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Sample records for large volcanic lake

  1. Yellowstone Lake: A Large Volcanic Lake Influenced by the Yellowstone Magmatic System

    NASA Astrophysics Data System (ADS)

    Shanks, W. C.; Morgan, L. A.

    2010-12-01

    Northern, central and West Thumb basins of Yellowstone Lake are within the Yellowstone Caldera, which collapsed due to the cataclysmic eruption of the Lava Creek Tuff at 0.64 Ma. Bathymetric, seismic reflection, and aeromagnetic mapping of Yellowstone Lake shows that the area inside the caldera hosts multiple post-caldera rhyolite lava flows, active faults and fissures, hundreds of sub-lacustrine hot spring vents and associated siliceous hydrothermal deposits, large and small hydrothermal explosion craters, and significant areas of hydrothermally altered sediments. All of these features are driven by hydrothermal upwelling related to an underlying partially molten magma reservoir. Yellowstone hydrothermal fluids originate predominantly from deeply circulating meteoric waters that are probably depth-limited by the brittle-ductile transition at temperatures of 350-400°C above the magmatic system. Brines (generated by phase-separation near the magma chamber) and degassed magmatic volatiles (CO2, H2S, HCl) both mix with circulating meteoric waters, resulting in a 350°C, CO2- and H2S-rich, deep thermal-reservoir fluid with about 310 mg/kg Cl. The deep reservoir fluid boils during ascent due to depressurization and may mix with local fluids. Sub-lacustrine hydrothermal vent fluids sampled by submersible remotely operated vehicle (ROV) show δD-Cl systematics that indicate the ascending fluids boil to ≥220°C with Cl increasing to ≤570 mg/kg and then mix with Yellowstone Lake water at or just below lake-floor hydrothermal vent sites. The geochemical composition of Yellowstone Lake water is strongly influenced by sub-lacustrine hydrothermal activity and magmatic volatiles. The evidence for this conclusion is twofold. First, Yellowstone Lake is strongly enriched in dissolved As, B, Cl, Cs, Ge, Li, Mo, Sb, and W relative to the weighted average of inflowing stream waters. Geochemical reaction modeling indicates that the composition of ascending hydrothermal fluids is

  2. Future volcanic lake research: revealing secrets from poorly studied lakes

    NASA Astrophysics Data System (ADS)

    Rouwet, D.; Tassi, F.; Mora-Amador, R. A.

    2012-04-01

    Volcanic lake research boosted after the 1986 Lake Nyos lethal gas burst, a limnic rather than volcanic event. This led to the formation of the IAVCEI-Commission on Volcanic Lakes, which grew out into a multi-disciplinary scientific community since the 1990's. At Lake Nyos, a degassing pipe is functional since 2001, and two additional pipes were added in 2011, aimed to prevent further limnic eruption events. There are between 150 and 200 volcanic lakes on Earth. Some acidic crater lakes topping active magmatic-hydrothermal systems are monitored continuously or discontinuously. Such detailed studies have shown their usefulness in volcanic surveillance (e.g. Ruapehu, Yugama-Kusatsu-Shiran, Poás). Others are "Nyos-type" lakes, with possible gas accumulation in bottom waters and thus potentially hazardous. "Nyos-type" lakes tend to remain stably stratified in tropical and sub-tropical climates (meromictic), leading to long-term gas build-up and thus higher potential risk. In temperate climates, such lakes tend to turn over in winter (monomictic), and thus liberating its gas charge yearly. We line out research strategies for the different types of lakes. We believe a complementary, multi-disciplinary approach (geochemistry, geophysics, limnology, biology, statistics, etc.) will lead to new insights and ideas, which can be the base for future following-up and monitoring. After 25 years of pioneering studies on rather few lakes, the scientific community should be challenged to study the many poorly studied volcanic lakes, in order to better constrain the related hazard, based on probabilistic approaches.

  3. Hazards of volcanic lakes: analysis of Lakes Quilotoa and Cuicocha, Ecuador

    NASA Astrophysics Data System (ADS)

    Gunkel, G.; Beulker, C.; Grupe, B.; Viteri, F.

    2008-01-01

    Volcanic lakes within calderas should be viewed as high-risk systems, and an intensive lake monitoring must be carried out to evaluate the hazard of potential limnic or phreatic-magmatic eruptions. In Ecuador, two caldera lakes - Lakes Quilotoa and Cuicocha, located in the high Andean region >3000 a.s.l. - have been the focus of these investigations. Both volcanoes are geologically young or historically active, and have formed large and deep calderas with lakes of 2 to 3 km in diameter, and 248 and 148 m in depth, respectively. In both lakes, visible gas emissions of CO2 occur, and an accumulation of CO2 in the deep water body must be taken into account. Investigations were carried out to evaluate the hazards of these volcanic lakes, and in Lake Cuicocha intensive monitoring was carried out for the evaluation of possible renewed volcanic activities. At Lake Quilotoa, a limnic eruption and diffuse CO2 degassing at the lake surface are to be expected, while at Lake Cuicocha, an increased risk of a phreatic-magmatic eruption exists.

  4. Volcanic lake systematics II. Chemical constraints

    USGS Publications Warehouse

    Varekamp, J.C.; Pasternack, G.B.; Rowe, G.L.

    2000-01-01

    A database of 373 lake water analyses from the published literature was compiled and used to explore the geochemical systematics of volcanic lakes. Binary correlations and principal component analysis indicate strong internal coherence among most chemical parameters. Compositional variations are influenced by the flux of magmatic volatiles and/or deep hydrothermal fluids. The chemistry of the fluid entering a lake may be dominated by a high-temperature volcanic gas component or by a lower-temperature fluid that has interacted extensively with volcanic rocks. Precipitation of minerals like gypsum and silica can strongly affect the concentrations of Ca and Si in some lakes. A much less concentrated geothermal input fluid provides the mineralized components of some more dilute lakes. Temporal variations in dilution and evaporation rates ultimately control absolute concentrations of dissolved constituents, but not conservative element ratios. Most volcanic lake waters, and presumably their deep hydrothermal fluid inputs, classify as immature acid fluids that have not equilibrated with common secondary silicates such as clays or zeolites. Many such fluids may have equilibrated with secondary minerals earlier in their history but were re-acidified by mixing with fresh volcanic fluids. We use the concept of 'degree of neutralization' as a new parameter to characterize these acid fluids. This leads to a classification of gas-dominated versus rock-dominated lake waters. A further classification is based on a cluster analysis and a hydrothermal speedometer concept which uses the degree of silica equilibration of a fluid during cooling and dilution to evaluate the rate of fluid equilibration in volcano-hydrothermal systems.

  5. Large Volcanic Rises on Venus

    NASA Technical Reports Server (NTRS)

    Smrekar, Suzanne E.; Kiefer, Walter S.; Stofan, Ellen R.

    1997-01-01

    Large volcanic rises on Venus have been interpreted as hotspots, or the surface manifestation of mantle upwelling, on the basis of their broad topographic rises, abundant volcanism, and large positive gravity anomalies. Hotspots offer an important opportunity to study the behavior of the lithosphere in response to mantle forces. In addition to the four previously known hotspots, Atla, Bell, Beta, and western Eistla Regiones, five new probable hotspots, Dione, central Eistla, eastern Eistla, Imdr, and Themis, have been identified in the Magellan radar, gravity and topography data. These nine regions exhibit a wider range of volcano-tectonic characteristics than previously recognized for venusian hotspots, and have been classified as rift-dominated (Atla, Beta), coronae-dominated (central and eastern Eistla, Themis), or volcano-dominated (Bell, Dione, western Eistla, Imdr). The apparent depths of compensation for these regions ranges from 65 to 260 km. New estimates of the elastic thickness, using the 90 deg and order spherical harmonic field, are 15-40 km at Bell Regio, and 25 km at western Eistla Regio. Phillips et al. find a value of 30 km at Atla Regio. Numerous models of lithospheric and mantle behavior have been proposed to interpret the gravity and topography signature of the hotspots, with most studies focusing on Atla or Beta Regiones. Convective models with Earth-like parameters result in estimates of the thickness of the thermal lithosphere of approximately 100 km. Models of stagnant lid convection or thermal thinning infer the thickness of the thermal lithosphere to be 300 km or more. Without additional constraints, any of the model fits are equally valid. The thinner thermal lithosphere estimates are most consistent with the volcanic and tectonic characteristics of the hotspots. Estimates of the thermal gradient based on estimates of the elastic thickness also support a relatively thin lithosphere (Phillips et al.). The advantage of larger estimates of

  6. Lake-floor sediment texture and composition of a hydrothermally-active, volcanic lake, Lake Rotomahana

    NASA Astrophysics Data System (ADS)

    Pittari, A.; Muir, S. L.; Hendy, C. H.

    2016-03-01

    Young volcanic lakes undergo a transition from rapid, post-eruptive accumulation of volcaniclastic sediment to slower pelagic settling under stable lake conditions, and may also be influenced by sublacustrine hydrothermal systems. Lake Rotomahana is a young (129 year-old), hydrothermally-active, volcanic lake formed after the 1886 Tarawera eruption, and provides a unique insight into the early evolution of volcanic lake systems. Lake-bottom sediment cores, 20-46 cm in length, were taken along a transect across the lake and characterised with respect to stratigraphy, facies characteristics (i.e., grain size, componentry) and pore water silica concentrations. The sediments generally comprise two widespread facies: (i) a lower facies of light grey to grey, very fine lacustrine silt derived from the unconsolidated pyroclastic deposits that mantled the catchment area immediately after the eruption, which were rapidly reworked and redeposited into the lake basin; and (ii) an upper facies of dark, fine-sandy diatomaceous silt, that settled from the pelagic zone of the physically stable lake. Adjacent to sublacustrine hydrothermal vents, the upper dark facies is absent, and the upper part of the light grey to grey silt is replaced by a third localised facies comprised of hydrothermally altered pale yellow to yellowish brown, laminated silt with surface iron-rich encrustations. Microspheres, which are thought to be composed of amorphous silica, although some may be halloysite, have precipitated from pore water onto sediment grains, and are associated with a decrease in pore water silicon concentration. Lake Rotomahana is an example of a recently-stabilised volcanic lake, with respect to sedimentation, that shows signs of early sediment silicification in the presence of hydrothermal activity.

  7. Sedimentation influx and volcanic interactions in the Fuji Five Lakes: implications for paleoseismological records

    NASA Astrophysics Data System (ADS)

    Lamair, Laura; Hubert-Ferrari, Aurélia; Yamamoto, Shinya; El Ouahabi, Meriam; Garrett, Ed; Shishikura, Masanobu; Schmidt, Sabine; Boes, Evelien; Obrochta, Stephen; Nakamura, Atsunori; Miyairi, Yosuke; Yokoyama, Yusuke; De Batist, Marc; Heyvaert, Vanessa M. A.

    2017-04-01

    can be linked to the modification of the lake watershed by Mount Fuji volcanism, leading to a decrease in the sediment volume that can be remobilized, and therefore disappearance of large sublacustrine landslides. Turbidites are deposited due to surficial remobilization of lake slope sediments most probably as a result of earthquake shaking. When studying sedimentological records of lakes to define the paleoearthquake record, eruptions of nearby volcanoes should be taken into account. This study suggests that a large magnitude earthquake occurring few decades after a volcanic eruption (with large scale scoria fall-out), might not be recorded in a lake, or would only be fingerprinted in the sedimentary record by small turbiditic flows.

  8. Large and small volcanic eruptions

    NASA Astrophysics Data System (ADS)

    Gudmundsson, Agust; Mohajeri, Nahid

    2013-04-01

    Despite great progress in volcanology in the past decades, we still cannot make reliable forecasts as to the likely size (volume, mass) of an eruption once it has started. Empirical data collected from volcanoes worldwide indicates that the volumes (or masses) of eruptive materials in volcanic eruptions are heavy-tailed. This means that most of the volumes erupted from a given magma chamber are comparatively small. Yet, the same magma chamber can, under certain conditions, squeeze out large volumes of magma. To know these conditions is of fundamental importance for forecasting the likely size of an eruption. Thermodynamics provides the basis for understanding the elastic energy available to (i) propagate an injected dyke from the chamber and to the surface to feed an eruption, and (ii) squeeze magma out of the chamber during the eruption. The elastic energy consists of two main parts: first, the strain energy stored in the volcano before magma-chamber rupture and dyke injection, and, second, the work done through displacement of the flanks of the volcano (or the margins of a rift zone) and the expansion and shrinkage of the magma chamber itself. Other forms of energy in volcanoes - thermal, seismic, kinetic - are generally important but less so for squeezing magma out of a chamber during an eruption. Here we suggest that for (basaltic) eruptions in rift zones the strain energy is partly related to minor doming above the reservoir, and partly to stretching of the rift zone before rupture. The larger the reservoir, the larger is the stored strain energy before eruption. However, for the eruption to be really large, the strain energy has to accumulate in the entire crustal segment above the reservoir and there will be additional energy input into the system during the eruption which relates to the displacements of the boundary of the rift-zone segment. This is presumably why feeder dykes commonly propagate laterally at the surface following the initial fissure

  9. Past, present and future of volcanic lake monitoring

    NASA Astrophysics Data System (ADS)

    Rouwet, Dmitri; Tassi, Franco; Mora-Amador, Raúl; Sandri, Laura; Chiarini, Veronica

    2014-02-01

    Volcanic lake research boosted after lethal gas burst occurred at Lake Nyos (Cameroon) in 1986, a limnic rather than a volcanic event. This led to the foundation of the IAVCEI-Commission on Volcanic Lakes, which grew out into a multi-disciplinary scientific community since the 1990s. We here introduce the first data base of volcanic lakes VOLADA, containing 474 lakes, a number that, in our opinion, is surprisingly high. VOLADA could become an interactive, open-access working tool where our community can rely on in the future. Many of the compiled lakes were almost unknown, or at least unstudied to date, whereas there are acidic crater lakes topping active magmatic-hydrothermal systems that are continuously or discontinuously monitored, providing useful information for volcanic surveillance (e.g., Ruapehu, Yugama, Poás). Nyos-type lakes, i.e. those hosted in quiescent volcanoes and characterized by significant gas accumulation in bottom waters, are potentially hazardous. These lakes tend to remain stably stratified in tropical and sub-tropical climates (meromictic), leading to long-term build-up of gas, which can be released after a trigger. Some of the unstudied lakes are possibly in the latter situation. Acidic crater lakes are easily recognized as active, whereas Nyos-type lakes can only be recognized as potentially hazardous if bottom waters are investigated, a less obvious operation. In this review, research strategies are lined out, especially for the “active crater lakes”. We make suggestions for monitoring frequency based on the principle of the “residence time dependent monitoring time window”. A complementary, multi-disciplinary (geochemistry, geophysics, limnology, statistics) approach is considered to provide new ideas, which can be the bases for future volcanic lake monitoring. More profound deterministic knowledge (e.g., precursory signals for phreatic eruptions, or lake roll-over events) should not only serve to enhance conceptual models of

  10. Volcanic Crater Lakes: Relaying Signals to Satellites for Decades

    NASA Astrophysics Data System (ADS)

    Murphy, S.; Wright, R.

    2016-12-01

    Volcanic crater lakes are a medium through which magmatic fluids can express themselves on the Earth's surface in a way that is visible from space. This is fortuitous because satellites have acquired time series of the world's crater lakes for decades. We leverage this archive to quantify the colour, temperature and size of 100 volcanic craters lakes over the last 25 years. These observations provide (typically unique) constraints on the physical properties of volcanic fluids that reach the surface of these target volcanoes. Mass flow rates at the subaqueous vent(s) can be constrained using HSV-color space. The premise being that the concentration of suspended sediments increases with flow rate due to turbidity in the lake. Increased sediment concentration raises the reflectivity of the lake in visible wavelengths (represented by its color value) and causes the lake color to become more gray in appearance (i.e. decreases color saturation). Chemical signatures (e.g. Ph and Eh) can also be constrained using a HSV-color space (e.g. transitions between red and green hues). Temperature changes can be caused by variations in the temperature and/or volume of magmatic fluid entering the near-surface system. Lake sizes are more difficult to quantify due to cloud cover, however, non-seasonal decrease in lake size over time indicates volcanic thermal regime change. Temporal signatures in one or more of these properties (e.g. increase in temperature and decrease in size) could aid forecasts in climates that favour aqueous lakes (i.e. around 15 % of active volcanoes). More generally, crater lakes can help us to better understand how volcanic fluid dynamics change over long periods of time. This knowledge could improve forecasts at volcanoes that do not exhibit crater lakes.

  11. Volcanic lakes of the Azores archipelago (Portugal): Geological setting and geochemical characterization

    NASA Astrophysics Data System (ADS)

    Cruz, J. V.; Antunes, P.; Amaral, C.; França, Z.; Nunes, J. C.

    2006-08-01

    A representative set of 30 lakes from the Azores archipelago (Portugal) has been studied to obtain data on their volcanic setting and water geochemistry. The majority of the studied lakes are located inside volcanic craters and subsidence calderas, while the remaining lakes are located in topographic depressions not associated with volcanic centres, in depressions of tectonic origin and inside lava caves. In general, the Azorean volcanic lakes are small, with surface areas between 8.94 × 10 - 4 km 2 and 4.35 km 2 and volumes between 2.4 × 10 3 and 4.78 × 10 7 m 3; median = 3.99 × 10 4 m 3, presenting maximum depths between 0.8 and 33 m. Mostly of the Na-Cl to Na-HCO 3 type, the lake waters are generally low temperature (11.9-24.6 °C), very dilute (TDS range between 11.0 and 356.2 mg/L; median = 36.8 mg/L) and a clear exception is Furna do Enxofre lake (Graciosa island) that shows a Mg trend. Two types of lake waters can be recognized: 1) one is characterized by Na/Cl ratio close to the seawater value and have evolved, and evolve by marine contribution; and 2) Na-HCO 3 type waters that, in addition to sea-salt input, have been influenced by other processes (e.g., water-rock interaction, hydrothermal seepage into the lake bottom) evident from higher total CO 2 content (365.1 mg/L) and SiO 2 content (74.9 mg/L), as well demonstrated by in the Furna do Enxofre lake. Nevertheless, volcanic contribution cannot be excluded for some lakes as Furna do Enxofre. Vertical profiles made at the deepest lakes of São Miguel reveal that major-ion content varies little with depth, largely independent of the occurrence of thermally driven density stratification in summer for some lakes. However, dissolved CO 2 increases with depth and is kept in the hypolimnion in summer, whereas the HCO 3- content is stable, suggesting that CO 2 release exceeds acidity neutralization by water-rock interaction. During winter, without stratification, the dissolved CO 2 increase is less sharp for

  12. Eruptive and environmental processes recorded by diatoms in volcanically-dispersed lake sediments from the Taupo Volcanic Zone, New Zealand

    USGS Publications Warehouse

    Harper, Margaret A.; Pledger, Shirley A.; Smith, Euan G. C.; Van Eaton, Alexa; Wilson, Colin J. N.

    2015-01-01

    Late Pleistocene diatomaceous sediment was widely dispersed along with volcanic ash (tephra) across and beyond New Zealand by the 25.4 ka Oruanui supereruption from Taupo volcano. We present a detailed analysis of the diatom populations in the Oruanui tephra and the newly discovered floras in two other eruptions from the same volcano: the 28.6 ka Okaia and 1.8 ka Taupo eruptions. For comparison, the diatoms were also examined in Late Pleistocene and Holocene lake sediments from the Taupo Volcanic Zone (TVZ). Our study demonstrates how these microfossils provide insights into the lake history of the TVZ since the Last Glacial Maximum. Morphometric analysis of Aulacoseira valve dimensions provides a useful quantitative tool to distinguish environmental and eruptive processes within and between individual tephras. The Oruanui and Okaia diatom species and valve dimensions are highly consistent with a shared volcanic source, paleolake and eruption style (involving large-scale magma-water interaction). They are distinct from lacustrine sediments sourced elsewhere in the TVZ. Correspondence analysis shows that small, intact samples of erupted lake sediment (i.e., lithic clasts in ignimbrite) contain heterogeneous diatom populations, reflecting local variability in species composition of the paleolake and its shallowly-buried sediments. Our analysis also shows a dramatic post-Oruanui supereruption decline in Cyclostephanos novaezelandiae, which likely reflects a combination of (1) reorganisation of the watershed in the aftermath of the eruption, and (2) overall climate warming following the Last Glacial Maximum. This decline is reflected in substantially lower proportions of C. novaezelandiae in the 1.8 ka Taupo eruption deposits, and even fewer in post-1.8 ka sediments from modern (Holocene) Lake Taupo. Our analysis highlights how the excellent preservation of siliceous microfossils in volcanic tephra may fingerprint the volcanic source region and retain a valuable record

  13. Reliable Floating Accumulation Chamber method for measuring CO2 emissions from volcanic crater lakes

    NASA Astrophysics Data System (ADS)

    Mazot, A.; Bernard, A. M.; Scott, B.

    2012-12-01

    Temporal variations in CO2 fluxes can be related to changes in the volcanic activity and may be important for the mitigation of the volcanic risk. On the recorded eruptions from 73 volcanoes hosting a lake some of them had devastating consequences on inhabited areas surrounding the volcanoes as the 1919 Kelud (Indonesia) eruption that killed 5160 people. Lake water contributed largely to the devastating lahars surrounding the volcano area. In order to measure CO2 flux from crater lakes it is necessary to measure fluxes at the water lake surface. CO2 degassing through the lake surface occurs by bubbling (convective /advective degassing) and diffusion through the water/air interface. CO2 flux survey on the surface of lakes has been performed by using the floating accumulation chamber method. With the CO2 flux measured at several sites that covered the entire lake the CO2 emission rate is quantified from the studying lake. This survey can be repeated to see any change in the CO2 degassing from the volcanic lake. Moreover, the CO2 flux surveys can give insight into the local structures present locally or regionally. In 2011, a CO2 flux campaign was performed on Lake Rotomahana, New Zealand. Lake Rotomahana was formed during the 1886 Mt. Tarawera eruption along a 17 km long fracture between Mt Tarawera and Waimangu. Pre-1886, there were two small lakes in the area occupied by present-day Lake Rotomahana. Violent phreatic and phreatomagmatic eruptions deepened and enlarged the two small lakes to form the Rotomahana Crater, now filled to a depth of ~125 m forming a lake five times larger. Today thermal activity occurs mainly along the western shore of the lake with intense bubbling areas occurring in the lake close to these geothermal manifestations. The mean CO2 flux calculated by sequential Gaussian simulation from the lake was 57 ± 5.7 g/m2/day with total emission of 549 ± 72 t/day. The mapping of the CO2 flux over the lake and the sublacustrine bottom vents detected

  14. Triggering of volcanic eruptions by large earthquakes

    NASA Astrophysics Data System (ADS)

    Nishimura, Takeshi

    2017-08-01

    When a large earthquake occurs near an active volcano, there is often concern that volcanic eruptions may be triggered by the earthquake. In this study, recently accumulated, reliable data were analyzed to quantitatively evaluate the probability of the occurrence of new eruptions of volcanoes located near the epicenters of large earthquakes. For volcanoes located within 200 km of large earthquakes of magnitude 7.5 or greater, the eruption occurrence probability increases by approximately 50% for 5 years after the earthquake origin time. However, no significant increase in the occurrence probability of new eruptions was observed at distant volcanoes or for smaller earthquakes. The present results strongly suggest that new eruptions are likely triggered by static stress changes and/or strong ground motions caused by nearby large earthquakes. This is not similar to the previously presented evidence that volcanic earthquakes at distant volcanoes are remotely triggered by surface waves generated by large earthquakes.

  15. Hydrological and chemical budgets in a volcanic caldera lake: Lake Kussharo, Hokkaido, Japan

    NASA Astrophysics Data System (ADS)

    Chikita, Kazuhisa A.; Nishi, Masataka; Fukuyama, Ryuji; Hamahara, Kazuhiro

    2004-05-01

    The contribution of groundwater output and input to lake chemistry was examined by estimating the hydrological and chemical budgets of a volcanic caldera lake, Lake Kussharo, Hokkaido, Japan. The lake level, meteorology, river water discharge and water properties were measured in the ice-covered period of February-March and in the open-water period of June-October in 2000. The inorganic chemistry was then analyzed for sporadically sampled surface water and hot spring water. The chemistry of lake water at pH of 6.91-7.57 and EC25 (electric conductivity at 25 °C) of 29.2-32.7 mS/m appears to be controlled by the input of two types of hot spring water: the inflowing Yunokawa River (pH of 2.27-2.54 and EC25 of 197.8-258.0 mS/m) and groundwater discharging directly on the shore (pH of 7.13-8.32, water temperature of 35.0-46.5 °C and EC25 of 53.1-152.0 mS/m). Excluding the days with rainfall or a great change in lake level, the water budget in June-October gave a net groundwater input of -7.41 to 2.97 m 3/s. A combination of the water budget with the chemical budget of two solutes, Na + and Cl -, led to the best estimate of groundwater output, Gout, at 3.82±3.02 m 3/s, the total fresh groundwater input, ∑ Gfresh, at 2.14±1.00 m 3/s, and the total groundwater input of hot springs, ∑ Gspa, at 0.46±0.05 m 3/s. This is comparable to G out=3.87 m3/ s, ∑G fresh=1.49 m3/ s and ∑G spa=0.41 m3/ s during the ice-covered period. The chemical flux by the freshwater input plays an important role in the alkalinity of lake water, as does the chemical flux by the shoreline hot springs. The large groundwater output could occur by the leakage through the highly permeable, underground pumice, distributed from the east-to-south lake basin to southeast of the outlet.

  16. Phosphorus fractionation in volcanic lake sediments (Azores - Portugal).

    PubMed

    Ribeiro, D C; Martins, G; Nogueira, R; Cruz, J V; Brito, A G

    2008-01-01

    The phosphorus distribution in volcanic sediments of three lakes that are under different anthropogenic pressures in São Miguel island (Azores - Portugal) was evaluated using a sequential extraction scheme. The P-fractionation scheme employs sequential extractions of sediment with NH4Cl, bicarbonate-dithionite (BD), NaOH (at room temperature), HCl and NaOH (at 85 degrees C) to obtain five P-fractions. The P-fractionation shows that in lakes with higher trophic status (Lake Furnas and Lake Sete Cidades), the NaOH extracted P is the dominant fraction, that contribute with more than 50% to total sedimentary phosphorus. The rank order of P-fractionation for these two lakes was NaOH>NaOH (85 degrees C)>HCl>BD>NH4Cl for Furnas lake and NaOH>HCl>NaOH (85 degrees C)>NH4Cl>BD for Sete Cidades lake. On the other hand, the trend of P contribution in the oligotrophic lake Fogo shows that the most inert P pools have the higher concentrations, with more than 50% of the P contribution from the last extraction step with NaOH at 85 degrees C. For this lake, the rank order of P-fractionation was NH4Cl>BD>NaOH>HCl>NaOH (85 degrees C). The Phosphorus Maximum Solubilization Potential (P-MSP) was also calculated and the results show that for the more bio-available P-fractions (first and second extraction step), the P-MSP values for Furnas and Sete Cidades lakes are sensibly higher than the results obtained in Fogo lake, an indication of the non-point diffuse load discharged in the first ones.

  17. Detecting river sediments to assess hazardous materials at volcanic lake using advanced remote sensing techniques

    NASA Astrophysics Data System (ADS)

    Saepuloh, Asep; Fitrianingtyas, Chintya

    2016-05-01

    The Toba Caldera formed from large depression of Quaternary volcanism is a remarkable feature at the Earth surface. The last Toba super eruptions were recorded around 73 ka and produced the Youngest Toba Tuff about 2,800 km3. Since then, there is no record of significant volcanic seismicity at Toba Volcanic Complex (TVC). However, the hydrothermal activities are still on going as presented by the existence of hot springs and alteration zones at the northwest caldera. The hydrothermal fluids probably containing some chemical compositions mixed with surficial water pollutant and contaminated the Toba Lake. Therefore, an environmental issues related to the existence of chemical composition and degradation of water clearness in the lake had been raised in the local community. The pollutant sources are debatable between natural and anthropogenic influences because some human activities grow rapidly at and around the lake such as hotels, tourisms, husbandry, aquaculture, as well as urbanization. Therefore, obtaining correct information about the source materials floating at the surface of the Toba Lake is crucial for environmental and hazard mitigation purposes. Overcoming the problem, we presented this paper to assess the source possibility of floating materials at Toba Lake, especially from natural sources such as hydrothermal activities of TVC and river stream sediments. The Spectral Angle Mapper (SAM) techniques using atmospherically corrected of Landsat-8 and colour composite of Polarimetric Synthetic Aperture Radar (PolSAR) were used to map the distribution of floating materials. The seven ground truth points were used to confirm the correctness of proposed method. Based on the SAM and PolSAR techniques, we could detect the interface of hydrothermal fluid at the lake surfaces. Various distributions of stream sediment were also detected from the river mouth to the lake. The influence possibilities of the upwelling process from the bottom floor of Toba Lake were also

  18. Morphology, volcanism, and mass wasting in Crater Lake, Oregon

    USGS Publications Warehouse

    Bacon, C.R.; Gardner, J.V.; Mayer, L.A.; Buktenica, M.W.; Dartnell, P.; Ramsey, D.W.; Robinson, J.E.

    2002-01-01

    Crater Lake was surveyed nearly to its shoreline by high-resolution multibeam echo sounding in order to define its geologic history and provide an accurate base map for research and monitoring surveys. The bathymetry and acoustic backscatter reveal the character of landforms and lead to a chronology for the concurrent filling of the lake and volcanism within the ca. 7700 calibrated yr B.P. caldera. The andesitic Wizard Island and central-plattform volcanoes are composed of sequences of lava deltas that record former lake levels and demonstrate simultaneous activity at the two vents. Wizard Island eruptions ceased when the lake was ~80 m lower than at present. Lava streams from prominent channels on the surface of the central platform descended to feed extensive subaqueous flow fields on the caldera floor. The Wizard Island and central-platform volcanoes, andesitic Merriam Cone, and a newly discovered probable lava flow on the eastern floor of the lake apparently date from within a few hundred years of caldera collapse, whereas a small rhydacite dome was emplaced on the flank of Wizard Island at ca. 4800 cal. yr B.P. Bedrock outcrops on the submerged caldera walls are shown in detail and, in some cases, can be correlated with exposed geologic units of Mount Mazama. Fragmental debris making up the walls elsewhere consists of narrow talus cones forming a dendritic pattern that leads to fewer, wider ridges downslope. Hummocky topography and scattered blocks up to ~280 m long below many of the embayments in the caldera wall mark debris-avalanche deposits that probably formed in single events and commonly are affected by secondary failures. The flat-floored, deep basins contain relatively fine-grained sediment transported from the debris aprons by sheet-flow turbidity currents. Crater Lake apparently filled rapidly (ca. 400-750 yr) until reaching a permeable layer above glaciated lava identified by the new survey in the northeast caldera wall at ~1845 m elevation

  19. Late Holocene volcanism at Medicine Lake Volcano, northern California Cascades

    USGS Publications Warehouse

    Donnelly-Nolan, Julie M.; Champion, Duane E.; Grove, Timothy L.

    2016-05-23

    Late Holocene volcanism at Medicine Lake volcano in the southern Cascades arc exhibited widespread and compositionally diverse magmatism ranging from basalt to rhyolite. Nine well-characterized eruptions have taken place at this very large rear-arc volcano since 5,200 years ago, an eruptive frequency greater than nearly all other Cascade volcanoes. The lavas are widely distributed, scattered over an area of ~300 km2 across the >2,000-km2 volcano. The eruptions are radiocarbon dated and the ages are also constrained by paleomagnetic data that provide strong evidence that the volcanic activity occurred in three distinct episodes at ~1 ka, ~3 ka, and ~5 ka. The ~1-ka final episode produced a variety of compositions including west- and north-flank mafic flows interspersed in time with fissure rhyolites erupted tangential to the volcano’s central caldera, including the youngest and most spectacular lava flow at the volcano, the ~950-yr-old compositionally zoned Glass Mountain flow. At ~3 ka, a north-flank basalt eruption was followed by an andesite eruption 27 km farther south that contains quenched basalt inclusions. The ~5-ka episode produced two caldera-focused dacitic eruptions. Quenched magmatic inclusions record evidence of intrusions that did not independently reach the surface. The inclusions are present in five andesitic, dacitic, and rhyolitic host lavas, and were erupted in each of the three episodes. Compositional and mineralogic evidence from mafic lavas and inclusions indicate that both tholeiitic (dry) and calcalkaline (wet) parental magmas were present. Petrologic evidence records the operation of complex, multi-stage processes including fractional crystallization, crustal assimilation, and magma mixing. Experimental evidence suggests that magmas were stored at 3 to 6 km depth prior to eruption, and that both wet and dry parental magmas were involved in generating the more silicic magmas. The broad distribution of eruptive events and the relative

  20. Oxygen Isotope Character of the Lake Owyhee Volcanic Field, Oregon

    NASA Astrophysics Data System (ADS)

    Blum, T.; Strickland, A.; Valley, J. W.

    2012-12-01

    Oxygen isotope analyses of zircons from lavas and tuffs from the Lake Owyhee Volcanic Field (LOVF) of east central Oregon unequivocally demonstrate the presence of mid-Miocene low-δ18O magmas (δ18Ozrc<4.7 ‰). Despite the growing data set of low-δ18O melts within, and proximal to, the Snake River Plain (SRP) Large Igneous Province, debate persists regarding both the mechanisms for low-δ18O magma petrogenesis, and their relative influence in the SRP. The LOVF is associated with widespread silicic volcanism roughly concurrent with the eruption of the Steens-Columbia River Basalt Group between ~17-15Ma. Silicic activity in the LOVF is limited to 16-15Ma, when an estimated 1100km3 of weakly peralkaline to metaluminous rhyolitic lavas and ignimbrites erupted from a series of fissures and calderas. Geographically, the LOVF overlaps the Oregon-Idaho Graben (OIG), and straddles the 87Sr/86Sr= 0.704 line which, together with the 0.706 line to the east, delineate the regional transition from the North American Precambrian continental crust to the east to younger Phanerozoic accreted terranes to the west. Here we report high accuracy ion microprobe analyses of δ18O in zircons using a 10-15μm spot, with average spot-to-spot precision ±0.28‰ (2SD), to investigate intra-grain and intra-unit δ18Ozrc trends for LOVF rhyolites. Due to its high closure temperature, chemical and physical resistance, and slow oxygen diffusion rates, zircon offers a robust record of magmatic oxygen isotope ratios during crystallization and provides constraints on the petrogenesis of Snake River Plain (SRP) low-δ18O melts. Individual zircons from LOVF rhyolites show no evidence of core-rim δ18O zoning, and populations exhibit ≤0.42‰ (2SD) intra-unit variability. Unit averages range from 2.2 to 4.3‰, with the lowest values in caldera-forming ignimbrites, but all units show evidence of crystallization from low-δ18O melts. Quartz and feldspar analyses by laser fluorination (precision

  1. The stable isotope geochemistry of volcanic lakes, with examples from Indonesia

    NASA Astrophysics Data System (ADS)

    Varekamp, J. C.; Kreulen, R.

    2000-04-01

    Stable isotope compositions ( δD, δ18O and δ34S) of volcanic lake waters, gas condensates and spring waters from Indonesia, Italy, Japan, and Russia were measured. The spring fluids and gas samples plot in a broad array between meteoric waters and local high-temperature volcanic gas compositions. The δD and δ18O data from volcanic lakes in East Indonesia plot in a concave band ranging from local meteoric waters to evaporated fluids to waters heavier than local high-temperature volcanic gases. We investigated isotopic fractionation processes in volcanic lakes at elevated temperatures with simultaneous mixing of meteoric waters and volcanic gases. An elevated lake water temperature gives enhanced kinetic isotope fractionation and changes in equilibrium fractionation factors, providing relatively flat isotope evolution curves in δ18O- δD diagrams. A numerical simulation model is used to derive the timescales of isotopic evolution of crater lakes as a function of atmospheric parameters, lake water temperature and fluxes of meteoric water, volcanic gas input, evaporation, and seepage losses. The same model is used to derive the flux magnitude of the Keli Mutu lakes in Indonesia. The calculated volcanic gas fluxes are of the same order as those derived from energy budget models or direct gas flux measurements in open craters (several 100 m 3 volcanic water/day) and indicate a water residence time of 1-2 decades. The δ34S data from the Keli Mutu lakes show a much wider range than those from gases and springs, which is probably related to the precipitation of sulfur in these acid brine lakes. The isotopic mass balance and S/Cl values suggest that about half of the sulfur input in the hottest Keli Mutu lake is converted into native sulfur.

  2. Rollover in volcanic crater lakes: a possible cause for Lake Nyos type disasters

    NASA Astrophysics Data System (ADS)

    Rice, A.

    2000-04-01

    Seemingly stably stratified fluids, that is a heavier layer of fluid underlying an upper layer of lighter fluid, can overturn if there is a heat flux through the system. Such events are termed ;rollover; in the engineering literature (occurring for instance in liquid natural gas tanks). They take place as well in lakes and ponds. In all such cases, the stratification starts off with the heavier, more dense fluid underlying lighter. Convection driven mixing at the stratification interface (due to the heat flux) as well as other processes serves to minimize with time the stabilizing density differences, which may eventually cause the stratification to invert. If gas has been contained under pressure in the lower layer, this gas may explosively vent from the fluid as it suddenly rises to the top such as occurs in liquid natural gas tanks where rollover is a hazard. These processes are quantifiable and are applied here to various scenarios that might refer to volcanic crater lakes whose lower layers are charged with volatiles. Provided herein are some examples of calculated conditions and calculated time of evolution leading to rollover with attendant release of gases from supersaturated ascending fluids. These calculations suggest rollover could occur in volcanic lakes. The August 1986 gas release at Lake Nyos is employed as an example. These estimates were made taking note that water is commonly supersaturated in CO2

  3. Volcanic flood simulation of magma effusion using FLO-2D for drainage of a caldera lake at the Mt. Baekdusan

    NASA Astrophysics Data System (ADS)

    Lee, Khil-Ha; Kim, Sung-Wook; Kim, Sang-Hyun

    2014-05-01

    Many volcanic craters and calderas are filled with large amounts of water that can pose significant flood hazards to downstream communities due to their high elevation and the potential for catastrophic releases of water. Recent reports pointed out the Baekdusan volcano that is located between the border of China and North Korea as a potential active volcano. Since Millennium Eruption around 1000 AD, smaller eruptions have occurred at roughly 100-year intervals, with the last one in 1903. Sudden release of huge volume of water stored in temporarily elevated caldera lakes are a recurrent feature of volcanic environments, due to the case with which outlet channels are blocked by and re-cut through, unwelded pyroclastic deposits. The volcano is showing signs of waking from a century-long slumber recently. Volcanic floods, including breakouts from volcanic lakes, can affect communities beyond the areas immediately affected by a volcanic eruption and cause significant hydrological hazards because floods from lake-filled calderas may be particularly large and high. Although a number of case studies have been presented in the literature, investigation of the underlying physical processes is required as well as a method for interpreting the process of the rapid release of water stored in a caldera lake. The development of various forecasting techniques to prevent and minimize economic and social damage is in urgent need. This study focuses on constructing a flood hazard map triggered by the magma effusion in the Baekdusan volcano. A physically-based uplift model was developed to compute the amount of water and time to peak flow. The ordinary differential equation was numerically solved using the finite difference method and Newton-Raphson iteration method was used to solve nonlinear equation. The magma effusion rate into the caldera lake is followed by examples at other volcanic activities. As a result, the hydrograph serves as an upper boundary condition when hydrodynamic

  4. ARE LAKES GETTING WARMER? REMOTE SENSING OF LARGE LAKE TEMPERATURES

    EPA Science Inventory

    Recent studies (Levitus et al., 2000) suggest a warning of the world ocean over the past 50 years. Freshwater lakes could also be getting warmer but thermal measurements to determine this are lacking. Large lake temperatures are vertically and horizontally heterogeneous and vary ...

  5. ARE LAKES GETTING WARMER? REMOTE SENSING OF LARGE LAKE TEMPERATURES

    EPA Science Inventory

    Recent studies (Levitus et al., 2000) suggest a warning of the world ocean over the past 50 years. Freshwater lakes could also be getting warmer but thermal measurements to determine this are lacking. Large lake temperatures are vertically and horizontally heterogeneous and vary ...

  6. Winter warming from large volcanic eruptions

    NASA Technical Reports Server (NTRS)

    Robock, Alan; Mao, Jianping

    1992-01-01

    An examination of the Northern Hemisphere winter surface temperature patterns after the 12 largest volcanic eruptions from 1883-1992 shows warming over Eurasia and North America and cooling over the Middle East which are significant at the 95 percent level. This pattern is found in the first winter after tropical eruptions, in the first or second winter after midlatitude eruptions, and in the second winter after high latitude eruptions. The effects are independent of the hemisphere of the volcanoes. An enhanced zonal wind driven by heating of the tropical stratosphere by the volcanic aerosols is responsible for the regions of warming, while the cooling is caused by blocking of incoming sunlight.

  7. Winter warming from large volcanic eruptions

    SciTech Connect

    Robock, A.; Mao, J.

    1992-01-01

    An examination of the Northern Hemisphere winter surface temperature patterns after the 12 largest volcanic eruptions from 1883-1992 shows warming over Eurasia and North America and cooling over the Middle East which are significant at the 95 percent level. This pattern is found in the first winter after tropical eruptions, in the first or second winter after midlatitude eruptions, and in the second winter after high latitude eruptions. The effects are independent of the hemisphere of the volcanoes. An enhanced zonal wind driven by heating of the tropical stratosphere by the volcanic aerosols is responsible for the regions of warming, while the cooling is caused by blocking of incoming sunlight.

  8. Winter warming from large volcanic eruptions

    NASA Technical Reports Server (NTRS)

    Robock, Alan; Mao, Jianping

    1992-01-01

    An examination of the Northern Hemisphere winter surface temperature patterns after the 12 largest volcanic eruptions from 1883-1992 shows warming over Eurasia and North America and cooling over the Middle East which are significant at the 95-percent level. This pattern is found in the first winter after tropical eruptions, in the first or second winter after midlatitude eruptions, and in the second winter after high latitude eruptions. The effects are independent of the hemisphere of the volcanoes. An enhanced zonal wind driven by heating of the tropical stratosphere by the volcanic aerosols is responsible for the regions of warming, while the cooling is caused by blocking of incoming sunlight.

  9. Late Cretaceous intraplate silicic volcanism in the Lake Chad region: incipient continental rift volcanism vs. Cameroon Line volcanism

    NASA Astrophysics Data System (ADS)

    Shellnutt, G.; Lee, T. Y.; Torng, P. K.; Yang, C. C.

    2015-12-01

    The crustal evolution of west-central Africa during the Cretaceous was directly related to plate motion associated with the opening of the central Atlantic Ocean. Late Cretaceous (~66 Ma) to recent magmatism related to the Cameroon Line stretches from Northern Cameroon (i.e. Golda Zuelva) to the Gulf of Guinea (i.e. Pagalu) and is considered to be due to mantle-crust interaction. The volcanic rocks at Hadjer el Khamis, west-central Chad, are considered to be amongst the oldest volcanic rocks of the Cameroon Line but their relationship is uncertain because they erupted during a period of a regional extension associated with the opening of the Late Cretaceous (~75 Ma) Termit basin. The silicic volcanic rocks can be divided into a peraluminous group and a peralkaline group with both rock types having similar chemical characteristics as within-plate granitoids. In situ U/Pb zircon dating yielded a mean 206Pb/238U age of 74.4 ± 1.3 Ma and indicates the rocks erupted ~10 million years before the next oldest eruption attributed to the Cameroon Line. The Sr isotopes (i.e. ISr = 0.7050 to 0.7143) show a wide range but the Nd isotopes (i.e. 143Nd/144Ndi = 0.51268 to 0.51271) are more uniform and indicate that the rocks were derived from a moderately depleted mantle source. Major and trace elemental modeling show that the silicic rocks likely formed by shallow fractionation of a mafic parental magma where the peraluminous rocks experienced crustal contamination and the peralkaline rocks did not. The silicic rocks are more isotopically similar to Late Cretaceous basalts in the Doba and Bongor basins (i.e. ISr = 0.7040 to 0.7060; 143Nd/144Ndi = 0.51267 to 0.51277) of southern Chad than to rocks of the Cameroon Line (i.e. ISr = 0.7026 to 0.7038; 143Nd/144Ndi = 0.51270 to 0.51300). Given the age and isotopic compositions, it is likely that the silicic volcanic rocks of the Lake Chad area are related to Late Cretaceous extensional tectonics rather than to Cameroon Line magmatism.

