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Sample records for campi flegrei caldera

  1. Historical activity at Campi Flegrei caldera, southern Italy

    USGS Publications Warehouse

    Dvorak, J.; Gasparini, P.

    1990-01-01

    We cannot forecast whether the activity since 968 will culminate in another eruption or whether Campi Flegrei will remain quiet for several hundred more years. This article summarizes the historical recorded of activity in Campi Flegrei, which, with varying degrees of reliability, spans 2,000 years, and emphasizes that further scientific studies of this caldera will improve our understanding of the behavior of longquiescent volcanic system. 

  2. Secondary hydrothermal mineral system in the Campi Flegrei caldera, Italy

    NASA Astrophysics Data System (ADS)

    Mormone, A.; Piochi, M.; Di Vito, M. A.; Troise, C.; De Natale, G.

    2012-04-01

    Mineral systems generally develop around the deep root of the volcanoes down to the degassing magma chamber due the selective enrichment process of elements within the host-rock. The mineralization process depends on i) volcanic structure, ii) magma and fluid chemistry, iii) host-rock type and texture, iv) temperature and pressure conditions, and v) action timing that affect the transport and precipitation conditions of elements in the solution. Firstly, it generates a hydrothermal system that in a later phase may generate considerable metallogenic mineralization, in terms of both spatial extension and specie abundance. The study of secondary assemblages through depth and, possibly, through time, together with the definition of the general geological, structural, mineralogical and petrological context is the background to understand the genesis of mineral-to-metallogenic systems. We report our study on the Campi Flegrei volcano of potassic Southern Italy belt. It is a sub-circular caldera characterized by an active high-temperature and fluid-rich geothermal system affected by seismicity and ground deformation in the recent decades. The circulating fluids originate at deeper level within a degassing magma body and give rise at the surface up to 1500 tonnes/day of CO2 emissions. Their composition is intermediate between meteoric water and brines. Saline-rich fluids have been detected at ~3000 in downhole. The hydrothermal alteration varies from argillitic to phillitic, nearby the caldera boundary, to propilitic to thermo-metamorphic facies towards its centre. The Campi Flegrei caldera was defined as analogue of mineralized system such as White Island (New Zealand) that is an example of an active magmatic and embryonic copper porphyry system. In order to enhance the knowledge of such a type of embryonic-like metallogenic system, we have carried out macroscopic and microscopic investigations, SEM-EDS and electron microprobe analyses on selected samples from deep wells

  3. Tectonic stress and renewed uplift at Campi Flegrei caldera, southern Italy: New insights from caldera drilling

    NASA Astrophysics Data System (ADS)

    Carlino, Stefano; Kilburn, Christopher R. J.; Tramelli, Anna; Troise, Claudia; Somma, Renato; De Natale, Giuseppe

    2015-06-01

    Deep drilling is a key tool for the investigation of active volcanoes in the modern Earth Sciences, as this provides the only means to obtain direct information on processes that occur at depth. Data acquired from drilling projects are fundamental to our understanding of volcano dynamics, and for mitigation of the hazards they pose for millions of people who live close to active volcanoes. We present here the first borehole measurement of the stress field in the crust of Campi Flegrei (southern Italy), a large active caldera, and one of the highest risk volcanoes worldwide. Measurements were performed to depths of ∼500 m during a pilot study for the Campi Flegrei Deep Drilling Project. These data indicate an extensional stress field, with a minimum horizontal stress of ca. 75% to 80% of the maximum horizontal stress, which is approximately equal to the vertical stress. The deviation from lithostatic conditions is consistent with a progressive increase in applied horizontal stress during episodes of unrest, since at least 1969. As the stress field is evolving with time, the outcome of renewed unrest cannot be assessed by analogy with previous episodes. Interpretations of future unrest must therefore accommodate the possibility that Campi Flegrei is approaching conditions that are more favourable to a volcanic eruption than has previously been the case. Such long-term accumulation of stress is not expected to be unique to Campi Flegrei, and so might provide a basis for improved forecasts of eruptions at large calderas elsewhere.

  4. Nonlinear forecasting analysis of inflation-deflation patterns of an active caldera (Campi Flegrei, Italy)

    USGS Publications Warehouse

    Cortini, M.; Barton, C.C.

    1993-01-01

    The ground level in Pozzuoli, Italy, at the center of the Campi Flegrei caldera, has been monitored by tide gauges. Previous work suggests that the dynamics of the Campi Flegrei system, as reconstructed from the tide gauge record, is chaotic and low dimensional. According to this suggestion, in spite of the complexity of the system, at a time scale of days the ground motion is driven by a deterministic mechanism with few degrees of freedom; however, the interactions of the system may never be describable in full detail. New analysis of the tide gauge record using Nonlinear Forecasting, confirms low-dimensional chaos in the ground elevation record at Campi Flegrei and suggests that Nonlinear Forecasting could be a useful tool in volcanic surveillance. -from Authors

  5. Identifying the locations of future eruptions within large calderas: Campi Flegrei, Southern Italy.

    NASA Astrophysics Data System (ADS)

    Charlton, Danielle; Kilburn, Christopher; Sobradelo, Rosa; Edwards, Stephen

    2016-04-01

    Large calderas, with surface areas of 100 km2 or more, are among the most populated active volcanoes on Earth. New vents commonly open at locations across the caldera floor. An important goal for hazard mitigation, therefore, is to develop reliable methods for evaluating the most likely location for a future eruption. A preferred approach is to analyse statistically the distributions of previous vents. Using the Campi Flegrei caldera as a test case, we here examine the sensitivity of results to starting assumptions, notably the choice of data set for defining preferred vent locations. Situated immediately west of Naples, in southern Italy, Campi Flegrei poses a direct threat to more than 300,000 people. It has been in episodic unrest since the late 1950s. The unrest is the first since the last eruption in Campi Flegrei in 1538 and suggests that the caldera may have re-entered a state with an increased probability of an eruption. Since the most recent episode of caldera collapse 15.5 ka BP, at least 60 intra-caldera eruptions have occurred across the 150 km2 that make up the modern onshore area of Campi Flegrei. The eruptions have been concentrated within three epochs: 15.5-9.5 ka BP (Epoch 1, c. 27 eruptions), 8.6-8.2 ka BP (Epoch 2; c. 6 eruptions) and 4.8-3.8 ka BP (Epoch 3; c. 27 eruptions). Recent statistical studies of future vent locations have assumed that (1) only data from Epoch 3 are relevant to modern Campi Flegrei, and (2) repeated eruptions from the same vent can be incorporated, whether they are independent events or belong to a connected sequence of activity. We have relaxed these assumptions to investigate data from all epochs and to distinguish between independent and related eruptions from the same vent. Quadrat and nearest-neighbour statistics show that eruptions from Epochs 1 and 2 were distributed within an annulus 3-5 km around modern Pozzuoli, but that, in agreement with previous studies, eruptions occurred preferentially NE-ENE of Pozzuoli

  6. Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption

    PubMed Central

    Di Vito, Mauro A.; Acocella, Valerio; Aiello, Giuseppe; Barra, Diana; Battaglia, Maurizio; Carandente, Antonio; Del Gaudio, Carlo; de Vita, Sandro; Ricciardi, Giovanni P.; Ricco, Ciro; Scandone, Roberto; Terrasi, Filippo

    2016-01-01

    Calderas are collapse structures related to the emptying of magmatic reservoirs, often associated with large eruptions from long-lived magmatic systems. Understanding how magma is transferred from a magma reservoir to the surface before eruptions is a major challenge. Here we exploit the historical, archaeological and geological record of Campi Flegrei caldera to estimate the surface deformation preceding the Monte Nuovo eruption and investigate the shallow magma transfer. Our data suggest a progressive magma accumulation from ~1251 to 1536 in a 4.6 ± 0.9 km deep source below the caldera centre, and its transfer, between 1536 and 1538, to a 3.8 ± 0.6 km deep magmatic source ~4 km NW of the caldera centre, below Monte Nuovo; this peripheral source fed the eruption through a shallower source, 0.4 ± 0.3 km deep. This is the first reconstruction of pre-eruptive magma transfer at Campi Flegrei and corroborates the existence of a stationary oblate source, below the caldera centre, that has been feeding lateral eruptions for the last ~5 ka. Our results suggest: 1) repeated emplacement of magma through intrusions below the caldera centre; 2) occasional lateral transfer of magma feeding non-central eruptions within the caldera. Comparison with historical unrest at calderas worldwide suggests that this behavior is common. PMID:27558276

  7. Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption.

    PubMed

    Di Vito, Mauro A; Acocella, Valerio; Aiello, Giuseppe; Barra, Diana; Battaglia, Maurizio; Carandente, Antonio; Del Gaudio, Carlo; de Vita, Sandro; Ricciardi, Giovanni P; Ricco, Ciro; Scandone, Roberto; Terrasi, Filippo

    2016-01-01

    Calderas are collapse structures related to the emptying of magmatic reservoirs, often associated with large eruptions from long-lived magmatic systems. Understanding how magma is transferred from a magma reservoir to the surface before eruptions is a major challenge. Here we exploit the historical, archaeological and geological record of Campi Flegrei caldera to estimate the surface deformation preceding the Monte Nuovo eruption and investigate the shallow magma transfer. Our data suggest a progressive magma accumulation from ~1251 to 1536 in a 4.6 ± 0.9 km deep source below the caldera centre, and its transfer, between 1536 and 1538, to a 3.8 ± 0.6 km deep magmatic source ~4 km NW of the caldera centre, below Monte Nuovo; this peripheral source fed the eruption through a shallower source, 0.4 ± 0.3 km deep. This is the first reconstruction of pre-eruptive magma transfer at Campi Flegrei and corroborates the existence of a stationary oblate source, below the caldera centre, that has been feeding lateral eruptions for the last ~5 ka. Our results suggest: 1) repeated emplacement of magma through intrusions below the caldera centre; 2) occasional lateral transfer of magma feeding non-central eruptions within the caldera. Comparison with historical unrest at calderas worldwide suggests that this behavior is common. PMID:27558276

  8. Reconstruction of caldera collapse and resurgence processes in the offshore sector of the Campi Flegrei caldera (Italy)

    NASA Astrophysics Data System (ADS)

    Steinmann, Lena; Spiess, Volkhard; Sacchi, Marco

    2015-04-01

    Large collapse calderas are associated with exceptionally explosive volcanic eruptions, which are capable of triggering a global catastrophe second only to that from a giant meteorite impact. Therefore, active calderas have attracted significant attention in both scientific communities and governmental institutions worldwide. One prime example of a large collapse caldera can be found in southern Italy, more precisely in the northern Bay of Naples within the Campi Flegrei Volcanic Area. The Campi Flegrei caldera covers an area of approximately 200 km² defined by a quasi-circular depression, half onland, half offshore. It is still under debate whether the caldera formation was related to only one ignimbritic eruption namely the Neapolitan Yellow Tuff (NYT) eruption at 15 ka or if it is a nested-caldera system related to the NYT and the Campanian Ignimbrite eruption at 39 ka. During the last 40 years, the Campi Flegrei caldera has experienced episodes of unrest involving significant ground deformation and seismicity, which have nevertheless not yet led to an eruption. Besides these short-term episodes of unrest, long-term ground deformation with rates of several tens of meters within a few thousand years can be observed in the central part of the caldera. The source of both short-term and long-term deformation is still under debate and possibly related to a shallow hydrothermal system and caldera resurgence attributed to a deeper magma chamber, respectively. Understanding the mechanisms for unrest and eruptions is of paramount importance as a future eruption of the Campi Flegrei caldera would expose more than 500,000 people to the risk of pyroclastic flows. This study is based on a dense grid (semi-3D) of high-resolution multi-channel seismic profiles acquired in the offshore sector of the Campi Flegrei caldera. The seismic lines show evidence for the escape of fluids and/or gases along weak zones such as faults, thereby supporting the existence of a hydrothermal

  9. Ground deformation at Campi Flegrei caldera using long water pipe tiltmeters and sea level gauges

    NASA Astrophysics Data System (ADS)

    Scarpa, R.; Capuano, P.; Tammaro, U.; Bilham, R.

    2012-04-01

    Campi Flegrei is a caldera complex located in the Campanian plain region of southern Italy, 15 km west of the city of Naples, and forms part of the Roman co-magmatic province which is a volcanic chain that characterizes the western coast of the country. The Campi Flegrei caldera was generated by several collapses produced by strong explosive eruptions. The main caldera at Campi Flegrei is 12 - 15km across and its rim is thought to have been formed during the catastrophic eruption, occurred 39 ky ago ca. which produced a deposit referred to as the Campanian Ignimbrite. Campi Flegrei area periodically experiences significant unrest episodes which include ground deformations, the so-called "bradisismo", recorded both by marine terraces, archaeological record and harbour structures. Following the last eruption (Monte Nuovo, 1538) a general subsidence has been interrupted by episodes of uplift, the most recent of which occurred in 1970-72 and 1982-84. In the past decade subsidence has been arrested and has been replaced by intermittent episodes of inflation with short time duration and various maximum amplitude. They occurred in 1989, 1994, 2000, 2004, 2005-06, 2009 and 2011 with duration of few months and maximum amplitude ranging between 3 and 11 cm. Since 2008 an array of water-pipe tiltmeters with lengths between 28 m and 278 m in tunnels on the flanks of the region of maximum inflation has been installed to avoid problems common to the traditional tiltmeters. The tiltmeters record inflation episodes upon which are superimposed local load tides, with amplitudes roughly an order of magnitude greater than the solid Earth body tides. In addition to the tides, the tiltmeters record a line spectrum of seiches in the Bay of Naples and in the Tyrrenian sea. We use data recorded by three tide gauges in the Bay of Pozzuoli to compare water pipe data with sea level to extract astronomical tidal components and seiches periods particularly between 20 minutes and 56 minutes that

  10. The Campi Flegrei Deep Drilling Project `CFDDP': Understanding the Magma-Aquifers Interaction at Large Calderas

    NASA Astrophysics Data System (ADS)

    de Natale, G.; Troise, C.; Sacchi, M.

    2007-05-01

    Campi Flegrei caldera is a good example of the most explosive volcanism on the Earth, a potential source of global catastrophes. Alike several similar volcanic areas (Yellowstone and Long Valley, USA; Santorini, Greece; Iwo Jima, Japan, etc.) its volcanic activity, i.e. eruptions and unrests, is dominated by physical mechanisms involving the strict interaction between shallow magma sources and geothermal systems. Furthermore, just like similar areas, it should be characterised by very large shallow magma chambers, filled by residual magma left after the ignimbritic caldera forming eruptions. However, neither the physical mechanisms of magma-water interaction, nor the evidence for such large magma chamber, have been ever clear enough to be used for detailed volcanological interpretation and eruption forecast. The CFDDP project aims to understand, for the first time, the location and rehology of large residual magma chambers and the mechanisms of interaction between magma and aquifer systems to generate eruptions and unrests. CFDDP is then structured as a large multidisciplinary project, with a main volcanological aim and with a further goal to launch a geothermal energy exploitation project in the area. A larger goal of the CFDDP project is to establish at Campi Flegrei, a densely urbanised area in a developed western country, a natural laboratory to study volcanic risk, environmental issues, monitoring technologies, geothermal energy exploitation.

  11. Investigating the activity of the Campi Flegrei caldera (Italy) through remote and in situ sensors (Invited)

    NASA Astrophysics Data System (ADS)

    Trasatti, E.; Polcari, M.; Bignami, C.; Bonafede, M.; Buongiorno, F.; Stramondo, S.

    2013-12-01

    Campi Flegrei is a nested caldera in Italy, whose structure includes submerged and continental parts at the western edge of the Bay of Naples. Together with Vesuvius and Etna, it is one of the Italian GeoHazard Supersites. The last eruption took place in 1538 A.D. and since then intense degassing, seismic swarms and several episodes of ground uplift have been observed. The area is characterized by one of the highest volcanic hazard in the world, due to the very high density of inhabitants. A major unrest episode took place in 1982-84, when the town of Pozzuoli, located at the caldera center, was uplifted by 1.80 m (~1 m/yr). During the following decades the area has been generally subsiding but minor uplift episodes of the order of few cm, seismic swarms and degassing episodes took place in 1989, 2000-01 and 2004-06, showing that the caldera is in a critical state on the verge of instability. Since March 1970 leveling surveys were regularly carried out to monitor the elevation changes. In the following decades many efforts have been done to monitor the different aspects of the activity of the area, and nowadays Campi Flegrei is subjected to intense geodetic, geophysical and geochemical monitoring. In the last 30 years a number of geophysical investigations has provided important constraints to the description of the subsurface structure and the historical volcanic activity. Surface deformation, microgravity changes and geochemical anomalies at Campi Flegrei have been interpreted either in terms of instabilities of the hydrothermal system or variations in the magmatic source. In particular, discerning between magmatic vs hydrothermal origin of the source responsible of the large uplift episode during 1982-84 (most probably due to deep magmatic source) and of the mini-uplifts (e.g. 2000 and 2004-06, most probably due to pressure variations in the shallow aquifer) may have important implications in terms of civil protection. In the last two decades, the precise and

  12. The Campi Flegrei Deep Drilling Project: understanding the structure and mechanisms of large collapse calderas

    NASA Astrophysics Data System (ADS)

    de Natale, Giuseppe; Troise, Claudia

    2010-05-01

    Large calderas are the most dangerous volcanoes on the Earth. They are produced by collapse during explosive super-eruptions, which are capable of triggering global catastrophes comparable to large meteorite impacts. The mechanisms of unrest and eruption at calderas are at a large extent unknown and, as demonstrated by volcanological research in the last decades, they may be very different from those characterizing more commonly studied stratovolcanoes. Campi Flegrei caldera (Italy) represents an ideal natural laboratory to fully understand mechanisms of caldera dynamics and to develop techniques for eruption forecast and effective risk mitigation. It is an active volcanic area marked by a quasi-circular caldera depression, formed by huge ignimbritic eruptions. The caldera has recently experienced intense deformation, originating uplift phenomena of more than 3.5 m in 15 years, with maximum rates of 1 m/year in the period 1982-1984, which caused the temporary evacuation of 30,000 people from the centre of Pozzuoli and exposed more than 500,000 to impending eruption risk (several millions in case of an ignimbritic eruption). This area will be the target of a leading International project, the ‘Campi Flegrei Deep Drilling Project', sponsored by ICDP, aimed to study in detail, by a crustal deviated drilling reaching the depth of about 4 km, the deep structure of the caldera. The role of deep drilling at this area is crucial. It could give a fundamental, precise insight into the substructure, the geometry and character of the geothermal systems and their role in the unrest episodes, as well as to explain magma chemistry and the mechanisms of magma-water interaction. One of the main goal will be giving a precise determination of the magma depth, based on the extrapolation of the geothermal gradient in purely conductive conditions, occurring below the maximum aquifer depth. The choice of Campi Flegrei as a target for the deep study of large calderas is justified by the

  13. Rock physics of fibrous rocks akin to Roman concrete explains uplifts at Campi Flegrei Caldera

    NASA Astrophysics Data System (ADS)

    Vanorio, Tiziana; Kanitpanyacharoen, Waruntorn

    2015-08-01

    Uplifts in the Campi Flegrei caldera reach values unsurpassed anywhere in the world (~2 meters). Despite the marked deformation, the release of strain appears delayed. The rock physics analysis of well cores highlights the presence of two horizons, above and below the seismogenic area, underlying a coupled process. The basement is a calc-silicate rock housing hydrothermal decarbonation reactions, which provide lime-rich fluids. The caprock above the seismogenic area has a pozzolanic composition and a fibril-rich matrix that results from lime-pozzolanic reactions. These findings provide evidence for a natural process reflecting that characterizing the cementitious pastes in modern and Roman concrete. The formation of fibrous minerals by intertwining filaments confers shear and tensile strength to the caprock, contributing to its ductility and increased resistance to fracture.

  14. Evidence for the buried rim of Campi Flegrei caldera from 3-d active seismic imaging

    NASA Astrophysics Data System (ADS)

    Zollo, A.; Judenherc, S.; Auger, E.; D'Auria, L.; Virieux, J.; Capuano, P.; Chiarabba, C.; de Franco, R.; Makris, J.; Michelini, A.; Musacchio, G.

    2003-10-01

    An extended marine, active seismic survey has been performed on September, 2001 in the gulfs of Naples and Pozzuoli by recording about 5000 shots at a network of 62 sea bottom and 72 on shore seismographs. 3-D images of the shallow caldera structure are obtained from the tomographic inversion of about 77000 first P arrival times using the Benz et al. [1996] tomographic technique. The buried rim of the Campi Flegrei caldera is clearly detected at about 800-2000 m depth, as an anular high P-velocity and high density body. It has a diameter of about 8-12 km and a height of 1-2 km. According to stratigraphic and sonic log data from deep boreholes and tomographic P velocities, the rim is likely formed by solidified lavas and/or tuffs with interbedded lava. This study confirms the existence for a depressed limestone basement beneath the caldera at less than 4 km depth, while no evidence are found for shallower magmatic bodies.

  15. Geochemical Clues on the Processes Controlling the 2005-2014 Unrest at Campi Flegrei Caldera, Italy

    NASA Astrophysics Data System (ADS)

    Chiodini, G.; Vandemeulebrouck, J.; Caliro, S.; D'auria, L.; De Martino, P.; Mangiacapra, A.; Petrillo, Z.

    2014-12-01

    The understanding of the mechanism which triggers unrests at active calderas is one of the most problematic issues of modern volcanology. In particular, magmatic intrusion vs. hydrothermal dynamics is one of the central questions to understand the signals of several restless calderas of the Earth, including, for example, Yellowstone, Long Valley, and Campi Flegrei. Here we focus on Campi Flegrei caldera, sited in the densely inhabited metropolitan area of Napoli, where an inflation stage showing an accelerating trend started in 2005 and reached a maximum vertical displacement of about 24 cm in July 2014. Fumarolic compositions compared with ground deformation data suggests that this ten year's accelerating uplift is mainly caused by the overlapping of two processes: (i) short time pulses caused by injection of magmatic fluids into the hydrothermal system, and (ii) a long time process of heating of the rocks. The short pulses are highlighted by comparing the residuals of ground deformation, fitted with an accelerating curve, with the fumarolic CO2/CH4 and He/CH4 ratios which are good indicators of the arrival of magmatic gases into the hydrothermal system. These two independent datasets show an impressive temporal correlation, with the same sequence of five peaks with a delay of ~ 200 days of the geochemical signal with respect to the geodetic one. The heating of the hydrothermal system is inferred by an evident increase in the fumarolic activity and by temperature-pressure gas-geoindicators. The accelerating ground deformation is paralleled in fact by an increase in the fumarolic CO/CO2 ratio and by a general decrease of the CH4/CO2ratio, both being sign of increased equilibration temperatures. Comparing the observed fumarolic compositions with the thermodynamically derived equilibrium values we infer that the heating is caused by the condensation of increasing amounts of steam. According to a recent interpretation of fumarolic inert gas species, which relates

  16. The Monte Nuovo eruption: the only historical event of the Campi Flegrei caldera

    NASA Astrophysics Data System (ADS)

    di Vito, Mauro Antonio; Arienzo, Ilenia; Buononato, Salvatore; Civetta, Lucia; Carandente, Antonio; D'Antonio, Massimo; di Renzo, Valeria; Orsi, Giovanni

    2010-05-01

    The Monte Nuovo eruption, the last event of the Campi Flegrei caldera, has been reconstructed through geological, volcanological and petrological investigations, and analyses of historical documents. The eruption, lasted one week and characterised by three vents, included three distinct phases. The main vent (MV) was located in the present crater, whereas two minor vents were along the southern (SV) and north-eastern (NEV) slopes of the Monte Nuovo tuff cone. The sequence of deposits has been subdivided in 5 members named A through E. The eruption began on September 29, 1538, at 7 p.m., and its first and main phase, lasted until the night of September 30. This phase generated almost continuous explosions mainly phreatomagmatic, producing pyroclastic density currents (pdćs) and minor short-lived, low eruption columns, which deposited members A and B. Member A, erupted in about 12 hours through the MV, forms the largest part of the cone. Phreatomagmatic explosions at the SV produced mainly pdćs which deposited Member B only in the southern sector of Monte Nuovo. Strombolian explosions at the SV and NEV deposited Member C over a narrow area. This activity was followed by a pause lasted two days. The eruption resumed on October 3 at 4 p.m. and lasted until the next night. This second phase of the eruption was characterized by a discontinuous sequence of low-energy phreatomagmatic and magmatic explosions at the MV, which deposited Member D. On October 6, at 4 p.m. explosive activity resumed and lasted few hours, mainly with low-energy magmatic explosions of a small dome, grown during the preceding two days, which produced Member E. During this phase 24 people died while climbing the slopes of the newly formed cone. The juvenile products of the Monte Nuovo eruption are phenocryst-poor rocks containing alkali feldspars and subordinate clinopyroxene and Fe-Ti oxides. The are light-coloured pumice and dark scoria fragments, and represent the most evolved magma erupted

  17. Trigger Mechanisms for Volcanic Eruptions at Campi Flegrei caldera (Southern-Italy) in the last 5ka of activity

    NASA Astrophysics Data System (ADS)

    Arienzo, I.; D'Antonio, M.; Moretti, R.; Cavallo, A.; Civetta, L.; Orsi, G.

    2012-12-01

    Products from the 3.98 ± 0.53 ka year-old Nisida eruption have been studied in order to investigate the role of magma mingling/mixing, degassing and crystal fractionation in triggering volcanic eruptions during the last 5 ka of volcanic activity at Campi Flegrei caldera (Southern Italy). Due to persistent unrest, the explosive character of its volcanism and the large population living within the caldera and its surroundings, the volcanic risk in this nested, resurgent caldera is among the highest on Earth and demands an accurate reconstruction of processes driving recent volcanism. We present major elements and isotope data on bulk rock, glass matrix and separated phenocrysts, along with major and volatile elements on clinopyroxene-hosted melt inclusions, of products from Nisida and other Campi Flegrei eruptions occurred in the last 5 ka. The new data, together with literature data, suggest that crystal fractionation may account for the chemical variability of the extruded melt, although additional processes, such as magma mingling/mixing and/or entrapment of antecrysts into the magma prior to eruption are required to explain the large isotopic variation displayed by the analyzed products. In particular, the Nisida eruption was triggered by the arrival of isotopically distinct (87Sr/86Sr ~ 0.7073), poorly differentiated (latite), volatile-rich magma (H2O up to 4 wt.%). This is in line with what already proposed for the Agnano-Monte Spina (~ 4.1 ka) and Minopoli 2 eruptions (~ 9.7 ka), both occurred in the eastern sector of the Campi Flegrei caldera affected by extension. Noteworthy, Campi Flegrei caldera is located at the intersection of regional NE-SW and NW-SE fault systems and characterized by large caldera-forming eruptions and resurgence of the caldera floor following a simple shearing mechanism. In particular, deep, latitic magmas, rose along portions of faults of the NE-SW system, in the eastern sector of the caldera affected by extensional processes

  18. Fiber-Reinforced Rocks Akin to Roman Concrete Help Explain Ground Deformation at Campi Flegrei Caldera

    NASA Astrophysics Data System (ADS)

    Vanorio, Tiziana; Kanitpanyacharoen, Waruntorn

    2016-04-01

    The caldera of Campi Flegrei is one of the active hydrothermal systems of the Mediterranean region experiencing notable unrest episodes in a densely populated area. During the last crisis of 1982-1984, nearly 40,000 people were evacuated for almost two years from the main town of Pozzuoli, the Roman Puteoli, due to the large uplifts (~2 m over two years) and the persistent seismic activity. The evacuation severely hampered the economy and the social make-up of the community, which included the relocation of schools and commercial shops as well as the harbor being rendered useless for docking. Despite the large uplifts, the release of strain appears delayed. Seismicity begins and reaches a magnitude of 4.0 only upon relatively large uplifts (~ 70-80 cm) contrary to what is generally observed for calderas exhibiting much lower deformation levels. Over and above the specific mechanism causing the unrest and the lack of identification of a shallow magmatic reservoir (< 4 km) by seismic data, there is a core question of how the subsurface rocks of Campi Flegrei withstand a large strain and have high strength. We performed a series of direct measurements on deep well cores by combining high-resolution microstructural and mineralogical analyses with the elastic and mechanical properties of well cores from the deep wells drilled in the area right before the unrest of 1982-1984 - San Vito (SV1 and SV2) and Mofete (MF1, MF2, MF5). The rock physics analysis of the well cores provides evidence for the existence of two horizons, above and below the seismogenic area, underlying a natural, coupled process. The basement is a calc-silicate rock housing hydrothermal decarbonation reactions, which provide lime-rich fluids. The caprock above the seismogenic area has a pozzolanic composition and a fibril-rich matrix made of intertwining filaments of ettringite and tobemorite, resulting from lime-pozzolanic reactions. These findings provide evidence for a natural process reflecting that

  19. The Project Serapis: High Resolution Seismic Imagingof The Campi Flegrei Caldera Structure

    NASA Astrophysics Data System (ADS)

    Zollo, A.; Virieux, J.; Capuano, P.; Chiarabba, C.; de Franco, R.; Makris, J.; Michelini, A.; Musacchio, G.; Serapis Group

    expected NE-SW and SE-NW structural trends and it has been designed to get 2D/3D images of the crustal structure at a regional scale. A denser 2D network of 35 OBSs has been deployed in the bay of Pozzuoli aimed at detecting and modeling reflected/converted waves from 1 the possible shallow to deep discontinuities beneath the Campi Flegrei caldera. The main target of this particular receiver lay-out is the detailed imaging of the magma chamber top, expected at 4-5 km depth, according to temperature measurements in wells and sparse seismic observations. About 5000 shots have been performed dur- ing the SERAPIS experiment, at an average spatial spacing of 125 m, for a total ship travel path of 620 km. All of the seismic lines have been re-sampled at least twice, using a staggered configuration, which results in a smaller source spacing (less than 65m). In the gulf of Pozzuoli the source array had a geometry of a 5x5 km grid, slightly shifted south with respect to the OBS array. Seismic signals produced by air- guns have been well detected up to 50-60 km distance and the whole Campi Flegrei, Ischia and Procida on-land networks have recorded high quality seismograms pro- duced by the gridded source array in the bay of Pozzuoli. Due to the extended and very dense source and receiver arrays used for SERAPIS, this campaign can provide an innovative contribution to the accurate reconstruction of the Campi Flegrei caldera structure and to the definition of its feeding system at depth. *SERAPIS group: Auger Emmanuel, Bernard Marie-Lise, Bobbio Antonella, Bonagura Mariateresa, Cantore Luciana, Convertito Vincenzo, D'Auria Luca, De Matteis Raffaella, Emolo Anto- nio, Festa Gaetano, Gasparini Paolo, Giberti Grazia, Herrero Andre, Improta Luigi, Lancieri Maria Flora, Nielsen Stefan, Nisii Vincenzo, Russo Guido, Satriano Clau- dio, Simini Mariella, Vassallo Maurizio, Bruno Pier Paolo, Buonocunto Ciro, Capello Marco, Del Pezzo Edoardo, Galluzzo Danilo, Gaudiosi Germana, Giuliana Alessio

  20. Geochemical clues on the origin of the current accelerating deformation of Campi Flegrei caldera

    NASA Astrophysics Data System (ADS)

    Chiodini, Giovanni

    2016-04-01

    An accelerating process of ground deformation is currently affecting the Campi Flegrei caldera. The deformation pattern is here explained with the overlapping of two processes: short time pulses that are caused by injection of magmatic fluids into the hydrothermal system, and a longer time process of heating of the rock. The short pulses were highlighted by comparing fumarolic compositions and ground deformations. The two independent data sets show the same sequence of anomalous peaks with a delay of ˜ 200 days of the geochemical signal with respect to the geodetic signal. This correspondence strongly support the occurrence of episodes of magmatic fluid injection into the hydrothermal system feeding the fumaroles of Solfatara. Seismic swarms, whose frequency is increasing in the time, accompanies each of this episode. The heating of the hydrothermal system, which parallels the long-period accelerating curve, is inferred by temperature-pressure gas geoindicators. Referring to a recent interpretation that relates variations in the fumarolic inert gas species to open system magma degassing, we infer that the heating is caused by an enrichment in water of the magmatic fluids, in addition to an increment in their flux and an increased frequency of the degassing events. A physical numerical model of the injection of magmatic fluids into the hydrothermal system nicely reproduces many of the observed data including the thermal evolution independently inferred from the fumarolic composition.

  1. The Campi Flegrei Deep Drilling Project: using borehole measurements to discriminate magmatic and geothermal effects in caldera unrest

    NASA Astrophysics Data System (ADS)

    De Natale, Giuseppe; Troise, Claudia; Carlino, Stefano; Troiano, Antonio; Giulia Di Giuseppe, Maria; Piochi, Monica; Somma, Renato; Tramelli, Anna; Kilburn, Christopher

    2015-04-01

    Large calderas are potentially the most risky volcanic areas in the world since they are capable of producing huge eruptions whose major effects can involve human life and activities from regional to global scale. Calderas worldwide are characterized by frequent episodes of unrest which, only in few cases, culminate with eruptions. This ambiguous behavior is generally explained in terms of magma intrusion or disturbance of geothermal fluids in the shallow crust, which are both source of ground deformations and seismicity. A major goal is to determine the relative contribution of each process, because the potential for eruptions significantly enhanced if magma movements emerge as the primary component. A very important case study is the active Campi Flegrei caldera, hosting part of the large city of Naples (Southern Italy). In the framework of the Campi Flegrei Deep Drilling Project new filed data from pilot borehole have been recorded (permeability and in situ stress) by using a novel procedure of Leak Off Test. These new data, particularly the actual permeability, are fundamental to calibrate the caldera unrest models at Campi Flegrei and, , to put constrains to forecast the maximum future eruptive scenario. We show here that these new data, integrated by fluid-dynamical modeling, allow to assess that only about a third of the maximum uplift recorded in 1982-1984 may be due to shallow aquifer perturbation, so that the remaining part should be due to magma inflow, corresponding to about 0.05 Km3 of new magma if we assume a sill-like reservoir located at 4 km of depth. Considering an almost equivalent magma inflow for the 1969-1972 unrest, which showed a similar uplift, we got a total magma inflow of 0.1 Km3. It is then very important to assess the times for cooling of such accumulated magma, in order to assess the eruption hazard.

  2. Investigation of hydrothermal activity at Campi Flegrei caldera using 3D simulations: extension to high temperature processes

    NASA Astrophysics Data System (ADS)

    Afanasyev, Andrey; Costa, Antonio; Chiodini, Giovanni

    2015-04-01

    Hydrothermal activity at Campi Flegrei caldera is simulated by using the multiphase code MUFITS (www.mufits.imec.msu.ru). We provide a brief description of the simulator covering the mathematical formulation and its applicability at elevated supercritical temperatures. Then we apply, for the first time, the code to hydrothermal systems investigating the Campi Flegrei caldera case. We consider both shallow subcritical regions and deep supercritical regions of the hydrothermal system. We impose sophisticated boundary conditions at the surface to provide a better description of the reservoir interactions with the atmosphere and the sea. Finally we carry out a parametric study and compare the simulation results with gas temperature and composition, gas and heat fluxes, and temperature measurements in the wells of that area. Results of the parametric study show that flow rate, composition, and temperature of the hot gas mixture injected at depth, and the initial geothermal gradient strongly control parameters monitored at Solfatara. Comparisons with observations show a very good match and suggest that the best guesses for the injected hot (~700 C) fluid mass flow rate is about 50-100 kg/s and the initial geothermal gradient is 120 C/km. Of particular interest resulted the comparison between the simulated thermal profiles and those measured in geothermal wells. Keeping in mind the uncertainties due to the heterogeneities of the system, the good match obtained for the wells in the eastern and north sectors of the caldera (located some km far from Solfatara) suggest that the model can reproduce the gross features of the Campi Flegrei hydrothermal system and implicitly support the hypothesis of a single (or major) deep source of magmatic fluid located close to the centre of the caldera. Surprising results were also obtained by comparing simulated and observed (Agnano well) temperature profiles in a zone close to the gas plume: in this case the simulations clearly suggested

  3. The dynamics of magma chamber refilling at the Campi Flegrei caldera.

    NASA Astrophysics Data System (ADS)

    Montagna, Chiara Paola; Vassalli, Melissa; Longo, Antonella; Papale, Paolo; Giudice, Salvatore; Saccorotti, Gilberto

    2010-05-01

    The volcanologic and petrologic reconstructions of several eruptions during the last tens of thousand years of volcanism at the Campi Flegrei caldera show that in most cases a small, chemically evolved, partially degassed magma chamber was refilled by magma of deeper origin shortly before the eruption. New magma input in a shallow chamber is revealed from a variety of indicators, well described in the literature, that include major-trace element and isotope heterogeneities, and crystal-liquid disequilibria (e.g., Arienzo et al., Bull. Volcanol., 2009). In the case of the 4100 BP Agnano Monte Spina eruption, representing the highest intensity and magnitude event of the last epoch of activity, it has been suggested that the refilling occurred within a few tens of hours from the start of the eruption. Notably, in such a case the two end-member magmas that mixed shortly before eruption onset are not recognized as individual members in the deposits, rather, their composition and characteristics are reconstructed from small scale disequilibria, revealing that a relatively short time was sufficient for efficient mixing of the liquid components. In order to investigate the dynamics of magma chamber refilling and mixing at Campi Flegrei we have applied the GALES code (Longo et al., Geophys. Res. Lett., 2006) in a series of numerical simulations. The initial and boundary conditions have been defined in the frame of two subsequent projects coordinated by INGV and funded by the Italian Civil Protection Department, that gather a large number of experts on Campi Flegrei, and are consistent with the bulk of knowledge on the deep magmatic system. In all cases an initial compositional interface is placed at a certain depth, with non-degassed, buoyant magma placed below. The simulations investigate both the dynamics in a very large, 8 km deep reservoir revealed by seismic tomography (Zollo et al., Geophys. Res. Lett., 2008), and those in shallower and smaller chamber systems

  4. The interplay between deformation and volcanic activity: new data from the central sector of the Campi Flegrei caldera

    NASA Astrophysics Data System (ADS)

    Isaia, Roberto; Sabatino, Ciarcia; Enrico, Iannuzzi; Ernesto, Prinzi; D'Assisi, Tramparulo Francesco; Stefano, Vitale

    2016-04-01

    The new excavation of a tunnel in the central sector of the Campi Flegrei caldera allowed us to collect new stratigraphic and structural data shedding light on the volcano-tectonic evolution of the last 10 ka. The analyzed sequences are composed by an alternation of volcanic, lacustrine, fluvial and marine sediments hosting several deformation structures such as faults, sedimentary dykes and fractures. A review of available well log togheter with the new data were used to perform a 3D reconstruction of paleo-surfaces resulted after the main volcanic and deformation episodes. Results show as the paleo-morphology was strictly controlled by faults and fractures that formed meso-scale channels and depressions subsequently filled by tephra and volcanoclastic sediments. The measured structures indicate an extensional deformation accompanying the ground uplift occurred in various stages of the caldera evolution. Stratigraphic relationships between structures and volcanic deposits further constrain the timing of the deformation phases. Presently an unrest phase of the Campi Flegrei caldera is marked by variations of different parameters such as ground deformation activities well recorded by GPS data, topographic leveling and satellite surveys. The results of this study provide further insight into the long term deformation pattern of the caldera and provide a key to interpret the ground deformation scenarios accompanying a possible resumption of volcanism.

  5. Phase relations and volatiles content of the Minopoli2 Campi Flegrei caldera shoshonitic magma

    NASA Astrophysics Data System (ADS)

    Mangiacapra, A.; Rutherford, M.; Civetta, L.

    2009-04-01

    New constraints on pre-eruption conditions of the Minopoli2 shoshonitic magma are provided by experimental studies. The products of this eruption represent the least evolved magma composition erupted in the first epoch of Campi Flegrei caldera activity (10.3-9.5 ka). Recent geochemical investigations (Mangiacapra et al.,2008)* on dissolved volatiles in the Minopoli2 phenocryst-hosted melt inclusions (MIs), revealed a H2O- and CO2-rich shoshonitic magma, stored at two depths (8-9 and 2-3 km) where it experienced both open-system degassing, driven by crystallization, and flushing with a CO2-rich gas phase coming from deeper levels. Phase equilibrium experiments dry and with 3.5wt% H2O have been guided by the dissolved H2O and CO2 in MIs. The phase equilibria of the shoshonite with 3.5 wt% H2O shows that the observed phenocryst assemblage (olivine, Ca-pyroxene, plagioclase and biotite) becomes stable at 1020±15 °C over the pressure range of 40 to 150 MPa and to higher pressures. The experimental data indicate that the shoshonite crystallised the phenocryst assemblage (15 vol%) at a depth of circa 9 Km and 1025 °C; only small degrees of additional crystallization occurred as the magma ascended to a depth of circa 3 km with degassing of some MIs. Sulphur speciation in glassy MIs was determined as ≥ 79% sulphate which is equivalent to a log fO2≥ NNO + 1.5. The low end of the fO2 range is interpreted to represent the pre-eruption magma at depth. The solubility of CO2 and H2O as a function of pressure in the Minopoli2 shoshonite have been experimentally calibrated. These results contribute to the understanding of magma chamber processes and conduit dynamics, relevant parameters for hazard assessment. * Mangiacapra A., R. Moretti, M. Rutherford, L. Civetta, G. Orsi and P. Papale (2008) The deep magmatic system of the Camp Flegrei caldera (Italy). Geophys. Res. Lett., 35, doi: 10.1029/2008GL035550

  6. Geodetic constraints to the source mechanism of the 2011-2013 unrest at Campi Flegrei (Italy) caldera

    NASA Astrophysics Data System (ADS)

    Trasatti, Elisa; Polcari, Marco; Bonafede, Maurizio; Stramondo, Salvatore

    2016-04-01

    Campi Flegrei (Italy) is a nested caldera and together with Vesuvius is one of the Italian GEO Geohazard Supersites (GSNL). The area is characterized by one of the highest volcanic hazard of the world, due to the very high density of inhabitants (1800/km²), the persistent activity of the system and the explosive character of volcanism. A major unrest episode took place in 1982-84, when the town of Pozzuoli, located at the caldera center, was uplifted by 1.80 m. Minor uplifts of few centimeters, seismic swarms and degassing episodes took place in 1989, 2000 and 2004-06. Since 2005 Campi Flegrei is uplifting, reaching a ground velocity of 9 cm/yr in 2012, showing that the caldera is in a critical state on the verge of instability. In this work, we present results from SAR Interferometry and geodetic data modelling at Campi Flegrei in the framework of the EU's FP7 MED-SUV Project. We exploit two COSMO-SkyMed data sets to map the deformation field during 2011-2013. The spatial distributions of the cumulative displacement from COSMO-SkyMed ascending/descending orbits show similar behaviors, confirming the bell-shaped pattern of the deformation at least within the inner rim of the caldera. The resulting data, together with GPS data from the Neapolitan Volcanoes Continuous GPS network (NeVoCGPS) is fitted through a geophysical inversion process using finite element forward models to account for the 3D heterogeneous medium. The best fit model is a north dipping mixed-mode dislocation source lying at ~5 km depth. The driving mechanism is ascribable to magma input into the source of the large 1982-1984 unrest (since similar source characteristics were inferred) that generates initial inflation followed by additional shear slip accompanying the extension of crack tips. The history and the current state of the system indicate that Campi Flegrei is able to erupt again. Constraining the defomation source may have important implications in terms of civil protection and the

  7. Geophysical monitoring of the submerged area of the Campi Flegrei caldera (Southern Italy): experiences and perspectives

    NASA Astrophysics Data System (ADS)

    Iannaccone, Giovanni; Guardato, Sergio; De Martino, Prospero; Donnarumma, Gian Paolo; Bobbio, Antonella; Chierici, Francesco; Pignagnoli, Luca; Beranzoli, Laura

    2016-04-01

    The monitoring system of the Campi Flegrei caldera is made up of a dense geophysical network of seismological and geodetic instruments with data acquired and processed at the Monitoring Center of INGV in Naples. As one third of the caldera is covered by the sea, a marine monitoring system has been operating since 2008 in the center of the gulf of Pozzuoli, where the sea depth is about 100 m at ~2.5 km from the coast. The main component of the monitoring system is CUMAS (Cabled Underwater Multidisciplinary Acquisition System), which consists of a sea floor module equipped with geophysical and oceanographic sensors (broad band seismometer, accelerometer, hydrophone, bottom pressure recorder and single point three component water-current meter) and status and control sensors. CUMAS is connected by cable to the top of an elastic beacon buoy equipped with the power supply and data transmission devices. The buoy consists of a float placed below sea level, surrounding and holding a steel pole that supports a turret structure above sea level. The pole, turret and float system are rigidly connected to the ballast on the sea bottom. Thus a GPS installed on the turret can record the vertical sea floor displacement related to the volcanic activity of the area. The GPS has operated since January 2012 with continuous acquisition lasting more than three years and has recorded a cumulative seafloor uplift of about 7-8 cm. The comparison of the pattern of the GPS buoy data with those of the land stations confirms a quasi-symmetrical vertical displacement field of the caldera area. Measurement of vertical sea floor displacement has also been obtained by the analysis of bottom pressure recorder data. These results, in conjunction with the analysis of seismic and hydrophone data, have encouraged us to extend the marine monitoring system with the deployment in the Gulf of Pozzuoli of three new similar systems. We also present preliminary results of the first few months of activity of

  8. Hydrothermal activity and subsurface soil complexity: implication for outgassing processes at Solfatara crater, Campi Flegrei caldera

    NASA Astrophysics Data System (ADS)

    Montanaro, Cristian; Mayer, Klaus; Scheu, Bettina; Isaia, Roberto; Mangiacapra, Annarita; Gresse, Marceau; Vandemeulebrouck, Jean; Moretti, Roberto; Dingwell, Donald B.

    2016-04-01

    The Solfatara area and its fumaroles are the main surface phenomena of the vigorous hydrothermal activity within the active Campi Flegrei caldera system. The existing fault system appears to have a major control on outgassing which in turn leads to a strong alteration of the volcanic products. Moreover the maar-nature of the crater, and its filling by more recent volcanic deposits, resulted in a complex fractured and multilayered cap to the rising gases. As a consequence the hydrothermal alteration differently affects the rocks within the crater, including pyroclastic fallout ash beds, pyroclastic density current deposits, breccias and lavas. The induced changes in both original microstructure and physical and mechanical properties of the rocks control the outgassing behavior. Here, we report results from a measurement survey conducted in July 2015, and aimed to characterize the in-situ physical (temperature, humidity) and mechanical (permeability, strength, stiffness) properties. The survey also included a mapping of the surficial hydrothermal features and their distributions. Chemical analyses and laboratory measurements (porosity, granulometry) of selected samples were additionally performed. Results show that the crater floor area comprises very different kinds of soils, from fine grained, thin laminated deposits around the two bubbling Fangaia mud pools, to crusted hummock formations along the SE and NE border of the crater. Dry and solid alunite-rich deposits are present in the western and southern part. Furthermore we observed evidences of a beginning of crust formation within the central part of the crater. A large range of surface temperatures, from boiling point to ambient temperature, were measured throughout the surveyed area. Outgassing occurs mainly along the crack system, which has also generated the crusted hummocks. Elsewhere the fluid circulation in the subsoil is favored by the presence of coarse and highly porous sulfur-hardened levels, whereas

  9. Comparison between 3D model of Pisciarelli area (Campi Flegrei caldera) through Terrestrial Laser Scanner

    NASA Astrophysics Data System (ADS)

    Caputo, Teresa; Somma, Renato; Marino, Ermanno; Terracciano, Rosario; Troise, Claudia; De Natale, Giuseppe

    2016-04-01

    The volcanic/geothermal area of Pisciarelli is located within Campi Flegrei caldera .This last is a densely populated area, including the Pozzuoli town and bordering the western side of the Naples city, this causes a high vulnerability and consequently a high volcanic risk. In the recent decades this area has experienced minor ground uplift episodes accompanied by low magnitude seismicity and by strong intensification of degassing activity in particular localized at Pisciarelli area. We present the results of the Terrestrial Laser Scanner (TLS), using a Reigl VZ1000®, analysis of Pisciarelli area performed in June 2013 and the comparison with the data acquired later in March 2014. We apply the TLS technique based on Time of Flight (TOF) method in order to define an accurate 3D digital model for detailed analysis of this area performing numerous scans from different points of view in the area. In this ways was ensured a good coverage of the whole investigated area in order to avoid shaded portion due to the high soil degassing activity. Such fact limits the capacity of laser penetration is caused by wavelength near infrared range. For each survey was obtained a Digital Terrain Model (DTM) from the reconstructed data and both were compared. In particular, we have identified two "critical" areas of interest that will be monitored more frequently. These are: 1) in the lower part of the studied area a major fault line that bounding the Agnano caldera moderately NE-dipping; 2) in the upper part of the study area a zone of depletion with its zone of accumulation. The DTM were georeferenced into the UTM-WGS84 reference frame. The aim of this work is to define a procedure to compare between 3D model applied to monitoring of this area. Also to evaluate of volumetric and morphologic changes and to recognizing unstable masses by comparison of 3D data. For this purpose other TLS surveys will be performed in the upcoming in this active volcanic/geothermal area.

  10. Impact of channelized flow on temperature distribution and fluid flow in restless calderas: Insight from Campi Flegrei caldera, Italy

    NASA Astrophysics Data System (ADS)

    Jasim, Alia; Whitaker, Fiona F.; Rust, Alison C.

    2015-09-01

    Magmatic hydrothermal systems develop by the imposition of a magmatically derived heat flux upon a shallow groundwater system. As such their dynamics can be intermittently perturbed by changing conditions within the associated magmatic system. Understanding the nature of the coupling between the magmatic and groundwater systems is thus key to discriminating geophysical signals of magmatic unrest from purely hydrothermal ones. Using a series of numerical groundwater models run with TOUGH2, we simulate the coupled groundwater-magmatic system at Campi Flegrei caldera, with particular emphasis on the impact of permeability developed within local fault systems and the dynamics of the system during magmatic unrest. Simulation results suggest that faults can play an important role in controlling the dynamics of recharge and heat transport within the shallow hydrothermal reservoir. Results specifically highlight that contrasts in permeability between faults and surrounding rock impact local temperature gradients, with faults either acting as preferential routes for recharge or discharge of groundwater, depending on fault/caldera fill permeability contrast and the vertical extent of the fault. Simulations of magmatic unrest with a step-wise increase in basal heat flux suggest that periodic geophysical and chemical signals may stem from the interaction between the development of gas at depth and the recharge-discharge dynamics of the reservoir. These results highlight the potential for the dynamics of magmatic-hydrothermal systems to be significantly impacted by the presence and nature of local fault systems. Where dynamic groundwater systems are involved, it is thus important to understand the impact of such geological elements when interpreting monitoring data such as ground deformation, seismicity and gas emissions.

  11. P-SV conversions at a shallow boundary beneath Campi Flegrei caldera (Italy) - evidence for the magma chamber

    SciTech Connect

    Ferrucci, F.; Hirn, A.; De Natale, G.; Virieux, J.; Mirabile, L. Inst. de Physique du Globe, Paris Osservatorio Vesuviano, Naples CNRS, Inst. de Geodynamique, Valbonne Ist. Universitario Navale, Naples )

    1992-10-01

    Seismograms from an active seismic experiment carried out at Campi Flegrei caldera (near Naples, Italy), show a large-amplitude SV-polarized shear wave, following by less than 1.5-s P waves reflected at wide angle from a deep crustal interface. Early arriving SV-polarized waves, with the same delay to direct P waves, are also observed in seismograms from a regional 280 km-deep, magnitude 5.1 earthquake. Such short delays of S to P waves are consistent with a P-SV conversion on transmission occurring at a shallow boundary beneath the receivers. The large amplitude of the converted-SV phase, along with that the P waves are near vertical, requires a boundary separating a very low rigidity layer from the upper caldera fill. The converted phases are interpreted as a seismic marker of a magma chamber. The top of this magma chamber is located slightly deeper than the deepest earthquakes observed during the 1982-1984 unrest of Campi Flegrei. 8 refs.

  12. Joint use of long water pipe tiltmeters and sea level gauges for monitoring ground deformation at Campi Flegrei caldera

    NASA Astrophysics Data System (ADS)

    Scarpa, Roberto; Capuano, Paolo; Tammaro, Umberto; Bilham, Roger

    2014-05-01

    The Campi Flegrei caldera, located in the Campanian Plain, Southern Italy, 15 km west of the city of Naples, is a nested, resurgent, and restless structure in the densely inhabited Neapolitan area. The main caldera at Campi Flegrei is 12 - 15 km across and its rim is thought to have been formed during the catastrophic eruption, occurred 39 ky ago ca., which produced a deposit referred to as the Campanian Ignimbrite. The volcanic hazards posed by this caldera and the related risk are extremely high, because of its explosive character and the about 1.5 million people living within the caldera. Campi Flegrei area periodically experiences significant unrest episodes which include ground deformations, the so-called 'bradisismo'. Following the last eruption (Monte Nuovo, 1538) a general subsidence has been interrupted by episodes of uplift, the most recent of which occurred in 1970-72 and 1982-84. Since 1950 the caldera is showing signs of unrest with ground uplift, seismicity, and composition variation of fumarole fluids. In particular, subsidence has been replaced by intermittent episodes of inflation with short time duration and various maximum amplitude. They occurred in 1989, 1994, 2000, 2005-06, 2008-09 and 2011-2014 with duration of few months and maximum amplitude ranging between 3 and 18 cm., approximately. In the last years an array of water-pipe tiltmeters with lengths between 28 m and 278 m in tunnels on the flanks of the region of maximum inflation has been installed to avoid problems common to the traditional tiltmeters. The tiltmeters record inflation episodes upon which are superimposed local load tides and the effects of the seiches in the Bay of Naples and in the Tyrrhenian sea. We use data recorded by three tide gauges in the Bay of Pozzuoli (Pozzuoli, Miseno, Nisida) to compare water pipe data with sea level to extract astronomical tidal components (diurnal and semidiurnal) and seiches periods (particularly between 20 minutes and 56 minutes) that

  13. Rapid differentiation in a sill-like magma reservoir: a case study from the campi flegrei caldera.

    PubMed

    Pappalardo, Lucia; Mastrolorenzo, Giuseppe

    2012-01-01

    In recent decades, geophysical investigations have detected wide magma reservoirs beneath quiescent calderas. However, the discovery of partially melted horizons inside the crust is not sufficient to put constraints on capability of reservoirs to supply cataclysmic eruptions, which strictly depends on the chemical-physical properties of magmas (composition, viscosity, gas content etc.), and thus on their differentiation histories. In this study, by using geochemical, isotopic and textural records of rocks erupted from the high-risk Campi Flegrei caldera, we show that the alkaline magmas have evolved toward a critical state of explosive behaviour over a time span shorter than the repose time of most volcanic systems and that these magmas have risen rapidly toward the surface. Moreover, similar results on the depth and timescale of magma storage were previously obtained for the neighbouring Somma-Vesuvius volcano. This consistency suggests that there might be a unique long-lived magma pool beneath the whole Neapolitan area. PMID:23050096

  14. Rapid differentiation in a sill-like magma reservoir: a case study from the campi flegrei caldera

    PubMed Central

    Pappalardo, Lucia; Mastrolorenzo, Giuseppe

    2012-01-01

    In recent decades, geophysical investigations have detected wide magma reservoirs beneath quiescent calderas. However, the discovery of partially melted horizons inside the crust is not sufficient to put constraints on capability of reservoirs to supply cataclysmic eruptions, which strictly depends on the chemical-physical properties of magmas (composition, viscosity, gas content etc.), and thus on their differentiation histories. In this study, by using geochemical, isotopic and textural records of rocks erupted from the high-risk Campi Flegrei caldera, we show that the alkaline magmas have evolved toward a critical state of explosive behaviour over a time span shorter than the repose time of most volcanic systems and that these magmas have risen rapidly toward the surface. Moreover, similar results on the depth and timescale of magma storage were previously obtained for the neighbouring Somma-Vesuvius volcano. This consistency suggests that there might be a unique long-lived magma pool beneath the whole Neapolitan area. PMID:23050096

  15. Disclosing Multiple Magma Degassing Sources Offers Unique Insights of What's Behind the Campi Flegrei Caldera Unrest

    NASA Astrophysics Data System (ADS)

    Moretti, R.; Civetta, L.; Orsi, G.; Arienzo, I.; D'Antonio, M.; Di Renzo, V.

    2013-12-01

    The definition of the structure and evolution of the magmatic system of Campi Flegrei caldera (CFc), Southern Italy, has been a fundamental tool for the assessment of the short-term volcanic hazard. The ensemble of geophysical and petrologic data show that the CFc magmatic system has been -and still is- characterized by two major reservoirs at different depths. From the deep one (around 8 km), less evolved magmas crystallize and degas, supplying fluids and magmas to the shallow (3-4 km) reservoirs. A thorough reconstruction of processes occurring in magma chamber/s prior and/or during the CFc eruptions has shown that magmas entering shallow reservoirs mixed with resident and crystallized batches. Also the 1982-85 unrest episode has been related to a magma intrusion of 2.1 x 10^7 m^3 at 3-4 km depth, on the basis of geophysical data (ground deformation, gravimetry, seismic imaging) and their interpretation. Thermodynamic evaluation of magma properties, at the time of emplacement, suggests for such an intrusion a bulk density of 2.000 kg/m^3 . Such a value testifies the high amount of exsolved volatiles within the system. The available record of geochemical and isotopic data on surface fumaroles, coupled with melt inclusion data, has already shown that dual (deep and shallow) magma degassing from such two reservoirs, as well as their interaction with the hydrothermal system, allows explaining the relevant fluctuations observed at crater fumaroles after the 1982-85 magma intrusion. An important role was played by the rapid crystallization (around 30 years) of the shallow magma, such that in the recent years gas discharges should be fuelled mostly by the deep magma. Such a process is well recorded in the fumarolic gas composition of the last ~10 years, but has to be reconciled with the unrest dynamics which took place after year 2000, characterized by a slow but continuous ground uplift. All geochemical indicators (major species and noble gases) point to three possible

  16. Retrieving the Stress Field Within the Campi Flegrei Caldera (Southern Italy) Through an Integrated Geodetical and Seismological Approach

    NASA Astrophysics Data System (ADS)

    D'Auria, Luca; Massa, Bruno; Cristiano, Elena; Del Gaudio, Carlo; Giudicepietro, Flora; Ricciardi, Giovanni; Ricco, Ciro

    2015-11-01

    We investigated the Campi Flegrei caldera using a quantitative approach to retrieve the spatial and temporal variations of the stress field. For this aim we applied a joint inversion of geodetic and seismological data to a dataset of 1,100 optical levelling measurements and 222 focal mechanisms, recorded during the bradyseismic crisis of 1982-1984. The inversion of the geodetic dataset alone, shows that the observed ground deformation is compatible with a source consisting of a planar crack, located at the centre of the caldera at a depth of about 2.56 km and a size of about 4 × 4 km. Inversion of focal mechanisms using both analytical and graphical approaches, has shown that the key features of the stress field in the area are: a nearly subvertical σ 1 and a sub-horizontal, roughly NNE-SSW trending σ 3. Unfortunately, the modelling of the stress fields based only upon the retrieved ground deformation source is not able to fully account for the stress pattern delineated by focal mechanism inversion. The introduction of an additional regional background field has been necessary. This field has been determined by minimizing the difference between observed slip vectors for each focal mechanism and the theoretical maximum shear stress deriving from both the volcanic (time-varying) and the regional (constant) field. The latter is responsible for a weak NNE-SSW extension, which is consistent with the field determined for the nearby Mt. Vesuvius volcano. The proposed approach accurately models observations and provides interesting hints to better understand the dynamics of the volcanic unrest and seismogenic processes at Campi Flegrei caldera. This procedure could be applied to other volcanoes experiencing active ground deformation and seismicity.

  17. 40Ar/39Ar dating of tuff vents in the Campi Flegrei caldera (southern Italy): Toward a new chronostratigraphic reconstruction of the Holocene volcanic activity

    USGS Publications Warehouse

    Fedele, L.; Insinga, D.D.; Calvert, A.T.; Morra, V.; Perrotta, A.; Scarpati, C.

    2011-01-01

    The Campi Flegrei hosts numerous monogenetic vents inferred to be younger than the 15 ka Neapolitan Yellow Tuff. Sanidine crystals from the three young Campi Flegrei vents of Fondi di Baia, Bacoli and Nisida were dated using 40Ar/39Ar geochronology. These vents, together with several other young edifices, occur roughly along the inner border of the Campi Flegrei caldera, suggesting that the volcanic conduits are controlled by caldera-bounding faults. Plateau ages of ∼9.6 ka (Fondi di Baia), ∼8.6 ka (Bacoli) and ∼3.9 ka (Nisida) indicate eruptive activity during intervals previously interpreted as quiescent. A critical revision, involving calendar age correction of literature 14C data and available 40Ar/39Ar age data, is presented. A new reference chronostratigraphic framework for Holocene Phlegrean activity, which significantly differs from the previously adopted ones, is proposed. This has important implications for understanding the Campi Flegrei eruptive history and, ultimately, for the evaluation of related volcanic risk and hazard, for which the inferred history of its recent activity is generally taken into account.

  18. Study of the 2011-2013 unrest at Campi Flegrei caldera (Italy) through InSAR and 3D modelling

    NASA Astrophysics Data System (ADS)

    Trasatti, Elisa; Polcari, Marco; Bignami, Christian; Bonafede, Maurizio; Buongiorno, Fabrizia; Stramondo, Salvatore

    2014-05-01

    Campi Flegrei is a nested caldera in Italy, at the western edge of the Bay of Naples. Together with Vesuvius and Mt Etna, it is one of the Italian GeoHazard Supersites. The area is characterized by one of the highest volcanic hazard in the world, due to the very high density of inhabitants (1800/km2), the persistent activity of the system and the explosive character of volcanism. A major unrest episode took place in 1982-84, when the town of Pozzuoli, located at the caldera center, was uplifted by 1.80 m (~1 m/yr). Minor uplifts of few cm, seismic swarms and degassing episodes took place in 1989, 2000 and 2004-06. Since 2005 Campi Flegrei is uplifting, reaching a ground velocity of 9 cm/yr in 2012, showing that the caldera is in a critical state on the verge of instability. In the present work we consider InSAR time series of the recent activity (2010-2013) detected by COSMO SkyMed satellite. In particular, the time series show a progressive velocity increase of ground deformation during 2012, while it slowed down in 2013 approaching zero. The cumulative displacement from COSMO SkyMed descending orbit (March 2011 - March 2013) show a semicircular pattern centered in Pozzuoli with a maximum LoS (Line of Sight) displacement of 11 cm and maximum velocity 9 cm/yr reached along the coastline. The spatial distribution of the cumulative displacement from COSMO SkyMed ascending orbit show a similar behavior, confirming the bell-shaped pattern of the deformation at least inside the inner rim of the caldera. The cumulative ascending LoS displacement between March 2013 - September 2013 is 1-2 cm, confirming the stall of the unrest after the first few months of 2013 as observed by GPS. Initially, several source geometries are adopted (sphere, spheroid, sill) to model the cumulative deformation between 2011 and 2013. All the sources are located offshore Pozzuoli at a depth of about 2 km. The sphere and spheroid result to dilate at an annual volume variation rate of the order of

  19. ROCK PHYSICS. Rock physics of fibrous rocks akin to Roman concrete explains uplifts at Campi Flegrei Caldera.

    PubMed

    Vanorio, Tiziana; Kanitpanyacharoen, Waruntorn

    2015-08-01

    Uplifts in the Campi Flegrei caldera reach values unsurpassed anywhere in the world (~2 meters). Despite the marked deformation, the release of strain appears delayed. The rock physics analysis of well cores highlights the presence of two horizons, above and below the seismogenic area, underlying a coupled process. The basement is a calc-silicate rock housing hydrothermal decarbonation reactions, which provide lime-rich fluids. The caprock above the seismogenic area has a pozzolanic composition and a fibril-rich matrix that results from lime-pozzolanic reactions. These findings provide evidence for a natural process reflecting that characterizing the cementitious pastes in modern and Roman concrete. The formation of fibrous minerals by intertwining filaments confers shear and tensile strength to the caprock, contributing to its ductility and increased resistance to fracture. PMID:26160377

  20. Permeability and continuous gradient temperature monitoring of volcanic rocks: new insights from borehole and laboratory analysis at the Campi Flegrei caldera (Southern Italy).

    NASA Astrophysics Data System (ADS)

    Carlino, Stefano; Piochi, Monica; Tramelli, Anna; Troise, Claudia; Mormone, Angela; Montanaro, Cristian; Scheu, Bettina; Klaus, Mayer; Somma, Renato; De Natale, Giuseppe

    2016-04-01

    The pilot borehole recently drilled in the eastern caldera of Campi Flegrei (Southern Italy), during the Campi Flegrei Deep Drill Project (CFDDP) (in the framework of the International Continental Scientific Drilling Program) allowed (i) estimating on-field permeability and coring the crustal rocks for laboratory experiments, and (ii) determining thermal gradient measurements down to ca. 500 m of depth. We report here a first comparative in situ and laboratory tests to evaluate the rock permeability in the very high volcanic risk caldera of Campi Flegrei, in which ground deformations likely occur as the persistent disturbance effect of fluid circulation in the shallower geothermal system. A large amount of petro-physical information derives from outcropping welded tuffs, cores and geophysical logs from previous AGIP's drillings, which are located in the central and western part of the caldera. We discuss the expected scale dependency of rock permeability results in relation with well-stratigraphy and core lithology, texture and mineralogy. The new acquired data improve the database related to physical property of Campi Flegrei rocks, allowing a better constrain for the various fluid-dynamical models performed in the tentative to understand (and forecast) the caldera behavior. We also present the first data on thermal gradient continuously measured through 0 - to 475 m of depth by a fiber optic sensor installed in the CFDDP pilot hole. As regards, we show that the obtained values of permeability, compared with those inferred from eastern sector of the caldera, can explain the different distribution of temperature at depth, as well as the variable amount of vapor phase in the shallow geothermal system. The measured temperatures are consistent with the distribution of volcanism in the last 15 ka.

  1. Crystallization and eruption ages of Breccia Museo (Campi Flegrei caldera, Italy) plutonic clasts and their relation to the Campanian ignimbrite

    NASA Astrophysics Data System (ADS)

    Gebauer, Samantha K.; Schmitt, Axel K.; Pappalardo, Lucia; Stockli, Daniel F.; Lovera, Oscar M.

    2014-01-01

    The Campi Flegrei volcanic district (Naples region, Italy) is a 12-km-wide, restless caldera system that has erupted at least six voluminous ignimbrites during the late Pleistocene, including the >300 km3 Campanian ignimbrite (CI) which originated from the largest known volcanic event of the Mediterranean region. The Breccia Museo (BM), a petrologically heterogeneous and stratigraphically complex volcanic deposit extending over 200 km2 in close proximity to Campi Flegrei, has long remained contentious regarding its age and stratigraphic relation to the CI. Here, we present crystallization and eruption ages for BM plutonic ejecta clasts that were determined via uranium decay series and (U-Th)/He dating of zircon, respectively. Despite mineralogical and textural heterogeneity of these syenitic clasts, their U-Th zircon rim crystallization ages are indistinguishable with an average age of 49.7 ± 2.5 ka (2σ errors; mean square of weighted deviates MSWD = 1.2; n = 34). A subset of these crystals was used to obtain disequilibrium-corrected (U-Th)/He zircon ages which average 41.7 ± 1.8 ka (probability of fit P = 0.54; n = 15). This age closely overlaps with published CI 40Ar/39Ar eruption ages (40.6 ± 0.1 ka) after recalibration to recently revised flux monitor ages. Concordant eruption ages for BM and CI agree with previous chemostratigraphic and paleomagnetic correlations, suggesting their origin from the same eruption. However, they are at variance with recalibrated 40Ar/39Ar ages which have BM postdate CI by 3 ± 1 ka. BM syenites show similar geochemical and Sr-Nd isotopical features of pre-caldera rocks erupted between 58 and 46 ka, but are distinctive from subsequent caldera-forming magmas. Energy-constrained assimilation and fractional crystallization modeling of Nd-Sr isotopic data suggests that pre-caldera magmas formed a carapace of BM-type intrusions in a mid-crust magma chamber (≥8 km depth) shielding the younger CI magma from contamination by

  2. Hydrothermal activity at Campi Flegrei caldera: rock mechanical properties and implications for outgassing and possible phreatic eruptions

    NASA Astrophysics Data System (ADS)

    Mayer, K.; Montanaro, C.; Scheu, B.; Isaia, R.; Mangiacapra, A.; Gresse, M.; Vandemeulebrouck, J.; Moretti, R.; Dingwell, D. B.

    2015-12-01

    The Solfatara and Pisciarelli fumaroles are the main surface manifestations of the vigorous hydrothermal activity within the Campi Flegrei caldera system. The existing fault system appears to have a major control on outgassing and leads to a strong alteration of the volcanic products in both areas. Consistent with the volcanic history of the area, Solfatara and Pisciarelli are posited as having the highest probability for the opening of new vents, and in particular for possible phreatic activity within the Campi Flegrei system. Hydrothermal alteration deeply affects all the rocks exposed within Solfatara sector, including lava domes, breccias, as well as pyroclastic fallout ash beds and pyroclastic density current deposits. This results in changes of the volcanic rock's original microstructure and of their physical and mechanical properties, which in turn control both the outgassing and their fragmentation behaviors. Here, samples from the wall rocks in the vicinity of the Solfatara and Pisciarelli fumaroles have been subjected to geochemical, physical and mechanical properties characterization. In addition, surficial Solfatara crater floor deposits were characterized and their properties, in particular permeability, were mapped. Results show that hydrothermal alteration increases porosity and permeability of the crater wall samples favoring outgassing, while decreasing the rock strength. At the crater floor the outgassing occurs mainly along the crack system, which has also generated crusted hummocks. Elsewhere the fluid circulation in the subsoil is favored by the presence of coarse and sulfur-hardened levels, whereas their surfacing is hindered by compacted fine-grained, low permeability layers. Decompression experiments were performed to simulate a phreatic eruption at shallow depth. We used crater-wall samples representing the rocks in the proximity of high degassing areas. Changes in the fragmentation behavior and ejection dynamics, depending on the

  3. The Evolution of the Campi Flegrei caldera (Italy): High- and low-frequency multichannel 2.5D seismic surveying for an amphibian IODP/ICDP drilling approach

    NASA Astrophysics Data System (ADS)

    Steinmann, Lena; Spiess, Volkhard; Sacchi, Marco

    2016-04-01

    Caldera-forming eruptions are considered as one of the most catastrophic natural events to affect the Earth's surface and human society. The half-submerged Campi Flegrei caldera, located in southern Italy, belongs to the world's most active calderas and, thus, has received particular attention in scientific communities and governmental institutions. Therefore, it has also become subject to a joint approach in the IODP and ICDP programmes. Despite ample research, no scientific consensus regarding the formation history of the Campi Flegrei caldera has been reached yet. So far, it is still under debate whether the Campi Flegrei caldera was formed by only one ignimbritic eruption, namely the Neapolitan Yellow Tuff (NYT) eruption at 15 ka or, if it is a nested-caldera system related to the NYT and the Campanian Ignimbrite (CI) eruption at 39 ka. In the last decades, the Campi Flegrei caldera has been characterized by short-term episodes of unrest involving considerable ground deformation (uplift and subsidence of several meters), seismicity and increased temperature at fumaroles. Furthermore, long-term deformation can be observed in the central part of the caldera with uplift rates of several tens of meters within a few thousand years. Recently, it has been proposed that the long-term deformation may be related to caldera resurgence, while short-term uplift episodes are probably triggered by the injection of magmatic fluids into a shallow hydrothermal system at ~2 km depth. However, both long-term and short term uplift could be interpreted as eruption precursor, thereby posing high-concern for a future eruption, which would expose more than 1.5 million people living in the surroundings of the volcanic district to extreme volcanic risks. During a joint Italian-German research expedition in 2008, a semi-3D grid (100-150 m profile spacing) of high-frequency (up to 1000 Hz) multichannel seismic data were acquired to support both the ongoing onshore ICDP and a proposed

  4. Hydrothermal fluid flow models of Campi Flegrei caldera, Italy constrained by InSAR surface deformation time series observations

    NASA Astrophysics Data System (ADS)

    Lundgren, P.; Lanari, R.; Manzo, M.; Sansosti, E.; Tizzani, P.; Hutnak, M.; Hurwitz, S.

    2008-12-01

    Campi Flegrei caldera, Italy, located along the Bay of Naples, has a long history of significant vertical deformation, with the most recent large uplift (>1.5m) occurring in 1983-1984. Each episode of uplift has been followed by a period of subsidence that decreases in rate with time and may be punctuated by brief episodes of lesser uplift. The large amplitude of the major uplifts that occur without volcanic activity, and the subsequent subsidence has been argued as evidence for hydrothermal amplification of any magmatic source. The later subsidence and its temporal decay have been argued as due to diffusion of the pressurized caldera fill material into the less porous surrounding country rock. We present satellite synthetic aperture radar (SAR) interferometry (InSAR) time series analysis of ERS and Envisat data from the European Space Agency, based on exploiting the Small Baseline Subset (SBAS) approach [Berardino et al., 2002]; this allows us to generate maps of relative surface deformation though time, beginning in 1992 through 2007, that are relevant to both ascending and descending satellite orbits. The general temporal behavior is one of subsidence punctuated by several lesser uplift episodes. The spatial pattern of deformation can be modeled through simple inflation/deflation sources in an elastic halfspace. Given the evidence to suggest that fluids may play a significant role in the temporal deformation of Campi Flegrei, rather than a purely magmatic or magma chamber-based interpretation, we model the temporal and spatial evolution of surface deformation as a hydrothermal fluid flow process. We use the TOUGH2-BIOT2 set of numerical codes [Preuss et al., 1999; Hsieh, 1996], which couple multi-phase (liquid-gas) and multi-component (H2O-CO2) fluid flow in a porous or fractured media with plane strain deformation and fluid flow in a linearly elastic porous medium. We explore parameters related to the depth and temporal history of fluid injection, fluid

  5. Timescales of magma processes occurred prior to recent Campi Flegrei caldera eruptions: first results from diffusion profiles on plagioclase phenocrysts

    NASA Astrophysics Data System (ADS)

    D'Antonio, Massimo; Arienzo, Ilenia; Fedele, Lorenzo; Iovine, Raffaella; Carmine Mazzeo, Fabio; Civetta, Lucia; Orsi, Giovanni; Wörner, Gerhard

    2015-04-01

    Knowledge of the timescales of magma rising and stagnation, as well as mingling/mixing processes occurring in the shallow plumbing system of an active volcano is crucial for volcanic hazard assessment and risk mitigation. Among few recently developed methodologies, high-precision, high spatial resolution analysis of major-, minor- and trace elements on zoned phenocrysts through electron microprobe techniques represents a powerful tool to provide good estimates of timescales of pre-eruptive magma rising, stagnation and/or mingling/mixing processes. To this purpose, volcanic rock samples of trachytic composition representative of the Agnano-Monte Spina eruption (4.7 ka CAL BP) occurred at the Campi Flegrei caldera (southern Italy) have been selected. The investigation has been carried out in the framework of Project V2 - Precursori di Eruzioni, funded by the Italian Dipartimento per la Protezione Civile - Istituto Nazionale di Geofisica e Vulcanologia. The investigated rock samples are pumice fragments from which double-polished, 100 µm thick thin sections have been prepared for analytical purposes. Back-scattered electrons (BSE) images have been acquired at the scanning electron microscope (SEM), in order to identify the plagioclase phenocrysts suitable to be analyzed successively, selected among those that best display their zoning. After a careful observation of the BSE images, major-, minor- and selected trace element contents have been determined through combined energy-dispersive and wavelength-dispersive system electron microprobe analyses (EDS-WDS-EMPA) on transects crossing the growth zones of the selected phenocrysts. This methodology has allowed reconstructing the diffusion profile of some key-elements through the growth zones of the investigated phenocrysts. Successively, the diffusion profiles have been combined with textural features obtained through BSE images in order to obtain diffusion models aimed at estimating the timescales of crystals

  6. Pyroclastic density current hazard maps at Campi Flegrei caldera (Italy): the effects of event scale, vent location and time forecasts.

    NASA Astrophysics Data System (ADS)

    Bevilacqua, Andrea; Neri, Augusto; Esposti Ongaro, Tomaso; Isaia, Roberto; Flandoli, Franco; Bisson, Marina

    2016-04-01

    Today hundreds of thousands people live inside the Campi Flegrei caldera (Italy) and in the adjacent part of the city of Naples making a future eruption of such volcano an event with huge consequences. Very high risks are associated with the occurrence of pyroclastic density currents (PDCs). Mapping of background or long-term PDC hazard in the area is a great challenge due to the unknown eruption time, scale and vent location of the next event as well as the complex dynamics of the flow over the caldera topography. This is additionally complicated by the remarkable epistemic uncertainty on the eruptive record, affecting the time of past events, the location of vents as well as the PDCs areal extent estimates. First probability maps of PDC invasion were produced combining a vent-opening probability map, statistical estimates concerning the eruptive scales and a Cox-type temporal model including self-excitement effects, based on the eruptive record of the last 15 kyr. Maps were produced by using a Monte Carlo approach and adopting a simplified inundation model based on the "box model" integral approximation tested with 2D transient numerical simulations of flow dynamics. In this presentation we illustrate the independent effects of eruption scale, vent location and time of forecast of the next event. Specific focus was given to the remarkable differences between the eastern and western sectors of the caldera and their effects on the hazard maps. The analysis allowed to identify areas with elevated probabilities of flow invasion as a function of the diverse assumptions made. With the quantification of some sources of uncertainty in relation to the system, we were also able to provide mean and percentile maps of PDC hazard levels.

  7. Texture and composition of pumices and scoriae from the Campi Flegrei caldera (Italy): Implications on the dynamics of explosive eruptions

    NASA Astrophysics Data System (ADS)

    Piochi, M.; Polacci, M.; de Astis, G.; Zanetti, A.; Mangiacapra, A.; Vannucci, R.; Giordano, D.

    2008-03-01

    The Campi Flegrei (CF) caldera is one of the most dangerous quiescent volcanic systems in the world. Its activity mostly resulted in low-magnitude explosive eruptions, such as that of the Monte Nuovo tuff cone that represents the last eruptive event within the caldera (A.D. 1538). However, there have been more energetic Plinian events, e.g., the Agnano Monte Spina eruption (4.1 ka), and very highly explosive, caldera-forming eruptions, e.g., the Campanian Ignimbrite eruption (39 ka). Here, we integrate new and literature data on the groundmass texture and composition of pyroclastic products from the three above eruptions with the aim of unraveling how volatiles content, degassing mechanisms, and crystallization processes influence magma explosivity and eruption dynamics at CF. Previous studies indicate that the investigated rocks share similar major element bulk and phenocryst chemistry; also similar is the water content of their trapped melt inclusions. These observations suggest that the magmas feeding these eruptions had comparable physicochemical properties during storage in the shallow crust. However, our investigations indicate that the studied rocks differ in texture and composition of the groundmass and viscosity of the related magmas. We ascribe such differences to the variable style of volatile exsolution and outgassing from the melt, primarily in response to changes of the rate of magma ascent to the surface. We conclude that the magma ascent rate was the key parameter in driving explosive eruptions at CF, and we suggest that this parameter may be influenced by magma-water interaction and/or magma chamber geometry and replenishment.

  8. Sustainability assessment of geothermal exploitation by numerical modelling: the example of high temperature Mofete geothermal field at Campi Flegrei caldera (Southern Italy)

    NASA Astrophysics Data System (ADS)

    Carlino, Stefano; Troiano, Antonio; Giulia Di Giuseppe, Maria; Tramelli, Anna; Troise, Claudia; Somma, Renato; De Natale, Giuseppe

    2015-04-01

    The active volcanic area of Campi Flegrei caldera has been the site of many geothermal investigations, since the early XX century. This caldera is characterised by high heat flow, with maximum value > 150 mWm-2, geothermal gradients larger than 200°Ckm-1 and diffuse magmatic gases discharge at the surface. These features encouraged an extensive campaign for geothermal investigation, started in 1939, with many drillings performed at Campanian volcanoes (Campi Flegrei and Ischia) and later at Vesuvius. Several wells aimed to the exploitation of high enthalpy geothermal energy, were drilled in the Campi Flegrei caldera, down to a maximum depth of ~3 km involving mainly two sites (Mofete and S.Vito geothermal fields) located in western and northern sector of caldera respectively. The most interesting site for geothermal exploitation was the Mofete zone, where a number of 4 productive wells were drilled and tested to produce electrical power. Based on data inferred from the productive tests it was established a potential electrical extractable power from Mofete field of at least 10MWe. More recently an empirical evaluation of the whole geothermal potential of the caldera provides a value of more than 1 GWe. The results of AGIP-ENEL exploration at Campi Flegrei highlighted the feasibility of geothermal exploitation. Here, we show for the first time the results of numerical simulations (TOUGH2 code ®) of fluids extraction and reinjection from the Mofete geothermal field, in order to produce at least 5MWe from zero emission power plant (Organic Rankine Cycle type). The simulation is aimed to understand the perturbation of the geothermal reservoir in terms of temperature, pressure change, and possible related seismicity, after different simulated time of exploitation. The modeling is mainly constrained by the data derived from geothermal exploration and productive tests performed since 1979 by AGIP-ENEL Companies. A general assessment of the maximum potential magnitude

  9. Mineralogical and petrological investigations of rocks cored from depths higher than 440m during the CFDDP drilling activities at the Campi Flegrei caldera (southern Italy).

