING (HIGH ROOF LINE); ELECTRICAL BUILDING (ONE-STORY, MADE OF PUMICE BLOCKS), TRA-648; AND HEAT EXCHANGER BUILDING (WITH BUILDING NUMBERS), TRA-644. NOTE PROJECTION OF ELECTRICAL BUILDING AT LEFT EDGE OF VIEW. CAMERA FACES NORTH. INL NEGATIVE NO. HD46-37-3. Mike Crane, Photographer, 4/2005 - Idaho National Engineering Laboratory, Test Reactor Area, Materials & Engineering Test Reactors, Scoville, Butte County, ID

Paleomagnetic evidence for high-temperature emplacement of the 1883 subaqueous pyroclastic flows from Krakatau Volcano, Indonesia

NASA Astrophysics Data System (ADS)

Mandeville, Charles W.; Carey, Steven; Sigurdsson, Haraldur; King, John

1994-05-01

The paroxysmal 1883 eruption of Krakatau volcano in Indonesia discharge at least 6.5 cu km (dense rock equivalent) of pyroclastic material into the shallow waters of the Sunda Straits within a 15-km radius of the volcano. Progressive thermal demagnetization studies of individually oriented pumice clasts from a core sample of the submarine pyroclastic deposits show that 41 out of 47 clasts exhibit single-component remanence with mean inclination of -24 deg. The partial thermoremanent magnetization components of both pumice and lithic clasts are well grouped in orientation, indicating that substantial cooling of clasts must have occurred following deposition. Estimated subaqueous emplacement temperature for such clasts is greater than 500 C. Rare two-component lithic fragments exhibit inflection points on vector endpoint diagrams that mark the temperature below which the fragments acquired magnetization of similar orientation. These inflection points range from 350 to 550 C, indicating a minimum subaqueous emplacement temperature of 350 C. Paleomagnetic evidence for high-emplacement temperature supports the hypothesis that proximal 1883 submarine pyroclastic deposits resulted from entrance of hot, subaerially generated pyroclastic flows into the sea. Similar deposits have been interpreted from the geologic record, but this is the first documented example of submarine pyroclastic flows from a historic eruption. The Kratatau deposits thus serve as an important modern analog for the study of pyroclastic flow/seawater interactions.

Various Surface Treatments to Implant Provisional Restorations and Their Effect on Epithelial Cell Adhesion: A Comparative In Vitro Study.

PubMed

Luchinskaya, Darya; Du, Rong; Owens, David M; Tarnow, Dennis; Bittner, Nurit

2017-02-01

The aim of this in vitro study was to investigate the ability of epithelial cells to attach to or proliferate on various mechanical or chemical surface treatments of an implant provisional material. Polyethyl methacrylate discs 10 mm in diameter and ∼0.2 to 0.75 mm in width were used in the study. Experimental discs were treated with either a mechanical (pumice, varnish for shine, or high polishing) or a chemical agent (alcohol, chlorhexidine, or steam) to provide cleaning and/or polishing. Using primary human epidermal keratinocytes, experiments were performed to test the adhesion or proliferation of cells on the discs with various surface treatments. Scanning electron microscope analysis, rhodamine staining, and cell counting using a hemocytometer corroborated all findings and illustrated that the highest cell adhesion was found to be in the smooth surface treatment groups and the poorest adhesion was found to be in the rough surface groups and chemical treatment group. Within the limitations of this study, the following clinical protocol is recommended for finishing, polishing, and disinfecting implant provisional restorations: coarse, medium, fine pumice → high polishing (if desired) → steam. It is recommended to avoid applying varnish in the perimucosal area near the epithelium. This study could establish the most appropriate way to handle provisional restorations in the peri-implant sulcus for improved soft tissue health, esthetics, and long-term stability.

Recurrent Mudflows at Popocatepetl Volcano: Impact on the Population over several Thousand Years and possible Precursors.

NASA Astrophysics Data System (ADS)

Martin, A. L.; Nieto, A.; Portocarrero, J.; Jaimes-Viera, M. D. C.; Fonseca, R.

2014-12-01

Popocatepetl Volcano in central Mexico has been erupting since 1994 with relatively small Strombolian and Vulcanian eruptions, expect for the 2 larger eruptions in 1997 and 2001 that produced more widespread pumice and ash fall, mud flows and in 2001, pumice flows. As part of the recent studies that have focused on monitoring eruptive behavior for risk reduction in this heavily populated area, we are updating the Hazard Map (1995). Here we present the results of the new data for the northwestern sector of the volcano where large mudflows reached 40km from the volcano toward Mexico City (14Ka). The 5Ka mudflows are overlain by several flows that covered pre-Columbian pre-classic settlements at around 2Ka BP. Buildings with ceramics from the classic and postclassic periods (around 1.5Ka and 0.9Ka BP) also indicate that settlements were abandoned and resettled several hundred years later. So far, it seems that inhabitants fled at the beginning of these larger eruptions, since no bodies have been found in the excavations. Since the XVI century, several smaller mudflows have reached the towns, but many are related with secondary deposits (for example, the Nexapa 2010 mudflow reached 15 km from the crater). Although this area has been inhabited for thousands of years, increased population shows that risk is considerable.

How Did Ca. 300 Years of Explosive Activity at Kilauea End?

NASA Astrophysics Data System (ADS)

Swanson, D. A.

2013-12-01

Kilauea experienced ~300 years of frequent explosive eruptions following caldera collapse in about 1500 CE, producing the Keanakāko';i Tephra. The first 200 years were dominated by juvenile-rich phreatomagmatic eruptions, and the next 100 years by lithic-rich phreatomagmatic and phreatic explosive events. For most of this time, the caldera was deep enough (≥600 m) to allow magma and hot rock to interact with external water at and below the water table. This situation changed after the deadly 1790 eruption. The first eruption was magmatic, involving high fountaining that deposited pumice across >25 km2 south of the caldera. The pumice is hard to find today; it was mostly eroded away soon after deposition and is found only in protected areas along drainages and next to obstacles. The deposit has a consistent internal stratigraphy regardless of its thickness (maximum of 12 cm): lower third mostly achneliths (Pele's hair and tears), upper two- thirds pumice bombs and lapilli. The fountaining, the first purely magmatic event since reticulite erupted in ca. 1500, probably signifies a rising magma column and early filling of the caldera. The next eruption was phreatic, depositing fine lithic ash a few millimeters thick across >45 km2 south of the caldera. It may record withdrawal of the magma column and collapse of part of the caldera floor to or below the water table. The magma column rose soon thereafter, and its free surface was above the water table for some time. This event is recorded by Pele's hair deposited on the lithic ash across >30 km2 south of the caldera. The hair forms a jackstraw mat <1 mm thick. Nothing coarser than hair is present, so it is probably not a product of tall fountains. An analog might be the open-vent activity at Halema';uma';u today, where spatter from the magma free-surface (a lava lake) produces Pele's hair that blows kilometers downwind, forming a paper-thin deposit that glistens in the sun like golden grain. Phreatic activity followed, depositing small lapilli now embedded in the hair and lithic ash. This was perhaps a vent-opening event for a dominantly phreatomagmatic eruption. The deposit of this eruption, mostly lithic but with scattered fluidal lapilli, is 0.5-2 cm thick and inversely graded across a depositional area of >40 km2 south of the caldera. Mean grain size along the dispersal axis decreases from 7 mm on the rim of the caldera to 2 mm 7 km south of the caldera, where the deposit disappears into forest. This subplinian eruption records interaction of groundwater with both conduit wallrock and magma, probably during renewed collapse. A few ballistic blocks fell near the caldera soon thereafter, recording separate explosive events after the main eruption. The last Keanakāko';i eruption, erupted some time before 1823, was a lava fountain that deposited golden pumice up to 3 m thick west of the caldera. The eruption clearly indicates that the caldera was filling and on its way to its present status. Thus the ca. 300 years of explosive activity ended with a bumpy transition from a deep to a relatively full caldera. The duration of the transition is unknown but shorter than about 30 years. During that time, at least two small collapses interrupted a generally rising magma column, which finally gained the upper hand and culminated in the mostly effusive activity of Kilauea ever since.

Structural Engineering. Loads. Design Manual 2.2.

DTIC Science & Technology

1981-11-01

cast, rolled 534 Locust 46 Bronze, 7.9 to 14% Sn 509 Maple, hard 43 Bronze, aluminum 481 Maple, white 33 Copper , cast, rolled 556 Oak, chestnut 54... Copper ore, pyrites 262 Oak, live 59 Gold, cast, hammered 1205 Oak, red, black 41 Gold, bars, stacked 1133 Oak, white 46 Gold, coin in bags 1084 Pine...Phosphate rock, apatite 200 Glass, crystal 184 Porphyry 172 Hay and straw - bales 20 Pumice, natural 40 Leather 59 Quartz, flint 165 Paper 58 Sandstone

Scanning Electron Microscopy and Petrography of Glassy Particles Produced by Lava Fountain Eruptions. Ph.D. Thesis - Final Report

NASA Technical Reports Server (NTRS)

Ladle, G. H.

1978-01-01

A conceptual model of a lava fountain consists of a vent, spatter ramparts, fountain column, downwind plume and associated pumice deposits. Glassy particles produced by lava fountain eruptions consist primarily of sideromelane glass and minor to moderate amounts of vesicles and crystals. Particles are classified on the basis of morphology as: (1) spherical, (2) elongate, (3) glass-coated mineral grain, (4) shard, (5) reticulite, (6) composite particle, and (7) lithic fragment.

LOFT. Containment and service building (TAN650). Section through east/west axis ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

LOFT. Containment and service building (TAN-650). Section through east/west axis of building as viewed from the north. Shows steel ladder to top of dome, gable roof of borated water tank enclosure, pumice block siding of pre-amp tower, metal siding of duct enclosure. Kaiser engineers 6413-11-STEP/LOFT-650-A-6. Date: October 1964. INEEL index code no. 036-650-00-486-122218 - Idaho National Engineering Laboratory, Test Area North, Scoville, Butte County, ID

Clinical Evaluation of an Acrylic Pontic ’Adhesively’ Bonded to Uncut Abutment Teeth: 18 Month Results

DTIC Science & Technology

1974-12-23

of pumice in a rotating rubber cup and rinsed. The teeth were isolated with gauze, etched for two minutes with a gel type ...indefinitely. The advantages of oral tissue compatability, ease of con- struction and superior esthetics in - herent in this prosthesis were offset to a...H.S., Heifetz, S.B. and McCune, R.J. The effective- ness of an adhesive sealant in preventing occlusal caries: Findings after two years in

Eruption-triggered avalanche, flood, and lahar at Mount St. Helens - Effects of winter snowpack

USGS Publications Warehouse

Waitt, R.B.; Pierson, T.C.; MacLeod, N.S.; Janda, R.J.; Voight, B.; Holcomb, R.T.

1983-01-01

An explosive eruption of Mount St. Helens on 19 March 1982 had substantial impact beyond the vent because hot eruption products interacted with a thick snowpack. A blast of hot pumice, dome rocks, and gas dislodged crater-wall snow that avalanched through the crater and down the north flank. Snow in the crater swiftly melted to form a transient lake, from which a destructive flood and lahar swept down the north flank and the North Fork Toutle River.

The mechanisms of fine particle generation and electrification during Mount St. Helens volcanic eruption

NASA Technical Reports Server (NTRS)

Cheng, R. J.

1982-01-01

Microscopical investigation of volcanic ash collected from ground stations during Mount St. Helens eruptions reveal a distinctive bimodel size distribution with high concentrations of particle ranges at (1) 200-100 microns and (2) 20-0.1 microns. Close examination of individual particles shows that most larger ones are solidified magma particles of porous pumice with numerous gas bubbles in the interior and the smaller ones are all glassy fragments without any detectable gas bubbles. Elemental analysis demonstrates that the fine fragments all have a composition similar to that of the larger pumice particles. Laboratory experiments suggest that the formation of the fine fragments is by bursting of glassy bubbles from a partially solidified surface of a crystallizing molten magma particle. The production of gas bubbles is due to the release of absorbed gases in molten magma particles when solubility decreases during phase transition. Diffusion cloud chamber experiments strongly indicate that sub-micron volcanic fragments are highly hygroscopic and extremely active as cloud condensation nuclei. Ice crystals also are evidently formed on those fragments in a supercooled (-20 C) cloud chamber. It has been reported that charge generation from ocean volcanic eruptions is due to contact of molten lava with sea water. This seems to be insufficient to explain the observed rapid and intense lightning activities over Mount St. Helens eruptions. Therefore, a hypothesis is presented here that highly electrically charged fine solid fragments are ejected by bursting of gas bubbles from the surface of a crystallizing molten magma particles.

Tephra dispersal during the Campanian Ignimbrite (Italy) eruption: implications for ultra-distal ash transport during the large caldera-forming eruption

NASA Astrophysics Data System (ADS)

Smith, Victoria C.; Isaia, Roberto; Engwell, Sam L.; Albert, Paul. G.

2016-06-01

The Campanian Ignimbrite eruption dispersed ash over much of the central eastern Mediterranean Sea and eastern Europe. The eruption started with a Plinian phase that was followed by a series of pyroclastic density currents (PDCs) associated with the collapse of the Plinian column and the caldera. The glass compositions of the deposits span a wide geochemical range, but the Plinian fallout and PDCs associated with column collapse, the Lower Pumice Flow, only erupted the most evolved compositions. The later PDCs, the Breccia Museo and Upper Pumice Flow, erupted during and after caldera collapse, tap a less evolved component, and intermediate compositions that represent mixing between the end-members. The range of glass compositions in the Campanian Ignimbrite deposits from sites across the central and eastern Mediterranean Sea allow us to trace the dispersal of the different phases of this caldera-forming eruption. We map the fallout from the Plinian column and the plumes of fine material associated with the PDCs (co-PDCs) across the entire dispersal area. This cannot be done using the usual grain-size methods as deposits in these distal regions do not retain characteristics that allow attribution to either the Plinian or co-PDC phases. The glass compositions of the tephra at ultra-distal sites (>1500 km from the vent) match those of the uppermost PDC units, suggesting that most of the ultra-distal dispersal was associated with the late co-PDC plume that was generated during caldera collapse.

Accessing the application of in situ cosmogenic 14C to surface exposure dating of amorphous SiO2

NASA Astrophysics Data System (ADS)

Cesta, J. M.; Goehring, B. M.; Ward, D. J.

2017-12-01

We assess the feasibility and utility of in situ cosmogenic 14C as a geochronometer for landforms composed of amorphous SiO2 through the comparison of 14C surface exposure ages to independently determined eruption ages on Obsidian Dome, California. Landforms composed of amorphous SiO2 phases are difficult to date by conventional cosmogenic nuclide methods due to several complications that may arise (e.g., inability to remove meteoric contamination). The onset of an increased understanding of production rates and analytical measurement of in situ 14C in SiO2 provides an opportunity to address this limitation. Obsidian Dome is a 600-year-old phreatomagmatic dome of the Mono-Inyo Craters located in Inyo County, California, and consists of vesicular pumice, obsidian, and rhyolite. Exposure ages from eight obsidian and banded pumice and obsidian surface samples range from 3947 ± 678 to 914 ± 134 years, all significantly older than the accepted radiocarbon age of 650-550 years. δ13C values for the samples range between +2.65‰ and +1.34‰ and show a negative correlation with CO2 yield. The `too old' exposure ages coupled with this negative correlation between δ13C and CO2 yield suggests the incorporation of an atmospheric component of 14C. Measurement of 14C concentrations in shielded, subsurface samples will assist in isolating the atmospheric 14C component and aid in correcting the surface exposure ages.

Influence of landscape structure, topography, and forest type on spatial variation in historical fire regimes, central Oregon, USA

USGS Publications Warehouse

Merschel, Andrew; Heyerdahl, Emily K.; Spies, Thomas A; Loehman, Rachel A.

2018-01-01

Context In the interior Northwest, debate over restoring mixed-conifer forests after a century of fire exclusion is hampered by poor understanding of the pattern and causes of spatial variation in historical fire regimes. Objectives To identify the roles of topography, landscape structure, and forest type in driving spatial variation in historical fire regimes in mixed-conifer forests of central Oregon. Methods We used tree rings to reconstruct multicentury fire and forest histories at 105 plots over 10,393 ha. We classified fire regimes into four types and assessed whether they varied with topography, the location of fuel-limited pumice basins that inhibit fire spread, and an updated classification of forest type. Results We identified four fire-regime types and six forest types. Although surface fires were frequent and often extensive, severe fires were rare in all four types. Fire regimes varied with some aspects of topography (elevation), but not others (slope or aspect) and with the distribution of pumice basins. Fire regimes did not strictly co-vary with mixed-conifer forest types. Conclusions Our work reveals the persistent influence of landscape structure on spatial variation in historical fire regimes and can help inform discussions about appropriate restoration of fire-excluded forests in the interior Northwest. Where the goal is to restore historical fire regimes at landscape scales, managers may want to consider the influence of topoedaphic and vegetation patch types that could affect fire spread and ignition frequency.

Hydrological performance of dual-substrate-layer green roofs using porous inert substrates with high sorption capacities.

PubMed

Wang, Xiaoou; Tian, Yimei; Zhao, Xinhua; Peng, Chenrui

2017-06-01

Given that the common medium in existing green roofs is a single layer composed of organic and inorganic substrates, seven pilot-scale dual-substrate-layer extensive green roofs (G1-G7), which include nutrition and adsorption substrate layers, were constructed in this study. The effectiveness of porous inert substrates (activated charcoal, zeolite, pumice, lava, vermiculite and expanded perlite) used as the adsorption substrate for stormwater retention was investigated. A single-substrate-layer green roof (G8) was built for comparison with G1-G7. Despite the larger total rainfall depth (mm) of six types of simulated rains (43.2, 54.6, 76.2, 87.0, 85.2 and 86.4, respectively), the total percent retention of G1-G7 varied between 14% and 82% with an average of 43%, exhibiting better runoff-retaining capacity than G8 based on the maximum potential rainfall storage depth per unit height of adsorption substrate. Regression analysis showed that there was a logarithmic relationship between cumulative rainfall depth with non-zero runoff and stormwater retention for G1-G4 and a linear relationship for G5-G8. To enhance the water retention capacity and extend the service life of dual-substrate-layer extensive green roofs, the mixture of activated charcoal and/or pumice with expanded perlite and/or vermiculite is more suitable as the adsorption substrate than the mixture containing lava and/or zeolite.

Geochemical and textural constraints on degassing processes in sub-Plinian eruptions: case-study of the Greenish Pumice eruption of Mount Somma-Vesuvius

NASA Astrophysics Data System (ADS)

Zdanowicz, G.; Boudon, G.; Balcone-Boissard, H.; Cioni, R.; Mundula, F.; Orsi, G.; Civetta, L.; Agrinier, P.

2018-04-01

Plinian eruptions are characterized by high intensity and an overall steady character, and result in a stable convective column. The main processes controlling the dynamics of such steady and stable plume systems have been extensively investigated. Conversely, sub-Plinian eruptions are unsteady, as recorded by the large variability of the products and deposits. Our knowledge of the processes creating this unsteadiness on various timescales remains limited, and still requires more observations as well as theoretical and experimental investigation. Here, we focus on the sub-Plinian eruption of the Greenish Pumice (GP, 19,265 ± 105 BP), Mt. Somma-Vesuvius (Italy). On the basis of coupled geochemical and textural analyses of samples from the well-established stratigraphy of the GP deposits, we investigate volatiles (H2O, CO2, F, Cl) to better constrain the unsteady sub-Plinian eruptive style. This allows us to carry out a detailed study of the degassing processes in relation to the eruption dynamics. We find that degassing by open-system processes generally dominates throughout the entire eruption, but alternates with episodes of closed-system degassing. The fluctuating degassing regimes, responsible for the variable magma ascent rate within the conduit, are also responsible for the eruptive column instability. Volatile behavior is well correlated with textural heterogeneities of the eruptive products. Both reflect higher conduit heterogeneity than for Plinian eruptions, where we find a higher horizontal gradient in magma ascent velocity due to a smaller conduit diameter.

FeTi oxide mineralogy and the origin of normal and reverse remanent magnetization in dacitic pumice blocks from Mt. Shasta, California

USGS Publications Warehouse

Lawson, C.A.; Nord, G.L.; Champion, D.E.

1987-01-01

Detailed mineralogical analyses and rock magnetic experiments have made it possible to directly identify the FeTi oxide phases responsible for the normal and reverse magnetic components of two dacitic pumice blocks from Mt. Shasta, California. Both samples contain a normal component carried by 100 ??m size multi-domain (MD) titanomagnetite (Usp11-24). One sample also contains a second normal component carried by < 10 ??m size pseudo-single domain (PSD) or single domain (SD) Ti-free magnetite (Usp1) found in the dacitic glass. The MD titanomagnetite and PSD or SD magnetite dominate the strong field magnetic signal, but only the PSD or SD magnetite has any influence on the remanence signal. Unlike the strong field signal, the remanence signal of both samples is dominated by a reverse NRM component. This reverse component is carried by 100 ??m size ferrian ilmenite (Ilm53-65). The compositions of the ilmenites in both samples are within the range of compositions (Ilm50-75) known to have the ability to acquire self-reversing thermoremanent magnetizations (TRM). The results of the Lowric-Fuller test indicate that the remanence signal is dominated by PSD or SD carriers. Because one sample contains only large MD titanomagnetite and no SD Ti-free magnetite (in addition to ferrian ilmenite), the ferrian ilmenite must be a PSD or SD carrier. Oxide and pyroxene geothermometry indicate the FeTi oxides in the pumice crystallized at temperatures between 880 and 945??C. This temperature range is within the disordered region of the ilmenite-hematite phase diagram for Ilm53-65. Previous work on synthetic Ilm70 and Ilm80 has shown that cooling through the order-disorder transition into the ordered region develops a transformation-induced microstructure consisting of cation-ordered domains with disordered domain boundaries. An Ilm58-59 grain from one of the Mt. Shasta samples was examined in the transmission electron microscope and was found to contain 100-200 A?? diameter cation-ordered domains. These domains arose during cooling through the transition temperature, which is estimated at 800??C for Ilm58-59. The presence of the disordered domain boundaries provides an explanation for the magnetic behavior of the ferrian ilmenite. (1) The disordered boundaries are the higher Curie point phase necessary for the operation of the self-reversal mechanism. (2) The disordered domain boundaries either inhibit the formation of magnetic domain walls or restrict magnetic domain wall movement accounting for the PSD or SD behavior of the ferrian ilmenite. ?? 1987.

Volcán Quizapu, Chilean Andes

USGS Publications Warehouse

Hildreth, Wes; Drake, Robert E.

1992-01-01

Quizapu is a flank vent of the basalt-to-rhyodacite Holocene stratocone, Cerro Azul, and lies at the focus of a complex Quaternary volcanic field on the Andean volcanic front. The Quizapu vent originated in 1846 when 5 km3 of hornblende-dacite magma erupted effusively with little accompanying tephra. Between ∼ 1907 and 1932, phreatic and strombolian activity reamed out a deep crater, from which 4 km3 of dacite magma identical to that of 1846 fed the great plinian event of 10–11 April 1932. Although a total of >9 km3 of magma was thus released in 86 years, there is no discernible subsidence. As the pre-plinian crater was lined by massive lavas, 1932 enlargement was limited and the total plinian deposit contains only ∼ 0.4 wt % lithics. Areas of 5-cm and 1-cm isopachs for compacted 1932 fallout are about half of those estimated in the 1930's, yielding a revised ejecta volume of ∼9.5 km3. A strong inflection near the 10-cm isopach (downwind ∼110 km) on a plot of log Thickness vs Area1/2 reflects slow settling of fine plinian ash — not of coignimbrite ash, as the volume of pyroclastic flows was trivial (<0.01 km3). About 17 vol.% of the fallout lies beyond the 1-cm isopach, and ∼ 82 wt% of the ejecta are finer than 1 mm. A least 18 hours of steady plinian activity produced an exceptionally uniform fall deposit. Observed column height (27–30 km) and average mass eruption rate (1.5x108 kg/s) compare well with values for height and peak intensity calculated from published eruption models. The progressive “aeolian fractionation” of downwind ash (for which Quizapu is widely cited) is complicated by the large compositional range of 1932 juvenile pumice (52–70% SiO2). The eruption began with andesitic scoria and ended with basaltic scoria, but >95% of the ejecta are dacitic pumice (67–68% SiO2); minor andesitic scoria and frothier rhyodacite pumice (70% SiO2) accompanied the dominant dacite. Phenocrysts (pl>hb∼opx>mt>ilm∼cpx) are similar in both abundance and composition in the 1846 (effusive) and 1932 (plinian) dacites. Despite the contrast in mode of eruption, bulk compositions are also indistinguishable. The only difference so far identified is a lower range of δ D values for 1846 hornblende, consistent with pre-eruptive degassing of the effusive batch.

The 2012 Copahue eruption: magnitude of gas fluxes and time scale of degassing

NASA Astrophysics Data System (ADS)

Varekamp, J. C.; Camfield, L.

2015-12-01

Copahue volcano (Argentina, 37.5 S, 71.5 W) erupted in 2000 and 2012 with initial phreato-magmatic blasts, violent Strombolian eruptions of several hours duration, followed by open conduit activity for days to months. The 2012 basal deposits 10 km S of Copahue are mm-sized ashes with hydrothermally altered debris, followed by up to 10cm pancake pumices, while denser cinders fell near the crater in the waning stages. The strombolian plume was ~ 6 km high and satellite images show its trajectory up to 200 km S. The pumices have finely porous rims (0.3mm vesicles) that were probably quenched by hydrothermal fluids and coarse interiors (several mm vesicles) that inflated during eruption. All the products have identical chemical composition and mineralogy, and only vary in degree of vesiculation. The 2012 products are the most mafic of the whole volcanic history of Copahue, with MgO ~ 4.5 %. The quench rim pumice glass contains 1160 ppm Cl while glass inclusions have up to 1800 ppm Cl. Water concentrations are 0.5-2.0 % (by difference with EMPA) and plagioclase hygrometry. Pre-eruptive conditions were 1080 oC and 1-2.5 kb pressure. The magmato-hydrothermal system is leaking fluids into the overlying crater lake and into a river. The hot springs have pH <1 and these fluids are up to 60% magmatic in origin. Annual river flux measurements and non-steady state modeling between 1997 and 2013 constrain the mean hydrothermal Cl flux at 1170 tonnes/month. The 2012 erupted magma mass is about 1012 gr, and from the measured total Cl loss between 2000 and 2012 and mean degassed Cl in the magma the volume of degassing magma is estimated at 1014-1015 grams. Much more magma was degassing than was erupted. Analyses of 226Ra-210Pb constrained the maximum degassing time at 8-10 years prior to the 2012 eruption. Almost all rock samples have 210Pb deficits, and so most gas escaped from the magma into the hydrothermal system. Nonetheless, the top of the magma reservoir accumulated bubbles, which caused overpressurization that led to the eruption. Calculations of bubble rise velocities help constrain the geometry of the underlying magma reservoir. The decadal eruption rhythm of Copahue is probably more determined by the time needed for bubble accumulation and associated pressure increase (about ten years) and less by new magma intrusions.

Material Properties Measurements for Selected Materials

NASA Technical Reports Server (NTRS)

Green, S. J.; Isbell, W. M.; Jones, A. H.; Maiden, C. J.; Perkins, R. D.; Shipman, F. H.

1968-01-01

Hugoniot equation of state measurements were made on Coconino sandstone, Vacaville basalt, Kaibab limestone, Mono Crater, pumice and Zelux (a polycarbonate resin) for pressures to 2 Mb. A single data point was obtained for fused quartz at 1.6 Mb. In addition to the hugoniot studies, the uniaxial compressive stress behavior of Vacaville basalt and Zelux was investigated at strain rates from about 10(exp -5)/sec to 10(exp 3)/second. The data presented include the stress - strain relations as a function of strain rate for these two materials.

A&M. TAN607. Construction view, facing southwest. At upper left of ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

A&M. TAN-607. Construction view, facing southwest. At upper left of view, north-wall equipment and operating galleries take shape on hot shop. Pumice-block side of storage pool section in center left of view. Water filter building (TAN-608) next to north wall of pool. Hot liquid waste building (TAN-616) at right of view. Note concrete construction of TAN-608 and 616. Date: January 18, 1954. INEEL negative no. 9604 - Idaho National Engineering Laboratory, Test Area North, Scoville, Butte County, ID

MOUNT SHASTA WILDERNESS STUDY AREA, CALIFORNIA.

USGS Publications Warehouse

Christiansen, Robert L.; Tuchek, Ernest T.

1984-01-01

The Mount Shasta Wilderness lies wholly on the slopes and summit area of Mount Shasta and consists almost entirely of the products of geologically young volcanism. Small deposits of volcanic cinders and pumice are present. The volcanic system of Mount Shasta is judged to have probable resource potential for geothermal energy but that potential is least within the wilderness study area boundaries. Because any geothermal energy resource beneath the volcano would lie at considerable depths, exploration or development would be most likely at lower altitudes on the gentler slopes outside the study area.

A postulated new source for the White River Ash, Alaska: A section in Geologic studies in Alaska by the US. Geological Survey, 1990

USGS Publications Warehouse

McGimsey, Robert G.; Richter, Donald H.; DuBois, Gregory D.; Miller, T.P.

1992-01-01

The White River Ash (Lerbekmo and others, 1968), product of two of the most voluminous pyroclastic eruptions in North America in the past 2,000 yr, blankets much of the Yukon Terrtory, Canada, and a small part of adjoining eastern Alaska. Lerbekmo and Campbell (1969) narrowed the source of the ash to an area northeast of the Mt. Bona-Mt. Churchill massif in the St. Elias Mountains of southern Alaska. Based on indirect evidence, Lerbekmo and Campbell (1969) further suggested that the vent was beneath the Klutlan Glacier, adjacent to a mound of coarse pumice, 16 km northeast of Mt. Bona. Recently discovered pumice and ash deposits and a possible vent structure near the summit of Mt. Churchill suggest an alternate source area. The White River Ash is a bilobate plinian fallout deposit covering more than 340,000 km2 and containing an estimated 25-50 km3 of tephra (Bostock, 1952; Berger, 1960; fig. 1). Radiocarbon ages indicate that the northern lobe was deposited about 1,887 yr B.P. and the eastern, and larger, lobe about 1,250 yr B.P. (Lerbekmo and others, 1975). The axes of the two lobes converge near Mt. Bona (16,420 ft (5,005 m)) and Mt. Churchill [15,638 ft (4,766 m)], which together form a prominent massif in the St. Elias Mountains. The Klutlan Glacier, a large valley glacier that flows eastward into Canada, has its principal source on the eastern flank of the massif. 

Qualitative and quantitative evaluation of human dental enamel after bracket debonding: a noncontact three-dimensional optical profilometry analysis.

PubMed

Ferreira, Fabiano G; Nouer, Darcy F; Silva, Nelson P; Garbui, Ivana U; Correr-Sobrinho, Lourenço; Nouer, Paulo R A

2014-09-01

The aim of this study was to undertake a qualitative and quantitative evaluation of changes on enamel surfaces after debonding of brackets followed by finishing procedures, using a high-resolution three-dimensional optical profiler and to investigate the accuracy of the technique. The labial surfaces of 36 extracted upper central incisors were examined. Before bonding, the enamel surfaces were subjected to profilometry, recording four amplitude parameters. Brackets were then bonded using two types of light-cured orthodontic adhesive: composite resin and resin-modified glass ionomer cement. Finishing was performed by three different methods: pumice on a rubber cup, fine and ultrafine aluminum oxide discs, and microfine diamond cups followed by silicon carbide brushes. The samples were subsequently re-analyzed by profilometry. Wilcoxon signed-rank test, Kruskal-Wallis test (p < 0.05) and a posteriori Mann-Whitney U test with Bonferroni correction (p < 0.0167) revealed a significant reduction of enamel roughness when diamond cups followed by silicon carbide brushes were used to finish surfaces that had remnants of resin-modified glass ionomer adhesive and when pumice was used to finish surfaces that had traces of composite resin. Enamel loss was minimal. The 3D optical profilometry technique was able to provide accurate qualitative and quantitative assessment of changes on the enamel surface after debonding. Morphological changes in the topography of dental surfaces, especially if related to enamel loss and roughness, are of considerable clinical importance. The quantitative evaluation method used herein enables a more comprehensive understanding of the effects of orthodontic bonding on teeth.

Character, mass, distribution, and origin of tephra-fall deposits of the 1989-1990 eruption of redoubt volcano, south-central Alaska

USGS Publications Warehouse

Scott, W.E.; McGimsey, R.G.

1994-01-01

The 1989-1990 eruption of Redoubt Volcano spawned about 20 areally significant tephra-fall deposits between December 14, 1989 and April 26, 1990. Tephra plumes rose to altitudes of 7 to more than 10 km and were carried mainly northward and eastward by prevailing winds, where they substantially impacted air travel, commerce, and other activities. In comparison to notable eruptions of the recent past, the Redoubt events produced a modest amount of tephra-fall deposits - 6 ?? 107 to 5 ?? 1010 kg for individual events and a total volume (dense-rock equivalent) of about 3-5 ?? 107 m3 of andesite and dacite. Two contrasting tephra types were generated by these events. Pumiceous tephra-fall deposits of December 14 and 15 were followed on December 16 and all later events by fine-grained lithic-crystal tephra deposits, much of which fell as particle aggregates. The change in the character of the tephra-fall deposits reflects their fundamentally different modes of origin. The pumiceous deposits were produced by magmatically driven explosions. The finegrained lithic-crystal deposits were generated by two processes. Hydrovolcanic vent explosions generated tephrafall deposits of December 16 and 19. Such explosions continued as a tephra source, but apparently with diminishing importance, during events of January and February. Ash clouds of lithic pyroclastic flows generated by collapse of actively growing lava domes probably contributed to tephra-fall deposits of all events from January 2 to April 26, and were the sole source of tephra fall for at least the last 4 deposits. ?? 1994.

Description and mineralogy of Tertiary volcanic ash partings and their relationship to coal seams, near Homer, Alaska

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reinink-Smith, L.M.

1985-04-01

Outcrops of Tertiary coal-bearing units in sea cliffs of the Kenai Peninsula provide an excellent study area for volcanic ash partings in coals. Twenty mid-to late-Miocene, 50-cm to 3-m thick coal seams exposed in the sea cliffs about 10 km west of Homer contain an average of 10 volcanic ash or lapilli tuff partings each. The bedding relationships of the coal with any one parting cannot be predicted, and the contacts of the partings with the coal range from very sharp to predominantly gradational. These bedding relationships provide clues about the surface on which the ashes fell and on whichmore » the coal was accumulating. For example, some ashes fell in standing water, others on irregular subaerial surfaces. The partings are in various stages of alteration to kaolinite and bentonite, and vary in thickness from a few millimeters to about 10 cm. The consistency and texture of the partings depend on the degree of alteration; the less altered partings display visible pumice fragments and euhedral feldspars, commonly within a finer grained matrix. Separate pumice fragments, excluding matrix, can also occur as partings in the coal. The more altered partings may be wet and plastic, or they may be well indurated claystones; the colors range from gray-yellow to dark brown. The indurated prints are more common in older part of the section. The coal seams may be capped by volcanic ash partings and are commonly underlain by a pencil shale of nonvolcanic origin.« less

The 7-8 August 2008 eruption of Kasatochi Volcano, central Aleutian Islands, Alaska

NASA Astrophysics Data System (ADS)

Waythomas, Christopher F.; Scott, William E.; Prejean, Stephanie G.; Schneider, David J.; Izbekov, Pavel; Nye, Christopher J.

2010-12-01

Kasatochi volcano in the central Aleutian Islands erupted unexpectedly on 7-8 August 2008. Kasatochi has received little study by volcanologists and has had no confirmed historical eruptions. The island is an important nesting area for seabirds and a long-term biological study site of the U.S. Fish and Wildlife Service. After a notably energetic preeruptive earthquake swarm, the volcano erupted violently in a series of explosive events beginning in the early afternoon of 7 August. Each event produced ash-gas plumes that reached 14-18 km above sea level. The volcanic plume contained large amounts of SO2 and was tracked around the globe by satellite observations. The cumulative volcanic cloud interfered with air travel across the North Pacific, causing many flight cancelations that affected thousands of travelers. Visits to the volcano in 2008-2009 indicated that the eruption generated pyroclastic flows and surges that swept all flanks of the island, accumulated several tens of meters of pyroclastic debris, and increased the diameter of the island by about 800 m. Pyroclastic flow deposits contain abundant accidental lithic debris derived from the inner walls of the Kasatochi crater. Juvenile material is crystal-rich silicic andesite that ranges from slightly pumiceous to frothy pumice. Fine-grained pyroclastic surge and fall deposits with accretionary lapilli cover the lithic-rich pyroclastic flow deposits and mark a change in eruptive style from episodic explosive activity to more continuous ash emission with smaller intermittent explosions. Pyroclastic deposits completely cover the island, but wave erosion and gully development on the flanks have begun to modify the surface mantle of volcanic deposits.

A comparison of retentive strength of implant cement depending on various methods of removing provisional cement from implant abutment

PubMed Central

Keum, Eun-Cheol

2013-01-01

PURPOSE This study evaluated the effectiveness of various methods for removing provisional cement from implant abutments, and what effect these methods have on the retention of prosthesis during the definitive cementation. MATERIALS AND METHODS Forty implant fixture analogues and abutments were embedded in resin blocks. Forty cast crowns were fabricated and divided into 4 groups each containing 10 implants. Group A was cemented directly with the definitive cement (Cem-Implant). The remainder were cemented with provisional cement (Temp-Bond NE), and classified according to the method for cleaning the abutments. Group B used a plastic curette and wet gauze, Group C used a rubber cup and pumice, and Group D used an airborne particle abrasion technique. The abutments were observed using a stereomicroscope after removing the provisional cement. The tensile bond strength was measured after the definitive cementation. Statistical analysis was performed using one-way analysis of variance test (α=.05). RESULTS Group B clearly showed provisional cement remaining, whereas the other groups showed almost no cement. Groups A and B showed a relatively smooth surface. More roughness was observed in Group C, and apparent roughness was noted in Group D. The tensile bond strength tests revealed Group D to have significantly the highest tensile bond strength followed in order by Groups C, A and B. CONCLUSION A plastic curette and wet gauze alone cannot effectively remove the residual provisional cement on the abutment. The definitive retention increased when the abutments were treated with rubber cup/pumice or airborne particle abraded to remove the provisional cement. PMID:24049563

Effect of two prophylaxis methods on marginal gap of Cl Vresin-modified glass-ionomer restorations.

PubMed

Kimyai, Soodabeh; Pournaghi-Azar, Fatemeh; Daneshpooy, Mehdi; Abed Kahnamoii, Mehdi; Davoodi, Farnaz

2016-01-01

Background. This study evaluated the effect of two prophylaxis techniques on the marginal gap of CI V resin-modified glass-ionomer restorations. Methods. Standard Cl V cavities were prepared on the buccal surfaces of 48 sound bovine mandibular incisors in this in vitro study. After restoration of the cavities with GC Fuji II LC resin-modified glass-ionomer, the samples were randomly assigned to 3 groups of 16. In group 1, the prophylactic procedures were carried out with rubber cup and pumice powder and in group 2 with air-powder polishing device (APD). In group 3 (control), the samples did not undergo any prophylactic procedures. Then the marginal gaps were measured. Two-way ANOVA was used to compare marginal gaps at the occlusal and gingival margins between the groups. Post hoc Tukey test was used for two-by-two comparisons. Statistical significance was set at P < 0.05. Results. There were significant differences in the means of marginal gaps in terms of prophylactic techniques (P < 0.001), with significantly larger marginal gaps in the APD group compared to the pumice and rubber cup group, which in turn exhibited significantly larger marginal gaps compared to the control group (P < 0.0005). In addition, the means of marginal gaps were significant in terms of the margin type (P < 0.001), with significantly larger gaps at gingival margins compared to the occlusal margins (P < 0.0005). Conclusion. The prophylactic techniques used in this study had a negative effect on the marginal gaps of Cl V resin-modified glass-ionomer restorations.

Tephra layers of blind Spring Valley and related upper pliocene and pleistocene tephra layers, California, Nevada, and Utah: isotopic ages, correlation, and magnetostratigraphy

USGS Publications Warehouse

Sarna-Wojcicki, Andrei M.; Reheis, Marith C.; Pringle, Malcolm S.; Fleck, Robert J.; Burbank, Doug; Meyer, Charles E.; Slate, Janet L.; Wan, Elmira; Budahn, James R.; Troxel, Bennie; Walker, James P.

2005-01-01

Numerical ages have been determined for a stratigraphic sequence of silicic tephra layers exposed at the Cowan Pumice Mine in Blind Spring Valley, near Benton Hot Springs, east-central California, as well as at Chalk Cliffs, north of Bishop, Calif. The tephra layers at these sites were deposited after eruptions from nearby sources, most of them from near Glass Mountain, and some from unknown sources. The ages were determined primarily by the laser-fusion 40Ar/39Ar method, mostly on sanidine feldspar; two were determined by conventional K-Ar analysis on obsidian clasts. These tephra layers, all underlying the Bishop ash bed and listed in order of concordant age and stratigraphic position, are: Tephra Unit Method Material Age Bishop Tuff (air-fall pumice) Ar/Ar sanidine 0.759?0.002 Ma* Upper tuffs of Glass Mountain Ar/Ar sanidine 0.87?0.02 Ma Upper tuffs of Glass Mountain Ar/Ar sanidine 1.13?0.19 Ma Lower tuffs of Glass Mountain K-Ar obsidian 1.86?0.09 Ma (avg of 2 dates) Ar/Ar sanidine 1.92?0.02 Ma (avg of 2 dates) Tuffs of Blind Spring Valley Ar/Ar sanidine 2.135?0.02 to sanidine 2.219?0.006 Ma (10 dates) Tuffs of Benton Hot Springs Ar/Ar plagioclase 2.81?0.02 Ma *Date published previously The above tephra layers were also petrographically examined and the volcanic glass shards of the layers were chemically analyzed using the electron microprobe and, for some samples, instrumental neutron activation analysis and X-ray fluorescence. The same types of chemical and petrographic analyses were conducted on stratigraphic sequences of tephra layers of suspected upper Pliocene and Pleistocene age in several past and present depositional basins within the region outside of Blind Spring Valley. Chemical characterization, combined with additional dates and with magnetostratigraphy of thick sections at two of the distal sites, allow correlation of the tephra layers at the Cowan Pumice Mine with layers present at the distal sites and provide age constraints for other intercalated tephra layers and sediments for which age data were previously lacking. The identification at several sections of the widespread Huckleberry Ridge ash bed, derived from the Yellowstone eruptive source area in Wyoming, as well as a new 40Ar/39Ar age on this ash bed from a proximal locality, provide additional age constraints to several of the distal sections. The dated or temporally bracketed distal units, in order of concordant age and stratigraphic position, are: Tephra Unit Method Material Age Tephra layers of Glass Mountain (undiff.) P-mag.*; correlation N/A 1.78 , 1.96, 1.96, 2.22, 2.57, <2.89 Ma Tephra layers of Benton Hot Springs Ar/Ar; correlation plagioclase 2.89?0.03 Ma *Magnetostratigraphic polarity determination At the Cowan Pumice Mine, only a partial section of the eruptive record is preserved, but the best materials for laser-fusion 40Ar/39Ar and other isotopic dating methods were obtained. In the more distal Willow Wash and Confidence Hills sections, both persistent depositional basins for most of late Pliocene time, more complete sections of upper Pliocene tephra layers were preserved. In the region of Glass Mountain, the tephra layers that make up each of the mapped and dated pyroclastic units are multiple and complex, but a progressive simplification of the stratigraphy away from the source area was observed for more distal sites in southern and southwestern California and in Utah. This progressive

The 1963–65 eruption of Irazú volcano, Costa Rica (the period of March 1963 to October 1964)

USGS Publications Warehouse

Murata, K.J.; Dondoli, C.; Saenz, R.

1966-01-01

The ash section was about 2 meters thick, 800 meters downwind from the vent in June 1964. In the section, deposits of the rainy season could be distinguished by their well developed stratification from those of the dry season. A zone containing three persistent pumice horizons represents the climactic period of December 1963 to January 1964. The cloudburst of December 10, 1963 is recorded by a highly rilled surface, and the strong winds of the dry season of 1964 are indicated by a rippled lag deposit.

40Ar/39Ar ages of the AD 79 eruption of Vesuvius, Italy

USGS Publications Warehouse

Lanphere, Marvin A.; Champion, Duane E.; Melluso, Leone; Morra, Vincenzo; Perrotta, Annamaria; Scarpati, Claudio; Tedesco, Dario; Calvert, Andrew T.

2007-01-01

The Italian volcano, Vesuvius, erupted explosively in AD 79. Sanidine from pumice collected at Casti Amanti in Pompeii and Villa Poppea in Oplontis yielded a weighted-mean 40Ar/39Ar age of 1925±66 years in 2004 (1σ uncertainty) from incremental-heating experiments of eight aliquants of sanidine. This is the calendar age of the eruption. Our results together with the work of Renne et al. (1997) and Renne and Min (1998) demonstrate the validity of the 40Ar/39Ar method to reconstruct the recent eruptive history of young, active volcanoes.

The latest explosive eruptions of Ciomadul (Csomád) volcano, East Carpathians - A tephrostratigraphic approach for the 51-29 ka BP time interval

NASA Astrophysics Data System (ADS)

Karátson, D.; Wulf, S.; Veres, D.; Magyari, E. K.; Gertisser, R.; Timar-Gabor, A.; Novothny, Á.; Telbisz, T.; Szalai, Z.; Anechitei-Deacu, V.; Appelt, O.; Bormann, M.; Jánosi, Cs.; Hubay, K.; Schäbitz, F.

2016-06-01

The most recent, mainly explosive eruptions of Ciomadul, the youngest volcano in the Carpatho-Pannonian Region, have been constrained by detailed field volcanological studies, major element pumice glass geochemistry, luminescence and radiocarbon dating, and a critical evaluation of available geochronological data. These investigations were complemented by the first tephrostratigraphic studies of the lacustrine infill of Ciomadul's twin craters (St. Ana and Mohoş) that received tephra deposition during the last eruptions of the volcano. Our analysis shows that significant explosive activity, collectively called EPPA (Early Phreatomagmatic and Plinian Activity), started at Ciomadul in or around the present-day Mohoş, the older crater, at ≥ 51 ka BP. These eruptions resulted in a thick succession of pyroclastic-fall deposits found in both proximal and medial/distal localities around the volcano, characterized by highly silicic (rhyolitic) glass chemical compositions (ca. 75.2-79.8 wt.% SiO2). The EPPA stage was terminated by a subplinian/plinian eruption at ≥ 43 ka BP, producing pumiceous pyroclastic-fall and -flow deposits of similar glass composition, probably from a "Proto-St. Ana" vent located at or around the younger crater hosting the present-day Lake St. Ana. After a quiescent period with a proposed lava dome growth in the St. Ana crater, a new explosive stage began, defined as MPA (Middle Plinian Activity). In particular, a significant two-phase eruption occurred at 31.5 ka BP, producing pyroclastic flows from vulcanian explosions disrupting the preexisting lava dome of Sf. Ana, and followed by pumiceous fallout from a plinian eruption column. Related pyroclastic deposits show a characteristic, less evolved rhyolitic glass composition (ca. 70.2-74.5 wt.% SiO2) and occur both in proximal and medial/distal localities up to 21 km from source. The MPA eruptions, that may have pre-shaped a crater similar to, but possibly smaller than, the present-day St. Ana crater, was followed by a so far unknown, but likewise violent last eruptive stage from the same vent, creating the final morphology of the crater. This stage, referred to as LSPA (Latest St. Ana Phreatomagmatic Activity), produced pyroclastic-fall deposits of more evolved rhyolitic glass composition (ca. 72.8-78.8 wt.% SiO2) compared to that of the previous MPA stage. According to radiocarbon age constraints on bulk sediment, charcoal and organic matter from lacustrine sediments recovered from both craters, the last of these phreatomagmatic eruptions - that draped the landscape toward the east and southeast of the volcano - occurred at 29.6 ka BP, some 2000 years later than the previously suggested last eruption of Ciomadul.

Pyroclastic density currents associated with the 2008-2009 eruption of Chaitén Volcano (Chile): forest disturbances, deposits, and dynamics

USGS Publications Warehouse

Major, Jon J.; Pierson, Thomas C.; Hoblitt, Richard P.; Moreno, Hugo

2013-01-01

Explosive activity at Chaitén Volcano in May 2008 and subsequent dome collapses over the following nine months triggered multiple, small-volume pyroclastic density currents (PDCs). The explosive activity triggered PDCs to the north and northeast, which felled modest patches of forest as far as 2 km from the caldera rim. Felled trees pointing in the down-current direction dominate the disturbance zones. The PDC on the north flank of Chaitén left a decimeters-thick, bipartite deposit having a basal layer of poorly sorted, fines-depleted pumice-and-lithic coarse ash and lapilli, which transitions abruptly to fines-enriched pumice-and-lithic coarse ash. The deposit contains fragments of mostly uncharred organics near its base; vegetation protruding above the deposit is uncharred. The nature of the forest disturbance and deposit characteristics suggest the PDC was dilute, of relatively low temperature (-1. It was formed by directionally focused explosions throughout the volcano's prehistoric, intracaldera lava dome. Dilute, low-temperature PDCs that exited the caldera over a low point on the east-southeast caldera rim deposited meters-thick fill of stratified beds of pumice-and-lithic coarse ash and lapilli. They did not fell large trees more than a few hundred of meters from the caldera rim and were thus less energetic than those on the north and northeast flanks. They likely formed by partial collapses of the margins of vertical eruption columns. In the Chaitén River valley south of the volcano, several-meter-thick deposits of two block-and-ash flow (BAF) PDCs are preserved. Both have a coarse ash matrix that supports blocks and lapilli predominantly of lithic rhyolite dome rock, minor obsidian, and local bedrock. One deposit was emplaced by a BAF that traveled an undetermined distance downvalley between June and November 2008, apparently triggered by partial collapse of a newly effused lava dome on that started growing on 12 May. A second, and larger, BAF related to another collapse of the new lava dome on 19 February 2009 traveled to within 3 km of the village of Chaitén, 10 km downstream of the volcano. It deposited as much as 8-10 m of diamict having sedimentary characteristics very similar to the previous BAF deposit. Charred trees locally encased within the BAD deposits suggest that the flows were of moderate temperature, perhaps as much as 300°C. Erosion of the BAD deposits filling the Chaitén River channel has delivered substantial sediment loads downstream, contributing to channel instability and challenged river management.

A closer look at the pyroclastic density current deposits of the May 18, 1980 eruption of Mt St Helens

NASA Astrophysics Data System (ADS)

Mackaman-Lofland, C. A.; Brand, B. D.; Dufek, J.

2010-12-01

Pyroclastic Density Currents (PDCs) are the most dangerous hazard associated with explosive volcanic eruptions. Due to the danger associated with observing these ground-hugging currents of searing hot gas, ash, and rock in real time, their processes are poorly understood. In order to understand flow dynamics, including what controls how far PDCs travel and how they interact with topography, it is necessary to study their deposits. The May 18th, 1980 eruption of Mt. St. Helens produced multiple PDCs, burying the area north of the volcano under 10s of meters of PDC deposits. Because the eruption is one of the best observed on record, individual flow units can be correlated to changes in eruptive intensity throughout the day (e.g., Criswell, 1987). Deep drainage erosion over the past 30 years has exposed the three-dimensional structure of the PDC deposits, making this intensive study possible. Up to six flow units have been identified along the large western drainage of the pumice plain. Each flow unit has intricate vertical and lateral facies changes and complex cross-cutting relationships away from source. The most proximal PDC deposits associated with the afternoon flows on May 18 are exposed 4 km from source in tributaries of the large drainage on the western side of the pumice plain. Hummocks from the debris avalanche are also exposed above and within these proximal drainages. It is apparent that the PDCs were often erosional, entraining large blocks from the hummocks and depositing them in close proximity downstream. The currents were also depositional, as thick sequences of PDC deposits are found in areas between hummocks, which thin to veneers above them. This indicates that the currents were interacting with complex topography early in their propagation, and is reflected by spatially variable bed conditions including rapid changes in bedding and granulometry characteristics within individual flow units. For example, within 20 lateral meters of a given flow unit, depositional features can vary from massive, diffusely-stratified to stratified, and cross stratified. We interpret this variability as a result of interaction with nearby topography, rapid sedimentation of large blocks, or a combination of the two; this implies rapid spatial and temporal instabilities in the current. For each flow unit we measure deposit thickness, bedding style, clast size, density and sorting, and degree of pumice rounding with distance from source. We use this data to better understand and interpret flow dynamics from depositional characteristics. The data we collect will be used to refine and validate numerical models of PDCs, ultimately providing a more accurate hazard assessment for explosive eruptions.

Remarkably preserved tephra from the 3430 Ma Strelley Pool Formation, Western Australia: Implications for the interpretation of Precambrian microfossils

NASA Astrophysics Data System (ADS)

Wacey, David; Saunders, Martin; Kong, Charlie

2018-04-01

The ∼3430 Ma Strelley Pool Formation (SPF), Pilbara, Western Australia contains some of the most diverse microfossil evidence for early life on Earth. Here we report an assemblage of tephra (scoria, tubular pumice, plus vesicular and non-vesicular volcanic glass shards) from two stratigraphic levels in the SPF, including morphotypes that closely resemble previously described microfossils from this unit and elsewhere. Clasts of scoria are characterised by numerous spheroidal vesicles, with subordinate eye- and lens-shaped morphotypes, commonly lined with anatase (TiO2) and small amounts of organic material. Their diameters range from 5-180 μm with 80% in the 10-50 μm range. Fragments of tubular pumice are also lined with anatase + / - carbon and have tube diameters of 5-15 μm. Other volcanic ejecta particles include a multitude of sub-angular shard particles with or without vesicles, plus more rounded vase-shaped, eye-shaped, and hair-like morphologies; once again, most of these are coated by anatase + / - carbon and are several tens of micrometres in size. Many of the tephra fragments are now entirely silicified with no compositional difference between the former volcanic glass, the vesicle infill and the clast matrix. However, some examples retain a partial aluminosilicate composition, either as a vesicle infilling phase or as isolated lath-like grains within the formerly glassy groundmass. Isolated occurrences of some of these tephra morphotypes strongly resemble simple microbial morphologies including pairs and clusters of cells (cf. scoria), filamentous microbes (cf. tubular pumice) and larger sheaths/cysts (cf. sub-rounded glass shards). Furthermore, some tephra-containing clasts occur in a SPF sandstone unit that hosts previously described microfossils, while others are interbedded with chert layers from which microfossils have also been described. In light of our new volcanogenic data, we evaluate the robustness of previous microfossil evidence from the SPF in the East Strelley greenstone belt. We find that the majority of previously illustrated microfossils from this greenstone belt possess multiple features that are consistent with a biological interpretation and are unlikely to be volcanogenic, but at least one previously illustrated specimen is here reinterpreted as volcanic in origin. The importance of this work is that it serves to highlight the common occurrence of volcanogenic microstructures resembling biological fossils (i.e. pseudo-fossils) in Archean environments that are habitable for life. Such structures have until now been largely overlooked in the assessment of putative Precambrian microfossils. Our data show that tephra-derived microstructures should be considered as a null hypothesis in future evaluations of potential signs of life on the early Earth, or on other planets.

Hydrogeologic investigations of the Miocene Nogales Formation in the Nogales Area, Upper Santa Cruz Basin, Arizona

USGS Publications Warehouse

Page, William R.; Gray, Floyd; Bultman, Mark W.; Menges, Christopher M.

2016-07-28

Hydrogeologic investigations were conducted to evaluate the groundwater resource potential for the Miocene Nogales Formation in the Nogales area, southern Arizona. Results indicate that parts of the formation may provide new, deeper sources of groundwater for the area. Geologic mapping determined the hydrogeologic framework of the formation by defining lithologic, mineralogic, and stratigraphic characteristics; identifying potential aquifers and confining units; and mapping faults and fractures which likely influence groundwater flow. Geophysical modeling was used to determine the basin geometry and thickness of the Nogales Formation and younger alluvial aquifers and to identify target areas (deep subbasins) which may prove to be productive aquifers.Volcaniclastic sandstone samples from the formation were analyzed for porosity, bulk density, saturated hydraulic conductivity, and fabric. Effective porosity ranges from 16 to 42 percent, bulk density from 1.6 to 2.47 grams per cubic centimeter, and saturated hydraulic conductivity (SHC) from 4 to 57 centimeters per day (4.9×10-5 to 6.7×10-4 centimeters per second). Thin sections show that sandstone framework grains consist of quartz, feldspar, biotite, hornblende, pumice, volcanic glass, and opaque minerals. The matrix in most samples consists of pumice fragments, and some contain predominantly silt and clay. Samples with a mostly silt and clay matrix have lower porosity and SHC compared to samples with mostly pumice, which have higher and wider ranges of porosity and SHC. Pore space in the Nogales Formation sediments includes moldic, intercrystalline, and fracture porosity. Some intercrystalline pore space is partially filled with calcite cement. About one third of the samples contain fractures, which correspond to fractures noted in outcrops in all members of the formation.Scanning electron microscope (SEM) and x-ray diffraction (XRD) analyses indicate that most of the samples contained the zeolite clinoptilolite and mixed-layer clay. X-ray diffraction analyses verified clinoptilolite as the only zeolite in Nogales Formation samples; they also verified the presence of smectite and illite clay and some kaolinite. Samples which contain greater amounts of clinoptilolite and lesser amounts of smectite have high porosity and SHC in narrow ranges. However, samples with abundant smectite and lesser amounts of clinoptilolite span the entire ranges of porosity and SHC for the formation.All members of the Nogales Formation are fractured and faulted as a result of Tertiary Basin and Range extensional deformation, which was broadly contemporaneous with deposition of the formation. These structures may have significant influence on groundwater flow in the upper Santa Cruz basin because, although many of the sediments in the formation have characteristics indicating they may be productive aquifers based only on porous-media flow, fracturing in these sediments may further enhance permeability and groundwater flow in these basin-fill aquifers by orders of magnitude.

The hydrological response to precipitations of a layered shallow sloping deposit: physical experiments and mathematical modeling

NASA Astrophysics Data System (ADS)

Damiano, Emilia; Greco, Roberto; Guida, Andrea; Olivares, Lucio; Picarelli, Luciano

2016-04-01

Although rainfall-induced landslides are frequent, so that they can be probably considered the most widespread natural hazards, fortunately the occurrence of an extreme rainfall event only rarely corresponds to the triggering of landslides. This is due to the fact that slopes, although often considered as separated systems in the stability analyses, are actually part of a larger, more complex hydrological system, with which continuously exchange water. Indeed, most of the slopes do not fail, and when they are subjected to heavy precipitation, effective draining mechanisms spontaneously develop, such as overland and subsurface runoff, and sometimes even new preferential flow paths originated by mechanical processes, such as piping erosion or deformation cracks. Hence, the triggering of a rainfall-induced landslide requires these dynamically evolving (non-linear) drainage processes to be incapable of releasing the excess of water (and pressure) accumulating within the slope. For the case of shallow sloping covers, the capability of the slope to effectively drain the infiltrating water depends on the hydraulic properties of the involved soils (hydraulic conductivity and water retention curves) and on the hydraulic boundary conditions (at the base of the cover, where it lays upon the bedrock, and at the foot of the slope), which are in turn strongly influenced by the initial moisture state (often indicated as a predisposing cause), owing to the non-linearity of the hydraulic processes. Such an already complex picture is furthermore complicated by heterogeneity. In this study, we focus our attention onto the effects of a layered soil cover with contrasting hydraulic properties on the infiltration and drainage processes in a shallow pyroclastic deposit. This is a typical situation along many pyroclastic-covered slopes of Campania (southern Italy), which present alternations of ashes (silty sands) and pumices (sands with gravel) deposited by volcanic eruptions, and where shallow landslides are sometimes triggered by intense and long-lasting precipitations. Several studies have already pointed out that layering may play a crucial role in the development of the infiltration process, as the coarse-grained pumice layers may behave as capillary barriers, leading to the formation of perched saturated zones. The hydrological behavior of such kind of layered slopes is investigated by means of small-scale infiltration experiments carried out in an instrumented flume in the laboratory. The interpretation of the experimental results is made with the help of a mathematical model of 2-D Richards equation, which allows shedding some light in the hydraulic properties of the pumices, which are hardly measurable with standard laboratory techniques. The obtained results show how, depending on initial moisture conditions, slope inclination angle and applied rainfall intensity, the response of the slope may be very different, and that the formation of a capillary barrier is not always observed.

Straddling the tholeiitic/calc-alkaline transition: the effects of modest amounts of water on magmatic differentiation at Newberry Volcano, Oregon

USGS Publications Warehouse

Mandler, Ben E.; Donnelly-Nolan, Julie M.; Grove, Timothy L.

2014-01-01

Melting experiments have been performed at 1 bar (anhydrous) and 1- and 2-kbar H2O-saturated conditions to study the effect of water on the differentiation of a basaltic andesite. The starting material was a mafic pumice from the compositionally zoned tuff deposited during the ~75 ka caldera-forming eruption of Newberry Volcano, a rear-arc volcanic center in the central Oregon Cascades. Pumices in the tuff of Newberry caldera (TNC) span a continuous silica range from 53 to 74 wt% and feature an unusually high-Na2O content of 6.5 wt% at 67 wt% SiO2. This wide range of magmatic compositions erupted in a single event makes the TNC an excellent natural laboratory in which to study the conditions of magmatic differentiation. Our experimental results and mineral–melt hygrometers/thermometers yield similar estimates of pre-eruptive H2O contents and temperatures of the TNC liquids. The most primitive (mafic) basaltic andesites record a pre-eruptive H2O content of 1.5 wt% and a liquidus temperature of 1,060–1,070 °C at upper crustal pressure. This modest H2O content produces a distinctive fractionation trend that is much more enriched in Na, Fe, and Ti than the calc-alkaline trend typical of wetter arc magmas, but slightly less enriched in Fe and Ti than the tholeiitic trend of dry magmas. Modest H2O contents might be expected at Newberry Volcano given its location in the Cascade rear arc, and the same fractionation trend is also observed in the rim andesites of the rear-arc Medicine Lake volcano in the southern Cascades. However, the Na–Fe–Ti enrichment characteristic of modest H2O (1–2 wt%) is also observed to the west of Newberry in magmas erupted from the arc axis, such as the Shevlin Park Tuff and several lava flows from the Three Sisters. This shows that modest-H2O magmas are being generated directly beneath the arc axis as well as in the rear arc. Because liquid lines of descent are particularly sensitive to water content in the range of 0–3 wt% H2O, they provide a quantitative and reliable tool for precisely determining pre-eruptive H2O content using major-element data from pumices or lava flows. Coupled enrichment in Na, Fe, and Ti relative to the calc-alkaline trend is a general feature of fractional crystallization in the presence of modest amounts of H2O, which may be used to look for “damp” fractionation sequences elsewhere.

Culture-Independent Identification of Manganese-Oxidizing Genes from Deep-Sea Hydrothermal Vent Chemoautotrophic Ferromanganese Microbial Communities Using a Metagenomic Approach

NASA Astrophysics Data System (ADS)

Davis, R.; Tebo, B. M.