  10. Stable isotope composition of Earth's large lakes

    NASA Astrophysics Data System (ADS)

    Jasechko, S.; Gibson, J. J.; YI, Y.; Birks, S. J.; Sharp, Z. D.

    2011-12-01

    Lakes cover about three percent of Earth's continental area. Large lakes can significantly influence lake shore and regional climates by increasing specific humidity during evaporation and by moderating air temperatures. Stable isotopes of oxygen and hydrogen can be used to quantify lake evaporation, providing a supplementary and often cost-advantageous alternative to conventional hydrologic approaches that require over lake monitoring. Further, stable isotopes in lake sediments are an established tool in paleolimnology; however, interpreting changes to a lake's past isotope composition requires a comprehensive understanding of contemporary controls. Here, δ18O and δ2H values of water in modern lakes exceeding roughly five hundred square kilometres are compiled (n > 35). Voluminous and seasonally mixed lakes - such as the North American Great Lakes - have the most homogenous stable isotope compositions, while perennially-stratified and shallow lakes show greater variability. A rudimentary stable isotope mass balance is used to assess evaporation fluxes from large lakes on Earth. The approach taken simultaneously constrains evaporation outputs for both oxygen and hydrogen stable isotopes by accounting for lake effects on the overlying atmosphere. Model development highlights important considerations such as isotopic stratification (Tanganyika), disequilibrium isotopic mass balances (Baikal), and non-steady hydrologic balances. Further, the isotope composition of Earth's continental surface water reservoir is calculated. This value - weighted to volume - is δ18O = -7.5±1.7 per mille relative to standard mean ocean water. The compiled data may be a useful tracer of continental evaporate in global atmospheric water cycle studies and could be coupled to climate models capable of incorporating oxygen-18 and deuterium tracers to improve or validate calculations of lake effects on regional water cycling.

  11. Biogeochemical impacts of volcanic eruptions on alkaline lake environments: A case study on Lake Van in the eastern Turkey

    NASA Astrophysics Data System (ADS)

    Olgun, Nazli; Çagatay, Namık; Aksu, Abdullah; Balkıs, Nuray; Kaiser, Jerome; Öveçoglu, Lütfi; Özcan, Mustafa

    2014-05-01

    Volcanic ashes ejected during explosive volcanic eruptions can release more than fifty-five soluble elements in contact with water, most of which have environmental significance such as fluoride, chloride, the nutrients like the fixed-nitrogen, phosphate, silica and a variety of key trace metals including iron. Deposition of volcanic ash onto the aqueous environments can therefore affect the water geochemistry and eventually the phytoplankton growth in the ash fallout regions. Alkaline (soda) lakes are distributed world-wide and located almost exclusively in the volcanic regions, which have been related to the long term dissolution of volcanic products. However, although alkali lakes are found in the high volcanic impact regions, the way in which the biogeochemistry of the alkaline lake waters is affected by the volcanic eruptions still remains unknown. Lake Van, located in the eastern Turkey, is the largest of the alkaline lakes on Earth and had been exposed to various volcanic ash fallouts produced by the historical eruptions of neighbouring semi-active volcanoes Nemrut, Süphan and Tendürek. Here, we present new data from geochemical analyses of Lake Van sediments, aiming to determine the potential changes in the primary productivity related to the volcanic eruptions, by using organic biomarkers such as pigments chlorin and fucoxanthin, long chain alkenons, total organic and inorganic carbon contents of sediment layers above and below the ten selected tephra fallout deposits dating back from 1 ka to 82 ka. Furthermore, we have performed microscopic observations of the microfossils (diatoms and coccoliths) in the Lake Van sediments. Our data pointed out variable changes related to different fallout deposits including significant positive (fertilizing affect) and negative (toxic affect) impacts and as well as nearly negligible changes in the biomarker concentrations in the sediments overlying the ten tephra layers compared to the underlying sediments. We suggest

  12. Winter warming from large volcanic eruptions

    SciTech Connect

    Robock, A.; Jianping Mao )

    1992-12-24

    An examination of the Northern Hemisphere winter surface temperature patterns after the 12 largest volcanic eruptions from 1883-1992 shows warming over Eurasia and North America and cooling over the Middle East which are significant at the 95% level. This pattern is found in the first winter after tropical eruptions, in the first or second winter after midlatitude eruptions, and in the second winter after high latitude eruptions. The effects are independent of the hemisphere of the volcanoes. An enhanced zonal wind driven by heating of the tropical stratosphere by the volcanic aerosols is responsible for the regions of warming, while the cooling is caused by blocking of incoming sunlight. 21 refs., 2 figs., 1 tab.

  13. Water-quality effects on Baker Lake of recent volcanic activity at Mount Baker, Washington

    USGS Publications Warehouse

    Bortleson, Gilbert Carl; Wilson, Reed T.; Foxworthy, B.L.

    1976-01-01

    , mineral-rich inflow depend mainly on: (1) the rate of flow and the character of Boulder Creek water at the time; (2) the relative rate of inflow of the feedwater from other streams; and (3) whether the reservoir is temperature-stratified (summer) or homothermal (winter). A distinct layer of Boulder Creek water was found in the lake in September 1975 extending at least 0.3 miles (.5 km) downreservoir. The greatest opportunity for water from Boulder Creek to persist as a layer and extend farthest before mixing with the other reservoir water is when Baker Lake is strongly stratified and Boulder Creek flow rate is large in relation to other feedwater. Baker Lake probably could assimilate indefinitely the acid loads measured during 1975, by dilution, chemical neutralization, and buffering of the acid-rich Boulder creek water. Minor elements found in Boulder Creek water included arsenic, selenium, and mercury; however, none of these would reach the limits recommended by the U.S. Environmental Protection Agency for public water supplies unless their concentrations increased to several times the amounts found during this study. Under the prevailing conditions, acid-rich Boulder Creek water apparently cannot accumulate as a pool, or persist as a layer long enough to reach Upper Baker Dam and attack the concrete. However, even if the acid load from Boulder Creek does not greatly increase, occasional light fish mortalities may result near the mouth of the creek. Greater acid and mineral loads, resulting from further increases in volcanic activity or other possible causes, could be more harmful, especially to the fish. Continued monitoring of Boulder Creek flow and water quality is needed to rapidly any changes in conditions at Sherman Crater, and to provide warning of possible greater impacts on Baker Lake from any future increases in Mount Baker activity.

  14. Late Archean mafic volcanism in the Rainy Lake area, Minnesota

    SciTech Connect

    Day, W.C.

    1985-01-01

    The Late Archean greenstone-granite terrane of the Rainy Lake area of Minnesota contains a bimodal suite of mafic and felsic volcanic and coeval intrusive rocks. New geochemical data show that the mafic rocks occur in three distinct suites: (1) low-Ti olivine- and quartz-tholeiite, (2) high-Ti quartz-tholeiite and basaltic andesite, and (3) calc-alkaline lamprophyric monzodiorite and quartz diorite. The low-Ti tholeiites have only slightly evolved Mg-numbers from 53-63, Ni=125-300 ppm, and MORB-like REE. In contrast, the high-Ti tholeiites are more evolved, with Mg*=26-48, Ni=43-135 ppm, and higher total REE. Compared to the tholeiitic suites, the monzodiorite suite has more primitive Mg-numbers, with Mg*=70-78, Ni<410 ppm, and anomalously high LREE. The two tholeiitic suites cannot be genetically related by simple fractionation from a single parent magma; however, lower degrees of partial melting (<8 percent) of a mantle source (spinel periodotite) with REE=2-4 times chondrites could have produced the high-Ti tholeiites, and higher degrees of melting (20-30 percent) of a similar source could have generated the low-Ti tholeiites. In contrast, the monzodiorite suite must have been generated from either a LREE-rich or (and) a garnet-bearing source (garnet periodotite). The authors conclude that shallow melting (<40-50 km) within the Archean mantle in the Rainy Lake area produced the tholeiitic rocks, and that deep melting (>40-50 km) generated the lamprophyric monzodiorites.

  15. Preliminary volcano hazard assessment for the Emmons Lake volcanic center, Alaska

    USGS Publications Warehouse

    Waythomas, Christopher; Miller, Thomas P.; Mangan, Margaret T.

    2006-01-01

    The Emmons Lake volcanic center is a large stratovolcano complex on the Alaska Peninsula near Cold Bay, Alaska. The volcanic center includes several ice- and snow-clad volcanoes within a nested caldera structure that hosts Emmons Lake and truncates a shield-like ancestral Mount Emmons edifice. From northeast to southwest, the main stratovolcanoes of the center are: Pavlof Sister, Pavlof, Little Pavlof, Double Crater, Mount Hague, and Mount Emmons. Several small cinder cones and vents are located on the floor of the caldera and on the south flank of Pavlof Volcano. Pavlof Volcano, in the northeastern part of the center, is the most historically active volcano in Alaska (Miller and others, 1998) and eruptions of Pavlof pose the greatest hazards to the region. Historical eruptions of Pavlof Volcano have been small to moderate Strombolian eruptions that produced moderate amounts of near vent lapilli tephra fallout, and diffuse ash plumes that drifted several hundreds of kilometers from the vent. Cold Bay, King Cove, Nelson Lagoon, and Sand Point have reported ash fallout from Pavlof eruptions. Drifting clouds of volcanic ash produced by eruptions of Pavlof would be a major hazard to local aircraft and could interfere with trans-Pacific air travel if the ash plume achieved flight levels. During most historical eruptions of Pavlof, pyroclastic material erupted from the volcano has interacted with the snow and ice on the volcano producing volcanic mudflows or lahars. Lahars have inundated most of the drainages heading on the volcano and filled stream valleys with variable amounts of coarse sand, gravel, and boulders. The lahars are often hot and would alter or destroy stream habitat for many years following the eruption. Other stratocones and vents within the Emmons Lake volcanic center are not known to have erupted in the past 300 years. However, young appearing deposits and lava flows suggest there may have been small explosions and minor effusive eruptive activity

  16. An aem-tem study of weathering and diagenesis, Abert Lake, Oregon: I. Weathering reactions in the volcanics

    USGS Publications Warehouse

    Banfield, J.F.; Jones, B.F.; Veblen, D.R.

    1991-01-01

    Abert Lake in south-central Oregon provides a site suitable for the study of sequential weathering and diagenetic events. In this first of two papers, transmission electron microscopy was used to characterize the igneous mineralogy, subsolidus alteration assemblage, and the structural and chemical aspects of silicate weathering reactions that occur in the volcanic rocks (basalts, basaltic andesites, and dacitic/ rhyolitic extrusive and pyroclastics) that outcrop around the lake. Olivine and pyroxene replacement occurred topotactically, whereas feldspar and glass alteration produced randomly oriented smectite in channels and cavities. The tetrahedral, octahedral, and interlayer compositions of the weathering products, largely dioctahedral smectites, varied with primary mineral composition, rock type, and as the result of addition of elements released from adjacent reaction sites. Weathering of the highly evolved, Fe-rich Jug Mountain complex at the north end of the lake produced a homogeneous smectite assemblage that contrasts with the heterogeneous smectite assemblage replacing the volcanics along the eastern margin of the lake. The variability within and between the smectite assemblages highlights the microenvironmental diversity, fluctuating redox conditions, and variable solution chemistry associated with mineral weathering reactions in the surficial environment. Late-stage exhalative and aqueous alteration of the volcanics redistributed many components and formed a variety of alkali and alkali-earth carbonate, chloride, sulfate, and fluoride minerals in vugs and cracks. Overall, substantial Mg, Si, Na, Ca, and K are released by weathering reactions that include the almost complete destruction of the Mg-smectite that initially replaced olivine. The leaching of these elements from the volcanics provides an important source of these constituents in the lake water. The nature of subsequent diagenetic reactions resulting from the interaction between the materials

  17. Quantification of the CO2 emitted from volcanic lakes in Pico Island (Azores)

    NASA Astrophysics Data System (ADS)

    Andrade, César; Cruz, José; Viveiros, Fátima; Branco, Rafael

    2017-04-01

    This study shows the results of the diffuse CO2 degassing surveys performed in lakes from Pico volcanic Island (Azores archipelago, Portugal). Detailed flux measurements using the accumulation chamber method were made at six lakes (Capitão, Caiado, Paul, Rosada, Peixinho and Negra) during two field campaigns, respectively, in winter (February 2016) and late summer (September 2016). Pico is the second largest island of the Azores archipelago with an area of 444.8 km2; the oldest volcanic unit is dated from about 300,000 years ago. The edification of Pico was mainly due to Hawaiian and Strombolian type volcanic activity, resulting in pahoehoe and aa lava flows of basaltic nature, as well as scoria and spatter cones. Three main volcanic complexes are identified in the island, namely (1) the so-called Montanha Volcanic Complex, corresponding to a central volcano located in the western side of the island that reaches a maximum altitude of 2351 m, (2) the São Roque-Piedade Volcanic Complex, and (3) the Topo-Lajes Volcanic Complex, this last one corresponding to the remnants of a shield volcano located in the south coast. The studied lakes are spread along the São Roque-Piedade Volcanic Complex at altitudes between 785 m and 898 m. Three are associated with depressions of undifferentiated origin (Caiado, Peixinho, Negra), two with depressions of tectonic origin (Capitão, Paul), while Rosada lake is located inside a scoria cone crater. The lakes surface areas vary between 1.25x10-2 and 5.38x10-2 km2, and the water column maximum depth is 7.9 m (3.5-7.9 m). The water storage ranges between 3.6x104 to 9.1x104 m3, and the estimated residence time does not exceed 1.8x10-1 years. A total of 1579 CO2 flux measurements were made during both surveys (868 in summer and 711 in the winter campaign), namely 518 in Caiado lake (293; 225), 358 in Paul (195; 163), 279 in Capitão (150, 129), 200 in Rosada (106, 94), 171 in Peixinho (71, 100) and 53 measurements in Negra lake. Negra

  18. A Holocene Lake Record from Laguna Del Maule (LdM) in the Chilean Andes: Climatic and Volcanic Controls on Lake Depositional Dynamics

    NASA Astrophysics Data System (ADS)

    Valero-Garces, B. L.; Frugone Alvarez, M.; Barreiro-Lostres, F.; Carrevedo, M. L.; Latorre Hidalgo, C.; Giralt, S.; Maldonado, A.; Bernárdez, P.; Prego, R.; Moreno-Caballud, A.

    2014-12-01

    Central Chile is a tectonically active, drought-prone region sensitive to latitudinal variations in large-scale cold fronts associated with fluctuations of the Pacific subtropical high. Holocene high-resolution records of climate and volcanic events could help inform more on the frequency of extensive droughts as well as volcanic and seismic hazards. LdM is a high altitude, volcanic lake located in the Transition Southern Volcanic Zone (~36°S, 2200 m.a.s.l). The LdM volcanic field is a very seismically and volcanically active zone in the Andes, with several caldera-forming eruptions over the last 1.5 Ma, and intense postglacial activity. In 2013, we recovered over 40 m of sediment cores at four sites of LdM and collected > 20 km of seismic lines. The cores were imaged, their physical and geochemical properties analysed with a Geotek MSCL and XRF scanner respectively, and sampled for TOC, TIC, TS, TN, BioSi, and bulk mineralogy. The chronology was constructed with a Bayesian age-depth model including 210Pb-137Cs, the Quizapú volcanic ash (1932 AD) and 17 AMS 14C dates. The 4.8 m long composite sequence spans the Late glacial and Holocene.Sediments are massive to banded, quartz and plagioclase-rich silts with variable diatom (BioSi, 15- 30 %) and organic matter content (TOC, 1-5 %). Four main units have been defined based on sedimentological and geochemical composition. The transition from Unit 4 to 3 is ascribed to the onset of the Holocene; Unit 2 spans the mid Holocene, and Unit 1 the last 4 ka. Higher (lower) TOC, Br/Ti and Fe/Mn ratios in units 1 and 3 (2 and 4) suggest higher (lower) organic productivity in the lake and dominant oxic (anoxic) conditions at the bottom of the lake. Up to 17 ash and lapilli layers mark volcanic events, mostly grouped in units 1 and 3. Periods of higher lake productivity (units 1 and 3) are synchronous to higher frequency of volcanic events. Some climate transitions (LIA, 4ka, 8ka and 11ka) are evident in the LdM sequence

  19. Comparing the Hazards From Large Volcanic Eruptions and Impacting Asteroids

    NASA Astrophysics Data System (ADS)

    Mason, B. G.; Pyle, D. M.

    2003-12-01

    Explosive volcanic eruptions and asteroid impacts leave craters that allow direct comparison of the scale and frequency of these severe events. We have compiled data on large volcanic eruptions over the past 45 million years, and used this to develop an improved quantitative assessment of the frequency of large volcanic eruptions, and to make a comparative assessment of the relative likelihood of the Earth being affected by severe volcanic eruptions, and impact events of equal severity. In terms of volcanic activity, the expected frequency of explosive eruptions involving > 1015 kg of rock lies between 1.3 and 22 events per million years. For the events that form terrestrial craters with diameters of order 10 - 25 km, the thermal energy release (during a volcanic eruption) is of the same order of magnitude as the kinetic energy release (from an asteroid impact), and ca. 1021 - 1022 J (2 x 105 - 2 x 106 Mt equivalent of TNT). Over the past 5 Ma, volcanic activity dominates the production rate of craters < 45 km diameter. This suggests that over short timescales (< 1 Ma), destructive volcanic eruptions are more frequent than impact events of a similar energy. A better comparison of the primary effects of both phenomena may be realised by considering the area destroyed by shock waves (impactors) or hot pyroclastic deposits (volcanoes). Using simple scalings, we show that the primary area destroyed by an impactor is about ten times that for an eruption. Using this area as a measure of severity, we can show that for events with a return period of 100,000 years or less, there are considerably more eruptions of a given severity than there are impact events. Impactor events only dominate for return periods of > 200,000 - 500,000 years. We conclude that smaller (< 1012 kg, < 1 km diameter) near-earth orbiters pose a significantly smaller hazard to humans than the regional effects of large (1014 - 1015 kg) volcanic eruptions.

  20. Intrabasin Variability of Volcanic Ash Stratigraphy in a Small Kettle Lake; Lorraine Lake, Anchorage, Alaska

    NASA Astrophysics Data System (ADS)

    Kathan, K. M.; Werner, A.; Kaufman, D. S.; Waythomas, C. F.; Wallace, K. L.

    2004-12-01

    Lorraine Lake is a small (0.53 km2) shallow (ca. 8 m) kettle located on the Elmendorf Moraine (Pleistocene age) 11 km northwest of Anchorage, Alaska. Situated in an area of low relief (49 m), the basin has a small drainage basin (1.3 km2), no inflow and remains ice covered for approximately six months of the year. This study was initiated to resolve the volcanic ash-fall record preserved in the Holocene lake sediments from this basin, and to evaluate intrabasinal variability of ash stratigraphies. It was hypothesized that tephra deposition varies spatially across the lake and that some locations exhibit a more complete record of ash fall than others. This variation may possibly be due to tephra being redistributed by wind on the frozen or open-water surface, carried by currents once it sinks, or mixed by bioturbation following deposition. Six sediment cores between 3.2 and 5.8 m long were recovered from the north, south, east, and west parts of the lake, which is divided into two (north and south) sub-basins. A total of 21 AMS 14C ages were obtained on terrestrial macrofossils and basal ages from three cores are greater than 14,500 cal yr. BP, confirming that the cores contain the entire postglacial sedimentary record. Eleven tephra deposits, ranging from invisible to several centimeters in thickness, were correlated among the cores based on their relative depths, spacing, color, texture, thickness, high magnetic susceptibility (MS), low loss-on-ignition, X-ray gray scale value, and abundance of magnetic minerals. Although other diffuse tephra units occur, these 11 clearly defined units are used to compare tephra deposition within the lake. Several physical characteristics were compared to evaluate possible intrabasin variability including stratigraphic thickness, and X-ray density stratigraphy. A numerical classification scheme was developed ranking visual and stratigraphic prominence based on thickness, purity of ash and nature (sharpness and continuity) of

  1. Volcanic Resurfacing as an Alternative Mechanism for Formation of Martian ``Crater Lake'' Features

    NASA Astrophysics Data System (ADS)

    Leverington, D. W.

    2004-05-01

    Martian impact craters associated with channels and inner terraces have previously been considered excellent candidates for the locations of ancient lacustrine environments. However, a study of thirty widely-distributed regions containing typical examples of purported crater lakes suggests instead that the channel and terrace features may have formed through igneous processes involving the flow and ponding of lava. While a variety of processes must have been responsible for early terrain evolution at these sites, it is apparent that more recent volcanic resurfacing events were the source of much of the crater fill present at the sites and in surrounding regions, and were responsible for the formation of features related to the flow, deposition, and subsidence of these materials. Evidence in support of an igneous origin for ``crater lake'' features includes: a) strong morphological similarity between channels and sinuous volcanic rilles on both Mars and the Moon; b) widespread association with crater fill of wrinkle ridges, lobate margins, and peripheral terraces and moats, all of which bear strong resemblance to corresponding lunar features considered to be indicative of the flow and subsidence of volcanic materials; c) similarity between the local surface texture of crater fill and that of materials found on the flanks of large Martian volcanoes; and d) cratering records and nighttime thermal properties of crater fill that are consistent with relatively dense and consolidated materials. The case for the igneous origin of terrace, channel, and fill features in the study areas is further strengthened by inconsistencies between the nature of these features and the lacustrine hypothesis. These findings have potentially important implications regarding our understanding of the evolution of Martian climate and the volatile history of the planet. They furthermore suggest that astrobiological conclusions made on the basis of earlier lacustrine interpretations may need to

  2. Variety and sustainability of volcanic lakes: Response to subaqueous thermal activity predicted by a numerical model

    NASA Astrophysics Data System (ADS)

    Terada, Akihiko; Hashimoto, Takeshi

    2017-08-01

    We use a numerical model to investigate the factors that control the presence or absence of a hot crater lake at an active volcano. We find that given a suitable pair of parameters (e.g., the enthalpy of subaqueous fumaroles and the ratio of mass flux of the fluid input at the lake bottom to lake surface area), hot crater lakes can be sustained on relatively long timescales. Neither a high rate of precipitation nor an impermeable layer beneath the lake bottom are always necessary for long-term sustainability. The two controlling parameters affect various hydrological properties of crater lakes, including temperature, chemical concentrations, and temporal variations in water levels. In the case of low-temperature crater lakes, increases in flux and enthalpy, which are a common precursor to phreatic or phreatomagmatic eruptions, result in an increase in both temperature and water level. In contrast, a decrease in water level accompanied by a rise in temperature occurs at high-temperature lakes. Furthermore, our model suggests that crater geometry is a key control on water temperature. For lakes with a conical topography, a perturbation in the water level due to trivial nonvolcanic activity, such as low levels of precipitation, can cause persistent increases in water temperature and chemical concentrations, and a decrease in the water level, even though subaqueous fumarolic activity does not change. Such changes in hot crater lakes which are not caused by changes in volcanic activity resemble the volcanic unrest that precedes eruptions.

  3. [Ichthyofauna and its community diversity in volcanic barrier lakes of Northeast China].

    PubMed

    Yang, Fu-Yi; Lü, Xian-Guo; Lou, Yan-Jing; Lou, Xiao-Nan; Xue, Bin; Yao, Shu-Chun; Xiao, Hai-Feng

    2012-12-01

    Based on the investigations of fish resources in Jingpo Lake and Wudalianchi Lakes in 2008-2011 and the historical data, this paper analyzed the characteristics of ichthyofauna and its community diversity in volcanic barrier lakes of Northeast China. The ichthyofauna in the volcanic barrier lakes of Northeast China was consisted of 64 native species, belonging to 47 genera, 16 families, and 9 orders, among which, one species was the second class National protected wild animal, four species were Chinese endemic species, and five species were Chinese vulnerable species. In the 64 recorded species, there were 44 species of Cypriniformes order and 37 species of Cyprinidae family dominated, respectively. The ichthyofauna in the volcanic barrier lakes of Northeast China was formed by 7 fauna complexes, among which, the eastern plain fauna complex was dominant, the common species from the South and the North occupied 53.1%, and the northern endemic species took up 46.9%. The Shannon, Fisher-alpha, Pielou, Margalef, and Simpson indices of the ichthyofauna were 2.078, 4.536, 0.575, 3.723, and 0.269, respectively, and the abundance distribution pattern of native species accorded with lognormal model. The Bray-Curtis, Morisita-Horn, Ochiai, Sørensen, and Whittaker indices between the communities of ichthyofauna in the volcanic barrier lakes of Northeast China and the Jingpo Lake were 0.820, 0.992, 0.870, 0.862 and 0.138, respectively, and those between the communities of ichthyofauna in the volcanic barrier lakes and the Wudalianchi Lakes were 0.210, 0.516, 0.838, 0.825, and 0.175, respectively. The ichthyofauna in volcanic barrier lakes of Northeast China was characterized by the mutual infiltration between the South and the North, and the overlap and transition between the Palaeoarctic realm and the Oricetal realm. It was suggested that the ichthyofauna community species diversity in the volcanic barrier lakes of Northeast China was higher, the species structure was more

  4. Wind-induced Microseisms from Large Lakes

    NASA Astrophysics Data System (ADS)

    Kerman, Bryan R.; Mereu, Robert F.; Roy, Denis

    The characteristics of microseisms measured by seismometers near the shore of Lake Ontario and Great Slave Lake are analyzed. For Lake Ontario the rms levels in the 1 to 3 Hz band are coherent between stations widely separated around its western basin indicating a common generative mechanism. A distinct onshore intermittent flux of Rayleigh-like wave energy was detected at the onshore sites for both lakes. Microseismic energy in this band is correlated with the wind speed. The correlation improves as the winds are averaged into the past until an optimum is reached corresponding to the time constant of water wave generation by changing wind speed. For a given fixed wind speed, the microseismic energy correlates with the average fetch of the wind over the lake. The sensitivity to fetch effects is similar for both onshore and offshore stations indicating that shoaling is probably not a source. Niagara Falls which also can have a wind-dependent flow from Lake Erie causes measurable effect to at least 25 km but does not noticeably affect stations at a distance of 150 km. It is suggested that the microseismic flux provides a natural, relatively inexpensive way to monitor the water wave field on such large lakes. Further, such seismic observations may provide useful insights into wave generation mechanisms, in particular a lake's response to variable wind speed, the onset of rough flow and the spatial variability of the wave field. Additionally a large lake may well prove to have a stronger source strength of microseisms than an ocean.

  5. Global monsoon precipitation responses to large volcanic eruptions.

    PubMed

    Liu, Fei; Chai, Jing; Wang, Bin; Liu, Jian; Zhang, Xiao; Wang, Zhiyuan

    2016-04-11

    Climate variation of global monsoon (GM) precipitation involves both internal feedback and external forcing. Here, we focus on strong volcanic forcing since large eruptions are known to be a dominant mechanism in natural climate change. It is not known whether large volcanoes erupted at different latitudes have distinctive effects on the monsoon in the Northern Hemisphere (NH) and the Southern Hemisphere (SH). We address this issue using a 1500-year volcanic sensitivity simulation by the Community Earth System Model version 1.0 (CESM1). Volcanoes are classified into three types based on their meridional aerosol distributions: NH volcanoes, SH volcanoes and equatorial volcanoes. Using the model simulation, we discover that the GM precipitation in one hemisphere is enhanced significantly by the remote volcanic forcing occurring in the other hemisphere. This remote volcanic forcing-induced intensification is mainly through circulation change rather than moisture content change. In addition, the NH volcanic eruptions are more efficient in reducing the NH monsoon precipitation than the equatorial ones, and so do the SH eruptions in weakening the SH monsoon, because the equatorial eruptions, despite reducing moisture content, have weaker effects in weakening the off-equatorial monsoon circulation than the subtropical-extratropical volcanoes do.

  6. Global monsoon precipitation responses to large volcanic eruptions

    PubMed Central

    Liu, Fei; Chai, Jing; Wang, Bin; Liu, Jian; Zhang, Xiao; Wang, Zhiyuan

    2016-01-01

    Climate variation of global monsoon (GM) precipitation involves both internal feedback and external forcing. Here, we focus on strong volcanic forcing since large eruptions are known to be a dominant mechanism in natural climate change. It is not known whether large volcanoes erupted at different latitudes have distinctive effects on the monsoon in the Northern Hemisphere (NH) and the Southern Hemisphere (SH). We address this issue using a 1500-year volcanic sensitivity simulation by the Community Earth System Model version 1.0 (CESM1). Volcanoes are classified into three types based on their meridional aerosol distributions: NH volcanoes, SH volcanoes and equatorial volcanoes. Using the model simulation, we discover that the GM precipitation in one hemisphere is enhanced significantly by the remote volcanic forcing occurring in the other hemisphere. This remote volcanic forcing-induced intensification is mainly through circulation change rather than moisture content change. In addition, the NH volcanic eruptions are more efficient in reducing the NH monsoon precipitation than the equatorial ones, and so do the SH eruptions in weakening the SH monsoon, because the equatorial eruptions, despite reducing moisture content, have weaker effects in weakening the off-equatorial monsoon circulation than the subtropical-extratropical volcanoes do. PMID:27063141

  7. Oxygen isotope evolution of the Lake Owyhee volcanic field, Oregon, and implications for the low-δ18O magmatism of the Snake River Plain-Yellowstone hotspot and other low-δ18O large igneous provinces

    NASA Astrophysics Data System (ADS)

    Blum, Tyler B.; Kitajima, Kouki; Nakashima, Daisuke; Strickland, Ariel; Spicuzza, Michael J.; Valley, John W.

    2016-11-01

    The Snake River Plain-Yellowstone (SRP-Y) hotspot track represents the largest known low-δ18O igneous province; however, debate persists regarding the timing and distribution of meteoric hydrothermal alteration and subsequent melting/assimilation relative to hotspot magmatism. To further constrain alteration relations for SRP-Y low-δ18O magmatism, we present in situ δ18O and U-Pb analyses of zircon, and laser fluorination δ18O analyses of phenocrysts, from the Lake Owyhee volcanic field (LOVF) of east-central Oregon. U-Pb data place LOVF magmatism between 16.3 and 15.4 Ma, and contain no evidence for xenocrystic zircon. LOVF δ18O(Zrc) values demonstrate (1) both low-δ18O and high-δ18O caldera-forming and pre-/post-caldera magmas, (2) relative increases in δ18O between low-δ18O caldera-forming and post-caldera units, and (3) low-δ18O magmatism associated with extension of the Oregon-Idaho Graben. The new data, along with new compilations of (1) in situ zircon δ18O data for the SRP-Y, and (2) regional δ18O(WR) and δ18O(magma) patterns, further constrain the thermal and structural associations for hydrothermal alteration in the SRP-Y. Models for low-δ18O magmatism must be compatible with (1) δ18O(magma) trends within individual SRP-Y eruptive centers, (2) along axis trends in δ18O(magma), and (3) the high concentration of low-δ18O magmas relative to the surrounding regions. When considered with the structural and thermal evolution of the SRP-Y, these constraints support low-δ18O magma genesis originating from syn-hotspot meteoric hydrothermal alteration, driven by hotspot-derived thermal fluxes superimposed on extensional tectonics. This model is not restricted to continental hotspot settings and may apply to several other low-δ18O igneous provinces with similar thermal and structural associations.

  8. Late Cretaceous intraplate silicic volcanic rocks from the Lake Chad region: An extension of the Cameroon volcanic line?

    NASA Astrophysics Data System (ADS)

    Shellnutt, J. G.; Lee, T.-Y.; Torng, P.-K.; Yang, C.-C.; Lee, Y.-H.

    2016-07-01

    Silicic volcanic rocks at Hadjer el Khamis, near Lake Chad, are considered to be an extension of the Cameroon volcanic line (CVL) but their petrogenetic association is uncertain. The silicic rocks are divided into peraluminous and peralkaline groups with both rock types chemically similar to within-plate granitoids. In situ U/Pb zircon dating yielded a mean 206Pb/238U age of 74.4 ± 1.3 Ma indicating the magmas erupted ˜10 million years before the next oldest CVL rocks (i.e., ˜66 Ma). The Sr isotopes (i.e., ISr = 0.7021-0.7037) show a relatively wide range but the Nd isotopes (i.e., 143Nd/144Ndi = 0.51268-0.51271) are uniform and indicate that the rocks were derived from a moderately depleted mantle source. Thermodynamic modeling shows that the silicic rocks likely formed by fractional crystallization of a mafic parental magma but that the peraluminous rocks were affected by low temperature alteration processes. The silicic rocks are more isotopically similar to Late Cretaceous basalts identified within the Late Cretaceous basins (i.e., 143Nd/144Ndi = 0.51245-0.51285) of Chad than the uncontaminated CVL rocks (i.e., 143Nd/144Ndi = 0.51270-0.51300). The age and isotopic compositions suggest the silicic volcanic rocks of the Lake Chad region are related to Late Cretaceous extensional volcanism in the Termit basin. It is unlikely that the silicic volcanic rocks are petrogenetically related to the CVL but it is possible that magmatism was structurally controlled by suture zones that formed during the opening of the Central Atlantic Ocean and/or the Pan-African Orogeny.

  9. Quilotoa volcano — Ecuador: An overview of young dacitic volcanism in a lake-filled caldera

    NASA Astrophysics Data System (ADS)

    Hall, Minard L.; Mothes, Patricia A.

    2008-09-01

    Quilotoa volcano, an example of young dacitic volcanism in a lake-filled caldera, is found at the southwest end of the Ecuador's volcanic front. It has had a long series of powerful plinian eruptions of moderate to large size (VEI = 4-6), at repetitive intervals of roughly 10-15 thousand years. At least eight eruptive cycles (labeled Q-I to Q-VIII with increasing age) over the past 200 ka are recognized, often beginning with a phreatomagmatic onset and followed by a pumice-rich lapilli fall, and then a sequence of pumice, crystal, and lithic-rich deposits belonging to surges and ash flows. These unwelded pyroclastic flows left veneers on hillsides as well as very thick accumulations in the surrounding valleys, the farthest ash flow having traveled about 17 km down the Toachi valley. The bulk volumes of the youngest flow deposits are on the order of 5 km 3, but that of Q-I's 800 yr BP ash-fall unit is about 18 km 3. In the last two eruption cycles water has had a more important role. Upon Quilotoa's low-relief volcanic edifice, three calderas are recognized; the formation of the oldest one predates the Q-IV cycle and the others occurred during the Q-II and Q-I cycles. Dacite lava domes are common along the present caldera rim and most were emplaced at the end of the Q-II cycle; older domes of dark dacite belong to the Q-III and IV cycles. The explosive onset of the Q-I cycle expulsed as much as 250 million m 3 of the lake's water, resulting in large debris flows that scoured the eastern flanks of the edifice and descended the Toachi river. Little variation in the mineralogy and chemistry of Quilotoa's eruptive products is observed, suggesting that the source is a homogeneous magma body at shallow depth. Both the pyroclastic material and the domes are composed chiefly of gray porphyritic dacites carrying large phenocrysts of plagioclase, amphibole, biotite, and occasionally quartz.

  10. Regional Triggering of Volcanic Activity Following Large Magnitude Earthquakes

    NASA Astrophysics Data System (ADS)

    Hill-Butler, Charley; Blackett, Matthew; Wright, Robert

    2015-04-01

    There are numerous reports of a spatial and temporal link between volcanic activity and high magnitude seismic events. In fact, since 1950, all large magnitude earthquakes have been followed by volcanic eruptions in the following year - 1952 Kamchatka M9.2, 1960 Chile M9.5, 1964 Alaska M9.2, 2004 & 2005 Sumatra-Andaman M9.3 & M8.7 and 2011 Japan M9.0. While at a global scale, 56% of all large earthquakes (M≥8.0) in the 21st century were followed by increases in thermal activity. The most significant change in volcanic activity occurred between December 2004 and April 2005 following the M9.1 December 2004 earthquake after which new eruptions were detected at 10 volcanoes and global volcanic flux doubled over 52 days (Hill-Butler et al. 2014). The ability to determine a volcano's activity or 'response', however, has resulted in a number of disparities with <50% of all volcanoes being monitored by ground-based instruments. The advent of satellite remote sensing for volcanology has, therefore, provided researchers with an opportunity to quantify the timing, magnitude and character of volcanic events. Using data acquired from the MODVOLC algorithm, this research examines a globally comparable database of satellite-derived radiant flux alongside USGS NEIC data to identify changes in volcanic activity following an earthquake, February 2000 - December 2012. Using an estimate of background temperature obtained from the MODIS Land Surface Temperature (LST) product (Wright et al. 2014), thermal radiance was converted to radiant flux following the method of Kaufman et al. (1998). The resulting heat flux inventory was then compared to all seismic events (M≥6.0) within 1000 km of each volcano to evaluate if changes in volcanic heat flux correlate with regional earthquakes. This presentation will first identify relationships at the temporal and spatial scale, more complex relationships obtained by machine learning algorithms will then be examined to establish favourable

  11. Impact of volcanism on the evolution of Lake Van I: evolution of explosive volcanism of Nemrut Volcano (eastern Anatolia) during the past >400,000 years

    NASA Astrophysics Data System (ADS)

    Sumita, Mari; Schmincke, Hans-Ulrich

    2013-05-01

    The historically active Nemrut Volcano (2,948 m asl) (Eastern Anatolia), rising close to the western shore of huge alkaline Lake Van, has been the source of intense Plinian eruptions for >530,000 years (drilled lake sediments). About 40 widespread, newly recognized trachytic and less common rhyolitic fallout tephras and ca. 12 interbedded ignimbrites, sourced in Nemrut Volcano, are documented in stratigraphic traverses throughout an area of >6,000 km2 mostly west of Lake Van. Phenocrysts in the moderately peralkaline trachytes and rarer large-volume comenditic rhyolites comprise anorthoclase, hedenbergite-augite, fayalite and, especially in trachytic units, augite, minor aenigmatite, apatite and quartz, and rare chevkinite and zircon. Dacitic to rhyolitic tephras from nearby calcalkalic Süphan Volcano (4,058 m asl), locally interbedded with Nemrut tephras, are characterized by disequilibrium phenocryst assemblages (biotite, augitic clinopyroxene and hypersthene, minor olivine, common crystal clots and/or, in some deposits, amphibole). The magma volume (DRE) of the largest Nemrut tephra sheet (AP-1) described in detail may exceed 30 km3. Extreme facies and systematic compositional changes are documented in the ca. 30 ka Nemrut Formation (NF) deposits formed from one large and complex eruption (thick rhyolitic fallout overlain by ignimbrite, welded agglutinate, overbank surge deposits, and final more mafic fallout deposits). Common evidence of magma mixing in Nemrut ignimbrites reflects eruption from compositionally zoned magma reservoirs. Several young Çekmece Formation trachytes overlying ca. 30 ka old NF deposits and the late trachytes of the NF deposits show compositional affinities to tephra from Süphan Volcano possibly due to temporary influx of Süphan magmas into the Nemrut system following the evacuation of >10 km3 magma (DRE) during the caldera-forming NF eruption. Axes of large fallout fans are dominantly SW-NE but W-E in the younger sheets resembling

  12. A viable microbial community in a subglacial volcanic crater lake, Iceland.

    PubMed

    Gaidos, Eric; Lanoil, Brian; Thorsteinsson, Thorsteinn; Graham, Andrew; Skidmore, Mark; Han, Suk-Kyun; Rust, Terri; Popp, Brian

    2004-01-01

    We describe a viable microbial community in a subglacial lake within the Grímsvötn volcanic caldera, Iceland. We used a hot water drill to penetrate the 300-m ice shelf and retrieved lake water and volcanic tephra sediments. We also acquired samples of borehole water before and after penetration to the lake, overlying glacial ice and snow, and water from a nearby subaerial geothermal lake for comparative analyses. Lake water is at the freezing point and fresh (total dissolved solids = 260 mg L(-1)). Detectable numbers of cells were found in samples of the lake water column and tephra sediments: 2 x 10(4) ml(-1) and 4 x 10(7) g(-1), respectively. Plate counts document abundant cold-adapted cultivable organisms in the lake water, but not in the borehole (before penetration) or glacial ice. Denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene fragments amplified from genomic DNA extracted from Grímsvötn samples indicates that the lake community is distinct from the assemblages of organisms in borehole water (before penetration) and the overlying ice and snow. Sequencing of selected DGGE bands revealed that many sequences are highly similar to known psychrophilic organisms or cloned DNA from other cold environments. Significant uptake of 14C-labeled bicarbonate occurred in dark, low-temperature incubations of lake water samples, indicating the presence of autotrophs. Acetylene reduction assays under similar incubation conditions showed no significant nitrogen fixation potential by lake water samples. This may be a consequence of the inhibition of diazotrophy by nitrogen in the lake.

  13. A Viable Microbial Community in a Subglacial Volcanic Crater Lake, Iceland

    NASA Astrophysics Data System (ADS)

    Gaidos, Eric; Lanoil, Brian; Thorsteinsson, Thorsteinn; Graham, Andrew; Skidmore, Mark; Han, Suk-Kyun; Rust, Terri; Popp, Brian

    2004-09-01

    We describe a viable microbial community in a subglacial lake within the Grímsvötn volcanic caldera, Iceland. We used a hot water drill to penetrate the 300-m ice shelf and retrieved lake water and volcanic tephra sediments. We also acquired samples of borehole water before and after penetration to the lake, overlying glacial ice and snow, and water from a nearby subaerial geothermal lake for comparative analyses. Lake water is at the freezing point and fresh (total dissolved solids = 260 mg L-1). Detectable numbers of cells were found in samples of the lake water column and tephra sediments: 2 × 104 ml-1 and 4 × 107 g-1, respectively. Plate counts document abundant cold-adapted cultivable organisms in the lake water, but not in the borehole (before penetration) or glacial ice. Denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene fragments amplified from genomic DNA extracted from Gr??msv??tn samples indicates that the lake community is distinct from the assemblages of organisms in borehole water (before penetration) and the overlying ice and snow. Sequencing of selected DGGE bands revealed that many sequences are highly similar to known psychrophilic organisms or cloned DNA from other cold environments. Significant uptake of 14C-labeled bicarbonate occurred in dark, low-temperature incubations of lake water samples, indicating the presence of autotrophs. Acetylene reduction assays under similar incubation conditions showed no significant nitrogen fixation potential by lake water samples. This may be a consequence of the inhibition of diazotrophy by nitrogen in the lake.

  14. First in-situ sensing of volcanic gas plume composition at Boiling Lake (Dominica, West Indies)

    NASA Astrophysics Data System (ADS)

    Di Napoli, R.; Aiuppa, A.; Allard, P.