    NASA Astrophysics Data System (ADS)

    Mormone, Angela; Piochi, Monica; Balassone, Giuseppina; Carlino, Stefano; Somma, Renato; Troise, Claudia; De Natale, Giuseppe

    2014-05-01

    The Campi Flegrei caldera is one of the highest-risk volcanic areas on the Earth and the drilling exploiting activities carried by the Azienda Geologica Italiana Petroli (AGIP) and the Società Anonima Forze Endogene Napoletane (SAFEN) since the '40 have produced the main constrains to the definition of the subsurface structure of the caldera. The eastern part of the caldera represents among the least known in the area in terms of both volcanic and geothermal evolution. Recently, in the 2012, the Campi Flegrei Deep Drilling Project (CFDDP) allowed performing a 506m hole in this sector of the caldera, i.e. in the Bagnoli Plain, where the western districts of the Neapolitan city developed. Here, we present the preliminary results from mineralogical, geochemical and petrological investigations of drilling core samples collected at -443 m and -506 m of depths. Scanning electron microscopy (SEM), microanalysis by energy dispersive spectroscopy (EDS) together with investigations by back-scattered electron mode (SEM-BSE), and powder X-Ray diffraction (XRD) allowed: 1) defining the primary sample lithology; 2) examining the features of both primary and secondary minerals; 3) describing the relationships among texture and secondary mineralization. Sr isotope analyses were furthermore performed on separated feldspars. Density measurements were also carried out on the bottom core. The investigated samples are representative of strongly altered, massive pyroclastic tuffs, which made of a chaotic ashy to sandy matrix including low crystalline juvenile scoria and pumice fragments. Textural features of secondary mineralization are consistent with circulation of hydrothermal fluids as the results of a wide geothermal resource in the caldera. Comparing the paleo-temperature inferred by authigenic minerals occurrence and the temperature measured at the bottom hole (~60°C) during geophysical logs, we suggest the cooling of the hydrothermal system in the eastern sector of the caldera.

  10. First observations of the fumarolic gas output from a restless caldera: Implications for the current period of unrest (2005-2013) at Campi Flegrei

    NASA Astrophysics Data System (ADS)

    Aiuppa, A.; Tamburello, G.; Napoli, R.; Cardellini, C.; Chiodini, G.; Giudice, G.; Grassa, F.; Pedone, M.

    2013-10-01

    The fumarolic gas output has not been quantified for any of the currently deforming calderas worldwide, due to the lack of suitable gas flux sensing techniques. In view of resumption of ground uplift (since 2005) and the associated variations in gas chemistry, Campi Flegrei, in southern Italy, is one of the restless calderas where gas flux observations are especially necessary. Here we report the first ever obtained estimate of the Campi Flegrei fumarolic gas output, based on a set of MultiGAS surveys (performed in 2012 and 2013) with an ad-hoc-designed measurement setup. We estimate that the current Campi Flegrei fumarolic sulphur (S) flux is low, on the order of 1.5-2.2 tons/day, suggesting substantial scrubbing of magmatic S by the hydrothermal system. However, the fumarolic carbon dioxide (CO2) output is ˜460±160 tons/day (mean±SD), which is surprisingly high for a dormant volcano in the hydrothermal stage of activity, and results in a combined (fumaroles + soil) CO2 output of ˜1560 tons/day. Assuming magma to be the predominant source, we propose that the current CO2 output can be supplied by either (i) a large (0.6-4.6 km3), deeply stored (>7 km) magmatic source with low CO2 contents (0.05-0.1 wt%) or (ii) by a small to medium-sized (˜0.01-0.1 km3) but CO2-rich (2 wt%) magma, possibly stored at pressures of ˜100 to 120 MPa. Independent geophysical evidence (e.g., inferred from geodetic and gravity data) is needed to distinguish between these two possibilities.

  11. Simulating the Dynamics of Magmatic Hydrothermal Systems in Restless Volcanoes: Insights into the Effect of Faulting at Campi Flegrei Caldera

    NASA Astrophysics Data System (ADS)

    Jasim, A.; Whitaker, F.; Rust, A.

    2014-12-01

    Magmatic hydrothermal systems are the superficial manifestation of high heat flux in groundwater systems and their dynamics can be intermittently perturbed by those of the magmatic system. The complex interplay between heat and fluid flow in hydrothermal systems must be understood in order to discriminate geophysical signals of magmatic unrest from purely hydrothermal ones. Starting from the Campi Flegrei model of Todesco et al. (2010), we investigate the impact of major geological discontinuities in permeability on: advective flow within the hydrothermal reservoir, subsurface pressure and temperature distributions and the relative contribution of volcanic and surface derived fluids to surficial discharge. In the baseline scenario (no faults), a steady state convective flow system develops within 4 ky in which the injection of hot fluids feeds a narrow plume (fumarole), which entrains water from the surrounding aquifer and depresses isotherms by up to 500 m in the zone 400-1500 m from fumarole. The addition of two steep faults 4 and 7 km from the fumarole (faults A and B) two orders of magnitude higher vertical permeability than the matrix, divides the flow field into three separate advective cells (fumarole, fault A and fault B). Faults focus recharge of shallow groundwater to the deeper reservoir, with the concomitant upwelling of hot water around faults leading to local thermal anomalies (+50 0C) at 500 m depth. Increasing fault permeability by an order of magnitude enhances this effect around fault B, but reverses the flow pattern at fault A which now serves as a conduit discharging fluids at up to 90 0C. Increasing matrix permeability results in interaction between the previously separate advective cells. The juxtaposition of low permeability rock at the faulted caldera margin focusses discharge of hot waters, fed by recharge via faults within the caldera. Simulations also evaluate the effect of unrest, highlighting the impact of fluid flow on subsurface

  12. Multiphysics numerical models of resurgent calderas ground deformation: The 1982-2010 Campi Flegrei (Southern Italy) case studies

    NASA Astrophysics Data System (ADS)

    Tizzani, Pietro

    2013-04-01

    Ground deformation signals in caldera region are the expression of near-surface and/or deep-seated physical processes. As most of the geophysical analysis, the interpretation of the deformation data is usually performed setting up inverse problems, which often use Monte Carlo optimization techniques like the Simulated Annealing and the Genetic Algorithm, in order to constrain the nature of the causative sources at depth. Usually, these methods exploit the problem's solution space by iterating forward analytical models, which consider simplified geometries and homogeneous linear elastic material properties. However, several recent studies have shown that oversimplified forward models may lead to misinterpretations of the retrieved source parameters. To overcome these limitations we consider the Finite Element (FE) method as a powerful numerical tool that allows implementing models with complex geometries, material heterogeneities, as well as time dependent physical processes. For this reason, FE models are a suitable candidate to fill the gap between the accuracy achieved on the observation of ground deformation in volcanic areas and the models used for its interpretation. In this context, we investigate the driving forces responsible of the long-term ground deformation of the Campi Flegrei (CF) caldera, Southern Italy, during the 1982-2010 time interval. To this purpose, we propose a new multiphysics numerical model that takes into account both the mechanical heterogeneities of the crust and the thermal conditions of geothermal system beneath the volcano. We perform a numerical Chain Rule Optimization Procedure (CROP) in a FEM environment, that considers different physical contexts linked along a common evolution line: starting from the thermal proprieties and mechanical heterogeneities of the upper crust, we develop a 3D time dependent thermo-fluid dynamic model of CF caldera. More specifically, by carrying out two subsequent optimization procedures based on

  13. Probabilistic tsunami hazard assessment related to underwater explosions in the Campi Flegrei caldera: Gulfs of Napoli and Pozzuoli (Tyrrhenian Sea, Italy).

    NASA Astrophysics Data System (ADS)

    Ulvrova, Martina; Selva, Jacopo; Paris, Raphael; Brizuela, Beatriz; Costa, Antonio; Grezio, Anita; Lorito, Stefano; Tonini, Roberto

    2016-04-01

    Tsunami caused by underwater volcanic explosions are typically characterized by short period waves and greater dispersion compared to tsunami generated by earthquakes, and the impact in the far-field is often limited. However, the effect of dispersion is reduced for underwater explosions occurring in shallow-water environments, as the length-to-depth ratio of the waves rapidly increase, and runup inland can be locally high. This effect was particularly illustrated by the 19 m runup at Karymsky Lake, Kamchatka, in 1996 (Belousov et al., 2010; Ulvrova et al., 2014). Hazards related to underwater volcanic explosions are challenging to evaluate and might be underestimated in some cases. In this study we consider different scenarios of explosions in the offshore part of the Campi Flegrei (Phlegraean Fields) caldera in the Pozzuoli - Naples region (Tyrrhenian Sea, Italy). The onshore eruptive history of the caldera is well documented (e.g. Orsi et al., 2004), but past and future activity offshore has been rarely discussed. The probability for eruptions in the submarine part of the caldera is perhaps low (Selva et al., 2012), but scenarios of tsunamis generated by underwater explosions and their impact in the proximal field (Bay of Pozzuoli) and far field (Bay of Naples) deserve to be considered due to high population density in the adjacent coastal areas. Initial surface displacement is estimated as a function of explosion energy at a given depth. We study 17 different potential vent locations within the Pozzuoli Bay, and 3 different vent radii (200 m, 650 m and 900 m), corresponding to the three representative eruptive scenarios identified in Orsi et al. (2009) and Selva et al. (2010). We then use these sources in a Bayesian Event Tree framework, following the procedure defined in Selva et al. (2010), in order to evaluate a first order Probabilistic Hazard Analysis for this type of tsunami sources for the Gulfs of Napoli and Pozzuoli. Belousov A., Voight B., Belousova M

  14. Magma injection beneath the urban area of Naples: a new mechanism for the 2012-2013 volcanic unrest at Campi Flegrei caldera.

    PubMed

    D'Auria, Luca; Pepe, Susi; Castaldo, Raffaele; Giudicepietro, Flora; Macedonio, Giovanni; Ricciolino, Patrizia; Tizzani, Pietro; Casu, Francesco; Lanari, Riccardo; Manzo, Mariarosaria; Martini, Marcello; Sansosti, Eugenio; Zinno, Ivana

    2015-01-01

    We found the first evidence, in the last 30 years, of a renewed magmatic activity at Campi Flegrei caldera from January 2012 to June 2013. The ground deformation, observed through satellite interferometry and GPS measurements, have been interpreted as the effect of the intrusion at shallow depth (3090 ± 138 m) of 0.0042 ± 0.0002 km(3) of magma within a sill. This interrupts about 28 years of dominant hydrothermal activity and occurs in the context of an unrest phase which began in 2005 and within a more general ground uplift that goes on since 1950. This discovery has implications on the evaluation of the volcanic risk and in the volcanic surveillance of this densely populated area. PMID:26279090

  15. Magma injection beneath the urban area of Naples: a new mechanism for the 2012-2013 volcanic unrest at Campi Flegrei caldera

    NASA Astrophysics Data System (ADS)

    D'Auria, Luca; Pepe, Susi; Castaldo, Raffaele; Giudicepietro, Flora; Macedonio, Giovanni; Ricciolino, Patrizia; Tizzani, Pietro; Casu, Francesco; Lanari, Riccardo; Manzo, Mariarosaria; Martini, Marcello; Sansosti, Eugenio; Zinno, Ivana

    2015-08-01

    We found the first evidence, in the last 30 years, of a renewed magmatic activity at Campi Flegrei caldera from January 2012 to June 2013. The ground deformation, observed through satellite interferometry and GPS measurements, have been interpreted as the effect of the intrusion at shallow depth (3090 ± 138 m) of 0.0042 ± 0.0002 km3 of magma within a sill. This interrupts about 28 years of dominant hydrothermal activity and occurs in the context of an unrest phase which began in 2005 and within a more general ground uplift that goes on since 1950. This discovery has implications on the evaluation of the volcanic risk and in the volcanic surveillance of this densely populated area.

  16. Magma injection beneath the urban area of Naples: a new mechanism for the 2012–2013 volcanic unrest at Campi Flegrei caldera

    PubMed Central

    D’Auria, Luca; Pepe, Susi; Castaldo, Raffaele; Giudicepietro, Flora; Macedonio, Giovanni; Ricciolino, Patrizia; Tizzani, Pietro; Casu, Francesco; Lanari, Riccardo; Manzo, Mariarosaria; Martini, Marcello; Sansosti, Eugenio; Zinno, Ivana

    2015-01-01

    We found the first evidence, in the last 30 years, of a renewed magmatic activity at Campi Flegrei caldera from January 2012 to June 2013. The ground deformation, observed through satellite interferometry and GPS measurements, have been interpreted as the effect of the intrusion at shallow depth (3090 ± 138 m) of 0.0042 ± 0.0002 km3 of magma within a sill. This interrupts about 28 years of dominant hydrothermal activity and occurs in the context of an unrest phase which began in 2005 and within a more general ground uplift that goes on since 1950. This discovery has implications on the evaluation of the volcanic risk and in the volcanic surveillance of this densely populated area. PMID:26279090

  17. MED SUV TASK 6.3 Capacity building and interaction with decision makers: Improving volcanic risk communication through volcanic hazard tools evaluation, Campi Flegrei Caldera case study (Italy)

    NASA Astrophysics Data System (ADS)

    Nave, Rosella; Isaia, Roberto; Sandri, Laura; Cristiani, Chiara

    2016-04-01

    In the communication chain between scientists and decision makers (end users), scientific outputs, as maps, are a fundamental source of information on hazards zoning and the related at risk areas definition. Anyway the relationship between volcanic phenomena, their probability and potential impact can be complex and the geospatial information not easily decoded or understood by not experts even if decision makers. Focusing on volcanic hazard the goal of MED SUV WP6 Task 3 is to improve the communication efficacy of scientific outputs, to contribute in filling the gap between scientists and decision-makers. Campi Flegrei caldera, in Neapolitan area has been chosen as the pilot research area where to apply an evaluation/validation procedure to provide a robust evaluation of the volcanic maps and its validation resulting from end users response. The selected sample involved are decision makers and officials from Campanian Region Civil Protection and municipalities included in Campi Flegrei RED ZONE, the area exposed to risk from to pyroclastic currents hazard. Semi-structured interviews, with a sample of decision makers and civil protection officials have been conducted to acquire both quantitative and qualitative data. The tested maps have been: the official Campi Flegrei Caldera RED ZONE map, three maps produced by overlapping the Red Zone limit on Orthophoto, DTM and Contour map, as well as other maps included a probabilistic one, showing volcanological data used to border the Red Zone. The outcomes' analysis have assessed level of respondents' understanding of content as displayed, and their needs in representing the complex information embedded in volcanic hazard. The final output has been the development of a leaflet as "guidelines" that can support decision makers and officials in understanding volcanic hazard and risk maps, and also in using them as a communication tool in information program for the population at risk. The same evaluation /validation process

  18. History of earthquakes and vertical ground movement in Campi Flegrei caldera, Southern Italy: comparison of precursory events to the A.D. 1538 eruption of Monte Nuovo and of activity since 1968

    USGS Publications Warehouse

    Dvorak, J.J.; Gasparini, P.

    1991-01-01

    The record of felt earthquakes around Naples Bay in southern Italy is probably complete since the mid-15th century. According to this record, intense earthquake swarms originating beneath Campi Flegrei, an explosive caldera located along the north coast of Naples Bay, have occurred only twice: (1) before the only historical eruption in Campi Flegrei in 1538; and (2) from mid-1983 to December 1984. Earthquake activity during the earlier period, which began at least a few years, and possibly as many as 30 years, before the 1538 eruption, damaged many buildings in the city of Pozzuoli, located near the center of Campi Flegrei. Minor seismic activity, which consisted of only a few felt earthquakes, occurred from 1970 to 1971. The second period of intense earthquake swarms lasted from mid-1983 to 1984, again damaging many buildings in Pozzuoli. Two periods of uplift along the shoreline within Campi Flegrei have also been noted since the mid-15th century: (1) during the few decades before the 1538 eruption; and (2) as two distinct episodes since 1968. Uplift of a few meters probably occurred a few decades before the 1538 eruption; uplift of as much as 3.0 m has occurred in Pozzuoli since 1968. These similarities strongly suggest that, for the first time in 440 years, the same process that caused intense local earthquake swarms and uplift in the early 1500's and led to an eruption in 1538, has again occurred beneath Campi Flegrei. Though no major seismicity or uplift has occurred since December 1984, because of the large amount of extensional strain accumulated during the past two decades, if a third episode of seismicity and rapid uplift occurs, it may lead to an eruption within several months after the resumption of activity. ?? 1991.

  19. 3D image of Brittle/Ductile transition in active volcanic area and its implication on seismicity: The Campi Flegrei caldera case study

    NASA Astrophysics Data System (ADS)

    Castaldo, Raffaele; Luca, D'auria; Susi, Pepe; Giuseppe, Solaro; Pietro, Tizzani

    2015-04-01

    The thermo-rheology of the rocks is a crucial aspect to understand the mechanical behavior of the crust in young and tectonically active area. As a consequence, several studies have been performed since last decades in order to understand the role of thermic state in the evolution of volcanic environments. In this context, we analyze the upper crust rheology of the Campi Flegrei active caldera (Southern Italy). Our target is the evaluation of the 3D geometry of the Brittle-Ductile transition beneath the resurgent caldera, by integrating the available geological, geochemical, and geophysical data. We first performed a numerical thermal model by using the a priori geological and geophysical information; than we employ the retrieved isothermal distribution to image the rheological stratification of the shallow crust beneath caldera. In particular, considering both the thermal proprieties and the mechanical heterogeneities of the upper crust, we performed, in a Finite Element environment, a 3D conductive time dependent thermal model through an numerical of solution of the Fourier equation. The dataset consist in temperature measurements recorded in several deep wells. More specifically, the geothermal gradients were measured in seven deep geothermal boreholes, located in three main distinct areas: Mofete, Licola, and San Vito. In addition, we take into account also the heat flow density map at the caldera surface calculated by considering the thermal measurements carried out in 30 shallow water wells. We estimate the isothermal distribution of the crust calibrating two model parameters: the heat production [W], associated to the magma injection episodes in the last 60 kyears within the magma chamber and the heat flow coefficient [W/m2*K] at the external surface. In particular, the optimization procedure has been performed using an exhaustive grid search, to minimize the differences between model and experimental measurements. The achieved results allowed us to

  20. Delayed earthquake-volcano interactions at Campi Flegrei Caledra, Italy

    NASA Astrophysics Data System (ADS)

    Lupi, Matteo; Frehner, Marcel; Saenger, Erik H.; Tisato, Nicola; Weis, Philipp; Geiger, Sebastian; Chiodini, Giovanni; Driesner, Thomas

    2015-04-01

    The Campi Flegrei Caldera near Naples, Italy, is arguably one of the world's prime examples of volcanic hazard in a heavily populated area. Over the last centuries the ground of the caldera went through cyclical phases of inflation and deflation. The inflation phase consists of rapid vertical ground movements associated with the emission of volcanic gases marked by a strong magmatic component. Such deformations are suggested to be caused by pulses of CO2-rich fluids injected into the caldera's shallow hydrothermal system or by the intrusion of magmatic bodies at shallow depths. We show that since 1945 the uplift crises occurring at the Campi Flegrei Caldera are caused by large regional earthquakes. Our results point out that maximum uplift rates in the caldera take place about three years after the occurrence of large earthquakes that imposed a log10(PGA[cm s-2]) greater than 0.18. These observations are supported by forward seismic simulations and with a semi-quantitative statistical analysis of ground surface displacements and Peak Ground Accelerations (PGA). Our proposed geomechanical model integrates and simplifies previous empirical concepts of upwelling fluids that pressurize the region beneath the Campi Flegrei causing ground surface uplift. Numerical simulations indicate that passing seismic body waves impose high dynamic strains at the upper boundary of the deep magma reservoir as well as at the brittle/ductile transition at about 3 km depth. Such dynamic strains induce short-lived brittle failure in nominally ductile regions causing the release of magmatic fluids. The approximately 3-years time lag between the earthquake and maximum surface uplift reflects the time during which the lithostatically pressured fluids ascend through hot, nominally ductile lithologies without expanding. After passing the brittle/ductile transition at ~3 km depth the H2O-CO2 mixture can expand and phase-separate, pressurizing the subsurface. This leads to a rapid ground uplift

  1. Testing and optimization of the seismic networks of Campi Flegrei (Southern Italy)

    NASA Astrophysics Data System (ADS)

    Tramelli, A.; Troise, C.; De Natale, G.; Orazi, M.

    2013-11-01

    The definition of the network resolution power is an important parameter to be considered when evaluating most of the seismic analysis, being connected to the location quality and earthquakes detectability. We estimated the resolving power of the seismic network of Campi Flegrei. The results show that the actual moment magnitude threshold is 0.5 in the Solfatara area, center of the caldera, but increases sharply going away from the center. We also estimated the theoretical resolution power of the actual seismic network of Campi Flegrei plus 5 hypothetical borehole stations, moving the borehole stations into 3 different wells. As expected, big improvements in the location parameters come from the use of borehole stations. The results show that a 3000 m deep borehole located close to the actual hypocentral area would allow to detect and locate the very low magnitude earthquakes, probably connected to the hydrothermal system characterizing the Campi Flegrei caldera. Finally, we performed an optimization analysis of the permanent seismic network of Campi Flegrei finding the best 3 station positions that would increase the resolution power of the network to locate earthquakes in the South and offshore part of the caldera. We evidenced that the actual network has an improvable resolution in the South and West part of the caldera.

  2. Mineralogical and sulfur isotopic characterization of the sulfur-bearing mineralization from the active degassing area of Campi Flegrei caldera (southern Italy)

    NASA Astrophysics Data System (ADS)

    Mormone, Angela; Piochi, Monica; Balassone, Giuseppina; Strauss, Harald; Troise, Claudia; De Natale, Giuseppe

    2015-04-01

    The Campi Flegrei caldera is a site of persistent hydrothermal circulation and gaseous emissions inside the Pozzuoli town and nearby the city of Napoli (Italy). The solfataric phenomena are associated with episodes of low-magnitude seismicity and vertical ground displacement since Roman times, evolving to the Monte Nuovo eruption in the 1538 AD. Pronounced geochemical anomalies, uplift rates up to 1 m/y and up to ten thousands microearthquakes per year also characterized the four most recent decades of unrest. The degassing phenomena are concentrated within the Solfatara crater, although, since 2006, the hydrothermal activity strongly increased in the Pisciarelli district, i.e. on the north-east slope of the tuff. We investigated sulfur-bearing mineral precipitates sampled from the active fumaroles both within the Solfatara and along the Pisciarelli slope. Mineral assemblage, texture and chemistry were determined for the efflorescence precipitated nearby the fumaroles and along the mud pool by x-ray diffraction, back-scattered electron microscope and electron diffuse microanalysis. δ34S compositions were also determined on separated sulfur-minerals. The new data have been compared with scattered literature data, including few existing for the previous '70 and '80 unrest episodes. Native sulfur and alunite are the main mineral phases that associate with alunogene, and, locally, pickeringite and potassium alum. Sporadically mereiterite, amarillite, and pyrite have been found as neogenesis mineralization along the outcropping rocks. The mud pool is rich in gypsum, potassium alum and pyrite. δ34S values range from -5.48 to 0.0‰, being slightly lower than previous data. The obtained results suggest that the Pisciarelli area is characterized by magmatic-hydrothermal, magmatic-steam and steam-heated environments, developed on a argillitic hydrothermal facies that thickens in correspondence of the degassing area. These environments develop and continuously evolve in

  3. SERAPIS project - 3D imaging of the Campi Flegrei caldera (southern Italy) : high resolution P-wave velocity tomography

    NASA Astrophysics Data System (ADS)

    Judenherc, S.; Zollo, A.; Auger, E.; Boschi, L.; Satriano, C.; Serapis Working Group

    2003-04-01

    In September 2001, the SERAPIS project was carried out as an extended active seismic survey in the gulfs of Naples and Pozzuoli. A dense array of 60 three-component on-land stations and 72 sea bottom seismographs (OBS) have been deployed to record more than 5000 air gun shots at a spacing of about 125~m. As a preliminary analysis, the first P-arrival times of a the small offset data in the central part of the region has been inverted using the codes of H.M. Benz. The linearized iterative inversion of 38000 arrival times provided a >80% variance reduction with a node spacing of 250m. At the first order, our model shows a 2-layer structure : low velocity volcanic sediments (2.5-3.5km/s) lying on an inclined high velocity limestone platform (>6km/s). The caldera itself is very well identified, the rim is characterized by a 500-1000m upward shift of the velocity isolines. The whole dataset is expected to provide a wider image with the same resolution (250m). It includes the detailed shape of the refractor beneath the caldera as well as its irregularities out of the bay which have been observered in the seismic sections.

  4. Dynamic model of intrusion of magma and/or magmatic fluids in the large-scale deformation source of the Campi Flegrei caldera (Italy).

    NASA Astrophysics Data System (ADS)

    Crescentini, Luca; Amoruso, Antonella; Luongo, Annamaria

    2015-04-01

    The Campi Flegrei (CF) caldera is located in a densely populated area close to Naples (Southern Italy). It is renowned as a site of continual slow vertical movements. After the last eruption in 1538, the caldera generally subsided until 1969 when minor uplift occurred. In the early 1970s this uplift became significant (~1.5 m max). A further large uplift episode occurred from 1982 to 1984 (~1.8 m max), and subsequently smaller uplift episodes have occurred since then. Amoruso et al. (2014a,b) have recently shown that the CF surface deformation field from 1980 to 2013 can be decomposed into two stationary parts. Large-scale deformation can be explained by a quasi-horizontal source, oriented NW to SE and mathematically represented by a pressurized finite triaxial ellipsoid (PTE) ~4 km deep, possibly related to the injection of magma and/or magmatic fluids from a deeper magma chamber into a sill, or pressurization of interconnected (micro)cavities. Residual deformation not accounted for by PTE is confined to the Solfatara fumarolic area and can be mathematically explained by a small (point) pressurized oblate spheroid (PS) ~2 km below the Solfatara fumarolic field, that has been equated with a poroelastic response of the substratum to pore pressure increases near the injection point of hot magmatic fluids into the hydrothermal system. A satisfying feature of this double source model is that the geometric source parameters of each are constant over the period 1980-2013 with the exception of volume changes (potencies). Several papers have ascribed CF deformation to the injection of magmatic fluids at the base of the hydrothermal system. All models predict complex spatial and temporal evolution of the deformation pattern and consequently contrast with the observed deformation pattern stationarity. Also recently proposed dynamic models of sill intrusion in a shallow volcanic environment do not satisfy the observed CF deformation pattern stationarity. We have developed an

  5. Contribution of 2009-2014 COSMO-SkyMed SAR data to the interpretation of the Campi Flegrei caldera, Italy, activity.

    NASA Astrophysics Data System (ADS)

    Amoruso, Antonella; Crescentini, Luca; Luongo, Annamaria; Zinno, Ivana; Casu, Francesco

    2015-04-01

    The Campi Flegrei (CF) caldera is located in a densely populated volcanic region in the northern suburbs of Naples (Southern Italy). The coast near CF is famous for its significant vertical motions since Roman times, which are documented by drowned and elevated harbor works that have recorded slow variations in local sea level. After the last eruption in 1538, the caldera subsided and it has been doing so more-or-less steadily since 1969 when minor uplift occurred. In the early 1970s this uplift became significant (~1.5 m max). A further large uplift episode occurred from 1982 to 1984 (~1.8 m max), and subsequently smaller uplift episodes have occurred later on. From 2006 to spring 2013, CF was mostly uplifting at an increasing rate. Uplifting started again during summer 2014. Amoruso et al. (2014a,b) have recently shown that the CF ground deformation field from 1980 to 2013 can be decomposed into two stationary parts. Large-scale deformation can be explained by a quasi-horizontal source, oriented NW to SE and mathematically represented by a pressurized finite triaxial ellipsoid (PTE) ~4 km deep, possibly related to the injection of magma and/or magmatic fluids from a deeper magma chamber into a sill. Residual deformation not accounted for by PTE is confined to the Solfatara fumarolic area and can be mathematically explained by a small (point) pressurized oblate spheroid (PS) ~2 km below the Solfatara fumarolic field, that has been equated with a poroelastic response of the substratum to pore pressure increases near the injection point of hot magmatic fluids into the hydrothermal system. A satisfying feature of this double source model is that the geometric source parameters of each are constant over the period 1980-2013 with the exception of volume changes (potencies); potency time histories for PTE and PS, to which the time evolutions of the two components of the ground displacement field are related, are somewhat similar but not identical. Amoruso et al. (2014a

  6. Geochemical evidences of magma dynamics at Campi Flegrei (Italy)

    NASA Astrophysics Data System (ADS)

    Caliro, S.; Chiodini, G.; Paonita, A.

    2014-05-01

    Campi Flegrei caldera, within the Neapolitan area of Italy, is potentially one of the most dangerous volcanoes in the world, and during the last decade it has shown clear signs of reactivation, marked by the onset of uplift and changes in the geochemistry of gas emissions. We describe a 30-year-long data set of the CO2-He-Ar-N2 compositions of fumarolic emissions from La Solfatara crater, which is located in the center of the caldera. The data display continuous decreases in both the N2/He and N2/CO2 ratios since 1985, paralleled by an increase in He/CO2. These variations cannot be explained by either processes of boiling/condensation in the local hydrothermal system or with changes in the mixing proportions between a magmatic vapor and hydrothermal fluids. We applied the magma degassing model of Nuccio and Paonita (2001, Earth Planet. Sci. Lett. 193, 467-481) using the most recent inert-gas solubilities in order to interpret these peculiar features in accordance with petrologic constraints derived from the ranges of the melt compositions and reservoir pressures at Campi Flegrei. The model simulations for mafic melts (trachybasalt and shoshonite) show a remarkably good agreement with the measured data. Both decompressive degassing of an ascending magma and mixing between magmatic fluids exsolved at various levels along the ascent path can explain the long-term geochemical changes. Recalling that (i) a sill-like reservoir of gases at a depth of 3-4 km seems to be the main source of ground inflation and (ii) there is petrologic and geophysical evidence for a reservoir of magma at about 8 km below Campi Flegrei, we suggest that the most-intense episodes of inflation occur when the gas supply to the sill-like reservoir comes from the 8 km-deep magma, although fluids exsolved by magma bodies at shallower depths also contribute to the gas budget. Our work highlights that, in caldera systems where the presence of hydrothermal aquifers commonly masks the magmatic signature

  7. Geochemical Monitoring In Campi Flegrei From 1970 To 2000.

    NASA Astrophysics Data System (ADS)

    Avino, R.; Caliro, S.; Chiodini, G.; del Gaudio, C.; di Matteo, V.; Pece, R.; Russo, M.

    At the present, the activity of Campi Flegrei caldera is characterized by strong fumarolic emissions at Solfatara and minor emissions at Baia and Mofete. Two bradyseismic crises, centred at Pozzuoli, interested the caldera in recent times: in 1969-1972 (maximum uplift of 1.7 m) and in 1982-1984 when the area was affected by a maximum uplift of 1.8 m and by several thousands earthquakes. More recently, three minor sudden ground uplifts and seismic swarms were recorded in 1989-90, in 1994 and in 2000. In the late `70s started a systemat ic work of geochemical surveillance based on the monitoring of the fumarolic fluids of Solfatara. In addition, in 1983 was added the monitoring of radon concentration, temperature and pH in the waters of three wells (Damiani, Costagliola and Tortorelli). Measures at Tortorelli were interrupted in 1993, because of technical problems, while Damiani and Costagliola are still monitored. The variations of radon, temperature and pH monitored in the three wells and compositional changes in Solfatara fumaroles show a clear correlation with the different phases of the bradyseismic crisis. Concurrent changes of physical and chemical parameters were recorded during 1989, 1994-1996 and 2000. The most complete set of geochemical data, which also includes measurements of the diffuse degassing at Solfatara, regards the last crisis. The soil uplift was accompanied by a significant increase of diffuse CO2 fluxes, increments in temperature and pressures of the hydrothermal system, estimated by gas-indicators, and by a marked increase of the radon content in the waters. The data suggest that variations of fluid pressure within the hydrothermal system are one of the main causes of ground deformation episodes at Campi Flegrei.

  8. Bouguer Anomaly of the Solfatara Hydrothermal Plume, Campi Flegrei

    NASA Astrophysics Data System (ADS)

    Young, N. K.; Gottsmann, J.

    2015-12-01

    Solfatara tuff cone is the most hydrothermally active area within Campi Flegrei caldera, a resurgent nested caldera near Naples, Italy. Hydrothermal gases and fluids are released most vigorously here and at Pisciarelli nearby. Models explaining the measured fumarole emissions and deformation require a plume of ascending hot water vapour and CO2 from depth. Here we present preliminary findings from a new gravity survey which aims at i) creating a high precision Bouguer anomaly map of Solfatara and ii) imaging the hydrothermal plume. We carried out a high spatial density gravity survey of Solfatara and the surrounding area using a Scintrex CG5 gravimeter and simultaneous benchmark localisation using a GNSS system. We created a dense grid of 51 stations within Solfatara crater, and a reduced density network of 37 further stations outside the crater to 3km distance. Other geophysical techniques such as electromagnetism, electrical resistivity, and active seismic imaging have resolved the subsurface architecture to depths between a few hundred meters to 3km depth. Our coverage and spacing should capture the details of the plume under Solfatara and have resolution to approximately 3km depth.

  9. Hydrothermal alteration favoring phreatic eruption processes at Solfatara (Campi Flegrei)

    NASA Astrophysics Data System (ADS)

    Mayer, Klaus; Scheu, Bettina; Montanaro, Cristian; Aßbichler, Donjá; Isaia, Roberto; Dingwell, Donald B.

    2015-04-01

    Solfatara and Pisciarelli fumaroles are the main surface manifestations of the strong hydrothermal activity within the Campi Flegrei caldera system and pointing to a significant risk for phreatic eruptions in this densely populated area. Phreatic eruptions, triggered by various processes are hardly predictable in occurrence time and size. Despite their hazard potential, these eruptions, as well as the influence of hydrothermal alteration on their likelihood, magnitude and style, have so far been largely overlooked in experimental volcanology. The physical properties and the mechanical behavior of volcanic rocks are highly dependent on their original magmatic microstructure and on any eventual alteration of those microstructures due to hydrothermal reactions. We have therefore investigated the potential effects of hydrothermal alteration on rock microstructure and, as a consequence, on fragmentation dynamics. Rock samples from the vicinity of the Solfatara and Pisciarelli fumaroles have been characterized 1) geochemically (X-ray fluorescence, X-ray diffraction), 2) physically (density, porosity, permeability and elastic wave velocity) and 3) mechanically (uniaxial compressive strength, tensile strength). We furthermore have investigated the effects of hydrothermal alteration on fragmentation processes using a shock-tube apparatus, operating with Argon gas, water vapor and superheated water at temperatures up to 400°C and maximum pressures of 20 MPa. Fragmentation and ejection dynamics in the presence of three different energy sources within the pores have been investigated: overpressure by 1) Argon gas; or 2) water vapor and due to 3) steam flashing of superheated water. Fragmentation speed, fragmentation efficiency and fragmented particle ejection velocity were measured. Our results indicate on the one hand, that steam flashing provides the highest energy - resulting in increased fragmentation speed and particle ejection velocity and also a significant higher

  10. Geochemical and B-Sr-Nd isotopic evidence for mingling and mixing processes in the magmatic system that fed the Astroni volcano (4.1-3.8 ka) within the Campi Flegrei caldera (southern Italy)

    NASA Astrophysics Data System (ADS)

    Tonarini, Sonia; D'Antonio, Massimo; Di Vito, Mauro Antonio; Orsi, Giovanni; Carandente, Antonio

    2009-02-01

    The Astroni volcano was built through seven eruptions that generated pyroclastic deposits and lava domes within the Campi Flegrei caldera (southern Italy) 4.1-3.8 ka BP. Whole-rock geochemical and B-Sr-Nd isotopic investigations were carried out on representative samples of all seven eruptions. The products vary from tephriphonolites to phonolites, and from latites to trachytes. They show textural, mineralogical and isotopic evidence of disequilibrium, including distinct clinopyroxene populations, rounded and/or resorbed plagioclase and alkali-feldspar, and reverse-zoned phenocrysts of all these mineral phases. The Sr, Nd and B isotopic composition of whole rocks is variable and correlated with the degree of chemical evolution, suggesting open-system processes in addition to fractional crystallisation. Moreover, significant Sr-isotopic disequilibrium between the phenocrysts and glass has been documented for one sample. The chemostratigraphy of the products indicates that Astroni eruptions 1 through 5 were fed by magmas of trachytic to phonolitic composition that were less enriched in radiogenic Sr and 11B up-section. This variability has been interpreted as the result of mingling between at least two distinct magmatic end-members, one more evolved and the other less evolved. Another heterogeneous batch of magma, resulting from almost complete mixing between the same two end-members, was drained during eruptions 6 and 7. The more evolved end-member, characterised by 87Sr/ 86Sr ≥ 0.7075, 143Nd/ 144Nd ≤ 0.51247 and δ11B ≥ - 8‰, was very similar to the magma that fed the final phases of the Agnano-Monte Spina eruption, which occurred a few centuries earlier in the Astroni vent area. The less evolved end-member had 87Sr/ 86Sr ≤ 0.70726, 143Nd/ 144Nd ≥ 0.51251 and δ11B ≤ 10‰, and was likely derived by fractional crystallisation of a mantle-derived magma. An abrupt decrease in both the Sr isotope ratio and the Th content, detected at the transition

  11. Spatiotemporal analysis and interpretation of 1993-2013 ground deformation at Campi Flegrei, Italy, observed by advanced DInSAR

    NASA Astrophysics Data System (ADS)

    Samsonov, Sergey V.; Tiampo, Kristy F.; Camacho, Antonio G.; Fernández, José; González, Pablo J.

    2014-09-01

    Campi Flegrei is one of the most hazardous volcanic areas in the world because of its close proximity to the city of Naples. Here we apply the multidimensional small baseline subset (MSBAS) differential interferometric synthetic aperture radar (DInSAR) technique to obtain vertical and horizontal components of ground deformation for Campi Flegrei at high spatial and temporal resolutions that span, for the first time, 20 years. The area underwent continuous subsidence from 1993 through 1999. Moderate uplift began in 2010 and substantially increased through 2012, reaching approximately 13 cm by 2013. We model the observed deformation to determine source parameters for subsidence and uplift epochs. Both the inflation and deflation mechanisms involve large, extended sources in a layered hydrothermal system whose location is controlled by the caldera structure and stratigraphy. The temporal resolution of MSBAS approaches that of GPS daily time series, with superior precision and spatial resolution, making it an excellent alternative for volcano monitoring.

  12. Geodetic Measurements and Modelling at Neapolitan Volcanoes(Southern Italy): Somma-Vesuvius and Campi Flegrei

    NASA Astrophysics Data System (ADS)

    de Natale, G.; Troise, C.; Pingue, F.; Obrizzo, F.

    2004-12-01

    We show the recent results about geodetic observations and modelling at two very explosive and densely populated volcanoes in Southern Italy, namely Somma-Vesuvius and Campi Flegrei caldera. The two areas, characterised by the highest volcanic risk in the World because of the density of population and exposed value, are among the best monitored ones in the World. Geodetic monitoring at these areas started more than 30 years ago, and was progressively improved in the last decade, including dense networks making use of both terrestrial and space techniques. The monitored period includes two strong unrests at Campi Flegrei caldera, not followed by eruptions, characterised by uplift of up to 3 m in few years, with rates up to 1 m/year, and intercurring subsidence with rates up to .08 m/year. Somma Vesuvius is on the contrary characterised, in the last 30 years, by a marked stability, except for a very localised subsidence at the young active center (Vesuvius) and a peculiar ring-like subsidence all around the volcanic edifice. The fast uplift and subsidence at Campi Flegrei has been modelled as due to shallow inflation sources and a dominant effect of passive slip along the ring faults bordering the collapsed area. Numerical modelling taking carefully into account the geometry of ring faults gives an accurate description of observed displacements. At Somma-Vesuvius, subsidence of Vesuvius cone is modelled in terms of gravitationally-induced slip along the contact limits between the older caldera and the younger active edifice. The ring-like subsidence around the whole edifice is modelled in terms of normal fault-like behaviour of the contacts among the loaded basement and the superimposed volcanic edifice, subject to the extensional tectonic stress of the area. Both models of ground deformations at the two areas appear very consistent with the behaviour of local volcano-tectonic seismicity, and enlighten the very important role played by volcano-tectonic structures in

  13. Residence times of alkali feldspar phenocrysts from magma feeding the Agnano-Monte Spina Eruption (4.7 ka), Campi Flegrei caldera (Napoli, southern Italy) based on Ba-zonation modelling

    NASA Astrophysics Data System (ADS)

    Iovine, Raffaella Silvia; Wörner, Gerhard; Carmine Mazzeo, Fabio; Arienzo, Ilenia; Fedele, Lorenzo; Civetta, Lucia; D'Antonio, Massimo; Orsi, Giovanni

    2016-04-01

    Timescales governing the development of crustal magma reservoirs are a key for understanding magmatic processes such as ascent, storage and mixing event. An estimate of these timescales can provide important constraints for volcanic hazard assessment of active volcanoes. We studied the Agnano-Monte Spina eruption (A-MS; 4.7 ka; VEI = 4; 0.85 km3 D.R.E. of magma erupted) of the Campi Flegrei caldera, one of the most dangerous volcanic areas on Earth. The A-MS eruption has been fed by magmas varying from more to less evolved trachyte whose variable 87Sr/86Sr and trace elements features suggest magma mixing between two end-members. Ba zonation profiles of alkali feldspar phenocrysts have been determined through combined energy-dispersive and wavelength-dispersive electron microprobe analyses (EDS-WDS-EMPA). We focused on distinct compositional breaks near the rim of the crystals that likely represent the last mixing event prior to eruption. We always chose the steepest gradients close to the crystal rims, taking into account that any effects related to cutting angles or crystal orientation should give longer apparent diffusion times. Two different approaches were undertaken: (1) a quantitative Ba compositional profiles were measured by point analyses along a short transect crossing growth discontinuities and (2) grey-scale profiles were taken parallel to the acquired point profiles. Assuming that Ba dominates the backscattered electron intensities in sanidines, greyscale gradients can be used as a diffusive tracer. BSE images were processed using the ImageJ® software, in order to extract a numerical greyscale profile. In both cases, each profile was interpolated through a non-linear Boltzmann fit curve with the Mathematica® software. A few traverses done at angles smaller than 90° to the compositional boundary interface were corrected by multiplying the distance values by the sinus of the traverse angle relative to the vertical on the interface. Our preliminary

  14. Processes and timescales of magma evolution prior to the Campanian Ignimbrite eruption (Campi Flegrei, Italy)

    NASA Astrophysics Data System (ADS)

    Arienzo, Ilenia; Heumann, Arnd; Wörner, Gerhard; Civetta, Lucia; Orsi, Giovanni

    2011-06-01

    The Campi Flegrei caldera collapsed 39 ka in the Neapolitan area (southern Italy) after the Campanian Ignimbrite eruption. This eruption, recognized as the largest and the most cataclysmic volcanic event in the Mediterranean area over the past 200 ka, extruded not less than 300 km 3 of trachytic magma. Controversy exists over the timescales required to assemble such large volume of silicic melt and thus whether large magmatic reservoirs can actually persist below active volcanic systems over prolonged periods of time. Uranium-series analyses have been performed on Campanian Ignimbrite whole-rocks, glass matrixes and separated minerals, and the obtained results have been interpreted in combination with data on Sr, Nd, and Pb isotopes from literature. The compositionally most evolved sample which is most radiogenic with respect to Sr isotopes records a reference age of 71 ka. By contrast, U-Th internal isochrones of the three compositionally least evolved samples give identical initial Th isotope ratios and yield consistent ages predating the eruption by up to 6.4 ka. The highest Pb and Nd isotopic ratios and 230Th/ 232Th activity ratios together with the oldest reference age of the most evolved samples suggest the existence of a resident magma body possibly related to a magmatic system that is known to have fed earlier magmatic activity in the Campi Flegrei area. Conversely, the younger age of the least evolved and least radiogenic magma dates the crystallization/differentiation event of a chemically and isotopically new magma batch entering the reservoir of the resident magma some few thousand years before the cataclysmic eruption. Therefore, the time preceding this large caldera-forming eruption during which the large volume of Campanian Ignimbrite magma assembled and mixed is 6.4 ± 2.1 ka.

  15. A detailed study of the site effects in the volcanic area of Campi Flegrei using empirical approaches

    NASA Astrophysics Data System (ADS)

    Tramelli, Anna; Galluzzo, Danilo; Del Pezzo, Edoardo; Di Vito, Mauro A.

    2010-08-01

    Campi Flegrei is a highly populated active caldera in the south of Italy. Several hundred thousand people live within this area, which is characterized by seismicity and ground deformation episodes, known as `bradyseism'. For this reason, this area falls into a high-risk category and thus the Italian Civil Defence requires a detailed site-effect estimation. To determine the local amplification of the seismic waves for a high number of sites, we have analysed the seismic recordings of three seismic networks that have been deployed in the Campi Flegrei area over different time periods. The first network was deployed during the bradyseismic crisis of 1982-1984. We selected 22 of the highest magnitude earthquakes that were recorded during this crisis. An additional 22 seismic events were selected from those recorded by the mobile seismic network that has been in operation in the Campi Flegrei area since 2006. The third data set comprises noise recorded by 34 seismic stations that were deployed during the active SERAPIS experiment in 2001 September. The generalized inversion technique and the H/V spectral ratio method were applied to the S waves and coda waves of the earthquakes recorded by the first two seismic networks, to determine the site-transfer functions of the recording stations. The seismic noise recorded by the third network was analysed using the Nakamura's technique. The results show that the high topographical and geological heterogeneity of the sites located inside the caldera has an important influence on the seismic-wave amplification. Consequently, the site-transfer functions can be different even at sites close to each other. The transfer functions of the sites located outside the caldera are much more regular, apparently due to the more regular topography and geology.

  16. Volcanic risk perception in the Campi Flegrei area

    NASA Astrophysics Data System (ADS)

    Ricci, T.; Barberi, F.; Davis, M. S.; Isaia, R.; Nave, R.

    2013-03-01

    The Campi Flegrei which includes part of the city of Naples, is an active volcanic system; its last eruption occurred in 1538 AD. More recently two significant crises occurred between 1969 and 72 and 1982-84 and were accompanied by ground movements (bradyseism) and seismic activity, forcing people of the town of Pozzuoli to be evacuated. Since 1984 development of a volcanic emergency plan has been underway. In 2000 Civil Protection published a risk map which defined the Red Zone, an area highly at risk from pyroclastic flows, which would need to be evacuated before an eruption. The first study to evaluate the volcanic risk perceptions of the people living within the Campi Flegrei area was completed in spring 2006, resulting in the largest sample ever studied on this topic except for one on Vesuvio area residents by Barberi et al. (2008). A 46 item questionnaire was distributed to 2000 of the approximately 300,000 residents of the Campi Flegrei Red Zone, which includes three towns and four neighborhoods within the city of Naples. A total of 1161 questionnaires were returned, for an overall response rate of 58%. Surveys were distributed to junior high and high school students, as well as to adult members of the general population. Results indicated that unlike issues such as crime, traffic, trash, and unemployment, volcanic hazards are not spontaneously mentioned as a major problem facing their community. However, when asked specific questions about volcanic risks, respondents believe that an eruption is likely and could have serious consequences for themselves and their communities and they are quite worried about the threat. Considering the events of 1969-72 and 1982-84, it was not surprising that respondents indicated earthquakes and ground deformations as more serious threats than eruptive phenomena. Of significant importance is that only 17% of the sample knows about the existence of the Emergency Plan, announced in 2001, and 65% said that they have not received

  17. Campi Flegrei Deep Drilling Project and geothermal activities in Campania Region (Southern Italy)

    NASA Astrophysics Data System (ADS)

    De Natale, Giuseppe; Troise, Claudia; Troiano, Antonio; Giulia Di Giuseppe, Maria; Mormone, Angela; Carlino, Stefano; Somma, Renato; Tramelli, Anna; Vertechi, Enrico; Sangianantoni, Agata; Piochi, Monica

    2013-04-01

    The Campanian volcanic area has a huge geothermal potential (Carlino et al., 2012), similar to the Larderello-Radicondoli-Amiata region, in Tuscany (Italy), which has been the first site in the World exploited for electric production. Recently, the Campi Flegrei Deep Drilling Project (CFDDP), sponsored by ICDP and devoted to understand and mitigate the extreme volcanic risk in the area, has also risen new interest for geothermal exploration in several areas of Italy. Following the new Italian regulations which favour and incentivise innovative pilot power plants with zero emission, several geothermal projects have started in the Campania Region, characterized by strict cooperation among large to small industries, Universities and public Research Centers. INGV department of Naples (Osservatorio Vesuviano) has the technical/scientific leadership of such initiatives. Most of such projects are coordinated in the framework of the Regional District for Energy, in which a large part is represented by geothermal resource. Leading geothermal projects in the area include 'FORIO' pilot plant project, aimed to build two small (5 MWe each one) power plants in the Ischia island and two projects aimed to build pilot power plants in the Agnano-Fuorigrotta area in the city of Naples, at the easternmost part of Campi Flegrei caldera. One of the Campi Flegrei projects, 'SCARFOGLIO', is aimed to build a 5 MWe geothermal power plant in the Agnano area, whereas the 'START' project has the goal to build a tri-generation power plant in the Fuorigrotta area, fed mainly by geothermal source improved by solar termodynamic and bio-mass. Meanwhile such projects enter the field work operational phase, the pilot hole drilling of the CFDDP project, recently completed, represents an important experience for several operational aspects, which should contitute an example to be followed by the next geothermal activities in the area. It has been furthermore a source of valuable data for geothermal

  18. Marine geo-hazard in the Campi Flegrei coastal area (Eastern Tyrrhenian sea)

    NASA Astrophysics Data System (ADS)

    Violante, C.; Angelino, A.; Buonocunto, F. P.; di Fiore, V.; Esposito, E.; Molisso, F.; Porfido, S.; Sacchi, M.

    2009-04-01

    The Campi Flegrei (i.e. "burning plains") are located on the eastern Tyrrhenian margin, an area characterized by active tectonics and volcanism since the Pleistocene. It is a densely urbanized coastal zone, including the bay of Pozzuoli, Procida and Ischia islands, where documented human activities have been developing for more than two thousand years. In the Pozzuoli area two major periods of eruptive volcanic activity occurred from 10.0 to 8.0 ky B.P and 4.5 to 3.7 ky B.P. These periods were followed by the September 1538 Monte Nuovo eruption. Numerous monogenic volcanoes formed close to the shoreline and volcanic debris interpreted as submarine counterpart of subaerial flow and surge, has been detected offshore. The most recent volcanic activity on Ischia island starts around 10.0 ky B.P. to which associates several eruptive centres mostly located in the western sector. The last eruption dates back to Arso flow in 1302. Nevertheless the landscape of Ischia is dominated by Mount Epomeo in the central part of the island, which is the highest peak (788 m). It is a volcano-tectonic structure that raised above sea level between 33 and 28 ka BP, due to the intrusion of magma at shallow depth. In the Campi Flegrei, magma-related activity is testified by extensive hydrothermalism, and recent episodes (1883 on Ischia, and 1970-71 and 1982-84 on Pozzuoli coast) of shallow seismicity and ground deformation, exceeding rates of 100 cm/year in the years 1983-1984. Volcanic and volcano-tectonic activity mainly associate with inferred resurgent calderas whose uplift have caused mass wasting phenomena, faulting and erosional activity both on land and at sea. Major geohazard features resulting from marine geophysical and sedimentological investigations include (1) extensive landslide deposits and associated hummocky topographies off Ischia volcanic island, (2) seafloor instabilities in the form of creep/slump, channelled sediment flow and deep sedimentary fan, (3) superficial

  19. Advanced DInSAR analysis at Campi Flegrei and Vesuvius, Italy

    NASA Astrophysics Data System (ADS)

    Tiampo, K. F.; Camacho, A. G.; Fernandez, J.; Gonzalez, P. J.; Samsonov, S. V.

    2015-12-01

    at Campi Flegrei involve large, extended sources in a layered hydrothermal system whose location is controlled by the caldera structure and stratigraphy. The temporal resolution of MSBAS approaches that of GPS daily timeseries, with superior precision and spatial resolution, making it an excellent alternative for volcano monitoring.

  20. The permeability and elastic moduli of tuff from Campi Flegrei, Italy: implications for ground deformation modelling

    NASA Astrophysics Data System (ADS)

    Heap, M. J.; Baud, P.; Meredith, P. G.; Vinciguerra, S.; Reuschlé, T.

    2014-01-01

    The accuracy of ground deformation modelling at active volcanoes is a principal requirement in volcanic hazard mitigation. However, the reliability of such models relies on the accuracy of the rock physical property (permeability and elastic moduli) input parameters. Unfortunately, laboratory-derived values on representative rocks are usually rare. To this end we have performed a systematic laboratory study on the influence of pressure and temperature on the permeability and elastic moduli of samples from the two most widespread lithified pyroclastic deposits at the Campi Flegrei volcanic district, Italy. Our data show that the water permeability of Neapolitan Yellow Tuff and a tuff from the Campanian Ignimbrite differ by about 1.5 orders of magnitude. As pressure (depth) increases beyond the critical point for inelastic pore collapse (at an effective pressure of 10-15 MPa, or a depth of about 750 m), permeability and porosity decrease significantly, and ultrasonic wave velocities and dynamic elastic moduli increase significantly. Increasing the thermal stressing temperature increases the permeability and decreases the ultrasonic wave velocities and dynamic elastic moduli of the Neapolitan Yellow Tuff; whereas the tuff from the Campanian Ignimbrite remains unaffected. This difference is due to the presence of thermally unstable zeolites within the Neapolitan Yellow Tuff. For both rocks we also find, under the same pressure conditions, that the dynamic (calculated from ultrasonic wave velocities) and static (calculated from triaxial stress-strain data) elastic moduli differ significantly. The choice of elastic moduli in ground deformation modelling is therefore an important consideration. While we urge that these new laboratory data should be considered in routine ground deformation modelling, we highlight the challenges for ground deformation modelling based on the heterogeneous nature (vertically and laterally) of the rocks that comprise the caldera at Campi

  1. Significance of the 1982-2014 Campi Flegrei seismicity: Preexisting structures, hydrothermal processes, and hazard assessment

    NASA Astrophysics Data System (ADS)

    Di Luccio, F.; Pino, N. A.; Piscini, A.; Ventura, G.

    2015-09-01

    We find that the double-difference relocated seismicity, which occurred over the last 30 years at Campi Flegrei, was triggered by the uprising of fluids preferentially concentrated along onshore and offshore NW striking preexisting caldera faults. Focal volumes of the 2005-2014 seismicity do not overlap that of the 1982-1984 period, when a major uplift of 1.8 m occurred in the central sector of the caldera. This indicates a transition from an elastic to a plastic behavior due to fluid saturation and heating of the rocks in the hydrothermal reservoir. The 2012-2014 deeper earthquakes are located in a low VP/VS zone at the western boundary of the hydrothermal reservoir, where a volume increase from a magmatic body at 3.5 km depth has been recognized. The progressive rheological change from elastic to plastic in the upper 4 km of the crust implies that a slow upward migration of magma may not necessarily be preceded by earthquakes or swarms.

  2. The Campi Flegrei caldera-hosted high-temperature and high-saline geothermal system in the Southern Italy: the implication of the geothermal resource as derived by the present state of the knowledge through 70 years of volcanological, structural, petrolog

    NASA Astrophysics Data System (ADS)

    Piochi, M.; Di Vito, M. A.; Mormone, A.; De Natale, G.; Tramelli, A.; Troise, C.; Carlino, S.

    2012-04-01

    The Campi Flegrei caldera (Italy) hosts a geothermal system characterized by: i) high thermal gradient (temperature up to 420°C at 3050 m b.s.l.), ii) high temperature (up to ~90-150°C at very shallow depth) fumaroles, iii) multiple meteoric to brine (TDS up to 33 g•l-1; temperature up to 95 °C) aquifers and iv) at least 1500 tonnes per day of CO2 emissions. This area is highly urbanized despite the repeated occurrence of ground deformation phenomena accompanied by seismicity with volcano-tectonic and long-period micro-earthquakes. The caldera has been widely studied by geologist and geophysicists. In particular, since '40s, the caldera has drawn scientific interest for its geothermal capability inducing the companies AGIP (Azienda Geologica Italiana Petroli) and SAFEN (Società Anonima Forze Endogene Napoletane) to drill more than one hundred 80-to-3100 m deep wells. However this experience did not reach the exploitation phase due to technological and communication problems. The geothermal potential (thermal and electric) is evaluated of about 6 GWy. The recent Campi Flegrei Deep Drilling Project [De Natale and Troise, 2011], sponsored by the International Continental Scientific Drilling Program, foresees the realization of medium-to-deep wells in the caldera with the ambition of stimulating interest in geothermal energy exploitation and technology development and, in addition of installing downhole monitoring systems. The geological knowledge of the area is the benchmark for the drilling sites selection. We reconstructed a multi-disciplinary conceptual model updated on the basis of the most recent scientific results and findings. In particular, the constrains (the most important are listed in brackets) comes from: i) boreholes (litho-stratigraphy, aquifer location, depth-related temperature), ii) fieldwork (stratigraphy, location of structural fractures and eruption vents), iii) petrology and melt inclusions (pressure and temperature of magma with

  3. The Rock Physics of Fiber-Reinforced Rocks Helps Explain Uplifts at Campi Flegrei Volcano-Hydrothermal System

    NASA Astrophysics Data System (ADS)

    Vanorio, T.; Kanitpanyacharoen, W.

    2015-12-01

    The caldera of Campi Flegrei is one of the active volcano-hydrothermal systems of the Mediterranean region experiencing notable unrest episodes in a densely populated area. One peculiar trait characterizes the unrest of this system: the ability of withstanding large uplifts before setting off a swarm of microeartquakes. Therefore, one core question is how the subsurface rocks of Campi Flegrei withstand such a large strain and have high strength. The rock physics analysis of well cores up to 3 km provides evidence for the existence of two horizons, above and below the seismogenic area, underlying a natural, coupled process. The basement is a calc-silicate rock housing hydrothermal decarbonation reactions, which provide lime-rich fluids. The impermeable caprock above the seismogenic area has a pozzolanic composition and a fibril-rich matrix made of intertwining filaments of ettringite and tobemorite, resulting from lime-pozzolanic reactions. These findings provide evidence for a natural process reflecting that of the engineering of the Roman concrete. The formation of fibrous minerals by intertwining filaments confers shear and tensile strength to the caprock, contributing to its ductility and increased resistance to fracture. The importance of these findings lies not only on the fibrous and compositionally nature of the caprock but also on its possible physicochemical deterioration. Given the P-T-XCO2 conditions regulating the decarbonation reactions, possible influx of new brine into the Campi Flegrei system dilutes the existing CO2, thus triggering further decarbonation reaction. This leads to the formation of additional CO2, methane, and steam. As these gases rise toward the surface, they are halted by the natural concrete-like layer, which would lead to pore pressure increase and subsequent ground deformations.

  4. Permeability of Campi Flegrei magmas: examples from the Campanian Ignimbrite and Monte Nuovo eruptions

    NASA Astrophysics Data System (ADS)

    Polacci, Margherita; Bouvet de Maisonneuve, Caroline; Giordano, Daniele; Piochi, Monica; Mancini, Lucia; Degruyter, Wim; Bachmann, Olivier

    2014-05-01

    We performed permeability measurements on trachy-phonolitic pyroclastic products from the Campanian Ignimbrite and Monte Nuovo, two explosive eruptions from the active Campi Flegrei caldera, Southern Italy. Viscous (Darcian) permeability spans a wide range between 1.22x10-14 and 9.31x10-11 m2. Inertial (non-Darcian) permeability follows the same trend as viscous permeability: it increases as viscous permeability increases, highlighting the strong direct correlation between these two parameters. We observe that vesicularity does not exert a first order control on permeability: the Monte Nuovo scoria clasts are the most permeable samples but not the most vesicular; pumice clasts from the Campanian Ignimbrite proximal facies, whose vesicularity is comparable with that of Monte Nuovo scoriae, are instead the least permeable. In addition, we find that sample geometry exhibits permeability anisotropy as samples oriented parallel to vesicle elongation are more permeable than those oriented perpendicular. We compare our results with permeability values of volcanic products from effusive and explosive activity, and discuss the role of melt viscosity and crystallinity on magma permeability.

  5. Assessing pyroclastic density current dynamics and hazard of Plinian events at Campi Flegrei (Italy) by using 3D numerical simulations

    NASA Astrophysics Data System (ADS)

    Esposti Ongaro, T.; Neri, A.; Todesco, M.

    2012-04-01

    Campi Flegrei is a densely populated widespread caldera located near the city of Naples. Current evaluation of volcanic hazard include the probable generation of pyroclastic density currents (PDC) produced by explosive events of variable size and uncertain vent location. In this study we investigate the dynamics and hazard of PDC produced by the partial collapse of the volcanic column by using the 3D transient multiphase flow model PDAC (Esposti Ongaro et al., Parallel Computing, 2007). The model allows to describe the temporal and spatial evolution of the stratified PDC by accounting for the multiparticle nature of the flow and the complex topography of the caldera. Employed eruptive intensity and pyroclast properties are representative of magmatic phases of the Agnano Monte Spina (AMS, 4100 BP) Plinian eruption, the largest explosive event of the last cycle of activity of the caldera. Eruptive centers are supposed to be located in the north-eastern part of the caldera, the area with the largest number of past vents. Several simulations were performed considering different collapsing regimes, flow conditions at the source and vent locations. Results illustrate the complex dynamics of flow propagation in the caldera settings and quantify the associated hazards. Fountain instabilities, recycling of collapsed material into the jet caused by the caldera walls, triggering of thermals and co-ignimbrite clouds by topographic reliefs, flow decoupling between dense and dilute streams, and generation of backflows are some of the processes simulated. The areas invaded by the PDC result affected by the inner topography of the caldera and therefore largely influenced by the assumed location of the vent. PDC result mostly confined by the outer caldera rims although they appear able to overcome Posillipo Hill and affect the eastern portions of the city of Naples. Comparisons with reconstructions of the AMS event are also discussed.

  6. Sr-O isotope systematics in the Campi Flegrei magma systems

    NASA Astrophysics Data System (ADS)

    Wörner, Gerhard; Iovine, Raffaella; Carmine Mazzeo, Fabio; D'Antonio, Massimo; Arienzo, Ilenia; Civetta, Lucia; Orsi, Giovanni

    2016-04-01

    a large range mostly between 7 and 10 ‰ VSMOW, maximum and minimum values reach from ~11 to ~6 ‰ VSMOW. Our data obtained so far show compositions that are very different from typical mantle values and that span a very large range towards heavy δ18O values compared to other magmatic compositions from the Italian Peninsula. We compare our clinopyroxene and olivine data with published clinopyroxene and olivine O-isotope data from other Italian volcanic centers (Alban Hills, Mts. Ernici, Ischia, Mt. Vesuvius, Aeolian Islands, Tuscany and Sardinia) and from subduction zones worldwide (Kamchatka, Lesser Antilles, Indonesia and Central Andean ignimbrites). Distinct trends and sources are recognized: (1) serpentinized mantle (Kamchatka), (2) sediment-enrichment in the mantle source (Indonesia, Vesuvius), (3) magma assimilation by old radiogenic continental crust (Alban Hills, Tuscany, Ischia), (4) assimilation by mafic crust (Andes). Sr-O-isotope values of Campi Flegrei and Vesuvius magmas fall on the same vertical trend in Sr-O isotope space that deviates profoundly from all other subduction-related magmas. This indicates that magmas are derived from (a) a mantle source variably modified by pelagic sediments (as for Vesuvius) that were later (b) assimilated by highly δ18O-enriched crustal material that did not further significantly affect the Sr-isotope composition. From Sr-O isotope relations, this crustal signal could be introduced through interaction with Mesozoic limestone and/or low-T altered volcanic material from previous volcanic activity in the Campi Flegrei caldera.

  7. The Breccia Museo formation, Campi Flegrei, southern Italy: Geochronology, chemostratigraphy and relationship with the Campanian Ignimbrite eruption

    USGS Publications Warehouse

    Fedele, L.; Scarpati, C.; Lanphere, M.; Melluso, L.; Morra, V.; Perrotta, A.; Ricci, G.

    2008-01-01

    The Breccia Museo is one of the most debated volcanic formations of the Campi Flegrei volcanic district. The deposit, made up of six distinctive stratigraphic units, has been interpreted by some as the proximal facies of the major caldera-forming Campanian Ignimbrite eruption, and by others as the product of several, more recent, independent and localized events. New geochemical and chemostratigraphical data and Ar - Ar age determinations for several units of the Breccia Museo deposits (???39 ka), correlate well with the Campanian Ignimbrite-forming eruption. The chemical zoning of the Breccia Museo deposits is interpreted here to be a consequence of a three-stage event that tapped a vertically zoned trachytic magma chamber. ?? Springer-Verlag 2008.

  8. Trace element partitioning between clinopyroxene and trachy-phonolitic melts: A case study from the Campanian Ignimbrite (Campi Flegrei, Italy)

    NASA Astrophysics Data System (ADS)

    Mollo, S.; Forni, F.; Bachmann, O.; Blundy, J. D.; De Astis, G.; Scarlato, P.

    2016-05-01

    The partitioning of trace elements between crystals and melts provides an important petrogenetic tool for understanding magmatic processes. We present trace element partition coefficients measured between clinopyroxene phenocrysts and trachy-phonolitic magmas at the Campi Flegrei (Italy), whose late Quaternary volcanism has been characterized by two major caldera-forming events (Campanian Ignimbrite at ~ 39 ka, and Neapolitan Yellow Tuff at ~ 15 ka). Our data indicate that the increase of trivalent rare earth elements and yttrium into the crystal lattice M2 site is facilitated by the charge-balancing substitution of Si4 + with Al3 + on the tetrahedral site. Higher concentrations of tetravalent and pentavalent high field strength elements on the M1 site are also measured when the average charge on this site is increased by the substitution of divalent cations by Alvi. In contrast, due to these charge balance requirements, divalent transitional elements become less compatible within the crystal lattice. On the basis of the lattice strain theory, we document that the incorporation of rare earth elements and yttrium in clinopyroxene is influenced by both compositional and physical parameters. Data from this study allow to update existing partitioning equations for rare earth elements in order to construct a self-consistent model for trachy-phonolitic magmas based on the lattice strain theory. The application of this model to natural products from the Campanian Ignimbrite, the largest caldera-forming eruption at the Campi Flegrei, reveals that the complex rare earth element pattern recorded by the eruptive products can be successfully described by the stepwise fractional crystallization of clinopyroxene and feldspar where the clinopyroxene-melt partition coefficient changes progressively as a function of the physicochemical conditions of the system.

  9. Steam-driven explosions at Solfatara volcano, Campi Flegrei: new insights from an experimental approach

    NASA Astrophysics Data System (ADS)

    Montanaro, Cristian; Bettina, Scheu; Klaus, Mayer; Giovanni, Orsi; Moretti, Roberto; Dingwell Donald, B.

    2014-05-01

    The Solfatara crater is a highly active hydrothermal site located in the central part of the Campi Flegrei Caldera (south-central Italy). Campi Flegrei is one of most active calderas in the world, characterized by intense unrest episodes involving massive ground deformation, high seismicity and continuous gas emissions from the Solfatara crater. These episodes are thought to be driven by the complex interaction between a deep magmatic source and a shallow hydrothermal system [Orsi et al., 1999]. The most recent unrest episode started in 2006, exhibiting an increase in the degassing activity, especially in the Pisciarelli field (SE of Solfatara crater). In such an active magmato-hydrothermal system steam-driven explosive eruptions (phreatic or hydrothermal) are a likely potential hazard - one that is difficult to predict in terms of timing and magnitude. Here we present an experimental approach based on a rapid decompression experiments to investigate the different scenarios likely for steam explosions in the Solfatara area. The experimental setup produces fragmentation precipitated by the release of Argon gas overpressure and assisted by water-to-steam flashing within the connected pore space of the tested samples. We have investigated varying P-T conditions and varying gas-to-liquid ratios. The experimental conditions used in this case study mimic those of a mixing zone present at the base of the hydrothermal system below Solfatara at a depth between 1000 and 1500 m (15-25 MPa) and temperatures from 270°C to 300°C [Caliro et al., 2007]. Neapolitan Yellow Tuff is used as sample material for the study as it is the stratigraphic unit expected at this depth in this region [Orsi et al. 1996]. Sensors monitor temperature and pressure evolution during the experiments, enabling the determination of the speed of fragmentation. A high-speed camera (10000 fps) is used to measure the ejection velocities of the gas-particle mixtures. The fragments generated are recovered and

  10. RICEN : Repeated InduCed Earthquakes and Noise at Solfatara, Campi Flegrei, Italy.

    NASA Astrophysics Data System (ADS)

    Festa, G.; Serra, M.; Amoroso, O.; Bruno, P. P.; Pilz, M.; Roux, P.; Russo, G.; Woith, H.; Zollo, A.

    2015-12-01

    RICEN is a series of three experiments whose goal is to study the changes in the elastic properties of the medium at small scales through repeated observations over time through the recognition of changes in seismic records acquired at a dense network. The investigation area is the Solfatara, a volcano in the Campi Flegrei caldera, characterized by an intense hydrothermal shallow activity. RICEN sampled the investigated area with passive and active seismic. For the active part, acquisition was performed by shooting the area with the MiniVIB and recording the ground motion at 240 seismic stations, placed on a regular in front of the Fangaia. Additional two 1D orthogonal profiles were acquired with sensors located at 2m distance. Ambient noise was instead recorded in the area for several days, including also the active part. Data from the first experiment and from the two profiles were processed and analysed. We obtained 3D P and S wave tomographic models of the subsoil covered by the grid. The P wave velocity model was obtained from a linearized inversion of P wave first arrivals, manually picked on cross-correlated minimum phase traces. The S model was obtained through the inversion of the phase and group velocities dispersion curves, measured on 96 overlapping sub-grids and for each of them assuming a 1D propagation medium. Dispersion curves were also available from ambient noise analysis. Moreover a 2D long profile was analysed to retrieve a tomographic 2D model of the area and the section migrated at depth to retrieve the bottom of the crater in the area. Finally statistical properties of the scattered field, such as the mean free path, were obtained from the analysis of the coherent vs incoherent wavefield and the enhanced backscattering. Velocity contrasts and the properties of the scattered field indicate a clear separation between gas rich and water rich regions.

  11. A strongly heterogeneous hydrothermal area imaged by surface waves: the case of Solfatara, Campi Flegrei, Italy.

    NASA Astrophysics Data System (ADS)

    Serra, Marcello; Festa, Gaetano; Roux, Philippe; Gresse, Marceau; Vandemeulebrouck, Jean; Zollo, Aldo

    2016-04-01

    We investigated the shallow structure of the Solfatara, a volcano within the Campi Flegrei caldera, southern Italy, using surface waves as a diagnostic tool. We analyzed data collected during the RICEN campaign, where a three-dimensional active seismic experiment was performed on a dense regular grid of 90 m × 115 m using a Vibroseis as the seismic source. After removal of the source time function, we analyzed the surface-wave contribution to the Green's function. Here, a one-dimensional approximation can hold for subgrids of 40 m × 40 m. Moreover, we stacked all of the signals in the subgrid according to source-receiver distance bins, despite the absolute location of the source and the receiver, to reduce the small scale variability in the data. We then analyzed the resulting seismic sections in narrow frequency bands between 7 Hz and 25 Hz. We obtained phase and group velocities from a grid search, and a cost function based on the spatial coherency of both the waveforms and their envelopes. We finally jointly inverted the dispersion curves of the phase and group velocities to retrieve a one-dimensional S-wave model local to the subgrid. Together, the models provided a three-dimensional description of the S-wave model in the area. We found that the maximum penetration depth is 15 m. In the first 4 m, we can associate the changes in the S-wave field to the temperature gradient, while at greater depths, the seismic images correlate with the resistivity maps, which indicate the water layer close to the Fangaia area, and an abrupt variation moving toward the north-east.

  12. A strongly heterogeneous hydrothermal area imaged by surface waves: the case of Solfatara, Campi Flegrei, Italy

    NASA Astrophysics Data System (ADS)

    Serra, Marcello; Festa, Gaetano; Roux, Philippe; Gresse, Marceau; Vandemeulebrouck, Jean; Zollo, Aldo

    2016-06-01

    We investigated the shallow structure of the Solfatara, a volcano within the Campi Flegrei caldera, southern Italy, using surface waves as a diagnostic tool. We analysed data collected during the RICEN campaign, where a 3-D active seismic experiment was performed on a dense regular grid of 90 m × 115 m using a Vibroseis as the seismic source. After removal of the source time function, we analysed the surface wave contribution to the Green's function. Here, a 1-D approximation can hold for subgrids of 40 m × 40 m. Moreover, we stacked all of the signals in the subgrid according to source-receiver distance bins, despite the absolute location of the source and the receiver, to reduce the small-scale variability in the data. We then analysed the resulting seismic sections in narrow frequency bands between 7 and 25 Hz. We obtained phase and group velocities from a grid search, and a cost function based on the spatial coherence of both the waveforms and their envelopes. We finally jointly inverted the dispersion curves of the phase and group velocities to retrieve a 1-D S-wave model local to the subgrid. Together, the models provided a 3-D description of the S-wave model in the area. We found that the maximum penetration depth is 15 m. In the first 4 m, we can associate the changes in the S-wave field to the temperature gradient, while at greater depths, the seismic images correlate with the resistivity maps, which indicate the water layer close to the Fangaia area and an abrupt variation moving towards the northeast.

  13. Electromagnetic outline of the Solfatara-Pisciarelli hydrothermal system, Campi Flegrei (Southern Italy)

    NASA Astrophysics Data System (ADS)

    Troiano, Antonio; Giulia Di Giuseppe, Maria; Patella, Domenico; Troise, Claudia; De Natale, Giuseppe

    2014-05-01

    We describe the results from a combined CSAMT and MT survey carried out in the Solfatara-Pisciarelli area, located in the central part of the Campi Flegrei composite caldera, west of Naples, Southern Italy. The Solfatara-Pisciarelli area represents the most active zone within the CF area, in terms of hydrothermal manifestations and local seismicity. Since 1969, the caldera is experiencing ground deformation, seismicity and geochemical fluid changes, which are particularly evident in this area. A 1 km long, nearly W-E directed CSAMT-MT profile crossing the fumaroles field was carried out with the aim of deducting an EM model of the structural setting of the hydrothermal system in the first 3 km depth. An interpretation of the EM modelled section is given in this paper, taking advantage from already existing seismic, gravity and geochemical data in the same area. Three well distinct EM zones have been outlined. The first EM zone is a very shallow, electrically conductive body localized beneath the westernmost segment of the profile, which, within a short distance of about 100 m, dips westwards from near surface down to some hundred metres depth. Mostly accounting for the very low resistivity (1-10 Ωm) and the exceedingly high values of vP/vS (>4), this shallow zone has been ascribed to a water-saturated, high-pressurized geothermal reservoir. The second EM zone, which has been localized below the west-central portion of the EM transect, appears as a composite body made of a nearly vertical plumelike structure that escapes at about 2.25 km depth from the top edge of the east side of a presumably horizontal platelike body. The plumelike structure rises up to the free surface in correspondence of the fumaroles field, whereas the platelike structure deepens at least down to the 3 km of maximum EM exploration depth. The combined interpretation of resistivity, wave velocity, gravity and geochemical data indicates the plumelike portion is likely associated with a steam

  14. The origin of a zoned ignimbrite: insights into the Campanian Ignimbrite magma chamber (Campi Flegrei, Italy)

    NASA Astrophysics Data System (ADS)

    Forni, Francesca; Bachmann, Olivier; Mollo, Silvio; De Astis, Gianfilippo

    2016-04-01

    The Campanian Ignimbrite (CI; Campi Flegrei, Italy), dated at 39 ka, is a widespread pyroclastic sequence emplaced during a cataclysmic caldera-forming eruption fed by trachytic to phonolitic magmas. The CI pyroclastic sequence is famous for its remarkable geochemical gradients,attributed to the presence of a vertically zoned magma chamber. Combining bulk-rock data with detailed phenocrysts and matrix glass analyses from well characterized stratigraphic units, we investigate the relatioships between such chemical zoning and the crystallinity variations observed along the CI pyroclastic sequence. Using geothermometers and hygrometers specifically calibrated for alkaline magmas, we reconstruct the reservoir storage conditions, revealing the presence of gradients in temperature and magma water content. In particular, we observe an increase in crystallinity and temperature and a decrease in magma evolution and water content from the bottom to the top of the sequence. We interpret these features as the result of protracted fractional crystallization leading to the formation of a cumulate crystal mush at the base of the eruptible reservoir, from which highly evolved, crystal-poor, water-rich and relatively cold melts were separated. The extracted melts, forming a buoyant, easily eruptible cap at the top of the magma chamber, fed the initial phases of the eruption, until caldera collapse and eruption of the deeper, more crystalline part of the system. This late-erupted, crystal-rich material, represents remobilized portions of the cumulate crystal mush, rejuvenated after mafic recharge. Our interpretation is supported by: 1) the bulk-rock positive Eu anomalies and the high Ba and Sr contents observed in the crystal-rich units, implying feldspar accumulation; 2) the positive Eu anomalies in the matrix glass of the crystal-rich units, testifying to the presence of liquid derived from partial melting of low temperature mineral phases within the crystal mush (feldspars and

  15. The origin of a zoned ignimbrite: Insights into the Campanian Ignimbrite magma chamber (Campi Flegrei, Italy)

    NASA Astrophysics Data System (ADS)

    Forni, Francesca; Bachmann, Olivier; Mollo, Silvio; De Astis, Gianfilippo; Gelman, Sarah E.; Ellis, Ben S.

    2016-09-01

    Caldera-forming eruptions, during which large volumes of magma are explosively evacuated into the atmosphere from shallow crustal reservoirs, are one of the most hazardous natural events on Earth. The Campanian Ignimbrite (CI; Campi Flegrei, Italy) represents a classical example of such events, producing a voluminous pyroclastic sequence of trachytic to phonolitic magma that covered several thousands of squared kilometers in the south-central Italy around 39 ka ago. The CI deposits are known for their remarkable geochemical gradients, attributed to eruption from a vertically zoned magma chamber. We investigate the relationships between such chemical zoning and the crystallinity variations observed within the CI pyroclastic sequence by combining bulk-rock data with detailed analyses of crystals and matrix glass from well-characterized stratigraphic units. Using geothermometers and hygrometers specifically calibrated for alkaline magmas, we reconstruct the reservoir storage conditions, revealing the presence of gradients in temperature and magma water content. In particular, we observe a decrease in crystallinity and temperature and an increase in magma evolution and water content from the bottom to the top of the magma chamber. We interpret these features as the result of protracted fractional crystallization leading to the formation of a cumulate crystal mush at the base of the eruptible reservoir, from which highly evolved, crystal-poor, water-rich and relatively cold melts were separated. The extracted melts, forming a buoyant, easily eruptible cap at the top of the magma chamber, fed the initial phases of the eruption, until caldera collapse and eruption of the deeper more crystalline part of the system. This late-erupted, crystal-rich material represents remobilized portions of the cumulate crystal mush, partly melted following hotter recharge. Our interpretation is supported by: 1) the positive bulk-rock Eu anomalies and the high Ba and Sr contents observed in

  16. The physical and chemical properties of tuffs from Campi Flegrei (Italy): the influence of thermal and stress-induced microcracking

    NASA Astrophysics Data System (ADS)

    Heap, M. J.; Laumann, A.; Hess, K.; Lavallee, Y.; Dingwell, D. B.; Meredith, P. G.; Orsi, G.

    2010-12-01

    Campi Flegrei caldera (Italy), 6km in diameter, poses great threat to densely-populated region in and surrounding Naples. Uplift, a result of the intrusion of magma, has been systematically recorded since the nineteenth century and indicates three major episodes of uplift, the latter of which continues to this day. Studies have postulated that this uplift is expected to continue for another 80-90 years and possibly increasing the likelihood of eruption. The majority of erupted material at Campi Flegrei is in the form of tuff. However, only recently have studies started to investigate how fundamental physical properties of tuff can alter with depth and temperature. Such properties may not only unravel key information on fluid and gas flow as well as seismic activity within the caldera, but they are essential parameters for ground deformation modelling and tomography used to monitor magma movement at depth. Here we present a comprehensive experimental dataset on how both the physical and chemical properties of three representative tuffs from the Campi Flegrei caldera change with increasing heat-treatment temperature (up to 1000oC). The tuffs are the grey Campanian Ignimbrite (CI), Neapolitan Yellow Tuff (NYT) and Piperno Tuff (PT). Thermal cracking analysis, using a fast-acquisition acoustic emission system, demonstrates that a substantial thermal microcrack population is produced in tuff upon heating to 1000oC and initiates after only a couple of hundred degrees. However, despite this, porosity change with increasing temperature is almost negligible and is most likely to be due to their already impressive initial connected porosity (ranging from 45-55%). Permeability measurements show that CI is two orders of magnitude more permeable than its counterparts (about 1 x10-10 m2 compared to about 1 x 10-12 m2). However, interestingly, CI does not show any increase in permeability with heat-treatment temperature, in contrast to NYT and PT who both show an increase of an

  17. Detailed investigation of Long-Period activity at Campi Flegrei by Convolutive Independent Component Analysis

    NASA Astrophysics Data System (ADS)

    Capuano, P.; De Lauro, E.; De Martino, S.; Falanga, M.