2013-12-01

Microbial activity has long been recognized as being important to the fate of manganese (Mn) in hydrothermal systems, yet we know very little about the organisms that catalyze Mn oxidation, the mechanisms by which Mn is oxidized or the physiological function that Mn oxidation serves in these hydrothermal systems. Hydrothermal vents with thick ferromanganese microbial mats and Mn oxide-coated rocks observed throughout the Pacific Ring of Fire are ideal models to study the mechanisms of microbial Mn oxidation, as well as primary productivity in these metal-cycling ecosystems. We sampled ferromanganese microbial mats from Vai Lili Vent Field (Tmax=43°C) located on the Eastern Lau Spreading Center and Mn oxide-encrusted rhyolytic pumice (4°C) from Niua South Seamount on the Tonga Volcanic Arc. Metagenomic libraries were constructed and assembled from these samples and key genes known to be involved in Mn oxidation and carbon fixation pathways were identified in the reconstructed genomes. The Vai Lili metagenome assembled to form 121,157 contiguous sequences (contigs) greater than 1000bp in length, with an N50 of 8,261bp and a total metagenome size of 593 Mbp. Contigs were binned using an emergent self-organizing map of tetranucleotide frequencies. Putative homologs of the multicopper Mn-oxidase MnxG were found in the metagenome that were related to both the Pseudomonas-like and Bacillus-like forms of the enzyme. The bins containing the Pseudomonas-like mnxG genes are most closely related to uncultured Deltaproteobacteria and Chloroflexi. The Deltaproteobacteria bin appears to be an obligate anaerobe with possible chemoautotrophic metabolisms, while the Chloroflexi appears to be a heterotrophic organism. The metagenome from the Mn-stained pumice was assembled into 122,092 contigs greater than 1000bp in length with an N50 of 7635 and a metagenome size of 385 Mbp. Both forms of mnxG genes are present in this metagenome as well as the genes encoding the putative Mn oxidases McoA and MopA. The greater diversity of Mn oxidase pathways in this metagenome suggests a more diverse Mn oxidizing microbial community in the cold pumice sample. Key enzymes for four of the six known carbon fixation pathways (the Calvin Cycle, the reductive TCA cycle, the Wood-Ljungdahl pathway, and the 3-hydroxypropionate/4-hydroxybutyrate Cycle) were also identified in both samples indicating primary production occurs via a diverse community of carbon fixing organisms. Together, these samples contain active, diverse populations of Mn oxidizing bacteria living in association with microbial communities supported by chemoautotrophic carbon fixation.

Late Miocene ignimbrites at the southern Puna-northern Sierras Pampeanas border (˜27°S): Stratigraphic correlation

NASA Astrophysics Data System (ADS)

Montero-López, Carolina; Guzmán, Silvina; Barrios, Fabiola

2015-10-01

New field observations and petrographic and geochemical data of pyroclastic deposits exposed along the Las Papas valley (border between southern Puna and northern Sierras Pampeanas, Argentina) and further north, lead us to propose a new stratigraphic correlation and classification of the late Miocene volcanism in this area. We redefine the Las Papas, Las Juntas, Aguada Alumbrera and Rosada ignimbrites and define the Agua Caliente and Del Medio ignimbrites. The whole set of ignimbrites are rhyolites and less frequently dacites of calc-alkaline affinity. In the present contribution we divide ignimbrites into the Agua Negra and Rincón groups, based mainly on their geochemical signature. The Agua Negra Group is formed by the Las Papas and Las Juntas ignimbrites, indurated and welded, lithic-rich, with crystal-poor pumices and crystal-rich matrix. The Rincón Group comprises the Agua Caliente, Aguada Alumbrera, Rosada and Del Medio ignimbrites, with variable welding degrees, lithic and crystal content. The greater enrichment of crystals in the matrix in comparison with the crystal content in pumices indicates significant elutriation during flow transport and thus volume estimations are to be considered lower bounds for the actual erupted volume. The total minimum estimated volume for the ignimbrites of the Agua Negra and Rincón groups is 2.8 km3 (2.3 km3 DRE). Field relationships and new analytical data indicate that the different acid ignimbrites that crop out in this small area are related to at least two different magma chambers. The widespread Quaternary volcanism in this area covers the older deposits, thus making it difficult to recognize the volcanic centers that produced these late Miocene ignimbrites.

Shear strengths of a gallium alloy bonded to human enamel following nine different surface treatments.

PubMed

Claire, J; Williams, P T

2001-03-01

Gallium and indium-containing alloys have demonstrated an ability to wet and bond to many types of materials including enamel. The purpose of this study was to evaluate and compare the bond strengths of a gallium-and-indium-containing alloy and a dental amalgam to human enamel surfaces. A flat enamel bonding surface was created by slicing recently extracted human molars with a 180-grit diamond wheel. Cylinders of amalgam or a gallium-indium alloy were bonded to the as-cut surfaces or to as-cut surfaces that had been pumiced, air-abraded or acid-etched for various times. Before testing, samples were stored under different conditions (100% humidity, immersed in water, thermocycled). The shear-bond strength was determined using a crosshead speed of 0.1 mm x min(-1). Sample size was 10. Data was subjected to ANOVA and a post-hoc Tukey's test. The bond strength of amalgam to enamel was zero. The bond strength of the gallium-indium alloy ranged between 6.5 MPa (10s etch with 10% phosphoric acid) and 4.2 MPa (pumiced enamel). Acid-etching significantly increased the bond strength (P>0.0001) The bond strength was not significantly affected by the type of mechanical surface preparation, storage conditions, thermocycling, etching times or acid concentrations. Bonding, particularly chemical bonding, suggests a greater potential for better wetting and therefore better sealing of a cavity. Since microleakage of restorations is one of the principal causes of restoration failure, materials that can bond may in turn posses enhanced resistance to microleakage and ultimately, resistance to restoration failure. The gallium-indium alloy evaluated in this study may be such an alloy.

Remnant colloform pyrite at the haile gold deposit, South Carolina: A textural key to genesis

USGS Publications Warehouse

Foley, N.; Ayuso, R.A.; Seal, R.R.

2001-01-01

Auriferous iron sulfide-bearing deposits of the Carolina slate belt have distinctive mineralogical and textural features-traits that provide a basis to construct models of ore deposition. Our identification of paragenetically early types of pyrite, especially remnant colloform, crustiform, and layered growth textures of pyrite containing electrum and pyrrhotite, establishes unequivocally that gold mineralization was coeval with deposition of host rocks and not solely related to Paleozoic tectonic events. Ore horizons at the Haile deposit, South Carolina, contain many remnants of early pyrite: (1) fine-grained cubic pyrite disseminated along bedding; (2) fine- grained spongy, rounded masses of pyrite that may envelop or drape over pyrite cubes; (3) fragments of botryoidally and crustiform layered pyrite, and (4) pyritic infilling of vesicles and pumice. Detailed mineral chemistry by petrography, microprobe, SEM, and EDS analysis of replaced pumice and colloform structures containing both arsenic compositional banding and electrum points to coeval deposition of gold and the volcanic host rocks and, thus, confirms a syngenetic origin for the gold deposits. Early pyrite textures are present in other major deposits of the Carolina slate belt, such as Ridgeway and Barite Hill, and these provide strong evidence for models whereby the sulfide ores formed prior to tectonism. The role of Paleozoic metamorphism was to remobilize and concentrate gold and other minerals in structurally prepared sites. Recognizing the significance of paragenetically early pyrite and gold textures can play an important role in distinguishing sulfide ores that form in volcanic and sedimentary environments from those formed solely by metamorphic processes. Exploration strategies applied to the Carolina slate belt and correlative rocks in the eastern United States in the Avalonian basement will benefit from using syngenetic models for gold mineralization.

Petrogenesis and depositional history of felsic pyroclastic rocks from the Melka Wakena archaeological site-complex in South central Ethiopia

NASA Astrophysics Data System (ADS)

Resom, Angesom; Asrat, Asfawossen; Gossa, Tegenu; Hovers, Erella

2018-06-01

The Melka Wakena archaeological site-complex is located at the eastern rift margin of the central sector of the Main Ethiopian Rift (MER), in south central Ethiopia. This wide, gently sloping rift shoulder, locally called the "Gadeb plain" is underlain by a succession of primary pyroclastic deposits and intercalated fluvial sediments as well as reworked volcaniclastic rocks, the top part of which is exposed by the Wabe River in the Melka Wakena area. Recent archaeological survey and excavations at this site revealed important paleoanthropological records. An integrated stratigraphic, petrological, and major and trace element geochemical study has been conducted to constrain the petrogenesis of the primary pyroclastic deposits and the depositional history of the sequence. The results revealed that the Melka Wakena pyroclastic deposits are a suite of mildly alkaline, rhyolitic pantellerites (ash falls, pumiceous ash falls and ignimbrites) and slightly dacitic ash flows. These rocks were deposited by episodic volcanic eruptions during early to middle Pleistocene from large calderas along the Wonji Fault Belt (WFB) in the central sector of the MER and from large silicic volcanic centers at the eastern rift shoulder. The rhyolitic ash falls, pumiceous ash falls and ignimbrites have been generated by fractional crystallization of a differentiating basaltic magma while the petrogenesis of the slightly dacitic ash flows involved some crustal contamination and assimilation during fractionation. Contemporaneous fluvial activities in the geomorphologically active Gadeb plain deposited overbank sedimentary sequences (archaeology bearing conglomerates and sands) along meandering river courses while a dense network of channels and streams have subsequently down-cut through the older volcanic and sedimentary sequences, redepositing the reworked volcaniclastic sediments further downstream.

The eruptive history and magmatic evolution of Aluto volcano: new insights into silicic peralkaline volcanism in the Ethiopian rift

NASA Astrophysics Data System (ADS)

Hutchison, William; Pyle, David M.; Mather, Tamsin A.; Yirgu, Gezahegn; Biggs, Juliet; Cohen, Benjamin E.; Barfod, Dan N.; Lewi, Elias

2016-12-01

The silicic peralkaline volcanoes of the East African Rift are some of the least studied volcanoes on Earth. Here we bring together new constraints from fieldwork, remote sensing, geochronology and geochemistry to present the first detailed account of the eruptive history of Aluto, a restless silicic volcano located in a densely populated section of the Main Ethiopian Rift. Prior to the growth of the Aluto volcanic complex (before 500 ka) the region was characterized by a significant period of fault development and mafic fissure eruptions. The earliest volcanism at Aluto built up a trachytic complex over 8 km in diameter. Aluto then underwent large-volume ignimbrite eruptions at 316 ± 19 ka and 306 ± 12 ka developing a 42 km2 collapse structure. After a hiatus of 250 ka, a phase of post-caldera volcanism initiated at 55 ± 19 ka and the most recent eruption of Aluto has a radiocarbon age of 0.40 ± 0.05 cal. ka BP. During this post-caldera phase highly-evolved peralkaline rhyolite lavas, ignimbrites and pumice fall deposits have erupted from vents across the complex. Geochemical modelling is consistent with rhyolite genesis from protracted fractionation (> 80%) of basalt that is compositionally similar to rift-related basalts found east of the complex. Based on the style and volume of recent eruptions we suggest that silicic eruptions occur at an average rate of 1 per 1000 years, and that future eruptions of Aluto will involve explosive emplacement of localised pumice cones and effusive obsidian coulees of volumes in the range 1-100 × 106 m3.

The Late-Holocene evolution of the Miseno area (south-western Campi Flegrei) as inferred by stratigraphy, petrochemistry and 40Ar/39Ar geochronology:Chapter 6 in Volcanism in the Campania Plain — Vesuvius, Campi Flegrei and Ignimbrites

USGS Publications Warehouse

Insinga, Donatella; Calvert, Andrew T.; Lanphere, Marvin A.; Morra, Vincenzo; Perrotta, Annamaria; Sacchi, Marco; Scarpati, Claudio; Saburomaru, James; Fedele, Lorenzo

2006-01-01

This study on terrestrial and marine successions increases the understanding of the Late-Holocene volcanological and stratigraphical evolution of the south-western part of Campi Flegrei caldera.Stratigraphic data derived from field studies of two major tuff vents located along the coastal zone, namely Porto Miseno and Capo Miseno, clearly indicate that the Porto Miseno tuff ring slightly predates the Capo Miseno tuff cone. 40Ar/39Ar step-heating experiments, carried out on fresh sanidine separates from pumice samples, yielded a plateau age of 5090±140 yr BP for Capo Miseno and 6490±510 yr BP for Porto Miseno vent, thus confirming field observations.The volcanoclastic input derived from this recent and intense eruptive activity played a major role in the inner-shelf stratigraphic evolution of the Porto Miseno Bay deposits that have been drilled up to 40 m depth off the crater rim. The cored succession is characterised by transgressive marine deposits (mostly volcanic sand) with two intercalated peat layers (t1 and t2), dated at 3560±40 yr BP and 7815±55 yr BP (14C), respectively, interbedded with a 1–5 m thick pumice layer (tephra C). Peat layers have been chronostratigraphically correlated with two widespread paleosols onland while petrochemical analyses allowed us to correlate tephra C with the Capo Miseno tuff cone deposits.The results presented in this study imply a Late-Holocene volcanic activity that is also well preserved in the marine record in this sector of the caldera where a new chronostratigraphic reconstruction of the eruptive events is required in order to better evaluate the hazard assessment of the area.

Source of the great A.D. 1257 mystery eruption unveiled, Samalas volcano, Rinjani Volcanic Complex, Indonesia

PubMed Central

Lavigne, Franck; Degeai, Jean-Philippe; Komorowski, Jean-Christophe; Guillet, Sébastien; Robert, Vincent; Lahitte, Pierre; Oppenheimer, Clive; Stoffel, Markus; Vidal, Céline M.; Surono; Pratomo, Indyo; Wassmer, Patrick; Hajdas, Irka; Hadmoko, Danang Sri; de Belizal, Edouard

2013-01-01

Polar ice core records attest to a colossal volcanic eruption that took place ca. A.D. 1257 or 1258, most probably in the tropics. Estimates based on sulfate deposition in these records suggest that it yielded the largest volcanic sulfur release to the stratosphere of the past 7,000 y. Tree rings, medieval chronicles, and computational models corroborate the expected worldwide atmospheric and climatic effects of this eruption. However, until now there has been no convincing candidate for the mid-13th century “mystery eruption.” Drawing upon compelling evidence from stratigraphic and geomorphic data, physical volcanology, radiocarbon dating, tephra geochemistry, and chronicles, we argue the source of this long-sought eruption is the Samalas volcano, adjacent to Mount Rinjani on Lombok Island, Indonesia. At least 40 km3 (dense-rock equivalent) of tephra were deposited and the eruption column reached an altitude of up to 43 km. Three principal pumice fallout deposits mantle the region and thick pyroclastic flow deposits are found at the coast, 25 km from source. With an estimated magnitude of 7, this event ranks among the largest Holocene explosive eruptions. Radiocarbon dates on charcoal are consistent with a mid-13th century eruption. In addition, glass geochemistry of the associated pumice deposits matches that of shards found in both Arctic and Antarctic ice cores, providing compelling evidence to link the prominent A.D. 1258/1259 ice core sulfate spike to Samalas. We further constrain the timing of the mystery eruption based on tephra dispersal and historical records, suggesting it occurred between May and October A.D. 1257. PMID:24082132

Kaguyak dome field and its Holocene caldera, Alaska Peninsula

USGS Publications Warehouse

Fierstein, J.; Hildreth, W.

2008-01-01

Kaguyak Caldera lies in a remote corner of Katmai National Park, 375??km SW of Anchorage, Alaska. The 2.5-by-3-km caldera collapsed ~ 5.8 ?? 0.2??ka (14C age) during emplacement of a radial apron of poorly pumiceous crystal-rich dacitic pyroclastic flows (61-67% SiO2). Proximal pumice-fall deposits are thin and sparsely preserved, but an oxidized coignimbrite ash is found as far as the Valley of Ten Thousand Smokes, 80??km southwest. Postcaldera events include filling the 150-m-deep caldera lake, emplacement of two intracaldera domes (61.5-64.5% SiO2), and phreatic ejection of lakefloor sediments onto the caldera rim. CO2 and H2S bubble up through the lake, weakly but widely. Geochemical analyses (n = 148), including pre-and post-caldera lavas (53-74% SiO2), define one of the lowest-K arc suites in Alaska. The precaldera edifice was not a stratocone but was, instead, nine contiguous but discrete clusters of lava domes, themselves stacks of rhyolite to basalt exogenous lobes and flows. Four extracaldera clusters are mid-to-late Pleistocene, but the other five are younger than 60??ka, were truncated by the collapse, and now make up the steep inner walls. The climactic ignimbrite was preceded by ~ 200??years by radial emplacement of a 100-m-thick sheet of block-rich glassy lava breccia (62-65.5% SiO2). Filling the notches between the truncated dome clusters, the breccia now makes up three segments of the steep caldera wall, which beheads gullies incised into the breccia deposit prior to caldera formation. They were probably shed by a large lava dome extruding where the lake is today.

The effects of growth and collapse on the magmatic system below Mt Taranaki, New Zealand.

NASA Astrophysics Data System (ADS)

Procter, Jonathan; Marcroft, Grace; Zellmer, Georg; Zernack, Anke

2017-04-01

Mt. Taranaki exhibits one of the best long-term records of volcanic growth and destruction of any volcano worldwide, making it ideal for understanding the long-term effects of changing lithostatic pressure, or loading and unloading, on the magma chamber and magma supply. The ring-plain around Mt. Taranaki houses volcaniclastic deposits that provide a near continuous record of the evolution of the volcano, yet these records have remained relatively unexploited when investigating the interrelated cyclical phases of volcano collapse and growth, the geochemical evolution of the centre, and the consequent time-varying hazard potential. In this study, we systematically sampled pumice-rich tephra and pumice-rich mass flow deposits that were stratigraphically immediately before and after the 24,801 ± 268 years BP Pungarehu Formation debris avalanche ( 7.5 km3). Crystals (clinopyroxene and plagioclase) were characterised in detail. Mg and Fe zoning across selected crystals from samples pre-and post-debris avalanche were found to have completely equilibrated, yet zoning patterns in Al remained intact and showed major differences in their formation, allowing for the calculation of diffusion rates. These have enabled the determination of maximum residence times (depths and pressure regimes) of the magma system. It is intended that this technique will be applied across the stratigraphic record, which contains 14 collapse events. This will provide insights into crustal magma transport and residence times, and the propagation of fissures and the buoyancy of the magma pre- and post-collapse, in order to characterise the evolution of the centre and quantify the long-term relationship between magmatic rise and volcano growth and destruction.

Formation of a spatter-rich pyroclastic density current deposit in a Neogene sequence of trachytic-mafic igneous rocks at Mason Spur, Erebus volcanic province, Antarctica

NASA Astrophysics Data System (ADS)

Martin, A. P.; Smellie, J. L.; Cooper, A. F.; Townsend, D. B.

2018-01-01

Erosion has revealed a remarkable section through the heart of a volcanic island, Mason Spur, in the southwestern Ross Sea, Antarctica, including an unusually well-exposed section of caldera fill. The near-continuous exposure, 10 km laterally and > 1 km vertically, cuts through Cenozoic alkalic volcanic rocks of the Erebus volcanic province (McMurdo Volcanic Group) and permits the study of an ancient volcanic succession that is rarely available due to subsequent burial or erosion. The caldera filling sequence includes an unusual trachytic spatter-rich lapilli tuff (ignimbrite) facies that is particularly striking because of the presence of abundant black fluidal, dense juvenile spatter clasts of trachytic obsidian up to 2 m long supported in a pale cream-coloured pumiceous lapilli tuff matrix. Field mapping indicates that the deposit is an ignimbrite and, together with petrological considerations, it is suggested that mixing of dense spatter and pumiceous lapilli tuff in the investigated deposit occurred during emplacement, not necessarily in the same vent, with the mixed fragmental material emplaced as a pyroclastic density current. Liquid water was not initially present but a steam phase was probably generated during transport and may represent water ingested during passage of the current as it passed over either wet ground, stream, shallow lake or (possibly) snow. Well-exposed caldera interiors are uncommon and that at Mason Spur is helping understand eruption dynamics associated with a complex large island volcano. The results of our study should help to elucidate interpretations of other, less well exposed, pyroclastic density current deposits elsewhere in Antarctica and globally.

From pumice to obsidian: eruptive behaviors that produce tephra-flow dyads. II- The 114ka trachyte eruption at Pu'u Wa'awa'a (Hawai'i).

NASA Astrophysics Data System (ADS)

Shea, T.; Leonhardi, T. C.; Giachetti, T.; Larsen, J. F.; Lindoo, A. N.

2014-12-01

Associations of tephra and lava flow/domes produced by eruptions involving evolved magmas are a common occurrence in various types of volcanic settings (e.g. Pu'u Wa'awa'a ~114ka, Hawaii; South Mono ~AD625, California; Newberry Big Obsidian flow ~AD700, Oregon; Big Glass Mountain ~AD1100, California; Inyo ~AD1350, California, Chaitén AD2008-2009, Chile; Cordón Caulle AD2011-2012, Chile), ejecting up to a few cubic km of material (tephra+flow/dome). Most, if not all, of these eruptions have in common the paradoxical coexistence of (1) eruptive styles which are inferred to be sustained in nature (subplinian and plinian), with (2) a pulsatory behavior displayed by the resulting fall deposits, and (3) the coeval ejection of vesicular tephra and pyroclastic obsidian. Through two case studies, we explore this apparent set of paradoxes, and their significance in understanding transitions from explosive to effusive behavior. In this second case study (also cf. Shea et al., same session), we present new field, textural and geochemical data pertaining to the 114ka Pu'u Wa'awa'a trachyte eruption in Hawai'i. This large volume (>5 km3) event produced both a tephra cone (~1.6 km in diameter) and a thick (>250 m) lava flow, which have been largely covered by the more recent basaltic Mauna Loa and Hualalai lava flows. The trachyte tephra contains juvenile material displaying a large textural variety (pumice, scoria, obsidian, microcrystalline trachyte and banded-clasts), which can be linked with the extent of degassing and the formation of feldspar microlites. Notably, the abundance of microlites can be used to reconstruct an ascent and devolatilization history that accounts for all the seemingly contradictory observations.

Santorini eruption radiocarbon dated to 1627-1600 B.C.

PubMed

Friedrich, Walter L; Kromer, Bernd; Friedrich, Michael; Heinemeier, Jan; Pfeiffer, Tom; Talamo, Sahra

2006-04-28

Precise and direct dating of the Minoan eruption of Santorini (Thera) in Greece, a global Bronze Age time marker, has been made possible by the unique find of an olive tree, buried alive in life position by the tephra (pumice and ashes) on Santorini. We applied so-called radiocarbon wiggle-matching to a carbon-14 sequence of tree-ring segments to constrain the eruption date to the range 1627-1600 B.C. with 95.4% probability. Our result is in the range of previous, less precise, and less direct results of several scientific dating methods, but it is a century earlier than the date derived from traditional Egyptian chronologies.

40Ar/39Ar ages of the AD 79 eruption of Vesuvius, Italy

NASA Astrophysics Data System (ADS)

Lanphere, Marvin; Champion, Duane; Melluso, Leone; Morra, Vincenzo; Perrotta, Annamaria; Scarpati, Claudio; Tedesco, Dario; Calvert, Andrew

2007-01-01

The Italian volcano, Vesuvius, erupted explosively in AD 79. Sanidine from pumice collected at Casti Amanti in Pompeii and Villa Poppea in Oplontis yielded a weighted-mean 40Ar/39Ar age of 1925±66 years in 2004 (1σ uncertainty) from incremental-heating experiments of eight aliquants of sanidine. This is the calendar age of the eruption. Our results together with the work of Renne et al. (1997) and Renne and Min (1998) demonstrate the validity of the 40Ar/39Ar method to reconstruct the recent eruptive history of young, active volcanoes.

Economic Drivers of Strategic & Critical Materials

DTIC Science & Technology

2012-05-01

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Chronology, morphology and stratigraphy of pumiceous pyroclastic-flow (ignimbrite) deposits from the eruption of Mount St. Helens on 18 May 1983

NASA Technical Reports Server (NTRS)

Criswell, C. W.; Elston, W. E.

1984-01-01

Between 1217 and 1620 hours (PDT), on May 18, 1980, the magmatic eruption column of Mount St. Helens formed an ash fountain and pyroclastic flows dominated the eruption process over tephra ejection. Eurption-rate pulsations generally increased to a maximum at 1600 to 1700 hrs. After 1620 hrs, the eruption assumed an open-vent discharge with strong, vertical ejection of tephra. Relative eruption rates (relative mass flux rates) of the pyroclastic flows were determined by correlating sequential photographs and SLAR images, obtained during the eruption, with stratigraphy and surface morphology of the deposits.

Geochemistry and Temperatures Recorded by Zircon During the Final Stages of the Youngest Toba Tuff Magma Chamber, Sumatra, Indonesia

NASA Astrophysics Data System (ADS)

Gaither, T.; Reid, M. R.; Vazquez, J. A.

2009-12-01

The ~74 ka eruption of the Youngest Toba Tuff (YTT) in Sumatra, Indonesia, was one of the largest single volcanic eruptions in geologic history, on par with other voluminous silicic eruptions such as the Huckleberry Ridge Tuff of Yellowstone and the Bishop Tuff of Long Valley, California. We are exploring how zircon and other accessory mineral phases record compositional and thermal changes that occurred in the YTT magma, and the important clues these crystal scale records hold for magma chamber dynamics and processes that lead up to supervolcano eruptions. In this study, we report trace element (REE, U, Th, Ti, and Hf) characteristics, Ti-in-zircon crystallization temperatures, and apparent REE partition coefficients obtained for YTT zircon rims. Twenty-nine zircons from pumices with a compositional range of 70-76 wt% SiO2 were analyzed on the UCLA Cameca ims 1270 ion microprobe. The grains were mounted so that only the outermost ~1.5 microns of the crystals were analyzed. Median Zr/Hf ratios of 34 to 38 characterize zircons from the pumices; the high silica rhyolite grains have lower Zr/Hf. Chondrite-normalized REE patterns are strongly LREE-depleted. Positive Ce anomalies are large (Ce/Ce* ranges up to 88) and Eu/Eu* varies by a factor of four (0.05 to 0.21). Eu/Eu*, Nd/Yb, and Th/U decrease with decreasing Zr/Hf, showing that the variation in zircon rim compositions may be related by co-precipitation of feldspar and allanite along with zircon. Titanium contents also decrease with decreasing Zr/Hf, suggesting that the chemical differences could be related to temperature changes. REE partition coefficients calculated from zircon rim compositions and pumice glass compositions give a good fit to a lattice strain model. They are also quite similar to the partition coefficients of Sano et al. (2002) which have been shown to be successful at reproducing melt compositions in other settings. Temperatures of crystallization calculated using the Ti-in-zircon geothermometer (Watson et al., 1996), assuming a melt aTiO2 of 0.5, yield very low median values (even without a possible pressure correction of -40 to -80°C), ranging from 640-667°C. Virtually all of the zircon rims record temperatures lower than eruption temperatures of 700-780°C estimated for the YTT by Chesner (1998) using FeTi oxide equilibria. It is possible that the low zircon temperatures reflect uncertainties in the Ti-in-zircon geothermometer but they are nonetheless permissive of re-entrainment of zircon from a near-solidus mush close to the time of eruption. The analytically significant chemical variations within the individual zircon populations, especially those of Zr/Hf, Eu/Eu*, and Nd/Yb, suggest that crystals from distinct compositional domains were brought together during a final merging/coalescence of magma that catalyzed the eruption.

GEOLOGICAL-GEOMORPHOLOGICAL ANALYSIS OF THE REGION OF GUADALAJARA, MEXICO AND ITS RELATION WITH SUBSIDENCE HAZARDS

NASA Astrophysics Data System (ADS)

Suarez-Plascencia, C.; Delgado-Argote, L. A.; Nunez-Cornu, F. J.

2009-12-01

The Metropolitan Area of Guadalajara (MAG) was built over pumice deposits generated during Quaternary activity in the Sierra la Primavera, that covered a thick sequence of basaltic, dacitic, rhyolitic lava flows, ignimbrites and fluvial-lacustrine deposits. The most complete stratigraphic section is observed in different sections of the Rio Grande de Santiago cliff, located north of the city. Five distinctive geoforms were identified: 1) the cliff of the Rio Grande de Santiago (CRGS) is a tectonic erosive depression with average depth of 500 m and 3.5 km width. Structurally, in the San Gaspar zone, south of the union of Verde river with Santiago river, we identified normal faults with left-lateral motion and oriented 191°/89° on basaltic lavas. In the Colimilla dam, 1297 meters above sea level, we observed lateral faulting with normal component (267°/81°) where jumps as high as 30 m were observed. Lava flows are sheared parallel to the Verde river. In the Puente Arcediano zone, where the base of the sequence is apparent, faults have a dominant orientation of 188°/75° on andesitic flows, whereas on pumice ignimbrites they show a shearing with a direction of 92°/84° parallel to the Verde river. 2) The Sierra la Primavera, to the southwest of MAG is a caldera formed by a series of domes, flows, and pyroclastic deposits with rhyolitic composition. 3) The southern Guadalajara volcanic chain system, which is formed by several volcanic cones and flows of basaltic-andesitic composition and Plio-Pleistocene age, oriented NW-SE, developed over the San Gaspar ignimbrite (4.8 m.a.). 4) Los Colomos and Alcalde-Barranquitas cliff system, which form dendrite networks developed on pumice deposits, where most of the cliffs were deep and narrow. The origin of the cliffs might be associated with observed faults or fracture zones in the CRGS. 5) Wavy plains of Atemajac and Tesistán valleys, which are characterized by hills and wide plains. The system of cliffs controlled the growth of the MAG on its N, W, and NW sectors until the 1940 decade. Starting the 1950 decade, however, urban developers began to slowly modify the relief units and to build landfills on los Colomos and Alcalde Barranquitas cliffs as well as to build one and two-storey houses. During the mid 1980 decade there began to appear reports of affectation of variable magnitude caused by sinking of buildings and infrastructures on this area of the city. These problems have forced the different municipal governments and private owners to pump large funds for the mitigation and prevention of damage, but the sinking is recurrent at the time of this writing. More than 1,100 sites of sinking were observed and related directly to areas where the relief has been modified for urban use.

Long-term changes in explosive and effusive behaviour at andesitic arc volcanoes: Chronostratigraphy of the Centre Hills Volcano, Montserrat

NASA Astrophysics Data System (ADS)

Coussens, Maya; Cassidy, Michael; Watt, Sebastian F. L.; Jutzeler, Martin; Talling, Peter J.; Barfod, Dan; Gernon, Thomas M.; Taylor, Rex; Hatter, Stuart J.; Palmer, Martin R.; Montserrat Volcano Observatory

2017-03-01

Volcanism on Montserrat (Lesser Antilles arc) has migrated southwards since the formation of the Silver Hills 2.5 Ma, and has formed three successively active volcanic centres. The Centre Hills volcano was the focus of volcanism from 1-0.4 Ma, before activity commenced at the currently active Soufrière Hills volcano. The history of activity at these two volcanoes provides an opportunity to investigate the pattern of volcano behaviour on an andesitic arc island over the lifetime of individual volcanoes. Here, we describe the pyroclastic stratigraphy of subaerial exposures around central Montserrat; identifying 11 thick (> 1 m) pumiceous units derived from sustained explosive eruptions of Centre Hills from 0.8-0.4 Ma. Over 10 other, less well- exposed pumiceous units have also been identified. The pumice-rich units are interbedded with andesite lava breccias derived from effusive, dome-forming eruptions of Centre Hills. The stratigraphy indicates that large (up to magnitude 5) explosive eruptions occurred throughout the history of Centre Hills, alongside effusive activity. This behaviour at Centre Hills contrasts with Soufrière Hills, where deposits from sustained explosive eruptions are much less common and restricted to early stages of activity at the volcano, from 175-130 ka. Subsequent eruptions at Soufriere Hills have been dominated by andesitic effusive eruptions. The bulk composition, petrography and mineral chemistry of volcanic rocks from Centre Hills and Soufrière Hills are similar throughout the history of both volcanoes, except for occasional, transient departures to different magma compositions, which mark shifts in vent location or dominant eruption style. For example, the final recorded eruption of Centre Hills, before the initiation of activity at Soufrière Hills, was more silicic than any other identified eruption on Montserrat; and the basaltic South Soufrière Hills episode marked the transition to the current stage of predominantly effusive Soufrière Hills activity. The compositional stability observed throughout the history of Centre Hills and Soufrière Hills suggests that a predominance towards effusive or explosive eruption styles is not driven by major compositional shifts of magma, but may reflect local changes in long-term magma storage conditions that characterise individual episodes (on 105 year timescales) of volcanism on Montserrat. Supplementary Table 2: Complete XRF analyses for all analysed samples Supplementary Table 3: Complete ICP-MS analyses for all analysed samples. Supplementary Table 4: Plagioclase composition and precision data from SEM analysis Supplementary Table 5: Clinopyroxene composition and precision data from SEM analysis Supplementary Table 6: Orthopyroxene composition and precision data from SEM analysis Supplementary Table 7: Amphibole composition and precision data from SEM analysis Supplementary Table 8: Glass compositions from EMP analysis Supplementary Table 9: Standard Deviation of glass compositions from EMP analysis. Supplementary Table 10: Isotopic composition of argon from plagioclase crystals from select units. Data obtained using an ARGUS V multi-collector mass spectrometer.

Impact of the AD 79 explosive eruption on Pompeii, I. Relations amongst the depositional mechanisms of the pyroclastic products, the framework of the buildings and the associated destructive events

NASA Astrophysics Data System (ADS)

Luongo, Giuseppe; Perrotta, Annamaria; Scarpati, Claudio

2003-08-01

A quantitative and qualitative evaluation of the damage caused by the products of explosive eruptions to buildings provides an excellent contribution to the understanding of the various eruptive processes during such dramatic events. To this end, the impact of the products of the two main phases (pumice fallout and pyroclastic density currents) of the Vesuvius AD 79 explosive eruption onto the Pompeii buildings has been evaluated. Based on different sources of data, such as photographs and documents referring to the archaeological excavations of Pompeii, the stratigraphy of the pyroclastic deposits, and in situ inspection of the damage suffered by the buildings, the present study has enabled the reconstruction of the events that occurred inside the city when the eruption was in progress. In particular, we present new data related to the C.J. Polibius' house, a large building located inside Pompeii. From a comparison of all of the above data sets, it has been possible to reconstruct, in considerable detail, the stratigraphy of the pyroclastic deposits accumulated in the city, to understand the direction of collapse of the destroyed walls, and to evaluate the stratigraphic level at which the walls collapsed. Finally, the distribution and style of the damage allow us to discuss how the emplacement mechanisms of the pyroclastic currents are influenced by their interaction with the urban centre. All the data suggest that both structure and shape of the town buildings affected the transport and deposition of the erupted products. For instance, sloping roofs 'drained' a huge amount of fall pumice into the 'impluvia' (a rectangular basin in the centre of the hall with the function to collect the rain water coming from a hole in the centre of the roof), thus producing anomalous deposit thicknesses. On the other hand, flat and low-sloping roofs collapsed under the weight of the pyroclastic material produced during the first phase of the eruption (pumice fall). In addition, it is evident that the walls that happened to be parallel to the direction of the pyroclastic density currents produced during the second eruptive phase were minimally damaged in comparison to those walls oriented perpendicular to the flow direction. We suggest that the lower depositional parts of the pyroclastic currents were partially blocked (locally reflected) and slowed down because of recurring encounters with the closely spaced walls within buildings. Locally, the percentage of demolished walls decreases down-current, which has been interpreted as a loss in kinetic energy within the depositional system of the flow. However, it seems that the upper transport system by-passed these obstacles, then supplied new pyroclasts to the depositional system that restored its physical characteristics and restored enough kinetic energy to demolish the next walls and buildings further along its path.

Investigating Degassing in Felsic and Mafic Magmas by 3-D Imaging of Vesicle Pathways

NASA Astrophysics Data System (ADS)

Polacci, M.; Baker, D. R.; Piochi, M.; Mancini, L.

2009-12-01

Volatiles are the motor of volcanic eruptions. Studies of vesiculation in erupted products can provide information on how volatiles exsolve, grow and are lost from magmas as lava and tephra fragments bear the fingerprints of such processes in vesicle and crystal textures. We summarize here the results of a series of X-ray computed microtomographic experiments that were performed on about 70 volcanic specimens of mainly basaltic and trachytic compositions. A first sample suite comprises samples collected from explosive activity at persistently degassing basaltic volcanoes, namely Stromboli (Aeolian Islands), Etna (Eastern Sicily) and Ambrym (Vanuatu Islands); a second suite consists of pumice and scoria clasts from Plinian to Subplinian to Vulcanian eruptions that occurred in the Campi Flegrei caldera (Southern Italy). The tomographic images provide us with a complete 3-D view of our sampled material through which it is possible to reconstruct the geometry of the vesicle network and explore how gas was transported in the investigated magmas. We find that basaltic scoriae exhibit two types of vesicles: large (~ mm^3), coalescing vesicles with complex, convoluted shapes and small-to-intermediate sized (<~1x10^-3 mm^3), spherical to sub-spherical, poorly connected or isolated vesicles. The former vesicles were interpreted as percolation pathways for gas to flow non-explosively to the volcano crater and thought to sustain the persistent passive gas release that characterizes these volcanoes. The fact that such vesicles were found in products erupted from active basaltic volcanoes located in different tectonic settings and characterized by different explosivity strongly suggests that basaltic systems appear to follow a common degassing pathway. However, not all explosive basaltic rocks contain large, coalescing vesicles. Pumice clasts from the much more violent, dangerous and less frequent paroxysmal explosions at Stromboli do not have this type of vesicles, demonstrating that basaltic volcanoes develop different vesicle textures and therefore degassing dynamics with increasing explosive activity. Trachytic pumices from highly explosive eruptions display a much finer structure in comparison to scoriae having sub-spherical to slightly deformed large vesicles and a large population of small spherical vesicles (1x10^-3 - <1x10^-5 mm^3). These two vesicle textures were mainly ascribed to the rapid ascent of a supersaturated magma under closed-system degassing, in comparison to the open-system conditions of basaltic magmas. Large interconnected vesicles that form micro-cracks are, however, found in some denser pyroclasts from Campi Flegrei. This suggests that gas was percolating in the conduit system before the eruption and that open-system degassing may be an effective way through which gas is lost in a moderately violent manner at the crater surface in some explosive felsic eruptions. Ultimately this study reveals that 3-D imaging of volcanic rocks is an essential tool for investigating degassing conditions in erupted magmas.

The flow dynamics of an extremely large volume pyroclastic flow, the 2.08-Ma Cerro Galán Ignimbrite, NW Argentina, and comparison with other flow types

USGS Publications Warehouse

Cas, Ray A.F.; Wright, Heather M.; Folkes, Christopher B.; Lesti, Chiara; Porreca, Massimiliano; Giordano, Guido; Viramonte, Jose G.

2011-01-01

The 2.08-Ma Cerro Galán Ignimbrite (CGI) represents a >630-km3 dense rock equivalent (VEI 8) eruption from the long-lived Cerro Galán magma system (∼6 Ma). It is a crystal-rich (35–60%), pumice (<10% generally) and lithic-poor (<5% generally) rhyodacitic ignimbrite, lacking a preceding plinian fallout deposit. The CGI is preserved up to 80 km from the structural margins of the caldera, but almost certainly was deposited up to 100 km from the caldera in some places. Only one emplacement unit is preserved in proximal to medial settings and in most distal settings, suggesting constant flow conditions, but where the pyroclastic flow moved into a palaeotopography of substantial valleys and ridges, it interacted with valley walls, resulting in flow instabilities that generated multiple depositional units, often separated by pyroclastic surge deposits. The CGI preserves a widespread sub-horizontal fabric, defined by aligned elongate pumice and lithic clasts, and minerals (e.g. biotite). A sub-horizontal anisotropy of magnetic susceptibility fabric is defined by minute magnetic minerals in all localities where it has been analysed. The CGI is poor in both vent-derived (‘accessory’) lithics and locally derived lithics from the ground surface (‘accidental’) lithics. Locally derived lithics are small (<20 cm) and were not transported far from source points. All data suggest that the pyroclastic flow system producing the CGI was characterised throughout by high sedimentation rates, resulting from high particle concentration and suppressed turbulence at the depositional boundary layer, despite being a low aspect ratio ignimbrite. Based on these features, we question whether high velocity and momentum are necessary to account for extensive flow mobility. It is proposed that the CGI was deposited by a pyroclastic flow system that developed a substantial, high particle concentration granular under-flow, which flowed with suppressed turbulence. High particle concentration and fine-ash content hindered gas loss and maintained flow mobility. In order to explain the contemporaneous maintenance of high particle concentration, high sedimentation rate at the depositional boundary layer and a high level of mobility, it is also proposed that the flow(s) was continuously supplied at a high mass feeding rate. It is also proposed that internal gas pressure within the flow, directed downwards onto the substrate over which the flow was passing, reduced the friction between the flow and the substrate and also enhanced its mobility. The pervasive sub-horizontal fabric of aligned pumice, lithic and even biotite crystals indicates a consistent horizontal shear force existed during transport and deposition in the basal granular flow, consistent with the existence of a laminar, shearing, granular flow regime during the final stages of transport and deposition.

Volcanic Processes and Geology of Augustine Volcano, Alaska

USGS Publications Warehouse

Waitt, Richard B.; Beget, James E.

2009-01-01

Augustine Island (volcano) in lower Cook Inlet, Alaska, has erupted repeatedly in late-Holocene and historical times. Eruptions typically beget high-energy volcanic processes. Most notable are bouldery debris avalanches containing immense angular clasts shed from summit domes. Coarse deposits of these avalanches form much of Augustine's lower flanks. A new geologic map at 1:25,000 scale depicts these deposits, these processes. We correlate deposits by tephra layers calibrated by many radiocarbon dates. Augustine Volcano began erupting on the flank of a small island of Jurassic clastic-sedimentary rock before the late Wisconsin glaciation (late Pleistocene). The oldest known effusions ranged from olivine basalt explosively propelled by steam, to highly explosive magmatic eruptions of dacite or rhyodacite shed as pumice flows. Late Wisconsin piedmont glaciers issuing from the mountainous western mainland surrounded the island while dacitic eruptive debris swept down the south volcano flank. Evidence is scant for eruptions between the late Wisconsin and about 2,200 yr B.P. On a few south-flank inliers, thick stratigraphically low pumiceous pyroclastic-flow and fall deposits probably represent this period from which we have no radiocarbon dates on Augustine Island. Eruptions between about 5,350 and 2,200 yr B.P. we know with certainty by distal tephras. On Shuyak Island 100 km southeast of Augustine, two distal fall ashes of Augustinian chemical provenance (microprobe analysis of glass) date respectively between about 5,330 and 5,020 yr B.P. and between about 3,620 and 3,360 yr B.P. An Augustine ash along Kamishak Creek 70 km southwest of Augustine dates between about 3,850 and 3,660 yr B.P. A probably Augustinian ash lying within peat near Homer dates to about 2,275 yr B.P. From before 2,200 yr B.P. to the present, Augustine eruptive products abundantly mantle the island. During this period, numerous coarse debris avalanches swept beyond Augustine's coast, most recently in A.D. 1883. The decapitated summit after the 1883 eruption, replaced by andesite domes of six eruptions since, shows a general process: collapse of steep summit domes, then the summit regrown by later dome eruptions. The island's stratigraphy is based on six or seven coarse-pumice tephra 'marker beds'. In upward succession they are layers G (2,100 yr B.P.), I (1,700 yr B.P.), H (1,400 yr B.P.), C (1,200-1,000 yr B.P.), M (750 yr B.P.), and B (390 yr B.P.). A coarse, hummocky debris-avalanche deposit older than about 2,100 yr B.P. - or perhaps a stack of three of them - lies along the east coast, the oldest exposed such bouldery diamicts on Augustine Island. Two large debris avalanches swept east and southeast into the sea between about 2,100 and 1,800 yr B.P. A large debris avalanche shed east and east-northeast into the sea between 1,700 and 14,00 yr B.P. Between about 1,400 and 1,100 yr B.P. debris avalanches swept into the sea on the volcano's south, southwest, and north-northwest. Pumiceous pyroclastic fans spread to the southeast and southwest, lithic pyroclastic flows and lahars (?) to the south and southeast. Pyroclastic flows, pyroclastic surges, and lahars swept down the west and south flanks between about 1,000 and 750 yr B.P. A debris avalanche swept into the sea on the west, and a small one on the south-southeast, between about 750 and 400 yr B.P. Large lithic pyroclastic flows shed to the southeast; smaller ones descended existing swales on the southwest and south. Between about 400 yr B.P. and historical time (late 1770s), three debris avalanches swept into the sea on the west-northwest, north-northwest, and north flanks. One of them (West Island) was large and fast: most of it rode to sea far beyond a former sea cliff, and its surface includes geomorphic evidence of having initiating a tsunami. Augustine's only conspicuous lava flow erupted on the north flank. During this prehistoric period numerous domes grew at th

Enhancement of eruption explosivity by heterogeneous bubble nucleation triggered by magma mingling.

PubMed

Paredes-Mariño, Joali; Dobson, Katherine J; Ortenzi, Gianluigi; Kueppers, Ulrich; Morgavi, Daniele; Petrelli, Maurizio; Hess, Kai-Uwe; Laeger, Kathrin; Porreca, Massimiliano; Pimentel, Adriano; Perugini, Diego

2017-12-04

We present new evidence that shows magma mingling can be a key process during highly explosive eruptions. Using fractal analysis of the size distribution of trachybasaltic fragments found on the inner walls of bubbles in trachytic pumices, we show that the more mafic component underwent fracturing during quenching against the trachyte. We propose a new mechanism for how this magmatic interaction at depth triggered rapid heterogeneous bubble nucleation and growth and could have enhanced eruption explosivity. We argue that the data support a further, and hitherto unreported contribution of magma mingling to highly explosive eruptions. This has implications for hazard assessment for those volcanoes in which evidence of magma mingling exists.

Geologic logs of geotechnical cores from the subsurface Sacramento-San Joaquin Delta, California

USGS Publications Warehouse

Maier, Katherine L.; Ponti, Daniel J.; Tinsley, John C.; Gatti, Emma; Pagenkopp, Mark

2014-01-01

This report presents and summarizes descriptive geologic logs of geotechnical cores collected from 2009–12 in the Sacramento–San Joaquin Delta, California, by the California Department of Water Resources. Graphic logs are presented for 1,785.7 ft of retained cores from 56 borehole sites throughout the Sacramento-San Joaquin Delta. Most core sections are from a depth of ~100–200 feet. Cores primarily contain mud, silt, and sand lithologies. Tephra (volcanic ash and pumice), paleosols, and gravels are also documented in some core sections. Geologic observations contained in the core logs in this report provide stratigraphic context for subsequent sampling and data for future chronostratigraphic subsurface correlations.

CENTENNIAL MOUNTAINS WILDERNESS STUDY AREA, MONTANA AND IDAHO.

USGS Publications Warehouse

Witkind, Irving J.; Ridenour, James

1984-01-01

A mineral survey conducted within the Centennial Mountains Wilderness study area in Montana and Idaho showed large areas of probable and substantiated resource potential for phosphate. Byproducts that may be derived from processing the phosphate include vanadium, chromium, uranium, silver, fluorine, and the rare earths, lanthanum and yttrium. Results of a geochemical sampling program suggest that there is little promise for the occurrence of base and precious metals in the area. Although the area contains other nonmetallic deposits, such as coal, building stone, and pumiceous ash they are not considered as mineral resources. There is a probable resource potential for oil and gas and significant amounts may underlie the area around the Peet Creek and Odell Creek anticlines.

HOT CELL BUILDING, TRA632, INTERIOR. HOT CELL NO. 1 (THE ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

HOT CELL BUILDING, TRA-632, INTERIOR. HOT CELL NO. 1 (THE FIRST BUILT) IN LABORATORY 101. CAMERA FACES SOUTHEAST. SHIELDED OPERATING WINDOWS ARE ON LEFT (NORTH) SIDE. OBSERVATION WINDOW IS AT LEFT OF VIEW (ON WEST SIDE). PLASTIC COVERS SHROUD MASTER/SLAVE MANIPULATORS AT WINDOWS IN LEFT OF VIEW. NOTE MINERAL OIL RESERVOIR ABOVE "CELL 1" SIGN, INDICATING LEVEL OF THE FLUID INSIDE THE THICK WINDOWS. HOT CELL HAS BEVELED CORNER BECAUSE A SQUARED CORNER WOULD HAVE SUPPLIED UNNECESSARY SHIELDING. NOTE PUMICE BLOCK WALL AT LEFT OF VIEW. INL NEGATIVE NO. HD46-28-1. Mike Crane, Photographer, 2/2005 - Idaho National Engineering Laboratory, Test Reactor Area, Materials & Engineering Test Reactors, Scoville, Butte County, ID

Multiple Magma Batches Recorded in Tephra Deposits from the Toba Complex, Sumatra.

NASA Astrophysics Data System (ADS)

Pearce, N. J. G.; Westgate, J.; Gatti, E.

2015-12-01

The Toba Caldera Complex is the largest Quaternary caldera on Earth, and has generated three voluminous and compositionally similar rhyolitic tuffs, viz. the Oldest (OTT, 800 ka), Middle (MTT, ~500 ka) and Youngest Toba Tuffs (YTT, 75 ka). These tephra deposits are widespread across Indonesia, Malaysia, South China Sea, Sea of Bengal, India and Indian Ocean and provide useful stratigraphic markers in oceanic, lacustrine and terrestrial environments. Single shard trace element analysis of these deposits reveals the changing availability of different batches of magma through time, with Sr, Ba and Y contents defining 5 discrete magma populations in YTT, 4 populations in MTT and only a single, low Ba population in OTT. Within an individual eruption these populations are clearly distinct, but between eruptions (e.g. MTT and YTT) some of these populations overlap while others do not, indicating both the longevity (and/or continuous supply of fresh material) and evolution of these magma batches in the Toba Complex. Major element compositions of the different groups show equilibration at different pressures (based on Q'-Ab'-Or'), with the equilibration of low Ba populations at ~160 MPa, increasing to depths of ~210 MPa for the highest Ba population. The proportions of different populations of glass in distal YTT shows that relatively little of the high Ba population makes it into the distal record across India, and that this population appears to be over-represented in the proximal free glass and pumice from the caldera walls. This data may shed light on magma availability and tephra dispersal during the YTT eruption. Similarly, the glass composition of individual pumices from proximal deposits record regional, compositional and temporal differences in the erupted products. These show, for example, the apparent mingling of some of the magma batches and also that the high Ba population appears early (i.e. stratigraphically lower) in the northern caldera wall.

Magma Chamber of the 26.5 ka Oruanui Eruption, Taupo Volcano, New Zealand

NASA Astrophysics Data System (ADS)

Liu, Y.; Anderson, A. T.; Wilson, C. J.; Davis, A. M.

2004-12-01

We have investigated melt inclusions and their host quartz crystals from the Bishop-Tuff-sized 26.5 ka Oruanui eruption at Taupo volcano, New Zealand. Compositions (major and trace elements, H2O and CO2) of melt inclusions and cathodoluminescence (CL) images of quartz were obtained for eight individual pumices from early, middle and late depositional units. All melt inclusions are high-silica weakly peraluminous rhyolites. Melt inclusions for different eruptive phases have similar ranges of H2O contents (3.8-5.2 wt %), but late-erupted samples have higher CO2 contents (mostly > 140 ppm). A positive correlation between CO2 and compatible trace elements such as Sr suggests that crystallization and melt entrapment occurred under gas-saturated conditions. Trace elements variations in melt inclusions are consistent with fractionation of 30-40 wt % crystals (plagioclase+quartz+pyroxene+amphibole). Crystal contents in pumices, trace-element contents in melt inclusions, and CL zoning patterns of quartz show no correlation with eruptive phases, suggesting that the Oruanui magma was well mixed before eruption. Some Oruanui quartz crystals contain distinctive CL zonings with a jagged ('restitic') core mantled by a black CL zone. Trace element variations in melt inclusions in the 'restitic' cores are consistent with fractionation of Ba-bearing minerals such as sanidine and/or biotite, both of which are rare or absent in rocks erupted from Taupo volcanic center. The above evidence suggests that Oruanui rhyolite is generated by assimilation of previous intruded rocks or country rocks, differentiated by crystal fractionation, and then mixed prior to eruption. Despite the differences in trace element and volatile contents, and crystal assemblages, both Bishop Tuff and Oruanui magmas involve crystal fractionation as one of the main differentiation mechanisms during their evolution. However, there are pronounced differences in the pre-eruptive stratification of the two chambers, which may reflect the tectonic settings, eruption rates, and ages of the systems.

Pre-eruptive conditions of dacitic magma erupted during the 21.7 ka Plinian event at Nevado de Toluca volcano, Central Mexico

NASA Astrophysics Data System (ADS)

Arce, J. L.; Gardner, J. E.; Macías, J. L.

2013-01-01

The Nevado de Toluca volcano in Central Mexico has been active over the last ca. 42 ka, during which tens of km3 of pyroclastic material were erupted and two important Plinian-type eruptions occurred at ca. 21.7 ka (Lower Toluca Pumice: LTP) and ca. 10.5 ka (Upper Toluca Pumice: UTP). Samples from both the LTP and UTP contain plagioclase, amphibole, iron-titanium oxides, and minor anhedral biotite, set in a vesicular, rhyolitic, glassy matrix. In addition, UTP dacites contain orthopyroxene. Analysis of melt inclusions in plagioclase phenocrysts yields H2O contents of 2-3.5 wt.% for LTP and 1.3-3.6 wt.% for UTP samples. Ilmenite-ulvospinel geothermometry yields an average temperature of ~ 868 °C for the LTP magma (hotter than the UTP magma, ~ 842 °C; Arce et al., 2006), whereas amphibole-plagioclase geothermometry yields a temperature of 825-859 °C for the LTP magma. Water-saturated experiments using LTP dacite suggest that: (i) amphibole is stable above 100 MPa and below 900 °C; (ii) plagioclase crystallizes below 250-100 MPa at temperatures of 850-900 °C; and (iii) pyroxene is stable only below pressures of 200-100 MPa and temperatures of 825-900 °C. Comparison of natural and experimental data suggests that the LTP dacitic magma was stored at 150-200 MPa (5.8-7.7 km below the volcano summit). No differences in pressure found between 21.7 ka and 10.5 ka suggest that these two magmas were stored at similar depths. Orthopyroxene produced in lower temperature LTP experiments is compositionally different to those found in UTP natural samples, suggesting that they originated in two different magma batches. Whole-rock chemistry, petrographic features, and mineral compositions suggest that magma mixing was responsible for the generation of the dacitic Plinian LTP eruption.

Volcanic Hazards Associated with the NE Sector of Tacaná Volcano, Guatemala.

NASA Astrophysics Data System (ADS)

Hughes, S. R.; Saucedo, R.; Macias, J.; Arce, J.; Garcia-Palomo, A.; Mora, J.; Scolamacchia, T.

2003-12-01

Tacaná volcano, with a height of 4,030 m above sea level, straddles the southern Mexico/Guatemala border. Last active in 1986, when there was a small phreatic event with a duration of a few days, this volcano presents an impending hazard to over 250,000 people. The NE sector of the volcano reveals the violent volcanic history of Tacaná that may be indicative of a serious potential risk to the area. Its earliest pyroclastic history appears to consist of fall, flow, and surge deposits, together with lavas, that have formed megablocks within a series of old debris avalanche deposits. This sector collapse event is overlain by a sequence of pumice fall and ash flow deposits, of which the youngest, less-altered pumice fall deposit shows a minimum thickness of > 4 m, with a dispersal axis trending toward the NE. A second debris avalanche deposit, separated from the above deposits by a paleosoil, is dominated by megablocks of lava and scoriaceous dome material. The current topography around the northeastern flank of the volcano is determined by a third, and most recent debris avalanche deposit, a thick (> 20 m) sequence of six block and ash flows dated at around 16,000 years BP, each separated by 1-10 cm thick ash cloud surge deposit, together with secondary lahar deposits. These are followed by a at least 4 lava flows that extend 2 km down the flank of the volcano. It appears that the most recent pyroclastic event at Tacaná is also recorded in this sector of the volcano: above the block and ash flows occurs a > 1 m thick ash flow unit that can be seen at least 5 km from the vent. Lastly, the Santa Maria Ash fall deposit, produced in 1902, has capped most of the deposits at Tacaná.

Integrating field, textural, and geochemical monitoring to track eruption triggers and dynamics: a case study from Piton de la Fournaise

NASA Astrophysics Data System (ADS)

Gurioli, Lucia; Di Muro, Andrea; Vlastélic, Ivan; Moune, Séverine; Thivet, Simon; Valer, Marina; Villeneuve, Nicolas; Boudoire, Guillaume; Peltier, Aline; Bachèlery, Patrick; Ferrazzini, Valérie; Métrich, Nicole; Benbakkar, Mhammed; Cluzel, Nicolas; Constantin, Christophe; Devidal, Jean-Luc; Fonquernie, Claire; Hénot, Jean-Marc

2018-04-01

The 2014 eruption at Piton de la Fournaise (PdF), La Réunion, which occurred after 41 months of quiescence, began with surprisingly little precursory activity and was one of the smallest so far observed at PdF in terms of duration (less than 2 days) and volume (less than 0.4 × 106 m3). The pyroclastic material was composed of golden basaltic pumice along with fluidal, spiny iridescent and spiny opaque basaltic scoria. Density analyses performed on 200 lapilli reveal that while the spiny opaque clasts are the densest (1600 kg m-3) and most crystalline (55 vol. %), the golden pumices are the least dense (400 kg m-3) and crystalline (8 vol. %). The connectivity data indicate that the fluidal and golden (Hawaiian-like) clasts have more isolated vesicles (up to 40 vol. %) than the spiny (Strombolian-like) clasts (0-5 vol. %). These textural variations are linked to primary pre-eruptive magma storage conditions. The golden and fluidal fragments track the hotter portion of the melt, in contrast to the spiny fragments and lava that mirror the cooler portion of the shallow reservoir. Exponential decay of the magma ascent and output rates through time revealed depressurization of the source during which a stratified storage system was progressively tapped. Increasing syn-eruptive degassing and melt-gas decoupling led to a decrease in the explosive intensity from early fountaining to Strombolian activity. The geochemical results confirm the absence of new input of hot magma into the 2014 reservoir and confirm the emission of a single shallow, differentiated magma source, possibly related to residual magma from the November 2009 eruption. Fast volatile exsolution and crystal-melt separation (second boiling) were triggered by deep pre-eruptive magma transfer and stress field change. Our study highlights the possibility that shallow magma pockets can be quickly reactivated by deep processes without mass or energy (heat) transfer and produce hazardous eruptions with only short-term elusive precursors.

Primary and secondary fragmentation of crystal-bearing intermediate magma

NASA Astrophysics Data System (ADS)

Jones, Thomas J.; McNamara, Keri; Eychenne, Julia; Rust, Alison C.; Cashman, Katharine V.; Scheu, Bettina; Edwards, Robyn

2016-11-01

Crystal-rich intermediate magmas are subjected to both primary and secondary fragmentation processes, each of which may produce texturally distinct tephra. Of particular interest for volcanic hazards is the extent to which each process contributes ash to volcanic plumes. One way to address this question is by fragmenting pyroclasts under controlled conditions. We fragmented pumice samples from Soufriere Hills Volcano (SHV), Montserrat, by three methods: rapid decompression in a shock tube-like apparatus, impact by a falling piston, and milling in a ball mill. Grain size distributions of the products reveal that all three mechanisms produce fractal breakage patterns, and that the fractal dimension increases from a minimum of 2.1 for decompression fragmentation (primary fragmentation) to a maximum of 2.7 by repeated impact (secondary fragmentation). To assess the details of the fragmentation process, we quantified the shape, texture and components of constituent ash particles. Ash shape analysis shows that the axial ratio increases during milling and that particle convexity increases with repeated impacts. We also quantify the extent to which the matrix is separated from the crystals, which shows that secondary processes efficiently remove adhering matrix from crystals, particularly during milling (abrasion). Furthermore, measurements of crystal size distributions before (using x-ray computed tomography) and after (by componentry of individual grain size classes) decompression-driven fragmentation show not only that crystals influence particular size fractions across the total grain size distribution, but also that free crystals are smaller in the fragmented material than in the original pumice clast. Taken together, our results confirm previous work showing both the control of initial texture on the primary fragmentation process and the contributions of secondary processes to ash formation. Critically, however, our extension of previous analyses to characterisation of shape, texture and componentry provides new analytical tools that can be used to assess contributions of secondary processes to ash deposits of uncertain or mixed origin. We illustrate this application with examples from SHV deposits.

The volcanic history of Volcán Alcedo, Galápagos Archipelago: a case study of rhyolitic oceanic volcanism

USGS Publications Warehouse

Geist, Dennis J.; Howard, Keith A.; Jellinek, A. Mark; Rayder, Scott

1994-01-01

Volcán Alcedo is one of the seven western Galápagos shields and is the only active Galápagos volcano known to have erupted rhyolite as well as basalt. The volcano stands 4 km above the sea floor and has a subaerial volume of 200 km3, nearly all of which is basalt. As Volcán Alcedo grew, it built an elongate domal shield, which was partly truncated during repeated caldera-collapse and partial-filling episodes. An outward-dipping sequence of basalt flows at least 250 m thick forms the steepest (to 33°) flanks of the volcano and is not tilted; thus a constructional origin for the steep upper flanks is favored. About 1 km3 of rhyolite erupted late in the volcano's history from at least three vents and in 2–5 episodes. The most explosive of these produced a tephra blanket that covers the eastern half of the volcano. Homogeneous rhyolitic pumice is overlain by dacite-rhyolite commingled pumice, with no stratigraphic break. The tephra is notable for its low density and coarse grain size. The calculated height of the eruption plume is 23–30 km, and the intensity is estimated to have been 1.2x108 kg/s. Rhyolitic lavas vented from the floor of the caldera and from fissures along the rim overlie the tephra of the plinian phase. The age of the rhyolitic eruptions is ≤120 ka, on the basis of K-Ar ages. Between ten and 20 basaltic lava flows are younger than the rhyolites. Recent faulting resulted in a moat around part of the caldera floor. Alcedo most resently erupted sometime between 1946 and 1960 from its southern flank. Alcedo maintains an active, transient hydrothermal system. Acoustic and seismic activity in 1991 is attributed to the disruption of the hydrothermal system by a regional-scale earthquake.

Estimation of septic tank setback distances based on transport of E. coli and F-RNA phages.

PubMed

Pang, Liping; Close, Murray; Goltz, Mark; Sinton, Lester; Davies, Helen; Hall, Carollyn; Stanton, Greg

2004-01-01

Setback distances between septic tank systems and the shorelines of Lake Okareka, New Zealand were determined from model simulations for a worst-case scenario, using the highest hydraulic conductivity and gradient measured in the field, removal rates of the microbial indicators (Escherichia coli and F-RNA phages) determined from a column experiment, and maximum values of the design criteria for the disposal system, and assuming an absence of an unsaturated zone, a continuous discharge of the raw effluent from a failed or non-complying treatment system (both indicators at concentrations of 1x10(7) counts/100 ml) into the groundwater and no sorption of pathogens in the aquifer. Modelling results suggest that the minimal setback distances were 16 m to satisfy the New Zealand Recreational Water Quality Guidelines for E. coli <126 per 100 ml (Ministry for the Environment, 1999) and 48 m to meet the Drinking-Water Standards for New Zealand 2000 for enteric virus <1 per 100 l (Ministry of Health, 2000). These distances may be applicable for other lakeshores in pumice sand aquifers with groundwater velocities <7 m/day. Findings of laboratory column and batch experiments provided an insight into the microbial attenuation and transport processes in pumice sand aquifers. Bacterial removal was predominately through filtration (87-88%) and partially by die-off (12-13%), while viral removal was by both die-off (45%) and filtration (55%). In addition, microbial die-off in groundwater without aquifer material (i.e., free microbes) was much lower than die-off in groundwater with aquifer material (i.e., sorbed microbes) and contributed only 2-6% to the total removal. This implies that the setback distances estimated from die-off rates for the free microbes, determined in the laboratory without considering aquifer media and other removal processes, which are often reported in the literature, could be larger than necessary.

Landslides from the February 4, 1976, Guatemala earthquake

USGS Publications Warehouse

Harp, Edwin L.; Wilson, Raymond C.; Wieczorek, Gerald F.