    2012-12-01

    Dominica, a small Caribbean island between Martinique (to the South) and Guadeloupe (to the North), is, because of the high number of potentially active volcanic centres, one of the most susceptible sites to volcanic risk in the Lesser Antilles arc. Seven major volcanic centres, active during the last 10ka, are considered likely to erupt again, and one of these is the Valley of Desolation volcanic complex. This is an area of 0.5 km2, located in on SW Dominica, where a number of small explosion craters, hot springs, bubbling pools and fumaroles testify for vigorous and persistent hydrothermal activity. Two main phreatic explosions have been documented in historical time (1880 and 1997), and the most likely centre of future activity is the Boiling Lake, a nearby high-T volcanic crater lake produced by an undated phreatic/phreato-magmatic explosion. Hot (80 to 90°C) and acidic (4-6) waters normally characterize the steady-state activity of the lake, whereby which vigorous gas upwelling in the lake's centre feeds a persistent steaming plume. Stability of the Boiling Lake has occasionally been interrupted in the past (since 1876) by crises, the most recent in 2004, involving rapid draining of the lake and changes in water temperature and pH, likely as a result of drastic decrease of hydrothermal fluid input into the lake. While the chemical and isotopic composition of the lake waters is well characterised, there are no compositional data available for the gas plume leaving the lake, due to inherent difficulties in direct gas sampling. Here, we present the results of the first direct measurements of the Boiling Lake's plume, performed by using the MultiGAS technique in February 2012. We acquired 0.5 Hz time-series of H2O, CO2, H2S and SO2 plume concentrations, which were seen to peak (with maximum background-corrected concentrations of 3680, 101 and 25 ppm for respectively H2O, CO2 and H2S) during phases of visible increase in lake outgassing. SO2 was virtually absent

  15. What We Can Learn from the Next Large Volcanic Eruption

    NASA Astrophysics Data System (ADS)

    Robock, A.

    2015-12-01

    The April 1982 eruption of El Chichón in México stimulated interest in the climate response to volcanic eruptions and produced very useful observations and modeling studies. The last large volcanic eruption, the June 15, 1991 eruption of Mt. Pinatubo in the Philippines, was the best observed eruption ever, and serves as a canonical example for studies of aerosol production and transport, climate response, and deposition on ice sheets. However, many aspects of both eruptions were poorly observed, climate model simulations of the response are imperfect, and new scientific issues, such as stratospheric sulfate geoengineering, raise new scientific questions that could be answered by better observations of the next large volcanic eruption. In this talk I will summarize what we know and do not know about large volcanic eruptions, and discuss new questions that can be addressed by being prepared for the next large eruption. These include: How and how fast will SO2 convert to sulfate aerosols? How will the aerosols grow? What will be the size distribution of the resulting sulfate aerosol particles? How will the aerosols be transported throughout the stratosphere? How much fine ash gets to the stratosphere, how long does it stay there, and what are its radiative and chemical impacts? How will temperatures change in the stratosphere as a result of the aerosol interactions with shortwave (particularly near IR) and longwave radiation? Are there large stratospheric water vapor changes associated with stratospheric aerosols? Is there an initial injection of water from the eruption? Is there ozone depletion from heterogeneous reactions on the stratospheric aerosols? As the aerosols leave the stratosphere, and as the aerosols affect the upper troposphere temperature and circulation, are there interactions with cirrus and other clouds?

  16. Revisiting the observed surface climate response to large volcanic eruptions

    NASA Astrophysics Data System (ADS)

    Wunderlich, Fabian; Mitchell, Daniel M.

    2017-01-01

    In light of the range in presently available observational, reanalysis and model data, we revisit the surface climate response to large tropical volcanic eruptions from the end of the 19th century until present. We focus on the dynamically driven response of the North Atlantic Oscillation (NAO) and the radiative-driven tropical temperature response. Using 10 different reanalysis products and the Hadley Centre Sea Level Pressure observational dataset (HadSLP2) we confirm a positive tendency in the phase of the NAO during boreal winters following large volcanic eruptions, although we conclude that it is not as clear cut as the current literature suggests. While different reanalyses agree well on the sign of the surface volcanic NAO response for individual volcanoes, the spread in the response is often large (˜ 1/2 standard deviation). This inter-reanalysis spread is actually larger for the more recent volcanic eruptions, and in one case does not encompass observations (El Chichón). These are all in the satellite era and therefore assimilate more atmospheric data that may lead to a more complex interaction for the surface response. The phase of the NAO leads to a dynamically driven warm anomaly over northern Europe in winter, which is present in all datasets considered. The general cooling of the surface temperature due to reduced incoming shortwave radiation is therefore disturbed by dynamical impacts. In the tropics, where less dynamically driven influences are present, we confirm a predominant cooling after most but not all eruptions. All datasets agree well on the strength of the tropical response, with the observed and reanalysis response being statistically significant but the modelled response not being significant due to the high variability across models.

  17. Morphotectonic setting of maar lakes in the Campo de Calatrava Volcanic Field (Central Spain, SW Europe)

    NASA Astrophysics Data System (ADS)

    Martín-Serrano, A.; Vegas, J.; García-Cortés, A.; Galán, L.; Gallardo-Millán, J. L.; Martín-Alfageme, S.; Rubio, F. M.; Ibarra, P. I.; Granda, A.; Pérez-González, A.; García-Lobón, J. L.

    2009-12-01

    In the Campo de Calatrava Volcanic Field (CCVF, Central Spain), the eruption of Pliocene-Pleistocene maar craters into two clearly distinct types of pre-volcanic rocks allows the observation and comparison of hard-substrate and soft-substrate maar lakes. Hard-substrate maars formed when phreatomagmatic processes affected the jointed, Paleozoic igneous and metamorphic rocks (hard substrate), giving rise to funnel-like maar lake basins. Soft-substrate maars resulted from phreatomagmatic volcanic processes affecting poorly-consolidated Pliocene sediments, forming bowl-like maar lake basins. Pre-volcanic bedrock determined the post-eruptive lacustrine architecture in the craters and favored a higher preservation of hard-substrate maars in comparison to soft-substrate maars. This is because the hard-substrate maars, surrounded by a deep stable crater wall, are more capable of collecting sediments in their basins. These sediments could be preserved for longer than similar deposits in broad, shallow maars with a soft substrate. Ancient soft-substrate maars do not usually preserve their original morphology well and can be identified only by their lacustrine deposits. Carbonate lacustrine/palustrine deposits surrounding a bowl-like depression are the remnants of this second type of maar lake, and allow reconstruction of the original morphology of ancient soft-substrate maar craters. Geophysical (electrical tomography ground surveys) and geomorphologic-geologic mapping techniques were combined with fieldwork and facies analysis in order to locate and accurately characterize the Pliocene-Pleistocene soft-substrate maar volcanic structures of the CCVF.

  18. Age of the youngest volcanism at Eagle Lake, northeastern California—40Ar/39Ar and paleomagnetic results

    USGS Publications Warehouse

    Clynne, Michael A.; Calvert, Andrew T.; Champion, Duane E.; Muffler, L.J.P.; Sawlan, Michael G.; Downs, Drew T.

    2017-03-22

    The age of the youngest volcanism at Eagle Lake, California, was investigated using stratigraphic, paleomagnetic, and 40Ar/39Ar techniques. The three youngest volcanic lava flows at Eagle Lake yielded ages of 130.0±5.1, 127.5±3.2 and 123.6±18.7 ka, and are statistically indistinguishable. Paleomagnetic results demonstrate that two of the lava flows are very closely spaced in time, whereas the third is different by centuries to at most a few millennia. These results indicate that the basalt lava flows at Eagle Lake are not Holocene in age, and were erupted during an episode of volcanism at about 130–125 ka that is unlikely to have spanned more than a few thousand years. Thus, the short-term potential for subsequent volcanism at Eagle Lake is considered low. 

  19. The effects and consequences of very large explosive volcanic eruptions

    NASA Astrophysics Data System (ADS)

    Self, S.

    2006-08-01

    Every now and again Earth experiences tremendous explosive volcanic eruptions, considerably bigger than the largest witnessed in historic times. Those yielding more than 450km3 of magma have been called super-eruptions. The record of such eruptions is incomplete; the most recent known example occurred 26000 years ago. It is more likely that the Earth will next experience a super-eruption than an impact from a large meteorite greater than 1km in diameter. Depending on where the volcano is located, the effects will be felt globally or at least by a whole hemisphere. Large areas will be devastated by pyroclastic flow deposits, and the more widely dispersed ash falls will be laid down over continent-sized areas. The most widespread effects will be derived from volcanic gases, sulphur gases being particularly important. This gas is converted into sulphuric acid aerosols in the stratosphere and layers of aerosol can cover the global atmosphere within a few weeks to months. These remain for several years and affect atmospheric circulation causing surface temperature to fall in many regions. Effects include temporary reductions in light levels and severe and unseasonable weather (including cool summers and colder-than-normal winters). Some aspects of the understanding and prediction of super-eruptions are problematic because they are well outside modern experience. Our global society is now very different to that affected by past, modest-sized volcanic activity and is highly vulnerable to catastrophic damage of infrastructure by natural disasters. Major disruption of services that society depends upon can be expected for periods of months to, perhaps, years after the next very large explosive eruption and the cost to global financial markets will be high and sustained.

  20. The effects and consequences of very large explosive volcanic eruptions.

    PubMed

    Self, S

    2006-08-15

    Every now and again Earth experiences tremendous explosive volcanic eruptions, considerably bigger than the largest witnessed in historic times. Those yielding more than 450km3 of magma have been called super-eruptions. The record of such eruptions is incomplete; the most recent known example occurred 26000 years ago. It is more likely that the Earth will next experience a super-eruption than an impact from a large meteorite greater than 1km in diameter. Depending on where the volcano is located, the effects will be felt globally or at least by a whole hemisphere. Large areas will be devastated by pyroclastic flow deposits, and the more widely dispersed ash falls will be laid down over continent-sized areas. The most widespread effects will be derived from volcanic gases, sulphur gases being particularly important. This gas is converted into sulphuric acid aerosols in the stratosphere and layers of aerosol can cover the global atmosphere within a few weeks to months. These remain for several years and affect atmospheric circulation causing surface temperature to fall in many regions. Effects include temporary reductions in light levels and severe and unseasonable weather (including cool summers and colder-than-normal winters). Some aspects of the understanding and prediction of super-eruptions are problematic because they are well outside modern experience. Our global society is now very different to that affected by past, modest-sized volcanic activity and is highly vulnerable to catastrophic damage of infrastructure by natural disasters. Major disruption of services that society depends upon can be expected for periods of months to, perhaps, years after the next very large explosive eruption and the cost to global financial markets will be high and sustained.

  1. Theoretical validation of ASTER_SW algorithm used for the monitoring of hot volcanic lakes

    NASA Astrophysics Data System (ADS)

    Bernard, A.; Campion, R. A.

    2009-12-01

    Volcanic lakes act as calorimeters trapping most of the heat released by the magmatic-hydrothermal system. Their temperatures are reflecting the balance between heat input from hydrothermal fluids and heat output by radiation and evaporation of the lake surface to the atmosphere. The lake surface temperature is one of the key parameters used to detect any changes occurring in the activity of the volcano. Many volcanic lakes are located in remote areas with difficult accessibility; these lakes are rarely visited or monitored. For these lakes remote sensing by satellite sensors can provide very useful information at relatively low cost. To retrieve surface temperatures of volcanic lakes, ASTER TIR images were analyzed with a recently developed algorithm based on a Split-Window method: ASTER_SW. The difference in brightness temperatures between bands 13 and 14 (BT13-BT14) is used to remove the atmospheric effects. The use of two TIR channels enables a differential absorption measurement in order to remove the effects of atmospheric vapor and other absorbing constituents. Further validation of the ASTER_SW algorithm was completed by applying it to a set of radiance simulations using a line-by-line radiative transfer code (Atmosphit). Parameters used for the simulations included: surface temperatures, atmospheric models and surface altitudes. The obtained spectra were integrated on the spectral response functions of ASTER and converted with the inverse of Planck’s law to get the Simulated Brightness Temperatures (SBT). The ASTER_SW algorithm was applied to the SBT. The coherence between ASTER_SW-derived temperatures and model surface temperatures was examined to test the validity and robustness of the algorithm. ASTER_SW proved to be accurate in most circumstances, revealing no systematic bias in any peculiar atmosphere or altitude. However, for very warm lakes (T>50°C), a small dependency on surface altitude is appearing in tropical atmospheres. The low frequency of

  2. The Geysers-Clear Lake area, California: thermal waters, mineralization, volcanism, and geothermal potential

    USGS Publications Warehouse

    Donnelly-Nolan, J. M.; Burns, M.G.; Goff, F.E.; Peters, E.K.; Thompson, J.M.

    1993-01-01

    Manifestations of a major thermal anomaly in the Geysers-Clear Lake area of northern California include the late Pliocene to Holocene Clear Lake Volcanics, The Geysers geothermal field, abundant thermal springs, and epithermal mercury and gold mineralization. The epithermal mineralization and thermal springs typically occur along high-angle faults within the broad San Andreas transform fault system that forms the western boundary of the North American plate in this area. The young volcanic rocks overlie Mesozoic marine rocks of the Great Valley sequence which have been thrust above the coeval Franciscan Complex and penecontemporaneously dropped back down along low-angle detachment faults. Geothermal power production has peaked at The Geysers and pressure declines indicate significant depletion of the fluid resource. It is proposed that recently discovered, isotopically shifted steam in the northwest Geysers area indicates the presence not of deep connate water but rather of boiled-down, boron-rich Franciscan evolved meteoric water. This water is likely to be present in limited quantities and will not provide a significant hot water resource for geothermal power production at The Geysers field or from the main Clear Lake volcanic field. -from Authors

  3. The relative influences of climate and volcanic activity on Holocene lake development inferred from a mountain lake in central Kamchatka

    NASA Astrophysics Data System (ADS)

    Self, A. E.; Klimaschewski, A.; Solovieva, N.; Jones, V. J.; Andrén, E.; Andreev, A. A.; Hammarlund, D.; Brooks, S. J.

    2015-11-01

    A sediment sequence was taken from a closed, high altitude lake (informal name Olive-backed Lake) in the central mountain range of Kamchatka, in the Russian Far East. The sequence was dated by radiocarbon and tephrochronology and used for multi-proxy analyses (chironomids, pollen, diatoms). Although the evolution of Beringian climate through the Holocene is primarily driven by global forcing mechanisms, regional controls, such as volcanic activity or vegetation dynamics, lead to a spatial heterogeneous response. This study aims to reconstruct past changes in the aquatic and terrestrial ecosystems and to separate the climate-driven response from a response to regional or localised environmental change. Radiocarbon dates from plant macrophytes gave a basal date of 7800 cal yr BP. Coring terminated in a tephra layer, so sedimentation at the lake started prior to this date, possibly in the early Holocene following local glacier retreat. Initially the catchment vegetation was dominated by Betula and Alnus woodland with a mosaic of open, wet, aquatic and semi-aquatic habitats. Between 7800 and 6000 cal yr BP the diatom-inferred lake water was pH 4.4-5.3 and chironomid and diatom assemblages in the lake were initially dominated by a small number of acidophilic/acid tolerant taxa. The frequency of Pinus pumila (Siberian dwarf pine) pollen increased from 5000 cal yr BP and threshold analysis indicates that P. pumila arrived in the catchment between 4200 and 3000 cal yr BP. Its range expansion was probably mediated by strengthening of the Aleutian Low pressure system and increased winter snowfall. The diatom-inferred pH reconstructions show that after an initial period of low pH, pH gradually increased from 5500 cal yr BP to pH 5.8 at 1500 cal yr BP. This trend of increasing pH through the Holocene is unusual in lake records, but the initially low pH may have resulted directly or indirectly from intense regional volcanic activity during the mid-Holocene. The chironomid

  4. Geologic map and structure sections of the Clear Lake Volcanics, Northern California

    USGS Publications Warehouse

    Hearn, B.C.; Donnelly-Nolan, J. M.; Goff, F.E.

    1995-01-01

    The Clear Lake Volcanics are located in the California Coast Ranges about 150 km north of San Francisco. This Quaternary volcanic field has erupted intermittently since 2.1 million years ago. This volcanic field is considered a high-threat volcanic system (Ewert and others, 2005) The adjacent Geysers geothermal field, largest power-producing geothermal field in the world, is powered by the magmatic heat source for the volcanic field. This report consists of three sheets that include the geologic map, one table, two figures, three cross sections, description of map units, charts of standard and diagrammatic correlation of map units, and references. This map supersedes U.S. Geological Survey Open-File Report 76-751. Descriptions of map units are grouped by geographic area. Summaries of the evolution, chemistry, structure, and tectonic setting of the Clear Lake Volcanics are given in Hearn and others (1981) and Donnelly-Nolan and others (1981). The geology of parts of the area underlain by the Cache Formation is based on mapping by Rymer (1981); the geology of parts of the areas underlain by the Sonoma Volcanics, Franciscan assemblage, and Great Valley sequence is based on mapping by McLaughlin (1978). Volcanic compositional map units are basalt, basaltic andesite, andesite, dacite, rhyodacite, and rhyolite, based on SiO2 content. Included in this report are maps showing the distribution of volcanic rocks through time and a chart showing erupted volumes of different lava types through time. A table gives petrographic data for each map unit by mineral type, abundance, and size. Most ages are potassium-argon (K/Ar) ages determined for whole-rock samples and mineral separates by Donnelly-Nolan and others (1981), unless otherwise noted. A few ages are carbon-14 ages or were estimated from geologic relationships. Magnetic polarities are from Mankinen and others (1978; 1981) or were determined in the field by B.C. Hearn, Jr., using a portable fluxgate magnetometer

  5. Lake Nyos disaster, Cameroon, 1986: the medical effects of large scale emission of carbon dioxide?

    PubMed

    Baxter, P J; Kapila, M; Mfonfu, D

    1989-05-27

    Carbon dioxide was blamed for the deaths of around 1700 people in Cameroon, west Africa, in 1986 when a massive release of gas occurred from Lake Nyos, a volcanic crater lake. The clinical findings in 845 survivors seen at or admitted to hospital were compatible with exposure to an asphyxiant gas. Rescuers noted cutaneous erythema and bullae on an unknown proportion of corpses and 161 (19%) survivors treated in hospital; though these lesions were initially believed to be burns from acidic gases, further investigation suggested that they were associated with coma states caused by exposure to carbon dioxide in air. The disaster at Lake Nyos and a similar event at Lake Monoun, Cameroon, two years previously provide new information on the possible medical effects of large scale emissions of carbon dioxide, though the presence of other toxic factors in these gas releases cannot be excluded.

  6. Managing Long-term Risks from Natural Hazards in a Dynamic Volcanic and Institutional Environment: The Spirit Lake Story

    NASA Astrophysics Data System (ADS)

    Grant, G.; Major, J. J.; Lewis, S.

    2016-12-01

    The 18 May 1980 eruption of Mount St. Helens, Washington, spawned a massive (109 m3) debris avalanche, a violent and extensive pyroclastic density current, lahars, pyroclastic flows, and ashfall. It fundamentally transformed the proximal landscape, and created potential secondary hazards that remain legacies of the eruption over 35 years later. The debris avalanche raised the level of Spirit Lake—a picturesque lake at the foot of the volcano—by 60 m and blocked its outlet. Abruptly, the lake went from charming to menacing, capable of releasing a potentially catastrophic outburst flood (108 m3) that could transform into a massive (109 m3) debris flow if rising lake water breached the blockage. To reduce risk of an uncontrolled breach, and under Presidential emergency declaration, the U.S. Army Corps of Engineers (USACE) bored a 2,590-m-long outlet tunnel through bedrock within the U.S. Forest Service (USFS)-administered Mount St. Helens National Volcanic Monument. Drainage through the tunnel maintains a safe lake level below a geologic contact in the blockage where seepage erosion could result in failure. Although the tunnel has performed its mission for over 30 years, episodic deformation has reduced its outlet capacity, necessitating expensive (>$1 million) repairs and closures which temporarily caused precarious lake rises, and prompted re-examination of the strategy to maintain a safe lake level. Here we discuss how federal researchers (USFS and U.S. Geological Survey) interact with Monument and USFS land managers, USACE, the National Academy of Sciences, and the public at large to develop and evaluate, under Congressional mandate, alternative strategies for reducing the risk of catastrophic flooding. Amidst this nexus of institutions, agendas, and perspectives, set against the backdrop of a rapidly evolving landscape subject to a trio of hazards (eruptions, earthquakes, floods), competing interests, costs, and natural risks must be balanced and managed.

  7. Survey and assessment of post volcanic activities of a young caldera lake, Lake Cuicocha, Ecuador

    NASA Astrophysics Data System (ADS)

    Gunkel, G.; Beulker, C.; Grupe, B.; Viteri, F.

    2009-05-01

    Cuicocha is a young volcano adjacent to the inactive Pleistocene Cotacachi volcano complex, located in the western cordilleras of the Ecuadorian Andes. A series of eruptions with intensive ash emission and collapse of the caldera occurred around 4500-3000 y BP. A crater 3.2 km in diameter and a maximum depth of 450 m was formed. Further eruptions of the volcano occurred 1300 y BP and formed four smaller domes within the caldera. Over the last few hundred years, a caldera lake has developed, with a maximum depth of 148 m. The lake water is characterized by sodium carbonate with elevated concentrations of manganese, calcium and chloride. Nowadays, an emission of gases, mainly CO2, and an input of warm spring water occur in Lake Cuicocha. The zone of high activity is in the western basin of the lake at a depth of 78 m, and continuous gas emissions with sediment resuspension were observed using sonar. In the hypolimnion of the lake, CO2 accumulation occurs up to 0.2% saturation, but the risk of a limnic eruption can be excluded at present. The lake possesses monomictic stratification behaviour, and during overturn an intensive gas exchange with the atmosphere occurs. Investigations concerning the sedimentation processes of the lake suggest only a thin sediment layer of up to 10-20 cm in the deeper lake basin; in the western bay, in the area of gas emissions, the lake bottom is partly depleted of sediment in the form of holes, and no lake colmation exists. Decreases in the lake water level of about 30 cm y-1 indicate a percolation of water into fractures and fissures of the volcano, triggered by a nearby earthquake in 1987.

  8. Terminal Pleistocene to early Holocene volcanic eruptions at Zuni Salt Lake, west-central New Mexico, USA

    NASA Astrophysics Data System (ADS)

    Onken, Jill; Forman, Steven

    2017-01-01

    Zuni Salt Lake (ZSL) is a large maar in the Red Hill-Quemado volcanic field located in west-central New Mexico in the southwestern USA. Stratigraphic analysis of sections in and around the maar, coupled with optically stimulated luminescence (OSL) and accelerator mass spectrometry (AMS) 14C dating, indicate that ZSL volcanic activity occurred between ˜13.4 and 9.9 ka and was most likely confined to a ≤500-year interval sometime between ˜12.3 and 11.0 ka. The basal volcanic unit consists of locally widespread basaltic ash fallout interpreted to represent a violent or wind-aided strombolian eruption tentatively attributed to Cerro Pomo, a scoria cone ˜10 km south of ZSL. Subsequent eruptions emanated from vents near or within the present-day ZSL maar crater. Strombolian eruptions of multiple spatter and scoria cones produced basaltic lava and scoria lapilli fallout. Next, a phreatomagmatic eruption created the maar crater and surrounding tephra rim and apron. ZSL eruptions ended with strombolian eruptions that formed three scoria cones on the crater floor. The revised age range of ZSL is younger and more precise than the 190-24 ka 2-sigma age range derived from previous argon dating. This implies that other morphologically youthful, argon-dated volcanoes on the southern margin of the Colorado Plateau might be substantially younger than previously reported.

  9. Volcanically far-flung lake sediments in New Zealand and their diatom contents.

    NASA Astrophysics Data System (ADS)

    Harper, Margaret; Pledger, Shirley; Smith, Euan; Van Eaton, Alexa; Wilson, Colin

    2015-04-01

    Explosive volcanic eruptions from the Taupo Volcanic Zone in New Zealand such as the Okaia (28.6 ka) and Oruanui (25.4 ka) through paleolake Huka and the Taupo eruption (1.8 ka) through paleolake Taupo dispersed measurable quantities of diatom valves (remains of siliceous microscopic algae) along with the tephra (Van Eaton et al. 2013). Diatoms preserved in tephra can inform us about the past histories of freshwater floras and lakes. For instance the possibly extinct endemic diatom Cyclostephanos novaezealandiae is 20 times commoner in the Late Pleistocene Oruanui and Okaia tephras than in recent lake sediment. We also found Aulacoseira valves (mainly A. ambigua) were generally shorter in the older tephras, possibly due to more turbid conditions in the glacial period due to stronger winds or less availability of nutrients. Some information on eruptive processes can also be derived from diatoms. Nearly all diatom assemblages in the Oruanui samples were remarkably similar, indicating they were well mixed by turbulence in the eruptive column. The exceptions were a proximal sample (11 km from vent) and the clasts of slightly older lake sediment enclosed in the ignimbrite. One clast was dominated by different Aulacoseira taxa (A. granulata and A. granulata var. angustissima). A vent in a shallower area of paleolake Huka could well have been the source of these diatoms. The proximal sample was deposited early in the eruption and on a ridge close to the rim of the paleolake, and is also likely to have come from a local vent. Caution should be used in interpreting diatoms in phreatomagmatic tephra in lake basins. Earlier Harper & Collen (2002) interpreted diatoms associated with the Okaia and Oruanui tephras in the Poukawa basin (125 km from vent) as indicating the existence of lakes formed when drainage was blocked by the tephra. However the strong resemblance of the assemblages and morphometry of Aulacoseira valves to those measured in our new samples shows they arrived

  10. Io volcanism

    SciTech Connect

    Carr, M.H.

    1985-01-01

    Io is the most volcanically active body in the Solar System. The Voyage spacecraft observed nine active eruption plumes in 1979, and detected numerous thermal anomalies. Loki the most active volcanic region has been emitting 1.5 x 10/sup 13/ W over the last few years. Many of the volcanic features have been interpreted as the result of sulfur volcanism because 1) the spectral reflectance of the surface resembles sulfur, 2) SO/sub 2/ has been positively identified, 3) the satellite leaves a trail of sulfur atoms in its wake; and 4) many of the hot spots have surfaces temperatures less than 400/sup 0/K, compatible with low-temperature melts. The evidence for sulfur has led to suggestions of sulfur lava flows hundreds of kilometers long, and sulfur lava lakes as large as Lake Erie. The observations are, however, equally compatible with basaltic volcanism. Modeling of the cooling of basaltic lava flows indicates that regions of basaltic volcanism on Io should have temperatures similar to those detected by the Voyager spacecraft. High eruption rates are required. High rates of fumarolic activity accompanying the eruptions and expulsion of volatiles by the plumes give the surface its sulfur-like spectral reflectance.

  11. Crustal and tectonic controls on large-explosive volcanic eruptions

    NASA Astrophysics Data System (ADS)

    Sheldrake, Tom; Caricchi, Luca

    2017-04-01

    Quantifying the frequency-Magnitude (f-M) relationship for volcanic eruptions is important to estimate volcanic hazard. Furthermore, understanding how this relationship varies between different groups of volcanoes can provide insights into the processes that control the size and rate of volcanic events. Using a Bayesian framework, which allows us to conceptualise the volcanic record as a series of individual and unique time series, associated by a common group behaviour, we identify variations in the size and rate of volcanism in different volcanic arcs. These variations in behaviour are linked to key parameters that include the motion of subduction, rate of subduction, age of the slab and thickness of the crust. The effects of these parameters on volcanism are interpreted in terms of variations in mantle productivity and the thermal efficiency of magma transfer in arc crustal systems. Understanding the link between subduction architecture, heat content of magmatic systems, and volcanic activity will serve to improve our capacity to quantify volcanic hazard in regions with limited geological and historical records of volcanic activity.

  12. Crustal Structure in Northern Malawi and Southern Tanzania surrounding Lake Malawi and the Rungwe Volcanic Province

    NASA Astrophysics Data System (ADS)

    Borrego, D.; Kachingwe, M.; Nyblade, A.; Shillington, D. J.; Gaherty, J. B.; Ebinger, C. J.; Accardo, N. J.; O'Donnell, J. P.; Mbogoni, G. J.; Mulibo, G. D.; Chindandali, P. R. N.; Mphepo, F.; Ferdinand-Wambura, R.; Tepp, G.

    2015-12-01

    Crustal Structure in Northern Malawi and Southern Tanzania surrounding Lake Malawi and the Rungwe Volcanic Province David Borrego, Marsella Kachingwe, Andrew Nyblade, Donna Shillington, James Gaherty, Cynthia Ebinger, Natalie Accardo, J.P. O'Donnell, Gabriel Mbogoni, Gabriel Mulibo, Richard Ferdinand, Patrick Chindandali, Felix Mphepo, Gabrielle Tepp, Godson Kamihanda We investigate crustal structure around the northern end of Lake Malawi and in the Rungwe Volcanic Province using teleseismic receiver functions from the SEGMeNT broadband seismic network. The SEGMeNT network includes 55 broadband stations deployed in northern Malawi and southern Tanzania, with station spacing of 20-50 km. Fourteen stations were deployed in August 2013, and an additional of 41 stations were added to the study region beginning June/July 2014. Fifteen stations are located in Malawi and 40 stations in Tanzania. Data from teleseismic earthquakes with magnitude 5.5 or greater in the 30 to 90 degrees distance range have been used to calculate P-wave receiver functions. Estimates of Moho depth and Vp/Vs ratios have been obtained by using the H-k stacking method and by jointly inverting the receiver functions with Rayleigh wave phase velocities. Preliminary results show an average Moho depth of 40 km and an average Vp/Vs ratio of 1.72. Little evidence is found for magmatic underplating beneath the Rungwe Volcanic Province.

  13. Tectonic versus volcanic origin of the summit depression at Medicine Lake Volcano, California

    SciTech Connect

    Mark Leon Gwynn

    2010-05-01

    Medicine Lake Volcano is a Quaternary shield volcano located in a tectonically complex and active zone at the transition between the Basin and Range Province and the Cascade Range of the Pacific Province. The volcano is topped by a 7x12 km elliptical depression surrounded by a discontinuous constructional ring of basaltic to rhyolitic lava flows. This thesis explores the possibility that the depression may have formed due to regional extension (rift basin) or dextral shear (pull-apart basin) rather than through caldera collapse and examines the relationship between regional tectonics and localized volcanism. Existing data consisting of temperature and magnetotelluric surveys, alteration mineral studies, and core logging were compiled and supplemented with additional core logging, field observations, and fault striae studies in paleomagnetically oriented core samples. These results were then synthesized with regional fault data from existing maps and databases. Faulting patterns near the caldera, extension directions derived from fault striae P and T axes, and three-dimensional temperature and alteration mineral models are consistent with slip across arcuate ring faults related to magma chamber deflation during flank eruptions and/or a pyroclastic eruption at about 180 ka. These results are not consistent with a rift or pull-apart basin. Limited subsidence can be attributed to the relatively small volume of ash-flow tuff released by the only known major pyroclastic eruption and is inconsistent with the observed topographic relief. The additional relief can be explained by constructional volcanism. Striae from unoriented and oriented core, augmented by striae measurements in outcrop suggest that Walker Lane dextral shear, which can be reasonably projected from the southeast, has probably propagated into the Medicine Lake area. Most volcanic vents across Medicine Lake Volcano strike north-south, suggesting they are controlled by crustal weakness related to Basin and

  14. TECTONIC VERSUS VOLCANIC ORIGIN OF THE SUMMIT DEPRESSION AT MEDICINE LAKE VOLCANO, CALIFORNIA

    SciTech Connect

    Mark Leon Gwynn

    2010-05-01

    Medicine Lake Volcano is a Quaternary shield volcano located in a tectonically complex and active zone at the transition between the Basin and Range Province and the Cascade Range of the Pacific Province. The volcano is topped by a 7x12 km elliptical depression surrounded by a discontinuous constructional ring of basaltic to rhyolitic lava flows. This thesis explores the possibility that the depression may have formed due to regional extension (rift basin) or dextral shear (pull-apart basin) rather than through caldera collapse and examines the relationship between regional tectonics and localized volcanism. Existing data consisting of temperature and magnetotelluric surveys, alteration mineral studies, and core logging were compiled and supplemented with additional core logging, field observations, and fault striae studies in paleomagnetically oriented core samples. These results were then synthesized with regional fault data from existing maps and databases. Faulting patterns near the caldera, extension directions derived from fault striae P and T axes, and three-dimensional temperature and alteration mineral models are consistent with slip across arcuate ring faults related to magma chamber deflation during flank eruptions and/or a pyroclastic eruption at about 180 ka. These results are not consistent with a rift or pull-apart basin. Limited subsidence can be attributed to the relatively small volume of ash-flow tuff released by the only known major pyroclastic eruption and is inconsistent with the observed topographic relief. The additional relief can be explained by constructional volcanism. Striae from unoriented and oriented core, augmented by striae measurements in outcrop suggest that Walker Lane dextral shear, which can be reasonably projected from the southeast, has probably propagated into the Medicine Lake area. Most volcanic vents across Medicine Lake Volcano strike north-south, suggesting they are controlled by crustal weakness related to Basin and

  15. Level rise episodes triggered by volcanic eruptions during the desiccation of Lake Lisan

    NASA Astrophysics Data System (ADS)

    Bookman, R.; Filin, S.; Avni, Y.; Marco, S.

    2012-12-01

    The June 1991 Pinatubo volcanic eruption perturbed the atmosphere, triggering short-term worldwide changes in surface and lower troposphere temperatures, precipitation, and runoff. The following winter was anomalously wet in the Levant, with a ~2-meter increase in the Dead Sea level that created a distinct morphological terrace along the lake's shore. Given the global radiative and chemical effects of volcanogenic aerosols on climatic systems, we tested the hypothesis that the 1991-92 winter shore terrace is a modern analogue to the linkage between past volcanic eruptions and a sequence of shore terraces on the cliffs around the Dead Sea Basin (DSB). Sixteen shore terraces, detected using airborne laser scanning data, were interpreted as indicating short-term level rises due to episodes of enhanced precipitation and runoff during the drop in Lake Lisan's (palaeo-Dead Sea) level at the end of the Last Glacial Maximum. The terraces were compared with a dated time series of volcanigenic sulfate from the GISP2 ice core, and similar numbers of sulfate peaks and shore terraces were found with significant correlation (R2=0.8) between the SO4 concentration and the physical and hydrological character of the terraces. We suggest that this correlation indicates a link between the explosivity of past eruptions, the magnitude of stratographic injection, and their impact on the northern hemisphere water balance. The record of such short-term climato-hydrological effects is made possible by the dramatic desiccation of Lake Lisan and may show the amplification of the volcanic atmospheric perturbation during the main climatic transition at the end of the Last Glacial Maximum. Detailed records of such events, albeit rare because of their vulnerability and short longevity, provide an important demonstration of global climatic teleconnections.

  16. Possible connection between large volcanic eruptions and level rise episodes in the Dead Sea Basin

    NASA Astrophysics Data System (ADS)

    Bookman, Revital; Filin, Sagi; Avni, Yoav; Rosenfeld, Daniel; Marco, Shmuel

    2014-05-01

    The June 1991 Pinatubo volcanic eruption perturbed the atmosphere, triggering short-term worldwide changes in surface and lower troposphere temperatures, precipitation, and runoff. The following winter was anomalously wet in the Levant, with a ~2-meter increase in the Dead Sea level that created a distinct morphological terrace along the lake's shore. Given the global radiative and chemical effects of volcanogenic aerosols on climatic systems, we tested the hypothesis that the 1991-92 winter shore terrace is a modern analogue to the linkage between past volcanic eruptions and a sequence of shore terraces on the cliffs around the Dead Sea Basin. Analysis of historical annual precipitation series from Jerusalem showed a significant positive correlation between the Dust Veil Index (DVI) of the modern largest eruptions and corresponding annual rainfall. The DVI was found to explain nearly 50% of the variability in the annual rainfall, such that greater DVI means more rainfall. Other factors that may affect the annual rainfall in the region as the Southern Oscillation Index (SOI) and the North Atlantic oscillations (NAO) were incorporated along with the DVI in a linear multiple regression model. It was found that the NAO did not contribute anything except for increased noise, but the added SOI increased the explained variability of rainfall to more than 60%. The atmospheric effect of the volcanic aerosol cloud produced after the Mt. Pinatubo eruption shows responses in the climate system on a hemispherical to global scale. Volcanic eruptions with a VEI of 6, as in the Pinatubo, occurred about once a century during the Holocene period at a rate that persisted throughout the last glacial-interglacial cycle, though with large variations in the mean. This occurrence is similar to the frequency of shore terrace build-up during the Lake Lisan desiccation. Sixteen shore terraces, detected using airborne laser scanning data, were interpreted as indicating short-term level rises

  17. Assessing Magmatic Processes and Hazards at two Basaltic Monogenetic Centers: Volcan Jorullo, Mexico, and Blue Lake Maar, Oregon

    NASA Astrophysics Data System (ADS)

    Johnson, E. R.; Cashman, K.; Wallace, P.; Delgado Granados, H.

    2007-05-01

    Although monogenetic basaltic volcanoes exhibit a wide variety of eruption styles, the origin of this diversity is poorly understood and often ignored when assessing volcanic hazards. To better understand magmatic processes and hazards associated with these eruptions, we have studied two monogenetic centers with differing behavior: Volcan Jorullo, a cinder cone in Mexico, and Blue Lake, a maar in the Oregon High Cascades. Although compositionally similar (medium-K basalt to basaltic andesite), their eruptive styles and products are quite different. Jorullo had violent strombolian eruptions that deposited alternating beds of ash and tephra, as well as lava flows. In contrast, Blue Lake exhibited initial phreatomagmatism that formed a 100m deep crater and produced surge deposits. This activity was followed by magmatic eruptions that produced deposits of tephra and bombs, but no lava flows. The diversity in eruptive style at these two centers reflects different magma ascent and crystallization processes, deduced using olivine-hosted melt inclusions. Jorullo melt inclusions trap variably degassed melts (0.5-5 wt% H2O; 0-1000 ppm CO2), with associated crystallization pressures that decrease from early (<4 kbars) to late (<100 bars) in the eruption. These data support the formation of a shallow storage region beneath the volcano that facilitated both crystallization and magma degassing, which is consistent with effusion of degassed lavas from the base of the cone throughout the eruption. In contrast, Blue Lake inclusions trap melts with a restricted range of volatiles (2.6-4 wt% H2O; 677-870 ppm CO2) corresponding to crystallization pressures of 2.2-3.2 kbars. This suggests that the magma feeding Blue Lake stalled in the upper crust and crystallized before ascending rapidly to the surface, without further crystallization of olivine or shallow storage. This is consistent with both the observed unstratified tephra deposits (indicating single rather than pulsatory eruptions

  18. Geosphere-Biosphere Interactions in Bio-Activity Volcanic Lakes: Evidences from Hule and Rìo Cuarto (Costa Rica)

    PubMed Central

    Cabassi, Jacopo; Tassi, Franco; Mapelli, Francesca; Borin, Sara; Calabrese, Sergio; Rouwet, Dmitri; Chiodini, Giovanni; Marasco, Ramona; Chouaia, Bessem; Avino, Rosario; Vaselli, Orlando; Pecoraino, Giovannella; Capecchiacci, Francesco; Bicocchi, Gabriele; Caliro, Stefano; Ramirez, Carlos; Mora-Amador, Raul

    2014-01-01

    Hule and Río Cuarto are maar lakes located 11 and 18 km N of Poás volcano along a 27 km long fracture zone, in the Central Volcanic Range of Costa Rica. Both lakes are characterized by a stable thermic and chemical stratification and recently they were affected by fish killing events likely related to the uprising of deep anoxic waters to the surface caused by rollover phenomena. The vertical profiles of temperature, pH, redox potential, chemical and isotopic compositions of water and dissolved gases, as well as prokaryotic diversity estimated by DNA fingerprinting and massive 16S rRNA pyrosequencing along the water column of the two lakes, have highlighted that different bio-geochemical processes occur in these meromictic lakes. Although the two lakes host different bacterial and archaeal phylogenetic groups, water and gas chemistry in both lakes is controlled by the same prokaryotic functions, especially regarding the CO2-CH4 cycle. Addition of hydrothermal CO2 through the bottom of the lakes plays a fundamental priming role in developing a stable water stratification and fuelling anoxic bacterial and archaeal populations. Methanogens and methane oxidizers as well as autotrophic and heterotrophic aerobic bacteria responsible of organic carbon recycling resulted to be stratified with depth and strictly related to the chemical-physical conditions and availability of free oxygen, affecting both the CO2 and CH4 chemical concentrations and their isotopic compositions along the water column. Hule and Río Cuarto lakes were demonstrated to contain a CO2 (CH4, N2)-rich gas reservoir mainly controlled by the interactions occurring between geosphere and biosphere. Thus, we introduced the term of bio-activity volcanic lakes to distinguish these lakes, which have analogues worldwide (e.g. Kivu: D.R.C.-Rwanda; Albano, Monticchio and Averno: Italy; Pavin: France) from volcanic lakes only characterized by geogenic CO2 reservoir such as Nyos and Monoun (Cameroon). PMID

  19. Geosphere-biosphere interactions in bio-activity volcanic lakes: evidences from Hule and Rìo Cuarto (Costa Rica).

    PubMed

    Cabassi, Jacopo; Tassi, Franco; Mapelli, Francesca; Borin, Sara; Calabrese, Sergio; Rouwet, Dmitri; Chiodini, Giovanni; Marasco, Ramona; Chouaia, Bessem; Avino, Rosario; Vaselli, Orlando; Pecoraino, Giovannella; Capecchiacci, Francesco; Bicocchi, Gabriele; Caliro, Stefano; Ramirez, Carlos; Mora-Amador, Raul

    2014-01-01

    Hule and Río Cuarto are maar lakes located 11 and 18 km N of Poás volcano along a 27 km long fracture zone, in the Central Volcanic Range of Costa Rica. Both lakes are characterized by a stable thermic and chemical stratification and recently they were affected by fish killing events likely related to the uprising of deep anoxic waters to the surface caused by rollover phenomena. The vertical profiles of temperature, pH, redox potential, chemical and isotopic compositions of water and dissolved gases, as well as prokaryotic diversity estimated by DNA fingerprinting and massive 16S rRNA pyrosequencing along the water column of the two lakes, have highlighted that different bio-geochemical processes occur in these meromictic lakes. Although the two lakes host different bacterial and archaeal phylogenetic groups, water and gas chemistry in both lakes is controlled by the same prokaryotic functions, especially regarding the CO2-CH4 cycle. Addition of hydrothermal CO2 through the bottom of the lakes plays a fundamental priming role in developing a stable water stratification and fuelling anoxic bacterial and archaeal populations. Methanogens and methane oxidizers as well as autotrophic and heterotrophic aerobic bacteria responsible of organic carbon recycling resulted to be stratified with depth and strictly related to the chemical-physical conditions and availability of free oxygen, affecting both the CO2 and CH4 chemical concentrations and their isotopic compositions along the water column. Hule and Río Cuarto lakes were demonstrated to contain a CO2 (CH4, N2)-rich gas reservoir mainly controlled by the interactions occurring between geosphere and biosphere. Thus, we introduced the term of bio-activity volcanic lakes to distinguish these lakes, which have analogues worldwide (e.g. Kivu: D.R.C.-Rwanda; Albano, Monticchio and Averno: Italy; Pavin: France) from volcanic lakes only characterized by geogenic CO2 reservoir such as Nyos and Monoun (Cameroon).