    2016-04-01

    This work is devoted to the analysis of seismic signals continuously recorded at Campi Flegrei Caldera (Italy) during the entire year 2006. The radiation pattern associated with the Long-Period energy release is investigated. We adopt an innovative Independent Component Analysis algorithm for convolutive seismic series adapted and improved to give automatic procedures for detecting seismic events often buried in the high-level ambient noise. The extracted waveforms characterized by an improved signal-to-noise ratio allows the recognition of Long-Period precursors, evidencing that the seismic activity accompanying the mini-uplift crisis (in 2006), which climaxed in the three days from 26-28 October, had already started at the beginning of the month of October and lasted until mid of November. Hence, a more complete seismic catalog is then provided which can be used to properly quantify the seismic energy release. To better ground our results, we first check the robustness of the method by comparing it with other blind source separation methods based on higher order statistics; secondly, we reconstruct the radiation patterns of the extracted Long-Period events in order to link the individuated signals directly to the sources. We take advantage from Convolutive Independent Component Analysis that provides basic signals along the three directions of motion so that a direct polarization analysis can be performed with no other filtering procedures. We show that the extracted signals are mainly composed of P waves with radial polarization pointing to the seismic source of the main LP swarm, i.e. a small area in the Solfatara, also in the case of the small-events, that both precede and follow the main activity. From a dynamical point of view, they can be described by two degrees of freedom, indicating a low-level of complexity associated with the vibrations from a superficial hydrothermal system. Our results allow us to move towards a full description of the complexity of

  18. Electromagnetic outline of the Solfatara-Pisciarelli hydrothermal system, Campi Flegrei (Southern Italy)

    NASA Astrophysics Data System (ADS)

    Troiano, A.; Di Giuseppe, M. G.; Patella, D.; Troise, C.; De Natale, G.

    2014-05-01

    We describe the results from a combined controlled source audio magnetotelluric (CSAMT) and natural source magnetotelluric (MT) survey carried out in the Solfatara-Pisciarelli (S-P) area, located in the central part of the Campi Flegrei (CF) composite caldera, west of Naples, Southern Italy. The S-P area represents the most active zone within the CF caldera, in terms of hydrothermal manifestations and local seismicity. Since 1969, the CF caldera is experiencing ground deformation, seismicity and geochemical fluid changes, which are particularly evident in the S-P area. A 1 km long, nearly W-E directed CSAMT-MT profile crossing the fumarole field was carried out in the S-P area with the aim of deducting a resistivity model of the structural setting of the hydrothermal system in the first 3 km depth. An interpretation of the modelled section across the profile is given in this paper, taking advantage from already existing seismic, gravity and geochemical data in the same area. Three well distinct zones have been outlined. The first zone is a very shallow, electrically conductive body localized beneath the westernmost segment of the profile, which, within a short distance of about 100 m, dips westwards from near surface down to some hundred metres in depth. Mostly accounting for the very low resistivity (1-10 Ω m) and the exceedingly high values of vP/vS (> 4), this shallow zone has been ascribed to a water-saturated, high-pressurized geothermal reservoir. The second zone, which has been localized below the west-central portion of the CSAMT-MT transect, appears as a composite body made up of a nearly vertical plumelike structure that escapes at about 2.25 km depth from the top edge of the east side of a presumably horizontal platelike body. The plumelike structure rises up to the free surface in correspondence of the fumarole field, whereas the platelike structure deepens at least down to the 3 km of maximum exploration depth. The combined interpretation of

  19. Mineralogical, geochemical and isotopic features of tuffs from the CFDDP drill hole: Hydrothermal activity in the eastern side of the Campi Flegrei volcano (southern Italy)

    NASA Astrophysics Data System (ADS)

    Mormone, A.; Troise, C.; Piochi, M.; Balassone, G.; Joachimski, M.; De Natale, G.

    2015-01-01

    A 506 m drill-hole has been recently drilled in the framework of the Campi Flegrei Deep Drilling Project (CFDDP) and the International Continental Scientific Drilling Program (ICDP) with the intention of coring the subsurface in the eastern sector of the Campi Flegrei caldera. The borehole, located in the western district of the Neapolitan city (Bagnoli Plain) 3 km to the east of the most active volcanic area and about 5 m above sea level, is now targeted for monitoring purposes. This paper reports the results obtained from the analysis of two short cores collected at depths of - 443 and - 506 m below the ground level. The cores sampled two pre-caldera tuffs. Observations performed by optical and scanning electron microscopy, energy dispersive spectroscopy and powder X-ray diffraction were used to achieve data on the primary lithology, both primary and secondary mineralogical assemblages, and the relationship between texture and secondary mineralization. Sr isotope ratios were determined on selected primary feldspars, whereas δ13C and δ18O analyses were performed on carbonates from veins and filled-voids in tuffs. Our results provide information on the hydrothermal system in the eastern sector of the caldera that was not among the goals in the previous drilling programs. Secondary mineralization suggests a saline hydrothermal environment characterized by fluids that progressively evolved from boiling toward more alkaline and cooler conditions. A paleo-temperature of ca. 160 °C has been inferred from authigenic mineral occurrences and calculated on the basis of equilibria between cored calcites and fluids presently emitted at the surface, by using carbon and oxygen isotope data. The temperature measured at the bottom of the drilling is about 80 °C.

  20. Time-lapse integrated geophysical imaging of magmatic injections and fluid-induced fracturing causing Campi Flegrei 1983-84 Unrest

    NASA Astrophysics Data System (ADS)

    De Siena, Luca; Crescentini, Luca; Amoruso, Antonella; Del Pezzo, Edoardo; Castellano, Mario

    2016-04-01

    Geophysical precursors measured during Unrest episodes are a primary source of geophysical information to forecast eruptions at the largest and most potentially destructive volcanic calderas. Despite their importance and uniqueness, these precursors are also considered difficult to interpret and unrepresentative of larger eruptive events. Here, we show how novel geophysical imaging and monitoring techniques are instead able to represent the dynamic evolution of magmatic- and fluid-induced fracturing during the largest period of Unrest at Campi Flegrei caldera, Italy (1983-1984). The time-dependent patterns drawn by microseismic locations and deformation, once integrated by 3D attenuation tomography and absorption/scattering mapping, model injections of magma- and fluid-related materials in the form of spatially punctual microseismic bursts at a depth of 3.5 km, west and offshore the city of Pozzuoli. The shallowest four kilometres of the crust work as a deformation-based dipolar system before and after each microseismic shock. Seismicity and deformation contemporaneously focus on the point of injection; patterns then progressively crack the medium directed towards the second focus, a region at depths 1-1.5 km south of Solfatara. A single high-absorption and high-scattering aseismic anomaly marks zones of fluid storage overlying the first dipolar centre. These results provide the first direct geophysical signature of the processes of aseismic fluid release at the top of the basaltic basement, producing pozzolanic activity and recently observed via rock-physics and well-rock experiments. The microseismicity caused by fluids and gasses rises to surface via high-absorption north-east rising paths connecting the two dipolar centres, finally beingq being generally expelled from the maar diatreme Solfatara structure. Geophysical precursors during Unrest depict how volcanic stress was released at the Campi Flegrei caldera during its period of highest recorded seismicity

  1. Volcanic CO2 flux measurement at Campi Flegrei by tunable diode laser absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Pedone, M.; Aiuppa, A.; Giudice, G.; Grassa, F.; Cardellini, C.; Chiodini, G.; Valenza, M.

    2014-04-01

    Near-infrared room temperature tunable diode lasers (TDL) have recently found increased usage in atmospheric chemistry and air monitoring research, but applications in volcanology are still limited to a few examples. Here, we explored the potential of a commercial infrared laser unit (GasFinder 2.0 from Boreal Laser Ltd) for measurement of volcanic CO2 mixing ratios, and ultimately for estimating the volcanic CO2 flux. Our field tests were conducted at Campi Flegrei near Pozzuoli, Southern Italy, where the GasFinder was used during three campaigns in October 2012, January 2013 and May 2013 to repeatedly measure the path-integrated mixing ratios of CO2 along cross sections of the atmospheric plumes of two major fumarolic fields (Solfatara and Pisciarelli). By using a tomographic post-processing routine, we resolved, for each of the two fields, the contour maps of CO2 mixing ratios in the atmosphere, from the integration of which (and after multiplication by the plumes' transport speeds) the CO2 fluxes were finally obtained. We evaluate a total CO2 output from the Campi Flegrei fumaroles of ˜490 Mg/day, in line with independent estimates based on in situ (Multi-GAS) observations. We conclude that TDL technique may enable CO2 flux quantification at other volcanoes worldwide.

  2. Permeability measurements of Campi Flegrei pyroclastic products: An example from the Campanian Ignimbrite and Monte Nuovo eruptions

    NASA Astrophysics Data System (ADS)

    Polacci, M.; Bouvet de Maisonneuve, C.; Giordano, D.; Piochi, M.; Mancini, L.; Degruyter, W.; Bachmann, O.

    2014-02-01

    In order to understand outgassing during volcanic eruptions, we performed permeability measurements on trachy-phonolitic pyroclastic products from the Campanian Ignimbrite and Monte Nuovo, two explosive eruptions from the active Campi Flegrei caldera, Southern Italy. Viscous (Darcian) permeability spans a wide range between 1.22 × 10- 14 and 9.31 × 10- 11 m2. Inertial (non-Darcian) permeability follows the same trend as viscous permeability: it increases as viscous permeability increases, highlighting the strong direct correlation between these two parameters. We observe that vesicularity does not exert a first order control on permeability: the Monte Nuovo scoria clasts are the most permeable samples but not the most vesicular; pumice clasts from the Campanian Ignimbrite proximal facies, whose vesicularity is comparable with that of Monte Nuovo scoriae, are instead the least permeable. In addition, we find that sample geometry exhibits permeability anisotropy as samples oriented parallel to vesicle elongation are more permeable than those oriented perpendicular. We compare our results with permeability values of volcanic products from effusive and explosive activity, and discuss the role of melt viscosity and crystallinity on magma permeability.

  3. Hydrothermal alteration of surficial rocks at Solfatara (Campi Flegrei): Petrophysical properties and implications for phreatic eruption processes

    NASA Astrophysics Data System (ADS)

    Mayer, Klaus; Scheu, Bettina; Montanaro, Cristian; Yilmaz, Tim I.; Isaia, Roberto; Aßbichler, Donjá; Dingwell, Donald B.

    2016-06-01

    Solfatara crater is located within the Campi Flegrei caldera to the west of Naples (Italy). It is one of the largest fumarolic manifestations known, and the rocks hosting the hydrothermal system are affected by intense hydrothermal alteration. Alteration can result in changes of degassing behavior, and in the formation of a cap rock thereby increasing the probability of phreatic eruptions. Here, we investigate the effects of alunitic (solfataric) alteration on the mineralogy, the physical properties (porosity, density, permeability) and the mechanical properties (strength) of the rocks involved, as well as its influence on fragmentation and ejection behavior. Our results show that the pristine mineralogy of deposits from the vicinity of the Solfatara cryptodome and from Pisciarelli is almost completely replaced by amorphous silica and alunite. The differences in the degree of alteration among the samples series are reflected in the investigated properties and behavior as well as in the analysis of the experimentally generated particles. Alunitic alteration increases porosity and permeability, whereas it reduces density, elastic wave velocity and strength leading to higher fragmentation and ejection speeds for the sample series examined in this study. Our results also show that alteration results in the generation of a high fraction of fines (particle sizes < 10 μm) during fragmentation, mainly composed of alunite crystals. Due to their potential for inducing chronic disease, dispersion of such material should represent a serious health hazard on a local scale and the evaluation of precautions should be considered.

  4. The campi flegrei (Italy) geothermal system: A fluid inclusion study of the mofete and San Vito fields

    USGS Publications Warehouse

    de, Vivo B.; Belkin, H.E.; Barbieri, M.; Chelini, W.; Lattanzi, P.; Lima, A.; Tolomeo, L.

    1989-01-01

    Vito 3 cores show an approach to fluid/rock Sr equilibrium with a fluid similar to modern ocean water in 87Sr/86Sr ratio. The Campi Flegrei volcanic system has evolved undersaturated products, mostly trachyte, and defines a large (??? 12 km) caldera. The hydrothermal system developed in this location can be used as an analog for fossil systems in similar trachytic environments. The potential for ore mineralization is expressed by the recognition, from fluid inclusion and drilling data, of ore-forming environments such as boiling and brine stratification. ?? 1989.

  5. Observatory response to a volcanic crisis: the Campi Flegrei simulation exercise

    NASA Astrophysics Data System (ADS)

    Papale, Paolo; De Natale, Giuseppe

    2015-04-01

    In Febraury 2014 a simulation exercise was conducted at Campi Flegrei, Italy, in order to test the scientific response capabilities and the effectiveness of communication with Civil Protection authorities. The simulation was organized in the frame of the EU-VUELCO project, and involved the participation of the Osservatorio Vesuviano of INGV (INGV-OV) corroborated by other INGV scientists involved for their specific competencies; and the Italian Civil Protection, which was supported by an expert team formed by selected experts from the Italian academy and by VUELCO scientists from several EU and Latin American countries. The simulation included a previously appointed group of four volcanologists covering a range of expertise in volcano seismology, geodesy, geochemistry, and with experience both on the Campi Flegrei system and on other volcanic systems and crises in the world. The duty of this 'volcano team' was that of producing consistent sets of signals, that were sent to INGV-OV at the beginning of each simulation phase. In turn, the observatory response was that of i) immediately communicate the relevant observations to the Civil Protection; ii) analyze the synthetic signals and observations and extract a consistent picture and interpretation, including the analysis and quantification of uncertainties; iii) organize all the information produced in a bulletin, that was sent to the Civil Protection at the end of each simulation phase and that contained, according to national established agreements, a) the information available, and b) its interpretation including forecasts on the possible medium-short term evolution. The test included four simulation phases and it was blind, as only the volcano team knew the evolution and the final outcome; the volcano team was located at the INGV buildings in Rome, far from INGV-OV in Naples and the Civil Protection Dept. still in Rome, and with no contacts with any of them for the entire duration of the simulation. In this

  6. Emergency preparedness: community-based short-term eruption forecasting at Campi Flegrei

    NASA Astrophysics Data System (ADS)

    Selva, Jacopo; Marzocchi, Warner; Civetta, Lucia; Del Pezzo, Edoardo; Papale, Paolo

    2010-05-01

    A key element in emergency preparedness is to define advance tools to assist decision makers and emergency management groups during crises. Such tools must be prepared in advance, accounting for all of expertise and scientific knowledge accumulated through time. During a pre-eruptive phase, the key for sound short-term eruption forecasting is the analysis of the monitoring signals. This involves the capability (i) to recognize anomalous signals and to relate single or combined anomalies to physical processes, assigning them probability values, and (ii) to quickly provide an answer to the observed phenomena even when unexpected. Here we present a > 4 years long process devoted to define the pre-eruptive Event Tree (ET) for Campi Flegrei. A community of about 40 experts in volcanology and volcano monitoring participating to two Italian Projects on Campi Flegrei funded by the Italian Civil Protection, has been constituted and trained during periodic meetings on the statistical methods and the model BET_EF (Marzocchi et al., 2008) that forms the statistical package tool for ET definition. Model calibration has been carried out through public elicitation sessions, preceded and followed by devoted meetings and web forum discussion on the monitoring parameters, their accuracy and relevance, and their potential meanings. The calibrated ET allows anomalies in the monitored parameters to be recognized and interpreted, assigning probability values to each set of data. This process de-personalizes the difficult task of interpreting multi-parametric sets of data during on-going emergencies, and provides a view of the observed variations that accounts for the averaged, weighted opinion of the scientific community. An additional positive outcome of the described ET calibration process is that of providing a picture of the degree of confidence by the expert community on the capability of the many different monitored quantities of recognizing significant variations in the state of

  7. Laboratory experiments and continuous fluid monitoring at Campi Flegrei to understand pressure transients in hydrothermal systems

    NASA Astrophysics Data System (ADS)

    Woith, Heiko; Mangiacapra, Annarita; Chiodini, Giovanni; Pilz, Marco; Walter, Thomas

    2015-04-01

    The hydrothermal system beneath Campi Flegrei is strongly affected by sub-surface processes as manifested by the existence of a geothermal "plume" below Solfatara (Bruno et al. 2007), associated with formation of new fumaroles and the spatial pattern of exhalation vents. Within the frame of MED-SUV (The MED-SUV project has received funding from the European Union Seventh Framework Programme (FP7) under Grant agreement no 308665), pressure tansients in the hydrothermal system of Campi Flegrei shall be studied using a combination of laboratory experiments and continuous pressure/temperature monitoring at fumaroles, mudpools, hot springs, and geothermal wells. Four groundwater monitoring sites were installed in September 2013: one in the Fangaia mud pool inside Solfatara and three within the geothermal area of Agnano, which is located roughly 3 km to the East of the Solfatara crater. In 2014 additional sensors were installed in Pisciarelli. Autonomous devices are being used to record the water level and water temperature at 10 minute intervals. Records reveal significant changes of the hydrothermal system in September 2013 at the Agnano main spring during the night from 23 to 24 September. Both, the water level and the water temperature dropped significantly, confirmed by visual inspection of the spa operators. The pool of the main spring almost emptied and the flow rate was significantly reduced, implying a profound change in the system. Similar water level drops occurred in the following months. Gas bubbles are likely to play a major role with respect to spatio-temporal variations in shallow fluid systems below Solfatara. Thus, additional to the field measurements we investigate potential bubble-related mechanisms capable to increase fluid pressure. The BubbleLab at GFZ has been setup. We are able to simulate earthquake ground motions with a shaking table, track the size and velocity of rising bubbles via a camera system, and quantify transients with a set of

  8. Volcanic CO2 mapping and flux measurements at Campi Flegrei by Tunable Diode Laser absorption Spectroscopy

    NASA Astrophysics Data System (ADS)

    Pedone, Maria; Aiuppa, Alessandro; Giudice, Gaetano; Grassa, Fausto; Chiodini, Giovanni; Valenza, Mariano

    2014-05-01

    Near-infrared room-temperature Tunable Diode Lasers (TDL) have recently found increased usage in atmospheric chemistry and air monitoring research, but applications in Volcanology are still limited to a few examples. Here, we explored the potentiality of a commercial infrared laser unit (GasFinder 2.0 from Boreal Laser Ltd) to measurement of volcanic CO2 flux emissions. Our field tests were conducted at Campi Flegrei (near Pozzuoli, Southern Italy), where the GasFinder was used (during three campaigns in October 2012, January 2013 and May 2013) to repeatedly measure the path-integrated concentrations of CO2 along cross-sections of the atmospheric plumes of the two main fumarolic fields in the area (Solfatara and Pisciarelli). By using ad-hoc designed field-set-up and a tomographic post-processing routine, we resolved, for each of the 2 manifestations, the contour maps of CO2 concentrations in their atmospheric plumes, from the integration of which (and after multiplication by the plumes' transport speeds) the CO2 fluxes were finally obtained [1]. The so-calculated fluxes average of 490 tons/day, which agrees well with independent evaluations of Aiuppa et al. (2013) [2] (460 tons/day on average), and support a significant contribution of fumaroles to the total CO2 budget. The cumulative (fumarole [this study] +soil [2]) CO2 output from Campi Flegrei is finally evaluated at 1600 tons/day. The application of lasers to volcanic gas studies is still an emerging (though intriguing) research field, and requires more testing and validation experiments. We conclude that TDL technique may valuably assist CO2 flux quantification at a number of volcanic targets worldwide. [1] Pedone M. et al. (2013) Gold2013:abs:5563, Goldschmidt Conference, session 11a. [2] Aiuppa A. et al. (2013) Geochemistry Geophysics Geosystems. doi: 10.1002/ggge.20261. [3] Chiodini G. et al. (2010) Journal of Geophysical Research, Volume 115, B03205. doi:10.1029/2008JB006258.

  9. Chemical and isotopic compositions of minerals and waters from the Campi Flegrei volcanic system, Naples, Italy

    NASA Astrophysics Data System (ADS)

    Valentino, G. M.; Cortecci, G.; Franco, E.; Stanzione, D.

    1999-08-01

    Based on their δ 34S signature, sulfate minerals and native sulfur around fumaroles and hot water pools from the Campi Flegrei volcanic area derive from supergenic oxidation of volcanic H 2S. Their mean δ 34S value (-0.2±1.7‰) matches with that of fumarolic H 2S at Solfatara (-0.3±0.3‰), as well as with the δ 34S of +1.4‰ obtained for total sulfur in fresh trachyte from the area. All δ 34S values indicate a mostly deep-seated origin for sulfur. Thermal waters were analysed for major and minor chemistry and for oxygen, hydrogen and sulfur isotope compositions. Pools at Pisciarelli are filled with evaporated meteoric water heated by rising (magmatic) gases. The water δ 18O (+3.8±1.3‰) and δ 2H (+6.5±2.2‰) values in these steam-heated waters are controlled by mixing and evaporation effects, and the δ 34S value of dissolved sulfate (-1.3±0.3‰) basically agrees with supergenic oxidation of deep-seated H 2S as the major source of sulfur. Instead, water from thermal springs and wells elsewhere in the Campi Flegrei appears to be a mixture between dilute meteoric and saline marine components. The latter may be local seawater from the bay of Pozzuoli. The δ 18O and δ 2H values of waters sampled during 1993-1994 range from -5.6 to +0.3‰ and from -33 to -3.4‰, respectively. The δ 34S values of dissolved sulfate range between -0.1 and +19.5‰. In general, sulfate is probably derived essentially from two sources, both within the volcanic cover, i.e., oxidation/dissolution of pyrite and anhydrite, and marine water. An occasional source of water and sulfate is represented by (magmatic) gases, which directly interact with shallow meteoric water as in the case of the Hotel Tennis well yielding steam-heated water with δ 18O=-1.5±0.2‰, δ 2H=-17±1‰ and δ 34S=-0.1‰.

  10. 14C age of the "Museum Breccia" (Campi Flegrei) and its relevance for the origin of the Campanian Ignimbrite

    USGS Publications Warehouse

    Lirer, L.; Rolandi, G.; Rubin, M.

    1991-01-01

    Field stratigraphic investigations and AMS 14C dating of carbon particles in paleosols has resulted in a framework of the sequence and age of the pyroclastic products in the Campi Flegrei area of Southern Italy. The Museum Breccia cannot be the early phase of the Campanian Ignimbrite, as was previously believed, but is from a smaller and later eruption with an age of approximately 17,900 y B.P. This date also precludes its correlation with the Neapolitan Yellow Tuff (12,000 y B.P.). ?? 1991.

  11. Texture and Composition of Pumice and Scoria Provide New Insights into the Dynamics of Explosive Eruptions at Campi Flegrei (Italy)

    NASA Astrophysics Data System (ADS)

    Polacci, M.; Piochi, M.; de Astis, G.; Zanetti, A.; Mangiacapra, A.; Vannucci, R.; Giordano, D.

    2007-12-01

    Campi Flegrei (CF), a nested caldera located west of the densely-inhabited city of Naples, has been the site of volcanic activity for the past 60 ka BP. The last eruption occurred in AD 1538, but geochemical and geophysical signals have been monitored for the last tens of years clearly indicating that the magmatic system is still active. Volcanic risk mitigation in this area is therefore a primary goal of the scientific community. Here we combine new and literature data on the texture and composition of pumice and scoria clasts of selected CF eruptions with the goal to investigate their relationship to, and implications for, the eruption dynamics. We focus on three events with decreasing eruption intensity and magnitude: the Campanian Ignimbrite (39 ka), Agnano Monte Spina (4.1 ka) and Monte Nuovo (AD 1538) eruptions. Previous studies indicate that phenocryst and major element bulk compositions, as well as the original volatile content, are comparable in samples from the investigated eruptions. From these observations we derive that similar pre-eruptive physico-chemical conditions governed magma storage in the shallow crust before the occurrence of the above eruptions. Our investigation displays however a significant heterogeneity among the studied samples in terms of crystal and vesicle texture and abundance, composition of microlites and glassy groundmass, residual groundmass water content, and, finally, rheological properties of the related magmas. We ascribe such textural, compositional and rheological variability to different mechanisms of volatile exsolution, separation from the melt and outgassing accompanying magma ascent along the conduit and generated primarily by changes in the magma ascent rate. Low ascent rates allow open-system degassing, groundmass crystallization in response to water exsolution and the development of permeable flow pathways through which volatiles escape non-explosively to the surface potentially decreasing the overall eruption

  12. Authigenic Mineral Cycling in Roman Seawater Concrete with Campi Flegrei Pumiceous Ash Pozzolan

    NASA Astrophysics Data System (ADS)

    Jackson, M. D.; Mulcahy, S. R.; Chen, H.; Li, Q.; Cappelletti, P.; Carraro, C.; Wenk, H. R.

    2015-12-01

    Alteration of Campi Flegrei pumiceous ash in Roman concrete harbor structures along the central Italian coast produced zeolite and Ca-silicate minerals that have reinforced cementitious fabrics for >2000 years. X-ray microdiffraction experiments and electron microprobe analyses show that diverse alteration paths produced authigenic phillipsite and Al-tobermorite in the pyroclasts, pores, and cementing matrix of mortars in Romacons drill cores from Portus Cosanus, Portus Neronis, and Baianus Sinus. These minerals have cation exchange capabilities for some radionuclides and heavy metal cations and are candidate sorbents for concrete waste encapsulations. Compositions of phillipsite in certain Portus Cosanus and Portus Neronis pumice clasts are similar to those in the Neapolitan Yellow Tuff. Dissolution of this phillipsite and alkali feldspar produced new, authigenic phillipsite with less Si, greater Al and Ca, Al-tobermorite, and poorly-crystalline binder in pumice vesicles. Conversely, alteration of trachytic glass to clay mineral (nontronite) in a Baianus Sinus tuff clast is associated with new, authigenic phillipsite and Al-tobermorite in the tuff and cementing matrix. The Al-tobermorite has lower Al/(Si+Al) and Ca/(Si+Al) compared to Al-tobermorite in relict lime clasts. These more siliceous crystals, similar to those in hydrothermally-altered basalt, have 11.3 Å d-spacing in [001]. Raman spectra show symmetrical bending of Si-O-Si and Si-O-Al linkages, Si-O and Si-Al symmetrical stretching, and possible Q3 Si and Al tetrahedral peaks that suggest cross-linking of silicate chains-an important factor in cation exchange. The authigenic crystals refine pore space, contribute to binding in interfacial zones, and obstruct microcrack propagation. The well-constrained history of temperature variations and seawater immersion could provide further information for understanding alteration in volcanoclastic deposits and predicting regenerative processes in high performance

  13. Influence of hydrothermal alteration on phreatic eruption processes in Solfatara (Campi Flegrei)

    NASA Astrophysics Data System (ADS)

    Mayer, K.; Scheu, B.; Montanaro, C.; Isaia, R.; Dingwell, D. B.

    2014-12-01

    The strong hydrothermal activity exhibited at Campi Flegrei by the Solfatara and Pisciarelli fumaroles points to a significant risk for phreatic eruptions in this densely populated area. Phreatic eruptions, triggered by various processes are hardly predictable in occurrence time and size. Despite their hazard potential, these eruptions, as well as the influence of hydrothermal alteration on their likelihood, magnitude and style, have so far been largely overlooked in experimental volcanology. The physical properties and the mechanical behavior of volcanic rocks are highly dependent on their original magmatic microstructure and on any eventual alteration of those microstructures due to hydrothermal reactions. We have therefore investigated the potential effects of hydrothermal alteration on rock microstructure and, as a consequence, on fragmentation dynamics. Rock samples from the vicinity of the Solfatara fumaroles have been characterized 1) geochemically (X-ray fluorescence, X-ray diffraction), 2) physically (density, porosity, permeability and elastic wave velocity) and 3) mechanically (uniaxial compressive strength, tensile strength). We have investigated the effects of hydrothermal alteration on fragmentation processes using a shock-tube apparatus, operating with Argon gas, water vapor and superheated water at temperatures up to 400°C and maximum pressures of 20 MPa. The three different energy sources within the pores initiating fragmentation, have been investigated: overpressure by 1) Argon gas; or 2) water vapor and due to 3) steam flashing of water. Fragmentation speed, fragmentation efficiency and fragmented particle ejection velocity were measured. Our results indicate, that steam flashing provides the highest energy - resulting in increased particle ejection velocity and higher fragmentation efficiency. Based on our results, we aim to constrain the influence of hydrothermal alteration on the dynamics of phreatic explosions and the effect on the amount of

  14. Abrupt magma chamber contraction and microseismicity at Campi Flegrei, Italy: Cause and effect determined from strainmeters and tiltmeters

    NASA Astrophysics Data System (ADS)

    Amoruso, Antonella; Crescentini, Luca; Scarpa, Roberto; Bilham, Roger; Linde, Alan T.; Sacks, I. Selwyn

    2015-08-01

    In March 2010 two borehole strainmeters and three Michelson tiltmeters within the Campi Flegrei volcanic system, Italy, registered an abrupt deformation signal that was followed 20 min later by seismic slip on a pair of onshore normal faults. We demonstrate that the observed strain changes were caused by a small but rapid volume decrease in a previously identified offshore ellipsoidal magma source or part of it. Although the total deflation was below the detectability of interferometric synthetic aperture radar and GPS, deflation observed rates were briefly 2 orders of magnitude more rapid than decadal inflation rates. We conclude that this high dilatational contraction rate was responsible for triggering seismicity and that this process may be responsible for the normal faulting often observed in the Campi Flegrei region. Our study quantifies the crucial role played by a transient, minor reduction in dilatational stress, in triggering slip on a fault near critical failure. Our subsurface measurements of strain and tilt registered anomalous deformation three sigma above background noise levels 17 min before the onset of microseismicity suggesting strain measurements have potential utility as an early warning system for the city of Naples.

  15. Hot fluid migration: an efficient source of ground deformation: application to the 1982 1985 crisis at Campi Flegrei-Italy

    NASA Astrophysics Data System (ADS)

    Bonafede, Maurizio

    1991-08-01

    Some solutions of the forced heat advection problem in compressible media are worked out employing a perturbative approach and their implication for thermoelastic deformation are discussed. A sharp temperature front, which migrates at a speed in the order of Darcy flow rate, develops in the medium, giving rise to significant deformation via thermal expansion. A thermally induced pressure source accompanies the temperature front, which may be significant only in very high temperature cases. Results are applied to interpreting the uplift episode of 1982-1984 at Campi Flegrei (C.F.), near Naples, Italy. A mechanism is envisaged for uplift at Campi Flegrei in which a sudden connection is established between a deep, hot, high-pressure fluid reservoir and a shallow, relatively cold, low-pressure aquifer. The inclusion of fluid migration in the deformation model allows simple explanations of several geochemical and geophysical observations made during the bradyseismic crisis. It appears that the proposed mechanism may explain the large observed uplift, without requiring unreasonable pressure increase within the magma chamber. Furthermore, the deformation source may be allowed to be shallower than the magma chamber, as required by any reasonable deformation model at C.F.

  16. Seafloor slow vertical displacement inferred by sea bottom pressure measurements in shallow water: an application to the Campi Flegrei volcanic area

    NASA Astrophysics Data System (ADS)

    Chierici, Francesco; Pignagnoli, Luca; Iannaccone, Giovanni; Guardato, Sergio; Locritani, Marina; Embriaco, Davide; Donnarumma, Gian Paolo; La Rocca, Adriano; Pinto, Salvatore; Beranzoli, Laura

    2016-04-01

    The vertical component of sea floor displacement in tectonic or volcanically active areas can be observed using sea bottom pressure recorders. These measurements are usually acquired in areas affected by strong dynamics with large vertical displacement and in deep water, where the noise induced by the sea state is low. Under these conditions the contribution of the variation of sea water density and the contribution of the instrumental drift - a typical feature of the bottom pressure recorders - can be negligible. We have developed a new methodology to monitor vertical sea floor displacement both in areas with small and slow deformation, and in shallow water. We take advantage of bottom pressure recorder data, augmented with ancillary sea level, barometric and water physical parameters measurements. We have applied this method to the data collected by a bottom pressure recorder deployed at 100 m w.d. in the Campi Flegrei Caldera as part of CUMAS multiparameter monitoring system. During several months of 2011 we have observed a small uplift episode related to the bradiseismic activity of the area. These observations are compatible with other geodetic data recorded in the region and provide unprecedented measurements of the vertical deformation in the marine area.

  17. The Italy's D.P.C. - I.N.G.V. Project UNREST: Realization of an integrated method for the definition of the unrest phases at Campi Flegrei.

    NASA Astrophysics Data System (ADS)

    Civetta, Lucia; Del Pezzo, Edoardo

    2010-05-01

    In this poster we present the framework of the Project "UNREST" and the preliminary results obtained in the first 18 months of activity. The Campi Flegrei resurgent caldera, where several hundred thousands people live, have been characterized during last decades by several bradiseismic crises which determined the partial evacuation of the population, as for the crises in 1969-72 and 1982-84. Recent studies have revealed a process of unrest which continues since the fifties, and which presents characteristics similar to the several centuries-decades long unrest period which led to the last eruption in AD 1538. In the frame of last INGV-DPC Agreement a method has been developed, which allows accounting of any information and associated uncertainty coming from historical, field, and modelling studies, and from the monitoring network, providing a probability on the state of the volcano and on the occurrence of an eruption. In the present project this method is explored and developed, particularly through the experimentation of methods for the definition of reference parameters and thresholds, and of criteria and procedures to make it an operational tool useful for volcano surveillance and crisis management. The research in the project include the following points: a) Definition of the reference database for the validation of models of pre-eruptive dynamics. The database will include geologic, geophysic, geochemical, hydrological and hystorical data. b) Quantitative analysis of measured signals, and formulation of hypotheses on source mechanisms. c) Definition of a general conceptual model for the magma-rocks-geothermal system at Campi Flegrei. d) Physico-mathematical modelling and numerical simulation of the magmatic and geothermal process dynamics, and of the space-time relationships between such dynamics and the geophysical and geochemical signals measured at the surface. e) Definition of the critical parameters for the definition of the different unrest phases, and

  18. Integrated multi-parameters Probabilistic Seismic Landslide Hazard Analysis (PSLHA): an innovative approach in the active volcano-tectonic area of Campi Flegrei (Italy)

    NASA Astrophysics Data System (ADS)

    Caccavale, M.; Matano, F.; Sacchi, M.; Somma, R.; Troise, C.; De Natale, G.

    2013-12-01

    The western coastal sector of Campania region (southern Italy) is characterised by the presence of the active volcano-tectonic area of Campi Flegrei. This area represents a very particular and interesting case-study for a probabilistic seismic hazard analysis (PSHA). The principal seismic source, related with the caldera, is not clearly constrained in the on-shore and off-shore areas. The well-known and monitored phenomenon of bradyseism affecting a large portion of case-study area is not modelled in the standard PSHA approach. From the environmental point of view the presence of very high exposed values in terms of population, buildings, infrastructures and palaces of high archaeological, natural and artistic value, makes this area a strategic natural laboratory to develop new methodologies. Moreover the geomorphological and geo-volcanological features lead to a heterogeneous coastline, made up by both beach and tuff cliffs, rapidly evolving for erosion and landslide (i.e. mainly rock fall and rock slide) phenomena that represent an additional hazard aspect. In the Campi Flegrei the possible occurrence of a moderate/large seismic event represents a serious threat for the inhabitants, for the infrastructures as well as for the environment. In the framework of Italian MON.I.C.A project (sinfrastructural coastlines monitoring) an innovative and dedicated probabilistic methodology has been applied to identify the areas with higher tendency of landslide occurrence due to the seismic effect. Resident population reported the occurrence of some small rock falls along tuff quarry slopes during the main shocks of the 1982-84 bradyseismic events. The PSHA methodology, introduced by Cornell (1968), combines the contributions to the hazard from all potential sources of earthquakes and the average activity rates associated to each seismogenic zone considered. The result of the PSHA is represented by the spatial distribution of a ground-motion (GM) parameter A, such as Peak

  19. Definition of Brittle Ductile Transition of the upper crust beneath the Campi Flegrei-Ischia Volcanic District and its impact on natural seismicity

    NASA Astrophysics Data System (ADS)

    Tizzani, Pietro; Castaldo, Raffaele; De Novellis, Vincenzo; Santilano, Alessandro; Gola, Gianluca; Pepe, Susi; D'Auria, Luca; Solaro, Giuseppe

    2016-04-01

    The thermo-rheology behaviour of the rocks is a crucial aspect to understand the mechanical behaviour of the crust of tectonically active area. As a consequence, several studies have been performed since last decades in order to clarify the role of thermic state in the evolution of volcanic areas. In this framework, the knowledge of the Brittle-Ductile transition inside the upper crust may provide insights to verify the roles that some hypothesized mechanisms, such as slab pull, crustal delamination might have played in the evolution of a tectonically active region. The goal of our study was the 3D imaging of the crust rheology beneath the active Campi Flegrei-Ischia Volcanic District and its impact on natural seismicity. Despite many works have been done on the internal structure of the active volcanoes, the determination of the 3D rheological stratification of the crust below the caldera has not yet been tackled. To fill this gap of knowledge, we proposed the definition of 3D geometry of the Brittle-Ductile transition calculated via numerical optimization modelling based on geological, geochemical, and geophysical available data. We first performed a 3D numerical modelling of thermal field by using the a priori geological and geophysical information starting to thermal proprieties and mechanical heterogeneities of the crust beneath the caldera. We developed a suitable 3D conductive/convective time-dependent thermal numerical model solving the Fourier equation and further we used the retrieved thermal model to image a 3D rheological stratification of the shallow crust below the volcanic district. Finally we demonstrate the role of the crustal rheology on seismicity cut off and its implication on maximum expected earthquakes magnitude.

  20. Interaction between hydrothermal and magmatic systems: modelling of magmatic gas release and ascent at Campi Flegrei (Italy)

    NASA Astrophysics Data System (ADS)

    Todesco, Micol; Afanasyev, Andrey; Montagna, Chiara Paola; Longo, Antonella

    2016-04-01

    We model the perturbation of a hydrothermal system caused by the gas release from sub-surface magma chambers. First, we simulate the evolution of the magmatic system composed by two magma reservoirs: a small and shallow chamber, filled with degassed phonolite, connected to a deeper reservoir of gas-rich shoshonite through a vertical dyke. The fluid-dynamics governing the replenishment of the upper chamber is computed with a 2D code solving conservation equations of mass, momentum and energy for a homogeneous multicomponent, multiphase Newtonian mixture, accounting for exsolution and dissolution of volatiles (H2O+CO2). We then assume that the volatiles that accumulate at the top of the upper chamber, escape from the reservoir and enter a steady state hydrothermal system. The response of the hydrothermal circulation is simulated with two multi-phase, multi-component porous media codes (MUFITS and TOUGH2) that describe the propagation of magmatic volatiles toward the surface. We create a simple model of Campi Flegrei hydrothermal system covering both shallow and deep regions where the temperature exceeds the critical temperature for water. Simulation results suggest that the rate at which volatiles are released from the magma chamber, the permeability distribution and the conditions of the hydrothermal system when degassing takes place can determine very different evolutions: accordingly, carbon dioxide may reach the surface within a time span ranging from weeks to millennia. The simulations indicate also that a single unrest event, associated with volatiles release from the chamber, can result in a periodic behaviour of observable parameters such as gas flux and fumarole composition. Duration of the period is of the order of 10 years, which is comparable with the time span between major unrest events observed at Campi Flegrei.

  1. A temporal record of pre-eruptive magmatic volatile contents at Campi Flegrei: Insights from texturally-constrained apatite analyses

    NASA Astrophysics Data System (ADS)

    Stock, Michael J.; Isaia, Roberto; Humphreys, Madeleine C. S.; Smith, Victoria C.; Pyle, David M.

    2016-04-01

    Apatite is capable of incorporating all major magmatic volatile species (H2O, CO2, S, Cl and F) into its crystal structure. Analysis of apatite volatile contents can be related to parental magma compositions through the application of pressure and temperature-dependent exchange reactions (Piccoli and Candela, 1994). Once included within phenocrysts, apatite inclusions are isolated from the melt and preserve a temporal record of magmatic volatile contents in the build-up to eruption. In this work, we measured the volatile compositions of apatite inclusions, apatite microphenocrysts and pyroxene-hosted melt inclusions from the Astroni 1 eruption of Campi Flegrei, Italy (Stock et al. 2016). These data are coupled with magmatic differentiation models (Gualda et al., 2012), experimental volatile solubility data (Webster et al., 2014) and thermodynamic models of apatite compositional variations (Piccoli and Candela, 1994) to decipher pre-eruptive magmatic processes. We find that apatite halogen/OH ratios decreased through magmatic differentiation, while melt inclusion F and Cl concentrations increased. Melt inclusion H2O contents are constant at ~2.5 wt%. These data are best explained by volatile-undersaturated differentiation over most of the crystallisation history of the Astroni 1 melt, with melt inclusion H2O contents reset at shallow levels during ascent. Given the high diffusivity of volatiles in apatite (Brenan, 1993), the preservation of volatile-undersaturated melt compositions in microphenocrysts suggests that saturation was only achieved 10 - 103 days before eruption. We suggest that late-stage transition into a volatile-saturated state caused an increase in magma chamber overpressure, which ultimately triggered the Astroni 1 eruption. This has major implications for monitoring of Campi Flegrei and other similar volcanic systems. Piccoli and Candela, 1994. Am. J. of Sc., 294, 92-135. Stock et al., 2016, Nat. Geosci. Gualda et al., 2012. J. Pet., 53, 875

  2. Comparison of multi-temporal TLS data for collapses and/or landslides monitoring of a coastal area: Coroglio cliff at Campi Flegrei (Italy).

    NASA Astrophysics Data System (ADS)

    Caputo, Teresa; Somma, Renato; Marino, Ermanno; Matano, Fabio; Troise, Claudia; De Natale, Giuseppe

    2015-04-01

    The area under consideration is the Coroglio cliff localized in the Campi Flegrei caldera (CFc). The latter is a volcanic area resulting by two major eruptive collapses. The first of these two catastrophic eruptions dating back to 39 ka and is defined as Ignimbrite Campana (IC). Its deposits cover an area of approximately 30,000 km2, while the volume of erupted magma was estimated at 150 km3. The second major eruption is the Neapolitan Yellow Tuff (NYT) dating back to 14.9 ka. It covers an area of about 1000 km2 and a volume of ejected material exceeding 40 km3. The Coroglio cliff constitutes the rocky front of Posillipo hill beaten by the sea. The Posillipo hill is a structural high located on the eastern rim of the CFc. It is the morphological evolution of the caldera rim of NYT. Lithologically consists of a tuff extremely lithified, associated to the eruption of NYT, overlaid by more recent products of the Campi Flegrei. The Coroglio cliff has an elevation of 150 m a.s.l. and a breadth of at least 200 m. It is composed of different lithologies, mostly of volcanic origin, and locally by paleosols. The proximity and the action of the sea and/or wind makes these materials highly erodible. Recently the Laser Scanning technique has shown to be a very useful tool not only to get an item of information and integration derived for measurement of landslide but also to monitor and predict the landslide. This study presents a Terrestrial Laser Scanning (TLS) application for the landslides monitoring by multi-temporal comparison laser scan data. The TLS seems to be a very appropriate tool for the geomorphology evolution of an area. The instrument used in this study is a long range TLS based on the Time of Flight method (TOF) manufactured by RIEGL®, model VZ 1000. Two measurement campaigns of the Coroglio cliff were performed after one year of each other. The first in May, 2013 and the second in June, 2014. The main objective was to define a 3D model for the site of

  3. Operational short-term Probabilistic Volcanic Hazard Assessment of tephra fallout: an example from the 1982-1984 unrest at Campi Flegrei

    NASA Astrophysics Data System (ADS)

    Sandri, Laura; Selva, Jacopo; Costa, Antonio; Macedonio, Giovanni; Marzocchi, Warner

    2014-05-01

    high eruption "scenario" respectively) and 700 possible vent positions within the CF Neapolitan Yellow Tuff caldera. The probabilities related to eruption dynamics, and estimated by BET_EF, are based on the set up of the code obtained specifically for CF during a 6-years long elicitation project, and on the actual monitoring parameters measured during the unrest and published in the literature. We take advantage here of two novel improvements: (i) a time function to describe how the probability of eruption evolves within the time window defined for the forecast, and (ii) the production of hazard curves and their confidence levels, a tool that allows a complete description of PVHA and its uncertainties. The general goal of this study is to show what, and how, pieces of scientific knowledge can be operationally transferred to decision makers, and specifically how this could have been translated in practice during the 1982-84 Campi Flegrei crisis, if scientists knew what we know today about this volcano.

  4. Quantitative models for magma degassing and ground deformation (bradyseism) at Campi Flegrei, Italy: Implications for future eruptions

    USGS Publications Warehouse

    Bodnar, R.J.; Cannatelli, C.; de Vivo, B.; Lima, A.; Belkin, H.E.; Milia, A.

    2007-01-01

    Campi Flegrei (Phlegrean Fields) is an active volcanic center near Naples, Italy. Numerous eruptions have occurred here during the Quaternary, and repeated episodes of slow vertical ground movement (bradyseism) have been documented since Roman times. Here, we present a quantitative model that relates deformation episodes to magma degassing and fracturing at the brittle-ductile transition in a magmatic-hydrothermal enviromnent. The model is consistent with field and laboratory observations and predicts that uplift between 1982 and 1984 was associated with crystallization of ???0.83 km3 of H2O-saturated magma at 6 km depth. During crystallization, ???6.2 ?? 1010 kg of H2O and 7.5 ?? 108 kg of CO2, exsolved from the magma and generated ???7 ?? 1015 J of mechanical (P??V) energy to drive the observed uplift. For comparison, ???1017 J of thermal energy was released during the 18 May 1980 lateral blast at Mount St. Helens. ?? 2007 The Geological Society of America.

  5. Degradation Pathways for Geogenic Volatile Organic Compounds (VOCs) in Soil Gases from the Solfatara Crater (Campi Flegrei, Southern Italy).

    NASA Astrophysics Data System (ADS)

    Tassi, F.; Venturi, S.; Cabassi, J.; Capecchiacci, F.; Nisi, B., Sr.; Vaselli, O.

    2014-12-01

    The chemical composition of volatile organic compounds (VOCs) in soil gases from the Solfatara crater (Campi Flegrei, Southern Italy) was analyzed to investigate the effects of biogeochemical processes occurring within the crater soil on gases discharged from the hydrothermal reservoir and released into the atmosphere through diffuse degassing. In this system, two fumarolic vents (namely Bocca Grande and Bocca Nuova) are the preferential pathways for hydrothermal fluid uprising. For our goal, the chemistry of VOCs discharged from these sites were compared to that of soil gases. Our results highlighted that C4-C9 alkanes, alkenes, S-bearing compounds and alkylated aromatics produced at depth were the most prone to degradation processes, such as oxidation-reduction and hydration-dehydration reactions, as well as to microbial activity. Secondary products, which were enriched in sites characterized by low soil gas fluxes, mostly consisted of aldheydes, ketons, esters, ethers, organic acids and, subordinately, alcohols. Benzene, phenol and hydrofluorocarbons (HCFCs) produced at depth were able to transit through the soil almost undisturbed, independently on the emission rate of diffuse degassing. The presence of cyclics was possibly related to an independent low-temperature VOC source, likely within sedimentary formations overlying the hydrothermal reservoir. Chlorofluorocarbons (CFCs) were possibly due to air contamination. This study demonstrated the strict control of biogeochemical processes on the behaviour of hydrothermal VOCs that, at least at a local scale, may have a significant impact on air quality. Laboratory experiments conducted at specific chemical-physical conditions and in presence of different microbial populations may provide useful information for the reconstruction of the degradation pathways controlling fate and behaviour of VOCs in the soil.

  6. Native sulfur, sulfates and sulfides from the active Campi Flegrei volcano (southern Italy): Genetic environments and degassing dynamics revealed by mineralogy and isotope geochemistry

    NASA Astrophysics Data System (ADS)

    Piochi, Monica; Mormone, Angela; Balassone, Giuseppina; Strauss, Harald; Troise, Claudia; De Natale, Giuseppe

    2015-10-01

    We investigated sulfur-bearing minerals from the Campi Flegrei caldera, southern Italy, in relation to the increase of hydrothermal activity phenomena since 2006, aimed at providing insights into the volcanic system dynamics. Mineral encrustations and muds were sampled between 2013 and 2015 at the long-standing degassing crater of the Solfatara tuff cone and its recently restless north-eastern Pisciarelli slope. Deep-seated sulfides were further separated from two drill cores (AGIP's Mofete boreholes: 1500 m and 2695 m depth). The mineral assemblage and texture of sampled encrustations were determined by X-ray diffraction, optical and scanning electron microscopy and X-ray microanalysis by energy dispersive spectrometry. Native sulfur and alunite dominate among the newly formed mineral phases. Other minerals are mostly alunogen, and locally pickeringite, potassium alum, hematite and pyrite. Mereiterite and amarillite sporadically occur. The mud pools are rich in gypsum, potassium alum and pyrite. Quartz and argillic phases, locally with analcime, are dispersed in the outcropping rocks. δ34S values were determined for shallow subsurface native sulfur (- 5.5 to 0.0‰) and alunite (- 1.7 to - 0.2‰), as well as for the deep-seated pyrite (3.3 to 7.4‰ in the depth range:1500-2695 m). δ18O values were measured for shallow native alunite (4.2 to 7.0‰). Pisciarelli alunite was finally analyzed for its 87Sr/86Sr ratio and 143Nd/144Nd ratios (0.707517 ± 6 and 0.512459 ± 6, respectively). Textural and isotopic data constrain the genesis of alunite at the expense of K-feldspars through rock alteration by hydrothermal fluids. We suggest that the caldera is a low-sulfidation system hosting acid-sulfate deposits in its active degassing area. The acid-sulfate environment developed on an argillitic facies that thins outwards and is characteristic for steam-heated and magmatic-steam environments. These environments developed in relation to the fractured settings that

  7. Continuous thermal infrared monitoring at Campi Flegrei and Vesuvius (Italy) by automated data processing: an effective surveillance tool of active volcanoes

    NASA Astrophysics Data System (ADS)

    Sansivero, Fabio; Vilardo, Giuseppe

    2014-05-01

    The INGV-Osservatorio Vesuviano Thermal Infrared Imagery Monitoring Network (TIIMNet) is made up of IR acquisition stations designed to continuously acquire IR scenes of diffuse degassing areas in the Neapolitan volcanic district. Every station consists of a RMS (Remote Monitoring Station) which manages the shooting functionalities of the IR camera and the connection to the surveillance Centre of INGV-Osservatorio Vesuviano in Naples. The first developed station was equipped with a NEC Thermo Tracer TS7302 IR camera (with 320x240 pixel FPA uncooled microbolometer); a newer one is equipped with a FLIR SC645 IR camera (with 640x480 pixel FPA uncooled microbolometer) and is supported by an in-house developed hardware which manages a fully real-time control of data acquisition and transfer procedures. As a whole, TIIMNet is composed of four permanent stations and three transportable ones. The first permanent NEC Station was installed at Vesuvius on July 2004 and dismissed on May 2007. A new permanent FLIR Station was set up on June 2011 and it acquires IR scenes from the inner SW slope of Vesuvius crater. In the Campi Flegrei caldera (Pozzuoli, Italy) a permanent NEC Station was operative at Solfatara since September 2004 and it acquired scenes of the major fumaroles area located on the SE inner slope at the intersection of two active, SW-NE and NW-SE main faults. A permanent FLIR Station has been installed at Solfatara on June 2013 and takes IR shots of a significant thermal anomaly on the Northern inner slope of the crater. At Pisciarelli locality, on the Solfatara NE outer slope, a transportable NEC Station was set up on October 2006 and dismissed on September 2013. It was abreast of a permanent FLIR Station on March 2013. Both stations stored IR scenes of the outer eastern flank of the Solfatara tuff-cone characterized by heavy water vapor and CO2 emissions close to an active NW-SE fault. IR scenes are acquired every night by the TIIMNet stations and in real time

  8. Application of laser scanning and opto-electronic devices for monitoring cliff instability in the Campi Flegrei coastal area: the Coroglio case study ( Napoli, Italy)

    NASA Astrophysics Data System (ADS)

    Somma, R.; Caputo, T.; Esposito, G.; Marino, E.; Matano, F.; Carlino, S.; Iuliano, S.; Sacchi, M.; Troise, C.; De Natale, G.

    2013-12-01

    This study introduces a Terrestrial Laser Scanning (TLS) application for the landslides monitoring and its experiment in Gulf of Pozzuoli coastal area (Italy). This area is a part of the Campi Flegrei volcanic district, one of the major volcanic risk zones of the world, with more than 300.000 people and a lot of infrastructures concentrated within it. The cliffs consist of very erodible volcanoclastic lithologies as same as tuffs and ignimbrites, affected by the erosive action of both sea and meteorological agents, very high erosion rate. Furthermore, in this area the bradyseismic phenomenon occurred too, producing differential displacement and fracturing. The Coroglio test site was chosen taking into account cliff's geological and geomorphological properties, as well as aspect, fractures, lithology, and elements at risk located upslope or downslope: The Coroglio site is characterized by lithified upper member of the NYT with stratified, wavy-to-planar alternations of coarse-grained, disorganized, matrix-supported layers, thinly-laminated discontinuous beds and massive, even fine ash layers. The accuracy of the technique used reaches a detailed level in landslide monitoring which allows this methodology to be complementary to the monitoring by setup a geodetic deformation monitoring network. With this aim we have firstly reconstructed a 3D model of the investigated cliff with the use of dedicated softwares and successively analyzed the main lithological, structural and geomorphologic elements related to cliff instability processes. What is possible to confirm after this first study, can be here resumed: (1) These tests were designed to set-up landslide monitoring in highly urbanised areas such as the Campi Flegrei; they are very important sites with a well-established road network, which can be affected by landslide phenomena as occurred in the past causing either traffic interruption and damage to infrastructures insisting along the landslides fronts. (2) In the

  9. Automatized near-real-time short-term Probabilistic Volcanic Hazard Assessment of tephra dispersion before eruptions: BET_VHst for Vesuvius and Campi Flegrei during recent exercises

    NASA Astrophysics Data System (ADS)

    Selva, Jacopo; Costa, Antonio; Sandri, Laura; Rouwet, Dmtri; Tonini, Roberto; Macedonio, Giovanni; Marzocchi, Warner

    2015-04-01

    Probabilistic Volcanic Hazard Assessment (PVHA) represents the most complete scientific contribution for planning rational strategies aimed at mitigating the risk posed by volcanic activity at different time scales. The definition of the space-time window for PVHA is related to the kind of risk mitigation actions that are under consideration. Short temporal intervals (days to weeks) are important for short-term risk mitigation actions like the evacuation of a volcanic area. During volcanic unrest episodes or eruptions, it is of primary importance to produce short-term tephra fallout forecast, and frequently update it to account for the rapidly evolving situation. This information is obviously crucial for crisis management, since tephra may heavily affect building stability, public health, transportations and evacuation routes (airports, trains, road traffic) and lifelines (electric power supply). In this study, we propose a methodology named BET_VHst (Selva et al. 2014) for short-term PVHA of volcanic tephra dispersal based on automatic interpretation of measures from the monitoring system and physical models of tephra dispersal from all possible vent positions and eruptive sizes based on frequently updated meteorological forecasts. The large uncertainty at all the steps required for the analysis, both aleatory and epistemic, is treated by means of Bayesian inference and statistical mixing of long- and short-term analyses. The BET_VHst model is here presented through its implementation during two exercises organized for volcanoes in the Neapolitan area: MESIMEX for Mt. Vesuvius, and VUELCO for Campi Flegrei. References Selva J., Costa A., Sandri L., Macedonio G., Marzocchi W. (2014) Probabilistic short-term volcanic hazard in phases of unrest: a case study for tephra fallout, J. Geophys. Res., 119, doi: 10.1002/2014JB011252

  10. Principles of volcanic risk metrics: Theory and the case study of Mount Vesuvius and Campi Flegrei, Italy

    NASA Astrophysics Data System (ADS)

    Marzocchi, Warner; Woo, Gordon

    2009-03-01

    Despite volcanic risk having been defined quantitatively more than 30 years ago, this risk has been managed without being effectively measured. The recent substantial progress in quantifying eruption probability paves the way for a new era of rational science-based volcano risk management, based on what may be termed "volcanic risk metrics" (VRM). In this paper, we propose the basic principles of VRM, based on coupling probabilistic volcanic hazard assessment and eruption forecasting with cost-benefit analysis. The VRM strategy has the potential to rationalize decision making across a broad spectrum of volcanological questions. When should the call for evacuation be made? What early preparations should be made for a volcano crisis? Is it worthwhile waiting longer? What areas should be covered by an emergency plan? During unrest, what areas of a large volcanic field or caldera should be evacuated, and when? The VRM strategy has the paramount advantage of providing a set of quantitative and transparent rules that can be established well in advance of a crisis, optimizing and clarifying decision-making procedures. It enables volcanologists to apply all their scientific knowledge and observational information to assist authorities in quantifying the positive and negative risk implications of any decision.

  11. First combined flux chamber survey of mercury and CO2 emissions from soil diffuse degassing at Solfatara of Pozzuoli crater, Campi Flegrei (Italy): Mapping and quantification of gas release

    NASA Astrophysics Data System (ADS)

    Bagnato, E.; Barra, M.; Cardellini, C.; Chiodini, G.; Parello, F.; Sprovieri, M.

    2014-12-01

    There have been limited studies to date targeting gaseous elemental mercury (GEM) flux from soil emission in enriched volcanic substrates and its relation with CO2 release and tectonic structures. In order to evaluate and understand the processes of soil-air exchanges involved at Solfatara of Pozzuoli volcano, the most active zone of Campi Flegrei caldera (Italy), an intensive field measurement survey has been achieved in September 2013 by using high-time resolution techniques. Soil-air exchange fluxes of GEM and CO2 have been measured simultaneously at 116 points, widely distributed within the crater. Quantification of gas flux has been assessed by using field accumulation chamber method in conjunction with a Lumex®-RA 915 + portable mercury vapor analyzer and a LICOR for CO2 determination, respectively. The spatial distribution of GEM and CO2 emissions correlated quite closely with the hydrothermal and geological features of the studied area. The highest GEM fluxes (from 4.04 to 5.9 × 10- 5 g m- 2 d- 1) were encountered close to the southern part of the crater interested by an intense fumarolic activity and along the SE-SW tectonic fracture (1.26 × 10- 6-6.91 × 10- 5 g GEM m- 2 d- 1). Conversely, the lowest values have been detected all along the western rim of the crater, characterized by a weak gas flux and a lush vegetation on a very sealed clay soil, which likely inhibited mercury emission (range: 1.5 × 10- 7-7.18 × 10- 6 g GEM m- 2 d- 1). Results indicate that the GEM exchange between soil and air inside the Solfatara crater is about 2-3 orders of magnitude stronger than that in the background areas (10- 8-10- 7 g m- 2 d- 1). CO2 soil diffuse degassing exhibited an analogous spatial pattern to the GEM fluxes, with emission rates ranging from about 15 to ~ 20,000 g CO2 m- 2 d- 1, from the outermost western zones to the south-eastern sector of the crater. The observed significant correlation between GEM and CO2 suggested that in volcanic system GEM

  12. Seismic Reflection Imaging Of Volcanic Structures Below Campi Flegrei Submerged Caldera And Correlation With Well Log Data

    NASA Astrophysics Data System (ADS)

    Bruno, P. P.; di Fiore, V.; Rapolla, A.

    The deep volcanic structure and the stratigraphic realstionships of some of the vol- canic banks (Penta Palummo, Miseno and Nisida) cropping out in the Gulfo of Poz- zuoli were outlined using multichannel seismic reflection data. Correlation between the main shallow volcanic reflectors and onshore well geology data was made using well logs. Synthetic seismograms are essential to associate well geology to seismic data during the seismo-stratigraphic interpretation. Unfortunately sonic and density logs were not performed in the geothermal exploration wells located along the CF shore. Therefore we derived the pseudovelocity by resistivity logs according to Faust (1951). We also calculated the pseudodensity using the empirical equation often called GardnerSs rule (Gardner et al.,1974). Synthetic seismograms of well SS.Vito 8T pro- & cedil;jected over line NA02 (located offshore at about three km from the well) show a good correlation with the shallow reflectors and allow to infer that many reflections origi- nate at the interface between tuff and lava. References. Faust, L.Y., 1951 Seismic velocity as a function of depth and geologic time. Geo- physics, 16, 2, pp. 192-206. Gardner G.H.F., Gardner L.W., and Gregory A.R.. 1974, Formation velocity and density U The diagnostic basic for stratigraphic trap. Geo- physics, 39, pp. 770-780.

  13. Viscosity of Campi Flregrei (Italy) magmas

    NASA Astrophysics Data System (ADS)

    Misiti, Valeria; Vetere, Francesco; Scarlato, Piergiorgio; Behrens, Harald; Mangiacapra, Annarita; Freda, Carmela

    2010-05-01

    ν is the viscosity in Pa×s, T the temperature in K, and w is the water content in wt%; a, b, c, d, e, g are the Vogel-Fulcher-Tamman parameters. Each of the two compositions shows its own VTF parameters. Following this equation we can now calculate viscosity values for the two compositions under the condition inferred for Campi Flegrei magma chambers, i.e., water content from 0.3 to 3 wt%, T=1393K (Mangiacapra et al., 2008). For melt with 0.3 wt% water content we obtain viscosity values (ν in Pas) of 102.68and 102.24 for shoshonite and latite, respectively. At higher water contents of about 3 wt% the viscosity difference decreases to 101.71 (shoshonite) and 101.51 (latite). One important application of these data is the estimate of flow regime and magma rising velocity from deep to shallow reservoirs. Given the inferred magma water contents (0.3 and 3 wt%), temperature (1393K) and depth of deep and shallow reservoirs (9 and 4 km, respectively, Mangiacapra et al., 2008) and assuming a 2 m dyke wide, we have calculated (Lister and Kerry, 1991) a rising time from deep to shallow reservoir in the order of few minutes, 4.4 and 5.9 for a shoshonitic magma with 3 and 0.3 wt% water content, respectively. The same order of magnitude (4.1 and 5.2) has been obtained for latitic magma with similar amount of water. Lister and Kerry (1991) Fluid mechanical models of cracks propagation and their application to magmatic transport and dyke. Journal of Geophysical Research 96, 10049-10077. Mangiacapra A., Moretti, R., Rutherford L., Civetta L., Orsi G., Papale P. (2008) The deep magmatic system of the Campi Flegrei caldera (Italy). Geophysical Research Letters 35, L21304.

  14. 3D Imaging of Brittle/Ductile transition of the crust beneath the resurgent calderas

    NASA Astrophysics Data System (ADS)

    Tizzani, P.; Castaldo, R.; Pepe, S.; Solaro, G.

    2012-04-01

    Rheology is a crucial factor to understand the mechanical behaviour and evolution of the crust in young and tectonically active belts. The aim of this paper is to investigate the rheological properties of the crust beneath resurgent calderas as Long Valley caldera (California USA) and Campi Flegrei (Southern Italy). Through the rheological proprieties of the calderas area, we highlight the driving process that determine the cut off of the local seismicity [K. Ito, 1993]. In this context, we consider the thermal proprieties and mechanical heterogeneity of the crust in order to develop a 3D conductive time dependent thermal model of the upper crust beneath the two calderas. More specifically we integrate geophysical information (gravimetric, seismic and boreholes data) available for the considered area in FEM environment [Manconi A. et al., 2010]. We performed a numerical solution of Fourier equation to carry out an advance optimization of the real measured data. We produce a set of forward models and propose, in order to analyse and solve the statistical problem, the Monte Carlo optimization procedures as Genetic Algorithm [Manconi A. et al., 2009]. In particular we search for the heat production, the volume source distribution and the surface emissivity parameters that providing the best-fit of the geothermal profiles data measured at boreholes, by solving the non stationary heat flow equation (Campanian Ignimbrite eruption about 40 kyr for Campi Flegrei caldera and Bishop tuff eruption about 700 kyr for Long Valley caldera). The performed thermal fields allow us to obtain the rheological stratification of the crust beneath two resurgent calderas; the models suggest that the uprising of a ductile layer which connects the upper mantle to the volcanic feeding system could determine the stress conditions that controlled the distribution of seismicity. In fact, the computed 3D imaging of Brittle/Ductile transition well agrees with the seismic hypocentral distribution

  15. Forecasting the fate of caldera unrest through statistical analysis of monitoring data

    NASA Astrophysics Data System (ADS)

    Di Lorenzo, Riccardo; Sandri, Laura; Acocella, Valerio

    2015-04-01

    eruptions are preceded by an unrest episode, but not all unrest episodes culminate in an eruption; Eruptive unrest episodes are tipically shorter than failed unrest episodes, as confirmed by different independent algorithms (KS test and Fisher analysis). The binary decision tree shows that 79% of the eruptive unrest episodes show high seismicity, degassing and last less than 9 months; without considering the unrest duration, virtually all the several tens of eruptive unrest episodes in closed (non recently erupting) magmatic systems show high seismicity and degassing over periods longer than a few days; This has potential implications for the ongoing, currently aseismic unrest at Campi Flegrei caldera. This statistical analysis will be improved including also the Newhall and Dzurisin 1988 data and performing the time series analysis of the measured parameters, in order to better constrain caldera unrest and its possible culmination in eruptions.

  16. Decadal to monthly timescales of magma transfer and reservoir growth at a caldera volcano.

    PubMed

    Druitt, T H; Costa, F; Deloule, E; Dungan, M; Scaillet, B

    2012-02-01

    Caldera-forming volcanic eruptions are low-frequency, high-impact events capable of discharging tens to thousands of cubic kilometres of magma explosively on timescales of hours to days, with devastating effects on local and global scales. Because no such eruption has been monitored during its long build-up phase, the precursor phenomena are not well understood. Geophysical signals obtained during recent episodes of unrest at calderas such as Yellowstone, USA, and Campi Flegrei, Italy, are difficult to interpret, and the conditions necessary for large eruptions are poorly constrained. Here we present a study of pre-eruptive magmatic processes and their timescales using chemically zoned crystals from the 'Minoan' caldera-forming eruption of Santorini volcano, Greece, which occurred in the late 1600s BC. The results provide insights into how rapidly large silicic systems may pass from a quiescent state to one on the edge of eruption. Despite the large volume of erupted magma (40-60 cubic kilometres), and the 18,000-year gestation period between the Minoan eruption and the previous major eruption, most crystals in the Minoan magma record processes that occurred less than about 100 years before the eruption. Recharge of the magma reservoir by large volumes of silicic magma (and some mafic magma) occurred during the century before eruption, and mixing between different silicic magma batches was still taking place during the final months. Final assembly of large silicic magma reservoirs may occur on timescales that are geologically very short by comparison with the preceding repose period, with major growth phases immediately before eruption. These observations have implications for the monitoring of long-dormant, but potentially active, caldera systems. PMID:22297973

  17. Numerical models for ground deformation and gravity changes during volcanic unrest: simulating the hydrothermal system dynamics of a restless caldera

    NASA Astrophysics Data System (ADS)

    Coco, A.; Gottsmann, J.; Whitaker, F.; Rust, A.; Currenti, G.; Jasim, A.; Bunney, S.

    2016-04-01

    Ground deformation and gravity changes in restless calderas during periods of unrest can signal an impending eruption and thus must be correctly interpreted for hazard evaluation. It is critical to differentiate variation of geophysical observables related to volume and pressure changes induced by magma migration from shallow hydrothermal activity associated with hot fluids of magmatic origin rising from depth. In this paper we present a numerical model to evaluate the thermo-poroelastic response of the hydrothermal system in a caldera setting by simulating pore pressure and thermal expansion associated with deep injection of hot fluids (water and carbon dioxide). Hydrothermal fluid circulation is simulated using TOUGH2, a multicomponent multiphase simulator of fluid flows in porous media. Changes in pore pressure and temperature are then evaluated and fed into a thermo-poroelastic model (one-way coupling), which is based on a finite-difference numerical method designed for axi-symmetric problems in unbounded domains.

    Informed by constraints available for the Campi Flegrei caldera (Italy), a series of simulations assess the influence of fluid injection rates and mechanical properties on the hydrothermal system, uplift and gravity. Heterogeneities in hydrological and mechanical properties associated with the presence of ring faults are a key determinant of the fluid flow pattern and consequently the geophysical observables. Peaks (in absolute value) of uplift and gravity change profiles computed at the ground surface are located close to injection points (namely at the centre of the model and fault areas). Temporal evolution of the ground deformation indicates that the contribution of thermal effects to the total uplift is almost negligible with respect to the pore pressure contribution during the first years of the unrest, but increases in time and becomes dominant after a long period of the simulation. After a transient increase over the first years of

  18. A coupled hydrothermal and mechanical model for estimating thermo-poroelastic deformation, gravity and magnetic changes in calderas

    NASA Astrophysics Data System (ADS)

    Coco, A.; Gottsmann, J.; Whitaker, F.; Rust, A.; Currenti, G. M.; Jasim, A.

    2014-12-01

    Increasing integration of satellite and ground-based geophysical observations in volcanic areas has dramatically enhanced our ability to detect and track complex processes that can be difficult to reconcile with models of elastic mechanical behavior of upper crust. This study uses a thermo-poroelastic model to evaluate ground deformation, magnetic and gravity changes caused by hydrothermal fluid circulation and pressurization of magma chambers, in which surface topography, crustal heterogeneities and the presence of faults are taken into account. We develop a numerical framework for more realistic assessment of geophysical observations associated with volcanic processes, with particular focus on calderas. The numerical model is fully coupled with TOUGH2, a commercial software simulating multi-phase and multi-component fluid flow and heat transfer. The two-way coupling is performed through: (i) the concept of effective stress, which is controlled by pore pressure and thermal expansion, and (ii) empirical expressions for porosity, permeability, and capillary pressure, which are dependent on the effective stress. The model is applied to Campi Flegrei to simulate a generic unrest period caused by a deep injection of hot water and CO2. Vertical uplift reaches 12 cm in 3 years, with associated thermomagnetic variations of c. 14 nT and gravity changes of c. 210 μGal, comparable to those observed during the 1982-84 bradyseism. Gravity and magnetic signals continuously increase for 2 years and approach steady state after 2.5 years. The contribution of thermal effects to total ground deformation is almost negligible in the first 3 years, but reaches half of the total after 15 years, and is dominant after 35 years. We also simulated the presence of faults and the contribution of a deeper magma chamber pressurization, which affect considerably the sub-surface circulation, and consequently the geophysical changes at the surface.

  19. Downsag calderas, ring faults, caldera sizes, and incremental caldera growth

    NASA Astrophysics Data System (ADS)

    Walker, G. P. L.

    1984-09-01

    According to present concepts, a caldera is a more or less circular volcanic depression larger than a crater which is caused by subsidence. It is commonly considered that the subsided mass consists of a block or blocks encircled by a ring fracture. Caldera collapse is generally correlated with a major explosive eruption. The present investigation is concerned with six features which do not conform well with the favored caldera model. Attention is given to downsagged calderas, the distribution of postcaldera vents in calderas, vent rings, the size of calderas and cauldrons, incremental caldera growth, and caldera-forming events. It is found that no single structural or genetic model applies to all calderas. Thus, the fact of subsidence may be the only common feature. It is pointed out that most known ring dikes occur in Precambrian crust. This may mean that the subsiding piston mechanism operates best where the crust is sufficiently rigid and strong.

  20. Long time series of soil CO2 degassing measurements at Solfatara of Pozzuoli (Campi Flegrei, Italy)

    NASA Astrophysics Data System (ADS)

    Cardellini, Carlo; Chiodini, Giovanni; Rosiello, Angelo; Bagnato, Emanula; Avino, Rosario; Frondini, Francesco; Caliro, Stefano; Beddini, Giulio; Donnini, Marco; Lelli, Matto

    2016-04-01

    Since 1998, 28 extensive soil CO2 flux surveys, each including 400-500 measurements by accumulation chamber method, were performed over a large area (about 1.45 km2) covering the Solfatara crater and its surroundings. The statistical analysis of CO2 flux values, coupled with the measurement of the CO2 efflux isotopic composition, allowed to characterize the different CO2 sources feeding soil degassing and to investigate their temporal variability. Using a geostatistical approach the spatial structure of the degassing area, as well as the total amount of released CO2, have been defined. The area is characterized by a well defined diffuse degassing structure interested by the release of deeply derived CO2 (Solfatara DDS), which geometry is strongly controlled by volcanic and tectonic structures. The extension of the Solfatara DDS varied in the time with two major enlargements, the first consisted in its doubling in 2003-2004 and the second in further enlargement of about 30% occurred between 2011 and 2012. Both DDS enlargement mainly interested the area external to the crater in correspondence of the NE-SW fault system of Pisciarelli area. This area is also characterized by a very large increase in fumarolic emissions, in terms of both flow rate and discharge temperatures since 2005. The first event of DDS enlargements was previously correlated with the occurrence in 2000 of a relatively deep seismic swarm, which was interpreted as the indicator of the opening of an easy-ascent pathway for the transfer of magmatic fluids towards the shallower portion of the hydrothermal system; the second enlargement well correlates with the recent unrest phase of the system, characterized by an acceleration of the ground uplift. The amount of released CO2 has been estimated ranging between about 700 t/d and about 1500 t/d (with errors between 9 and 15 %) until the January 2015 when there was an increase up to 2800 t/d. After this maximum emission rate the flux slightly decrease during 2015 reaching again an CO2 output of 1500 t/d at November 2015. The CO2 variations in the last two years seems to follow the trend depicted by ground deformations, with increases of fluxes during the uplift accelerations and decreases of fluxes during the phases of relative "no-uplift". The comparison of the CO2 flux data with the chemical composition of the main fumaroles suggests that the variation of in the DDS extension is correlated to processes of condensation of the vapor plume feeding the Solfatara manifestation accompanied by an overall increase of the temperatures, caused by the arrival of increasing amounts of magmatic fluids

  1. Principles of Volcano Risk Metrics: theory and the case study of Mt. Vesuvius and Campi Flegrei.

    NASA Astrophysics Data System (ADS)

    Marzocchi, W.; Woo, G.

    2009-04-01

    Despite volcanic risk having been defined quantitatively more than thirty years ago, it has been always managed without being effectively measured. Yet, the recent substantial progress in quantifying eruption probability paves the way for a new era of rational science-based volcano risk management, that we name Volcanic Risk Metrics (VRM). In this talk, we propose some principles of VRM, based on two main components: a probabilistic volcanic hazard assessment and eruption forecasting, and a cost/benefit analysis. In a nutshell, the method assists managers in decision-making under uncertainty, weighing appropriately the cost and benefit of actions to mitigate the effects of a threat having a specific probability of occurrence. The strategy has the potential to rationalize decision-making across a broad spectrum of volcanological questions: what areas should be covered by emergency plan? What early preparations should be made for a volcano crisis? When should the call for evacuation be made? The strategy has the paramount advantage of providing a set of quantitative and transparent 'rules' that can be established before a crisis, optimizing and clarifying decision-making procedures. It places volcanologists at the centre of decision-making, applying all their scientific knowledge and observational information to assist authorities in quantifying the positive and negative risk implications of any decision.

  2. Caldera demonstration model

    USGS Publications Warehouse

    Venezky, Dina; Wessells, Stephen

    2010-01-01

    A caldera is a large, usually circular volcanic depression formed when magma is withdrawn or erupted from a shallow underground magma reservoir. It is often difficult to visualize how calderas form. This simple experiment using flour, a balloon, tubing, and a bicycle pump, provides a helpful visualization for caldera formation.

  3. Diffuse Soil CO2 Degassing at Solfatara of Pozzuoli (Campi Flegrei, Italy): 1998-2015, Sixteen Years of Flux Measurement.

    NASA Astrophysics Data System (ADS)

    Cardellini, C.; Chiodini, G.; Caliro, S.; Quareni, F.; Frondini, F.; Rosiello, A.; Avino, R.; Bagnato, E.

    2015-12-01

    Solfatara of Pozzuoli is one of the largest studied volcanic-hydrothermal system of the world releasing a large amount of deeply derived fluids. Since 1998, extensive soil CO2 flux surveys where performed using the accumulation chamber method over a large area (1.45 km2). The statistical analysis of CO2 flux, coupled with the investigation of the CO2 efflux isotopic composition, allowed to characterize the different CO2 sources and to investigate their temporal variability. The geostatistical elaboration of CO2 fluxes allowed to define the spatial structure of the degassing area, as well as the total amount of released CO2, pointing out the presence of a well defined diffuse degassing structure interested by the release of deeply derived CO2 (Solfatara DDS). The extension of the DDS experienced relevant variations with two major enlargements, the first consisted in its doubling in 2003-2004 and the second in further enlargement of about 30% in 2011-2012. These variations mainly occurred external to the crater area in correspondence of a NE-SW fault system (Pisciarelli area). The first event was previously correlated with the occurrence in 2000 of a relatively deep seismic swarm, which was interpreted as the indicator of the opening of an easy-ascent pathway for the transfer of magmatic fluids towards the shallower portion of the hydrothermal system; the second enlargement well correlates with the recent unrest phase of the system, characterized by an acceleration of the ground uplift. The amount of released CO2 has been estimated ranging between about 700 t/d and about 1500 t/d (with errors between 9 and 15 %) until the January 2015 when there was an increase up to 2800 t/d. The CO2 variations in the last two years seems to follow the trend depicted by ground deformations, with increases of fluxes during the uplift accelerations and decreases of fluxes during the phases of relative "no-uplift". The comparison of the CO2 flux data with the chemical composition of the main fumaroles suggests that the variation of in the DDS extension is correlated to processes of condensation of the vapor plume feeding the Solfatara manifestation accompanied by an overall increase of the temperatures, caused by the arrival of increasing amounts of deep fluids, possibly magmatic.

  4. Monitoring the geothermal fluid using time lapse electrical resistivity tomography: The Pisciarelli fumarolic field test site (Campi Flegrei, South Italy)

    NASA Astrophysics Data System (ADS)

    Fedele, Alessandro; Giulia Di Giuseppe, Maria; Troiano, Antonio; Somma, Reanto; Caputo, Teresa; Patella, Domenico; Troise, Claudia; De Natale, Giuseppe

    2015-04-01

    Pisciarelli area is a fumarolic field subject to very short time morphological changes. A number of critical problems affect this area, i.e. increase of temperature of the fumaroles above the average background temperature, local seismicity and occurrence of fumaroles mixed with jets of boiling water. The presence of a very shallow aquifer seem to have the control on the behavior and composition of the fumaroles. This fumarolic field is still largely unknown regarding geophysical surveys mainly because of its limited space, surrounded on the eastern side by intense urbanization inside the large Agnano crater (Troiano et al. 2014). Currently is mainly affected by geochemical, thermal and seismic monitoring which may not fully explain the behaviour of fluids surface. Many monitoring or time lapse (TL) applications are discussed in literature (e.g., White, 1994; Daily et al., 1995; Barker and Moore, 1998; Ramirez and Daily, 2001; Carter, 2002; Slater et al., 2002; Singha and Gorelick, 2005; Cassiani et al., 2006; Swarzenski et al., 2006; de Franco et al., 2009). However all these experiments are devoted to the use of the ERT for tracer tests or in contaminant hydrology and are characterized by a short monitoring period due to the complexity and problems of long-time instrument maintenance. We propose and present a first approach of a geophysical monitoring by time lapse electrical resistivity in a fumarolic field. The profiles were acquired in January 2013, in January, March, May, July, September and November 2014 respectively. They cross the Pisciarelli area following approximately the NS direction and were characterized by a 2.5 m electrode spacing and maximum penetration depth of about 20 m. and will supply fundamental evidences on the possible seasonal resistivity fluctuations or if the resistivity changes are indicative of an increase in volcanic gases present in the hydrothermal system.

  5. Comparative proximal features of the main Plinian deposits (Campanian Ignimbrite and Pomici di Base) of Campi Flegrei and Vesuvius

    NASA Astrophysics Data System (ADS)

    Scarpati, Claudio; Sparice, Domenico; Perrotta, Annamaria

    2016-07-01

    The proximal Plinian fall deposits of the Campanian Ignimbrite (CI; 38 ky, Fedele et al., 2008) and Pomici di Base (PdB; 18 ky, Bertagnini et al., 1998) have been investigated in order to understand the contribution of each part of the plume to the proximal sedimentation. Following Houghton et al. (2004b) we consider three main transport regimes: jet phase (producing facies Fb), buoyant region of the plume (producing facies Fa) and direct lateral ejection (producing facies Fc). As well documented in medial locations (Sparks et al., 1992, 1997; Ernst et al., 1996), transport regimes can develop different facies even in proximal locations according to the dynamics of the eruptive column. Our proximal deposits show stratification and diffuse bedding allowing us to introduce two new facies: stratified Fa (sFa) and diffuse bedded Fb (dbFb). These facies retain the transport regime previously proposed for Fa (buoyant plume) and Fb (jet phase) but their lithological features are influenced by near-vent depositional conditions. Lithology and sedimentological data (grain-size, componentry, maximum clasts) suggest that most of the sedimentation occurred mainly from the buoyant plume with simultaneous contribution from the other two different dynamic regimes. Coarse clasts falling from the lower margins of the plume strongly affected the sedimentation of the CI proximal fall deposit with a minor contribution from lithic clasts ballistically emplaced and partial collapses of the plume forming pyroclastic density currents. In contrast, the PdB proximal fall deposit was strongly affected by coarse clasts emplaced directly from the vent through parabolic trajectories, with very little contribution of material emplaced from the lower part of the plume. These differences can be attributed to different vent/conduit processes acting during the eruptions.