1981-01-01

The M (Richter magnitude) = 7.5 Guatemala earthquake of February 4, 1976, generated more than 10,000 landslides throughout an area of approximately 16,000 km2. These landslides caused hundreds of fatalities as well as extensive property damage. Landslides disrupted both highways and the railroad system and thus severely hindered early rescue efforts. In Guatemala City, extensive property damage and loss of life were due to ground failure beneath dwellings built too close to the edges of steeply incised canyons. We have recorded the distribution of landslides from this earthquake by mapping individual slides at a scale of 1:50,000 for most of the landslide-affected area, using high-altitude aerial photography. The highest density of landslides was in the highlands west of Guatemala City. The predominant types of earthquake-triggered landslides were rock falls and debris slides of less than 15,000 m3 volume; in addition to these smaller landslides, 11 large landslides had volumes of more than 100,000 m3. Several of these large landslides posed special hazards to people and property from lakes impounded by the landslide debris and from the ensuing floods that occurred upon breaching and rapid erosion of the debris. The regional landslide distribution was observed to depend on five major factors: (1) seismic intensity; (2) lithology: 90 percent of all landslides were within Pleistocene pumice deposits; (3) slope steepness; (4) topographic amplification of seismic ground motion; and (5) regional fractures. The presence of preearthquake landslides had no apparent effect on the landslide distribution, and landslide concentration in the Guatemala City area does not correlate with local seismic-intensity data. The landslide concentration, examined at this scale, appears to be governed mainly by lithologic differences within the pumice deposits, preexisting fractures, and amplification of ground motion by topography-all factors related to site conditions.

Relating the physical properties of volcanic rocks to the characteristics of ash generated by experimental abrasion

NASA Astrophysics Data System (ADS)

Buckland, Hannah M.; Eychenne, Julia; Rust, Alison C.; Cashman, Katharine V.

2018-01-01

Interactions between clasts in pyroclastic density currents (PDCs) generate volcanic ash that can be dispersed to the atmosphere in co-PDC plumes, and due to its small size, is far-travelled. We designed a series of experiments to determine the effects of pyroclast vesicularity and crystal content on the efficiency and type of ash generated by abrasion. Two different pyroclastic materials were used: (1) basaltic-andesite pyroclasts from Fuego volcano (Guatemala) with 26-46% vesicularity and high groundmass crystallinity and (2) tephri-phonolite Avellino pumice (Vesuvius, Italy) with 55-75% vesicularity and low groundmass crystallinity. When milled, both clast types produced bimodal grain size distributions with fine ash modes between 4 and 5φ (32-63 μm). Although the vesicular Avellino pumice typically generated more ash than the denser Fuego pyroclasts, the ash-generating potential of a single pyroclast was independent of density, and instead governed by heterogeneous crystal and vesicle textures. One consequence of these heterogeneities was to cause the vesicular Avellino clasts to split in addition to abrading, which further enhanced abrasion efficiency. The matrix characteristics also affected ash shape and componentry, which will influence the elutriation and transport properties of ash in the atmosphere. The experimental abrasion successfully replicated some of the characteristics of natural co-PDC ash samples, as shown by similarities in the Adherence Factor, which measures the proportion of attached matrix on phenocrysts, of both the experimentally generated ash and natural co-PDC ash samples. Our results support previous studies, which have shown that abrasion is an effective mechanism for generating fine ash that is similar in size ( 5φ; 30 μm) to that found in co-PDC deposits. We further show that both the abundance and nature (shape, density, components, size distribution) of those ash particles are strongly controlled by the matrix properties of the abraded pyroclasts.

Stratigraphy of the Grande Savane Ignimbrite Sequence, Dominica, Lesser Antilles

NASA Astrophysics Data System (ADS)

Schneider, S.; Smith, A. L.; Deuerling, K.; Killingsworth, N.; Daly, G.

2007-12-01

The island of Dominica, located in the central part of the Lesser Antilles island arc has eight potentially active volcanoes. One of these, Morne Diablotins, is a composite stratovolcano with several superimposed stratigraphic sequences ranging in age from Pliocene (4-2 Ma) to "Younger" Pleistocene (<1.8 Ma). The most recent major eruptive activity from this volcano was a series of Plinian eruptions that produced ignimbrites that gave dates of >22,000 and >40,000 years B.P. The ignimbrite sequences form four flow fans that reached both the east and west coasts of the island. One of these flow fans, the Grande Savane, on the west coast of the island, also extends off-shore for a distance of at least 14 km as a distinctive submarine fan. Stratigraphical studies of the on- shore deposits that make up this fan indicate an older sequence of block and ash flow deposits, within which occurs a distinctive vulcanian fall deposit. These are overlain, with no evidence of an intervening paleosol, by a sequence of ignimbrites containing welded horizons (ranging in thickness from around 4 m to 16m). The lack of fall deposits beneath the ignimbrites suggest they may have been formed by instantaneous continuous collapse of the eruption column. This whole succession is overlain by a series of planar and dune bedded pumiceous surge deposits with interbedded pumiceous lapilli fall and ash fall deposits, that extend laterally outside of the main area of ignimbrite deposition. Beds within this upper sequence often contain accretionary lapilli and gas cavities suggesting magma-water interaction. The youngest deposits from Morne Diablotins appear to be valley- fill deposits of both ignimbrite and block and ash flow. A comparison of the of the Grande Savane pyroclastic sequence with the Pointe Ronde (west coast) and Londonderry (east coast) pyroclastic flow fans will provide information on the eruptive history of this major Plinian episode.

Identifying the Volcanic Eruption Depicted in a Neolithic Painting at Çatalhöyük, Central Anatolia, Turkey

PubMed Central

Schmitt, Axel K.; Danišík, Martin; Aydar, Erkan; Şen, Erdal; Ulusoy, İnan; Lovera, Oscar M.

2014-01-01

A mural excavated at the Neolithic Çatalhöyük site (Central Anatolia, Turkey) has been interpreted as the oldest known map. Dating to ∼6600 BCE, it putatively depicts an explosive summit eruption of the Hasan Dağı twin-peaks volcano located ∼130 km northeast of Çatalhöyük, and a birds-eye view of a town plan in the foreground. This interpretation, however, has remained controversial not least because independent evidence for a contemporaneous explosive volcanic eruption of Hasan Dağı has been lacking. Here, we document the presence of andesitic pumice veneer on the summit of Hasan Dağı, which we dated using (U-Th)/He zircon geochronology. The (U-Th)/He zircon eruption age of 8.97±0.64 ka (or 6960±640 BCE; uncertainties 2σ) overlaps closely with 14C ages for cultural strata at Çatalhöyük, including level VII containing the “map” mural. A second pumice sample from a surficial deposit near the base of Hasan Dağı records an older explosive eruption at 28.9±1.5 ka. U-Th zircon crystallization ages in both samples range from near-eruption to secular equilibrium (>380 ka). Collectively, our results reveal protracted intrusive activity at Hasan Dağı punctuated by explosive venting, and provide the first radiometric ages for a Holocene explosive eruption which was most likely witnessed by humans in the area. Geologic and geochronologic lines of evidence thus support previous interpretations that residents of Çatalhöyük artistically represented an explosive eruption of Hasan Dağı volcano. The magmatic longevity recorded by quasi-continuous zircon crystallization coupled with new evidence for late-Pleistocene and Holocene explosive eruptions implicates Hasan Dağı as a potential volcanic hazard. PMID:24416270

The effect of prophylaxis method on microtensile bond strength of indirect restorations to dentin.

PubMed

Soares, C J; Pereira, J C; Souza, S J B; Menezes, M S; Armstrong, S R

2012-01-01

The aim of this study was to evaluate the effect of different materials used for dentin prophylaxis on the microtensile bond strengths (μTBS) of adhesively cemented indirect composite restorations. Sixty bovine incisors had the buccal surface ground with wet #600-grit silicon carbide abrasive paper to obtain a flat exposed superficial dentin and were submitted to different prophylaxis protocols, as follows: 3% hydrogen peroxide (HydP); 0.12% chlorhexidine (Chlo); sodium bicarbonate jet (SodB); 50-μm aluminum oxide air abrasion (AirA); pumice paste (PumP), and control group-water spray (Cont). After prophylaxis protocols a resin composite block (3.0 mm × 5.0 mm × 5.0 mm) was adhesively cemented using dual resin cement (Rely X ARC). After 24 hours of water storage, specimens were serially sectioned perpendicular to the bonded interface into 1-mm-thick slices. Each specimen was trimmed with a diamond bur to an hourglass shape with a cross-sectional area of approximately 1.0 mm(2) at the bonded area. Specimens were tested (μTBS) at 0.5 mm/min using a universal testing machine. Scanning electron microscopy was used to examine the effects of prophylaxis techniques on dentin. Bond strength data (MPa) were analyzed by one-way analysis of variance and failure mode by Fisher test (α=0.05). μTBS data, means (SD), were (different superscripted letters indicate statistically significant differences): AirA, 25.2 (7.2)(a); PumP, 24.1 (7.8)(a); Chlo, 21.5 (5.6)(a); Cont, 20.6 (8.1)(a); HydP(,) 15.5 (7.6)(b); and SodB(,) 11.5 (4.4)(c). The use of aluminum oxide air abrasion, pumice paste, and chlorhexidine before acid etching did not significantly affect μTBS to dentin; however, the use of hydrogen peroxide and sodium bicarbonate jet significantly reduced μTBS.

Quartz phenocrysts preserve volcanic stresses at Long Valley and Yellowstone calderas

NASA Astrophysics Data System (ADS)

Befus, K. S.; Leonhardi, T. C.; Manga, M.; Tamura, N.; Stan, C. V.

2016-12-01

Magmatic processes and eruptions are the consequence of stresses active in volcanic environments. Few techniques are presently available to quantify those stresses because they operate in subsurface and/or hazardous environments, and thus new techniques are needed to advance our understanding of key processes. Here, we provide a dataset of volcanic stresses that were imparted to quartz crystals that traveled through, and were hosted within, pyroclastic and effusive eruptions from Long Valley and Yellowstone calderas. We measured crystal lattice deformation with submicron spatial resolution using the synchrotron X-ray microdiffraction beamline (12.3.2) at the Advanced Light Source, Lawrence Berkeley National Laboratory. Quartz from all units produces diffraction patterns with residual strains locked in the crystal lattice. We used Hooke's Law and the stiffness constants of quartz to calculate the stresses that caused the preserved residual strains. At Long Valley caldera, quartz preserves stresses of 187±80 MPa within pumice clasts in the F1 fall unit of the Bishop Tuff, and preserves stresses of 120±45 MPa from the Bishop Tuff welded ignimbrite. At Yellowstone caldera quartz preserves stresses of 115±30 and 140±60 MPa within pumices from the basal fall units of the Mesa Falls Tuff and the Tuff of Bluff Point, respectively. Quartz from near-vent and flow-front samples from Summit Lake lava flow preserves stresses up to 130 MPa, and show no variation with distance travelled. We believe that subsurface processes cause the measured residual stresses, but it remains unclear if they are relicts of fragmentation or from the magma chamber. The residual stresses from both Long Valley and Yellowstone samples roughly correlate to lithostatic pressures estimated for the respective pre-eruption magma storage depths. It is possible that residual stress in quartz provides a new geobarometer for crystallization pressure. Moving forward, we will continue to perform analyses and experiments on natural and synthetic crystals to better determine the source of residual stresses.

Microbial colonization in diverse surface soil types in Surtsey and diversity analysis of its subsurface microbiota

NASA Astrophysics Data System (ADS)

Marteinsson, V.; Klonowski, A.; Reynisson, E.; Vannier, P.; Sigurdsson, B. D.; Ólafsson, M.

2015-02-01

Colonization of life on Surtsey has been observed systematically since the formation of the island 50 years ago. Although the first colonisers were prokaryotes, such as bacteria and blue-green algae, most studies have been focused on the settlement of plants and animals but less on microbial succession. To explore microbial colonization in diverse soils and the influence of associated vegetation and birds on numbers of environmental bacteria, we collected 45 samples from different soil types on the surface of the island. Total viable bacterial counts were performed with the plate count method at 22, 30 and 37 °C for all soil samples, and the amount of organic matter and nitrogen (N) was measured. Selected samples were also tested for coliforms, faecal coliforms and aerobic and anaerobic bacteria. The subsurface biosphere was investigated by collecting liquid subsurface samples from a 181 m borehole with a special sampler. Diversity analysis of uncultivated biota in samples was performed by 16S rRNA gene sequences analysis and cultivation. Correlation was observed between nutrient deficits and the number of microorganisms in surface soil samples. The lowest number of bacteria (1 × 104-1 × 105 cells g-1) was detected in almost pure pumice but the count was significantly higher (1 × 106-1 × 109 cells g-1) in vegetated soil or pumice with bird droppings. The number of faecal bacteria correlated also to the total number of bacteria and type of soil. Bacteria belonging to Enterobacteriaceae were only detected in vegetated samples and samples containing bird droppings. The human pathogens Salmonella, Campylobacter and Listeria were not in any sample. Both thermophilic bacteria and archaea 16S rDNA sequences were found in the subsurface samples collected at 145 and 172 m depth at 80 and 54 °C, respectively, but no growth was observed in enrichments. The microbiota sequences generally showed low affiliation to any known 16S rRNA gene sequences.

Microbial colonisation in diverse surface soil types in Surtsey and diversity analysis of its subsurface microbiota

NASA Astrophysics Data System (ADS)

Marteinsson, V.; Klonowski, A.; Reynisson, E.; Vannier, P.; Sigurdsson, B. D.; Ólafsson, M.

2014-09-01

Colonisation of life on Surtsey has been observed systematically since the formation of the island 50 years ago. Although the first colonisers were prokaryotes, such as bacteria and blue-green algae, most studies have been focusing on settlement of plants and animals but less on microbial succession. To explore microbial colonization in diverse soils and the influence of associate vegetation and birds on numbers of environmental bacteria, we collected 45 samples from different soils types on the surface of the island. Total viable bacterial counts were performed with plate count at 22, 30 and 37 °C for all soils samples and the amount of organic matter and nitrogen (N) was measured. Selected samples were also tested for coliforms, faecal coliforms aerobic and anaerobic bacteria. The deep subsurface biosphere was investigated by collecting liquid subsurface samples from a 182 m borehole with a special sampler. Diversity analysis of uncultivated biota in samples was performed by 16S rRNA gene sequences analysis and cultivation. Correlation was observed between N deficits and the number of microorganisms in surface soils samples. The lowest number of bacteria (1 × 104-1 × 105 g-1) was detected in almost pure pumice but the count was significant higher (1 × 106-1 × 109 g-1) in vegetated soil or pumice with bird droppings. The number of faecal bacteria correlated also to the total number of bacteria and type of soil. Bacteria belonging to Enterobacteriaceae were only detected in vegetated and samples containing bird droppings. The human pathogens Salmonella, Campylobacter and Listeria were not in any sample. Both thermophilic bacteria and archaea 16S rDNA sequences were found in the subsurface samples collected at 145 m and 172 m depth at 80 °C and 54 °C, respectively, but no growth was observed in enrichments. The microbiota sequences generally showed low affiliation to any known 16S rRNA gene sequences.

Composite Calderas: The Long and Short of it

NASA Astrophysics Data System (ADS)

Gravley, D. M.; Hasegawa, T.; Nakagawa, M.; Wilson, C. J.

2006-12-01

Calderas formed in supereruptions are normally linked to a single magma body. However, caldera formation, regional tectonics, and multiple magma bodies may interact to form composite structures with complex geometries. The term composite caldera is often used without reference as to whether the `composite' is in time or space. Three examples of composite caldera styles from New Zealand and Japan show field, geophysical, geochemical and isotopic evidence to suggest that current models for the size, shape and evolution of calderas may be too simplistic. In our examples, multiple separate magma bodies distributed in either space or time, or both, may play a significant role in composite caldera formation. Multiple, clustered collapse events incremental in time: Akan caldera in Hokkaido appears to be a single, rectangular shaped caldera. However, the identification of 17 eruptive units spanning >1 Myr suggests that the caldera evolved incrementally over time and space. New gravity data shows that the caldera is actually a daisy-chain of 3 distinct collapse structures that can be correlated, using lithic componentry, to 3 major geochemical groups in the eruptive products. Multiple, clustered collapse events in a single eruption sequence: Shikotsu caldera in Hokkaido was originally thought to have formed following the eruption of a single large zoned magma chamber. However, the caldera-related deposits are characterized by several geochemically distinct pumice types that can not have been accommodated in a single magma system. Our studies suggest that the variations in pumice compositions are consistent with multiple distinct magma bodies feeding coeval eruptions from several vent sources within an area that collapsed to form a single caldera. Paired calderas with linking eruption-related regional faulting: Rotorua and Ohakuri calderas in New Zealand are 30 km apart and formed in close succession during a complex but virtually continuous eruption sequence at ca. 240 ka. The distinct calderas are joined in dumb-bell fashion by an intervening zone of eruption-related and immediately post-eruptive faulting and collapse.

A Spectroscopic Study On Two Glasses With Different Vesicularity From The Astroni Tephra (phlegraean Fields, Italy): Implications On Bubble Expansion

NASA Astrophysics Data System (ADS)

Slejko, F. F.; Petrini, R.

Bubble growth in ascending viscous magmas by volatile exsolution from the melt structure is important in causing the magma fragmentation which determines the trans- form from a lava flow to a pyroclastic explosion. Volatile solubility and speciation in the melt vary during pressure and temperature changes. The pressure drop which oc- curs as a magma rises towards the surface in a volcanic conduit, causes the release of the volatiles dissolved in the melt and the progressive growth in the size of bubbles against the retarding forces to expansion generated by the polymeric interconnections in the silicate melt structure. At some critical growth rate with respect to the relax- ation time of the melt structure, the disruption of the interbubbles walls in the melt marks the fragmentation threshold, with the transition from a viscous bubbly liquid to a fast-uprising gas carrying on fragments of vesiculated magma. Highly polymer- ized, silica-rich melts are characterised by relaxation times which may be long com- pared to the quick growth and deformation of bubbles during rapid magma decom- pression and cooling, and the glassy pumices which form may retain informations on the vesiculation and degassing processes which occurred close to the fragmentation depth. Furthermore, the formation of vesicles during the cooling and decompression of an ascending volatile-supersaturated high-silica magma is strongly favoured by the occurrence of bubble nucleating sites in the melt. In order to investigate the influ- ence of the structure and iron speciation on bubble growth during explosive volcan- ism, a dense glass and a vesiculated pumice glass coexisting in the same pyroclastic unit of the Astroni volcano tephra in the Phlegraean Fields Caldera (4.1-3.8 ka BP) were investigated by 29Si 2D phase adjusted spinning sidebands (PASS) NMR, 1H MAS NMR, electron spin resonance (ESR) and Mössbauer spectroscopy. 29Si 2D PASS spectra show that silicon copolymerizes in the structure dominantly by Q3 and Q4 groups, with partly overlapping chemical shift. Spectrum fittings indicate that the dense glass is characterised by a larger abundance of Q3 species compared to the vesiculated pumice, suggesting a less polymerized structure. 1H MAS spectra reveal a larger amount of hydrogen concentration in the dense glass, partly attributable to structural hydroxyl groups possibly in Q3-OH terminations depolymerizing the glass structure. The less polymerized structure of the dense glass could have allowed an easier volatile exsolution, preventing the bubble formation. The EPR spectra indicate that the Fe3+ has similar surroundings in both samples, suggesting that Fe3+ is likely to occur in both network forming and modifying sites. Nevertheless, the vesiculated glass is characterised by a significantly higher amount of magnetite particles, which could have enhanced the bubble nucleation. Mössbauer spectra show four doublets attributable to ferric iron in both tetrahedral and octahedral sites and ferrous iron only in octahedral coordination. The oxidation of Fe2+ to Fe3+ observed in the vesicu- lated glass with respect to the dense glass could be an evidence of pressure drop with consequent bubble expansion.

Silicon Isotopic Fractionation in a Tropical Soil-Plant System

NASA Astrophysics Data System (ADS)

Opfergelt, S.; Delstanche, S.; Cardinal, D.; Andre, L.; Delvaux, B.

2006-12-01

Silica fluxes to soil solutions and water streams are controlled by both abiotic and biotic processes occurring in a Si soil-plant cycle that can be significant in comparison with Si weathering input and hydrological output. The quantification of Si-isotopic fractionation by these processes is highly promising to study the Si soil-plant cycle. Therein, the fate of aqueous monosilicic acid H4SiO4, as produced by silicate weathering, may take four paths: (1) uptake by plants and recycling through falling litter, (2) formation of clay minerals, (3) specific adsorption onto Al and Fe oxides, (4) leaching in drainage waters and export from watersheds. Here we report on detailed Si-isotopic compositions of various Si pools in a tropical soil-plant system involving old stands of banana (Musa acuminata Colla, cv Grande Naine) cropped on a weathering sequence of soils derived from andesitic volcanic ash and pumice deposits in Cameroon, West Africa. Si-isotopic compositions were measured by MC-ICP-MS in dry plasma mode with external Mg doping with a reproducibility of 0.08 permil (2stdev). Results were expressed as delta29Si vs NBS28. The compositions were determined in plant parts, bulk soils, clay fractions (less than 2um) and stream waters used for crop irrigation. Of the weathering sequence, we selected young (Y) and old (O) volcanic soils (vs). Yvs are rich in weatherable minerals, and contain large amounts of pumice gravels; their clay fraction (10-35 percent) contains allophane, halloysite and ferrihydrite. Oppositely, Ovs are strongly weathered and fine clayey soils (75-96 percent clay) rich in halloysite, kaolinite, gibbsite and goethite. Intra-plant fractionation between roots and shoots and within shoots confirmed our previous data measured on banana plants grown in hydroponics. The bulk plant isotopic composition was heavier at Ovs than at Yvs giving a fractionation factor per atomic mass unit between plants and their irrigation water Si source (+0.61 permil) of -0.33 (Ovs) and -0.56 permil (Yvs), close to the fractionation factor previously measured in hydroponics (-0.40 permil). The average delta29Si of phytoliths in banana plants was +0.17 permil. In the topsoil, the isotopic composition of Yvs ( 0.21 permil) was close to that of unweathered pumice (-0.20 permil). The Ovs were significantly lighter (-0.73 permil), confirming published data pointing to lighter isotopic composition with increased weathering. Heavier bulk plants at Ovs might be related to a heavier residual soil solution due to: (i) the formation of lighter clay minerals at Ovs (clay fraction: -0.94 permil) than at Yvs (-0.60 permil), and (ii) the quantitative adsorption of silica onto iron oxides (see Delstanche et al., 2006, AGU), more abundant in weathered Ovs. Our data support the view that plants can induce a strong imprint on the continental cycle of silicon, just as clay formation and possibly Si adsorption onto iron oxides can do. The quantification of Si-isotopic fractionation in the soil-plant system requires, however, further studies involving all the Si pools to achieve a comprehensive understanding of this cycle.

The origin of the magnetic fabric and the significance of AIRM in reconstructing the emplacement dynamics of ignimbrites: a case study from the Central Anatolian Volcanic Province, Turkey

NASA Astrophysics Data System (ADS)

Agrò, A.; Zanella, E.; Le Pennec, J.; Temel, A.

2012-12-01

The investigation of the magnetic fabric is a very effective tool in the study of the emplacement and depositional processes of volcanic rocks. The analysis of the anisotropy of magnetic susceptibility (AMS) has been increasingly applied to pyroclastic deposits with the main purpose of getting information about the petrofabric, understanding the flow dynamics, and inferring flow directions and vent position. One of the most crucial points, which prejudice the reliability of any volcanological reconstructions is understanding the meaning of the AMS, discriminating among primary and secondary fabric and identifying the carriers of the AMS signal. The AMS fabric of a volcanic rock is the complex result of various factors: contribution of the paramagnetic fraction, type of ferromagnetic grains (MD or SD), rheology of the flow, interaction of the flow with paleotopography and disturbances due to the intrinsic heterogeneities. In this study we investigate the magnetic fabric of the Late Miocene Kizilkaya ignimbrite (Central Anatolian Volcanic Province, Turkey) through measures of anisotropy of magnetic susceptibility (AMS), isothermal remanent magnetization (AIRM) and anhysteretic remanent magnetization (AARM). Sampling has been performed at seven localities at different stratigraphic heights (a total of 35 sites yielding about 600 specimens) within the ignimbrite's devitrified layer. Our measurements and observations reveal that the magnetic mineralogy is complex: the main magnetic carrier is represented by Ti-magnetite which occurs as free grains in the matrix and as inclusions in pumice and lithic clasts, as well as in glass shards; in certain levels it is also detected the presence of a more oxidized Ti-magnetite and haematite. The AMS fabric varies vertically along each section; based on the angle between the direction of the magnetic lineation k1 and that of the foliation plunge k3, three types of fabric are evidenced: normal, oblique and transverse. The anisotropy of the magnetic fabric was firstly enhanced by discarding all specimens whose density values differ more than +/- 1σ from the site mean value. This resulted in the elimination of the oblique fabrics (i.e. the angle formed by k1 and k3 is comprised between 35 and 55°), which are interpreted as an orientation disturbance due to local occurrence of pumices and lithic clasts in the specimens. Moreover, the consistency of the directions of k1 and k3 for specimens with normal fabric supports a primary origin of the magnetic fabric. Secondly, we measured the AIRM of the specimens with low lithic and pumice content, to determine the orientation of the ferromagnetic minerals fraction. Preliminary data indicate that MD Ti-magnetite is the main carrier of the fabric, which in turn suggests that the magnetic fabric is a reliable proxy for flow directions. Data are preliminary, but the Kizilkaya case study suggests that AMS data only cannot be enough to resolve reliable volcanological reconstruction, and AIRM may be required to separate the effect of the various minerals and thus possible overprints which mask the fabric from the emplacement dynamics.

Shallow conduit processes of the 1991 Hekla eruption, Iceland

NASA Astrophysics Data System (ADS)

Gudnason, J.; Thordarson, T.; Houghton, B. F.

2013-12-01

On January 17, 1991 at 17:00 hrs, the 17th eruption of Hekla since 1104AD began. Lasting for almost two months, it produced 0.02 km3 of icelandite tephra and ~0.15km3 of icelandite lava. This eruption was the third of four eruptions since 1980 with a recurrence period of approximately 10 years, as opposed to a recurrence interval of c. 55 years for the eruptions in the period 1104AD to 1947AD. [1] The last four Hekla eruptions are typified by a 0.5-2 hour-long initial phase of subplinian intensity and discharge ranging from 2900-6700 m3/s [2]. In all 4 events the inital phase was followed by a sustained and relatively low-discharge(<20 m3/s) effusive phase, which in the case of Hekla 1991 lasted until the 11th March 1991 [1]. The initial phase of the 1991 event lasted for ~50 minutes and sustained an eruption plume that rose to 11.5 km in about 10 minutes [1]. The plume was dispersed to the NNE at velocities of 60-70 km/hr producing a well-sorted tephra fall covering >20,000 km2. Here we examine the first phase of the Hekla 1991 eruption with focus on vesiculation and fragmentation processes in the shallow conduit and ash production. Samples of the tephra fall were collected on snow immediately after the initial phase at multiple sites providing a representative spatial coverage within the 0.1mm isopach [3]. This set was augmented by samples collected in 2012 to provide tighter coverage of near vent region. Grain size of all samples has been measured down to 1 micron. Density measurements have been conducted on 4 near-vent pumice samples (100 clasts each) and the pumice vesicle size distribution has been determined in a selected subset of clasts. The reconstructed whole deposit grain size distribution exhibits a unimodal, log-normal distribution peaking at -3 phi, typical of dry, magmatic fragmentation. Pumice densities range from 520-880 kg/m3 and exhibit a tight unimodal and log-normal distribution indicating a mean vesicularity of 77% to 79% for the magma erupted during the initial phase. Along with preliminary results for bubble number density and vesicle size distribution this implies a single late-stage homogeneous bubble nucleation and very uniform conditions of magma fragmentation during this short-lived initial phase of the Hekla 1991 eruption. 1. Gudmundsson, A., et al., The 1991 eruption of Hekla, Iceland. Bulletin of Volcanology, 1992. 54(3): p. 238-246. 2. Höskuldsson, Á., Óskarsson, N., Pedersen, R., Grönvold, K., Vogfjörd, K. & Ólafsdóttir, R. 2007. The millennium eruption of Hekla in February 2000. Bull Volcanol, 70:169-182. 3. Larsen, G., E.G. Vilmundardóttir, and B. Thorkelsson, Heklugosid 1991: Gjóskufall og gjóskulagid frá fyrsta degi gossins. Náttúrufrædingurinn, 1992. 61(3-4): p. 159-176.

Mineral resource potential map of the Gila-San Francisco Wilderness Study Area, Graham and Greenlee counties, Arizona

USGS Publications Warehouse

Richter, Donlad H.; Klein, Douglas P.; Lawrence, Viki A.; Lane, Michael

1982-01-01

The mineral resource potential of the Gila-San Francisco Wilderness Study Area (AZ-040-022/023/024) is low (fig. 2). Although favorable geologic environments for placer gold deposits and manganese vein deposits are present in the study area, the probability of discovering economically exploitable deposits of these metals is low, and not encouraging. Even more speculative is the study area's porphyry copper potential which is based solely on the possibility of favorable host terranes underlying the study area at depth. The study area does contain substantial deposits of pumice, but their economic significance is probably minor. A part of the study area has been previously designated a Known Geothermal Resource Area (KGRA).

THREE SISTERS WILDERNESS, OREGON.

USGS Publications Warehouse

MacLeod, Norman S.; Causey, J. Douglas

1984-01-01

A mineral survey of the Three Sisters Wilderness, Oregon indicated little promise for the occcurrence of metallic mineral resources. Block pumice suitable for commercial uses occurs at an undeveloped claim at Rock Mesa in the wilderness, but numerous other sources occur outside the wilderness closer to markets. A broad area centered around South Sister volcano is among the most favorable targets for geothermal resources in the Oregon Cascade Range, based on the very young age and large volume of silicic volcanic rocks that occur in this area. Deep exploration holes could be drilled in areas outside the wilderness south of South Sister to provide data on the subsurface thermal and hydrologic regimes in the southern part of the area most likely to contain geothermal resources.

Water, CO2, Cl, and F in melt inclusions in phenocrysts from three Holocene explosive eruptions, Crater Lake, Oregon

USGS Publications Warehouse

Bacon, C.R.; Newman, S.; Stolper, E.

1992-01-01

Rare melt inclusions ~100 ??m in diameter trapped near the boundaries of corroded patchy zones in plagioclase phenocrysts from Plinian pumice of three Holocene eruptions were analyzed by IR spectroscopy for molecular H2O, OH groups, and CO2 and by electron microprobe for Cl and F. The three rhyodacitic eruptions, each of which began with a Plinian phase, occurred over ~200 yr. The Llao Rock and Cleetwood eruptions ended with degassed lava flows and the subsequent climatic eruption with voluminous ignimbrite. Location of melt inclusions near boundaries of patchy zones, which are mantled by oscillatory-zoned overgrowths, suggests that their H2O concentrations represent magmatic values significantly before eruption. -from Authors

Geochemistry of the 1989-1990 eruption of redoubt volcano: Part I. Whole-rock major- and trace-element chemistry

USGS Publications Warehouse

Nye, C.J.; Swanson, S.E.; Avery, V.F.; Miller, T.P.

1994-01-01

The 1989-1990 eruption of Redoubt Volcano produced medium-K calc-alkaline andesite and dacite of limited compositional range (58.2-63.4% SiO2) and entrained quenched andesitic inclusions (55% SiO2) which bear chemical similarities to the rest of the ejecta. The earliest (December 15) magmas are pumiceous, often compositionally banded, and the majority is relatively mafic ( 60 wt.%). They have Mg, Cr, Ni, Sc, and V contents higher than the andesites, but lower than Redoubt basalts and basaltic andesites. Thus, they may be crystallization products of andesites, but do not represent the cumulate residue of basalt fractionation. The xenoliths were probably derived from a shallow or intermediate crustal chamber. ?? 1994.

Volcanic stratigraphy and geochemistry of the Soufrière Volcanic Centre, Saint Lucia with implications for volcanic hazards

NASA Astrophysics Data System (ADS)

Lindsay, Jan M.; Trumbull, Robert B.; Schmitt, Axel K.; Stockli, Daniel F.; Shane, Phil A.; Howe, Tracy M.

2013-05-01

The Soufrière Volcanic Complex (SVC), Saint Lucia, represents one of the largest silicic centres in the Lesser Antilles arc. It comprises extensive pumiceous pyroclastic flow deposits, lava flows as well as Peléan-style domes and dome collapse block-and-ash-flow deposits. These deposits occur within and around the Qualibou Depression, a ~ 10-km diameter wide sector collapse structure. To date, vent locations for SVC pyroclastic deposits and their relationship to the sector collapse have been unclear because of limited stratigraphic correlation and few radiometric ages. In this study we reconstruct the geologic history of the SVC in light of new and recently published (U-Th)/He, U-Th and U-Pb zircon chronostratigraphic data, aided by mineralogical and geochemical correlation. Compositionally, SVC deposits are monotonous medium-K, calc-alkaline rocks with 61.6 to 67.7 wt.% SiO2 and display similar trace element abundances. Combined U-Th and (U-Th)/He zircon dating together with 14C ages and mineral fingerprinting reveals significant explosive eruptions at 640, 515, 265, 104, 60 and 40 ka (producing deposits previously grouped together as the "Choiseul" unit) and at 20 ka (Belfond unit). The mineralogically and geochemically distinct Belfond unit is a large, valley-filling pumiceous pyroclastic flow deposit distributed to the north, northeast, south and southeast of the Qualibou Depression that was probably deposited during a single plinian eruption. The unit previously referred to as ‘Choiseul tuff' is much less well defined. The typical Choiseul unit comprises a series of yellowish-white, crystal-poor, non-welded pumiceous pyroclastic deposits cropping out to the north and southeast of the Qualibou depression; however its age is poorly constrained. A number of other units previously mapped as Choiseul can be distinguished based on age, and in some cases mineral and whole rock chemistry. Pyroclastic deposits at Micoud (640 ± 19 ka), Bellevue (264 ± 8 ka), Anse John (104 ± 4 ka) and La Pointe (59.8 ± 2.1 ka), Anse Noir and Piaye were all previously grouped with or associated with the Choiseul tuff (all uncertainties 1σ). We suggest that these units represent individual periods of activity spanning a range of ages, whereas Choiseul pumice at the type locality has yielded a (U-Th)/He zircon age of 515 ± 19 ka. Their overall geochemical and mineralogical similarities with the Choiseul at the type locality suggest that they might have all originated from the same centre. Morne Tabac (532 ± 21 ka) is a dome truncated by the depression escarpment, whereas Morne Bonin (273 ± 15 ka), Gros Piton and Petit Piton (71 ± 3 ka and 109 ± 4 ka, resp.), Belfond (13.6 ± 0.4 ka) and Terre Blanche (15.3 ± 0.4 ka) are domes within the Qualibou Depression. Belfond and Terre Blanche have whole rock geochemistry and mineral assemblages similar to the Belfond pyroclastic flow deposit, thus possibly representing late-erupted degassed portions of the magma that produced the Belfond pyroclastics. The geochemical characteristics and similar zircon age distributions of the silicic lava domes and pyroclastics of the SVC suggest that these share a common magma source beneath the Qualibou depression. The distribution of the pyroclastic flows and the wide range in their eruption ages makes it unlikely that these were erupted during caldera-forming activity, and we instead invoke a series of smaller-volume explosive eruptions from the area of the current depression, the earliest of which occurred from a large proto-Qualibou edifice that subsequently underwent sector collapse. Activity from this proto-Qualibou centre may have ceased sometime between 38 and 59 ka ago, it therefore seems unlikely given our present understanding that there will be another eruption from the southern central highland region. However, the young dome-forming activity in the Qualibou depression may have occurred in or close to the Holocene, and there have been dome collapse events and explosion craters formed since then. A new dome eruption or renewed activity at a dome within the depression, growing in the style of the ongoing Soufrière Hills lava dome on the nearby island of Montserrat, is possible; as is a future plinian eruption from this area. Such an eruption would not only have a devastating impact on Saint Lucia, but would also have significant regional and global impacts.

The Novarupta-Katmai eruption of 1912 - largest eruption of the twentieth century; centennial perspectives

USGS Publications Warehouse

Hildreth, Wes; Fierstein, Judy

2012-01-01

The explosive outburst at Novarupta (Alaska) in June 1912 was the 20th century's most voluminous volcanic eruption. Marking its centennial, we illustrate and document the complex eruptive sequence, which was long misattributed to nearby Mount Katmai, and how its deposits have provided key insights about volcanic and magmatic processes. It was one of the few historical eruptions to produce a collapsed caldera, voluminous high-silica rhyolite, wide compositional zonation (51-78 percent SiO2), banded pumice, welded tuff, and an aerosol/dust veil that depressed global temperature measurably. It emplaced a series of ash flows that filled what became the Valley of Ten Thousand Smokes, sustaining high-temperature metal-transporting fumaroles for a decade. Three explosive episodes spanned ~60 hours, depositing ~17 km3 of fallout and 11±2 km3 of ignimbrite, together representing ~13.5 km3 of zoned magma. No observers were nearby and no aircraft were in Alaska, and so the eruption narrative was assembled from scattered villages and ship reports. Because volcanology was in its infancy and the early investigations (1915-23) were conducted under arduous expeditionary conditions, many provocative misapprehensions attended reports based on those studies. Fieldwork at Katmai was not resumed until 1953, but, since then, global advances in physical volcanology and chemical petrology have gone hand in hand with studies of the 1912 deposits, clarifying the sequence of events and processes and turning the eruption into one of the best studied in the world. To provide perspective on this century-long evolution, we describe the geologic and geographic setting of the eruption - in a remote, sparsely inhabited wilderness; we review the cultural and scientific contexts at the time of the eruption and early expeditions; and we compile a chronology of the many Katmai investigations since 1912. Products of the eruption are described in detail, including eight layers of regionwide fallout, nine packages of ash flows, and three lava domes that followed the explosive pyroclastic episodes. Changes in the proportions of coerupting rhyolite, dacite, and andesite pumice documented for the fallout and ash-flow successions, which are locally interbedded, permit close correlation of those synchronously emplaced sequences and their varied facies. Petrological correlation of the sequence of deposits near Novarupta with ash layers at Kodiak village, 170 km downwind, where three episodes of ashfall were recorded (to the hour), provides key constraints on timing of the eruptive events. Syneruptive collapse of a kilometer-deep caldera took place atop Mount Katmai, a stratovolcano centered 10 km east of the eruption site at Novarupta, owing to drainage of magma from beneath the Katmai edifice. Correlation of ~50 earthquakes recorded at distant seismic stations (including 14 shocks of magnitude 6.0 to 7.0) to fitful caldera collapse provides further constraints on eruption timing, because layers of nonjuvenile breccia and mud ejected from Mount Katmai during collapse pulses are intercalated with the pumice-fall layers from Novarupta. Structure of the Novarupta vent, a 2-km-wide depression backfilled by welded tuff and inferred to be funnel-shaped at depth, is described in detail, as is the 4-km-wide caldera at Mount Katmai. Discussions are also provided concerning: (1) the impact on global climate of the great mass of sulfur-poor but halogen-rich aerosol ejected into the atmosphere by the rhyolite-dominated eruption; (2) chemical and mineralogical effects of the fumarolic acid gases; and (3) the timing of several syneruptive landslide deposits sandwiched within the pumice-fall sequence. Secondary posteruption phenomena characterized include impounded lakes, ash-rich debris flows, phreatic craters on the ignimbrite sheet, responses of glaciers to the fallout blanket and to beheading by caldera collapse, growth of new glaciers inside the caldera, and gradual filling of the caldera lake. Structure, composition, and ages of the several andesite-dacite stratovolcanoes, closely clustered near Novarupta, all of which remain fumarolically and seismically active, are summarized. But among them only Mount Katmai extends compositionally to include basalt and rhyolite. The petrological affinities of 1912 magmas erupted at Novarupta with pre-1912 Katmai lavas are outlined, and various chemical, mineralogical, isotopic, and experimental data are assembled to construct a model of preeruptive magma storage beneath Mount Katmai. The monograph concludes by comparing the 1912 eruption with several other well-studied large explosive eruptions, 14 of them historical and 9 prehistoric. Finally, we retrospectively review the historical difficulties in understanding what had actually taken place at Katmai in 1912 and the century of progress in volcano science that has allowed most of it to be figured out.

Klinkenberg effect in hydrodynamics of gas flow through anisotropic porous materials

NASA Astrophysics Data System (ADS)

Wałowski, Grzegorz; Filipczak, Gabriel

2017-10-01

This study discusses results of experiments on hydrodynamic assessment of gas flow through backbone (skeletal) porous materials with an anisotropic structure. The research was conducted upon materials of diversified petrographic characteristics, both natural origin (rocky, pumice) and process materials (char and coke). The study was conducted for a variety of hydrodynamic conditions, using air, as well as for nitrogen and carbon dioxide. The basis for assessing hydrodynamics of gas flow through porous material was a gas stream that results from the pressure forcing such flow. The results of measurements indicate a clear impact of the type of material on the gas permeability, and additionally - as a result of their anisotropic internal structure - to a significant effect of the flow direction on the value of gas stream.

Experimental shock metamorphism of lunar soil

NASA Technical Reports Server (NTRS)

Schaal, R. B.; Horz, F.

1980-01-01

Shock experiments in the pressure range 15-73 GPa were performed on lunar soil 15101 in order to investigate the effect of a single impact event on the formation of soil breccias and agglutinates. The study has demonstrated that the propagation of a shock wave emanating from a single impact in porous particulate samples causes collision and shear of grains, collapse of pore spaces, and compaction which is sufficient to indurate soil at low pressures (15-18 GPa) without significant melting (less than 5%). These low pressures create soil breccias or weakly shocked soil fragments from loose regolith. At pressures above 65 GPa, shock melting produces a pumiceous whole-soil glass which is equivalent to agglutinate glass, glass fragments, or ropy glasses depending on the abundance of lithic fragments and relict grains.

The regulation of crystalline silica: an industry perspective.

PubMed

Elzea, J M

1997-01-01

Silica is ubiquitous in the earth's crust. It occurs in trace to large quantities in rocks and soil. Because it is so common, the regulation of silica has affected a large number of industries, including the mining industry and any industry that uses quartz in the manufacture of a products. Mineral commodities that contain silica include diatomite, bentonite, kaolinite, talc, pyrophyllite, sand and gravel, perlite, pumice, dimension stone, and barite. Products that contain minerals, many of which are associated with silica, include paint, paper, rubber, plastic, pharmaceuticals, food, cement, plaster, cat litter, potting soil, plaster board, and miscellaneous construction materials. In collaboration with some agencies and academic centers, the silica industry is supporting research to lower health risks and to improve the methods of detecting this common material.

Chronology and pyroclastic stratigraphy of the May 18, 1980, eruption of Mount St. Helens, Washington

NASA Technical Reports Server (NTRS)

Criswell, C. William

1987-01-01

The eruption of Mount St. Helens on May 18, 1980 can be subdivided into six phases: the paroxysmal phase I, the early Plinian phase II, the early ash flow phase III, the climactic phase IV, the late ash flow phase V, and phase VI, the activity of which consisted of a low-energy ash plume. These phases are correlated with stratigraphic subunits of ash-fall tephra and pyroclastic flow deposits. Sustained vertical discharge of phase II produced evolved dacite with high S/Cl ratios. Ash flow activity of phase III is attributed to decreases in gas content, indicated by reduced S/Cl ratios and increased clast density of the less evolved gray pumice. Climactic events are attributed to vent clearing and exhaustion of the evolved dacite.

Calcite-impregnated defluidization structures in littoral sands of Mono Lake, California

USGS Publications Warehouse

Cloud, P.; Lajoie, K.R.

1980-01-01

Associated locally with well-known tufa mounds and towers of Mono Lake, California, are subvertical, concretionary sand structures through which fresh calcium-containing artesian waters moved up to sites of calcium carbonate precipitation beneath and adjacent to the lake. The structures include closely spaced calcite-impregnated columns, tubes, and other configurations with subcylindrical to bizarre cross sections and predominantly vertical orientation in coarse, barely coherent pumice sands along the south shore of the lake. Many structures terminate upward in extensive calcareous layers of caliche and tufa. Locally they enter the bases of tufa mounds and towers. A common form superficially resembles root casts and animal burrows except that branching is mostly up instead of down. Similar defluidization structures in ancient sedimentary rocks have been mistakenly interpreted as fossil burrows.

Pre-eruptive storage conditions of the Holocene dacite erupted from Kizimen Volcano, Kamchatka

USGS Publications Warehouse

Browne, B.; Izbekov, P.; Eichelberger, J.; Churikova, T.

2010-01-01

This study describes an investigation of the pre-eruptive conditions (T, P and fO2) of dacite magma erupted during the KZI cycle (12,000-8400 years ago) of Kizimen Volcano, Kamchatka, the earliest, most voluminous and most explosive eruption cycle in the Kizimen record. Hydrothermal, water-saturated experiments on KZI dacite pumice coupled with titanomagnetite-ilmenite geothermometry calculations require that the KZI dacite existed at a temperature of 823 ?? 20??C and pressures of 125-150 MPa immediately prior to eruption. This estimate corresponds to a lithologic contact between Miocene volcaniclastic rocks and Pliocene-Pleistocene volcanic rocks located at a depth of 5-6 km beneath the Kizimen edifice, which may have facilitated the accumulation of atypically large volumes of gas-rich dacite during the KZI cycle.

A multidisciplinary approach for high-resolution reconstruction of the eruptive past of La Soufrière (Guadeloupe) over the last 12 000 years: Implications for hazards assessment.

NASA Astrophysics Data System (ADS)

Legendre, Yoann; Komorowski, Jean-Christophe; Boudon, Georges

2010-05-01

La Soufrière de Guadeloupe is a dangerous andesitic composite volcano characterized over the last 12 000 years by numerous phreatic eruptions that alternate with few magmatic eruptions, including the last magmatic and best-studied "Soufrière" subplinian eruption in 1530 AD, and unusually numerous flank-collapse events. Field analysis of the deposits provide constraints for values of the physical input parameters for simple models which provide with first-order simulation of eruptive phenomena, and from which quantitative probabilistic hazard maps can be elaborated in which epistemic and aleatory uncertainty can be incorporated and quantified. The study of yesterday's eruptions provide key insights for elaborating realistic simulations and describing potential eruptive scenarios for tomorrow's eruptions. However hazard assessment is biased towards eruptions of significant magnitude that produce extensive, and relatively thick deposits. Nevertheless, eruptions of moderate magnitude which are often more frequent, can significantly affect vulnerable island communities living at short distances from the vent. However, their deposits are ephemeral in the geologic record on account of intense erosion from tropical rainfall, important soil development and erosion by the emplacement of recurrent pyroclastic density currents, debris avalanches, and mudflows. We have developed a novel approach by using a manual sediment corer to obtain undisturbed sedimentary eruptive archives in sheltered zones on the volcano where a longer eruption record has been preserved. We describe two such cores (6.32 and 6.64 m long) that extend over at least 8700 years and that contain several thin tephra layers missing at the outcrop scale. We combine these new data with the analysis of more than 120 stratigraphic sections on outcrops studied over the last decade to provide a new eruptive chronology for La Soufriere volcano over the last 12 000 years. This chronology is robustly constrained by 105 new 14C age dates of wood, charcoal, and paleosoil samples that complete the existing 14C database (total of about 261 dates). A multidisciplinary analysis (sedimentology, lithology, microtextures, magnetic susceptibility) of the sediment cores and field data has allowed us to identify hidden, and missing eruptions, and to re-interpret mis-identified eruptions. For the last 12 000 years we have identified at least 5 distinct new pumice fallout deposits, some of which are associated with pumice pyroclastic flow deposits. We also identified several deposits formed by magmatic turbulent pyroclastic density currents (blasts) mostly associated with flank-collapse events. Thus, the number of Holocene magmatic eruptions has significantly increased compared to previous knowledge. More over we have identified eruptive sequences that consist of a diverse range of phenomena including edifice-collapse, associated laterally directed explosions (blasts), pumice fallout with column-collapse and dome growth similar to the AD1530 most recent magmatic eruption. The magmatic eruptive rate could be twice as important with 11-13 magmatic eruptions in 12 000 years, a rate of about 0.92-1.08 magmatic eruption by 1000 years. This new data will allow a better determination of the recurrence, magnitude, intensity, and the spatio-temporal evolution of deposit types that define different eruptive scenarios. Hence, this high-resolution reconstruction of the eruptive past will provide the basis for an improved probabilistic hazard and risk assessment for La Soufrière of Guadeloupe, a dangerous volcano, currently experiencing prolongued unrest since 1992.

Significance of a near-source tephra-stratigraphic sequence to the eruptive history of Hayes Volcano, south-central Alaska

USGS Publications Warehouse

Wallace, Kristi; Coombs, Michelle L.; Hayden, Leslie A.; Waythomas, Christopher F.

2014-01-01

Bluffs along the Hayes River valley, 31 km northeast and 40 km downstream from Hayes Volcano, reveal volcanic deposits that shed new light on its eruptive history. Three thick (>10 cm) and five thin (<10 cm) tephra-fall deposits are dacitic in whole rock composition and contain high proportions of amphibole to pyroxene and minor biotite and broadly correlate to Hayes tephra set H defined by earlier investigators. Two basal ages for the tephra-fall sequence of 3,690±30 and 3,750±30 14C yr B.P. are also consistent with the Hayes tephra set H timeframe. Distinguishing among Hayes tephra set H units is critical because the set is an important time-stratigraphic marker in south-central Alaska and this section provides a new reference section for Hayes tephra set H. Analysis of Fe-Ti oxide grains in the tephras shows promise for identifying individual Hayes deposits. Beneath the dacitic tephra sequence lies an older, poorly sorted tephra (tephra A) that contains dacite and rhyolite lapilli and whose basal age is 4,450±30 14C yr B.P. Immediately below the tephra-fall sequence (Unit III) lies a series of mass-flow deposits that are rich in rhyodacitic clasts (Unit II). Below Unit II and possibly coeval with it, is a 20–30 m thick pumiceous pyroclastic-flow deposit (Unit I) that extends to the valley floor. Here informally named the Hayes River ignimbrite, this deposit contains pumice clasts of rhyolite with quartz, sanidine, plagioclase, and biotite phenocrysts, an assemblage that is unique among known Quaternary volcanic products of Hayes and other Alaskan volcanoes. Units I, II, and tephra A of Unit III represent at least two previously unrecognized eruptions of Hayes Volcano that occurred prior to ~3,700 yr B.P. No compositionally equivalent distal tephra deposits correlative with Hayes Volcano rhyodacites or rhyolites have yet been identified, perhaps indicating that some of these deposits are pre-Holocene, and were largely removed by glacial ice during the last ice age. More field and analytical work is needed to further refine the eruptive history of Hayes Volcano.

Insights into Proximal-Medial Pyroclastic Density Current Deposits at a High-Risk Glaciated Volcano: Mt Ruapehu, New Zealand

NASA Astrophysics Data System (ADS)

Cowlyn, J.; Kennedy, B.; Gravley, D. M.; Cronin, S. J.; Pardo, N.; Wilson, T. M.; Leonard, G.; Townsend, D.; Dufek, J.

2014-12-01

Pyroclastic density currents (PDCs) are a destructive volcanic hazard. Quantifying the types, frequency and magnitudes of PDC events in the geological record is essential for effective risk management. However small-medium volume valley-confined PDC deposits have low preservation potential, especially when emplaced in active drainages or onto snow or ice. Where PDC deposits are preserved they can be difficult to distinguish from other surficial deposits and are frequently misinterpreted or overlooked. This is the case at Mt. Ruapehu; a much visited, high-risk active volcano in New Zealand with no historical PDCs. Through systematic field observations we identified several young proximal-medial andesitic PDC deposits exposed on Ruapehu's eastern flanks. The oldest deposits (Ohinewairua PDCs, <13.6 ka) are massive pumice-rich deposits that are preserved at least 7km from source (North Crater) and correlate with Ruapehu's largest plinian eruptions. Overlying these, the pumice-rich Pourahu PDC deposit reaches >10km from source (South Crater) and correlates with Ruapehu's last known plinian eruption (~11.6 ka). Several younger locally preserved PDC deposits (Tukino PDCs) with denser juvenile clasts represent proximal PDCs from smaller eruptions at South Crater. Finally, a variably welded, bedded deposit containing clasts of welded spatter is interpreted to represent multiple failures of near-vent (North Ruapehu) accumulations of erupted material. Here, PDC initiation appears to have been controlled by the topographic gradient and deposition rate, without requiring a collapsing eruption column. The Ruapehu deposits highlight the limited preservation of PDC deposits, which appears to be favoured at PDC margins. Lateral and vertical flow stratification means the resulting deposits may not then represent the bulk flow. Additionally, deposit textures, distributions, and associations with moraines indicate that many of Ruapehu's PDCs encountered glacial ice during transport. This affected their distribution, mobility and preservation, and has implications for assessing the PDC hazard at Ruapehu and other glaciated volcanoes. The deposits reinforce that hazardous PDCs threatening life and infrastructure may be generated even from small eruptions and across a wide range of eruption styles.

The Western North American Cretaceous-Tertiary (K-T) boundary interval and its content of shock-metamorphosed minerals: Implications concerning the K-T boundary impact-extinction theory

NASA Technical Reports Server (NTRS)

Izett, G. A.

1988-01-01

At 20 sites in the Raton Basin of Colorado and New Mexico, and at several other sites in Wyoming, Montana, and Canada, a pair of claystone units, an Ir abundance anomaly, and a concentration of shock-metamorphosed minerals mark the palynological K-T boundary. The K-T boundary claystone, which is composed of kaolinite and small amounts of illite/smectite mixed-layer clay, is similar in most respects to kaolinite tonstein layers in coal beds. At some, but not all, K-T boundary localities, the boundary claystone contains solid kaolinite and hollow and solid goyazite spherules, 0.05 to 1.2 mm in diameter. The upper unit, the K-T boundary impact layer, consists chiefly of kaolinite and various amounts of illite/smectite mixed-layer clay. The impact layer and boundary claystone are similar chemically, except that the former has slightly more Fe, K, Ba, Cr, Cu, Li, V, and Zn than the latter. The facts that the boundary claystone and impact layer contain anomalous amounts of Ir, comprise a stratigraphic couplet at Western North American sites, and form thin, discrete layers, similar to air-fall units (volcanic or impact), suggest that the claystone units are of impact origin. Significantly, the impact layer contains as much as 2 percent clastic mineral grains, about 30 percent of which contain multiple sets of shock lamellae. Only one such concentration of shocked minerals has been found near the K-T boundary. The type of K-T boundary shock-metamorphosed materials (quartzite and metaquartzite) in the impact layer and the lack of shock lamellae in quartz and feldspar of pumice lapilli and granitic xenoliths in air-fall pumice units of silicic tuffs, such as the Bishop Tuff, eliminate the possibility that the shock-metamorphosed minerals in the K-T impact layer are of volcanic origin. The global size distribution and abundance of shock-metamorphosed mineral grains suggest that the K-T impact occurred in North America.

Dynamics of an unusual cone-building trachyte eruption at Pu`u Wa`awa`a, Hualālai volcano, Hawai`i

NASA Astrophysics Data System (ADS)

Shea, Thomas; Leonhardi, Tanis; Giachetti, Thomas; Lindoo, Amanda; Larsen, Jessica; Sinton, John; Parsons, Elliott

2017-04-01

The Pu`u Wa`awa`a pyroclastic cone and Pu`u Anahulu lava flow are two prominent monogenetic eruptive features assumed to result from a single eruption during the trachyte-dominated early post-shield stage of Hualālai volcano (Hawaíi). Púu Wa`awa`a is composed of complex repetitions of crudely cross-stratified units rich in dark dense clasts, which reversely grade into coarser pumice-rich units. Pyroclasts from the cone are extremely diverse texturally, ranging from glassy obsidian to vesicular scoria or pumice, in addition to fully crystalline end-members. The >100-m thick Pu`u Anahulu flow is, in contrast, entirely holocrystalline. Using field observations coupled with whole rock analyses, this study aimed to test whether the Pu`u Wa`awa`a tephra and Pu`u Anahulu lava flows originated from the same eruption, as had been previously assumed. Crystal and vesicle textures are characterized along with the volatile contents of interstitial glasses to determine the origin of textural variability within Pu`u Wáawáa trachytes (e.g., magma mixing vs. degassing origin). We find that (1) the two eruptions likely originated from distinct vents and magma reservoirs, despite their proximity and similar age, (2) the textural diversity of pyroclasts forming Pu`u Wa`awa`a can be fully explained by variable magma degassing and outgassing within the conduit, (3) the Pu`u Wa`awa`a cone was constructed during explosions transitional in style between violent Strombolian and Vulcanian, involving the formation of a large cone and with repeated disruption of conduit plugs, but without production of large pyroclastic density currents (PDCs), and (4) the contrasting eruption styles of Hawaiian trachytes (flow-, cone-, and PDC-forming) are probably related to differences in the outgassing capacity of the magmas prior to reaching the surface and not in intrinsic compositional or temperature properties. These results further highlight that trachytes are "kinetically faster" magmas compared to dacites or rhyolites, likely degassing and crystallizing more rapidly.

3D imaging of vesicles in hyaloclastic fragments - clues to syn-eruptive shear conditions

NASA Astrophysics Data System (ADS)

Helo, C.; Flaws, A.; Hess, K.; Franz, A.; Clague, D. A.; Dingwell, D. B.

2011-12-01

3D imaging of stretched vesicles in hyaloclastic fragments has been used to investigate the shear environment of mild pyroclastic eruptions at mid-ocean ridges. X-ray computed tomography offers an attractive non-invasive method to investigate geomaterials at a high resolution for the geometry of the different phases. In this study, we have imaged vesicles within two types of basaltic glass fragments. Stretched, ellipsoid-shaped vesicles in thin limu o Pele and tubular vesicles in a pumiceous fragment. Both types originate from pyroclastic activity on Axial Seamount, Juan de Fuca ridge. Rapid quenching of the glass has prevented extensive bubble relaxation and information about syn-eruptive shear and differential stress conditions is stored, as the dimensions of a stretched bubble directly relates to the extent and mode of shearing. The X-ray tomography data was processed using a set of codes based on edge detection and ellipsoid fitting to acquire quantitative information on the shape of the stretched vesicles. Preliminary results demonstrate, that the geometry of the stretched vesicles, e.g., the elongation of the vesicle with respect to the calculated undeformed radius, is in accordance with simple shear scenarios. Stored differential stress ranges from 5 kPa to 90 kPa with shear rates between 3.2x102 s-1 and 5.7x3 s-1 within a single limu o Pele fragment. This range may be explained by either variable time available for relaxation as the cooling front proceeds through the fragment, complex interplay in space and time between fragmentation and quenching, bubble clusters mutually inhibiting each others extend of deformation, or any combination of these. Bubble relaxation time scales are less then 0.005 s providing constraints on the timeframe for cooling to the glass transition. Qualitative analyses of the tube pumice indicates that the tubular structures grow in length by coalescence of vertically aligned ellipsoid-shaped vesicles, and in width by coalescence of horizontally contiguous vesicles. Pyroclastic fragments produced in deep-sea environments thus offer the opportunity to explore in-situ shear and stress conditions prevailing during eruption, even in very low viscous systems.

The alkaline Meidob volcanic field (Late Cenozoic, northwest Sudan)

NASA Astrophysics Data System (ADS)

Franz, Gerhard; Breitkreuz, Christoph; Coyle, David A.; El Hur, Bushra; Heinrich, Wilhelm; Paulick, Holger; Pudlo, Dieter; Smith, Robyn; Steiner, Gesine

1997-08-01

The Meidob volcanic field (MVF) forms part of the Darfur Volcanic Province and developed from 7 Ma to 5 ka as indicated by K/Ar, thermoluminescence and 14C ages. It is situated in an uplifted high of the Pan-African basement, which consists of greenstones, high-grade gneisses and granites, and which is covered by Cretaceous sandstone. The MVF basaltic lavas, which originated from more than 300 scoria cones, formed a lava plateau of 50×100 km and up to 400 m thickness in the time between 7 and < 0.3 Ma. Young phonolitic mesa flows, together with rare trachyticbenmoreitic lava flows, trachytic pumice fallout deposits, ignimbrites and maars, form the central part of the field. The total amount of volcanic rocks is between 1400 and 1800 km 3, with 98 vol.% being basaltic rocks, which results in an integrated magma output rate of ˜ 0.0002 km 3 a -1. A combination of age data of the lavas with erosional features yields uplift rates for the Darfur Dome of ˜30 m Ma- 1 in the MVF area. Magma was generated by 3-5% melting of predominantly asthenospheric mantle with a HIMU contribution. Fractionation of olivine, pyroxene, An-poor plagioclaseanorthoclase, magnetite and apatite leads to a differentiation from basanite to phonolite. Assimilation of crustal rocks near the top of the phonolitic upper crustal magma chambers - facilitated by volatile enrichment - produced magmas which gave way to benmoreitic and trachytic lavas, as well as to trachytic ignimbrites and pumice fallout deposits. Ultramafic cumulate xenoliths indicate the existence of major magma reservoirs at the crust-mantle boundary during MVF activity. Magma ascent occurred in a tensional regime, which changed its orientation at around 1 Ma. Early during MVF development, west-east and subordinately northeastsouthwest trending lineaments were active whereas volcanic activity younger than 1 Ma took place along northwest-southeast and northeast-southwest trending systems. The Central African Fault Zone, a transcontinental, lithospheric shear zone, played an important role for the rise of magmas in the Darfur Dome.

The Cordón Caulle rhyolite lava flow: an exceptional case study

NASA Astrophysics Data System (ADS)

Magnall, N.; James, M. R.; Tuffen, H.; Schipper, C. I.; Castro, J. M.; Vye-Brown, C.; Davies, A. G.; Farquharson, J.

2017-12-01

Rhyolites comprise the most silica-rich lavas, and rhyolitic lava flows can reach tens of kilometres in length. Interpretations of ancient and historic rhyolite lava flows suggest protracted emplacement due to relatively slow cooling of these massive bodies and have identified late stage events such as the formation of pumice diapirs. However, our understanding of emplacement processes has long remained limited by the lack of observations from an active flow. The 2011-2012 eruption of Puyehue-Cordón Caulle in southern Chile resulted in the first scientifically observed emplacement of an extensive (0.4 km3, 5 km long), crystal-poor rhyolite lava flow and has provided an unparalleled opportunity to further our understanding of flow dynamics. Here, we summarise our work on this lava flow, which has combined satellite and field observations, microstructural characterisation of samples, and numerical modelling. Early observations showed that advance of the 40 m thick flow stalled after 150 days of eruption, due to interactions with topographic barriers and the formation of a retarding surface crust. Following this, numerous breakouts formed from the flow fronts and margins, attaining lengths of ≤2 km. Microstructural characterisation supports the model that the breakouts formed due to continued lava supply to the stalled portions of the flow front along preferential thermal pathways, coupled with late-stage vesiculation of the flow core. This led to pressure increase, inflation, and eventual rupturing of the surface crust. These breakouts have been classified into four morphological types (domed, petaloid, rubbly, and cleft split) that reflect processes of advance and inflation. Some breakouts continued to advance and form after the eruption ended, with numerical modelling and direct observations suggesting mobility of the lava years after the eruption ended. Unlike other rhyolite flows, pumice diapirs were not observed at Cordón Caulle, instead late stage volatile exsolution (with associated vapour-phase cristobalite formation), core vesiculation, and resultant inflation contributed to breakout formation. Insights gained from Cordón Caulle aid in the interpretation of ancient silicic lavas and help anticipate the hazards posed by future, potentially lengthy, eruptions of rhyolitic lava.

Evaluating Reflectance Spectroscopy as a Method of Rapid Cryptotephra Identification using Component Analysis: Tephrochronology of the Lesser Antilles Arc

NASA Astrophysics Data System (ADS)

Fisher, E. A.