  20. Impact of volcanism on the evolution of Lake Van II: Temporal evolution of explosive volcanism of Nemrut Volcano (eastern Anatolia) during the past ca. 0.4 Ma

    NASA Astrophysics Data System (ADS)

    Sumita, Mari; Schmincke, Hans-Ulrich

    2013-03-01

    Thirty-two new single crystal ages document 400 000 years of widespread explosive volcanism of historically active Nemrut Volcano towering over huge alkaline Lake Van (Eastern Anatolia). The dated deposits were selected to monitor the volcanic and compositional evolution of Nemrut Volcano through time and thus to provide a rigorous temporal framework for the tephra record of the PaleoVan Drilling Project. Tephra samples were taken from large-volume deposits or those that occur in medial to distal localities, well-exposed stratigraphic sections or from the initial phase of an eruptive sequence. Mainly fallout deposits were chosen because most ignimbrites show more complex and corroded feldspar populations owing to compositional zoning and magma mixing. Moreover, fallout deposits held the promise to be more clearly identifiable with—and correlatable to—> 300 tephra layers in the PaleoVan drill cores, even though commonly in amounts marginal or insufficient in thickness to allow well-supported single crystal dating. The crystals dated are dominantly anorthoclase, the main phenocryst phase in the trachytic to rhyolitic, slightly to strongly peralkaline Nemrut magmas. Ages obtained so far range from ca. 400 ka to ca. 30 ka for Nemrut Volcano. The causes of significant changes in the frequency, volume and composition of tephra layers per unit time are discussed in terms of external (erosion, climate changes, geodynamic factors) and internal forcing (changes in magma supply and composition and incubation periods preceding large volume rhyolitic eruptions). For example, the low frequency of tephra layers deposited prior to ca. 200 ka may be due to low explosive activity, severe erosion between MIS 9 and MIS 11, or both. Nevertheless, the overall frequency of explosive eruptions appears to have increased during the past ca. 200 ka. We also recognize a slight peak in explosive eruptions during warm periods (e.g. MIS 5 and MIS 7) and speculate on lithospheric unloading

  1. Occurrence, spatiotemporal distribution, and ecological risks of steroids in a large shallow Chinese lake, Lake Taihu.

    PubMed

    Zhou, Li-Jun; Zhang, Bei-Bei; Zhao, Yong-Gang; Wu, Qinglong L

    2016-07-01

    Steroids have been frequently detected in surface waters, and might pose adverse effects on aquatic organisms. However, little information is available regarding the occurrence and spatiotemporal distribution of steroids in lake environments. In addition to pollution sources, the occurrence and spatiotemporal distribution of steroids in lake environments might be related to lake types (shallow or deep), lake hydrodynamics, and sorption-desorption processes in the water-sediment systems. In this study, the occurrence, spatiotemporal distribution, and ecological risks of 36 steroids in a large shallow lake were evaluated by investigating surface water and sediment samples at 32 sites in Lake Taihu over two seasons. Twelve and 15 analytes were detected in aqueous and sedimentary phases, respectively, with total concentrations ranging from 0.86 to 116ng/L (water) and from 0.82 to 16.2ng/g (sediment, dry weight). Temporal variations of steroid concentrations in the water and sediments were statistically significant, with higher concentrations in winter. High concentrations of steroids were found in the seriously polluted bays rather than in the pelagic zone of the lake. Strong lake currents might mix pelagic waters, resulting in similar concentrations of steroids in the pelagic zone. Mass balance analysis showed that sediments in shallow lakes are in general an important sink for steroids. Steroids in the surface water and sediments of Lake Taihu might pose potential risks to aquatic organisms. Overall, our study indicated that the concentrations and spatiotemporal distribution of steroids in the large shallow lake are influenced simultaneously by pollution sources and lake hydrodynamics. Steroids in the large shallow Lake Taihu showed clear temporal and spatial variations and lake sediments may be a potential sink of steroids. Copyright © 2016 Elsevier B.V. All rights reserved.

  2. Patterns in benthic biodiversity link lake trophic status to structure and potential function of three large, deep lakes.

    PubMed

    Hayford, Barbara L; Caires, Andrea M; Chandra, Sudeep; Girdner, Scott F

    2015-01-01

    Relative to their scarcity, large, deep lakes support a large proportion of the world's freshwater species. This biodiversity is threatened by human development and is in need of conservation. Direct comparison of biodiversity is the basis of biological monitoring for conservation but is difficult to conduct between large, insular ecosystems. The objective of our study was to conduct such a comparison of benthic biodiversity between three of the world's largest lakes: Lake Tahoe, USA; Lake Hövsgöl, Mongolia; and Crater Lake, USA. We examined biodiversity of common benthic organism, the non-biting midges (Chironomidae) and determined lake trophic status using chironomid-based lake typology, tested whether community structure was similar between the three lakes despite geographic distance; and tested whether chironomid diversity would show significant variation within and between lakes. Typology analysis indicated that Lake Hövsgöl was ultra-oligotrophic, Crater Lake was oligotrophic, and Lake Tahoe was borderline oligotrophic/mesotrophic. These results were similar to traditional pelagic measures of lake trophic status for Lake Hövsgöl and Crater Lake but differed for Lake Tahoe, which has been designated as ultra-oligotrophic by traditional pelagic measures such as transparency found in the literature. Analysis of similarity showed that Lake Tahoe and Lake Hövsgöl chironomid communities were more similar to each other than either was to Crater Lake communities. Diversity varied between the three lakes and spatially within each lake. This research shows that chironomid communities from these large lakes were sensitive to trophic conditions. Chironomid communities were similar between the deep environments of Lake Hövsgöl and Lake Tahoe, indicating that chironomid communities from these lakes may be useful in comparing trophic state changes in large lakes. Spatial variation in Lake Tahoe's diversity is indicative of differential response of chironomid

  3. Subaerial records of large-scale explosive volcanism and tsunami along an oceanic arc, Tonga, SW Pacific

    NASA Astrophysics Data System (ADS)

    Cronin, S. J.; Smith, I. E.

    2015-12-01

    We present a new chronology of major terrestrial eruptions and tsunami events for the central Tongan Arc. The active Tonga-Kermadec oceanic arc extends 2500 km northward of New Zealand and hosts many tens of submarine volcanoes with around a dozen forming islands. Despite its obious volcanic setting, the impacts of explosive volcanism and volcano-tectonic related tsunami are an often overlooked in archaeological and paleo-botanical histories, mainly due the lack of good Holocene subaerial exposures. The inhabited small uplifted coral platform islands east of the volcanic arc in Tonga collectively cover only <550 km2. Inspired by local mythology of gods flying overhead with baskets of ash, and an analysis of the high-level wind distribution patterns, lake and wetland sites were investigated along the Tongan chain. In most cases former lagoon basins lifted above sea-level by a combination of tectonic rise and the lowering of mean sea levels by around 2 m since the Mid-Holocene form closed lake or swampy depressions. Coring reveaed between 6 and 20 mineral layers at each site, withn humic sediment or peat. Over thirty new radiocarbon dates were collected to develop a chronology for the sequences and the mineral layers were examined mineralogically and geochemically. These sites reveal mainly tephra fall layers of <6500 cal. years B.P., including several very large and regionally significant tephras. Erupted compositions range from basaltic to dacitic, with some showing compositional change during eruption. In addition, some large eruptions appear to have generated regionally significant tsunami, represented by characteristically mixed sandy layers with lithologies including shell fragment, foraminifera and volcanic particles.

  4. Stratified tephra records from lake sediment archives: Holocene eruptions of the Virunga Volcanic Province, East African Rift

    NASA Astrophysics Data System (ADS)

    Lane, Christine; Scholz, Christopher; Poppe, Sam; Schmid, Martin; Ross, Kelly Ann

    2016-04-01

    Lake sediments preserve rare stratified records of explosive volcanism, often with accompanying chronological controls or climatostratigraphic detail. In proximal areas where outcrop stratigraphies are complex, exposures isolated and sediments frequently eroded, the lacustrine archive provides a means to check the order of events and identify additional eruptions not preserved on land. The visible volcanic ash (tephra) record within lake sediments may be limited by eruption volume, distance from source and high sedimentation rates. A more complete eruption history can be detected through the study of non-visible tephra layers. Such "cryptotephra" records may be revealed through non-destructive core-scanning methods, such as XRF-scanning or magnetic susceptibility measurements, or by more thorough laboratory processes and microscopic analysis. Compositional analysis of tephra glass shards using WDS-EPMA and LA-ICP-MS provide a means to provenance eruptions, to cross-correlate between multiple sediment cores, and to establish connections between the lacustrine record and proximal outcrops. Here we present the results of such a "tephrostratigraphic" approach applied to the Holocene volcanic record of the Virunga Volcanic Province (VVP). More than 10 explosive volcanic eruptions, attributed to multiple volcanic centres, are evidenced over the last 12,000 years. This unique insight into the frequency of explosive eruptions from the VVP, demonstrates the potential of visible and cryptotephra investigations in lacustrine sediment archives as a means of studying past, present and future volcanic hazards.

  5. The legacy of large regime shifts in shallow lakes.

    PubMed

    Ramstack Hobbs, Joy M; Hobbs, William O; Edlund, Mark B; Zimmer, Kyle D; Theissen, Kevin M; Hoidal, Natalie; Domine, Leah M; Hanson, Mark A; Herwig, Brian R; Cotner, James B

    2016-12-01

    Ecological shifts in shallow lakes from clear-water macrophyte-dominated to turbid-water phytoplankton-dominated are generally thought of as rapid short-term transitions. Diatom remains in sediment records from shallow lakes in the Prairie Pothole Region of North America provide new evidence that the long-term ecological stability of these lakes is defined by the legacy of large regime shifts. We examine the modern and historical stability of 11 shallow lakes. Currently, four of the lakes are in a clear-water state, three are consistently turbid-water, and four have been observed to change state from year to year (transitional). Lake sediment records spanning the past 150-200 yr suggest that (1) the diatom assemblage is characteristic of either clear or turbid lakes, (2) prior to significant landscape alteration, all of the lakes existed in a regime of a stable clear-water state, (3) lakes that are currently classified as turbid or transitional have experienced one strong regime shift over the past 150-200 yr and have since remained in a regime where turbid-water predominates, and (4) top-down impacts to the lake food-web from fish introductions appear to be the dominant driver of strong regime shifts and not increased nutrient availability. Based on our findings we demonstrate a method that could be used by lake managers to identify lakes that have an ecological history close to the clear-turbid regime threshold; such lakes might more easily be returned to a clear-water state through biomanipulation. The unfortunate reality is that many of these lakes are now part of a managed landscape and will likely require continued intervention.

  6. The volcanic, sedimentologic, and paleolimnologic history of the Crater Lake caldera floor, Oregon:Evidence for small caldera evolution

    USGS Publications Warehouse

    Nelson, C. Hans; Bacon, Charles R.; Robinson, Stephen W.; Adam, David P.; Bradbury, J. Platt; Barber, John H.; Schwartz, Deborah; Vagenas, Ginger

    1994-01-01

    Apparent phreatic explosion craters, caldera-floor volcanic cones, and geothermal features outline a ring fracture zone along which Mount Mazama collapsed to form the Crater Lake caldera during its climactic eruption about 6,850 yr B.P. Within a few years, subaerial deposits infilled the phreatic craters and then formed a thick wedge (10-20 m) of mass flow deposits shed from caldera walls. Intense volcanic activity (phreatic explosions, subaerial flows, and hydrothermal venting) occurred during this early postcaldera stage, and a central platform of subaerial andesite flows and scoria formed on the caldera floor.Radiocarbon ages suggest that deposition of Iacustrine hemipelagic sediment began on the central platform about 150 yr after the caldera collapse. This is the minimum time to fill the lake halfway with water and cover the platform assuming present hydrologic conditions of precipitation and evaporation but with negligible leakage of lake water. Wizard Island formed during the final part of the 300-yr lake-filling period as shown by its (1) upper subaerial lava flows from 0 to -70 m below present water level and lower subaqueous lava flows from -70 to -500 m and by (2) lacustrine turbidite sand derived from Wizard Island that was deposited on the central platform about 350 yr after the caldera collapse. Pollen stratigraphy indicates that the warm and dry climate of middle Holocene time correlates with the early lake deposits. Diatom stratigraphy also suggests a more thermally stratified and phosphate-rich environment associated respectively with this climate and greater hydrothermal activity during the early lake history.Apparent coarse-grained and thick-bedded turbidites of the early lake beds were deposited throughout northwest, southwest, and eastern basins during the time that volcanic and seismic activity formed the subaqueous Wizard Island, Merriam Cone, and rhyodacite dome. The last known postcaldera volcanic activity produced a subaqueous rhyodacite

  7. Isotopic and geophysical constraints on the structure andevolution of the Clear Lake volcanic system

    SciTech Connect

    Hammersley, L.; DePaolo, D.

    2005-03-09

    New Sr and Nd isotopic data are combined with availableinformation on the composition and petrology of lavas and the thermal andseismic structure of the underlying crust to develop a detailed model forthe deep structure and magmatic processes of the Clear Lake volcanicsystem in northern California. The isotopic data require a two-stagemodel for magmatic evolution. In stage I, basaltic magma (eNd=+6 to +8;87Sr/86Sr=0.703 to 0.7035; SiO2V50 percent) is fed from the mantle intothe lower and middle crust and evolves through combined crustalassimilation and fractional crystallization to basaltic andesite (eNd=+5to +0.4; 87Sr/86Sr=0.70328 to 0.70485; SiO2655 percent to 57 percent). Instage II, the basaltic andesite magmas are transported upward and areeither erupted at the surface or stored in shallow magma chambers wherethey evolve by fractional crystallization to form dacitic and rhyoliticmagmas (SiO2665 percent to 70 percent). High-silica rhyolites (SiO2675percent; high 87Sr/86Sr) show evidence that further crustal assimilationcan occur where upper crustal temperatures are elevated. Calculateddensities of Clear Lake lavas indicate that basalt should pond at a depthof 12-18 km where seismic data show a pronounced density boundary withinthe crust. Thermodynamic models of assimilation require that mid-crustaltemperatures are at least 600-800 8C to allow for enough assimilation toexplain the isotopic data. Both surface heat flow and thermobarometry ofcrustal xenoliths in andesites are consistent with these inferred hightemperatures. The Clear Lake volcanic system provides an opportunity tocross-calibrate petrological, geochemical and geophysical approaches. Theresults confirm that magma supply, magma buoyancy, and crustaltemperatures control magmatic evolution. A temporal trend of increasingeNd over the past 2 million years suggests that magma supply in the ClearLake volcanic field has been increasing and is still high. This isconsistent with high heat flow in the area

  8. The large volcanic eruptions at different latitude bands and patterns of winter temperature changes over China

    NASA Astrophysics Data System (ADS)

    Hao, Zhixin; Sun, Di

    2016-04-01

    Based on the chronology of 29 large volcanic eruptions events (Volcanic Explosivity Index≥4) since 1951 and gridded temperature dataset from China Meteorological Data Sharing Service System, we identified the patterns of winter temperature changes over China after the large volcanic eruptions, comparing with the mean temperature within the five years before, then we analyzed the related dynamic mechanisms of different patterns by NCEP reanalysis data and model output data from Community Earth System Model (CESM). The results showed that the winter temperature decreased more than 1°C in East China after volcanic eruptions on middle-lower latitudes and equatorial bands. After volcanic eruptions on different latitudes, the temperature spatial patterns were summarized as two types, which included that temperature was cooling centered on Northeast and warming in Tibets, and its opposite pattern. The first pattern was usually detected after tropical volcanic eruptions in spring/summer and it also appeared after volcanic eruptions on high latitudes in spring/autumn. After middle-lower latitude volcanic eruptions, the variation of geopotential height on 500hPa showed that the positive anomaly was existed at the East of Ural mountain, which caused the temperature decreased in Northwest , Central East and Southeast when east asian trough was intensified. After high latitudes volcanic eruptions, the zonal circulation was more obvious at middle latitudes, the cold air was not easy to transport,therefore winter temperature increased in China except for the Yangtze River Basin. The result of full forcing experiments by CESM showed that temperature decreased at most regions after large volcanic eruptions on equatorial /high bands, and troughs and wedges were developed on 500 hPa. The variation of geopotential height was nearly reversed after volcanic eruptions on high latitudes, only the temperature of Tibetan Plateau decreased. But how the variation of geopotential height

  9. The large volcanic eruptions at different latitude bands and patterns of winter temperature changes over China

    NASA Astrophysics Data System (ADS)

    Sun, D.; Hao, Z.; Zheng, J.

    2015-12-01

    Based on the chronology of 29 large volcanic eruptions events (Volcanic Explosivity Index≥4) since 1951 and gridded temperature dataset from China Meteorological Data Sharing Service System, we identified the patterns of winter temperature changes over China after the large volcanic eruptions, comparing with the mean temperature within the five years before, then we analyzed the related dynamic mechanisms of different patterns by NCEP reanalysis data and model output data from Community Earth System Model (CESM). The results showed that the winter temperature decreased more than 1°C in East China after volcanic eruptions on middle-lower latitudes and equatorial bands. After volcanic eruptions on different latitudes, the temperature spatial patterns were summarized as two types, which included that temperature was cooling centered on Northeast and warming in Tibets, and its opposite pattern. The first pattern was usually detected after equatorial volcanic eruptions in spring/summer and it also appeared after volcanic eruptions on high latitudes in spring/autumn. After middle-lower latitude volcanic eruptions, the variation of geopotential height on 500hPa showed that the positive anomaly was existed at the East of Ural mountain, which caused the temperature decreased in Northwest , Central East and Southeast when east asian trough was intensified. After high latitudes volcanic eruptions, the zonal circulation was more obvious at middle latitudes, the cold air was not easy to transport therefore winter temperature increased in China except for the Yangtze River Basin. The result of full forcing experiments by CESM showed that temperature decreased at most regions after large volcanic eruptions on equatorial /high bands, and troughs and wedges were developed on 500 hPa. The variation of geopotential height was nearly reversed after volcanic eruptions on high latitudes, only the temperature of Tibetan Plateau decreased. But how the variation of geopotential height

  10. Depth gradients in food web processes linking large lake habitats

    EPA Science Inventory

    In large lakes around the world, shifts in ecological communities are often associated with water depth. This suggests that there may be concomitant changes in patterns of resource allocation. Using Lake Superior as an example, we explored this idea through stable isotope analyse...

  11. Depth gradients in food web processes linking large lake habitats

    EPA Science Inventory

    In large lakes around the world, shifts in ecological communities are often associated with water depth. This suggests that there may be concomitant changes in patterns of resource allocation. Using Lake Superior as an example, we explored this idea through stable isotope analyse...

  12. The Lepanto Cu–Au deposit, Philippines: A fossil hyperacidic volcanic lake complex

    USGS Publications Warehouse

    Berger, Byron R.; Henley, Richard W.; Lowers, Heather; Pribil, Michael

    2014-01-01

    Hyperacidic lakes and associated solfatara in active volcanoes are the expression of magmatic gas expansion from source to surface. Here we show for the first time, that the vein system that comprises the ~ 2 Ma high-sulfidation, Lepanto copper–gold deposit in the Mankayan district (Philippines) was associated with a contemporary hyperacidic volcanic lake complex—possibly the first such lake recognized in the geological record. A 15–20‰ difference in sulfur isotopic composition between barite and sulfides and sulfosalts in the vent fumarole encrustations supports the interpretation that SO2-rich volcanic gas vented into the base of the lake and marginal to it and ties the mineralization directly to magmatic gas expansion, fracture propagation, and mineralization that occurred through a series of decompression steps within the feeder fracture network. These data confirm that crater lake environments such as Kawah Ijen (Java, Indonesia) provide modern day analogs of the Lepanto and other high sulfidation Cu–Au depositing environments.We also provide extensive analysis of sulfosalt–sulfide reactions during vein formation within the hyperacidic lake complex. Pyrite ±  silica deposited first at high temperature followed by enargite that preserves the vapor–solid diffusion of, for example, antimony, tin, and tellurium into the vapor from the crystallizing solid. Subsolidus, intra-crystalline diffusion continued as temperature declined. Pyrite and enargite are replaced by Fe-tennantite in the lodes which initially has low Sb/(Sb + As) atomic ratios around 13.5% close to the ideal tennantite formula, but evolves to higher ratios as crystallization proceeds. Fumarole encrustation clasts and sulfosalts in the lake sediment are more highly evolved with a larger range of trace element substitutions, including antimony. Substitution of especially Zn, Te, Ag, and Sn into tennantite records metal and semi-metal fractionation between the expanding magmatic

  13. Simulating Volcanic Plumes: From Micro To Large Scales

    NASA Astrophysics Data System (ADS)

    Graf, H.-F.; Textor, Ch.

    Longer lasting atmospheric effects of volcanic activity are mainly due to sulfuric aerosols formed from gaseous sulfur emissions. The fate of the sulfur depends strongly on microphysical processes inside the eruption plume, which are influenced by envi- ronmental conditions in the surrounding atmosphere. A powerful numerical simulation model "ATHAM" is presented that treats these pro- cesses at a comparatively high level of realism. Results of this model concerning the efficiency of stratospheric injection of sulfur gases and other species as well as vol- canic ashes will be discussed. The SO2 injected into the stratosphere is transformed into sulfur acid particles which can be globally distributed and can affect climate for few years after strong eruptions. These processes also can be modelled successfully and examples of volcanic climate effects will be shown for different eruptions. Besides these effects of strongly explosive eruptions also permanent degassing plays a key role in atmospheric chemistry and climate. Model simulations underlining the super-proportional effect of tropospheric sulfur emissions from volcanic sources will demonstrate the need for more complete monitoring of volcanic degassing.

  14. Dynamic response to valley breeze circulation in Santa María del Oro, a volcanic lake in Mexico

    NASA Astrophysics Data System (ADS)

    Serrano, David; Filonov, Anatoliy; Tereshchenko, Irina

    2002-07-01

    The paper discusses the dynamic response to valley breeze circulation in Santa Maria del Oro, a volcanic lake in Mexico. Hourly records of wind measurements were used to construct a hydrodynamical model of the level fluctuations of the lake's water as well as integrated drift currents. The calculations show that the valley breeze circulation stimulates barotropic seiches in the lake with a period of 2.6 minutes and maximal level in the southwest part up to 18 mm. The drift current form two circulating rings having an opposite directions: anticyclonical in northern part of the lake and cyclonical in the southern. At the external edge of these rings the current speed can reach 20 cm/s. The measurements have shown that most part of the year the lake is strongly stratified. The maximal vertical temperature gradients are over 1°C/m in November and August, in a layer of 17-20 m.

  15. Large lake models - uses, abuses, and future

    SciTech Connect

    Sonzogni, W.C.; Canale, R.P.; Lam, D.C.L.; Lick, W.; Mackay, D.; Minns, C.K.; Richardson, W.L.; Scavia, D.; Smith, V.; Strachan, W.M.J.

    1987-01-01

    Mathematical modeling has played and should continue to play an important role in Great Lakes management and scientific development. Great Lakes modeling is entering a phase of relative maturity in which expectations are more realistic than in the past. For example, it is now realized that the modeling process itself is valuable even if the resulting models are not immediately useful for management. The major thrust in the past has been water quality (eutrophication) modeling, but there has been a recent shift toward developing toxic substances models. Modelers and model users have been limited by a lack of knowledge of Great Lakes processes, limited data availability, and incomplete or improper validation. In the future, greater emphasis is needed on specifying prediction uncertainty and conducting proper model validation - including calibration, verification, and post-audits. Among the Great Lakes modeling activities likely to have the greatest payoff in the near future are (1) the development and refinement of toxic substances models, (2) post-auditing and improvement of eutrophication models, and (3) the adaptation of models for use on personal computers to allow greater model utilization.

  16. Trends in evaporation of a large subtropical lake

    NASA Astrophysics Data System (ADS)

    Hu, Cheng; Wang, Yongwei; Wang, Wei; Liu, Shoudong; Piao, Meihua; Xiao, Wei; Lee, Xuhui

    2017-07-01

    How rising temperature and changing solar radiation affect evaporation of natural water bodies remains poor understood. In this study, evaporation from Lake Taihu, a large (area 2400 km2) freshwater lake in the Yangtze River Delta, China, was simulated by the CLM4-LISSS offline lake model and estimated with pan evaporation data. Both methods were calibrated against lake evaporation measured directly with eddy covariance in 2012. Results show a significant increasing trend of annual lake evaporation from 1979 to 2013, at a rate of 29.6 mm decade-1 according to the lake model and 25.4 mm decade-1 according to the pan method. The mean annual evaporation during this period shows good agreement between these two methods (977 mm according to the model and 1007 mm according to the pan method). A stepwise linear regression reveals that downward shortwave radiation was the most significant contributor to the modeled evaporation trend, while air temperature was the most significant contributor to the pan evaporation trend. Wind speed had little impact on the modeled lake evaporation but had a negative contribution to the pan evaporation trend offsetting some of the temperature effect. Reference evaporation was not a good proxy for the lake evaporation because it was on average 20.6 % too high and its increasing trend was too large (56.5 mm decade-1).

  17. Constraints on the history of open-basin lakes on Mars from the timing of volcanic resurfacing

    NASA Astrophysics Data System (ADS)

    Goudge, T. A.; Mustard, J. F.; Head, J. W.; Fassett, C. I.

    2011-12-01

    A catalogue of 30 open-basin lakes on Mars [1] have been identified as volcanically resurfaced based on distinct morphology and mineralogy. Associated morphologies include: (1) smooth floor deposits with lobate margins; (2) high crater retention, especially at small crater sizes; (3) wrinkle ridges on the smooth floor deposits; (4) embayment of basin perimeters and older, stratigraphically underlying deposits; (5) "moat" structures surrounding the edge of the basin, suggesting subsidence of the volcanic fill [2]; (6) high thermal inertia based on THEMIS nighttime IR data [3]; and (7) roughness signatures characteristic of smooth, volcanic material [4]. In addition to studying the morphology of the open-basin lakes, the mineralogies of the floor deposits have been analyzed using orbital spectroscopy data returned from the CRISM and OMEGA instruments. This analysis reveals that these resurfaced basins contain strong mafic mineral signatures isolated to their interiors when clear spectroscopic signatures are visible. An analysis of the CRISM and OMEGA spectra reveal the presence of both olivine and pyroxene, based on distinct mineral absorptions at 1 and 2 μm, in many resurfaced basins; however, olivine appears to be the dominant mafic mineral in the majority of these units. These mineral signatures provide further evidence for the volcanic resurfacing of the studied open-basin lakes. Additionally, the studied open-basin lakes lack any evidence for mineralogical and morphologic features that would be expected for lava-water interaction. This indicates that these open-basin lakes were completely devoid of surficial water at the time of volcanic resurfacing. Ages for the resurfacing events have been determined through crater size-frequency distributions and indicate that the process of volcanic resurfacing occurred throughout the Hesperian and into the Amazonian, with the majority of basins being resurfaced in the earliest parts of the Hesperian, near the Noachian

  18. Emmons Lake Volcanic Center, Alaska Peninsula: Source of the Late Wisconsin Dawson tephra, Yukon Territory, Canada

    USGS Publications Warehouse

    Mangan, M.T.; Waythomas, C.F.; Miller, T.P.; Trusdell, F.A.

    2003-01-01

    The Emmons Lake Volcanic Center on the Alaska Peninsula of southwestern Alaska is the site of at least two rhyolitic caldera-forming eruptions (C1 and C2) of late Quaternary age that are possibly the largest of the numerous caldera-forming eruptions known in the Aleutian arc. The deposits produced by these eruptions are widespread (eruptive volumes of >50 km3 each), and their association with Quaternary glacial and eolian deposits on the Alaska Peninsula and elsewhere in Alaska and northwestern Canada enhances the likelihood of establishing geochronological control on Quaternary stratigraphic records in this region. The pyroclastic deposits associated with the second caldera-forming eruption (C2) consist of loose, granular, airfall and pumice-flow deposits that extend for tens of kilometres beyond Emmons Lake caldera, reaching both the Bering Sea and Pacific Ocean coastlines north and south of the caldera. Geochronological and compositional data on C2 deposits indicate a correlation with the Dawson tephra, a 24 000 14C BP (27 000 calibrated years BP), widespread bed of silicic ash found in loess deposits in west-central Yukon Territory, Canada. The correlation clearly establishes the Dawson tephra as the time-stratigraphic marker of the last glacial maximum.

  19. Paleomagnetic study of the Portage Lake Volcanics exposed in the Quincy Mine

    NASA Astrophysics Data System (ADS)

    Michels, Alexander C.

    A detailed paleomagnetic and rock-magnetic investigation was conducted on thirty six basaltic flows of the ˜1095 Ma Portage Lake Volcanics. The flows were sampled along the East Adit of the Quincy Mine (Hancock, MI). Thirty two flows yielded well-defined primary magnetization directions carried by magnetite. A secondary magnetization component carried by hematite was also found in twenty nine flows. After correction for serial correlation between the flows, nineteen independent mean directions were calculated. The corresponding paleomagnetic pole is located at 25.5 °N, 182.1 °W (A95 = 3.5°). The new pole overlaps with the pole from the ˜1087 Ma Lake Shore Traps suggesting a standstill of the North American plate during that time period. The low angular dispersion of virtual geomagnetic poles (S = 7.9°) suggests that the flows were erupted within a short time period, or that the strength of geomagnetic secular variation was lower than that of the recent field.

  20. An oligarchic microbial assemblage in the anoxic bottom waters of a volcanic subglacial lake.

    PubMed

    Gaidos, Eric; Marteinsson, Viggo; Thorsteinsson, Thorsteinn; Jóhannesson, Tomas; Rúnarsson, Arni Rafn; Stefansson, Andri; Glazer, Brian; Lanoil, Brian; Skidmore, Mark; Han, Sukkyun; Miller, Mary; Rusch, Antje; Foo, Wilson

    2009-04-01

    In 2006, we sampled the anoxic bottom waters of a volcanic lake beneath the Vatnajökull ice cap (Iceland). The sample contained 5 x 10(5) cells per ml, and whole-cell fluorescent in situ hybridization (FISH) and PCR with domain-specific probes showed these to be essentially all bacteria, with no detectable archaea. Pyrosequencing of the V6 hypervariable region of the 16S ribosomal RNA gene, Sanger sequencing of a clone library and FISH-based enumeration of four major phylotypes revealed that the assemblage was dominated by a few groups of putative chemotrophic bacteria whose closest cultivated relatives use sulfide, sulfur or hydrogen as electron donors, and oxygen, sulfate or CO(2) as electron acceptors. Hundreds of other phylotypes are present at lower abundance in our V6 tag libraries and a rarefaction analysis indicates that sampling did not reach saturation, but FISH data limit the remaining biome to <10-20% of all cells. The composition of this oligarchy can be understood in the context of the chemical disequilibrium created by the mixing of sulfidic lake water and oxygenated glacial meltwater.

  1. Primary alkaline magmas associated with the Quaternary Alligator Lake volcanic complex, Yukon Territory, Canada

    NASA Astrophysics Data System (ADS)

    Eiché, G. E.; Francis, D. M.; Ludden, J. N.

    1987-02-01

    The Alligator Lake complex is a Quaternary alkaline volcanic center located in the southern Yukon Territory of Canada. It comprises two cinder cones which cap a shield consisting of five distinct lava units of basaltic composition. Units 2 and 3 of this shield are primitive olivine-phyric lavas (13.5 19.5 cation % Mg) which host abundant spinel lherzolite xenoliths, megacrysts, and granitoid fragments. Although the two lava types have erupted coevally from adjacent vents and are petrographically similar, they are chemically distinct. Unit 2 lavas have considerably higher abundances of LREE, LILE, and Fe, but lower HREE, Y, Ca, Si, and Al relative to unit 3 lavas. The 87Sr/86Sr and 143Nd/144Nd isotopic ratios of these two units are, however, indistinguishable. The differences between these two lava types cannot be explained in terms of low pressure olivine fractionation, and the low concentrations of Sr, Nb, P, and Ti in the granitoid xenoliths relative to the primitive lavas discounts differential crustal contamination. The abundance of spinel lherzolite xenoliths and the high Mg contents in the lavas of both units indicates that their compositional differences originated in the upper mantle. The Al and Si systematics of these lavas suggests that, compared to unit 3 magmas, the unit 2 magmas may have segregated at greater depths from a garnet lherzolite mantle. The identical isotopic composition and similar ratios of highly incompatible elements in these two lava units argues against their differences being a consequence of random metasomatism or mantle heterogeneity. The lower Y and HREE contents but higher concentrations of incompatible elements in the unit 2 lavas relative to unit 3 can be most simply explained by differential partial melting of similar garnet-bearing sources. The unit 2 magmas thus appear to have been generated by smaller degrees of melting at a greater depth than the unit 3 magmas. The contemporaneous eruption of two distinct but

  2. Non-volcanic tremor driven by large transient shear stresses

    USGS Publications Warehouse

    Rubinstein, J.L.; Vidale, J.E.; Gomberg, J.; Bodin, P.; Creager, K.C.; Malone, S.D.

    2007-01-01

    Non-impulsive seismic radiation or 'tremor' has long been observed at volcanoes and more recently around subduction zones. Although the number of observations of non-volcanic tremor is steadily increasing, the causative mechanism remains unclear. Some have attributed non-volcanic tremor to the movement of fluids, while its coincidence with geodetically observed slow-slip events at regular intervals has led others to consider slip on the plate interface as its cause. Low-frequency earthquakes in Japan, which are believed to make up at least part of non-volcanic tremor, have focal mechanisms and locations that are consistent with tremor being generated by shear slip on the subduction interface. In Cascadia, however, tremor locations appear to be more distributed in depth than in Japan, making them harder to reconcile with a plate interface shear-slip model. Here we identify bursts of tremor that radiated from the Cascadia subduction zone near Vancouver Island, Canada, during the strongest shaking from the moment magnitude Mw = 7.8, 2002 Denali, Alaska, earthquake. Tremor occurs when the Love wave displacements are to the southwest (the direction of plate convergence of the overriding plate), implying that the Love waves trigger the tremor. We show that these displacements correspond to shear stresses of approximately 40 kPa on the plate interface, which suggests that the effective stress on the plate interface is very low. These observations indicate that tremor and possibly slow slip can be instantaneously induced by shear stress increases on the subduction interface - effectively a frictional failure response to the driving stress. ??2007 Nature Publishing Group.

  3. Non-volcanic tremor driven by large transient shear stresses.

    PubMed

    Rubinstein, Justin L; Vidale, John E; Gomberg, Joan; Bodin, Paul; Creager, Kenneth C; Malone, Stephen D

    2007-08-02

    Non-impulsive seismic radiation or 'tremor' has long been observed at volcanoes and more recently around subduction zones. Although the number of observations of non-volcanic tremor is steadily increasing, the causative mechanism remains unclear. Some have attributed non-volcanic tremor to the movement of fluids, while its coincidence with geodetically observed slow-slip events at regular intervals has led others to consider slip on the plate interface as its cause. Low-frequency earthquakes in Japan, which are believed to make up at least part of non-volcanic tremor, have focal mechanisms and locations that are consistent with tremor being generated by shear slip on the subduction interface. In Cascadia, however, tremor locations appear to be more distributed in depth than in Japan, making them harder to reconcile with a plate interface shear-slip model. Here we identify bursts of tremor that radiated from the Cascadia subduction zone near Vancouver Island, Canada, during the strongest shaking from the moment magnitude M(w) = 7.8, 2002 Denali, Alaska, earthquake. Tremor occurs when the Love wave displacements are to the southwest (the direction of plate convergence of the overriding plate), implying that the Love waves trigger the tremor. We show that these displacements correspond to shear stresses of approximately 40 kPa on the plate interface, which suggests that the effective stress on the plate interface is very low. These observations indicate that tremor and possibly slow slip can be instantaneously induced by shear stress increases on the subduction interface-effectively a frictional failure response to the driving stress.

  4. Comparison between mechanisms of CO2 degassing from El Chichon volcanic lake, México, and Specchio di Venere lake, Pantelleria, Italia.

    NASA Astrophysics Data System (ADS)

    Jácome Paz, M. P.; Taran, Y.; Inguaggiato, S.; Collard, N.; Vita, F.; Pecoraino, G.

    2014-12-01

    We present results of the CO2 diffuse emission from the surface of two volcanic lakes: El Chichón (EC) in Mexico and Specchio di Venere (SV) on Pantelleria Island, Italy. Both lakes are drainless, have similar sizes (~2x105 m2) and similar input-output dynamics. However, they are drastically different in water chemistry. The SV lake is alkaline (pH >9) and of a high near constant salinity, whereas EC lake is acidic (pH 2.3) and of a low variable salinity. In the vicinity of both lakes there are thermal grounds with steam vents and hot springs and a high CO2 soil flux. The SV lake has high alkalinity (~70 meq/L), whereas the EC lake is characterized by high concentration of dissolved CO2. CO2 flux measurements from the surface of both lakes were made with the "floating" accumulation chamber. During the flux measuring, gas samples were taken for carbon isotopic analysis. Soil flux measurements were also made in the crater of El Chichon volcano and on the area adjacent to the SV lake. The preliminary results of CO2 fluxes indicate EC lake has a high CO2 flux with a mean value of 3500 g m-2 d-1, with the highest values alignment across NW-SE and NE-SW faults and a high degassing by bubbling gases, especially near the strongest NE fumarolic field. While SV has a mean value of the CO2 flux ~ 10 g m-2 d-1 and limited bubbling on the lake surface. High CO2 flux was measured from the soil near the lake at the Mofeta place. A net mean diffusion flux (without bubbles) from EC lake is about 350 times higher than that from SV lake (3500 g m-2 d-1 vs 10 g m-2 d-1). SV has the total CO2 flux by diffusion of ~3 ton d-1 from an area of 0.3 km2 and the total flux of 0.44 ton d-1 by bubbling areas at SW and S zones. The EC lake has the total CO2 flux of 840 ton d-1 from an area of 0.24 km2. The total CO2 output from SV is nevertheless about two times higher taking into account the seepage from the lake (~ 8 kg s-1) of highly carbonated water.

  5. Large Volume 18O-depleted Rhyolitic Volcanism: the Bruneau-Jarbidge Volcanic Field, Idaho

    NASA Astrophysics Data System (ADS)

    Boroughs, S.; Wolff, J.; Bonnichsen, B.; Godchaux, M. M.; Larson, P. B.

    2003-12-01

    The Bruneau-Jarbidge (BJ) volcanic field is located in southern Idaho at the intersection of the western and eastern arms of the Snake River Plain. The BJ region is an oval structural basin of about 6000 km2, and is likely a system of nested caldera and collapse structures similar to, though larger than, the Yellowstone Volcanic Plateau. BJ rocks are high-temperature rhyolite tuffs, high-temperature rhyolite lavas, and volumetrically minor basalts. Exposed volumes of individual rhyolite units range up to greater than 500 km3. We have analyzed feldspar and, where present, quartz from 30 rhyolite units emplaced throughout the history of the BJ center. All, including the Cougar Point Tuff, are 18O depleted (δ 18OFSP = -1.3 to 3.7‰ ), while petrographically, temporally, and chemically similar lavas erupted along the nearby Owyhee Front have "normal" rhyolite magmatic δ 18O values of 7 - 9‰ . There is no evidence for significant modification of δ 18O values by post-eruptive alteration. No correlation exists between δ 18O and age, magmatic temperature, major element composition or trace element abundances among depleted BJ rhyolites. The BJ and WSRP rhyolites possess the geochemical characteristics (depressed Al, Ca, Eu, and Sr contents, high Ga/Al and K/Na) expected of liquids derived from shallow melting of calc-alkaline granitoids with residual plagioclase and orthopyroxene (Patino-Douce, Geology v.25 p.743-746, 1997). The classic Yellowstone low δ 18O rhyolites are post-caldera collapse lavas, but at BJ, both lavas and caldera-forming ignimbrites are strongly 18O-depleted. The total volume of low δ 18O rhyolite may be as high as 10,000 km3, requiring massive involvement of meteoric-hydrothermally altered crust in rhyolite petrogenesis. Regional hydrothermal modification of the crust under the thermal influence of the Yellowstone hotspot apparently preceded voluminous rhyolite generation at Bruneau-Jarbidge.

  6. Feedback between deglaciation and volcanism in arc settings: the example of the Mount Mazama volcanic system, Crater Lake, Oregon

    NASA Astrophysics Data System (ADS)

    Branecky, C.; Farner, M. J.; Keller, T.; Lanza, F.; Siravo, G.; Gonnermann, H. M.; Huybers, P. J.; Manga, M.; van der Wal, W.

    2015-12-01

    Previous studies have found correlations between glacial cycles and volcanism. Any such feedback mechanisms could have important implications for climate through variations in volcanic outgassing. Although decompression melting has been established as a cause for increased volcanism during deglaciation at mid-ocean ridge systems (Jull and McKenzie, 1996), it has not been determined how changes in glacial loading affect other settings such as volcanic arcs. We examine the Mount Mazama volcanic system, Oregon, where pulses of volcanism have been suggested to follow major deglaciations (Bacon et al. 2006). A statistical test regarding the timing of eruptions is first developed, and its application to eruption dates demonstrates statistically significant clustering of eruptions following deglaciation. To explore potential causes for the identified changes in probability of eruptions, the effects of glacial unloading on melt production are computed using a 1D mantle melting model, and the effect of ice unloading on shallow crustal stress conditions is tested with a viscoelastic stress model. Combining these effects into a simple eruption model, we propose that variations in melt supply rates from the mantle and changing stress conditions around a shallow crustal magma reservoir modulate eruption probability during glacial cycles. This model illustrates the physical plausibility of glacial variability causing the identified changes in eruption rates at Mt Mazama.

  7. Asphalt Volcanism as a Model to Understand the Geochemical Nature of Pitch Lake, a Planetary Analog for Titan and the Implications towards Methane Flux into Earth's Atmosphere.

    NASA Astrophysics Data System (ADS)

    Khan, A.

    2016-12-01

    Pitch Lake is located in the southwest peninsula of the island near La Brea in Trinidad and Tobago, covering an area of approximately 46 hectares. It was discovered in the year 1595 and is the largest of three natural asphalt lakes that exist on Earth. Pitch Lake is a large oval shaped reservoir composed of dominantly hydrocarbon compounds, but also includes minor amounts of clay and muddy water. It is a natural liquid asphalt desert, which is nourished by a form of petroleum consisting of mostly asphaltines from the surrounding oil-rich region. The hydrocarbons mix with mud and gases under high pressure during upward seepage, and the lighter portion evaporates or is volatilized, which produces a high-viscosity liquid asphalt residue. The residue on and near the surface is a hydrocarbon matrix, which poses extremely challenging environmental conditions to microorganisms characterized by an average low water activity in the range of 0.49 to 0.75, recalcitrant carbon substrates, and toxic chemical compounds. Nevertheless, an active microbial community of archaea and bacteria, many of them novel strains, was found to inhabit the liquid hydrocarbon matrix of Pitch Lake. Geochemical analyses of minerals, done by our team, which revealed sulfates, sulfides, silicates, and metals, normally associated with deep-water hydrothermal vents leads to our new hypothetical model to describe the origins of Pitch Lake and its importance to atmospheric and earth sciences. Pitch Lake is likely the terrestrial equivalent of an offshore submarine asphalt volcano just as La Brea Tar Pits are in some ways an on-land version of the asphalt volcanoes discovered off shore of Santa Barbara by Valentine et al. in 2010. Asphalt volcanism possibly also creates the habitat for chemosynthetic life that is widespread in this lake, as reported by Schulze-Makuch et al. in 2011 and Meckenstock et al. in 2014.

  8. Geology of the Mid-Miocene Rooster Comb Caldera and Lake Owyhee Volcanic Field, eastern Oregon: Silicic volcanism associated with Grande Ronde flood basalt

    NASA Astrophysics Data System (ADS)

    Benson, Thomas R.; Mahood, Gail A.