  6. PREFACE: Collapse Calderas Workshop

    NASA Astrophysics Data System (ADS)

    Gottsmann, Jo; Aguirre-Diaz, Gerardo

    2008-10-01

    Caldera-formation is one of the most awe-inspiring and powerful displays of nature's force. Resultant deposits may cover vast areas and significantly alter the immediate topography. Post-collapse activity may include resurgence, unrest, intra-caldera volcanism and potentially the start of a new magmatic cycle, perhaps eventually leading to renewed collapse. Since volcanoes and their eruptions are the surface manifestation of magmatic processes, calderas provide key insights into the generation and evolution of large-volume silicic magma bodies in the Earth's crust. Despite their potentially ferocious nature, calderas play a crucial role in modern society's life. Collapse calderas host essential economic deposits and supply power for many via the exploitation of geothermal reservoirs, and thus receive considerable scientific, economic and industrial attention. Calderas also attract millions of visitors world-wide with their spectacular scenic displays. To build on the outcomes of the 2005 calderas workshop in Tenerife (Spain) and to assess the most recent advances on caldera research, a follow-up meeting was proposed to be held in Mexico in 2008. This abstract volume presents contributions to the 2nd Calderas Workshop held at Hotel Misión La Muralla, Querétaro, Mexico, 19-25 October 2008. The title of the workshop `Reconstructing the evolution of collapse calderas: Magma storage, mobilisation and eruption' set the theme for five days of presentations and discussions, both at the venue as well as during visits to the surrounding calderas of Amealco, Amazcala and Huichapan. The multi-disciplinary workshop was attended by more than 40 scientist from North, Central and South America, Europe, Australia and Asia. Contributions covered five thematic topics: geology, geochemistry/petrology, structural analysis/modelling, geophysics, and hazards. The workshop was generously supported by the International Association of Volcanology and the Chemistry of The Earth's Interior

  7. Emi Koussi Caldera

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This is a view of the Emi Koussi Caldera captured by the Expedition Six Crew Observation (CEO) experiment aboard the International Space Station (ISS). Rising 2.3 km above the surrounding sandstone plains, Emi Koussi is a 6.5 km wide volcano located at the south end of the Tibesti Mountains in the central Sahara desert. The volcano is one of several in the Tibesti massif and has been used as a close analog to the famous Martian volcano Elysium Mons. Major charnels can be seen on volcanoes on both planets that indicate low points in caldera rims where lava spilled out of the pre-collapsed craters.

  8. Pavonis Mons Caldera

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Pavonis Mons is the middle of the three large volcanoes on the Tharsis bulge. This visible THEMIS image covers the edge of the volcano's caldera. Outside of the caldera, numerous lava flows and impact craters can be seen. In addition, there are a few small features which may be cinder cones. The best example is on the left hand side of the image, about two thirds of the way down from the top. There is an elevation difference of about 4.2 kilometers from the top of the volcano to the caldera floor. This image shows evidence for repeated episodes of mass wasting of the caldera wall, likely due to subsidence of the caldera over time.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

    Image information: VIS instrument. Latitude 0.8, Longitude 246.9 East (113.1 West). 19 meter/pixel resolution.

  9. Pavonis Mons Summit Caldera

    NASA Technical Reports Server (NTRS)

    2002-01-01

    [figure removed for brevity, see original site]

    This image shows part of the summit caldera of Pavonis Mons. Pavonis the middle of three Tharsis volcanos that form a line southeast of Olympus Mons and northwest of Vallis Marineris. On Earth volcanic calderas usually form when a massive eruption has emptied out the magma chamber and the 'roof' of the chamber collapses into the resultant space. It is likely that summit calderas on Martian volcanoes form in a similar manner.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  10. Arsia Mons Caldera Rim

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    This VIS image shows part of the caldera rim and floor of Arsia Mons. The arcuate fractures along the rim indicate multiple periods of activity -- both eruptions and collapse after eruptions. The floor of the caldera is very flat, having been filled by lava.

    Image information: VIS instrument. Latitude -9, Longitude 238.8 East (121.2 West). 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  11. Long Valley caldera GIS Database

    NASA Astrophysics Data System (ADS)

    Williams, M. J.; Battaglia, M.; Hill, D.; Langbein, J.; Segall, P.

    2002-12-01

    In May of 1980, a strong earthquake swarm that included four magnitude 6 earthquakes struck the southern margin of Long Valley Caldera associated with a 25-cm, dome-shaped uplift of the caldera floor. These events marked the onset of the latest period of caldera unrest that continues to this day. This ongoing unrest includes recurring earthquake swarms and continued dome-shaped uplift of the central section of the caldera (the resurgent dome) accompanied by changes in thermal springs and gas emissions. Analysis of combined gravity and geodetic data confirms the intrusion of silicic magma beneath Long Valley caldera. In 1982, the U.S. Geological Survey under the Volcano Hazards Program began an intensive effort to monitor and study geologic unrest in Long Valley Caldera. This database provides an overview of the studies being conducted by the Long Valley Observatory in Eastern California from 1975 to 2000. The database includes geological, monitoring and topographic datasets related to the Long Valley Caldera, plus a number of USGS publications on Long Valley (e.g., fact-sheets, references). Datasets are available as text files or ArcView shapefiles. Database CD-ROM Table of Contents: - Geological data (digital geologic map) - Monitoring data: Deformation (EDM, GPS, Leveling); Earthquakes; Gravity; Hydrologic; CO2 - Topographic data: DEM, DRG, Landsat 7, Rivers, Roads, Water Bodies - ArcView Project File

  12. A comprehensive classification of collapse calderas

    NASA Astrophysics Data System (ADS)

    Geyer, A.; Marti, J.; Acocella, V.; Aguirre-Diaz, G. J.; Cas, R. A.

    2012-12-01

    Collapse calderas are volcanic depressions that result from the disruption of the magma chamber roof during an eruption or lateral intrusion of magma. Their formation implies a perturbation of the structure and dynamics of the associated magma chambers. Collapse calderas are present in any geodynamic environment and may be associated with a wide range of magma compositions. Caldera morphology and structure yield information on subsidence mechanisms, evolutionary stage of collapse and the associated magma chamber, while any eruptive product provides the clues on magma composition and eruption dynamics. The term "caldera" has been commonly used to define certain sizes of collapses in volcanic areas, rather than a specific process. Moreover, several different classifications of collapse caldera have been proposed considering separately various aspects such as morphology, structure, composition, style of subsidence, size, eruption dynamics, or tectonic controls. However, the causative relationships between the resulting caldera types are not always well defined, thus causing confusion on the causes and results of each caldera process. This study has two main goals. 1) First, we provide a timely definition for calderas: we propose to restrict the term collapse caldera to those cases in which there is a direct interaction of the structures controlling collapse with an underlying magma chamber, independently of its size. 2) We present a comprehensive classification of collapse calderas based on an event tree structure that considers a hierarchy of criteria that we analyse in a logical sequence. This classification allows identifying any collapse caldera as a function of its dynamic, geometric, evolutionary and compositional conditions.

  13. Venus - Sag Caldera 'Sachs Patera

    NASA Technical Reports Server (NTRS)

    1991-01-01

    This image of Sachs Patera on Venus is centered at 49 degrees north, 334 degrees east. Defined as a sag-caldera, Sachs is an elliptical depression 130 meters (81 feet) in depth, spanning 40 kilometers (25 miles) in width along its longest axis. The morphology implies that a chamber of molten material drained and collapsed, forming a depression surrounded by concentric scarps spaced 2-to-5 kilometers (1.2- to-3 miles) apart. The arc-shaped set of scarps, extending out to the north from the prominent ellipse, is evidence for a separate episode of withdrawal; the small lobe-shaped extension to the southwest may represent an additional event. Solidified lava flows 10-to-25 kilometers (6-to-16 miles) long, give the caldera its flower-like appearance. The flows are a lighter tone of gray in the radar data because the lava is blockier in texture and consequently returns more radar waves. Much of the lava, which was evacuated from the chamber, probably traveled to other locations underground, while some of it may have surfaced further south. This is unlike calderas on Earth, where a rim of lava builds up in the immediate vicinity of the caldera.

  14. New light on caldera evolution - Askja, Iceland

    SciTech Connect

    Brown, G.C.; Everett, S.P.; Rymer, H.; McGarvie, D.W.; Foster I. )

    1991-04-01

    The large multiple-caldera volcanic system of Askja, central Iceland, is composed principally of subglacial basaltic hyaloclastite-pillow-lava formations and postglacial basaltic scoria and flows. Traditionally, such calderas are believed to be formed by downfaulting and ring-fracture collapse. Whereas this certainly applies to the smaller A.D. 1875 caldera, the older main caldera may have developed positive relief during subglacial construction of laterally confined hyaloclastite ridges above erupting fractures. This is supported by the evidence of a large negative gravity anomaly that reaches minima over the marginal low-density ridges but which is less negative within the caldera, where relatively dense postglacial lavas are believed to cover a more limited hyaloclastite succession beneath the caldera floor.

  15. Long term monitoring at Solfatara of Pozzuoli (Campi Flegrei, Italy): 1998-2014, fifteen years of soil CO2 flux measurement.

    NASA Astrophysics Data System (ADS)

    Cardellini, Carlo; Chiodini, Giovanni; Rosiello, Angelo; Bagnato, Emanuela; Avino, Rosario; Frondini, Francesco; Donnini, Marco; Caliro, Stefano

    2015-04-01

    With a flux of deeply derived fluids of ~5000 t/d and an energetic release of ~100 MW Solfatara of Pozzuoli is one of the largest studied volcanic-hydrothermal system of the world. Since 1998, soil CO2 flux surveys where performed using the accumulation chamber method over a large area (1.45 km2), including the volcanic apparatus and its surroundings. The statistical elaboration of CO2 flux, also coupled with the investigation of the CO2 efflux isotopic composition, allowed to characterize both the CO2 flux connected to by biological activity in the soil and that feed to the degassing of the hydrothermal system. A geostatistical elaboration of CO2 fluxes based on sequential Gaussian simulations, allowed to define the spatial structure of the degassing area, pointing out the presence of a well defined diffuse degassing structure interested by the release of deeply derived CO2 (Solfatara DDS). Solfatara DDS results well correlated to volcanic and tectonic structures interesting the crater area and the eastern area of Pisciarelli. With the same approach the total amount of CO2 release was estimated to range between 754 t/d and 1530 t/d in the last fifteen year (with an error in the estimate varying between 9 and 15 %). Also the extension of the DDS experienced relevant variations varying between 4.5x105 m2 to 12.3 x105 m2. In particular two major changes occurred in the extension of the DDS, the first consisted in its doubling in 2003-2004 and the second in further enlargement of ~ 30% in 2011-2012, the last occurring after period of decreasing trend which interrupted 4-5 years of relative stability. These variations mainly occurred external to the crater area in correspondence of a NE-SW fault system where fluxes increased from background to values typical of the endogenous source. The first event was previously correlated with the occurrence in 2000 of a relatively deep seismic swarm, which was interpreted as the indicator of the opening of an easy-ascent pathway for the transfer of magmatic fluids towards the shallower portion of the hydrothermal system; the second event of DDS enlargement well correlates with the recent unrest phase of the system, characterised by an acceleration of the ground uplift. The comparison of the CO2 flux data with the chemical composition of the main fumaroles suggests that the enlargements in the extension of the DDS are controlled by processes of pressurization of the buried gas plume feeding the Solfatara manifestation.

  16. A chemostratigraphic study of the Campanian Ignimbrite eruption (Campi Flegrei, Italy): Insights on magma chamber withdrawal and deposit accumulation as revealed by compositionally zoned stratigraphic and facies framework

    NASA Astrophysics Data System (ADS)

    Fedele, L.; Scarpati, C.; Sparice, D.; Perrotta, A.; Laiena, F.

    2016-09-01

    Petrochemical analyses of juvenile samples from twenty stratigraphic sections of the Campanian Ignimbrite medial deposits, located from 30 to 79 km from the vent, are presented here. Sampling has accurately followed a well-defined stratigraphic framework and the new component facies scheme. The Campanian Ignimbrite succession is formed by a basal plinian pumice fall deposit, overlain by a complex architecture of pyroclastic density current deposits emplaced from a single sustained pyroclastic density current through a mechanism of vertical and lateral accretion. The deposit is broadly zoned, from more evolved trachyte at its base to less evolved trachyte at its top, and is similarly less evolved with increasing distance from the area of emission. Irregular chemical trends are locally observed and interpreted to represent only a limited, "patchy" record of the entire vertical geochemical trend. The petrochemical variation observed horizontally was ascribed to changes in the flow dynamics and interaction between the advancing flow and the underlying topography. The results of this study were used to propose a unified volcanological-petrological model for the Campanian Ignimbrite eruption, taking into account the emplacement of both the proximal (i.e., the "Breccia Museo" formation) and medial deposits.

  17. Caldera in Sippar Sulcus, Ganymede

    NASA Technical Reports Server (NTRS)

    2001-01-01

    An irregularly shaped caldera, or pit, within the bright swath called Sippar Sulcus on Jupiter's moon Ganymede dominates this image taken by NASA's Galileo spacecraft. The high-standing interior of the caldera is interpreted as evidence of the flow of a viscous material.

    Elevation modeling indicates the height of the westernmost caldera floor material (arrow) is comparable to adjacent grooved material but decreases towards the east (right), where it is similar to nearby, lower-lying smooth terrain. The smooth terrain, generally lacking grooves or stripes, extends across the upper half of the image and crosscuts a similar but grooved band at the lower right. Analysis of such high-resolution images in combination with estimates of the features' relative elevations is helping scientists interpret the roles of volcanism and tectonics in creating the bright terrain on Ganymede.

    This image was prepared by the Lunar and Planetary Institute, Houston, and included in a report by Dr. Paul Schenk et al. in the March 1, 2001, edition of the journal Nature.

    The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Galileo mission for NASA's Office of Space Science, Washington, D.C.

    Images and data received from Galileo are posted on the Galileo mission home page at http://www.jpl.nasa.gov/galileo. Background information and educational context for the images can be found at http://www.jpl.nasa.gov/galileo/sepo.

  18. Nonstatistical dynamics on the caldera.

    PubMed

    Collins, Peter; Kramer, Zeb C; Carpenter, Barry K; Ezra, Gregory S; Wiggins, Stephen

    2014-07-21

    We explore both classical and quantum dynamics of a model potential exhibiting a caldera: that is, a shallow potential well with two pairs of symmetry related index one saddles associated with entrance/exit channels. Classical trajectory simulations at several different energies confirm the existence of the "dynamical matching" phenomenon originally proposed by Carpenter, where the momentum direction associated with an incoming trajectory initiated at a high energy saddle point determines to a considerable extent the outcome of the reaction (passage through the diametrically opposing exit channel). By studying a "stretched" version of the caldera model, we have uncovered a generalized dynamical matching: bundles of trajectories can reflect off a hard potential wall so as to end up exiting predominantly through the transition state opposite the reflection point. We also investigate the effects of dissipation on the classical dynamics. In addition to classical trajectory studies, we examine the dynamics of quantum wave packets on the caldera potential (stretched and unstretched). These computations reveal a quantum mechanical analogue of the "dynamical matching" phenomenon, where the initial expectation value of the momentum direction for the wave packet determines the exit channel through which most of the probability density passes to product. PMID:25053305

  19. Nonstatistical dynamics on the caldera

    SciTech Connect

    Collins, Peter; Wiggins, Stephen; Kramer, Zeb C. Ezra, Gregory S.; Carpenter, Barry K.

    2014-07-21

    We explore both classical and quantum dynamics of a model potential exhibiting a caldera: that is, a shallow potential well with two pairs of symmetry related index one saddles associated with entrance/exit channels. Classical trajectory simulations at several different energies confirm the existence of the “dynamical matching” phenomenon originally proposed by Carpenter, where the momentum direction associated with an incoming trajectory initiated at a high energy saddle point determines to a considerable extent the outcome of the reaction (passage through the diametrically opposing exit channel). By studying a “stretched” version of the caldera model, we have uncovered a generalized dynamical matching: bundles of trajectories can reflect off a hard potential wall so as to end up exiting predominantly through the transition state opposite the reflection point. We also investigate the effects of dissipation on the classical dynamics. In addition to classical trajectory studies, we examine the dynamics of quantum wave packets on the caldera potential (stretched and unstretched). These computations reveal a quantum mechanical analogue of the “dynamical matching” phenomenon, where the initial expectation value of the momentum direction for the wave packet determines the exit channel through which most of the probability density passes to product.

  20. The worldwide collapse caldera database (CCDB): A tool for studying and understanding caldera processes

    NASA Astrophysics Data System (ADS)

    Geyer, Adelina; Marti, Joan

    2015-04-01

    Collapse calderas are one of the most important volcanic structures not only because of their hazard implications, but also because of their high geothermal energy potential and their association with mineral deposits of economic interest. In 2008 we presented a new general worldwide Collapse Caldera DataBase (CCDB), in order to provide a useful and accessible tool for studying and understanding caldera collapse processes. The principal aim of the CCDB is to update the current field based knowledge on calderas, merging together the existing databases and complementing them with new examples found in the bibliography, and leaving it open for the incorporation of new data from future studies. Currently, the database includes over 450 documented calderas around the world, trying to be representative enough to promote further studies and analyses. We have performed a comprehensive compilation of published field studies of collapse calderas including more than 500 references, and their information has been summarized in a database linked to a Geographical Information System (GIS) application. Thus, it is possible to visualize the selected calderas on a world map and to filter them according to different features recorded in the database (e.g. age, structure). The information recorded in the CCDB can be grouped in seven main information classes: caldera features, properties of the caldera-forming deposits, magmatic system, geodynamic setting, pre-caldera volcanism,caldera-forming eruption sequence and post-caldera activity. Additionally, we have added two extra classes. The first records the references consulted for each caldera. The second allows users to introduce comments on the caldera sample such as possible controversies concerning the caldera origin. During the last seven years, the database has been available on-line at http://www.gvb-csic.es/CCDB.htm previous registration. This year, the CCDB webpage will be updated and improved so the database content can be

  1. Mineralized and unmineralized calderas in Spain; Part I, evolution of the Los Frailes Caldera

    USGS Publications Warehouse

    Cunningham, C.G.; Arribas, A., Jr.; Rytuba, J.J.; Arribas, A.

    1990-01-01

    The Cabo de Gata volcanic field of southeastern Spain contains several recently-recognized calderas. Some of the calderas are mineralized with epithermal gold, alunite, and base metal deposits, and others are barren, and yet they formed under generally similar conditions. Comparison of the magmatic, geochemical, and physical evolution of the Los Frailes, Rodalquilar, and Lomilla calderas provides insight into the processes of caldera evolution that led to precious-metal mineralization. The Los Frailes caldera formed at 14.4 Ma and is the oldest caldera. It formed in response to multiple eruptions of hornblende dacite magma. Following each eruption, the area collapsed and the caldera was invaded by the sea. Dacite domes fill the lower part of the caldera. Pyroxene andesites were erupted through the solidified core of the caldera and were probably initially responsible for magma generation. The Los Frailes caldera did not evolve to rhyolites nor was it subjected to the amount of structural development that the younger, mineralized Rodalquilar and Lomilla calderas were. ?? 1990 Springer-Verlag.

  2. Evolution of the Olympus Mons Caldera, Mars

    NASA Technical Reports Server (NTRS)

    Mouginis-Mark, Peter J.; Robinson, Mark S.; Zuber, Maria T.

    1990-01-01

    Extensive high-resolution (15 to 20 m/pixel) coverage of Olympus Mons volcano permits the investigation of the sequence of events associated with the evolution of the nested summit caldera. The sequence of the intra-caldera events is well illustrated by image data collected on orbits 473S and 474S of Viking Orbiter 1. These data cover both the oldest and youngest portions of the caldera floor. The chronology inferred from the observations is presented which in turn can be interpreted in terms of the internal structure of the volcano (i.e., magma chamber depth and the existence of dikes).

  3. Calderas and mineralization: volcanic geology and mineralization in the Chianti caldera complex, Trans-Pecos Texas

    SciTech Connect

    Duex, T.W.; Henry, C.D.

    1981-01-01

    This report describes preliminary results of an ongoing study of the volcanic stratigraphy, caldera activity, and known and potential mineralization of the Chinati Mountains area of Trans-Pecos Texas. Many ore deposits are spatially associated with calderas and other volcanic centers. A genetic relationship between calderas and base and precious metal mineralization has been proposed by some and denied by others. Steven and others have demonstrated that calderas provide an important setting for mineralization in the San Juan volcanic field of Colorado. Mineralization is not found in all calderas but is apparently restricted to calderas that had complex, postsubsidence igneous activity. A comparison of volcanic setting, volcanic history, caldera evolution, and evidence of mineralization in Trans-Pecos to those of the San Juan volcanic field, a major mineral producer, indicates that Trans-Pecos Texas also could be an important mineralized region. The Chianti caldera complex in Trans-Pecos Texas contains at least two calderas that have had considerable postsubsidence activity and that display large areas of hydrothermal alteration and mineralization. Abundant prospects in Trans-Pecos and numerous producing mines immediately south of the Trans-Pecos volcanic field in Mexico are additional evidence that ore-grade deposits could occur in Texas.

  4. Research Spotlight: Extraordinary uplift of Yellowstone caldera

    NASA Astrophysics Data System (ADS)

    Tretkoff, Ernie

    2011-02-01

    In Yellowstone National Park, located in Wyoming, Montana, and Idaho, the Yellow­stone caldera, which extends about 40 kilometers by 60 kilometers, began in 2004 a period of accelerated uplift, with rates of uplift as high as 7 centimeters per year. From 2006 to 2009 the uplift rate slowed. Global Positioning System (GPS) and interferometric synthetic aperture radar (InSAR) ground deformation measurements described by Chang et al. show that in the northern caldera, uplift decreased from 7 centimeters per year in 2006 to 5 in 2008 and 2 in 2009. In the southwestern portion of the caldera, uplift decreased from 4 centimeters per year in 2006 to 2 in 2008 and 0.5 in 2009, demonstrating a spatial pattern of ground motion decrease from southwest to northeast along the caldera. (”Geophysical Research Letters, doi:10.1029/2010GL045451, 2010)

  5. Caldera Formation on the Vance Seamounts

    NASA Astrophysics Data System (ADS)

    Clague, D.; Paduan, J.; Cousens, B.; Cornejo, L.; Perfit, M.; Wendt, R.; Stix, J.; Helo, C.

    2006-12-01

    The Vance Seamounts are a chain of near-ridge volcanoes located just west of the southern Juan de Fuca Ridge. The six volcanoes are built on ocean crust ranging from 0.78 Ma at the southeastern end to 2.55 Ma in the northwest. Morphologic analysis indicates that the volcanoes were constructed sequentially and get younger to the southeast towards the ridge axis. Like many near-ridge volcanoes, some of the Vance Seamounts have large offset calderas that presumably formed above evacuated shallow magma chambers within the upper ocean crust. In summer 2006, we completed 6 dives using MBARI's ROV Tiburon to study the formation of these calderas. The floor of each caldera consists of flat-lying volcaniclastite, under about 25 cm of pelagic sediment. Some caldera floors have mounds of post-caldera pillow flows. The caldera walls have a lower section covered by talus and an upper section of interbedded massive flows with columnar joints (to 11 m thick) and pillow basalts. The top of each caldera wall has a unit of volcanic mudstone to sandstone ranging from 20 cm to 2 m thick. The fine matrix of many of these samples is green hydrothermal clay. The finest siltstone to mudstone samples appear to be layers of massive tan hydrothermal clays. Talus fragments, lava and volcaniclastite outcrops are universally coated and cemented by 1 to 4 cm-thick deposits of hydrothermal Mn-oxide crusts, even on the youngest of the volcanoes. Volcanic particles in the sandstones are mostly dense angular glass, but bubble-wall fragments (limu o Pele) are present and indicate formation during low-energy pyroclastic eruptions. Without the few percent limu o Pele fragments, the glass fragments would resemble those inferred to form by quench granulation. We suggest that quench granulation is actually pyroclastic fragmentation that occurs as coalesced magmatic gas bubbles disrupt the molten lava surface at the vents. Our observations confirm that the more southeasterly offset calderas truncated thick

  6. Intracaldera volcanism and sedimentation - Creede Caldera, Colorado

    SciTech Connect

    Heiken, G.; Krier, D.; Snow, M.G.

    1997-06-01

    Within the Creede caldera, Colorado, many of the answers to its postcaldera volcanic and sedimentary history lie within the sequence of tuffaceous elastic sedimentary rocks and tuffs known as the Creede Formation. The Creede Formation and its interbedded ash deposits were sampled by research coreholes Creede 1 and 2, drilled during the fall of 1991. In an earlier study of the Creede Formation, based on surface outcrops and shallow mining company coreholes, Heiken and Krier concluded that the process of caldera structural resurgence was rapid and that a caldera lake had developed in an annulus ({open_quotes}moat{close_quotes}) located between the resurgent dome and caldera wall. So far we have a picture of intracaldera activity consisting of intermittent hydrovolcanic eruptions within a caldera lake for the lower third of the Creede Formation, and both magmatic and hydrovolcanic ash eruptions throughout the top two-thirds. Most of the ash deposits interbedded with the moat sedimentary rocks are extremely fine-grained. Ash fallout into the moat lake and unconsolidated ash eroded from caldera walls and the slopes of the resurgent dome were deposited over stream delta distributaries within relatively shallow water in the northwestern moat, and in deeper waters of the northern moat, where the caldera was intersected by a graben. Interbedded with ash beds and tuffaceous siltstones are coarse-grained turbidites from adjacent steep slopes and travertine from fissure ridges adjacent to the moat. Sedimentation rates and provenance for elastic sediments are linked to the frequent volcanic activity in and near the caldera; nearly all of the Creede Formation sedimentary rocks are tuffaceous.

  7. Italian super-eruption larger than thought

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2012-07-01

    Recent research suggested that the super-eruption of the Campi Flegrei caldera volcano in southern Italy about 40,000 years ago may have played a part in wiping out, or forcing the migration of, the Neanderthal and modern human populations in the eastern Mediterranean regions that were covered in ash. Now a new modeling study by Costa et al. suggests that this eruption may have been even larger than previously thought. This Campi Flegrei eruption produced a widespread ash layer known as Campanian Ignimbrite (CI). Using ash thickness measurements collected at 115 sites and a three-dimensional ash dispersal model, the researchers found that the CI super-eruption would have spread 250-300 cubic kilometers of ash across a 3.7-million-square kilometer region—2 to 3 times previous ash volume estimates.

  8. Stress evolution during caldera collapse

    NASA Astrophysics Data System (ADS)

    Holohan, E. P.; Schöpfer, M. P. J.; Walsh, J. J.

    2015-07-01

    The mechanics of caldera collapse are subject of long-running debate. Particular uncertainties concern how stresses around a magma reservoir relate to fracturing as the reservoir roof collapses, and how roof collapse in turn impacts upon the reservoir. We used two-dimensional Distinct Element Method models to characterise the evolution of stress around a depleting sub-surface magma body during gravity-driven collapse of its roof. These models illustrate how principal stress orientations rotate during progressive deformation so that roof fracturing transitions from initial reverse faulting to later normal faulting. They also reveal four end-member stress paths to fracture, each corresponding to a particular location within the roof. Analysis of these paths indicates that fractures associated with ultimate roof failure initiate in compression (i.e. as shear fractures). We also report on how mechanical and geometric conditions in the roof affect pre-failure unloading and post-failure reloading of the reservoir. In particular, the models show how residual friction within a failed roof could, without friction reduction mechanisms or fluid-derived counter-effects, inhibit a return to a lithostatically equilibrated pressure in the magma reservoir. Many of these findings should be transferable to other gravity-driven collapse processes, such as sinkhole formation, mine collapse and subsidence above hydrocarbon reservoirs.

  9. The Chacana caldera complex in Ecuador

    NASA Astrophysics Data System (ADS)

    Hall, Minard L.; Mothes, Patricia A.

    2008-10-01

    The Chacana caldera, located immediately east of Quito, capital of Ecuador, forms the most-northern edifice of Ecuadorõs rhyolite province. It is a 50X30 km Pleistocene structure that has remained active into historic times. Vitrophyres, welded tuffs, and ignimbrites of rhyolitic and dacitic composition constitute the outer flanks, meantime syngenetic breccias and tuffs, capped later by extensive dacite lava flows and basin sediments, filled the calderaõs depression. A notable resurgence occurred that lifted quiet-water sediments to over 4000 m in elevation. The area has numerous hot springs, and little seismic activity.

  10. Mineralized and unmineralized calderas in Spain; Part II, evolution of the Rodalquilar caldera complex and associated gold-alunite deposits

    USGS Publications Warehouse

    Rytuba, J.J.; Arribas, A., Jr.; Cunningham, C.G.; McKee, E.H.; Podwysocki, M.H.; Smith, James G.; Kelly, W.C.; Arribas, A.

    1990-01-01

    The Rodalquilar caldera complex is located in the western part of the Cabo de Gata volcanic field in southeastern Spain and is the first documented example of epithermal gold-alunite mineralization within a caldera in Europe. The Rodalquilar caldera is an oval collapse structure having a maximum diameter of 8 km and formed at 11 Ma from eruption of the Cinto ash-flow tuff. The oval Lomilla caldera, with a diameter of 2 km, is nested within the central resurgent dome of the older Rodalquilar caldera. The Lomilla caldera resulted from the eruption of the Lazaras ash-flow tuff which was ponded within the moat of the Rodalquilar caldera. The last phase of volcanic activity in the caldera complex was the emplacement of hornblende andesite flows and intrusions. This magmatic event resulted in structural doming of the caldera, opening of fractures and faults, and provided the heat source for the large hydrothermal systems which deposited quartz-alunite type gold deposits and base metal vein systems. The gold-alunite deposits are enclosed in areas of intense acid sulfate alteration and localized in ring and radial faults and fractures present in the east wall of the Lomilla caldera. Like other acid-sulfate type deposits, the Rodalquilar gold-alunite deposits are closely related in time and space to porphyritic, intermediate composition magma emplaced along caldera structures but unrelated to the caldera forming magmatic system. ?? 1990 Springer-Verlag.

  11. A Comparison of Historic Caldera-Forming Events

    NASA Astrophysics Data System (ADS)

    Stix, J.

    2002-12-01

    Recent field, experimental, and theoretical studies of calderas have advanced our understanding of how calderas form. With this in mind, I compare and contrast the styles and mechanisms of caldera development for five historic events: Katmai 1912, Kilauea 1924, Fernandina 1968, Pinatubo 1991, and Miyakejima 2000. As well as affording an opportunity to compare felsic and mafic systems, these examples allow us to identify systematic similarities and differences during the process of caldera formation. Critical questions include the following. (1) What are durations of caldera formation, as well as precursory signals and triggering mechanisms? (2) Why is there frequently a mismatch between caldera volumes at the surface and magma volume changes in the subsurface? (3) What are the relative proportions of erupted magma vs. magma which is drained and/or transported laterally in the subsurface? (4) How much magma is displaced, either by eruption or by drainage, before a caldera starts forming at the surface? (5) Does caldera subsidence occur en masse, incrementally, or somewhere between these two extremes of behavior? (6) Does subsidence of the caldera block help magma to be evacuated from the chamber, or is the subsidence process a passive response to magma withdrawal by other means? In addition to addressing the above questions, I will discuss how caldera formation influences the development of "open" and "closed" magmatic systems. Finally, I will discuss the problems of scaling, as the historic examples discussed here are 1-3 orders of magnitude smaller than large-scale caldera-forming ignimbrite eruptions.

  12. Renewed Geodetic Unrest at Santorini Caldera, Greece

    NASA Astrophysics Data System (ADS)

    Newman, A. V.; Stiros, S. C.; Moschas, F.; Saltogianni, V.; Feng, L.; Farmer, G. T.; Psimoulis, P.; Jiang, Y.

    2012-04-01

    Santorini Caldera, in the southern Aegean, is part of a well-developed, and very active volcanic system fueled by subduction along the Hellenic arc that is responsible for the largest volcanic eruption in human history (~1650 B.C.). After approximately 50 years of relative seismic quiescence within the caldera and an episode of minor inflation, the volcano has recently reawakened with an exponentially increasing inflation signal, beginning in January 2011. The GPS network, including 3 continuous stations and biennial surveys of 19 campaign stations, showed essentially no deformation between 2006 and 2010. Following a cluster of microseismicity within the caldera two surveys in June and August 2011 were made, while two additional permanent GPS stations were installed. From this data, we found uplift and nearly-radial expansion up to 1 cm/month. This deformation is well-explained by a Mogi-source at the northern part of the caldera, with an approximately 6-10 million m3 volumetric growth at approximately 4 km depth, and tendency for development of a new dome offshore. It is likely that stresses from this magma source are responsible for a cluster of microseismity that began in January 2011 along a radial lineament of young volcanics, called the 'Kameni Line'.

  13. Petrological cycles and caldera-forming events

    NASA Astrophysics Data System (ADS)

    Bachmann, O.; Deering, C. D.

    2012-12-01

    Many caldera-forming events can be framed within broad petrological cycles; volcanic stratigraphy typically defines a trend from mafic to more silicic magmas with time, culminating in the catastrophic evacuation of an upper crustal reservoir filled with the silicic magma, followed by a return to the eruption of more mafic magmas shortly after caldera collapse. Understanding how such cycles develop has clear implications for characterizing the current state of an active system. Here, we focus on a detailed examination of the well-exposed Quaternary Kos-Nisyros eruptive sequence (eastern Aegean arc) to frame a potential model for such cycles. On the basis of zircon U/Th/Pb ages, building the upper crustal magma chamber large enough to induce caldera collapse required at least a few hundred thousand years. This timeframe is necessary not only for the accumulation of large amounts of viscous, gas-rich silicic magma, but also to heat the upper crust sufficiently to allow the developing reservoir to be maintained above the solidus. In the Kos-Nisyros volcanic center, small eruptions precede the caldera-forming event and mark this period of thermal maturation as the system transitions from intermediate to silicic magma, reaching the most-evolved state only shortly prior to the caldera-forming event, the Kos Plateau Tuff (> 60 km3 of volatile-rich, high-silica rhyolite). The Kos Plateau Tuff was then followed by small-volume eruptions of more mafic magma (basaltic andesite, andesite, and dacites) that are characterized by a drier mineral assemblage. With time, the system transitioned back to cold, wet, high-SiO2 rhyolite. We suggest that the changes in magma composition and mineralogy following the caldera-forming event are due to a near-complete crystallization of the non-erupted mush in the upper crustal reservoir as it is abruptly decompressed during eruption. This rapid crystallization (1) leads to the formation of a porphyritic texture in the crystalline residual - a

  14. Microearthquakes at Valles Caldera, New Mexico: Improved Detection and Location with Two Additional Caldera Stations

    NASA Astrophysics Data System (ADS)

    Roberts, P. M.; House, L. S.; Ten Cate, J. A.

    2015-12-01

    The Los Alamos Seismic Network (LASN) has operated for 43 years, providing data to locate more than 2,500 earthquakes in north-central New Mexico. Roughly 1-2 earthquakes are detected and located per month within about 150 km of Los Alamos, a total of over 900 from 1973 to present. LASN's primary purpose is to monitor seismicity close to the Los Alamos National Laboratory (LANL) for seismic hazards; monitoring seismicity associated with the nearby Valles Caldera is secondary. Until 2010 the network was focused on monitoring seismic hazards and comprised only 7 stations, all near LANL or in the nearby Jemez Mountains. Just one station—PER, installed in 1998—was close enough to Valles Caldera to be able to detect microearthquakes located in or near the caldera. An initial study of the data from station PER between 1998 and 2002 identified and located 13 events with magnitudes less than 0.5 using the single-station hodogram technique. Those events were all located south of the caldera within a few kilometers of PER. Recently, two new digital broadband stations were installed inside the caldera, one on a northeastern ring-fracture dome, station CDAB, and the other on a northwestern dome, station SAMT. Also, station PER was upgraded with digital broadband instrumentation. Thus, LASN now can detect and record microearthquakes as small as magnitude -1.5 near the caldera, and they can be located using multiple arrival times. Several recent events located near station SAMT on the caldera's ring fracture are the first that have been seen in that area. Additional events were recorded (by all three stations) and located in the area south of the caldera where the earlier hodogram-only events were located. These new multi-station event recordings allow a more quantitative assessment of the uncertainties in the initial single-station hodogram locations. Each event is located using multiple arrival times as well as the hodogram method at as many as three stations. Thus

  15. Core lithology, Valles caldera No. 1, New Mexico

    SciTech Connect

    Gardner, J.N.; Goff, F.; Goff, S.; Maassen, L.; Mathews, K.; Wachs, D.; Wilson, D.

    1987-04-01

    Vallas caldera No. 1 (VC-1) is the first Continental Scientific Drilling Program research core hole in the Vallas caldera and the first continuously cored hole in the region. The hole penetrated 298 m of moat volcanics and caldera-fill ignimbrites, 35 m of volcaniclastic breccia, and 523 m of Paleozoic carbonates, sandstones, and shales with over 95% core recovery. The primary research objectives included coring through the youngest rhyolite flow within the caldera; obtaining structural and stratigraphic information near the intersection of the ring-fracture zone and the pre-caldera Jemez fault zone; and penetrating a high-temperature hydrothermal outflow plume near its source. This report presents a compilation of lithologic and geophysical logs and photographs of core that were collected while drilling VC-1. It is intended to be a reference tool for researchers interested in caldera processes and associated geologic phenomena.

  16. The Long Valley Caldera GIS database

    USGS Publications Warehouse

    Battaglia, Maurizio; Williams, M.J.; Venezky, D.Y.; Hill, D.P.; Langbein, J.O.; Farrar, C.D.; Howle, J.F.; Sneed, M.; Segall, P.

    2003-01-01

    This database provides an overview of the studies being conducted by the Long Valley Observatory in eastern California from 1975 to 2001. The database includes geologic, monitoring, and topographic datasets related to Long Valley caldera. The CD-ROM contains a scan of the original geologic map of the Long Valley region by R. Bailey. Real-time data of the current activity of the caldera (including earthquakes, ground deformation and the release of volcanic gas), information about volcanic hazards and the USGS response plan are available online at the Long Valley observatory web page (http://lvo.wr.usgs.gov). If you have any comments or questions about this database, please contact the Scientist in Charge of the Long Valley observatory.

  17. California's restless giant: the Long Valley Caldera

    USGS Publications Warehouse

    Hill, David P.; Bailey, Roy A.; Hendley, James W., II; Stauffer, Peter H.; Marcaida, Mae

    2014-01-01

    Scientists have monitored geologic unrest in the Long Valley, California, area since 1980. In that year, following a swarm of strong earthquakes, they discovered that the central part of the Long Valley Caldera had begun actively rising. Unrest in the area persists today. The U.S. Geological Survey (USGS) continues to provide the public and civil authorities with current information on the volcanic hazard at Long Valley and is prepared to give timely warnings of any impending eruption.

  18. Buried caldera of mauna kea volcano, hawaii.

    PubMed

    Porter, S C

    1972-03-31

    An elliptical caldera (2.1 by 2.8 kilometers) at the summit of Mauna Kea volcano is inferred to lie buried beneath hawaiite lava flows and pyroclastic cones at an altitude of approximately 3850 meters. Stratigraphic relationships indicate that hawaiite eruptions began before a pre-Wisconsin period of ice-cap glaciation and that the crest of the mountain attained its present altitude and gross form during a glaciation of probable Early Wisconsin age. PMID:17842285

  19. Eruptive History of Ikeda Caldera, Southern Kyushu, Japan

    NASA Astrophysics Data System (ADS)

    Inakura, H.; Naruo, H.; Okuno, M.; Kobayashi, T.; Tamura, T.

    2015-12-01

    Ikeda caldera is a small-scale caldera (about 4 km in diameter), located in the southern tip of the Satsuma Peninsula, southern Kyushu, Japan. The information on the onset of the caldera-forming eruption is gone due to the catastrophic eruption, but Ikeda caldera is a relatively small-scale eruption that the information before the eruption may have been conserved. We conducted a geological research to understand the eruptive history of Ikeda caldera, including a study of the processes leading to the catastrophic eruption. Pre-caldera activity began at about 20 cal kBP by Iwamoto ash and the effusion of Senta lava, which may have similar composition as the caldera-forming eruption. The caldera-forming eruption began at 6.4 cal kBP with a phreatic explosion that produced the Ikezaki tephra. The phreatic eruption was followed by Osagari scoria, Mizusako scoria and Ikeda pumice plinian eruption. During the climactic stage, Ikeda ignimbrite was erupted and reclaimed the coastal area at that time, and formed the ignimbrite plateau along the coast. Immediately after this event, four maars were formed to the southeast of the caldera. Yamagawa maar, which is the largest and is located at the southeastern end of the fissure vent, erupted pumiceous base surge (Yamagawa base surge), but other maars ejected small amount of accidental materials. During the late stage of the Ikeda eruption, phreatomagmatic eruption occurred at the bottom of the caldera floor, and erupted the Ikedako ash which covered a wide area. The Central lava dome was generated at the late stage of this eruption. After Ikedako ash deposition, secondary explosion of Ikeda ignimbrite occurred mainly along the coastal area, generating small-scale base surge deposits. About two thousand years after the caldera-forming eruption at 4.8 cal kBP, new magmatic activity began on the margin of the caldera rim, and generated Nabeshimadake lava dome.

  20. Caldera-Fill Sediments at Toba Caldera, Sumatra, Indonesia: A Field Reconnaissance Report

    NASA Astrophysics Data System (ADS)

    Chesner, C. A.; Barbee, O. A.; Lesmana, Z.; Nasution, A.

    2013-12-01

    The 74 ka Toba Caldera in northern Sumatra offers a unique opportunity to study caldera-fill sedimentation and its implications on the dynamic post-collapse history of Earth's largest Quaternary resurgent caldera. Although the complete 74,000 year sedimentation record is hidden beneath Lake Toba, a significant portion (~20-74 ka) of the post-caldera sedimentary sequence has been uplifted above lake level and is exposed on the 45 x 18 km Samosir Island resurgent dome. This extensive sedimentary record, over 100 m thick in places, is exposed by stream incision, and in resurgent dome fault scarps. Reconnaissance mapping and sampling of the sedimentary veneer covering Samosir Island was conducted in 2012-2013 to supplement recent sub-bottom seismic reflection profiling (chirp sonar) of the younger sediments and provide the basis for a more detailed caldera-fill sedimentation study at Toba. Our preliminary mapping indicates that distinct lacustrine and fluvial sedimentary sequences occur on Samosir Island. The lacustrine sequence dominates the surface exposures across the island and consists of interbedded clays, silts, sands, and diatomites. Different depositional environments and processes are suggested by regional variations in the componentry (i.e. abundance of diatoms, pumice clasts, reworked lake sediment clasts, rafted pumice blocks, etc.), but no significant ash-beds have been identified. An underlying coarse-grained indurated fluvial sequence is exposed in deeply incised drainages and fault scarps. This sequence consists mostly of coarse oxidized sands in eastern Samosir (approximately in the center of the caldera) that thicken and become coarser in western Samosir towards the caldera wall, where breccias and debris flows are also common. Blocks and boulders up to several meters in diameter derived from the basement rocks in the western caldera walls suggest a wedge of alluvial sediments formed before the lake reached its maximum level. Samples have been

  1. Caldera processes and magma-hydrothermal systems continental scientific drilling program: thermal regimes, Valles caldera research, scientific and management plan

    SciTech Connect

    Goff, F.; Nielson, D.L.

    1986-05-01

    Long-range core-drilling operations and initial scientific investigations are described for four sites in the Valles caldera, New Mexico. The plan concentrates on the period 1986 to 1993 and has six primary objectives: (1) study the origin, evolution, physical/chemical dynamics of the vapor-dominated portion of the Valles geothermal system; (2) investigate the characteristics of caldera fill and mechanisms of caldera collapse and resurgence; (3) determine the physical/chemical conditions in the heat transfer zone between crystallizing plutons and the hydrothermal system; (4) study the mechanism of ore deposition in the caldera environment; (5) develop and test high-temperature drilling techniques and logging tools; and (6) evaluate the geothermal resource within a large silicic caldera. Core holes VC-2a (500 m) and VC-2b (2000 m) are planned in the Sulphur Springs area; these core holes will probe the vapor-dominated zone, the underlying hot-water-dominated zone, the boiling interface and probable ore deposition between the two zones, and the deep structure and stratigraphy along the western part of the Valles caldera fracture zone and resurgent dome. Core hole VC-3 will involve reopening existing well Baca number12 and deepening it from 3.2 km (present total depth) to 5.5 km, this core hole will penetrate the deep-crystallized silicic pluton, investigate conductive heat transfer in that zone, and study the evolution of the central resurgent dome. Core hole VC-4 is designed to penetrate deep into the presumably thick caldera fill in eastern Valles caldera and examine the relationship between caldera formation, sedimentation, tectonics, and volcanism. Core hole VC-5 is to test structure, stratigraphy, and magmatic evolution of pre-Valles caldera rocks, their relations to Valles caldera, and the influences of regional structure on volcanism and caldera formation.

  2. The Las Cañadas caldera (Tenerife, Canary Islands): an overlapping collapse caldera generated by magma-chamber migration

    NASA Astrophysics Data System (ADS)

    Marti, J.; Gudmundsson, A.

    2000-12-01

    The Las Cañadas caldera is one of the most important geological structures of Tenerife. Stratigraphic, structural, volcanological, petrological, geochronological, and geophysical data suggest that the Las Cañadas caldera resulted from multiple vertical collapse episodes that occurred during the construction of the Las Cañadas edifice Upper Group. Three long-term (≥200 ka) cycles of phonolitic explosive activity, each culminating with a caldera collapse, have been identified in the Upper Group. During the construction of the Upper Group, the focus of felsic volcanism migrated from west to east. Using the results of field observations, experimental analogue models and numerical studies, we propose that the formation of the overlapping Las Cañadas collapse caldera is related to the migration of the associated magma chamber. Our model implies that each collapse of this overlapping caldera partly, or completely, destroyed the feeding magma chamber. This destruction led to changes in the local stress field that favoured the formation of a new chamber at one side of the previous one, resulting in magma-chamber migration. The proposed model accounts for the formation of the Las Cañadas caldera. In particular, it explains the geometrical relationships, stratigraphy and chronology of the caldera wall deposits. Comparison with other overlapping collapse calderas suggests that our model may apply to other overlapping calderas.

  3. Yellowstone and Long Valley - A Comparison of Two Restless Calderas

    NASA Astrophysics Data System (ADS)

    Hill, D. P.; Smith, R. B.

    2007-12-01

    Three large, silicic calderas in the conterminous United States have explosively erupted volumes > 300 km3 within in the last 2 million years -- Yellowstone caldera (Wyoming) Long Valley caldera (California) and the Vallez caldera (New Mexico) all located in extensional tectonic environments. All have shown varying levels of historic unrest. Pronounced unrest episodes at Yellowstone and Long Valley calderas over the past three decades stimulated extensive research on these two closely monitored calderas, and we explore some emerging similarities and differences. Yellowstone caldera is underlain by a long-lived (> 17 my) upper-mantle hot-spot that has fed a series of caldera-forming, extending to the southwest across southern Idaho to central Oregon including three caldera-forming eruptions from the Yellowstone caldera system in the last 2 my, the most recent at 600,000 ybp. It is marked by relatively low density and low seismic velocities extending to depths of at least 400 km and a regional topographic swell with elevations exceeding 2000 m. The extensive Yellowstone hydrothermal system has a thermal output of 5 GW. The most recent magmatic eruption dated at 70,000 ybp. By comparison, Long Valley caldera is underlain by a relatively modest "hot-spot", the locus of which appears to be influenced by a dilatational jog between the dextral Eastern California Shear Zone and the Walker Lane and westward delamination of the dense lithospheric root of the adjacent Sierra Nevada. The Long Valley system has fed multiple eruptions of over the past 4 my and a single caldera-forming eruption at 760,000 ybp. It is marked by a limited topographic swell but with the elevation of the caldera floor and adjacent basins comparable to the 2000-plus m elevation of the Yellowstone swell. Long Valley caldera hydrothermal system has a thermal output of 0.3 GW (including a 40 MW geothermal power plant). The most recent eruptions from the Long Valley Caldera- Mono Domes volcanic field

  4. The Cerro Aguas Calientes caldera, NW Argentina: An example of a tectonically controlled, polygenetic collapse caldera, and its regional significance

    NASA Astrophysics Data System (ADS)

    Petrinovic, I. A.; Martí, J.; Aguirre-Díaz, G. J.; Guzmán, S.; Geyer, A.; Paz, N. Salado

    2010-07-01

    Polygenetic, silicic collapse calderas are common in the central Andes. Here we describe in detail the Cerro Aguas Calientes caldera in NW Argentina, which comprises two caldera-forming episodes that occurred at 17.15 Ma and 10.3 Ma. We analyse the significance of its structural setting, composition, size and the subsidence style of both caldera episodes. We find that the caldera eruptions had a tectonic trigger. In both cases, an homogeneous dacitic crystal-rich (>60 vol.% of crystals) reservoir of batholithic size became unstable due to the effect of increasing regional transpression, which favoured local dilation through minor strike-slip faults from which ring faults nucleated and permitted caldera collapse. Both calderas are similar in shape, location and products. The 17.15 Ma caldera has an elliptical shape (17 × 14 km) elongated in a N30° trend; both intracaldera and extracaldera ignimbrites covered an area of around 620 km 2 with a minimum volume estimate of 140 km 3 (DRE). The 10.3 Ma episode generated another elliptical caldera (19 × 14 km), with the same orientation as the previous one, from which intracaldera and outflow ignimbrites covered a total area of about 1700 km 2, representing a minimum eruption volume of 350 km 3(DRE). In this paper we discuss the significance of the Cerro Aguas Calientes caldera in comparison with other well known examples from the central Andes in terms of tectonic setting, eruption mechanisms, and volumes of related ignimbrites. We suggest that our kinematic model is a common volcano-tectonic scenario during the Cenozoic in the Puna and Altiplano, which may be applied to explain the origin of other large calderas in the same region.

  5. The Cerro Aguas Calientes caldera, NW Argentina: an example of a tectonically controlled, polygenetic, collapse caldera, and its regional significance

    NASA Astrophysics Data System (ADS)

    Petrinovic, Ivan A.; Martí, Joan; Aguirre-Diaz, Gerardo J.; Guzmán, Silvina R.; Geyer, Adelina; Grosse, Pablo; Salado Paz, Natalia

    2010-05-01

    Polygenetic, silicic collapse calderas such as Cerro Galán, Pastos Grandes, La Pacana, Vilama, Negra Muerta, Farallón Negro, Cerro Guacha, among others are common in the central Andes. Here we describe in detail the Cerro Aguas Calientes caldera in NW Argentina, which comprises two caldera-forming episodes occurred at 17.15 Ma and 10.3 Ma, respectively. We analyse the significance of its structural setting, composition, size and the subsidence style of both caldera episodes. Our results reveal that the caldera eruptions had a tectonic trigger. In both cases, an homogeneous dacitic crystal-rich (>60 vol. % of crystals) reservoir of batholitic size became unstable due to the effect of increasing regional transpression, favouring local dilation throughout minor strike slip faults from which ring faults nucleated and permitted caldera collapse. Both episodes are similar in shape, location and products of the resulting calderas. The 17.15 Ma caldera has an elliptical shape (17 × 14 km) and is elongated in a N30° trend; both intracaldera and extracaldera ignimbrites covered an area of around 620 km2 with a minimum volume estimate of 138 km3 (DRE). The 10.3 Ma episode generated another elliptical caldera (19 ×14 km), with the same orientation as the previous one, from which intracaldera and outflow ignimbrites covered a total area of about 1,700 km2, representing a minimum eruption volume of 341 km3 (DRE). In this work we discuss the significance of the Cerro Aguas Calientes caldera in comparison with other well known examples from the central Andes in terms of tectonic setting, eruption mechanisms, and volumes of related ignimbrites. We suggest that our kinematic model is a common volcano-tectonic scenario during the Cenozoic in the Puna and Altiplano, which may be applied to explain the origin of other large calderas in the same region.

  6. Setting A Stopwatch for Post-Caldera Effusive Rhyolite Eruptions at Yellowstone caldera, Wyoming

    NASA Astrophysics Data System (ADS)

    Till, C. B.; Vazquez, J. A.; Boyce, J. W.

    2015-12-01

    Rejuvenation of previously intruded silicic magma is an important process leading to effusive rhyolite, which is the most common product of volcanism at calderas with protracted histories of eruption and unrest such as Yellowstone caldera (Wyoming), Long Valley caldera (California), and Valles caldera (New Mexico) in the United States. Although orders of magnitude smaller in volume than rare caldera-forming supereruptions, these relatively frequent effusions of rhyolite are comparable to the largest eruptions of the 20th century and pose a considerable volcanic hazard. However, the physical pathway from rejuvenation to eruption of silicic magma is unclear, particularly because the time between reheating of a subvolcanic intrusion and eruption is poorly quantified. This study uses trace element diffusion in sanidine crystals measured at nanometer-scale with NanoSIMS to reveal that rejuvenation of a near-solidus or subsolidus silicic intrusion occurred within ~10 months following a protracted period (220 k.y.) of volcanic repose, and resulted in effusion of ~3 km3 of high-silica rhyolite lava at the onset of Yellowstone's last volcanic interval. In addition we find that the frequently made assumption in geospeedometry of a step-function initial condition can be inaccurate despite petrographic evidence for resorption, and can be addressed by interrogating diffusion time scale concordance between multiple trace elements that are geochemically similar. The results of this study reveal that a sufficiently energetic rejuvenation of Yellowstone's shallow crystal-melt mush and/or hydrothermally altered wall rock could lead to an effusive eruption within months. Fortunately, any significant rejuvenation of the reservoir is likely to be associated with deformation or seismicity and identifiable by geophysical monitoring.

  7. Land- and resource-use issues at the Valles Caldera

    SciTech Connect

    Intemann, P.R.

    1981-01-01

    The Valles Caldera possesses a wealth of resources from which various private parties as well as the public at large can benefit. Among the most significant of these are the geothermal energy resource and the natural resource. Wildlife, scenic, and recreational resources can be considered components of the natural resource. In addition, Native Americans in the area value the Valles Caldera as part of their religion. The use of land in the caldera to achieve the full benefits of one resource may adversely affect the value of other resources. Measures can be taken to minimize adverse affects and to maximize the benefits of all the varied resources within the caldera as equitably as possible. An understanding of present and potential land and resource uses in the Caldera, and who will benefit from these uses, can lead to the formulation of such measures.

  8. Elongate summit calderas as Neogene paleostress indicators in Antarctica

    USGS Publications Warehouse

    Paulsen, T.S.; Wilson, T.J.

    2007-01-01

    The orientations and ages of elongate summit calderas on major polygenetic volcanoes were compiled to document Miocene to Pleistocene Sh (minimum horizontal stress) directions on the western and northern flanks of the West Antarctic rift system. Miocene to Pleistocene summit calderas along the western Ross Sea show relatively consistent ENE long axis trends, which are at a high angle to the Transantarctic Mountain Front and parallel to the N77ºE Sh direction at Cape Roberts. The elongation directions of many Miocene to Pleistocene summit calderas in Marie Byrd Land parallel the alignment of polygenetic volcanoes in which they occur, except several Pleistocene calderas with consistent NNE to NE trends. The overall pattern of elongate calderas in Marie Byrd Land is probably due to a combination of structurally controlled orientations and regional stress fields in which Sh is oriented NNE to NE at a moderate to high angle to the trace of the West Antarctic rift system.

  9. The graben caldera of Guanajuato, Mexico

    NASA Astrophysics Data System (ADS)

    Aguirre-Diaz, G. J.; Tristán-González, M.; Labarthe-Hernández, G.; Marti, J.

    2013-05-01

    Guanajuato has been an important gold and silver mineral district of Mexico since the 16th century until Present. Famous mines such as Rayas, La Valenciana and El Cubo, are part of this important mining development. Stratigraphy and structures are well known, and major faults and vein systems are precisely mapped. The series include a Mesozoic metamorphosed volcano-sedimentary sequence interpreted as a tectonically accreted terrane during Early Cretaceous subduction; a >1000 m thick red beds sequence, apparently Eocene and interpreted originally as molasses posterior to K/T Laramide orogeny, but more probably fanglomerates filling a graben formed during mid-Tertiary extension; an Eocene-Miocene volcanic sequence that accumulated in this tectonic basin and the surrounding area, including andesitic lavas, silicic ignimbrites and surge deposits, and rhyolitic domes. Pyroclastic rocks have not been studied with a volcanological approach, with the purpose of understanding the physical volcanic processes that formed them. Randall (1994) suggested a caldera source for some of them. Our purpose is to describe the volcanic processes involved in the mid-Tertiary units of Guanajuato. There are dacitic and andesitic lavas that were apparently contemporaneous with deposition of the Red Conglomerate of Guanajuato. The ignimbrites correspond to the Sierra Madre Occidental volcanic province. These units were originated as two main pyroclastic densety currents sequences that formed the Loseros-Bufa and the Calderones formations. The former is rhyolitic and the later andesitic-dacitic. Loseros is composed of a series of thin-bedded to laminated pyroclastic surge deposits in continuous and concordant contact with overlying Bufa massive ignimbrite. Bufa ignimbrite is partly welded, with columnar jointing, completely devitrified, and highly silicified by post-deposition hydrothermalism and/or vapor phase alteration. Co-ignimbrite lithic lag breccias are observed at several sites in

  10. Central San Juan caldera cluster: regional volcanic framework

    USGS Publications Warehouse

    Lipman, Peter W.

    2000-01-01

    Eruption of at least 8800 km3 of dacitic-rhyolitic magma as 9 major ash-slow sheets (individually 150-5000 km3) was accompanied by recurrent caldera subsidence between 28.3 and about 26.5 Ma in the central San Juan Mountains, Colorado. Voluminous andesitic-decitic lavas and breccias were erupted from central volcanoes prior to the ash-flow eruptions, and similar lava eruptions continued within and adjacent to the calderas during the period of explosive volcanism, making the central San Juan caldera cluster an exceptional site for study of caldera-related volcanic processes. Exposed calderas vary in size from 10 to 75 km in maximum diameter, the largest calderas being associated with the most voluminous eruptions. After collapse of the giant La Garita caldera during eruption if the Fish Canyon Tuff at 17.6 Ma, seven additional explosive eruptions and calderas formed inside the La Garita depression within about 1 m.y. Because of the nested geometry, maximum loci of recurrently overlapping collapse events are inferred to have subsided as much as 10-17 km, far deeper than the roof of the composite subvolcanic batholith defined by gravity data, which represents solidified caldera-related magma bodies. Erosional dissection to depths of as much as 1.5 km, although insufficient to reach the subvolcanic batholith, has exposed diverse features of intracaldera ash-flow tuff and interleaved caldera-collapse landslide deposits that accumulated to multikilometer thickness within concurrently subsiding caldera structures. The calderas display a variety of postcollapse resurgent uplift structures, and caldera-forming events produced complex fault geometries that localized late mineralization, including the epithermal base- and precious-metal veins of the well-known Creede mining district. Most of the central San Juan calderas have been deeply eroded, and their identification is dependent on detailed geologic mapping. In contrast, the primary volcanic morphology of the

  11. Seismic imaging of the Medicine Lake Caldera

    SciTech Connect

    Zucca, J.J.; Evans, J.R.; Kasameyer, P.W.

    1987-04-01

    Medicine Lake Volcano, a broad shield volcano about 50 km east of Mount Shasta in northern California, produced rhylotic eruptions as recently as 400 years ago. Because of this recent activity it is of considerable interest to producers of geothermal energy. The USGS and LLNL conducted an active seismic experiment designed to explore the area beneath and around the caldera. This experiment had two purposes: To produce high-quality velocity and attenuation images of the young magma body presumed to be the source for the young volcanic features, and to collect a dataset that can be used to develop and test seismic imaging methods that may be useful for understanding other geothermal systems. Eight large explosions were detonated in a 50 km radius circle around the volcano, a distance chosen to produce strong upward traveling signals through the area of interest. The data were inverted using Aki's method to produce three-dimensional velocity and attenuation images of the sub-surface. Preliminary interpretation shows low velocity and attenuation on the flanks of the volcano, and coincident high attenuation values and low velocities (-20%) from 3 to 5 km beneath the center of the caldera. This zone may be a region of partial melt which fed the youngest eruptions.

  12. Arcuate Fractures in Olympus Mons Caldera

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    This VIS image shows part of the caldera at the summit of Olympus Mons -- a huge volcano. The arcuate (curved) fractures seen on the right side of the caldera floor were likely formed when later eruptions occurred -- note the smoother, younger section to the left.

    Image information: VIS instrument. Latitude 18.2, Longitude 226.9 East (133.1 West). 19 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  13. Regional and local tectonics at Erta Ale caldera, Afar (Ethiopia)

    NASA Astrophysics Data System (ADS)

    Acocella, Valerio

    2006-10-01

    Erta Ale volcano lies along the on-shore Red Sea Rift (northern Afar, Ethiopia), separating the Nubia and Danakil plates. Erta Ale has a NNW-SSE elongated caldera, with a subvertical rim scarp, hosting a lava lake. Structural field work was aimed at defining the deformation pattern around the caldera. The caldera consists of along-rim and across-rim structures, resulting from local and regional (maximum extension ˜NE-SW) stress fields, respectively. These structures cross-cut each other at high angles, suggesting that the two stress fields remain distinct, each prevailing during rifting or caldera collapse. The local along-rim extensional fractures are gravity-driven structures that formed due to the retreat of the caldera wall after collapse, and are confined to the region of caldera subsidence. The across-rim structures are mainly located to the N and S of the caldera, where they form rift zones each accommodating a similar amount of extension (˜6.3 m), but displaying different trends and extension directions. Analogue models of interacting fractures are consistent with the Southern Rift being representative of the regional fault kinematics, while the Northern Rift is a local perturbation, resulting from the interaction between two right-stepping rift segments along the Erta Ale Range.

  14. Historical unrest at large calderas of the world

    SciTech Connect

    Newhall, C.A.; Dzurisin, D.

    1989-09-01

    This is a remarkable reference for researchers interested in volcanic hazards and silicic volcanism. Because of long repose and often obscure shapes and large size calderas are a volcanic type less obvious and less well studied. Because they represent potentially highly dangerous and highly explosive volcanos which could have large-scale and even global impact when they erupt, it is very important to understand their behavior. This new volume represents an extensive effort at compiling real observations at earth's calderas. The authors manage to incorporate a very impressive list of original references that go far beyond standard volcanological literature and also often extend back many centuries to include the perspective of longer historic time at some calderas. If volcanologists are serious about eruption forecasting, they must be willing to dig out and absorb the lessons of historic observations as well as design instruments and make good measurements. There is an initial introductory chapter of 27 pages which attempts to lead the way to interpretation of various patterns of caldera unrest, based on synthesis of the various individual cases. The meat of the volumes is in sections on the individual calderas, enriched with many maps and figures documenting the caldera unrest. A valuable asset of the compilation is its broad scope, which incorporates the activity of related or possibly related cones, domes, solfataras, etc., with the parent ( ) caldera.

  15. Stratigraphy of Reforma Caldera, Baja California Sur, Mexico

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    The Reforma caldera is located at ~35 km to the northwest of Santa Rosalía in the central part of the Baja California peninsula. It has 10 km in diameter and a maximum height of 1200 masl in the center and between 100 and 500 masl in its slopes. Reforma is within a tectonic zone affected by two fault systems: A NW-SE normal fault system linked to the opening of the Gulf of California, and a NNW-SSE and NW-SE strike-slip fault system associated with an active Riedel system. Reforma was built upon Cretaceous granites that outcrop at the caldera center, Miocene to Pliocene volcano-sedimentary rocks of the Comondú group, and Miocene marine sediments of the Santa Rosalía basin. On top of these rocks outcrop at least four submarine to subaerial ignimbrites interbedded with marine fossiliferous beds and the lower Pleistocene deposits associated to the Reforma caldera. These deposits are formed by a ignimbrite that shifts to different lithofacies that change gradually their welding, here dubbed basal, transitional, intermediate, and upper (all of then enriched in black fiammes), followed by a pumice-rich, white fiammes, and vitrophyre lithofacies, which are distributed around the 9 km wide caldera and have been associated to the caldera formation episode. Deposits related to post-caldera volcanism are andesite-basaltic lava flows erupted along the caldera rim through localized feeding dikes and andesitic and rhyolitic domes, and scoria cinder cones exposed inside and outside the caldera. On top of these deposits rest the middle Pleistocene Aguajito caldera deposits.

  16. AmeriFlux US-Vcp Valles Caldera Ponderosa Pine

    DOE Data Explorer

    Litvak, Marcy [University of New Mexico

    2016-01-01

    This is the AmeriFlux version of the carbon flux data for the site US-Vcp Valles Caldera Ponderosa Pine. Site Description - The Valles Caldera Ponderosa Pine site is located in the 1200km2 Jemez River basin of the Jemez Mountains in north-central New Mexico at the southern margin of the Rocky Mountain ecoregion. The Ponderosa Pine forest is the warmest and lowest (below 2700m) zone of the forests in the Valles Caldera National Preserve. Its vegetation is composed of a Ponderosa Pine (Pinus Ponderosa) overstory and a Gambel Oak (Quercus gambelii) understory.

  17. Recent crustal subsidence at Yellowstone Caldera, Wyoming

    USGS Publications Warehouse

    Dzurisin, D.; Savage, J.C.; Fournier, R.O.

    1990-01-01

    Following a period of net uplift at an average rate of 15??1 mm/year from 1923 to 1984, the east-central floor of Yellowstone Caldera stopped rising during 1984-1985 and then subsided 25??7 mm during 1985-1986 and an additional 35??7 mm during 1986-1987. The average horizontal strain rates in the northeast part of the caldera for the period from 1984 to 1987 were: {Mathematical expression}1 = 0.10 ?? 0.09 ??strain/year oriented N33?? E??9?? and {Mathematical expression}2 = 0.20 ?? 0.09 ??strain/year oriented N57?? W??9?? (extension reckoned positive). A best-fit elastic model of the 1985-1987 vertical and horizontal displacements in the eastern part of the caldera suggests deflation of a horizontal tabular body located 10??5 km beneath Le Hardys Rapids, i.e., within a deep hydrothermal system or within an underlying body of partly molten rhyolite. Two end-member models each explain most aspects of historical unrest at Yellowstone, including the recent reversal from uplift to subsidence. Both involve crystallization of an amount of rhyolitic magma that is compatible with the thermal energy requirements of Yellowstone's vigorous hydrothermal system. In the first model, injection of basalt near the base of the rhyolitic system is the primary cause of uplift. Higher in the magmatic system, rhyolite crystallizes and releases all of its magmatic volatiles into the shallow hydrothermal system. Uplift stops and subsidence starts whenever the supply rate of basalt is less than the subsidence rate produced by crystallization of rhyolite and associated fluid loss. In the second model, uplift is caused primarily by pressurization of the deep hydrothermal system by magmatic gas and brine that are released during crystallization of rhyolite and them trapped at lithostatic pressure beneath an impermeable self-sealed zone. Subsidence occurs during episodic hydrofracturing and injection of pore fluid from the deep lithostatic-pressure zone into a shallow hydrostatic-pressure zone

  18. Imaging radar observations of Askja Caldera, Iceland

    NASA Technical Reports Server (NTRS)

    Malin, M. C.; Evans, D.; Elachi, C.

    1978-01-01

    A 'blind' test involving interpretation of computer-enhanced like- and cross-polarized radar images is used to evaluate the surface roughness of Askja Caldera, a large volcanic complex in central Iceland. The 'blind' test differs from earlier analyses of radar observations in that computer-processes images and both qualitative and quantitative analyses are used. Attention is given to photogeologic examination and subsequent survey-type field observations, along with aerial photography during the field trip. The results indicate that the 'blind' test of radar interpretation of the Askja volcanic area can be considered suitable within the framework of limitations of radar data considered explicitly from the onset. The limitations of the radar techniques can be eliminated by using oblique-viewing conditions to remove geometric distortions and slope effects.

  19. Real-time measurements of Hg0 and H2S at La Solfatara Crater (Campi Flegrei, Southern Italy) and Mt. Amiata volcano (Siena, Central Italy): a new geochemical approach to estimate the distribution of air contaminants

    NASA Astrophysics Data System (ADS)

    Cabassi, J.; Calabrese, S.; Tassi, F.; Venturi, S.; Capecchiacci, F.; Di Lonardo, C.; D'Alessandro, W.; Vaselli, O.

    2014-12-01

    The emission of Hg and H2S from natural and anthropogenic sources may have a great environmental impact in urban areas as well as in the surroundings of active and passive degassing volcanoes. Mercury is present in the atmosphere mainly in its elemental form (Hg0~98 %), which has a relatively high volatility, low solubility and chemical inertness. Hydrogen sulfide, one of the most abundant gas species in volcanic fluids, is highly poisoning and corrosive. In this study, an innovative real-time method for the measurements of Hg0 and H2S concentrations in air was carried out at La Solfatara Crater, a hydrothermally altered tuff-cone nested in the town of Pozzuoli (Southern Italy), and at Mt. Amiata volcano (Central Italy), where a world-class Hg mining district abandoned in the seventies and a presently-exploited geothermal field for the production of electrical energy occur. The main aims were (i) to test this new methodological approach and (ii) to investigate Hg0 and H2S concentrations and the chemical-physical parameters regulating their spatial distribution in polluted areas. A portable Zeeman atomic absorption spectrometer with high frequency modulation of light polarization (Lumex RA-915M) was used in combination with a pulsed fluorescence gas analyzer (Thermo Scientific Model 450i) to measure Hg0 and H2S, respectively. The instruments were synchronized and set at high-frequency acquisition (10 sec and 1 min, respectively). Measurements were carried out along pathways (up to 12 km long) at an average speed of <10 km/h and coupled with GPS data and meteorological parameters. In selected sites, passive samplers were positioned to determine the time-integrated Hg0 and H2S concentrations to be compared with the real-time measurements. The results indicate that this approach is highly efficient and effective in providing reliable and reproducible Hg0 and H2S concentrations and can be used to identify and characterize gas emitters in different environments.

  20. Magma storage in a strike-slip caldera

    PubMed Central

    Saxby, J.; Gottsmann, J.; Cashman, K.; Gutiérrez, E.

    2016-01-01

    Silicic calderas form during explosive volcanic eruptions when magma withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of magma reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of magma constrains potential vent locations for future eruptions. PMID:27447932

  1. Magma storage in a strike-slip caldera

    NASA Astrophysics Data System (ADS)

    Saxby, J.; Gottsmann, J.; Cashman, K.; Gutiérrez, E.

    2016-07-01

    Silicic calderas form during explosive volcanic eruptions when magma withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of magma reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of magma constrains potential vent locations for future eruptions.

  2. Magma storage in a strike-slip caldera.

    PubMed

    Saxby, J; Gottsmann, J; Cashman, K; Gutiérrez, E

    2016-01-01

    Silicic calderas form during explosive volcanic eruptions when magma withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of magma reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of magma constrains potential vent locations for future eruptions. PMID:27447932

  3. Intracaldera volcanism and sedimentation-Creede caldera, Colorado

    SciTech Connect

    Heiken, G.; Krier, D.; Snow, M.G.; McCormick, T.

    1994-12-31

    Within the Creede caldera, Colorado, many of the answers to its postcaldera volcanic and sedimentary history lie within the sequence of tuffaceous clastic sedimentary rocks and tuffs known as the Creede Formation. The Creede Formation and its interbedded ash deposits were sampled by research coreholes Creede 1 and 2, drilled during the fall of 1991. In an earlier study of the Creede Formation, based on surface outcrops and shallow mining company coreholes, Heiken and Krier (1987) concluded that the process of caldera structural resurgence was rapid and that a caldera lake had developed in an annulus (``moat``) located between the resurgent dome and caldera wall. So far we have a picture of intracaldera activity consisting of intermittent hydrovoleanic eruptions within a caldera lake for the lower third of the Creede Formation, and both magmatic and hydrovolcanic ash eruptions throughout the top two-thirds. Most of the ash deposits interbedded with the moat sedimentary rocks are extremely fine-grained. Ash fallout into the moat lake and unconsolidated ash eroded from caldera walls and the slopes of the resurgent dome were deposited over stream delta distributaries within relatively shallow water in the northwestern moat, and in deeper waters of the northern moat, where the caldera was intersected by a graben. Interbedded with ash beds and tuffaceous siltstones are coarse-grained turbidites from adjacent steep slopes and travertine from fissure ridges adjacent to the moat. Sedimentation rates and provenance for clastic sediments are linked to the frequent volcanic activity in and near the caldera; nearly all of the Creede Formation sedimentary rocks are tuffaceous.

  4. The Unique Formation of the Nili Patera Caldera on Mars

    NASA Astrophysics Data System (ADS)

    Skok, J. R.; Karunatillake, S.; Fawdon, P.

    2014-12-01

    Caldera formation is common on the large volcanoes of Mars. Of these, the Nili Patera caldera in Syrtis Major appears unique. Set at one end of a 200 km long depression, the caldera manifests both extrusive [Christensen et al., 2005] and potentially intrusive [Wray et al., 2013] evolved silica-rich units, hydrothermal systems [Skok et al., 2010], and other post-caldera-formation volcanic structures such as the Nili Tholus cone. Nili Patera distinguishes itself by the depth of collapse. While other Martian caldera collapse less than thickness of the volcanics, Nili Patera's floor lies ~1800 m below the plains elevations: ~1300 m below the estimated 500 m mean thickness of Syrtis Major [Hiesinger and Head, 2004]. Other calderas lack morphologic evidence of late-stage volcanic constructs, while dust cover precludes spectroscopic evidence of evolved compositions in many calderas. If Nili Patera is unique, the question then is why? We examine the qualities that distinguish Nili Patera not just from calderas on other volcanoes but also from the neighboring Meroe Patera, due south within the same elongate depression. The Noachian-aged material below Syrtis Major have been observed to be altered and phyllosilicate-rich [Ehlmann et al., 2009, Marzo et al., 2010]. Access to this water-rich substrate could have driven the surface hydrothermal system. The eruption of evolved lavas would not be caused by the substrate composition, but could instead result from the collapse. Basaltic volcanoes on Earth often have evolved plutons created by repeated partial melting. The massive collapse of Nili Patera could have provided a mechanism for this unit to erupt, while remaining buried in other volcanoes. We examine multiple hypotheses for why this deep collapse is only observed in Nili Patera and how the observed lithologies here may relate to the evolution of other Martian volcanoes. The regional-scale compositional signature, that the Syrtis Major province shares with other major

  5. Radar observations of a volcanic terrain: Askja Caldera, Iceland

    NASA Technical Reports Server (NTRS)

    Evans, D. L.

    1978-01-01

    Surface roughness spectra of nine radar backscatter units in the Askja caldera region of Iceland were predicted from computer-enhanced like- and cross-polarized radar images. A field survey of the caldera was then undertaken to check the accuracy of the preliminary analysis. There was good agreement between predicted surface roughness of backscatter units and surface roughness observed in the field. In some cases, variations in surface roughness could be correlated with previously mapped geologic units.

  6. Gravity and fault structures, Long Valley caldera, California

    SciTech Connect

    Carle, S.F.; Goldstein, N.E.

    1987-07-01

    The main and catastrophic phase of eruption in Long Valley occurred 0.73 m.y. ago with the eruption of over 600 km/sup 3/ of rhyolitic magma. Subsequent collapse of the roof rocks produced a caldera which is now elliptical in shape, 32 km east-west by 17 km north-south. The caldera, like other large Quarternary silicic ash-flow volcanoes that have been studied by various workers, has a nearly coincident Bouguer gravity low. Earlier interpretations of the gravity anomaly have attributed the entire anomaly to lower density rocks filling the collapsed structure. However, on the basis of many additional gravity stations and supporting subsurface data from several new holes, a much more complex and accurate picture has emerged of caldera structure. From a three-dimensional inversion of the residual Bouguer gravity data we can resolve discontinuities that seem to correlate with extensions of pre-caldera faults into the caldera and faults associated with the ring fracture. Some of these faults are believed related to the present-day hydrothermal upflow zone and the zone of youngest volcanic activity within the caldera.

  7. Can the structure of an explosive caldera affect eruptive behaviour?

    NASA Astrophysics Data System (ADS)

    Willcox, C. P.; Branney, M.; Carrasco-Nuñez, G.; Barford, D.

    2010-12-01

    Explosive caldera volcanoes cause catastrophic events at the Earth’s surface, yet we know little about how their internal structures evolve with time, and whether this can affect both differentiation and eruptive behaviour. Distinguishing how structural evolution impacts upon eruption behaviour and periodicity is challenging because the resolution of eruption frequencies can be difficult at ancient exhumed calderas, whereas at young volcanoes, most of the caldera floor faults and associated conduits are hidden. Some exhumed calderas reveal caldera floor faults and conduits; some of these apparently underwent a single collapse event that was piecemeal, i.e. fragmentation into several, variously subsided fault-blocks (e.g. Scafell caldera, UK). In contrast, the present study tests whether some caldera volcanoes may become more intensely fractured with time as a result of successive distinct caldera-collapse eruptions (“multi-cyclic calderas”). It has been proposed that this scenario could lead to an increase in eruption frequency, with smaller eruptions over time. Magma leakage through the increasingly fractured volcano might also lead to less evolved compositions with time due to shorter residence times. We have returned to the volcano where this hypothesis was formulated, the ~ 20 km diameter, hydrothermally active Los Humeros caldera in eastern central México. We aim to see how well the structural evolution of this modern caldera can be reconstructed, and whether changes in structure affected the styles and periodicity of large explosive eruptions. How a caldera evolves structurally could have important implications for predicting future catastrophic eruptions. Detailed structural mapping (e.g. of fault scarps, vent positions, and tilted strata), documentation of draping and cross-cutting field relations, together with logging, optical and SEM petrography, XRF major and trace element geochemistry and new 40Ar-39Ar and radiocarbon dating of the pyroclastic

  8. Geology and structure of the Malpaso caldera and El Ocote ignimbrite, Aguascalientes, Mexico

    NASA Astrophysics Data System (ADS)

    Nieto-Obregón, Jorge; Aguirre-Díaz, Gerardo

    2008-10-01

    A new caldera, named Malpaso, is reported west of the city of Aguascalientes, Mexico. The Malpaso caldera is a volcano-tectonic depression, highly fractured and faulted, and was filled by voluminous pyroclastic products related to the caldera collapse. Due to these characteristics it as a graben caldera. It is truncated by younger normal faults of the Calvillo and Aguascalientes grabens. In this work we present a summary of the geologic and structural observations on this caldera, as well as a description of the main caldera product, the high-grade El Ocote ignimbrite.

  9. Evolution of volcanic and tectonic features in caldera settings and their importance in the localization of ore deposits

    USGS Publications Warehouse

    Rytuba, J.J.

    1994-01-01

    Many calderas are located along regionally important fault zones that are intermittently active before and after the caldera cycle. In mineralized calderas, the ore deposits are controlled by structures developed during caldera formation and by regional faults which intersect and reactivate the caldera-related structures. The paper discusses the importance of the different stages of caldera formation in connection with the localization of ore deposits. -from Author

  10. Post-Silent Canyon caldera structural setting for Pahute Mesa

    SciTech Connect

    Warren, R.G.; Byers, F.M. Jr.; Orkild, P.P.

    1985-12-31

    At Pahute Mesa, Nevada Test Site, the Silent Canyon caldera of about 14 Ma age is almost completely concealed beneath ash-flow tuffs of the 11.5 Ma old Rainier Mesa Member of the Timber Mountain Tuff. Structures unequivocally related to the caldera are not observed in the Rainier Mesa Member. Structure contours on top of Rainier Mesa Member at Pahute Mesa define a series of elongate, fault-bounded blocks. Between the East Boxcar and Almendro Faults these blocks tilt eastward away from westward-dipping normal faults and elsewhere they also have a strong northward component of dip, away from Timber Mountain caldera. Episodic movement along these faults controlled thicknesses of members of Paintbrush Tuff (13.3 - 12.7 Ma) and tuffs and lavas of Area 20 (14 - 13.3 Ma), which have steeper eastward and northward components of dip than the overlying Rainier Mesa Member and also thicken eastward within each structural block. Fault blocks north of Timber Mountain caldera on Pahute Mesa are very similar to blocks described at Yucca mountain south of the caldera, and probably were generated by regional Basin and Range extension and four episodes of caldera-forming volcanism at Timber Mountain. Faults bounding these blocks on Pahute Mesa formed during early episodes of caldera-forming volcanism at Timber Mountain and reactivated during later episodes, so that fault displacements and bedding plane attitudes increase with age. Because these faults have episodic activity, even a relatively small post-Rainier Mesa displacement may define the location of important displacement within underlying units.