2015-12-01

The reactivation of Montserrat's South Soufrière-Soufrière Hills volcanic complex has impelled the creation of tephrochronologic records in the Lesser Antilles Arc in order to assess volcanic hazards to human safety. Developing an eruptive history of Montserrat by recording tephra layers preserved in marine sediment is hindered by the lack of a rapid, non-destructive method for detecting cryptotephra, tephra deposits invisible to the naked eye, in marine cores. Identifying cryptotephra is important because some cryptotephra layers represent primary tephra emplacement from small proximal eruptions, events that if excluded from a volcanic record could mischaracterize a volcano's eruptive frequency over time. VSWIR [0.4-2.5 μm] reflectance spectroscopy is a candidate for rapid, non-destructive cryptotephra detection in marine sediment cores because it can detect tephra in hemipelagic sediment using summary parameters sensitive to iron content and clay minerals (McCanta et al. 2014, AGU abstract OS53D-1086). Spectra from marine cores U1396C-1H-1A through U1396C-1H-5A, collected during International Ocean Discovery Program (IODP) mission 340, reveal 29 potential cryptotephra layers (McCanta et al. 2014, AGU abstract OS53D-1086). This study seeks to determine the effectiveness of reflectance spectroscopy at identifying cryptotephra by measuring the abundance of volcanic materials (i.e., glass shards/vesicular pumice and non-vesicular lava clasts) in these layers ( LeFriant et al. 2008; Cassidy et al. 2014). Component analysis was conducted on select core intervals with both cryptotephra-identifying peaks in reflectance parameters, and tephra-indicative peaks in core scanning XRF and magnetic susceptibility parameters (McCanta et al. 2014, AGU abstract OS53D-1086). Samples in this subset show abundances of non-vesicular lava and vesicular pumice clasts above expected background abundances, supporting the existence of cryptotephra at these locations (Fig. 1; LeFriant et al. 2008; Cassidy et al. 2014). This suggests that reflectance spectroscopy is an effective means of identifying cryptotephra in situ, and when employed in concert with other core scanning techniques could facilitate widespread rapid identification of cryptotephra in future tephrochronology studies.

Deep-sea tsunami deposits in the Miocene Nishizaki Formation of Boso Peninsula, Central Japan

NASA Astrophysics Data System (ADS)

Lee, I. T.; Ogawa, Y.

2003-12-01

Many sets of deep-sea deposits considered to be formed by return flow of tsunami were found from the middle Miocene Nishizaki Formation of Boso Peninsula, Central Japan, which is located near the convergent plate boundary at present as well as in the past, and has been frequently attacked by tsunami. The characteristics of the tsunami deposits in the Nishizaki Formation are as follows. Each set consists of 10-20 beds with parallel laminations formed under upper plane regime composed of alternated pumiceous beds in white and black colors. The white bed comprises coarse sands and pebbles with thickness of 5-10 cm. In contrast, the black bed is made of silts with thickness less than 1 cm. Among the 10-20 beds, the grain size is coarsest in the middle part of the set in general. The uppermost bed of each set shows cross-lamination formed by lower plane regime, gradually changing into finer graded bed on top. Sometimes, the lower part of the parallel laminated bed is associated with an underlying debrite or turbidite bed. Each set of these parallel-laminated beds is lenticular in shape thinning to the east in consistent with the generally eastward paleocurrent of the cross-lamination at the top. Such sedimentary characteristics are different from any event deposits reported in deep-sea but similar to the deep-sea K/T boundary deposits in the Caribbean region. Statistically, tsunami waves occur totally 12-13 times. Among them the height of 5-6th wave is known to be strongest. Interval time of each return flow is known to be 30-40 minutes, enough to settle the finer clastics at each bed top. The parallel-laminated parts have common dish structure and never trace fossils, indicating rather rapid deposition for the whole parts of the set. Consequently, the sedimentary characteristics shown from the parallel-laminated beds of the Nishizaki Formation are attributed to the return flow of tsunami to the deep-sea. We considered that such deep-sea parallel-laminated deposits of pumiceous clastics occur just after a large earthquake which forms the debrite or turbidite at the lowermost part.

The relationship between plutonism and volcanism: zircon ages from granitoid clasts in recent pyroclastic deposits from Tarawera volcano

NASA Astrophysics Data System (ADS)

Shane, P. A.; Storm, S.; Schmitt, A. K.; Lindsay, J.

2011-12-01

In Quaternary magmatic systems that have not undergone extensive uplift that would expose their intrusive roots, co-magmatic (and xenolithic) plutonic clasts entrained in eruptive deposits are an important source of information on the temporal relationship between plutonism and volcanism. Granitoid clasts in pyroclastic deposits of the 0.7 ka (Kaharoa) eruption from the Tarawera volcano of the Okataina Volcanic Centre (OVC), New Zealand, provide a rare insight to the plutonic processes beneath one of the most productive Quaternary rhyolite centers on Earth. SIMS U-Th and U-Pb data on 79 granitoid zircon crystals from six clasts reveal a unimodal age spectrum yielding a weighted average model age of 211 ± 4 ka (MSWD = 1.1). This crystallization event coincides with relative quiescence in OVC volcanism. A few outlier antecrysts date back to ~700 ka, a period significantly longer than the known volcanic record at OVC (probably ~330 ka). In contrast, zircon crystallization in co-erupted pumice and lava of the 0.7 ka Kaharoa event, and that of the three preceding rhyolite eruptions, occurred mostly during 0-50 ka. Thus, the granitoid clasts represent part of the system immediately beneath the volcano that survived assimilation and/or destruction in subsequent eruption and caldera collapse episodes. Brittle deformation features, incipient alteration and low-d18O whole-rock compositions (+3%) are consistent with a shallow solid carapace that has interacted with hydrothermal fluids. However, d18O SIMS analyses of zircons (+5.4 ± 0.2 %; n = 11) are consistent with magmatic compositions, and thus meteoric interaction occurred post-emplacement. The Kaharoa granitoids contrast with those ejected in the ~60 ka caldera-forming Rotoiti event, that were partly molten and display zircon age spectra indistinguishable from that in co-erupted pumices, suggesting the latter were derived from contemporaneous crystal mush. The 0.7 ka Kaharoa case shows that, over time, eruptible parts of a magmatic reservoir can become armored by a solidified intrusive carapace that minimizes interaction with other parts of the magmatic system and the surrounding wall-rocks. Thus, plutonic and volcanic evolution can diverge even in close proximity of the same magmatic system.

Numerical simulations of impacts involving porous bodies. II. Comparison with laboratory experiments

NASA Astrophysics Data System (ADS)

Jutzi, Martin; Michel, Patrick; Hiraoka, Kensuke; Nakamura, Akiko M.; Benz, Willy

2009-06-01

In this paper, we compare the outcome of high-velocity impact experiments on porous targets, composed of pumice, with the results of simulations by a 3D SPH hydrocode in which a porosity model has been implemented. The different populations of small bodies of our Solar System are believed to be composed, at least partially, of objects with a high degree of porosity. To describe the fragmentation of such porous objects, a different model is needed than that used for non-porous bodies. In the case of porous bodies, the impact process is not only driven by the presence of cracks which propagate when a stress threshold is reached, it is also influenced by the crushing of pores and compaction. Such processes can greatly affect the whole body's response to an impact. Therefore, another physical model is necessary to improve our understanding of the collisional process involving porous bodies. Such a model has been developed recently and introduced successfully in a 3D SPH hydrocode [Jutzi, M., Benz, W., Michel, P., 2008. Icarus 198, 242-255]. Basic tests have been performed which already showed that it is implemented in a consistent way and that theoretical solutions are well reproduced. However, its full validation requires that it is also capable of reproducing the results of real laboratory impact experiments. Here we present simulations of laboratory experiments on pumice targets for which several of the main material properties have been measured. We show that using the measured material properties and keeping the remaining free parameters fixed, our numerical model is able to reproduce the outcome of these experiments carried out under different impact conditions. This first complete validation of our model, which will be tested for other porous materials in the future, allows us to start addressing problems at larger scale related to small bodies of our Solar System, such as collisions in the Kuiper Belt or the formation of a family by the disruption of a porous parent body in the main asteroid belt.

New high-capacity, calcium-based sorbents, calcium silicate sorbents. Final report, 1993--August 31, 1994

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kenney, M.C.; Chiang, R.K.; Fillgrove, K.L.

1995-02-01

A search is being carried out for new calcium-based S0{sub 2} sorbents for induct injection. More specifically, a search is being carried out for induct injection calcium silicate sorbents that are highly cost effective. The objectives for the current year include the study of sorbents made from Ca(OH){sub 2}, from mixtures of Ca(OH){sub 2} and SiO{sub 2}, and from portland cement. They also include the study of sorbents made from model compounds. During this year, sorbents prepared from Ca(OH){sub 2} and from mixtures of Ca(OH){sub 2} and fumed SiO{sub 2} were investigated. The results show that very good SiO{sub 2}-modifiedmore » Ca(OH){sub 2} sorbents in which the Si-to-Ca reactant ratio is low can be prepared from Ca(OH){sub 2} and fumed SiO{sub 2}. Sorbents prepared from Ca(OH){sub 2} and natural SiO{sub 2} or natural SiO{sub 2} sources were also studied. The results obtained show that very good SiO{sub 2}-modified Ca(OH){sub 2} sorbents and calcium silicate hydrate sorbents, C-S-H sorbents, can be prepared from Ca(OH){sub 2} and diatomite, pumice or perlite, minerals that are readily available. In addition. sorbents prepared from Ca{sub 3}SiO{sub 5} and {beta}-Ca{sub 2}SiO{sub 4} and from mixtures of these compounds and SiO{sub 2} were studied. The results secured demonstrate that very good C-S-H rich sorbents can be prepared from these compounds and from mixtures of them with SiO{sub 2}. They also provide information useful for interpreting the cement sorbent results. Sorbents prepared from cement and from mixtures of cement and natural SiO{sub 2} or SiO{sub 2} sources were investigated as well. The results secured show that cement and mixtures of it with diatomite, pumice or perlite rapidly yield excellent sorbents with the proper reaction conditions.« less

Progress made in understanding Mount Rainier's hazards

USGS Publications Warehouse

Sisson, T.W.; Vallance, J.W.; Pringle, P.T.

2001-01-01

At 4392 m high, glacier-clad Mount Rainier dominates the skyline of the southern Puget Sound region and is the centerpiece of Mount Rainier National Park. About 2.5 million people of the greater Seattle-Tacoma metropolitan area can see Mount Rainier on clear days, and 150,000 live in areas swept by lahars and floods that emanated from the volcano during the last 6,000 years (Figure 1). These lahars include the voluminous Osceola Mudflow that floors the lowlands south of Seattle and east of Tacoma, and which was generated by massive volcano flank-collapse. Mount Rainier's last eruption was a light dusting of ash in 1894; minor pumice last erupted between 1820 and 1854; and the most recent large eruptions we know of were about 1100 and 2300 years ago, according to reports from the U.S. Geological Survey.

The Laramide Mesa formation and the Ojo de Agua caldera, southeast of the Cananea copper mining district, Sonora, Mexico

USGS Publications Warehouse

Cox, Dennis P.; Miller, Robert J.; Woodbourne, Keith L.

2006-01-01

The Mesa Formation extends from Cananea, Mexico, southeast to the Sonora River and is the main host rock of Laramide porphyry copper deposits in the Cananea District and at the Alacran porphyry prospect to the east. The Mesa consists of two members-a lower andesite and an upper dacite. The lowest part of the dacite member is a crystal tuff about 100 m thick. This tuff is the outfall of a caldera centered near the village of Ojo de Agua, dated by 40Ar/39Ar at 65.8 Ma ?0.4. The Ojo de Agua Caldera is about 9 km in diameter and is filled by a light gray biotite dacite tuff with abundant flattened pumice fragments. The volume of the caldera is estimated to be 24 km3.

Minerals yearbook, 1991: California. Annual report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carrillo, F.V.; Davis, J.F.; Alfors, J.T.

1993-05-01

The report has been prepared under a Memorandum of Understanding between the U.S. Bureau of Mines, U.S. Department of the Interior, and the California Department of Conservation, Division of Mines and Geology, for collecting information on all nonfuel minerals. California ranked second among the States, after Arizona, in the value of nonfuel minerals produced in 1991, accounting for almost 10% of the U.S. total. The value of the commodities produced during the year decreased about 9% to $2.5 billion, following last year's 4% decline. California was the sole producer of boron and tungsten and led all States in the productionmore » of asbestos, portland cement, diatomite, calcined gypsum, rare-earth concentrates, and construction sand and gravel. It was second in natural calcium chloride, gold, magnesium compounds, pumice, industrial sand and gravel, and soda ash.« less

Long-distance transport of a West Atlantic stony coral on a plastic raft.

PubMed

Hoeksema, Bert W; Pedoja, Kevin; Poprawski, Yohann

2018-05-30

The occurrence of wide-spread coral species around isolated reefs and over long stretches of deep ocean cannot be explained by larval dispersal alone; their larval stage is too short for that, especially in brooding species (Nunes et al. 2011, de Souza et al. 2017). Rafting on natural substrates, such as volcanic pumice fragments, wooden logs and coconut shells has been recognized as an alternative means for transport in reef corals (Fielden 1893, Crossland 1952, Jokiel 1984). Fouling on ship hulls and oil platforms is a relatively new, anthropogenic way for coral migration and because it is fast, it escalates the risk of alien species introductions (Creed et al. 2017). This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Explosive eruption, flank collapse and megatsunami at Tenerife ca. 170 ka.

PubMed

Paris, Raphaël; Bravo, Juan J Coello; González, María E Martín; Kelfoun, Karim; Nauret, François

2017-05-15

Giant mass failures of oceanic shield volcanoes that generate tsunamis potentially represent a high-magnitude but low-frequency hazard, and it is actually difficult to infer the mechanisms and dynamics controlling them. Here we document tsunami deposits at high elevation (up to 132 m) on the north-western slopes of Tenerife, Canary Islands, as a new evidence of megatsunami generated by volcano flank failure. Analyses of the tsunami deposits demonstrate that two main tsunamis impacted the coasts of Tenerife 170 kyr ago. The first tsunami was generated during the submarine stage of a retrogressive failure of the northern flank of the island, whereas the second one followed the debris avalanche of the subaerial edifice and incorporated pumices from an on-going ignimbrite-forming eruption. Coupling between a massive retrogressive flank failure and a large explosive eruption represents a new type of volcano-tectonic event on oceanic shield volcanoes and a new hazard scenario.

Shallow-storage conditions for the rhyolite of the 1912 eruption at Novarupta, Alaska

USGS Publications Warehouse

Coombs, Michelle L.; Gardner, James E.

2001-01-01

Recent studies have proposed contrasting models for the plumbing system that fed the 1912 eruption of Novarupta, Alaska. Here, we investigate the conditions under which the rhyolitic part of the erupted magma last resided in the crust prior to eruption. Geothermometry suggests that the rhyolite was held at ∼800-850 °C, and analyses of melt inclusions suggest that it was fluid saturated and contained ∼4 wt% water. Hydrothermal, water-saturated experiments on rhyolite pumice reveal that at those temperatures the rhyolite was stable between 40 and 100 MPa, or a depth of 1.8-4.4 km. These results suggest that pre-eruptive storage and crystal growth of the rhyolite were shallow; if the rhyolite ascended from greater depths, it did so slowly enough for unzoned phenocrysts to grow as it passed through the shallow crust.

Mobility of pyroclastic flows and surges at the Soufriere Hills Volcano, Montserrat

USGS Publications Warehouse

Calder, E.S.; Cole, P.D.; Dade, W.B.; Druitt, T.H.; Hoblitt, R.P.; Huppert, H.E.; Ritchie, L.; Sparks, R.S.J.; Young, S.R.

1999-01-01

The Soufriere Hills Volcano on Montserrat has produced avalanche-like pyroclastic flows formed by collapse of the unstable lava dome or explosive activity. Pyroclastic flows associated with dome collapse generate overlying dilute surges which detach from and travel beyond their parent flows. The largest surges partially transform by rapid sedimentation into dense secondary pyroclastic flows that pose significant hazards to distal areas. Different kinds of pyroclastic density currents display contrasting mobilities indicated by ratios of total height of fall H, run-out distance L, area inundated A and volume transported V. Dome-collapse flow mobilities (characterised by either L/H or A/V 2/3) resemble those of terrestrial and extraterrestrial cold-rockfalls (Dade and Huppert, 1998). In contrast, fountain-fed pumice flows and fine-grained, secondary pyroclastic flows travel slower but, for comparable initial volumes and heights, can inundate greater areas.

Mount Pinatubo, Philippine Islands as seen from STS-59

NASA Image and Video Library

1994-04-10

STS059-L14-170 (9-20 April 1994) --- Orient with the sea at the left. Then Subic Bay is at the lower left corner, and Clark Air Force Base (abandoned after the eruption) is to the lower right of the volcano. A turquoise lake occupies the caldera just below the center of the photograph. Mount Pinatubo erupted in June, 1991 after several hundred years of quiescence. Eruptive activity has nearly ceased, but every torrential rain in this monsoonal climate causes renewed mud flows of a viscous slurry composed of volcanic ash and pumice. Shuttle crews have been photographing the mountain at every opportunity, to add documentation to unmanned-satellite, aerial, and ground-based observations of changes. SRL scientists will use the excellent radar imagery obtained during STS-59 to help discriminate among different kinds of volcanic material, and to extend their observations to other volcanoes around the world using future, perhaps unmanned, radar satellites. Linhof photograph.

Keeping watch over Colombia’s slumbering volcanoes

USGS Publications Warehouse

Ordoñez, Milton; López, Christian; Alpala, Jorge; Narváez, Lourdes; Arcos, Dario; Battaglia, Maurizio

2015-01-01

Located in the Central Cordillera (Colombian Andes), Nevado del Ruiz is a volcanic complex, topped by glaciers, rising 5,321 m above sea level. A relatively small explosive eruption from Ruiz's summit crater on November 13, 1985, generated an eruption column and sent a series of pyroclastic flows and surges across the volcano's ice-covered summit. Pumice and meltwater produced by the hot pyroclastic flows and surges swept into gullies and channels on the slopes of Ruiz as a series of lahars. Within two hours of the beginning of the eruption, lahars had traveled 100 km and left behind a wake of destruction: more than 25,000 people were killed (23,000 in the town of Armero and 2,000 in the town of Chinchiná), about 5,000 injured, and more than 5,000 homes destroyed along the Chinchiná, Gualí, and Lagunillas rivers.

Volcanic Ash fall Impact on Vegetation, Colima 2005

NASA Astrophysics Data System (ADS)

Garcia, M. G.; Martin, A.; Fonseca, R.; Nieto, A.; Radillo, R.; Armienta, M.

2007-05-01

An ash sampling network was established arround Colima Volcano in 2005. Ash fall was sampled on the North, Northeast, East, Southeast, South, Southwest and West of the volcano. Samples were analyzed for ash components, geochemistry and leachates. Ash fall ocurred on April (12), May (10, 23), June (2, 6, 9, 10, 12, 14), July (27), September (27), October (23) and November (24). Most of the ash is made of andesitic dome-lithics but shows diferences in crystal, juvenile material and lithic content. In May, some samples contained grey and dark pumice (scoria). Texture varies from phi >4 to phi 0. Leachate concentration were low: SO4 (7.33-54.19) Cl- (2.29-4.97) and F- (0.16-0.37). During 2005, Colima Volcano's ash fall rotted some of the guava and peach fruits and had a drying effect on spearment and epazote plants. Even these small ash amounts could have hindered sugar cane and agave growth.

The May 2003 eruption of Anatahan volcano, Mariana Islands: Geochemical evolution of a silicic island-arc volcano

USGS Publications Warehouse

Wade, J.A.; Plank, T.; Stern, R.J.; Tollstrup, D.L.; Gill, J.B.; O'Leary, J. C.; Eiler, J.M.; Moore, R.B.; Woodhead, J.D.; Trusdell, F.; Fischer, T.P.; Hilton, David R.

2005-01-01

The first historical eruption of Anatahan volcano began on May 10, 2003. Samples of tephra from early in the eruption were analyzed for major and trace elements, and Sr, Nd, Pb, Hf, and O isotopic compositions. The compositions of these tephras are compared with those of prehistoric samples of basalt and andesite, also newly reported here. The May 2003 eruptives are medium-K andesites with 59-63 wt.% SiO2, and are otherwise homogeneous (varying less than 3% 2?? about the mean for 45 elements). Small, but systematic, chemical differences exist between dark (scoria) and light (pumice) fragments, which indicate fewer mafic and oxide phenocrysts in, and less degassing for, the pumice than scoria. The May 2003 magmas are nearly identical to other prehistoric eruptives from Anatahan. Nonetheless, Anatahan has erupted a wide range of compositions in the past, from basalt to dacite (49-66 wt.% SiO2). The large proportion of lavas with silicic compositions at Anatahan (> 59 wt.% SiO2) is unique within the active Mariana Islands, which otherwise erupt a narrow range of basalts and basaltic andesites. The silicic compositions raise the question of whether they formed via crystal fractionation or crustal assimilation. The lack of 87Sr/86Sr variation with silica content, the MORB-like ??18O, and the incompatible behavior of Zr rule out assimilation of old crust, altered crust, or zircon-saturated crustal melts, respectively. Instead, the constancy of isotopic and trace element ratios, and the systematic variations in REE patterns are consistent with evolution by crystal fractionation of similar parental magmas. Thus, Anatahan is a type example of an island-arc volcano that erupts comagmatic basalts to dacites, with no evidence for crustal assimilation. The parental magmas to Anatahan lie at the low 143Nd/144Nd, Ba/La, and Sm/La end of the spectrum of magmas erupted in the Marianas arc, consistent with 1-3 wt.% addition of subducted sediment to the mantle source, or roughly one third of the sedimentary column. The high Th/La in Anatahan magmas is consistent with shallow loss of the top 50 m of the sedimentary column during subduction. ?? 2005 Elsevier B.V. All rights reserved.

Erosional self-channelization of pyroclastic density currents - Evidence from ground-penetrating radar imaging at Mt. St. Helens, Washington (USA)

NASA Astrophysics Data System (ADS)

Gase, A.; Brand, B. D.; Bradford, J.

2016-12-01

The causes and consequences of substrate erosion are among the least understood attributes of pyroclastic density current (PDC) dynamics. Field evidence of substrate erosion is often limited by the location and quality of exposed PDC deposits. Here we present evidence for one of the most spatially extensive cases of PDC erosion to date, found within the 18 May 1980 deposits of Mt. St. Helens, Washington (USA). An 8 m deep and 300 m wide PDC scour and fill feature, which extends into PDC deposits from earlier in the eruption, is exposed along a distal outcrop of the shallow-dipping (<15º) pumice plain. Near surface geophysical techniques allow us to investigate the nature, extent, and cause of this large scour. We used 50 MHz ground-penetrating radar to track the distal scour from outcrop toward its source. Beginning 700 m up-flow from the large scour and fill exposure, the feature progressively widens from 205 m to 280 m and deepens from 10 m to 13 m, suggesting the PDCs became more erosive along the length of the scour. We extended our transects across the pumice plain to locate additional scours and to establish the topography at the time of erosion. We found a second 420 m wide and 11 m deep scour that extends at least 500 m from its inception point. Apparent dips of the sides of both channels are asymmetrical, due to pronounced erosion on the up-slope side of the flow in cross-section. Our data show no evidence of subsurface topographic irregularities or high slope angles up-flow from either erosional feature. These features imply large PDCs from semi-sustained or fluctuating eruptions can self-channelize by erosional mechanisms. Our findings suggest that (1) concentrated PDCs are capable of producing large scours on shallow slopes with negligible surface roughness, analogous to the erosional channels of submarine turbidity currents, (2) substrate properties, including partial fluidization of fresh PDC deposits, may facilitate substrate erosion during semi-sustained eruptions, and (3) large PDCs can undergo self-channelization, whereby axial zones of high flow energy erode channels that confine subsequent flows. Erosion and self-channelization of this nature is not accounted for in models of concentrated PDCs, which may result in underestimates of run-out distance.

Paleointensity in ignimbrites and other volcaniclastic flows

NASA Astrophysics Data System (ADS)

Bowles, J. A.; Gee, J. S.; Jackson, M. J.

2011-12-01

Ash flow tuffs (ignimbrites) are common worldwide, frequently contain fine-grained magnetite hosted in the glassy matrix, and often have high-quality 40Ar/39Ar ages. This makes them attractive candidates for paleointensity studies, potentially allowing for a substantial increase in the number of well-dated paleointensity estimates. However, the timing and nature of remanence acquisition in ignimbrites are not sufficiently understood to allow confident interpretation of paleointensity data from ash flows. The remanence acquisition may be a complex function of mineralogy and thermal history. Emplacement conditions and post-emplacement processes vary considerably between and within tuffs and may potentially affect the ability to recover ancient field intensity information. To better understand the relevant magnetic recording assemblage(s) and remanence acquisition processes we have collected samples from two well-documented historical ignimbrites, the 1980 ash flows at Mt. St. Helens (MSH), Washington, and the 1912 flows from Mt. Katmai in the Valley of Ten Thousand Smokes (VTTS), Alaska. Data from these relatively small, poorly- to non-welded historical flows are compared to the more extensive and more densely welded 0.76 Ma Bishop Tuff. This sample set enables us to better understand the geologic processes that destroy or preserve paleointensity information so that samples from ancient tuffs may be selected with care. Thellier-type paleointensity experiments carried out on pumice blocks sampled from the MSH flows resulted in a paleointensity of 55.8 μT +/- 0.8 (1 standard error). This compares favorably with the actual value of 56.0 μT. Excluded specimens of poor technical quality were dominantly from sites that were either emplaced at low temperature (<350°C) or were subject to post-emplacement hydrothermal alteration. The VTTS experienced much more wide-spread low-temperature hydrothermal activity than did MSH. Pumice-bearing ash matrix samples from this locality are characterized by at least two magnetic phases, one of which appears to carry a chemical remanent magnetization. Paleointensities derived from the second phase give results that vary widely but which may be correlated with degree of hydrothermal alteration or hydration. Preliminary data from the Bishop Tuff suggests that vapor-phase alteration at high (>600°C) temperatures does not corrupt the paleointensity signal, and additional data will be presented which explores this more fully.

Assessing New and Old Methods in Paleomagnetic Paleothermometry: A Test Case at Mt. St. Helens, USA

NASA Astrophysics Data System (ADS)

Bowles, J. A.; Gerzich, D.; Jackson, M. J.

2017-12-01

Paleomagnetic data can be used to estimate deposit temperatures (Tdep) of pyroclastic density currents (PDCs). The typical method is to thermally demagnetize oriented lithic clasts incorporated into the PDC. If Tdep is less than the maximum Curie temperature (Tc), the clast is partially remagnetized in the PDC, and the unblocking temperature (Tub) at which this remagnetization is removed is an estimate of Tdep. In principle, juvenile clasts can also be used, and Tub-max is taken as the minimum Tdep. This all assumes blocking (Tb) and unblocking temperatures are equivalent and that the blocking spectrum remains constant through time. Recent evidence shows that Tc in many titanomagnetites is a strong function of thermal history due to a crystal-chemical reordering process. We therefore undertake a study designed to test some of these assumptions and to assess the extent to which the method may be biased by a Tb spectrum that shifts to higher T during cooling. We also explore a new magnetic technique that relies only on stratigraphic variations in Tc. Samples are from the May 18, 1980 PDCs at Mt. St. Helens, USA. Direct temperature measurements of the deposits were 297 - 367°C. At sites with oriented lithics, standard methods provide a Tdep range that overlaps with measured temperatures, but is systematically higher by a few 10s of °C. By contrast, pumice clasts all give Tdep_min estimates that greatly exceed lithic estimates and measured temperatures. We attribute this overestimate to two causes: 1) Tc and Tub systematically increase with depth as a result of the reordering process. This results in Tdep_min estimates that vary by 50°C and increase with depth. 2) MSH pumice is multi-domain, where Tub > Tb, resulting in a large overestimate in Tdep. At 5 sites, stratigraphic variations in Tc were conservatively interpreted in terms of Tdep as <300°C or >300°C. More sophisticated modeling of the time-temperature-depth evolution of Tc allows us to place tighter constraints on some deposits, and our preliminary interpretation suggests that PDC pulses became successively hotter throughout the day. This new method allows us to evaluate subtle temporal/spatial variabilities that may not be evident from direct measurements made at the surface. It also allows Tdep estimates to be made on PDCs where no lithic clasts are present.

Magmatic and Volcanic Processes Interpreted from Recent Ash Emissions from Nevado del Ruiz, Colombia

NASA Astrophysics Data System (ADS)

Wall, K. T.; Harpel, C. J.; Martinez, L. M.; Ceballos, J. A.; Cortés, G. P.

2017-12-01

Nevado del Ruiz is a composite volcano located in the Colombian Central Cordillera. It is the modern edifice of the Nevado del Ruiz Volcanic Complex that has been active since 1.8 Ma. Through historic times, Ruiz has exhibited decades-long eruptive stages that include minor explosions and fumarolic activity bracketing one major magmatic event. Modern eruptive activity began with seismic unrest in 1984, a small explosive eruption on September 11, 1985, and the catastrophic lahar-generating eruption of November 13, 1985. Since then, Ruiz has periodically erupted plumes up to a few kilometers above the crater, including a phreatomagmatic eruption on September 1, 1989, eruptions on May 29 (1 km plume) and June 30 (8 km plume) 2012, and frequent minor ash emissions from 2015 through the present. We have examined a suite of samples from the 1985, 1989, 2012, and 2015 eruptions to assess the origin of erupted materials (juvenile vs. non-juvenile) and nature of eruptive and subvolcanic processes (e.g. fresh intrusion, phreatic explosion). The November 1985 ash is dominated by beige to light gray pumice and free crystals, while samples from September 1985 and the 1989 through 2015 eruptions contain other fresh looking angular to subangular particles, including dense glassy to microcrystalline chips and vesicular glass shards. If juvenile, as we suspect, these components indicate phreatomagmatic to magmatic eruptive processes. Vesicular glass ranges from colorless to brown, often within the same sample, suggesting that bimodal magmatic sources, as recorded by mingled pumices of November 1985, have continued to play a role in eruptions at Ruiz. In particular, ash from 1989 contains vesicular glass that is 65% colorless to beige and 35% brown. Sparse, very dark brown vesicular glass appears in ash from June 2012—a larger eruption than that of May 2012—and is also observed in some 2015 samples, suggesting a more prominent mafic component. In addition to our observations from binocular microscopy, we will present results from SEM and electron microprobe analyses that further clarify the magmatic conditions that produced these dense and vesicular glassy components, and that test our hypothesis that these particles represent juvenile material from continued phreatomagmatic to magmatic eruptions at Ruiz.

Lithic breccia and ignimbrite erupted during the collapse of Crater Lake Caldera, Oregon

USGS Publications Warehouse

Druitt, T.H.; Bacon, C.R.

1986-01-01

The climactic eruption of Mount Mazama (6845 y.B.P.) vented a total of ???50 km3 of compositionally zoned rhyodacitic to basaltic magma from: (a) a single vent as a Plinian pumice fall deposit and the overlying Wineglass Welded Tuff, and (b) ring vents as ignimbrite and coignimbrite lithic breccia accompanying the collapse of Crater Lake caldera. New field and grain-size data for the ring-vent products are presented in this report. The coarse-grained, poorly bedded, clast-supported lithic breccia extends as far as 18 km from the caldera center. Like the associated ignimbrite, the breccia is compositionally zoned both radially and vertically, and silicic, mixed, and mafic types can be recognized, based on the proportion of rhyodacitic pumice. Matrix fractions in silicic breccias are depleted of fines and are lithic- and crystal-enriched relative to silicic ignimbrite due to vigorous gas sorting during emplacement. Ignimbrite occurs as a proximal veneer deposit overlying the breccia, a medial (??? 8 to ??? 25 km from the caldera center), compositionally zoned valley fill as much as > 110 m thick, and an unzoned distal ({slanted equal to or greater-than} 20 km) facies which extends as far as 55 km from the caldera. Breccia within ??? 9 km of the caldera center is interpreted as a coignimbrite lag breccia formed within the deflation zone of the collapsing ring-vent eruption columns. Expanded pyroclastic flows of the deflation zone were probably vertically graded in both size and concentration of blocks, as recently postulated for some turbidity currents. An inflection in the rate of falloff of lithic-clast size within the lithic breccia at ??? 9 km may mark the outer edge of the deflation zone or may be an artifact of incomplete exposure. The onset of ring-vent activity at Mt. Mazama was accompanied by a marked increase in eruptive discharge. Pyroclastic flows were emplaced as a semicontinuous stream, as few ignimbrite flow-unit boundaries are evident. As eruption from the ring vents progressed, flow-runout distance and the extent of breccia deposition decreased due to (a) greater internal flow friction, and (b) decreasing eruption column heights. Effect (b) probably resulted from a progressive decrease in magmatic gas content and discharge rate. Waning discharge may have been promoted by the tapping of more viscous, crystal-rich magma, collapse of conduit walls, and declining caldera collapse rate. ?? 1986.

Ability of Hand Hygiene Interventions Using Alcohol-Based Hand Sanitizers and Soap To Reduce Microbial Load on Farmworker Hands Soiled during Harvest.

PubMed

de Aceituno, Anna Fabiszewski; Bartz, Faith E; Hodge, Domonique Watson; Shumaker, David J; Grubb, James E; Arbogast, James W; Dávila-Aviña, Jorgé; Venegas, Fabiola; Heredia, Norma; García, Santos; Leon, Juan S

2015-11-01

Effective hand hygiene is essential to prevent the spread of pathogens on produce farms and reduce foodborne illness. The U.S. Food and Drug Administration Food Safety Modernization Act Proposed Rule for Produce Safety recommends the use of soap and running water for hand hygiene of produce handlers. The use of alcohol-based hand sanitizer (ABHS) may be an effective alternative hygiene intervention where access to water is limited. There are no published data on the efficacy of either soap or ABHS-based interventions to reduce microbial contamination in agricultural settings. The goal of this study was to assess the ability of two soap-based (traditional or pumice) and two ABHS-based (label-use or two-step) hygiene interventions to reduce microbes (coliforms, Escherichia coli, and Enterococcus spp.) and soil (absorbance of hand rinsate at 600 nm [A600]) on farmworker hands after harvesting produce, compared with the results for a no-hand-hygiene control. With no hand hygiene, farmworker hands were soiled (median A600, 0.48) and had high concentrations of coliforms (geometric mean, 3.4 log CFU per hand) and Enterococcus spp. (geometric mean, 5.3 log CFU per hand) after 1 to 2 h of harvesting tomatoes. Differences in microbial loads in comparison to the loads in the control group varied by indicator organism and hygiene intervention (0 to 2.3 log CFU per hand). All interventions yielded lower concentrations of Enterococcus spp. and E. coli (P < 0.05), but not of coliforms, than were found in the control group. The two-step ABHS intervention led to significantly lower concentrations of coliforms and Enterococcus spp. than the pumice soap and label-use ABHS interventions (P < 0.05) and was the only intervention to yield significantly fewer samples with E. coli than were found in the control group (P < 0.05). All interventions removed soil from hands (P < 0.05), soap-based interventions more so than ABHS-based interventions (P < 0.05). ABHS-based interventions were equally as effective as hand washing with soap at reducing indicator organisms on farmworker hands. Based on these results, ABHS is an efficacious hand hygiene solution for produce handlers, even on soiled hands.

Pre-eruptive conditions of the Hideaway Park topaz rhyolite: Insights into metal source and evolution of magma parental to the Henderson porphyry molybdenum deposit, Colorado

USGS Publications Warehouse

Mercer, Celestine N.; Hofstra, Albert H.; Todorov, Todor I.; Roberge, Julie; Burgisser, Alain; Adams, David T.; Cosca, Michael A.

2015-01-01

The Hideaway Park tuff is the only preserved extrusive volcanic unit related to the Red Mountain intrusive complex, which produced the world-class Henderson porphyry Mo deposit. Located within the Colorado Mineral Belt, USA, Henderson is the second largest Climax-type Mo deposit in the world, and is therefore an excellent location to investigate magmatic processes leading to Climax-type Mo mineralization. We combine an extensive dataset of major element, volatile, and trace element abundances in quartz-hosted melt inclusions and pumice matrix glass with major element geochemistry from phenocrysts to reconstruct the pre-eruptive conditions and the source and evolution of metals within the magma. Melt inclusions are slightly peraluminous topaz rhyolitic in composition and are volatile-charged (≤6 wt % H2O, ≤600 ppm CO2, ∼0·3–1·0 wt % F, ∼2300–3500 ppm Cl) and metal-rich (∼7–24 ppm Mo, ∼4–14 ppm W, ∼21–52 ppm Pb, ∼28–2700 ppm Zn, <0·1–29 ppm Cu, ∼0·3–1·8 ppm Bi, ∼40–760 ppb Ag, ∼690–1400 ppm Mn). Melt inclusion and pumice matrix glass chemistry reveal that the Hideaway Park magma evolved by large degrees of fractional crystallization (≤60–70%) during quartz crystallization and melt inclusion entrapment at pressures of ≤300 MPa (≤8 km depth), with little to no crystallization upon shallow ascent and eruption. Filter pressing, crystal settling, magma recharge and mixing of less evolved rhyolite melt, and volatile exsolution were important processes during magma evolution; the low estimated viscosities (∼105–1010 Pa s) of these H2O- and F-rich melts probably enhanced these processes. A noteworthy discrepancy between the metal contents in the pumice matrix glass and in the melt inclusions suggests that after quartz crystallization ceased upon shallow magma ascent and eruption, the Hideaway Park magma exsolved an aqueous fluid into which Mo, Bi, Ag, Zn, Mn, Cs, and Y strongly partitioned. Given that the Henderson deposit contains anomalous abundances of not only Mo, but also W, Pb, Zn, Cu, Bi, Ag, and Mn, we suggest that these metals were sourced from similar fluids exsolved from unerupted portions of the same magmatic system. Trace element ratios imply that Mo was sourced deep, from either the lower crust or metasomatized mantle. The origin of sulfur remains unresolved; however, given the extremely low S solubility of rhyolite melts in the shallow crust we favor the possibility that another source of S might supplement or account for that present in the ore deposit, probably the comagmatic, mantle-derived lamprophyres that occur in minor quantities with the voluminous topaz rhyolites in the area. To account for the 437 Mt of MoS2 (∼1·0 × 106 t Mo) present in the Henderson ore deposit, a volume of ∼45 km3 of Hideaway Park rhyolite magma would have been necessary to supply the Mo (a cylindrical pluton measuring 3·1 km × 6·0 km) along with sparging of ∼6·8 × 105 t of S from ∼0·05 km3 of lamprophyre magma. Based on a weighted mean 40Ar/39Ar age of 27·58 ± 0·24 Ma, similar melt geochemistry, and characteristically F-rich biotite phenocrysts, we conclude that the Hideaway Park tuff was cogenetic with the intrusions at Red Mountain that formed the Henderson deposit.

The eruption history of the quaternary Eifel volcanic fields: Implications from the ELSA - Tephra - Stack

NASA Astrophysics Data System (ADS)

Förster, Michael; Sirocko, Frank

2015-04-01

Numerous tephra layers occur in maar sediments in the quaternary Eifel volcanic fields. The sediments were systematically drilled and cored since 1998 by the Eifel Laminated Sediment Archive project (ELSA) (Sirocko et al. 2013). These maar sediments are laminated and the tephra is easily recognizeable by a coarser grain size. Additionaly, tephra layers appear dark grey to black in color. The ashes were sieved to a fraction of 250 - 100 µm and sorted into grains of: reddish and greyish sandstone, quartz, amphibole, pyroxene, scoria and pumice, sanidine, leucite and biotite. A minimum of 100 grains for each tephra layer were used for a sediment petrographic tephra characterisation (SPTC). The grain counts resemble the vol. -% of each grain species. Three types of tephra could be identified by their distinctive grain pattern: (1) phreatomagmatic tephra, rich in basement rocks like greyish/reddish sandstone and quartz. (2) Strombolian tephra, rich in scoria and mafic minerals like pyroxene. (3) evolved tephra, rich in sanidine and pumice. 16 drill-cores, covering the last 500 000 years have been examined. Younger cores were dated by 14C ages and older cores by optical stimulated luminescence. Independently from this datings, the drill-cores were cross-correlated by pollen and the occurences of specific marker-tephra layers, comprising characteristic grain-types. These marker-tephra layers are especially thick and of evolved composition with a significant abundance of sanidine and pumice. The most prominent tephra layers of this type are the Laacher See tephra, dated to 12 900 b2k by Zolitschka (1998), the 40Ar/39Ar dated tephra layers of Dümpelmaar, Glees and Hüttenberg, dated to 116 000 b2k, 151 000 b2k and 215 000 b2k by van den Bogaard & Schmincke (1990), van den Bogaard et al. (1989). These datings set the time-frame for the eruption-phases of the quaternary Eifel Volcanic Fields. Our study refines these findings and shows that phases of activity are very periodically, peaking at 450 000 to 500 000, 140 000, 100 000 and 50 000 b2k in the West Eifel Volcanic Field and 400 000, 200 000, 150 000 and 12 900 b2k in the East Eifel Volcanic Field. These phases are seperated by long dormant intervals and cluster around times of climate and sea level changes. The youngest phase of intense activity in the West Eifel Volcanic Field occured from ~60 000 to 27 800 b2k. All young maar volcanoes with open maar lakes like the Pulvermaar, Meerfelder Maar and Dauner Maar Group erupted in this cluster. Only one maar postdates this interval of increased activity, the 11 000 b2k Ulmener Maar. References Sirocko, F., Dietrich, S., Veres, D., Grootes, P. M., Schaber-Mohr, K., Seelos, K., Nadeau, M.-J., Kromer, B., Rothacker, L., Röhner, M., Krbetschek, M., Appleby, P., Hambach, U., Rolf, C., Sudo, M., & Grim, S. (2013). Multi-proxy dating of Holocene maar lakes and Pleistocene dry maar sediments in the Eifel, Germany. Quaternary Science Reviews, 62, 56-76. van den Bogaard, P., Hall, C. M., Schmincke, H. U., & York, D. (1989). Precise single-grain 40Ar/39 Ar dating of a cold to warm climate transition in Central Europe. Nature 342, 523 - 525 van den Bogaard, P. & Schmincke, H. U. (1990). Die Entwicklungsgeschichte des Mittelrheinraumes und die Eruptionsgeschichte des Osteifel-Vulkanfeldes. Rheingeschichte zwischen Mosel und Maas. deuqua-Führer, 1, 166-190. Zolitschka, B. (1998). A 14,000 year sediment yield record from western Germany based on annually laminated lake sediments. Geomorphology, 22(1), 1-17.

Identification and quantitative determination of diphenylarsenic compounds in abandoned toxic smoke canisters.

PubMed

Hanaoka, Shigeyuki; Nomura, Koji; Kudo, Shinichi

2005-09-02

Knowledge of the exact nature of the constituents of abandoned chemical weapons (ACW) is a prerequisite for their orderly destruction. Here we report the development of analytical procedures to identify diphenylchloroarsine (DA/Clark I), diphenylcyanoarsine (DC/Clark II) and related substances employed in one of the munitions known as "Red canister". Both DA and DC are relatively unstable under conventional analytical procedures without thiol derivatization. Unfortunately however, thiol drivatization affords the same volatile organo-arsenic derivative from several different diphenylarsenic compounds, making it impossible to identify and quantify the original compounds. Further, diminishing the analytical interference caused by the celluloid powder used as a stacking material in the weapons, is also essential for accurate analysis. In this study, extraction and instrumental conditions have been evaluated and an optimal protocol was determined. The analysis of Red canister samples following this protocol showed that most of the DA and DC associated with pumice had degraded to bis(diphenylarsine)oxide (BDPAO), while those associated with celluloid were dominantly degraded to diphenylarsinic acid (DPAA).

Petrographic and geochemical characteristics of a section through the Tiva Canyon Tuff at Antler Ridge, Yucca Mountain, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singer, F.R.; Widmann, B.L.; Dickerson, R.P.

1994-12-31

The Tiva Canyon Tuff of the Paintbrush Group of Miocene age caps much of Yucca Mountain, Nevada and is a compositionally zoned, compound cooling, pyroclastic flow that ranges from a dominantly high-silica rhyolitic base to a quartz-latitic caprock. Petrographic and geochemical studies have focused on rigorously defining the internal stratigraphy of this unit to support the detailed mapping of the Ghost Dance fault and other structures in the central fault block of Yucca Mountain. This study shows that devitrification textures and vapor phase mineralogy, in addition to other physical attributes such as pumice variability (flattening) and crystal content, can bemore » used as distinguishing criteria to better define lithologic zones within the Tiva Canyon Tuff. In addition, the study also shows that the petrographic textures and chemistry of the groundmass vary systematically within recognizable lithologic zones and may be used to characterize and vertically divide litho-stratigraphic zones within the Tiva Canyon Tuff.« less

Functional characteristics and influence factors of microbial community in sewage sludge composting with inorganic bulking agent.

PubMed

Wang, Ke; Mao, Hailong; Li, Xiangkun

2018-02-01

The metabolic function of microbial community dominated organics and nutrients transformation in aerobic composting process. In this study, the metabolic characteristics of bacterial and fungal communities were evaluated in 60 days composting of sludge and pumice by using FUNGuild and PICRUSt, respectively. The results showed that microbial community structure and metabolic characteristics were distinctively different at four composting periods. Bacterial genes related to carbohydrate metabolisms decreased during the first 30 days, but bacterial sequences associated with oxidative phosphorylation and fatty acids synthesis were enhanced in curing phase. Most of fungal animal pathogen and plant pathogen disappeared after treatment, and the abundance of saprotroph fungi increased from 44.3% to 97.8%. Oxidation reduction potential (ORP) significantly increased from -28 to 175 mV through incubation. RDA analysis showed that ORP was a crucial factor on the succession of both bacterial and fungal communities in sludge composting system. Copyright © 2017. Published by Elsevier Ltd.

Map showing surface ruptures associated with the Mammoth Lakes, California, earthquakes of May 1980

USGS Publications Warehouse

Clark, M.M.; Yount, J.C.; Vaughn, P.R.; Zepeda, R.L.

1982-01-01

This map shows surface ruptures associated with the M 6 Mammoth Lakes earthquakes of May 25-27, 1980 (Sherburne, 1980). The ruptures were mapped during USGS field investigations May 28 to June 4 and July 14-19, 1980. The map also includes some of the ruptures recorded by California Division of Mines and Geology investigators May 26-31, June 26-27, and July 7-11, 1980 (Taylor and Bryant, 1980). Because most of the surface ruptures developed in either unconsolidated pumice, alluvium, or till (and many were on slopes of scarps created by earlier faulting), wind, rain and animals quickly erased many of the ruptures. In places, the minimum detectable slip was 3-10 mm. Thus the lines on the map do not record all of the ruptures that formed at the time of the earthquake. Many of the areas were we show gaps between lines on the map probably had cracks originally. 

Explosive eruption, flank collapse and megatsunami at Tenerife ca. 170 ka

PubMed Central

Paris, Raphaël; Bravo, Juan J. Coello; González, María E. Martín; Kelfoun, Karim; Nauret, François

2017-01-01

Giant mass failures of oceanic shield volcanoes that generate tsunamis potentially represent a high-magnitude but low-frequency hazard, and it is actually difficult to infer the mechanisms and dynamics controlling them. Here we document tsunami deposits at high elevation (up to 132 m) on the north-western slopes of Tenerife, Canary Islands, as a new evidence of megatsunami generated by volcano flank failure. Analyses of the tsunami deposits demonstrate that two main tsunamis impacted the coasts of Tenerife 170 kyr ago. The first tsunami was generated during the submarine stage of a retrogressive failure of the northern flank of the island, whereas the second one followed the debris avalanche of the subaerial edifice and incorporated pumices from an on-going ignimbrite-forming eruption. Coupling between a massive retrogressive flank failure and a large explosive eruption represents a new type of volcano-tectonic event on oceanic shield volcanoes and a new hazard scenario. PMID:28504256

Textural constraints on effusive silicic volcanism - Beyond the permeable foam model

NASA Technical Reports Server (NTRS)

Fink, Jonathan H.; Anderson, Steven W.; Manley, Curtis R.

1992-01-01

The paper reports textural observations and presents isotopic evidence from active and recent silicic lava flows which show that at least some vesiculation occurs during surface advance of extrusions, after magma has reached the earth's surface. This view is in contrast to the widely promoted 'permeable foam' model, which states that all volatiles escape during ascent of the magma, and that all dense glassy material in lava flows forms from the collapse of pumiceous lava, i.e., that silicic lavas emerge as highly inflated foam flows. The permeable foam model also implies the unlikely requirement that explosive-to-effusive transitions be associated with an increase in the eruption rate. A more comprehensive model for the emplacement of silicic extrusions that allows for early gas loss during ascent, as well as late-stage vesiculation, is presented. The way in which the redistribution of volatiles during surface flow can increase explosive hazards from silicic lavas days, weeks, or months after the lava emerges from the event is discussed.

Immobilized glucose oxidase--catalase and their deactivation in a differential-bed loop reactor.

PubMed

Prenosil, J E

1979-01-01

Glucose oxidase containing catalase was immobilized with a copolymer of phenylenediamine and glutaraldehyde on pumice and titania carrier to study the enzymatic oxidation of glucose in a differential-bed loop reactor. The reaction rate was found to be first order with respect to the concentration of limiting oxygen substrate, suggesting a strong external mass-transfer resistance for all the flow rates used. The partial pressure of oxygen was varied from 21.3 up to 202.6 kPa. The use of a differential-bed loop reactor for the determination of the active enzyme concentration in the catalyst with negligible internal pore diffusion resistance is shown. Catalyst deactivation was studied, especially with respect to the presence of catalase. It is believed that the hydrogen peroxide formed in the oxidation reaction deactivates catalase first; if an excess of catalase is present, the deactivation of glucose oxidase remains small. The mathematical model subsequently developed adequately describes the experimental results.

Radiocarbon dates for lava flows and pyroclastic deposits on Sao Miguel, Azores

USGS Publications Warehouse

Moore, R.B.; Rubin, M.

1991-01-01

We report 63 new radiocarbon analyses of samples from Sao Miguel, the largest island in the Azores archipelago. The samples are mainly carbonized tree roots and other plant material collected from beneath 20 mafic lava flows and spatter deposits and from within and beneath 42 trachytic pyroclastic flow, pyroclastic surge, mudflow, pumice-fall and lacustrine deposits and lava flows. One calcite date is reported. These dates establish ages for 48 previously undated lava flows and pyroclastic deposits, and revise three ages previously reported. These data are critical to deciphering the Holocene and late Pleistocene eruptive history of Sao Miguel and evaluating its potential volcanic hazards. Average dormant intervals during the past 3000 years are about 400 years for Sete Cidades volcano, 145 years for volcanic Zone 2, 1150 years for Agua de Pau volcano and 320 years for Furnas volcano. No known eruptions have occurred in volcanic Zone 4 during the past 3000 years. -from Authors

Chronology of the 2007 eruption of Stromboli and the activity of the Scientific Synthesis Group

NASA Astrophysics Data System (ADS)

Barberi, Franco; Civetta, Lucia; Rosi, Mauro; Scandone, Roberto

2009-05-01

On 27 February 2007, at 12.49 GMT, a new eruption of Stromboli took place with the effusion of a lava flow from a fracture cutting the flank of the NE cone, which rapidly reached the sea. The eruption had been heralded by an increase in the amplitude of tremor and flank movement since at least the 14th of February. Short-term precursors were an increase in the rate of occurrence of small landslides within the "Sciara del Fuoco" scar on the North-western flank of the volcano. A new effusive vent opened at 18.30 GMT on the Sciara del Fuoco at an height of 400 m asl. The new lava emission caused the sudden termination of the summit flow and initiated a period of non-stationary lava outpouring which ended on 2 April, 2007. The eruption has been characterized by a rapid decrease in the eruption rate after the first days and subsequently by episodic pulse increases. On the 15th of March, the increase in lava outpouring, monitored by a thermal camera, heralded by 9 min the occurrence of a violent paroxysmal explosion with the formation of an impulsive eruption column and the emission of small pumices mingled with black scoriae. The pumice had a bulk composition similar to that of the lava and of the black scoriae, but with a distinct lower content of phenocrysts. A similar feature has been repeatedly observed during the major explosive paroxysms of Stromboli. Short term precursors of the paroxysm were recorded by strainmeter and tiltmeter stations. The volcano monitoring activity has been made by a joint team of researchers from the INGV sections of Catania, Napoli, Palermo and Rome, along with researchers from the Universities of Florence, Pisa, Roma Tre, and Palermo. The scientific activity was coordinated by a Synthesis Group made up by scientists responsible for the different monitoring techniques of INGV and Universities and by the volcanic experts of Commissione Nazionale Grandi Rischi of the Prime Minister Office (Civil Protection Department). The group made a daily evaluation of the state of the volcano and transmitted its recommendations to the Civil Protection Department (DPC). Several prevention measures were adopted by DPC, the main of which were the evacuation of the coast zone when strong acceleration of the Sciara del Fuoco slope motion (occurred twice) could led to a dangerous tsunami by flank collapse (as last occurred on 30 December 2002) and four days before the 15 March paroxysm when access was prohibited to the part of the volcano above 290 m asl.

Lava dome morphometry and geochronology of the youngest eruptive activity in Eastern Central Europe: Ciomadul (Csomád), East Carpathians, Romania

NASA Astrophysics Data System (ADS)

Karátson, D.; Telbisz, T.; Harangi, Sz.; Magyari, E.; Kiss, B.; Dunkl, I.; Veres, D.; Braun, M.

2012-04-01

Volcanic evolution of the Ciomadul (Csomád) lava dome complex, site of the youngest (Late Pleistocene, late Marine Isotope Stage 3) eruptive activity in the Carpathians, has been studied by advanced morphometry and radiometric (U/Pb, U/He and 14C) geochronology. The volcano produced alternating effusive and intermittent explosive eruptions from individual domes, typical of common andesitic-dacitic lava domes. A comparative morphometry shows steep ≥30° mean slopes of domes' upper flank and the Csomád domes fit well to the 100-200 ka domes worldwide. Morphometric ages obtained from the mean slope vs age precipitation correlation results in ≤100 ka ages. The morphometric approach is supported by U/Pb and U/He chronology: preliminary results of zircon dating indicate ages ranging between 200(250) and 30 ka. The youngest ages of the data set obtained both from lavas and pumiceous pyroclastics argue for a more or less coeval effusive and explosive volcanism. Based also on volcanological data, we propose vulcanian eruptions and explosive dome collapses especially toward the end of volcanic activity. Moreover, radiometric chronology suggests that, possibly subsequently to the peripheral domes, a central lava dome complex built up ≤100 ka ago. This dome complex, exhibiting even more violent, up to sub-plinian explosions, emplaced pumiceous pyroclastic flow and fall deposits as far as 17 km. We propose that the explosive activity produced caldera-forming eruptions as well, creating a half-caldera. This caldera rim is manifested by the asymmetric morphology of the central edifice: the present-day elevated ridge of Ciomadul Mare (Nagy Csomád), encompassing the twin craters of Mohoş (Mohos) peat bog and Sf. Ana (Szent [St.] Anna). These latter craters may have been formed subsequently, ca. ~100-30 ka ago, after the caldera formation. Drilling of lacustrine sediments in the St. Anna crater shows that beneath the Holocene gyttja several meters of Late Pleistocene sediment occurs. Although we did not reach the very bottom of the crater, radiometric dating of the lowest layer indicates that the formation of the crater exceeds 26,000 cal yr BP. This is in accordance with magnetic susceptibility curves and pollen results from the lake sediments, as well as the 31,450 cal yr BP radiocarbon age of the youngest dated eruption at Csomád. Research has been funded by Hungarian National Grants OTKA K68587 and NF101362.

Partial self-reversal of TRM in baked soils and ceramics from Ecuador

NASA Astrophysics Data System (ADS)

Roperch, Pierrick; Chauvin, Annick; Valdez, Francisco

2012-11-01

Partial self-reversed thermoremanent magnetizations (SRTRMs) were observed in samples of baked soils, hearths and ceramics from the Rumipamba archeological site near Quito (Ecuador) and ceramics from sites near the town of Esmeraldas (Ecuador). The SRTRMs were recognized at room temperature on few samples but cooling the samples in liquid nitrogen enhanced the intensity of the SRTRM and measurement at 77°K enables its rapid detection in many samples from these sites. Alternating field demagnetization of the SRTRM indicate median destructive field of the order of 50 mT and thermal demagnetization give unblocking temperatures in the temperature range 280-380 °C. The magnetic carriers of the SRTRM are stable to heating in air or in vacuum up to 600 °C suggesting that titanomaghemite should not be the magnetic carrier of the SRTRM. The studied baked clays and ceramics contain detrital material of mainly volcanic origin. Ti-poor titanomagnetite is the main magnetic carrier identified by strong field data or susceptibility measurements versus temperature. Ilmeno-hematite grains were recognized with microscope observations under reflected light. Scanning electron microscope observations with energy dispersive X-ray spectrometry indicate a Ti/Fe ratio corresponding to an ilmenite content of ˜0.55. We also compared the magnetic properties of the partially self-reversed baked clays with those of the self-reversed Pinatubo pumices. The SRTRMs were measured upon cooling from room temperature to 20°K with the MPMS. Upon cooling to 20°K the SRTRM show a nearly tenfold increase in intensity with respect to the room temperature measurement. The baked clay and ceramics from Ecuador carrying the SRTRM share similar magnetic properties with the Pinatubo pumices (unblocking temperatures, low temperature behavior) supporting the interpretation that detrital hemoilmenite originating from the Holocene activity of the numerous Ecuadorian volcanoes is the main carrier of the SRTRM in the archeological samples. In some samples, anisotropy tensors of SRTRM show large anisotropy degree (>2). The high anisotropy observed when the total magnetization is the sum of a normal thermoremanent magnetization (TRM) and a SRTRM is likely amplified because the anisotropy carried by the SRTRM is larger than the one carried by the normal component. A component of SRTRM may be hidden in archeological materials containing detrital hemoilmenites related to dacitic/andesitic volcanism and this may affect the determination of paleointensity of the earth magnetic field especially when non thermal method are used.

Unusual ice diamicts emplaced during the December 15, 1989 eruption of redoubt volcano, Alaska

USGS Publications Warehouse

Waitt, R.B.; Gardner, C.A.; Pierson, T.C.; Major, J.J.; Neal, C.A.

1994-01-01

Ice diamict comprising clasts of glacier ice and subordinate rock debris in a matrix of ice (snow) grains, coarse ash, and frozen pore water was deposited during the eruption of Redoubt Volcano on December 15, 1989. Rounded clasts of glacier ice and snowpack are as large as 2.5 m, clasts of Redoubt andesite and basement crystalline rocks reach 1 m, and tabular clasts of entrained snowpack are as long as 10 m. Ice diamict was deposited on both the north and south volcano flanks. On Redoubt's north flank along the east side of Drift piedmont glacier and outwash valley, ice diamict accumulated as at least 3 units, each 1-5 m thick. Two ice-diamict layers underlie a pumice-lithic fall tephra that accumulated on December 15 from 10:15 to 11:45 AST. A third ice diamict overlies the pumiceous tephra. Some of the ice diamicts have a basal 'ice-sandstone' layer. The north side icy flows reached as far as 14 km laterally over an altitude drop of 2.3 km and covered an area of about 5.7 km2. On Crescent Glacier on the south volcano flank, a composite ice diamict is locally as thick as 20 m. It travelled 4.3 km over an altitude drop of 1.7 km, covering about 1 km2. The much higher mobility of the northside flows was influenced by their much higher water contents than the southside flow(s). Erupting hot juvenile andesite triggered and turbulently mixed with snow avalanches at snow-covered glacier heads. These flows rapidly entrained more snow, firn, and ice blocks from the crevassed glacier. On the north flank, a trailing watery phase of each ice-diamict flow swept over and terraced the new icy deposits. The last (and perhaps each) flood reworked valley-floor snowpack and swept 35 km downvalley to the sea. Ice diamict did not form during eruptions after December 15 despite intervening snowfalls. These later pyroclastic flows swept mainly over glacier ice rather than snowpack and generated laharic floods rather than snowflows. Similar flows of mixed ice grains and pyroclastic debris resulted from the November 13, 1985 eruption of Nevado del Ruiz volcano and from eruptions of snowclad Mount St. Helens in 1982-1984. Such deposits at snowclad volcanoes are initially broad and geomorphically distinct, but they soon become extensively reworked and hard to recognize in the geologic record. ?? 1994.

Long-range hazard assessment of volcanic ash dispersal for a Plinian eruptive scenario at Popocatépetl volcano (Mexico): implications for civil aviation safety

NASA Astrophysics Data System (ADS)

Bonasia, Rosanna; Scaini, Chiara; Capra, Lucia; Nathenson, Manuel; Siebe, Claus; Arana-Salinas, Lilia; Folch, Arnau

2014-01-01

Popocatépetl is one of Mexico's most active volcanoes threatening a densely populated area that includes Mexico City with more than 20 million inhabitants. The destructive potential of this volcano is demonstrated by its Late Pleistocene-Holocene eruptive activity, which has been characterized by recurrent Plinian eruptions of large magnitude, the last two of which destroyed human settlements in pre-Hispanic times. Popocatépetl's reawakening in 1994 produced a crisis that culminated with the evacuation of two villages on the northeastern flank of the volcano. Shortly after, a monitoring system and a civil protection contingency plan based on a hazard zone map were implemented. The current volcanic hazards map considers the potential occurrence of different volcanic phenomena, including pyroclastic density currents and lahars. However, no quantitative assessment of the tephra hazard, especially related to atmospheric dispersal, has been performed. The presence of airborne volcanic ash at low and jet-cruise atmospheric levels compromises the safety of aircraft operations and forces re-routing of aircraft to prevent encounters with volcanic ash clouds. Given the high number of important airports in the surroundings of Popocatépetl volcano and considering the potential threat posed to civil aviation in Mexico and adjacent regions in case of a Plinian eruption, a hazard assessment for tephra dispersal is required. In this work, we present the first probabilistic tephra dispersal hazard assessment for Popocatépetl volcano. We compute probabilistic hazard maps for critical thresholds of airborne ash concentrations at different flight levels, corresponding to the situation defined in Europe during 2010, and still under discussion. Tephra dispersal mode is performed using the FALL3D numerical model. Probabilistic hazard maps are built for a Plinian eruptive scenario defined on the basis of geological field data for the "Ochre Pumice" Plinian eruption (4965 14C yr BP). FALL3D model input eruptive parameters are constrained through an inversion method carried out with the semi-analytical HAZMAP model and are varied by sampling them using probability density functions. We analyze the influence of seasonal variations on ash dispersal and estimate the average persistence of critical ash concentrations at relevant locations and airports. This study assesses the impact that a Plinian eruption similar to the Ochre Pumice eruption would have on the main airports of Mexico and adjacent areas. The hazard maps presented here can support long-term planning that would help minimize the impacts of such an eruption on civil aviation.

Provenance of Miocene submarine fans in the Shikoku Basin: Results from NanTroSEIZE and implications for stratigraphic correlation of subduction inputs

NASA Astrophysics Data System (ADS)

Pickering, K. T.; Underwood, M.; Moore, G. F.