    2016-01-01

    The Lake Owyhee Volcanic Field (LOVF) of eastern Oregon consists of rhyolitic caldera centers and lava fields contemporaneous with and spatially related to Mid-Miocene Columbia River flood basalt volcanism. Previous studies delineated two calderas in the southeastern part of LOVF near Owyhee Reservoir, the result of eruptions of two ignimbrites, the Tuff of Leslie Gulch and the Tuff of Spring Creek. Our new interpretation is that these two map units are differentially altered parts of a single ignimbrite produced in a major phreatomagmatic eruption at ~ 15.8 Ma. Areas previously mapped as Tuff of Spring Creek are locations where the ignimbrite contains abundant clinoptilolite ± mordenite, which made it susceptible to erosion. The resistant intracaldera Tuff of Leslie Gulch has an alteration assemblage of albite ± quartz, indicative of low-temperature hydrothermal alteration. Our new mapping of caldera lake sediments and pre- and post-caldera rhyolitic lavas and intrusions that are chemically similar to intracaldera Tuff of Leslie Gulch point to a single ~ 20 × 25 km caldera, which we name the Rooster Comb Caldera. Erosion of the resurgently uplifted southern half of the caldera created dramatic exposures of intracaldera Tuff of Leslie Gulch cut by post-caldera rhyolite dikes and intrusions that are the deeper-level equivalents of lava domes and flows that erupted into the caldera lake preserved in exposures to the northeast. The Rooster Comb Caldera has features in common with more southerly Mid-Miocene calderas of the McDermitt Volcanic Field and High Rock Caldera Complex, including formation in a basinal setting shortly after flood basalt eruptions ceased in the region, and forming on eruption of peralkaline ignimbrite. The volcanism at Rooster Comb Caldera postdates the main activity at McDermitt and High Rock, but, like it, begins ~ 300 ky after flood basalt volcanism begins in the area, and while flood basalts don't erupt through the silicic focus, are

  9. Lake Nyos disaster, Cameroon, 1986: the medical effects of large scale emission of carbon dioxide?

    PubMed Central

    Baxter, P. J.; Kapila, M.; Mfonfu, D.

    1989-01-01

    Carbon dioxide was blamed for the deaths of around 1700 people in Cameroon, west Africa, in 1986 when a massive release of gas occurred from Lake Nyos, a volcanic crater lake. The clinical findings in 845 survivors seen at or admitted to hospital were compatible with exposure to an asphyxiant gas. Rescuers noted cutaneous erythema and bullae on an unknown proportion of corpses and 161 (19%) survivors treated in hospital; though these lesions were initially believed to be burns from acidic gases, further investigation suggested that they were associated with coma states caused by exposure to carbon dioxide in air. The disaster at Lake Nyos and a similar event at Lake Monoun, Cameroon, two years previously provide new information on the possible medical effects of large scale emissions of carbon dioxide, though the presence of other toxic factors in these gas releases cannot be excluded. Images FIG 2 a FIG 2 b FIG 2 c FIG 2 d FIG 2 e FIG 3 FIG 4 PMID:2502283

  10. Global baseline data on phosphorus pollution of large lakes

    NASA Astrophysics Data System (ADS)

    Fink, Gabriel; Flörke, Martina; Alcamo, Joseph

    2016-04-01

    Lakes are exposed to harmful eutrophication which is the most concerning water quality issue on global scale. Eutrophication is caused by phosphorous pollution in most lakes. Hence, global consistent base line data on phosphorus loadings are needed to assess future sustainable development. We used the modeling framework WaterGAP3 to calculate present total phosphorus loadings to the world's largest lakes. Estimates of modeled total phosphorus (TP) loadings as well as the contributions of different sectors were successfully validated against measured data. Based on these findings, annual total phosphorus loadings to lakes were calculated for diffuse and point sources according to the different sectors domestic, manufacturing, urban surface runoff, agriculture and background for the time period 1990 to 2010. Our results show high phosphorus loadings into lakes in southern latitudes. On global average, industrial fertilizer is the main anthropogenic source while background loadings are low in comparison. Nevertheless, both features indicate a high potential to reduce the exposure to eutrophication in lakes which are faced with high phosphor inputs. The global average of TP loadings was 7% higher in the time period 2005-2010 than in the period 1990-1995. The global average in 2005-2010 results from an increase in TP loadings of 79% in South America, which was dampened by a decrease in Europe, North America, and Asia. Chinese lakes were exposed to massive increasing phosphorus loadings, too. Both increasing and decreasing trends are caused primarily by changing industrial fertilizer application rates. In conclusion, this study provides a consistent and model based synopsis of global trends and sources of phosphorus loadings to large lakes. The estimates of phosphorus pollution of lakes present a basis for assessing and managing the global eutrophication problem.

  11. Evidence for sub-lacustrine volcanic activity in Lake Bolsena (central Italy) revealed by high resolution seismic data sets

    NASA Astrophysics Data System (ADS)

    Lindhorst, Katja; Krastel, Sebastian; Wagner, Bernd; Schuerer, Anke

    2017-06-01

    The Bolsena caldera that formed between 0.6 and 0.2 Ma has a well preserved structural rim, which makes it an ideal site to study the tectonic and volcanic evolution of calderas. However, the main area is covered by a 150 m deep lake which makes it rather difficult to investigate the subsurface structure directly. To overcome this problem new high resolution hydro-acoustic surveys using a multichannel reflection seismic system and a sediment echo-sounder system were conducted in September 2012. As space was limited we used a rowing boat towed by a rubber boat to handle a 36 m long and 24 channel streamer to receive seismic reflections produced using a Mini GI-Gun (0.25 l). The subsurface structure of Lake Bolsena was imaged up to a sediment depth of 190 m, which is estimated to have filled over a period of 333 kyrs. However, massive pyroclastic flow deposits found in the deeper parts of the basin indicate an initial infill of volcanic deposits from two adjacent younger calderas, the Latera (W) and Montefiascone (SE) calderas. Our data suggest that the caldera has a long history of active volcanism, because the lacustrine sediments show post-sedimentary influences of geothermal fluids. We mapped several mound structures at various stratigraphic depths. Two volcanic structures outcrop at the modern lake surface implying recent activity. One of these structures is hardly covered by sediments and has a crater-like feature in its summit. The other structure shows a pockmark-like depression on top. Another observable feature is a partially sediment filled crater located in the western part of the lake which further implies the existence of a magma chamber located beneath the Bolsena caldera. Since the late Pleistocene and Holocene, the sedimentation was mainly hemipelagic evidenced by a sediment drape of up to 10 m thick sediment drape on the uppermost sediments. Beneath the drape we found evidence for a distal tephra layer likely related to an explosive eruption from

  12. Patterns in Benthic Biodiversity Link Lake Trophic Status to Structure and Potential Function of Three Large, Deep Lakes

    PubMed Central

    Hayford, Barbara L.; Caires, Andrea M.; Chandra, Sudeep; Girdner, Scott F.

    2015-01-01

    Relative to their scarcity, large, deep lakes support a large proportion of the world’s freshwater species. This biodiversity is threatened by human development and is in need of conservation. Direct comparison of biodiversity is the basis of biological monitoring for conservation but is difficult to conduct between large, insular ecosystems. The objective of our study was to conduct such a comparison of benthic biodiversity between three of the world’s largest lakes: Lake Tahoe, USA; Lake Hövsgöl, Mongolia; and Crater Lake, USA. We examined biodiversity of common benthic organism, the non-biting midges (Chironomidae) and determined lake trophic status using chironomid-based lake typology, tested whether community structure was similar between the three lakes despite geographic distance; and tested whether chironomid diversity would show significant variation within and between lakes. Typology analysis indicated that Lake Hövsgöl was ultra-oligotrophic, Crater Lake was oligotrophic, and Lake Tahoe was borderline oligotrophic/mesotrophic. These results were similar to traditional pelagic measures of lake trophic status for Lake Hövsgöl and Crater Lake but differed for Lake Tahoe, which has been designated as ultra-oligotrophic by traditional pelagic measures such as transparency found in the literature. Analysis of similarity showed that Lake Tahoe and Lake Hövsgöl chironomid communities were more similar to each other than either was to Crater Lake communities. Diversity varied between the three lakes and spatially within each lake. This research shows that chironomid communities from these large lakes were sensitive to trophic conditions. Chironomid communities were similar between the deep environments of Lake Hövsgöl and Lake Tahoe, indicating that chironomid communities from these lakes may be useful in comparing trophic state changes in large lakes. Spatial variation in Lake Tahoe’s diversity is indicative of differential response of chironomid

  13. Tectonics of the baikal rift deduced from volcanism and sedimentation: a review oriented to the Baikal and Hovsgol lake systems.

    PubMed

    Ivanov, Alexei V; Demonterova, Elena I

    2009-01-01

    As known from inland sedimentary records, boreholes, and geophysical data, the initiation of the Baikal rift basins began as early as the Eocene. Dating of volcanic rocks on the rift shoulders indicates that volcanism started later, in the Early Miocene or probably in the Late Oligocene. Prominent tectonic uplift took place at about 20 Ma, but information (from both sediments and volcanics) on the initial stage of the rifting is scarce and incomplete. A comprehensive record of sedimentation derived from two stacked boreholes drilled at the submerged Akademichesky ridge indicates that the deep freshwater Lake Baikal existed for at least 8.4 Ma, while the exact formation of the lake in its roughly present-day shape and volume is unknown. Four important events of tectonic/environmental changes at about approximately 7, approximately 5, approximately 2.5, and approximately 0.1 Ma are seen in that record. The first event probably corresponds to a stage of rift propagation from the historical center towards the wings of the rift system. Rifting in the Hovsgol area was initiated at about this time. The event of ~5 Ma is a likely candidate for the boundary between slow and fast stages of rifting. It is reflected in a drastic change of sedimentation rate due to isolation of the Akademichesky ridge from the central and northern Lake Baikal basins. The youngest event of 0.1 Ma is reflected by the (87)0Sr/ (86)Sr ratio increase in Lake Baikal waters and probably related to an increasing rate of mountain growth (and hence erosion) resulting from glacial rebounding. The latter is responsible for the reorganization of the outflow pattern with the termination of the paleo-Manzurka outlet and the formation of the Angara outlet. The event of approximately 2.5 Ma is reflected in the decrease of the (87)Sr/(86)Sr and Na/Al ratios in Lake Baikal waters. We suggest that it is associated with a decrease of the dust load due to a reorganization of the atmospheric circulations in Mainland

  14. Sedimentary and Volcanic Records of the Laschamp and Mono Lake Excursions from Australia and New Zealand

    NASA Astrophysics Data System (ADS)

    Ingham, E. M.; Roberts, A. P.; Turner, G. M.; Heslop, D.; Ronge, T.; Conway, C.; Leonard, G.; Townsend, D.; Tiedemann, R.; Lamy, F.; Calvert, A. T.

    2014-12-01

    Geomagnetic excursions are short-lived deviations of the geomagnetic field from the normal range of secular variation. Despite significant advances in geomagnetic excursion research over the past 20 years, fundamental questions remain concerning the typical duration and global morphology of excursional geomagnetic fields. To answer such questions, more high-resolution, chronologically well-constrained excursion records are required, particularly from the Southern Hemisphere. We present preliminary paleomagnetic records of the Laschamp (~41 ka) and Mono Lake (~35 ka) excursions from three marine sediment cores from the Bounty Trough, New Zealand margin, and complementary volcanic records of the Laschamp excursion from lavas of Mt Ruapehu, New Zealand. Relatively high sedimentation rates of 12 - 26 cm/kyr in the Bounty Trough during glacial periods allow identification of excursional field behavior at each of the studied core locations. Each core displays one or two excursional events, with rapid directional swings between stable normal polarity and reversed excursional directions, each associated with coincident relative paleointensity minima. These anomalous paleomagnetic directions are interpreted to represent the Laschamp and Mono Lake excursions, based on a combination of tephrochronology, radiocarbon dating, and cyclostratigraphy (defined from core-scanning X-ray fluorescence and magnetic susceptibility records). Beside these records, we present results from fourteen lava flows, on Mt Ruapehu, for which 40Ar-39Ar dating indicates ages of between 39 and 45 ka. The step heating 40Ar-39Ar experiments produced particularly flat age plateaus, with corresponding 2 s.d. errors mostly approaching 1 kyr. The youngest and oldest flows carry normal polarity magnetization, however six flows, dated between 41 and 43 ka, display transitional field characteristics. Three of these flows display a declination swing of around 180o, which coincides with a previously published

  15. Functional groups and activities of bacteria in a highly acidic volcanic mountain stream and lake in Patagonia, Argentina.

    PubMed

    Wendt-Potthoff, Katrin; Koschorreck, M

    2002-01-01

    Acidic volcanic waters are naturally occurring extreme habitats that are subject of worldwide geochemical research but have been little investigated with respect to their biology. To fill this gap, the microbial ecology of a volcanic acidic river (pH approximately equal to 0-1.6), Rio Agrio, and the recipient lake Caviahue in Patagonia, Argentina, was studied. Water and sediment samples were investigated for Fe(II), Fe(III), methane, bacterial abundances, biomass, and activities (oxygen consumption, iron oxidation and reduction). The extremely acidic river showed a strong gradient of microbial life with increasing values downstream and few signs of life near the source. Only sulfide-oxidizing and fermentative bacteria could be cultured from the upper part of Rio Agrio. However, in the lower part of the system, microbial biomass and oxygen penetration and consumption in the sediment were comparable to non-extreme aquatic habitats. To characterize similarities and differences of chemically similar natural and man-made acidic waters, our findings were compared to those from acidic mining lakes in Germany. In the lower part of the river and the lake, numbers of iron and sulfur bacteria and total biomass in sediments were comparable to those known from acidic mining lakes. Bacterial abundance in water samples was also very similar for both types of acidic water (around 10(5) mL(-1)). In contrast, Fe(II) oxidation and Fe(III) reduction potentials appeared to be lower despite higher biogenic oxygen consumption and higher photosynthetic activity at the sediment-water interface. Surprisingly, methanogenesis was detected in the presence of high sulfate concentrations in the profundal sediment of Lake Caviahue. In addition to supplementing microbiological knowledge on acidic volcanic waters, our study provides a new view of these extreme sites in the general context of aquatic habitats.

  16. Geology of the Ivanhoe Hg-Au district, northern Nevada: Influence of Miocene volcanism, lakes, and active faulting on epithermal mineralization

    USGS Publications Warehouse

    Wallace, A.R.

    2003-01-01

    The mercury-gold deposits of the Ivanhoe mining district in northern Nevada formed when middle Miocene rhyolitic volcanism and high-angle faulting disrupted a shallow lacustrine environment. Sinter and replacement mercury deposits formed at and near the paleosurface, and disseminated gold deposits and high-grade gold-silver veins formed beneath the hot spring deposits. The lacustrine environment provided abundant meteoric water; the rhyolites heated the water; and the faults, flow units, and lakebeds provided fluid pathways for the hydrothermal fluids. A shallow lake began to develop in the Ivanhoe area about 16.5 Ma. The lake progressively expanded and covered the entire area with fine-grained lacustrine sediments. Lacustrine sedimentation continued to at least 14.4 Ma, and periodic fluctuations in the size and extent of the lake may have been responses to both climate and nearby volcanism. The eruption of rhyolite and andesite flows and domes periodically disrupted the lacustrine environment and produced interfingered flows and lake sediments. The major pulse of rhyolitic volcanism took place between 15.16 ± 0.05 and 14.92 ± 0.05 Ma. High-angle faulting began in the basement about 15.2 Ma, penetrated to and disrupted the paleosurface after 15.10 ± 0.06 Ma, and largely ceased by 14.92 ± 0.05 Ma. Ground motion related to both faulting and volcanism created debris flows and soft-sediment deformation in the lakebeds. Mercury-gold mineralization was coeval with rhyolite volcanism and high-angle faulting, and it took place about 15.2 to 14.9 Ma. At and near the paleosurface, hydrothermal fluids migrated through tuffaceous sediments above relatively impermeable volcanic and Paleozoic units, creating chalcedonic, cinnabar-bearing replacement bodies and sinters. Disseminated gold was deposited in sedimentary and volcanic rocks beneath the mercury deposits, although the hydrologic path between the two ore types is unclear. Higher-grade gold-silver deposits formed in

  17. Geochemistry of the Albano and Nemi crater lakes in the volcanic district of Alban Hills (Rome, Italy)

    NASA Astrophysics Data System (ADS)

    Carapezza, M. L.; Lelli, M.; Tarchini, L.

    2008-12-01

    Lake Albano, located 20 km to the SE of Rome, is hosted within the most recent crater of the quiescent Alban Hills volcanic complex that produced hydromagmatic eruptions in Holocene times. Stratigraphic, archaeological and historical evidence indicates that the lake level underwent important variations in the Bronze Age. Before the IV century B.C. several lahars were generated by water overflows from the lake and in the IV century B.C. Romans excavated a drainage tunnel. The lake is located above a buried carbonate horst that contains a pressurized medium-enthalpy geothermal reservoir from which fluids escape to the surface to produce many important gas manifestations of mostly CO 2. Previous studies recognized the presence of gas emissions also from the crater bottom. In 1997 the possibility of a Nyos-type event triggered by a lake rollover was considered very low, because the CO 2 water concentration at depth was found to be far from saturation. However, considering the high population density nearby, the Italian Civil Protection Department recommended that periodical monitoring be carried out. To this scope we initiated in 2001 a systematic geochemical study of the lake. Thirteen vertical profiles have been repeatedly carried out in 2001-2006, especially in the deepest part of the lake (167 m in 2006), measuring T, pH, dissolved O 2 and electrical conductivity. Water samples were collected from various depths and chemically and isotopically analysed. Two similar profiles have been measured also in the nearby Nemi crater lake. Results indicate that in the 4.5 years of monitoring the pressure of gas dissolved in the Lake Albano deep waters remained much lower than the hydrostatic pressure. A CO 2 soil survey carried out on the borders of the two lakes, indicates the presence of some zones of anomalous degassing of likely magmatic origin. A water overturn or a heavy mixing of deep and shallow waters likely occurred in winter 2003-2004, when cold rainfall cooled the

  18. Effects of concurrent stratospheric sulfur geoengineering and a large volcanic eruption

    NASA Astrophysics Data System (ADS)

    Laakso, Anton; Partanen, Antti-Ilari; Kokkola, Harri; Lehtinen, Kari; Korhonen, Hannele

    2013-04-01

    Solar radiation management by stratospheric sulfur injection is one of the most discussed geoengineering methods. Injecting sulfur to the stratosphere could be seen as an analogy of large volcanic eruptions, where a large amount of sulfate particles is formed in the stratosphere. These particles reflect solar radiation back to space and thus cool the climate. Effects of stratospheric sulfur injection and large volcanic eruption are both widely studied cases. However effects of large volcanic eruption in case where stratospheric sulfur geoengineering is used has not studied before. This could lead to temporary extra cooling effect when there would be strong radiative forcing from a volcanic eruption and geoengineering. In this study we use the global aerosol-climate model ECHAM5-SALSA to investigate effects from a case where there is an increased amount of sulfate particles in the stratosphere from both a volcanic eruption and geoengineering. The ECHAM5-SALSA describes aerosol distribution by 10 size bins and calculates the microphysical processes of nucleation, condensation, coagulation and hydration. As a baseline, we have studied a case where 8 Tg of sulfur is injected to 20 km height to the equator for geoengineering purposes. On top of that, we have studied volcanic eruptions corresponding in magnitude to the Pinatubo eruption in 1991, where about 8.5 Tg of sulfur was released to the stratosphere. Preliminary results shows that when the eruption takes place in the tropics, the total global radiative forcing from concurrent geoengineering and volcanic eruption is clearly smaller than if the forcing is calculated as the sum of separate cases. Results also show that recovery of the global forcing from volcanic eruption is 2.6 times faster if the eruption takes place in a situation where geoengineering is used. Thus, simultaneous geoengineering and volcanic eruption do not lead to long-lasting extra cooling. If the volcanic eruption takes place in the Arctic, the

  19. Contrasted effects of climate change on temperate large lakes oxygen-depletion (Lakes Geneva, Bourget, Annecy)

    NASA Astrophysics Data System (ADS)

    Jenny, Jean-Philippe; Arnaud, Fabien; Dorioz, Jean-Marcel; Alric, Benjamin; Sabatier, Pierre; Perga, Marie-Elodie

    2013-04-01

    Among manifestations of the entry in a new geological era -The Anthropocene- marked by the fingerprinting of human activities in global ecology, the development of persistent zones of oxygen-depletion particularly threatens aquatic ecosystems. This results in a loss of fisheries, a loss of biodiversity, an alteration of food-webs and even, in extreme cases, mass mortality of fauna1. Whereas hypoxia -defined as dissolved oxygen ≤2 mg/l- has long been considered as a consequence of the sole eutrophication, recent studies showed it also depends on climate change. Despite basic processes of oxygen-depletion are well-known, till now no study evaluated the contrasted effects of climate changes on a long-term perspective. Here we show that climate change paced fluctuation of hypoxia in 3 large lakes (Lake Geneva, Lake Bourget and Lake Annecy) that were previously disturbed by unprecedented nutrient input. Our approach couples century-scale paleo-reconstruction of 1) hypoxia, 2) flood regime and 3) nutrient level, thanks to an exceptional 80 sediment core data collection taken in three large lakes (Geneva, Bourget, Annecy), and monitoring data. Our results show that volume of hypoxia can be annually estimated according to varve records through large lakes. Quantitative additive models were then used to identify and hierarchy environmental forcings on hypoxia. Flood regime and air temperatures hence appeared as significant forcing factors of hypolimnetic hypoxia. Noticeably, their effects are highly contrasted between lakes, depending on specific lake morphology and local hydrological regime. We hence show that greater is the lake specific river discharge the more is the control of winter mixing and the lower is the control of thermal stratification on oxygen depletion. Our study confirms that the perturbation of food web due to nutrient input led to a higher vulnerability of aquatic ecosystems to climate change. We further show specific hydrological regime play a crucial

  20. Rocky 7 prototype Mars rover field geology experiments 1. Lavic Lake and sunshine volcanic field, California

    USGS Publications Warehouse

    Arvidson, R. E.; Acton, C.; Blaney, D.; Bowman, J.; Kim, S.; Klingelhofer, G.; Marshall, J.; Niebur, C.; Plescia, J.; Saunders, R.S.; Ulmer, C.T.

    1998-01-01

    Experiments with the Rocky 7 rover were performed in the Mojave Desert to better understand how to conduct rover-based, long-distance (kilometers) geological traverses on Mars. The rover was equipped with stereo imaging systems for remote sensing science and hazard avoidance and 57Fe Mo??ssbauer and nuclear magnetic resonance spectrometers for in situ determination of mineralogy of unprepared rock and soil surfaces. Laboratory data were also obtained using the spectrometers and an X ray diffraction (XRD)/XRF instrument for unprepared samples collected from the rover sites. Simulated orbital and descent image data assembled for the test sites were found to be critical for assessing the geologic setting, formulating hypotheses to be tested with rover observations, planning traverses, locating the rover, and providing a regional context for interpretation of rover-based observations. Analyses of remote sensing and in situ observations acquired by the rover confirmed inferences made from orbital and simulated descent images that the Sunshine Volcanic Field is composed of basalt flows. Rover data confirmed the idea that Lavic Lake is a recharge playa and that an alluvial fan composed of sediments with felsic compositions has prograded onto the playa. Rover-based discoveries include the inference that the basalt flows are mantled with aeolian sediment and covered with a dense pavement of varnished basalt cobbles. Results demonstrate that the combination of rover remote sensing and in situ analytical observations will significantly increase our understanding of Mars and provide key connecting links between orbital and descent data and analyses of returned samples. Copyright 1998 by the American Geophysical Union.

  1. Paleomagnetism of the ~1.1 GA Portage Lake Volcanics (Michigan, USA)

    NASA Astrophysics Data System (ADS)

    Kulakov, E.; Smirnov, A. V.

    2014-12-01

    The ~1094 Ma Portage Lake Volcanics (PLV) consist of more than 200 lava flows and represent the most voluminous phase of the North American Midcontinent Rift (MCR) extrusive magmatism. Paleomagnetism of the PLV basalts has been investigated since the 1960s, but most of the paleomagnetic datasets are affected by remagnetization due to an extensive mineralization event that affected the PLV flows in the central part of the Keweenaw Peninsula. We report new paleomagnetic data from 74 and 35 PLV lava flows exposed at the eastern tip of the Keweenaw Peninsula and on Isle Royale, respectively. These lava flows represent the uppermost part of the PLV sequence and are much less affected by mineralization and metamorphism than their counterparts in the center of the Keweenaw Peninsula and the older PLV flows. Detailed thermal demagnetization reveals multiple natural remanent magnetization (NRM) components. In addition to a soft, low-temperature NRM component, removed by heating to 350-375°C, two components carried by magnetite were observed. A secondary magnetite component was isolated between ~375 and 525°C. The characteristic component of NRM was isolated between ~525°C and 585°C. The primary origin of this component is supported by positive paleomagnetic field tests. While the magnetite components have the same declination, the primary remanence is characterized by systematically steeper inclinations. The PLV lava flows also reveal a high-temperature NRM component carried by hematite. The direction of the hematite remanence is indistinguishable from that of the primary magnetite component. The new high-quality paleomagnetic pole for the PLV is obtained. We will discuss implications of the new paleomagnetic data for the MCR evolution as well as for the North American apparent polar wander path and plate motion rate at ~ 1.1 Ga.

  2. Horizontal differences in ecosystem metabolism of a large shallow lake

    NASA Astrophysics Data System (ADS)

    Idrizaj, Agron; Laas, Alo; Anijalg, Urmas; Nõges, Peeter

    2016-04-01

    The causes of horizontal differences in metabolic activities between lake zones are still poorly understood. We carried out a two-year study of lake metabolism in two contrasting parts of a large shallow lake using the open-water technique based on high-frequency measurements of dissolved oxygen concentrations. We expected that the more sheltered and macrophyte-rich southern part of the lake receiving a high hydraulic load from the main inflow will exhibit equal or higher rate of metabolic processes compared to the open pelagic zone, and higher temporal variability, including anomalous metabolic estimates such as negative gross primary production (GPP) or community respiration (CR) due to rapid water exchange. Our results showed that anomalous metabolic estimates occurred at both stations with a similar frequency and were related rather to certain wind directions, which likely contributed to stronger water exchange between the littoral and pelagic zones. Periods of auto- and heterotrophy (daily mean NEP> or <0) had a 50:50 distribution at the Central Station while the proportions were 30:70 at the Southern Station. High areal GPP estimated in our study exceeding nearly twice the long-term average 14C primary production, showed the advantages of the free-water technique in integrating the metabolism of all communities, a large part of which has remained undetected by the traditional bottle or chamber incubation techniques.

  3. Jurassic Lake T'oo'dichi': a large alkaline, saline lake, Morrison Formation, eastern Colorado Plateau

    USGS Publications Warehouse

    Turner, C.E.; Fishman, N.S.

    1991-01-01

    Recognition of alkaline, saline-lake deposits in the Morrison Formation significantly alters interpretations of depositional environments of this formation, and it also has important implications for paleoclimatic interpretation. Late Jurassic climate was apparently much more arid than had previously been thought. In fact, sedimentologic evidence suggests that the lake basin was typically dry for extended periods and enjoyed only brief wet intervals. This conclusion has important consequences for environmental interpretation of the habitat that was favorable for large herbivorous dinosaurs, which thrived in the Late Jurassic. -from Authors

  4. Large-Scale Atmospheric Variability and the Great Salt Lake

    NASA Astrophysics Data System (ADS)

    Moon, Young-Il.

    The impact of climate variability on the hydrologic cycle is of importance from the point of view of understanding the underlying dynamics of the system. The regional climate is governed primarily by the topography, vegetal cover, geomorphological characteristics, and the large scale atmospheric circulation. Regional climate is strongly affected by the nature of temporal variations in the atmospheric circulation. There is a large literature concerning potential hydrologic changes coming from various climatic change scenarios. Thus, we need to understand how the climate system influences hydrologic variability. Water-level fluctuations of Great Salt Lake (GSL) are a subject of concern and interest to industries along the shore, governmental officials, and the general public. Utah's rate of population growth is among the highest in the nation. Economic impacts of reduced water supply on industrial growth and agriculture are thus likely to be very significant if projected climate change scenarios occur. The ability to identify a relationship between Great Salt Lake (GSL) and atmospheric circulation patterns is important for understanding the response of lake volume to climatic variability. In particular, the impact of variability for atmospheric circulation is strong in the Western United States, where water resources are limited. The proposed research was motivated by an interest in how variations in climate may influence hydrologic extremes. Climatic variability and predictability is a function of the time and space scales of interest. Persistent droughts and wet periods typically have long time scales and large spatial extent. Closed basin lakes can act as amplifiers of climatic variability, and represent a space-time integration of basin hydrologic processes. The study (1) showed relationships between the time variability of the volume of the Great Salt Lake (GSL) and selected atmospheric circulation indices, (2) developed and applied nonlinear measures of

  5. Possible connection between large volcanic eruptions and level rise episodes in the Dead Sea Basin

    NASA Astrophysics Data System (ADS)

    Bookman, R.; Filin, S.; Avni, Y.; Rosenfeld, D.; Marco, S.

    2014-12-01

    The June 1991 Pinatubo volcanic eruption perturbed the atmosphere, triggering short-term worldwide changes in climate. The following winter was anomalously wet in the Levant, with a ~2-meter increase in the Dead Sea level that created a morphological terrace along the lake's shore. Given the global effects of volcanogenic aerosols, we tested the hypothesis that the 1991-92 shore terrace is a modern analogue to the linkage between past volcanic eruptions and a sequence of shore terraces in the Dead Sea Basin. Analysis of precipitation series from Jerusalem showed a significant positive correlation between the Dust Veil Index (DVI) of the modern eruptions and annual rainfall. The DVI was found to explain nearly 50% of the variability in the annual rainfall, such that greater DVI means more rainfall. Other factors that may affect the annual rainfall in the region as the Southern Oscillation Index (SOI) and the North Atlantic oscillations (NAO) were incorporated along with the DVI in a linear multiple regression model. It was found that the NAO did not contribute anything except for increased noise, but the added SOI increased the explained variability of rainfall to more than 60%. Volcanic eruptions with a VEI of 6, as in the Pinatubo, occurred about once a century during the Holocene and the last glacial-interglacial cycle. This occurrence is similar to the frequency of shore terrace build-up during the Lake Lisan desiccation. Sixteen shore terraces, detected using airborne laser scanning data, were interpreted as indicating short-term level rises due to episodes of enhanced precipitation and runoff during the dramatic drop in Lake Lisan's (palaeo-Dead Sea) level at the end of the LGM. The terraces were compared with a time series of volcanogenic sulfate from the GISP2 record, and similar numbers of sulfate concentration peaks and terraces were found. Furthermore, a significant correlation was found between SO4 concentration peaks and the terraces heights. This

  6. Large-scale volcanism associated with coronae on Venus - Implications for formation and evolution

    NASA Technical Reports Server (NTRS)

    Roberts, Kari M.; Head, James W.

    1993-01-01

    Large-scale volcanism, in the form of areally extensive flow fields, is a previously unrecognized important aspect of the evolution of at least 41 percent of all coronae on Venus. The timing and scale of many coronae flow fields is consistent with an origin due to the arrival and pressure-release melting of material in the head of a mantle plume or diapir. The production of voluminous amounts of volcanism at some coronae is proposed to be the result of larger plume size and/or the intersection of mantle upwellings with regions of lithospheric extension and rifting.

  7. Temporal dynamics and drivers of ecosystem metabolism in a large subtropical shallow lake (lake Taihu).

    PubMed

    Hu, Zhenghua; Xiao, Qitao; Yang, Jinbiao; Xiao, Wei; Wang, Wei; Liu, Shoudong; Lee, Xuhui

    2015-04-01

    With continuous measurements of dissolved oxygen, temperature, irradiance, and wind speed, as well as frequent measurements of pH, oxidation-reduction potential, and algal chlorophyll, temporal dynamics and drivers of ecosystem metabolism in a large nutrient-rich shallow lake (Lake Taihu) are tested in this study. The results show that the dissolved oxygen concentrations in the lake fluctuate annually. They increase in autumn and winter with a peak value of 14.19 mg·L-1 in winter, and decrease in spring and summer with a trough value of 6.40 mg·L-1 in summer. Gross primary production (GPP), ecosystem respiration (R), and net ecosystem production (NEP) increase in summer, with their peak values in late summer and autumn, and decrease in winter and spring. Mean values of GPP, R and NEP are 1.75 ± 0.06 (Mean ± SE), 1.52 ± 0.05, and 0.23 ± 0.03 g O2 m-3·d-1, respectively. It is also found that water temperature and surface irradiance are the best predictors of GPP and R, while water temperature (wind speed) has a significantly positive (negative) relationship with NEP. The findings in this study suggest that Lake Taihu is a net autotrophic ecosystem, and water temperature and surface irradiance are the two important drivers of lake metabolism.

  8. Temporal Dynamics and Drivers of Ecosystem Metabolism in a Large Subtropical Shallow Lake (Lake Taihu)

    PubMed Central

    Hu, Zhenghua; Xiao, Qitao; Yang, Jinbiao; Xiao, Wei; Wang, Wei; Liu, Shoudong; Lee, Xuhui

    2015-01-01

    With continuous measurements of dissolved oxygen, temperature, irradiance, and wind speed, as well as frequent measurements of pH, oxidation-reduction potential, and algal chlorophyll, temporal dynamics and drivers of ecosystem metabolism in a large nutrient-rich shallow lake (Lake Taihu) are tested in this study. The results show that the dissolved oxygen concentrations in the lake fluctuate annually. They increase in autumn and winter with a peak value of 14.19 mg·L−1 in winter, and decrease in spring and summer with a trough value of 6.40 mg·L−1 in summer. Gross primary production (GPP), ecosystem respiration (R), and net ecosystem production (NEP) increase in summer, with their peak values in late summer and autumn, and decrease in winter and spring. Mean values of GPP, R and NEP are 1.75 ± 0.06 (Mean ± SE), 1.52 ± 0.05, and 0.23 ± 0.03 g O2 m−3·d−1, respectively. It is also found that water temperature and surface irradiance are the best predictors of GPP and R, while water temperature (wind speed) has a significantly positive (negative) relationship with NEP. The findings in this study suggest that Lake Taihu is a net autotrophic ecosystem, and water temperature and surface irradiance are the two important drivers of lake metabolism. PMID:25837347

  9. Possible connection between large volcanic eruptions and level rise episodes in the Dead Sea Basin

    NASA Astrophysics Data System (ADS)

    Bookman, Revital; Filin, Sagi; Avni, Yoav; Rosenfeld, Daniel; Marco, Shmuel

    2014-04-01

    The June 1991 Pinatubo volcanic eruption perturbed the atmosphere, triggering short-term worldwide changes in surface and lower troposphere temperatures, precipitation, and runoff. The following winter was anomalously wet in the Levant, with a ˜2-m increase in the Dead Sea level that created a distinct morphological terrace along the lake's shore. Given the global radiative and chemical effects of volcanogenic aerosols on climatic systems, we tested the hypothesis that the 1991-92 winter shore terrace is a modern analogue to the linkage between past volcanic eruptions and a sequence of shore terraces on the cliffs around the Dead Sea Basin (DSB). Sixteen shore terraces, detected using airborne laser scanning data, were interpreted as indicating short-term level rises due to episodes of enhanced precipitation and runoff during the dramatic drop in Lake Lisan's (palaeo-Dead Sea) level at the end of the Last Glacial Maximum. The terraces were compared with a dated time series of volcanogenic sulfate from the GISP2 ice core, and similar numbers of sulfate concentration peaks and shore terraces were found. Furthermore, a significant correlation was found between SO4 concentration peaks and the heights of the terraces. This correlation may indicate a link between the explosivity of past eruptions, the magnitude of stratospheric injection, and their impact on the northern hemisphere water balance. The record of such short-term climato-hydrological effects is made possible by the dramatic desiccation of Lake Lisan. Detailed records of such events, albeit rare because of their vulnerability and short longevity, provide an important demonstration of global climatic teleconnections.

  10. On numerical simulation of the global distribution of sulfate aerosol produced by a large volcanic eruption

    SciTech Connect

    Pudykiewicz, J.A.; Dastoor, A.P.

    1994-12-31

    Volcanic eruptions play an important role in the global sulfur cycle of the Earth`s atmosphere and can significantly perturb the global atmospheric chemistry. The large amount of sulfate aerosol produced by the oxidation of SO{sub 2} injected into the atmosphere during volcanic eruptions also has a relatively big influence on the radiative equilibrium of the Earth`s climatic system. The submicron particles of the sulfate aerosol reflect solar radiation more effectively than they trap radiation in the infrared range. The effect of this is observed as cooling of the Earth`s surface. The modification of the global radiation budget following volcanic eruption can subsequently cause significant fluctuations of atmospheric variables on a subclimatic scale. The resulting perturbation of weather patterns has been observed and well documented since the eruptions of Mt. Krakatau and Mt. Tambora. The impact of the sulfate aerosol from volcanic eruptions on the radiative equilibrium of the Earth`s atmosphere was also confirmed by the studies done with Global Circulation Models designed to simulate climate. The objective of the present paper is to present a simple and effective method to estimate the global distribution of the sulfate aerosol produced as a consequence of volcanic eruptions. In this study we will present results of the simulation of global distribution of sulfate aerosol from the eruption of Mt Pinatubo.

  11. Evaluation of climate impacts after a large volcanic eruption during stratospheric sulfur injections

    NASA Astrophysics Data System (ADS)

    Laakso, Anton; Kokkola, Harri; Partanen, Antti-Ilari; Niemeier, Ulrike; Timmreck, Claudia; Lehtinen, Kari; Hakkarainen, Hanne; Korhonen, Hannele

    2016-04-01

    Solar radiation management (SRM) by injecting sulfur to the stratosphere is one of the most discussed geoengineering methods, because it has been suggested to be affordable and effective and its impacts have been thought to be predictable based on volcanic eruptions. Injecting sulfur to the stratosphere could be seen as an analogy of large volcanic eruptions, where large amounts of sulfur dioxide are released into the stratosphere. In the atmosphere sulfur dioxide oxidizes and forms aqueous sulfuric acid aerosols which reflect incoming solar radiation back to space. If SRM is ever used to cool the climate it is possible that a large volcanic eruption could happen also during the SRM, which would lead temporally to a very strong cooling. The simulations in this study were performed in two steps. In the first step, we used the aerosol-climate model MAECHAM5-HAM-SALSA to define global aerosol fields in scenarios with stratospheric sulfur injections and/or a volcanic eruption. In the second step of the study we performed climate simulations using Max-Planck-Institute's Earth system model (MPI-ESM) by using aerosol fields defined by MAECHAM5-HAM-SALSA. We studied scenarios of volcanic eruptions in two different locations and seasons and during the SRM sulfur injections and without injections. According to our simulations the radiative impacts of the eruption and SRM are not additive and the radiative effects and climate changes occurring after the eruption depend strongly on whether SRM is continued or suspended after the eruption. Adding to this, sulfate burden and radiative forcing after the volcanic eruption decrease significantly faster if the volcanic eruption happens during the geoengineering injections. In this situation, sulfur from the eruption does not only form new particles but it also condenses into pre-existing particles. Furthermore, the new small particles that are formed after the eruption coagulate effectively with the existing larger particles from

  12. Eruptive and depositional characteristics of the Loolmurwak and Eledoi maar volcanoes, Lake Natron - Engaruka monogenetic volcanic field, northern Tanzania

    NASA Astrophysics Data System (ADS)

    Berghuijs, J. F.; Mattsson, H. B.; Bosshard, S. A.

    2012-04-01

    The Eledoi and Loolmurwak maars form two of the largest craters within the Lake Natron - Engaruka monogenetic volcanic field (northern Tanzania), an area consisting of approximately 200 vents scattered between four large central volcanoes. We here describe depositional characteristics of the two maars, as observed in the field, and present preliminary findings on the petrographic textures which can provide insights into the eruption dynamics. Most maar volcanoes are considered to be the result of explosive phreatomagmatic volcanic eruptions (in which ascending magma interacts with external water). However, our field observations indicate that neither Loolmurwak nor Eledoi provides clear evidence of wet eruption or deposition. The overall arid climate in the area, in combination with the higher elevation of these maars with respect to their surroundings, makes the availability of external water, necessary to drive a phreatomagmatic eruption, questionable. Features indicative of phreatomagmatism, such as accretionary lapilli, vesiculated tuffs or plastering against objects, were not observed. Rather, most observations points toward dry eruption modes for these eruptions. The ejecta ring of Eledoi is strongly asymmetrical, with the finer deposit fractions concentrated on its NW side, suggesting a dry eruption column that allowed effective eolian segregation of differently sized pyroclasts during deposition. Subspherical melt blobs, cored with single olivine, clinopyroxene and phlogopite crystals that reach up to 11 cm in diameter, occur abundantly at Loolmurwak. Many of these melt blobs show slight flattening parallel to the bedding plane, which indicates that they were emplaced as molten droplets. The abundance of large phlogopite phenocrysts in the Loolmurwak deposits points towards a volatile-rich magma. The occurrence of mantle xenoliths, 20-30 cm in diameter, implies that the magma traveled from the upper mantle to the surface in less than two days. The rapid

  13. Patterns of volcanism, weathering, and climate history from high-resolution geochemistry of the BINGO core, Mono Lake, California, USA

    NASA Astrophysics Data System (ADS)

    Zimmerman, S. R.; Starratt, S.; Hemming, S. R.

    2012-12-01

    Mono Lake, California is a closed-basin lake on the east side of the Sierra Nevada, and inflow from snowmelt dominates the modern hydrology. Changes in wetness during the last glacial period (>12,000 years ago) and over the last 2,000 years have been extensively described, but are poorly known for the intervening period. We have recovered a 6.25 m-long core from ~3 m of water in the western embayment of Mono Lake, which is shown by initial radiocarbon dates to cover at least the last 10,000 years. The sediments of the core are variable, ranging from black to gray silts near the base, laminated olive-green silt through the center, to layers of peach-colored carbonate nodules interbedded with gray and olive silts and pea-green organic ooze. Volcanic tephras from <1 to 8 cm thick occur throughout. Results of 0.5 cm-resolution scanning-X-Ray fluoresence (XRF) analysis describe changes in lithology due to volcanism, erosion, and changing lake level and chemistry. Titanium (Ti) is chemically and biologically unreactive, and records the dominant input, from weathering of Sierra Nevada granite to the west and Miocene and Pliocene volcanic rocks of the Bodie and Adobe Hills to the north, east, and south. The rhyolitic tephras of the Mono-Inyo Craters are much lower in TiO2 than the bedrock (<0.1% vs. 1-2%), and are an unweathered source of K2O (3.5-5%), and thus form dramatic peaks in the K/Ti ratio. Calcium (Ca) and Sr are well correlated throughout the core, and normalization of both by K (detritus + tephra) corresponds with occurrence of carbonate-rich layers. These are a mixture of authigenic precipitates directly precipitated and eroded into the lake during periods of regression. The lowermost 1.5 m of the BINGO core contains the highest proportion of detrital input to Mono Lake over the last ~12,000 years, recorded by high Si, Ti, K, and Fe, in black to dark-gray, fine-grained silts above 10 cm of pure light gray silt. Based on radiocarbon dates of >10,000 calibrated

  14. Midcontinent rift volcanism in the Lake Superior region: Sr, Nd, and Pb isotopic evidence for a mantle plume origin

    SciTech Connect

    Nicholson, S.W. Univ. of Minnesota, MN ); Shirey, S.B. )

    1990-07-10

    Between 1091 and 1098 Ma, most of a 15- to 20-km thickness of dominantly tholeiitic basalt erupted in the Midcontinent Rift System of the Lake Superior region, North American. The Portage Lake Volcanics in Michigan, which are the youngest MRS flood basalts, fall into distinctly high- and low-TiO{sub 2} types having different liquid lines of descent. Incompatible trace elements in both types of tholeiites are enriched compared to depleted or primitive mantle (La/Yb = 4.3-5.3; Th/Ta = 2.12-2.16; Zr/Y = 4.3-4.4), and both basalt types are isotopically indistinguishable. Sr, Nd, and Pb isotopic compositions of the Portage Lake tholeiites have {sup 87}Sr/{sup 86}Sr{sub i} {approx}0.7038, {epsilon}{sub Nd(1095 Ma)} {approx}0 {plus minus} 2, and {mu}{sub 1} {approx}8.2. Model ages with respect to a depleted mantle source (T{sub DM}) average about 1950-2100 Ma. Portage Lake rhyolits fall into two groups. Type I rhyolites have Nd and Pb isotopic characteristics ({epsilon}{sub Nd(1095 Ma)} {approx}0 to {minus}4.7; {mu}{sub 1} {approx}8.2-7.8) consistent with contamination of tholeiitic rocks by 5-10% Archean crust. The one type II rhyolite analyzed has Nd and Pb isotopic compositions ({epsilon}{sub Nd(1095 Ma)} {approx}{minus}13 to {minus}16; {mu}{sub 1} {approx}7.6-7.7) which are consistent with partial melting of Archean crust. Early Proterozoic crust was not a major contaminant of MRS rocks in the Lake Superior region. Most reported Nd and Pb isotopic compositions of MRS tholeiites from the main stage of volcanism in the Lake Superior region and of the Duluth Complex are comparable to the Nd and Pb isotopic data for Portage lake tholeiites. The isotopic enrichment of the MRS source compared to depleted mantle is striking and must have occurred at least 700 m.y. before 1100 Ma.