  11. Is the Valles caldera entering a new cycle of activity?

    SciTech Connect

    Wolff, J.A.; Gardner, J.N.

    1995-05-01

    The Valles caldera formed during two major rhyolitic ignimbrite eruptive episodes (the Bandelier Tuff) at 1.61 and 1.22 Ma, after some 12 m.y. of activity in the Jemez Mountains volcanic field, New Mexico. Several subsequent eruptions between 1.22 and 0.52 Ma produced dominantly high-silica rhyolite lava domes and tephras within the caldera. These were followed by a dormancy of 0.46 m.y. prior to the most recent intracaldera activity, the longest hiatus since the inception of the Bandelier magma system at approximately 1.8 Ma. The youngest volcanic activity at approximately 60 ka produced the SW moat rhyolites, a series of lavas and tuffs that display abundant petrologic evidence of being newly generated melts. Petrographic textures conform closely to published predictions for silicic magmas generated by intrusion of basaltic magma into continental crust. The Valles caldera may currently be the site of renewed silicic magma generation, induced by intrusion of mafic magma at depth. Recent seismic investigations revealed the presence of a large low-velocity anomaly in the lower crust beneath the caldera. The generally aseismic character of the caldera, despite abundant regional seismicity, may be attributed to a heated crustal column, the local effect of 13 m.y. of magmatism and emplacement of mid-crustal plutons. 24 refs., 3 figs.

  12. Continental Scientific Drilling Program: Valles Caldera, New Mexico

    SciTech Connect

    1993-01-01

    The U.S. Continental Scientific Drilling Program attempts to develop a better understanding of the geologic and hydrologic mechanisms within the continental crust, under the auspices of an interagency group comprising the US Department of Energy, the National Science Foundation, and the U.S. Geological Survey. Ten years of research and drilling in the Valles caldera of northern New Mexico has provided a new understanding of volcanism and geothermal systems within a large caldera. Situated at the intersection of the Rio Grande rift and the Jemez volcanic lineament, the Valles caldera and Toledo calderas were formed during two massive eruptions 1.1 and 1.5 M a that vented approximately 300 to 400 km{sup 3} of high-silica rhyolitic tephra. The research at the Valles/Toledo caldera has provided more than 3000 m of corehole samples, which are stored in a repository in Grand Junction, Colorado, and are accessible to the public. This research has also helped support theories of mineral deposition within hydrothermal systems-hot water circulating through breccias, leaching elements from the rocks, and later depositing veins of economically valuable materials.

  13. Caldera collapse unloading volcanoes: the textbook case of Fernandina, Galapagos

    NASA Astrophysics Data System (ADS)

    Corbi, F.; Rivalta, E.; Pinel, V.; Maccaferri, F.; Acocella, V.

    2014-12-01

    Calderas are topographical depressions resulting from the yielding of magma chambers roof after large eruptions or intrusive events. On the outer slope, most calderas display radial fissures and, in limited cases, also circumferential fissures. Despite many hypotheses, the conditions controlling the formation of radial and/or circumferential fissures, and thus the shallow magma transfer within the volcano slopes, are still poorly understood. Here we demonstrate with numerical and analog models that the mass redistribution associated with caldera formation promotes shallow sill-shaped magma chambers and controls the orientation of eruptive fissures. We find that depending on the initial injection depth, dikes will bend or twist about an axis parallel to propagation resulting in circumferential and radial eruptive fissures, respectively. This mechanism is governed by the competition between gravitational unloading pressure and dike overpressure. We apply our results to Fernandina (Galapagos, Ecuador), the best case of caldera with radial and circumferential fissures, showing that the predicted stress field caused by the caldera unloading is consistent with the pattern of eruptive fissures and the dynamics of magma propagation.

  14. Science guide for the Long Valley Caldera deep hole

    SciTech Connect

    Rundle, J.B.; Eichelberger, J.C.

    1989-05-01

    The Magma Energy Program of the US Department of Energy, Geothermal Technology Division, is planning to begin drilling a deep (6 km) exploration well in Long Valley Caldera, California, in September 1988. The location of the well is in the central part of the caldera, coincident with a large number of shallow (5-7 km) geophysical anomalies identified through many independent investigations. Results from the hole will permit the following: direct investigation of the geophysical anomalies interpreted to be magma; investigation of the patterns and conditions of deep fluid circulation and heat transport below the caldera floor; determination of the amount of collapse and subsequent resurgence of the central portion of Long Valley caldera; and determination of the intrusion history of the central plutonic complex beneath the caldera, and establishment of the relationship of intrusive to eruptive events. The hole will thus provide a stringent test of the hypothesis that magma is still present within the central plutonic complex. If the interpretation of geophysical anomalies is confirmed, the hole will provide the first observations of the environment near a large silicic magma chamber. 80 refs., 7 figs., 2 tabs.

  15. A geophysical-geological transect of the Silent Canyon caldera complex, Pahute Mesa, Nevada

    SciTech Connect

    Ferguson, J.F.; Cogbill, A.H.; Warren, R.G.

    1994-03-10

    Revision of lithological logs for boreholes penetrating the volcanic center at Pahute Mesa, Neveda, has led to a thorough review of the volcanic stratigraphy and geologic structure. The authors have combined this review with a compilation of old and newly acquired gravity and seismic travel time data, producing a unified interpretation along a northwest to southeast profile. The analysis supports a new interpretation of the Silent Canyon caldera complex. The caldera is found to be more asymmetric than previously suggested, with the southeastern boundary formed by linear, high-angle normal faults and a more gently sloping northwestern boundary. The total thickness of volcanic units within the caldera complex does not appear to exceed 5 km. The shallow structure at Pahute Mesa could have a profound effect on the seismic response for regional and teleseismic signals from this nuclear test site. The Silent Canyon caldera complex is actually a set of nested calderas first filled by thick (>1 km) postcaldera lavas and subsequently buried by outflow sheets of the Timber Mountain caldera to the south. Thick, postcaldera lavas filled a half-graben structure formed west of the West Greeley fault, dropping the tops of the youngest caldera-forming units to depths in excess of 2 km. Therefore the western boundary of the caldera complex is poorly defined. East of the West Greeley fault, two overlapping calderas are defined, and stratigraphic data suggest the presence of even older calderas. The youngest caldera, the calc-alkaline Area 20 caldera, is well defined from drill hole data. The Area 20 caldera overlaps the 13.6 Ma peralkaline Grouse Canyon caldera, which is less well defined, but apparently collapsed in trap-door style along the Almendro fault. For both these calderas, collapse continued after the main caldera-forming eruption, concurrent with the accumulation of thick (>1 km) lavas within the peripheral collapse zones. 67 refs., 13 figs.

  16. Ash-flow eruptive megabreccias of the Manhattan and Mount Jefferson calderas, Nye County, Nevada

    SciTech Connect

    Shawe, D.R.; Snyder, D.B.

    1988-01-01

    A detailed field study of ash-flow megabreccias associated with the Manhattan and Mount Jefferson calderas shows that megaclasts were brecciated in sub-caldera level before incorporation in ash flows. This evidence in addition to the presence of some clast lithologies that are nowhere recognized in caldera walls and the occurrence of some megabreccia units as outflow suggest an origin by eruption rather than by collapse of caldera walls. Geophysical investigations and a mathematical analysis are presented in the paper.

  17. Carbonatite ring-complexes explained by caldera-style volcanism

    PubMed Central

    Andersson, Magnus; Malehmir, Alireza; Troll, Valentin R.; Dehghannejad, Mahdieh; Juhlin, Christopher; Ask, Maria

    2013-01-01

    Carbonatites are rare, carbonate-rich magmatic rocks that make up a minute portion of the crust only, yet they are of great relevance for our understanding of crustal and mantle processes. Although they occur in all continents and from Archaean to present, the deeper plumbing system of carbonatite ring-complexes is usually poorly constrained. Here, we show that carbonatite ring-complexes can be explained by caldera-style volcanism. Our geophysical investigation of the Alnö carbonatite ring-complex in central Sweden identifies a solidified saucer-shaped magma chamber at ~3 km depth that links to surface exposures through a ring fault system. Caldera subsidence during final stages of activity caused carbonatite eruptions north of the main complex, providing the crucial element to connect plutonic and eruptive features of carbonatite magmatism. The way carbonatite magmas are stored, transported and erupt at the surface is thus comparable to known emplacement styles from silicic calderas. PMID:23591904

  18. Stable Isotopes of Tilted Ignimbrite Calderas in Nevada

    NASA Astrophysics Data System (ADS)

    John, D. A.; Watts, K. E.; Hofstra, A. H.; Colgan, J. P.; Henry, C.; Bindeman, I. N.

    2013-12-01

    Mid-Tertiary calderas are exceptionally well exposed in tilted fault blocks of the northern Great Basin, facilitating detailed evolutionary models of their magmatic-hydrothermal systems. The 29.4 Ma Job Canyon caldera, the oldest of 3 overlapping calderas in the Stillwater Range, west-central Nevada, is tilted ~90° exposing a 10-km-thick section of the crust. Large parts of the >7 km-diameter caldera system, including >2 km thickness of intracaldera rhyolitic tuff, lower parts of an ~2 km thick sequence of post-caldera intermediate lavas, and the upper 500 m of the resurgent granodioritic IXL pluton, were pervasively altered to propylitic, argillic, and sericitic assemblages. Sparse quartz×calcite veins cut the tuff. δ18O values of altered whole rock samples range from +4.8 to -9.1‰ but are mostly -6 to -9‰ at paleodepths >2 km. Calculated magmatic δ18O and δD values range from +6.4 to 8.2‰ and ~-70‰, respectively. Calculated fluid compositions using temperatures from fluid inclusions and mineral assemblages are δ18OH2O=-9.5 to -15‰ and δDH2O=-125 to -135‰ (chlorite) and -70 to -80‰ (epidote). Chlorite-whole rock data suggest fluids that were derived from moderately 18O-exchanged meteoric water. Fault blocks in north-central Nevada expose a >5 km upper crustal cross section through the 12-17 x 20 km, 34 Ma Caetano caldera, including >3 km thickness intracaldera rhyolitic Caetano Tuff. Asymmetric caldera subsidence left a depression >1 km deep partly filled with a lake. Magma resurgence and emplacement of shallow granite porphyry plutons drove a hydrothermal system that altered >120 km2 of the caldera to depths >1.5 km. Alteration was focused in an early granite porphyry intrusion and surrounding upper Caetano Tuff and lacustrine sediments. Early pervasive quartz-kaolinite-pyrite alteration grades outward and downward into more restricted quartz-illite/smectite-pyrite alteration. Hematite, quartz, and barite veins and hydrothermal breccias cut

  19. New observations at Iwo-Jima caldera, Volcano Islands, Japan

    NASA Astrophysics Data System (ADS)

    Ukawa, U. M.; Fujita, E.; Hill, D.; Kobayashi, T.; Lowenstern, J.; Newhall, C.

    2003-04-01

    Small phreatic eruptions on opposite sides of Iwo-Jima in September and October 2001 marked the beginning of several changes in this largely submarine caldera and trapdoor resurgence of its floor. The northern part of Motoyama, roughly the center of the caldera floor, has risen >120 m in the past 420 years at an average rate of ˜25 cm/y; uplift in the past year has been substantially faster. The main cause of uplift at Iwo-Jima is fresh, episodic(?) magma influx into a reservoir whose top is ˜ 2 km below the caldera floor. Despite roughly 10 million m3/y apparent magma influx, degassing seems to minimize magmatic eruptions.

  20. Carbonatite ring-complexes explained by caldera-style volcanism.

    PubMed

    Andersson, Magnus; Malehmir, Alireza; Troll, Valentin R; Dehghannejad, Mahdieh; Juhlin, Christopher; Ask, Maria

    2013-01-01

    Carbonatites are rare, carbonate-rich magmatic rocks that make up a minute portion of the crust only, yet they are of great relevance for our understanding of crustal and mantle processes. Although they occur in all continents and from Archaean to present, the deeper plumbing system of carbonatite ring-complexes is usually poorly constrained. Here, we show that carbonatite ring-complexes can be explained by caldera-style volcanism. Our geophysical investigation of the Alnö carbonatite ring-complex in central Sweden identifies a solidified saucer-shaped magma chamber at ~3 km depth that links to surface exposures through a ring fault system. Caldera subsidence during final stages of activity caused carbonatite eruptions north of the main complex, providing the crucial element to connect plutonic and eruptive features of carbonatite magmatism. The way carbonatite magmas are stored, transported and erupt at the surface is thus comparable to known emplacement styles from silicic calderas. PMID:23591904

  1. Core log: Valles caldera No. 2A, New Mexico

    SciTech Connect

    Starguist, V.L.

    1988-01-01

    Scientific core hole VC-2A was drilled into the western ring-fracture zone at Sulphur Springs in the Valles caldera, New Mexico. VC-2A, the second scientific core hole in the caldera, was cored through a faulted and brecciated sequence of intracauldron tuffs and volcaniclastic rocks to a depth of 528 m. As of November 1, 1986, the unequilibrated bottom-hole temperature was 212/degree/C. The rocks penetrated are intensely altered and host sub-ore grade stockwork molybdenite mineralization between 25 and 125 m. This report contains a detailed core log to aid researchers in their studies of the Valles caldera magma hydrothermal system. 3 refs., 2 figs.

  2. Magma energy exploratory well Long Valley caldera, Mono County, California

    SciTech Connect

    Bender-Lamb, S.

    1991-04-01

    Intensive study of Long Valley over the past 15 years indicates evidence for magma at depths accessible to drilling. The Department of Energy's Magma Energy Extraction Program is currently drilling a 20,000 foot exploratory well into the Long Valley caldera. The purpose of this program is to determine the feasibility of producing electrical power from magma. If the magma energy experiment is successful, the Long Valley caldera could hypothetically supply the electrical power needs of California for 100 years at present power consumption rates. The paper describes calderas, the potential of geothermal energy, Long Valley geology, the Long Valley magma energy exploratory well, the four phases of the exploratory well drilling program, and Phase 1 results.

  3. Pyroclastic conduits of the late Cenozoic collapse calderas from Japan

    NASA Astrophysics Data System (ADS)

    Yoshida, T.; Iwahashi, A.; Takahashi, T.; Nagahashi, Y.

    2006-12-01

    There are many late Cenozoic calderas in Japan. Many of the late Cenozoic calderas are the large-scale collapse calderas of the piston-cylinder type, and consist of collapsed volcanic basin surrounded by arcuate ring faults or array of vents and the surrounding pyroclastic flow deposits. Yoshida (1984) reported intrusive breccia dikes between the subsided block and wall rocks of the Ishizuchi cauldron, SW Japan. The intrusive breccias consist of tuff and tuff breccias containing many kinds of rock fragments. Contacts with surrounding rocks are sharp. Some breccia dikes along the marginal ring fracture zone of the cauldron, which are composed of welded pyroclastic rocks, probably fill vents from which the surrounding pyroclastic flow deposits were discharged. The matrix of the intrusive breccia is welded ash and/or clastic powder. Fragments vary in size from millimeters to several meters. Local continuity of structures from one fragment to another indicates that the brecciation was not a consequence of explosive action; these are interpreted as intrusive breccias produced by fluidization processes, probably associated with pyroclastic explosions. These breccias were intruded upward to their present positions as part of a fluidization system. Intrusive breccia and tuff within the ring fault complex contain a eutaxitic foliation oriented nearly parallel to contacts. This feature is thought to result from inwardly directed pressures exerted by the dike walls during caldera collapse following eruption of the pyroclastic flows. The eutaxitic foliation indicates that the intrusive breccia and tuff were emplaced as a fluidized system of gas, solid particles, and probably liquid droplets. Mt. Taiheizan is located 20km northeast of Akita, NE Japan. There is the late Miocene to early Pliocene Nibetsu cauldron on Mt. Taiheizan. Recent study revealed the details of a contemporary arcute pyroclastic conduit consisting of felsic tuff. This Hirasawa felsic tuff dyke is about 5 km

  4. Geophysical expression of the batholith beneath Questa Caldera, New Mexico

    NASA Astrophysics Data System (ADS)

    Cordell, Lindrith; Long, Carl L.; Jones, David W.

    1985-11-01

    Gravity gradients delineate uncharacteristically straight, north-south trending graben faults in the Rio Grande rift west of Questa caldera, and gravity and audiomagnetotelluric (AMT) data show north-south trending low-density and high-resistivity zones from the caldera southward. A gravity inversion technique was used to isolate the gravity anomaly of the caldera and related intrusive rocks from the complicated Bouguer gravity field. The residual gravity anomaly together with AMT data reported in a companion paper by C. L. Long seem to delineate the subcaldera batholith. Geophysical models indicate this to be a north-south trending dikelike or beamlike body about 25 km long, 5 km wide, and >4 km thick, thickness estimate being limited by the penetration depth of the AMT soundings. The north-south trend is not consistent with the regional pattern of early Miocene southwest directed extension and instead may reflect passive control by preexisting north-south strike-slip faults.

  5. Workshop on recent research in the Valles caldera

    SciTech Connect

    Heiken, G.

    1985-02-01

    Over the last 5 years, there has been increased interest in the geology of the Jemez Mountains volcanic field, New Mexico. Of special interest is the Toledo-Valles caldera complex, which is targeted for research coring as part of the Continental Scientific Drilling Program. The general topics covered in this workshop were (1) hydrothermal systems and rock-water interactions, (2) volcanology and structural framework of the Jemez volcanic field, (3) determining the presence or absence of melt below the Valles caldera, and (4) deep coring and drilling technology. Separate abstracts were prepared for each presentation.

  6. AmeriFlux US-Vcm Valles Caldera Mixed Conifer

    DOE Data Explorer

    Litvak, Marcy [University of New Mexico

    2016-01-01

    This is the AmeriFlux version of the carbon flux data for the site US-Vcm Valles Caldera Mixed Conifer. Site Description - The Valles Caldera Mixed Conifer site is located in the 1200 km2 Jemez River basin in north-central New Mexico. Common to elevations ranging from 3040 to 2740 m in the region, the mixed conifer stand, within the entirety of the tower footprint in all directions, provides an excellent setting for studying the seasonal interaction between snow and vegetation.

  7. Evaluating volumes for magma chambers and magma withdrawn for caldera collapse

    NASA Astrophysics Data System (ADS)

    Geshi, Nobuo; Ruch, Joel; Acocella, Valerio

    2014-06-01

    We develop an analytical model to infer the total volume of a magma chamber associated with caldera collapse and the critical volume of magma that must be withdrawn to induce caldera collapse. The diameter of caldera border fault, depth to the magma chamber, and volumes of magma erupted before the onset of collapse and of entire eruption are compiled for 14 representative calderas. The volume of erupted magma at the onset of collapse aligns between the total erupted volume of the other representative caldera-forming eruptions and the volume of eruptions without collapse during the post-caldera stage, correlating with the structural diameter of the calderas. The total volume of magma chamber is evaluated using a piston-cylinder collapse model, in which the competition between the decompression inside magma chamber and friction along the caldera fault controls the collapse. Estimated volumes of the magma chambers associated with caldera collapse are 3-10 km3 for Vesuvius 79 A.D. to 3000-10 500 km3 for Long Valley, correlating with the cube of caldera diameters. The estimated volumes of magma chamber are always larger than the total volume of erupted magma for caldera formation, suggesting that the magma chambers are never completely emptied by the caldera-forming eruptions. The minimum volumes of erupted magma to trigger collapse are calculated from the correlation between the caldera diameters and the evaluated volume of magma chambers. The minimum eruptive volume for the collapse correlates with the square of the caldera radius r and the square of the depth to the magma chamber h, and inversely correlates with the bulk modulus of magma, which is mainly controlled by the bubble fraction in the magma. A bubble fraction between 5 and 10% at the onset of collapse may explain the distribution of the erupted volumes at the onset of collapse of the calderas in nature.

  8. Computer analysis of mammography phantom images (CAMPI): an application to the measurement of microcalcification image quality of directly acquired digital images.

    PubMed

    Chakraborty, D P

    1997-08-01

    The purpose of this investigation was to apply the recently developed CAMPI (computer analysis of mammography phantom images) method to a Fischer Mammotest Stereotactic Digital Biopsy machine. Another aim was to further elucidate the nature of the empirically introduced CAMPI measures. Images of an American College of Radiology (ACR) accreditation phantom centered on the largest two speck groups were obtained on this machine under a variety of x-ray conditions. An additional measure, alternative SNR (ASNR) is introduced which is complementary to the SNR measure. Analyses of the Mammotest images revealed that the mAs and kVp dependencies of the CAMPI measures could be understood from basic imaging physics principles. It is shown that: (1) the measures reflect the expected linearity of the digital detector and Poisson photon statistics; (2) under automatic exposure control (AEC) conditions the signal (SIG) measure is proportional to subject contrast; and (3) under AEC conditions the noise (NOI) measure is proportional to the square root of the average absorbed photon energy. Correspondence with basic imaging physics principles shows that the measures are significantly free of artifacts. Precision of the CAMPI measures exceeds that of human observers by orders of magnitude. CAMPI measures are expected to be more relevant to clinical mammography than Fourier metrics as the measurements are done on objects of arbitrary shape and size that were designed by the manufacturer to resemble various detection tasks in mammography. It is concluded that CAMPI can perform objective and highly precise evaluations of phantom image quality in mammography. It could be used as a sophisticated quality control tool, as a replacement for the current ACR/MQSA phantom evaluation program, and to evaluate the rapidly evolving digital mammography technology. PMID:9284251

  9. Caldera formation at Tendurek, East Turkey

    NASA Astrophysics Data System (ADS)

    Bathke, H.; Sudhaus, H.; Shirzaei, M.; Walter, T. R.

    2012-04-01

    Volcanoes of eastern Turkey have been historically active and are located in an active tectonic system with abundant faults and fissures. Tendurek is a low relief shield volcano with an edifice height of about 3580 m and covers an area of 650km2. It has an elliptical shape and the two summit craters and a flank crater are arranged in the direction of the long axis. The summit area is surrounded by an also elliptical ring fracture system with a 9km long axis and a 6km minor axis. This system is more developed in the south than in the north, therefore it is called a half caldera. Tendurek is located in an active tectonic region with right lateral motion near to the Balik Gölü fault, and has been affected by significant tectonic earthquakes, such as in 1840 (M7.4). The last eruption occurred in 1855, since then it is considered to be dormant. Little is known about the deep magma plumbing system, and the state of its current activity. Here we report on a radar interferometric study where we combine SAR images acquired by the Envisat satellite in the years from 2004- 2008 and 2003- 2010 in ascending and descending orbits, respectively. We used the software's ROI_Pac and Doris to create interferograms. The StaMPS software was used to analyze the temporal evolution and to estimate a mean annual velocity of the deformation signal in both tracks. Due to the poor coherence in the summit area, less stable pixel have been identified there in the processing. Where at the lower flanks and further away from the volcanic edifice a lot of stable pixel could be identified. These data allows us to investigate the ground deformation pattern at unprecedented spatial detail. We observe various localized but evident deformation occurrences, associated with volcanic activity at Tendurek volcano. Deformation affected the upper region of the volcano, including the summit craters within the dimension of the previously mentioned ring fault system at a very low rate. By using a genetic

  10. Root zone of the late Proterozoic Salma caldera, northeastern Arabian Shield, Kingdom of Saudi Arabia.

    USGS Publications Warehouse

    Kellogg, K.S.

    1985-01-01

    The eroded root of the late Proterozoic Salma caldera crops out in a striking, roughly elliptical feature, about 27 km long and 22 km wide, near the NE edge of the Arabian Shield, The caldera is genetically part of an elongate alkalic granitic massif (Jabal Salma) that extends 35 km from the caldera to the SW. Comenditic ash flow tuff and lava(?) of the caldera fill, probably more than 1 km thick, are the oldest recognized rocks of the caldera complex. These rocks were erupted during caldera collapse associated with the rapid evacuation of the upper, mildly peralkalic part of a zoned magma reservoir. Within the caldera fill, a massive, lithic-rich intracaldera rhyolite, probably a lava in excess of 1 km thick, is overlain by a layered ash flow sequence. Numerous megabreccia blocks, probably derived from the caldera wall, occur in the massive rhyolite. No apparent structural doming of the exposed volcanic rocks along the E side of the caldera took place; the layered ash flows commonly dip steeply toward the center of the caldera. Postemplacement deformation and metamorphism of the caldera are mimimal. Small-displacement strike-slip faults cut the complex, which is tilted to the NE by no more than about 2o.-from Author

  11. An ion microprobe study of individual zircon phenocrysts from voluminous post-caldera rhyolites of the Yellowstone caldera

    NASA Astrophysics Data System (ADS)

    Watts, K. E.; Bindeman, I. N.; Schmitt, A. K.

    2010-12-01

    Following the formation of the Yellowstone caldera from the 640 ka supereruption of the Lava Creek Tuff (LCT), a voluminous episode of post-caldera volcanism filled the caldera with >600 km3 of low-δ18O rhyolite. Such low-δ18O signatures require remelting of 100s of km3 of hydrothermally altered (18O-depleted) rock in the shallow crust. We present a high resolution oxygen isotope and geochronology (U-Th and U-Pb) study of individual zircon crystals from seven of these voluminous post-caldera rhyolites in order to elucidate their genesis. Oxygen isotope and geochronology analyses of zircon were performed with an ion microprobe that enabled us to doubly fingerprint 25-30 µm diameter spots. Host groundmass glasses and coexisting quartz were analyzed in bulk for oxygen isotopes by laser fluorination. We find that zircons from the youngest (200-80 ka) post-caldera rhyolites have oxygen isotopic compositions that are in equilibrium with low-δ18O host groundmass glasses and quartz and are unzoned in oxygen and U-Th age. This finding is in contrast to prior work on older (500-250 ka) post-caldera rhyolites, which exhibit isotopic disequilibria and age zoning, including the presence of clearly inherited zircon cores. Average U-Th crystallization ages and δ18O zircon values for Pitchstone Plateau flow (81±7 ka, 2.8±0.2‰), West Yellowstone flow (118±8 ka, 2.8±0.1‰), Elephant Back flow (175±22 ka, 2.7±0.2‰) and Tuff of Bluff Point (176±20 ka, 2.7±0.1‰) are overlapping or nearly overlapping in age and identical in oxygen isotope composition within uncertainty (2 SE). New U-Pb geochronology and oxygen isotope data for the North Biscuit Basin flow establish that it has an age (188±33 ka) and δ18O signature (2.8±0.2‰) that is distinctive of the youngest post-caldera rhyolites. Conversely, the South Biscuit Basin flow has a heterogeneous zircon population with ages that range from 550-250 ka. In this unit, older and larger (200-400 µm) zircons have more

  12. Igneous evolution of a complex laccolith-caldera, the Solitario, Trans-Pecos Texas: Implications for calderas and subjacent plutons

    USGS Publications Warehouse

    Henry, C.D.; Kunk, M.J.; Muehlberger, W.R.; McIntosh, W.C.

    1997-01-01

    The Solitario is a large, combination laccolith and caldera (herein termed "laccocaldera"), with a 16-km-diameter dome over which developed a 6 x 2 km caldera. This laccocaldera underwent a complex sequence of predoming sill, laccolith, and dike intrusion and concurrent volcanism; doming with emplacement of a main laccolith; ash-flow eruption and caldera collapse; intracaldera sedimentation and volcanism; and late intrusion. Detailed geologic mapping and 40Ar/39Ar dating reveal that the Solitario evolved over an interval of approximately 1 m.y. in three distinct pulses at 36.0, 35.4, and 35.0 Ma. The size, duration, and episodicity of Solitario magmatism are more typical of large ash-flow calderas than of most previously described laccoliths. Small volumes of magma intruded as abundant rhyolitic to trachytic sills and small laccoliths and extruded as lavas and tuffs during the first pulse at 36.0 Ma. Emplacement of the main laccolith, doming, ash-flow eruption, and caldera collapse occurred at 35.4 Ma during the most voluminous pulse. A complex sequence of debris-flow and debris-avalanche deposits, megabreccia, trachyte lava, and minor ash-flow tuff subsequently filled the caldera. The final magmatic pulse at 35.0 Ma consisted of several small laccoliths or stocks and numerous dikes in caldera fill and along the ring fracture. Solitario rocks appear to be part of a broadly cogenetic, metaluminous suite. Peralkaline rhyolite lava domes were emplaced north and west of the Solitario at approximately 35.4 Ma, contemporaneous with laccolith emplacement and the main pulse in the Solitario. The spatial and temporal relation along with sparse geochemical data suggest that the peralkaline rhyolites are crustal melts related to the magmatic-thermal flux represented by the main pulse of Solitario magmatism. Current models of laccolith emplacement and evolution suggest a continuum from initial sill emplacement through growth of the main laccolith. Although the Solitario

  13. Lithium in the McDermitt caldera, Nevada and Oregon

    USGS Publications Warehouse

    Glanzman, R.K.; McCarthy, J.H., Jr.; Rytuba, J.J.

    1978-01-01

    Anomalously high concentrations of lithium in fluviatile-lacustrine sediments near McDermitt, Nevada, may constitute a potential resource. These sediments are associated with a caldera about 45 km in diameter that is a result of volcanic activity, subsidence and sedimentation chiefly of Miocene age. The sediments originally were vitroclastic and now consist chiefly of authigenic zeolites, clay minerals, feldspar and quartz. Calcite occurs as thin beds, nodules and cement Gypsum is presnt but sparse. Most of the clay beds in the caldera contain 0.01-0.1% Li and have well above the average Li concentration for continental clays (0.006%) (Ronov et al.1). Individual smectitic clay samples from the western and southern part of the caldera contain as much as 0.65% Li and are associated with analcime and K-feldspar. Two beds, each 0.6m thick, contain 0.35% Li. Clay samples from the northern part of the caldera contain as much as 0.36% Li, and are associated with clinoptilolite and erionite. The clay beds are thinner in the north; in one section a bed 0.3 m thick contains 0.36% Li, and in another section a bed 0.1 m thick contains 0.30% Li. Lithium is probably derived from volcanic material and then incorporated into the clay beds during alteration. ?? 1978.

  14. Magmas and reservoirs beneath the Rabaul caldera (Papua New Guinea)

    NASA Astrophysics Data System (ADS)

    Bouvet de Maisonneuve, C.; Costa Rodriguez, F.; Huber, C.

    2013-12-01

    The area of Rabaul (Papua New Guinea) consists of at least seven - possibly nine - nested-calderas that have formed over the past 200 ky. The last caldera-forming eruption occurred 1400 y BP, and produced about 10 km3 of crystal-poor, two-pyroxene dacite. Since then, five effusive and explosive eruptive episodes have occurred from volcanic centres along the caldera rim. The most recent of these was preceded by decade-long unrest (starting in 1971) until the simultaneous eruption of Vulcan and Tavurvur, two vents on opposite sides of the caldera in 1994. Most eruptive products are andesitic in composition and show clear signs of mixing/mingling between a basalt and a high-K2O dacite. The hybridization is in the form of banded pumices, quenched mafic enclaves, and hybrid bulk rock compositions. In addition, the 1400 y BP caldera-related products show the presence of a third mixing component; a low-K2O rhyodacitic melt or magma. Geochemical modeling considering major and trace elements and volatile contents shows that the high-K2O dacitic magma can be generated by fractional crystallization of the basaltic magma at shallow depths (~7 km, 200 MPa) and under relatively dry conditions (≤3 wt% H2O). The low-K2O rhyodacitic melt can either be explained by extended crystallization at low temperatures (e.g. in the presence of Sanidine) or the presence of an additional, unrelated magma. Our working model is therefore that basalts ascend to shallow crustal levels before intruding a main silicic reservoir beneath the Rabaul caldera. Storage depths and temperatures estimated from volatile contents, mineral-melt equilibria and rock densities suggest that basalts ascend from ~20 km (~600 MPa) to ~7 km (200 MPa) and cool from ~1150-1100°C before intruding a dacitic magma reservoir at ~950°C. Depending on the state of the reservoir and the volumes of basalt injected, the replenishing magma may either trigger an eruption or cool and crystallize. We use evidence from major and

  15. Elastic and Transport Properties of Steam-Cured Pozzolanic-Lime Rock Composites Upon CO2 Injection

    NASA Astrophysics Data System (ADS)

    Emery, D. E.; Vanorio, T.

    2015-12-01

    Understanding the relationship between pozzolanic ash-lime reactions and the rock physics properties of the resulting rock microstructure is important for monitoring unrest conditions in volcanic-hydrothermal systems as well as devising concrete with enhanced performance. The recent discovery in the depths of the Campi Flegrei volcanic-hydrothermal systems of a natural process forming a fiber-reinforced, concrete-like rock with enhanced elastic and strength properties calls for further research to investigate the physico-chemical conditions contributing to undermine or enhance the properties of the subsurface rocks of volcanic-hydrothermal systems and, in turn, build upon those processes that the ancient Romans unwittingly exploited to create their famous concrete. To study this, we prepared 8 samples by mixing the pozzolana volcanic ash, slaked lime, aggregates of Neapolitan Yellow tuff, and seawater from Campi Flegrei in the same ratios as the ancient Romans. Each sample contained a lime-to-pozzolana ratio of 1:2 by weight and a water-to-binder (pozzolana plus lime) ratio of 0.4 by weight. Neapolitan Yellow tuff made up 20% of the weight of the mixture. To mimic the conditions of the caldera, we used mineral seawater from a well in the Campi Flegrei region rich in sulfate, bicarbonate, calcium, potassium, and magnesium ions. The samples were cured under steam conditions as well. We measured baseline properties of porosity, permeability, and the acoustic velocity through the samples in order to calculate the bulk, shear, and Young's modulus. Subsequently, half of the samples were injected with CO2- rich aqueous solution and the changes in their microstructure and physical properties measured. Our findings show how a steam- and sulfur-alkaline- rich environment affects both transport and elastic properties of the samples and how they may change in response to microstructural changes due to potential chemical instabilities such as possible new flux of CO2 into a

  16. La Pacana caldera, N. Chile: a re-evaluation of the stratigraphy and volcanology of one of the world's largest resurgent calderas

    NASA Astrophysics Data System (ADS)

    Lindsay, J. M.; de Silva, S.; Trumbull, R.; Emmermann, R.; Wemmer, K.

    2001-04-01

    La Pacana caldera in the Central Andes of northern Chile is one of the largest and best exposed resurgent calderas in the world. The caldera had previously been recognised as the source of the regionally-extensive Atana ignimbrite, but additional field and stratigraphic evidence, along with new K-Ar age determinations and geochemical data have led to a revision of the geology and development of this major Andean caldera. In particular, this information allows more realistic estimates of eruptive volumes and has implications for the style of ignimbrite eruption. Two major ignimbrites appear to have originated from La Pacana caldera, based on their thickness variations, lateral distributions and stratigraphic relations: the crystal-poor, rhyolitic Toconao ignimbrite (4-5 Ma) and the crystal-rich, dacitic Atana ignimbrite (4 Ma). Following caldera collapse and formation of the resurgent Atana block, several crystal-rich dacitic-rhyolitic domes formed along the margin of the resurgent block. New K-Ar ages show that this post-caldera volcanism continued from 4 to 2 Ma, indicating that the La Pacana magmatic system was active for at least 2 Ma after the main eruption. The Atana ignimbrite extends west, south and east of La Pacana caldera. Our work shows that the ignimbrite sequence northeast of the caldera, formerly mapped as Atana outflow, represents two new units which we name the upper and lower Tara ignimbrites. The distribution of the Tara ignimbrites points to a source to the north. The upper Tara ignimbrite comprises four flow units with interbedded surge and fall deposits and a characteristic, heterogeneous pumice population. It occurs in the La Pacana moat and onlaps the resurgent block. These field relations and a new K-Ar age of 3.8 Ma show convincingly that this ignimbrite erupted after formation of La Pacana caldera. The lower Tara ignimbrite is a single extensive flow unit, and has an age of 5.6 Ma. Two outcrops of lag breccia occur adjacent to the caldera

  17. Subsurface structure of Valles Caldera; a resurgent cauldron in northern New Mexico. [Abstract only

    SciTech Connect

    Goff, F.

    1983-03-01

    Valles Caldera is a 1.1 My old silicic cauldron lying at the intersection of the Rio Grande rift and northeast-trending Jemez Lineament. Geothermal exploration in the caldera region during the last 10 years provides subsurface data which refine our knowledge of deep caldera structure, but raise some questions concerning current models of resurgent cauldrons. For example, a detailed gravity investigation using 730 stations (Segar, 1974) shows a circular negative gravity anomaly centered over the caldera (as expected) but also indicates a strong northeast-trending grain of fault blocks in pre-caldera rocks, that are generally down-faulted to the southeast toward the Rift. Gravity data do not define a diapir structure beneath the resurgent dome attributable to tumescent magma; instead of a northeast-trending horst underlies the Redondo Peak segment of the dome. Interpretation of stratigraphy from many geothermal wells suggests that the caldera and resurgent dome are floored by untilted fault blocks (Hulen and Nielson, 1982). In addition, drilling to Precambrian basement and depths of 3.2 km has not encountered a large intrusive rhyolite that might logically produce tumescence of the dome. The new data indicate that the subsurface structural configuration of Valles Caldera is controlled by pre-caldera tectonics and that a more complicated mechanism is required to explain the resurgent dome standing high inside the caldera. A refined mechanism of resurgence might be one result of CSDP drilling at Valles Caldera.

  18. Campylobacter in broiler slaughter samples assessed by direct count on mCCDA and Campy-Cefex agar.

    PubMed

    Gonsalves, Camila Cristina; Borsoi, Anderlise; Perdoncini, Gustavo; Rodrigues, Laura Beatriz; do Nascimento, Vladimir Pinheiro

    2016-01-01

    Campylobacter spp. cause foodborne illnesses in humans primarily through the consumption of contaminated chicken. The aim of this study was to evaluate the United States Department of Agriculture's (USDA) recommended methodology, protocol MLG 41.02, for the isolation, identification and direct plate counting of Campylobacter jejuni and C. coli samples from the broiler slaughtering process. A plating method using both mCCDA and Campy-Cefex agars is recommended to recover Campylobacter cells. It is also possible to use this method in different matrices (cloacal swabs and water samples). Cloacal swabs, samples from pre-chiller and post-chiller carcasses and samples of pre-chiller, chiller and direct supply water were collected each week for four weeks from the same flock at a slaughterhouse located in an abattoir in southern Brazil. Samples were analyzed to directly count Campylobacter spp., and the results showed a high frequency of Campylobacter spp. on Campy-Cefex agar. For the isolated species, 72% were identified as Campylobacter jejuni and 38% as Campylobacter coli. It was possible to count Campylobacter jejuni and Campylobacter coli from different samples, including the water supply samples, using the two-agar method. These results suggest that slaughterhouses can use direct counting methods with both agars and different matrices as a monitoring tool to assess the presence of Campylobacter bacteria in their products. PMID:27237112

  19. Geochemistry of hydrothermal plume in the Suiyo Seamount Caldera.

    NASA Astrophysics Data System (ADS)

    Shitashima, K.; Maeda, Y.

    2002-12-01

    Chemical compounds of the hot basalt origin are discharged into the deep ocean via hydrothermal plume by the deep-sea hydrothermal activity. The hydrothermal plume is widely diffused to the ocean by mixing with ambient seawater. Chemical reactions and interactions with microorganisms in the diffusion process of the hydrothermal plume are important to comprehend the oceanic geochemical cycles. Recently, it has been clarified that the variation of hydrothermal activity is greatly controlled in the tidal current. Not only geochemical observation but also physical observation, such as water current measurement, are necessary for the understanding of the deep-sea hydrothermal systems including the behavior of hydrothermal plume. In order to observe the diffusion process of hydrothermal plumes, sampling and chemical mapping of the hydrothermal plume and measurement of water current were carried out at the Suiyo Seamount Caldera during research cruises under the ?Archaean Park? project funded by MEXT. The three-dimensional acoustic current meters were moored at the height of 13m and 125m above the bottom in the Suiyo Seamount Caldera. At the 13m height, average water current speed and current direction were 10.46 cm/second and 228.1 degrees, respectively, and maximum water current speed was over 40.46 cm/second. On the other hand, average water current speed and current direction at the 125m height were 3.87 cm/second and 57.8 degrees, respectively. The strong water current of the southwest direction in 24 hours periods existed near bottom of the caldera. In addition, downward current and water temperature depreciation were observed, when there was the strong current in 24 hours periods. These results suggest that the low-temperature ocean water around the Suiyo Seamount flows toward the bottom of caldera periodically. The mini CTDT-RMS mounted twelve 1.2L Niskin bottles and the in-situ pH sensor were installed on the ROV or manned submersible. The hydrothermal plume

  20. Regional audiomagnetotelluric study of the Questa Caldera, New Mexico

    NASA Astrophysics Data System (ADS)

    Long, Carl L.

    1985-11-01

    Audiomagnetotelluric (AMT) soundings at Questa caldera were made in the course of a mineral resource study of the Columbine-Hondo and Latir Peak Wilderness areas, New Mexico, in the fall of 1980 and 1981. This regional electrical survey covered an area of approximately 518 km2 and consisted of 92 AMT stations at an average spacing of approximately 3 km. An AMT apparent resistivity map and one-dimensional models delineate several major lithologic and structural features. A large north-south resistivity high is interpreted to outline a largely concealed batholith 20 km long, 2-6 km wide, and >4 km thick. Two high-resistivity east-west trends coincide with the mapped margins of the Questa caldera, indicating the electrically contrasting rocks at its boundary. Apparent resistivity lows coincide with areas of hydrothermal alteration known to contain stockwork molybdenum deposits.

  1. Geology and eruptive mechanisms of Masaya Caldera Complex, Nicaragua

    SciTech Connect

    Williams, S.N.

    1983-01-01

    Results of detailed geologic field mapping and analysis of eruptive mechanisms at Masaya Caldera Complex, Nicaragua are presented. Eruptions began at least 50,000 and possibly 460,000 y.b.p. The Las Sierras Formation, regarded as Plio-Pleistocene in age, forms the local basement. A central vent of group or vents in the developing Masaya volcanic complex produced diverse deposits, all of basaltic composition. Eruption of a pyroclastic flow-surge sequence at 2250-6500 y.b.p. culminated in wholesale collapse of a caldera with a volume of 15.3 km/sup 3/. The bulk volume of the ignimbrite is 2.2-3.4 kkm/sup 3/ and the surge deposit is 4.9-5.5 km/sup 3/. Pre-historic lava production rates of 1.9-5.5 x 10/sup 6/ m/sup 3//year are similar to rates at other volcanoes but 26-76 times greater than the historic rate of production. The average lava effusion rate of 32 m/sup 3//sec during the 1772 eruption is at least an order of magnitude greater than observed effusion rates at other Central American volcanoes, and helps explain the unusual shield-like morphology of the volcano. Pyroclastic eruptions of several types have played an important role in the evolution of the volcano. Fissure-type eruptions, unknown elsewhere in Central America, have created numerous ash and scoria deposits. Two widespread scoria-fall deposits, locally known as the Fontana Lapilli an San Judas Formation, are the first documented plinian airfall deposts of basaltic composition. The Masaya-type caldera is redefined as a caldera associated with voluminous explosive eruptions of much less than 100 km/sup 3/ of mafic magma from a summit vent.

  2. Preliminary Hot Dry Rock geothermal evaluation of Long Valley Caldera, California

    SciTech Connect

    Gambill, D.T.

    1981-03-01

    Long Valley Caldera, formed during the catastrophic eruption of the Bishop Tuff 0.7 Myr ago, straddles the border between the Sierra Nevada and the Basin and Range tectonic provinces in eastern California. The caldera contains rhyolitic to basaltic flows, tuffs, and domes from 3.2 Myr to 450 yr old. Sierra Nevada frontal faults intersect the northwest and southeast parts of the caldera. The dominant feature within the caldera is a resurgent dome in the west-central section, which formed between about 0.7 and 0.5 Myr b.p. Teleseismic data indicate a low P-wave velocity zone below the western part of the caldera, indicating a magma chamber between 7 and 25 km depth. This conclusion is supported by gravity data. Heat flow just west of the caldera is 3.75 HFU. Just east of the caldera, measured heat flow is about 2 HFU. However, a deep well on the eastern edge of the resurgent dome has a gradient of 38/sup 0/C/km from 0.66 to 1.2 km suggesting that the magma chamber, which produced Long Valley, is largely crystallized below the resurgent dome. The high heat flow beneath the western caldera may be a manifestation of shallow silicic magma associated with the recent Inyo Craters. These data indicate a smaller magma source may lie below the western caldera. The resurgent dome and the area just west of the caldera are cited for additional Hot Dry Rock prospection. The higher temperature gradient and lack of caldera fill beyond the west margin of the caldera combine to make this area promising for future HDR evaluation.

  3. Uplift, thermal unrest and magma intrusion at Yellowstone caldera.

    PubMed

    Wicks, Charles W; Thatcher, Wayne; Dzurisin, Daniel; Svarc, Jerry

    2006-03-01

    The Yellowstone caldera, in the western United States, formed approximately 640,000 years ago when an explosive eruption ejected approximately 1,000 km3 of material. It is the youngest of a series of large calderas that formed during sequential cataclysmic eruptions that began approximately 16 million years ago in eastern Oregon and northern Nevada. The Yellowstone caldera was largely buried by rhyolite lava flows during eruptions that occurred from approximately 150,000 to approximately 70,000 years ago. Since the last eruption, Yellowstone has remained restless, with high seismicity, continuing uplift/subsidence episodes with movements of approximately 70 cm historically to several metres since the Pleistocene epoch, and intense hydrothermal activity. Here we present observations of a new mode of surface deformation in Yellowstone, based on radar interferometry observations from the European Space Agency ERS-2 satellite. We infer that the observed pattern of uplift and subsidence results from variations in the movement of molten basalt into and out of the Yellowstone volcanic system. PMID:16511491

  4. On the formation of calderas during ignimbrite eruptions

    USGS Publications Warehouse

    Druitt, T.H.; Sparks, R.S.J.

    1984-01-01

    Many large calderas result from the eruption of substantial volumes (tens or hundreds of km3) of silicic pyroclastics. Such events often begin with an airfall phase and progress to the generation of voluminous ignimbrites1-3. We propose here that many such eruptions involve two well-defined stages, based on a simple analysis of magma chamber pressure variations during an eruption. The first stage begins when an overpressured magma chamber fractures the country rock and forms a conduit to the surface. The chamber pressure decreases rapidly to values less than lithostatic pressure. We show that only small to moderate volumes of magma, representing a small fraction of the total chamber, can be erupted during this stage. In the second stage, caldera collapse results from a further decrease in magma pressure, which causes the chamber roof to fracture catastrophically and deform. Subsidence of the roof attempts to re-establish lithostatic pressures within the chamber and can drive substantial volumes of magma to the surface. Geological relationships in pyroclastic deposits associated with large caldera eruptions provide independent evidence for this model. ?? 1984 Nature Publishing Group.

  5. Faulting history of the Long Valley caldera, eastern California

    SciTech Connect

    Foster, J.G. . School of Natural Science)

    1993-03-01

    The faulting history that produced the Sierra Nevada Range can be seen, in part, on the eastern contact of the Sierra Nevada Block with the Owens Valley Block. By surveying a series of remnant lake shore lines in the Long Valley Caldera of eastern California, the deformation and faulting history of the area can be inferred. These beaches are ideal for studying the faulting history of the area as their location is so near the contact of the two plates. The caldera sits on the Owens Valley Block just east of the major fault which separates it from the Sierra Nevada Block. It encompasses a ten mile by twenty mile area, which was filled with a lake after its creation some 730,000 years ago. Over time, the lake slowly lowered due to erosion of its sill, successive upward tilting of the Sierra Nevada Block, and consequent downward tilting of the Owens Valley Block. These changes in the attitude of the caldera floor and the beaches of the lake left the successive, non-parallel shore lines that have now been surveyed, mapped, and dated relative to each other. Together with the regional structures and history of the area, the remnant deformed shore lines can be used to develop a picture of the faulting history of the area and its relation to the rising of the Sierra Nevada Mountains.

  6. Uplift, thermal unrest and magma intrusion at Yellowstone caldera

    USGS Publications Warehouse

    Wicks, C.W.; Thatcher, W.; Dzurisin, D.; Svarc, J.

    2006-01-01

    The Yellowstone caldera, in the western United States, formed ???640,000 years ago when an explosive eruption ejected ???1,000 km3 of material. It is the youngest of a series of large calderas that formed during sequential cataclysmic eruptions that began ???16 million years ago in eastern Oregon and northern Nevada. The Yellowstone caldera was largely buried by rhyolite lava flows during eruptions that occurred from ???150,000 to ???70,000 years ago. Since the last eruption, Yellowstone has remained restless, with high seismicity, continuing uplift/subsidence episodes with movements of ???70 cm historically to several metres since the Pleistocene epoch, and intense hydrothermal activity. Here we present observations of a new mode of surface deformation in Yellowstone, based on radar interferometry observations from the European Space Agency ERS-2 satellite. We infer that the observed pattern of uplift and subsidence results from variations in the movement of molten basalt into and out of the Yellowstone volcanic system. ?? 2006 Nature Publishing Group.

  7. A core hole in the southwestern moat of the Long Valley caldera: Early results

    SciTech Connect

    Wollenberg, H.A.; Sorey, M.L.; Farrar, C.D.; White, A.F.; Flexser, S.; Bartel, L.C.

    1986-12-01

    A continuously cored hole penetrated 715m into the southwestern moat of the Long Valley caldera. Temperatures in the post-caldera deposits increase rapidly with depth over the upper 335m to 202/sup 0/C, then remain nearly isothermal into the Bishop Tuff to the bottom of the hole. The depth to the Bishop is the shallowest, and the temperatures observed are among the highest in holes drilled in the caldera. The hole identifies a potential geothermal resource for the community of Mammoth Lakes, constrains the position of the principal heat source for the caldera's hydrothermal system, and serves as access for monitoring changes in water level, temperatures, and fluid chemistry.

  8. Geologic Map of Mount Mazama and Crater Lake Caldera, Oregon

    USGS Publications Warehouse

    Bacon, Charles R.

    2008-01-01

    Crater Lake partly fills one of the most spectacular calderas of the world, an 8-by-10-km basin more than 1 km deep formed by collapse of the volcano known as Mount Mazama (fig. 1) during a rapid series of explosive eruptions about 7,700 years ago. Having a maximum depth of 594 m, Crater Lake is the deepest lake in the United States. Crater Lake National Park, dedicated in 1902, encompasses 645 km2 of pristine forested and alpine terrain, including the lake itself, virtually all of Mount Mazama, and most of the area of the geologic map. The geology of the area was first described in detail by Diller and Patton (1902) and later by Williams (1942), whose vivid account led to international recognition of Crater Lake as the classic collapse caldera. Because of excellent preservation and access, Mount Mazama, Crater Lake caldera, and the deposits formed by the climactic eruption constitute a natural laboratory for study of volcanic and magmatic processes. For example, the climactic ejecta are renowned among volcanologists as evidence for systematic compositional zonation within a subterranean magma chamber. Mount Mazama's climactic eruption also is important as the source of the widespread Mazama ash, a useful Holocene stratigraphic marker throughout the Pacific Northwest, adjacent Canada, and offshore. A detailed bathymetric survey of the floor of Crater Lake in 2000 (Bacon and others, 2002) provides a unique record of postcaldera eruptions, the interplay between volcanism and filling of the lake, and sediment transport within this closed basin. Knowledge of the geology and eruptive history of the Mount Mazama edifice, greatly enhanced by the caldera wall exposures, gives exceptional insight into how large volcanoes of magmatic arcs grow and evolve. Lastly, the many smaller volcanoes of the High Cascades beyond the limits of Mount Mazama are a source of information on the flux of mantle-derived magma through the region. General principles of magmatic and eruptive

  9. Relating seismic swarms and deformation in Long Valley Caldera, California

    NASA Astrophysics Data System (ADS)

    Montgomery-Brown, E. K.; Ellsworth, W. L.; Hill, D. P.; Shelly, D. R.; Langbein, J. O.; Lisowski, M.; Llenos, A. L.

    2013-12-01

    Earthquake swarm activity in the South Moat Seismic Zone (SMSZ) in Long Valley caldera began increasing following the onset of slow inflation of the resurgent dome in 2011. From 1980 through 1999 the caldera produced recurring earthquake swarms in the SMSZ accompanied by an 80-cm uplift of the resurgent dome. Since 2000, the caldera has been quieter than from 1980 to 1999, but it experienced a gradual 7-cm uplift episode in 2002-2003 and currently the caldera has been gradually uplifting since 2011 at less than half of the peak uplift velocity observed in the late 1990's. Two of the recent swarms in October/November of 2012 and March 2013 have been accompanied by small deformation transients during which caldera uplift paused for about a week despite otherwise steady inflation. To better understand this recent activity, we cross correlate seismic velocity waveforms from individual events recorded by the Long Valley seismic network to identify similar clusters (families) of earthquakes and analyze their temporal recurrence. Then, we use representative waveforms from each family as templates to search the continuous waveforms from the deep borehole seismometers in the Long Valley Exploratory Well (MDH1) for repeating, yet smaller, earthquakes. MDH1 consists of two three-component instruments, located 2592 m and 2263 m below ground level, that provide 6 channels with very low background noise relative to surface seismometers. The cross correlations identify about 25 times more earthquakes with most magnitudes ranging from -1 to +0.5, determined from an empirical relationship between catalog magnitude and observed amplitude on MDH1. We apply an ETAS model to the augmented catalog to detect subtle changes in background earthquake rates that might suggest a change in stressing rate. For comparison with the change in seismicity rates, a geodetically determined stress change is estimated from a simple model of the continuous GPS data. We model the uplift from 2011 to

  10. Late-stage volatile saturation as a potential trigger for explosive volcanic eruptions

    NASA Astrophysics Data System (ADS)

    Stock, Michael J.; Humphreys, Madeleine C. S.; Smith, Victoria C.; Isaia, Roberto; Pyle, David M.

    2016-03-01

    Magma reservoirs are thought to grow relatively slowly, assembling incrementally under volatile-saturated conditions. Eruptions may be triggered by injections of volatile-rich melt, or generation of over-pressure due to protracted crystallization. Here, we analyse fluorine, chlorine and water in apatite crystals trapped at different stages of magma evolution, and in melt inclusions from clinopyroxene and biotite crystals expelled during an explosive eruption of the Campi Flegrei caldera, Italy, about 4,000 years ago. We combine our geochemical analyses with thermodynamic modelling to reconstruct the evolution of magmatic volatile contents leading up to the explosive eruption. We find that the magma reservoir remained persistently water-undersaturated throughout most of its lifetime. Even crystals in contact with the melt shortly before eruption show that the magma was volatile-undersaturated. Our models suggest that the melt reached volatile saturation at low temperatures, just before eruption. We suggest that late-stage volatile saturation probably triggered the eruption, and conclude that `priming’ of the magma system for eruption may occur on timescales much shorter than the decadal to centennial timescales thought typical for magma reservoir assembly. Thus, surface deformation pulses that record magma assembly at depth beneath Campi Flegrei and other similar magmatic systems may not be immediately followed by an eruption; and explosive eruptions may begin with little warning.

  11. Geophysical expression of caldera related volcanism, structures and mineralization in the McDermitt volcanic field

    NASA Astrophysics Data System (ADS)

    Rytuba, J. J.; Blakely, R. J.; Moring, B.; Miller, R.

    2013-12-01

    The High Rock, Lake Owyhee, and McDermitt volcanic fields, consisting of regionally extensive ash flow tuffs and associated calderas, developed in NW Nevada and SE Oregon following eruption of the ca. 16.7 Ma Steens flood basalt. The first ash flow, the Tuff of Oregon Canyon, erupted from the McDermitt volcanic field at 16.5Ma. It is chemically zoned from peralkaline rhyolite to dacite with trace element ratios that distinguish it from other ash flow tuffs. The source caldera, based on tuff distribution, thickness, and size of lithic fragments, is in the area in which the McDermitt caldera (16.3 Ma) subsequently formed. Gravity and magnetic anomalies are associated with some but not all of the calderas. The White Horse caldera (15.6 Ma), the youngest caldera in the McDermitt volcanic field has the best geophysical expression, with both aeromagnetic and gravity lows coinciding with the caldera. Detailed aeromagnetic and gravity surveys of the McDermitt caldera, combined with geology and radiometric surveys, provides insight into the complexities of caldera collapse, resurgence, post collapse volcanism, and hydrothermal mineralization. The McDermitt caldera is among the most mineralized calderas in the world, whereas other calderas in these three Mid Miocene volcanic fields do not contain important hydrothermal ore deposits, despite having similar age and chemistry. The McDermitt caldera is host to Hg, U, and Li deposits and potentially significant resources of Ga, Sb, and REE. The geophysical data indicate that post-caldera collapse intrusions were important in formation of the hydrothermal systems. An aeromagnetic low along the E caldera margin reflects an intrusion at a depth of 2 km associated with the near-surface McDermitt-hot-spring-type Hg-Sb deposit, and the deeper level, high-sulfidation Ga-REE occurrence. The Li deposits on the W side of the caldera are associated with a series of low amplitude, small diameter aeromagnetic anomalies that form a continuous

  12. Geologic evolution of the Donguinyó-Huichapan caldera complex, central Mexican Volcanic Belt, Mexico

    NASA Astrophysics Data System (ADS)

    Aguirre-Díaz, Gerardo J.; López-Martínez, Margarita

    2009-01-01

    The Donguinyó-Huichapan caldera complex is located 110 km to the NNW of Mexico City, in the central sector of the Mexican Volcanic Belt. It is a 10 km in diameter complex apparently with two overlapping calderas, each one related to an ignimbrite sequence that contrasts in composition, mineralogy, welding, distribution, and physical aspect. The geologic evolution of this complex includes the following phases, 1) A first caldera formed at 5.0 ± 0.3 Ma, with the eruption of several discrete pulses of andesitic to trachydacitic pyroclastic flows that produced a series of densely welded ignimbrites; 2) At 4.6 ± 0.3 Ma, several small shield volcanoes and cinder cones built the rim of this caldera and erupted basaltic-andesite and andesitic lava flows; 3) At 4.2 ± 0.2 Ma, a second caldera was formed associated to the eruption of the Huichapan Tuff, which is a rhyolitic pyroclastic sequence consisting of minor unwelded ignimbrites, pumice fall and surge deposits, and a voluminous welded ignimbrite; 4) Also yielding an age of 4.2 ± 0.2 Ma, several trachydacitic lava domes were extruded along the new ring fracture and formed the rim of the Huichapan caldera, as well as five intra-caldera domes of dacitic and trachydacitic composition. Peripheral volcanism includes a large 2.5 ± 0.1 Ma shield volcano that was emplaced on the Huichapan caldera rim. The two calderas that form the Donguinyó-Huichapan complex have contrasting differences in volcanic styles that were apparently due to their differences in composition. Products erupted by the Donguinyó caldera are basaltic-andesite to trachydacitic in composition, whereas Huichapan caldera products are all high-silica rhyolites.

  13. Geologic map of the Caetano caldera, Lander and Eureka counties, Nevada

    USGS Publications Warehouse

    Colgan, Joseph P.; Henry, Christopher D.; John, David A.

    2011-01-01

    The Eocene (34 Ma) Caetano caldera in north-central Nevada offers an exceptional opportunity to study the physical and petrogenetic evolution of a large (20 km by 10–18 km pre-extensional dimensions) silicic magma chamber, from precursor magmatism to caldera collapse and intrusion of resurgent plutons. Caldera-related rocks shown on this map include two units of crystal-rich intracaldera tuff totaling over 4 km thickness, caldera collapse breccias, tuff dikes that fed the eruption, hydrothermally altered post-eruption rocks, and two generations of resurgent granitic intrusions (John et al., 2008). The map also depicts middle Miocene (about 16–12 Ma) normal faults and synextensional basins that accommodated >100 percent extension and tilted the caldera into a series of ~40° east-dipping blocks, producing exceptional 3-D exposures of the caldera interior (Colgan et al., 2008). This 1:75,000-scale map is a compilation of published maps and extensive new mapping by the authors (fig. 1), and supersedes a preliminary 1:100,000-scale map published by Colgan et al. (2008) and John et al. (2008). New mapping focused on the margins of the Caetano caldera, the distribution and lithology of rocks within the caldera, and on the Miocene normal faults and sedimentary basins that record Neogene extensional faulting. The definition of geologic units and their distribution within the caldera is based entirely on new mapping, except in the northern Toiyabe Range, where mapping by Gilluly and Gates (1965) was modified with new field observations. The distribution of pre-Cenozoic rocks outside the caldera was largely compiled from existing sources with minor modifications, with the exception of the northeastern caldera margin (west of the Cortez Hills Mine), which was remapped in the course of this work and published as a stand-alone 1:6000-scale map (Moore and Henry, 2010).

  14. Satellites images, digitized topography, and the recognition of the Xela Caldera, Quezaltenango Valley, Guatemala

    SciTech Connect

    Foley, D. . Dept. of Earth Sciences); McEwen, A.; Duffield, W. ); Heiken, G. )

    1992-01-01

    The authors propose, based on reconnaissance geology studies and interpretation of landforms as depicted by Landsat Thematic Mapper (TM) images combined with digitized topography, that the Quezaltenango basin of Guatemala is part of a caldera. The Quezaltenango basin is an elliptical depression, about 12 by 25 km and about 500 m deep. The proposed Xela Caldera extends beyond the basin more than 10 km to the north. The geomorphological features of the area that are typical of a geologically young large-scale caldera include bounding walls that have steep interior and gentle exterior slopes; broad flat areas at the base of the walls; at least one large block, about 3 by 12 km, that only partly floundered as the caldera collapsed; resurgence of a younger volcanic dome, flow and small-scale caldera complex (last active in 1818); younger volcanoes located along the structural margin of the major caldera (one of which is currently active) lobate features on the caldera margins that may indicate a multiple sequence of eruptions; and an active, high-temperature geothermal system. The valley is coincident with a gravity low. Extensive ash-flow tuff sheets that have no identified source are located north of the caldera, and may be the outflow deposits. The Xela caldera is similar in size to the Atitlan caldera, which lies about 50 km southeast of Quezaltenango. The Xela Caldera, if confirmed by future studies, may contain undiscovered geothermal resources, may present a significant geologic hazard to the more than 400,000 people who occupy the Quezaltenango valley, and may be a new member of the list of magmatic systems that have the capability to change global climate for several years.

  15. Geologic map of the Caetano caldera, north-central Nevada: One of the world's best-exposed and most informative calderas

    NASA Astrophysics Data System (ADS)

    Colgan, J. P.; Henry, C. D.; John, D. A.

    2011-12-01

    The 34.0 Ma Caetano caldera formed during eruption of ~1100 km3 of crystal-rich rhyolite (72-78% SiO2). Miocene extension cut and tilted the originally 20 x 12-18 km caldera into a set of ~40° east-dipping fault blocks that expose the entire caldera to its floor, including minor pre-caldera volcanic rocks, two units of intracaldera Caetano Tuff up to 4 km thick, ash-flow tuff feeder dikes, caldera collapse breccias, post-collapse resurgent intrusions, and the caldera structural margin and topographic wall. Geologic mapping at scales ranging from 1:6,000 to 1:75,000 allows the volcanic and structural history of this caldera system to be reconstructed at a level of detail available for few calderas worldwide. The caldera was not built on an older volcanic edifice, although it was preceded by ~6 Ma of regional intrusive magmatism, including 35.7 Ma rhyolite dikes emplaced during formation of nearby Carlin-type gold deposits. Only a very small volume of andesitic lava erupted locally prior to formation of the caldera itself (about 1.2 Ma before). The caldera floor subsided asymmetrically as an apparently coherent block during the eruption. Early eruption and subsidence was likely rapid, allowing the lower intracaldera tuff to pond as a single cooling unit up to 3 km thick in the eastern part of the caldera. Later subsidence was greater in the western part, where the upper intracaldera tuff is up to 2 km thick but thins to <0.5 km to the east. This phase of the eruption was episodic enough that fine-grained sediments accumulated between ash-flow cooling units, but extensive 40Ar/39Ar dating indicates that the entire volcanic interval lasted <100 ka. Collapse occurred dominantly along a single ring fracture, but a composite ring fracture is preserved on the northeastern margin. Here, greatest collapse (up to 4 km) occurred along an inner fracture that transitions upward from a discrete fault zone to a topographic wall. The topographic wall here (and elsewhere in the

  16. Deformation of the Aniakchak Caldera, Alaska, mapped by InSAR

    USGS Publications Warehouse

    Kwoun, Oh-Ig; Lu, Zhiming

    2004-01-01

    The deformation of Aniakchak volcano is investigated using 19 ERS-1 / 2 interferometric synthetic aperture radar (InSAR) data from 1992 through 2002. InSAR images from the different time intervals reveal that the10-km-wide caldera has been subsiding during the time of investigation. The pattern of subsidence does not following the pyroclastic flows from the last eruption of the caldera in 1931. The maximum subsidence is near the center of the caldera, with a rate of up to 13 mm/yr. Deformation outside the caldera is insignificant. Least squares inversion of the multi-temporal deformation maps indicates that the subsidence rate has been relatively constant. Field observations have identified numerous fumaroles inside the caldera. In 1973, temperatures of 80??C were measured at a depth of 15 cm in loose volcanic rubble adjacent to the small cinder cone (about 1.5 km northeast of the vent of the 1931 eruption), whereas springs near a caldera lake had a temperature of 25??C in July 1993. Therefore, we suggest the observed subsidence at Aniakchak caldera is most likely caused by the reduction of pore fluid pressure of a hydrothermal system located a few kilometers beneath the caldera.

  17. How caldera collapse shapes the shallow emplacement and transfer of magma in active volcanoes

    NASA Astrophysics Data System (ADS)

    Corbi, F.; Rivalta, E.; Pinel, V.; Maccaferri, F.; Bagnardi, M.; Acocella, V.

    2015-12-01

    Calderas are topographic depressions formed by the collapse of a partly drained magma reservoir. At volcanic edifices with calderas, eruptive fissures can circumscribe the outer caldera rim, be oriented radially and/or align with the regional tectonic stress field. Constraining the mechanisms that govern this spatial arrangement is fundamental to understand the dynamics of shallow magma storage and transport and evaluate volcanic hazard. Here we show with numerical models that the previously unappreciated unloading effect of caldera formation may contribute significantly to the stress budget of a volcano. We first test this hypothesis against the ideal case of Fernandina, Galápagos, where previous models only partly explained the peculiar pattern of circumferential and radial eruptive fissures and the geometry of the intrusions determined by inverting the deformation data. We show that by taking into account the decompression due to the caldera formation, the modeled edifice stress field is consistent with all the observations. We then develop a general model for the stress state at volcanic edifices with calderas based on the competition of caldera decompression, magma buoyancy forces and tectonic stresses. These factors control: 1) the shallow accumulation of magma in stacked sills, consistently with observations; 2) the conditions for the development of circumferential and/or radial eruptive fissures, as observed on active volcanoes. This top-down control exerted by changes in the distribution of mass at the surface allows better understanding of how shallow magma is transferred at active calderas, contributing to forecasting the location and type of opening fissures.

  18. Implications of a Caldera Origin of the Lunar Crater Copernicus

    NASA Astrophysics Data System (ADS)

    Green, J.

    2007-12-01

    The forthcoming renaissance in lunar exploration will focus on many objectives such as Copernicus. Copernicus appears to be a caldera for at least 8 reasons. If a caldera we see (1) transient activity (2) no overturned impact flap at the crater margins (3) internal sinuous leveed lava flow channels (4) a lava covered floor (5) terraces of different ages (6) multiple central volcanoes, one showing a directed volcanic blast (7) olivine-rich komatiitic lavas on central volcanoes and (8) magmatic inflation/deflation on caldera flanks localizing craterlets and extinct fumaroles in "loop" patterns. Regarding (6), directed volcanic blasts can remove a segment of the volcano wall as evidenced in terrestrial analogs at Mt. St. Helens and Bezymianny. Impact mechanisms to produce this feature in Copernicus are contrived. For (7) Clementine spectral data show a high olivine content of the central mountains on Copernicus which I interpret as forsteritic spinifex mineralization in komatiitic lavas and not as impact rebound of olivine-rich deep seated rocks. (8) MacDonald (1956) documented loop patterns on the flank of Halemaumau in Hawaii defining arcuate fractures localizing fumaroles and craterlets. Inflation/deflation of subjacent magma bodies are interpreted as the cause for these loops. Inflation/deflation mechanisms on caldera flanks are common around terrestrial calderas. "Loop" patterns on the flank of Copernicus localizing "gouge" craterlets have been interpreted as ballistic features resulting from the meteorite impact of this crater. Questioned is the logic of a linear N26E trending array of fragments within Copernicus to serve as a source of ballistic projectiles to form the loops localizing conjugate craterlets. The fused craterlet axes on the lunar loops do not point back to a presumed impact center in Copernicus. The axes are oriented parallel to a regional northwest (N35-60W) fracture zone. Implications for an endogenic origin of Copernicus would involve

  19. Structural controls on diffuse degassing in the Las Cañadas caldera, Tenerife, Canary Islands

    NASA Astrophysics Data System (ADS)

    Galindo, I.; Soriano, C.; Martí, J.; Pérez, N.

    2003-04-01

    The Las Cañadas caldera is an elliptical depression located in the central part of the Tenerife Island. The active Teide stratovolcano stands in the centre of the depression, which is limited to the south by the caldera wall, up to 500 m high above the caldera floor. Mapping most of the caldera wall at 1:5000 has provided new insights on its stratigraphy, structure, and geological evolution. Three major ENE-WSW normal faults have been mapped on the caldera wall in the area comprised between El Llano de Ucanca and Los Azulejos, where an intense hydrothermal alteration affects the lower stratigraphic levels of the caldera wall. Hydrothermal alteration is rather distinctive in this area, showing bluish to greenish colours. Most of the phonolitic cone sheets and radial dykes of the caldera wall do not show distinctive hydrothermal features, as do show the phonolitic pyroclastic rocks and lavas of the lower parts of the caldera wall. This suggests the main episodes of dyke intrusion in the Las Cañadas caldera postdate hydrothermal alteration. ENE-WSW normal faults involve dyke swarms and rocks of the upper stratigraphic levels of the caldera wall, and show displacements of up to 100 m. Unfortunately the upper possible age of these faults is poorly constrained since no contact relationship has been observed between fault planes and the rocks of the uppermost stratigraphic levels of the caldera wall. The rocks of the caldera wall adjacent to the faults are intensely fractured at the macro and mesoscale. In addition to field mapping, a soil gas survey was carried out at the caldera depression. Soil CO2 efflux and H2 concentration were measured reaching values of 12 gm-2d-1 and 4 ppmV, respectively. Spatial distribution of these species showed that positive anomalies coincide with the surface expression of the three major faults and their adjacent intensely fractured zone. The high CO2 and H2 values and their coincidence with major normal faults suggests that degassing in

  20. Aeromagnetic Study of Tke Huichapan Caldera; Central Volcanic Belt

    NASA Astrophysics Data System (ADS)

    Gonzalez, T.; Martin, A.; Alfaro, G.; Oyarzabal, E.

    2013-12-01

    Analysis of the aeromagnetic anomalies over the central sector of the Mexican Volcanic Belt sheds new light on the structure of the Huichapan Caldera. This volcanic center located 100 Km to the north- northwest of Mexico City is approximately 10 km in diameter and related to an ignimbrite sequence. Milan et al, (1993) and. Aguirre-Diaz and Lopez-Martinez (2009) mapped Huichapan area and described the geology and petrology of the erupted products in the region. Aguirre-Diaz and Lopez-Martinez (2009) suggest the idea of two overlapping calderas related to an ignimbrite sequence. The analyzed region is a rectangular area, approximately from 20.25 N to 20.42 N and between 99.42 W and 99.6 W. The total field aeromagnetic data was obtained with a Geometrics G-803 proton magnetometer at a flight altitude of 300 m above ground level. For the analysis of the anomalies, the data was further smoothed to construct a 1 km regularly spaced grid. The anomaly map was compared with the surface geology and larger anomalies were correlated with major volcanic features. Since our main interest was in mapping the subsurface intrusive and volcanic bodies, the total field magnetic anomalies were reduced to the pole by using the double integral Fourier method. The reduced to the pole anomaly map results in a simplified pattern of isolated positive and negative anomalies, which show an improved correlation with all major volcanic structures. For the analysis and interpretation of the anomalies, the reduced to the pole anomalies were continued upward at various reference levels. These operations result in smoothing of the anomaly field by the filtering of high frequency anomalies that may be related to shallow sources. Two profiles were selected that cross the major anomalies on the Huichapan Caldera. The Talwani algorithm for 2-D polygonal bodies has been used for calculating the theoretical anomalies.

  1. Magnetotelluric Investigation of Melt Storage Beneath Okmok Caldera, Alaska

    NASA Astrophysics Data System (ADS)

    Bennington, N. L.; Bedrosian, P.; Key, K.; Zelenak, G.

    2015-12-01

    Alaska accounts for nearly 99% of the seismic moment release within the US. Much of this is associated with the Aleutian volcanic arc, the most tectonically active region in North America, and an ideal location for studying arc magmatism. Okmok is an active volcano located in the central Aleutian arc, defined by a pair of nested, 10 km diameter calderas. The subdued topography of Okmok, relative to other Aleutian volcanoes, improves access and permits dense sampling within the caldera closer to the underlying magmatic system. Okmok volcano was selected as the site of study for this project due to frequent volcanic activity and the presence of a crustal magma reservoir as inferred from previous coarse resolution seismic studies. In June-July 2015, we carried out an amphibious geophysical field deployment at Okmok. Onshore work in and around the volcano included collection of an array of magnetotelluric (MT) stations and installation of a temporary, year-long seismic array. A ring of 3D offshore MT deployments made around the island augments the onshore array. An additional 2D tectonic-scale profile spans the trench, volcanic arc, and backarc. This new geophysical data will be used to gain a greater understanding of Aleutian arc melt generation, migration, and storage beneath an active caldera. We present results from the analysis of the newly collected amphibious 3D MT data. This data will be used to model the distribution and migration of melt within Okmok's crustal magma reservoir. Initial processing of the data shows strong MT signal levels, in particular from a geomagnetic storm that occurred from June 21-23, 2015. A companion abstract discussing the 2D tectonic scale MT profile, which constrains the mantle and deep crust beneath Okmok volcano, is discussed by Zelenak et al.

  2. Insight into vent opening probability in volcanic calderas

    NASA Astrophysics Data System (ADS)

    Giudicepietro, Flora; Macedonio, Giovanni; D'Auria, Luca; Martini, Marcello

    2016-04-01

    This study provides insight into the possible behavior of volcanic calderas in pre-eruptive phase and into the most probable location of the areas prone to vent opening hazard, for cases where sill emplacement is an important element of the shallow magma transport system. We consider that the evolution of the stress field is the main factor that controls the vent opening processes in volcanic calderas and we think that the intrusion of sills is one of the most common mechanism governing caldera unrest. Therefore, we have investigated the spatial and temporal evolution of the stress field due to the emplacement of a sill at shallow depth to provide insight on vent opening probability. We carried out several numerical experiments by using a physical model, to assess the role of the magma properties (viscosity), host rock characteristics (Young's modulus and thickness), and dynamics of the intrusion process (mass flow rate) in controlling the stress field. Results show that that high magma viscosity produces larger stress values, while low magma viscosity leads to lower stresses and favors the radial spreading of the sill. Also high-rock Young's modulus gives high stress intensity, whereas low values of Young's modulus produce a dramatic reduction of the stress associated with the intrusive process. The maximum intensity of tensile stress is concentrated at the front of the sill and propagates radially with it, over time. In our simulations, we find that maximum values of tensile stress occur in ring-shaped areas with radius ranging between 350m and 2500m from the injection point, depending on the model parameters. We infer that the probability of vent opening is higher in these areas.

  3. Thermal history of caldera-forming magmatic systems

    NASA Astrophysics Data System (ADS)

    Bradshaw, R. W.; Kent, A. J.; Cooper, K. M.; Huber, C.

    2015-12-01

    Large, caldera-forming silicic eruptions require the assembly and storage of a large volume of magma, and are though to result from either (1) rare high magma flux events needed to maintain melt-rich (eruptible) magma for extended timescales, or (2) magma accumulation at lower magma fluxes, storage for extended timescales as low temperature crystal mushes and rapid rejuvenation prior to eruption. The thermal history of these magmas prior to eruption thus provides an important clue into the processes that lead to eruption, but has been difficult to quantify. However in-situ measurement of Sr and other trace elements in plagioclase, coupled with diffusion models, can be used to constrain the time magmas spend at different temperatures. Progressive differentiation of plagioclase from a silicic magma produces plagioclase with lower Sr at low An—producing a positive correlation between Sr and An, which is the opposite of what is predicted by equilibrium partitioning. Forward modeling of the temperature-dependent diffusion of Sr from this initial disequilibrium condition toward equilibrium concentrations, based on partitioning relationships of An and Sr, gives an estimate of the time individual crystals spend at specific temperatures. Preliminary high spatial resolution LA-ICP-MS analysis of Sr in plagioclase from five caldera-forming eruptions show overall positive correlations of Sr and An, suggesting that little diffusive re-equilibration has occurred. Thus, over the lifetime that these magmas reside in the upper crust (>10 k.y.) they likely spend less than a few thousand years at temperatures above 750 °C (the approximate temperature of rheological lockup). These results suggest that the magmas that feed many large caldera-forming eruptions are kept in cold storage for long timescales, and that rapid rejuvenation of mush occurs without extended thermal conditioning prior to eruption.

  4. Post-caldera faulting of the Late Quaternary Menengai caldera, Central Kenya Rift (0.20°S, 36.07°E)

    NASA Astrophysics Data System (ADS)

    Riedl, Simon; Melnick, Daniel; Mibei, Geoffrey K.; Njue, Lucy; Strecker, Manfred R.

    2015-04-01

    A structural geological analysis of young caldera volcanoes is necessary to characterize their volcanic activity, assess their geothermal potential, and decipher the spatio-temporal relationships of faults on a larger tectonic scale. Menengai caldera is one of several major Quaternary trachytic caldera volcanoes that are aligned along the volcano-tectonic axis of the Kenya Rift, the archetypal active magmatic rift and nascent plate boundary between the Nubia and Somalia plates. The caldera covers an area of approximately 80 km² and is among the youngest and also largest calderas in the East African Rift, situated close to Nakuru - a densely populated urban area. There is an increasing interest in caldera volcanoes in the Kenya Rift, because these are sites of relatively young volcanic and tectonic activity, and they are considered important sites for geothermal exploration and future use for the generation of geothermal power. Previous studies of Menengai showed that the caldera collapsed in a multi-event, multiple-block style, possibly as early as 29 ka. In an attempt to characterize the youngest tectonic activity along the volcano-tectonic axis in the transition between the Central and Northern Kenya rifts we first used a high-resolution digital surface model, which we derived by structure-from-motion from an unmanned aerial vehicle campaign. This enabled us to identify previously unrecognized normal faults, associated dyke intrusions and volcanic eruptive centers, and transfer faults with strike-slip kinematics in the caldera interior and its vicinity. In a second step we verified these structures at outcrop scale, assessed their relationship with known stratigraphic horizons and dated units, and performed detailed fault measurements, which we subsequently used for fault-kinematic analysis. The most important structures that we mapped are a series of north-northeast striking normal faults, which cross-cut both the caldera walls and early Holocene lake

  5. Mesozoic ash-flow caldera fragments in southeastern Arizona and their relation to porphyry copper deposits.

    USGS Publications Warehouse

    Lipman, P.W.; Sawyer, D.A.

    1985-01-01

    Jurassic and Upper Cretaceous volcanic and associated granitic rocks in SE Arizona are remnants of large composite silicic volcanic fields, characterized by voluminous ash-flow tuffs and associated calderas. Presence of 10-15 large caldera fragments is inferred primarily from 1) ash-flow deposits over 1 km thick, having features of inter-caldera ponding; 2) 'exotic-block' breccia within a tuff matrix, interpreted as caldera-collapse megabreccia; and 3) local granitic intrusion along arcuate structural boundaries of the thick volcanics. Several major porphyry copper deposits are associated with late granitic intrusions within the calderas or along their margins. Such close spatial and temporal association casts doubt on models that associate porphyry copper deposits exclusively with intermediate composition strato-volcanoes. -L.C.H.

  6. Long Valley Caldera 2003 through 2014: overview of low level unrest in the past decade

    USGS Publications Warehouse

    Wilkinson, Stuart K.; Hill, David P.; Langbein, John O.; Lisowski, Michael; Mangan, Margaret T.

    2014-01-01

    Long Valley Caldera is located in California along the eastern escarpment of the Sierra Nevada Range. The caldera formed about 760,000 years ago as the eruption of 600 km3 of rhyolite magma (Bishop Tuff) resulted in collapse of the partially evacuated magma chamber. Resurgent doming in the central part of the caldera occurred shortly afterwards, and the most recent eruptions inside the caldera occurred about 50,000 years ago. The caldera remains thermally active, with many hot springs and fumaroles, and has had significant deformation and seismicity since at least 1978. Periods of intense unrest in the 1980s to early 2000s are well documented in the literature (Hill and others, 2002; Ewert and others, 2010). In this poster, we extend the timeline forward, documenting seismicity and deformation over the past decade.