2013-12-01

Seismo-stratigraphy, coring and LWD during IODP Expeditions 319, 322, and 333 (Sites C0011 / C0012) show three Miocene submarine fans in the NE Shikoku Basin, with broadly coeval deposits at ODP Site 1177 and DSDP Site 297, NW Shikoku Basin. Pickering et al. (2013) have shown that the sediment dispersal patterns for these fans have major implications for paleogeographies at that time. The oldest, Middle Miocene Kyushu Fan is the finest grained, has a sheet-like geometry, and was fed by quartz-rich sediment gravity-flows derived mostly from an ancestral landmass in the East China Sea. This likely sediment provenance is further supported by U-Pb zircon and fission track analysis of both zircons and apatites from sediments taken from the forearc and trench of the Nankai Trough, together with rivers from southwest Japan, that point to the influence of the Yangtze River in supplying into the Shikoku Basin prior to rifting of the Okinawa Trough at 10 to 6 Ma (Clift et al. 2013). During prolonged hemipelagic mud deposition at C0011-C0012 (12.2 to 9.1 Ma), sand supply continued at Sites 1177 and 297. Sand delivery to much of the Shikoku Basin, however, probably halted during a phase of sinistral strike-slip and oblique plate motion, after which the Daiichi Zenisu Fan (9.1 to 8.0 Ma) was fed by submarine channels. The youngest fan (Daini Zenisu; 8.0 to 7.6 Ma) has sheet-like geometry with thick-bedded, coarse-grained pumiceous sandstones. The pumice fragments were fed from a mixed provenance that included the collision zone of the Izu-Bonin and Honshu arcs. The shift from channelized to sheet-like flows was probably favored by renewal of relatively rapid northward subduction, which accentuated the trench as a bathymetric depression. Understanding the stratigraphic position and 3-D geometry of the sandbodies has important implications for stratigraphic correlation throughout the northern Shikoku Basin, together with subduction-related processes, including the potential for focused fluid flow and fluid overpressures above and below the plate-boundary fault. References Pickering, K.T., Underwood, M.B., Saito, S., Naruse, H., Kutterolf, S., Scudder, R., Park, J.-O., Moore, G.F. & Slagle, A. 2013. Geochemistry, Geophysics, Geosystems, 14, doi:10.1002/ggge.20107 Clift, P.D., Carter, A., Nicholson, U. & Masago, H. 2013. Tectonics, doi: 10.1002/tect.20033

Results of Physical Property Measurements Obtained during the CHIKYU Cruise CK16-01 to Hydrothermal Fields of the Middle Okinawa Trough

NASA Astrophysics Data System (ADS)

Tanikawa, W.; Masaki, Y.; Komori, S.; Torimoto, J.; Makio, M.; Ohta, Y.; Nozaki, T.; Ishibashi, J. I.; Kumagai, H.; Maeda, L.; Hamada, Y.

2016-12-01

The middle Okinawa trough, along the Ryukyu-arc on the margin of the western Pacific, fosters several hydrothermal fields. The cruise CK16-01 of D/V CHIKYU targeted the Iheya-North Field and Noho hydrothermal site. More than ten-days extensive coring was carried out with Logging While Drilling (LWD) and deployment of Kuroko cultivation apparatus between February 29th to March 17th2016. Here we present the results of the physical property measurements obtained using Chikyu's on-board laboratory. Cores were sampled among three sites where the seafloor environments were quite different: the Noho site (C9017), a site between the Natsu and Aki sites of the Iheya-North field (C9021), and the Iheya-North Aki site (C9023). Site C9017 was near the center of the hydrothermal activity, and the obtained core was limited 36 m in length and 30 % in the recovery rate. At 70 mbsf (meters below seafloor), the grain density and bulk density of the sediment reached their maxim (3.7 g/m3 and 2.7 g/cm3, respectively), while thermal conductivity reached its lowest value (0.6 W/m·K). Site C9021 yielded a 54 m core, with a core recovery rate of 50 %. Coarse pumiceous layers were found at 68 mbsf, with a hydrothermally altered layer appearing below 68 mbsf. The mean grain density value was 2.4 g/cm3 and was uniform throughout the core. The mean bulk density value of the pumiceous layers was 1.3 g/cm3, and of the hydrothermally altered layer was 2.1 g/cm3. Site C9023 was close to the active hydrothermal chimneys of the Iheya-North Aki site, and yielded 33 m of core with a core recovery rate of 16 %. Massive sulfide layers were found below 48 mbsf with grain density and bulk density values varying between 2.8-4.7 g/cm3 and 1.5-3.9 g/cm3, respectively. Magnetic susceptibility exhibited a high anomaly in a sedimented anhydrite layer found between 95 and 135 mbsf, and a high porosity and low resistivity zone was found below 150 mbsf. Together, these data from drilling cores and onboard analysis provide the first insights into the physical properties of hydrothermal fields in the Okinawa trough. This work was supported by the Council for Science, Technology and Innovation (CSTI) Cross-ministerial Strategic Innovation Promotion Program (SIP), "Next-generation technology for ocean resources exploration" (Lead agency: JAMSTEC)

Rapid assembly and rejuvenation of a large silicic magmatic system: Insights from mineral diffusive profiles in the Kidnappers and Rocky Hill deposits, New Zealand

NASA Astrophysics Data System (ADS)

Cooper, George F.; Morgan, Daniel J.; Wilson, Colin J. N.

2017-09-01

The timescales over which magmas in large silicic systems are reactivated, assembled and stored remains a fundamental question in volcanology. To address this question, we study timescales from Fe-Mg interdiffusion in orthopyroxenes and Ti diffusion in quartz from the caldera-forming 1200 km3 Kidnappers and 200 km3 Rocky Hill eruptions from the Mangakino volcanic centre (Taupo Volcanic Zone, New Zealand). The two eruptions came from the same source area, have indistinguishable 40Ar/39Ar ages (∼1.0 Ma) and zircon U-Pb age spectra, but their respective deposits are separated by a short period of erosion. Compositions of pumice, glass and mineral species in the collective eruption deposits define multiple melt dominant bodies but indicate that these shared a common magmatic mush zone. Diffusion timescales from both eruptions are used to build on chemical and textural crystal signatures and interpret both the crystal growth histories and the timing of magma accumulation. Fe-Mg interdiffusion profiles in orthopyroxenes imply that the three melt-dominant bodies, established through extraction of melt and crystals from the common source, were generated within 600 years and with peak accumulation rates within 100 years of each eruption. In addition, a less-evolved melt interacted with the Kidnappers magma, beginning ∼30 years prior to and peaking within 3 years of the eruption. This interaction did not directly trigger the eruption, but may have primed the magmatic system. Orthopyroxene crystals with the same zoning patterns from the Kidnappers and Rocky Hill pumices yield consistently different diffusion timescales, suggesting a time break between the eruptions of ∼20 years (from core-rim zones) to ∼10 years (outer rim zones). Diffusion of Ti in quartz reveals similarly short timescales and magmatic residence times of <30 years, suggesting quartz is only recording the last period of crystallization within the final eruptible melt. Accumulation of the eruptible magma for these two, closely successive eruptions was accomplished over centuries to decades, in contrast to the gestation time of the magmatic system of ∼200 kyr, as indicated by zircon age patterns. The magmatic system was able to recover after the Kidnappers eruption in only ∼10-20 years to accumulate enough eruptible melt and crystals for a second ∼ 200 km3 eruption. Our data support concepts of large silicic systems being stored as long-lived crystal mushes, with eruptible melts generated over extraordinarily short timescales prior to eruption.

Somma-Vesuvius Plinian Eruptions fed by mafic magma: insights from bubbles in melt inclusions

NASA Astrophysics Data System (ADS)

Esposito, R.; Redi, D.; Cannatelli, C.; Danyushevsky, L. V.; Lima, A.; Bodnar, R. J.; De Vivo, B.

2014-12-01

Mt. Somma-Vesuvius Plinian eruptions were first described by Pliny the younger in 79 AD during the infamous eruption that destroyed Pompeii. Today, such eruptions are still a concern to the nearly 3 million people living in the Naples metropolitan area. Understanding the source for Mt. Somma-Vesuvius magma and the coexisting volatile phase is vital to better constrain the long-term eruptive behavior of this volcano. In the present study, ~ 50 olivine phenocrysts were selected from lavas and pumices produced during mild effusive events referred to as inter-Plinian eruptions, and from highly explosive Plinian eruptions that occurred at Mt. Somma-Vesuvius between 33000 ka and 1631 AD. Selected olivine phenocrysts containing MI were examined petrographically and analyzed for Fo content. Fo varies from 69 to 73 mole% for inter-Plinian olivine crystals and from 84 to 90 mole% with one zoned olivine containing 76-81 mole% Fo, for Plinian olivine crystals. Investigated MI vary from slightly crystallized to highly crystallized. Selected crystallized MI were reheated using the Vernadsky stage, and quenched to a homogeneous glass (Group 1) or glass plus a vapor bubble (Group 2). On one hand, MI of Group 1 are hosted in olivine ranging from Fo72 to Fo76 and were all erupted from the Pompeii eruption (white pumice deposit). On the other hand, MI of Group 2 are trapped in olivine ranging from Fo69 to Fo81 and from Fo84 to Fo90, and the hosts are representative of both Plinian and inter-Plinian events. The only eruption where Group-1 and Group-2 MI coexist is the Pompeii eruption. Group 2 MIs were further analyzed by Raman to test for the presence of volatiles (CO2 or H2O) in the vapor bubbles. CO2 was detected in all MI analyzed. CO2 density was determined using the distance between the two Fermi-diad peaks, and ranges between 0.14 and 0.55 g/cm3. Six MI also showed evidence for H2O in the vapor bubble. In addition, carbonates were detected at the glass-vapor interface of five MI. This study shows that the CO2-rich fluid phase, which might exsolve from Plinian melts contain a significant amount of H2O. In addition, the first melting temperature of the fluids in the vapor bubble (~ -58ºC) suggests that volatile components, other than CO2, are included in the vapor bubbles.

Eruption and emplacement of a laterally extensive, crystal-rich, and pumice-free ignimbrite (the Cretaceous Kusandong Tuff, Korea)

NASA Astrophysics Data System (ADS)

Sohn, Y. K.; Son, M.; Jeong, J. O.; Jeon, Y. M.

2009-10-01

The Cretaceous Kusandong Tuff, Korea, is a thin (1-5 m thick) but laterally extensive (~ 200 km) silicic ignimbrite emplaced in a fluviolacustrine basin adjacent to a continental volcanic arc. The tuff has been used as an excellent key bed because of its great lateral continuity and unique lithology, characterized by the virtual absence of juvenile clasts and an abundance of quartz and feldspar crystals (up to 55-73 vol.%). The tuff is mostly massive and ungraded and locally shows crude internal layering, basal inverse grading and near-top normal grading of crystals, either erosional or non-erosional lower surfaces, and flat-lying to imbricated grain fabrics. Fragile intraformational clasts of mudstone and tuff are also included. These features provide only ambiguous information on the properties of the responsible pyroclastic density currents: i.e. whether they were dense and laminar or dilute and turbulent. The overall lateral continuity and sheet-like geometry of the tuff suggests, however, that the transport system of the currents was highly expanded, dilute, and turbulent. A plug-flow or slab-flow model cannot explain the origin of crude internal layering, imbricated grain fabrics, and the high crystal content, which is most likely the result of vigorous sorting processes within a dilute and turbulent current. Features indicative of deposition from a dense and laminar transporting medium are locally present, suggesting that a dense and laminar depositional system could develop locally at the base of the dilute and turbulent transport system. The virtual absence of juvenile clasts in the tuff is interpreted to be due to rapid ascent, sudden decompression, and full fragmentation of silicic magma into fine glass shards and crystals. Scarcity of basement-derived accidental components together with the absence of pumiceous fallout deposits beneath the tuff is interpreted to be due to shallow-level fragmentation of magma followed by immediate generation of pyroclastic density currents from shallow-level blasts at the onset of eruption. The eruption occurred through multiple vent sites in a short period of time, producing a seemingly single but actually composite ignimbrite unit. Such an eruption was probably possible because of a regional tectonic event within the basin or in its vicinity. It is proposed that a composite ignimbrite with the characteristics of the Kusandong Tuff can be an exemplary product of syntectonic volcanism that can provide an insight into the interpretation of structural and stratigraphic evolution of a sedimentary basin.

Dynamics of Conduit Flow and Fragmentation of Trachytic Versus Rhyolitic Eruptions

NASA Astrophysics Data System (ADS)

Papale, P.; Giordano, D.; del Seppia, D.; Romano, C.; Dingwell, D. B.

We have performed a systematic investigation of the dynamics of ascent and fragmen- tation of trachitic magmas from Phlegrean Fields, and have compared such dynamics with those of the more common and more thoroughly investigated rhyolitic eruptions. The investigation involved experimental as well as numerical studies. Knowledge of the viscosity of trachytic magmas is crucial, since viscosity is one of the most im- portant controlling factors in magma ascent dynamics. We have performed a series of measurements of the dry and hydrous viscosity of trachytic liquids representative of the glassy portion of pumice from the Campanian Ignimbrite, Agnano Monte Spina, and Monte Nuovo eruptions of Phlegrean Fields, spanning a time interval from 36,000 BP to 1538 AD, and an intensity range of about 4 orders of magnitude. The results show that for water contents larger than 1-2 wt% trachytic viscosities are within one order of magnitude less than rhyolitic viscosities. On the contrary, the calculated sol- ubility of water in trachytic liquids is significantly higher than in rhyolitic liquids. We have simulated the steady, multiphase flow of gas and liquid magma, or pyro- clasts above fragmentation, for trachytic and rhyolitic compositions, by parameteris- ing quantities like the total water content and the conduit size. All else being equal, the higher water solubility of trachytes and substantially similar liquid viscosity with respect to rhyolites yields a lower mixture viscosity and lower pressure gradient in the deep conduit region for the former magma type. This results in the achievement of fragmentation conditions, calculated as the condition at which the strain rate in magma becomes too large to be supported by viscous flow, which are hundreds to thousands of meters higher in the conduit for trachytes than for rhyolites. The fragmentation vesic- ularity of trachytes is also systematically larger than that of rhyolites, still remaining in the 0.6 U 0.85 range which is typical of pumice from magmatic eruptions through- out the world. In spite of such large differences in the internal conduit dynamics, the conduit exit conditions are remarkably similar for the two magma types (all other conditions being equal), according to the similar large scale features of rhyolitic and trachytic explosive eruptions. Finally, despite the lower magma viscosity of trachytes with respect to rhyolites, the delayed fragmentation and longer high-viscosity bubbly flow region of the former can result in larger overall mechanical energy dissipation by viscous forces, and lower mass flow rates for trachitic than for rhyolitic eruptions.

An experimental study of the fluid-melt partitioning of volatiles (H2O, CO2, S) during the degassing of ascending basalt

NASA Astrophysics Data System (ADS)

Le Gall, Nolwenn; Pichavant, Michel; Di Carlo, Ida; Scaillet, Bruno

2017-04-01

We performed decompression experiments to constrain the fluid-melt partitioning of volatiles (H2O, CO2, S) in ascending basalt magmas associated with violent eruptions. Experiments were conducted in an internally heated pressure vessel under oxidizing conditions (fO2: NNO+1.1) so that all sulphur occurs as sulfate (S6+) in the melt. Volatile-bearing (2.72 ± 0.02 wt% H2O, 1291 ± 85 ppm CO2, 1535 ± 369 ppm S) melts, prepared from Stromboli pumice, were synthesized at 1200°C and 200 MPa, decompressed between 150 and 25 MPa at constant rates of 39 and 78 kPa/s (or 1.5 and 3 m/s), and rapidly quenched. Run products were characterized both chemically (by IR spectroscopy and electron microprobe analysis) and texturally (by scanning electron microscopy), and then compared with Stromboli pumice products (glass inclusions, volcanic gases). In H2O-CO2-S-bearing basaltic melts, bubbles start to nucleate heterogeneously on Fe sulfides for supersaturation pressures ΔPHeN ≤ 1 MPa and to nucleate homogeneously for ΔPHoN < 50 MPa (ΔPHeN and ΔPHoN are the difference between the saturation pressure and the pressure at which heterogeneous and homogeneous bubble nucleation are observed, respectively). Bubble growth, coalescence and outgassing occur in addition to continuous bubble nucleation, which is sustained by the preservation of CO2 supersaturated melts during decompression. In addition to model the degassing behaviour of sulphur (and also of CO2 and H2O), our experiments aim to assist in the interpretation of geochemical observables. On the one hand, the volatile degassing trend recorded by Stromboli natural glasses (unsealed glass embayments) was closely experimentally simulated, with a coupled decrease of H2O and S whereas CO2 concentrations remain elevated. On the other hand, the experimental H2O/CO2 and CO2/SO2 fluid molar ratios, calculated by mass balance, both reproduced or closely approached the lower ranges of gas ratios measured at Stromboli for quiescent magma degassing and explosive activity. Compared to models that attribute a deep origin to CO2-rich fluxes and high CO2/SO2 gas ratios, our experimental observations support a model of low pressure (Pf << 25 MPa) explosive degassing of CO2-rich melts generated as a result of disequilibrium degassing to generate Strombolian paroxysms.

Preliminary report on the ground-water resources of the Klamath River basin, Oregon

USGS Publications Warehouse

Newcomb, Reuben Clair; Hart, D.H.

1958-01-01

The Klamath River basin, including the adjacent Lost River basin, includes about 5,500 square miles of plateaus, mountain-slopes and valley plains in south-central Oregon. The valley plains range in altitude from about 4,100 feet in the south to more than 4,500 feet at the northern end; the mountain and plateau lands rise to an average altitude of 6,000 feet at the drainage divide, some peaks rising above 9,000 feet. The western quarter of the basin is on the eastern slope of the Cascade Range and the remainder consists of plateaus, mountains, and valleys of the basin-and-range type. The rocks of the Klamath River basin range in age from Recent to Mesozoic. At the southwest side of the basin in Oregon, pre-Tertiary metamorphic, igneous, and sedimentary rocks, which form extensive areas farther west, are overlain by sedimentary rocks of Eocene age and volcanic rocks of Eocene and Oligocene age. These early Tertiary rocks dip east toward the central part of the Klamath River basin. The complex volcanic rocks of high Cascades include three units: the lowest unit consists of a sequence of basaltic lava flows about 800 feet thick; the medial unit is composed of volcanic-sedimentary and sedimentary rocksthe Yonna formation200 to 2,000 feet thick; the uppermost unit is a sequence of basaltic lava flows commonly about 200 feet thick. These rocks dip east from the Cascade Range and are the main bedrock formations beneath most of the basin. Extensive pumice deposits, which emanated from ancestral Mount Mazama, cover large areas in the northwestern part of the basin. The basin has an overall synclinal structure open to the south at the California boundary where it continues as the Klamath Lake basin in California. The older rocks dip into the basin in monoclinal fashion from the adjoining drainage basins. The rocks are broken along rudely rectangular nets of closely spaced normal faults, the most prominent set of which trends northwest. The network of fault displacements includes two main grabens, the Klamath and the Langell, which were downthrown approximately 50 and 1,000 feet, respectively. The average annual precipitation varies with the altitude, the higher parts of the Cascade Range getting more than 60 inches, and the semiarid valley plains receive as little as 13 inches in some places. Most precipitation occurs in the winter. The principal tributaries, Williamson and Sprague Rivers, rise near the higher parts of the eastern rim of the basin, flow through narrow valley plains to the western part, and discharge into Upper Klamath Lake. Wood River and associated creeks also empty into Upper Klamath Lake after draining southward along along the eastern foot of the Cascade Range. The Klamath River receives the outflow from Upper Klamath Lake, via Link River and Lake Ewauna, and flows southwestward through Keno Gap and hance through a youthful canyon, to its lower valley in California. The ground water occurs largely in an unconfined, or water-table, condition, though areas of local confinement are present. The regional water table is graded to a base level about equal to that of the major drainage on the valley plains. The slop of the water table, where water is confined, or the piezometric surface is downstream at about the same grade as that of the surface drainage in each of the larger valleys, and ground-water divides occur between the upper parts of adjacent major valleys. The principal water-bearing units are the lower lava rocks and upper lava rocks of the volcanic rocks of high Cascades, the pumice of Quaternary age, and the alluvium. In places layers of coarse fragmental material in the Yonna formation (Newcomb, 1958) also transmit water. The water-bearing units, especially the breccia layers of the lava rocks and the pumice, yield large amounts of water to wells and provide natural discharge outlets for the ground water. The spring outflows to the Williamson and Wood Rivers-Crooked Creek drainage, mea

Effects of a non-rinse conditioner on the enamel of primary teeth.

PubMed

Fava, Marcelo; Myaki, Silvio Issáo; Arana-Chavez, Victor Elias; Fava-de-Moraes, Flavio

2003-01-01

The aim of this in vitro study was to evaluate by scanning electron microscopy the morphological aspects of the enamel of primary teeth after etching with 36% phosphoric acid or a non-rinse conditioner. Ten naturally exfoliated anterior primary teeth were selected. The samples were subjected to prophylaxis with pumice paste and water using a low-speed hand piece. Etching was done on the buccal surface. Specimens were divided into 2 groups: G1 (n=10): etching with 36% phosphoric acid gel - Conditioner 36 (Dentsply) for 20 s, followed by water rinse for 15 s; G2 (n=10): etching with NRC - Non Rinse Conditioner (Dentsply) for 20 s, followed by air drying for 15 s. The samples were dehydrated, mounted on metal stubs, coated with gold and observed with Jeol JSM-6100 scanning electron microscope. Electron-micrographic analysis showed that both etching agents were effective for etching the enamel of primary teeth causing the formation of microporosities on the enamel surface, although the etching pattern was more effective with the use of 36% phosphoric acid gel.

Plaque, gingival bleeding and calculus formation after supragingival scaling with and without polishing: a randomised clinical trial.

PubMed

Zanatta, Fabricio Batistin; Pinto, Tatiana Militz; Kantorski, Karla Zanini; Rösing, Cassiano Kuchenbecker

2011-01-01

The aim of this study was to compare the effect of polishing after scaling and root planing on supragingival plaque, calculus formation, and gingival bleeding. The study was designed as a split-mouth randomised clinical trial. Seventy-six patients were submitted to supragingival scaling on the six mandibular anterior teeth with manual curettes until a smooth surface was achieved. Subsequently, quadrants were randomly selected to be polished (test) or not (control) with a rubber cup and pumice. One, two and three weeks following treatment, a blinded examiner evaluated the visible plaque index, gingival bleeding index and the presence of supragingival calculus on the lingual tooth surfaces. The results showed that unpolished surfaces exhibited higher mean percentages of visible plaque in the third week. No statistically significant differences were observed between unpolished and polished sites related to gingival bleeding. Calculus formation was higher on unpolished sites than on polished sites at 2 and 3 weeks. Dental polishing after supragingival scaling contributed to reducing plaque and calculus formation. Polishing exerts an inhibitory effect on plaque and calculus formation.

SAN JOAQUIN ROADLESS AREA, CALIFORNIA.

USGS Publications Warehouse

McKee, Edwin H.; Capstick, Donald O.

1984-01-01

The San Joaquin Roadless Area is composed of three noncontiguous areas on the eastern side of the Sierra Nevada in Madera County, California. The results of geologic, geochemical, and mining-activity and production surveys in the central part of the area indicate little promise for the occurrence of metallic-mineral or energy resources in the area. Sand, gravel, and pumice exist in the area but occurrences are small and isolated and farther from major markets than similar deposits outside the roadless area. Rocks in the area are exhibited in exposures of unaltered and nonmineralized granitic and metavolcanic rock along the steep western wall of the glacially carved valley of the Middle Fork of the San Joaquin River. Drainage in the area consists of seeps along fractures in the cliff or small cascading streams, a hydraulic setting not favorable for the development of placer deposits. No mines or prospect workings were found in the roadless area. Alteration zones within the granitic and metamorphic rock that crop out within the area are small, isolated, and consist only of limonitic staining and bleached quartzose rock.

Effects of sucrose amendment on ammonia assimilation during sewage sludge composting.

PubMed

Meng, Liqiang; Li, Weiguang; Zhang, Shumei; Wu, Chuandong; Wang, Ke

2016-06-01

The aim of this study was to evaluate the laboratory-scale composting of sewage sludge and pumice mixtures that were amended with sucrose. The variation in temperature, pH, NH4(+)-N, ammonia emission, bacterial community, ammonia assimilating bacteria (AAB) populations and enzymatic activity related to ammonia assimilation were detected. The addition of sucrose increased the AAB population by 2.5-3.5 times, reduced ammonia emission by 24.7-31.1% compared with the control treatment, and promoted the growth of Bacillus and Wautersiella. The activities of glutamate dehydrogenase (GDH), glutamate synthase (GS) and glutamine synthetase (GOGAT), were enhanced by the addition of sucrose. GDH made a substantial contribution to ammonia assimilation when the ammonia concentration was high (⩾1.5g/kg) in the thermophilic phase. The GS/GOGAT cycle played an important role at low ammonia concentrations (⩽1.1g/kg) in the cooling phase. These results suggested that adding sucrose to sludge compost could promote ammonia assimilation and reduce ammonia emission. Copyright © 2016 Elsevier Ltd. All rights reserved.

The Avellino 3780-yr-B.P. catastrophe as a worst-case scenario for a future eruption at Vesuvius

PubMed Central

Mastrolorenzo, Giuseppe; Petrone, Pierpaolo; Pappalardo, Lucia; Sheridan, Michael F.

2006-01-01

A volcanic catastrophe even more devastating than the famous anno Domini 79 Pompeii eruption occurred during the Old Bronze Age at Vesuvius. The 3780-yr-B.P. Avellino plinian eruption produced an early violent pumice fallout and a late pyroclastic surge sequence that covered the volcano surroundings as far as 25 km away, burying land and villages. Here we present the reconstruction of this prehistoric catastrophe and its impact on the Bronze Age culture in Campania, drawn from an interdisciplinary volcanological and archaeoanthropological study. Evidence shows that a sudden, en masse evacuation of thousands of people occurred at the beginning of the eruption, before the last destructive plinian column collapse. Most of the fugitives likely survived, but the desertification of the total habitat due to the huge eruption size caused a social–demographic collapse and the abandonment of the entire area for centuries. Because an event of this scale is capable of devastating a broad territory that includes the present metropolitan district of Naples, it should be considered as a reference for the worst eruptive scenario at Vesuvius. PMID:16537390

Mineralization of reactive azo dyes present in simulated textile waste water using down flow microaerophilic fixed film bioreactor.

PubMed

Balapure, Kshama; Bhatt, Nikhil; Madamwar, Datta

2015-01-01

The present research emphasizes on degradation of azo dyes from simulated textile wastewater using down flow microaerophilic fixed film reactor. Degradation of simulated textile wastewater (COD 7200mg/L and dye concentration 300mg/L) was studied in a microaerophilic fixed film reactor using pumice stone as a support material under varying hydraulic retention time (HRT) and organic loading rate (OLR). The intense metabolic activity of the inoculated bacterial consortium in the reactor led to 97.5% COD reduction and 99.5% decolorization of simulated wastewater operated under OLR of 7.2kgCODm(3)/d and 24h of HRT. FTIR, (1)H NMR and GC-MS studies revealed the formation of lower molecular weight aliphatic compounds under 24h of HRT, leading to complete mineralization of simulated wastewater. The detection of oxido-reductive enzyme activities suggested the enzymatic reduction of azo bonds prior to mineralization. Toxicity studies indicated that microbial treatment favors detoxification of simulated wastewater. Copyright © 2014 Elsevier Ltd. All rights reserved.

Ustica Island (Tyrrhenian Sea, Italy): from shoaling to emergent stage

NASA Astrophysics Data System (ADS)

Marinoni, L. B.; Pasquaré, G.; Vezzoli, L.

2003-04-01

Ustica is a volcanic island located in the southern Tyrrhenian sea, ~60 km NW of Sicily. As usual for volcanic ocean islands, its exposed part (8.6 km2, 248 m max elevation, mostly of Pleistocene age), is a small fraction of the whole edifice which rises from ~2000 m depth. Its 5-pointed-star shape is slightly elongated in a NE direction. A new geological field survey was carried out at scale 1:10000 and locally at 1:2000, establishing informal stratigraphic units that on the whole fit a common scheme of evolution for volcanic ocean islands. In this framework, the whole pre-existing stratigraphy has been revised. Ustica has a variety of volcanic deposits from submarine (basaltic effusive to explosive) to subaereal (effusive, explosive and highly explosive -Plinian?). Moreover, Ustica is one of the few places in the world where a transition of deposits from shoaling to emergent stage crop out. In fact, its oldest deposits consist of: (a) a flank-facies association of submarine lavas (variably-shaped pillows, pillow breccias and hyaloclastites) with biocalcarenite-biocalcirudite lenses, dipping coastward in the E, S and W outer parts of the island; this association is arranged in steep foreset beds (lava deltas) and is capped by flat-lying transitional to subaereal massive lava flows and surf-shaped boulder conglomerates; the geometry of this association may suggest a progressive island uplift or sea lowering during this period; (b) shallow-water to emergent tuff cone deposits in the NW part of the island. In the centre of the island, subsequent activity built a pile, now deeply eroded, of subaereal basaltic lava flows capped by a scoria cone. A previously unknown outcrop where a pumice fall layer is exposed, allows a distinction into two members of a unit that was known as formed by pyroclastic surges only. Higher in the succession, the Ustica Pumice formation (for which 4 members are defined) is underlain by a palaeosoil, and is likely the remnant of a caldera-forming eruption, which possibly dismantled the northern part of the island. It may be suggested that a later flank collapse affected the W side of the island, exposing seamount-stage deposits and allowing small fissural eruptions. The northern part of the island was then rebuilt by hydro-magmatic littoral deposits, subaereal aa flows, and thick columnar lava flows. At the NE corner of the island, a littoral tuff cone (the only cone of the island which is roughly preserved in its original shape) gave the last volcanic activity in Ustica. Acknowledgement: LBM benefited of a grant from Milan University under the supervision of Prof. G.Pasquaré in the framework of a joint venture with SGN.

Topographic controls on pyroclastic density current dynamics: Insight from 18 May 1980 deposits at Mount St. Helens, Washington (USA)

NASA Astrophysics Data System (ADS)

Brand, Brittany D.; Bendaña, Sylvana; Self, Stephen; Pollock, Nicholas

2016-07-01

Our ability to interpret the deposits of pyroclastic density currents (PDCs) is critical for understanding the transport and depositional processes that control PDC dynamics. This paper focuses on the influence of slope on flow dynamics and criticality as recorded in PDC deposits from the 18 May 1980 eruption of Mt. St. Helens (USA). PDC deposits are found along the steep flanks (10°-30°) and across the pumice plain ( 5°) up to 8 km north of the volcano. Granulometry, componentry and descriptions of depositional characteristics (e.g., bedform morphology) are recorded with distance from source. The pumice plain deposits are primarily thick (3-12 m), massive and poorly-sorted, and represent deposition from a series of concentrated PDCs. By contrast, the steep flank deposits are stratified to cross-stratified, suggesting deposition from PDCs where turbulence strongly influenced transport and depositional processes. We propose that acceleration of the concentrated PDCs along the steep flanks resulted in thinning of the concentrated, basal region of the current(s). Enhanced entrainment of ambient air, and autofluidization from upward fluxes of air from substrate interstices and plunging breakers across rugged, irregular topography further inflated the currents to the point that the overriding turbulent region strongly influenced transport and depositional mechanisms. Acceleration in combination with partial confinement in slot canyons and high surface roughness would also increase basal shear stress, further promoting shear and traction transport in the basal region of the current. Conditions along the steep flank resulted in supercritical flow, as recorded by regressive bedforms, which gradually transitioned to subcritical flow downstream as the concentrated basal region thickness increased as a function of decreasing slope and flow energy. We also find that (1) PDCs were erosive into the underlying granular substrate along high slopes (> 25°) where currents were partially confined in steep slot canyons, suggesting that basal shear stress is an important control on erosive capacity, and (2) bedform amplitude, wavelength and the presence of regressive bedforms increase with increasing slope and proximity to source along the steep flank, suggesting a link between bedform morphology, flow velocity, and flow criticality. While our results indicate that slope and irregular topography strongly influence PDC dynamics, criticality and erosive capacity, the influence of these conditions on ultimate flow runout distance is unclear. The work here also highlights the issue that relationships between the controls on bedform size and morphology in density stratified flows remain poorly constrained, limiting our ability to extract important information about the currents that produced them. These final two points warrant further exploration through the combination of field, experimental and numerical approaches.

The VEI-7 Millennium eruption, Changbaishan-Tianchi volcano, China/DPRK: New field, petrological, and chemical constraints on stratigraphy, volcanology, and magma dynamics

NASA Astrophysics Data System (ADS)

Pan, Bo; de Silva, Shanaka L.; Xu, Jiandong; Chen, Zhengquan; Miggins, Daniel P.; Wei, Haiquan

2017-09-01

Field relations, petrography, bulk and micro-scale chemistry reveal that the most recent history of hazardous Changbaishan-Tianchi volcano should be revised with important implications for volcanic hazard in NE Asia. Currently, the two most recent large eruptions are identified separately as a VEI 5 trachytic Baguamiao eruption (BGM) and the much heralded VEI 7, late 946 CE (Common Era) "Millennium" eruption (ME) of comendite. However, we find that the former is part of the latter based on the following evidence: (1) trachytic fallout of the BGM lies directly on the comendite tephra of the ME without any indication of depositional hiatus; (2) abundant mingled trachyte-comendite pumice in the tephra deposits; (3) similar chemistry of mingled pumice and its components to those in the BGM and ME products; (4) correlation of bimodal glass shard compositions in the distal 'B-Tm' ash from the Japan Sea with comendite and trachyte glass from the BGM and ME products. Based on the above evidence, we suggest that the great Millennium eruption of 946 CE should be revised finally to include the BGM trachyte as its final stage. Furthermore, deposits attributed to two other trachytic eruptions in 1668 and/or 1702 CE (also called Baguamiao by some authors), and 1903 CE referred to in historic accounts were also examined. Our field observations, petrography, bulk and micro-scale chemistry combined with previously published Ra/Th ages indicate that all these trachytes are either primary deposits of the ME or its reworked deposits. Thus our findings do not support two separate post-ME eruptions and require that volcanic hazard assessment at Changbaishan volcano include this new interpretation. Recently published geochronological data integrated with our new petrochemical and volcanological framework informs the magma dynamics leading to the ME. The ME comendite, derived from a parental trachyte similar to the BGM started accumulating at shallow levels around 12 ka to 8 ka. Around 4 to 1.6 ka the BGM trachyte sensu strictu separated from its basaltic parent and started accumulating and crystallizing separately from the ME comendite. Just prior to the ME eruption, mingling of trace amounts of a third more mafic hybrid is implicated by the composition of mafic glass selvedges. The strong evidence for mixing of all these endmembers in the eruption products suggests that recharge mixing and overturn of this predominantly comendite-trachyte system occurred during the 1 ka ME. The common occurrence of comendite and trachyte in the last 100 ka (also maybe 1 Ma) at Changbaishan-Tianchi suggests that conditions for trachyte-comendite magma interactions are prevalent in the magma system of Changbaishan and maybe crucial in catastrophic eruptions there.

Tropical cyclone Pam field survey in Vanuatu

NASA Astrophysics Data System (ADS)

Fritz, Hermann M.; Pilarczyk, Jessica E.; Kosciuch, Thomas; Hong, Isabel; Rarai, Allan; Harrison, Morris J.; Jockley, Fred R.; Horton, Benjamin P.

2016-04-01

Severe tropical cyclone Pam (Cat. 5, SSHS) crossed the Vanuatu archipelago with sustained winds of 270 km/h on March 13 and 14, 2015 and made landfall on Erromango. Pam is the most intense tropical cyclone to make landfall on Vanuatu since the advent of satellite imagery based intensity estimates in the 1970s. Pam caused one of the worst natural disaster in Vanuatu's recorded history. Eleven fatalities were directly attributed to cyclone Pam and mostly due to lack of shelter from airborne debris. On March 6 Pam formed east of the Santa Cruz Islands causing coastal inundation on Tuvalu's Vaitupu Island located some 1100 km east of the cyclone center. Pam intensified while tracking southward along Vanuatu severely affecting the Shefa and Tafea Provinces. An international storm surge reconnaissance team was deployed to Vanuatu from June 3 to 17, 2015 to complement earlier local surveys. Cyclone Pam struck a remote island archipelago particularly vulnerable to the combined cyclonic multi-hazards encompassing extreme wind gusts, massive rainfall and coastal flooding due to a combination of storm surge and storm wave impacts. The team surveyed coastal villages on Epi, the Shepherd Islands (Tongoa and Mataso), Efate (including Lelepa), Erromango, and Tanna. The survey spanned 320 km parallel to the cyclone track between Epi and Tanna encompassing more than 45 sites including the hardest hit settlements. Coastal flooding profiles were surveyed from the shoreline to the limit of inundation. Maximum coastal flood elevations and overland flow depths were measured based on water marks on buildings, scars on trees, rafted debris and corroborated with eyewitness accounts. We surveyed 91 high water marks with characteristic coastal flood levels in the 3 to 7 m range and composed of storm surge with superimposed storm waves. Inundation distances were mostly limited to a few hundred meters but reached 800 m on Epi Island. Wrack lines containing pumice perfectly delineated the inundation at many sites and were mapped as line features. Coral boulders of more than 1 m diameter were measured on Erromango. Along each island that was sampled, Cyclone Pam deposited a 1 - 20 cm thick sedimentary layer consisting of foraminfera-bearing sand and pumice cobbles. Infrastructure damage on traditional and modern structures was assessed. Eyewitnesses were interviewed at most sites to document the chronology of the wind and coastal flooding events, survival strategies, cyclone and tsunami awareness, evacuation procedures, shelter locations and ancestral knowledge. Field observations were compared with surveyed eyewitness accounts of historic events such as severe tropical cyclone Uma in 1987. The measured cyclone Pam high water marks will facilitate the interpretation of the collected sedimentary evidence and serve as benchmarks for modeling studies.

Geology of proximal, small-volume trachyte-trachyandesite pyroclastic flows and associated surge deposits, Roccamonfina volcano, Italy

NASA Astrophysics Data System (ADS)

Giannetti, Bernardino

1998-01-01

This paper describes the 232 ka B.P. MTTT trachyte-trachyandesite pyroclastic succession of Roccamonfina volcano. This small-volume, proximal sequence crops out along Mulino di Sotto, Paratone, and Pisciariello ravines in the southwest sector of the central caldera, and covers a minimum extent of 3.5 km 2 area. It is made up of seven pyroclastic flows and pyroclastic surge units consisting of trachytic ash matrix containing juvenile trachyandesitic scoria and dense lava fragments, pumice clasts of uncertain trachyandesite, and a foreign trachyandesitic lithic facies. Two stratigraphic markers allow correlation of the units. No paleosoils and Plinian fallout have been observed at the base and within the succession. Some lateral grading of scoria and lithic clasts suggests that MTTT derived from three distinct source vents. The sequence consists of a basal ash flow passing laterally to laminated surge deposits (Unit A). This is overlain by a reversely graded scoria and pumice lapilli flow (Unit B) which is in turn overlain by a thinly cross-stratified scoria lapilli surge (Unit C). Unit C is capped by a prominent ash-and-scoria flow (Unit D). A ground layer (Marker MK1) divides Unit D from a massive ignimbrite which grades upcurrent to sand-wave surge deposits (Unit E). Another ground layer (Marker MK2) separates Unit E from Unit F. This unit consists of a basal ignimbrite passing laterally to bedded surge deposits with convolute structures (subunit Fl), and grading upcurrent to a subhorizontally plane-laminated ash cloud (subunit F2) containing near the top a layer of millimetric lithic clasts embedded in fine ash. The succession is closed by the pyroclastic flow Unit G. Surge Unit C can be interpreted in terms of vertical gradients in turbulence, particle concentration, and velocity during flowage, whereas the bedded surge parts present in the massive deposits of Units A and E-F1 can be related to abrupt changes of velocity down the steep slopes of ravines. Reverse grading in Unit B is probably due to grain dispersive pressures. The convolute structures within Fl are related to zones of diagenetic cementation associated with groundwater. Finally, the laminated, fine-grained nature of subunit F2 is interpreted as due to ash clouds elutriated from the basal part of Unit F. Stratigraphic markers MK1-MK2 are ground layer breccias formed by settling of lithic and scoria clasts from overlying units E and F, respectively. Vesiculation and morphologies of glass shards of the MTTT succession suggest that eruptions were essentially driven by magmatic explosions which had an appreciable hydromagmatic component.

Two coarse pyroclastic flow deposits, northern Mono-Inyo Craters, CA

NASA Astrophysics Data System (ADS)

Dennen, R. L.; Bursik, M. I.; Stokes, P. J.; Lagamba, M.; Fontanella, N.; Hintz, A. R.; Jayko, A. S.

2010-12-01

The ~1350 A.D., rhyolitic North Mono eruption, Mono-Inyo Craters, CA, included the extrusion and destruction of Panum Dome and associated clastic deposits. Overlying the tephras of the North Mono sequence, the Panum deposits include a block-and-ash flow (BAF) deposit, covering ~3.5 km2. Blocks within the deposit are typically lithic rhyolite and banded gray micro-vesicular glass, showing white, almost powdery marks ranging from circular to linear in shape. These marks are interpreted as friction marks resulting from collisions between clasts. The deposit also contains bread-crusted obsidians with pressed-in clasts as well as reticulite with a bread-crusted surface texture. Near the centerline of the deposit is a ridge-topping train of jigsaw fractured blocks, often with reddish-orange alteration. One house sized jigsaw block sits upstream of a long, thinning pile of reddish orange debris; this “flow shadow” indicates that the block remained relatively stationary while the block and ash flow continued to propagate around it. The bread-crusted reticulite is most common at proximal localities. It is proposed that the dome destruction included a debris avalanche emplacing the train of jigsaw fractured blocks and creating a topographic high, the block-and-ash flow (the farthest reaching deposit from this event) which flowed around the debris avalanche deposits, and a final “lateral expansion” of a magma foam, creating the reticulite seen concentrated at proximal locations. Another coarse pyroclastic flow (here termed the “lower blast deposit”) underlies the North Mono tephra. It is more obsidian rich and finer grained than the Panum BAF. The lower blast deposit may have originated from Pumice Pit vent, which is now capped with an older dome ~0.5 km southeast of Panum. The lower blast deposit extends farther from the Panum vent than does the Panum BAF deposit, and apparently was mistaken for the Panum BAF deposit by previous workers. Hence the run-out distance of the Panum BAF is smaller than previously reported. Thus, there are multiple, coarse pyroclastic flow-like deposits at the northern end of the Mono-Inyo Craters, reflecting multiple phases of dome destruction. The lower blast deposit is proposed to be a blast event predating the Panum eruption, possibly originating from Pumice Pit. The Panum BAF consists of three main facies, formed by three separate, sequential events. A debris avalanche deposited a train of jigsaw clasts along a narrow path, followed by a block and ash flow that spread material over a wider region. Finally, molten rhyolite was exposed by the earlier events, resulting in rapid foam expansion and creation of a bread crusted reticulite-bearing facies.

The origin of a coarse lithic breccia in the 34 ka caldera-forming Sounkyo eruption, Taisetsu volcano group, central Hokkaido, Japan

NASA Astrophysics Data System (ADS)

Yasuda, Y.; Suzuki-Kamata, K.

2018-05-01

The 34 ka Sounkyo eruption produced 7.6 km3 of tephra ( 5 km3 DRE) as fallout, ignimbrite, and lithic breccia units, forming a small, 2-km-diameter summit caldera in the Taisetsu volcano group, Japan. The Sounkyo eruption products are made up of five eruptive units (SK-A to -E) in proximal regions, corresponding to the distal deposits, a 1- to 2-m-thick pumice fallout and the Px-type ignimbrite up to 220 m thick. The eruption began with a fallout phase, producing unstable low eruption columns during the earlier phase to form a <7-m-thick succession of well-stratified fallouts (SK-A1 and the lower part of the distal fallout). The eruption column reached up to 25 km high (subplinian to plinian) and became more stable at the late of the phase, producing a < 60-m-thick, pumice-dominated fallout (SK-A2 and the upper part of the distal fallout). The second phase, the climax of the Sounkyo eruption, produced a widespread, valley-filling ignimbrite in both proximal and distal regions (SK-B and the Px-type ignimbrite). At the end of the climactic phase, the waning of the eruption led to extensive failure of the walls of the shallow conduit, generating a dense, lithic-rich, low-mobile pyroclastic density current (PDC) to form a >27-m-thick, unstratified and ungraded, coarse lithic breccia (SK-C). The failure in turn choked the conduit, and then the eruption stopped. After a short eruptive hiatus, the eruption resumed with a short-lived fall phase, establishing an eruption column up to 16 km high and producing a <6-m-thick scoria fallout (SK-D). Finally, the eruption ended with the generation of PDCs by eruption column collapse to form a 5- to 15-m-thick ignimbrite in the proximal area (SK-E). Volume relationships between the caldera, ejected magma, and ejected lithic fragments suggest that the caldera was not essentially formed by caldera collapse but, instead, by vent widening as a consequence of explosive erosion and failure of the shallow conduit. The dominance of shallow-origin volcanic rocks in the lithic fraction throughout the Sounkyo eruption products implies the development of a flaring funnel-shaped vent. Hence, the occurrence of lithic breccias within small caldera-forming eruption products does not necessarily reflect either the existence or the timing of caldera collapse, as commonly assumed in literature. Lithic breccias commonly overlie climactic ignimbrite/fallout deposits in small caldera-forming eruptions, and an alternative explanation is that this reflects the collapse of the shallow conduit after an eruption climax, whose walls had been highly fractured and had become unstable owing to progressive erosion.

Complex proximal deposition during the Plinian eruptions of 1912 at Novarupta, Alaska

USGS Publications Warehouse

Houghton, Bruce F.; Wilson, C.J.N.; Fierstein, J.; Hildreth, W.

2004-01-01

Proximal (<3 km) deposits from episodes II and III of the 60-h-long Novarupta 1912 eruption exhibit a very complex stratigraphy, the result of at least four transport regimes and diverse depositional mechanisms. They contrast with the relatively simple stratigraphy (and inferred emplacement mechanisms) for the previously documented, better known, medial-distal fall deposits and the Valley of Ten Thousand Smokes ignimbrite. The proximal products include alternations and mixtures of both locally and regionally dispersed fall ejecta, and numerous thin complex deposits of pyroclastic density currents (PDCs) with no regional analogs. The locally dispersed component of the fall deposits forms sector-confined wedges of material whose thicknesses halve radially from and concentrically about the vent over distances of 100-300 m (cf. several kilometers for the medial-distal fall deposits). This locally dispersed fall material (and many of the associated PDC deposits) is rich in andesitic and banded pumices and richer in shallow-derived wall-rock lithics in comparison with the coeval medial fall units of almost entirely dacitic composition. There are no marked contrasts in grain size in the near-vent deposits, however, between locally and widely dispersed beds, and all samples of the proximal fall deposits plot as a simple continuation of grain size trends for medial-distal samples. Associated PDC deposits form a spectrum of facies from fines-poor, avalanched beds through thin-bedded, landscape-mantling beds to channelized lobes of pumice-block-rich ignimbrite. The origins of the Novarupta near-vent deposits are considered within a spectrum of four transport regimes: (1) sustained buoyant plume, (2) fountaining with co-current flow, (3) fountaining with counter-current flow, and (4) direct lateral ejection. The Novarupta deposits suggest a model where buoyant, stable, regime-1 plumes characterized most of episodes II and III, but were accompanied by transient and variable partitioning of clasts into the other three regimes. Only one short period of vent blockage and cessation of the Plinian plume occurred, separating episodes II and III, which was followed by a single PDC interpreted as an overpressured "blast" involving direct lateral ejection. In contrast, regimes 2 and 3 were reflected by spasmodic sedimentation from the margins of the jet and perhaps lower plume, which were being strongly affected by short-lived instabilities. These instabilities in turn are inferred to be associated with heterogeneities in the mixture of gas and pyroclasts emerging from the vent. Of the parameters that control explosive eruptive behavior, only such sudden and asymmetrical changes in the particle concentration could operate on time scales sufficiently short to explain the rapid changes in the proximal 1912 products. ?? Springer-Verlag 2003.

Review of eruptive activity at Tianchi volcano, Changbaishan, northeast China: implications for possible future eruptions

NASA Astrophysics Data System (ADS)

Wei, Haiquan; Liu, Guoming; Gill, James

2013-04-01

One of the largest explosive eruptions in the past several thousand years occurred at Tianchi volcano, also known as Changbaishan, on the China-North Korea border. This historically active polygenetic central volcano consists of three parts: a lower basaltic shield, an upper trachytic composite cone, and young comendite ash flows. The Millennium Eruption occurred between 938 and 946 ad, and was preceded by two smaller and chemically different rhyolitic pumice deposits. There has been at least one additional, small eruption in the last three centuries. From 2002 to 2005, seismicity, deformation, and the helium and hydrogen gas contents of spring waters all increased markedly, causing regional concern. We attribute this event to magma recharge or volatile exhalation or both at depth, followed by two episodes of addition of magmatic fluids into the overlying aquifer without a phreatic eruption. The estimated present magma accumulation rate is too low by itself to account for the 2002-2005 unrest. The most serious volcanic hazards are ash eruption and flows, and lahars. The available geological information and volcano monitoring data provide a baseline for comprehensive assessment of future episodes of unrest and possible eruptive activity.

Young cumulate complex beneath Veniaminof caldera, Aleutian arc, dated by zircon in erupted plutonic blocks

USGS Publications Warehouse

Bacon, C.R.; Sison, T.W.; Mazdab, F.K.

2007-01-01

Mount Veniaminof volcano, Alaska Peninsula, provides an opportunity to relate Quaternary volcanic rocks to a coeval intrusive complex. Veniaminof erupted tholeiitic basalt through dacite in the past ???260 k.y. Gabbro, diorite, and miarolitic granodiorite blocks, ejected 3700 14C yr B.P. in the most recent caldera-forming eruption, are fragments of a shallow intrusive complex of cumulate mush and segregated vapor-saturated residual melts. Sensitive high-resolution ion microprobe (SHRIMP) analyses define 238U-230Th isochron ages of 17.6 ?? 2.7 ka, 5+11/-10 ka, and 10.2 ?? 4.0 ka (2??) for zircon in two granodiorites and a diorite, respectively. Sparse zircons from two gabbros give 238-230Th model ages of 36 ?? 8 ka and 26 ?? 7 ka. Zircons from granodiorite and diorite crystallized in the presence of late magmatic aqueous fluid. Although historic eruptions have been weakly explosive Strombolian fountaining and small lava effusions, the young ages of plutonic blocks, as well as late Holocene dacite pumice, are evidence that the intrusive complex remains active and that evolved magmas can segregate at shallow levels to fuel explosive eruptions. ?? 2007 The Geological Society of America.

Assessment of porous material anisotropy and its effect on gas permeability

NASA Astrophysics Data System (ADS)

Wałowski, Grzegorz

2017-10-01

The results of experimental research upon the assessment of porous material anisotropy and its effect on gas permeability of porous materials with respect to the gas flow. The conducted research applied to natural materials with an anisotropic gap-porous structure and - for comparative purposes - to model materials such as coke, pumice and polyamide agglomerates. The research was conducted with the use of a special test stand that enables measuring the gas permeability with respect to three flow orientations compared with symmetric cubic-shaped samples. The research results show an explicit impact of the flow direction on the permeability of materials porous, which results from their anisotropic internal structures. The anisotropy coefficient and permeability effective coefficient of such materials was determined and an experimental evaluation of the value of this coefficient was conducted with respect to the gas stream and the total pressure drop across the porous deposit. The process of gas permeability was considered in the category of hydrodynamics of gas flow through porous deposits. It is important to broaden the knowledge of gas hydrodynamics assessment in porous media so far unrecognised for the development of a new generation of clean energy sources, especially in the context of biogas or raw gas production.

Soil and Crop management: Lessons from the laboratory biosphere 2002-2004

NASA Astrophysics Data System (ADS)

Silverstone, S.; Nelson, M.; Alling, A.; Allen, J.

During the years 2002 and 2003, three closed system experiments were carried out in the "Laboratory Biosphere" facility located in Santa Fe, New Mexico. The program involved experimentation with "Hoyt" Soy Beans, USU Apogee Wheat and TU-82-155 sweet potato using a 5.37 m2 soil planting bed which was 30 cm deep. The soil texture, 40% clay, 31% sand and 28% silt (a clay loam), was collected from an organic farm in New Mexico to avoid chemical residues. Soil management practices involved minimal tillage, mulching and returning crop residues to the soil after each experiment. Between experiment #2 and #3, the top 15 cm of the soil was amended using a mix of peat moss, green sand, humates and pumice to improve soil texture, lower soil pH and increase nutrient availability. Soil analyses for all three experiments are presented to show how the soils have changed with time and how the changes relate to crop selection and rotation, soil selection and management, water management and pest control. The experience and information gained from these experiments are being applied to the future design of the Mars On Earth facility.

Stratigraphic relationships and timing of the 2012 Havre submarine silicic volcanic eruption revealed by high resolution bathymetric mapping and observations by underwater vehicles.

NASA Astrophysics Data System (ADS)

Carey, R.; Soule, S. A.; Houghton, B. F.; White, J. D. L.; Manga, M.; Wysoczanski, R. J.; Tani, K.; McPhie, J.; Fornari, D. J.; Jutzeler, M.; Caratori Tontini, F.; Ikegami, F.; Jones, M.; Murch, A.; Fauria, K.; Mitchell, S. J.; Cahalan, R. C.; Conway, C.; McKenzie, W.

2015-12-01

The 2012 deep rhyolitic caldera eruption of Havre volcano in the Kermadec arc is the first historic observed submarine eruption that produced a pumice raft observed at the ocean's surface. Ship-based bathymetric surveys before and after the eruption permit the intricacies of eruption styles, products and timescales to be quantified. In 2015 we mapped this submarine volcano in unprecedented detail with two submergence vehicles in tandem, facilitating a wide and comprehensive geological survey and sampling mission. These efforts and observations show highly complex and often simultaneous eruptive behavior from more than 14 vents along two 3 km-long fissures that represent massive ruptures of the caldera walls. This survey also revealed an important role for pre- and inter-eruptive periods of mass wasting processes derived from the intrusion of magma and destablisation of caldera walls. The detailed characterization of the eruption products, and quantification of timescales provides the scientific community with the first glimpse of the nature of submarine, intermediate magnitude, deep silicic caldera eruptions and permits unanswered yet first order fundamental questions of submarine eruption and transport processes to be addressed in the decades to come.

Confirmation of a late middle Pleistocene age for the Omo Kibish 1 cranium by direct uranium-series dating.

PubMed

Aubert, Maxime; Pike, Alistair W G; Stringer, Chris; Bartsiokas, Antonis; Kinsley, Les; Eggins, Stephen; Day, Michael; Grün, Rainer

2012-11-01

While it is generally accepted that modern humans evolved in Africa, the specific physical evidence for that origin remains disputed. The modern-looking Omo 1 skeleton, discovered in the Kibish region of Ethiopia in 1967, was controversially dated at ~130 ka (thousands of years ago) by U-series dating on associated Mollusca, and it was not until 2005 that Ar-Ar dating on associated feldspar crystals in pumice clasts provided evidence for an even older age of ~195 ka. However, questions continue to be raised about the age and stratigraphic position of this crucial fossil specimen. Here we present direct U-series determinations on the Omo 1 cranium. In spite of significant methodological complications, which are discussed in detail, the results indicate that the human remains do not belong to a later intrusive burial and are the earliest representative of anatomically modern humans. Given the more archaic morphology shown by the apparently contemporaneous Omo 2 calvaria, we suggest that direct U-series dating is applied to this fossil as well, to confirm its age in relation to Omo 1. Copyright © 2012 Elsevier Ltd. All rights reserved.

Practice of Sealants and Preventive Resin Restorations Among Malaysian Dentists.

PubMed

Chin, Zhe W; Chong, Wai S; Mani, Shani A

2016-01-01

To assess the knowledge, attitude and utilisation regarding fissure sealants (FS) and preventive resin restorations (PRR) among Malaysian dentists. A questionnaire consisting of 35 questions was distributed by mail or an online survey to 425 registered dentists selected according to place of work by stratified random sampling. One hundred fifty-three dentists responded to the survey. A positive attitude towards FS and PRR was noted among most Malaysian dentists. About half of the respondents used FS/PRR occasionally (48.4%), while few (13.7%) applied them routinely. The majority of the dentists agreed that minimally invasive dentistry is important and FS are effective in caries prevention, using them on high caries-risk individuals. Most of the dentists used pumice or paste to clean teeth before placing FS/PRR. A significant number of dentists used a bonding agent prior to placing FS. Although only 57.5% dentists were aware of guidelines for FS use, most dentists agreed that guidelines are important. Although there was a positive attitude towards FS/PRR, few dentists applied them routinely. Some of the steps undertaken for placement of FS and PRR were outdated. Updating local guidelines for dentists to ensure uniform practice of FS and PRR is justified.

Magnetic grain-size variations through an ash flow sheet: influence on magnetic properties and implications for cooling history

USGS Publications Warehouse

Rosenbaum, J.G.

1993-01-01

Rock magnetic studies of tuffs are essential to the interpretation of paleomagnetic data derived from such rocks, provide a basis for interpretation of aeromagnetic data over volcanic terranes, and yield insights into the depositional and cooling histories of ash flow sheets. A rhyolitic ash flow sheet, the Miocene-aged Tiva Canyon Member of the Paintbrush Tuff, contains both titanomagnetite phenocrysts, present in the magma prior to eruption, and cubic Fe-oxide microcrystals that grew after emplacement. Systematic variations in the quantity and magnetic grain size of the microcrystals produce large variations in magnetic properties through a section of the ash flow sheet penetrated in a borehole on the Nevada Test Site. Microcrystals are important contributors to remanent magnetization and magnetic susceptibility in two 15-m-thick zones at the top and bottom. Within these zones the size of microcrystals decreases both toward the quenched margins and toward the interior of the sheet. The decrease in microcrystal size toward the interior of the sheet is interpreted to indicate the presence of a cooling break; possibly represented by a concentration of pumice. -from Author

Reestablishment of endogonaceae on Mount St. Helens: survival of residuals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allen, M.F.; MacMahon, J.A.; Andersen, D.C.

1984-01-01

The 18 May 1980 eruption of Mount St. Helens resulted in the burial of relatively well developed soils under variable depths of sterile tephra and ash. During summer 1982, we examined a series of sites and estimated the numbers of spores of Endogonaceae that had been transported from the buried soil to the new ground surface by either abiotic or biotic vectors. There was no difference between spore counts of Endogone spp. or Glomus spp. in the buried soils of forests and clear-cuts; spores were rare in the tephra at any site. In areas featuring less than or equal tomore » 50 cm of tephra, spores were transported to the surface by gophers (in previous clear-cut areas) and by ants (in previous forest and clear-cut habitats). In the Pumice Plain, an area devoid of gophers and ants, erosion exposed spores to the surface. We found no evidence to suggest that endogonaceous fungi grow back up root systems from buried horizons. We hypothesize that small-scale perturbations (erosion, gopher and ant mounds) following the major volcanic disturbance may drive succession by exposing buried mycorrhizal and decomposer fungi. 26 references, 2 figures, 3 tables.« less

Building of tropical beach ridges, northeastern Queensland, Australia: Cyclone inundation and aeolian decoration

NASA Astrophysics Data System (ADS)

Tamura, Toru; Nicholas, William; Brooke, Brendan; Oliver, Thomas

2016-04-01

Processes associated with tropical cyclones are thought responsible for building coarse sand beach ridges along the northeastern Queensland coast, Australia. While these ridges are expected to be geological records of the past cyclone, they question the general consensus of the aeolian genesis of sandy beach ridges. To explore the ridge-forming process, we carried out the GPR survey, auger drilling, pit excavation, grain-size analysis, and OSL dating for coarse sand beach ridges at the Cowley Beach, northeastern Queensland. The Cowley Beach is a mesotidal beach characterized by a low-tide terrace and steep beach face. Ten beach ridges are recognized along the survey transect that extends 700 m inland from the shore. 37 OSL ages are younger seawards, indicating the seaward accretion of the ridge sequence over the last 2700 years. The highest ridge is +5.1 m high above AHD (Australian Height Datum). Two GPR units are bounded by a groundwater surface at c. +1.5 m AHD. The upper unit is characterized by horizontal to hummocky reflectors punctuated by seaward dipping truncation surfaces. These reflectors in places form dome-like structure that appears to be the nucleus of a beach ridge. The shape and level (+2.5 m AHD) of the dome are similar to those of the present swash berm. The lower unit shows a sequence of reflectors that dip at an angle of present beach face. The sequence is dissected by truncation surfaces, some of which are continuous to those in the upper unit. Coarse sand mainly forms beach ridge deposits below +4.0 m AHD, while a few higher ridges have an upward fining layer composed of medium sand above +4.0 m, which is finer than aeolian ripples found on the backshore during the survey. In addition, pumice gravel horizons underlie the examined ridge crests. The sequence of seaward dipping reflectors indicates that the Cowley Beach, like other many sandy beaches, has prograded during onshore sand accretion by fairweather waves and has been eroded by storms waves. It is evident that increased water level and high waves associated with tropical cyclones are responsible for ridge building between +2.5 and +4.0 m AHD. However, astronomical tide should be critical rather than rare, intense cyclones for frequent coastal inundations up to +4.0 m AHD, just 1.5 m higher than the high-tide swash limit. The medium-grained sand layer on a few beach ridges higher than +4.0 m AHD can be accounted for by aeolian origin, but pumice gravels indicate the contribution of cyclone inundation. The building process of the ridges at Cowley Beach is thus most likely a mixture of fairweather swash and cyclone inundation modulated by tides, and aeolian processes during cyclonic and non-cyclonic conditions. For the reconstruction of the past cyclone based on these ridges, the roles of higher astronomical tides and aeolian processes should be taken into account.

Oxygen isotope study of the Long Valley magma system, California: isotope thermometry and convection in large silicic magma bodies

NASA Astrophysics Data System (ADS)

Bindeman, Ilya; Valley, John

2002-07-01

Products of voluminous pyroclastic eruptions with eruptive draw-down of several kilometers provide a snap-shot view of batholith-scale magma chambers, and quench pre-eruptive isotopic fractionations (i.e., temperatures) between minerals. We report analyses of oxygen isotope ratio in individual quartz phenocrysts and concentrates of magnetite, pyroxene, and zircon from individual pumice clasts of ignimbrite and fall units of caldera-forming 0.76 Ma Bishop Tuff (BT), pre-caldera Glass Mountain (2.1-0.78 Ma), and post-caldera rhyolites (0.65-0.04 Ma) to characterize the long-lived, batholith-scale magma chamber beneath Long Valley Caldera in California. Values of δ18O show a subtle 1‰ decrease from the oldest Glass Mountain lavas to the youngest post-caldera rhyolites. Older Glass Mountain lavas exhibit larger ( 1‰) variability of δ18O(quartz). The youngest domes of Glass Mountain are similar to BT in δ18O(quartz) values and reflect convective homogenization during formation of BT magma chamber surrounded by extremely heterogeneous country rocks (ranging from 2 to +29‰). Oxygen isotope thermometry of BT confirms a temperature gradient between "Late" (815 °C) and "Early" (715 °C) BT. The δ18O(quartz) values of "Early" and "Late" BT are +8.33 and 8.21‰, consistent with a constant δ18O(melt)=7.8+/-0.1‰ and 100 °C temperature difference. Zircon-melt saturation equilibria gives a similar temperature range. Values of δ18O(quartz) for different stratigraphic units of BT, and in pumice clasts ranging in pre-eruptive depths from 6 to 11 km (based on melt inclusions), and document vertical and lateral homogeneity of δ18O(melt). Worldwide, five other large-volume rhyolites, Lava Creek, Lower Bandelier, Fish Canyon, Cerro Galan, and Toba, exhibit equal δ18O(melt) values of earlier and later erupted portions in each of the these climactic caldera-forming eruptions. We interpret the large-scale δ18O homogeneity of BT and other large magma chambers as evidence of their longevity (>105 years) and convection. However, remaining isotopic zoning in some quartz phenocrysts, trace element gradients in feldspars, and quartz and zircon crystal size distributions are more consistent with far shorter timescales (102-104 years). We propose a sidewall-crystallization model that promotes convective homogenization, roofward accumulation of more evolved and stagnant, volatile-rich liquid, and develops compositional and temperature gradients in pre-climactic magma chamber. Crystal + melt + gas bubbles mush near chamber walls of variable δ18O gets periodically remobilized in response to chamber refill by new hotter magmas. One such episode of chamber refill by high-Ti, Sr, Ba, Zr, and volatile-richer magma happened 103-104 years prior to the 0.76-Ma caldera collapse that caused magma mixing at the base, mush thawing near the roof and walls, and downward settling of phenocrysts into this hybrid melt.