  15. What Causes the Relationship Between Large Impact Basin Rims and Volcanism on Mars?

    NASA Astrophysics Data System (ADS)

    Kiefer, W. S.; Weller, M. B.

    2016-12-01

    Several large impact basins on Mars have concentrations of volcanism on their rims. Hellas (2300 km diameter) is largely surrounded by slightly younger volcanism in its rim zone, including Hadriacus Mons, Tyrrhenus Mons, Amphitrites Patera, Peneus Patera, and Noachis Terra. Isidis (1900 km diameter) has Syrtis Major on its western rim zone. Utopia (3300 km diameter) has Elysium Mons and Hecates Tholus on its southeast rim zone. All of these volcanos were active beginning shortly after basin formation, although in some cases at least minor volcanism continued for more than a billion years after basin formation. These spatial and temporal relationships suggest a possible causal relationship between the impact basins and the volcanos, although it is worth noting that the Argyre impact basin (1850 km diameter) does not have volcanism in its rim zone. For near-vertical impacts, the impact heats a region 500 km across and 400 km deep. Portions of the mantle are heated above the solidus, and this impact melt escapes from the mantle to the surface in a few thousand years by Darcy flow. The residual mantle is at its solidus and can rise viscously due to its thermal buoyancy. Mantle flow models indicate that the ascending mantle will produce magma by adiabatic decompression melting for 20-30 million years after impact basin formation. For near-vertical impacts, this melting is focused near the basin center and is likely too brief in duration to explain the age range of volcanism. Oblique impacts will shift the center of the impact heating zone towards the basin rim. The amount, distribution, and timing of decompression melting in the oblique impact case are currently being calculated using three-dimensional mantle convection simulations. An additional factor that may play a role is the deposition of a porous ejecta layer in the rim zone. The low thermal conductivity of this layer may lead to long term heating of the mantle beneath the rim zone.

  16. Large-scale Explosive Silicic Volcanic Eruptions in Maine, USA: Where, When, and Why

    NASA Astrophysics Data System (ADS)

    Seaman, S. J.; Van Lankvelt, A.; Williams, M. L.

    2014-12-01

    Two magmatic belts in Maine host essentially undeformed, well-preserved Silurian to Devonian volcanic sequences that include thick ash flow tuffs and rhyolitic lava flows. The Coastal Maine volcanic belt consists of at least five bimodal volcanic complexes (419 to 424 +/- 2 Ma) hosting volcanic sequences 1-4 km thick, spanning approximately 160 km of the Maine coastline. Entire cross-sections of the volcanic-plutonic complexes are visible, providing excellent sites to study the volcano/pluton interface. The Central Maine belt also extends approximately 160 km, northeast to southwest, across central Maine, and also hosts several bimodal plutonic/volcanic complexes. Rocks in the Central Maine belt range from 400 to 410 Ma (Hubacher and Lux, 1987; Bradley et al., 1996). The largest complex in the Central Maine belt is the ~407 Ma (Rankin and Tucker, 1995) Katahdin granite and Moxie mafic intrusive complex and the coeval Traveler Rhyolite, a monotonous two-member, 3200-meter-thick pyroclastic succession. In Rankin and Hon (1987), Hon argued that the original volume of the Traveler rhyolite was at least 5000 km3, making it one of the largest silicic caldera eruptions in the rock record. Both the Coastal Maine volcanic belt and the Central Maine belt are on the Gander terrane, a peri-Gondwanan crustal block that accreted to Laurentia during the Salinic orogeny. Accretion of the block was complete by ~421 Ma (Pollock et al., 2012), but by then the Avalon terrane was accreting to Gander. Either back-arc extension associated with subduction of oceanic lithosphere on the leading edge of the Avalonian plate, or delamination of that plate beneath Gander resulted in back-arc extension, decompression melting of the mantle, and partial melting of thick crust. The Central Maine belt, farther inboard of the downgoing Avalonian slab, developed similar bimodal, extension-related magmatism by approximately 410 Ma. Large silicic caldera eruptions developed in these belts as a result of

  17. Seismic Structure of Volcanic Edifice and Lava Lake at the Lucky Strike Volcano, Mid-Atlantic Ridge

    NASA Astrophysics Data System (ADS)

    Arnulf, A. F.; Singh, S. C.; Harding, A. J.; Kent, G.; Crawford, W. C.

    2010-12-01

    The top of the oceanic crust is formed by a heterogeneous process of magmatic eruptions and tectonic deformation at ocean spreading centres, creating 200-1000 m thick extrusive layer, sometimes called as layer 2A, thickness of which depends on spreading rate. The base of this layer is defined by a high velocity gradient zone where velocity increases from 2.5 km/s to 4.5 km/s. Although, wide-angle reflection image from this gradient zone and/or a velocity contour of 4.5 km/s provides idea of thickness Layer 2A, it has been difficult to obtain seismic images of this region with resolutions comparable to the length scales of the geologic processes. Drilling could be used to overcome the resolution gap but on its own would be prohibitively expensive. Using a combination of a synthetic ocean bottom experiment (SOBE) and three-dimensional tomographic technique, here we show the high resolution 3D velocity structure of the Lucky Strike volcano at Mid-Atlantic Ridge. We find that the upper oceanic crust is laterally heterogeneous on 2-3 km scales, with unusually low velocity (< 2.2 km/s) underneath the Lucky Strike volcanic edifices down to 300 m below the seafloor and normal velocity in layer 2A underneath the lava lake. Such a low velocity could be due to high porosity (> 25 %), suggestive of recently erupted, higly fractured pillow lavas. The location of the hydrothermal vent fields seems to lie at the boundary of high-porosity volcanic edifices and low porosity lava lake. A new reflector distinct from the usually imaged layer 2A-2B transition zone and consistent with a constructional origin is also observed at the base of the volcanic edifices. The strong lateral and vertical heterogeneities and the presence of secondary layer above classical Layer 2A might explain the controvery about the origin of seismic Layer 2A, i.e. volcanic versus alteration front. The new technique provides an image of the oceanic crust comparable to that of seafloor geology, leading to new

  18. Large Holocene lakes and climate change in the Chihuahuan Desert

    NASA Astrophysics Data System (ADS)

    Castiglia, Peter J.; Fawcett, Peter J.

    2006-02-01

    Lake-level variations preserved as beach ridges in the Laguna El Fresnal and Laguna Santa María subbasins, northern Mexico, record millennially spaced episodes of increased precipitation during the Holocene epoch. We find that the early, middle, and late Holocene were punctuated by periods wet enough to establish large pluvial lakes in currently dry basins in the Chihuahuan Desert; the largest dated pluvial lake covered ˜5650 km2 during the early Holocene. Constructional beach ridges in these subbasins are 221 ± 33 14C yr B.P. (Little Ice Age equivalent), 3815 ± 52 to 4251 ± 59 14C yr B.P. (early Neoglacial), 6110 ± 80 to 6721 ± 68 14C yr B.P. (mid-Holocene), and 8269 ± 64 to 8456 ± 97 14C yr B.P. (early Holocene), dates that correlate with other millennially spaced wet or cold events in the Northern Hemisphere. We attribute these wet episodes to increased precipitation, cooler temperatures, and reduced evaporation following southward shifts in winter storm tracks, which are related to long-term El Niño Southern Oscillation variability during the Holocene.

  19. The effects of recent uplift and volcanism on deposition in Mono Lake, California, from seismic-reflection (CHIRP) profiles

    NASA Astrophysics Data System (ADS)

    Colman, S. M.; Hemming, S. R.; Stine, S.; Zimmerman, S. R. H.

    2014-05-01

    About 150 km of high-resolution, seismic reflection (Compressed High-Intensity Radar Pulse) profiles (approximately 20 m penetration) were collected in Mono Lake in order to define the uppermost sedimentary architecture of the basin, which has been heavily impacted by recent volcanic, tectonic, and climatic processes. The study also provides an important background for ongoing efforts to obtain paleoenvironmental records from sediment cores in the lake. The history of four seismic-stratigraphic units in the upper 20 m of section are inferred from the data, and the interpretations are generally consistent with previous interpretations of lake history for the past 2000 years, including a major lowstand at 1941 m. No shorelines below the previously documented major lowstand at 1941 m were found. A relatively steep slope segment, whose toe is at about 1918 m, and which occurs on the southern and western margins of the deep basin of the lake, is interpreted as the relict foreset slope of deposition from prograding western tributaries. This topography is unconformably overlain by a unit of interbedded tephra and lake sediments of variable lithology, which contains tephra of the North Mono (600-625 cal yr BP) eruption in its upper part. The tephra-rich unit is overlain by a mostly massive mudflow deposit that is locally more than 18 m thick and that is distributed in a radial pattern around Paoha Island. The evidence suggests that within the past few hundred years, rapid uplift of Paoha Island through thick, preexisting lake deposits led to widespread slope failures, which created a terrain of disrupted, intact blocks near the island, and a thick, fluid mudflow beyond. As is common in mudflows, the mudflow moved up the depositional slope of the lake floor, terminating against the preexisting slopes, likely in multiple surges. Since about 1700 Common Era, fine-grained, well-laminated sediments have accumulated in the deep parts of the lake at anomalously rapid rates

  20. Historical seismicity of the Mont Dore volcanic province (Auvergne, France) unraveled by a regional lacustrine investigation: New insights about lake sensitivity to earthquakes

    NASA Astrophysics Data System (ADS)

    Chassiot, Léo; Chapron, Emmanuel; Di Giovanni, Christian; Lajeunesse, Patrick; Tachikawa, Kazuyo; Garcia, Marta; Bard, Edouard

    2016-06-01

    Lake sediments are relevant natural seismographs over long time scale. However, because tectonic events are not systematically recorded in lake sediments, one forthcoming challenge for paleoseismology is to better assess lake sensitivity to earthquakes. To this end, a limnogeological investigation, including hydroacoustic mapping techniques, core sampling and multi-proxy sediment analyses, has been conducted within four small volcanic lakes located in the Mont Dore province (Auvergne, France), an area with a moderate seismo-tectonic activity. Results show the existence of several gravity reworking processes in the lakes over the last millennium. Around AD 1300, the occurrence of synchronous events in lakes Pavin, Chauvet, Montcineyre and Guéry (100 km2 area) highlights an undocumented earthquake as a common trigger for slope failures in disconnected basins. At regional scale, the record of this tectonic event may have been favored by human-induced increase in sediment load (Chauvet and Montcineyre) and/or after an abrupt lake-level drop (Pavin) affecting the sediment stability. In addition, synchronous turbidites and mass-wasting deposits (MWD) recorded in lakes Pavin and Guéry provide evidence for a seismic activity during the XIXth century. Potential triggers are historical earthquakes that occurred either in the Mont Dore area or in the southern part of the Limagne fault at this time. Despite moderate seismic activity in this intraplate volcanic domain, these results highlight the role of tectonics as a major trigger in the sedimentary processes dominating these lacustrine infills. Within the diversity of studied sites, it appears that lake sensitivity to earthquakes was not constant over time. This sensitivity can be expressed as a combination of external factors, namely earthquake magnitude and lake-epicenter distance and internal factors such as lake morphology, nature of sediment, lake-level fluctuations and human-induced changes in catchment sedimentary

  1. Ash from the Toba supereruption in Lake Malawi shows no volcanic winter in East Africa at 75 ka.

    PubMed

    Lane, Christine S; Chorn, Ben T; Johnson, Thomas C

    2013-05-14

    The most explosive volcanic event of the Quaternary was the eruption of Mt. Toba, Sumatra, 75,000 y ago, which produced voluminous ash deposits found across much of the Indian Ocean, Indian Peninsula, and South China Sea. A major climatic downturn observed within the Greenland ice cores has been attributed to the cooling effects of the ash and aerosols ejected during the eruption of the Youngest Toba Tuff (YTT). These events coincided roughly with a hypothesized human genetic bottleneck, when the number of our species in Africa may have been reduced to near extinction. Some have speculated that the demise of early modern humans at that time was due in part to a dramatic climate shift triggered by the supereruption. Others have argued that environmental conditions would not have been so severe to have such an impact on our ancestors, and furthermore, that modern humans may have already expanded beyond Africa by this time. We report an observation of the YTT in Africa, recovered as a cryptotephra layer in Lake Malawi sediments, >7,000 km west of the source volcano. The YTT isochron provides an accurate and precise age estimate for the Lake Malawi paleoclimate record, which revises the chronology of past climatic events in East Africa. The YTT in Lake Malawi is not accompanied by a major change in sediment composition or evidence for substantial temperature change, implying that the eruption did not significantly impact the climate of East Africa and was not the cause of a human genetic bottleneck at that time.

  2. Discovery of a Plains Caldera Complex and Extinct Lava Lake in Arabia Terra, Mars: Implications for the Discovery of Additional Highland Volcanic Source Regions

    NASA Technical Reports Server (NTRS)

    Bleacher, Jacob; Michalski, Joseph

    2012-01-01

    Several irregularly shaped topographic depressions occur near the dichotomy boundary in northern Arabia Terra, Mars. The geomorphology of these features suggests that they formed by collapse, opposed to meteor impact. At least one depression (approx.55 by 85 km) displays geologic features indicating a complex, multi-stage collapse history. Features within and around the collapse structure indicate volcanic processes. The complex occurs within Hesperian ridged plains of likely volcanic origin and displays no crater rim or evidence for ejecta. Instead the depression consists of a series of circumferential graben and down-dropped blocks which also display upper surfaces similar to ridged plain lavas. Large blocks within the depression are tilted towards the crater center, and display graben that appear to have originally been linked with circumferential graben outside of the complex related to earlier collapse events. A nearly 700 m high mound exists along a graben within the complex that might be a vent. The deepest depression displays two sets of nearly continuous terraces, which we interpret as high-stands of a drained lava lake. These features appear similar to the black ledge described during the Kilauea Iki eruption in 1959. A lacustrine origin for the terraces seems unlikely because of the paucity of channels found in or around the depression that could be linked to aqueous surface processes. In addition, there is no obvious evidence for lacustrine sediments within the basin. Together with the presence of significant faulting that is indicative of collapse we conclude that this crater complex represents a large caldera formed in the Late Noachian to Early Hesperian. Other linear and irregular depressions in the region also might be linked to ancient volcanism. If that hypothesis is correct, it suggests that northern Arabia Terra could contain a large, previously unrecognized highland igneous province. Evacuation of magma via explosive and effusive activity

  3. Depositional evolution of the Early Cretaceous Sihetun Lake and implications for regional climatic and volcanic history in western Liaoning, NE China

    NASA Astrophysics Data System (ADS)

    Jiang, Baoyu; Fürsich, Franz T.; Hethke, Manja

    2012-06-01

    Numerous well-known fossils of the Jehol Biota, including early birds, feathered theropods, primitive mammals, and putative early angiosperms, have been discovered in lacustrine deposits (Lake Sihetun) of the Lower Cretaceous Yixian Formation of western Liaoning province, NE China. Based on extensive field investigations and four high-resolution excavations, we document in detail the spatio-temporal changes of sedimentary facies, facies associations and limnic community relicts, reconstruct the depositional history, and discuss the significance of these deposits regarding the regional climatic and volcanic history. Four phases are recognized in the history of Lake Sihetun. They are: (1) a phase of fluctuating but gradually rising water level indicated by subaerial and shallow-water lacustrine deposits, (2) a lake with beach-nearshore facies along the marginal areas and suspension-dominated lake floor facies in central areas, (3) a lake phase with a lake floor dominated by hyperpycnal flows, and (4) progradation of a fan delta. Two distinct depositional conditions are observed: stratified and unstratified lake intervals. The former occurred mainly during the second phase and produced clay-poor and clay-rich laminae, whereas the latter developed during the other three phases, and were dominated by deposition of subaqueous sedimentary density flows. These alternations of depositional conditions in offshore lacustrine deposits suggest that the Yixian Formation may have formed under a transitional climate regime fluctuating gradually from warm and dry to warm and humid conditions. Resurgent volcanism is inferred to have become stronger during the late phase of lake development based on distribution of deposits characterizing the unstratified lake interval and volcanic rocks of the overlying Upper Lava unit, a higher content of primary pyroclastic fragments, and evidence of strong syndepositional disturbance.

  4. AMS radiocarbon analyses from Lake Baikal, Siberia: Challenges of dating sediments from a large, oligotrophic lake

    USGS Publications Warehouse

    Colman, Steven M.; Jones, Glenn A.; Rubin, M.; King, J.W.; Peck, J.A.; Orem, W.H.

    1996-01-01

    A suite of 146 new accelerator-mass spectrometer (AMS) radiocarbon ages provides the first reliable chronology for late Quaternary sediments in Lake Baikal. In this large, highly oligotrophic lake, biogenic and authigenic carbonate are absent, and plant macrofossils are extremely rare. Total organic carbon is therefore the primary material available for dating. Several problems are associated with the TOC ages. One is the mixture of carbon sources in TOC, not all of which are syndepositional in age. This problem manifests itself in apparent ages for the sediment surface that are greater than zero. However, because most of the organic carbon in Lake Baikal sediments is algal (autochthonous) in origin, this effect is limited to about 1000+500 years, which can be corrected, at least for young deposits. The other major problem with dating Lake Baikal sediments is the very low carbon contents of glacial-age deposits, which makes them extremely susceptible to contamination with modern carbon. This problem can be minimized by careful sampling and handling procedures. The ages show almost an order of magnitude difference in sediment-accumulation rates among different sedimentary environments in Lake Baikal, from about 0.04 mm/year on isolated banks such as Academician Ridge, to nearly 0.3 mm/year in the turbidite depositional areas beneath the deep basin floors, such as the Central Basin. The new AMS ages clearly indicate that the dramatic increase in diatom productivity in the lake, as evidenced by increases in biogenic silica and organic carbon, began about 13 ka, in contrast to previous estimates of 7 ka for the age of this transition. Holocene net sedimentation rates may be less than, equal to, or greater than those in the late Pleistocene, depending on the site. This variability reflects the balance between variable terrigenous sedimentation and increased biogenic sedimentation during interglaciations. The ages reported here, and the temporal and spatial variation in

  5. Responses of large volcanic eruptions in the instrumental and documentary climatic data over Central Europe

    NASA Astrophysics Data System (ADS)

    Písek, Jan; Brázdil, Rudolf

    2006-03-01

    Responses of large volcanic eruptions in selected long temperature series from Austria, the Czech Republic and Germany as well as in three global radiation series in Central Europe are studied. In the example of seven large tropical eruptions (Krakatau 1883; Pelée, Soufriére and Santa María 1902; Agung, 1963; El Chichón, 1982; Mt Pinatubo, 1991) it has been demonstrated that volcanic signal in regional series is not so strongly expressed as in the hemispheric scale owing to different local effects and circulation patterns. This is also valid in the case of two further discussed eruptions of Tambora (1815) and Katmai (1912). The responses of eruptions in areas closer to Central Europe such as Iceland or Italy are more important. In nine analysed cases with VEI = 4-5 with a single exception of the Hekla eruption (1917), cold seasons were observed to follow the eruption. Responses to the Lakagígar eruption (1783) of Iceland with important impacts are also discussed in detail. Moreover, correlation between temperatures (annual and winter half-year series) and NAOI is prevailingly smaller for the period following eruptions than in the period preceding eruptions. The importance of documentary evidence as a valuable source of the information about the impacts of volcanic eruptions is demonstrated.

  6. Spatial heterogeneity of cyanobacterial communities and genetic variation of microcystis populations within large, shallow eutrophic lakes (Lake Taihu and Lake Chaohu, China).

    PubMed

    Cai, Yuanfeng; Kong, Fanxiang; Shi, Limei; Yu, Yang

    2012-01-01

    Cyanobacteria, specifically Microcystis, usually form massive blooms in eutrophic freshwater lakes. Cyanobacterial samples were collected from eight sites of both Lake Taihu and Lake Chaohu in late summer to determine the diversity and distribution pattern of cyanobacteria and Microcystis in large, shallow, entropic lakes with significant spatial heterogeneity and long-term Microcystis bloom. Molecular methods based on denaturing gradient gel electrophoresis and clone library analysis were used. A similar heterogeneous distribution pattern of cyanobacteria in both lakes was observed. Most parts of these two lakes with high trophic level were dominated by Microcystis. However, in the regions with low trophic levels as well as low concentrations of chlorophyll a, Synechococcus occupied a considerable percentage. Different morphospecies and genotypes dominated the bloom-forming Microcystis populations in these two lakes. Microcystis viridis and Microcystis novacekii were dominant in Lake Chaohu, whereas Microcystis flos-aquae was dominant in Lake Taihu. Only 2 of thel3 Microcystis operational taxonomic units were shared between these two lakes. Analysis of molecular variance based on 16S to 23S internal transcribed spacer sequences indicated the significAnt genetic differentiation of Microcystis between these two lakes (F(ST) = 0.19, p < 0.001). However, only 19.46% of the genetic variability was explained by the population variation between lakes, whereas most (80.54%) of the genetic variability occurred within the lakes. Phylogenetic analysis revealed no phylogeographic structure of Microcystis population in these two lakes, as illustrated by their cosmopolitan nature. Our results revealed that spatial heterogeneity within lakes has more impact on the cyanobacterial diversity than geographical isolation in a local scale.

  7. Depth gradients in food-web processes linking habitats in large lakes: Lake Superior as an exemplar ecosystem

    USGS Publications Warehouse

    Sierszen, Michael E.; Hrabik, Thomas R.; Stockwell, Jason D.; Cotter, Anne M; Hoffman, Joel C.; Yule, Daniel L.

    2014-01-01

    Support of whole-lake food webs through trophic linkages among pelagic, profundal and littoral habitats appears to be integral to the functioning of large lakes. These linkages can be disrupted though ecosystem disturbance such as eutrophication or the effects of invasive species and should be considered in native species restoration efforts.

  8. Building a large magma chamber at Mount Mazama, Crater Lake, Oregon

    NASA Astrophysics Data System (ADS)

    Wright, H. M.; Karlstrom, L.; Bacon, C. R.

    2012-12-01

    Crater Lake caldera, Oregon, a structure produced by the 50 km3 eruption of Mount Mazama ~7.7 ka, is one of only three identified Quaternary calderas in the Cascades volcanic chain (Hildreth 2007). What were the conditions necessary to build a large volume magma chamber capable of producing this caldera-forming eruption at Mount Mazama? Using the well-documented >400,000 year volcanic history at Mazama (Bacon and Lanphere 2006), an approximation of vent locations for each eruptive unit (Bacon 2008), and a compilation of over 900 whole-rock compositions from Mount Mazama and regional volcanic rocks, we examine questions of magma chamber assembly in an active volcanic arc. These questions include: (1) is magmatic input approximately constant in composition between Mazama and regional monogenetic volcanic centers? (2) how did melt evolution differ in the two cases (Mazama vs. regional volcanism)? (3) is there spatiotemporal evidence in eruption data (including eruptive volume and chemistry) for a growing magma chamber at depth? and (4) does stability of that chamber require pre-warming of the surrounding country rock? An assumption of approximately constant major-element composition magmatic input is consistent with observed compositional overlap between basaltic to basaltic andesitic eruptive products at Mount Mazama and its vicinity (within 15 km of the volcano). MELTS modeling (Ghiorso and Sack 1995) from an initial composition of magnesian basaltic andesite of monogenetic Red Cone (erupted at a distance of ~8 km from the climactic vent) is consistent with water-saturated magmatic evolution at relatively shallow depths (<500 MPa, with the caveat that shallow pressure calibration data are largely lacking from MELTS models). Within this pressure range, differences in whole-rock compositions indicate that regional magmatic rocks evolved at shallower depths and/or drier conditions than those at the Mazama center. Observations of eruptive ages, compositions, vent

  9. Lava lakes on Io: Observations of Io's volcanic activity from Galileo NIMS during the 2001 fly-bys

    USGS Publications Warehouse

    Lopes, R.M.C.; Kamp, L.W.; Smythe, W.D.; Mouginis-Mark, P.; Kargel, J.; Radebaugh, J.; Turtle, E.P.; Perry, J.; Williams, D.A.; Carlson, R.W.; Doute, S.

    2004-01-01

    Galileo's Near-Infrared Mapping Spectrometer (NIMS) obtained its final observations of Io during the spacecraft's fly-bys in August (I31) and October 2001 (I32). We present a summary of the observations and results from these last two fly-bys, focusing on the distribution of thermal emission from Io's many volcanic regions that give insights into the eruption styles of individual hot spots. We include a compilation of hot spot data obtained from Galileo, Voyager, and ground-based observations. At least 152 active volcanic centers are now known on Io, 104 of which were discovered or confirmed by Galileo observations, including 23 from the I31 and I32 Io fly-by observations presented here. We modify the classification scheme of Keszthelyi et al. (2001, J. Geophys. Res. 106 (E12) 33 025-33 052) of Io eruption styles to include three primary types: promethean (lava flow fields emplaced as compound pahoehoe flows with small plumes 200 km high plumes and rapidly-emplaced flow fields), and a new style we call "lokian" that includes all eruptions confined within paterae with or without associated plume eruptions). Thermal maps of active paterae from NIMS data reveal hot edges that are characteristic of lava lakes. Comparisons with terrestrial analogs show that Io's lava lakes have thermal properties consistent with relatively inactive lava lakes. The majority of activity on Io, based on locations and longevity of hot spots, appears to be of this third type. This finding has implications for how Io is being resurfaced as our results imply that eruptions of lava are predominantly confined within paterae, thus making it unlikely that resurfacing is done primarily by extensive lava flows. Our conclusion is consistent with the findings of Geissler et al. (2004, Icarus, this issue) that plume eruptions and deposits, rather than the eruption of copious amounts of effusive lavas, are responsible for Io's high resurfacing rates. The origin and longevity of islands within ionian

  10. Cooling following large volcanic eruptions corrected for the effect of diffuse radiation on tree rings

    NASA Astrophysics Data System (ADS)

    Robock, Alan

    2005-03-01

    The lack of a larger cooling in proxy records of climate change following large volcanic eruptions such as those of Tambora in 1815 and Krakatau in 1883 has long been a puzzle for climatologists. These records, however, may have been biased by enhanced tree growth for several years following each eruption induced by additional diffuse radiation caused by the stratospheric volcanic aerosol clouds from the eruptions. By comparing proxy reconstructions of climate with and without tree ring data, this effect is demonstrated for the five largest eruptions for the period 1750-1980. When proxy records of Northern Hemisphere climate change are corrected for this proposed diffuse effect, there is no impact on climate change for time scales longer than 20 years. However, it now appears that there was a hemispheric cooling of about 0.6°C for a decade following the unknown volcanic eruption of 1809 and Tambora in 1815, and a cooling of 0.3°C for several years following the Krakatau eruption of 1883.

  11. Dynamic coupling of volcanic CO2 flow and wind at the HorseshoeLake tree kill, Mammoth Mountain, CA

    SciTech Connect

    Lewicki, J.L.; Hilley, G.E.; Tosha, T.; Aoyagi, R.; Yamamoto, K.; Benson, S.M.

    2006-11-20

    We investigate spatio-temporal relationships between soilCO2 flux (FCO2), meteorological variables, and topography over a ten-dayperiod (09/12/2006 to 09/21/2006) at the Horseshoe Lake tree kill,Mammoth Mountain, CA. Total CO2 discharge varied from 16 to 52 t d-1,suggesting a decline in CO2 emissions over decadal timescales. Weobserved systematic changes in FCO2 in space and time in association witha weather front with relatively high wind speeds from the west and lowatmospheric pressures. The largest FCO2 changes were observed inrelatively high elevation areas. The variations in FCO2 may be due todynamic coupling of wind-driven airflow through the subsurface and flowof source CO2 at depth. Our results highlight the influence of weatherfronts on volcanic gas flow in the near-surface environment and how thisinfluence can vary spatially within a study area.

  12. Spatial distribution and temporal variability of stable water isotopes in a large and shallow lake.

    PubMed

    Xiao, Wei; Wen, Xuefa; Wang, Wei; Xiao, Qitao; Xu, Jingzheng; Cao, Chang; Xu, Jiaping; Hu, Cheng; Shen, Jing; Liu, Shoudong; Lee, Xuhui

    2016-01-01

    Stable isotopic compositions of lake water provide additional information on hydrological, meteorological and paleoclimate processes. In this study, lake water isotopic compositions were measured for more than three years in Lake Taihu, a large and shallow lake in southern China, to investigate the isotopic spatial and seasonal variations. The results indicated that (1) the whole-lake mean δ(2)H and δ(18)O values of the lake water varied seasonally from -48.4 ± 5.8 to -25.1 ± 3.2 ‰ and from -6.5 ± 0.9 to -3.5 ± 0.8 ‰, respectively, (2) the spatial pattern of the lake water isotopic compositions was controlled by the direction of water flow and not by local evaporation rate, and (3) using a one-site isotopic measurement to represent the whole-lake mean may result in unreasonable estimates of the isotopic composition of lake evaporation and the lake water residence time in poorly mixed lakes. The original data, documented here as an online supplement, provides a good reference for testing sensitivity of lake water budget to various isotopic sampling strategies. We propose that detailed spatial measurement of lake water isotopic compositions provides a good proxy for water movement and pollutant and alga transports, especially over big lakes.

  13. Large-volume volcanic edifi ce failures in Central America and associated hazards

    USGS Publications Warehouse

    Siebert, L.; Alvarado, Guillermo E.; Vallance, J.W.; Van Wyk de Vries, B.

    2006-01-01

    Edifi ce-collapse phenomena have, to date, received relatively little attention in Central America, although ??40 major collapse events (??0.1 km3) from about two dozen volcanoes are known or inferred in this volcanic arc. Volcanoes subjected to gravitational failure are concentrated at the arc's western and eastern ends. Failures correlate positively with volcano elevation, substrate elevation, edifi ce height, volcano volume, and crustal thickness and inversely with slab descent angle. Collapse orientations are strongly infl uenced by the direction of slope of the underlying basement, and hence are predominately perpendicular to the arc (preferentially to the south) at its extremities and display more variable failure directions in the center of the arc. The frequency of collapse events in Central America is poorly constrained because of the lack of precise dating of deposits, but a collapse interval of ??1000-2000 yr has been estimated during the Holocene. These high-impact events fortunately occur at low frequency, but the proximity of many Central American volcanoes to highly populated regions, including some of the region's largest cities, requires evaluation of their hazards. The primary risks are from extremely mobile debris avalanches and associated lahars, which in Central America have impacted now-populated areas up to ??50 km from a source volcano. Lower probability risks associated with volcanic edifi ce collapse derive from laterally directed explosions and tsunamis. The principal hazards of the latter here result from potential impact of debris avalanches into natural or man-made lakes. Much work remains on identifying and describing debris-avalanche deposits in Central America. The identifi cation of potential collapse sites and assessing and monitoring the stability of intact volcanoes is a major challenge for the next decade. ?? 2006 Geological Society of America.

  14. Large-volume volcanic edifice failures in Central America and associated hazards

    USGS Publications Warehouse

    Siebert, Lee; Alvarado, Guillermo E.; Vallance, James W.; van Wyk de Vries, Benjamin

    2006-01-01

    Edifice-collapse phenomena have, to date, received relatively little attention in Central America, although ∼40 major collapse events (≥0.1 km3) from about two dozen volcanoes are known or inferred in this volcanic arc. Volcanoes subjected to gravitational failure are concentrated at the arc's western and eastern ends. Failures correlate positively with volcano elevation, substrate elevation, edifice height, volcano volume, and crustal thickness and inversely with slab descent angle. Collapse orientations are strongly influenced by the direction of slope of the underlying basement, and hence are predominately perpendicular to the arc (preferentially to the south) at its extremities and display more variable failure directions in the center of the arc.The frequency of collapse events in Central America is poorly constrained because of the lack of precise dating of deposits, but a collapse interval of ∼1000–2000 yr has been estimated during the Holocene. These high-impact events fortunately occur at low frequency, but the proximity of many Central American volcanoes to highly populated regions, including some of the region's largest cities, requires evaluation of their hazards. The primary risks are from extremely mobile debris avalanches and associated lahars, which in Central America have impacted now-populated areas up to ∼50 km from a source volcano. Lower probability risks associated with volcanic edifice collapse derive from laterally directed explosions and tsunamis. The principal hazards of the latter here result from potential impact of debris avalanches into natural or man-made lakes. Much work remains on identifying and describing debris-avalanche deposits in Central America. The identification of potential collapse sites and assessing and monitoring the stability of intact volcanoes is a major challenge for the next decade.

  15. Natural origin arsenic in aquatic organisms from a deep oligotrophic lake under the influence of volcanic eruptions.

    PubMed

    Juncos, Romina; Arcagni, Marina; Rizzo, Andrea; Campbell, Linda; Arribére, María; Guevara, Sergio Ribeiro

    2016-02-01

    Volcanic eruptions are recognized sources of toxic elements to freshwater, including arsenic (As). In order to study the short term changes in the bioaccumulation of naturally occurring As by aquatic organisms in Lake Nahuel Huapi (Argentina), located close to the Puyehue-Cordón Caulle volcanic complex (PCCVC), we described As concentrations at different trophic levels and food web transfer patterns in three sites of the lake prior to the last PCCVC eruption (June 2011), and compared As concentrations in biota before and after the eruption. The highest As concentrations and greater variations both between sites and position in the water column, were observed in phytoplankton (3.9-64.8 µg g(-1) dry weight, DW) and small zooplankton (4.3-22.3 µg g(-1) DW). The pattern of As accumulation in aquatic organisms (whole body or muscle) was: primary producers (phytoplankton) > scrapper mollusks (9.3-15.3 µg g(-1) DW) > filter feeding mollusks (5.4-15.6 µg g(-1) DW) > omnivorous invertebrates (0.4-9.2 µg g(-1) DW) > zooplankton (1.2-3.5 µg g(-1) DW) > fish (0.2-1.9 µg g(-1) DW). We observed As biodilution in the whole food web, and in salmonids food chains, feeding on fish prey; but biomagnification in the food chain of creole perch, feeding on benthic crayfish. The impact of the 2011 PCCVC eruption on the As levels of biota was more evident in pelagic-associated organisms (zooplankton and planktivorous fish), but only in the short term, suggesting a brief high bioavailability of As in water after ash deposition. In benthic organisms As variations likely responded to shift in diet due to coverage of the littoral zone with ashes. Copyright © 2015 Elsevier Ltd. All rights reserved.

  16. Development and application of indices using large volcanic databases for a global hazard and risk assessment

    NASA Astrophysics Data System (ADS)

    Brown, Sarah; Auker, Melanie; Cottrell, Elizabeth; Delgado Granados, Hugo; Loughlin, Sue; Ortiz Guerrero, Natalie; Sparks, Steve; Vye-Brown, Charlotte; Taskforce, Indices

    2015-04-01

    The Global Volcano Model (GVM) and IAVCEI were commissioned by the United Nations Office for Disaster Risk Reduction to produce a global assessment of volcanic hazard and risk for the Global Assessment Report 2015 (GAR15). This involved presenting both an introduction to volcanology and developing indices to assess hazard and risk on a global scale. To this end two open-access databases were of utmost importance: the Global Volcanism Program's Volcanoes of the World (http://www.volcano.si.edu) and the Large Magnitude Explosive Volcanic Eruptions database (LaMEVE; http://www.bgs.ac.uk/vogripa/). Indices were developed to enable a relative global assessment cognisant of data uncertainty and availability to broadly identify how hazard and risk varies around the world, the extent of monitoring and strengths and limitations in knowledge. The accessibility of both physical (e.g. volcano, eruption) and social data is crucial to our understanding of past behaviour, forecasting probable future behaviour and the potential impacts on communities. Such data is regionally highly variable and the eruption record worsens back in time. The Volcanic Hazard Index (VHI) was designed to quantify hazard levels globally, based on the Holocene eruption record. Vulnerability to eruptions was measured using the Population Exposure Index, which weights the population within 100 km of volcanoes by area and historical fatalities. The combination of these indices provides an indicator of population risk at individual volcanoes. The VHI was also combined with the total populations living within 30 km of volcanoes in each country to develop an understanding of the global distribution of volcano threat, and to rank countries by this measure. About half of the historically active volcanoes have insufficient information to adequately calculate VHI and these are highlighted as requiring future research. A database currently in development, GLOVOREMID, collates monitoring data to understand

  17. Large Early Permian eruptive complexes in northern Saxony, Germany: Volcanic facies analysis and geochemical characterization

    NASA Astrophysics Data System (ADS)

    Hübner, Marcel; Breitkreuz, Christoph; Repstock, Alexander; Heuer, Franziska

    2017-04-01

    In the course of formation of extensional basins during the Early Permian a widespread volcanic activity led to the deposition of volcanic and volcanosedimentary units in Saxony (Walter 2006, Hoffmann et al. 2013). Situated east of Leipzig, the North Saxonian Volcanic Complex (NSVC) hosts two large caldera complexes, the Rochlitz and Wurzen Volcanic Systems, with diameters of 90 and 52 km, respectively. Volume estimates (> 1000 km3) qualify these as supereruptions according to Mason et al. (2004). In addition to the large caldera systems, the NSVC hosts several small pyroclastic flow deposits ranging from crystal-poor (e.g. Cannewitz and vitrophyric Ebersbach ignimbrites) to crystal-rich units (Wermsdorf and Dornreichenbach ignimbrites). Additionally rhyolitic lava and subvolcanic units are present. The Chemnitz basin (Schneider et al. 2012), located to the south of the NSVC, harbours caldera-outflow facies deposits of the Rochlitz eruption (Fischer 1991), i.e. the partially vitrophyric Planitz ignimbrite. The Rochlitz and Wurzen caldera-fill ignimbrites exhibit relatively high crystal contents with maxima up to 52 and 58 vol.-%, for corresponding 66 and 68 wt.-% SiO2. This is comparable with the 'monotonous intermediates' (Hildreth 1981) in the Cenozoic western USA investigated by Huber et al. (2012). In contrast, the Planitz ignimbrite in the Chemnitz basin reveals predominantly crystal-poor pyroclastics (<10 vol.-%) with higher SiO2-contents (from 67 to 79 wt.-%). For the comparative study of the NSVC and the Planitz ignimbrite, we use detailed investigation of the volcanosedimentary facies, whole rock geochemical data (> 70 analyses), and mineral geochemistry to reconstruct the eruption history and magma genesis of this large Late Paleozoic magmatic complex in Central Europe. Volcanic textures and geochemical trends indicate magma mingling and mixing to have been important during the formation of the Wurzen caldera system. Geothermometric and -barometric

  18. The effect of large impacts on the mantle dynamics and volcanism of Mercury

    NASA Astrophysics Data System (ADS)

    Roberts, J. H.; Barnouin-Jha, O. S.

    2009-12-01

    The flybys of Mercury by MESSENGER, along with those of Mariner 10, have now imaged over 90% of the planet's surface [1]. Images of the Caloris and Rembrandt impact basins, along with several smaller impact structures reveal evidence for interior volcanism subsequent to impact formation [1,2]. Furthermore, crater counts indicate that a smooth plain just beyond the rim of Caloris are at least coeval and possibly younger than volcanic materials within the basin [2,3]. These plains are probably volcanic in origin, and might be associated with the long-term aftermath of Caloris' formation. The broad influence of Caloris on the surface of Mercury indicates that it might also affect heat flow within the mantle and thereby, the core dynamics. Here we investigate possible links between large impacts on Mercury, the volcanism within (and in the case of Caloris, surrounding) the basins, and effects on the planet's dynamo. While the impact cannot have formed the melts directly, the thermal impulse from such a large impact can alter the underlying mantle dynamics, potentially producing subsequent volcanism and altering the heat-flow at the core-mantle boundary. A finite element model of thermochemical convection in a spherical shell [4,5] is used to explore the consequences of the formation of large impacts in the Mercurian mantle. Composition is tracked using a particle tracer method [6]. The impactor size is determined from the observed basin using standard methods of crater scaling [7,8]. The impact is treated as an instantaneous temperature increase that decays away from the impact center [9]. Mantle melting is parameterized as a function of pressure, temperature, and modal cpx based on modeling and experiments of peridotite melting [10]. Melt residue and unmelted mantle are tracked seperately. Melt is removed to the surface; vapor is ignored. We find that even a Caloris-forming impact cannot significantly heat the core, assuming reasonable impact parameters, and should

  19. Large volcanic aerosol load in the stratosphere linked to Asian monsoon transport.

    PubMed

    Bourassa, Adam E; Robock, Alan; Randel, William J; Deshler, Terry; Rieger, Landon A; Lloyd, Nicholas D; Llewellyn, E J Ted; Degenstein, Douglas A

    2012-07-06

    The Nabro stratovolcano in Eritrea, northeastern Africa, erupted on 13 June 2011, injecting approximately 1.3 teragrams of sulfur dioxide (SO(2)) to altitudes of 9 to 14 kilometers in the upper troposphere, which resulted in a large aerosol enhancement in the stratosphere. The SO(2) was lofted into the lower stratosphere by deep convection and the circulation associated with the Asian summer monsoon while gradually converting to sulfate aerosol. This demonstrates that to affect climate, volcanic eruptions need not be strong enough to inject sulfur directly to the stratosphere.

  20. Theoretical wave modeling of large wave ripples in volcaniclastic sediments, Ordovician Llewelyn Volcanic Group, North Wales

    NASA Astrophysics Data System (ADS)

    Fritz, William J.

    1991-11-01

    Volcaniclastic sedimentary rocks of Ordovician age underlying the Garth Tuff member of the Capel Curig Volcanic Formation, North Wales were deposited on a shallow marine shelf. Deposition at the Capel Curig anticline 2 km southwest of Capel Curig was on a high-energy proximal offshore to foreshore. Analysis of large wave ripples and associated sedimentary structures suggests a shallow marine depositional environment, above storm wave base and in water depths of 10-30 m. This estimate of water depth from wave calculations is similar to that estimated by facies analysis.

  1. Volcanism in Eastern Africa

    NASA Technical Reports Server (NTRS)

    Cauthen, Clay; Coombs, Cassandra R.