  7. Principal component analysis of geodetically measured deformation in Long Valley caldera, eastern California, 1983-1987

    USGS Publications Warehouse

    Savage, J.C.

    1988-01-01

    Geodetic measurements of deformation at Long Valley caldera provide two examples of the application of principal component analysis. A 40-line trilateration network surrounding the caldera was surveyed in midsummer 1983, 1984, 1985, 1986, and 1987. Principal component analysis indicates that the observed deformation can be represented by a single coherent source. The time dependence for that source displays a rapid rate of deformation in 1983-1984 followed by less rapid but uniform rate in the 1984-1987 interval. The spatial factor seems consistent with expansion of a magma chamber beneath the caldera plus some shallow right-lateral slip on a vertical fault in the south moat of the caldera. An independent principal component analysis of the 1982, 1983, 1984, 1985, 1986, and 1987 leveling across the caldera requires two self-coherent sources to explain the deformation. -from Author

  8. Analogue of Caldera Dynamics: the Controlled Salt Cavern Collapse

    NASA Astrophysics Data System (ADS)

    Jousset, P. G.; Rohmer, J.

    2012-12-01

    Caldera collapse (or pit-crater) dynamics are inferred from geological observations and laboratory experiments. Here, we present an analogue of caldera collapse at field scale and possible analogy with large scale caldera dynamics. Through an original exploitation technique in sedimentary environment, a salt layer is emptied, leaving a brine-filled cavern, which eventually collapses after overburden falls into the cavern. Such a collapse was monitored in East France by many instruments (including GPS, extensometers, geophones, broadband seismological sensors, tiltmeter, gravity meter, … ), which allowed us to describe mechanisms of the collapse. Micro-seismicity is a good indicator of spatio-temporal evolution of physical properties of rocks prior to catastrophic events like volcanic eruptions or landslides and may be triggered by a number of causes including dynamic characteristics of processes in play or/and external forces. We show evidence of triggered micro-seismicity observed in the vicinity of this underground salt cavern prone to collapse by a remote M~7.2 earthquake, which occurred ~12000 kilometres away. High-dynamic broadband records reveal the strong time-correlation between a dramatic change in the rate of local high-frequency micro-seismicity and the passage of low-frequency seismic waves, including body, Love and Rayleigh surface waves. Pressure was lowered in the cavern by pumping operations of brine out of the cavern. We demonstrate the near critical state of the cavern before the collapse by means of 2D axisymmetric elastic finite-element simulations. Stress oscillations due to the seismic waves may have exceeded the strength required for the rupture of the complex media made of brine and rock triggering micro-earthquakes and leading to damage of the overburden and eventually collapse of the salt cavern. The increment of stress necessary for the failure of a Dolomite layer is of the same order or magnitude as the maximum dynamic stress magnitude

  9. Dilational processes accompanying earthquakes in the Long Valley Caldera

    USGS Publications Warehouse

    Dreger, Douglas S.; Tkalcic, Hrvoje; Johnston, M.

    2000-01-01

    Regional distance seismic moment tensor determinations and broadband waveforms of moment magnitude 4.6 to 4.9 earthquakes from a November 1997 Long Valley Caldera swarm, during an inflation episode, display evidence of anomalous seismic radiation characterized by non-double couple (NDC) moment tensors with significant volumetric components. Observed coseismic dilation suggests that hydrothermal or magmatic processes are directly triggering some of the seismicity in the region. Similarity in the NDC solutions implies a common source process, and the anomalous events may have been triggered by net fault-normal stress reduction due to high-pressure fluid injection or pressurization of fluid-saturated faults due to magmatic heating.

  10. A multidisciplinary study of the 2014-2015 Bárðarbunga caldera collapse, Iceland

    NASA Astrophysics Data System (ADS)

    Tumi Gudmundsson, Magnus; Jonsdóttir, Kristin; Hooper, Andy; Holohan, Eoghan; Halldorsson, Saemundur

    2016-04-01

    The collapse of the ice-filled Bárðarbunga caldera in central Iceland occurred in autumn and winter, when weather was highly unsettled and conditions for monitoring in many ways difficult. Nevertheless several detailed time series could be obtained on the collapse and to a degree the associated flood-basalt eruption in Holuhraun. This was achieved through applying an array of sensors, that were ground, air and satellite based, partly made possible through the EU-funded FUTUREVOLC supersite project. This slow caldera collapse lasted six months, ending in February 2015. The array of sensors used, coupled with the long duration of the event, allowed unprecedented detail in observing a caldera collapse. The deciphering of the course of events required the use of aircraft altimeter surveys of the ice surface, seismic and GPS monitoring, the installation of a GPS station on the glacier surface in the centre of the caldera that continuously recorded the subsidence. Full Stokes 3-D modelling of the 700-800 m thick ice in the caldera, constrained by observations, was applied to remove the component of ice deformation that had a minor effect on the measured subsidence. The maximum subsidence of the subglacial caldera floor was about 65 meters. The combined interpretation of geochemical geobarometers, subsidence geometry with GPS and InSAR deformation signals, seismicity and distinct element deformation modelling of the subsidence provided unprecedented detail of the process and mechanism of caldera collapse. The collapse involved the re-activation of pre-existing ring faults, and was initiated a few days after magma started to drain from underneath the caldera towards the eventual eruption site in Holuhraun, 45 km to the northeast. The caldera collapse was slow and gradual, and the flow rate from underneath the caldera correlates well with the lava flow rate in Holuhraun, both in terms of total volume and variations in time.

  11. A tectonic model of the Askja caldera system based on FEM analysis

    NASA Astrophysics Data System (ADS)

    Browning, John; Gudmundsson, Agust; Thordarson, Thorvaldur

    2015-04-01

    The Askja volcanic system lies on the boundary between the Eurasian and North American tectonic plates and is an example of a multiple caldera formed in an extensional regime. Askja is composed of at least three calderas, the last of which formed during an explosive eruption in A.D. 1875. The caldera floor has been subsiding almost continuously since 1983; total subsidence in this period is around 1.1 metres. Perhaps surprisingly, there has been no slip or movement on the caldera bounding ring-faults during this subsidence period. Various models have been proposed to explain this unusual signal. Previous models suggest two magma sources, one shallow at around 3 km depth and one much larger at around 16 km depth. In this model, subsidence is caused by depressurisation in both sources as a result of cooling contraction and crystallisation. In other models subsidence results from magma being squeezed out of the shallow chamber laterally; or somehow draining back into a deep seated reservoir. In this study we examine the contribution of regional extension and structural discontinuities to the current subsidence of Askja caldera. Using a finite element numerical analysis, we ascertain the state of stresses at Askja caldera over time based on several different magma body geometries. We calculate surface displacements expected from extension around a shallow magma body, and place these findings in the context of Icelandic calderas. In addition we investigate the likely stress effects of the Askja caldera on the associated part of the Northern Volcanic Zone. The proposed model seeks to understand the volcano-tectonic conditions at Askja during caldera formation, as well as during rifting episodes. The models presented will be useful in assessing likely future rifting events and fissure swarm activity in Askja caldera, and neighbouring volcanoes.

  12. Intracaldera volcanic activity, Toledo caldera and embayment, Jemez Mountains, New Mexico

    SciTech Connect

    Heiken, G.; Goff, F.; Stix, J.; Shafiqullah, M.; Garcia, S.; Hagan, R.

    1986-02-10

    The Toledo caldera was formed at 1.47 +- 0.06 Ma during the catastrophic eruption of the lower member, Bandelier Tuff. The caldera was obscured at 1.12 +- 0.03 Ma during eruption of the equally voluminous upper member of the Bandelier Tuff that led to formation of the Valles caldera. Earlier workers interpreted a 9-km-diameter embayment, located NE of the Valles caldera (Toledo embayment), to be a remnant of the Toledo caldera. Drill hole data and new K-Ar dates of Toledo intracaldera domes redefine the position of Toledo caldera, nearly coincident with and of the same dimensions as the younger Valles caldera. the Toledo embayment may be of tectonic origin or a small Tschicoma volcanic center caldera. This interpretation is consistent with distribution of the lower member of the Bandelier Tuff and with several other field and drilling-related observations. Explosive activity associated with Cerro Toledo Rhyolite domes is recorded in tuff deposits located between the lower and upper members of the Bandelier Tuff on the northeast flank of the Jemez Mountains. Recorded in the tuff deposits are seven cycles of explosive activity. Most cycles consists of phreatomagmatic tuffs that grade upward into Plinian pumice beds. A separate deposit, of the same age and consisting of pyroclastic surges and flows, is associated with Rabbit Mountain, located on the southeast rim of the Valles-Toledo caldera complex. These are the surface expression of what may be a thicker, more voluminous intracaldera tuff sequence. The combined deposits of the lower and upper members of the Bandelier Tuff, Toledo and Valles intracaldera sediments, tuffs, and dome lavas form what we interpret to be a wedge-shaped caldera fill. This sequence is confirmed by deep drill holes and gravity surveys.

  13. Growth of intra-caldera lava domes controlled by various modes of caldera collapse, the Štiavnica volcano-plutonic complex, Western Carpathians

    NASA Astrophysics Data System (ADS)

    Tomek, Filip; Žák, Jiří; Holub, František V.; Chlupáčová, Marta; Verner, Kryštof

    2016-02-01

    The Štiavnica volcano-plutonic complex is an erosional relic of Miocene caldera-stratovolcano in the Western Carpathians. The complex exposes a vertical section from the volcano basement through subvolcanic intrusions and a ring fault to volcanic edifice, comprising mostly andesitic lava flows and domes. This paper examines internal structure, magnetic fabric as derived from the anisotropy of magnetic susceptibility (AMS), and emplacement dynamics of three intra-caldera andesite domes (referred to as Domes 1-3) located near the presumed ring fault. Magnetic fabrics, carried by multi-domain titanomagnetite and titanomaghemite, are interpreted as recording various mechanisms of dome growth controlled by active caldera collapse. Dome 1 is explained as a lava coulée, fed by conduits located along the ring fault, with a long lava outflow down the sloping caldera floor. Dome 2 represents an elongated, ring fault-parallel dome wherein the lava flowed a short distance over a flat floor. Dome 3 is interpreted as a composite dome fed from multiple linear fissures opened at a high angle to the ring fault. Subsequently, the dome was intruded by ring fault-parallel dikes that may have potentially fed overlying, now largely eroded lava domes and flows. Finally, we suggest that all domes formed during collapse of the Štiavnica caldera and the various mechanisms of their growth reflect different stages of the caldera evolution from piston (Dome 2) through trap-door (Dome 1) to piecemeal (Dome 3).

  14. The Twin Peaks caldera: A window into the emplacement and evolution of a Caldera-filling ignimbrite

    SciTech Connect

    Jellinek, A.M.; Geist, D. . Dept. of Geology)

    1993-04-01

    The Twin Peaks caldera, about 13 km west of Challis, Idaho, is an elliptical Valles-sized caldera with dimensions of 20 x 14 km. The tuff of Challis Creek (TCR) is largely a caldera-fill ignimbrite sequence that was emplaced about 45 Ma during the last stages of the Eocene Challis volcanic episode. Post-volcanic block faulting and erosion have deeply-dissected the TCR section resulting in over 1,200 meters of vertical exposure. This feature has provided a rare opportunity to both describe intracaldera-fill cooling facies and explore the pre-, syn-, and post-emplacement mechanisms controlling their development. Hardyman (1983) delineated two major intracaldera cooling units on the basis of rock texture, degree of welding, crystallinity, and pumice color relative to the matrix. In this study these two cooling units have been expanded to include one simple cooling unit, T0 (at least 140 m thick), and two compound units, T1 (140--670 m thick) and T2 (at least 800 m thick), with three and eight distinct facies respectively. The cooling units and their associated facies are defined on the basis of field observations of: (1) macroscopic textures and degree of welding, (2) weathering color, (3) matrix color, crystallinity, and lithic content, and, (4) pumice crystallinity, flattening, and color relative to the matrix. Petrographic observations of: (1) mineral assemblages and styles of phenocryst fragmentation, (2) alignment of glass shards and their relative, compaction and contortion around phenocrysts, and (3) the extent of compaction and contortion and crystallinity of collapsed pumice structures have further refined facies determinations. A preliminary model for the T2 compound cooling unit suggests that the development of the eight T2 facies can be explained by post-emplacement collapse of pore space combined with the exsolution of volatiles followed by further compaction and welding.

  15. Renewed inflation of Long Valley Caldera, California (2011 to 2014)

    NASA Astrophysics Data System (ADS)

    Montgomery-Brown, E. K.; Wicks, C. W.; Cervelli, P. F.; Langbein, J. O.; Svarc, J. L.; Shelly, D. R.; Hill, D. P.; Lisowski, M.

    2015-07-01

    Slow inflation began at Long Valley Caldera in late 2011, coinciding with renewed swarm seismicity. Ongoing deformation is concentrated within the caldera. We analyze this deformation using a combination of GPS and InSAR (TerraSAR-X) data processed with a persistent scatterer technique. The extension rate of the dome-crossing baseline during this episode (CA99 to KRAC) is 1 cm/yr, similar to past inflation episodes (1990-1995 and 2002-2003), and about a tenth of the peak rate observed during the 1997 unrest. The current deformation is well modeled by the inflation of a prolate spheroidal magma reservoir ˜7 km beneath the resurgent dome, with a volume change of ˜6 × 106 m3/yr from 2011.7 through the end of 2014. The current data cannot resolve a second source, which was required to model the 1997 episode. This source appears to be in the same region as previous inflation episodes, suggesting a persistent reservoir.

  16. Origin of Hot Creek Canyon, Long Valley caldera, California

    SciTech Connect

    Maloney, N.J. . Dept. of Geological Sciences)

    1993-04-01

    Hot Creek has eroded a canyon some thirty meters deep across the Hot Creek rhyolite flows located in the southeastern moat of Long Valley Caldera. Maloney (1987) showed that the canyon formed by headward erosion resulting from spring sapping along hydrothermally altered fractures in the rhyolite, and the capture of Mammoth Creek. This analysis ignored the continuing uplift of the central resurgent dome. Reid (1992) concluded that the downward erosion of the canyon must have kept pace with the uplift. Long Valley Lake occupied the caldera until 100,000 to 50,000 years before present. The elevation of the shoreline, determined by trigonometric leveling, is 2,166 m where the creek enters the canyon and 2,148 m on the downstream side of the rhyolite. The slope of the strand line is about equal to the stream gradient. The hill was lower and the stream gradient less at the time of stream capture. Rotational uplift increased the stream gradient which increased the rate of downward erosion and formed the V-shaped canyon

  17. Renewed inflation of Long Valley Caldera, California (2011 to 2014)

    USGS Publications Warehouse

    Montgomery-Brown, Emily; Wicks, Chuck; Cervelli, Peter F.; Langbein, John O.; Svarc, Jerry L.; Shelly, David R.; Hill, David P.; Lisowski, Michael

    2015-01-01

    Slow inflation began at Long Valley Caldera in late 2011, coinciding with renewed swarm seismicity. Ongoing deformation is concentrated within the caldera. We analyze this deformation using a combination of GPS and InSAR (TerraSAR-X) data processed with a persistent scatterer technique. The extension rate of the dome-crossing baseline during this episode (CA99 to KRAC) is 1 cm/yr, similar to past inflation episodes (1990–1995 and 2002–2003), and about a tenth of the peak rate observed during the 1997 unrest. The current deformation is well modeled by the inflation of a prolate spheroidal magma reservoir ∼7 km beneath the resurgent dome, with a volume change of ∼6 × 106 m3/yr from 2011.7 through the end of 2014. The current data cannot resolve a second source, which was required to model the 1997 episode. This source appears to be in the same region as previous inflation episodes, suggesting a persistent reservoir.

  18. Months between rejuvenation and volcanic eruption at Yellowstone caldera, Wyoming

    USGS Publications Warehouse

    Till, Christy B.; Vazquez, Jorge A.; Boyce, Jeremy W

    2015-01-01

    Rejuvenation of previously intruded silicic magma is an important process leading to effusive rhyolite, which is the most common product of volcanism at calderas with protracted histories of eruption and unrest such as Yellowstone, Long Valley, and Valles, USA. Although orders of magnitude smaller in volume than rare caldera-forming super-eruptions, these relatively frequent effusions of rhyolite are comparable to the largest eruptions of the 20th century and pose a considerable volcanic hazard. However, the physical pathway from rejuvenation to eruption of silicic magma is unclear particularly because the time between reheating of a subvolcanic intrusion and eruption is poorly quantified. This study uses geospeedometry of trace element profiles with nanometer resolution in sanidine crystals to reveal that Yellowstone’s most recent volcanic cycle began when remobilization of a near- or sub-solidus silicic magma occurred less than 10 months prior to eruption, following a 220,000 year period of volcanic repose. Our results reveal a geologically rapid timescale for rejuvenation and effusion of ~3 km3 of high-silica rhyolite lava even after protracted cooling of the subvolcanic system, which is consistent with recent physical modeling that predict a timescale of several years or less. Future renewal of rhyolitic volcanism at Yellowstone is likely to require an energetic intrusion of mafic or silicic magma into the shallow subvolcanic reservoir and could rapidly generate an eruptible rhyolite on timescales similar to those documented here.

  19. Highly evolved rhyolitic glass compositions from the Toba Caldera, Sumatra

    SciTech Connect

    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 of 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.

  20. The hydrothermal system of Long Valley Caldera, California

    USGS Publications Warehouse

    Sorey, M.L.; Lewis, Robert Edward; Olmsted, F.H.

    1978-01-01

    Long Valley caldera, an elliptical depression covering 450 km 2 on the eastern front of the Sierra Nevada in east-central California, contains a hot-water convection system with numerous hot springs and measured and estimated aquifer temperatures at depths of 180?C to 280?C. In this study we have synthesized the results of previous geologic, geophysical, geochemical, and hydrologic investigations of the Long Valley area to develop a generalized conceptual and mathematical model which describes the gross features of heat and fluid flow in the hydrothermal system. Cenozoic volcanism in the Long Valley region began about 3.2 m.y. (million years) ago and has continued intermittently until the present time. The major event that resulted in the formation of the Long Valley caldera took place about 0.7 m.y. ago with the eruption of 600 km 3 or more of Bishop Tuff of Pleistocene age, a rhyolitic ash flow, and subsequent collapse of the roof of the magma chamber along one or more steeply inclined ring fractures. Subsequent intracaldera volcanism and uplift of the west-central part of the caldera floor formed a subcircular resurgent dome about 10 km in diameter surrounded by a moat containing rhyolitic, rhyodacitic, and basaltic rocks ranging in age from 0.5 to 0.05 m.y. On the basis of gravity and seismic studies, we estimate an aver- age thickness of fill of 2.4 km above the precaldera granitic and metamorphic basement rocks. A continuous layer of densely welded Bishop Tuff overlies the basement rocks, with an average thickness of 1.4 km; the fill above the welded Bishop Tuff consists of intercalated volcanic flows and tuffs and fluvial and lacustrine deposits. Assuming the average grain density of the fill is between 2.45 and 2.65 g/cm 3 , we calculate the average bulk porosity of the total fill as from 0.11 to 0.21. Comparison of published values of porosity of the welded Bishop Tuff exposed southeast of the caldera with calculated values indicates average bulk porosity

  1. Radon-222 in groundwater of the Long Valley caldera, California

    NASA Astrophysics Data System (ADS)

    Wollenberg, H. A.; Smith, A. R.; Mosier, D. F.; Flexser, S.; Clark, M.

    1984-03-01

    In the Long Valley caldera, where seismicity has continued essentially uninterrupted since mid-1980 and uplift is documented, samples of water from hot, warm, and cold springs have been collected since September, 1982, and their222Rn concentrations analyzed. Concurrently, rocks encompassing the hydrologic systems feeding the springs were analyzed for their radioelement contents, because their uranium is the ultimate source of the222Rn in the water. The222Rn concentration in the springs varies inversely with their temperature and specific conductance. High concentrations (1500 to 2500 picocuries per liter) occur in dilute cold springs on the margins of the caldera, while low contents (12 to 25 pCi/l) occur in hot to boiling springs. Springwater radon concentrations also correlate slightly with the uranium content of the encompassing rocks. A continuous monitoring system was installed in August, 1983, at a spring issuing from basalt, to provide hourly records of radon concentration. A gamma detector is submerged in a natural pool, and we have observed that the radioactivity measured in this manner is due almost entirely to the222Rn concentration of the water. Initial operation shows diurnal and semidiurnal variations in the222Rn concentration of the springwater that are ascribed to earth tides, suggesting that those variations are responding to small changes in stress in the rocks encompassing the hydrologic system.

  2. Radon in groundwater of the Long Valley Caldera, California

    SciTech Connect

    Flexser, S.; Wollenberg, H.A.; Smith, A.R.

    1987-04-01

    In the Long Valley caldera, an area of recently (approx.550 y) active volcanism and current seismic activity, /sup 222/Rn concentrations in hot, warm, and cold spring waters have been measured since 1982. Rn contents of the waters correlate inversely with temperature and specific conductance, with high concentrations (1500 to 2500 pCi/l) occurring in dilute cold springs on the margins of the caldera, and low concentrations (12 to 25 pCi/l) in hot to boiling springs. Rn correlates only slightly with the uranium contents of the wide range of rocks which host the hydrological system feeding the springs. These environmental effects on the radon record may mask responses to small or distant seismic, volcanic, or crustal deformation events. To date, anomalous changes in water-borne Rn have been observed in connection with at least one earthquake, which occurred close to the monitoring site. This continuing study points out that an understanding of the geological setting, its associated hydrological system, and environmental influences is necessary to properly evaluate concentrations and changes in groundwater radioactivity.

  3. A New Model for Episodic Caldera Deformation at Yellowstone

    NASA Astrophysics Data System (ADS)

    Cervelli, P. F.; Gervais, S. M.; Lowenstern, J. B.; Wicks, C. W.

    2012-12-01

    For nearly 90 years, geodetic measurements at Yellowstone have shown recurring episodes of uplift and subsidence confined mostly to the caldera but also extending into the Norris Geyser Basin. The most recent such episode began in late 2004 with the onset of caldera-wide uplift that continued for about 5 years before switching to subsidence in late 2009. The physical mechanism driving the deformation is unknown, though several researchers have proposed kinematic models that can reproduce the observed data. The "Lake" earthquake swarm, which occurred in the northern part of Yellowstone Lake from December 2008 through January 2009, provides a new constraint on caldera deformation models. The timing of the swarm correlates with an abrupt change in local deformation, which preceded the gradual transition from uplift to subsidence in late 2009. Thus, caldera deformation, at least in the vicinity of Yellowstone Lake, consists of two (or more) distinct parts, implying the existence of two (or more) distinct deformation sources. This fresh information leads us to propose a new kinematic model for deformation at Yellowstone, which we develop from the last 15 years of continuous GPS and InSAR data. Our new model consists of three deformation sources: (1) a cauldron block source that is subject to a constant displacement at its base while its surrounding ring fault remains locked; (2) a pressurizing (or depressurizing) spherical cavity near the Norris Geyser Basin, which is known to deform separately from the caldera; and (3) a pressurizing (or depressurizing) spherical cavity at the Sour Creek Dome, which we infer from the abrupt change in deformation rate after the Lake Swarm. We use the GPS and InSAR data from the period of strongest signal, summer 2005 through summer 2007, to optimize the geometry of the three sources: the locations and depths of the spherical cavity, and the perimeter of the cauldron block. We then, while holding their geometry fixed, estimate the

  4. Lithologic descriptions and temperature profiles of five wells in the southwestern Valles caldera region, New Mexico

    SciTech Connect

    Shevenell, L.; Goff, F.; Miles, D.; Waibel, A.; Swanberg, C.

    1988-01-01

    The subsurface stratigraphy and temperature profiles of the southern and western Valles caldera region have been well constrained with the use of data from the VC-1, AET-4, WC 23-4, PC-1 and PC-2 wells. Data from these wells indicate that thermal gradients west of the caldera margin are between 110 and 140)degrees)C/km, with a maximum gradient occurring in the bottom of PC-1 equal to 240)degrees)C/km as a result of thermal fluid flow. Gradients within the caldera reach a maximum of 350)degrees)C/km, while the maximum thermal gradient measured southwest of the caldera in the thermal outflow plume is 140)degrees)C/km. The five wells exhibit high thermal gradients (>60)deghrees)C/km) resulting from high conductive heat flow associated with the Rio Grande rift and volcanism in the Valles caldera, as well as high convective heat flow associated with circulating geothermal fluids. Gamma logs run in four of the five wells appear to be of limited use for stratigraphic correlations in the caldera region. However, stratigraphic and temperature data from the five wells provide information about the structure and thermal regime of the southern and western Valles caldera region. 29 refs., 9 figs. 2 tabs.

  5. History and results of VC-1, the first CSDP corehole in Valles caldera, New Mexico

    SciTech Connect

    Goff, F.; Rowley, J.; Gardner, J.N.; Hawkins, W.; Goff, S.; Pisto, L.; Polk, G.

    1985-01-01

    Valles Caldera No. 1 (VC-1) is the first Continental Scientific Drilling Program (CSDP) corehole drilled in the Valles caldera and the first continuously cored hole in the caldera region. The objectives of VC-1 were to penetrate a hydrothermal outflow plume near its source, to obtain structural and stratigraphic information near the intersection of the ring-fracture zone and the pre-caldera Jemez fault zone, and to core the youngest volcanic unit inside the caldera (Banco Bonito obsidian, 0.13 Ma). VC-1 penetrates 298 m of moat volcanics and caldera-fill ignimbrites, 35 m of pre-caldera volcaniclastic breccia, and 523 m of Paleozoic carbonates, sandstones and shales, with over 95% core recovery. Hydrothermal alterations are concentrated in sheared, brecciated and fractured zones from the volcaniclastic breccia to total depth with both the intensity and rank of alterations increasing with depth. Alterations consist primarily of clays, calcite, pyrite, quartz, and chlorite, but chalcopyrite has been identified as high as 518 m and molybdenite has been identified in a fractured zone at 847 m. Thermal aquifers were penetrated at various intervals from about 510 m on down. 11 refs., 5 figs.

  6. Changes in magma storage conditions following caldera collapse at Okataina Volcanic Center, New Zealand

    NASA Astrophysics Data System (ADS)

    Rubin, Allison; Cooper, Kari M.; Leever, Marissa; Wimpenny, Josh; Deering, Chad; Rooney, Tyrone; Gravley, Darren; Yin, Qing-zhu

    2016-01-01

    Large silicic volcanic centers produce both small rhyolitic eruptions and catastrophic caldera-forming eruptions. Although changes in trace element and isotopic compositions within eruptions following caldera collapse have been observed at rhyolitic volcanic centers such as Yellowstone and Long Valley, much still remains unknown about the ways in which magma reservoirs are affected by caldera collapse. We present 238U-230Th age, trace element, and Hf isotopic data from individual zircon crystals from four eruptions from the Okataina Volcanic Center, Taupo Volcanic Zone, New Zealand, in order to assess changes in trace element and isotopic composition of the reservoir following the 45-ka caldera-forming Rotoiti eruption. Our data indicate that (1) mixing of magmas derived from crustal melts and mantle melts takes place within the shallow reservoir; (2) while the basic processes of melt generation likely did not change significantly between pre- and post-caldera rhyolites, post-caldera zircons show increased trace element and isotopic heterogeneity that suggests a decrease in the degree of interconnectedness of the liquid within the reservoir following collapse; and (3) post-caldera eruptions from different vents indicate different storage times of the amalgamated melt prior to eruption. These data further suggest that the timescales needed to generate large volumes of eruptible melt may depend on the timescales needed to increase interconnectedness and achieve widespread homogenization throughout the reservoir.

  7. A Sr-isotopic comparison between thermal waters, rocks, and hydrothermal calcites, Long Valley caldera, California

    USGS Publications Warehouse

    Goff, F.; Wollenberg, H.A.; Brookins, D.C.; Kistler, R.W.

    1991-01-01

    The 87Sr/86Sr values of thermal waters and hydrothermal calcites of the Long Valley caldera geothermal system are more radiogenic than those of young intracaldera volcanic rocks. Five thermal waters display 87Sr/86Sr of 0.7081-0.7078 but show systematically lighter values from west to east in the direction of lateral flow. We believe the decrease in ratio from west to east signifies increased interaction of deeply circulating thermal water with relatively fresh volcanic rocks filling the caldera depression. All types of pre-, syn-, and post-caldera volcanic rocks in the west and central caldera have (87Sr/86Sr)m between about 0.7060 and 0.7072 and values for Sierra Nevada granodiorites adjacent to the caldera are similar. Sierran pre-intrusive metavolcanic and metasedimentary rocks can have considerably higher Sr-isotope ratios (0.7061-0.7246 and 0.7090-0.7250, respectively). Hydrothermally altered volcanic rocks inside the caldera have (87Sr/86Sr)m slightly heavier than their fresh volcanic equivalents and hydrothermal calcites (0.7068-0.7105) occupy a midrange of values between the volcanic/plutonic rocks and the Sierran metamorphic rocks. These data indicate that the Long Valley geothermal reservoir is first equilibrated in a basement complex that contains at least some metasedimentary rocks. Reequilibration of Sr-isotope ratios to lower values occurs in thermal waters as convecting geothermal fluids flow through the isotopically lighter volcanic rocks of the caldera fill. ?? 1991.

  8. Effects of topography on facies and compositional zonation in caldera-related ignimbrites

    SciTech Connect

    Valentine, G.A.; Wohletz, K.H.; Kieffer, S.W.

    1992-02-01

    Large-scale fluid dynamical processes during explosive eruptions within calderas are examined numerically by solving the full set of two-phase hydrodynamic equations with a topographic barrier, representing the rim of a caldera. The effect of the caldera rim on eruption dynamics depends on the relative locations of the rim and the impact zone where tephra collapsing from the eruption column strikes the ground. The distance of the impact zone from the vent is proportional to the collapse (fountain) height of the eruption column. Three significantly different eruption patterns have been observed in the simulations: (1) If the impact zone is outside the caldera rim, relatively continuous pyroclastic flow occurs outside the caldera. (2) If the impact zone is on or near the caldera rim, an initial pyroclastic current flow out of the caldera and is followed by a lapse in outflow during which the cladera fills up with ash. (3) If the impact zone is inside the rim, all initial pyroclastic flows are contained within the caldera unless the flows have sufficiently high initial densities and velocities to carry them over the rim. In most cases, recirculation of pyroclasts into the base of the column causes fountain height to decrease dramatically with time due to the {open_quotes}choking{close_quotes} effect of the ash. This recycling of ash in turn reduces the ability of pyroclastic flows to surmount the rim. The numerical models suggest several processes that cause the formation of multiple cooling and flow units in deposits outside a caldera from a single eruption of steady discharge. Compositional gaps may occur in outflow ignimbrite due entirely to interaction of eruption and emplacement dynamics with topography; sharp compositional gradients within a magma chamber are not necessarily implied by compositional gaps in outflow units. 35 refs., 10 figs., 1 tab.

  9. Oligocene volcanism and multiple caldera formation in the Chinati Mountains, Presidio County, Texas

    SciTech Connect

    Cepeda, J.C.; Henry, C.D.

    1983-01-01

    The Chinati Mountains caldera, which lies in Trans-Pecos Texas in the southern Basin and Range Province, was formed by eruption of the Mitchell Mesa Rhyolite. Volcanism in the Chinati Mountains area began several million years before formation of the Chinati Mountains caldera. Rocks of the Morita Ranch Formation, Infiernito caldera, and Shely Group ring the caldera on the south, east, and north. After its collapse, the caldera was filled by rhyolitic to trachytic lava flows and an ash-flow tuff of the Chinati Mountains Group. These include, from oldest to youngest, the lower trachyte, middle trachyte, lower rhyolite, upper trachyte, and upper rhyolite (ash-flow tuff). The Chinati Mountains Group was then intruded by the West Chinati Stock, the resurgent dome of the caldera. Three cycles of rhyolitic to trachytic magmatism, all derived from a zoned magma chamber, are represented by (1) Mitchell Mesa Rhyolite to lower and middle trachytes, (2) lower rhyolite to upper trachyte, and (3) upper rhyolite to West Chinati Stock. Dominant caldera collapse followed eruption of the Mitchell Mesa Rhyolite, but collapse is also associated with rhyolitic eruptions in the second and third cycles. The entire sequence erupted between 32 and 33 mya. The Chinati Mountains area is the site of one major, inactive silver mine and numerous prospects for silver, lead, zinc, copper, molybdenum, uranium, and fluorite. The Shafter silver district produced 31 million ounces of silver from Permian dolomitic limestones just south of the southern boundary of the caldera. Major prospects are associated with a quartz-monzonite porphyry intrusion (copper-molybdenum) just west of Shafter and with the West Chinati Stock (silver, lead, zinc, copper, and fluorite). All mineralization is probably genetically related to the caldera. 74 references, 15 figures, 3 tables.

  10. Upper crustal structure of the Yellowstone Caldera from seismic delay time analyses and gravity correlations

    SciTech Connect

    Lehman, J.A.; Smith, R.B.; Schilly, M.M.; Braile, L.W.

    1982-04-10

    The 1978 Yellowstone-Snake River Plain seismic experiment provided detailed refraction data that were recorded across a two-dimensional array of seismographs in Yellowstone National Park. A delay time analysis was applied to 173 crystalline basement P/sub g/ arrivals from these data to determine the three-dimensional distribution of velocities and the layer configuration of the upper crust beneath the Yellowstone caldera. The P wave velocity structure of the caldera is characterized by a surface layer of combined sediments and rhyolite flows, averaging 2.8 km/s, that range in thickness from 1.5 to 2.0 km. Adjacent to the caldera, the crystalline upper crustal layer has a velocity of 6.05 +- 0.01 km/s, but this layer decreases by 6% to 5.70 km/s beneath the caldera and extends northeast 15 km beyond the caldera. Smaller zones of very low P velocity, 4.0 km/s, a 30% velocity reduction compared to the 6.05 km/s layer, occur in the upper crust beneath the northeastern caldera rim and beneath the southwest caldera in the vicinity of the Upper and Midway Geyser basins. A three-dimensional gravity interpretation based upon densities derived from the seismic model suggests that the regional gravity low of -60 mGal over the caldera correlates directly with (1) the surface layer of combined sediments and rhyolite flows, (2) the low-velocity, 5.7-km/s, upper crustal layer, and (3) the 4.0-km/s low-velocity zone beneath the northeastern caldera rim. An interpretation of the seismic velocities and densities, based on experimental data and theoretical models is made.

  11. Subsurface architecture of a strike-slip collapse structure: insights from Ilopango caldera, El Salvador

    NASA Astrophysics Data System (ADS)

    Saxby, Jennifer; Gottsmann, Joachim; Cashman, Katherine; Gutierrez, Eduardo

    2016-04-01

    While most calderas are created by roof collapse along ring-like faults into an emptying magma reservoir during a large and violent explosive eruption, an additional condition for caldera formation may be tectonically induced extensional stresses. Here we provide geophysical insights into the shallow sub-volcanic plumbing system of a collapse caldera in a major strike-slip tectonic setting by inverting Bouguer gravity data from the Ilopango caldera in El Salvador. Despite a long history of catastrophic eruptions with the most recent in 500 A.D., the internal architecture of the caldera has not been investigated, although studies of the most recent eruption have not identified the ring faults commonly associated with caldera collapse. The gravity data show that low-density material aligned along the principal stress orientations of the El Salvador Fault Zone (ESFZ) forms a pronounced gravity low beneath the caldera. Extending to around 6 km depth, the low density structure likely maps a complex stacked shallow plumbing system composed of magmatic and fractured hydrothermal reservoirs. A substantial volume of the plumbing system must be composed of a vapour phase to explain the modeled negative density contrasts. We use these constraints to map the possible multi-phase parameter space contributing to the subsurface architecture of the caldera and propose that the local extension along the complex ESFZ controls accumulation, ascent and eruption of magma at Ilopango. The data further suggest that future eruptions at Ilopango could be facilitated by rapid rise of magma along conjugate fault damage zones through a mechanically weak crust under tension. This may explain the absence of clear ring fault structures at the caldera.

  12. Limited Boron Isotopic Variation Between Caldera-Forming and Post-Caldera Low-δ 18O Rhyolites from Yellowstone Caldera

    NASA Astrophysics Data System (ADS)

    Schmitt, A. K.

    2004-12-01

    Post-collapse rhyolites from within Yellowstone caldera show prominent excursions to δ 18O values (VSMOW) as low as ˜0 ‰ that provide strong evidence for significant non-lithospheric oxygen input into magmas, presumably via infiltration of meteoric waters (1). Very little, however, is known about the behavior of other stable isotope systems, such as boron, in low δ 18O rhyolites and their potential for unraveling the mechanisms by which brines and magmas interact. Ion microprobe measurements of quartz-hosted melt inclusions from two low-δ 18O rhyolite flows (South Biscuit Basin SBB and Middle Biscuit Basin MBB) yielded average δ 11B values (NIST SRM 951) of -1.5 and -0.9 ‰ , respectively. These values overlap within error with those for glassy obsidian matrix from SBB and MBB. Melt inclusions from two caldera-forming tuff eruptions (Lava Creek Tuff LCT and Huckleberry Ridge Tuff HRT), known to have 'normal' oxygen isotopic compositions, also yielded indistinguishable δ 11B values of -1.8 ‰ . Recent petrologic studies (1) suggested that bulk remelting of hydrothermally altered volcanic rocks, specifically HRT, in the down-dropped roof of the magma chamber produced the low-δ 18O magmas. The lack of strong boron isotopic variations (within ±2‰ ) between 'normal' and low-δ 18O rhyolites, however, contrasts with published evidence for strong 11B-depletion in hydrothermal altered rhyolite encountered in Yellowstone drill-wells (δ 11B = -9.7 ‰ ; 2). This implies that boron isotopic fractionation due to interaction with hydrothermal fluids was either absent in the source region of the SBB and MBB magmas, or became masked due to subsequent processes. From preliminary mixing calculations it is concluded that assimilation of 11B- and 18O-depleted rocks by fresh rhyolite recharge could be a compositionally and thermally viable alterative to bulk remelting. (1) I. N. Bindeman and J. W. Valley (2001) J Petrol 42, 1491-1517; (2) M. R. Palmer and N. C. Sturchio

  13. Three-dimensional p-velocity structure of the summit caldera of Newberry Volcano, Oregon

    SciTech Connect

    Stauber, D.A.; Iyer, N.M.; Mooney, W.D.; Dawson, P.B.

    1985-01-01

    A three-dimensional high-resolution seismic study of the summit caldera of Newberry Volcano, Oregon, was conducted by the US Geological Survey using an adaptation of the method applied by Mercessian et al. (1984). Preliminary interpretation of the traveltime residuals reveals a ring of high P-velocity material coinciding with the inner ring fault system of the caldera in the upper 2 km. A zone of lower P velocities extends deeper than 2 km in the center of the caldera. 9 refs., 5 figs.

  14. Helium soil-gas survey of the aurora uranium deposit, McDermitt Caldera Complex, Oregon

    SciTech Connect

    Reimer, G.M.

    1986-11-10

    Two soil gas helium surveys were carried out in a section of the McDermitt caldera complex of mineralized volcanic rocks in Oregon. A regional helium anomaly was found and is thought to be associated with uranium-rich tuffaceous fill of the caldera and the Aurora uranium deposit, which occurs near the northeastern rim of the Caldera. Local hydrology may have an effect on the displacement of the helium anomaly from the uranium deposit and be a carrier of helium from sources at depth. This study suggests that helium surveys may be useful in a volcanic environment by helping to select areas for exploratory drilling for uranium deposits.

  15. GEOLOGIC HISTORY AND URANIUM POTENTIAL OF THE BIG JOHN CALDERA, SOUTHERN TUSHAR MOUNTAINS, UTAH.

    USGS Publications Warehouse

    Steven, Thomas A.; Cunningham, Charles G.; Anderson, John J.

    1984-01-01

    The Big John caldera is an obscure subsidence structure on the western flank of the Tushar Mountains, within the Marysvale volcanic field of west-central Utah. The caldera subsided about 23 m. y. ago in response to ash-flow eruptions that deposited the Delano Peak Tuff Member of the Bullion Canyon Volcanics. During caldera development and subsequent filling and erosion, several geologic environments were formed that were favorable for the concentration of uranium; these environments form the focus of this report describing the major geologic features and main mining areas of the Marysvale volcanic field.

  16. An overview of the Valles Caldera National Preserve: the natural and cultural resources

    USGS Publications Warehouse

    Parmenter, Robert R.; Steffen, Anastasia; Allen, Craig D.

    2007-01-01

    The Valles Caldera National Preserve is one of New Mexico’s natural wonders and a popular area for public recreation, sustainable natural resource production, and scientific research and education. Here, we provide a concise overview of the natural and cultural history of the Preserve, including descriptions of the ecosystems, flora and fauna. We note that, at the landscape scale, the Valles caldera appears to be spectacularly pristine; however, humans have extracted resources from the Preserve area for many centuries, resulting in localized impacts to forests, grasslands and watersheds. The Valles Caldera Trust is now charged with managing the Preserve and providing public access, while preserving and restoring these valuable public resources.

  17. Geometry of Caldera Superfaults and Emplacement of Their Associated Intrusions

    NASA Astrophysics Data System (ADS)

    Hildyard, R.; Kokelaar, P.

    2006-12-01

    Caldera collapse generally involves large-scale fault movements, in some cases involving an annular structure (ring-fault) but commonly involving several intersecting fault strands. Fault displacements are typically hundreds of meters in hours or days. The geometry of caldera faults has often been depicted as inward dipping and bounding a coherent crustal block, but such `key-stone'-like geometry does not facilitate subsidence unless associated with overall extension. Recent modelling, experimentation and comparison with natural analogs show that bounding faults typically dip outwards. Reappraisal of the deeply dissected Glencoe Volcano in Scotland has shown that the archetypal bounding `ring-fault' and associated intrusions, which define an ellipse 14x8 km, comprise near vertical, outward-dipping structures that have accommodated ~700 m of subsidence. Along certain sections, pseudotachylyte occurs at the margins of voluminous (1-2000 m wide) fault intrusions of rhyolite, monzonite, diorite, tonalite and granite. The pseudotachylyte and rhyolite show various mingling relationships indicating a fluid and particulate-state interaction during emplacement. The inner contacts, against the subsided country rocks, are planar while the outer contacts are highly irregular, both on a large scale (100's m) and a small scale (10 cm -1 m). In one section, a fault strand cuts a hydrothermal system recorded by veins of quartz, epidote, pyrite and sericite. We infer that both friction melts and magmas were transformed explosively to froth or spray where they encountered rapid decompression along dilatant sections of the active superfaults. The friction melts were driven upwards, plastering separate fault surfaces, and were rapidly followed by fragmented rhyolite magma and then fluid magma that formed fault intrusions. The irregular outer contacts of the fault intrusions are interpreted as recording instantaneous explosive disruption of pressurized hydrothermal systems that were

  18. Volcano-tectonic architecture of a Caldera Complex, Karthala volcano, Grande Comore: new field observations

    NASA Astrophysics Data System (ADS)

    Poppe, S.; Kervyn, M.; Soulé, H.; Cnudde, V.; De Kock, T.; Jacobs, P.

    2012-04-01

    Karthala volcano on the oceanic island of Grande Comore, West-Indian Ocean, is one of worlds' largest active alkaline basalt shield volcanoes, with 5 eruptions since 1991. In the last century the volcanic activity mainly concentrated within the 3.5 x 2.8 km large area of the summit caldera complex. Limited study has so far been carried out to unravel the structure and geometry of the summit caldera complex, the collapse chronology and the recent changes caused by the 2005 - 2007 eruption phases. Two exploratory missions to the Karthala summit in July 2011 led to an updated overview of the volcano-tectonic structures, evidence of the local orientation of the principle stresses and a preliminary stratigraphy of the 400 m deep rock sequence exposed in the caldera walls. Three overlapping caldera's build the main structure of the complex, with vertically-subsided blocks forming intermediate terraces along the caldera structures. Within these blocks, several graben-like structures with N-S and N135°E orientations are evidencing a secondary influence of extension during or after the overall vertical collapse. One of the southwestern caldera blocks shows a 'tilted block' morphology, with a caldera-inward rotation. 'Choungou Changouméni', a nested pit crater in the Northern caldera, was 30 m deep in 1965 and has now been almost completely filled with pyroclastic deposits and lava flows. Caldera walls in the whole complex consist of massif meter-thick alkali-basalt flows with decimetric intercalations of weathered pyroclastic layers, and are topped by scoria and tuff cones. The caldera floor itself is covered by volcanic ash, lapilli, and massif scoriaceous surfaces of ancient flows. At the intersection of the 3 main caldera structures two deep explosion craters are located, together named 'Choungou Chahalé'. These were the centres of recent phreatic activity. Their vertical walls show a sequence of thick alkali basalt flows and hold numerous cross-cutting dykes which

  19. Comparison of hydrothermal alteration of carboniferous carbonate and siliclastic rocks in the Valles caldera with outcrops from the Socorro caldera, New Mexico

    NASA Astrophysics Data System (ADS)

    Armstrong, Augustus K.; Renault, Jacques R.; Oscarson, Robert L.

    1995-08-01

    Continental Scientific Drilling Program (CSDP) drill hole VC-2B [total depth 1761.7 m (5780 ft); maximum temperature 295 °C] was continuously cored through the Sulphur Springs hydrothermal system in the western ring-fracture zone of the 1.14 Ma Valles caldera. Among other units, the hole penetrated 760.2 m (2494.1 ft) of Paleozoic carbonate and siliciclastic strata underlying caldera fill and precaldera volcanic and epiclastic rocks. Comparison of the VC-2B Paleozoic rocks with corresponding lithologies within and around the 32.1 Ma Socorro caldera, 192 km ( 119 miles) to the south-southwest, provides insight into the variability of alteration responses to similar caldera-related hydrothermal regimes. The Pennsylvanian Madera Limestone and Sandia Formation from VC-2B preserve many of the sedimentological and diagenetic features observed in these units on a regional basis and where unaffected by high temperatures or hydrothermal activity. Micrites in these formations in VC-2B are generally altered and mineralized only where fractured or brecciated, that is, where hydrothermal solutions could invade carbonate rocks which were otherwise essentially impermeable. Alteration intensity (and correspondingly inferred paleopermeability) is only slightly higher in carbonate packstones and grainstones, low to intermediate in siltstones and claystones, and high in poorly cemented sandstones. Hydrothermal fracture-filling phases in these rocks comprise sericite (and phengite), chlorite, allanite, apatite, an unidentified zeolite and sphene in various combinations, locally with sphalerite, galena, pyrite and chalcopyrite. Terrigenous feldspars and clays are commonly altered to chlorite and seriate, and euhedral anhydrite "porphyroblasts" with minor chlorite occur in Sandia Formation siltstone. Fossils are typically unaltered, but the walls of some colonial bryozoans in the Madera Limestone are altered to the assemblage chlorite-sericite-epidote-allanite. La, Ce and Nd are

  20. Oblique synoptic images, produced from digital data, display strong evidence of a "new" caldera in southwestern Guatemala

    USGS Publications Warehouse

    Duffield, W.; Heiken, G.; Foley, D.; McEwen, A.

    1993-01-01

    The synoptic view of broad regions of the Earth's surface as displayed in Landsat and other satellite images has greatly aided in the recognition of calderas, ignimbrite plateaus and other geologic landforms. Remote-sensing images that include visual representation of depth are an even more powerful tool for geologic interpretation of landscapes, but their use has been largely restricted to the exploration of planets other than Earth. By combining Landsat images with digitized topography, we have generated regional oblique views that display compelling evidence for a previously undocumented late-Cenozoic caldera within the active volcanic zone of southwestern Guatemala. This "new" caldera, herein called Xela, is a depression about 30 km wide and 400-600 m deep, which includes the Quezaltenango basin. The caldera depression is breached only by a single river canyon. The caldera outline is broadly circular, but a locally scalloped form suggests the occurrence of multiple caldera-collapse events, or local slumping of steep caldera walls, or both. Within its northern part, Xela caldera contains a toreva block, about 500 m high and 2 km long, that may be incompletely foundered pre-caldera bedrock. Xela contains several post-caldera volcanoes, some of which are active. A Bouguer gravity low, tens of milligals in amplitude, is approximately co-located with the proposed caldera. The oblique images also display an extensive plateau that dips about 2?? away from the north margin of Xela caldera. We interpret this landform to be underlain by pyroclastic outflow from Xela and nearby Atitla??n calderas. Field mapping by others has documented a voluminous rhyolitic pumiceous fallout deposit immediately east of Xela caldera. We speculate that Xela caldera was the source of this deposit. If so, the age of at least part of the caldera is between about 84 ka and 126 ka, the ages of deposits that stratigraphically bracket this fallout. Most of the floor of Xela caldera is covered

  1. Oblique synoptic images, produced from digital data, display strong evidence of a ``new'' caldera in southwestern Guatemala

    NASA Astrophysics Data System (ADS)

    Duffield, Wendell; Heiken, Grant; Foley, Duncan; McEwen, Alfred

    1993-03-01

    The synoptic view of broad regions of the Earth's surface as displayed in Landsat and other satellite images has greatly aided in the recognition of calderas, ignimbrite plateaus and other geologic landforms. Remote-sensing images that include visual representation of depth are an even more powerful tool for geologic interpretation of landscapes, but their use has been largely restricted to the exploration of planets other than Earth. By combining Landsat images with digitized topography, we have generated regional oblique views that display compelling evidence for a previously undocumented late-Cenozoic caldera within the active volcanic zone of southwestern Guatemala. This "new" caldera, herein called Xela, is a depression about 30 km wide and 400-600 m deep, which includes the Quezaltenango basin. The caldera depression is breached only by a single river canyon. The caldera outline is broadly circular, but a locally scalloped form suggests the occurrence of multiple caldera-collapse events, or local slumping of steep caldera walls, or both. Within its northern part, Xela caldera contains a toreva block, about 500 m high and 2 km long, that may be incompletely foundered pre-caldera bedrock. Xela contains several post-caldera volcanoes, some of which are active. A Bouguer gravity low, tens of milligals in amplitude, is approximately co-located with the proposed caldera. The oblique images also display an extensive plateau that dips about 2° away from the north margin of Xela caldera. We interpret this landform to be underlain by pyroclastic outflow from Xela and nearby Atitlán calderas. Field mapping by others has documented a voluminous rhyolitic pumiceous fallout deposit immediately east of Xela caldera. We speculate that Xela caldera was the source of this deposit. If so, the age of at least part of the caldera is between about 84 ka and 126 ka, the ages of deposits that stratigraphically bracket this fallout. Most of the floor of Xela caldera is covered with

  2. Volcanology. A large magmatic sill complex beneath the Toba caldera.

    PubMed

    Jaxybulatov, K; Shapiro, N M; Koulakov, I; Mordret, A; Landès, M; Sens-Schönfelder, C

    2014-10-31

    An understanding of the formation of large magmatic reservoirs is a key issue for the evaluation of possible strong volcanic eruptions in the future. We estimated the size and level of maturity of one of the largest volcanic reservoirs, based on radial seismic anisotropy. We used ambient-noise seismic tomography below the Toba caldera (in northern Sumatra) to observe the anisotropy that we interpret as the expression of a fine-scale layering caused by the presence of many partially molten sills in the crust below 7 kilometers. This result demonstrates that the magmatic reservoirs of present (non-eroded) supervolcanoes can be formed as large sill complexes and supports the concept of the long-term incremental evolution of magma bodies that lead to the largest volcanic eruptions. PMID:25359969

  3. Caldera collapse in the Galápagos Islands, 1968

    USGS Publications Warehouse

    Simkin, T.; Howard, K.A.

    1970-01-01

    The summit caldera of Isla Fernandina, a large, uninhabited basaltic shield volcano, was further enlarged by 1 to 2 km3 in June 1968. A small quake and large vapor cloud on 11 June were followed 4 hours later by a remarkable volcanic ash cloud and, after another hour, by a major explosion recorded at infrasonic stations throughout the hemisphere. Seismic activity increased to a peak on 19 June, when more than 200 events per day were recorded by a seismograph 140 km away. Several hundred quakes were in the magnitude range 4.0 to 5.4 mb, but few such events were recorded after 23 June. Unusual lightning accompanied the major cloud, and, during the evening of 11 June, distant observers reported red glow and flashes from the area. Fine ash fell that night and much of the next day to distances at least 350 km from the volcano.

  4. Localized Temporal Gravity Investigations at Long Valley Caldera

    NASA Astrophysics Data System (ADS)

    Markiel, J. M.; Gabbert, R.; Smith, E.; Ingalls, S.; Beale, J.; Factor, J.; Holmes, S. A.

    2012-12-01

    Accurately modeling temporal changes in the gravity field of the Earth is now a central concern of modern geodesy. Investigations in temporal gravity are currently the focus of considerable research on a global basis as reported by the IAG, Commission 2.2: Gravity Field [IAG, 2011]. These large scale investigations utilizing the GRACE/GOCE satellite datasets have demonstrated considerable time dependent variations in gravity as the result of mass changes, most notably owing to variations in water/ice regimes. However, these gravity missions are relatively recent, and so the length of the temporal period is limited to sub-decadal extent. Similarly, the long wavelength resolution of the satellite data precludes the derivation of a spatially dense, localized gravity model. The analysis of gravity changes on a localized basis is quite limited owing to the lack of quality gravity collections over a period of decades. Investigations over decadal time periods are accordingly unique. In this paper, we report the results of our recent investigations at Long Valley Caldera, California, USA with respect to localized temporal gravity changes. Leveraging early gravity acquisitions by Jachens and Roberts [1985] and Battaglia, et al, [2003], we analyze the recent (2012) gravity collections to establish a three decade study of gravity changes at the Long Valley Caldera site. Since all the data was collected at the same locations for each gravity survey (1982~1985, 1999, 2012), the resulting study is able to minimize errors associated with interpolation. Additionally, we compare the recent localized gravity model with the GRACE/GOCE gravity signature and analyze the correlation between the local and global models. Approved for public release 12-430

  5. Chemistry and isotopic composition of fumarole discharges of Furnas caldera

    NASA Astrophysics Data System (ADS)

    Ferreira, Teresa; Oskarsson, Niels

    1999-09-01

    Two fumarole grounds at Lagoa das Furnas and Furnas village and a fumarole on the bank of Ribeira dos Tambores are located on a west-east tectonic lineament across the topographic low of the Furnas caldera. The discharge of the fumaroles derives from steam separation from shallow (100-200 m) aquifers at temperatures of about 180°C. As inferred from nitrogen/argon relations and deuterium-oxygen isotope relations the hydrothermal fluid is derived from local precipitation after some 10% steam fractionation in the fumarole conduits. Sulphur isotope ratios of the discharge, being close to those of juvenile rock sulphur, indicate extensive rock-leaching within the aquifers. The carbon isotope composition of the fumarole discharge and carbon dioxide saturated waters encountered across the caldera floor suggests that the source of carbon is regional outgassing of mantle derived juvenile carbon dioxide. Chemistry of the acid gases, carbon dioxide and hydrogen sulphide in the discharge indicates a slight fractionation induced by different boiling in the shallow hydrothermal aquifers. Traces of hydrogen and methane contained in the discharge bear no relation to the low temperature water-steam equilibria of the Furnas fumaroles. Assuming a deeper origin of these gases, a simple model for binary mixtures of methane and hydrogen indicates that these gases are derived from supercritical conditions, presumably equilibrated within hot rocks below the hydrothermal system. The remarkably stable ratios of hydrogen and methane, also considering their inferred deep origin, suggest that these gases might be considered for future chemical monitoring of the fumarole discharge in Furnas.

  6. Field trip guide to the Valles Caldera and its geothermal systems

    SciTech Connect

    Goff, F.E.; Bolivar, S.L.

    1983-12-01

    This field trip guide has been compiled from extensive field trips led at Los Alamos National Laboratory during the past six years. The original version of this guide was designed to augment a workshop on the Valles Caldera for the Continental Scientific Drilling Program (CSDP). This workshop was held at Los Alamos, New Mexico, 5-7 October 1982. More stops were added to this guide to display the volcanic and geothermal features at the Valles Caldera. The trip covers about 90 miles (one way) and takes two days to complete; however, those who wish to compress the trip into one day are advised to use the designated stops listed in the Introduction. Valles Caldera and vicinity comprise both one of the most exciting geothermal areas in the United States and one of the best preserved Quaternary caldera complexes in the world.

  7. Maars to calderas: end-members on a spectrum of explosive volcanic depressions

    NASA Astrophysics Data System (ADS)

    Palladino, Danilo; Valentine, Greg; Sottili, Gianluca; Taddeucci, Jacopo

    2015-07-01

    We discuss maar-diatremes and calderas as end-members on a spectrum of negative volcanic landforms (depressions) produced by explosive eruptions (note - we focus on calderas formed during explosive eruptions, recognizing that some caldera types are not related to such activity). The former are dominated by ejection of material during numerous discrete phreatomagmatic explosions, brecciation, and subsidence of diatreme fill, while the latter are dominated by subsidence over a partly evacuated magma chamber during sustained, magmatic volatile-driven discharge. Many examples share characteristics of both, including landforms that are identified as maars but preserve deposits from non-phreatomagmatic explosive activity, and ambiguous structures that appear to be coalesced maars but that also produced sustained explosive eruptions with likely magma reservoir subsidence. A convergence of research directions on issues related to magma-water interaction and shallow reservoir mechanics is an important avenue toward developing a unified picture of the maar-diatreme-caldera spectrum.

  8. Temporal gravity and height changes of the Yellowstone caldera, 1977 - 1994

    USGS Publications Warehouse

    Arnet, F.; Kahle, H.-G.; Klingele, E.; Smith, R.B.; Meertens, Charles M.; Dzurisin, D.

    1997-01-01

    This paper describes the longest record of gravity measurements in the area of the Yellowstone caldera, Wyoming. The temporal gravity changes, at the ??12 ??Gal (10-8 ms-2) precision level, are compared with changes in heights from leveling and GPS. The gravity field decreased across the caldera from 1977 to 1983 during the uplift and attained a maximum decrease of up to -60 ?? 12 ??Gal along the Caldera axis. The gravity field then reversed polarity to increasing values, of up to 60 ?? 12 ??Gal between 1986 and 1993. The ratio between height and gravity changes varied during the entire time, but converged over the latter period following the free-air gravity gradient. General ground deformation deduced from leveling showed caldera-wide uplift of ???15 mm/a during the period of gravity decrease, then from leveling and GPS, subsidence of ??? 25 mm/a during the gravity increase. Copyright 1997 by the American Geophysical Union.

  9. Inner structure of La Pacana Caldera (Central Andes, Chile) using gravimetry data

    NASA Astrophysics Data System (ADS)

    Delgado, F.; Pavez Alvarado, A.

    2010-12-01

    La Pacana caldera is located in the Altiplano Puna Volcanic Complex in the Chilean Andes and is a 60 by 35 km NS elongated body. It is one of the largest resurgent calderas in the world, comparable to the supervolcanoes of La Garita, Toba and Yellowstone. It has been described as being formed 4 My ago during an eruption with a VEI of 8,7, which makes it the fifth largest eruption ever in the geological record. This eruption was followed by a subsidence of 0,9 up to 2 km according to previous studies. Different models for this caldera formation were proposed but with a lack of sub surface information. We hence carried a gravimetry study to investigate its inner structure and to better off constrains on these proposed models. The residual Bouguer anomaly (figure 1) is asymetric with multiple high and low gravity, with an average amplitude of -14 mGal, which reaches -24 mGal near the resurgent dome, interpreted as the deepest part of the caldera. Based on this, we propose that the main collapse zone is not related to the topographic border, but to resurgent dome edges. This is compatible with a piecemeal collapse geometry. There are several gravity highs below strato-volcanoes and postcaldera domes within La Pacana caldera, which are interpreted as magmatic reservoirs. Our data combined with previous geological studies allowed us to separate La Pacana in two nested calderas and to trace its NNW, N and NNE borders, previously unrecognized features. The 2,5 D forward modelling cross sections constrained with geological data showed that the maximum caldera depth is 1,3 km with a minimum of 0,6 km in its southern part. We finally suggest that caldera rims are surrounded by paleozoic basement uplifted by thrust fault systems. La Pacana's residual Bouguer anomaly is small (1/2) when compared with the ones associated to other supervolcanoes (Toba, Yellowstone). La Pacana caldera constitutes then an anomaly for supervolcanoes internal structure due to its interpreted low

  10. Recent geologic history of lake Atitlán, a caldera lake in western Guatemala

    USGS Publications Warehouse

    Newhall, C.G.; Paull, C.K.; Bradbury, J.P.; Higuera-Gundy, A.; Poppe, L.J.; Self, S.; Bonar, Sharpless N.; Ziagos, J.

    1987-01-01

    Heat-flow measurements inside and just outside the caldera are high (290 and 230 mW m−2), suggesting hydrothermal convection and a shallow heat source. High heat flow, a geological record of post-caldera silicic eruptions, and unexplained fluctuations of lake level (episodic tumescence ofthe lake floor?) suggest that magma remains beneath Lake Atitlán and that future eruptions are possible.

  11. Investigation of the groundwater system at Masaya Caldera, Nicaragua, using transient electromagnetics and numerical simulation

    USGS Publications Warehouse

    MacNeil, R.E.; Sanford, W.E.; Connor, C.B.; Sandberg, S.K.; Diez, M.

    2007-01-01

    The distribution of groundwater beneath Masaya Volcano, in Nicaragua, and its surrounding caldera was characterized using the transient electromagnetic method (TEM). Multiple soundings were conducted at 30 sites. Models of the TEM data consistently indicate a resistive layer that is underlain by one or more conductive layers. These two layers represent the unsaturated and saturated zones, respectively, with the boundary between them indicating the water-table elevation. A map of the TEM data shows that the water table in the caldera is a subdued replica of the topography, with higher elevations beneath the edifice in the south-central caldera and lower elevations in the eastern caldera, coinciding with the elevation of Laguna de Masaya. These TEM data, combined with regional hydrologic data, indicate that the caldera in hydrologically isolated from the surrounding region, with as much as 60??m of difference in elevation of the groundwater table across caldera-bounding faults. The water-table information and estimates of fluxes of water through the system were used to constrain a numerical simulation of groundwater flow. The simulation results indicate that basalt flows in the outer parts of the caldera have a relatively high transmissivity, whereas the central edifice has a substantially lower transmissivity. A layer of relatively high transmissivity must be present at depth within the edifice in order to deliver the observed flux of water and steam to the active vent. This hydrologic information about the caldera provides a baseline for assessing the response of this isolated groundwater system to future changes in magmatic activity. ?? 2007.

  12. How caldera collapse shapes the shallow emplacement and transfer of magma in active volcanoes

    NASA Astrophysics Data System (ADS)

    Corbi, Fabio; Rivalta, Eleonora; Pinel, Virginie; Maccaferri, Francesco; Bagnardi, Marco; Acocella, Valerio

    2016-04-01

    Calderas are topographic depressions formed by the collapse of a partly drained magma reservoir. At volcanic edifices with calderas, eruptive fissures can circumscribe the outer caldera rim, be oriented radially and/or align with the regional tectonic stress field. Constraining the mechanisms that govern this spatial arrangement is fundamental to understand the dynamics of shallow magma storage and transport and evaluate volcanic hazard. Here we use numerical models to show that the previously unappreciated unloading effect of caldera formation may contribute significantly to the stress budget of a volcano. We first test this hypothesis against the ideal case of Fernandina, Galápagos, where previous models only partly explained the peculiar pattern of circumferential and radial eruptive fissures and the geometry of the intrusions determined by inverting the deformation data. We show that by taking into account the decompression due to the caldera formation, the modeled edifice stress field is consistent with all the observation. We then develop a general model for the stress state at volcanic edifices with calderas based on the competition of caldera decompression, magma buoyancy forces and tectonic stresses. These factors control the shallow accumulation of magma in stacked sills, consistently with observations as well as the conditions for the development of circumferential and/or radial eruptive fissures, as observed on active volcanoes. This top-down control exerted by changes in the distribution of mass at the surface allows better understanding of how shallow magma is transferred at active calderas, contributing to forecasting the location and type of opening fissures.

  13. The Denham Caldera on Raoul Volcano: dacitic volcanism in the Tonga Kermadec arc

    NASA Astrophysics Data System (ADS)

    Worthington, Tim J.; Gregory, Murray R.; Bondarenko, Vladislav

    1999-05-01

    Denham Caldera, on Raoul Volcano in the Tonga-Kermadec arc, is a simple collapse structure. It is 6.5×4 km 2 across, >0.3 km deep, represents an erupted magma volume of 8-16 km 3, and is considerably larger than previously estimated. Caldera formation was contemporaneous with an eruption of homogeneous dacitic magma at 2.2 ka. Tephra from this event is preserved as a pumice fall and pyroclastic flow sequence up to 120 m thick on Raoul Island. Offshore, this sequence forms a submarine deposit diminishing in thickness from 120 m near the northern caldera rim to 80 m at a distance of 3.5 km, where it rests upon an erosional planation surface of 17-20 ka age incised into older volcaniclastic rocks. Both the caldera volume and ejecta distribution of the 2.2 ka eruption are comparable to the caldera volume and ejecta distribution of the 1883 Krakatau eruption. Resurgent volcanism has built at least six submarine pyroclastic cones along a north-northeast trending lineament crossing Denham Caldera. Redistribution of pumiceous dacite from these cones, including ephemeral islands that emerged during the 1814 and 1870 eruptions, has contributed to recent shoaling in Denham Bay. A smaller eruption occurred in 1964-65, and hydrothermal activity persists at several sites along the lineament. Voluminous felsic volcanism at intra-oceanic arcs is usually associated with crustal extension, and was unexpected in the Tonga-Kermadec arc. However, because the tectonic fabric within the active back-arc Havre Trough is oblique to the Kermadec arc, rifts within the trough apparently propagate to the volcanic front and transfer extensional strain to the arc, thereby promoting the ascent of felsic magma. The orientation of Denham Caldera, as well as that of Macauley Caldera 110 km further south, thus reflect the stress field of the Havre Trough and not the predominant field of the arc.

  14. Tephrostratigraphy and eruptive history of post-caldera stage of Toya Volcano, Hokkaido, northern Japan

    NASA Astrophysics Data System (ADS)

    Miyabuchi, Yasuo; Okuno, Mitsuru; Torii, Masayuki; Yoshimoto, Mitsuhiro; Kobayashi, Tetsuo

    2014-06-01

    A detailed tephrostratigraphy of Toya Volcano in Hokkaido, northern Japan has been constructed to evaluate the post-caldera eruptive history of the volcano. The tephrostratigraphic sequence preserved above the Toya ignimbrite reaches a total thickness of 8 m southeast of the caldera. After the caldera formation (115-112 ka), there was a long quiescent period of more than 60 ka years. The first post-caldera activity started with Nakajima Osarugawa pumice-fall deposit (Nj-Os) inside the caldera at 48 ka. Eruptive activity at Nakajima Volcano resumed at 30 ka with Nakajima Sekinai pumice-fall deposit (Nj-Sk), and was followed by continuous emission of fine ash including abundant accretionary lapilli. Soon after the Nakajima pyroclastic eruption Usu Volcano began its activity with discharges of basaltic ash and scoria (forming the Usu prehistoric tephra) and extrusion of homogeneous lavas namely Usu somma lava, resulting in the formation of the initial volcanic edifice. Subsequently, a large sector collapse occurred between 30 and 20 ka that emplaced the Zenkoji debris avalanche with little break after the formation of the initial Usu volcanic edifice. After the sector collapse, the volcano remained dormant for about 20-30 ka years. Eruptive activity at Usu Volcano resumed in 1663 AD with the most explosive plinian eruption in the post-caldera stage of Toya Volcano. Since then, seven eruptions have been recorded in 1769, 1822, 1853, 1910, 1943-1945, 1977-1978 and 2000 at multi-decadal interval. Total tephra volume during the post-caldera stage is estimated at about 0.9 km3 (dense rock equivalent: DRE), whereas total lava volume is calculated at about 2.3 km3. Therefore, the average magma discharge rate during the post-caldera stage of Toya Volcano is estimated at about 0.03 km3/ky, which is one or two order smaller than those of other Quaternary volcanoes in Japan.

  15. Proceedings of the second workshop on hydrologic and geochemical monitoring in the Long Valley Caldera

    SciTech Connect

    Sorey, M.L.; Farrar, C.D.; Wollenberg, H.A.

    1986-12-01

    A workshop was held to review the results of hydrologic and geochemical monitoring and scientific drilling in the Long Valley caldera. Such monitoring is being done to detect changes in the hydrothermal system induced by ongoing magmatic and techonic processes. Data from a 2400-ft deep core hole completed in June 1986 were presented at the 1986 workshop and participants discussed the need and rationale for siting locations for future scientific drilling in the caldera.

  16. Towards a detailed distal tephrostratigraphy in the Central Mediterranean: The last 20,000 yrs record of Lago Grande di Monticchio

    NASA Astrophysics Data System (ADS)

    Wulf, Sabine; Kraml, Michael; Keller, Jörg

    2008-10-01

    A detailed compilation of distal tephrostratigraphy comprising the last 20,000 yrs is given for the Central Mediterranean region. A total of 47 distinct ash layers identified in the maar lake sediments of Lago Grande di Monticchio (Basilicata, Southern Italy) are compared with proximal and distal terrestrial-marine tephra deposits in the circum-central Mediterranean region. The results of these studies provide valuable information for reconstructing the Late Pleistocene and the Holocene dispersal of pyroclastic deposits from south Italian explosive volcanoes, in particular Somma-Vesuvius, the Campi Flegrei caldera, Ischia Island and Mount Etna. Prominent tephras are discussed with respect to their reliability as dating and correlation tools in sedimentary records. Ashes from Plinian eruptions of Somma-Vesuvius (i.e. Avellino, Mercato, Greenish, Pomici di Base), for instance, are well-defined by their distribution patterns and their unique composition. The widespread Y-1 tephra from Mount Etna, on the other hand, derived most likely from two distinct Plinian events with changing wind conditions, and therefore becomes a less reliable stratigraphic marker. Statistical-numerical calculations are presented in order to discriminate between Holocene tephras from the Campi Flegrei caldera (i.e. Astroni 1-3, Agnano Monte Spina, Averno 1, Lagno Amendolare), since these ashes are characterized by an almost indistinguishable chemical fingerprint. As a highlight, numerous Campanian eruptions of proposed low-intensity have been identified in the distal site of Monticchio suggesting a revision of existing tephra dispersal maps and re-calculation of eruptive conditions. In summary, the tephra record of Monticchio is one of the key successions for linking both, terrestrial records from Central-southern Italy and marine sequences from the Tyrrhenian, Adriatic and Ionian Seas.

  17. A GEOLOGICAL AND GEOPHYSICAL STUDY OF THE BACA GEOTHERMAL FIELD, VALLES CALDERA, NEW MEXICO

    SciTech Connect

    Wilt, M.; Haar, S.V.

    1982-03-01

    The Baca location {number_sign}1 geothermal field is located in north-central New Mexico within the western half of the Plio-Pleistocene valles Caldera. Steam and hot water are produced primarily from the northeast-trending Redondo Creek graben, where downhole temperatures exceed 500 F. Stratigraphically the reservoir region can be described as a five-layer sequence that includes (1) caldera fill and the upper units of the Bandelier ash flow tuff, (2) the lower members of this tuff, which comprise the main reservoir rock at Baca, (3) the Pliocene Paliza Canyon volcanics, (4) Tertiary sands and Paleozoic sedimentary rocks, and (5) Precambrian granitic basement. Production is controlled by fractures and faults that are ultimately related to activity in the Rio Grande Rift system. Geophysically, the caldera is characterized by a gravity minimum and a resistivity low. A 40-mgal gravity minimum over the caldera is due mostly to the relatively low-density volcanics and sediments that fill the caldera and probably bears no relation to deep-seated magmatic sources. Two-dimensional gravity modeling indicates that the depth to Precambrian basement in Redondo Canyon is probably at least 3 km and may exceed 5 km in eastern parts of the caldera. Telluric and magnetotelluric surveys have shown that the reservoir region is associated with low resistivity and that a deep low-resistivity zone correlates well with the depth of the primary reservoir inferred from well data.

  18. The Reporoa Caldera, Taupo Volcanic Zone: source of the Kaingaroa Ignimbrites

    USGS Publications Warehouse

    Nairn, I.A.; Wood, C.P.; Bailey, R.A.

    1994-01-01

    The Reporoa Caldera occupies the northern end of the Reporoa Depression, previously described as a tectonic fault-angle depression. Earlier confirmation of the topographic basin as a caldera had been hindered by the lack of an associated young pyroclastic flow deposit of large enough volume to have caused caldera collapse. New exposures on the eastern margin of the Reporoa basin reveal thick lithic lag breccias (>30 m) interbedded within the 0.24 Ma Kaingaroa Ignimbrites. These ignimbrites were previously attributed to the adjacent Okataina Volcanic Centre. Lag breccia thicknesses and maximum clast sizes decrease rapidly outward from the caldera rim, and discrete breccias are absent from ignimbrite sections more than 3 km from the rim. The lithic lag breccias, together with structural and geophysical evidence, confirm Reporoa Caldera as the source of the c. 100 km3 Kaingaroa Ignimbrites, adding another major rhyolitic volcanic centre to the seven previously recognized in the Taupo Volcanic Zone. Other, older, calderas may also be present in the Reporoa Depression. ?? 1994 Springer-Verlag.

  19. Three-dimensional gravity modeling of the geologic structure of Long Valley caldera

    SciTech Connect

    Carle, S.F.

    1988-11-10

    A 48-mGal gravity low coincides with Long Valley caldera and is mainly attributed to low-density caldera fill. Gravity measurements by Unocal Geothermal have been integrated with U.S. Geological Survey data, vastly improving gravity station coverage throughout the caldera. A strong regional gravity trend is mainly attributed to isostasy. A ''best fitting'' (based on regional control of basement densities) Airy-Heiskanen isostatic model was used for the regional correction. A three-dimensional, multiple-unit gravity modeling program with iterative capabilities was developed to model the residual gravity. The density structure of Long Valley caldera and vicinity was modeled with 22 discrete density units, most of which were based on geologic units. Information from drill hole lithologies, surface geology, and structural geology interpretations constrain the model. Some important points revealed by the three-dimensional gravity modeling are that (1) the volume of ejected magma associated with the Bishop Tuff eruption is greater than previously thought, (2) the caldera structure is strongly influenced by precaldera topography and the extensions of major, active faults, (3) the main west ring fracture is coincident with the Inyo Domes--Mono Craters fracture system, (4) a relatively low-density region probably underlies the caldera, and (5) a silicic magma chamber may underlie Devils Postpile. copyright American Geophysical Union 1988

  20. Reanalysis of S-to-P amplitude ratios for gross attenuation structure, Long Valley caldera, California

    SciTech Connect

    Sanders, C.O.

    1993-12-01

    Because of the strong interest in the magmatism and volcanism at Long Valley caldera, eastern California, and because of recent sifnigicant improvements in our knowledge of the caldera velocity structure and earthquake locations, I have reanalyzed the local-earthquake S-to-P amplitude-ratio data of Sanders (1984) for the gross three-dimensional attenuation structure of the upper 10 km of Long Valley caldera. The primary goals of the analysis are to provide more accurate constraints on the depths of the attenuation anomalies using improved knowledge of the ray locations and an objective inversion procedure. The new image of the high S wave attenuation anomaly in the west-central cadlera suggests that the top of the principal anomaly is at 7-km depth, which is 2 km deeper than previously determined. Because of poor resolution in much of the region, some of the data remain unsatisfied by the final attenuation model. This unmodeled data may imply unresolved attenuation anomalies, perhaps small anomalies in the kilometer or two just above the central-caldera anomaly and perhaps a larger anomaly at about 7-km depth in the northwest caldera or somewhere beneath the Mono Craters. The central-caldera S wave attenuation anomaly has a location similar to mapped regions of low teleseismic P wave velocity, crustal inflation, reduced density, and aseismicity, strongly suggesting magmatic association.

  1. Catastrophic isotopic modification of rhyolitic magma at times of caldera subsidence, Yellowstone plateau volcanic field.

    USGS Publications Warehouse

    Hildreth, W.; Christiansen, R.L.; O'Neil, J.R.

    1984-01-01

    This Wyoming volcanic field has undergone repeated eruption of rhyolitic magma strongly depleted in 18O. Large calderas subsided 2.0, 1.3 and 0.6 m.y. ago on eruption of ash-flow sheets. More than 60 other rhyolite lavas and tuffs permit reconstruction of the long-term chemical and isotopic evolution of the silicic system. Narrow delta 18O ranges in the ash-flow sheets contrast with wide delta 18O variation in post-caldera lavas. The earliest post-collapse lavas are 3-6per mille lighter than the preceding ash-flow sheets. The 18O depletions were short-lived events that immediately followed caldera subsidence and sequences of post-caldera lavas record partial recovery toward pre-caldera delta 18O values. Contemporaneous extra-caldera rhyolites show no effects of the repeated depletions. Although some contamination by foundering roof rocks seems to be required, water was probably the predominant contaminant.-W.H.B.

  2. Exploration of Geothermal Natural Resources from Menengai Caldera at Naruku, Kenya

    NASA Astrophysics Data System (ADS)

    Patlan, E.; Wamalwa, A.; Thompson, L. E.; Kaip, G.; Velasco, A. A.

    2011-12-01

    The Menengai Caldera, a large, dormant volcano, lies near the city of Naruku, Kenya (0.20°S, 36.07°E) and presents a significant natural geothermal energy resource that will benefit local communities. Kenya continues to explore and exploit its only major energy resource: geothermal energy. The Geothermal Development Company (GDC) of Kenya and University of Texas at El Paso (UTEP) have initially deployed seven seismic stations to address the volcanic hazards and associated processes that occurs through the analysis of data collection from seismic sensors that record ground motion. Seven more sensors are planned to be deployed in Aug. 2011. In general, the internal state and activity of the caldera is an important component to the understanding of porosity of the fault system, which is derived from the magma movement of the hot spot, and for the exploitation of geothermal energy. We analyze data from March to May 2011 to investigate the role of earthquakes and faults in controlling the caldera processes, and we find 15 events occurred within the caldera. We will utilize the double difference earthquake location algorithm (HypoDD) to analyze the local events in order to find active faulting of the caldera and the possible location of the magma chamber. For future work, we will combine the exiting data with the new seismic station to image the location of the caldera magma chamber.

  3. The Silent Canyon Caldera Complex--A three-dimensional model based on drill-hole stratigraphy and gravity inversion

    SciTech Connect

    Sawyer, D.A.; Anderson, M.L.; Hildenbrand, T.G; McKee, E.H.; Rowley, P.R.

    1999-12-13

    The structural framework of Pahute Mesa, nevada, is dominated by the Silent Canyon caldera complex, a buried, multiple collapse caldera complex. Using the boundary surface between low density Tertiary volcanogenic rocks and denser granitic and weakly metamorphosed sedimentary rocks (basement) as the outer faults surfaces for the modeled collapse caldera complex, it is postulated that the caldera complex collapsed on steeply dipping arcuate faults two, possibly three, times following eruption of at least two major ash-flow tuffs. The caldera and most if its eruptive products are now deeply buried below the surface of Pahute Mesa. Relatively low-density rocks in the caldera complex produce one of the largest gravity lows in the western conterminous United States.

  4. Relation of mercury, uranium, and lithium deposits to the McDermitt caldera complex, Nevada-Oregon

    USGS Publications Warehouse

    Rytuba, James J.; Glanzman, Richard K.

    1979-01-01

    The McDermitt caldera complex, located along the Nevada-Oregon border, is a Miocene collapse structure 45 km in diameter. Large-volume rhyolitic and peralkaline ash-flow tufts were erupted from 17.9-15.8 m.y. ago, leading to the formation of overlapping and nested calderas. Emplacement of rhyolitic ring domes, located primarily along the western margin of the calderas, represents the last phase of volcanic activity.