Volcanic eruptions and seismicity of Mt. Baekdu (Changbai) occurred in the historical time

NASA Astrophysics Data System (ADS)

Kang, T.; Baag, C.; Chu, K.

2011-12-01

Recently, it was reported that the Mt. Baekdu had large volcanic eruptions at least two times in the geological and historical times and the lake Cheonji (Tianchi in Chinese) had formed by collapse of the summit part of the mountain. The last one of the four eruptions occurred in the historical time. Geologists tried to measure the date of eruptions using carbon isotope, but the results show diversity ranging approximately form AD 8 to 14 centuries corresponding to the dates of two dynasties of Balhae (Bohai in Chinese) and Goryeo. Unfortunately, there is no distinct record of the eruptions in this period in historical literatures. In the current study, we could infer that the last great volcanic eruption occurred in the winter time with strong northwestern seasonal wind, considering the distribution of pumice on the satellite images and the thickness of the pumice layers measured at sites in relationship with the climatic environment. On the other hand, some researchers interpreted five events appearing in historical documents written in the Joseon dynasty to be related to volcanic eruptions of Mt. Baekdu. These events occurred in the years 1413, 1597, 1668, 1702, and 1903. Their interpretations have been widely cited in journals and books, However based on critical reviews of historical literature including Joseon Wangjo Sillok (Annals of the Joseon Dynasty), we find that three events of the five were not related to volcanic eruptions of the Mt. Baekdu. Events in the years 1413 and 1668 were phenomena of Asian dust. The event in 1903 recorded in a Chinese literature is found to be a shower type of rain drop with hail accompanied by thunder and lightning. Only the two events in 1597 and 1702 are confirmed to be related to volcanic activities of Mt. Baekdu. According to Joseon Wangjo Sillok, a large earthquake of maximum intensity 9 (Modified Mercalli Intensity, MMI) and its aftershocks occurred at the border region of Samsu county in Hamgyeongdo Province in the year 1597. The document reveals that they were detected in Hamgyeongdo (MMI 6) and in Chungcheongdo (MMI 4) for three days. The mainshock was accompanied by a volcanic explosion at Wangtian that is located at 35km southwest from Mt. Baekdu. The place is one of the three eruption centers of the Mt. Baekdu volcanic body. A document from China reveals that a large earthquake with estimated magnitude 7.0 and aftershocks occurred in the gulf of Bohai on the same days as those of the Samsu earthquakes in Hamgyeongdo province. The shakes and disturbances observed eight times in Hamgyeongdo province might not directly come from the large earthquake in the gulf of Bohai. However, the two series of earthquakes reported at two different places on the same days imply that there may be close relationships in genesis between two events.

Volcanic Centers of the Northern McCullough Range, Southern Nevada USA: a View of Pre- Extensional Volcanism in the Colorado River Extensional Corridor

NASA Astrophysics Data System (ADS)

Honn, D. K.; Johnsen, R.; Smith, E. I.

2007-05-01

The northern McCullough Range, just south of Las Vegas, Nevada, is being developed by the US Bureau of Land Management as the Sloan Canyon National Conservation Area to preserve its natural history. Compared to adjacent ranges, the northern McCullough Range was relatively undeformed by Miocene extension in the Colorado River Extensional Corridor. Therefore, the well preserved volcanic centers within the McCullough Range provide an excellent opportunity to study pre-extensional volcanism. There are at least seven volcanic centers in the northern McCullough Range; this study focuses on the Cactus Hill, McCullough Wash, and Eldorado Valley Volcanoes in the central McCullough Range, and the Henderson Caldera in the northern McCullough Range. The Cactus Hill volcano is a 200 m thick section of flows and agglomerates that form a broad basalt-andesite cone, nearly 2 km in diameter. This cone is cut by two (2-3 m wide) basalt dikes and at least 8 dacite domes. Each of the domes is associated with a broad debris apron. The McCullough Wash volcano is composed of at least 6 dacite domes and carapace breccias that reflect periods of dome growth and collapse. The Eldorado Valley Volcano, another series of dacite domes and flows, is the source of a 250 m thick breccia unit (Eldorado Valley breccia). The breccia is a block and ash deposit (with beds up to 1.5 m thick) containing spectacular blocks (1 cm - 3 m in diameter) and bombs (10 cm - 6 m in diameter) that are interbedded with flows from the McCullough Wash and Cactus Hill volcanoes. Interbedding of dacite breccia of the Eldorado Valley Volcano with dacitic, andesitic and basaltic dome debris from the Cactus Hill volcano reflect coeval mafic and felsic volcanism. The Henderson caldera at the northern tip of the McCullough Range is formed by a arc of domes that erupted a series of biotite dacite flows. The caldera is also filled by domes and flows of hornblende andesite, ash-flow tuff and mesobreccia deposits. The tuff of the Henderson caldera (~20 m thick) grades from a pumice poor base to a pumice rich top and contains lithic fragments of andesite that reflect the explosive truncation of the central McCullough Range stratovolcano (2500 to 3000 m thick section of andesite flows). Mesobreccia occurs along the southern margin of the caldera and contains andesite clasts (< 25 cm) within a matrix of the tuff of the Henderson caldera. The ongoing study the volcanic centers of the McCullough Range provide geologic data for the development of the Sloan Canyon National Conservation Area as well as providing insight into the evolution of the Colorado River extensional corridor.

Hydrogen isotope investigation of amphibole and glass in dacite magmas erupted in 1980-1986 and 2005 at Mount St. Helens, Washington

USGS Publications Warehouse

Underwood, S.J.; Feeley, T.C.; Clynne, M.A.

2013-01-01

In active, shallow, sub-volcanic magma conduits the extent of the dehydrogenation–oxidation reaction in amphibole phenocrysts is controlled by energetic processes that cause crystal lattice damage or conditions that increase hydrogen diffusivity in magmatic phases. Amphibole phenocrysts separated from dacitic volcanic rocks erupted from 1980 to 1986 and in 2005 at Mount St. Helens (MSH) were analyzed for δD, water content and Fe3+/Fe2+, and fragments of glassy groundmass were analyzed for δD and water content. Changes in amphibole δD values through time are evaluated within the context of carefully observed volcanic eruption behavior and published petrological and geochemical investigations. Driving forces for amphibole dehydrogenation include increase in magma oxygen fugacity, decrease in amphibole hydrogen fugacity, or both. The phenocryst amphibole (δD value c. –57‰ and 2 wt % H2O) in the white fallout pumice of the May 18, 1980 plinian eruptive phase is probably little modified during rapid magma ascent up an ∼7 km conduit. Younger volcanic rocks incorporate some shallowly degassed dacitic magma from earlier pulses, based on amphibole phenocryst populations that exhibit varying degrees of dehydrogenation. Pyroclastic rocks from explosive eruptions in June–October 1980 have elevated abundances of mottled amphibole phenocrysts (peaking in some pyroclastic rocks erupted on July 22, 1980), and extensive amphibole dehydrogenation is linked to crystal damage from vesiculation and pyroclastic fountain collapse that increased effective hydrogen diffusion in amphibole. Multiple amphibole δD populations in many 1980 pyroclastic rocks combined with their groundmass characteristics (e.g. mixed pumice textures) support models of shallow mixing prior to, or during, eruption as new, volatile-rich magma pulses blended with more oxidized, degassed magma. Amphibole dehydrogenation is quenched at the top surface of MSH dacite lava lobes, but the diversity in the δDamph populations in original fresh lava flow surfaces may occur from blending magma domains with different ascent histories in the sub-volcanic environment immediately before eruption. Multi-stage open-system magma degassing operated in each parcel of magma rising toward the surface, whereas the magma below ∼7 km was a relatively closed system, at least to the October 1986 eruption based on the large population of minimally dehydrogenated, rim-free amphibole in the lavas. Magma degassing and possibly H isotope exchange with low-δD fluids around the roof zone may have accompanied the ∼1·5 km upward migration of the 1980 magma body. The low-δDamph (c. –188 to –122‰) oxy-amphibole phenocrysts in lava spines extruded in May 2005 reflect dehydrogenation as ascending viscous magma degassed and crystallized, and fractures that admitted oxygen into the hot solidified lava spine interior facilitated additional iron oxidation.

Effect of adhesive remnant removal on enamel topography after bracket debonding

PubMed Central

Cardoso, Larissa Adrian Meira; Valdrighi, Heloísa Cristina; Vedovello, Mario; Correr, Américo Bortolazzo

2014-01-01

INTRODUCTION: At orthodontic treatment completion, knowledge about the effects of adhesive remnant removal on enamel is paramount. OBJECTIVE: This study aimed at assessing the effect of different adhesive remnant removal methods on enamel topography (ESI) and surface roughness (Ra) after bracket debonding and polishing. METHODS: A total of 50 human premolars were selected and divided into five groups according to the method used for adhesive remnant removal: high speed tungsten carbide bur (TCB), Sof-Lex discs (SL), adhesive removing plier (PL), ultrasound (US) and Fiberglass burs (FB). Metal brackets were bonded with Transbond XT, stored at 37oC for 24 hours before debonding with adhesive removing plier. Subsequently, removal methods were carried out followed by polishing with pumice paste. Qualitative and quantitative analyses were conducted with pre-bonding, post-debonding and post-polishing analyses. Results were submitted to statistical analysis with F test (ANOVA) and Tukey's (Ra) as well as with Kruskal-Wallis and Bonferroni tests (ESI) (P < 0.05). RESULTS: US Ra and ESI were significantly greater than TCB, SL, PL and FB. Polishing minimized Ra and ESI in the SL and FB groups. CONCLUSION: Adhesive remnant removal with SL and FB associated with polishing are recommended due to causing little damage to the enamel. PMID:25628087

Textural evidence for high-grade ignimbrites formed by low-explosivity eruptions, Paraná Magmatic Province, southern Brazil

NASA Astrophysics Data System (ADS)

Luchetti, Ana Carolina F.; Gravley, Darren M.; Gualda, Guilherme A. R.; Nardy, Antonio J. R.

2018-04-01

The Paraná-Etendeka Province is a Lower Cretaceous huge bimodal tholeiitic volcanic province (1 million·km3) that predated the Gondwana breakup. Its silicic portion makes up a total volume of at least 20,000 km3 and in southern Brazil it comprises the Chapecó porphyritic high-Ti trachydacites-dacites and the Palmas microporphyritic-aphyric low-Ti dacites-rhyolites. The widespread silicic sheets are debated in the literature because they bear similarities between lavas and high grade ignimbrites. Here we provide new observations and interpretations for flow units with large, dark, and vesicle-poor lens-shaped blobs surrounded by a light-colored matrix. The textural features (macro- to micro-scale) of these blobs are different from typical pumice and/or fiamme and support a low explosivity pyroclastic origin, possibly low-column fountain eruptions with discharge rates high enough to produce laterally extensive high-grade ignimbrites. Such an interpretation, combined with a conspicuous absence of lithic fragments in the deposits, is aligned with a lack of identified calderas in the Paraná-Etendeka Province. Maximum timescales of crystallization associated with the juvenile blobs and estimated from CSD slopes are on the order of millennia for phenocryst populations and on the order of decades for microphenocryst populations.

Mineralogical Characterization of the Miocene Olcese Formation, Southern San Joaquin Valley, California

NASA Astrophysics Data System (ADS)

Lopez, K. A.; Baron, D.; Guo, J.; Woolford, J. M.

2016-12-01

The early to middle Miocene Olcese Formation in the southern San Joaquin Valley of California consists of shallow marine shelf sands in its lower and upper parts, and non-marine, frequently pumiceous sands in its middle part, and varies in thickness up to 1800 ft. There is little known as to the origin, nature, quantity, and distribution of clay minerals throughout the formation. This study examined 95 sidewall core samples from three wells, as well as 388 cutting samples from four wells and 12 samples from 3 outcrops. Well samples were from depths between 1,800 and 4,000 ft. Qualitative and quantitative mineralogy including clay minerals of the sidewall samples and selected cutting samples was determined by powder X-ray diffraction (XRD). XRD analyses were supplemented by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) and petrographic microscopy of selected samples. The main minerals of bulk samples include composite clay, quartz, potassium feldspar/plagioclase, calcite, and clinoptilolite. Content of composite clay varies between 17% and 51%. The clay-size fraction is predominantly composed of smectite, illite, kaolinite and chlorite with smectite being the most abundant. Smectite and clinoptilolite may be the alteration products of deeper burial of volcanic materials. The formation permeability could be significantly lowered by these authigenic minerals.

Geologic and geomorphic controls on the occurrence of fens in the Oregon Cascades and implications for vulnerability and conservation

USGS Publications Warehouse

Aldous, A.; Gannett, Marshall W.; Keith, Mackenzie K.; O'Connor, James E.

2015-01-01

Montane fens are biologically diverse peat-forming wetlands that develop at points of groundwater discharge. To protect these ecosystems, it is critical to understand their locations on the landscape and the hydrogeologic systems that support them. The upper Deschutes Basin has a groundwater flow system that supports baseflow in many rivers, but little is known about the wetland types and groundwater dependence of the thousands of wetlands within the watershed. In 292 randomly selected wetlands, we quantified landscape metrics thought useful for discriminating montane fens from non-peat-forming wetlands. We inspected these wetlands and classified 67 of them as fens. Of the landscape metrics, only geology reliably differentiated fens from other types of wetlands. Nearly all fens develop in low-permeability glacial till found at approximately 1400–1800 m in elevation, and are concentrated in areas mantled by pumice deposits that originated primarily from the eruption of Mt. Mazama approximately 7700 years BP. Stratigraphic and hydrologic factors indicate the fens are supplied by perched aquifers in glacial till, instead of the deeper regional aquifer system. Their hydrogeologic setting makes the fens highly vulnerable to expected changes to recharge associated with climate change, but not to groundwater pumping from the regional aquifer.

Adverse reactions to orthodontic materials.

PubMed

Sifakakis, I; Eliades, T

2017-03-01

Adverse effects can arise from the clinical use of orthodontic materials, due to the release of constituent substances (ions from alloys and monomers, degradation by-products, and additives from polymers). Moreover, intraoral aging affects the biologic properties of materials. The aim of this review is to present the currently identified major adverse effects of the metallic and polymeric components found in orthodontic appliances and materials. Corrosion in metallic orthodontic attachments releases metal ions, mainly iron, chromium, and nickel. The latter has received the greatest attention because of its reported potential for an allergic response. The formation of an oxide layer may inhibit the outward movement of ions, thereby acting as an obstacle for release. Titanium alloys have superior corrosion resistance than stainless steel. The efficiency of polymerisation is considered an essential property for all polymers. A poor polymer network is susceptible to the release of biologically reactive substances, such as bisphenol-A (BPA), which is capable of inducing hormone-related effects. The close proximity of a light-curing tip to the adhesive, pumice prophylaxis after bonding, indirect irradiation and mouth rinsing during the first hour after bonding may decrease BPA release. The adverse effects of some orthodontic materials should be considered during material selection and throughout orthodontic treatment, in order to minimise possible undesirable implications. © 2017 Australian Dental Association.

Comparison of Ejecta Distributions from Normal Incident Hypervelocity Impact on Lunar Regolith Simulant

NASA Technical Reports Server (NTRS)

Edwards, David L.; Cooke, William; Scruggs, Rob; Moser, Danielle E.

2008-01-01

The National Aeronautics and Space Administration (NASA) is progressing toward long-term lunar habitation. Critical to the design of a lunar habitat is an understanding of the lunar surface environment; of specific importance is the primary meteoroid and subsequent ejecta environment. The document, NASA SP-8013, was developed for the Apollo program and is the latest definition of the ejecta environment. There is concern that NASA SP-8013 may over-estimate the lunar ejecta environment. NASA's Meteoroid Environment Office (MEO) has initiated several tasks to improve the accuracy of our understanding of the lunar surface ejecta environment. This paper reports the results of experiments on projectile impact into powered pumice and unconsolidated JSC-1A Lunar Mare Regolith stimulant (JSC-1A) targets. The Ames Vertical Gun Range (AVGR) was used to accelerate projectiles to velocities in excess of 5 km/s and impact the targets at normal incidence. The ejected particles were detected by thin aluminum foil targets placed around the impact site and angular distributions were determined for ejecta. Comparison of ejecta angular distribution with previous works will be presented. A simplistic technique to characterize the ejected particles was formulated and improvements to this technique will be discussed for implementation in future tests.

Dextran templating for the synthesis of metallic and metal oxide sponges

NASA Astrophysics Data System (ADS)

Walsh, Dominic; Arcelli, Laura; Ikoma, Toshiyuki; Tanaka, Junzo; Mann, Stephen

2003-06-01

Silver or gold-containing porous frameworks have been used extensively in catalysis, electrochemistry, heat dissipation and biofiltration. These materials are often prepared by thermal reduction of metal-ion-impregnated porous insoluble supports (such as alumina and pumice), and have surface areas of about 1 m2 g-1, which is typically higher than that obtained for pure metal powders or foils prepared electrolytically or by infiltration and thermal decomposition of insoluble cellulose supports. Starch gels have been used in association with zeolite nanoparticles to produce porous inorganic materials with structural hierarchy, but the use of soft sacrificial templates in the synthesis of metallic sponges has not been investigated. Here we demonstrate that self-supporting macroporous frameworks of silver, gold and copper oxide, as well as composites of silver/copper oxide or silver/titania can be routinely prepared by heating metal-salt-containing pastes of the polysaccharide, dextran, to temperatures between 500 and 900 °C. Magnetic sponges were similarly prepared by replacing the metal salt precursor with preformed iron oxide (magnetite) nanoparticles. The use of dextran as a sacrificial template for the fabrication of metallic and metal oxide sponges should have significant benefits over existing technologies because the method is facile, inexpensive, environmentally benign, and amenable to scale-up and processing.

Effect of operating temperature on styrene mass transfer characteristics in a biotrickling filter.

PubMed

Parnian, Parham; Zamir, Seyed Morteza; Shojaosadati, Seyed Abbas

2017-05-01

To study the effect of operating temperature on styrene mass transfer from gas to liquid phase in biotrickling filters (BTFs), overall mass transfer coefficient (K L a) was calculated through fitting test data to a general mass balance model under abiotic conditions. Styrene was used as the volatile organic compound and the BTF was packed with a mixture of pall rings and pumice. Operating temperature was set at 30°C and 50°C for mesophilic and thermophilic conditions, respectively. K L a values increased from 54 to 70 h -1 at 30°C and from 60 to 90 h -1 at 50°C, respectively, depending on the countercurrent gas to liquid flow ratio that varied in the range of 7.5-32. Evaluation of styrene mass transfer capacity (MTC) showed that liquid-phase mass transfer resistance decreased as the flow ratio increased at constant temperature. MTC also decreased with an increase in operating temperature. Both gas-liquid partition coefficient and K L a increased with increasing temperature; however the effect on gas-liquid partition coefficient was more significant and served to increase mass transfer limitations. Thermophilic biofiltration on the one hand increases mass transfer limitations, but on the other hand may enhance the biodegradation rate in favor of enhancing BTFs' performance.

Mantle wedge infiltrated with saline fluids from dehydration and decarbonation of subducting slab

PubMed Central

Kawamoto, Tatsuhiko; Yoshikawa, Masako; Kumagai, Yoshitaka; Mirabueno, Ma. Hannah T.; Okuno, Mitsuru; Kobayashi, Tetsuo

2013-01-01

Slab-derived fluids play an important role in heat and material transfer in subduction zones. Dehydration and decarbonation reactions of minerals in the subducting slab have been investigated using phase equilibria and modeling of fluid flow. Nevertheless, direct observations of the fluid chemistry and pressure–temperature conditions of fluids are few. This report describes CO2-bearing saline fluid inclusions in spinel-harzburgite xenoliths collected from the 1991 Pinatubo pumice deposits. The fluid inclusions are filled with saline solutions with 5.1 ± 1.0% (wt) NaCl-equivalent magnesite crystals, CO2-bearing vapor bubbles, and a talc and/or chrysotile layer on the walls. The xenoliths contain tremolite amphibole, which is stable in temperatures lower than 830 °C at the uppermost mantle. The Pinatubo volcano is located at the volcanic front of the Luzon arc associated with subduction of warm oceanic plate. The present observation suggests hydration of forearc mantle and the uppermost mantle by slab-derived CO2-bearing saline fluids. Dehydration and decarbonation take place, and seawater-like saline fluids migrate from the subducting slab to the mantle wedge. The presence of saline fluids is important because they can dissolve more metals than pure H2O and affect the chemical evolution of the mantle wedge. PMID:23716664

Timescales of magmatic processes prior to the ˜4.7 ka Agnano-Monte Spina eruption (Campi Flegrei caldera, Southern Italy) based on diffusion chronometry from sanidine phenocrysts

NASA Astrophysics Data System (ADS)

Iovine, Raffaella Silvia; Fedele, Lorenzo; Mazzeo, Fabio Carmine; Arienzo, Ilenia; Cavallo, Andrea; Wörner, Gerhard; Orsi, Giovanni; Civetta, Lucia; D'Antonio, Massimo

2017-02-01

Barium diffusion chronometry applied to sanidine phenocrysts from the trachytic Agnano-Monte Spina eruption (˜4.7 ka) constrains the time between reactivation and eruption of magma batches in the Campi Flegrei caldera. Backscattered electron imaging and quantitative electron microprobe measurements on 50 sanidine phenocrysts from representative pumice samples document core-to-rim compositional zoning. We focus on compositional breaks near the crystal rims that record magma mixing processes just prior to eruption. Diffusion times were modeled at a magmatic temperature of 930 °C using profiles based on quantitative BaO point analyses, X-ray scans, and grayscale swath profiles, yielding times ≤60 years between mixing and eruption. Such short timescales are consistent with volcanological and geochronological data that indicate that at least six eruptions occurred in the Agnano-San Vito area during few centuries before the Agnano-Monte Spina eruption. Thus, the short diffusion timescales are similar to time intervals between eruptions. Therefore, the rejuvenation time of magma residing in a shallow reservoir after influx of a new magma batch that triggered the eruption, and thus pre-eruption warning times, may be as short as years to a few decades at Campi Flegrei caldera.

Inter-laboratory comparison of X-ray fluorescence analyses of eruptive products of El Chichón Volcano, Chiapas, Mexico

USGS Publications Warehouse

Tilling, Robert I.; Bornhorst, Theodore J.; Taggart, Joseph E.; Rose, William I.; McGee, James J.

1987-01-01

An inter-laboratory comparison has been made of X-ray fluorescence analyses of 10 samples of lava and pumices from El Chichón Volcano, Chiapas, Mexico. Some determinations of major-element constituents agree within analytical uncertainty, whereas others exchibit significant bias. Analyses carried out at the Michigan Technological University (MTU) laboratory are systematically lower in MgO (26–48%), Fetotal(5–18%), CaO (4–15%) and higher in K2O (0–15%) than analyses made at the U.S. Geological Survey (USGS) Denver laboratory. These differences are ascribed in part to a complex combination of calibration assumptionsand mineralogical and particle-size effects inherent in the use of pressed rock-powder pellets in the analytical procedure of the MTU laboratory. Other, but as yet unknown, differences in sample preparation and/or analytical technique may also be important; effects related to natural sample inhomogeneityare believed to be insignificant. The inter-laboratory differences in the analytical data complicated accurate assessment of whether El Chichón magmas have changed composition during the past 300 000 a. Knowledge of such change is needed for understanding petrogenetic history and for such related studies as evaluation of volcanic hazards.

Pleistocene volcaniclastic units from North-Eastern Sicily (Italy): new evidence for calc-alkaline explosive volcanism in the Southern Tyrrhenian Sea

NASA Astrophysics Data System (ADS)

Di Bella, Marcella; Italiano, Francesco; Sabatino, Giuseppe; Tripodo, Alessandro; Baldanza, Angela; Casella, Sergio; Pino, Paolo; Rasa', Riccardo; Russo, Selma

2016-08-01

A well-preserved volcaniclastic sequence crops out in Pleistocene marine sediments along the Tyrrhenian coastline of the Calabrian-Peloritani arc (Sicily, Italy), testifying the occurrence of Lower-Middle Pleistocene volcanic activity in Southern Tyrrhenian Sea. The presence of dominant highly vesicular and minor blocky glassy particles indicates that the volcanic clasts were originated by explosive events related to the ascent and violent emission of volatile-rich magmas accompanied by and/or alternated with hydromagmatic fragmentation due to magma-sea water interaction. Field investigations and sedimentological features of the studied volcaniclastic units suggest a deposition from sediment-water density flows. The chemical classification of the pumice clasts indicates prevalent rhyolitic and dacitic compositions with calc-alkaline to high-K calc-alkaline affinity. The geochemical features of immobile trace elements together with the presence of orthopyroxene are indicative of a provenance from an arc-type environment. The age (from 980-910 to 589 ka), the chemical composition and the evidence of subaerial explosive volcanic activity constrain the origin nature and temporal evolution of the arc-type volcanism in the Southern Tyrrhenian domain. Finally, the new information here provided contribute to a better understanding of the temporal geodynamic evolution of this sector of the Mediterranean domain.

Late Quaternary distal tephra-fall deposits in lacustrine sediments, Kenai Peninsula, Alaska

USGS Publications Warehouse

de Fontaine, C.S.; Kaufman, D.S.; Scott, Anderson R.; Werner, A.; Waythomas, C.F.; Brown, T.A.

2007-01-01

Tephra-fall deposits from Cook Inlet volcanoes were detected in sediment cores from Tustumena and Paradox Lakes, Kenai Peninsula, Alaska, using magnetic susceptibility and petrography. The ages of tephra layers were estimated using 21 14C ages on macrofossils. Tephras layers are typically fine, gray ash, 1-5??mm thick, and composed of varying proportions of glass shards, pumice, and glass-coated phenocrysts. Of the two lakes, Paradox Lake contained a higher frequency of tephra (0.8 tephra/100 yr; 109 over the 13,200-yr record). The unusually large number of tephra in this lake relative to others previously studied in the area is attributed to the lake's physiography, sedimentology, and limnology. The frequency of ash fall was not constant through the Holocene. In Paradox Lake, tephra layers are absent between ca. 800-2200, 3800-4800, and 9000-10,300??cal yr BP, despite continuously layered lacustrine sediment. In contrast, between 5000 and 9000??cal yr BP, an average of 1.7 tephra layers are present per 100 yr. The peak period of tephra fall (7000-9000??cal yr BP; 2.6 tephra/100 yr) in Paradox Lake is consistent with the increase in volcanism between 7000 and 9000 yr ago recorded in the Greenland ice cores. ?? 2007 Elsevier Inc. All rights reserved.

Mantle wedge infiltrated with saline fluids from dehydration and decarbonation of subducting slab.

PubMed

Kawamoto, Tatsuhiko; Yoshikawa, Masako; Kumagai, Yoshitaka; Mirabueno, Ma Hannah T; Okuno, Mitsuru; Kobayashi, Tetsuo

2013-06-11

Slab-derived fluids play an important role in heat and material transfer in subduction zones. Dehydration and decarbonation reactions of minerals in the subducting slab have been investigated using phase equilibria and modeling of fluid flow. Nevertheless, direct observations of the fluid chemistry and pressure-temperature conditions of fluids are few. This report describes CO2-bearing saline fluid inclusions in spinel-harzburgite xenoliths collected from the 1991 Pinatubo pumice deposits. The fluid inclusions are filled with saline solutions with 5.1 ± 1.0% (wt) NaCl-equivalent magnesite crystals, CO2-bearing vapor bubbles, and a talc and/or chrysotile layer on the walls. The xenoliths contain tremolite amphibole, which is stable in temperatures lower than 830 °C at the uppermost mantle. The Pinatubo volcano is located at the volcanic front of the Luzon arc associated with subduction of warm oceanic plate. The present observation suggests hydration of forearc mantle and the uppermost mantle by slab-derived CO2-bearing saline fluids. Dehydration and decarbonation take place, and seawater-like saline fluids migrate from the subducting slab to the mantle wedge. The presence of saline fluids is important because they can dissolve more metals than pure H2O and affect the chemical evolution of the mantle wedge.

Paleo-geomorphic evolution of the Ciomadul volcano (East Carpathians, Romania) using integrated volcanological, stratigraphical and radiometric data

NASA Astrophysics Data System (ADS)

Karátson, Dávid; Wulf, Sabine; Veres, Daniel; Gertisser, Ralf; Telbisz, Tamás; Magyari, Enikö

2016-04-01

Ciomadul volcano is the youngest eruptive center of the Carpatho-Pannonian Region (CPR), located at the southernmost end of the Intra-Carpathian Volcanic Range, and within this, the Harghita Mountains in the East Carpathians. As a result of multi-disciplinary, ongoing studies (Karátson et al. 2013 and in review; Magyari et al. 2014; Veres et al. in prep.; Wulf et al. in review), we have obtained a number of constraints on the paleo-geomorphic evolution of the volcano. Our studies clarified that this volcano, a lava dome complex with a twin-crater (i.e. the older Mohos peat bog and the younger St. Ana lake), produced frequent explosive eruptions between 50 and 29 ky. As a result, a set of superimposed volcanic landforms were created, the chronology of which in some cases can be well constrained, in other cases further studies are required to infer their timing. Ciomadul evolved as a moderately explosive dacitic dome complex possibly for several hundred ka (see controversial chronology in Karátson et al. 2013, Harangi et al. 2015 and Szakács et al. 2015), resulting in a set of adjoining lava domes and a central complex. There is no evidence for crater-forming eruptions during that time, although the possibility of moderate explosions cannot be ruled out. Field relations show that the first exposive products are phreatomagmatic tuff series, called Turia type, dated at ca. 50 ka. These tephra units could be linked to the formation of a "Paleo-Mohos" crater, and possibly to the northern half-caldera rim which consists of massive lava dome rock and hosts Ciomadul Mare, the highest point of the volcano (1300 m). After this first explosive activity, volcanism seems to have migrated toward the W, at the site of the later St. Ana crater. Following plinian eruption(s) at ca. 47-43 ka, the explosive activity went dormant, and a lava dome might have grown up in a possibly small "Proto-St. Ana" crater. At 31-32 ka, a succession of violent magmatic explosive eruptions occurred, called "TGS" (Targu Seciuesc) eruptions. Noteworthy, these products can be pointed out from drilling in the Mohos crater, inactive by that time, the tuff units being intercalated between lacustrine deposits. The TGS eruptions, further shaping St. Ana crater, started with lava dome disruption and pumiceous block-and-ash flows, and possibly terminated by a plinian event distributing pumice fall to the SE. Finally, after some ka dormancy, the youngest eruption of Ciomadul, again of phreatomagmatic type, took place at ca. 29 ka ("Latest St. Ana" eruption). Its products can be also recovered from Mohos crater, and at the same time they drape the landscape to the S and E. That this eruption was a really violent, crater-forming event, accounting for the relatively large crater of present-day St. Ana (~1600 m), can be explained by the wide distribution of this latest tephra, identified as far as 350 km from vent near Odessa ('Roxolany tephra').

The June 2014 eruption of Piton de la Fournaise: Insights from field, textural and geochemical data

NASA Astrophysics Data System (ADS)

Gurioli, Lucia; Vlastelic, Ivan; Di Muro, Andrea; Boudoire, Guillaume; Moune, Séverine; Bachelery, Patrick; Villeneuve, Nicolas

2015-04-01

The June 20st, 2014 eruption of Piton de la Fournaise (PdF) represents the first eruption after 3.5 years of quiescence of this very active basaltic volcano. The eruption occurred on the SE slopes of the central cone and was short-lived, lasting only 20 hours and producing a short (1.5 km long) lava flow and a very weak (low) hawaiian to strombolian activity along the eruptive fissure. Here we discuss the first detailed dataset on PdF products integrating field, componentry, texture and chemical data on the 2014 eruptive products. The most intense activity occurred close to the lower tip of the eruptive fracture and dispersed a very small scoria fall out deposit. The deposit is inversely graded from lapilli to bombs, with minor coarse ash and comprises mainly juvenile scoriae with (very) minor, non-juvenile fragments of old scoriae and lava. The juvenile component is characterized by three groups of scoria: (i) spiny-opaque, (ii) spiny-iridescent, and (iii) fluidal, along with golden pumice. Density analyses performed on 200 coarse lapilli reveal a correlation between porosity and morphology, so that the spiny-opaque clasts are the densest (up to 1.60 x 103 kg m-3, for a vesicularity of 45%) and the golden pumice are the lightest (minimum density of 0.4 x 103 kg m-3 for a vesicularity of up to 86 %; DRE: 2.88 x 103 kg m-3). The increase in vesicularity correlates with an increase in number of small vesicles and a decrease in the large, coalesced vesicles. The connectivity data also indicate that the fluidal and golden (hawaiian-like) clasts have more isolated vesicles (up to 40%) than the spiny (strombolian-like) clasts (0-5%). The strong variation in density is controlled not only by the vesicularity, but also by the crystal content: the densest, spiny opaque fragments are the richest in microphenocrysts and microlites of plagioclase, pyroxene and olivine. The glass chemistry of each of the four clast types allows us to correlate porosity and oxide content: while MgO increases (from 4 to 6%) with porosity, FeOt decreases (from 18 down to 11%) evidencing the relatively more primitive signature of the lightest component. The spiny-opaque fragments are always mingled with fresher, microlite-poorer magma at their edges. The observed trends can be explained by variation in magma degassing and ascent velocity. We interpret the fluidal and golden fragments to be the fastest and less degassed magma that arrived from a relatively deeper source. The ascent of this small volume of magma triggered the eruption and underwent rapid decompression as is apparent from the large number of small vesicles, low microphenocrysts content and almost no microlites. The densest, spiny scoriae are thus old, shallow and degassed magma (possibly emplaced during the large 2007 eruption) that was passively involved in the event. This interpretation is consistent with the very shallow location of pre- and syn-eruptive seismic hypocenters (< 2 km below volcano summit) and the short duration of geophysical and geochemical precursors.

Geology of the peralkaline volcano at Pantelleria, Strait of Sicily

USGS Publications Warehouse

Mahood, G.A.; Hildreth, W.

1986-01-01

Situated in a submerged continental rift, Pantelleria is a volcanic island with a subaerial eruptive history longer than 300 Ka. Its eruptive behavior, edifice morphologies, and complex, multiunit geologic history are representative of strongly peralkaline centers. It is dominated by the 6-km-wide Cinque Denti caldera, which formed ca. 45 Ka ago during eruption of the Green Tuff, a strongly rheomorphic unit zoned from pantellerite to trachyte and consisting of falls, surges, and pyroclastic flows. Soon after collapse, trachyte lava flows from an intracaldera central vent built a broad cone that compensated isostatically for the volume of the caldera and nearly filled it. Progressive chemical evolution of the chamber between 45 and 18 Ka ago is recorded in the increasing peralkalinity of the youngest lava of the intracaldera trachyte cone and the few lavas erupted northwest of the caldera. Beginning about 18 Ka ago, inflation of the chamber opened old ring fractures and new radial fractures, along which recently differentiated pantellerite constructed more than 25 pumice cones and shields. Continued uplift raised the northwest half of the intracaldera trachyte cone 275 m, creating the island's present summit, Montagna Grande, by trapdoor uplift. Pantellerite erupted along the trapdoor faults and their hingeline, forming numerous pumice cones and agglutinate sheets as well as five lava domes. Degassing and drawdown of the upper pantelleritic part of a compositionally and thermally stratified magma chamber during this 18-3-Ka episode led to entrainment of subjacent, crystal-rich, pantelleritic trachyte magma as crenulate inclusions. Progressive mixing between host and inclusions resulted in a secular decrease in the degree of evolution of the 0.82 km3 of magma erupted during the episode. The 45-Ka-old caldera is nested within the La Vecchia caldera, which is thought to have formed around 114 Ka ago. This older caldera was filled by three widespread welded units erupted 106, 94, and 79 Ka ago. Reactivation of the ring fracture ca. 67 Ka ago is indicated by venting of a large pantellerite centero and a chain of small shields along the ring fault. For each of the two nested calderas, the onset of postcaldera ring-fracture volcanism coincides with a low stand of sea level. Rates of chemical regeneration within the chamber are rapid, the 3% crystallization/Ka of the post-Green Tuff period being typical. Highly evolved pantellerites are rare, however, because intervals between major eruptions (averaging 13-6 Ka during the last 190 Ka) are short. Benmoreites and mugearites are entirely lacking. Fe-Ti-rich alkalic basalts have erupted peripherally along NW-trending lineaments parallel to the enclosing rift but not within the nested calderas, suggesting that felsic magma persists beneath them. The most recent basaltic eruption (in 1891) took place 4 km northwest of Pantelleria, manifesting the long-term northwestward migration of the volcanic focus. These strongly differentiated basalts reflect low-pressure fractional crystallization of partial melts of garnet peridotite that coalesce in small magma reservoirs replenished only infrequently in this continental rift environment. ?? 1986 Springer-Verlag.

An experimental study of permeability development as a function of crystal-free melt viscosity

NASA Astrophysics Data System (ADS)

Lindoo, A.; Larsen, J. F.; Cashman, K. V.; Dunn, A. L.; Neill, O. K.

2016-02-01

Permeability development in magmas controls gas escape and, as a consequence, modulates eruptive activity. To date, there are few experimental controls on bubble growth and permeability development, particularly in low viscosity melts. To address this knowledge gap, we have run controlled decompression experiments on crystal-free rhyolite (76 wt.% SiO2), rhyodacite (70 wt.% SiO2), K-phonolite (55 wt.% SiO2) and basaltic andesite (54 wt.% SiO2) melts. This suite of experiments allows us to examine controls on the critical porosity at which vesiculating melts become permeable. As starting materials we used both fine powders and solid slabs of pumice, obsidian and annealed starting materials with viscosities of ∼102 to ∼106 Pas. We saturated the experiments with water at 900° (rhyolite, rhyodacite, and phonolite) and 1025 °C (basaltic andesite) at 150 MPa for 2-72 hrs and decompressed samples isothermally to final pressures of 125 to 10 MPa at rates of 0.25-4.11 MPa/s. Sample porosity was calculated from reflected light images of polished charges and permeability was measured using a bench-top gas permeameter and application of the Forchheimer equation to estimate both viscous (k1) and inertial (k2) permeabilities. Degassing conditions were assessed by measuring dissolved water contents using micro-Fourier-Transform Infrared (μ-FTIR) techniques. All experiment charges are impermeable below a critical porosity (ϕc) that varies among melt compositions. For experiments decompressed at 0.25 MPa/s, we find the percolation threshold for rhyolite is 68.3 ± 2.2 vol.%; for rhyodacite is 77.3 ± 3.8 vol.%; and for K-phonolite is 75.6 ± 1.9 vol.%. Rhyolite decompressed at 3-4 MPa/s has a percolation threshold of 74 ± 1.8 vol.%. These results are similar to previous experiments on silicic melts and to high permeability thresholds inferred for silicic pumice. All basaltic andesite melts decompressed at 0.25 MPa/s, in contrast, have permeabilities below the detection limit (∼10-15 m2), and a maximum porosity of 63 vol.%. Additionally, although the measured porosities of basaltic andesite experiments are ∼10-35 vol.% lower than calculated equilibrium porosities, μ-FTIR analyses confirm the basaltic andesite melts remained in equilibrium during degassing. We show that the low porosities and permeabilities are a consequence of short melt relaxation timescales during syn- and post-decompression degassing. Our results suggest that basaltic andesite melts reached ϕc > 63 vol.% and subsequently degassed; loss of internal bubble pressure caused the bubbles to shrink and their connecting apertures to seal before quench, closing the connected pathways between bubbles. Our results challenge the hypothesis that low viscosity melts have a permeability threshold of ∼30 vol.%, and instead support the high permeability thresholds observed in analogue experiments on low viscosity materials. Importantly, however, these low viscosity melts are unable to maintain high porosities once the percolation threshold is exceeded because of rapid outgassing and collapse of the permeable network. We conclude, therefore, that melt viscosity has little effect on percolation threshold development, but does influence outgassing.

Syneruptive deep magma transfer and shallow magma remobilization during the 2011 eruption of Shinmoe-dake, Japan—Constraints from melt inclusions and phase equilibria experiments

NASA Astrophysics Data System (ADS)

Suzuki, Yuki; Yasuda, Atsushi; Hokanishi, Natsumi; Kaneko, Takayuki; Nakada, Setsuya; Fujii, Toshitsugu

2013-05-01

The 2011 Shinmoe-dake eruption started with a phreatomagmatic eruption (Jan 19), followed by climax sub-Plinian events and subsequent explosions (Jan 26-28), lava accumulation in the crater (end of January), and vulcanian eruptions (February-April). We have studied a suite of ejecta to investigate the magmatic system beneath the volcano and remobilization processes in the silicic magma mush. Most of the ejecta, including brown and gray colored pumice clasts (Jan 26-28), ballistically ejected dense lava (Feb 1), and juvenile particles in ash from the phreatomagmatic and vulcanian events are magma mixing products (SiO2 = 57-58 wt.%; 960-980 °C). Mixing occurred between silicic andesite (SA) and basaltic andesite (BA) magmas at a fixed ratio (40%-30% SA and 60%-70% BA). The SA magma had SiO2 = 62-63 wt.% and a temperature of 870 °C, and contains 43 vol.% phenocrysts of pyroxene, plagioclase, and Fe-Ti oxide. The BA magma had SiO2 = 55 wt.% and a temperature of 1030 °C, and contains 9 vol.% phenocrysts of olivine and plagioclase. The SA magma partly erupted without mixing as white parts of pumices and juvenile particles. The two magmatic end-members crystallized at different depths, requiring the presence of two separate magma reservoirs; shallower SA reservoir and deeper BA reservoir. An experimental study reveals that the SA magma had been stored at a pressure of 125 MPa, corresponding to a depth of 5 km. The textures and forms of phenocrysts from the BA magma indicate rapid crystallization directly related to the 2011 eruptive activity. The wide range of H2O contents of olivine melt inclusions (5.5-1.6 wt.%) indicates that rapid crystallization was induced by decompression, with olivine crystallization first (≤ 250 MPa), followed by plagioclase addition. The limited occurrence of olivine melt inclusions trapped at depths of < 5 km is consistent with the proposed magma system model, because olivine crystallization ceased after magma mixing. Our petrological model is consistent with a geophysical model that explains whole crustal deformation as being due to a single source located 7-8 km northwest of the Shinmoe-dake summit. However, even the shallowest estimated source of this deformation (7.5-6.2 km) is deeper than the SA reservoir, which thus requires a contribution of deeper BA magmas to the observed deformation. Remobilization of mush-like SA magma occurred in two stages before the early sub-Plinian event. Firstly, precursor mixing with BA magma and associated heating occurred (925-871 °C; stage-1 of ≥ 350 h), followed by final mixing with BA magma (stage-2). MgO profiles of magnetite phenocrysts define timescales of 0.7-15.2 h from this final mixing to eruption. The mixed and heated magmas, and stagnant mush that existed in the SA reservoir in the precursor stage, were finally erupted together. Magnetite phenocrysts in the Feb 18 ash reveal the occurrence of continuous erosion of the stagnant mush during the course of the 2011 eruptive activity.

Analysis of Regolith Simulant Ejecta Distributions from Normal Incident Hypervelocity Impact

NASA Technical Reports Server (NTRS)

Edwards, David L.; Cooke, William; Suggs, Rob; Moser, Danielle E.

2008-01-01

The National Aeronautics and Space Administration (NASA) has established the Constellation Program. The Constellation Program has defined one of its many goals as long-term lunar habitation. Critical to the design of a lunar habitat is an understanding of the lunar surface environment; of specific importance is the primary meteoroid and subsequent ejecta environment. The document, NASA SP-8013 'Meteoroid Environment Model Near Earth to Lunar Surface', was developed for the Apollo program in 1969 and contains the latest definition of the lunar ejecta environment. There is concern that NASA SP-8013 may over-estimate the lunar ejecta environment. NASA's Meteoroid Environment Office (MEO) has initiated several tasks to improve the accuracy of our understanding of the lunar surface ejecta environment. This paper reports the results of experiments on projectile impact into powdered pumice and unconsolidated JSC-1A Lunar Mare Regolith simulant targets. Projectiles were accelerated to velocities between 2.45 and 5.18 km/s at normal incidence using the Ames Vertical Gun Range (AVGR). The ejected particles were detected by thin aluminum foil targets strategically placed around the impact site and angular ejecta distributions were determined. Assumptions were made to support the analysis which include; assuming ejecta spherical symmetry resulting from normal impact and all ejecta particles were of mean target particle size. This analysis produces a hemispherical flux density distribution of ejecta with sufficient velocity to penetrate the aluminum foil detectors.

Petro-chemical features and source areas of volcanic aggregates used in ancient Roman maritime concretes

NASA Astrophysics Data System (ADS)

Marra, F.; Anzidei, M.; Benini, A.; D'Ambrosio, E.; Gaeta, M.; Ventura, G.; Cavallo, A.

2016-12-01

We present and discuss data from petrographic observation at the optical microscope, electron microprobe analyses on selected glass shards, and trace-element analyses on 14 mortar aggregates collected at the ancient harbors and other maritime structures of Latium and Campania, spanning the third century BCE through the second CE, aimed at identify the volcanic products employed in the concretes and their area of exploitation. According to Latin author Vitruvius assertion about the ubiquitous use of Campanian pozzolan in the ancient Roman sea-water concretes, results of this study show a very selective and homogeneous choice in the material employed to produce the concretes for the different investigated maritime structures, evidencing three main pumice compositions, all corresponding to those of the products of the post-Neapolitan Yellow Tuff activity of the Phlegraean Fields, and a systematic use of the local Neapolitan Yellow Tuff to produce the coarse aggregate of these concretes. However, mixing with local products of the Colli Albani volcanic district, located 20 km east of Rome, has been evidenced at two fishponds of Latium, in Punta della Vipera and Torre Astura. Based on these petrographic and geochemical data, we conclude that the selective use of pozzolan from Campania, rather than of unproved different chemical properties, was the consequence of a series of logistic, economic, industrial and historical reasons.

Enamel microabrasion: An overview of clinical and scientific considerations

PubMed Central

Pini, Núbia Inocencya Pavesi; Sundfeld-Neto, Daniel; Aguiar, Flavio Henrique Baggio; Sundfeld, Renato Herman; Martins, Luis Roberto Marcondes; Lovadino, José Roberto; Lima, Débora Alves Nunes Leite

2015-01-01

Superficial stains and irregularities of the enamel are generally what prompt patients to seek dental intervention to improve their smile. These stains or defects may be due to hypoplasia, amelogenesis imperfecta, mineralized white spots, or fluorosis, for which enamel microabrasion is primarily indicated. Enamel microabrasion involves the use of acidic and abrasive agents, such as with 37% phosphoric acid and pumice or 6% hydrochloric acid and silica, applied to the altered enamel surface with mechanical pressure from a rubber cup coupled to a rotatory mandrel of a low-rotation micromotor. If necessary, this treatment can be safely combined with bleaching for better esthetic results. Recent studies show that microabrasion is a conservative treatment when the enamel wear is minimal and clinically imperceptible. The most important factor contributing to the success of enamel microabrasion is the depth of the defect, as deeper, opaque stains, such as those resulting from hypoplasia, cannot be resolved with microabrasion, and require a restorative approach. Surface enamel alterations that result from microabrasion, such as roughness and microhardness, are easily restored by saliva. Clinical studies support the efficacy and longevity of this safe and minimally invasive treatment. The present article presents the clinical and scientific aspects concerning the microabrasion technique, and discusses the indications for and effects of the treatment, including recent works describing microscopic and clinical evaluations. PMID:25610848

Evidence for water influx from a caldera lake during the explosive hydromagmatic eruption of 1790, Kilauea volcano, Hawaii

USGS Publications Warehouse

Mastin, L.G.

1997-01-01

In 1790 a major hydromagmatic eruption at the summit of Kilauea volcano, Hawaii, deposited up to 10 m of pyroclastic fall and surge deposits and killed several dozen Hawaiian natives who were crossing the island. Previous studies have hypothesized that the explosivity of this eruption was due to the influx of groundwater into the conduit and mixing of the groundwater with ascending magma. This study proposes that surface water, not groundwater, was the agent responsible for the explosiveness of the eruption. That is, a lake or pond may have existed in the caldera in 1790 and explosions may have taken place when magma ascended into the lake from below. That assertion is based on two lines of evidence: (1) high vesicularity (averaging 73% of more than 3000 lapilli) and high vesicle number density (105-107 cm-3 melt) of pumice clasts suggest that some phases of the eruption involved vigorous, sustained magma ascent; and (2) numerical calculations suggest that under most circumstances, hydrostatic pressure would not be sufficient to drive water into the eruptive conduit during vigorous magma ascent unless the water table were above the ground surface. These results are supported by historical data on the rate of infilling of the caldera floor during the early 1800s. When extrapolated back to 1790, they suggest that the caldera floor was below the water table.

Influence of chemical and mechanical polishing on water sorption and solubility of denture base acrylic resins.

PubMed

Rahal, Juliana Saab; Mesquita, Marcelo Ferraz; Henriques, Guilherme Elias Pessanha; Nóbilo, Mauro Antonio Arruda

2004-01-01

Influence of polishing methods on water sorption and solubility of denture base acrylic resins was studied. Eighty samples were divided into groups: Classico (CL), and QC 20 (QC) - hot water bath cured; Acron MC (AC), and Onda Cryl (ON) - microwave cured; and submitted to mechanical polishing (MP) - pumice slurry, chalk powder, soft brush and felt cone in a bench vise; or chemical polishing (CP) - heated monomer fluid in a chemical polisher. The first desiccation process was followed by storage in distilled water at 37 +/- 1 degrees C for 1 h, 1 day, 1, 2, 3 and 4 weeks. Concluding each period, water sorption was measured. After the fourth week, a second desiccation process was done to calculate solubility. Data were submitted to analysis of variance, followed by Tukey test (p

The effect of immediate dentin sealing and optical powder removal method on the fracture resistance of CAD/CAM-fabricated endocrowns.

PubMed

El-Damanhoury, Hatem M; Gaintantzopoulou, Marianna

2016-01-01

To evaluate the effect of immediate dentin sealing and optical powder removal method on the fracture resistance of CAD/CAM-fabricated ceramic endocrowns. Seventy-eight extracted premolars were endodontically treated. Standardized endocrown preparations were done in 60 teeth. Teeth were divided equally (n = 10) depending on the treatment of dentin (delayed sealing [DS] or immediate sealing [IS]), and the methods of optical powder removal (air-water spray washing [AW]; microabrasion [MA]; or aqueous suspension of pumice [PB], followed by air-water spray washing). After cementation, specimens were thermocycled (5,000 cycles, 5°C/50°C) and stored in distilled water for 1 week. Specimens were loaded in compression using a universal testing machine until failure. Failure load was recorded, and modes of failure were examined under a stereomicroscope. Micromorphological evaluation of different dentin treatments was done under SEM (n = 3). Results were analyzed using two-way ANOVA and Bonferroni post hoc multiple comparison tests (α = 0.05). Fracture resistance of all IS groups was significantly lower than DS groups, except for AW. There was no statistically significant difference between powder removal methods. Immediate dentin sealing does not improve the fracture resistance of endocrown restorations. Air-water spray washing is adequate to remove the optical powder after optical scanning impression taking.

Earth Observations taken by the Expedition 14 crew

NASA Image and Video Library

2007-01-11

ISS014-E-11872 (11 Jan. 2007) --- Pagan Island, Northern Mariana Islands, is featured in this image photographed by an Expedition 14 crewmember on the International Space Station. According to scientists, the Mariana Islands are part a volcanic island arc -- surface volcanoes formed from magma generation as one tectonic plate is overridden (or subducted) beneath another. In the case of the Mariana Islands, the Pacific Plate is being subducted beneath the Philippine Plate along the famously deep Mariana Trench (more than 11 kilometers below sea level). Pagan Island (right) is comprised of two stratovolcanoes (tall, typically cone-shaped structures formed by layers of dense crystallized lava and less-dense ash and pumice) connected by a narrow isthmus of land. Mount Pagan, the larger of the two volcanoes, forms the northeastern portion of the island and has been the most active historically. The most recent major eruption took place in 1981, but since then numerous steam- and ash-producing events have been observed at the volcano -- the latest reported one occurring between Dec. 5-8, 2006. This image records volcanic activity on Jan. 11, 2007 that produced a thin plume (most probably steam, say NASA scientists, possibly with minor ash content) that extended westwards away from Mount Pagan. The island is sparsely populated, and monitored for volcanic activity by the United States Geological Survey and the Commonwealth of the Mariana Islands.

Paleoclimate change in the Nakuru basin, Kenya, at 119 - 109 ka derived from δ18Odiatom and diatom assemblages and 40Ar/39Ar geochronology

NASA Astrophysics Data System (ADS)

Bergner, Andreas; Deino, Alan; Leng, Melanie; Gasse, Francoise

2016-04-01

A 4.5m-thick diatomite bed deposited during the cold interval of the penultimate interglacial at ~119 - 109 ka documents a period in which a deep freshwater lake filled the Nakuru basin in the Central Kenya Rift (CKR), East Africa. Palaeohydrological conditions of the basin are reconstructed for the paleolake highstand using δ18Odiatom and characterization of diatom assemblages. The age of the diatomite deposit is established by precise 40Ar/39Ar-dating of intercalated pumice tuffs. The paleolake experienced multiple hydrological fluctuations on sub-orbital (~1,500 to 2,000 years) time scales. The magnitude of the δ18Odiatom change (+/- 3‰) and significant changes in the plankton-littoral ratio of the diatom assemblage (+/- 25%) suggest that the paleolake record can be interpreted in the context of long-term climatic change in East Africa. Using 40Ar/39Ar age control and nominal diatomite-sedimentation rates we establish a simplified age model of paleohydrological vs. climatic change, from which we conclude that more humid conditions prevailed in equatorial East Africa during the late Pleistocene over a relatively long time interval of several thousands years. Then, extreme insolation at eccentricity maximum and weakened zonal air-pressure gradients in the tropics favored intensified ITCZ-like convection over East Africa and deep-freshwater lake conditions.

[Surface characteristics of the acrylic resins according to the polishing methods].

PubMed

Vitalariu, Anca Mihaela; Lazăr, Lenuţa; Buruiană, Tinca; Diaconu, Diana; Tatarciuc, Monica Silvia

2011-01-01

The objective of this study was to evaluate the effect of the polishing technique and glazing on the porosity of the dental resins. The studied resins were: Castapress/Vertex, Prothyl Hot/Zermack, Rapid Simplified/Vertex, Duracryl Plus/Spofa Dental, Vertex-Soft/Vertex, Superacryl Plus/Spofa Dental. Thirty specimens, five for every resin, of 50/25/2 cm in size were done. One surface of each sample was polished with extrahard tungsten carbide burs, the other surface being polished with extrahard extrafine and diamond burs. The final polishing was done using a conventional method: pumice, water and lathe bristle brush for 90 seconds, 1500 rpm and soft leather polishing wheel for 90 seconds, 3000 rpm. Twenty surfaces were glazed after polishing with Glaze/Bosworth. Vertex Soft specimens were not polished because this is a resilient material. Surface porosity of the acrylic resin specimens was measured by optical microscopy. The lowest porosity was obtained by conventional polishing combined with glazing techniques. No differences between glazed and non/glazed self-curing resin specimens were noticed, but there were differences between self-curing and heat-curing resins. Conventional lathe polishing method is an effective and reliable technique for polishing dental resins. Specimens of self-curing resin had a higher porosity than heat curing resin following the same surface treatment. Higher surface smoothness was obtained by conventional lathe polishing completed by glazing.

Surface and subsurface facies architecture of a small hydroexplosive, rhyolitic centre in the Mesoproterozoic Gawler Range Volcanics, South Australia

NASA Astrophysics Data System (ADS)

Roache, M. W.; Allen, S. R.; McPhie, J.

2000-12-01

At Menninnie Dam, South Australia, a drilling program has revealed a complete section through the subsurface feeder system and erupted products of a small, hydroexplosive, rhyolitic centre within the Mesoproterozoic Gawler Range Volcanics. Porphyritic rhyolite intruded near-vertical faults in the Palaeoproterozoic basement and at less than a few hundred metres depth, interacted with fault-hosted (hot?) groundwater. Hydrofracturing of the wall rock occurred in advance of and at the margins of the rhyolitic intrusions. The rhyolitic intrusions have peperitic margins and grade into discordant lithic-rich PB facies. The advancing fragmentation front intersected the palaeosurface, triggering phreatic eruptions that deposited a poorly sorted, lithic-rich explosion breccia. Rhyolite then rose to the surface through the intrusive breccias and shallow-seated magma-water interaction occurred in the conduit within <50 m of the surface. As the magma discharge rate increased, ;dry; explosive activity prevailed. A fall deposit, the top of which is welded, was deposited close to the vent, and in more distal locations (>800 m from the inferred source), the products include muddy sandstone and pumice breccia. At the end of the eruption, rhyolitic lava was extruded in the form of a small dome. The presence of contemporaneous Pb-Zn-Ag mineralisation in the wall rocks suggests that an active hydrothermal system may have been involved in the formation of the Menninnie Dam hydroexplosive volcanic centre.

Volcano-related materials in concretes: a comprehensive review.

PubMed

Cai, Gaochuang; Noguchi, Takafumi; Degée, Hervé; Zhao, Jun; Kitagaki, Ryoma

2016-04-01

Massive volcano-related materials (VRMs) erupted from volcanoes bring the impacts to natural environment and humanity health worldwide, which include generally volcanic ash (VA), volcanic pumice (VP), volcanic tuff (VT), etc. Considering the pozzolanic activities and mechanical characters of these materials, civil engineers propose to use them in low carbon/cement and environment-friendly concrete industries as supplementary cementitious materials (SCMs) or artificial/natural aggregates. The utilization of VRMs in concretes has attracted increasing and pressing attentions from research community. Through a literature review, this paper presents comprehensively the properties of VRMs and VRM concretes (VRMCs), including the physical and chemical properties of raw VRMs and VRMCs, and the fresh, microstructural and mechanical properties of VRMCs. Besides, considering environmental impacts and the development of long-term properties, the durability and stability properties of VRMCs also are summarized in this paper. The former focuses on the resistance properties of VRMCs when subjected to aggressive environmental impacts such as chloride, sulfate, seawater, and freezing-thawing. The latter mainly includes the fatigue, creep, heat-insulating, and expansion properties of VRMCs. This study will be helpful to promote the sustainability in concrete industries, protect natural environment, and reduce the impacts of volcano disaster. Based on this review, some main conclusions are discussed and important recommendations regarding future research on the application of VRMs in concrete industries are provided.

Campylobacter jejuni inactivation in New Zealand soils.

PubMed

Ross, C M; Donnison, A M

2006-11-01

The study was undertaken to determine the inactivation rate of Campylobacter jejuni in New Zealand soils. Farm dairy effluent (FDE) inoculated at c. 10(5) ml(-1) with C. jejuni was applied to intact soil cores at a rate of 2 l m(-2). Four soils were used: Hamilton (granular); Taupo (pumice); Horotiu and Waihou (allophanic). After FDE application cores were incubated at 10 degrees C for up to 32 days. For all four soils all the FDE remained within the cores and at least 99% of C. jejuni were retained in the top 5 cm. Campylobacter jejuni had declined to the limit of detection (two C. jejuni 100 g(-1)) by 25 days in Hamilton and Taupo soils and by 32 days in Waihou soil. In contrast, in Horotiu soil the decline was only three orders of magnitude after 32 days. Simulated heavy rainfall was applied 4 and 11 days after FDE application and only about 1% of the applied C. jejuni were recovered in leachates. This study demonstrated that at least 99% of applied C. jejuni were retained in the top 5 cm of four soils where they survived for at least 25 days at 10 degrees C. Soil retention of C. jejuni is efficient at FDE application rates that prevent drainage losses. The low infectious dose of C. jejuni and its ability to survive up to 25 days have implications for stock management on dairy farms.

A Hydrothermal-Sedimentary Context for the Origin of Life

PubMed Central

Hickman-Lewis, K.; Hinman, N.; Gautret, P.; Campbell, K.A.; Bréhéret, J.G.; Foucher, F.; Hubert, A.; Sorieul, S.; Dass, A.V.; Kee, T.P.; Georgelin, T.; Brack, A.

2018-01-01

Abstract Critical to the origin of life are the ingredients of life, of course, but also the physical and chemical conditions in which prebiotic chemical reactions can take place. These factors place constraints on the types of Hadean environment in which life could have emerged. Many locations, ranging from hydrothermal vents and pumice rafts, through volcanic-hosted splash pools to continental springs and rivers, have been proposed for the emergence of life on Earth, each with respective advantages and certain disadvantages. However, there is another, hitherto unrecognized environment that, on the Hadean Earth (4.5–4.0 Ga), would have been more important than any other in terms of spatial and temporal scale: the sedimentary layer between oceanic crust and seawater. Using as an example sediments from the 3.5–3.33 Ga Barberton Greenstone Belt, South Africa, analogous at least on a local scale to those of the Hadean eon, we document constant permeation of the porous, carbonaceous, and reactive sedimentary layer by hydrothermal fluids emanating from the crust. This partially UV-protected, subaqueous sedimentary environment, characterized by physical and chemical gradients, represented a widespread system of miniature chemical reactors in which the production and complexification of prebiotic molecules could have led to the origin of life. Key Words: Origin of life—Hadean environment—Mineral surface reactions—Hydrothermal fluids—Archean volcanic sediments. Astrobiology 18, 259–293. PMID:29489386

Comparison of the bond strength of stainless steel orthodontic brackets bonded to crown porcelains.

PubMed

Chay, Siew Han; Wattanapayungkul, Pranee; Yap, Adrian U Jin; Loh, Poey Ling; Chung, Sew Meng

2005-05-01

The bond strengths and mode of failure of stainless steel orthodontic brackets bonded to the newer all-ceramic crown systems has not been fully investigated. To compare the shear-peel bond strengths and modes of failure of stainless steel Begg orthodontic brackets bonded to all-ceramic crown systems (Finesse, Empress II) and a conventional feldsphatic crown porcelain (Vita Omega 900). Fifteen flat-surface discs of three crown porcelains (Finesse, Vita Omega 900, Empress II) were made and mounted in acrylic moulds. The discs were pumiced, etched with phosphoric acid, primed with silane, and a flat stainless steel Begg bracket bonded to each disc with a chemical cure composite resin (Unite Bond). The discs were stored for one week in water and debonded with a sheer-peel load in an Instron uniaxial testing system with a crosshead speed of 0.5 mm/min. The composite remnants on the ceramic surfaces were classified using the Adhesive Remnant Index (ARI). The bond strength of Finesse (15.03 +/- 1.90 MPa) was significantly greater (p < 0.001) than Vita Omega 900 11.51 +/- 2.35 MPa) and Empress II (11.12 +/- 1.78 MPa). There were no significant differences among the ARI scores. The mode of failure was a mixture of adhesive and cohesive failure. The results indicate that the bond strengths of stainless steel orthodontic brackets bonded to Finesse and Empress II porcelains are clinically acceptable.

Clinical evaluation of the efficacy of an in-office desensitizing paste containing 8% arginine and calcium carbonate in providing instant and lasting relief of dentin hypersensitivity.