    1996-01-01

    In 1891, the Virunga Mountains of Eastern Zaire were first acknowledged as volcanoes, and since then, the Virunga Mountain chain has demonstrated its potentially violent volcanic nature. The Virunga Mountains lie across the Eastern African Rift in an E-W direction located north of Lake Kivu. Mt. Nyamuragira and Mt. Nyiragongo present the most hazard of the eight mountains making up Virunga volcanic field, with the most recent activity during the 1970-90's. In 1977, after almost eighty years of moderate activity and periods of quiescence, Mt. Nyamuragira became highly active with lava flows that extruded from fissures on flanks circumscribing the volcano. The flows destroyed vast areas of vegetation and Zairian National Park areas, but no casualties were reported. Mt. Nyiragongo exhibited the same type volcanic activity, in association with regional tectonics that effected Mt. Nyamuragira, with variations of lava lake levels, lava fountains, and lava flows that resided in Lake Kivu. Mt. Nyiragongo, recently named a Decade volcano, presents both a direct and an indirect hazard to the inhabitants and properties located near the volcano. The Virunga volcanoes pose four major threats: volcanic eruptions, lava flows, toxic gas emission (CH4 and CO2), and earthquakes. Thus, the volcanoes of the Eastern African volcanic field emanate harm to the surrounding area by the forecast of volcanic eruptions. During the JSC Summer Fellowship program, we will acquire and collate remote sensing, photographic (Space Shuttle images), topographic and field data. In addition, maps of the extent and morphology(ies) of the features will be constructed using digital image information. The database generated will serve to create a Geographic Information System for easy access of information of the Eastem African volcanic field. The analysis of volcanism in Eastern Africa will permit a comparison for those areas from which we have field data. Results from this summer's work will permit

  2. Development of new measuring technique using sound velocity for CO2 concentration in Cameroonian volcanic lakes

    NASA Astrophysics Data System (ADS)

    Sanemasa, M.; Saiki, K.; Kaneko, K.; Ohba, T.; Kusakabe, M.; Tanyileke, G.; Hell, J.

    2012-12-01

    1. Introduction Limnic eruptions at Lakes Monoun and Nyos in Cameroon, which are sudden degassing of magmatic CO2 dissolved in the lake water, occurred in 1984 and 1986, respectively. The disasters killed about 1800 people around the lakes. Because of ongoing CO2 accumulation in the bottom water of the lakes, tragedy of limnic eruptions will possibly occur again. To prevent from further disasters, artificial degassing of CO2 from the lake waters has been undergoing. Additionally, CO2 monitoring of the lake waters is needed. Nevertheless, CO2 measurement is done only once or twice a year because current methods of CO2 measurement, which require chemical analysis of water samples, are not suitable for frequent measurement. In engineering field, on the other hand, a method to measure salt concentration using sound velocity has been proposed (Kleis and Sanchez, 1990). This method allows us to evaluate solute concentration fast. We applied the method to dissolved CO2 and examined the correlation between sound velocity and CO2 concentration in laboratory experiment. Furthermore, using the obtained correlation, we tried to estimate the CO2 concentration of waters in the Cameroonian lakes. 2. Laboratory experiment We examined the correlation between sound velocity and CO2 concentration. A profiler (Minos X, made by AML oceanography) and pure water were packed in cylindrical stainless vessel and high-pressure CO2 gas was injected to produce carbonated water. The profiler recorded temperature, pressure and sound velocity. Change of sound velocity was defined as difference of sound velocity between carbonated water and pure water under the same temperature and pressure conditions. CO2 concentration was calculated by Henry's law. The result indicated that the change of sound velocity [m s-1] is proportional to CO2 concentration [mmol kg-1], and the coefficient is 0.021 [m kg s-1 mmol-1]. 3. Field application Depth profiles of sound velocity, pressure, and temperature of Lakes

  3. Midcontinent rift volcanism in the Lake Superior region: Sr, Nd, and Pb isotopic evidence for a mantle plume origin

    USGS Publications Warehouse

    Nicholson, S.W.; Shirey, S.B.

    1990-01-01

    Between 1091 and 1098 Ma, most of a 15- to 20-km thickness of dominantly tholeiitic basalt erupted in the Midcontinent Rift System of the Lake Superior region, North America. The Portage Lake Volcanics in Michigan, which are the younget MRS flood basalts, fall into distinctly high- and low-TiO2 types having different liquid lines of descent. Incompatible trace elements in both types of tholeiites are enriched compared to depleted or primitive mantle and both basalt types are isotopically indistinguishable. The isotopic enrichment of the MRS source compared to depleted mantle is striking and must have occurred at least 700 m.y. before 1100 Ma. There are two likely sources for such magmatism: subcontinental lithospheric mantle enriched during the early Proterozoic or enriched mantle derived from an upwelling plume. Decompression melting of an upwelling enriched mantle plume in a region of lithosphere thinned by extension could have successfully generated the enormous volume (850 ?? 103 km3) of relatively homogeneous magma in a restricted time interval. -from Authors

  4. Cyanobacteria biennal dynamic in a volcanic mesotrophic lake in central Italy: Strategies to prevent dangerous human exposures to cyanotoxins.

    PubMed

    Manganelli, Maura; Stefanelli, Mara; Vichi, Susanna; Andreani, Paolo; Nascetti, Giuseppe; Scialanca, Fabrizio; Scardala, Simona; Testai, Emanuela; Funari, Enzo

    2016-06-01

    Vico Lake, a volcanic meso-eutrophic lake in Central Italy, whose water is used for drinking and recreational activities, experienced the presence of the microcystins (MC) producing cyanobacterium Planktothrix rubescens. In order to assess the human health risks and to provide the local health authorities with a scientific basis for planning tailored monitoring activities, we studied P. rubescens ecology and toxicity for two years. P. rubescens generally dominated the phytoplankton community, alternating with Limnothrix redekei, potentially toxic. P. rubescens was distributed throughout the water column during winter; in summer it produced intense blooms where drinking water is collected (-20 m); here MC were detected all year round (0.5-5 μg/L), with implications for drinking water quality. In surface waters, MC posed no risk for recreational activities in summer, while in winter surface blooms and foams (containing up to 56 μg MC/L) can represent a risk for people and children practicing water sports and for animals consuming raw water. Total phosphorus, phosphate and inorganic nitrogen were not relevant to predict densities nor toxicity; however, a strong correlation between P. rubescens density and aminopeptidase ectoenzymatic activity, an enzyme involved in protein degradation, suggested a role of organic nitrogen for this species. The fraction of potentially toxic population, determined both as mcyB(+)/16SrDNA (10-100%) and as the MC/mcyB(+) cells (0.03-0.79 pg MC/cell), was much more variable than usually observed for P. rubescens. Differently from other Italian and European lakes, the correlation between cell density or the mcyB(+) cells and MC explained only ∼50 and 30% of MC variability, respectively: for Vico Lake, monitoring only cell or the mcyB(+) cell density is not sufficient to predict MC concentrations, and consequently to protect population health. Finally, during a winter bloom one site has been sampled weekly, showing that

  5. Protracted volcanism after large impacts: Evidence from the Sudbury impact basin

    NASA Astrophysics Data System (ADS)

    Ubide, Teresa; Guyett, Paul C.; Kenny, Gavin G.; O'Sullivan, Edel M.; Ames, Doreen E.; Petrus, Joseph A.; Riggs, Nancy; Kamber, Balz S.

    2017-04-01

    Morphological studies of large impact structures on Mercury, Venus, Mars, and the Moon suggest that volcanism within impact craters may not be confined to the shock melting of target rocks. This possibility prompted reinvestigation of the 1.85 Ga subaqueous Sudbury impact structure, specifically its 1.5 km thick immediate basin fill (Onaping Formation). Historically, breccias of this formation were debated in the context of an endogenic versus an impact-fallback origin. New field, petrographic, and in situ geochemical data document an array of igneous features, including vitric shards, bombs, sheet-like intrusions, and peperites, preserved in exquisite textural detail. The geochemistry of vitric materials is affected by alteration, as expected for subaqueous magmatic products. Earlier studies proposed an overall andesitic chemistry for all magmatic products, sourced from the underlying impact melt sheet. The new data, however, suggest progressive involvement of an additional, more magnesian, and volatile-rich magma source with time. We propose a new working model in which only the lower part of the Onaping Formation was derived by explosive "melt-fuel-coolant interaction" when seawater flooded onto the impact melt sheet in the basin floor. By contrast, we suggest that the upper 1000 m were deposited during protracted submarine volcanism and sedimentary reworking. Magma was initially sourced from the impact melt sheet and up stratigraphy, from reservoirs at greater depth. It follows that volcanic deposits in large impact basins may be related to magmatism caused by the impact but not directly associated with the impact-generated melt sheet.

  6. Pre-Venus-Transit Dark Lunar Eclipse Reveals a Very Large Volcanic Eruption in 1761

    NASA Astrophysics Data System (ADS)

    Pang, Kevin

    2009-01-01

    Kepler's third law states Sun-planet distances in AU. International observations of the solar parallax during the 1761/1769 Venus transits gave us the first AU in miles. Benjamin Franklin promoted American participation in the project. While serving as Ambassador to France he observed that a "dry fog” from the 1783 Laki eruption in Iceland had obscured the Sun, and led to a cold summer and winter. Using Benjamin Franklin's method I analyzed photometric observations of the dark lunar eclipse made just before the 1761 Venus transit, ice core, tree ring, and Chinese weather data, and conclude that a very large previously unknown volcanic eruption in early 1761 had cooled the world climate. Observers worldwide found the 18 May 1761 totally eclipsed Moon very dark or invisible, e.g., Wargentin could not see the Moon for 38 minutes even with a 2-ft telescope (Phil. Trans. 52, 208, 1761-1762). Since the totally eclipsed Moon is illuminated only by sunlight refracted by the Earth's atmosphere, the obscuration must have been very severe. Ice cores from Greenland and Antarctica have large sulfuric acid contents in 1761-1762, precipitated from the global volcanic acid cloud (Zeilinski, J. Geophys. Res. 102, 26625, 1997). Frost-damaged rings in American bristlecone pines confirm that 1761 was very cold (LaMarche, Nature 307, 121, 1984). Contemporary Chinese chronicles report that heavy sustained snow fell from the Tropic of Cancer to the Yellow River. Wells and rivers froze, e.g., Taihu "Great Lake” and nearby Yangtze tributaries were not navigable. Innumerable trees, birds and livestock perished, etc. All observations are consistent with the above conclusion. Finally Benjamin Franklin's criteria for a climate-altering volcanic eruption are still universally used. Moreover his legacy continues to inspire climate researchers. See Pang, Eos 74, no. 43, 106, 1993; and as cited in "Earth in Balance,” Al Gore, p. 379, 1993.

  7. Effect of a large and very shallow lake on local summer precipitation over the Lake Taihu basin in China

    NASA Astrophysics Data System (ADS)

    Gu, Hongping; Ma, Zhuguo; Li, Mingxing

    2016-08-01

    Lake Taihu is the third largest freshwater lake in China and is situated in the Middle and lower Yangtze River delta. It is characterized by its shallowness (~1.9 m), large area (~2338 km2), and high turbidity in recent years. The lake's effect on local summer precipitation is first studied in this paper through the use of an atmosphere-lake coupled model. By enlarging the light extinction coefficient, modifying the radiation scheme, and setting the roughness length to constants, the coupled model after adjustment realistically reproduces the thermal stratification and magnitude of diurnal variation over Lake Taihu, with mean biases of 0.7°C for lake surface temperature and 0.4°C for near-surface air temperature, respectively. Based on this calibrated coupled model, two high-resolution numerical simulations with and without the lake (lake grid cells replaced by cropland) were conducted to identify the lake effects. The results show that an overall effect of Lake Taihu on local summer precipitation is negative during daytime and positive during nighttime and the precipitation pattern may be modified to some extent. The lake effect varies between areas and with time of day and occurs primarily on the downwind shore. A composite analysis for a representative decreased precipitation region reveals that during daytime in the summer, the combination of decreased air temperature and latent heat flux, along with intensified divergence and downdraft, acts together to stabilize the lower atmosphere and suppress thermal convective activities, ultimately resulting in less precipitation over this region.

  8. Successive collapses of the El Estribo volcanic complex in the Pátzcuaro Lake, Michoacán, Mexico

    NASA Astrophysics Data System (ADS)

    Pola, A.; Macías, J. L.; Garduño-Monroy, V. H.; Osorio-Ocampo, S.; Cardona-Melchor, S.

    2014-12-01

    The El Estribo volcanic complex is located in the north-central part of Michoacán State (Mexico) within the Michoacán-Guanajuato Volcanic Field. It consists of a ~ 126 kr shield volcano crowned by a cinder cone, separated by a paleosol dated at 28,360 ± 170 BP. The shield volcano has been cut by the E-W normal Pátzcuaro fault that exposes 200-m of piled up lavas flows. Our field reconstruction suggests that two collapses have been originated from this fault. Two debris avalanche deposits with hummocky topography are exposed between this fault and the southern shore of the Pátzcuaro Lake. The basal debris avalanche deposit (BDAD) covers lacustrine sediments and is covered by a paleosol that at 28,110 ± 720 yr BP yielding a minimum age for the event. It had a maximum run out of 3.2 km with a H/L of 0.0062. The upper debris avalanche deposit (UDAD) is overlain by a paleosol dated at 14,110 ± 60 yr BP that yields a minimum age of the event. It had a maximum run out of 2.3 km with a H/L of 0.0086. No pyroclastic deposits have been found in association with these debris avalanches and the shield volcano rocks show signs of intense hydrothermal alteration or abundant clay minerals for which we assume that failure was triggered by seismic-tectonic activity. The older debris avalanche was more mobile because it moved on water and on top of water-saturated sediments deforming them and likely originating a tsunami across the lake. Instead, the younger debris avalanche moved across the previous rugged hummocky topography of the basal avalanche resulting in a more restricted dispersion. These collapse events of El Estribo, the morphology of the scarp and historic and modern seismicity indicate that a future failure represents a serious threat to the surrounding communities of the Pátzcuaro Lake. Consequently, some preventive measurements as seismic and deformation rate monitoring are necessary. Today five villages with circa 1500 inhabitants live upon the mass waste

  9. Ash from the Toba supereruption in Lake Malawi shows no volcanic winter in East Africa at 75 ka

    PubMed Central

    Lane, Christine S.; Chorn, Ben T.; Johnson, Thomas C.

    2013-01-01

    The most explosive volcanic event of the Quaternary was the eruption of Mt. Toba, Sumatra, 75,000 y ago, which produced voluminous ash deposits found across much of the Indian Ocean, Indian Peninsula, and South China Sea. A major climatic downturn observed within the Greenland ice cores has been attributed to the cooling effects of the ash and aerosols ejected during the eruption of the Youngest Toba Tuff (YTT). These events coincided roughly with a hypothesized human genetic bottleneck, when the number of our species in Africa may have been reduced to near extinction. Some have speculated that the demise of early modern humans at that time was due in part to a dramatic climate shift triggered by the supereruption. Others have argued that environmental conditions would not have been so severe to have such an impact on our ancestors, and furthermore, that modern humans may have already expanded beyond Africa by this time. We report an observation of the YTT in Africa, recovered as a cryptotephra layer in Lake Malawi sediments, >7,000 km west of the source volcano. The YTT isochron provides an accurate and precise age estimate for the Lake Malawi paleoclimate record, which revises the chronology of past climatic events in East Africa. The YTT in Lake Malawi is not accompanied by a major change in sediment composition or evidence for substantial temperature change, implying that the eruption did not significantly impact the climate of East Africa and was not the cause of a human genetic bottleneck at that time. PMID:23630269

  10. Large volumes of rejuvenated volcanism in Samoa: Evidence supporting a tectonic influence on late-stage volcanism

    NASA Astrophysics Data System (ADS)

    Konter, Jasper G.; Jackson, Matthew G.

    2012-06-01

    Hot spot volcanoes are commonly constructed in a characteristic sequence of stages. After the volumetrically dominant shield stage, a protracted period of quiescence ends with a final stage of activity: rejuvenated volcanism. The mechanism responsible for generating rejuvenated volcanism is not generally agreed upon. New data obtained for samples 200 m down-section in a deeply incised canyon on Savai`i (Samoa) are unusually enriched isotopically and indicate a relatively voluminous rejuvenated stage compared to other intraplate volcanoes. Using a modified flexural model originally proposed for Hawai`i, we suggest that the location of Samoa near the Tonga Trench terminus causes plate flexure resulting in upward flow of the shallow mantle driving partial melting. In particular, subduction-related plate bending in the Samoan region may cause a larger flexural amplitude than generated by volcanic loading in Hawai`i. The larger amplitude may explain the larger volume of rejuvenated melt in Samoa, constrained by our new data. Moreover, we argue that Sr-Nd-Pb-Os-He-Ne isotopes in Samoan rejuvenated lavas are all consistent with sampling of a lithospheric component that is characterized by a metasomatic imprint from the Pacific Plate's earlier passage over the Rarotonga hot spot. Furthermore, temperature estimates for the melts suggest a drop in temperature during the predicted shallower melting due to flexural uplift, compared to the conditions during shield volcanism. Thus, flexural bending and metasomatism of the Samoan lithosphere may have generated the voluminous and geochemically distinct Samoan rejuvenated lavas, implying the lithosphere may play an important role during this stage in non- Hawaiian hot spots.

  11. Estimation of the CO2 flux from Furnas volcanic Lake (São Miguel, Azores)

    NASA Astrophysics Data System (ADS)

    Andrade, César; Viveiros, Fátima; Cruz, J. Virgílio; Coutinho, Rui; Silva, Catarina

    2016-04-01

    A study on diffuse CO2 degassing was undertaken at Furnas lake (São Miguel island, Azores) in order to estimate the total diffuse CO2 output and identify anomalous degassing areas over the lake. Furnas lake is located in Furnas Volcano, the easternmost of the three active central volcanoes of the São Miguel island. The lake has an area of 1.87 km2 and a maximum length and width equal to 2025 and 1600 m, respectively. The maximum depth of the water column is 15 m and the estimated water storage is 14 × 106 m3. Lake water temperature is cold, with temperature values between 13 °C and 15 °C in the winter period and 18.9 °C to 19.3 °C in early autumn, and the variation along the water column suggests a monomictic character. The major-ion relative composition is in decreasing order Na+ > K+ > Ca2+ > Mg2 + for cations and HCO3- > Cl- > SO42- for anions, and conductivity and pH measurements, respectively in the range of 152 to 165 μS cm- 1 and 5.3 to 8.7, suggests that Furnas has neutral-diluted waters and can be classified as a non-active lake. Diffuse CO2 flux measurements were made using the accumulation chamber method with a total of 1537 and 2577 measurements performed in two different sampling campaigns. The total amount of diffuse CO2 emitted to the atmosphere was estimated between 28 and 321 t km- 2 d- 1, respectively, in the second and first sampling campaigns, corresponding to ~ 52 and ~ 600 t d- 1. The main anomalous degassing area identified over the Furnas lake during both surveys is probably associated to a WNW-ESE trending tectonic structure. Other secondary areas are also suggested to be tectonically influenced. Identified anomalous areas showed similarities to the ones observed during previous soil CO2 degassing studies.

  12. Discovery of an Active Microbial Community in a Subglacial Volcanic Crater Lake, Iceland

    NASA Astrophysics Data System (ADS)

    Gaidos, E.; Lanoil, B.; Thorsteinsson, T.; Graham, A.; Skidmore, M.; Decarlo, E.; Popp, B.

    2002-12-01

    Grímsvötn, an active volcano beneath the Vatnajökull glacier in Iceland, hosts a subglacial caldera lake (Gudmundsson, Sigmundsson and Björnsson 1997 Nature 389, 954). Except for earlier geochemical measurements (Ágústsdóttir and Brantley 1994 J. Geophys. Res. 99, 9505), the lake and its possible biota have remained unexplored. In June 2002 we penetrated the 300-meter ice sheet over the lake using hot-water drilling and collected water and tephra sediment samples. The 85oC drilling water and chemical sterilization of equipment were used to minimize sample contamination. Samples of borehole water, glacial ice, and snow were also obtained. Lake water was at the freezing point and samples had no sulfidic smell indicative of anaerobic conditions. One sample from the borehole actively degassed after retrieval. Waters were slightly acidic (pH ≈ 5) and fresh ([Na] = 5 ppm) with low sulfate (2 ppm). Elevated transition metal levels measured by ICP-MS are being analyzed. Direct (DAPI stain) cell counts in water and sediment average 2 x 104 cells ml-1 and 4 x 107 cells ml-1, respectively. Counts on R2A plates incubated under aerobic conditions at 22oC and 6oC for one week were 1-2 x 104 and 5 x 103 CFU/ml, respectively. These values may reflect growth during sample shipment, however, growth at 6oC indicates the presence of psychrophilic or at least psychrotolerant organisms in the lake. Colonies from lake and post-penetration borehole samples were distinct from those of the borehole, ice and snow. Incubations of lake samples at 4oC showed incorporation of 14C (from bicarbonate). Incubations of other aliquots with a nitrogen-acetylene mixture indicated production of ethylene suggestive of nitrogenase activity. DNA will be extracted and analyzed to determine if the microbial community is distinct from that in the overlying snow and ice.

  13. The origin of a large (> 3 km) maar volcano by coalescence of multiple shallow craters: Lake Purrumbete maar, southeastern Australia

    NASA Astrophysics Data System (ADS)

    Jordan, S. C.; Cas, R. A. F.; Hayman, P. C.

    2013-03-01

    Lake Purrumbete maar is located in the intraplate, monogenetic Newer Volcanics Province in southeastern Australia. The extremely large crater of 3000 m in diameter formed on an intersection of two fault lines and comprises at least three coalesced vents. The evolution of these vents is controlled by the interaction of the tectonic setting and the properties of both hard and soft rock aquifers. Lithics in the maar deposits originate from country rock formations less than 300 m deep, indicating that the large size of the crater cannot only be the result of the downwards migration of the explosion foci in a single vent. Vertical crater walls and primary inward dipping beds evidence that the original size of the crater has been largely preserved. Detailed mapping of the facies distributions, the direction of transport of base surges and pyroclastic flows, and the distribution of ballistic block fields, form the basis for the reconstruction of the complex eruption history,which is characterised by alternations of the eruption style between relatively dry and wet phreatomagmatic conditions, and migration of the vent location along tectonic structures. Three temporally separated eruption phases are recognised, each starting at the same crater located directly at the intersection of two local fault lines. Activity then moved quickly to different locations. A significant volcanic hiatus between two of the three phases shows that the magmatic system was reactivated. The enlargement of especially the main crater by both lateral and vertical growth led to the interception of the individual craters and the formation of the large circular crater. Lake Purrumbete maar is an excellent example of how complicated the evolution of large, seemingly simple, circular maar volcanoes can be, and raises the question if these systems are actually monogenetic.

  14. Mercury as a proxy for Large Igneous Province volcanism: A comparison of Mesozoic events

    NASA Astrophysics Data System (ADS)

    Percival, L.; Jenkyns, H. C.; Mather, T. A.; Hesselbo, S. P.; Ruhl, M.; Tedeschi, L. R.; Whiteside, J. H.; Woelders, L.; Giraud, F.; Pittet, B.; Grosheny, D.; Baudin, F.; Reboulet, S.

    2016-12-01

    Mass extinction events and other episodes of palaeoceanographic and palaeoclimatic upheaval, such as Ocean Anoxic Events (OAEs), have punctuated global climate over the last 300 million years. Many of these events have been causally linked with Large Igneous Provinces (LIPs), which represent the geologically abrupt emplacement of millions of cubic kilometres of (chiefly) basaltic material. Evidence for such a relationship comes both from a coincidence in radiometrically determined ages of many LIPs with the apparent age of an extinction/climate perturbation, and also from the sedimentary record, where stratigraphic horizons recording palaeoclimatic events commonly also record perturbations in sedimentary proxies for volcanism. Numerous recent studies have highlighted Hg/TOC (mercury/total organic carbon) excursions in both terrestrial and marine sedimentary archives recording mass extinctions. Because the main natural source of mercury to the modern environment is volcanic outgassing, such Hg/TOC excursions have been used to support a precise temporal link between many extinction events and continental flood basalts (subaerial LIPs) of the same age. Here we review and compare new and published Hg/TOC data from the sedimentary records of a number of palaeoclimatic events such as mass extinctions and OAEs. The first Hg/TOC data are also presented from records of OAE1a (121Ma) and OAE2 (94Ma), both of which have been associated with the emplacement of subaqueous LIPs (oceanic plateaus). Comparing the mercury records of multiple events is crucial to further understanding of the controls on Hg/TOC as a volcanic proxy, as well as the processes governing relationships between different environmental perturbations and LIPs. Of particular interest is the impact associated with LIP location (e.g. subaerial vs subaqeous; low- vs high-latitude), and its potential to generate additional thermogenic volatiles.

  15. Radiative and climate impacts of a large volcanic eruption during stratospheric sulfur geoengineering

    NASA Astrophysics Data System (ADS)

    Laakso, A.; Kokkola, H.; Partanen, A.-I.; Niemeier, U.; Timmreck, C.; Lehtinen, K. E. J.; Hakkarainen, H.; Korhonen, H.

    2015-08-01

    Both explosive volcanic eruptions, which emit sulfur dioxide into the stratosphere, and stratospheric geoengineering via sulfur injections can potentially cool the climate by increasing the amount of scattering particles in the atmosphere. Here we employ a global aerosol-climate model and an earth system model to study the radiative and climate impacts of an erupting volcano during solar radiation management (SRM). According to our simulations, the radiative impacts of an eruption and SRM are not additive: in the simulated case of concurrent eruption and SRM, the peak increase in global forcing is about 40 % lower compared to a corresponding eruption into a clean background atmosphere. In addition, the recovery of the stratospheric sulfate burden and forcing was significantly faster in the concurrent case since the sulfate particles grew larger and thus sedimented faster from the stratosphere. In our simulation where we assumed that SRM would be stopped immediately after a volcano eruption, stopping SRM decreased the overall stratospheric aerosol load. For the same reasons, a volcanic eruption during SRM lead to only about 1/3 of the peak global ensemble-mean cooling compared to an eruption under unperturbed atmospheric conditions. Furthermore, the global cooling signal was seen only for 12 months after the eruption in the former scenario compared to over 40 months in the latter. In terms of the global precipitation rate, we obtain a 36 % smaller decrease in the first year after the eruption and again a clearly faster recovery in the concurrent eruption and SRM scenario. We also found that an explosive eruption could lead to significantly different regional climate responses depending on whether it takes place during geoengineering or into an unperturbed background atmosphere. Our results imply that observations from previous large eruptions, such as Mt Pinatubo in 1991, are not directly applicable when estimating the potential consequences of a volcanic eruption

  16. Mercury as a proxy for Large Igneous Province volcanism: A comparison of Mesozoic events

    NASA Astrophysics Data System (ADS)

    Percival, Lawrence; Jenkyns, Hugh; Mather, Tamsin; Hesselbo, Stephen; Ruhl, Micha; Whiteside, Jessica; Dickson, Alexander; Jarvis, Ian

    2017-04-01

    Mass extinction events and other episodes of palaeoceanographic and palaeoclimatic upheaval, such as Ocean Anoxic Events (OAEs), have punctuated global climate throughout the Phanerozoic Aeon. Many of these events from the last 300 million years have been causally linked with Large Igneous Provinces (LIPs), which represent the geologically abrupt emplacement of millions of cubic kilometres of (chiefly) basaltic material. Evidence for such a relationship comes both from a coincidence in radiometrically determined ages of many LIPs with the apparent age of an extinction/climate perturbation, and also from the sedimentary record, where stratigraphic horizons recording palaeoclimatic events commonly also record perturbations in sedimentary proxies for volcanism. Numerous recent studies have highlighted Hg/TOC (mercury/total organic carbon) excursions in both terrestrial and marine sedimentary archives recording mass extinctions. Because the main natural source of mercury to the modern environment is volcanic outgassing, such Hg/TOC excursions have been used to support a precise temporal link between many major environmental perturbations and the formation of LIPs. Here, we present new Hg/TOC data from the end-Triassic extinction and Late Cretaceous OAE 2, and compare it to previously published data from records of the end-Permian, end-Triassic, Early Toarcian OAE, Early Aptian OAE 1a, Cenomanian-Turonian OAE 2, and end-Cretaceous events. Comparing the mercury records of multiple events is crucial to further understanding of the controls on Hg/TOC as a volcanic proxy, as well as the processes governing relationships between different environmental perturbations and LIPs. Of particular interest is the influence of LIP location (e.g. subaerial vs subaqeous; low- vs high-latitude), and the potential generation of additional thermogenic volatiles during LIP emplacement.

  17. Long term average rates of large-volume explosive volcanism are not average

    NASA Astrophysics Data System (ADS)

    Connor, C.; Kiyosugi, K.

    2011-12-01

    How good are our estimates of long term recurrence rates of large magnitude explosive volcanic eruptions? To investigate this question, we created a data set of all known explosive eruptions in Japan since 1.8 Ma and VEI magnitude 4 or greater. This data set contains 696 explosive eruptions. We use this data set to consider the change in apparent recurrence rate of large volume explosive eruptions through time. Assuming there has been little change in recurrence rate of volcanism since 2.25 Ma, apparent changes are due to erosion of explosive eruption deposits and a lower rate of identification of older deposits preserved in the geologic record. Surprisingly, one half of the eruptions in the data set occurred within the last 65 ka. 77% of the total eruptions occurred since 200 ka; the oldest eruption in the database is 2.25 Ma. Overall, there is a roughly exponential decrease in the numbers of eruptions of a given magnitude identified in the geological record as a function of time. This result clearly indicates that even large magnitude eruptions are significantly under-reported. In addition, percentages of explosive eruptions in the entire data set by eruption magnitude are: VEI 4 (40%), VEI 5 (42%), VEI 6 (13%) and VEI 7 (5%). Because it is reasonable to assume that smaller eruptions occur much more frequently, fewer VEI 4 eruptions than VEI 5 eruptions indicates that small eruptions are missing in this data set. We quantify these variations by plotting survivor functions, noting that there is little change in apparent rate of activity (or the preservation potential of deposits) with geographic and tectonic setting in Japan. These data indicate that eruption probabilities based on long term recurrence rate may underestimate rates of activity. This result also indicates there is considerable uncertainty about the future recurrence rate of large magnitude eruptions, as our best estimates of frequency are based on an unrealistically short record.

  18. Sulfur Lakes and Sulfur-rich Volcanic Hydrothermal Systems on the Mariana Arc

    NASA Astrophysics Data System (ADS)

    Butterfield, D. A.; Resing, J. A.; Chadwick, W. W.; Embley, R. W.; Lupton, J. E.; Nakamura, K.; Lilley, M. D.; Huber, J. A.

    2007-12-01

    During the Submarine Ring of Fire expeditions in 2004 and 2006, and the Natsushima NT-05-18 expedition in 2005 we investigated and sampled hydrothermal systems on ten submarine volcanoes in the Mariana arc between 13.5 and 23.1 degrees N. The high volatile content of the volcanic arc environment is evident in the CO2 and SO2 dominated fluids sampled and differentiates volcanic arc hydrothermal chemistry from more rock- buffered mid-ocean ridge systems. Sulfur-dominated sites appear to be common on submarine arc volcanoes at water depths shallower than 700 meters. At NW Rota-1 volcano, there is clear evidence of ongoing eruptive activity producing clouds of particulate and molten sulfur as well as mm to m-size glassy volcanic ejecta. The hydrothermal system at NW Rota-1 represents a direct connection to a sub-seafloor magma body, and is one of the only known sites in the world where we can directly sample the solid, liquid and gaseous products of a submarine magmatic hydrothermal system. Fluids (30 to 260 deg C) sampled directly from an eruptive vent have pH as low as 1.0, with a high content of particulate sulfur, excess sulfurous and sulfuric acid, and very low H2S content. Fluids percolating through volcaniclastic sand adjacent to the vent reached 100 deg C and had higher silica, slightly higher pH, and millimolar levels of H2S. The chemistry of both types of fluids is indicative of input of volcanic SO2 and incomplete disproportionation into sulfuric acid and either H2S (in volcaniclastic sands) or elemental sulfur (in the eruptive vent). Highly acidic aqueous fluids attack the basaltic substrate, and carry high levels of iron and aluminum. Daikoku (21.3°N) and Nikko (23.1°N) submarine volcanoes both host active molten sulfur ponds and a wide variety of sulfur flows and deposits. The remarkable molten sulfur pools (~180-200°C) occur without widespread focused venting of hot water and may be maintained by active magmatic degassing of hot CO2/SO2-rich gases

  19. Sedimentation, volcanism, and ancestral lakes in the Valles Marineris: Clues from topography

    NASA Technical Reports Server (NTRS)

    Lucchitta, B. K.; Isbell, N. K.; Howington-Kraus, A.

    1993-01-01

    Compilation of a simplified geologic/geomorphic map onto a digital terrain model of Valles Marineris has permitted quantitative evaluations of topographic parameters. The study showed that, if their interior layered deposits are lacustrine, the ancestral Valles Marineris must have consisted of isolated basins. If, on the other hand, the troughs were interconnected as they are today, the deposits are most likely to volcanic origin, and the mesas in the peripheral troughs may be table mountains. The material eroded from the trough walls was probably not sufficient to form all of the interior layered deposits, but it may have contributed significantly to their formation.

  20. Volcanic Infillings of Large Basins on Mercury as Indicators of Mantle Thermal State and Composition

    NASA Astrophysics Data System (ADS)

    Padovan, Sebastiano; Tosi, Nicola; Plesa, Ana-Catalina; Ruedas, Thomas

    2017-04-01

    The crust of Mercury is mostly the cumulative result of partial melting in the mantle associated with solid-state convection [1]. The details of how the surface composition represents the result of dynamical processes in the interior are difficult to elucidate. Explanations for the observed geochemically varied surface include a heterogeneous mantle, the effects of ancient giant impacts, an evolving mantle composition, or a combination of these processes [e.g., 2]. Here we explore the effects of large impacts on mantle dynamics and associated melt production. With the convection code GAIA we compute thermal evolution histories of Mercury compatible with the expected amount of heat producing elements in the mantle and with the crustal thickness inferred from gravity and topography data. We estimate the thermal anomalies in the mantle generated by large impacts using scaling laws [3]. Impactors have a velocity of 42 km/s and an impact angle of 45°, as appropriate for Mercury [4]. Their size is varied in order to produce basins with diameters in the range from 715 km (Rembrandt) to 1550 km (Caloris). Depending on the timing of the impact, the melt erupting in the basin interior is a combination of convective melt generated at depth and shallow melt resulting from shallow impact-induced convective currents. The volcanic infillings following an impact happening early in the evolution of the planet, when convection is still vigorous, are dominated by convective melt. Later in the evolution, the erupted melt shows the signature of the impact-induced shallow melt. We show that the properties of melt sheets within the young large basins Caloris and Rembrandt depend on the mantle thermal state and composition. In particular, we predict the source depth of the volcanic plains within large young basins to be different from the source depth of older surface units, a result that can help explaining the peculiar composition of the volcanic plains inside Caloris [2, 5]. [1] Tosi

  1. Volcanic hazard alert issued for the Long Valley-Mono Lake area of California

    USGS Publications Warehouse

    Kerr, R. A.

    1982-01-01

    The ski resort of Mammoth Lakes, nestled against the east front of the Sierra Nevada just east of Yosemite National Park, knows about natural hazards. It is still being shaken by an unusual sequence of earthquakes that started in 1978 and included four earthquakes of magnitude 6 within 48 hours of each other in May 1980. An earthquake hazard watch is still in effect. 

  2. Constraining timescales of pre-eruptive events within large silicic volcanic centers

    NASA Astrophysics Data System (ADS)

    Rubin, A. E.; Cooper, K. M.; Kent, A. J.; Costa Rodriguez, F.; Till, C. B.

    2015-12-01

    Large silicic volcanic centers produce catastrophic supervolcanic eruptions. As a result it is necessary to understand what's happening within these centers, and on what timescales, in order to anticipate and prepare for such eruptions. A widely accepted model for many rhyolitic volcanic systems is that of a long-lived mush from which melt is periodically extracted and erupted. However, what remains unclear are 1) the specific processes by which melt is amalgamated and extracted from this mush and 2) the timescales over which these occur. Processes occurring close to eruption likely include amalgamation (and potentially homogenization) of melt, melt extraction, crystallization of major phases, and final magma ascent. Numerical and geochemical models have been used to constrain timescales of mush rejuvenation, and contrast between short timescales for mush reactivation (e.g., <<1000 years, depending on the reservoir) and others demonstrating much longer timescales at super-solidus conditions (e.g., 100s of kyrs). Timescales calculated from intra-crystalline diffusion profiles suggest that many crystals spend very short amounts of time (decades to centuries) at near-solidus temperatures prior to eruption. At the Okataina Volcanic Center (OVC) in New Zealand, geochemical and isotopic data suggest that melts are extracted from a long-lived, heterogeneous mush prior to eruption. Despite this protracted existence, combined U-series ages and diffusion profiles in OVC zircon and plagioclase crystals suggest that crystallization often occurs within the final hundreds to thousands of years prior to eruption, and at most, a few percent of a crystal's total history is spent at above-solidus conditions. Within these brief amounts of time, diffusion techniques can be linked to specific pre-eruptive processes in order to constrain timescales of melt extraction from a mush (likely decades to centuries), intrusions of new melt and/or magma mixing (likely years to decades), and

  3. Large volcanic eruptions and the PETM: Geochemistry from the Fur Formation, Denmark

    NASA Astrophysics Data System (ADS)

    Jones, Morgan; Svensen, Henrik; Tegner, Christian; Planke, Sverre; Willumsen, Pi

    2015-04-01

    The opening of the North Atlantic Ocean during the early Cenozoic was accompanied by substantial volcanism that resulted in the deposition of numerous ash layers over much of northern Europe. This volcanism was contemporaneous with the extreme greenhouse climate of the Palaeocene-Eocene Thermal Maximum (PETM), and is therefore of particular interest for volcanism-climate interactions. The island of Fur, northern Denmark, contains abundant outcrops of volcanic ash layers deposited in a shallow marine environment. Over 179 distinct ash horizons (those greater than ~1 cm are numbered #-39 to #+140) are found within the ~60 m thick Fur Formation. The ash layers are predominantly black and composed of volcanic glass particles ranging from silt to sand in size. Each bed is normally graded and lacks any evidence of significant reworking. There were no volcanoes in the vicinity of Fur during this time, and the outcrops are >700 km from the break-up axis, indicating that at least some of the ash layers were formed during very large eruptions and transported a long way from the source volcanoes. A few thick grey ash layers (e.g. #-33 and #+19) are believed to have originated from volcanoes in East Greenland. Here we present geochemical data from two key sections within the Fur Formation, a beach section at Stolleklint where ashes #-34 to #-31 are exposed, and a quarry section at Jenshøj that covers ashes #+17 to #+35. The #-33 and #+19 ashes are both prominent marker horizons around 15-20 cm thick. The Stolleklint section is clay rich while the quarry section is dominated by diatomite. At Stolleklint, bulk rock total organic carbon (TOC) δ13C values throughout a 1.5 m section are relatively steady at -30.7 to -31.7 o typical of the carbon isotope excursion values of the PETM at Fur. Just above ash layer #-33, δ13C = -27.9 o characteristic of post-PETM values. The bulk rock TOC is high, 1.5 to 4 wt. %. The post-PETM quarry section is much poorer in organic material (0

  4. The Aerosol Cloud of a large Volcanic Eruption: Simulation of Evolution and Climatic Influence

    NASA Astrophysics Data System (ADS)

    Niemeier, U.; Timmreck, C.; Rast, J. S.

    2009-04-01

    Super eruptions exert an extreme forcing on the Earth System. The emitted volcanic aerosol stays several years in the stratosphere, causing strong radiative effects with consequences for atmospheric processes. The interactive simulation of formation, dispersal and temporal development of a very large volcanic cloud is a challenging task for every aerosol climate model. For our studies we use the middle atmosphere general circulation model MAECHAM5 including the global aerosol module HAM. HAM calculates the aerosol microphysics of sulfate and other species and their source and sink processes. The model setup has been validated for the Pinatubo eruption, showing good agreement with satellite data. The results show a realistic atmospheric life cycle of the aerosols, including removal processes and the caused radiative forcings. The simulations are carried out for a possible Northern Hemisphere mid-latitude super eruption located at Yellowstone National Park, because it seems to be one of the most likely possible sites for such an event at higher latitudes, and for a tropical one. The discussion includes the evolution of the sulfate aerosol, the radiative forcing and changes in atmospheric transport and circulation. We also show the influence of the model set up, e.g. resolution, OH-limitation, on the results.

  5. Pyrosequencing analysis of bacterial communities in Lake Bosten, a large brackish inland lake in the arid northwest of China.

    PubMed

    Zhang, Lei; Gao, Guang; Tang, Xiangming; Shao, Keqiang; Gong, Yi

    2016-06-01

    The bacteria inhabiting brackish lake environments are poorly known, and there are few studies on the microbial diversity of these environments. Lake Bosten, a large brackish inland lake, is the largest lake in Xinjiang Province in northwestern China. Because sediments record past limnic changes, the analysis of sedimentary bacteria in Lake Bosten may help elucidate bacterial responses to environmental change. We employed 454 pyrosequencing to investigate the diversity and bacterial community composition in Lake Bosten. A total of 48 230 high-quality sequence reads with 16 314 operational taxonomic units were successfully obtained from the 4 selected samples, and they were numerically dominated by members of the Deltaproteobacteria (17.1%), Chloroflexi (16.1%), Betaproteobacteria (12.6%), Bacteroidetes (6.6%), and Firmicutes (5.7%) groups, accounting for more than 58.1% of the bacterial sequences. The sediment bacterial communities and diversity were consistently different along the 2 geographic environmental gradients: (i) freshwater-brackish water gradient and (ii) oligotrophic-mesotrophic habitat gradient. Deltaproteobacteria, Chloroflexi, and Betaproteobacteria were amplified throughout all of the sampling sites. More Bacteroidetes and Firmicutes were found near the Kaidu River estuary (site 14). Our investigation showed that Proteobacteria did not display any systematic change along the salinity gradient, and numerous 16S rRNA sequences could not be identified at the genus level. Our data will provide a better understanding of the diversity and distribution of bacteria in arid region brackish lakes.

  6. Gyre formation within embayments of a large lake (Lake Geneva, Switzerland)

    NASA Astrophysics Data System (ADS)

    Razmi, A.; Barry, D.; Bouffard, D.; Le Dantec, N.; Lemmin, U.; Wuest, A.

    2013-12-01

    Numerical simulations were carried out to examine gyre formation within open, wide lacustrine embayments. The present study was motivated by observed differences in gyre formation within two open and wide embayments (located at Vidy and Morges in Lake Geneva, Switzerland). These two embayments are located within about 3 km of each other on the northern shore of Lake Geneva, and are subjected to similar pelagic currents. Vidy is deeper and has a greater aspect ratio than Morges. The flow field in the embayments was modeled using a previously validated 3D hydrodynamic model (Delft3D-FLOW). The model solved the Reynolds-Averaged Navier-Stokes equations, combined with a k-ɛ turbulence closure in σ (lakebed-following) coordinates. Our study focused on the influence of the embayment geometry on the (uniform) longshore (pelagic) current, specifically the occurrence and magnitude of circulation within the embayment. We built a set of numerical experiments using synthetic embayments, and systematically examined embayment geometry, thereby capturing the differences between the Vidy and Morges embayments. The numerical experiments considered single rectilinear embayments with different aspect ratios (i.e., 1-6), depth, shore-parallel flow rates, and embayment corner angle between 0°-50°. The circulation magnitude changes abruptly for an angle of about 40°. Embayments with angles greater than 40° have much greater circulation then those with lesser angles, other factors remaining the same. Of the factors considered (i.e., aspect ratio, offshore current velocity, corner angle, bottom slope, and viscosity), bottom slope and the viscosity have almost no impact on embayment circulation. For uniform offshore current patterns, gyres form in embayments with large aspect ratios (up to ~3). For the Vidy and Morges embayments, the results showed that gyre formation is more likely in Morges due to its smaller aspect ratio, a finding that is supported by field data gathered in

  7. Large, Moderate or Small? The Challenge of Measuring Mass Eruption Rates in Volcanic Eruptions

    NASA Astrophysics Data System (ADS)

    Gudmundsson, M. T.; Dürig, T.; Hognadottir, T.; Hoskuldsson, A.; Bjornsson, H.; Barsotti, S.; Petersen, G. N.; Thordarson, T.; Pedersen, G. B.; Riishuus, M. S.