  5. Building and interpreting a database to understand recent caldera unrest from monitoring data

    NASA Astrophysics Data System (ADS)

    Di Lorenzo, Riccardo; Acocella, Valerio; Scandone, Roberto; Geshi, Nobuo

    2014-05-01

    Calderas are among the most spectacular, dangerous and active volcanoes on the Earth. Activation of seismicity, surface deformation and anomalous degassing are commonly observed at many calderas, denoting unrest. The unrest can be intermittent, lasting for months to years, or persistent, over decades to centuries. Although most caldera unrest episodes do not lead to an eruption, the possibility of an impending eruption warrants detailed monitoring and study. To better understand caldera unrest, we built a database from all available publications and reports on the recent unrest episodes at calderas in the world. We focused our attention on the unrest episodes which have occurred in the last 25 years, being complementary to Newhall and Dzurisin (1988). We considered the monitoring data from more than 45 unresting calderas, 35 of which characterized by eruptions. Attention has been given to seismicity, deformation and gas variations, along with their possible interaction. The database consists of an excel sheet containing the: (a) caldera descriptive parameters (caldera name, UTM coordinates, maximum and minimum diameter, area, date of last eruption, magma composition); (b) seismic data (width, maximum and minimum depth of area undergoing seismicity, frequency and duration and maximum magnitude; (c) geodetic data (location and width of deformed area, intensity and duration of the deformation); (d) geochemical data (location of anomalies, changes in maximum temperature, variations in chemical composition, duration of the anomaly, pH changes); (e) presence of eruptions and their characterization. The preliminary analysis of the database confirms that all eruptions are preceded by an unrest episode, but not all unrest episodes culminate in an eruption; this suggests that these indicators are a necessary condition to establish the state of unrest, which may anticipate an impending eruption; however, the indicators are not always adequate to determine the occurrence of

  6. Elysium Mons Volcano - Detail of Southern Caldera Wall and Floor

    NASA Technical Reports Server (NTRS)

    1998-01-01

    On July 4, 1998--the first anniversary of the Mars Pathfinder landing--Mars Global Surveyor's latest images were radioed to Earth with little fanfare. The images received on July 4, 1998, however, were very exciting because they included a rare crossing of the summit caldera of a major martian volcano. Elysium Mons is located at 25oN, 213oW, in the martian eastern hemisphere. Elysium Mons is one of three large volcanoes that occur on the Elysium Rise-- the others are Hecates Tholus (northeast of Elysium Mons) and Albor Tholus (southeast of Elysium Mons). The volcano rises about 12.5 kilometers (7.8 miles) above the surrounding plain, or about 16 kilometers (9.9 miles) above the martian datum-- the 'zero' elevation defined by average martian atmospheric pressure and the planet's radius.

    Elysium Mons was discovered by Mariner 9 in 1972. It differs in a number of ways from the familiar Olympus Mons and other large volcanoes in the Tharsis region. In particular, there are no obvious lava flows visible on the volcano's flanks. The lack of lava flows was apparent from the Mariner 9 images, but the new MOC high resolution image--obtained at 5.24 meters (17.2 feet) per pixel--illustrates that this is true even when viewed at higher spatial resolution.

    Elysium Mons has many craters on its surface. Some of these probably formed by meteor impact, but many show no ejecta pattern characteristic of meteor impact. Some of the craters are aligned in linear patterns that are radial to the summit caldera--these most likely formed by collapse as lava was withdrawn from beneath the surface, rather than by meteor impact. Other craters may have formed by explosive volcanism. Evidence for explosive volcanism on Mars has been very difficult to identify from previous Mars spacecraft images. This and other MOC data are being examined closely to better understand the nature and origin of volcanic features on Mars.

    The three MOC images, 40301 (red wide angle), 40302 (blue wide angle

  7. Seismic and gravity signature of the Ischia Island Caldera (Italy)

    NASA Astrophysics Data System (ADS)

    Capuano, P.; de Matteis, R.; Russo, G.

    2009-04-01

    The Campania (Italy) coasts are characterized by the presence of several volcanoes. The island of Ischia, located at the northwestern end of the Gulf of Naples, belongs to the Neapolitan Volcanic District together with Phlegrean Fields and Vesuvius, having all these Pleistocene volcanoes erupted in historical times, and it is characterized by diffuse hydrothermal phenomena The island represents the emergent part of a more extensive volcanic area developed mainly westward of the island, with underwater volcanoes aligned along regional fault patterns. The activity of Ischia volcano is testified by the occurrence of eruptions in historical times, the presence of intense hydrothermal phenomena, and by seismic activity (e.g. the 1883 Casamicciola earthquake). Ischia is populated by about 50,000 inhabitants increasing, mainly in the summer, due to thriving tourism business, partially due to its active volcanic state. Hazard assessment at active, densely populated volcanoes is critically based on knowledge of the volcanoes past behavior and the definition of its present state. As a contribution to the definition of the present state of the Ischia island volcano, we obtain a model of the shallow crust using geophysical observables through seismic tomography and 3D gravity inversion. In particular we use travel times collected during the Serapis experiment on the island and its surroundings and free air anomaly. A new 3D gravity inversion procedure has been developed to take better into account the shape and the effects of topography approximating it by a triangular mesh. Below each triangle, a sequence of triangular prisms is built, the uppermost prism having the upper face coincident with the triangle following the topography. The inversion is performed searching for a regularized solution using the minimum norm stabilizer. The main results inferable from the 3D seismic and gravity images are the definition of the caldera rims hypothesize by many authors along the

  8. Upper crustal structure of the Yellowstone Caldera from seismic delay time analyses and gravity correlations

    NASA Astrophysics Data System (ADS)

    Lehman, Jay A.; Smith, Robert B.; Schilly, Michael M.; Braile, Lawrence W.

    1982-04-01

    The 1978 Yellowstone-Snake River Plain seismic experiment provided detailed refraction data that were recorded across a two-dimensional array of seismographs in Yellowstone National Park. A delay time analysis was applied to 173 crystalline basement Pg arrivals from these data to determine the three-dimensional distribution of velocities and the layer configuration of the upper crust beneath the Yellowstone caldera. The P wave velocity structure of the caldera is characterized by a surface layer of combined sediments and rhyolite flows, averaging 2.8 km/s, that range in thickness from 1.5 to 2.0 km. Adjacent to the caldera, the crystalline upper crustal layer has a velocity of 6.05±0.01 km/s, but this layer decreases by 6% to 5.70 km/s beneath the caldera and extends northeast 15 km beyond the caldera. Smaller zones of very low P velocity, 4.0 km/s, a 30% velocity reduction compared to the 6.05 km/s layer, occur in the upper crust beneath the northeastern caldera rim and beneath the southwest caldera in the vicinity of the Upper and Midway Geyser basins. A three-dimensional gravity interpretation based upon densities derived from the seismic model suggests that the regional gravity low of -60 mGal over the caldera correlates directly with (1) the surface layer of combined sediments and rhyolite flows, (2) the low-velocity, 5.7-km/s, upper crustal layer, and (3) the 4.0-km/s low-velocity zone beneath the northeastern caldera rim. An interpretation of the seismic velocities and densities, based on experimental data and theoretical models, suggests that the 6.05-km/s (ρ = 2.70 g/cm3) regional Pg velocity is characteristic of crystalline basement rocks such as the Precambrian granitic gneisses that are exposed north and south of the Yellowstone caldera. The 5.7-km/s velocity layer (ρ = 2.65 g/cm3) is interpreted to be a 10-km-thick hot body of granitic composition. The 4.0-km/s low-velocity body (ρ = 2.40 g/cm3) beneath the northeastern caldera rim is associated

  9. Possible tectonomagnetic effect observed from mid-1989, to mid-1990, in Long Valley caldera, California

    SciTech Connect

    Mueller, R.J.; Johnston, M.J.S.; Langbein, J.O. )

    1991-04-01

    Precise measurements of local magnetic fields have been obtained with a differentially connected array of three proton magnetometers in the Long Valley caldera region since 1984. Two magnetometers are located inside the caldera with a third reference magnetometer located 26 km southeast of the caldera. After correction for secular variation, it is apparent that an anomalous 2 nT decrease in the magnetic field occurred from mid-1989 to mid-1990 at the magnetometer located closest to the center of the resurgent dome inside the caldera. During this period a significant increase in geodetic strain rate of 8.5 ppm/yr was observed on the two-color geodimeter network within the caldera from October, 1989, to mid-1990 and a dramatic increase in seismic activity occurred from December, 1989 to July, 1990. A simple dilatational point-source model with pressure increasing by 52 Mpa from October 1989 to August 1990 at a depth of about 7 km beneath the center of the resurgent dome can be fit to the strain data. If this same model is used to calculate piezomagnetic fields in the caldera, the results obtained agree with the observed local magnetic field data provided the Curie point isotherm is at a depth of {le}5 km. Taken together, these magnetic, seismic and geodetic data suggest that an episode of active magmatic intrusion occurred from late 1989 to mid-1990 at a depth of about 7-8 km beneath the resurgent dome within the Long Valley caldera. Other indications of this intrusion should be evident in measurements of leveling, local gravity, and seismic imaging data.

  10. Geologic map of the Cochetopa Park and North Pass Calderas, northeastern San Juan Mountains, Colorado

    USGS Publications Warehouse

    Lipman, Peter W.

    2012-01-01

    The San Juan Mountains in southwestern Colorado have long been known as a site of exceptionally voluminous mid-Tertiary volcanism, including at least 22 major ignimbrite sheets (each 150-5,000 km3) and associated caldera structures active at 33-23 Ma. Recent volcanologic and petrologic studies in the San Juan region have focused mainly on several ignimbrite-caldera systems: the southeastern area (Platoro complex), western calderas (Uncompahgre-Silverton-Lake City), and the central cluster (La Garita-Creede calderas). Far less studied has been the northeastern San Juan region, which occupies a transition between earlier volcanism in central Colorado and large-volume younger ignimbrite-caldera foci farther south and west. The present map is based on new field coverage of volcanic rocks in seventeen 7.5' quadrangles in northeastern parts of the volcanic field, high-resolution age determinations for 120 new sites, and petrologic studies involving several hundred new chemical analyses. This mapping and the accompanying lab results (1) document volcanic evolution of the previously unrecognized North Pass caldera and the morphologically beautifully preserved but enigmatic Cochetopa basin, including unique features not previously described from ignimbrite calderas elsewhere; (2) provide evidence for a more rapid recurrence of large ignimbrite eruptions than previously known elsewhere; (3) quantify the regional time-space-volume progression from the earlier Sawatch magmatic trend southward into the San Juan region; and (4) permit more rigorous comparison between the broad mid-Tertiary magmatic belt in the western U.S. Cordillera and the type continental-margin arc volcanism in the central Andes.

  11. Qualitative and Quantitative Assessment of Naturals Hazards in the Caldera of Mount Bambouto (West Cameroon)

    NASA Astrophysics Data System (ADS)

    Zangmo Tefogoum, G.; Kagou Dongmo, A.; Nkouathio, D. G.; Wandji, P.

    2009-04-01

    Mount Bambouto is polygenic stratovolcano of the Cameroon Volcanic Line, build between 21 Ma and 4,5Ma (Nkouathio et al., 2008). It is situated at about 200 km NE of mount Cameroon, at 09°55' and 10°15' East and, 05°25' and 05°50' Nord. This volcano covers an area of 500 Km2 and culminates at 2740 m at Meletan hill and bears a collapse caldera (13 x 8 km). Fissural, extrusive and explosive dynamism are responsible of the construction in three main stages this volcano including the edification of a sommital large rim caldera. Mount Bambouto structure gives rise to different natural hazards, of volcanological origin and meteorological origin. In the past time, landslides, floodings, firebush, blocks collapse took place in this area with catastrophic impact on the population. New research program had been carried out in the caldera concerning qualitative and quantitative evaluation of natural risks and catastrophes. The main factors of instability are rain, structure of the basement, slopes, lithology and anthropic activities; particularly, the occurrence of exceptional rainfall due to global change are relevant; this gives opportunity to draw landslides hazards zonation map of the Bambouto caldera which is the main risk in this area. We evaluate the financial potential of the caldera base on the average income of breeding, farming, school fees and the cost of houses and equipments for each family. The method of calculation revealed that, the yearly economy of the mounts Bambouto caldera represents about 2 billions FCFA. Some recommendations have been made in order to prevent and reduced the potential losses and the number of victims in particular by better land use planning. These help us to estimate the importance of destruction of the environment and biodiversity in case of catastrophes. We conclude that in the Bambouto caldera there is moderate to high probability that destructive phenomena due to landslides occurs within the upcoming years with enormous

  12. 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.

  13. The Tala Tuff, La Primavera caldera Mexico. Pre-eruptive conditions and magma processes before eruption

    NASA Astrophysics Data System (ADS)

    Sosa-Ceballos, G.

    2015-12-01

    La Primavera caldera, Jalisco Mexico, is a Pleistocenic volcanic structure formed by dome complexes and multiple pyroclastic flows and fall deposits. It is located at the intersection of the Chapala, Colima, and Tepic grabens in western Mexico. The first volcanic activity associated to La Primavera started ~0.1 Ma with the emission of pre-caldera lavas. The caldera collapse occurred 95 ka and is associated to the eruption of ~20 km3of pumice flows known as the Tala tuff (Mahood 1980). The border of the caldera was replaced by a series of domes dated in 75-30 ky, which partially filled the inner depression of the caldera with pyroclastic flows and falls. For more than a decade the Federal Commission of Electricity in Mexico (CFE) has prospected and evaluated the geothermal potential of the Cerritos Colorados project at La Primavera caldera. In order to better understand the plumbing system that tapped the Tala tuff and to investigate its relation with the potential geothermal field at La Primavera we performed a series of hydrothermal experiments and studied melt inclusions hosted in quartz phenocrysts by Fourier Infra red stectroscopy (FTIR). Although some post caldera products at La Primavera contain fayalite and quartz (suggesting QFM conditions) the Tala tuff does not contain fayalite and we ran experiments under NNO conditions. The absence of titanomagnetite does not allowed us to calculate pre-eruptive temperature. However, the stability of quartz and plagioclase, which are natural phases, suggest that temperature should be less than 750 °C at a pressure of 200 MPa. The analyses of H2O and CO2 dissolved in melt inclusions yielded concentrations of 2-5 wt.% and 50-100 ppm respectively. This data confirm that the pre-eruptive pressure of the Tala tuff is ~200 MPa and in addition to major elements compositions suggest that the Tala tuff is either, compositionally zoned or mixed with other magma just prior to eruption.

  14. MGS-TES thermal inertia study of the Arsia Mons Caldera

    USGS Publications Warehouse

    Cushing, G.E.; Titus, T.N.

    2008-01-01

    Temperatures of the Arsia Mons caldera floor and two nearby control areas were obtained by the Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES). These observations revealed that the Arsia Mons caldera floor exhibits thermal behavior different from the surrounding Tharsis region when compared with thermal models. Our technique compares modeled and observed data to determine best fit values of thermal inertia, layer depth, and albedo. Best fit modeled values are accurate in the two control regions, but those in the Arsia Mons' caldera are consistently either up to 15 K warmer than afternoon observations, or have albedo values that are more than two standard deviations higher than the observed mean. Models of both homogeneous and layered (such as dust over bedrock) cases were compared, with layered-cases indicating a surface layer at least thick enough to insulate itself from diurnal effects of an underlying substrate material. Because best fit models of the caldera floor poorly match observations, it is likely that the caldera floor experiences some physical process not incorporated into our thermal model. Even on Mars, Arsia Mons is an extreme environment where CO2 condenses upon the caldera floor every night, diurnal temperatures range each day by a factor of nearly 2, and annual average atmospheric pressure is only around one millibar. Here, we explore several possibilities that may explain the poor modeled fits to caldera floor and conclude that temperature dependent thermal conductivity may cause thermal inertia to vary diurnally, and this effect may be exaggerated by presence of water-ice clouds, which occur frequently above Arsia Mons. Copyright 2008 by the American Geophysical Union.

  15. Variation of Fracturing Pressures with Depth Near the Valles Caldera

    SciTech Connect

    Dash, Zora; Murphy, Hugh

    1983-12-15

    Hydraulic Fracturing at the Fenton Hill Hot Dry Rock Geothermal site near the Valles Caldera has yielded fracturing pressures from 14 to 81 MPa (2030 to 11,750 psi) at depths ranging from 0.7 to 4.4 km (2250 to 14,400 ft). This data can be fit to a fracture gradient of 19 MPa/km (0.84 psi/ft), except for an anomalous region between 2.6 to 3.2 km where fracturing pressures are about 20 MPa lower than estiamted using the above gradient. This anomaly coincides with a biotite granodiorite intrusive emplaced into a heterogeneous jointed metamorphic complex comprised of gneisses, schists and metavolcanic rocks. Microseismic events detected with sensitive downhole geophones suggest that shear failure is an important process during hydraulic fracturing of such jointed rock. Consequently the usual relation between minimum earth stress and fracture opening pressure, based upon classic tensile failure, cannot be used apriori; fracture opening pressure is instead a complex function of joint orientation and all three components of principal earth stress.

  16. Scientific core hole VC-2A, Valles Caldera, New Mexico

    SciTech Connect

    Musgrave, J.; Goff, S. ); Turner, T. , Salt Lake City, UT )

    1990-10-01

    This report details the remedial action activities that were necessary to complete scientific core hole Valles caldera {number sign}2A (VC-2A) before it was relinquished to the landowners. Sandia National Laboratories, acting as the Geoscience Research Drilling Office (GRDO), managed the coring operations. Los Alamos National Laboratory (Los Alamos) obtained the proper drilling permits with the New Mexico State Engineers Office (SEO). A legal agreement between Los Alamos and the landowners states that the Laboratory will give the landowners the completed core hold with casing, well head, and other hardware at the end of May 1991, or earlier if scientific investigations were completed. By May 1988, the Science Team completed the planned scientific investigations in the VC-2A core hole. Upon the insistence of the GRDO, the New Mexico Oil Conservation Division (OCD) inspected the core hole, declared jurisdiction, and required that the 11.43- by 11.43-cm annular cement job be repaired to comply with OCD regulations. These regulations state that there must be a return to surface of cement in all cementing operations. We successfully completed a squeeze cementing operation and relinquished the core hold to the landowners in November 1988 to the satisfaction of the OCD, SEO, the landowners, and Los Alamos. 7 refs., 4 figs., 1 tab.

  17. Volcanic calderas delineate biogeographic provinces among Yellowstone thermophiles.

    PubMed

    Takacs-Vesbach, Cristina; Mitchell, Kendra; Jackson-Weaver, Olan; Reysenbach, Anna-Louise

    2008-07-01

    It has been suggested that the distribution of microorganisms should be cosmopolitan because of their enormous capacity for dispersal. However, recent studies have revealed that geographically isolated microbial populations do exist. Geographic distance as a barrier to dispersal is most often invoked to explain these distributions. Here we show that unique and diverse sequences of the bacterial genus Sulfurihydrogenibium exist in Yellowstone thermal springs, indicating that these sites are geographically isolated. Although there was no correlation with geographic distance or the associated geochemistry of the springs, there was a strong historical signal. We found that the Yellowstone calderas, remnants of prehistoric volcanic eruptions, delineate biogeographical provinces for the Sulfurihydrogenibium within Yellowstone (chi(2): 9.7, P = 0.002). The pattern of distribution that we have detected suggests that major geological events in the past 2 million years explain more of the variation in sequence diversity in this system than do contemporary factors such as habitat or geographic distance. These findings highlight the importance of historical legacies in determining contemporary microbial distributions and suggest that the same factors that determine the biogeography of macroorganisms are also evident among bacteria. PMID:18363714

  18. Fernandina caldera collapse morphology in geometric and dynamic comparison to sandbox models, subsidence sinks over nuclear-explosion cavities, and some other calderas

    NASA Astrophysics Data System (ADS)

    Howard, K. A.

    2009-12-01

    The 1968 collapse structure of Fernandina caldera (1.5 km3 collapsed) and also the smaller Darwin Bay caldera in Galápagos each closely resembles morphologically the structural zoning of features found in depressions collapsed into nuclear-explosion cavities (“sinks” of Houser, 1969) and in coherent sandbox-collapse models. Coherent collapses characterized by faulting, folding, and organized structure contrast with spalled pit craters (and lab experiments with collapsed powder) where disorganized piles of floor rubble result from tensile failure of the roof. Subsidence in coherent mode, whether in weak sand in the lab, stronger desert alluvium for nuclear-test sinks, or in hard rock for calderas, exhibits consistent morphologic zones. Characteristically in the sandbox and the nuclear-test analogs these include a first-formed central plug that drops along annular reverse faults. This plug and a surrounding inward-tilted or monoclinal ring (hanging wall of the reverse fault) contract as the structure expands outward by normal faulting, wherein peripheral rings of distending material widen the upper part of the structure along inward-dipping normal faults and compress inner zones and help keep them intact. In Fernandina, a region between the monocline and the outer zone of normal faulting is interpreted, by comparison to the analogs, to overlie the deflation margin of an underlying magma chamber. The same zoning pattern is recognized in structures ranging from sandbox subsidence features centimeters across, to Alae lave lake and nuclear-test sinks tens to hundreds of meters across, to Fenandina’s 2x4 km-wide collapse, to Martian calderas tens of kilometers across. Simple dimensional analysis using the height of cliffs as a proxie for material strength implies that the geometric analogs are good dynamic analogs, and validates that the pattern of both reverse and normal faulting that has been reported consistently from sandbox modeling applies widely to calderas.

  19. Eruptive and noneruptive calderas, northeastern San Juan Mountains, Colorado: Where did the ignimbrites come from?

    USGS Publications Warehouse

    Lipman, P.W.; McIntosh, W.C.

    2008-01-01

    The northeastern San Juan Mountains, the least studied portion of this well-known segment of the Southern Rocky Mountains Volcanic Field are the site of several newly identified and reinterpreted ignimbrite calderas. These calderas document some unique eruptive features not described before from large volcanic systems elsewhere, as based on recent mapping, petrologic data, and a large array of newly determined high-precision, laser-fusion 40Ar/39Ar ages (140 samples). Tightly grouped sanidine ages document exceptionally brief durations of 50-100 k.y. or less for individual Oligocene caldera cycles; biotite ages are more variable and commonly as much as several hundred k.y. older than sanidine from the same volcanic unit. A previously unknown ignimbrite caldera at North Pass, along the Continental Divide in the Cochetopa Hills, was the source of the newly distinguished 32.25-Ma Saguache Creek Tuff (???400-500 km3). This regionally, distinctive crystal-poor alkalic rhyolite helps fill an apparent gap in the southwestward migration from older explosive activity, from calderas along the N-S Sawatch locus in central Colorado (youngest, Bonanza Tuff at 33.2 Ma), to the culmination of Tertiary volcanism in the San Juan region, where large-volume ignimbrite eruptions started at ca. 29.5 Ma and peaked with the enormous Fish Canyon Tuff (5000 km3) at 28.0 Ma. The entire North Pass cycle, including caldera-forming Saguache Creek Tuff, thick caldera-filling lavas, and a smaller volume late tuff sheet, is tightly bracketed at 32.25-32.17 Ma. No large ignimbrites were erupted in the interval 32-29 Ma, but a previously unmapped cluster of dacite-rhyolite lava flows and small tuffs, areally associated with a newly recognized intermediate-composition intrusion 5 ?? 10 km across (largest subvolcanic intrusion in San Juan region) centered 15 km north of the North Pass caldera, marks a near-caldera-size silicic system active at 29.8 Ma. In contrast to the completely filled North Pass

  20. Bonanza, an "Extreme" Resurgent Ignimbrite-Caldera Cycle in the San Juan Mountains, Colorado

    NASA Astrophysics Data System (ADS)

    Lipman, P. W.; McIntosh, W. C.; Zimmerer, M. J.

    2012-12-01

    Among large calderas associated with ignimbrite super-eruptions, the 33.2 Ma Bonanza caldera of the Southern Rocky Mountain volcanic field displays compositional and structural features that provide near-endmember examples of ignimbrite eruptive processes. Bonanza, source of a compositionally complex regional ignimbrite sheet erupted at 33.19±0.04 Ma, is a subsequent resurgently domed structure ~20 km diameter that subsided >3 km during eruption of ~1,000 km3 of ignimbrite. Among its exceptional features: (1) extreme compositional gradients in the associated Bonanza Tuff (mafic dacite to silicic rhyolite; 59-76.5% SiO2); (2) multiple alternations of mafic and silicic zones, rather than simple upward gradient from silicic to mafic; (3) similarly large compositional diversity among postcollapse caldera-fill lavas and exposed roof zones of resurgent intrusions; (4) compositional contrasts among outflow sectors (mainly rhyolite to east, dacite to west); (5) brief time span for the entire caldera cycle (33.2-32.9 Ma); (6) a uniquely steep-sided resurgent dome (dips of 40-50o on west and 70-80o on east flanks); (7) unique exposure levels due to later structural tilting and rugged present-day topography--from postcollapse lavas, to thickly ponded intracaldera ignimbrite and interleaved landslide breccia, down through precaldera volcanic floor, into underlying Paleozoic and Precambrian basement that are intruded by resurgent plutons. Some near-original caldera morphology remains defined by present-day landforms (western topographic rim, resurgent core, ring-fault valley), while tilting and deep erosion provide exceptional three-dimensional exposures of fill, floor, and resurgent structures. An ~2.5-km-thick section of intracaldera ignimbrite on the western flank of the resurgent dome is complexly compositionally zoned (up to nine gradational alternations of rhyolite and dacite, interleaved with collapse-breccia lenses), underlain by caldera-floor intermediate

  1. Structural deformation and sedimentation in an active Caldera, Rabaul, Papua New Guinea

    USGS Publications Warehouse

    Greene, H. Gary; Tiffin, D.L.; McKee, C.O.

    1986-01-01

    Recent seismic and tectonic activity in Rabaul Caldera, Papua New Guinea, suggests that magma is accumulating at a shallow depth beneath this partially submerged structure and that a new volcano may be developing. Changes in onshore elevation since 1971 (as much as 2 m on south Matupit Island) indicate that rapid and large-scale uplifts have occurred on the seafloor near the center of the caldera. The frequency of seismic events within the caldera has also increased during this period. Earthquake locations define an elliptical ring surrounding the center of this uplift within the caldera. A marine geophysical survey in 1982 by the U.S. Geological Survey's R/V "S.P. Lee" in Rabaul Caldera shows the development of a bulge in the seafloor near the center of the caldera. High-resolution seismic reflection profiles show that this bulge consists of two domal uplifts bounded and separated by two major north-south-trending fault zones. Deformed sediments overlie these zones; a prominent slump flanks the area of the bulge. Five major acoustic units were identified in the seismic reflection profiles: an acoustic basement and four sedimentary units consisting of irregularly layered, cross-layered, contorted, and well-layered sequences. The acoustic basement is probably composed of crystalline volcanic rocks, and the layered acoustic units are probably sediments, primarily ash deposited in different environments. The cross-layered, irregularly layered, and contorted units appear to have been deposited in a dynamic environment subjected to strong currents, seismicity, and/or mass wasting, while the well-layered units were deposited in a low-energy environment. Locally, well-layered sequences interfinger with the other sedimentary units, indicating a transitional environment that alternated between high-energy and low-energy depositional processes. A submarine channel cuts most of the acoustic units and appears to be the conduit for sediment transport out of the caldera; it

  2. Inversion for sources of crustal deformation and gravity change at the Yellowstone caldera

    SciTech Connect

    Vasco, D.W.; Taylor, C.L. ); Smith, R.B. )

    1990-11-10

    The Yellowstone caldera was formed in the latest of three explosive eruptions of rhyolites and ash flow tuffs totaling 3,700 km{sup 3} at 2, 1.2, and 0.6 m.y. before present. Its youthful volcanic history, widespread hydrothermal activity, intense seismicity, and extremely high heat flow, in excess of 30 times the continental average, marks the Yellowstone volcanic system as a giant caldera at unrest. Orthometric height increases of the caldera of up to 76 cm, measured from precise leveling surveys from 1923 to 1975-1977, were inverted to determine volume expansion source models for the caldera-wide deformation. For the 1923 to 1977 uplift episode, two regions of expansion were found: (1) in the northern part of the caldera near the Sour Creek resurgent dome of {approximately}0.37 km{sub 3}, and (2) in the southern part of the caldera, near the Mallard Lake resurgent dome of {approximately}0.41 km{sub 3}. Both bodies occur in the upper crust from near-surface depths to 6.0 km, but the largest volume expansions were found in the 3.0-6.0 km depth range. The southern caldera source volume, near the Mallard Lake dome, may extend down to 9.0 km. From 1976 to 1987, nearly simultaneous measurements of elevation and gravity changes were made on a profile across the northern caldera during a period of net uplift. Models of the temporal gravity variation infer that the volume increase for the northern caldera source must lie above 9.0 km and involved a density perturbation greater than +0.002 g/cm{sup 3}. The modeled volumetric sources are in the same general locations as bodies of low P wave velocities, high seismic attenuation, and large negative Bouguer gravity anomalies. It is likely that the modeled volumetric increases were caused by migration of magmas and/or the introduction of large volumes of hydrothermal fluids into the upper crust.

  3. Under Construction: Rebuilding Kīlauea's Shallow Magma Storage System After Caldera Collapse

    NASA Astrophysics Data System (ADS)

    Swanson, D. A.; Wright, T. L.

    2015-12-01

    Draining of Kīlauea's upper level magma reservoir system in ~1500 CE led to a N-S elongate, roughly circular structural caldera ~6.5 km in diameter surrounding a prominent topographic caldera (TC) 4 x 3 km in diameter. The TC was probably at least 600 m deep with a volume of ~4-6 km3. The reservoir system has been rebuilding since then, mostly during the past 200 y of relatively high magma supply. Current reservoir locations are well defined geodetically (Poland et al., 2014) but do not match the presumed configuration of magma storage before the caldera collapse, if the common assumption holds that collapse width equals reservoir width. For example, magma does not underlie the northern 1-2 km of the TC, as judged by relatively high P-wave velocities (Dawson et al., 1999) and lack of deformation related to magma storage. The northernmost reservoir, near Halemaumau, is within the TC, but an order of magnitude more magma fills the south caldera reservoir south of the TC (Poland et al., 2014). Currently, the Halemaumau reservoir is shallower than the south caldera reservoir (1-2 km vs. 3-4 km), but in the 1960s magma was likely stored 3-3.5 km deep near Halemaumau (Wright and Klein, 2014). Many deformation centers are south of the TC and have an E-W spread of ~4 km. These observations suggest an evolving storage system that, if drained today, would not form a caldera of the size or location of the TC. Yet the TC is at the summit of the volcano, the site of an older caldera (Holcomb, 1987) and a positive Bouguer gravity anomaly (Kauahikaua et al., 2000), and is apparently the preferred location of reservoir draining and caldera collapse. We think the reservoir system will continue to evolve, expanding and centering itself below the topographic caldera, which will likely be where the next collapse takes place. Dawson et al., 1999, GRL. Holcomb, 1987, USGS PP 1350. Kauahikaua et al., 2000, Geology. Poland et al., 2014, USGS PP 1801. Wright and Klein, 2014, USGS PP 1806.

  4. Magma Storage, Recharge and the Caldera Cycle at Rabaul, Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Fabbro, G.; Bouvet de Maisonneuve, C.; Sindang, M.

    2015-12-01

    Many calderas have a history of repeated caldera-forming eruptions, interspersed with periods of more minor activity. Rabaul, for instance, has had at least 11 ignimbrite-forming eruptions over the last 200 ky. The most recent of these was the '1400 BP' eruption, which led to caldera collapse. Since then, there has been multiple smaller eruptions, including the ongoing activity from Tavurvur and Vulcan. An important question facing volcanology today is what controls the size of eruptions at calderas such as Rabaul.Detailed stratigraphic sampling of the 1400BP eruption reveals that prior to eruption, the magma reservoir below Rabaul contained a well-mixed dacite with whole-rock SiO2 contents of 65.0-66.4 wt%. The dacite contains a single phenocryst assemblage of plag (An44-52), cpx (En43-46Fs13-15Wo40-41), opx (En69-71Fs25-28Wo3) and magnetite, along with minor apatite. The homogeneity of the dacite is underscored by the narrow range of compositions of both the matrix glass and the melt inclusions (67.8-69.0 wt% SiO2). The only exception to this is at the top of the ignimbrite, representing some of the last magma to have been withdrawn. Dispersed throughout the dacitic pumices are darker, more mafic blebs. Streaks of mingled magma with a range of SiO2 contents, down to 59.9 wt% SiO2 are also found in the pumice, suggesting that a mafic recharge magma was intruded into the base of the reservoir shortly before eruption. High TiO2 contents rule out the direct involvement of basalt, and instead imply the magma that intruded into the reservoir was an andesite with at least 56 wt% SiO2. Phenocrysts related to this recharge magma are rare, and the crystals found in the dark blebs are identical in composition to those found in the dacite, indicating that the recharge was aphyric. The present-day, post-caldera recharge magma is different to the pre-1400 BP recharge magma: it is basaltic. This suggests that the plumbing system of Rabaul is different during the pre-caldera and

  5. Quiescent deformation of the Aniakchak Caldera, Alaska mapped by InSAR

    USGS Publications Warehouse

    Kwoun, Oh-Ig; Lu, Zhiming; Neal, C.; Wicks, C., Jr.

    2006-01-01

    The 10-km-wide caldera of the historically active Aniakchak volcano, Alaska, subsides ???13 mm/yr, based on data from 19 European Remote Sensing Satellite (ERS-1 and ERS-2) interferometric synthetic aperture radar (InSAR) images from 1992 through 2002. The pattern of subsidence does not reflect the distribution of pyroclastic deposits from the last eruption in 1931 and therefore is not related to compaction of fragmental debris. Weighted least-squares inversion of the deformation maps indicates a relatively constant subsidence rate. Modeling the deformation with a Mogi point source locates the source of subsidence at ???4 km below the central caldera floor, which is consistent with the inferred depth of magma storage before the 1931 eruption. Magmatic CO2 and He have been measured at a warm soda spring within the caldera, and several sub-boiling fumaroles persist elsewhere in the caldera. These observations suggest that recent subsidence can be explained by the cooling or degassing of a shallow magma body (???4 km deep), and/or the reduction of the pore-fluid pressure of a cooling hydrothermal system. Ongoing deformation of the volcano detected by InSAR, in combination with magmatic gas output from at least one warm spring, and infrequent low-level bursts of seismicity below the caldera, indicate that the volcanic system is still active and requires close attention for the timely detection of possible hazards. ?? 2006 Geological Society of America.

  6. Geologic Map of the Central San Juan Caldera Cluster, Southwestern Colorado

    USGS Publications Warehouse

    Lipman, Peter W.

    2006-01-01

    The San Juan Mountains are the largest erosional remnant of a composite volcanic field that covered much of the southern Rocky Mountains in middle Tertiary time. The San Juan field consists mainly of intermediate-composition lavas and breccias, erupted about 35-30 Ma from scattered central volcanoes (Conejos Formation) and overlain by voluminous ash-flow sheets erupted from caldera sources. In the central San Juan Mountains, eruption of at least 8,800 km3 of dacitic-rhyolitic magma as nine major ash flow sheets (individually 150-5,000 km3) was accompanied by recurrent caldera subsidence between 28.3 Ma and about 26.5 Ma. Voluminous andesitic-dacitic lavas and breccias erupted from central volcanoes prior to the ash-flow eruptions, and similar lava eruptions continued within and adjacent to the calderas during the period of more silicic explosive volcanism. Exposed calderas vary in size from 10 to 75 km in maximum dimension; the largest calderas are associated with the most voluminous eruptions.

  7. The link between circumferential dikes and eruptive fissures around calderas: insights from numerical and analog models

    NASA Astrophysics Data System (ADS)

    Corbi, Fabio; Rivalta, Eleonora; Pinel, Virginie; Maccaferri, Francesco; Acocella, Valerio

    2016-04-01

    Active calderas are seldom associated with circumferential eruptive fissures along their rim, but eroded portions of extinct magmatic complexes reveal widespread evidence of circumferential dikes. This discrepancy suggests that, while the conditions to emplace circumferential dikes below volcanoes are easily met, mechanisms must exist to arrest the dikes before they reach the surface. Here we explain this discrepancy with laboratory experiments of air injection into a gelatin medium shaped to mimic a volcanic edifice with caldera. Our models show that the ascending dikes experience a variable degree of deflection, depending on the competition between dike overpressure, Pe, and the forcing induced by the topographic load, Pl. When Pl/Pe = 4.3 - 4.5 the analog dikes proceed almost insensitive to the stress rotation and erupt within the caldera. When Pl/Pe = 4.8 - 5.3 the analog dikes closely propagate orthogonal to the least compressive stress σ3 and stall below the caldera rim in a circumferential arrangement. Progressive buoyancy increase through repeated supply of fluid is fundamental for the occurrence of circumferential fissures. Complementary numerical models explain the observed circumferential arrangement and validate the experiments. These results contribute defining the shallow magma transfer and related hazard assessment within calderas.

  8. Tilted middle Tertiary ash-flow calderas and subjacent granitic plutons, southern Stillwater Range, Nevada: cross sections of an Oligocene igneous center

    USGS Publications Warehouse

    John, D.A.

    1995-01-01

    Steeply tilted late Oligocene caldera systems in the Stillwater caldera complex record a number of unusual features including extreme thickness of caldera-related deposits, lack of evidence for structural doming of the calderas and preservation of vertical compositional zoning in the plutonic rocks. The Stillwater caldera complex comprises three partly overlapping ash-flow calderas and subjacent plutonic rocks that were steeply tilted during early Miocene extension. The Job Canyon caldera, the oldest (ca. 29-28 Ma) caldera, consists of two structural blocks. The 25 to 23 Ma Poco Canyon and Elevenmile Canyon calderas and underlying Freeman Creek pluton overlap in time and space with each other. Caldera collapse occurred mostly along subvertical ring-fracture faults that penetrated to depths of >5 km and were repeatedly active during eruption of ash-flow tuffs. The calderas collapsed as large piston-like blocks, and there is no evidence for chaotic collapse. Preserved parts of caldera floors are relatively flat surfaces several kilometers across. -from Author

  9. Accelerated uplift and magmatic intrusion of the Yellowstone caldera, 2004 to 2006.

    PubMed

    Chang, Wu-Lung; Smith, Robert B; Wicks, Charles; Farrell, Jamie M; Puskas, Christine M

    2007-11-01

    The Yellowstone caldera began a rapid episode of ground uplift in mid-2004, revealed by Global Positioning System and interferometric synthetic aperture radar measurements, at rates up to 7 centimeters per year, which is over three times faster than previously observed inflation rates. Source modeling of the deformation data suggests an expanding volcanic sill of approximately 1200 square kilometers at a 10-kilometer depth beneath the caldera, coincident with the top of a seismically imaged crustal magma chamber. The modeled rate of source volume increase is 0.1 cubic kilometer per year, similar to the amount of magma intrusion required to supply the observed high heat flow of the caldera. This evidence suggests magma recharge as the main mechanism for the accelerated uplift, although pressurization of magmatic fluids cannot be ruled out. PMID:17991858

  10. A core hole into the hydrothermal system of the Long Valley caldera

    SciTech Connect

    Wollenberg, H.; White, A.; Flexser, S.; Sorey, M.; Farrar, C.

    1987-03-01

    To investigate the present-day hydrothermal system, the ''Shady Rest'' hole was continuously cored 715m into the southwestern moat of the Long Valley caldera. The hole intersected 100m of glacial till and 300m of postcaldera rhyolite before entering the welded Bishop Tuff and bottoming in that unit. A sharp temperature rise over the upper 350m, and near-isothermal conditions below reflect the presence of approx.200/sup 0/C water moving through open, calcite-lined fractures in silicified Early Rhyolite and Bishop Tuff. The depth to the Bishop is the shallowest encountered in holes in the caldera, and the temperatures measured are among the hottest observed in wells drilled within the caldera.

  11. A geochemical survey using heavy mineral concentrates in the Mount Belknap caldera vicinity, Utah

    USGS Publications Warehouse

    Tucker, R.E.; Miller, W. Roger; Motooka, J.M.

    1982-01-01

    Geochemical surveys of the rocks, heavy-mineral concentrates, and surface and spring waters in the vicinity of the Mount Belknap caldera, Tushar Mountains, west-central Utah, were conducted during the summers of 1978 and 1979. Anomalous concentrations of mostly lithophile elements, particularly niobium, beryllium, lead, yttrium, tin, zinc, manganese, and molybdenum in the magnetic and nonmagnetic fraction of heavy-mineral concentrates derived from stream sediment suggest that late stage, highly differentiated felsic rocks were involved in the eruptive history of the Mount Belknap caldera. Q-mode factor analysis was used to characterize the geochemical assemblages within the survey area, and the areal distribution of high-factor scores associated with mineralization indicates favorable target areas for future exploration. The results of these studies indicate that porphyry-type molybdenum and possible associated vein-type uranium mineralized deposits may exist in or near the Mount Belknap caldera.

  12. Deep-sea Vector Magnetic Anomalies over the Bayonnaise Knoll Caldera (Izu-Ogasawara Arc) (Invited)

    NASA Astrophysics Data System (ADS)

    Honsho, C.; Ura, T.; Kim, K.

    2013-12-01

    The Bayonnaise Knoll caldera is located on the eastern margin of the backarc rift zone of the Izu-Ogasawara island arc. The caldera rim is ~3 km in diameter and 100-200 m high from the caldera floor 840-920 m deep. A large active hydrothermal field associated with sulfide deposit, called the Hakurei site, has been found at the foot of the southeastern caldera wall. We conducted deep-sea magnetic measurements using autonomous underwater vehicles to map ~75 % of an area 3 km by 4 km in the caldera. The magnetic vector field data were collected at 40-150 m altitude along the survey lines spaced 80-200 m apart. We improved the conventional correction method applied for removing the effect of vehicle magnetization, which greatly enhanced the precision of the resulting vector anomalies and allowed us to use the vector anomaly instead of the total intensity anomaly for inversion analysis. The magnetization distribution obtained using the vector anomaly was significantly different from the one obtained using the total intensity anomaly, especially in areas where the survey tracks were widely spaced. The aliasing effect appears in areas of sparse data distribution, and the magnetic field is more correctly calculated from the vector anomaly than the total intensity anomaly. The magnetization distribution in the caldera has two major features: a ~1.5-km wide belt of high magnetization, trending NNW-SSE through the caldera, and a clear low magnetization zone, ~300 m x ~500 m wide, extending over the Hakurei site. The high magnetization belt is considered to reflect basaltic volcanism associated with the backarc rifting that occurred after the formation of the Bayonnaise Knoll. The low magnetization zone is interpreted as the alteration zone resulting from the hydrothermal activity. Several zones of localized high magnetization are recognized within the high magnetization belt, some of them in the caldera wall adjacent to the low magnetization zone of the Hakurei site. We

  13. Geologic Model of the Baca Geothermal Reservoir, Valles Caldera, New Mexico

    SciTech Connect

    Nielson, Dennis L.; Hulen, Jeffrey B.

    1983-12-15

    The caldera environment represents a complex interaction of volcanic, structural, and often, hydrothermal processes. As a result calderas are often targets for geothermal exploration and development. From the standpoint of the reservoir engineer, such geothermal systems would be hosted by rocks that display a complex interplay of stratigrphic permeability, structural permeability, and changing permeability which results from the process of hydrothermal alteration and new fracture generation. The purpose of this paper is to present a geolgic model of the Baca geothermal reservoir which is situated in New Mexico. The geologic history of the Valles caldera is presented in Smith and Bailey (1968). The data we present is largely based on our studies of subsurface samples from Union Oil Company's Baca project area. Additional results of our work have been published previously (Hulen and Nielson, 1982, 1983; Nielson and Hulen, in press).

  14. Valles caldera region, New Mexico, and the emerging continental scientific drilling program

    SciTech Connect

    Goff, F.; Gardner, J.N.

    1988-06-10

    Valles caldera is best known in recent years as an excellent example of a resurgent caldera and as the site of a high-temperature geothermal system. However, Valles caldera and the surrounding Jemez Mountains volcanic field possess a rich history of geologic research that dates back to the late 1880s. Through the years, the research focus has changed as different economic and scientific factors have exerted their influence. Early work emphasized mining activity, while modern work has stressed volcanology and, later, geothermal development. Only in the last 5 years has it been possible to view the region as a dynamic, integrated magma-hydrothermal system having a complex evolution lasting more than 13 m.y.

  15. Hydrologic and geochemical monitoring in Long Valley caldera, Mono County, California, 1986. Water Resources Investigation

    SciTech Connect

    Farrar, C.D.; Sorey, M.L.; Sore, S.A.; Rojstaczer, S.A.; Steinemann, A.C.

    1989-01-01

    The U.S. Geological Survey continued to monitor hydrologic and geochemical conditions in the Long Valley caldera during 1986. The monitoring is directed toward detecting changes in the hydrologic system caused by tectonic or magmatic processes. Data collected during 1986 include chemical and isotopic composition of water from selected stream sites, springs, and wells; pumpage from four geothermal wells; flow rates of selected springs and stream sites; mean daily water or gas temperatures at selected sites; mean daily atmospheric pressures and water levels at selected wells, and precipitation records for two sites. Seismicity within the caldera persisted at a relatively low level compared with the more active periods of 1978-84. The most significant events of seismicity that affected hydrologic monitoring sites in Long Valley during 1986 occurred during July, in response to the Chalfant Valley earthquakes, centered about 20 miles southeast of the caldera.

  16. Graben calderas of the Sierra Madre Occidental: The case of Guanajuato, central Mexico

    NASA Astrophysics Data System (ADS)

    Aguirre-Diaz, G. J.; Tristán-González, M.; Labarthe-Hernández, G.; Marti, J.

    2013-12-01

    The Sierra Madre Occidental (SMO) volcanic province is characterized by voluminous silicic ignimbrites that reach an accumulated thickness of 500 to 1500 m. A single ignimbrite can reach up to 350 m thick in its outflow facies. This ignimbrite sequence formed mostly within 38-23 Ma, building up a total estimated volume of ca. 580,000 km3 making the SMO the largest ignimbrite province of the world. We have showed that several and probably most of the SMO ignimbrites were erupted from fissures associated to Basin and Range fault systems or grabens (Geology, 2003), thus naming these volcano-tectonic structures as graben calderas (Caldera Volcanism book, Elsevier, 2008). Generally, the sequence observed in graben calderas include, from oldest to youngest, alluvial fan deposits combined with lacustrine deposits, pyroclastic surge deposits and minor volume ignimbrites, a large-volume ignimbrite that could be massive or made of successive layers, and sometimes silicic lava domes and/or mafic fissural lavas both with vents aligned with the graben trend. Fallout deposits, plinian or non-plinian, are not observed in the sequence. Thus, onset of caldera collapse represented by the major ignimbrite must occur just after deposition of continental sediments within the graben domain. A similar volcano-tectonic development is observed in pull-apart grabens. Therefore, extensional or transtensional tectonics, before and during caldera collapse, and the emplacement of a subgraben shallow silicic magma chamber are the necessary conditions for the development of graben calderas. We describe here the case of the Guanajuato graben caldera, located in the central part of Mexico and in the southeastern portion of the SMO volcanic province. The caldera is part of the economically important mining district of Guanajuato, with 28 silver mines, some active since the 16th century. The caldera structure, a rectangle of 10 x 16 km, was controlled by NW and NE regional fault systems. Most ore

  17. The largest caldera-forming eruptions in Kamchatka: geochronology, definition, volumes, and petrologic and isotopic investigation

    NASA Astrophysics Data System (ADS)

    Bindeman, I. N.; Leonov, V.; Shipley, N. K.

    2012-12-01

    The continental arc of Kamchatka has the highest magma production rates in the world and arguably the largest number of calderas per unit arc length, which are in response to rapid head-on collision at a subduction angle of ~45°. Kamchatkan caldera sizes and volumes of ignimbrite eruptions some of the world's largest, but rapid volcanic and tectonic uplift and burial, rapid erosion rates, and bulldozing effects of multiple glaciations have reshaped Pleistocene and older calderas. This has left behind remnants of isolated, yet thick, often intracaldera-only ignimbrite sequences. While the contribution of Kamchatkan arc volcanism to global Pleistocene volcanism and oscillating Pleistocene climate is of prime importance, the combination of harsh climate, remoteness, poor road infrastructure, and heavy vegetation cover make fieldwork and recognition of caldera volcanics challenging. We present new results of geologic, geochronologic, geochemical and isotopic investigation of two of the largest caldera in Kamchatka - Pauzhetka (27x18km, 0.44Ma) and Karymshina (30x16km, 1.78 Ma). In both places large-volume climactic ignimbrites are represented by quartz-, zircon-, and biotite- bearing, but sanidine-free rhyolitic to high-silica rhyolitic tuffs. These compositional characteristics and evolved trace elemental ratios indicate a high degree of differentiation rarely achieved in other silicic rocks of the Kamchatka arc and worldwide. Crystallinity of ignimbrites ranges from high (35%) to relatively low (10%). Preliminary investigation of chemical and isotopic variations in pre-caldera sequences in both calderas demonstrates diverse peripheral eruptions of basaltic to dacitic compositions, with predominance of the former. The search for the precursor high-silica rhyolite continues. At Karymshina, pre-caldera magmas have a greater diversity of Sr (0,703283-0,703552) and Nd (0,513046- 0,512962) ratios, and moderately diverse and elevated δ18O values (5.5-7.5‰). In contrast

  18. The 2014-2015 slow collapse of the Bárðarbunga caldera, Iceland

    NASA Astrophysics Data System (ADS)

    Tumi Gudmundsson, Magnus; Jónsdóttir, Kristín; Roberts, Matthew; Ófeigsson, Benedikt G.; Högnadóttir, Thórdís; Magnússon, Eyjólfur; Jarosch, Alexander H.; Pálsson, Finnur; Einarsson, Páll; Sigmundsson, Freysteinn; Drouin, Vincent; Hjörleifsdóttir, Vala; Reynolds, Hannah I.; Dürig, Tobias; Vogfjörd, Kristín; Hensch, Martin; Munoz-Cobo Belart, Joaquin; Oddsson, Björn

    2015-04-01

    The Bárðarbunga caldera is located in central Iceland, under in NW corner of Vatnajökull ice cap. The caldera is about 65 km2 in area, with 500-600 m high topographic rims and is fully covered with up to 800 m thick ice. On 16 August 2014 an intense earthquake swarm started in Bárðarbunga, the beginning of a major volcano-tectonic rifting event forming a 45 km long dyke extending from the caldera to Holuhraun lava field outside the northern margin of Vatnajökull (Sigmundsson et al., 2014). A large basaltic, effusive fissure eruption began in Holuhraun on 31 August that by January had formed a lava field of volume in excess of one cubic kilometre. The collapse of the caldera is expected to have begun a few days after the onset of the earthquake swarm, probably coinciding with the first M5 earthquake. This slow caldera collapse has been monitored through repeated mapping of the gradually increasing subsidence bowl (~80 km2 in December) with airborne profiling of the ice surface, satellite mapping, an online GPS station set up in September on the glacier surface in the centre of the caldera with a strong motion sensor added in November, and indirectly through recording of seismic activity. Satellite interferograms constrain both ice movements and the rate of collapse. The rate of collapse was greatest in the first two weeks or 0.5-1 m/day in the centre, but has since gradually declined with time. The daily rate was 0.1-0.2 m/day in January, when the maximum lowering had reached about 60 m. A gradual widening of the subsidence bowl has been observed since early September. It is asymmetric, deepest in the NE part of the caldera. Downwards displacement extends outside the pre-existing topographic caldera rims, particularly on the south side where the rims have subsided by over 10 meters. Ice-flow modelling indicates that the ice is mostly passively subsiding with the caldera floor. Thus, horizontal ice flow has had little effect on the shape of the subsidence bowl

  19. Accelerated uplift and magmatic intrusion of the Yellowstone caldera, 2004 to 2006

    USGS Publications Warehouse

    Chang, W.-L.; Smith, R.B.; Wicks, C.; Farrell, J.M.; Puskas, C.M.

    2007-01-01

    The Yellowstone caldera began a rapid episode of ground uplift in mid-2004, revealed by Global Positioning System and interferometric synthetic aperture radar measurements, at rates up to 7 centimeters per year, which is over three times faster than previously observed inflation rates. Source modeling of the deformation data suggests an expanding volcanic sill of ???1200 square kilometers at a 10-kilometer depth beneath the caldera, coincident with the top of a seismically imaged crustal magma chamber. The modeled rate of source volume increase is 0.1 cubic kilometer per year, similar to the amount of magma intrusion required to supply the observed high heat flow of the caldera. This evidence suggests magma recharge as the main mechanism for the accelerated uplift, although pressurization of magmatic fluids cannot be ruled out.

  20. Aeromagnetic mapping of the structure of Pine Canyon caldera and Chisos Mountains intrusion, Big Bend National Park, Texas

    USGS Publications Warehouse

    Drenth, B.J.; Finn, C.A.

    2007-01-01

    Analysis of aeromagnetic and gravity data reveals new details of the structure, igneous geology, and temporal evolution of the prominent, enigmatic ca.32 Ma Pine Canyon caldera and the Chisos Mountains (Big Bend National Park, Texas). The main caldera-filling Pine Canyon Rhyolite, the oldest member of the South Rim Formation, is reversely magnetized, allowing it to be used as a key marker bed for determining caldera fill thickness. Modeling of gravity and magnetic anomalies indicates that the Pine Canyon Rhyolite is probably thicker in the northeastern part of the caldera. Lineaments in the magnetic data suggest the presence of buried faults beneath the caldera that may have led to increased downdrop in the northeast versus the southwest, allowing a thicker section of caldera fill to accumulate there. The Pine Canyon caldera has been interpreted as a downsag caldera because it lacks surficial faulting, so these inferred faults are the first mapped features there that could be responsible for caldera collapse. The caldera boundary correlates well with the margins of a gravity low. General features of the caldera match well with basic models of downsag calderas, meaning that the Pine Canyon caldera may be a classic example of downsagging, of which few well-described examples exist, in terms of a geophysical signature. The source of a long-wavelength magnetic high over the Chisos Mountains is interpreted as a previously unknown broad intrusion, the long axis of which trends parallel to a major crustal boundary related to the Ouachita orogeny or an even earlier Precambrian margin. This feature represents the largest intrusion (28-34 km diameter, 1-4 km thick, 700-3000 km3 in volume) in an area where relatively small laccoliths are ubiquitous. The intrusion most likely represents a long-lived (>1 m.y.) reservoir replenished by small batches of magma of varying composition, as reflected in the variation of eruptive products from the Pine Canyon and Sierra Quemada

  1. Geothermal Systems of the Yellowstone Caldera Field Trip Guide

    SciTech Connect

    Foley, Duncan; Neilson, Dennis L.; Nichols, Clayton R.

    1980-09-08

    Geothermal studies are proceedings on two fronts in the West Yellowstone area. High-temperature resources for the generation of electricity are being sought in the Island Park area, and lower temperatures resources for direct applications, primarily space heating, are being explored for near the town of West Yellowstone. Potential electric geothermal development in the Island Park area has been the subject of widespread publicity over fears of damage to thermal features in Yellowstone Park. At the time of writing this guide, companies have applied for geothermal leases in the Island Park area, but these leases have not yet been granted by the US Forest Service. The Senate is now discussing a bill that would regulate geothermal development in Island Park; outcome of this debate will determine the course of action on the lease applications. The Island Park area was the site of two cycles of caldera activity, with major eruptions at 2.0 and 1.2 million years ago. The US Geological Survey estimates that 16,850 x 10{sup 18} joules of energy may remain in the system. Geothermal resources suitable for direct applications are being sought in the West Yellowstone vicinity by the Montana Bureau of Mines and Geology, under funding from the US Department of Energy. West Yellowstone has a mean annual temperature of 1-2 C. Research thus far suggests that basement rocks in the vicinity are at a depth of about 600 m and are probably similar to the rocks exposed north of Hebgen Lake, where Precambrian, Paleozoic and Mesozoic rocks have been mapped. A few sites with anomalously warm water have been identified near the town. Work is continuing on this project.

  2. Travel Time Distribution Modeling in the Valles Caldera, New Mexico

    NASA Astrophysics Data System (ADS)

    Broxton, P. D.; Troch, P. A.; Brooks, P. D.; Lyon, S. W.; Gustafson, J. R.; Veatch, W. C.

    2007-12-01

    Modeling the transit times of catchment waters is of paramount importance in hydrology. The distribution of the time it takes for individual water molecules to move through a hydrologic system (a.k.a., the travel time distribution) is a fundamental characterization of a catchment. Travel time distributions are affected by a variety of physical characteristics of catchments (e.g., vegetation type, degree of soil development) that depend on the amount of solar energy the catchment receives. These characteristics, therefore, can be considered a function of aspect. The goal of this research is to constrain travel time distributions on a series of eight radial mountain streams having different slope aspects on Redondo Peak, a resurgent dome in the center of the Valles Caldera, near Los Alamos, New Mexico. Redondo Peak is an excellent natural laboratory for this type of experiment because all aspects are represented on different sides of the mountain while the internal geology and climate are relatively consistent. To model the transit time distributions of each catchment, variations of chemical load of the snowpack, isotopic compositions of meltwater samples, and snowcover distribution data from closely related studies are coupled with periodic stream and precipitation samples that are analyzed for stable water isotopes content. Additional information comes from a network of temperature sensors to monitor the distribution of snowmelt and headwater stream discharge as well as a series of flumes to capture the flows from the streams. The travel time distributions determined in this project provide a bottom up approach to verify catchment-scale models.

  3. Vertical collapse origin of Las Cañadas caldera (Tenerife, Canary Islands) revealed by 3-D magnetotelluric inversion

    NASA Astrophysics Data System (ADS)

    Piña-Varas, P.; Ledo, J.; Queralt, P.; Marcuello, A.; Bellmunt, F.; Ogaya, X.; Pérez, N.; Rodriguez-Losada, J. A.

    2015-03-01

    Tenerife island geology is one of the most complexes of the Canaries archipelago. This complexity is evidenced by the existing controversy regarding the lateral or vertical collapse origin of the Las Cañadas caldera. The resistivity structure of the Las Cañadas caldera has been determined by the 3-D inversion of 188 broadband magnetotelluric data. The resistivity distribution obtained in the final model shows clear evidences of the presence of a vertical structure under the Teide, associated to the buried northern wall of the caldera. Additionally, the characteristics of the main resistivity structure, a ring-shaped low-resistivity body (<10 Ω m) interpreted as a hydrothermal clay alteration cap, would point out the presence of a handwall for the Icod Valley lateral landslide located under the Teide, but not in the southern caldera wall (current wall). All these support the vertical collapse hypothesis to explain the origin of the Las Cañadas caldera.

  4. Consequences of frictional melting and catastrophic dilation along caldera superfaults: Glencoe, Scotland

    NASA Astrophysics Data System (ADS)

    Clesham, Stephen; Kokelaar, Peter; Lavallee, Yan; Faulkner, Dan

    2014-05-01

    The Glencoe Caldera records complex piecemeal caldera collapse along superfaults with slip rates in sufficient to induce frictional melting. The deeply dissected volcano exposes outer fault segments with cm-scale bands of pseudotachylyte in contact with breccias, cataclasites and magmatic fault intrusions along the fault plane. Processes of frictional melting, cataclasis and intrusion were closely associated and the various materials show evidence for fluid-state mixing. At shallow depths, where the caldera faults dip outwards, rapid subsidence of the caldera footwall led to catastrophic dilation and the formation of free surfaces at low pressures. Decompressed hydrothermal systems were explosively excavated to form irregular voids behind the original fault surfaces. In such dilatant sections of the fault, frictional melts and then magma intrusions were fragmented and explosively transformed to froths or sprays that coated newly-formed void walls. We suggest that these processes are likely to have formed the lithic breccias with hydrothermally altered and thermally spalled clasts - common in caldera-related ignimbrites. Mineralogy and clast-size distribution analysis indicate that some pseudotachylytes formed virtually in-situ, from the (Dalradian) metamorphic basement psammites and quartzites, while others were apparently sourced at considerable depths. Lithic clasts and xenoliths within the fault intrusions and pseudotachylytes imply a granitic source, probably the Rannoch Moor pluton, which in turn suggests transport of frictional melt for at least several hundreds of metres up the caldera fault, conceivably as fluidized froth. Modelling and reproduction of pseudotachylyte using laboratory friction experiments are intended to investigate the conditions that generated these rocks, and to explore their mobility as melts and fragmented products, shedding light on the processes of friction in volcanic environments.

  5. Characterizing analogue caldera collapse with computerized X-ray micro-tomography

    NASA Astrophysics Data System (ADS)

    Poppe, Sam; Holohan, Eoghan; Boone, Matthieu; Pauwels, Elin; Cnudde, Veerle; Kervyn, Matthieu

    2013-04-01

    Analogue models in the past mainly explored caldera collapse structures by documenting 2D model cross-sections. Kinematic aspects and 3D structures of caldera collapse are less well understood, although they are essential to interpret recent field and monitoring data. We applied high resolution radiography and computerized X-ray micro-tomography (µCT) to image the deformation during analogue fluid withdrawal in small-scale caldera collapse models. The models test and highlight the possibilities and limitations of µCT-scanning to qualitatively image and quantitatively analyse deformation of analogue volcano-tectonic experiments. High resolution interval radiography sequences document '2.5D' surface and internal model geometry, and subsidence kinematics of a collapsing caldera block into an emptying fluid body in an unprecedented way. During the whole drainage process, all subsidence was bound by caldera ring faults. Subsidence was associated with dilatation of the analogue granular material within the collapsing column. The temporal subsidence rate pattern within the subsiding volume comprised three phases: 1) Upward ring fault propagation, 2) Rapid subsidence with the highest subsidence rates within the uppermost subsiding volume, 3) Relatively slower subsidence rates over the whole column with intermittent subsidence rate acceleration. Such acceleration did almost never affect the whole column. By using radiography sequences it is possible in a non-destructive manner to obtain a continuous observation of fault propagation, down sag mechanisms and the subsequent development of collapse structures. Multi-angle µCT scans of the collapse result allow for a full virtual 3D reconstruction of the model. This leads to an unprecedented 3D view on fault geometries. The developed method is a step towards the quantitative documentation of volcano-tectonic models that would render data interpretations immediately comparable to monitoring data available from recent

  6. Scientific core hole Valles caldera No. 2b (VC-2b), New Mexico

    SciTech Connect

    Garner, J.N.; Hulen, J.B.; Lysne, P.; Jacobson, R.; Goff, F.; Nielson, D.L.; Pisto, L.; Criswell, C.W.; Gribble, R.; Utah Univ. Research Inst., Salt Lake City, UT; Sandia National Labs., Albuquerque, NM; Los Alamos National Lab., NM; Utah Univ. Research Inst., Salt Lake City, UT; Tonto Drilling Services, Inc., Salt Lake City, UT; Los Alamo

    1989-01-01

    Research core hole was continuously cored to 1.762 km on the western flank of the caldera's resurgent dome in 1988. Bottom hole temperature is about 295{degree}C within Precambrian (1.5 Ga) quartz monzonite, deep within the liquid-dominated portions of the Sulphur Springs hydrothermal system. VC-2b may be the deepest, hottest, continuously cored hole in North America. Core recovery was 99.2%. The only major drilling problems encountered were when temperatures at the bit exceeded 225{degree}C below depths of about 1000 m. The result of these conditions was loss of viscosity and/or lubricity in the mud, apparently caused by breakdown of the high temperature polymers. Lithologies in caldera-fill indicate the drill site may be proximal to ignimbrite vents and that an intracaldera lake with temperatures approaching boiling formed soon after the caldera itself. Structural correlations between VC-2b and the 528-m-deep companion hole VC-2a indicate the earlier Toledo caldera (1.45 Ma; Otowi Member tuffs) and even older Lower Tuffs caldera experienced no structural resurgence similar to the 1.12 million year old Valles caldera. The hydrothermal system penetrated by these bores, consists of a shallow vapor-rich cap, which has evolved from an earlier 200{degree}C liquid-dominated system, overlying stacked, liquid-dominated zones up to about 300{degree}C. Geochemistry of mud returns collected during drilling suggests chloride-rich geothermal fluids were entering the bore and mixing with the drilling fluids in the fractured lower Paleozoic and Precambrian sections. 23 refs., 5 figs., 1 tab.

  7. Recrystallization and anatexis along the plutonic-volcanic contact of the Turkey Creek caldera, Arizona

    USGS Publications Warehouse

    du Bray, E.A.; Pallister, J.S.

    1999-01-01

    Unusual geologic and geochemical relations are preserved along the contact between intracaldera tuff and a resurgent intrusion within the 26.9 Ma Turkey Creek caldera of southeast Arizona. Thick intracaldera tuff is weakly argillically altered throughout, except in zones within several hundred meters of its contact with the resurgent intrusion, where the groundmass of the tuff has been variably converted to granophyre and unaltered sanidine phenocrysts are present. Dikes of similarly granophyric material originate at the tuff-resurgent intrusion contact and intrude overlying intracaldera megabreccia and tuff. Field relations indicate that the resurgent intrusion is a laccolith and that it caused local partial melting of adjacent intracaldera tuff. Geochemical and petrographic relations indicate that small volumes of partially melted intracaldera tuff assimilated and mixed with dacite of the resurgent intrusion along their contact, resulting in rocks that have petrographic and compositional characteristics transitional between those of tuff and dacite. Some of this variably contaminated, second-generation magma coalesced, was mobilized, and was intruded into overlying intracaldera rocks. Interpretation of the resurgent intrusion in the Turkey Creek and other calderas as intracaldera laccoliths suggests that intrusions of this type may be a common, but often unrecognized, feature of calderas. Development of granophyric and anatectic features such as those described here may be equally common in other calderas. The observations and previously undocumented processes described here can be applied to identification and interpretation of similarly enigmatic relations and rocks in other caldera systems. Integration of large-scale field mapping with detailed petrographic and chemical data has resulted in an understanding of otherwise intractable but petrologically important caldera-related features.

  8. Gas Chemistry of Submarine Hydrothermal Venting at Maug Caldera, Mariana Arc

    NASA Astrophysics Data System (ADS)

    Embley, R. W.; Lupton, J. E.; Butterfield, D. A.; Lilley, M. D.; Evans, L. J.; Olson, E. J.; Resing, J. A.; Buck, N.; Larson, B. I.; Young, C.

    2014-12-01

    Maug volcano consists of 3 islands that define the perimeter of a submerged caldera that was formed by an explosive eruption. The caldera reaches a depth of ~225 meters, and has a prominent central cone or pinnacle that ascends within 20 meters of the sea surface. Our exploration of Maug began in 2003, when a single hydrocast in the caldera detected a strong suspended particle and helium plume reaching a maximum of δ3He = 250% at ~180 meters depth, clearly indicating hydrothermal activity within the caldera. In 2004 we returned armed with the ROPOS ROV, and two ROPOS dives discovered and sampled low temperature (~4 °C) diffuse venting associated with bacterial mats on the NE flank of the central pinnacle at 145 m depth. Samples collected with titanium gas tight bottles were badly diluted with ambient seawater but allowed an estimate of end-member 3He/4He of 7.3 Ra. Four vertical casts lowered into the caldera in 2004 all had a strong 3He signal (δ3He = 190%) at 150-190 meters depth. A recent expedition in 2014 focused on the shallow (~10 m) gas venting along the caldera interior. Scuba divers were able to collect samples of the gas bubbles using evacuated SS bottles fitted with plastic funnels. The gas samples had a consistent ~170 ppm He, 8 ppmNe, 60% CO2, 40%N2, and 0.8% Ar, and an end-member 3He/4He ratio of 6.9 Ra. This 3He/4He ratio falls within the range for typical arc volcanoes. The rather high atmospheric component (N2, Ar, Ne) in these samples is not contamination but appears to be derived from subsurface exchange between the ascending CO2 bubbles and air saturated seawater. A single vertical cast in 2014 had a maximum δ3He = 55% at 140 m depth, much lower than in 2003 and 2004. This decrease is possibly due to recent flushing of the caldera by a storm event, or may reflect a decrease in the deep hydrothermal activity. This area of shallow CO2 venting in Maug caldera is of particular interest as a natural laboratory for studying the effects of ocean

  9. Spasmodic tremor and possible magma injection in long valley caldera, eastern california.

    PubMed

    Ryall, A; Ryall, F

    1983-03-25

    Intensive microearthquake swarms with the appearance of volcanic tremor have been observed in the southwest part of Long Valley caldera, southeastern California. This activity, possibly associated with magma injection, began 6 weeks after several strong (magnitude 6+) earthquakes in an area south of the caldera and has continued sporadically to the present time. The earthquake sequence and magmatic activity are part of a broad increase in tectonic activity in a 15,000-square-kilometer region surrounding the "White Mountains seismic gap," an area with high potential for the next major earthquake in the western Great Basin. PMID:17735195

  10. Reconstruction of the most recent volcanic eruptions from the Valles caldera, New Mexico

    NASA Astrophysics Data System (ADS)

    Wolff, J. A.; Brunstad, K. A.; Gardner, J. N.

    2011-01-01

    Products of the latest eruptions from the Valles caldera, New Mexico, consist of the El Cajete Pyroclastic Beds and Battleship Rock Ignimbrite, a sequence of pyroclastic fall and density current deposits erupted at ~ 55 ka, capped by the later Banco Bonito Flow erupted at ~ 40 ka, and collectively named the East Fork Member of the Valles Rhyolite. The stratigraphy of the East Fork Member has been the subject of conflicting interpretations in the past; a long-running investigation of short-lived exposures over a period of many years enables us to present a more complete event stratigraphy for these eruptions than has hitherto been possible. The volume of rhyolitic magma erupted during the 55 ka event may have been more than 10 km 3, and for the 40 ka event can be estimated with rather more confidence at 4 km 3. During the earlier event, plinian eruptions dispersed fallout pumice over much of the Valles caldera, the southern Jemez Mountains, and the Rio Grande rift. We infer a fallout thickness of several decimeters at the site of the city of Santa Fe, and significant ash fall in eastern New Mexico. In contrast, pyroclastic density currents were channeled within the caldera moat and southwestward into the head of Cañon de San Diego, the principal drainage from the caldera. Simultaneous (or rapidly alternating) pyroclastic fallout and density current activity characterized the ~ 55 ka event, with density currents becoming more frequent as the eruption progressed through two distinct stages separated by a brief hiatus. One early pyroclastic surge razed a forest in the southern caldera moat, in a similar manner to the initial blast of the May 18, 1980 eruption of Mt. St. Helens. Ignimbrite outflow from the caldera through the drainage notch may have been restricted in runout distance due to steep, rugged topography in this vicinity promoting mixing between flows and air, and the formation of phoenix clouds. Lavas erupted during both the ~ 55 and ~ 40 ka events were

  11. There's more than one way to build a caldera magma chamber: Evidence from volcanic-plutonic relationships at three faulted Rio-Grande-rift calderas

    NASA Astrophysics Data System (ADS)

    Zimmerer, M. J.; McIntosh, W. C.

    2011-12-01

    The temporal and chemical relationships of volcanic and plutonic rocks of the Questa (NM), Mt. Aetna (CO), and Organ caldera (NM) complexes were investigated to establish the origin of these silicic magmas. Rio Grande Rift faulting at these systems has exposed both intracaldera sequences and subvolcanic plutons. Ar/Ar and U/Pb ages reveal the timing of volcanic activity and pluton emplacement and cooling. We observe a link between ignimbrite zoning patterns and the temporal-chemical relationship of volcanic and plutonic rocks. The Questa caldera erupted the high-SiO2 peralkaline Amalia Tuff (AT) at 25.4 Ma. Volumetrically minor phases of two resurgent plutons and a ring dike are compositionally similar to the AT. The age of the ring dike (25.4 Ma) is indistinguishable to AT, suggesting that the peralkaline intrusions are nonerupted AT. The remaining pluton ages are 100 ka to 6.1 Ma younger than AT and are too young to be the AT residual crystal mush. The Mt. Princeton batholith and nested Mt. Aetna caldera are interpreted to be the sources for the 37.3 Ma, low-SiO2 rhyolitic Wall Mountain Tuff (WMT) and the 34.3 Ma, dacitic Badger Creek Tuff (BCT). U/Pb and Ar/Ar ages of Mt. Princeton batholith (36.5 to 35.1 Ma) indicate that it was emplaced and rapidly cooled during the interval between the WMT and BCT eruptions, and that any WMT age intrusions are now eroded. During the eruption of the BCT, the fully crystallized Mt. Princeton batholith collapsed into the Mt. Aetna caldera. Intrusions along the margins of the Mt. Aetna caldera are compositionally identical the BCT and contain zircons 100 to 500 ka older than the tuff, suggesting that the BCT magma chamber was incrementally emplaced prior to caldera eruption. The Organ caldera complex erupted three ignimbrites: a basal high-silica 36.5 Ma rhyolite, a middle intermediate-silica 36.2 Ma rhyolite, and an upper 36.0 Ma low-silica rhyolite. The intracaldera sequence is intruded by the Organ Needle pluton. U/Pb zircon

  12. Tensor CSAMT survey over the Sulphur Springs thermal area, Valles Caldera, New Mexico, U.S.A. Part 1: Implications for structure of the western caldera

    SciTech Connect

    Wannamaker, P.E.

    1997-03-01

    An extensive tensor controlled-source audiomagnetotelluric (CSAMT) survey has been carried out over the Sulphur Springs geothermal area, Valles Caldera, New Mexico. Forty-five sites were acquired using two crossed transmitter bipoles placed approximately 13 km south of the center of the survey. The soundings in the Sulphur Springs area were arranged in four profiles to cross major structural features. CSAMT and magnetotelluric (MT) data taken outside Valles Caldera were constrained by drill logs and imply resistive Bandelier Tuff, underlain by conductive Paleozoic sediments, and further underlain by resistive, primarily Precambrian crystalline rocks. Model cross-sections within the caldera were derived using 2-D parameterized inversion constrained by drilling, with layered-earth inversion for starting models. Southeast of the Sulphur Creek fault, the upper 200 m of the section are of relatively low resistivity and correspond to unconsolidated land-slide and debris flows. The Bandelier Tuff below exhibits higher but variable resistivities because of alteration controlled by local faulting. Beneath the Bandelier Tuff, the Paleozoic sedimentary layer is only moderately less resistive than it is outside the caldera, with the lowest values occurring northwest of Sulphur Creek. Its low resistivity per se does not necessarily represent a hydrothermal aquifer. The Sulphur Creek fault appears to be a locus of substantial change in structural relief; upthrow of stratigraphy and basement to its west appears to be about 400--500 m. A major normal fault down to the southeast is located under the topographic expression of Freelove Canyon, which is up to 1 km farther southeast than suggested by previous geologic sections. High resistivities possibly corresponding to a vapor zone in the upper 500 m near VC-2B and VC-2A are not consistent with the CSAMT data.

  13. Elastic and Transport Properties of Steam-Cured Pozzolanic-Lime Rock Composites Upon CO2 Injection

    NASA Astrophysics Data System (ADS)

    Emery, Dan; Vanorio, Tiziana

    2016-04-01

    Understanding the effect of pozzolanic ash-lime reactions on the rock physics properties of the resulting rock microstructure is important for monitoring unrest conditions in volcanic-hydrothermal systems as well as for devising concrete with enhanced performance. By mixing pozzolana ash with lime, the ancient Romans unwittingly incorporated these reactions in the production of their famous concrete. Recently, it has been discovered that a fiber-reinforced, concrete-like rock is forming naturally at depth of 1.5 km within the Campi Flegrei volcanic-hydrothermal systems due to upwelling lime-rich fluids permeating a pozzolana rich layer. This study aims to investigate possible physico-chemical conditions contributing to both enhance and undermine the properties of the subsurface rocks of volcanic-hydrothermal systems and, in turn, build upon those processes that the ancient Romans exploited to create their famous concrete. We prepared samples by mixing the pozzolana volcanic ash, slaked lime, aggregates of Neapolitan Yellow tuff, and seawater from Campi Flegrei in the same ratios as the ancient Romans. To mimic the conditions of the caldera, we used alkaline water from a well in the Campi Flegrei region rich in sulfate, bicarbonate, calcium, potassium, and magnesium ions. Yet, the samples were cured for 28 days in steam-rich environment to favor hydration and hence, enhancing the stability of calcium- alumino-silicate hydrates and setting strength of the rock samples. We measured baseline properties of porosity, permeability, P-wave velocity, and S-wave velocity of the samples as well as imaged the fibrous microstructure. P and S-wave velocities were used to derive bulk, shear, and Young's moduli. Subsequently, samples were injected with an aqueous carbon dioxide, CO2 (aq), solution and the changes in their microstructure and physical properties measured. Exposure of the concrete-like rock samples to CO2 -rich fluid lowers pH below 12.5, thus affecting the stability

  14. Elastic and transport properties of steam-cured pozzolanic-lime rock composites upon CO2 injection

    NASA Astrophysics Data System (ADS)

    Emery, Dan; Vanorio, Tiziana

    2016-04-01

    Understanding the relationship between pozzolanic ash-lime reactions and the rock physics properties of the resulting rock microstructure is important for monitoring unrest conditions in volcanic-hydrothermal systems as well as devising concrete with enhanced performance. By mixing pozzolanic ash with lime, the ancient Romans incorporated these reactions in the production of concrete. Recently, it has been discovered that a fiber-reinforced, concrete-like rock is forming naturally in the depths of the Campi Flegrei volcanic-hydrothermal systems (Vanorio and Kanitpanyacharoen, 2015). We investigate the physico-chemical conditions contributing to undermine or enhance the laboratory measured properties of the subsurface rocks of volcanic-hydrothermal systems and, in turn, build upon those processes that the ancient Romans unwittingly exploited to create their famous concrete. We prepared samples by mixing the pozzolana volcanic ash, slaked lime, aggregates of Neapolitan Yellow tuff, and seawater from Campi Flegrei in the same ratios as the ancient Romans. To mimic the conditions of the caldera, we used mineral seawater from a well in the Campi Flegrei region rich in sulfate, bicarbonate, calcium, potassium, and magnesium ions. The samples were cured by steam. We measured baseline properties of porosity, permeability, P-wave velocity, and S-wave velocity of the samples. P and S-wave velocities were used to derive bulk, shear, and Young's moduli. Subsequently, half of the samples were injected with CO2-rich aqueous solution and the changes in their microstructure and physical properties measured. One sample was subjected to rapid temperature changes to determine how porosity and permeability changed as a function of the number of thermal shocks. Exposure of CO2 to the concrete-like rock samples destabilized fibrous mineral forming and decreased the samples' ability to deform without breaking. We show that steam- and sulfur-alkaline- rich environments affect both

  15. The geothermal potential of the Campania volcanic district and new heat exchanger technologies for exploitation of highly urbanised areas.

    NASA Astrophysics Data System (ADS)

    Carlino, S.; Somma, R.; Troiano, A.; Di Giuseppe, M. G.; Troise, C.; De Natale, G.

    2012-04-01

    The geothermal research in Campania region (Italy), started since the 1930, and continued until the '80 by the SAFEN, ENEL and AGIP companies. Such exploration activity highlighted that most of the volcanic districts of the Campania Region have a very high geothermal gradient and heat flow. In particular, inside the Campi Flegrei caldera and at Ischia island the geothermal gradient measured inside the deep wells reaches temperatures above 100° C between few tens and few hundreds of metres of depth, while the heat flow varies between 120-160 mWm-2 at Agnano and Mofete (Campi Flegrei main drill sites) to more than 500 mWm-2 at Ischia island (south-western sector). A general review of the available literature data (temperature at depth, stratigraphic sections, logs etc.) of the deep wells (down to 3 km b.s.l.) allowed us to quantify the geothermal potential (thermal and electric) of such district. The geothermal potential is about 6 GWy for the Campi Flegrei (Mofete and S. Vito sectors) and 11 GWy for the Ischia island (south-western sector) showing a geothermal reservoir with water and vapour dominant respectively. This results in strong potential interest for economic exploitation of the geothermal resource, both in the range of low-medium enthalpy at few hundreds of meters depth and of high enthalpy at depths of 1-2 km. In this study we try to model the effectiveness of new technologies of boreholes heat exchangers, which would allow to avoid fluid withdrawal, then strongly decreasing the environmental impact. The proposed technology consists of a double-pipe placed in a borehole heat exchange that can work coupled with an ORC. The two pipes, one inside the other, are located in the well in order to transfer the thermal energy to the working fluid during the descent in the external pipe and then go back through the internal pipe properly isolated. We propose a complete design of the borehole heat exchangers. The design activity is performed on a theoretical basis

  16. Cytoskeletal F-actin polymerization from cytosolic G-actin occurs in the phagocytosing immunocytes of arthropods (Limulus polyphemus and Gromphadorhina portentosa): does [cAMP]i play any role?

    PubMed

    Gupta, A P; Campenot, E S

    1996-09-01

    Phagocytosis is a major defense reaction in arthropods and is accomplished by two blood cells (hemocytes), the granulocyte (GRs) and plasmatocytes (PLs), collectively called immunocytes. Immunocytes (principally the GRs) from two arthropods, Limulus polyphemus (horseshoe crab) and Gromphadorhina portentosa (Madagascar hissing cockroach) effectively phagocytose fluorescein isothiocyanate (FITC)-conjugated fluoresbrite microspheres (FITC-FM) and chicken (Gallus domesticus) erythrocytes within 1 hr of incubation. Although actin polymerization and changes in intracellular cAMP ([cAMP]i) levels occur during the early stages of phagocytosis in vertebrates, these two phenomena have not been studied in arthropod immunocytes. Using the DNase I inhibition assay, we found a decrease in cytosolic G-actin and an increase in the cytoskeletal F-actin in the phagocytosing immunocytes; the total actin in both resting and phagocytosing immunocytes remained constant. These results showed an 86% increase in F-actin in G. portentosa immunocytes and a 29% increase in those of L. polyphemus after 1 hr of initial incubation with FITC-FM. As in some vertebrates, the role of [cAMP]i in the early stages of phagocytosis in these two animals- and perhaps in arthropods in general-is variable; although we detected some negligible amounts of [cAMP]i (0.10-0.80 pmol/cell at different time intervals) in L. polyphemus immunocytes, it was inconclusive whether those in G. portentosa also contained [cAMP]i. Even in L. polyphemus, the difference in the amounts of [cAMP]i in resting and phagocytosing cells was insignificant (P > 0.05). It was also inconclusive whether [Ca2+]i and/or [Mg2+]i play any roles in the early stages of phagocytosis in the two arthropods in this study. These results suggest that the two phenomena (F-actin polymerization and levels of [cAMP]i in arthropods) are basically similar to those in vertebrate neutrophils and macrophages, which suggests that certain immunological

  17. A short review of our current understanding of the development of ring faults during collapse caldera formation

    NASA Astrophysics Data System (ADS)

    Geyer, Adelina; Marti, Joan

    2014-09-01

    The term collapse caldera refers to those volcanic depressions resulting from the sinking of the chamber roof due to the rapid withdrawal of magma during the course of an eruption. During the last three decades, collapse caldera dynamics has been the focus of attention of numerous, theoretical, numerical and experimental studies. Nonetheless, even if there is a tendency to go for a general and comprehensive caldera dynamics model, some key aspects remain unclear, controversial or completely unsolved. This is the case of ring fault nucleation points and propagation and dip direction. Since direct information on calderas’ deeper structure comes mainly from partially eroded calderas or few witnessed collapses, ring faults layout at depth remains still uncertain. This has generated a strong debate over the detailed internal fault and fracture configuration of a caldera collapse and, in more detail, how ring faults initiate and propagate. We offer here a very short description of the main results obtained by those analogue and theoretical/mathematical models applied to the study of collapse caldera formation. We place special attention on those observations related to the nucleation and propagation of the collapse-controlling ring faults. This summary is relevant to understand the current state-of-the-art of this topic and it should be taken under consideration in future works dealing with collapse caldera dynamics.