PubMed

Schiff, Thomas; Delgado, Evaristo; Zhang, Yun Po; Cummins, Diane; DeVizio, William; Mateo, Luis R

2009-03-01

To determine the efficacy of an in-office desensitizing paste containing 8% arginine and calcium carbonate relative to that of a commercially-available pumice prophylaxis paste in reducing dentin hypersensitivity instantly after a single application following a dental scaling procedure and to establish the duration of sensitivity relief over a period of 4 weeks and 12 weeks. This was a single-center, parallel group, double-blind, stratified clinical study conducted in San Francisco, California, USA. Qualifying adult male and female subjects who presented two hypersensitive teeth with a tactile hypersensitivity score (Yeaple Probe) between 10-50 grams of force and an air blast hypersensitivity score of 2 or 3 (Schiff Cold Air Sensitivity Scale) were stratified according to their baseline hypersensitivity scores and randomly assigned within strata to one of two treatment groups: (1) A Test Paste, a desensitizing paste containing 8% arginine and calcium carbonate (Colgate-Palmolive Co); and (2) A Control Paste, Nupro pumice prophylaxis paste (Dentsply Professional). Subjects received a professionally-administered scaling procedure, after which they were re-examined for tactile and air blast dentin hypersensitivity (Post-Scaling Examinations). The assigned pastes were then applied as the final step to the professional dental cleaning procedure. Tactile and air blast dentin hypersensitivity examinations were again performed immediately after paste application. Subjects were provided with a commercially-available non-desensitizing dentifrice containing 0.243% sodium fluoride (Crest Cavity Protection, Procter & Gamble Co.) and an adult soft-bristled toothbrush and were instructed to brush their teeth for 1 minute, twice daily at home using only the toothbrush and dentifrice provided, for the next 12 weeks. Subjects returned to the testing facility 4 and 12 weeks after the single application of Test or Control paste, having refrained from all oral hygiene procedures and chewing gum for 8 hours and from eating and drinking for 4 hours, prior to each follow-up visit. Assessments of tactile and air blast hypersensitivity, and examinations of oral soft and hard tissue were repeated at these 4- and 12-week examinations. 68 subjects completed the 12-week study. No statistically significant differences from baseline scores were indicated at the Post-Scaling Examinations for either the Test Paste or Control Paste groups. Immediately following product application and 4 weeks after product application, subjects assigned to the Test Paste group exhibited statistically significant improvements from baseline with respect to baseline-adjusted mean air blast (44.1% and 45.9% respectively) and mean tactile hypersensitivity scores (156.2% and 170.3% respectively). At the same time points, subjects assigned to the Control Paste group exhibited statistically significant improvements from baseline with respect to baseline-adjusted mean air blast (15.1% and 8.9% respectively) and mean tactile hypersensitivity scores (43.1% and 8.3% respectively). Immediately following application of the assigned paste and 4 weeks later, the Test Paste group demonstrated statistically significant reductions in dentin hypersensitivity with respect to baseline-adjusted mean air blast (34.1% and 40.6% respectively) and mean tactile hypersensitivity scores (79.0% and 149.6% respectively), compared to the Control Paste group. No statistically significant differences were exhibited between paste groups at the Post-Scaling and 12-week examinations with respect to mean tactile and baseline-adjusted mean air blast hypersensitivity scores.

Degassing at Anatahan volcano during the May 2003 eruption: Implications from petrology, ash leachates, and SO 2 emissions

NASA Astrophysics Data System (ADS)

de Moor, J. M.; Fischer, T. P.; Hilton, D. R.; Hauri, E.; Jaffe, L. A.; Camacho, J. T.

2005-08-01

On 10 May 2003, Anatahan volcano (located at 16°21' N 145°40' E on the Mariana arc) entered its first historical eruptive episode, sending ash to > 12 km into the atmosphere. Abundant accretionary lapilli, quenched pumice textures, and hydrothermal minerals in the earliest eruptive deposits indicate hydromagmatic interaction and active mining of the pre-eruptive hydrothermal system. Whole-rock compositions of the products erupted within the first week are chemically homogenous, with SiO 2 ˜61%, MgO ˜2.1%, K 2O ˜1.4%, Na 2O ˜4.1% and Fe 2O 3 ˜9.1%. The products are classified as medium-K andesites with tholeiitic affinity. Slightly more silicic matrix glass compositions (up to 63% SiO 2 in microlite-rich matrices) overlap with whole rock, suggesting limited crystal fractionation with microlite crystallization responsible for the more evolved residual melt. Decreasing corrected LOI values (2.3-1.4 wt.%) upsection are consistent with waning hydrothermal mineral contributions as the eruption progressed. Oxygen fugacity calculations based on the ferric to ferrous iron ratio of bulk samples indicate an oxidized magma with ΔNNO ˜+1. Two-pyroxene equilibrium thermometry suggests magmatic temperatures of 1050-1100 °C. Matrix glass volatile contents show a degassed residual melt, with < 0.5 wt.% H 2O, 1000-2000 ppm Cl, 480-780 ppm F, 50-150 ppm S, and < 5 ppm CO 2. A magmatic SO 2 flux of 3-4.5 kt/day was measured by COSPEC on 21 May. Ash leachate data indicate a decreasing S/Cl ratio (3.3-0.7) in the eruptive plume between 10 and 21 May, with a relatively constant Cl concentration. Assuming a constant Cl flux, an SO 2 flux of 14-22 kt/day is calculated for 10 May. The average S concentration from ash leachates (1230 mg/kg) suggests that at least 25% of the SO 2 (˜60 kt) erupted from Anatahan between 10 and 21 May was removed from the plume by the precipitation of sulphate salts in the eruption column, adsorbtion onto ash particles and subsequent deposition. Molar ratios in ash leachates elucidate CaSO 4 and NaCl as the most likely soluble salts formed in the plume. Total element abundances, molar S/Ca > 1 and Ca, Mg, Na, and K ratios in the leachates suggest a hydrothermal fluid contribution to elements present as water soluble salts adsorbed onto ash. Sulfur budget calculations based on estimates of pre-eruptive magmatic and residual melt S contents, mass of erupted magma, and total SO 2 output fluxes require an additional source of S other than the erupted magma. Multiple lines of evidence, including high SO 2 emissions early in the eruption, the presence of accretionary lapilli and hydrothermal minerals in the early eruptive deposits, quenched pumice textures, and cation and anion ratios and abundances in ash leachates suggest that a S-rich free volatile phase exsolved from a large magma body. Magmatic volatiles were stored as components of the hydrothermal system (pressurized gases, hydrothermal fluids, and/or hydrothermal minerals) to be remobilized early in the eruption to contribute to the total SO 2 output.

Deposits from the 12 July Dome Collapse and Explosive Activity at Soufriere Hills Volcano, 12-15 July 2003

NASA Astrophysics Data System (ADS)

Edmonds, M.; Herd, R.; Strutt, M.; Mann, C.

2003-12-01

A large dome collapse took place on 12-13 July 2003 at Soufriere Hills Volcano. This event was the largest in magnitude during the 1995-2003 eruption and involved over 120 million m3 andesite dome and talus material. The collapse took place over 18 hours and culminated in an explosive phase that continued intermittently until 15 July 2003. Prior to the collapse, the total volume of the dome was 230 million m3 and was made up of remnants of lava erupted 1997-2001, talus material and fresh andesite dome lava erupted during the last two years. Talus made up around 50% of the total dome volume. This paper describes and interprets the pyroclastic flow and airfall deposits from this event, using other monitoring data and empirical evidence to reconstruct the dome collapse. The airfall and pyroclastic flow deposits were studied in detail over the weeks following the collapse. Airfall deposits were studied at 45 locations around the island and 75 samples were collected for analysis. The surge deposit stretched over 10 km2 on land and 35 pits were dug at intervals through it. The sections were described and sampled, yielding a further 60 samples for grain size analysis. Further sampling was carried out on the block and ash deposits in the Tar River Valley and on the Tar River Fan. Pumices from the post-collapse explosion sequence were collected and their densities measured and mass coverage estimated. Deposit maps for airfall, lithics and pumices were constructed for all of the individual events and a map to show the distribution of the main surge unit was generated. The collapse was monitored in real-time using the MVO seismic network and observations from the field. The sequence of events was as follows. From 09:00 to 18:00, low-energy pyroclastic flows took place, confined to the Tar River Valley, which reached the sea at the mouth of Tar River. These flows gradually increased in energy throughout the day but were not associated with energetic, large surges. By 18:00 the pyroclastic flows had increased in volume and were causing phreatic explosions as large, hot blocks hit the sea on the Tar River Fan. By 20:00 the pyroclastic flows had changed in character and were associated with a larger seismic signal and powerful surges that traveled up to 3 km off the coast over the surface of the sea. The most energetic phase of the eruption took place between 22:30 12 July and 01:30 13 July. The dome collapse of 12-13 July culminated in several very large individual pyroclastic flows, representing the collapse of the massive, hot, gas-rich interior of the lava dome. One very large flow was associated with a destructive and energetic surge that swept over topography to the north of the Tar River, killed 40-50 cows, removed trees at their bases and caused large clasts to become embedded in trees at a height of 1.5 m above the ground surface north of Irish Ghaut. The unloading of such large masses of lava dome from over the vent area caused large and powerful explosions. The mapping of the deposits from this event has shed light on the origins of the surge and the timing of large phreatic and magmatic explosions and has led to a new understanding of the hazard potential of large surges derived from the Tar River Valley during large dome collapses at Soufriere Hills Volcano.

Dacitic ash-flow sheet near Superior and Globe, Arizona

USGS Publications Warehouse

Peterson, Donald W.

1961-01-01

Remnants of a dacitic ash-flow sheet near Globe, Miama, and Superia, Arizona cover about 100 square miles; before erosion the area covered by the sheet was at least 400 square miles and perhaps as much as 1,500 square miles. Its maximum thickness is about 2,000 feet, its average thickness is about 500 feet, and its original volume was at least 40 cubic miles. It was erupted on an eroded surface with considerable relief. The main part of the deposit was thought by early workers to be a lava flow. Even after the distinctive character of welded tuffs and related rocks was discovered, the nature and origin of this deposit remained dubious because textures did not correspond to those in other welded tuff bodies. Yet a lava flow as silicic as this dacite would be viscous instead of spreading out as an extensive sheet. The purpose of this investigation has been to study the deposit, resolve the inconsistencies, and deduce its origin and history. Five stratigraphic zones are distinguished according to differences in the groundmass. From bottom to top the zones are basal tuff, vitrophyre, brown zone, gray zone, and white zone. The three upper zones are distinguished by colors on fresh surfaces, for each weathers to a similar shade of light reddish brown. Nonwelded basal tuff grades upward into the vitrophyre, which is a highly welded tuff. The brown and gray zones consist of highly welded tuff with a lithoidal groundmass. Degree of welding decreases progressively upward through the gray and the white zones, and the upper white zone is nonwelded. Textures are clearly outlined in the lower part of the brown zone, but upward they become more diffuse because of increasing devitrification. In the white zone, original textures are essentially obliterated, and the groundmass consists of spherulites and microcrystalline intergrowths. The chief groundmass minerals are cristobalite and sanidine, with lesser quartz and plagioclase. Phenocrysts comprise about 40 percent of the rock, and their relative proportions are fairly uniform. Almost three-fourths of the phenocrysts are plagioclase, one-tenth quartz, one-tenth biotite, and the remainder sanidine, magnetite, and hornblende, with accessory sphene, zircon, and appetite. Pumice fragments are nearly equidimensional near the top of the sheet, and downward they become progressively more flattened until they finally disappear. The zones and the pumice fragment flattening ration (ratio of length to height) provide means for recognizing several faults within the sheet. Twelve new chemical analyses are nearly uniform in composition. If named according to chemical composition, the rock would be a quartz latite, but when named according to phenocrysts, it is a dacite. From the field occurrence and the interpretation of relict textures, it is concluded that the deposit is an ash-flow sheet containing large amounts of welded tuff, and that it was emplaced by a type of nuee ardente instead of a lava flow or air-fall shower. The nature of zoning and trend of flattening ratios indicate a series of eruptions in rapid enough succession for the sheet to form a single cooling unit. Except in the lower part of the sheet, original textures were obscured by devitrification and crystallization during cooling. Nearly uniform mineralogy and chemistry suggest a single magnetic source. A nearly circular area, about 3? miles in diameter, of altered dacite and earlier volcanic rocks, bounded by intricately faulted and brecciated older rocks, may be the site of a caldera that represents the source of the eruptions.

Multibeam Mapping of the West Andaman Fault, NW Sumatra Fault, Andaman Volcanic Arc and Their Tectonic and Magmatic Implications

NASA Astrophysics Data System (ADS)

Kattoju, K. A.; Mudholkar, A. V.; Murty, G.; Vadakkeyakath, Y.; Singh, S. C.; Kiranmai, S.; Moeremans, R.

2012-12-01

West Andaman Fault (WAF) is a major structural feature in the Andaman Offshore region that plays an important role in modulating the strain partitioning within the Andaman Sea, well known for its complex tectonics and seismic hazard potential. However, detailed configuration of the WAF and its interaction with the Sumatra fault system in the Andaman sector are not well understood. Here we present near complete coverage of about 800 km long section of the WAF with special emphasis on the zone of confluence of the WAF and the Sumatra Fault systems, and the adjacent volcanic arc in the offshore region of the Great Nicobar Island. We have examined the fault system, and the volcanic arc feature by combining the newly acquired multibeam bathymetry data with the available data northwest of Sumatra. New multibeam map revealed a pattern of faults that are formed in the region of joining of the Seulimeum (SEU) and Aceh strands (AS) of the Sumatra fault with the WAF off Great Nicobar Island. Sandwiched between these faults, at this location, is a 50 km long and 7 km wide conspicuous NS elongated block that rises to 500 m from an adjacent seafloor of about 2000 m. The surface of the block has a westward dipping topographic fabric. Serpentinites were recovered from the eastern cliff of this block, suggestive of mantle origin. A deformed zone with corrugated surface is documented southeast of this elongated block at water depth ranging from 1000 to 1500 m. The mantle block and the deformed zone are bifurcated by a fault, which might be a branch of the WAF. Further south the expression of the Sumatra platform, northern boundary of the Aceh basin pinching out to WAF, extension of the SEU, AS strands towards south, and the northern limit of Weh basin are observed. The other prominent feature that is documented for the first time is the expression of the Andaman volcanic arc. Twenty-three submarine volcanoes of varying sizes have been mapped between 6°30‧N to 8°15‧N. Magnetic anomaly highs were noticed over the volcanic arc corresponding to volcanoes at 6°50‧N and 7°25‧N. The dredge samples from some of these volcanoes comprise of rhyolites, andesites with glass rind and plagioclase phenocrysts. Pumice was recovered at two volcanoes and also at a volcano north of the Andaman spreading center at 10°34‧N. Andesites were also recovered from the faults east of WAF bordering the Sewell rise. Recovery of these rock types is indicative of ascending melts from the recycled subducting lithosphere while the presence of pumice suggests the occurrence of submarine explosive volcanism. The volcanic arc is traced from the south off Sumatra region up to 12°N, which joins the Barren Island and the Narcondam Island volcanoes in the north. Our mapping and seabed sampling results provide for the first time, configuration of a section of the WAF, the Sumatra fault system and the volcanic arc, and provide insights into the interaction of these major fault systems with the volcanic arc in the Andaman Sea.

New 40Ar/39Ar age of the Bishop Tuff from multiple sites and sediment rate calibration for the Matuyama-Brunhes boundary

USGS Publications Warehouse

Sarna-Wojcicki, A. M.; Pringle, M.S.; Wijbrans, J.

2000-01-01

Precise dating of sanidine from proximal ash flow Bishop Tuff and air fall Bishop pumice and ash, California, can be used to derive an absolute age of the Matuyama Reversed-Brunhes Normal (M-B) paleomagnetic transition, identified stratigraphically close beneath the Bishop Tuff and ash at many sites in the western United States. An average age of 758.9 ?? 1.8 ka, standard error of the mean (SEM), was obtained for individual sanidine crystals or groups of several crystals, determined from ???70 individual analyses of sanidine separates from 11 sample groups obtained at five localities. The basal air fall pumice (757.7 ?? 1.8 ka) and overlying ash flow tuff (762.2 ?? 4.7 ka) from near the source yield essentially the same dates within errors of analysis, suggesting that the two units were emplaced close in time. A date on distal Bishop air fall ash bed at Friant, California, ???100 km to the west of the source area, is younger, 750.1 ?? 4.3 ka, but not significantly different within analytical error (??1 standard deviation). Previous dates of the Bishop Tuff, obtained by others using conventional K-Ar and the fission track method on zircons, ranged from ???650 ka to ???1.0 Ma. The most recent, generally accepted date by the K-Ar method on sanidine was 738 ?? 3 ka. We infer, as others before, that many K-Ar dates on sanidine feldspar are too young owing to incomplete degassing of radiogenic Ar during fusion in the K-Ar technique and that many older K-Ar dates are too old owing to detrital or xenocrystic contamination in the larger samples that are necessary for the technique. The new dates are similar to recent 40Ar/39Ar ages of the Bishop Tuff determined on individual samples by others but are derived from a larger proximal sample population and from multiple analysis of each sample. The results provide a definitive and precise age calibration of this widespread chronostratigraphic marker in the western United States and northeastern Pacific Ocean. We calculated the age of the M-B transition at five sites, assuming constant sedimentation rates, the age of the Bishop ash bed and one or more well-dated chronostratigraphic horizons above and below the Bishop Tuff ash bed and M-B transition, and stratigraphic separations between these datum levels. The age of the M-B transition is 774.2 ?? 2.8 ka, based on the average of eight such calculations, close to other recent determinations, and similar to that determined from the astronomically tuned polarity timescale. Our approach provides an alternative and surprisingly precise method for determining the age of the M-B and other chronostratigraphic levels. The above dates, calculated using U.S. Geological Survey values of 27.92 Ma for the Taylor Creek (TC) sanidine can be recalculated to other widely used values for these monitors. For example, using recently published values of 28.34 Ma (TC) and 523.1 Ma (McLure Mountain hornblende, MMhb-1), the resulting ages are ???774 ka for the Bishop Tuff and ash bed and ???789 ka for the M-B transition. Copyright 2000 by the American Geophysical Union.

Effusive silicic volcanism in the Central Andes: The Chao dacite and other young lavas of the Altiplano-Puna Volcanic Complex

NASA Technical Reports Server (NTRS)

De Silva, S. L.; Self, S.; Francis, P. W.; Drake, R. E.; Ramirez, Carlos R.

1994-01-01

The largest known Quaternary silicic lava body in the world is Cerro Chao in north Chile, a 14-km-long coulee with a volume of at least 26 cu km. It is the largest of a group of several closely similar dacitic lavas erupted during a recent (less than 100,000 year old) magmatic episode in the Altiplano-Puna Volcanic Complex (APVC; 21-24 deg S) of the Centra; Andean Volcanic Zone. The eruption of Chao proceeded in three phases. Phase 1 was explosive and produced approximately 1 cu km of coarse, nonwelded dacitic pumice deposits and later block and ash flows that form an apron in front of the main lava body. Phase 2 was dominantly effusive and erupted approximately 22.5 cu km of magma in the form of a composite coulee covering approximately 53 sq km with a 400-m-high flow front and a small cone of poorly expanded pumice around the vent. The lava is homogeneous with rare flow banding and vesicular tops and selvages. Ogives (flow ridges) reaching heights of 30 m form prominent features on its surface. Phase 3 produced a 6-km-long, 3-km-wide flow that emanated from a collapsed dome. Ogives are subdued, and the lava is glassier than that produced in previous phases. All the Chao products are crystal-rich high-K dacites and rhyodacites with phenocrysts of plagioclase, quartz, hornblende, biotite, sphene, rare snidine, and oxides. Phenocryst contents reach 40-60 vol % (vesicle free) in the main phase 2 lavas but are lower in the phase 1 (20-25%) and phase 3 (approximately 40%) lavas. Ovoid andesitic inclusions with vesicular interiors and chilled margins up to 10 cm are found in the later stages of phase 2 and compose up to 5% of the phase 3 lava. There is little evidence for preeruptive zonation of the magma body in composition, temperature (approximately 840 C), fO2 (19(exp -11), or water content, so we propose that eruption of the Chao complex was driven by intrusion of fresh, hot andesitic magma into a crystallizing and largely homogeneous body of dacitic magma. Morphological measurements suggest that the Chao lavas had internal plastic viscosities of 10(exp 10) to 10(exp 12) Pa s, apparent viscosities of 10(exp 9) Pa s, surface viscosities of 10(exp 15) to 10(exp 24) Pa s, and a yield strength of 8 x 10(exp 5) Pa. These estimates indicate that Chao would have exhibited largely similar rheological properties to other silicic lava extrusions, notwithstanding its high phenocryst content. We suggest that Chao's anomalous size is a function of both the relatively steep local slope (20 deg to 3 deg) and the available volume of magma. The eruption duration for Chao's emplacement is thought to have been about 100 to 150 years, with maximum effusion rates of about 25 cu m/s for short periods. Four other lavas in the vicinity with volumes of approximately 5 cu km closely resemble Chao and are probably comagnetic. The suite as a whole shares a petrologic and chemical similarity with the voluminous regional Tertiary to Pleistocene ignimbrites of the APVC and may be derived from a zone of silicic magmatism that is thought to have been active since the late Tertiary. Chao and the other young lavas may represent either the waning of this system or a new episode fueled by intrusions of mafic magma.

Pre-eruptive storage conditions and continuous decompression relations of rhyodacite magma erupted from Chaos Crags, Lassen Volcanic Center, California

NASA Astrophysics Data System (ADS)

Quinn, E. T.; Andrews, B. J.; Schwab, B. E.; Clynne, M. A.

2013-12-01

We performed a series of hydrothermal (high-temperature and -pressure) phase equilibrium experiments on a natural rhyodacite pumice from the 1103 ×13 years BP pyroclastic flow from the Chaos Crags, Lassen Volcanic Center, California. The pumice (LQ13-01, collected at the same location as LC84-417 (69.58 wt. % SiO2) by Clynne) is from the lower pyroclastic flow member of the group 1 lavas, the most silicic products known of Chaos Crags. Group 1 lavas are homogeneous (69-70 wt. % SiO2), petrographically and compositionally similar with rare to sparse mafic inclusions, and comprise the earliest emplaced units of Chaos Crags, the lower, middle, and upper pyroclastic flows, and domes A and B, whereas group 2 are comparatively heterogeneous (67-69 wt. % SiO2), with increasing abundance (10-15%) of mafic inclusions throughout the emplacement sequence, and comprise domes C through F. The phase assemblage in the natural sample used as experimental starting material comprises phenocrysts of quartz, plagioclase feldspars with rims of ~An35, biotite, hornblende, and Fe-Ti oxides in a vesiculated glassy matrix. Trace mafic enclaves are also present, but were removed from experimental starting material. All experiments were performed at the Smithsonian Institution. Experiments were run under H2O-saturated conditions at pressures of 75 MPa to 200 MPa and temperatures of 750°C to 900°C, at oxygen fugacity NNO+1 (×0.5-log-units), for 93 to 132 hours. EPMA and SEM analyses of experimental products show quartz is stable from <200 MPa at 750°C to <150 MPa at 800°C and is not stable at temperatures >800°C, within the investigated range. Amphibole is stable from >75 MPa at 750°C to >100 MPa at 800°C to 200 MPa at <850°C, and is not stable ≤75 MPa or ≥850°C. Biotite is stable at <800°C at 75 MPa to <825°C at 200 MPa, and not stable for any pressure at ≥850°C. Pyroxene, not present in the starting material is stable for 200MPa at >775°C and all pressures at temperatures ≥825°C, within the investigated range. FTIR analysis of quartz-hosted melt inclusions contain 4.0-5.0 wt. % H2O (average 4.3 wt. %), suggesting saturation pressures of 100-110 MPa (calculated using model of Papale et al., 2006). Comparison of the natural samples with the experimentally determined phase diagram and melt inclusions, suggests pre-eruptive storage conditions of 110-125 MPa and 775°C; given FeTi-oxide temperatures of 850 °C, magma may have been heated by as much as 75-100°C immediately prior to eruption. Ongoing work includes EPMA analysis of plagioclase feldspars and amphiboles to further constrain An-stability and hornblende-cummingtonite relations , respectively, and analysis of titanomagnetite-ilmenite pairs. Continuous decompression experiments are underway with rates ranging from 0.3 MPa/hr to 7.5 MPa/hr, corresponding to total decompression times of 16 hours to 18 days.

Effect of particle entrainment on the runout of pyroclastic density currents

NASA Astrophysics Data System (ADS)

Fauria, Kristen E.; Manga, Michael; Chamberlain, Michael

2016-09-01

Pyroclastic density currents (PDCs) can erode soil and bedrock, yet we currently lack a mechanistic understanding of particle entrainment that can be incorporated into models and used to understand how PDC bulking affects runout. Here we quantify how particle splash, the ejection of particles due to impact by a projectile, entrains particles into dilute PDCs. We use scaled laboratory experiments to measure the mass of sand ejected by impacts of pumice, wood, and nylon spheres. We then derive an expression for particle splash that we validate with our experimental results as well as results from seven other studies. We find that the number of ejected particles scales with the kinetic energy of the impactor and the depth of the crater generated by the impactor. Last, we use a one-dimensional model of a dilute, compressible density current—where runout distance is controlled by air entrainment and particle exchange with the substrate—to examine how particle entrainment by splash affects PDC density and runout. Splash-driven particle entrainment can increase the runout distance of dilute PDCs by an order of magnitude. Furthermore, the temperature of entrained particles greatly affects runout and PDCs that entrain ambient temperature particles runout farther than those that entrain hot particles. Particle entrainment by splash therefore not only increases the runout of dilute PDCs but demonstrates that the temperature and composition of the lower boundary have consequences for PDC density, temperature, runout, hazards and depositional record.

Revised chronostratigraphy of recurrent ignimbritic eruptions in Dominica (Lesser Antilles arc): Implications on the behavior of the magma plumbing system

NASA Astrophysics Data System (ADS)

Boudon, Georges; Balcone-Boissard, Hélène; Solaro, Clara; Martel, Caroline

2017-09-01

Ignimbritic eruptions represent catastrophic events due to the magma volume involved and the related consequences on Earth's environment in relation with the released gases and the tephra dispersal. Dominica has been recognized as hosting one of the major ignimbritic eruptions of the last 200 ky in the Lesser Antilles arc, called the Roseau Tuff. But more recent works have evidenced several pumiceous events instead of a single large one. Here we propose a revised chronostratigraphy of the explosive activity that occurred in the last tens of thousands years based on three field trips, new 14C ages, detailed lithological and geochemical investigations, in particular a precise characterization of trace element glass chemistry. This eruptive history reconstruction is mainly based on outcrops along the coast and in the valley, since the luxury vegetation in the center of the island mostly precludes sections close to the central volcanic centers. We thus confirm that the Roseau event has been overestimated and that we may recognize five main ignimbritic events: Grande Savane, Layou ( 51 ka), Grand Bay, Roseau ( 33 ka), Grand Fond ( 24 ka). We discuss the possible volcanic center at their origin, in addition to correlations with some Plinian events of lower magnitude that were identified in the Roseau valley and in the southern part of Dominica. This study may help to better constrain the eruptive history of the most active volcanic island of the Lesser Antilles arc, which has important implications on hazard mitigation.

New 1.5 million-year-old Homo erectus maxilla from Sangiran (Central Java, Indonesia).

PubMed

Zaim, Yahdi; Ciochon, Russell L; Polanski, Joshua M; Grine, Frederick E; Bettis, E Arthur; Rizal, Yan; Franciscus, Robert G; Larick, Roy R; Heizler, Matthew; Aswan; Eaves, K Lindsay; Marsh, Hannah E

2011-10-01

Sangiran (Solo Basin, Central Java, Indonesia) is the singular Homo erectus fossil locale for Early Pleistocene Southeast Asia. Sangiran is the source for more than 80 specimens in deposits with (40)Ar/(39)Ar ages of 1.51-0.9 Ma. In April 2001, we recovered a H. erectus left maxilla fragment (preserving P(3)- M(2)) from the Sangiran site of Bapang. The find spot lies at the base of the Bapang Formation type section in cemented gravelly sands traditionally called the Grenzbank Zone. Two meters above the find spot, pumice hornblende has produced an (40)Ar/(39)Ar age of 1.51 ± 0.08 Ma. With the addition of Bpg 2001.04, Sangiran now has five H. erectus maxillae. We compare the new maxilla with homologs representing Sangiran H. erectus, Zhoukoudian H. erectus, Western H. erectus (pooled African and Georgian specimens), and Homo habilis. Greatest contrast is with the Zhoukoudian maxillae, which appear to exhibit a derived pattern of premolar-molar relationships compared to Western and Sangiran H. erectus. The dental patterns suggest distinct demic origins for the earlier H. erectus populations represented at Sangiran and the later population represented at Zhoukoudian. These two east Asian populations, separated by 5000 km and nearly 800 k.yr., may have had separate origins from different African/west Eurasian populations. Copyright © 2011 Elsevier Ltd. All rights reserved.

Evaluation of the potential for debris and hyperconcentrated flows in Capulin Canyon as a result of the 1996 Dome fire, Bandelier National Monument, New Mexico

USGS Publications Warehouse

Cannon, Susan H.

1997-01-01

The Dome fire of April 1996 burned 6684 ha in Bandelier National Monument and the adjacent Sante Fe National Forest. The potential for significant debris- and hyperconcentrated-flow activity in Capulin Canyon is evaluated through 1) a systematic consideration of geologic and geomorphic factors that characterize the condition of the hillslope materials and channels following the fire, 2) examination of sedimentologic evidence for past debris-flow activity in the canyon, and 3) evaluation of the response of the watershed through the 1996 summer monsoon season. The lack of accumulations of dry-ravel material on the hillslopes or in channels, the absence of a continuous hydrophobic layer, the relatively intact condition of the riparian vegetation and of the fibrous root mat on the hillslopes, and the lack of evidence of widespread past debris- and hyperconcentrated-flow activity, even with evidence of past fires, indicate a low potential for debris-flow activity in Capulin Canyon. In addition, thunderstorms during the summer monsoon of 1996 resulted in abundant surface overland flow on the hillslopes which transported low-density pumice, charcoal, ash and some mineral soil downslope as small-scale and non-erosive debris flows. In some places cobble- and boulder-sized material was moved short distances. A moderate potential for debris- and hyperconcentrated-flow activity is identified for the two major tributary canyons to Capulin Canyon based on evidence of both summer of 1996 and possible historic significant debris-flow activity.

Lithofacies of Spencer Formation, western Tualatin Valley, Oregon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Atta, R.O.

The Spencer Formation crops out in a narrow band that trends north-northwest on the western edge of the Willamette and Tualatin Valleys, Oregon. It apparently conformably overlies mud rocks of either the Yamhill or the Nestucca Formation and is conformably overlain by the Pittsburgh Bluff Formation. The Spencer Formation consists of two members (informal): a lower highly micaceous sandstone (800-1000 ft) and an upper member that is micaceous siltstone and mudstone (1000-1300 ft). The lower member includes an upper part that is light-gray to creamy-gray, silty to muddy, pebbly lithic arkose to feldspathic litharenite, with minor arkose. Sorting is poormore » and beds may be laminated to ripple cross-laminated or massive and bioturbated with abundant mollusk shells, carbonized wood, and burrows. The lower part of the lower member is medium-gray to greenish-gray, silty, pumiceous lithic arkose to feldspathic litharenite. The texture tends to be more uniform and better sorted than that of the upper part of the member. Bedding is commonly massive due to bioturbation. The upper member is medium to dark-gray mudstone with thin pebble-conglomerate lenses. It intertongues with the lower member. Bioturbation, burrows, and carbonized wood are common. The trend in depositional environments appears to be from outer to mid-neritic (lower part, lower member) to shallow neritic, nearshore, and lagoonal (upper part, lower member, and upper member). The provenance of the Spencer Formation includes both proximal volcanics and distant plutonic and high-grade metamorphics.« less

Spatial distribution of damage around faults in the Joe Lott Tuff Member of the Mount Belknap Volcanics, Utah: A mechanical analog for faulting in pyroclastic deposits on Mars

USGS Publications Warehouse

Okubo, Chris H.

2012-01-01

Volcanic ash is thought to comprise a large fraction of the Martian equatorial layered deposits and much new insight into the process of faulting and related fluid flow in these deposits can be gained through the study of analogous terrestrial tuffs. This study identifies a set of fault-related processes that are pertinent to understanding the evolution of fault systems in fine-grained, poorly indurated volcanic ash by investigating exposures of faults in the Miocene-aged Joe Lott Tuff Member of the Mount Belknap Volcanics, Utah. The porosity and granularity of the host rock are found to control the style of localized strain that occurs prior to and contemporaneous with faulting. Deformation bands occur in tuff that was porous and granular at the time of deformation, while fractures formed where the tuff lost its porous and granular nature due to silicic alteration. Non-localized deformation of the host rock is also prominent and occurs through compaction of void space, including crushing of pumice clasts. Significant off-fault damage of the host rock, resembling fault pulverization, is recognized adjacent to one analog fault and may reflect the strain rate dependence of the resulting fault zone architecture. These findings provide important new guidelines for future structural analyses and numerical modeling of faulting and subsurface fluid flow through volcanic ash deposits on Mars.

Effects of fluidization of the host sediment on peperite textures: A field example from the Cretaceous Buan Volcanics, SW Korea

NASA Astrophysics Data System (ADS)

Gihm, Yong Sik; Kwon, Chang Woo

2017-04-01

In the Cretaceous Buan Volcanics (SW Korea), blocky and fluidal peperites are hosted in a massive pumiceous lapilli tuff intruded by intermediate dikes. Blocky peperites, the most abundant species, are characterized by polyhedral or platy juvenile clasts and a jigsaw-crack texture. Fluidal peperites occur only along dike margins, where the host sediments are composed of well sorted, fine to very fine ash (fine-grained zone), and are characterized by fluidal or globular juvenile clasts with irregular or ragged margins. The fine-grained zone is interpreted to form by grain size segregation caused by upward moving pore water (fluidization) that has resulted from heat transfer from intruding magma toward waterlogged host sediments during intrusion. With the release of pore water and the selective entrainment of fine-grained ash, fine-grained zones formed within the host sediments. Subsequent interactions between the fine-grained zone and the intruding magma resulted in ductile deformation of the magma before fragmentation, which generated fluidal peperites. Outside the fine-grained zone, intruding magma fragmented in a brittle manner because of the relative deficiency of both pore water and fine-grained ash, resulting in the formation of blocky peperites. The results of this study suggest that redistribution of constituent particles (ash) and interstitial fluids during fluidization resulted in heterogeneous physical conditions of the host sediments, which influenced peperite-forming processes, as reflected by the different peperite textures.

Production of Poly-γ-Glutamate (PGA) Biopolymer by Batch and Semicontinuous Cultures of Immobilized Bacilluslicheniformis strain-R

PubMed Central

Berekaa, Mahmoud M.; El Aassar, Samy A.; El-Sayed, Samia M.; EL Borai, Aliaa M.

2009-01-01

Production of Polyglutamate (PGA) biopolymer by immobilized Bacillus licheniformis strain-R was intensively investigated. Preliminary experiments were carried out to address the most suitable immobilization methodology. Entrapment of Bacillus cells in alginate–agar led optimal PGA production (36.75 g/l), with 1.32-and 2.18-fold increase in comparison with alginate-or K-carrageenan-immobilized cells, respectively. During semicontinuous cultivation of agar-alginate gel-cell mixture, production of PGA by 10 ml mixture was increased from 2nd to 3rd run whereas, increased till the 4th run using 15ml mixture. Adsorption was the most suitable immobilization technique for production of PGA and the sponge cubes was the preferred matrix recording 43.2 g/l of PGA with the highest cell adsorption. Furthermore, no PGA was detected when B. licheniformis cells were adsorbed on wood and pumice. Although luffa pulp-adsorbed cells recorded the highest PGA production (50.4 g/l), cell adsorption was the lowest. Semicontinuous cultivation of B. licheniformis cells adsorbed on sponge led to increase of PGA production till the 3rd run and reached 55.5 g/l then slightly decreased in the 4th run. The successful use of fixed-bed bioreactor for semicontinuous cultivation of B. licheniformis cells held on sponge cubes (3 runs, 96 hours/run) provides insight for the potential biotechnological production of PGA by immobilized cells. PMID:24031418

Phase-equilibrium geobarometers for silicic rocks based on rhyolite-MELTS. Part 4: Plagioclase, orthopyroxene, clinopyroxene, glass geobarometer, and application to Mt. Ruapehu, New Zealand

NASA Astrophysics Data System (ADS)

Harmon, Lydia J.; Cowlyn, James; Gualda, Guilherme A. R.; Ghiorso, Mark S.

2018-01-01

A new phase equilibria geobarometer determines magmatic storage and crystallization conditions, including pressure, temperature, oxygen fugacity ({f_{{{o}_2}}}), and the presence of a fluid phase for glass-bearing rocks containing the assemblage plagioclase + pyroxene(s). This newly developed geobarometer can better constrain crystallization conditions of shallow (< 500 MPa; < 20 km), glass-bearing andesites to dacites. The geobarometer utilizes rhyolite-MELTS to determine crystallization conditions in natural pumice and scoria samples. The validity of the geobarometer is tested by comparing it to results from experiments. Uncertainties are assessed using Monte Carlo simulations. We apply the geobarometer to the plag + opx + cpx-bearing system of Mt. Ruapehu, in the southern Taupo Volcanic Zone, New Zealand. The samples from Mt. Ruapehu are tested from 5 to 400 MPa and from super-liquidus to 90% crystalline ( 1200 to 700 °C). Mt. Ruapehu serves as a methodological testing ground for the geobarometer, and results from our geobarometer agree with recent Mt. Ruapehu studies. Results show a distribution of crystallization pressures ranging from 50 to 150 MPa ( 2.0 to 5.9 km) for different eruptions, with modes of 110 MPa ( 4.3 km) and 130 MPa ( 5.1 km). These are consistent with field interpretations of different eruptive styles based on juvenile clast textures and previous knowledge of the magma plumbing system. Mt. Ruapehu magmas are fluid saturated, with {f_{{{o}_2}}} of ΔQFM + 1 (NNO).

New geophysical views of Mt.Melbourne Volcano (East Antarctica)

NASA Astrophysics Data System (ADS)

Armadillo, E.; Gambetta, M.; Ferraccioli, F.; Corr, H.; Bozzo, E.

2009-05-01

Mt. Melbourne volcano is located along the transition between the Transantarctic Mountains and the West Antarctic Rift System. Recent volcanic activity is suggested by the occurrence of blankets of pyroclastic pumice and scoria fall around the eastern and southern flanks of Mt Melbourne and by pyroclastic layers interbedded with the summit snows. Geothermal activity in the crater area of Mount Melbourne may be linked to the intrusion of dykes within the last 200 years. Geophysical networks suggest that Mount Melbourne is a quiescent volcano, possibly characterised by slow internal dynamics. During the 2002-2003 Italian Antarctic campaign a high-resolution aeromagnetic survey was performed within the TIMM (Tectonics and Interior of Mt. Melbourne area) project. This helicopter-borne survey was flown at low-altitude and in drape-mode configuration (305 m above terrain) with a line separation less than 500 m. Our new high-resolution magnetic maps reveal the largely ice-covered magmatic and tectonic patters in the Mt. Melbourne volcano area. Additionally, in the frame of the UK-Italian ISODYN-WISE project (2005-06), an airborne ice-sounding radar survey was flown. We combine the sub-ice topography with images and models of the interior of Mt. Melbourne volcano, as derived from the high resolution aeromagnetic data and land gravity data. Our new geophysical maps and models also provide a new tool to study the regional setting of the volcano. In particular we re-assess whether there is geophysical evidence for coupling between strike-slip faulting, the Terror Rift, and Mount Melbourne volcano.

Lake sediments provide the first eruptive history for Corbetti, a high-risk Main Ethiopian Rift volcano

NASA Astrophysics Data System (ADS)

Martin-Jones, Catherine M.; Lane, Christine S.; Pearce, Nicholas J. G.; Smith, Victoria C.; Lamb, Henry F.; Schaebitz, Frank; Viehberg, Finn; Brown, Maxwell C.; Frank, Ute; Asrat, Asfawossen

2017-04-01

A recent World Bank report found that 49 of Ethiopia's 65 known Holocene volcanoes pose a high-risk to the surrounding population. One of these volcanoes, Corbetti, located in the densely populated Main Ethiopian Rift (MER), has only one documented Holocene eruption. Any risk assessment for Corbetti is therefore highly uncertain. Reliable hazard forecasting is dependent on the completeness of volcanic records. In the case of Ethiopian Rift volcanoes complete records are hindered by frequently poorly exposed, buried and inaccessible proximal outcrops. Lake sediments can yield comprehensive, stratigraphically-resolved dossiers of past volcanism. Here we use volcanic ash (tephra) layers preserved in sediments from three MER lakes to provide the first record of Holocene volcanism for Corbetti. It shows that Corbetti has erupted explosively throughout the Holocene at an average return period of 800 years. Based on the thickness and dispersal of the tephras, at least six eruptions were of a large magnitude, and there were four eruptions in the past 2000 years. Future explosive eruptions are likely and these could have significant societal impacts, they could blanket nearby Awassa and Shashamene, home to 260,000 people, with pumice deposits. Our data indicate that the threat posed by Corbetti has been significantly underestimated. These data can be used to refine regional volcano monitoring and develop evacuation plans. This lake sediment-tephrostratigraphic approach shows significant potential for application throughout the East African Rift system, and is essential to understanding volcanic hazards in this rapidly developing region.

Latest Pleistocene crustal cannibalization at Baekdusan (Changbaishan) as traced by oxygen isotopes of zircon from the Millennium Eruption

NASA Astrophysics Data System (ADS)

Cheong, Albert Chang-sik; Sohn, Young Kwan; Jeong, Youn-Joong; Jo, Hui Je; Park, Kye-Hun; Lee, Youn Soo; Li, Xian-Hua

2017-07-01

The silicic volcanism of Baekdusan (Changbaishan), which is on the border between North Korea and China, was initiated in the Late Pleistocene and culminated in the 10th century with a powerful (volcanic explosivity index = 7) commendite-trachyte eruption commonly referred to as the "Millennium Eruption." This study presents oxygen isotope data of zircon in trachydacitic pumices ejected during the Millennium Eruption, together with whole-rock geochemical and Sr-Nd-Pb isotopic data that manifest once again the A-type and EM1 affinities of the Millennium Eruption magma. The zircon crystals, dated by previous studies at ca. 12-9 ka, show a moderate inter-grain variation in δ18O from 3.69‰ to 5.03‰. These values are consistently lower than the normal mantle range, and interpreted to have resulted from the digestion of meteoric-hydrothermally altered intracaldera rocks in the shallow magma chamber beneath Baekdusan just prior to the crystallization of the zircons, rather than from derivation from low-δ18O sources deep in the mantle. The whole-rock geochemical/isotopic considerations suggest that the magma mainly self-cannibalized the earlier erupted volcanic carapace around the magma chamber. This study highlights the usefulness of zircon oxygen isotopes for characterizing past volcanic activity that has now been commonly eroded away and implies that the generation of Yellowstone-type low-δ18O magma is not a rare phenomenon in large-volume silicic eruptions.

Causes of complexity in a fallout dominated plinian eruption sequence: 312 ka Fasnia Member, Diego Hernández Formation, Tenerife, Spain

NASA Astrophysics Data System (ADS)

Edgar, C. J.; Cas, R. A. F.; Olin, P. H.; Wolff, J. A.; Martí, J.; Simmons, J. M.

2017-10-01

The 312 ka Fasnia eruption from the Las Cañadas Caldera on Tenerife, Canary Islands, Spain, produced a complex sequence of twenty-two intercalated units, including 7 pumice fall, 7 ignimbrite and 8 ash surge and fall deposits that define two distinct eruption sequences (Lower and Upper Fasnia sequences). The fallout units themselves are internally complex, reflecting waxing and waning of the eruption column, while many of the ignimbrites reflect multiple intra-plinian partial column collapse events associated with the injection of lithic clasts into the eruption column. The Lower and Upper Fasnia eruption phases were each terminated by caldera collapse and complete column collapse events. Probable blockage of the conduit and vent system during Lower Fasnia caldera collapse event briefly terminated the eruption, resulting in a short-lived period of erosion and sedimentation prior to the onset of the Upper Fasnia phase. The transition to the Upper Fasnia eruption phase coincided with the eruption of more geochemically homogeneous pyroclasts. In total, 62 km3 of tephra were erupted, including 49 km3 of juvenile clasts and > 12 km3 of lithic clasts. The DRE volume of magma erupted was 13 km3 (Lower Fasnia > 5 km3, Upper Fasnia > 8 km3), two thirds of which ( 9-10 km3) was deposited purely by fallout. The Fasnia Member is one of the most complex plinian sequences known.

Crew Earth Observations (CEO) taken during Expedition Six

NASA Image and Video Library

2003-02-16

ISS006-E-28546 (16 February 2003) --- Popocatepetl and Iztaccíhuatl Volcanoes in Mexico are featured in this digital image photographed by an Expedition 6 crewmember on the International Space Station (ISS). As part of the circum-Pacific “Ring of Fire”, Mexico hosts several of the world’s most continually active volcanoes including the massive Popocatepetl (Aztec for “Smoking Mountain”). This detailed oblique photograph also depicts a neighboring volcano, Iztaccíhuatl (the “Woman in White”). Popocatepetl has produced small, intermittent eruptions since 1994. In addition to the constant potential of eruptions producing ash deposits, pyroclastic flows, and lava, the summit of Popocatepetl also hosts glaciers. These can melt during eruptions to form mudflows that blanket areas to the south. In contrast to Popocatepetl’s well-defined symmetrical cone, Iztaccíhuatl is formed from several overlapping smaller cones that trend north-northwest to south-southeast. Glaciers and year-round snow are also present on Iztaccíhuatl (white regions along the peaks). According to NASA scientists, deep valleys have been eroded into the massive apron of ash and pumice deposits, glacial outwash, and alluvium to the east of the volcano. Despite its close proximity, similar age, and similar geologic character to Popocatepetl, Iztaccíhuatl has not erupted in historic times. This has encouraged the establishment of numerous agricultural fields (visible as faint rectilinear patterns in the lower half of the image) on the eastern flank of the mountain.

Evaluation of different configurations of hybrid membrane bioreactors for treatment of domestic wastewater.

PubMed

Cuevas-Rodríguez, G; Cervantes-Avilés, P; Torres-Chávez, I; Bernal-Martínez, A

2015-01-01

Four membrane bioreactors (MBRs) with the same dimensions were studied for 180 days: three hybrid growth membrane bioreactors with biofilm attached in different packing media and a conventional MBR (C-MBR). The four MBRs had an identical membrane module of hollow fiber with a nominal porous diameter of 0.4 μm. The MBRs were: (1) a C-MBR; (2) a moving bed membrane bioreactor (MB-MBR), which was packed with 2 L of carrier Kaldnes-K1, presenting an exposed surface area of 678.90 m²/m³; (3) a non-submerged organic fixed bed (OFB-MBR) packed with 6.5 L of organic packing media composed of a mixture of cylindrical pieces of wood, providing an exposed surface area of 178.05 m²/m³; and (4) an inorganic fixed bed non-submerged membrane bioreactor (IFB-MBR) packed with 6 L of spherical volcanic pumice stone with an exposed surface area of 526.80 m²/m³. The four MBRs were fed at low organic loading (0.51 ± 0.19 kgCOD/m³ d). The results were recorded according to the behavior of the total resistance, transmembrane pressure (TMP), permeability, and removal percentages of the nutrients during the experimental time. The results showed that the MB-MBR presented the better performance on membrane filtration, while the higher nutrient removals were detected in the OFB-MBR and IFB-MBR.

The assessment of orthodontic bonding defects: optical coherence tomography followed by three-dimensional reconstruction

NASA Astrophysics Data System (ADS)

Rominu, R.; Sinescu, C.; Rominu, M.; Negrutiu, M.; Petrescu, E.; Pop, D.; Podoleanu, A. Gh.

2011-10-01

Orthodontic bonding is a simple yet important procedure that can influence the outcome of treatment in case it is performed incorrectly. An orthodontic treatment shadowed by repeated bonding failures can become unduly long and will decrease patient trust and compliance. Optical coherence tomography has been widely used in ophtalmology but is relatively new to dentistry. Using OCT one can detect aerial inclusions within the orthodontic adhesive or even identify incongruence between the bracket base and the tooth surface. The aim of our study was to identify bonding defects and reconstruct them three-dimensionally in order to be able to characterize them more accurately. We bonded 30 sound human permanent teeth with ceramic orthodontic brackets using a no-mix self-curing orthodontic adhesive. Prior to bonding all teeth were stored in tap water at 4°C and then professionally cleaned with rotary brushes and pumice. The samples were processed by the same person and the rotary brushes were changed after every fifth tooth. All interfaces were investigated by means of OCT and 4 defects were found. Subsequently, the defects were reconstructed threedimensionally using an open-source program. By identifying and reconstructing bonding defects we could assess the quality of the bonding procedure. Since bonding tends to be more accurate in vitro where the environmental conditions are close to ideal, it is probable that defects found in vivo be even greater in number, which leads to the conclusion that this type of investigation is potentially valuable.

Stratigraphy of Late Pleistocene-Holocene pyroclastic deposits of Tacana Volcano, Mexico-Guatemala

NASA Astrophysics Data System (ADS)

Macias, J. L.; Arce, J. L.; Garcia-Palomo, A.; Mora, J. C.; Saucedo, R.; Hughes, S.; Scolamacchia, T.

2005-12-01

Tacana volcano (4,060 masl), the highest peak of the Tacana Volcanic Complex, is an acitve volcano located on the Mexico-Guatemala border. Tacana resumed phreatic activity in 1950 and again in 1986. After this last event, the volcano became the locus of attention of authorities and local scientists began to study the complex. Tacana's stratigraphic record has been studied using radiocarbon dating and these indicate that the volcano has been very active in the past producing at least 12 explosive eruptions during the last 40 ka years as follow: a) Four partial dome destruction events with the generation of block-and-ash flow deposits at 40, 28, <26, and 16 ka. b) Four small-volume phreatomagmatic events that emplaced dilute density currents at 10.6, 7.5, 6, and 2.5 ka. c) Four eruptions that emplaced pumice-rich fall deposits, three of them widely dispersed towards the NE flank of the volcano in Guatemala and dated at ~32, <24 and <14 ka, and finally a 0.8 ka fall deposit restricted to the crater vicinity that might represent the youngest magmatic eruption of the volcano. Although refining of these stratigraphic sequence is still underway, the eruptive chronology of Tacana volcano cleary indicates that explosive eruptions producing plinian fall and pyroclastic density currents have taken place every 1 to 8 ka years. This record constrasts with the small phreatic eruptions that occur 1-2 per century. So, this indicates that Tacana volcano is more active than previously considered and these results must be considered for future researches on hazards maps and mitigation.

Evaluation of the effect of different methods of microabrasion and polishing on surface roughness of dental enamel.

PubMed

Bertoldo, Carlos; Lima, Debora; Fragoso, Larissa; Ambrosano, Glaucia; Aguiar, Flavio; Lovadino, Jose

2014-01-01

The microabrasion technique of enamel consists of selectively abrading the discolored areas or causing superficial structural changes in a selective way. In microabrasion technique, abrasive products associated with acids are used, and the evaluation of enamel roughness after this treatment, as well as surface polishing, is necessary. This in-vitro study evaluated the enamel roughness after microabrasion, followed by different polishing techniques. Roughness analyses were performed before microabrasion (L1), after microabrasion (L2), and after polishing (L3).Thus, 60 bovine incisive teeth divided into two groups were selected (n=30): G1- 37% phosphoric acid (37%) (Dentsply) and pumice; G2- hydrochloric acid (6.6%) associated with silicon carbide (Opalustre - Ultradent). Thereafter, the groups were divided into three sub-groups (n=10), according to the system of polishing: A - Fine and superfine granulation aluminum oxide discs (SofLex 3M); B - Diamond Paste (FGM) associated with felt discs (FGM); C - Silicone tips (Enhance - Dentsply). A PROC MIXED procedure was applied after data exploratory analysis, as well as the Tukey-Kramer test (5%). No statistical differences were found between G1 and G2 groups. L2 differed statistically from L1 and showed superior amounts of roughness. Differences in the amounts of post-polishing roughness for specific groups (1A, 2B, and 1C) arose, which demonstrated less roughness in L3 and differed statistically from L2 in the polishing system. All products increased enamel roughness, and the effectiveness of the polishing systems was dependent upon the abrasive used.

IODP Expedition 351 Lithostratigraphy: Volcaniclastic Record of Izu-Bonin-Mariana (IBM) Arc Initiation

NASA Astrophysics Data System (ADS)

Barth, A. P.; Brandl, P. A.; Li, H.; Hickey-Vargas, R.; Jiang, F.; Kanayama, K.; Kusano, Y.; Marsaglia, K. M.; McCarthy, A.; Meffre, S.; Savov, I. P.; Tepley, F. J., III; Yogodzinski, G. M.

2014-12-01

The destruction of lithospheric plates by subduction is a fundamentally important process leading to arc magmatism and the creation of continental crust, yet subduction initiation and early magmatic arc evolution remain poorly understood. For many arc systems, onset of arc volcanism and early evolution are obscured by metamorphism or the record is deeply buried; however, initial products of arc systems may be preserved in forearc and backarc sedimentary records. IODP Expedition 351 recovered this history from the dispersed ash and pyroclast record in the proximal rear-arc of the northern IBM system west of the Kyushu-Palau Ridge. Drilling at Site U1438 in the Amami Sankaku Basin recovered a thick volcaniclastic record of subduction initiation and the early evolution of the Izu-Bonin Arc. A 160-m thick section of Neogene sediment overlies 1.3 kilometers of Paleogene volcaniclastic rocks with andesitic average composition; this volcaniclastic section was deposited on mafic volcanic basement rocks. The thin upper sediment layer is primarily terrigenous, biogenic and volcaniclastic mud and ooze with interspersed ash layers. The underlying Eocene to Oligocene volcaniclastic rocks are 33% tuffaceous mudstone, 61% tuffaceous sandstone, and 6% conglomerate with volcanic and rare sedimentary clasts commonly up to pebble and rarely to cobble size. The clastic section is characterized by repetitive conglomerate and sandstone-dominated intervals with intervening mudstone-dominated intervals, reflecting waxing and waning of coarse arc-derived sediment inputs through time. Volcanic lithic clasts in sandstones and conglomerates range from basalt to rhyolite in composition and include well-preserved pumice, reflecting a lithologically diverse and compositionally variable arc volcanic source.

A comparison of the effects of toothbrushing and handpiece prophylaxis on retention of sealants.

PubMed

Kolavic Gray, Shellie; Griffin, Susan O; Malvitz, Dolores M; Gooch, Barbara F

2009-01-01

Tooth surface cleaning before acid etching is considered to be an important step in the retention of resin-based pit-and-fissure sealants. The authors reviewed and summarized instructions for cleaning tooth surfaces from five manufacturers of 10 unfilled resin-based sealants marketed in the United States. The authors also searched electronic databases for studies that directly compared the effects of different surface-cleaning methods on sealant retention and for systematic reviews of the effectiveness of sealants. They explored the association between surface-cleaning methods and sealant retention in the studies included in the systematic reviews. They calculated the summary weighted retention rates for studies that used either a handpiece or toothbrush prophylaxis. All of the sealant manufacturers' instructions for use (IFU) recommended cleaning the tooth before acid etching. None of the IFU directly stated that a handpiece was required to perform the cleaning, but five IFU implied the use of handpiece prophylaxis. None of the IFU recommended surface-altering procedures in caries-free teeth. Direct evidence from two clinical trials showed no difference in complete sealant retention between surfaces cleaned mechanically with pumice or prophylaxis paste and those cleaned with air-water syringe or dry toothbrushing. Indirect evidence from 10 studies found that weighted summary retention by year after sealant placement in studies that used toothbrush prophylaxis was greater than or equivalent to values for studies that used handpiece prophylaxis. Levels of sealant retention after surface cleaning with toothbrush prophylaxis were at least as high as those associated with hand-piece prophylaxis. This finding may translate into lower resource costs for sealant placement.

Extreme U-Th disequilibrium in rift-related basalts, rhyolites and granophyric granite and the timescale of rhyolite generation, intrusion and crystallization at Alid volcanic center, Eritrea

USGS Publications Warehouse

Lowenstern, J. B.; Charlier, B.L.A.; Clynne, M.A.; Wooden, J.L.

2006-01-01

Rhyolite pumices and co-erupted granophyric (granite) xenoliths yield evidence for rapid magma generation and crystallization prior to their eruption at 15·2 ± 2·9 ka at the Alid volcanic center in the Danikil Depression, Eritrea. Whole-rock U and Th isotopic analyses show 230Th excesses up to 50% in basalts <10 000 years old from the surrounding Oss lava fields. The 15 ka rhyolites also have 30–40% 230Th excesses. Similarity in U–Th disequilibrium, and in Sr, Nd, and Pb isotopic values, implies that the rhyolites are mostly differentiated from the local basaltic magma. Given the (230Th/232Th) ratio of the young basalts, and presumably the underlying mantle, the (230Th/232Th) ratio of the rhyolites upon eruption could be generated by in situ decay in about 50 000 years. Limited (∼5%) assimilation of old crust would hasten the lowering of (230Th/232Th) and allow the process to take place in as little as 30 000 years. Final crystallization of the Alid granophyre occurred rapidly and at shallow depths at ∼20–25 ka, as confirmed by analyses of mineral separates and ion microprobe data on individual zircons. Evidently, 30 000–50 000 years were required for extraction of basalt from its mantle source region, subsequent crystallization and melt extraction to form silicic magmas, and final crystallization of the shallow intrusion. The granophyre was then ejected during eruption of the comagmatic rhyolites.

Frequent eruptions of Mount Rainier over the last ˜2,600 years

NASA Astrophysics Data System (ADS)

Sisson, T. W.; Vallance, J. W.

2009-08-01

Field, geochronologic, and geochemical evidence from proximal fine-grained tephras, and from limited exposures of Holocene lava flows and a small pyroclastic flow document ten-12 eruptions of Mount Rainier over the last 2,600 years, contrasting with previously published evidence for only 11-12 eruptions of the volcano for all of the Holocene. Except for the pumiceous subplinian C event of 2,200 cal year BP, the late-Holocene eruptions were weakly explosive, involving lava effusions and at least two block-and-ash pyroclastic flows. Eruptions were clustered from ˜2,600 to ˜2,200 cal year BP, an interval referred to as the Summerland eruptive period that includes the youngest lava effusion from the volcano. Thin, fine-grained tephras are the only known primary volcanic products from eruptions near 1,500 and 1,000 cal year BP, but these and earlier eruptions were penecontemporaneous with far-traveled lahars, probably created from newly erupted materials melting snow and glacial ice. The most recent magmatic eruption of Mount Rainier, documented geochemically, was the 1,000 cal year BP event. Products from a proposed eruption of Mount Rainier between AD 1820 and 1854 (X tephra of Mullineaux (US Geol Surv Bull 1326:1-83, 1974)) are redeposited C tephra, probably transported onto young moraines by snow avalanches, and do not record a nineteenth century eruption. We found no conclusive evidence for an eruption associated with the clay-rich Electron Mudflow of ˜500 cal year BP, and though rare, non-eruptive collapse of unstable edifice flanks remains as a potential hazard from Mount Rainier.

Evolution of a Holocene delta driven by episodic sediment delivery and coseismic deformation, Puget Sound, Washington, USA

USGS Publications Warehouse

Barnhardt, W.A.; Sherrod, B.L.

2006-01-01

Episodic, large-volume pulses of volcaniclastic sediment and coseismic subsidence of the coast have influenced the development of a late Holocene delta at southern Puget Sound. Multibeam bathymetry, ground-penetrating radar (GPR) and vibracores were used to investigate the morphologic and stratigraphic evolution of the Nisqually River delta. Two fluvial–deltaic facies are recognized on the basis of GPR data and sedimentary characteristics in cores, which suggest partial emplacement from sediment-rich floods that originated on Mount Rainier. Facies S consists of stacked, sheet-like deposits of andesitic sand up to 4 m thick that are continuous across the entire width of the delta. Flat-lying, highly reflective surfaces separate the sand sheets and comprise important facies boundaries. Beds of massive, pumice- and charcoal-rich sand overlie one of the buried surfaces. Organic-rich material from that surface, beneath the massive sand, yielded a radiocarbon age that is time-correlative with a series of known eruptive events that generated lahars in the upper Nisqually River valley. Facies CF consists of linear sandbodies or palaeochannels incised into facies S on the lower delta plain. Radiocarbon ages of wood fragments in the sandy channel-fill deposits also correlate in time to lahar deposits in upstream areas. Intrusive, sand-filled dikes and sills indicate liquefaction caused by post-depositional ground shaking related to earthquakes. Continued progradation of the delta into Puget Sound is currently balanced by tidal-current reworking, which redistributes sediment into large fields of ebb- and flood-oriented bedforms.

Melt fracturing and healing: A mechanism for degassing and origin of silicic obsidian

USGS Publications Warehouse

Cabrera, A.; Weinberg, R.F.; Wright, H.M.N.; Zlotnik, S.; Cas, Ray A.F.

2011-01-01

We present water content transects across a healed fault in pyroclastic obsidian from Lami pumice cone, Lipari, Italy, using synchrotron Fourier transform infrared spectroscopy. Results indicate that rhyolite melt degassed through the fault surface. Transects define a trough of low water content coincident with the fault trace, surrounded on either side by high-water-content plateaus. Plateaus indicate that obsidian on either side of the fault equilibrated at different pressure-temperature (P-T) conditions before being juxtaposed. The curves into the troughs indicate disequilibrium and water loss through diffusion. If we assume constant T, melt equilibrated at pressures differing by 0.74 MPa before juxtaposition, and the fault acted as a low-P permeable path for H2O that diffused from the glass within time scales of 10 and 30 min. Assuming constant P instead, melt on either side could have equilibrated at temperatures differing by as much as 100 ??C, before being brought together. Water content on the fault trace is particularly sensitive to post-healing diffusion. Its preserved value indicates either higher temperature or lower pressure than the surroundings, indicative of shear heating and dynamic decompression. Our results reveal that water contents of obsidian on either side of the faults equilibrated under different P-T conditions and were out of equilibrium with each other when they were juxtaposed due to faulting immediately before the system was quenched. Degassing due to faulting could be linked to cyclical seismic activity and general degassing during silicic volcanic activity, and could be an efficient mechanism of producing low-water-content obsidian. ?? 2011 Geological Society of America.

BISON ANTIQUUS OCCURRENCE AND PLEISTOCENE-HOLOCENE STRATIGRAPHY, CANADA DEL BUEY, PAJARITO PLATEAU, NEW MEXICO

DOE Office of Scientific and Technical Information (OSTI.GOV)

RENEAU, STEVEN L.; DRAKOS, PAUL G.; MORGAN, GARY S.

2007-02-12

A Bison. (probable Bison antiguus) distal humerus fragment was found within a Pleistocene colluvial deposit on a hillslope above Canada del Buey near White Rock, New Mexico. The Bison fossil is preserved within a buried soil with an inferred age of ca. 50-100 ka, based on soil properties and on stratigraphic position below a deposit of ca. 50-60 ka EI Cajete pumice. This represents the second oldest dated Bison in New Mexico, and one of the few occurrences of this genus in the northern mountains of the state. It is also only the second record of a Pleistocene vertebrate frommore » Los Alamos County, and is a rare occurrence of a pre-25 ka Bison fossil in good stratigraphic context. Hillslopes in the study area are underlain by a sequence of truncated Pleistocene and Holocene soils that are inferred to represent colluvial deposition and soil formation followed by erosion in the mid Pleistocene (buried soil 'b3'), the late Pleistocene (buried soil 'b2'), and the mid-to-late Holocene (buried soil 'b1'). The surface soil is developed in depOSits that overlie 600-800 year-old Ancestral Puebloan sites. Colluvium is dominated by relatively fine-grained (fine to very fine sand) slopewash colluvium deposited by overland flow, but also includes rocky colluvium on hillslopes below mesas. The fine-grained colluvium is likely derived mainly from reworking of eolian deposits. Episodic colluvial deposition appears to, at least in part, accompany and follow episodic eolian events, with intervening periods dominated by erosion and the development of truncated soils.« less

Impact of rhizobial inoculation and reduced N supply on biomass production and biological N2 fixation in common bean grown hydroponically.

PubMed

Kontopoulou, Charis-Konstantina; Liasis, Epifanios; Iannetta, Pietro Pm; Tampakaki, Anastasia; Savvas, Dimitrios

2017-10-01

Testing rhizobial inoculation of common bean (Phaseolus vulgaris L.) in hydroponics enables accurate quantification of biological N 2 fixation (BNF) and provides information about the potential of reducing inorganic N fertilizer use. In view of this background, common bean grown on pumice was inoculated with Rhizobium tropici CIAT899 (Rt) and supplied with either full-N (total nitrogen 11.2 mmol L -1 ), 1/3 of full-N or N-free nutrient solution (NS). BNF was quantified at the early pod-filling stage using the 15 N natural abundance method. Full-N supply to Rt-inoculated plants resulted in markedly smaller nodules than less- or zero-N supply, and no BNF. Rt inoculation of full-N-treated plants did not increase biomass and pod yield compared with non-inoculation. Restriction (1/3 of full-N) or omission of inorganic N resulted in successful nodulation and BNF (54.3 and 49.2 kg N ha -1 , corresponding to 58 and 100% of total plant N content respectively) but suppressed dry shoot biomass from 191.7 (full-N, +Rt) to 107.4 and 43.2 g per plant respectively. Nutrient cation uptake was reduced when inorganic N supply was less or omitted. Rt inoculation of hydroponic bean provides no advantage when full-N NS is supplied, while 1/3 of full-N or N-free NS suppresses plant biomass and yield, partly because the restricted NO 3 - supply impairs cation uptake. © 2017 Society of Chemical Industry. © 2017 Society of Chemical Industry.

Fitful and protracted magma assembly leading to a giant eruption, Youngest Toba Tuff, Indonesia

USGS Publications Warehouse

Reid, Mary R; Vazquez, Jorge A.

2017-01-01

The paroxysmal eruption of the 74 ka Youngest Toba Tuff (YTT) of northern Sumatra produced an extraordinary 2800 km3 of non-welded to densely welded ignimbrite and co-ignimbrite ash-fall. We report insights into the duration of YTT magma assembly obtained from ion microprobe U-Th and U-Pb dates, including continuous age spectra over >50% of final zircon growth, for pumices and a welded tuff spanning the compositional range of the YTT. A relatively large subpopulation of zircon crystals nucleated before the penultimate caldera-related eruption at 501 ka, but most zircons yielded interior dates 100-300 ka thereafter. Zircon nucleation and growth was likely episodic and from diverse conditions over protracted time intervals of >100 to >500 ka. Final zircon growth is evident as thin rim plateaus that are in Th/U chemical equilibrium with hosts, and that give crystallization ages within tens of ka of eruption. The longevity and chemical characteristics of the YTT zircons, as well as evidence for intermittent zircon isolation and remobilization associated with magma recharge, is especially favored at the cool and wet eutectoid conditions that characterize at least half of the YTT, wherein heat fluxes could dissolve major phases but have only a minor effect on larger zircon crystals. Repeated magma recharge may have contributed to the development of compositional zoning in the YTT but, considered together with limited allanite, quartz, and other mineral dating and geospeedometry, regular perturbations to the magma reservoir over >400 ka did not lead to eruption until 74 ka ago.

Fluidization of host sediments and its impacts on peperites-forming processes, the Cretaceous Buan Volcanics, Korea

NASA Astrophysics Data System (ADS)

Kwon, Chang Woo; Gihm, Yong Sik

2017-07-01

In the Cretaceous Buan Volcanics (SW Korea), blocky and fluidal peperites are developed in a bed of poorly sorted, massive pumiceous lapilli tuff (hot sediments) as a result of the vertical to subvertical intrusion of the trachyandesitic dikes into the bed. Blocky peperites are composed of polyhedral or platy juvenile clasts with a jigsaw-crack texture. Fluidal peperites are characterized by fluidal or globular juvenile clasts with irregular or ragged margins. The blocky peperites are ubiquitous in the host sediments, whereas the fluidal peperites only occur in fine-grained zone (well sorted fine to very fine ash) that are aligned parallel to the dike margin. The development of the fine-grained zone within the poorly sorted host sediments is interpreted to form by grain size segregation caused by upward moving pore water (fluidization) that has resulted from heat transfer from intruding magma toward the waterlogged host sediments during intrusion. With the release of pore water and the selective entrainment of fine-grained ash, the fine-grained zone formed within the host sediments. Subsequent interactions between the fine-grained zone and the intruding magma resulted in ductile deformation of the magma, which generated fluidal peperites. Outside the fine-grained zone, because of the relative deficiency of both pore water and fine-grained ash, intruding magma fragmented in a brittle manner, resulting in the formation of blocky peperites. The results of this study suggest that redistribution of constituent particles (ash) and interstitial fluids during fluidization resulted in heterogeneous physical conditions of the host sediments, which influenced peperite-forming processes.

The mineral industry of Ethiopia: present conditions and future prospects

NASA Astrophysics Data System (ADS)

Assefa, Getaneh

Despite a record of mineral activity that dates back to Biblical times and the occurrence of a wide variety of minerals, as well as continuing efforts to discover major ore deposits, Ethiopia's mineral resources ahve remained of minor importance in the world economy. Mineral production in the last 20 years, for example, forms less than 1% of the estimated GDP. Well known minerals andmineral products available in the country in commercial quantities are: gold, platinum, manganese ore, natural agas, clays and clay products, feldspars, gypsum and anhydrite, slat, lime, limestone, cement, sand, structural and crushed stones, marble, mineral water and pumice. There are also vast reserves of water and geothermal power. Recently discovered deposits (over the last 20 years), with major reserves that may attain an important role in mineral production in the future, include potash salts, copper ore and diatomites. Minerals which are known to occur in Ethiopia, but of which supplies are deficient, or which have not yet been proved to exist in economic quantities are: nickel, iron, chromium, mineral fuels (oil, coal and uranium), sulphur, asbesttos, mica, talc, barytes, fluorites, borates, soda-ash, phosphates, wolframite, abrasives (garnet), molybdenite and vanadium. Within the last few years there has been an increasing appreciation of the economic significance of a mineral industry and a definite attempt to foster it. Mineral ownership is vested in the state are cotnrolled by the MInistry of Mines, Energy and Water Resources. The law relating to foreign investment in mines is liberal. The plans for the future have to provide for detailed and intensive exploration of the country's mineral resources, manufacture and fabrication.

The Effect of Fluid and Solid Properties on the Auxetic Behavior of Porous Materials Having Rock-like Microstructures

NASA Astrophysics Data System (ADS)

Wollner, U.; Vanorio, T.; Kiss, A. M.

2017-12-01

Materials with a negative Poisson's Ratio (PR), known as auxetics, exhibit the counterintuitive behavior of becoming wider when uniaxially stretched and thinner when compressed. Though negative PR is characteristic of polymer foams or cellular solids, tight as well as highly porous rocks have also been reported to exhibit a negative Poisson's ratio, both from dynamic (PRd) and static measurements. We propose a novel auxetic structure based on pore-space configuration observed in rocks. First, we performed 2D and 3D imaging of a pumice and tight basalt to analyze their rock microstructure as well as similarities to natural structures of auxetic materials - e.g., cork. Based on these analyses, we developed a theoretical auxetic 3D model consisting of rotating rigid bodies having pore configurations similar to those observed in rocks. To alleviate the mechanical assumption of rotating bodies, the theoretical model was modified to include crack-like features being represented by intersecting, elliptic cylinders. We then used a 3D printer to create a physical version of the modified model, whose PRd was tested. We also numerically explored how the compressibility of fluids located in the pore-space of the modified model as well as how the elastic properties of the material from which the model is made of affect its auxetic behavior. We conclude that for a porous medium composed of a single material saturated with a single fluid (a) the more compliant the fluid is and (b) the lower the PR of the solid material, the lower the PR value of the composite material.

Earth Observations taken by Expedition 38 crewmember

NASA Image and Video Library

2014-01-21

ISS038-E-035123 (21 Jan. 2014) --- Apoyeque Volcano, Nicaragua is featured in this image photographed by an Expedition 38 crew member on the International Space Station. The Chiltepe Peninsula, highlighted in this photograph, extends into Lake Managua in west-central Nicaragua. The peninsula is formed from part of a large ignimbrite shield, a geologic structure created by deposition of primarily low density materials (such as pumice) ejected during violent, explosive eruptive activity. Ignimbrite deposits are most commonly emplaced during large pyroclastic flows - gravity-driven mixtures of rock, ash, and volcanic gases that can cover hundreds of kilometers at speeds of hundreds of kilometers per hour - with ignimbrite shields formed over geologic time by successive flows. The Apoyeque caldera, filled with a 2.8-kilometer-wide and 400-meter-deep lake, dominates the center of the peninsula. Geological evidence indicates that Apoyeque last erupted around 50 BCE (plus or minus 100 years). The Laguna Xiloa maar - a volcanic crater formed by the explosive interaction of magma and groundwater - is located immediately to the southeast of Apoyeque and is also filled with a lake. According to scientists, Laguna Xiloa last erupted approximately 6,100 years ago. More recently, a swarm of small earthquakes was detected near Apoyeque in 2012. These seismic swarms, when detected in volcanically active areas, may indicate movement of magma prior to an eruption. The capital city of Managua, not visible in the image, is located approximately 15 kilometers to the southeast of Apoyeque, while the town of Bosques de Xiloa is considerably closer (approximately four kilometers).

Influences of urban fabric on pyroclastic density currents at Pompeii (Italy): 2. Temperature of the deposits and hazard implications

NASA Astrophysics Data System (ADS)

Zanella, E.; Gurioli, L.; Pareschi, M. T.; Lanza, R.

2007-05-01

During the A.D. 79 eruption of Vesuvius, Italy, the Roman town of Pompeii was covered by 2.5 m of pyroclastic fall pumice and then partially destroyed by pyroclastic density currents (PDCs). Thermal remanent magnetization measurements performed on the lithic and roof tile fragments embedded in the PDC deposits allow us to quantify the variations in the temperature (Tdep) of the deposits within and around Pompeii. These results reveal that the presence of buildings strongly influenced the deposition temperature of the erupted products. The first two currents, which entered Pompeii at a temperature around 300-360°C, show drastic decreases in the Tdep, with minima of 100-140°C, found in the deposits within the town. We interpret these decreases in temperature as being the result of localized interactions between the PDCs and the city structures, which were only able to affect the lower part of the currents. Down flow of Pompeii, the lowermost portion of the PDCs regained its original physical characteristics, emplacing hot deposits once more. The final, dilute PDCs entered a town that was already partially destroyed by the previous currents. These PDCs left thin ash deposits, which mantled the previous ones. The lack of interaction with the urban fabric is indicated by their uniform temperature everywhere. However, the relatively high temperature of the deposits, between 140 and 300°C, indicates that even these distal, thin ash layers, capped by their accretionary lapilli bed, were associated with PDCs that were still hot enough to cause problems for unsheltered people.

Reconstructing 800 years of historical eruptive activity at Popocatépetl Volcano, Mexico

NASA Astrophysics Data System (ADS)

Martin-Del Pozzo, Ana Lillian; Rodríguez, Alan; Portocarrero, Jorge

2016-03-01

Pictorial and written documents spanning 800 years were analyzed for information about historical eruptions at Popocatépetl volcano. These documents were prepared by several indigenous groups as well as by the Spanish conquistadors and missionaries during their military campaigns and long-term evangelization and colonization and later on, by Indian nobles and Spanish historians. Pre-Columbian drawings show flames coming out of Popocatépetl's crater while later descriptions from the Spanish colonial period in Mexico (1521 to 1821) refer to ash emission and ballistics, lahars, and some pumice falls, similar to what were depicted in the thirteenth to sixteenth century drawings. Graphic information from the pre-Columbian codices, colonial maps, and paintings referring to the eruptions were correlated with historical accounts and religious chronicles, thereby leading to the reconstruction of a more detailed sequence of eruptive events. From such information, it was possible for us to prepare ash distribution maps for the 1540, 1592, and 1664 eruptions. Most of the known historical eruptions seem to be similar to those that have been occurring at Popocatépetl since 1994, indicating the importance of ash emission and crater dome formation throughout its recent eruptive history. The strongest eruptions occurred in 1510, 1519, 1540, 1580, 1664, and 2001; these produced widespread ash falls that affected both populated and rural areas. Duration of eruptive episodes during the past 800 years were estimated to have ranged from less than a year to more than 30 years, separated by repose periods ranging between 7 and over 100 years.

A distinct source and differentiation history for Kolumbo submarine volcano, Santorini volcanic field, Aegean arc.

PubMed

Klaver, Martijn; Carey, Steven; Nomikou, Paraskevi; Smet, Ingrid; Godelitsas, Athanasios; Vroon, Pieter

2016-08-01

This study reports the first detailed geochemical characterization of Kolumbo submarine volcano in order to investigate the role of source heterogeneity in controlling geochemical variability within the Santorini volcanic field in the central Aegean arc. Kolumbo, situated 15 km to the northeast of Santorini, last erupted in 1650 AD and is thus closely associated with the Santorini volcanic system in space and time. Samples taken by remotely-operated vehicle that were analyzed for major element, trace element and Sr-Nd-Hf-Pb isotope composition include the 1650 AD and underlying K2 rhyolitic, enclave-bearing pumices that are nearly identical in composition (73 wt.% SiO 2 , 4.2 wt.% K 2 O). Lava bodies exposed in the crater and enclaves are basalts to andesites (52-60 wt.% SiO 2 ). Biotite and amphibole are common phenocryst phases, in contrast with the typically anhydrous mineral assemblages of Santorini. The strong geochemical signature of amphibole fractionation and the assimilation of lower crustal basement in the petrogenesis of the Kolumbo magmas indicates that Kolumbo and Santorini underwent different crustal differentiation histories and that their crustal magmatic systems are unrelated. Moreover, the Kolumbo samples are derived from a distinct, more enriched mantle source that is characterized by high Nb/Yb (>3) and low 206 Pb/ 204 Pb (<18.82) that has not been recognized in the Santorini volcanic products. The strong dissimilarity in both petrogenesis and inferred mantle sources between Kolumbo and Santorini suggests that pronounced source variations can be manifested in arc magmas that are closely associated in space and time within a single volcanic field.

The location and timing of magma degassing during Plinian eruptions

NASA Astrophysics Data System (ADS)

Giachetti, T.; Gonnermann, H. M.

2014-12-01

Water is the most abundant volatile species in explosively erupting silicic magmas and significantly affects magma viscosity, magma fragmentation and the dynamics of the eruption column. The effect that water has on these eruption processes can be modulated by outgassing degassing from a permeable magma. The magnitude, rate and timing of outgassing during magma ascent, in particular in relation to fragmentation, remains a subject of debate. Here we constrain how much, how fast and where the erupting magma lost its water during the 1060 CE Plinian phase of the Glass Mountain eruption of Medicine Lake Volcano, California. Using thermogravimetric analysis coupled with numerical modeling, we show that the magma lost >90% of its initial water upon eruption. Textural analyses of natural pumices, together with numerical modeling of magma ascent and degassing, indicate that 65-90% of the water exsolved before fragmentation, but very little was able to outgas before fragmentation. The magma attained permeability only within about 1 to 10 seconds before fragmenting and during that time interval permeable gas flow resulted in only a modest amount of gas flux from the un-fragmented magma. Instead, most of the water is lost shortly after fragmentation, because gas can escape rapidly from lapilli-size pyroclasts. This results in an efficient rarefaction of the gas-pyroclast mixture above the fragmentation level, indicating that the development of magma permeability and ensuing permeable outgassing are a necessary condition for sustain explosive eruptions of silicic magma. Magma permeability is thus a double-edged sword, it facilitates both, the effusive and the explosive eruption of silicic magma.

Effect of temporary cements on the microtensile bond strength of self-etching and self-adhesive resin cement.

PubMed

Carvalho, Edilausson Moreno; Carvalho, Ceci Nunes; Loguercio, Alessandro Dourado; Lima, Darlon Martins; Bauer, José

2014-11-01

The aim of this study was to evaluate the microtensile bond strength (µTBS) of self-etching and self-adhesive resin cement systems to dentin affected by the presence of remnants of either eugenol-containing or eugenol-free temporary cements. Thirty extracted teeth were obtained and a flat dentin surface was exposed on each tooth. Acrylic blocks were fabricated and cemented either with one of two temporary cements, one zinc oxide eugenol (ZOE) and one eugenol free (ZOE-free), or without cement (control). After cementation, specimens were stored in water at 37°C for 1 week. The restorations and remnants of temporary cements were removed and dentin surfaces were cleaned with pumice. Resin composite blocks were cemented to the bonded dentin surfaces with one of two resin cements, either self-etching (Panavia F 2.0) or self-adhesive (RelyX U-100). After 24 h, the specimens were sectioned to obtain beams for submission to µTBS. The fracture mode was evaluated under a stereoscopic loupe and a scanning electron microscope (SEM). Data from µTBS were submitted to two-way repeated-measure ANOVA and the Tukey test (alpha = 0.05). The cross-product interaction was statistically significant (p < 0.0003). The presence of temporary cements reduced the bond strength to Panavia self-etching resin cements only (p < 0.05). Fracture occurred predominantly at the dentin-adhesive interface. The presence of eugenol-containing temporary cements did not interfere in the bond strength to dentin of self-adhesive resin cements.

[Combination of phosphorus solubilizing and mobilizing fungi with phosphate rocks and volcanic materials to promote plant growth of lettuce (Lactuca sativa L.)].

PubMed

Velázquez, María S; Cabello, Marta N; Elíades, Lorena A; Russo, María L; Allegrucci, Natalia; Schalamuk, Santiago

Arbuscular mycorrhizal fungi (AMF) increase the uptake of soluble phosphates, while phosphorus solubilizing fungi (S) promote solubilization of insoluble phosphates complexes, favoring plant nutrition. Another alternative to maintaining crop productivity is to combine minerals and rocks that provide nutrients and other desirable properties. The aim of this work was to combine AMF and S with pyroclastic materials (ashes and pumices) from Puyehue volcano and phosphate rocks (PR) from Rio Chico Group (Chubut) - to formulate a substrate for the production of potted Lactuca sativa. A mixture of Terrafertil®:ashes was used as substrate. Penicillium thomii was the solubilizing fungus and Rhizophagus intraradices spores (AMF) was the P mobilizer (AEGIS® Irriga). The treatments were: 1) Substrate; 2) Substrate+AMF; 3) Substrate+S; 4) Substrate+AMF+S; 5) Substrate: PR; 6) Substrate: PR+AMF; 7) Substrate: PR+S and 8) Substrate: PR+AMF+S. Three replicates were performed per treatment. All parameters evaluated (total and assimilable P content in substrate, P in plant tissue and plant dry biomass) were significantly higher in plants grown in substrate containing PR and inoculas with S and AMF. This work confirms that the combination of S/AMF with Puyehue volcanic ashes, PR from the Río Chico Group and a commercial substrate promote the growth of L. sativa, thus increasing the added value of national geomaterials. Copyright © 2017 Asociación Argentina de Microbiología. Publicado por Elsevier España, S.L.U. All rights reserved.

Storage conditions of the mafic and silicic magmas at Cotopaxi, Ecuador

NASA Astrophysics Data System (ADS)

Martel, Caroline; Andújar, Joan; Mothes, Patricia; Scaillet, Bruno; Pichavant, Michel; Molina, Indira

2018-04-01

The 2015 reactivation of the Cotopaxi volcano urges us to understand the complex eruptive dynamics of Cotopaxi for better management of a potential major crisis in the near future. Cotopaxi has commonly transitioned from andesitic eruptions of strombolian style (lava flows and scoria ballistics) or nuées ardentes (pyroclastic flows and ash falls) to highly explosive rhyolitic ignimbrites (pumiceous pyroclastic flows), which entail drastically different risks. To better interpret geophysical and geochemical signals, Cotopaxi magma storage conditions were determined via existing phase-equilibrium experiments that used starting materials chemically close to the Cotopaxi andesites and rhyolites. The results suggest that Cotopaxi's most mafic andesites (last erupted products) can be stored over a large range of depth from 7 km to ≥16 km below the summit (pressure from 200 to ≥400 MPa), 1000 °C, NNO +2, and contain 4.5-6.0±0.7 wt% H2O dissolved in the melt in equilibrium with 30-40% phenocrysts of plagioclase, two pyroxenes, and Fe-Ti oxides. These mafic andesites sometimes evolve towards more silicic andesites by cooling to 950 °C. Rhyolitic magmas are stored at 200-300 MPa (i.e. 7-11 km below the summit), 750 °C, NNO +2, and contain 6-8 wt% H2O dissolved in a nearly aphyric melt (<5% phenocrysts of plagioclase, biotite, and Fe-Ti oxides). Although the andesites produce the rhyolitic magmas by fractional crystallization, the Cotopaxi eruptive history suggests reactivation of either reservoirs at distinct times, likely reflecting flux or time fluctuations during deep magma recharge.

Preliminary results of high resolution magneto-biostratigraphy of continental sequences in Chapala Basin, Southwestern Mexico

NASA Astrophysics Data System (ADS)

Mendez Cardenas, D. L.; Benammi, M.

2007-05-01

Chapala Lake is south from Guadalajara, Jalisco State (Southwestern Mexico). Belongs to a series of Pliocenic lakes along the Mexican Volcanic Belt. It is localized in the Chapala rift, and the entire area is controlled by the tectonic setting of the Colima, Tepic and Chapala rifts, constituting the triple junction rift-rift-rift. The deposits studied belong to volcanosedimentary sequences, composed by lacustrine and fluvial associations alternated with units of ash and pumice. The faunistic component reported consists at least of 27 mammals species, and the sediments were there're in have to work with special attention for seek rodents by handpicking. Probably these rodents will be the clue to determine the deposits correlation. Core demagnetization shows that they are low-coercivity magnetic minerals like magnetite or Ti-magnetite. It was verified that the characteristic magnetization corresponds to MNRp and the inversion test resulted good. Rodents are represented by Geomynae, Sigmondontinae and Sciurinae. The Geomynae family is the most common, and the faunistic association indicates Blancan age. This also allows a correlation with the polarity pattern in the GSS between 3,6 and 2,6 Ma. Actually, is known that this kind of studies in continental sequences supported with paleontological record of vertebrates could give us a more precised calibration of the age of such deposits. Allowing better understanding of the evolution of these mammals and their path trough geological record. This work shows the preliminary results of rodents palaeontology and high resolution magneto-stratigraphy in the units from to Chapala Basin.

Curie temperatures of titanomagnetite in ignimbrites: Effects of emplacement temperatures, cooling rates, exsolution, and cation ordering

NASA Astrophysics Data System (ADS)

Jackson, Mike; Bowles, Julie A.

2014-11-01

Pumices, ashes, and tuffs from Mt. St. Helens and from Novarupta contain two principal forms of titanomagnetite: homogeneous grains with Curie temperatures in the range 350-500°C and oxyexsolved grains with similar bulk composition, containing ilmenite lamellae and having Curie temperatures above 500°C. Thermomagnetic analyses and isothermal annealing experiments in combination with stratigraphic settings and thermal models show that emplacement temperatures and cooling history may have affected the relative proportions of homogeneous and exsolved grains and have clearly had a strong influence on the Curie temperature of the homogeneous phase. The exsolved grains are most common where emplacement temperatures exceeded 600°C, and in laboratory experiments, heating to over 600°C in air causes the homogeneous titanomagnetites to oxyexsolve rapidly. Where emplacement temperatures were lower, Curie temperatures of the homogeneous grains are systematically related to overburden thickness and cooling timescales, and thermomagnetic curves are generally irreversible, with lower Curie temperatures measured during cooling, but little or no change is observed in room temperature susceptibility. We interpret this irreversible behavior as reflecting variations in the degree of cation ordering in the titanomagnetites, although we cannot conclusively rule out an alternative interpretation involving fine-scale subsolvus unmixing. Short-range ordering within the octahedral sites may play a key role in the observed phenomena. Changes in the Curie temperature have important implications for the acquisition, stabilization, and retention of natural remanence and may in some cases enable quantification of the emplacement temperatures or cooling rates of volcanic units containing homogeneous titanomagnetites.

Application of the method of temporal moments to interpret solute transport with sorption and degradation

NASA Astrophysics Data System (ADS)

Pang, Liping; Goltz, Mark; Close, Murray

2003-01-01

In this note, we applied the temporal moment solutions of [Das and Kluitenberg, 1996. Soil Sci. Am. J. 60, 1724] for one-dimensional advective-dispersive solute transport with linear equilibrium sorption and first-order degradation for time pulse sources to analyse soil column experimental data. Unlike most other moment solutions, these solutions consider the interplay of degradation and sorption. This permits estimation of a first-order degradation rate constant using the zeroth moment of column breakthrough data, as well as estimation of the retardation factor or sorption distribution coefficient of a degrading solute using the first moment. The method of temporal moment (MOM) formulae was applied to analyse breakthrough data from a laboratory column study of atrazine, hexazinone and rhodamine WT transport in volcanic pumice sand, as well as experimental data from the literature. Transport and degradation parameters obtained using the MOM were compared to parameters obtained by fitting breakthrough data from an advective-dispersive transport model with equilibrium sorption and first-order degradation, using the nonlinear least-square curve-fitting program CXTFIT. The results derived from using the literature data were also compared with estimates reported in the literature using different equilibrium models. The good agreement suggests that the MOM could provide an additional useful means of parameter estimation for transport involving equilibrium sorption and first-order degradation. We found that the MOM fitted breakthrough curves with tailing better than curve fitting. However, the MOM analysis requires complete breakthrough curves and relatively frequent data collection to ensure the accuracy of the moments obtained from the breakthrough data.

Effect of different surface treatments on microtensile bond strength of two resin cements to aged simulated composite core materials.

PubMed

Esmaeili, Behnaz; Alaghehmand, Homayoon; Shakerian, Mohadese

2015-01-01

Roughening of the aged composite resin core (CRC) surface seems essential for durable adhesion. The aim of this study was to investigate the influence of various surface treatments and different resin cements on microtensile bond strength (µ TBS) between two aged core build-up composites (CBCs) and feldspathic ceramic. A total of 16 composite blocks made of two CBCs, Core.it and Build-it were randomly assigned to four surface treatment groups after water storage and thermocycling (2 weeks and 500 cycles). Experimental groups included surface roughening with air abrasion (AA), hydrofluoric acid, pumice, and laser and then were bonded to computer-aided design/computer-aided manufacturing feldspathic ceramic blocks using two resin cements, Panavia F2 (PF), and Duo-link (DL). The µ TBS was tested, and the fracture mode was assessed. The data were analyzed with multiple analysis of variance to estimate the contribution of different surface treatments, resin cements, and two aged CRCs on µ TBS. Statistical significance level was set at α < 0.05. Surface treatment and cement type significantly affected bond strength (P < 0.001) but the type of CRC did not (P = 0.468). Between roughening methods, the highest and the lowest values of µ TBS were sequentially obtained in AA and Er.YAG laser groups. The highest bond strength was in AA group cemented with PF (31.83 MPa). The most common failure mode was cohesive fracture in the cement. Different surface treatments had different effects on µ TBS of aged CRCs to feldspathic ceramics. PF was significantly better than DL.

Contrasting styles of post-caldera volcanism along the Main Ethiopian Rift: Implications for contemporary volcanic hazards

NASA Astrophysics Data System (ADS)

Fontijn, Karen; McNamara, Keri; Zafu Tadesse, Amdemichael; Pyle, David M.; Dessalegn, Firawalin; Hutchison, William; Mather, Tamsin A.; Yirgu, Gezahegn

2018-05-01

The Main Ethiopian Rift (MER, 7-9°N) is the type example of a magma-assisted continental rift. The rift axis is populated with regularly spaced silicic caldera complexes and central stratovolcanoes, interspersed with large fields of small mafic scoria cones. The recent (latest Pleistocene to Holocene) history of volcanism in the MER is poorly known, and no eruptions have occurred in the living memory of the local population. Assessment of contemporary volcanic hazards and associated risk is primarily based on the study of the most recent eruptive products, typically those emplaced within the last 10-20 ky. We integrate new and published field observations and geochemical data on tephra deposits from the main Late Quaternary volcanic centres in the central MER to assess contemporary volcanic hazards. Most central volcanoes in the MER host large mid-Pleistocene calderas, with typical diameters of 5-15 km, and associated ignimbrites of trachyte and peralkaline rhyolite composition. In contrast, post-caldera activity at most centres comprises eruptions of peralkaline rhyolitic magmas as obsidian flows, domes and pumice cones. The frequency and magnitude of events varies between individual volcanoes. Some volcanoes have predominantly erupted obsidian lava flows in their most recent post-caldera stage (Fentale), whereas other have had up to 3 moderate-scale (VEI 3-4) explosive eruptions per millennium (Aluto). At some volcanoes we find evidence for multiple large explosive eruptions (Corbetti, Bora-Baricha, Boset-Bericha) which have deposited several centimetres to metres of pumice and ash in currently densely populated regions. This new overview has important implications when assessing the present-day volcanic hazard in this rapidly developing region. Supplementary Table 2 Main Ethiopian Rift outcrop localities with brief description of geology. All coordinates in Latitude - Longitude, WGS84 datum. Sample names (as listed in Supplementary Table 3a) follow outcrop name followed by a letter (e.g. A, B, etc.). Supplementary Table S3a. EMP data for all samples analysed in this study. Outcrop coordinates for terrestrial outcrops (names starting with "MER") are listed in Supplementary Table S2. Points refer to individual analysis spots, each on an individual patch of glass, avoiding visible crystals. Analyses suggesting an influence of (hidden) crystals have been omitted. Samples are grouped by volcano (South to North, Fig 1) and units are identified where possible. Only the most widely distributed units are given a unique name. Other units are identified as "NA" followed by the unit number of their corresponding section (in stratigraphic order, #1 being the youngest). Run refers to date analyses were acquired; corresponding secondary standard analyses and analytical conditions for all runs, ordered by date, are listed in Supplementary Table S3b. Analyses are normalised to volatile-free composition. Cl was also omitted from normalisation because it was not analysed for all samples. Supplementary Table S3b EMP analyses of secondary glass standards (non-normalised) run together with samples. All analyses were run at 15 kV accelerating voltage, 6 (or 4) nA beam current, and 10 (or 5) μm beam width. Standards were run at the start, regularly during and at the end of each run to monitor data quality. Error bars, also reported with the samples, are calculated as 2 x relative standard deviation on the standard analyses and hence represent precision of the data. Data accuracy is colour-coded on the average for each standard analysis during each run: green values are within 1s of the preferred values, orange within 2s, and red out of the 2s range. Standards used are ATHO-G (rhyolite), NIST-612 (synthetic glass), StHs6/80-G (andesite/dacite) and ML3B-G (basalt), and cover the range of expected values in our sample set. Preferred values, after Jochum et al. (2006, 2011), can also be consulted on GeoREM (http://georem.mpch-mainz.gwdg.de/).

Insights From Field Geology Into the Styles and Timings of Large Silicic Explosive `Supereruptions'

NASA Astrophysics Data System (ADS)

Wilson, C. J.

2006-12-01

The evocative terms `supereruption' (and `supervolcano'), whilst eminently saleable to the media, conceal the fact that, apart from knowing that such large eruptions (>300 km3, magma) actually have occurred, we understand very little about the dynamics of such events. Field studies of 3 supereruption deposits suggest that we are missing information on the timing and eruptive styles that is essential in assessing the dynamics and impacts of past and future large eruptions. The 26.5 ka Oruanui eruption in New Zealand (ca. 530 km3, magma) shows evidence in the form of erosion intervals and/or reworked horizons for spasmodic activity, including a hiatus of weeks plus other shorter breaks, that interrupted 10 phases of activity. Following the plinian fall unit of phase 1, there was a time break long enough for local reworking (and possibly emplacement of a small dome), thus of the order of weeks in duration. Other breaks, during which minor wind- or water-reworking took place are observed between phases 4 and 5, and 9 and 10, and were of the order of days. Two other horizons saw the complete settling out of 10-20 micron-sized ash particles before commencement of the next phase of the eruption, and thus may represent breaks of hours. The whole eruption was a series of large-scale outbreaks of generally increasing vigor, daisy-chained to form a single geological event, but one which would represent recurrent hazards, and uncertainties in eruptive activity if repeated today. The 0.76 Ma Bishop Tuff eruption (ca. 600 km3, magma), on the other hand, displays evidence only for one short time break, represented by settling out of fine ash at the top of a plinian pumice fall unit. Most of the eruption volume may have been emplaced over only about 6 days. Such an eruption, although catastrophic when placed in today's societal context, at least was over relatively rapidly. The immense 2.06 Ma Huckleberry Ridge Tuff (HRT) eruption (ca. 2500 km3, magma) shows evidence for prolonged time breaks, possibly of months to years, at several stages. During deposition of the basal pre- ignimbrite fall deposit, horizons of wind- and/or water-reworked material occur, suggesting that normal weather processes (wind, hail deposition, rainfall) may have affected the deposits during breaks in deposition. Between the three major ignimbrite units (A, B and C), there is local evidence for cooling below temperatures required for welding across their mutual boundaries and partial cessation of vapour-phase alteration in the earlier unit where the ignimbrites thin against topographic highs. A false impression of continuity in HRT emplacement is given by a lack of significant density contrasts across unit boundaries in areas where the deposits were thick enough to cause high temperatures and concomitant welding across the mutual contacts. All three eruptions show evidence for partial or complete simultaneity of plinian pumice fall deposition with co- generation and emplacement of ignimbrite. The widespread notions of fall and flow activity being antipathetic and of the former leading to the latter are too simple, especially given the demonstrable development of multiple vent sites in the Oruanui and Bishop eruptions. All three eruptions show that there is a wealth of information to be gained from detailed field studies that can provide powerful constraints on eruption dynamics, although it is apparent that there is no simple model that can be applied to supereruptions. Two out of the three examples were prolonged for months or years, and assessing when the eruption would have actually finished, or foreseeing the climactic stage(s) which would have caused the greatest impact, would have been problematic.

Crystallization of tholeiitic basalt in Alae Lava Lake, Hawaii

USGS Publications Warehouse

Peck, D.L.; Wright, T.L.; Moore, J.G.

1966-01-01

The eruption of Kilauea Volcano August 21-23, 1963, left 600,000 cubic meters of basaltic lava in a lava lake as much as 15 meters deep in Alae pit crater. Field studies of the lake began August 27 and include repeated core drilling, measurements of temperature in the crust and melt, and precise level surveys of the lake surface. The last interstitial melt in the lake solidified late in September 1964; by mid August 1965 the maximum temperature was 690??C at a depth of 11.5 meters. Pumice air-quenched from about 1140??C contains only 5 percent crystals - clinopyroxene, cuhedral olivine (Fo 80), and a trace of plagioclase, (An 70). Drill cores taken from the zone of crystallization in the lake show that olivine continued crystallizing to about 1070??C; below that it reacts with the melt, becoming corroded and mantled by pyroxene and plagioclase. Below 1070??C, pyroxene and plagioclase crystallized at a constant ratio. Ilmenite first appeared at about 1070??C and was joined by magnetite at about 1050??C; both increased rapidly in abundance to 1000??C. Apatite first appeared as minute needles in interstitial glass at 1000??C. Both the abundance and index of refraction of glass quenched from melt decreased nearly linearly with falling temperature. At 1070??C the quenched lava contains about 65 percent dark-brown glass with an index of 1.61; at 980??C it contains about 8 percent colorless glass with an index of 1.49. Below 980??C, the percentage of glass remained constant. Progressive crystallization forced exsolution of gases from the melt fraction; these formed vesicles and angular pores, causing expansion of the crystallizing lava and lifting the surface of the central part of the lake an average of 19.5 cm. The solidified basalt underwent pneumatolitic alteration, including deposition of cristobalite at 800??C, reddish alteration of olivine at 700??C, tarnishing of ilmenite at 550??C, deposition of anhydrite at 250??C, and deposition of native sulfur at 100??C. Ferric-ferrous ratios suggest that oxidation with maximum intensity between 550??C and 610??C moved downward in the crust as it cooled; this was followed by reduction at a temperature of about 100??C. The crystallized basalt is a homogeneous fine-grained rock containing on the average 48.3 percent by volume intergranular pyroxene (augite > pigeonite), 34.2 percent plagioclase laths (An60 70), 7.9 percent interstitial glass, 6.9 percent opaques (ilmenite > magnetite), 2.7 percent olivine (Fo70 80), and a trace of apatite. Chemical analyses of 18 samples, ranging from initially quenched pumice to lava cored more than a year after the eruption from the center and from near the base of the lake, show little variation from silica-saturated tholeiitic basalt containing 50.4 percent SiO2, 2.4 percent Na2O, and 0.54 percent K2O. Apparently there was no significant crystal settling and no appreciable vapor-phase transport of these components during the year of crystallization. However, seven samples of interstitial liquid that had been filter-pressed into gash fractures and drill holes from partly crystalline mush near the base of the crust show large differences from the bulk composition of the solidified crust-lower MgO, CaO, and Al2O3; and higher total iron, TiO2, Na2O, K2O, P2O5, and F, and, in most samples, SiO2. The minor elements Ba, Ga, Li, Y, and Yb and possibly Cu tend to be enriched in the filter-pressed liquids, and Cr and possibly Ni tend to be depleted. ?? 1966 Stabilimento Tipografico Francesco Giannini & Figli.

Experimental and petrological constraints on long-term magma dynamics and post-climactic eruptions at the Cerro Galán caldera system, NW Argentina

NASA Astrophysics Data System (ADS)

Grocke, Stephanie B.; Andrews, Benjamin J.; de Silva, Shanaka L.

2017-11-01

Cerro Galán in NW Argentina records > 3.5 Myr of magmatic evolution of a major resurgent caldera complex. Beginning at 5.72 Ma, nine rhyodacitic ignimbrites (68-71 wt% SiO2) with a combined minimum volume of > 1200 km3 (Dense Rock Equivalent; DRE) have been erupted. The youngest of those ignimbrites is the eponymous, geochemically homogenous, caldera-forming 2.08 ± 0.02 Ma Cerro Galán Ignimbrite (CGI; > 630 km3 DRE). Following this climactic supereruption, structural and magmatic resurgence led to the formation of a resurgent dome and post-climactic lava domes and their associated pyroclastic deposits. A clear transition from amphibole to sanidine-bearing magmas occurred during the evolution of Cerro Galán and is inferred to represent a shallowing of the magma system. We test this hypothesis here using experimental phase equilibria. We conducted a series of phase equilibria experiments on the post-climactic dome lithologies under H2O-saturated conditions using cold seal Waspaloy pressure vessels with an intrinsic log fO2 of NNO + 1 ± 0.5 across a temperature-pressure range of 750-900 °C and 50-200 MPa (PH2O = Ptotal), respectively. Petrologic and geochemical analysis of the post-climactic lithologies shows that the natural phase assemblage (plagioclase + quartz + biotite + sanidine + Fe-Ti oxides ± apatite ± zircon) is stable at < 50 MPa (PH2O) and 805-815 °C. Applying experimental results to the CGI pumice, which has the same phenocryst phase assemblage and modal abundance, whole rock and phenocryst chemistry, and overlapping temperature and fO2 as the post-climactic deposits, suggests that these pre-eruptive conditions (PH2O < 50 MPa) are relevant for the magmas that sourced the climactic CGI supereruption as well. Amphibole in the early Cerro Galán ignimbrites (Toconquis Group; 5.72-4.51 Ma, and the Cueva Negra Ignimbrite, 3.77 ± 0.08 Ma) records crystallization across a range of pressures (500 to 200 ± 60 MPa). In the interval between the eruption of the Cueva Negra ignimbrite and the CGI (2.08 ± 0.02 Ma) the complex magma system shallowed and stalled at low pressures (< 100 MPa), resulting in a more simple magma reservoir configuration represented by a large-volume, geochemically homogenous magma body. The shallowing of the Cerro Galán magma system during this time explains the marked transition from amphibole to sanidine-bearing magmas and seems to characterize many large silicic caldera-forming magma systems that erupt over million year timescales to generate long-lived volcanic complexes. The post-climactic history of Cerro Galán is informed through a detailed investigation of the textural differences among the post-climactic dome lithologies, and a comparison of those textures with previously published decompression experiments. These suggest that the highly vesiculated, pumiceous clasts with rare microlites represent magma stored within the core of the lava dome that decompressed relatively rapidly (0.003-0.0003 MPa s-1) and evolved via closed system degassing. Resulting over-pressure of the dome may have triggered superficial explosion. In contrast, dense clasts with abundant crystalline silica precipitates represent more typical dome-forming magmas that decompressed more slowly (< 0.00005 MPa s-1), evolved via open system degassing, and form the outer carapace of a lava dome. Integrating decompression histories with results from new phase equilibria experiments suggests that during post-climactic volcanic activity at Cerro Galán, remnant CGI dome-forming magmas ascended from the shallow magma reservoir (< 4 km) to motivate resurgent uplift and erupt as lava domes either explosively as vesiculated clasts or effusively as dense clasts that make up the outer structure of lava domes.

Geochemical and isotopic (Nd-Pb-Sr-O) variations bearing on the genesis of volcanic rocks from Vesuvius, Italy

USGS Publications Warehouse

Ayuso, R.A.; de Vivo, B.; Rolandi, G.; Seal, R.R.; Paone, A.

1998-01-01

Alkaline volcanism produced by Monte Somma-Vesuvius volcano includes explosive plinian and subplinian activity in addition to effusive lava flows. Pumice, scoria, and lava (150 samples) exhibit major- and trace-element gradients as a function of SiO2 (58.9-47.2 wt%) and MgO (0-7.8 wt%); Mg value are ???50. Internally gradational chemical groups or cycles are distinguished by age: (1) 25 000 to 14 000 yr B.P.; (2) 8000 yr B.P. to A.D. 79; and (3) A.D. 79 to 1944. A small number of lavas, dikes and scora were also analysed from the Somma formation (~ 35 000 to 25 000 yr B.P.). Within each group, contents of Na2O + K2O increas with decreasing MgO along distinct rocks. Nb/Y values are variable from 0.66 to 3.14 (at SiO2 ??? 50 wt%) generally in the range of alkaline and ultra-alkaline rocks. Variations in contents of some majro elements (e.g., P and Ti), and trace elements (e.g., Th, Nb, Ta, Zr, Hf, Pb, La, and Sc), as well as contrasting trends in ratios of various elements (e.g., Ta/Yb, Hf/U, Th/Ta, Th/Hf, Th/Yb, etc.) are also generally consistent with the group subdivisions. For example, Th/Hf increases from ??? 5 to ??? 10 with decreasing age for the Vesuvius system as a whole, yielding similar compositions in the least evolved rocks (low-silica, high-MgO, imcompatible element-poor) erupted at the end of each cycle. Internal variations within individual eruptions also systematically changed generally towards a common mafic composition at the end of each cycle, thus reflecting the dominanit volume in the magma chamber. At the start of a new eruptive cycle, the rocks are relatively enriched in incompatible elements; younger groups also contain higher abundances than other groups. N-MORB-normalized multielement diagrams exhibit selective enrichments of Sr, K, Rb, Th, and the light rare-earth elements; deep Nb and Ta negative anomalies commonly seen in rocks generated at orogenic margins are absent in the light rare-earth elements; deep Nb and Ta netgative anomalies commonly seen in rocks generated at orogenic margins are absent in our samples. Sr isotopic compositions are known to be variable within some of the units, in agreement with our data (87Sr/86Sr ~ 0.70699 to 0.70803) and with contributions from several isotopic components. Isotopic compositions for ??18O (7.3 to 10.2%), Pb for mineral separates and whole rocks (206Pb/204Pb ~ 18.947 to 19.178, 207Pb/204/Pb ~ 15.617 to 15.769, 208Pb/204Pb ~38.915 to 39.345), and Nd (143Nd ~ 0.51228 to 0.51251) also show variability. Oxygen isotope data show that pumices have higher ??18O values than cogenetic lavas, and that ??18O values and SiO2 are correlated. Radiogenic and stable isotope data plot within range of isotopic compositions for the Roman comagmatic province. Fractional crystallization cannot account for the radiogenic isotopic compositions of the Vesuvius magmas. We favor instead the combined effects of heterogeneous magma sources, together with isotopic exchange near the roof of the magma chamber. We suggest that metasomatized continental mantle lithosphere is the principal source of the magmas. This kind of enriched mantle was melted and reactivated in an area of continental extension (incipient rift setting) without direct reliance on contemporaneous subduction processes but possibly with input from mantle sources that resemble those that produce ocean island basalts.

Sulfur and oxygen isotopic systematics of the 1982 eruptions of El Chichón Volcano, Chiapas, Mexico

USGS Publications Warehouse

Rye, R.O.; Luhr, J.F.; Wasserman, M.D.

1984-01-01

Thermometers based on sulfur and oxygen isotopic compositions of anhydrite, pyrrhotite, titanomagnetite, and plagioclase crystals from fresh pumices of the 1982 eruptions of El Chichón Volcano indicate a pre-eruption temperature of 810 ± 40°C, confirming textural evidence that the anhydrite precipitated directly from the melt. The isotopic composition of sulfate leached from fresh ashfall samples shows it to be a mixture of anhydrite microphenocrysts and adsorbed sulfate derived from oxidized sulfur (SO2) in the eruption plume. The leachate data show no evidence for rapid oxidation of significant amounts of H2S in the eruption cloud even though the fugacity ratio of H2S/SO2 in the gas phase of the magma was >400. This may indicate kinetic inhibition of H2S to SO2 conversion in the eruption cloud. Prior to eruption, the magma contained an estimated 2.6 wt. % sulfur (as SO3). The estimated δ 34S of the bulk magma is 5.8‰. Such a high value may reflect assimilation of 34S-enriched evaporites or the prior loss of 34S-depleted H2S to a fluid or gas phase during formation of a small prophyry-type hydrothermal system or ore deposit. In either case, the original magma must have been very sulfur rich. It is likely that the initial high sulfur content of the magma and at least some of its 34S enrichment reflects involvement of subducted volcanogenic massive sulfides deposits during Benioff-zone partial melting. Isotopic data on mineralized, accidental lithic fragments support the possible development of a porphyry-type system at El Chichón.

A distinct source and differentiation history for Kolumbo submarine volcano, Santorini volcanic field, Aegean arc

PubMed Central

Carey, Steven; Nomikou, Paraskevi; Smet, Ingrid; Godelitsas, Athanasios; Vroon, Pieter

2016-01-01

Abstract This study reports the first detailed geochemical characterization of Kolumbo submarine volcano in order to investigate the role of source heterogeneity in controlling geochemical variability within the Santorini volcanic field in the central Aegean arc. Kolumbo, situated 15 km to the northeast of Santorini, last erupted in 1650 AD and is thus closely associated with the Santorini volcanic system in space and time. Samples taken by remotely‐operated vehicle that were analyzed for major element, trace element and Sr‐Nd‐Hf‐Pb isotope composition include the 1650 AD and underlying K2 rhyolitic, enclave‐bearing pumices that are nearly identical in composition (73 wt.% SiO2, 4.2 wt.% K2O). Lava bodies exposed in the crater and enclaves are basalts to andesites (52–60 wt.% SiO2). Biotite and amphibole are common phenocryst phases, in contrast with the typically anhydrous mineral assemblages of Santorini. The strong geochemical signature of amphibole fractionation and the assimilation of lower crustal basement in the petrogenesis of the Kolumbo magmas indicates that Kolumbo and Santorini underwent different crustal differentiation histories and that their crustal magmatic systems are unrelated. Moreover, the Kolumbo samples are derived from a distinct, more enriched mantle source that is characterized by high Nb/Yb (>3) and low 206Pb/204Pb (<18.82) that has not been recognized in the Santorini volcanic products. The strong dissimilarity in both petrogenesis and inferred mantle sources between Kolumbo and Santorini suggests that pronounced source variations can be manifested in arc magmas that are closely associated in space and time within a single volcanic field. PMID:27917071

Under trees and water at Crater Lake National Park, Oregon

USGS Publications Warehouse

Robinson, Joel E.; Bacon, Charles R.; Wayne, Chris

2012-01-01

Crater Lake partially fills the caldera that formed approximately 7,700 years ago during the eruption of a 12,000-ft-high volcano known as Mount Mazama. The caldera-forming, or climactic, eruption of Mount Mazama devastated the surrounding landscape, left a thick deposit of pumice and ash in adjacent valleys, and spread a blanket of volcanic ash as far away as southern Canada. Prior to the climactic event, Mount Mazama had a 400,000-year history of volcanic activity similar to other large Cascade volcanoes such as Mounts Shasta, Hood, and Rainier. Since the caldera formed, many smaller, less violent eruptions occurred at volcanic vents below Crater Lake's surface, including Wizard Island. A survey of Crater Lake National Park with airborne LiDAR (Light Detection And Ranging) resulted in a digital elevation map of the ground surface beneath the forest canopy. The average resolution is 1.6 laser returns per square meter yielding vertical and horizontal accuracies of ±5 cm. The map of the floor beneath the surface of the 1,947-ft-deep (593-m-deep) Crater Lake was developed from a multibeam sonar bathymetric survey and was added to the map to provide a continuous view of the landscape from the highest peak on Mount Scott to the deepest part of Crater Lake. Four enlarged shaded-relief views provide a sampling of features that illustrate the resolution of the LiDAR survey and illustrate its utility in revealing volcanic landforms and subtle features of the climactic eruption deposits. LiDAR's high precision and ability to "see" through the forest canopy reveal features that may not be easily recognized-even when walked over-because their full extent is hidden by vegetation, such as the 1-m-tall arcuate scarp near Castle Creek.

Isotope geochemistry of recent magmatism in the Aegean arc: Sr, Nd, Hf, and O isotopic ratios in the lavas of Milos and Santorini-geodynamic implications

USGS Publications Warehouse

Briqueu, L.; Javoy, M.; Lancelot, J.R.; Tatsumoto, M.

1986-01-01

In this comparative study of variations in the isotopic compositions (Sr, Nd, O and Hf) of the calc-alkaline magmas of the largest two volcanoes, Milos and Santorini, of the Aegean arc (eastern Mediterranean) we demonstrate the complexity of the processes governing the evolution of the magmas on the scale both of the arc and of each volcano. On Santorini, the crustal contamination processes have been limited, effecting the magma gradually during its differentiation. The most differentiated lavas (rhyodacite and pumice) are also the most contaminated. On Milos, by contrast, these processes are very extensive. They are expressed in the 143Nd/144Nd vs. 87Sr/86Sr diagram as a continuous mixing curve between a mantle and a crustal end member pole defined by schists and metavolcanic rocks outcropping on these volcanoes. In contrast with Santorini, the least differentiated lavas on Milos are the most contaminated. These isotopic singularities can be correlated with the geodynamic evolution of the Aegean subduction zone, consisting of alternating tectonic phases of distension and compression. The genesis of rhyolitic magmas can be linked to the two phases of distension, and the contamination of the calc-alkaline mantle-derived magmas with the intermediate compressive phase. The isotopic characteristics of uncontaminated calc-alkaline primitive magmas of Milos and Santorini are directly comparable to those of magmas generated in subduction zones for which a contribution of subducted sediments to partial melts from the mantle is suggested, such as in the Aleutian, Sunda, and lesser Antilles island arcs. However, in spite of the importance of the sediment pile in the eastern Mediterranen oceanic crust (6-10 km), the contribution of the subducted terrigenous materials remains of limited amplitude. ?? 1986.

Strong hydrothermal eruption 600 BP inside Golovnin caldera, Kunashir Island, Kurile arc

NASA Astrophysics Data System (ADS)

Belousov, Alexander; Belousova, Marina; Kozlov, Dmitry

2017-04-01

Hydrothermal explosions are difficult to predict and thus they pose serious hazard to visitors of hydrothermal areas. Here we present results of mapping of airfall deposit of strong prehistoric hydrothermal eruption that was the latest eruptive event in the limits of Golovnin caldera in the southern part of Kunashir Island, Kurile arc. This caldera was formed 30 Ka BP (Razhigaeva et al. 1998) that was followed by extrusion of two dacitic lava domes in the central part of the caldera. The studied hydrothermal eruption occurred at active hydrothermal area located at the southern foot of the Vostochny (Eastern) lava dome. This eruption formed a 350-m wide and 40 m deep crater surrounded by low-profile ring of the ejected material. Part of the crater is occupied by 17-m-deep Kipiashee Lake having intensive hydrothermal discharge on its bottom. The ejected material is represented by yellow-white and yellow-brown poorly sorted sandy gravels and sands with admixture of clay. This clastic material was formed by fragmentation of hydrothermally altered pumice tuffs (former sediments of the intracaldera lake). The airfall deposit has nearly circular distribution around the crater. The deposit thickness decreases from 5-7 m at the crater rim to 5 cm on the distances 2-3 km; thickness half-distance (bt) is estimated as 4.1. Volume of the deposit calculated by the method of Fierstein and Nathenson (1992) is 0.007 cub.km. Radiocarbon dating of soil buried directly under the deposit provided calibrated age 1300-1420 AD. This eruption can be considered as a model for future hydrothermal explosions inside the Golovnin caldera. This study was supported by grant of Russian Science Foundation #15-17-20011.

Extraordinary sediment delivery and rapid geomorphic response following the 2008–2009 eruption of Chaitén Volcano, Chile

USGS Publications Warehouse

Major, Jon J.; Bertin, Daniel; Pierson, Thomas C.; Amigo, Alvaro; Iroume, Andres; Ulloa, Hector; Castro, Jonathan M.

2016-01-01

The 10 day explosive phase of the 2008–2009 eruption of Chaitén volcano, Chile, draped adjacent watersheds with a few cm to >1 m of tephra. Subsequent lava-dome collapses generated pyroclastic flows that delivered additional sediment. During the waning phase of explosive activity, modest rainfall triggered an extraordinary sediment flush which swiftly aggraded multiple channels by many meters. Ten kilometer from the volcano, Chaitén River channel aggraded 7 m and the river avulsed through a coastal town. That aggradation and delta growth below the abandoned and avulsed channels allow estimates of postdisturbance traction-load transport rate. On the basis of preeruption bathymetry and remotely sensed measurements of delta-surface growth, we derived a time series of delta volume. The initial flush from 11 to 14 May 2008 deposited 0.5–1.5 × 106 m3 of sediment at the mouth of Chaitén River. By 26 May, after channel avulsion, a second delta amassed about 2 × 106 m3 of sediment; by late 2011 it amassed about 11 × 106 m3. Accumulated sediment consists of low-density vesicular pumice and lithic rhyolite sand. Rates of channel aggradation and delta growth, channel width, and an assumed deposit bulk density of 1100–1500 kg m−3 indicate mean traction-load transport rate just before and shortly after avulsion (∼14–15 May) was very high, possibly as great as several tens of kg s−1 m−1. From October 2008 to December 2011, mean traction-load transport rate declined from about 7 to 0.4 kg−1 m−1. Despite extraordinary sediment delivery, disturbed channels recovered rapidly (a few years).

Conditions for generation of fire-related debris flows, Capulin Canyon, New Mexico

USGS Publications Warehouse

Cannon, S.H.; Reneau, Steven L.

2000-01-01

Comparison of the responses of three drainage basins burned by the Dome fire of 1996 in New Mexico is used to identify the hillslope, channel and fire characteristics that indicate a susceptibility specifically to wildfire-related debris flow. Summer thunderstorms generated three distinct erosive responses from each of three basins. The Capulin Canyon basin showed widespread erosive sheetwash and rilling from hillslopes, and severe flooding occurred in the channel; the North Tributary basin exhibited extensive erosion of the mineral soil to a depth of 5 cm and downslope movement of up to boulder-sized material, and at least one debris flow occurred in the channel; negligible surface runoff was observed in the South Tributary basin. The negligible surface runoff observed in the South Tributary basin is attributed to the limited extent and severity of the fire in that basin. The factors that best distinguish between debris-flow producing and flood-producing drainages are drainage basin morphology and lithology. A rugged drainage basin morphology, an average 12 per cent channel gradient, and steep, rough hillslopes coupled with colluvium and soil weathered from volcaniclastic and volcanic rocks promoted the generation of debris flows. A less rugged basin morphology, an average gradient of 5 per cent, and long, smooth slopes mantled with pumice promoted flooding. Flood and debris-flow responses were produced without the presence of water-repellent soils. The continuity and severity of the burn mosaic, the condition of the riparian vegetation, the condition of the fibrous root mat, accumulations of dry ravel and colluvial material in the channel and on hillslopes, and past debris-flow activity, appeared to have little bearing on the distinctive responses of the basins. Published in 2000 by John Wiley and Sons, Ltd.

Xenopumice erupted on 15 October 2011 offshore of El Hierro (Canary Islands): a subvolcanic snapshot of magmatic, hydrothermal and pyrometamorphic processes

NASA Astrophysics Data System (ADS)

Del Moro, S.; Di Roberto, A.; Meletlidis, S.; Pompilio, M.; Bertagnini, A.; Agostini, S.; Ridolfi, F.; Renzulli, A.

2015-06-01

On 15 October 2011, a submarine eruption offshore of El Hierro Island gave rise to floating volcanic products, known as xenopumices, i.e., pumiceous xenoliths partly mingled and coated with the juvenile basanitic magma. Over the last few years, no consensus in the scientific community in explaining the origin of these products has been reached. In order to better understand the formation of xenopumice, we present a textural, mineralogical, and geochemical study of the possible magmatic, hydrothermal, and pyrometamorphic processes, which usually operate in the plumbing systems of active volcanoes. We carried out a comprehensive SEM investigation and Sr-Nd-Pb isotope analyses on some samples representative of three different xenopumice facies. All the data were compared with previous studies, new data for El Hierro extrusives and a literature dataset of Canary Islands igneous and sedimentary rocks. In the investigated xenopumices, we emphasize the presence of restitic magmatic phases as well as crystallization of minerals (mainly olivine + pyroxene + magnetite aggregates) as pseudomorphs after pre-existing mafic phenocrysts, providing evidence of pyrometamorphism induced by the high-T juvenile basanitic magma. In addition, we identify veins consisting of zircon + REE-oxides + mullite associated with Si-rich glass and hydrothermal quartz, which indicate the fundamental role played by hydrothermal fluid circulation in the xenopumice protolith. The petrological data agree with a pre-syneruptive formation of the xenopumice, when El Hierro basanite magma intruded hydrothermally altered trachyandesite to trachyte rocks and triggered local partial melting. Therefore, the El Hierro xenopumice represents a snapshot of the transient processes at the magma-wall rock interface, which normally occurs in the feeding system of active volcanoes.

Tulelake, California: The last 3 million years

USGS Publications Warehouse

Adam, D.P.; Sarna-Wojcicki, A. M.; Rieck, Hugh J.; Bradbury, J.P.; Dean, W.E.; Forester, R.M.

1989-01-01

The Tulelake basin, formed by east-west extension and faulting during the past several million years, contains at least 550 m of lacustrine sediment. Interdisciplinary studies of a 334 m-long cored section from the town of Tulelake, California, near the center of the basin, document a 3-m.y. record of environmental changes. The core consists of a thick sequence of diatomaceous clayey, silty, and marly lacustrine sediments interbedded with numerous tephra layers. Paleomagnetic study puts the base of the core at about 3.0 Ma. Twelve widespread silicic tephra units provide correlations with other areas and complement age control provided by magnetostratigraphy; mafic and silicic tephra units erupted from local sources are also common in the core. Widespread tephra units include the Llao Rock pumice (=Tsoyawata, 7 ka), the Trego Hot Springs Bed (23 ka), and the Rockland (0.40 Ma), Lava Creek (0.62 Ma), and Rio Dell (1.5 Ma) ash beds, as well as several ash beds also found at Summer Lake, Oregon, and an ash bed originally recognized in DSDP hole 173 in the northeastern Pacific. Several tephra layers found in the core also occur in lacustrine beds exposed around the margins of the basin and elsewhere in the ancestral lacustrine system. Diatoms are present throughout the section. Pollen is present in most of the section, but some barren zones are found in the interval between 50 and 140 m; the greatest change in behavior of the pollen record takes place just above the top of the Olduvai Normal-Polarity Subchronozone. Ostracodes are present only in high-carbonate (>10% CaCO3) intervals. Evolutionary changes are found in the diatom and ostracode records. Bulk geochemical analyses show significant changes in elemental composition of the sediment through time. ?? 1989.

Using an intelligent system to aid in tephra layer correlation of the tephra beds of the Mono-Inyo Craters, California

NASA Astrophysics Data System (ADS)

Hanson-Hedgecock, S.; Bursik, M.; Rogova, G.

2008-12-01

We are developing an intelligent system to correlate tephra layers by using the lithologic and geochemical characteristics of field samples, to aid geologists in interpreting eruption patterns in volcanic fields. Understanding the eruption history of a volcanic field from stratigraphic studies is important for forecasting future eruptive behavior and hazards. The intelligent system is used to define groups of tephra source vents and to correlate tephra layers based on a combination of geochemical data and lithostratigraphic characteristics. The tephra beds of the Mono-Inyo Craters, California, are used to test the ability of the intelligent system for tephra layer correlation. The data processing is performed by a suite of both unsupervised and supervised classifiers, built and combined within the framework of the Dempster-Shafer theory of evidence. We have developed algorithms to calculate isopleth maps of thickness, lithic and pumice size that are used in the processing of the lithostratigraphic data. This spatial information is important in the determination of eruption patterns and is used by an evidential nearest neighbor classifier to correlate tephra layers. Integrating a better isopleth approximation function and expert knowledge about stratigraphic order of the tephra layers into the classifier improves the lithostratigraphic correlation from 56% to 87% of layers correctly identified. Geochemical data for defining groups of tephra sources are processed by a suit of fuzzy k-means classifiers. Improved clustering results of geochemical data are achieved by the fusion of individual clustering results with an evidential combination method. The intelligent system aids correlation by showing matches and disparities between data patterns from different outcrops that may have been overlooked. The intelligent system produces a useful recognition result, while dealing with the uncertainty from sparse data and the imprecise description of layer characteristics.

Frequent eruptions of Mount Rainier over the last ∼2,600 years

USGS Publications Warehouse

Sisson, T.W.; Vallance, J.W.

2009-01-01

Field, geochronologic, and geochemical evidence from proximal fine-grained tephras, and from limited exposures of Holocene lava flows and a small pyroclastic flow document ten–12 eruptions of Mount Rainier over the last 2,600 years, contrasting with previously published evidence for only 11–12 eruptions of the volcano for all of the Holocene. Except for the pumiceous subplinian C event of 2,200 cal year BP, the late-Holocene eruptions were weakly explosive, involving lava effusions and at least two block-and-ash pyroclastic flows. Eruptions were clustered from ∼2,600 to ∼2,200 cal year BP, an interval referred to as the Summerland eruptive period that includes the youngest lava effusion from the volcano. Thin, fine-grained tephras are the only known primary volcanic products from eruptions near 1,500 and 1,000 cal year BP, but these and earlier eruptions were penecontemporaneous with far-traveled lahars, probably created from newly erupted materials melting snow and glacial ice. The most recent magmatic eruption of Mount Rainier, documented geochemically, was the 1,000 cal year BP event. Products from a proposed eruption of Mount Rainier between AD 1820 and 1854 (X tephra of Mullineaux (US Geol Surv Bull 1326:1–83, 1974)) are redeposited C tephra, probably transported onto young moraines by snow avalanches, and do not record a nineteenth century eruption. We found no conclusive evidence for an eruption associated with the clay-rich Electron Mudflow of ∼500 cal year BP, and though rare, non-eruptive collapse of unstable edifice flanks remains as a potential hazard from Mount Rainier.