  18. The Oligocene Creede Formation, Colorado: The sedimentary record of a deep lake within a resurgent caldera

    SciTech Connect

    Larsen, D.; Smith, G.A. . Dept. of Earth and Planetary Sciences)

    1993-04-01

    The Oligocene Creede Formation is the sedimentary fill of the Creede caldera in the Tertiary San Juan volcanic field in southern Colorado. Scientific drill core and outcrop studies of Creede strata allow an evaluation of the post-collapse sedimentary environments present within a caldera. Although the Creede Formation is structurally disrupted, correlation of fallout tuffs in exposed strata to those in the cores has clarified stratigraphic relationships. Following ash-fallout from the caldera-forming eruption, up to 121 meters of coarse grained debris-flow strata and rockfall debris with interstratified basinward ephemeral lake deposits were deposited. The presence of pseudomorphs after ikaite and up-section increase in carbonate facies suggest that the lake water was somewhat alkaline and cold (near freezing), and evolved chemically with time. A late-stage drop in lake level combined with integration of basin-feeding drainages and decreased subsidence lead to basinward progradation of coarser deltaic and lacustrine fan deposits. Sedimentation patterns suggest that subsidence occurred largely in the northern half of the caldera, and decreased late in the lake's history allowing the basin to fill with sediment.

  19. Monitoring super-volcanoes: Geophysical and geochemical signals at Yellowstone and other large caldera systems

    USGS Publications Warehouse

    Lowenstern, J. B.; Smith, R.B.; Hill, D.P.

    2006-01-01

    Earth's largest calderas form as the ground collapses during immense volcanic eruptions, when hundreds to thousands of cubic kilometres of magma are explosively withdrawn from the Earth's crust over a period of days to weeks. Continuing long after such great eruptions, the resulting calderas often exhibit pronounced unrest, with frequent earthquakes, alternating uplift and subsidence of the ground, and considerable heat and mass flux. Because many active and extinct calderas show evidence for repetition of large eruptions, such systems demand detailed scientific study and monitoring. Two calderas in North America, Yellowstone (Wyoming) and Long Valley (California), are in areas of youthful tectonic complexity. Scientists strive to understand the signals generated when tectonic, volcanic and hydrothermal (hot ground water) processes intersect. One obstacle to accurate forecasting of large volcanic events is humanity's lack of familiarity with the signals leading up to the largest class of volcanic eruptions. Accordingly, it may be difficult to recognize the difference between smaller and larger eruptions. To prepare ourselves and society, scientists must scrutinize a spectrum of volcanic signals and assess the many factors contributing to unrest and toward diverse modes of eruption. ?? 2006 The Royal Society.

  20. Deformation of the Wineglass Welded Tuff and the timing of caldera collapse at Crater Lake, Oregon

    USGS Publications Warehouse

    Kamata, H.; Suzuki-Kamata, K.; Bacon, C.R.

    1993-01-01

    Four types of deformation occur in the Wineglass Welded Tuff on the northeast caldera rim of Crater Lake: (a) vertical tension fractures; (b) ooze-outs of fiamme: (c) squeeze-outs of fiamme; and (d) horizontal pull-apart structures. The three types of plastic deformation (b-d) developed in the lower part of the Wineglass Welded Tuff where degree of welding and density are maximum. Deformation originated from concentric normal faulting and landsliding as the caldera collapsed. The degree of deformation of the Wineglass Welded Tuff increases toward the northeast part of the caldera, where plastic deformation occurred more easily because of a higher emplacement temperature probably due to proximity to the vent. The probable glass transition temperature of the Wineglass Welded Tuff suggests that its emplacement temperature was ???750??C where the tuff is densely welded. Calculation of the conductive cooling history of the Wineglass Welded Tuff and the preclimactic Cleetwood (lava) flow under assumptions of a initially isothermal sheet and uniform properties suggests that (a) caldera collapse occurred a maximum of 9 days after emplacement of the Wineglass Welded Tuff, and that (b) the period between effusion of the Cleetwood (lava) flow and onset of the climactic eruption was <100 years. If cooling is controlled more by precipitation during quiescent periods than by conduction, these intervals must be shorter than the calculated times. ?? 1993.

  1. Wall-rock argillic alteration and uranium mineralization of the northwestern Strel'tsovka caldera

    NASA Astrophysics Data System (ADS)

    Andreeva, O. V.; Golovin, V. A.; Petrov, V. A.

    2010-02-01

    Alteration of rocks and localization of uranium mineralization in the northwestern Strel’tsovka caldera are exemplified in the Dal’nee deposit. In the main parameters of hydrothermal mineralization (temperature, pH, pressure, and composition of solution), the Dal’nee deposit differs from the deposits of the Strel’tsovka ore field located in the central part of the caldera. The localization of high-grade stratiform orebodies are interpreted in light of kinematic relations between steeply and gently dipping faults that formed in the tectonic setting of the NE-SW-trending, long-living, right-lateral, strike-slip faulting. The wide halos of argillic alteration and the structural control of uranium mineralization are caused by the fact that the deposit is located at the margin of the geological block, which has developed since the Late Triassic in a regime of extension (pull-apart) to form a depression, which is arranged en echelon relative to the main caldera and comparable to it in area. Currently, this depression is overlapped by sediments of the Sukhoi Urulyungui Basin. Such a structure markedly increases the probability of finding hidden uranium ores associated with low-temperature argillic alteration in the volcanosedimantary rocks and granitoid basement of the northwestern Strel’tsovka caldera.

  2. Isotope geochemistry of thermal and nonthermal waters in the Valles caldera, Jemez Mountains, northern New Mexico

    SciTech Connect

    Vuataz, F.D.; Goff, F.

    1986-02-10

    Over 100 stable isotope and 45 tritium analyses from thermal and nonthermal waters of the Jemez Mountains region, New Mexico, have been used to define the hydrodynamics of the Valles caldera (Baca) geothermal system and related geothermal fluids of the region. Evaluation of 36 cold meteoric waters yields an equation for the Jemez Mountains meteoric water line of deltaD = 8delta/sup 18/O+12, while further evaluation of nine cold meteoric waters yields an equation relating recharge elevation to deuterium content of E(meters) = -44.9 (deltaD)-1154. Based on the deuterium content of five Baca well waters (223/sup 0/--294/sup 0/C), the average recharge elevation of the Valles geothermal system ranges from 2530 to 2890 m. This range of elevations falls between the elevations of the lowest point of the caldera floor (2400 m) and the summit of the resurgent dome inside the caldera (3430 m). Thus stable isotopes indicate that the caldera depression probably serves as a recharge basin for the deep geothermal system. Although cold spring waters of the Jemez Mountains region consist of meteoric water, tritium analyses show that most of them contain water between 20 and 75 years old.

  3. Structure and stratigraphy beneath a young phreatic vent: South Inyo Crater, Long Valley caldera, California

    SciTech Connect

    Eichelberger, J.C.; Vogel, T.A.; Younker, L.W.; Dan Miller, C.; Heiken, G.H.; Wohletz, K.H.

    1988-11-10

    An 861-m-long hole has been cored on a slanted trajectory that passed directly beneath South Inyo Crater in the west moat of Long valley Caldera, California. The purpose of the hole was to investigate the magmatic behavior that led to surface deformation and phreatic activity during the 600-year-old eruption of the Inyo vent chain. The hole was sited 216 m southwest of the crater, passed beneath its center at a depth of 566 m, and terminated 79 m northeast of the crater center at a depth of 810 m. Metamorphic basement was encountered at a depth of 779 m. The volcanic and sedimentary sequence consists solely of post-Bishop Tuff caldera fill, including 319 m of moat basalt and 342 m of early rhyolite, and is nearly 900 m thinner than in a Unocal Corporation well 900 m to the southeast. Apparently, a major fault lies between the two holes and forms part of the western structural boundary of the caldera, 3--4 km inboard of its topographic boundary. Breccia zones that intrude the caldera fill were intersected at 12.0--9.3 m and 1.2--0.8 m SW and 8.5--25.1 m NE of the crater center.

  4. A three-dimensional gravity model of the geologic structure of Long Valley caldera

    SciTech Connect

    Carle, S.F.; Goldstein, N.E.

    1987-03-01

    Several attempts to define and interpret this anomaly have been made in the past using 2-D and 3-D models. None of the previous interpretations have yielded definitive results, but in fairness, the interpretation here has benefited from a larger gravity data base and more subsurface control than available to previous workers. All published 3-D models simplistically assumed constant density of fill. All 2-D models suffered from the inherent three-dimensionality of the complicated density structure of Long Valley caldera. In addition, previous interpreters have lacked access to geological data, such as well lithologies and density logs, seismic refraction interpretations, suface geology, and structural geology interpretations. The purpose of this study is to use all available gravity data and geological information to constrain a multi-unit, 3-D density model based on the geology of Long Valley caldera and its vicinity. Insights on the geologic structure of the caldera fill can help other geophysical interpretations in determining near-surface effects so that deeper structure may be resolved. With adequate control on the structure of the caldera fill, we are able to examine the gravity data for the presence of deeper density anomalies in the crust. 20 refs., 7 figs.

  5. Topographic modelling of caldera analogues using Structure from Motion - Multiview stereo-photogrammetry

    NASA Astrophysics Data System (ADS)

    Ulusoy, İnan; Aydın, Eda; Evren Çubukçu, H.

    2016-04-01

    Analogue caldera models have long been used in volcanology to investigate structural evolution of volcanoes during tumescence and collapse periods. Influence of tectonic forces on volcanic features are also in the scope of those experiments. As well as interior modelling of the caldera experiments, topographic modelling is essential for digital monitoring and quantification purposes. Topographic modelling of those sandbox models is possible using laser scanning techniques. Particle tracking using still images is another way to demonstrate and quantify the structure and movement during the experiment. The quantum leap in the digital photography and computation tools and ease of access to both, provides the use of a new modelling technique in various scales and applications in Geology. Although the roots are older, Structure from Motion - Multiview stereo-photogrammetry (SfM-MVS) is a relatively new technique for surface modelling via several high resolution photographs. We have used SfM-MVS to digitally model the elevation of the tumescence and collapse cycles in analogue caldera experiments. Several sandbox experiments have been modelled using SfM-MVS technique stage by stage during tumescence and collapse periods. It has been possible to evaluate the structural evolution of the collapse models. Additionally, using particle tracking via still images acquired during the experiments, we have modelled the superficial evolution of the caldera structure. SfM-MVS is an effective low budget method for modelling in decimetric scale down to millimetre/micrometre precision.

  6. Monitoring super-volcanoes: geophysical and geochemical signals at Yellowstone and other large caldera systems.

    PubMed

    Lowenstern, Jacob B; Smith, Robert B; Hill, David P

    2006-08-15

    Earth's largest calderas form as the ground collapses during immense volcanic eruptions, when hundreds to thousands of cubic kilometres of magma are explosively withdrawn from the Earth's crust over a period of days to weeks. Continuing long after such great eruptions, the resulting calderas often exhibit pronounced unrest, with frequent earthquakes, alternating uplift and subsidence of the ground, and considerable heat and mass flux. Because many active and extinct calderas show evidence for repetition of large eruptions, such systems demand detailed scientific study and monitoring. Two calderas in North America, Yellowstone (Wyoming) and Long Valley (California), are in areas of youthful tectonic complexity. Scientists strive to understand the signals generated when tectonic, volcanic and hydrothermal (hot ground water) processes intersect. One obstacle to accurate forecasting of large volcanic events is humanity's lack of familiarity with the signals leading up to the largest class of volcanic eruptions. Accordingly, it may be difficult to recognize the difference between smaller and larger eruptions. To prepare ourselves and society, scientists must scrutinize a spectrum of volcanic signals and assess the many factors contributing to unrest and toward diverse modes of eruption. PMID:16844648

  7. Galileo's Last Fly-Bys of Io: NIMS Observations of Loki, Tupan, and Emakong Calderas

    NASA Technical Reports Server (NTRS)

    Lopes, Rosaly M. C.; Kamp, L. W.; Davies, A. G.; Smythe, W. D.; Carlson, R. W.; Doute, S.; McEwen, A.; Turtle, E. P.; Leader, F.; Mehlman, R.

    2002-01-01

    NIMS results from the 2001 Galileo fly-bys of Io will be presented, focusing on three calderas that may contain lava lakes. Preliminary results from the January 2002 Io fly-by will be presented. Additional information is contained in the original extended abstract.

  8. Steady subsidence of a repeatedly erupting caldera through InSAR observations: Aso, Japan

    NASA Astrophysics Data System (ADS)

    Nobile, Adriano; Acocella, Valerio; Ruch, Joel; Aoki, Yosuke; Borgstrom, Sven; Siniscalchi, Valeria; Geshi, Nobuo

    2016-04-01

    The relation between unrest and eruption at calderas is still poorly understood. Aso caldera, Japan, shows minor episodic eruptions, mainly phreatic, associated with steady subsidence. We analyse the recent deformation of Aso using SAR images from 1993 to 2011 and compare this with the eruptive activity. Although the dataset suffers from limitations (e.g., atmospheric effects, coherence loss, low signal to noise ratio), we observe a steady subsidence signal from 1996 to 1998, that suggests an overall contraction of a magmatic source below the caldera centre, from 4.5 to 7 km depth. Because of the similar volumes of the contracting source and erupted material, we propose that the contraction may have been induced by the release of the magmatic fluids feeding the eruptions. If confirmed by further data, this hypothesis suggests that degassing processes play a crucial role in triggering minor eruptions within open conduit calderas, as at Aso. These features underline the importance of defining any eruptive potential also from deflating magmatic systems with open conduit.

  9. Hydrothermal fluid flow and deformation in large calderas: Inferences from numerical simulations

    USGS Publications Warehouse

    Hurwitz, S.; Christiansen, L.B.; Hsieh, P.A.

    2007-01-01

    Inflation and deflation of large calderas is traditionally interpreted as being induced by volume change of a discrete source embedded in an elastic or viscoelastic half-space, though it has also been suggested that hydrothermal fluids may play a role. To test the latter hypothesis, we carry out numerical simulations of hydrothermal fluid flow and poroelastic deformation in calderas by coupling two numerical codes: (1) TOUGH2 [Pruess et al., 1999], which simulates flow in porous or fractured media, and (2) BIOT2 [Hsieh, 1996], which simulates fluid flow and deformation in a linearly elastic porous medium. In the simulations, high-temperature water (350??C) is injected at variable rates into a cylinder (radius 50 km, height 3-5 km). A sensitivity analysis indicates that small differences in the values of permeability and its anisotropy, the depth and rate of hydrothermal injection, and the values of the shear modulus may lead to significant variations in the magnitude, rate, and geometry of ground surface displacement, or uplift. Some of the simulated uplift rates are similar to observed uplift rates in large calderas, suggesting that the injection of aqueous fluids into the shallow crust may explain some of the deformation observed in calderas.

  10. Structural controls on the emission of magmatic carbon dioxide gas, Long Valley Caldera, USA

    NASA Astrophysics Data System (ADS)

    Lucic, Gregor; Stix, John; Wing, Boswell

    2015-04-01

    We present a degassing study of Long Valley Caldera that explores the structural controls upon emissions of magmatic carbon dioxide gas. A total of 223 soil gas samples were collected and analyzed for stable carbon isotopes using a field-portable cavity ring-down spectrometer. This novel technique is flexible, accurate, and provides sampling feedback on a daily basis. Sampling sites included major and minor volcanic centers, regional throughgoing faults, caldera-related structures, zones of elevated seismicity, and zones of past and present hydrothermal activity. The classification of soil gases based on their δ13C and CO2 values reveals a mixing relationship among three end-members: atmospheric, biogenic, and magmatic. Signatures dominated by biogenic contributions (~4 vol %, -24‰) are found on the caldera floor, the interior of the resurgent dome, and areas associated with the Hilton Creek and Hartley Springs fault systems. With the introduction of the magmatic component (~100 vol %, -4.5‰), samples acquire mixing and hydrothermal signatures and are spatially associated with the central caldera and Mammoth Mountain. In particular, they are concentrated along the southern margin of the resurgent dome where the interplay between resurgence-related reverse faulting and a bend in the regional fault system has created a highly permeable fracture network, suitable for the formation of shallow hydrothermal systems. This contrasts with the south moat, where despite elevated seismicity, a thick sedimentary cover has formed an impermeable cap, inhibiting the ascent of fluids and gases to the surface.

  11. The first report of the aphids of the Valles Caldera National Preserve, New Mexico, USA

    Technology Transfer Automated Retrieval System (TEKTRAN)

    We report 50 species, belonging to 26 genera of aphids (Hemiptera: Aphididae), collected within and near the boundary of the Valles Caldera National Preserve in the Jemez Mountains of northern New Mexico, USA. Of these, 35 (70%) represent new distribution records for New Mexico. Plant genera/species...

  12. Theoretical Investigations into the Quantitative Mechanisms Underlying the Regulation of [cAMP]i, Membrane Excitability and [Ca(2+)]i during GLP-1 Stimulation in Pancreatic β Cells.

    PubMed

    Takeda, Yukari

    2016-01-01

      Upon elevation of plasma glucose concentration, pancreatic β-cells generate bursts of action potentials to induce cyclic changes in [Ca(2+)]i regulating insulin release. Glucose-dependent insulin secretion is synergistically enhanced by glucagon-like peptide-1 (GLP-1), which increases [cAMP]i and activates protein kinase A (PKA) and exchange protein activated by cAMP (Epac). The insulinotropic effect of GLP-1 is mediated, at least in part, by modulating multiple ion channels/transporters at the plasma membrane and ER through PKA- and EPAC-dependent mechanisms, which increase membrane excitability and intracellular Ca(2+) release. However, because of complex interactions between multiple cellular factors involved in the GLP-1 effects, quantitative aspects of the molecular/ionic mechanisms have not yet been determined. We thus performed simulation studies and mathematical analysis to investigate how GLP-1 signals control [cAMP]i and subsequently modify the bursting activities and Ca(2+) dynamics. First, a GLP-1 receptor signal transduction model was developed and introduced to our β-cells model. Secondly, modulatory effects of PKA/Epac on ion channels/transporters were incorporated based on experimental studies. Increases in the frequency and duration of the bursting activity observed during GLP-1 stimulation were well reconstructed by our model, and lead potential analysis quantitatively determined the functional role of each ion channel/transporter in modifying the burst pattern. Finally, an IP3R model was developed to reproduce GLP-1-induced Ca(2+) transients/oscillations. Instantaneous equilibrium analysis and bifurcation analysis also elucidated the quantitative mechanisms involved in generating IP3R-mediated Ca(2+) mobilization. The results of this theoretical analysis of the effects of GLP-1 on membrane excitability/Ca(2+) dynamics are discussed in this review. PMID:26935088

  13. Fluid-Rock Interaction in the Miocene Tejeda Caldera, Gran Canaria, Canary Islands

    NASA Astrophysics Data System (ADS)

    Donoghue, E.; Troll, V. R.; Harris, C.; Walter, T. R.; Pérez Torrado, F. J.

    2007-12-01

    Rhyolite-trachyte tuffs deposited within the Miocene Tejeda caldera (Mogán Group 14-13.3Ma) show evidence of severe fluid-rock interaction. The altered tuffs are restricted to a peripheral zone directly inside the caldera margin, and occur at four distinct horizons within the mid-upper Mogán ignimbrite succession. Upper-Mogán tuffs display pervasive intermediate argillic alteration (smectite+illite+zeolites+adularia) and silicification (microcrystalline quartz+amorphous silica), indicative of low-temperature (≤250°C) near-neutral pH conditions. Quartz+kaolinite+muscovite+chlorite+calcite alteration of mid-Mogán tuffs and breccias may reflect boiling of higher-temperature, acidic hydrothermal fluids at depth. Si+Na+K+Pb+Sr+Rb were highly mobile during fluid-rock interaction, whereas Ti+Zr+Nb were dominantly refractory. Altered intra-caldera tuffs (n=65) have higher δ18O values than equivalent unaltered extra-caldera ignimbrites, reflecting an overall low-temperature near-surface environment in which meteoric water (δD ca.-15‰, δ18O ca.-3‰) was the dominant fluid source. A decrease in δ18O from upper- to mid- Mogán altered tuffs is consistent with an increase in fluid temperature with depth. Unaltered ignimbrites have δD values of -110 to -168‰ (n=6) and ≤0.2wt% H2O, indicative of Rayleigh-type H2O-exsolution. Altered tuffs have δD values of -52 to -117‰ (n=75) and up to 4wt% H2O, reflecting interaction with steam (δD\\ll-15‰) or an evolved low-δD fluid. Apparently unaltered ignimbrites between altered horizons (n=13), and shield basalts directly outside the caldera margin (n=6), have elevated δD and H2O values relative to equivalent unaltered rocks, indicative of minor alteration. Supported by numerical modelling, our Gran Canaria data reflect an intrusion-related, structurally controlled epithermal system, in which fluids and/or vapours migrated through intra-caldera tuffs via channelised, porous flow. This study may help to unravel the

  14. Evidence from cosmic-ray exposure dating based on 36Cl for the pre-Minoan caldera on Santorini, Greece

    NASA Astrophysics Data System (ADS)

    Athanassas, Constantin; Bourlès, Didier; Braucher, Regis; Druitt, Tim; Nomikou, Paraskevi; Léanni, Laetitia

    2016-04-01

    The physiography of Santorini prior to the Minoan (Late Bronze Age) eruption (17th century BCE) is of great archaeological interest, given the importance of Santorini as a commercial centre and port in the Minoan empire. However, the paleogeography of the pre-Minoan caldera has been a point of controversy: Heiken and McCoy (1984) advocated the existence, in the southern part of the present-day caldera, of a pre-existing caldera formed during the 172 ka Lower Pumice eruption, whereas Druitt and Francaviglia (1992), based on the presence of in situ plinian pumice from the Minoan eruption adhering to the modern cliff, conceived the pre-Minoan (22 ka) caldera as having occupied much of the northern basin of the present-day caldera. With the goal of settling the debate we performed cosmic ray exposure dating employing in situ-produced cosmogenic 36Cl to date different generations of caldera cliffs at Santorini, and hence to identify those cliffs predating the Minoan eruption. Our methodology involved the determination of the in situ-produced cosmogenic 36Cl in basaltic and andesitic rocks cropping out in the cliffs. The samples returned 36Cl CRE ages consistent with previously published field mapping of cliff populations based on geomorphological and stratigraphic arguments (Druitt and Francaviglia 1992), suggesting that much of the present cliff line of northern Santorini predated the Minoan eruption, or was superficially modified by landslips and rockfalls during that eruption. The 36Cl CRE ages enable us to better define the paleogeography of the pre-Minoan caldera. References [1] Druitt, T. H. and Francaviglia, V.1992. Caldera formation on Santorini and the physiography of the islands in the Late Bronze Age. Bulletin of Volcanology 54, 484-493. [2] Heiken G and McCoy F (1984) Caldera development during the Minoan eruption, Thira, Cyclades, Greece. Journal of Geophysical Research: 89 (B10), 8841-8862.

  15. Nonlinear teleseismic tomography at Long Valley caldera, using three-dimensional minimum travel time ray tracing

    SciTech Connect

    Weiland, C.M.; Steck, L.K.; Dawson, P.B.

    1995-10-10

    The authors explore the impact of three-dimensional minimum travel time ray tracing on nonlinear teleseismic inversion. This problem has particular significance when trying to image strongly contrasting low-velocity bodies, such as magma chambers, because strongly refracted/and/or diffracted rays may precede the direct P wave arrival traditionally used in straight-ray seismic tomography. They use a simplex-based ray tracer to compute the three-dimensional, minimum travel time ray paths and employ an interative technique to cope with nonlinearity. Results from synthetic data show that their algorithm results in better model reconstructions compared with traditional straight-ray inversions. The authors reexamine the teleseismic data collected at Long Valley caldera by the U.S. Geological Survey. The most prominent feature of their result is a 25-30% low-velocity zone centered at 11.5 km depth beneath the northwestern quandrant of the caldera. Beneath this at a depth of 24.5 km is a more diffuse 15% low-velocity zone. In general, the low velocities tend to deepen to the south and east. The authors interpret the shallow feature to be the residual Long Valley caldera magma chamber, while the deeper feature may represent basaltic magmas ponded in the midcrust. The deeper position of the prominent low-velocity region in comparison to earlier tomographic images is a result of using three-dimensional rays rather than straight rays in the ray tracing. The magnitude of the low-velocity anomaly is a factor of {approximately}3 times larger than earlier models from linear arrival time inversions and is consistent with models based on observations of ray bending at sites within the caldera. These results imply the presence of anywhere from 7 to 100% partial melt beneath the caldera. 40 refs., 1 fig., 1 tab.

  16. Crustal-scale perspective on the rapid development of Oligocene silicic calderas and related underlying plutonic systems, western Nevada USA

    NASA Astrophysics Data System (ADS)

    Colgan, J. P.; John, D. A.; Henry, C.; Watts, K. E.

    2015-12-01

    Geologic mapping, U-Pb zircon ages, and 40Ar/39Ar sanidine ages document the timing and extent of Oligocene magmatism in the southern Stillwater Range and Clan Alpine Mountains of western Nevada, where Miocene extension has exposed five nested silicic calderas and related granitic plutons to crustal depths locally ≥9 km. The ≤29.4-28.8 Ma Job Canyon caldera in the Stillwater Range is filled with ~4 km of intracaldera tuff and lava flows; the 28.4 Ma IXL pluton intrudes intracaldera tuff and extends to ≥9 km depth. The 29 Ma Deep Canyon caldera covers ~250 km2 of the Clan Alpine Mountains, but only the upper ~1 km is exposed. The ≤26.0-25.2 Ma Poco Canyon caldera in the Stillwater Range is filled with two distinct intracaldera tuffs totaling 4.5 km thick, underlain by the 24.8 Ma Freeman Creek pluton exposed to depths ≥8 km. The small 25.3 Ma Louderback Mountains caldera in the SW Clan Alpine Mountains is filled with ~600 m of intracaldera tuff deposited on Oligocene rhyolite lava flows. The 25.1 Ma Elevenmile Canyon caldera spans ~1600 km2 in the Stillwater Range, Clan Alpine Mountains, and Desatoya Mountains, where it overlaps or cross cuts older calderas. Its total volume is ≥2500 km3, mostly consisting of the 1-4 km thick tuff of Elevenmile Canyon. 24.9-25.5 Ma silicic intrusive rocks underlie the Louderback Mountains and Elevenmile Canyon calderas to depths ≥6-8 km, locally surrounding septa of basement rock and older Oligocene igneous rocks. Two magmatic pulses, each lasting ~1 m.y. and associated with the 29 and 25 Ma caldera complexes, replaced almost the entire Mesozoic upper crust with Oligocene intrusive and extrusive rock to depths ≥9 km over a 1500 km2 area (pre-extension). Magma emplacement was most likely accommodated by downward transfer of country rocks and accompanied by isostatic surface uplift. If other Great Basin calderas are similar, the dense concentration of shallowly exposed calderas in central Nevada may be underlain by a

  17. 4D volcano gravimetry

    USGS Publications Warehouse

    Battaglia, Maurizio; Gottsmann, J.; Carbone, D.; Fernandez, J.

    2008-01-01

    Time-dependent gravimetric measurements can detect subsurface processes long before magma flow leads to earthquakes or other eruption precursors. The ability of gravity measurements to detect subsurface mass flow is greatly enhanced if gravity measurements are analyzed and modeled with ground-deformation data. Obtaining the maximum information from microgravity studies requires careful evaluation of the layout of network benchmarks, the gravity environmental signal, and the coupling between gravity changes and crustal deformation. When changes in the system under study are fast (hours to weeks), as in hydrothermal systems and restless volcanoes, continuous gravity observations at selected sites can help to capture many details of the dynamics of the intrusive sources. Despite the instrumental effects, mainly caused by atmospheric temperature, results from monitoring at Mt. Etna volcano show that continuous measurements are a powerful tool for monitoring and studying volcanoes.Several analytical and numerical mathematical models can beused to fit gravity and deformation data. Analytical models offer a closed-form description of the volcanic source. In principle, this allows one to readily infer the relative importance of the source parameters. In active volcanic sites such as Long Valley caldera (California, U.S.A.) and Campi Flegrei (Italy), careful use of analytical models and high-quality data sets has produced good results. However, the simplifications that make analytical models tractable might result in misleading volcanological inter-pretations, particularly when the real crust surrounding the source is far from the homogeneous/ isotropic assumption. Using numerical models allows consideration of more realistic descriptions of the sources and of the crust where they are located (e.g., vertical and lateral mechanical discontinuities, complex source geometries, and topography). Applications at Teide volcano (Tenerife) and Campi Flegrei demonstrate the

  18. New constraints on the pyroclastic eruptive history of the Campanian volcanic Plain (Italy)

    USGS Publications Warehouse

    de Vivo, B.; Rolandi, G.; Gans, P.B.; Calvert, A.; Bohrson, W.A.; Spera, F.J.; Belkin, H.E.

    2001-01-01

    The ???150 km3 (DRE) trachytic Campanian Ignimbrite, which is situated north-west of Naples, Italy, is one of the largest eruptions in the Mediterranean region in the last 200 ky. Despite centuries of investigation, the age and eruptive history of the Campanian Ignimbrite is still debated, as is the chronology of other significant volcanic events of the Campanian Plain within the last 200-300 ky. New 40Ar/39Ar geochronology defines the age of the Campanian Ignimbrite at 39.28 ?? 0.11 ka, about 2 ky older than the previous best estimate. Based on the distribution of the Campanian Ignimbrite and associated uppermost proximal lithic and polyclastic breccias, we suggest that the Campanian Ignimbrite magma was emitted from fissures activated along neotectonic Apennine faults rather than from ring fractures defining a Campi Flegrei caldera. Significantly, new volcanological, geochronological, and geochemical data distinguish previously unrecognized ignimbrite deposits in the Campanian Plain, accurately dated between 157 and 205 ka. These ages, coupled with a xenocrystic sanidine component >315 ka, extend the volcanic history of this region by over 200 ky. Recent work also identifies a pyroclastic deposit, dated at 18.0 ka, outside of the topographic Campi Flegrei basin, expanding the spatial distribution of post-Campanian Ignimbrite deposits. These new discoveries emphasize the importance of continued investigation of the ages, distribution, volumes, and eruption dynamics of volcanic events associated with the Campanian Plain. Such information is critical for accurate assessment of the volcanic hazards associated with potentially large-volume explosive eruptions in close proximity to the densely populated Neapolitan region.

  19. Geothermal hydrology of Valles Caldera and the southwestern Jemez Mountains, New Mexico

    USGS Publications Warehouse

    Trainer, Frank W.; Rogers, Robert J.; Sorey, M.L.

    2000-01-01

    The Jemez Mountains in north-central New Mexico are volcanic in origin and have a large central caldera known as Valles Caldera. The mountains contain the Valles geothermal system, which was investigated during 1970-82 as a source of geothermal energy. This report describes the geothermal hydrology of the Jemez Mountains and presents results of an earlier 1972-75 U.S. Geological Survey study of the area in light of more recent information. Several distinct types of thermal and nonthermal ground water are recognized in the Jemez Mountains. Two types of near-surface thermal water are in the caldera: thermal meteoric water and acid sulfate water. The principal reservoir of geothermal fluids is at depth under the central and western parts of the caldera. Nonthermal ground water in Valles Caldera occurs in diverse perched aquifers and deeper valley-fill aquifers. The geothermal reservoir is recharged by meteorically derived water that moves downward from the aquifers in the caldera fill to depths of 6,500 feet or more and at temperatures reaching about 330 degrees Celsius. The heated geothermal water rises convectively to depths of 2,000 feet or less and mixes with other ground water as it flows away from the geothermal reservoir. A vapor zone containing steam, carbon dioxide, and other gases exists above parts of the liquid-dominated geothermal zone. Two subsystems are generally recognized within the larger geothermal system: the Redondo Creek subsystem and the Sulphur Creek subsystem. The permeability in the Redondo Creek subsystem is controlled by stratigraphy and fault-related structures. Most of the permeability is in the high-angle, normal faults and associated fractures that form the Redondo Creek Graben. Faults and related fractures control the flow of thermal fluids in the subsystem, which is bounded by high-angle faults. The Redondo Creek subsystem has been more extensively studied than other parts of the system. The Sulphur Springs subsystem is not as well

  20. Volcano geodesy: The search for magma reservoirs and the formation of eruptive vents

    USGS Publications Warehouse

    Dvorak, J.J.; Dzurisin, D.

    1997-01-01

    Routine geodetic measurements are made at only a few dozen of the world's 600 or so active volcanoes, even though these measurements have proven to be a reliable precursor of eruptions. The pattern and rate of surface displacement reveal the depth and rate of pressure increase within shallow magma reservoirs. This process has been demonstrated clearly at Kilauea and Mauna Loa, Hawaii; Long Valley caldera, California; Campi Flegrei caldera, Italy; Rabaul caldera, Papua New Guinea; and Aira caldera and nearby Sakurajima, Japan. Slower and lesser amounts of surface displacement at Yellowstone caldera, Wyoming, are attributed to changes in a hydrothermal system that overlies a crustal magma body. The vertical and horizontal dimensions of eruptive fissures, as well as the amount of widening, have been determined at Kilauea, Hawaii; Etna, Italy; Tolbachik, Kamchatka; Krafla, Iceland; and Asal-Ghoubbet, Djibouti, the last a segment of the East Africa Rift Zone. Continuously recording instruments, such as tiltmeters, extensometers, and dilatometers, have recorded horizontal and upward growth of eruptive fissures, which grew at rates of hundreds of meters per hour, at Kilauea; Izu-Oshima, Japan; Teishi Knoll seamount, Japan; and Piton de la Fournaise, Re??union Island. In addition, such instruments have recorded the hour or less of slight ground movement that preceded small explosive eruptions at Sakurajima and presumed sudden gas emissions at Galeras, Colombia. The use of satellite geodesy, in particular the Global Positioning System, offers the possibility of revealing changes in surface strain both local to a volcano and over a broad region that includes the volcano.

  1. Understanding the link between circumferential dikes and eruptive fissures around calderas based on numerical and analog models

    NASA Astrophysics Data System (ADS)

    Corbi, Fabio; Rivalta, Eleonora; Pinel, Virginie; Maccaferri, Francesco; Acocella, Valerio

    2016-06-01

    Active calderas are seldom associated with circumferential eruptive fissures, but eroded magmatic complexes reveal widespread circumferential dikes. This suggests that, while the conditions to emplace circumferential dikes are easily met, mechanisms must prevent them from reaching the surface. We explain this discrepancy with experiments of air injection into gelatin shaped as a volcano with caldera. Analog dikes show variable deflection, depending on the competition between overpressure, Pe, and topographic unloading, Pl; when Pl/Pe = 4.8-5.3, the dikes propagate orthogonal to the least compressive stress. Due to the unloading, they become circumferential and stall below the caldera rim; buoyancy is fundamental for the further rise and circumferential fissure development. Numerical models quantitatively constrain the stress orientation within the gelatin, explaining the observed circumferential dikes. Our results explain how dikes propagate below the rim of felsic and mafic calderas, but only in the latter they are prone to feed circumferential fissures.

  2. Geothermal data for 95 thermal and nonthermal waters of the Valles Caldera - southern Jemez Mountains region, New Mexico

    SciTech Connect

    Goff, F.; McCormick, Trujillo, P.E. Jr.; Counce, D.; Grigsby, C.O.

    1982-05-01

    Field, chemical, and isotopic data for 95 thermal and nonthermal waters of the southern Jemez Mountains, New Mexico are presented. This region includes all thermal and mineral waters associated with Valles Caldera and many of those located near the Nacimiento Uplift, near San Ysidro. Waters of the region can be categorized into five general types: (1) surface and near surface meteoric waters; (2) acid-sulfate waters (Valles Caldera); (3) thermal meteoric waters (Valles Caldera); (4) deep geothermal and derivative waters (Valles Caldera); and (5) mineralized waters near San Ysidro. Some waters display chemical and isotopic characteristics intermediate between the types listed. The object of the data is to help interpret geothermal potential of the Jemez Mountains region and to provide background data for investigating problems in hydrology, structural geology, hydrothermal alterations, and hydrothermal solution chemistry.

  3. Hydrogeochemical data for thermal and nonthermal waters and gases of the Valles Caldera- southern Jemez Mountains region, New Mexico

    SciTech Connect

    Shevenell, L.; Goff, F.; Vuataz, F.; Trujillo, P.E. Jr.; Counce, D.; Janik, C.J.; Evans, W.

    1987-03-01

    This report presents field, chemical, gas, and isotopic data for thermal and nonthermal waters of the southern Jemez Mountains, New Mexico. This region includes all thermal and mineral waters associated with Valles Caldera and many of those located near the Nacimiento Uplift, north of San Ysidro. Waters of the region can be categorized into five general types: (1) surface and near-surface meteoric waters; (2) acid-sulfate waters at Sulphur Springs (Valles Caldera); (3) thermal meteoric waters in the ring fracture zone (Valles Caldera); (4) deep geothermal waters of the Baca geothermal field and derivative waters in the Soda Dam and Jemez Springs area (Valles Caldera); and (5) mineralized waters near San Ysidro. Some waters display chemical and isotopic characteristics intermediate between the types listed. Data in this report will help in interpreting the geothermal potential of the Jemez Mountains region and will provide background for investigating problems in hydrology, structural geology, hydrothermal alterations, and hydrothermal solution chemistry.

  4. Probing the source and timing of rejuvenation and hybridization in post-caldera rhyolite magmas at Yellowstone Caldera

    NASA Astrophysics Data System (ADS)

    Till, C.; Vazquez, J. A.; Boyce, J. W.; Stelton, M. E.

    2013-12-01

    We find petrographic, isotopic and geochemical evidence for rejuvenation and recycling of subvolcanic intrusions within low δ18O intracaldera rhyolite lavas erupted following the formation of Yellowstone Caldera. In order to resolve the timing and compositional end-members involved in rejuvenation and hybridization of Yellowstone's subvolcanic magma reservoir, we have analyzed the Pb isotopic composition of clinopyroxene and sanidine phenocrysts and performed U-Pb dating of zircons from the South Biscuit Basin (SBB) and Scaup Lake (SCL) rhyolite lava flows. Both SBB and SCL erupted ca. 260 ka based on indistinguishable 40Ar/39Ar ages [1,2] and represent a renewed episode of postcaldera volcanism after a hiatus of ~200 kyr. Zoned phenocrysts of quartz, clinopyroxene, orthopyroxene, plagioclase, and sanidine and accessory zircon and Fe-Ti oxides characterize both SBB and SCL. SCL and SBB clinopyroxene have identical compositions and core-to-rim zoning patterns in Fe, Mg, and trace elements and commonly exhibit exsolution lamellae in their cores, suggesting that subsolidus conditions were attained during the early evolution of these rhyolites. The exsolution-bearing cores are mantled by a zone of relatively high Mg/Fe and low HREE & Rb, which is in turn overgrown by a rim with slightly lower Mg/Fe, and higher HREE & Rb. This zoning pattern suggests rejuvenation of subsolidus rhyolite by the influx of at least two less evolved, hotter silicic magmas. Diffusion modeling of Fe-Mg concentration profiles in clinopyroxene suggests that these events occurred on the order of 103 yrs prior to eruption. To identify the source of the rejuvenated rhyolite and delimit intra-grain variability, we analyzed the Pb-isotopic compositions of the SBB and SCL clinopyroxene zones via LA-MC-ICPMS. The different zones within SBB and SCL clinopyroxene yield indistinguishable Pb-isotope compositions with 208Pb/206Pb=2.165-2.185 and 207Pb/206Pb=0.882-0.890, which matches the Pb

  5. Conductive heat flux in VC-1 and the thermal regime of Valles Caldera, Jemez Mountains, New Mexico

    NASA Astrophysics Data System (ADS)

    Sass, J. H.; Morgan, Paul

    1988-06-01

    Over 5% of heat in the western United States is lost through Quaternary silicic volcanic centers, including the Valles caldera in north central New Mexico. These centers are the sites of major hydrothermal activity and upper crustal metamorphism, metasomatism, and mineralization, producing associated geothermal resources. We present new heat flow data from Valles caldera core hole 1 (VC-1), drilled in the southwestern margin of the Valles caldera. Thermal conductivities were measured on 55 segments of core from VC-1, waxed and wrapped to preserve fluids. These values were combined with temperature gradient data to calculate heat flow. Above 335 m, which is probably unsaturated, heat flow is 247±16 mW m-2. The only deep temperature information available is from an uncalibrated commercial log made 19 months after drilling. Gradients, derived from uncalibrated temperature logs, and conductivities are inversely correlated between 335 and 737 m, indicating a conductive thermal regime, and component heat fluxes over three depth intervals (335-539 m, 549-628 m, and 628-737 m) are in excellent agreement with each other with an average of 504±15 mW m-2. Temperature logs to 518 m depth with well-calibrated temperature sensors result in a revised heat flow of 463±15 mW m. We use shallow thermal gradient data from 75 other sites in and around the caldera to interpret the thermal regime at the VC-1 site. A critical review of published thermal conductivity data from the Valles caldera yields an average thermal conductivity of ≥1 W m-1 K-1 for the near-surface tuffaceous material, and we assume that shallow gradient values (°C km-1) are approximately numerically equal to heat flow (mW m-2). Heat loss from the caldera is asymmetrically distributed, with higher values (400 mW m-2 or higher) concentrated in the west-southwestern quadrant of the caldera. This quadrant also contains the main drainage from the caldera and the youngest volcanism associated with the caldera. We

  6. 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

  7. Evolution of the Creede Caldera and its relation to mineralization in the Creede mining district, Colorado

    USGS Publications Warehouse

    Barton, Paul B.; Rye, Robert O.; Bethke, Philip M.

    2000-01-01

    At 25 Ma a major epithermal silver and base metal deposit formed in rhyolitic welded tuff near Creede, Colorado. Nearly 24000 metric tons of silver, appreciable lead, and small amounts of zinc, copper, and gold, have been produced from large, crustified veins under Bachelor and Bulldog Mountains north and northwest of Creede. Prior geologic, hydrologic, and stable-isotope studies showed that ore deposition was associated with the mixing and boiling of waters from diverse sources and suggester that a critical part of the ore-forming fluid may have originated within the ancient lake and sediments of the lacustrine Creede Formation that filled the Creede caldera. Two drill holes that sampled the heretofore hidden lower half of the Creede Formation are the focus of this book. The Creede caldera formed at 26.9 Ma within a high constructional plateau of silicic ashflows that covered and were sporadically interlayed with, intermediate lavas and lahars from large stratovolcanoes. The Creede caldera lake had an inflow evaporation balance that did not permit rapid filling to create a brim-full deep lake. Thus salts were evaporatively concentrated; but, with the exception of possible gypsum, no evaporite minerals preserved. Cool springs deposited travertine as mounds and contributed to limestone interlaminations within the sediment. The lake bottom was anoxic, and bacterial reduction of sulfate led to extreme sulfur isotopic fractionation in diagenetic pyrite. The caldera gradually resurged, converting the initial equant lake into an arcuate moat. Resurgent doming, alluvial fans, lacustrine sediments, ashfalls, and lava domes displaced water, lifted the lake so that it overlapped what later became the southern edge of the mineralized are, and eventually filled the basin. At 25.1 Ma an unseen pluton intruded beneath the northen part of the Creede district and created a convecting olume that drew in brine from the Creede caldera fill, meteotic water from highlands to the north

  8. Aeromagnetic evidence for a volcanic caldera(?) complex beneath the divide of the West Antarctic Ice Sheet

    USGS Publications Warehouse

    Behrendt, John C.; Finn, C.A.; Blankenship, D.; Bell, R.E.

    1998-01-01

    A 1995-96 aeromagnetic survey over part of the Sinuous Ridge (SR) beneath the West Antarctic Ice Sheet (WAIS) divide shows a 70-km diameter circular pattern of 400-1200-nT anomalies suggesting one of the largest volcanic caldera(?) complexes on earth. Radar-ice-sounding (RIS) shows the northern part of this pattern overlies the SR, and extends south over the Bentley Subglacial Trench (BST). Modeled sources of all but one the caldera(?) anomalies are at the base of <1-2-km thick ice and their volcanic edifices have been glacially removed. The exception is a 700-m high, 15-km wide 'volcano' producing an 800-nT anomaly over the BST. 'Intrusion' of this 'volcano' beneath 3 km of ice probably resulted in pillow basalt rather than easily removed hyaloclastite erupted beneath thinner ice. The background area (-300 to -500-nT) surrounding the caldera(?) is possibly caused by a shallow Curie isotherm. We suggest uplift of the SR forced the advance of the WAIS.A 1995-96 aeromagnetic survey over part of the Sinuous Ridge (SR) beneath the West Antarctic Ice Sheet (WAIS) divide shows a 70-km diameter circular pattern of 400-1200-nT anomalies suggesting one of the largest volcanic caldera(?) complexes on earth. Radar-ice-sounding (RIS) shows the northern part of this pattern overlies the SR, and extends south over the Bentley Subglacial Trench (BST). Modeled sources of all but one the caldera(?) anomalies are at the base of < 1-2-km thick ice and their volcanic edifices have been glacially removed. The exception is a 700-m high, 15-km wide 'volcano' producing an 800-nT anomaly over the BST. 'Intrusion' of this 'volcano' beneath 3 km of ice probably resulted in pillow basalt rather than easily removed hyaloclastite erupted beneath thinner ice. The background area (-300 to -500-nT) surrounding the caldera(?) is possibly caused by a shallow Curie isotherm. We suggest uplift of the SR forced the advance of the WAIS.

  9. A geological and geophysical appraisal of the Baca geothermal field, Valles Caldera, New Mexico

    NASA Astrophysics Data System (ADS)

    Wilt, Michael; Vonder Haar, Stephen

    1986-03-01

    The Baca location #1 geothermal field is located in north-central New Mexico within the western half of the Plio-Pleistocene Valles Caldera. Steam and hot water are produced primarily from the northeast-trending Redondo Creek graben, where downhole temperatures exceed 260°C at depths of less than 2 km. Stratigraphically the reservoir region can be described as a five-layer sequence that includes Tertiary and Quaternary volcanic rocks, and Mesozoic and Tertiary sediments overlying Precambrian granitic basement. Production is mainly controlled by fractures and faults that are ultimately related to activity in the Rio Grande Rift system. Geophysically, the caldera is characterized by a gravity minimum and a resistivity low in its western half. A 40-mgal gravity minimum over the caldera is due mostly to the relatively low-density volcanics and sediments that fill the caldera and probably bears no relation to deep-seated magmatic sources. Two-dimensional gravity modeling indicates that the depth to Precambrian basement in Redondo Canyon is probably at least 3 km and may exceed 5 km in eastern parts of the caldera. Telluric and magnetotelluric surveys have shown that the reservoir region is associated with low resistivity and that a deep low-resistivity zone correlates well with the depth of the primary reservoir inferred from well data. Telluric and magnetotelluric data have also identified possible fault zones in the eastern and western sections of the production region that may form boundaries to the Redondo Creek reservoir. These data also suggest that the reservoir region is located at the intersection of lineaments that trend north-south and northeast-southwest. Magnetotelluric results indicate deep low resistivity at the western edge of the caldera which may be associated with deep hot fluids. On the basis of geophysical and well data, we make three estimates of reservoir dimensions. The estimates of the areal extent of the reservoir range from 10 to 30 km 2

  10. Dynamics of the Askja caldera landslide, July 2014, from seismic signal analysis

    NASA Astrophysics Data System (ADS)

    Schöpa, Anne; Burtin, Arnaud; Hovius, Niels; Green, Robert G.

    2016-04-01

    A voluminous landslide occurred at the Askja caldera in the Icelandic highlands on July 21st, 2014. The next day, flood marks of at least ten tsunami waves, that had reached the northern shore of the caldera lake, could be mapped out. The highest flood marks were found up to 60 m above the lake level close to famous tourist spots underlining the high hazard potential of the area. Since the landslide happened at night, no direct observations of the mass movement nor of the subsequent tsunami waves in the caldera lake were made. We present the analysis of seismic data from a network of 58 seismic stations that recorded data during the event. The seismic data give valuable information on the triggering, initiation, timing, and propagation of the landslide, with additional details on precursory signals before and oscillation waves in the caldera lake after the main landslide. From the set of seismic wave forms, characteristic features were extracted that could be used for early warning proposes. The seismic data reveals that the main slope failure along the southeastern caldera wall was a large, single event starting at 23.24 UTC. The main part of the energy was released in the first two minutes followed by smaller events, before the background noise level was re-established some 40 minutes after the main failure. Subsequent mass movements, much lower in amplitude, occurred during the following hours. About 20 minutes before the main failure, the background noise level started to rise. Ground velocities were up to three times higher that the background level with dominant frequencies between 2-4 Hz. The increase in background noise level is visible in stations up to 30 km away from the landslide area. This velocity increase is followed by a prominent velocity drop five minutes before the main failure. The spatial distribution of the velocity decrease with its centre at the detachment area of the landslide has an elliptical outline with a long axis oriented NE-SW. This

  11. Postcaldera volcanism and hydrothermal activity revealed by autonomous underwater vehicle surveys in Myojin Knoll caldera, Izu-Ogasawara arc

    NASA Astrophysics Data System (ADS)

    Honsho, Chie; Ura, Tamaki; Kim, Kangsoo; Asada, Akira

    2016-06-01

    Myojin Knoll caldera, one of the submarine silicic calderas lying on the volcanic front of the northern Izu-Ogasawara arc, has attracted increasing attention since the discovery of a large hydrothermal field called the Sunrise deposit. Although numerous submersible surveys have been conducted in Myojin Knoll caldera, they have not sufficiently explored areas to produce a complete picture of the caldera and understand the origin of the Sunrise deposit. We conducted comprehensive deep-sea surveys using an autonomous underwater vehicle and obtained high-resolution bathymetric and magnetic data and sonar images from ~70% of the caldera. The detailed bathymetric map revealed that faulting and magma eruptions, possibly associated with an inflation-deflation cycle of the magma reservoir during postcaldera volcanism, had generally occurred in the caldera wall. The main dome of the central cone was covered with lava flows and exhibits exogenous growth, which is unusual for rhyolitic domes. The magnetization distribution in the central cone indicates preferential magma intrusion along a NW-SE direction. It is presumed that magma migrated along this direction and formed a rhyolite dome at the foot of the southeastern caldera wall, where the Sunrise deposit occurs. The Sunrise deposit is composed mainly of three ridges extending in slope directions and covers ~400 × ~400 m. Magnetization reduction in the deposit area is small, indicating that the alteration zone beneath the Sunrise deposit is slanting rather than vertical. It is presumed that several slanting and near-vertical volcanic vents serve as pathways of hydrothermal fluid in Myojin Knoll caldera.

  12. Magma Evolution During a Single Caldera Cycle: Insights from Melt Inclusions of the 3.49 Ma Tara Supereruption, Guacha Caldera, SW Bolivia

    NASA Astrophysics Data System (ADS)

    Grocke, S.; de Silva, S. L.; Wallace, P. J.; Iriarte, R.

    2012-12-01

    Melt inclusions in quartz phenocrysts erupted during the 3.49 Ma Tara Ignimbrite supereruption (>800 km3 DRE) from the Guacha Caldera complex in SW Bolivia provide the rare opportunity to examine the magma evolution during a complete resurgent caldera cycle. Data from naturally glassy, crystal- and vapor-bubble free quartz-hosted melt inclusions from pumices in the climactic plinian and ignimbrite phase and lavas from the post-resurgent domes combined with data on matrix glass and whole rock compositions reveal that the three eruptive phases were genetically related and potentially derived from an andesitic magma represented by scoria in the ignimbrite. Variations in Cl, H2O, B and Li suggest the presence of a separate vapor phase in the pre-climactic Tara magma. H2O contents in the plinian pumice overlap with those in the ignimbrite pumice (2.2 to 6.0 and 2.1 to 5.4 wt.% H2O, respectively) but the ignimbrite-forming magma contains higher CO2 (<630 versus <300 ppm) suggesting a vertically arranged pre-climactic magma column from 7.5 km to 4 km. The initial plinian fall-producing eruption tapped a less-evolved, crystal-poor (~10%) roofward liquid that syneruptively mixed with the more crystalline (~45%) climactic, ignimbrite-forming magma. Melt inclusions from the highly-differentiated post-climactic magma contain no detectable CO2 and ~2% H2O in melt inclusions and connote a shallowing (<2 km) post-climactic magma system that crystallized a new generation of quartz crystals and accompanied the resurgent doming of the Guacha II caldera floor. The eruptive transition during the climactic eruption was not controlled by the volatile budget of the melt but more likely by external factors such as vent geometry and conduit evolution. Post climactic effusive volcanism reflects the degassed nature of the remnant magma.

  13. Rhyolitic calderas of the Yukon-Tanana Terrane, east central Alaska: volcanic remnants of a mid-Cretaceous magmatic arc

    USGS Publications Warehouse

    Bacon, C.R.; Foster, H.L.; Smith, James G.

    1990-01-01

    Four large but poorly exposed rhyolitic calderas are present in the Yukon-Tanana terrane (YTT) in east central Alaska. At least two are mid-Cretaceous in age (~93 Ma). Similar volcanic rocks, the South Fork Volcanics, occur northeast of the Tintina fault in Yukon Territory. Evidence for the calderas consists of thick deposits of devitrified crystal- and lithic-rich densely welded tuff, interpreted as caldera fill, associated with lava domes or shallow intrusive rocks. Coeval outflow sheets have been largely stripped by erosion. The calderas are preserved within a northeast trending depression extending across the axis of the elongate mid-Cretaceous plutonic province. Trace element abundances in andesites and rhyolites associated with the caldera structures are similar to those of volcanic and plutonic rocks of subduction-related magmatic arcs developed on continental crust and thus are suggestive of formation in such an environment. Late Cretaceous and early Tertiary igneous rocks in the YTT near the calderas are interpreted to have been emplaced in a more extensional setting when the subduction-related magmatic front was farther oceanward. -Authors

  14. A catastrophic flood caused by drainage of a caldera lake at Aniakchak Volcano, Alaska, and implications for volcanic hazards assessment

    USGS Publications Warehouse

    Waythomas, C.F.; Walder, J.S.; McGimsey, R.G.; Neal, C.A.

    1996-01-01

    Aniakchak caldera, located on the Alaska Peninsula of southwest Alaska, formerly contained a large lake (estimated volume 3.7 ?? 109 m3) that rapidly drained as a result of failure of the caldera rim sometime after ca. 3400 yr B.P. The peak discharge of the resulting flood was estimated using three methods: (1) flow-competence equations, (2) step-backwater modeling, and (3) a dam-break model. The results of the dam-break model indicate that the peak discharge at the breach in the caldera rim was at least 7.7 ?? 104 m3 s-1, and the maximum possible discharge was ???1.1 ?? 106 m3 s-1. Flow-competence estimates of discharge, based on the largest boulders transported by the flood, indicate that the peak discharge values, which were a few kilometers downstream of the breach, ranged from 6.4 ?? 105 to 4.8 ?? 106 m3 s-1. Similar but less variable results were obtained by step-backwater modeling. Finally, discharge estimates based on regression equations relating peak discharge to the volume and depth of the impounded water, although limited by constraining assumptions, provide results within the range of values determined by the other methods. The discovery and documentation of a flood, caused by the failure of the caldera rim at Aniakchak caldera, underscore the significance and associated hydrologic hazards of potential large floods at other lake-filled calderas.

  15. The Silent Canyon caldera: a three-dimensional model as part of a Pahute Mesa-Oasis Valley, Nevada, hydrogeologic model

    USGS Publications Warehouse

    McKee, Edwin H.; Phelps, Geoffery A.; Mankinen, Edward A.

    2001-01-01

    A 3-dimensional caldera model based on gravity inversion, drill-hole data, and geologic mapping offers the framework for a hydrogeologic evaluation of the Silent Canyon caldera in the central part of Pahute Mesa, Nevada. It has been recognized for several decades that the central part of Pahute Mesa is the site of a buried caldera called the Silent Canyon caldera. Conceptually, the structural framework of the Silent Canyon caldera is based on the idea of collapse of the caldera roof over a shallow magma chamber to form a structural basin following violent volcanic eruptions. Calderas are common in certain volcanic regions of the world, and most well-exposed calderas are broadly similar to each other, particularly the arcuate or circular shape of their collapse depression. There are other reasons for modeling the Silent Canyon caldera as a circular feature in addition to knowledge that calderas throughout the world are generally circular features. The Silent Canyon caldera is the site of one of the largest gravity lows in the Western United States, indicating a thick accumulation of low-density rocks such as lavas and tuffs—a fact confirmed by drilling on Pahute Mesa. This gravity low is bowl-shaped, and the uppermost volcanic units on Pahute Mesa form a circular outcrop pattern of inward-dipping tuff interpreted to be the result of their filling the upper part of the bowl-shaped depression. Together, these features are consistent with, and indicative of, a circular collapse structural model for the Silent Canyon caldera. The collapse depression of the Silent Canyon caldera, bounded by arcuate faults, is filled with as much as 6 km (19,800 ft) of volcanic and sedimentary rocks that are considerably less dense than the underlying and surrounding basement rocks. The boundary surface between less dense caldera fill and more dense basement is modeled as the caldera ring fault. Rocks in the upper part of the caldera fill are penetrated by drilling, and the drill

  16. Using InSAR to investigate long term caldera unrest: case studies from Yellowstone and Long Valley

    NASA Astrophysics Data System (ADS)

    battaglia, maurizio

    2016-04-01

    Interpreting geodetic measurements can be particularly difficult in the case of slow, years-to-decades deformation, such as that commonly observed at large Quaternary silicic calderas. For example, Yellowstone caldera has shown a complex behavior over recent decades: uplift of resurgent domes within the caldera started sometime after 1923, reaching a total of 90 cm, but in 1984 the deformation reversed to subsidence at a rate of 1-2 cm/yr until 1992. Starting in 1992, the deformation began migrating from one resurgent dome to the other, and deformation was also detected along the caldera boundary - the so-called Northern Caldera Rim - starting in the mid-1990s. Evidence from geodetic surveys suggests that magma intrusion and/or pressurization of hydrothermal fluids may both drive uplift at Yellowstone. Geodetic measurements at Long Valley caldera have also revealed multiple episodes of caldera uplift, but in contrast to Yellowstone, deformation is largely restricted to the caldera's single resurgent dome. The fact that the energy released during the resurgent dome uplift is much larger than that which can be explained by seismic activity within and around the caldera, together with the observation that the onset of accelerated deformation precedes increases in earthquake activity by several weeks, suggests that the major source of caldera unrest is probably magma intrusion beneath the resurgent dome. Here we present time series of surface deformation for Yellowstone and Long Valley retrieved by applying the SBAS InSAR technique. We estimate the average regional deformation signal by using the mean velocity values derived from coherent SAR pixels belonging to areas outside the caldera. This tectonic signal is removed from the InSAR displacement and we modeled the InSAR, leveling, and gravity measurements to retrieve the best fitting source parameters. For Yellowstone caldera, different distinct sources, either hydrothermal or magmatic, have been intermittently

  17. Geologic map of the Crystal Peak Caldera, west-central Utah

    SciTech Connect

    Steven, T.A.

    1989-01-01

    In early Oligocene time, an area 16 by 10 km across near Crystal Peak was suddenly converted from a dissected plateau to a steep-sided topographic basin; this was coincident with eruption of the Tunnel Spring tuff. Subsidence was complex; the western part of the basin seems underlain by an oval-shaped block (caldera) bounded by steep walls; whereas, the eastern part of the basin is less deeply subsided and contains thinner and more irregularly distributed fill. A gravity low closely mirrors the subsided area. In middle Oligocene time, two major ash-flow formations of the Needles Range Group invaded the caldera where they formed coherent sheets interlayered with locally derived gravels.

  18. Gravity anomalies, caldera structure, and subsurface geology in the Rotorua area, New Zealand

    SciTech Connect

    Hunt, T.M. )

    1992-04-01

    This paper discusses a re-examination of gravity which indicates that Rotorua Caldera does not have the circular, negative gravity anomaly typical of other rhyolitic calderas. New gravity measurements and residual gravity anomalies in Rotorua City are consistent with numerous rhyolite domes and ignimbrite sheets, interbedded with a thick sequence of poorly-compacted sediments. Within the city a gravity high extends from the shore of Lake Rotorua south to Whakarewarewa and is associated with a buried ridge, formed by the coalescing of two rhyolite domes. A gravity low centered near Linton Park suggests that rhyolites are thin or absent in this area and sediments extend to a depth of about 1 km. A quantitative analysis of the residual gravity anomalies was limited by insufficient information about the density, extent, and thickness of the material underlying the rhyolites, and the uncertainty in the distribution and density of silicification within the sediments.

  19. Decrease in deformation rate observed by two-color laser ranging in Long Valley Caldera

    USGS Publications Warehouse

    Linker, M.F.; Langbein, J.O.; McGarr, A.

    1986-01-01

    After the January 1983 earthquake swarm, the last period of notable seismicity, the rapid rate of deformation of the south moat and resurgent dome of the Long Valley caldera diminished. Frequently repeated two-color laser ranging measurements made within a geodetic network in the caldera during the interval June 1983 to November 1984 reveal that, although the deformation accumulated smoothly in time, the rate of extension of many of the baselines decreased by factors of 2 to 3 from mid-1983 to mid-1984. Areal dilatation was the dominant signal during this period, with rates of extension of several baselines reaching as high as 5 parts per million per annum during the summer of 1983. Within the south moat, shear deformation also was apparent. The cumulative deformation can be modeled as the result of injection of material into two points located beneath the resurgent dome in addition to shallow right lateral slip on a vertical fault in the south moat.

  20. The structural setting of the Ischia Island Caldera (Italy): first evidence from seismic and gravity data

    NASA Astrophysics Data System (ADS)

    Capuano, Paolo; De Matteis, Raffaella; Russo, Guido

    2015-09-01

    Ischia Island is one of the active volcanoes of the Neapolitan area (Italy). Hazard assessment of active, densely populated volcano is primarily based on knowledge of the volcano's past behaviour and of its present state. As a contribution to the definition of the present structural setting of Ischia Island, we constructed a new model of the shallow crust using geophysical data: seismic wave travel times and Bouguer anomaly data. We analysed these data sets through seismic tomography and gravity data inversion. The main results inferable from the 3D seismic and gravity images are the definition of the caldera rim along the perimeter of the island, as hypothesized by many authors, and the presence of a high velocity and density area inside the caldera consistent with extension of the resurgent block that characterizes the recent deformation of the island.

  1. Late Cretaceous Middle Fork caldera and its resurgent granite porphyry intrusion, east-central Alaska

    NASA Astrophysics Data System (ADS)

    Bacon, C. R.; Dusel-Bacon, C.; Aleinikoff, J. N.; Slack, J. F.

    2012-12-01

    Named for the Middle Fork of the North Fork of the Fortymile River, the Middle Fork caldera encompasses a 10 x 20 km area of rhyolite welded tuff and granite porphyry ~100 km west of the Yukon border. Intracaldera tuff has ≤4 mm quartz and feldspar phenocrysts and cm-sized fiamme; its maximum exposed thickness is 850 m. Less densely welded tuff near the caldera margins locally contains 1-2 cm K-feldspar megacrysts and pumice clasts to 6 cm. Zircon from intracaldera tuff yields a SHRIMP-RG U-Pb age of 68.7 ± 1.1 Ma (all ages 95% confidence). Granite porphyry occupies much of an 8 x 12 km area having 650 m of relief within the western part of the caldera fill. Zircon from the porphyry gives a SHRIMP-RG U-Pb age of 68.4 ± 1.0 Ma. These ages agree with a previous 40Ar/39Ar biotite age of 69.1 ± 0.5 Ma for proximal outflow tuff. The crystal-rich intracaldera tuff contains embayed quartz, plagioclase>K-feldspar, biotite, and Fe-Ti oxide phenocrysts in a very fine-grained crystalline groundmass. The porphyry carries 40-50% of larger phenocrysts of the same phases (skeletal quartz to 1 cm; K-feldspar to 2 cm, rarely to 4 cm) in a fine-grained groundmass characterized by abundant 50-100 μm quartz. Compositions of 3 tuff and 3 porphyry samples overlap, form a limited differentiation series at 69-72% SiO2, have arc geochemical signatures, and yield subparallel chondrite-normalized rare earth element patterns with light REE enrichment, concave-upward heavy REE, and small negative Eu anomalies. Although their phenocrysts differ in size (owing to fragmentation of crystals in the tuff) and abundance, the similar mineralogy, composition (in spite of crystal concentration in the tuff), and indistinguishable ages of the tuff and porphyry indicate that the magmas were closely related. A rare magmatic enclave (54% SiO2, arc geochemical signature) in the porphyry may be similar to parental magma and provides evidence of mafic magma and thermal input. The porphyry is interpreted

  2. Crustal deformation at long Valley Caldera, eastern California, 1992-1996 inferred from satellite radar interferometry

    USGS Publications Warehouse

    Thatcher, W.; Massonnet, D.

    1997-01-01

    Satellite radar interferometric images of Long Valley caldera show a pattern of surface deformation that resembles that expected from analysis of an extensive suite of ground-based geodetic data. Images from 2 and 4 year intervals respectively, are consistent with uniform movement rates determined from leveling surveys. Synthetic interferograms generated from ellipsoidal-inclusion source models based on inversion of the ground-based data show generally good agreement with the observed images. Two interferograms show evidence for a magmatic source southwest of the caldera in a region not covered by ground measurements. Poorer image quality in the 4 year interferogram indicates that temporal decorrelation of surface radar reflectors is progressively degrading the fringe pattern in the Long Valley region. Copyright 1997 by the American Geophysical Union.

  3. Volatiles from the 1994 Eruptions of Rabaul: Understanding Large Caldera Systems

    PubMed

    Roggensack; Williams; Schaefer; Parnell

    1996-07-26

    The 1994 eruption of Rabaul, in Papua New Guinea, involved a small plinian eruption at Vulcan and a vulcanian eruption on the opposite side of the caldera at Tavurvur. Vulcan's ash leachates indicate seawater interaction that is consistent with earlier observations of low sulfur dioxide emissions and the presence of ice crystals in the initial plinian eruption cloud. In contrast, Tavurvur ash leachates indicate no seawater interaction, and later sulfur dioxide emissions remained high despite low-level eruptive activity. Silicic melt inclusions indicate that the andesitic melt contained about 2 weight percent water and negligible carbon dioxide. Mafic melt inclusions in Tavurvur ash have water and carbon dioxide contents that vary systematically over the course of the eruption. The mafic melt inclusions suggest that a mafic dike intruded from below the silicic chamber and provide further evidence that mafic intrusions drive caldera unrest. PMID:8662536

  4. Gradual caldera collapse at Bárdarbunga volcano, Iceland, regulated by lateral magma outflow.

    PubMed

    Gudmundsson, Magnús T; Jónsdóttir, Kristín; Hooper, Andrew; Holohan, Eoghan P; Halldórsson, Sæmundur A; Ófeigsson, Benedikt G; Cesca, Simone; Vogfjörd, Kristín S; Sigmundsson, Freysteinn; Högnadóttir, Thórdís; Einarsson, Páll; Sigmarsson, Olgeir; Jarosch, Alexander H; Jónasson, Kristján; Magnússon, Eyjólfur; Hreinsdóttir, Sigrún; Bagnardi, Marco; Parks, Michelle M; Hjörleifsdóttir, Vala; Pálsson, Finnur; Walter, Thomas R; Schöpfer, Martin P J; Heimann, Sebastian; Reynolds, Hannah I; Dumont, Stéphanie; Bali, Eniko; Gudfinnsson, Gudmundur H; Dahm, Torsten; Roberts, Matthew J; Hensch, Martin; Belart, Joaquín M C; Spaans, Karsten; Jakobsson, Sigurdur; Gudmundsson, Gunnar B; Fridriksdóttir, Hildur M; Drouin, Vincent; Dürig, Tobias; Aðalgeirsdóttir, Guðfinna; Riishuus, Morten S; Pedersen, Gro B M; van Boeckel, Tayo; Oddsson, Björn; Pfeffer, Melissa A; Barsotti, Sara; Bergsson, Baldur; Donovan, Amy; Burton, Mike R; Aiuppa, Alessandro

    2016-07-15

    Large volcanic eruptions on Earth commonly occur with a collapse of the roof of a crustal magma reservoir, forming a caldera. Only a few such collapses occur per century, and the lack of detailed observations has obscured insight into the mechanical interplay between collapse and eruption. We use multiparameter geophysical and geochemical data to show that the 110-square-kilometer and 65-meter-deep collapse of Bárdarbunga caldera in 2014-2015 was initiated through withdrawal of magma, and lateral migration through a 48-kilometers-long dike, from a 12-kilometers deep reservoir. Interaction between the pressure exerted by the subsiding reservoir roof and the physical properties of the subsurface flow path explain the gradual, near-exponential decline of both collapse rate and the intensity of the 180-day-long eruption. PMID:27418515

  5. Deep Borehole Measurements for Characterizing the Magma/Hydrothermal System at Long Valley Caldera, CA

    SciTech Connect

    Carrrigan, Charles R.

    1989-03-21

    The Magma Energy Program of the Geothermal Technology Division is scheduled to begin drilling a deep (6 km) exploration well in Long Valley Caldera, California in 1989. The drilling site is near the center of the caldera which is associated with numerous shallow (5-7 km) geophysical anomalies. This deep well will present an unparalleled opportunity to test and validate geophysical techniques for locating magma as well as a test of the theory that magma is still present at drillable depths within the central portion of the caldera. If, indeed, drilling indicates magma, the geothermal community will then be afforded the unique possibility of examining the coupling between magmatic and hydrothermal regimes in a major volcanic system. Goals of planned seismic experiments that involve the well include the investigation of local crustal structure down to depths of 10 km as well as the determination of mechanisms for local seismicity and deformation. Borehole electrical and electromagnetic surveys will increase the volume and depth of rock investigated by the well through consideration of the conductive structure of the hydrothermal and underlying regimes. Currently active processes involving magma injection will be studied through observation of changes in pore pressure and strain. Measurements of in situ stress from recovered cores and hydraulic fracture tests will be used in conjunction with uplift data to determine those models for magmatic injection and inflation that are most applicable. Finally, studies of the thermal regime will be directed toward elucidating the coupling between the magmatic source region and the more shallow hydrothermal system in the caldera fill. To achieve this will require careful logging of borehole fluid temperature and chemistry. In addition, studies of rock/fluid interactions through core and fluid samples will allow physical characterization of the transition zone between hydrothermal and magmatic regimes.

  6. Renewed uplift at the Yellowstone caldera measured by leveling surveys and satellite radar interferometry

    USGS Publications Warehouse

    Dzurisin, D.; Wicks, C.; Thatcher, W.

    1999-01-01

    A first-order leveling survey across the northeast part of the Yellowstone caldera in September 1998 showed that the central caldera floor near Le Hardy Rapids rose 24 ?? 5 mm relative to the caldera rim at Lake Butte since the previous survey in September 1995. Annual surveys along the same traverse from 1985 to 1995 tracked progressive subsidence near Le Hardy Rapids at an average rate of -19 ?? 1 mm/year. Earlier, less frequent surveys measured net uplift in the same area during 1923-1976 (14 ?? 1 mm/year) and 1976-1984 (22 ?? 1 mm/year). The resumption of uplift following a decade of subsidence was first detected by satellite synthetic aperture radar interferometry, which revealed approximately 15 mm of uplift in the vicinity of Le Hardy Rapids from July 1995 to June 1997. Radar interferograms show that the center of subsidence shifted from the Sour Creek resurgent dome in the northeast part of the caldera during August 1992 to June 1993 to the Mallard Lake resurgent dome in the southwest part during June 1993 to August 1995. Uplift began at the Sour Creek dome during August 1995 to September 1996 and spread to the Mallard Lake dome by June 1997. The rapidity of these changes and the spatial pattern of surface deformation suggest that ground movements are caused at least in part by accumulation and migration of fluids in two sill-like bodies at 5-10 km depth, near the interface between Yellowstone's magmatic and deep hydrothermal systems.

  7. Seismic velocity structure and earthquake relocation for the magmatic system beneath Long Valley Caldera, eastern California

    NASA Astrophysics Data System (ADS)

    Lin, Guoqing

    2015-04-01

    A new three-dimensional (3-D) seismic velocity model and high-precision location catalog for earthquakes between 1984 and 2014 are presented for Long Valley Caldera and its adjacent fault zones in eastern California. The simul2000 tomography algorithm is applied to derive the 3-D Vp and Vp/Vs models using first-arrivals of 1004 composite earthquakes obtained from the original seismic data at the Northern California Earthquake Data Center. The resulting Vp model reflects geological structures and agrees with previous local tomographic studies. The simultaneously resolved Vp/Vs model is a major contribution of this study providing an important complement to the Vp model for the interpretation of structural heterogeneities and physical properties in the study area. The caldera is dominated by low Vp anomalies at shallow depths due to postcaldera fill. High Vp and low Vp/Vs values are resolved from the surface to ~ 3.4 km depth beneath the center of the caldera, corresponding to the structural uplift of the Resurgent Dome. An aseismic body with low Vp and high Vp/Vs anomalies at 4.2-6.2 km depth below the surface is consistent with the location of partial melt suggested by previous studies based on Vp models only and the inflation source locations based on geodetic modeling. The Sierran crystalline rocks outside the caldera are generally characterized with high Vp and low Vp/Vs values. The newly resolved velocity model improves absolute location accuracy for the seismicity in the study area and ultimately provides the basis for a high-precision earthquake catalog based on similar-event cluster analysis and waveform cross-correlation data. The fine-scale velocity structure and precise earthquake relocations are useful for investigating magma sources, seismicity and stress interaction and other seismological studies in Long Valley.

  8. Dynamic magmatic processes at a continental rift caldera, observed using satellite geodesy

    NASA Astrophysics Data System (ADS)

    Lloyd, Ryan; Biggs, Juliet; Birhanu, Yelebe; Wilks, Matt; Gottsmann, Jo; Kendall, Mike; Lewi, Elias

    2016-04-01

    Large silicic calderas are a key feature of developing continental rifts, such as the Main Ethiopian Rift (MER), and are often observed to be deforming. Corbetti is one such example of a Holocene caldera in the MER that is undergoing deformation. However, the cause of the unrest, and the relationship to rift processes such as magma storage, transport and extension remain poorly understood. To investigate, we use InSAR (ascending and descending Cosmo-SkyMed data) and continuous GPS to observe the temporal and spatial evolution of sustained uplift at the Corbetti Caldera. Within the caldera, which was thought to have formed ~200 ka, there is evidence for numerous periods of resurgent volcanism in the form of plinian eruptions as well as effusive obsidian flows. How the sources of these varying styles of volcanism are reconciled at depth and in time is currently poorly constrained. Previous research has shown that pre-rift structures have a significant influence on the strain field, and hence on the magmatic and hydrothermal processes which drive it. The Cosmo-SkyMed data used in this study was specifically chosen such that each ascending image has a corresponding descending image acquired as contemporaneously as possible. This is necessary, given the rate of uplift, so as to reduce the number of assumptions when constructing time-series from multiple look directions, and when incorporating GPS data. We decompose the ascending and descending line-of-site deformation signals into vertical and east-west components and use finite source modeling to constrain the depth and geometry of the source of deformation. These results are then compared to available seismic, dynamic microgravity and magnetotelluric data to better understand this system, and how it is related to the volcanic hazard and local geothermal resources.

  9. Caldera formation and varied eruption styles on North Pacific seamounts: the clastic lithofacies record

    NASA Astrophysics Data System (ADS)

    Portner, Ryan A.; Clague, Dave A.; Paduan, Jennifer B.

    2014-08-01

    Detailed examination of volcaniclastic and sedimentary rocks collected from the Taney (30 Ma), President Jackson (4 Ma), Vance (3 Ma) and Alarcon (2 Ma) near-ridge seamount chains of the North Pacific reveals seven clastic lithofacies that record various modes of eruption, magma fragmentation, and particle dispersal. Lithofacies are distinguished by differences in lithology, bedding habit, compositional heterogeneity, and relationship to volcanic landforms. Breccia lithofacies were produced through mechanical fragmentation during caldera collapse (polymict) or effusive eruptions onto steep slopes (monomict). Rare globular lapilli mudstone lithofacies contain clasts with morphologies formed by magma-sediment mingling processes (peperite). Seamount summit pyroclastic deposits include proximal lapilli tuff with vesicular pyroclasts, and more distal limu o Pele tuff lithofacies. Much finer-grained hydrothermal mudstone/tuff lithofacies occurs around caldera rims and contains greenschist minerals, hydrothermal clays and basaltic ash that record subsurface phreatomagmatic fragmentation processes. Very fine-grained ash is transported to distal regions by oceanic currents and hydrothermal plumes, and is a component of the regional pelagic sediment budget. Pyroclastic lithofacies only occur on seamount summits suggesting formation during the latter stages of seamount evolution. As a seamount drifts away from an adjacent ridge axis and associated heat source, its magma supply is reduced allowing for magmatic gas buildup and mild explosive eruptions. During this stage, the diminished melt supply under the seamount is unable to fully compensate for extension along the ridge axis and vertical seamount growth. Lateral intrusion into spreading-related structures in this stage causes magma withdrawal and caldera formation. Formation of caldera ring faults also promotes seawater ingress into subseafloor hydrothermal cells, which interact with magma conduits causing phreatomagmatic

  10. Hydrothermal outflow plume of Valles caldera, New Mexico, and a comparison with other outflow plumes

    SciTech Connect

    Goff, F.; Shevenell, L.; Gardner, J.N.; Vuataz, F.; Grigsby, C.O.

    1988-06-10

    Stratigraphic, temperature gradient, hydrogeochemical, and hydrologic data have been integrated with geologic data from previous studies to show the structural configuration of the Valles caldera hydrothermal outflow plume. Hydrologic data suggest that 25--50% of the discharge of the Valles outflow is confined to the Jemez fault zone, which predates caldera formation. Thermal gradient data from bores penetrating the plume show that shallow gradients are highest in the vicinity of the Jemez fault zone (up to 190 /sup 0/C/km). Shallow heat flow above the hydrothermal plume is as high as 500 mW m/sup -2/ near core hole VC-1 (Jemez fault zone) to 200 mW m/sup -2/ at Fenton Hill (Jemez Plateau). Chemical and isotopic data indicate that two source reservoirs within the caldera (Redondo Creek and Sulphur Springs reservoirs) are parents to mixed fluids flowing in the hydrothermal plume. However, isotopic data, borehole data, basic geology, and inverse relations between temperature and chloride content at major hot springs indicate that no single reservoir fluid and no single diluting fluid are involved in mixing. The Valles caldera hydrothermal plume is structurally dominated by lateral flow through a belt of vertical conduits (Jemez fault zone) that strike away from the source reservoir. Stratigraphically confined flow is present but dispersed over a wide area in relatively impermeable rocks. The Valles configuration is contrasted with the configuration of the hydrothermal plume at Roosevelt Hot Springs, which is dominated by lateral flow through a near-surface, widespread, permeable aquifer. Data from 12 other representative geothermal systems show that outflow plumes occur in a variety of magmatic and tectonic settings, have varying reservoir compositions, and have different flow characteristics.

  11. Characterizing magma storage at Aira caldera and Sakurajima volcano (Japan) from geodetic inversions

    NASA Astrophysics Data System (ADS)

    Hickey, J.; Gottsmann, J.; Iguchi, M.; Nakamichi, H.

    2014-12-01

    Aira caldera is located within Kagoshima Bay at the southern end of Kyushu, in Japan. Sakurajima, a post-caldera andesitic stratovolcano, sits on the calderas southern rim and is Japan's most active volcano. Historical records of activity at Sakurajima are punctuated with larger events: for example, in 1914 a major flank eruption ejected 0.52 km3 of pumice and ash, and 1.34 km3 of lava. The co-eruptive subsidence accompanying this eruption was around one metre in the vertical component, as determined from leveling surveys. Repeat surveys, and the addition of modern GPS data indicate that the present day level of ground uplift is approaching the level inferred before the 1914 eruption. This st