    2015-12-01

    The potential impact of a volcanic eruption is highly dependent on its eruption rate. In explosive eruptions ash may pose an aviation hazard that can extend several thousand kilometers away from the volcano. Models of ash dispersion depend on estimates of the volcanic source, but such estimates are prone to high error margins. Recent explosive eruptions, including the 2010 eruption of Eyjafjallajökull in Iceland, have provided a wealth of data that can help in narrowing these error margins. Within the EU-funded FUTUREVOLC project, a multi-parameter system is currently under development, based on an array of ground and satellite-based sensors and models to estimate mass eruption rates in explosive eruptions in near-real time. Effusive eruptions are usually considered less of a hazard as lava flows travel slower than eruption clouds and affect smaller areas. However, major effusive eruptions can release large amounts of SO2 into the atmosphere, causing regional pollution. In very large effusive eruptions, hemispheric cooling and continent-scale pollution can occur, as happened in the Laki eruption in 1783 AD. The Bárdarbunga-Holuhraun eruption in 2014-15 was the largest effusive event in Iceland since Laki and at times caused high concentrations of SO2. As a result civil protection authorities had to issue warnings to the public. Harmful gas concentrations repeatedly persisted for many hours at a time in towns and villages at distances out to 100-150 km from the vents. As gas fluxes scale with lava fluxes, monitoring of eruption rates is therefore of major importance to constrain not only lava but also volcanic gas emissions. This requires repeated measurements of lava area and thickness. However, most mapping methods are problematic once lava flows become very large. Satellite data on thermal emissions from eruptions have been used with success to estimate eruption rate. SAR satellite data holds potential in delivering lava volume and eruption rate estimates

  8. Spatial identification of critical nutrient loads of large shallow lakes: Implications for Lake Taihu (China).

    PubMed

    Janssen, Annette B G; de Jager, Victor C L; Janse, Jan H; Kong, Xiangzhen; Liu, Sien; Ye, Qinghua; Mooij, Wolf M

    2017-08-01

    Ongoing eutrophication frequently causes toxic phytoplankton blooms. This induces huge worldwide challenges for drinking water quality, food security and public health. Of crucial importance in avoiding and reducing blooms is to determine the maximum nutrient load ecosystems can absorb, while remaining in a good ecological state. These so called critical nutrient loads for lakes depend on the shape of the load-response curve. Due to spatial variation within lakes, load-response curves and therefore critical nutrient loads could vary throughout the lake. In this study we determine spatial patterns in critical nutrient loads for Lake Taihu (China) with a novel modelling approach called Spatial Ecosystem Bifurcation Analysis (SEBA). SEBA evaluates the impact of the lake's total external nutrient load on the local lake dynamics, resulting in a map of critical nutrient loads for different locations throughout the lake. Our analysis shows that the largest part of Lake Taihu follows a nonlinear load-response curve without hysteresis. The corresponding critical nutrient loads vary within the lake and depend on management goals, i.e. the maximum allowable chlorophyll concentration. According to our model, total nutrient loads need to be more than halved to reach chlorophyll-a concentrations of 30-40 μg L(-1) in most sections of the lake. To prevent phytoplankton blooms with 20 μg L(-1) chlorophyll-a throughout Lake Taihu, both phosphorus and nitrogen loads need a nearly 90% reduction. We conclude that our approach is of great value to determine critical nutrient loads of lake ecosystems such as Taihu and likely of spatially heterogeneous ecosystems in general. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

  9. Draft genome of iron-oxidizing bacterium Leptospirillum sp. YQP-1 isolated from a volcanic lake in the Wudalianchi volcano, China.

    PubMed

    Yan, Lei; Zhang, Shuang; Yu, Gaobo; Ni, Yongqing; Wang, Weidong; Hu, Huixin; Chen, Peng

    2015-12-01

    Leptospirillum sp. YQP-1, a member of iron-oxidizing bacteria was isolated from volcanic lake in northeast China. Here, we report the draft genome sequence of the strain YQP-1 with a total genome size of 3,103,789 bp from 85 scaffolds (104 contigs) with 58.64% G + C content. The genome sequence can be accessed at DDBJ/EMBL/GenBank under the accession no. LIEB00000000.

  10. Characterization of endocrine-disruption and clinical manifestations in large-mouth bass from Florida lakes

    SciTech Connect

    Gross, D.A.; Gross, T.S.; Johnson, B.; Folmar, L.

    1995-12-31

    Previous efforts from this laboratory have documented altered endocrine function and sexual differentiation for alligators and turtles from Lake Apopka in Central Florida. This lake has been exposed to a variety of contaminants which are potentially endocrine-disrupting. Therefore, a survey of large mouth bass populations was conducted on several lakes in North Central Florida to examine reproductive and clinical health. Large-mouth bass were collected from lakes Apopka, Griffin, Jessup and Woodruff. Approximately 24 fish (12 males and 12 females) were collected from each lake during the spawning (March--April) and non-reproductive (July--August) seasons. Plasma samples were collected for analysis of estrogen, testosterone and 11-keto-testosterone concentrations. Gonadal and liver tissues were collected for histological analysis. General blood chemistry analyses and parasite surveys were also conducted to estimate general health. Additionally, fillet samples were collected and analyzed for pesticide levels. Fish from Lake Apopka had unusual concentrations of estrogen and 11-keto-testosterone in plasma when compared to bass from Lakes Woodruff, Jessup and Griffin. Parasites loads were significantly higher for bass from lake Apopka than from the other lakes. Male bass on Apopka had depressed concentrations of 11-keto-testosterone, skewing the E/T ratios upward while female bass had higher concentrations of estrogens than females from the other lakes, again resulting in skewed E/T ratios. These skewed E/T ratios are similar to those observed for alligators on the same lake and raise the possibility that they are caused by contaminants. However, contaminant levels in fillets did not differ significantly between lakes. These studies indicate potentially altered reproductive and immunological function for large-mouth bass living in a contaminated lake.

  11. Catastrophic volcanism

    NASA Technical Reports Server (NTRS)

    Lipman, Peter W.

    1988-01-01

    Since primitive times, catastrophes due to volcanic activity have been vivid in the mind of man, who knew that his activities in many parts of the world were threatened by lava flows, mudflows, and ash falls. Within the present century, increasingly complex interactions between volcanism and the environment, on scales not previously experienced historically, have been detected or suspected from geologic observations. These include enormous hot pyroclastic flows associated with collapse at source calderas and fed by eruption columns that reached the stratosphere, relations between huge flood basalt eruptions at hotspots and the rifting of continents, devastating laterally-directed volcanic blasts and pyroclastic surges, great volcanic-generated tsunamis, climate modification from volcanic release of ash and sulfur aerosols into the upper atmosphere, modification of ocean circulation by volcanic constructs and attendent climatic implications, global pulsations in intensity of volcanic activity, and perhaps triggering of some intense terrestrial volcanism by planetary impacts. Complex feedback between volcanic activity and additional seemingly unrelated terrestrial processes likely remains unrecognized. Only recently has it become possible to begin to evaluate the degree to which such large-scale volcanic processes may have been important in triggering or modulating the tempo of faunal extinctions and other evolutionary events. In this overview, such processes are examined from the viewpoint of a field volcanologist, rather than as a previous participant in controversies concerning the interrelations between extinctions, impacts, and volcanism.

  12. Large iron isotope fractionation at the oxic-anoxic boundary in Lake Nyos

    NASA Astrophysics Data System (ADS)

    Teutsch, Nadya; Schmid, Martin; Müller, Beat; Halliday, Alex N.; Bürgmann, Helmut; Wehrli, Bernhard

    2009-07-01

    The degassing of volcanic Lake Nyos (Cameroon) provides the opportunity to study the strong isotopic variation of dissolved Fe(II) in a well constrained redox cycle and to identify the governing processes by reaction-transport modeling. Two depth profiles sampled in the lake in March 2004 and 2005 reveal an increase in iron concentrations and δ57Fe from around 1 mg L - 1 and - 1.88‰ at 55 m depth up to 344 mg L - 1 and + 0.83‰ at the bottom of the lake, respectively. A steep increase in δ57Fe was observed across the oxic-anoxic boundary. As many biological and geochemical processes are known to fractionate Fe isotopes, we used a calibrated reaction-transport model to disentangle the processes governing the Fe cycle. The model combines the isotopic signatures of dissolved Fe(II) and settling Fe(III) particles with the concentration profiles and settling fluxes of the Fe particles in the lake. We show that the strong shift in δ57Fe is caused by isotopic fractionation via dissimilatory Fe reduction across the oxic-anoxic boundary of Lake Nyos. The shift towards more positive values below the oxic-anoxic interface could be attributed to vertical mixing of a heavier component from the bottom of the lake.

  13. Large Eddy Simulation of gas-particle kinematic decoupling and turbulent entrainment in volcanic plumes

    NASA Astrophysics Data System (ADS)

    Cerminara, Matteo; Esposti Ongaro, Tomaso; Neri, Augusto

    2016-10-01

    In the framework of the IAVCEI (International Association of Volcanology and Chemistry of the Earth Interior) intercomparison study on volcanic plume models, we present three-dimensional (3D) numerical simulations carried out with the ASHEE (ASH Equilibrium Eulerian) model. The ASHEE model solves the compressible balance equations of mass, momentum, and enthalpy of a gas-particle mixture and is able to describe the kinematic decoupling for particles characterized by Stokes number (i.e., the ratio between the particle equilibrium time and the flow characteristic time) lower than 0.2 (or particles smaller than about 1 mm). The computational fluid dynamic model is designed to accurately simulate a turbulent flow field using a Large Eddy Simulation approach, and is thus suited to analyze the role of particle non-equilibrium in the dynamics of turbulent volcanic plumes. The two reference scenarios analyzed correspond to a weak (mass eruption rate = 1.5 * 106 kg/s) and a strong volcanic plume (mass eruption rate = 1.5 * 109 kg/s) in absence of wind. For each scenario, we compare the 3D results, averaged in space and time, with theoretical results obtained from integral plume models. Such an approach enables quantitative evaluation of the effects of grid resolution and the subgrid-scale turbulence model, and the influence of gas-particle non-equilibrium processes on the large-scale plume dynamics. We thus demonstrate that the uncertainty on the numerical solution associated with such effects can be significant (of the order of 20%), but still lower than that typically associated with input data and integral model approximations. In the Weak Plume case, 3D results are consistent with the predictions of integral models in the jet and plume regions, with an entrainment coefficient around 0.10 in the plume region. In the Strong Plume case, the self-similarity assumption is less appropriate and the entrainment coefficient in the plume region is more unstable, with an average

  14. Physical mechanisms that lead to large-scale gas accumulation in a volcanic conduit

    NASA Astrophysics Data System (ADS)

    Collombet, Marielle; Burgisser, Alain

    2016-04-01

    The eruption of viscous magma at the Earth's surface often gives rise to abrupt regime changes. The transition from the gentle effusion of a lava dome to brief but powerful explosions is a common regime change. This transition is often preceded by the sealing of the shallow part of the volcanic conduit and the accumulation of volatile-rich magma underneath, a situation that collects the energy to be brutally released during the subsequent explosion. While conduit sealing is well-documented, volatile accumulation has proven harder to characterize. We use a 2D conduit flow model including gas loss within the magma and into the wallrock to find steady-state magma flow configurations in the effusive regime. Model outputs yield a strongly heterogeneous distribution of the gas volume fraction underneath a dense, impermeable magma cap. Gas accumulates in inclined structures hundredths of meters long and several meters thick. These structures probably constitute the gas pockets that accumulate explosive energy and that were intuited by previous studies. We tested the numerical robustness of our results by simulating the fragmented state of the magma contained within the pockets, by testing various fragmentation criteria, and by varying computational gird size. These gas pockets are robust features that occur regardless of wallrock permeability (from very permeable at 10-12 m2 to quasi impermeable at 10-16 m2) but that are sensitive to the volume to surface ratio of the volcanic conduit. One implication is that the formation of these large degassing structures probably plays an essential role in the triggering of violent explosions. Such large scale outgassing feature may also bring a partial answer to the long standing issue of the observed gas transfer across entire magmatic systems despite high magma viscosity and no obvious physical mechanism of transfer.

  15. Multiple sources of selenium in ancient seafloor hydrothermal systems: Compositional and Se, S, and Pb isotopic evidence from volcanic-hosted and volcanic-sediment-hosted massive sulfide deposits of the Finlayson Lake District, Yukon, Canada

    NASA Astrophysics Data System (ADS)

    Layton-Matthews, Daniel; Leybourne, Matthew I.; Peter, Jan M.; Scott, Steven D.; Cousens, Brian; Eglington, Bruce M.

    2013-09-01

    Volcanic-hosted massive sulfide (VHMS) and volcanic-sediment-hosted massive sulfide (VSHMS; i.e., hosted by both volcanic and sedimentary rocks) deposits in the Finlayson Lake District, Yukon, Canada, provide a unique opportunity to study the influence of seafloor and sub-seafloor hydrothermal processes on the formation of Se-poor (GP4F VHMS deposit; 7 ppm Se average), intermediate (Kudz Ze Kayah—KZK VHMS deposit; 200 ppm Se average), and Se-enriched (Wolverine VSHMS deposit; 1100 ppm Se average) mineralization. All three deposits are hosted by mid-Paleozoic (˜360-346 Ma) felsic volcanic rocks, but only the Wolverine deposit has voluminous coeval carbonaceous argillites (black shales) in the host rock package. Here we report the first application of Se isotope analyses to ancient seafloor mineralization and use these data, in conjunction with Pb and S isotope analyses, to better understand the source(s) and depositional process(es) of Se within VHMS and VSHMS systems. The wide range of δ82Se (-10.2‰ to 1.3‰, relative to NIST 3149), δ34S (+2.0‰ to +12.8‰ CDT), and elevated Se contents (up to 5865 ppm) within the Wolverine deposit contrast with the narrower range of δ82Se (-3.8‰ to -0.5‰), δ34S (9.8‰ to 13.0‰), and lower Se contents (200 ppm average) of the KZK deposit. The Wolverine and KZK deposits have similar sulfide depositional histories (i.e., deposition at the seafloor, with concomitant zone refining). The Se in the KZK deposit is magmatic (leaching or degassing) in origin, whereas the Wolverine deposit requires an additional large isotopically negative Se source (i.e. ˜-15‰ δ82Se). The negative δ82Se values for the Wolverine deposit are at the extreme light end for measured terrestrial samples, and the lightest observed for hypogene sulfide minerals, but are within calculated equilibrium values of δ82Se relative to NIST 3149 (˜30‰ at 25 °C between SeO4 and Se2-). We propose that the most negative Se isotope values at the

  16. Yeast diversity in the acidic Rio Agrio-Lake Caviahue volcanic environment (Patagonia, Argentina).

    PubMed

    Russo, Gabriel; Libkind, Diego; Sampaio, José P; van Broock, Maria R

    2008-09-01

    The Rio Agrio and Lake Caviahue system (RAC), in Northwestern Patagonia, is a natural acidic environment. The aims of this study were to characterize the yeast community and to provide the first ecological assessment of yeast diversity of this extreme aquatic environment. Yeast occurrence and diversity were studied at seven sites where the water pH varied between 1.8 and 6.7. Yeast CFU counts in the river ranged from 30 to 1200 CFU L(-1), but in the Lake the values were lower (30-60 CFU L(-1)). A total of 25 different yeast species were found, 11 of which belonged to undescribed taxa. Among these was an unusual strongly acidophilic Cryptococcus species. The RAC yeast community resembles that of acidic aquatic environments resulting from anthropic activities such as the São Domingos mines in Portugal and the Rio Tinto in Spain, respectively. The isolated yeast species were organized into different grades of adaptation to the RAC aquatic system. Based on the proposed grades, Rhodotorula mucilaginosa, Rhodosporidium toruloides and two novel Cryptococcus species were the most adapted species. These Cryptococcus species are apparently specialists of acidic aquatic environments, and might bear physiological features that possibly account for their ability to thrive in such extreme environments.

  17. Protocol to reconstruct historical contaminant loading to large lakes: the Lake Michigan sediment record of mercury.

    PubMed

    Rossmann, Ronald

    2010-02-01

    Samples of opportunity from Pb-210 dated sediment cores collected from Lake Michigan between 1994 and 1996 were analyzed for mercury. The storage of anthropogenic and total (post-1850) mercury in the lake is calculated to be 186 and 228 t, respectively. By setting the sum of mercury stored in a representative core equal to the mercury storage within the entire lake, the time variation of annual mercury loading to the lake is calculated. The modern (1980-2002) mercury flux to the lake represented by the surface of the core at the time of collection in 1994 was 21.4 microg/m(2)/y. The preindustrial flux (< or =1850) was 3.09 microg/m(2)/y, and the peak flux in 1946 was 53.3 microg/m(2)/y. These yield modern and peak enrichment factors of 6.92 and 17.2, respectively. Modern fluxes exceed published atmospheric deposition estimates and, therefore, include terrestrial point sources, atmospheric deposition to watersheds, and atmospheric deposition to the lake. The modern net mercury load to the lake's sediments was 1157 kg/y in 1994. The atmosphere is estimated to contribute 91% of this load directly to the lake.

  18. Eruption probabilities for the Lassen Volcanic Center and regional volcanism, northern California, and probabilities for large explosive eruptions in the Cascade Range

    USGS Publications Warehouse

    Nathenson, Manuel; Clynne, Michael A.; Muffler, L.J. Patrick

    2012-01-01

    Chronologies for eruptive activity of the Lassen Volcanic Center and for eruptions from the regional mafic vents in the surrounding area of the Lassen segment of the Cascade Range are here used to estimate probabilities of future eruptions. For the regional mafic volcanism, the ages of many vents are known only within broad ranges, and two models are developed that should bracket the actual eruptive ages. These chronologies are used with exponential, Weibull, and mixed-exponential probability distributions to match the data for time intervals between eruptions. For the Lassen Volcanic Center, the probability of an eruption in the next year is 1.4x10-4 for the exponential distribution and 2.3x10-4 for the mixed exponential distribution. For the regional mafic vents, the exponential distribution gives a probability of an eruption in the next year of 6.5x10-4, but the mixed exponential distribution indicates that the current probability, 12,000 years after the last event, could be significantly lower. For the exponential distribution, the highest probability is for an eruption from a regional mafic vent. Data on areas and volumes of lava flows and domes of the Lassen Volcanic Center and of eruptions from the regional mafic vents provide constraints on the probable sizes of future eruptions. Probabilities of lava-flow coverage are similar for the Lassen Volcanic Center and for regional mafic vents, whereas the probable eruptive volumes for the mafic vents are generally smaller. Data have been compiled for large explosive eruptions (>≈ 5 km3 in deposit volume) in the Cascade Range during the past 1.2 m.y. in order to estimate probabilities of eruption. For erupted volumes >≈5 km3, the rate of occurrence since 13.6 ka is much higher than for the entire period, and we use these data to calculate the annual probability of a large eruption at 4.6x10-4. For erupted volumes ≥10 km3, the rate of occurrence has been reasonably constant from 630 ka to the present, giving

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

    PubMed

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

    2016-01-01

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

  20. Shatsky Rise: Constraining Duration of Volcanism in a Jurassic Large Igneous Province

    NASA Astrophysics Data System (ADS)

    Heaton, D. E.; Koppers, A. A.

    2013-12-01

    Here we present new high-precision 40Ar/39Ar ages from Shatsky Rise, an oceanic plateau (2.7 × 106 km3) composed of three large volcanic edifices: TAMU, ORI and Shirsov Massif. TAMU Massif (~144.8 × 1.2 Ma; Mahoney et al., 2004) was the first to form at the intersection of an ancient triple junction and is now considered to be the largest singular shield volcano ever to have formed on Earth (Sager et al. 2013; accepted for publication in Nature Geosciences). ORI and Shirsov Massif appear to have formed later in time, following the northward migration of the triple junction. However, it remains unclear whether mechanisms involved in the formation of this triple junction and related mid-ocean ridge volcanism created Shatsky Rise, or whether a plume source is required to explain its significant size and volume. With the age determinations presented here we will attempt to constrain the duration of magmatism, reveal the eruption rates of the Shatsky Rise shield volcanoes, and determine the nature of the age progression along the Shatsky Rise massifs, if it exists. In addition, we will relate the Shatsky Rise volcanic history to the formation of numerous seamounts on and around the Shatsky Rise area. Overall, 50 groundmass and plagioclase separates from across Shatsky Rise and the related seamounts were carefully picked and processed. Thirty-four samples were analyzed from TAMU massif, coming from IODP Expedition 324 Site U1347 (17 samples), ODP Leg 198 Site 1213B (14 samples) and dredging cruise TN037 (3 samples). Seventeen samples were analyzed from ORI Massif, coming from IODP Expedition 324 Sites U1349 and U1350 (16 samples) and a single dredge along the flank of the massif from TN037 (1 sample). Four samples were analyzed from Shirsov Massif, all from IODP Expedition 324 Site U1346. Samples were variably altered but were treated with an extensive acid leaching regimen (Koppers et al., 2004), including 2 x 15 minutes of 5% HF treatments for plagioclases. Samples

  1. Multiple isotopic components in Quaternary volcanic rocks of the Cascade Arc near Crater lake, Oregon

    USGS Publications Warehouse

    Bacon, C.R.; Gunn, S.H.; Lanphere, M.A.; Wooden, J.L.

    1994-01-01

    Quaternary lavas and pyroclastic rocks of Mount Mazama, Crater lake caldera, and the surrounding area have variable Sr, Nd, and Pb isotopic compositions. High-alumina olivine tholeiites have 87Ar/86Ar ratios of 0.70346-0.70364; basaltic andesite, 0.70349-0.70372; shoshonitic basaltic andesite, 0.70374-0.70388; and andesite, 0.70324-0.70383. Dacites of Mount Mazama have 87Sr/ 86Sr ratios of 0.70348-0.70373. Most rhyodacites converge on 0.7037. Andesitic to mafic-cumulate scoriae of the climatic eruption, and enclaves in pre-climactic rhyodacites, cluster in two groups but show nearly the entire 87Sr/86Sr range of the data set, confirming previously suggested introduction of diverse parental magmas into the growing climactic chamber. Magma evolution is described. -from Authors

  2. Did volcanic activity of the Emeishan large igneous province expand in Wuchiapingian times?

    NASA Astrophysics Data System (ADS)

    Bagherpour, Borhan; Bucher, Hugo; Yuan, Dong-Xun; Shen, Shu-zhong; Leu, Marc; Zhang, Chao

    2017-04-01

    Emplacement of the Emeishan Large Igneous Province (ELIP) in the Capitanian (Middle Permian) is associated with several environmental changes (e.g. facies change, carbon cycle perturbation and temperature rise) across the Guadalupian-Lopingian (G-L) interval in South China. However, most of the reported changes are within the Capitanian stage or close to the G-L boundary. Here, we report an episode of drastic environmental changes from the Pingtang syncline (S. Guizhou) that is similar with the previously known ones but which is significantly younger. The studied section represents a protracted and stepwise facies change from a benthos rich, thick-bedded and light grey shallow water limestone (Unit A) to a 30 m-thick unit with thin-bedded dark (OM-rich) radiolarian-spiculitic facies (Unit B). The latter is overlain by an 8 m-thick unit of volcaniclastic sandstone and silts defining a succession of decimetric, cyclic and thinning upward layers (Unit C). The base of the overlying medium-bedded limestone unit (Unit D) contain radiolarian and sponge spicules whose abundance progressively decrease up section with a progressive replacement by abundant benthic faunas concomitant with the transition to thick bedded limestone. A total of five conodont index species (assigned to Clarkina) of early Wuchiapingian age were recognized from Unit A and Unit B. The observed facies transition from Unit A to Unit B indicates a drastic drowning event. Unit C represents a distal turbiditic succession and the overlying Unit D shows an upward shallowing trend back to the initial shallow marine condition. Compilation of sedimentary records across G-L in South China reveals that such drowning events tend to cluster within three discrete time intervals. The drowning events may or may not end with deposition of either volcanics or volcaniclastics. Two first clusters display drowning events overlain by ELIP volcanic rocks or volcaniclastics of ELIP origin and are of Capitanian age. Only the

  3. Depth gradients in food web processes linking large lake habitats -presentation

    EPA Science Inventory

    In large lakes around the world, shifts in ecological communities are often associated with water depth. This suggests that there may be concomitant changes in patterns of resource allocation. Using Lake Superior as an example, we explored this idea through stable isotope analyse...

  4. Depth gradients in food web processes linking large lake habitats -presentation

    EPA Science Inventory

    In large lakes around the world, shifts in ecological communities are often associated with water depth. This suggests that there may be concomitant changes in patterns of resource allocation. Using Lake Superior as an example, we explored this idea through stable isotope analyse...

  5. Coupled evolution of magma chambers and flow in conduits during large volcanic eruptions

    NASA Astrophysics Data System (ADS)

    Karlstrom, L.; Manga, M.; Rudolph, M. L.

    2010-12-01

    The largest silicic and mafic volcanic eruptions in the geologic record, Supervolcano and Large Igneous Province (LIP) eruptions, are distinguished by differences in surface emplacement mode, geologic context, magma volatile content, viscosity, and reservoir depth. However, these large eruptions also share several common features. Individual eruptions of both types emplace roughly the same total volume (10^3 - 10^4 km^3) of remarkably homogeneous magma that likely comes from a single reservoir. In addition, they both release large quantities of volatiles, and hence individual eruptions may significantly perturb global climate. We have developed a model that couples conduit flow and magma chamber deformation, allowing us to study both eruption types. Steady, one-dimensional multiphase flow of magma containing crystals, exsolved water, and CO_2 in a cylindrical conduit is coupled to pressure evolution within an ellipsoidal magma chamber beneath a free surface. LIP eruptions are characterized by gas-driven flow of mafic lava that may be sustained past the cessation of chamber overpressure, much like a siphon. Eruptions cease when the yield strength of the country rocks is reached and the (generally Moho-level) chamber or the conduit implodes, resulting in steady discharge and atmospheric volatile loading. In contrast, more shallow silicic lavas such as the Fish Canyon Tuff erupt through rapid mobilization of a long-lived crystal-rich mush. The crystal-rich mush is a yield strength fluid, which we model using the von Mises criterion for mobilization. If the trigger for mobilization of the mush leads directly to eruption, time-progressive yielding due to mass removal results in a fluid magma chamber that grows as the eruption proceeds, until free-surface stresses induce roof collapse and caldera formation. Chamber pressure evolution may be buffered by the mobilization of the mush, maintaining overpressure and high discharge throughout the eruption. This model suggests

  6. Hydrologic interconnection between the volcanic aquifer and springs, Lake Tana basin on the Upper Blue Nile

    NASA Astrophysics Data System (ADS)

    Nigate, Fenta; Van Camp, Marc; Kebede, Seifu; Walraevens, Kristine

    2016-09-01

    Hydrochemical and stable isotope (δ18O, δ2H) data were used to identify the recharge sources of major springs and the hydraulic interconnection between the volcanic aquifer and springs in the Gilgel Abay catchment and adjacent areas. The hydrochemical data analysis showed that all water samples of springs and shallow wells have freshwater chemistry, Casbnd HCO3 to Casbnd Mgsbnd HCO3 types. This is mainly controlled by dissolution/hydrolysis of silicate minerals. The analyzed stable isotope data indicate that springs water, except Dengel Mesk, Kurt Bahir and Bility springs, and well waters, except Dangila well, fall close to the LMWL. This clearly shows that the infiltrated rainwater did not undergo much evaporation and δ18O values for spring water and groundwater are nearly equal to the value of Ethiopian summer rainfall, which is -2.5‰. Therefore, generally both stable isotope and hydrochemical data show the recharge source to springs and shallow groundwater is primarily from precipitation. Furthermore, data suggest that rock-water interaction has remained relatively limited, pointing to relatively short residence times, and local recharge rather than regional recharge.

  7. Magmatic gas emissions at Holocene volcanic features near Mono Lake, California, and their relation to regional magmatism

    NASA Astrophysics Data System (ADS)

    Bergfeld, Deborah; Evans, William C.; Howle, James F.; Hunt, Andrew G.

    2015-02-01

    Silicic lavas have erupted repeatedly in the Mono Basin over the past few thousand years, forming the massive domes and coulees of the Mono Craters chain and the smaller island vents in Mono Lake. We report here on the first systematic study of magmatic CO2 emissions from these features, conducted during 2007-2010. Most notably, a known locus of weak steam venting on the summit of North Coulee is actually enclosed in a large area (~ 0.25 km2) of diffuse gas discharge that emits 10-14 t/d of CO2, mostly at ambient temperature. Subsurface gases sampled here are heavily air-contaminated, but after standard corrections are applied, show average δ13C-CO2 of - 4.72‰, 3He/4He of 5.89RA, and CO2/3He of 0.77 × 1010, very similar to the values in fumarolic gas from Mammoth Mountain and the Long Valley Caldera immediately to the south of the basin. If these values also characterize the magmatic gas source at Mono Lake, where CO2 is captured by the alkaline lake water, a magmatic CO2 upflow beneath the lake of ~ 4 t/d can be inferred. Groundwater discharge from the Mono Craters area transports ~ 13 t/d of 14C-dead CO2 as free gas and dissolved carbonate species, and adding in this component brings the estimated total magmatic CO2 output to 29 t/d for the two silicic systems in the Mono Basin. If these emissions reflect intrusion and degassing of underlying basalt with 0.5 wt.% CO2, a modest intrusion rate of 0.00075 km3/yr is indicated. Much higher intrusion rates are required to account for CO2 emissions from Mammoth Mountain and the West Moat of the Long Valley Caldera.

  8. Post-11,000-year volcanism at Medicine Lake Volcano, Cascade Range, northern California

    SciTech Connect

    Donnelly-Nolan, J.M.; Champion, D.E.; Trimble, D.A. ); Miller, C.D. ); Grove, T.L. )

    1990-11-10

    Eight eruptions produced about 5.3 km{sup 3} of basaltic lava during an interval of a few hundred years about 10,500 years B.P. After a hiatus of about 6,000 years, eruptive activity resumed with a small andesite eruption at about 4,300 years B.P. Approximately 2.5 km{sup 3} of lava with compositions ranging from basalt to rhyolite vented in nine eruptions during an interval of about 3,400 years in late Holocene time. The most recent eruption occurred about 900 years B.P. A compositional gap in SiO{sub 2} values of erupted lavas occurs between 58 and 63%. The gap is spanned by chilled magmatic inclusions in late Holocene silicic lavas. Late Holocene andesitic to rhyolitic lavas were probably derived by fractionation, assimilation, and mixing from high-alumina basalt parental magma, possibly from basalt intruded into the volcano during the early mafic episode. Some eruptions have produced both tholeiitic and calc-alkaline compositions. The eruptive activity is probably driven by intrusions of basalt that occur during east-west stretching of the crust in an extensional tectonic environment. Vents are typically aligned parallel or subparallel to major structural features, most commonly within 30{degree} of north. Intruded magma should provide adequate heat for commercial geothermal development if sufficient fluids can be found. The nature and timing of future volcanic activity cannot be predicted from the observed pattern, but eruptions high on the edifice could produce high-silica products that might be accompanied by explosive activity, whereas eruptions lower on the flanks are likely to vent more fluid mafic lavas.

  9. Morphology, distribution, and estimated eruption volumes for intracaldera tuffs associated with volcanic-hosted massive sulfide deposits in the Archean Sturgeon Lake Caldera Complex, Northwestern Ontario

    NASA Astrophysics Data System (ADS)

    Hudak, George J.; Morton, Ronald L.; Franklin, James M.; Peterson, Dean M.

    The Archean Sturgeon Lake Caldera Complex (SLCC) comprises a well-preserved, north-facing homoclinal sequence of greenschist facies metamorphosed intrusive, volcanic, and sedimentary strata. This piecemeal caldera complex is at least 25 km in strike length and contains nearly 3000 meters of dominantly subaqueously deposited intracaldera fill. Episodes of subaerial and subaqueous explosive felsic volcanism produced rhyodacitic to rhyolitic tuffs and lapilli tuffs. Progressing stratigraphically upward, the most voluminous are: a) the High Level Lake Tuff (˜16km3 b) the Mattabi Tuff (˜27km3) and c) the Middle L Tuff (˜7km3). The subaerially erupted, subaerially and locally subaqueously deposited High Level Lake Tuff comprises an 80-300 meter-thick unit composed of basal, poorly sorted, massive to normal graded, quartz-phyric, locally spherulitic tuffs and lapilli tuffs (30—150m thick) that are overlain by thin-bedded tuffs (<1-5m thick). The subaqueously erupted and deposited Mattabi Tuff contains up to thirteen individual flow units, each comprising two distinct depositional facies: a) lower, quartz-phyric, poorly sorted, ungraded, massive tuffs and lapilli tuffs (20-250 meters thick; and b) upper, laminated to medium bedded, typically normal graded tuffs (1-13 meters thick). The subaqueously erupted and deposited Middle L Tuff is also characterized by two distinct lithofacies: a) lower graded, quartz- and, rarely, potassium feldspar-phyric tuffs and lapilli tuffs (5-120m thick); and b) overlying, well-sorted, laminated to thickly bedded, normal graded tuffs (volcanic-hosted massive sulfide (VHMS) ore bodies in the SLCC. At Sturgeon Lake, VHMS ore deposition appears to be favored by processes associated with the generation of voluminous subaqueous explosive eruptions.

  10. Depth gradients in food web processes linking habitats in large lakes: Lake Superior as an exemplar ecosystem

    EPA Science Inventory

    In large lakes around the world, water depth is often associated with shifts in ecological communities. Depth-based changes in the abundance and distribution of invertebrate and fish species suggest that there may be concomitant changes in patterns of resource allocation. Using L...

  11. Depth gradients in food web processes linking habitats in large lakes: Lake Superior as an exemplar ecosystem

    EPA Science Inventory

    In large lakes around the world, water depth is often associated with shifts in ecological communities. Depth-based changes in the abundance and distribution of invertebrate and fish species suggest that there may be concomitant changes in patterns of resource allocation. Using L...

  12. Discovery of large conical stromatolites in Lake Untersee, Antarctica.

    PubMed

    Andersen, D T; Sumner, D Y; Hawes, I; Webster-Brown, J; McKay, C P

    2011-05-01

    Lake Untersee is one of the largest (11.4 km(2)) and deepest (>160 m) freshwater lakes in East Antarctica. Located at 71°S the lake has a perennial ice cover, a water column that, with the exception of a small anoxic basin in the southwest of the lake, is well mixed, supersaturated with dissolved oxygen, alkaline (pH 10.4) and exceedingly clear. The floor of the lake is covered with photosynthetic microbial mats to depths of at least 100 m. These mats are primarily composed of filamentous cyanophytes and form two distinct macroscopic structures, one of which--cm-scale cuspate pinnacles dominated by Leptolyngbya spp.--is common in Antarctica, but the second--laminated, conical stromatolites that rise up to 0.5 m above the lake floor, dominated by Phormidium spp.--has not previously been reported in any modern environment. The laminae that form the conical stromatolites are 0.2-0.8 mm in thickness consisting of fine clays and organic material; carbon dating implies that laminations may occur on near decadal timescales. The uniformly steep sides (59.6 ± 2.5°) and the regular laminar structure of the cones suggest that they may provide a modern analog for growth of some of the oldest well-described Archean stromatolites. Mechanisms underlying the formation of these stromatolites are as yet unclear, but their growth is distinct from that of the cuspate pinnacles. The sympatric occurrence of pinnacles and cones related to microbial communities with distinct cyanobacterial compositions suggest that specific microbial behaviors underpin the morphological differences in the structures. © 2011 Blackwell Publishing Ltd.

  13. Post-11,000-year volcanism at Medicine Lake Volcano, Cascade Range, northern California

    USGS Publications Warehouse

    Donnelly-Nolan, J. M.; Champion, D.E.; Miller, C.D.; Grove, T.L.; Trimble, D.A.

    1990-01-01

    Eruptive activity during the past 11,000 years at Medicine Lake volcano has been episodic. Eight eruptions produced about 5.3 km3 of basaltic lava during an interval of a few hundred years about 10 500 years B.P. After a hiatus of about 6000 years, eruptive activity resumed with a small andesite eruption at about 4300 years B.P. Approximately 2.5 km3 of lava with compositions ranging from basalt to rhyolite vented in nine eruptions during an interval of about 3400 years in late Holocene time. The most recent eruption occurred about 900 years B.P. A compositional gap in SiO2 values of erupted lavas occurs between 58 and 63%. The gap is spanned by chilled magmatic inclusions in late Holocene silicic lavas. Late Holocene andesitic to rhyolitic lavas were probably derived by fractionation, assimilation, and mixing from high-alumina basalt parental magma, possibly from basalt intruded into the volcano during the early mafic episode. Eruptive activity is probably driven by intrusions of basalt that occur during E-W stretching of the crust in an extensional tectonic environment. Vents are typically aligned parallel or subparallel to major structural features, most commonly within 30?? of north. Intruded magma should provide adequate heat for commercial geothermal development if sufficient fluids can be found. -from Authors

  14. Diverse lavas from closely spaced volcanoes drawing from a common parent: Emmons Lake Volcanic Center, Eastern Aleutian Arc

    USGS Publications Warehouse

    Mangan, M.; Miller, T.; Waythomas, C.; Trusdell, F.; Calvert, A.; Layer, P.

    2009-01-01

    Emmons Lake Volcanic Center (ELVC) on the lower Alaskan Peninsula is one of the largest and most diverse volcanic centers in the Aleutian Arc. Since the Middle Pleistocene, eruption of ~ 350 km3 of basalt through rhyolite has produced a 30 km, arc front chain of nested calderas and overlapping stratovolcanoes. ELVC has experienced as many as five major caldera-forming eruptions, the most recent, at ~ 27 ka, produced ~ 50 km3 of rhyolitic ignimbrite and ash fall. These violent silicic events were interspersed with less energetic, but prodigious, outpourings of basalt through dacite. Holocene eruptions are mostly basaltic andesite to andesite and historically recorded activity includes over 40 eruptions within the last 200 yr, all from Pavlof volcano, the most active site in the Aleutian Arc. Geochemical and geophysical observations suggest that although all ELVC eruptions derive from a common clinopyroxene + spinel + plagioclase fractionating high-aluminum basalt parent in the lower crust, magma follows one of two closely spaced, but distinct paths to the surface. Under the eastern end of the chain, magma moves rapidly and cleanly through a relatively young (~ 28 ka), hydraulically connected dike plexus. Steady supply, short magma residence times, and limited interaction with crustal rocks preserve the geochemistry of deep crustal processes. Below the western part of the chain, magma moves haltingly through a long-lived (~ 500 ka) and complex intrusive column in which many generations of basaltic to andesitic melts have mingled and fractionated. Buoyant, silicic melts periodically separate from the lower parts of the column to feed voluminous eruptions of dacite and rhyolite. Mafic lavas record a complicated passage through cumulate zones and hydrous silicic residues as manifested by disequilibrium phenocryst textures, incompatible element enrichments, and decoupling of REEs and HFSEs ratios. Such features are absent in mafic lavas from the younger part of the chain

  15. Poyang Lake basin: a successful, large-scale integrated basin management model for developing countries.

    PubMed

    Chen, Meiqiu; Wei, Xiaohua; Huang, Hongsheng; Lü, Tiangui

    2011-01-01

    Protection of water environment while developing socio-economy is a challenging task for lake regions of many developing countries. Poyang Lake is the largest fresh water lake in China, with its total drainage area of 160,000 km2. In spite of rapid development of socio-economy in Poyang Lake region in the past several decades, water in Poyang Lake is of good quality and is known as the "last pot of clear water" of the Yangtze River Basin in China. In this paper, the reasons of "last pot of clear water" of Poyang Lake were analysed to demonstrate how economic development and environmental protection can be coordinated. There are three main reasons for contributing to this coordinated development: 1) the unique geomorphologic features of Poyang Lake and the short water residence time; 2) the matching of the basin physical boundary with the administrative boundary; and 3) the implementation of "Mountain-River-Lake Program" (MRL), with the ecosystem concept of "mountain as source, river as connection flow, and lake as storage". In addition, a series of actions have been taken to coordinate development, utilisation, management and protection in the Poyang Lake basin. Our key experiences are: considering all basin components when focusing on lake environment protection is a guiding principle; raising the living standard of people through implementation of various eco-economic projects or models in the basin is the most important strategy; preventing soil and water erosion is critical for protecting water sources; and establishing an effective governance mechanism for basin management is essential. This successful, large-scale basin management model can be extended to any basin or lake regions of developing countries where both environmental protection and economic development are needed and coordinated.

  16. Yardea Dacite -large-volume, high-temperature felsic volcanism from the Middle Proterozoic of South Australia

    SciTech Connect

    Creaser, R.A.; White, A.J.R. )

    1991-01-01

    The Yardea Dacite is a large-volume felsic volcanic unit from the Middle Proterozoic Gawler Range Volcanics of South Australia; it has been previously described as an ignimbrite. However, some samples contain no petrographic evidence for a pyroclastic origin, but have characteristics compatible with final crystallization from a nonfragmented magma. These samples may have erupted as lavas, but others are likely to be extremely densely welded ignimbrites, suggesting a compound nature for the unit. Geothermometry and phase equilibria indicate that the Yardea Dacite originated from a high-temperature ({approximately}1,000{degree}C) felsic magma with a low water content ({le}2%). The Yardea Dacite is not associated with a known caldera of the Valles type, and shares many characteristics of recently described Cenozoic felsic volcanic rocks from the western United States, interpreted as rheoignimbrites or as unusually extensive lavas.

  17. Floating Wetland Islands Help Restore Large PA Lake

    EPA Pesticide Factsheets

    One of Pennsylvania’s largest natural lakes has been removed from the state’s list of impaired waters following years of EPA-funded work to control phosphorus pollution. One of the innovative actions taken to meet the goal was use of 5 floating wetlands.

  18. Floating Wetland Islands Help Restore Large Pennsylvania Lake

    EPA Pesticide Factsheets

    One of Pennsylvania’s largest lakes has been removed from the list of impaired waters following years of EPA-funded work to control phosphorus pollution. One of the innovative actions taken to meet the goal was deployment of five floating wetland islands.

  19. Diatom assemblages promote ice formation in large lakes.

    PubMed

    D'souza, N A; Kawarasaki, Y; Gantz, J D; Lee, R E; Beall, B F N; Shtarkman, Y M; Koçer, Z A; Rogers, S O; Wildschutte, H; Bullerjahn, G S; McKay, R M L

    2013-08-01

    We present evidence for the directed formation of ice by planktonic communities dominated by filamentous diatoms sampled from the ice-covered Laurentian Great Lakes. We hypothesize that ice formation promotes attachment of these non-motile phytoplankton to overlying ice, thereby maintaining a favorable position for the diatoms in the photic zone. However, it is unclear whether the diatoms themselves are responsible for ice nucleation. Scanning electron microscopy revealed associations of bacterial epiphytes with the dominant diatoms of the phytoplankton assemblage, and bacteria isolated from the phytoplankton showed elevated temperatures of crystallization (T(c)) as high as -3 °C. Ice nucleation-active bacteria were identified as belonging to the genus Pseudomonas, but we could not demonstrate that they were sufficiently abundant to incite the observed freezing. Regardless of the source of ice nucleation activity, the resulting production of frazil ice may provide a means for the diatoms to be recruited to the overlying lake ice, thereby increasing their fitness. Bacterial epiphytes are likewise expected to benefit from their association with the diatoms as recipients of organic carbon excreted by their hosts. This novel mechanism illuminates a previously undescribed stage of the life cycle of the meroplanktonic diatoms that bloom in Lake Erie and other Great Lakes during winter and offers a model relevant to aquatic ecosystems having seasonal ice cover around the world.

  20. Diatom assemblages promote ice formation in large lakes

    PubMed Central

    D'souza, N A; Kawarasaki, Y; Gantz, J D; Lee, R E; Beall, B F N; Shtarkman, Y M; Koçer, Z A; Rogers, S O; Wildschutte, H; Bullerjahn, G S; McKay, R M L

    2013-01-01

    We present evidence for the directed formation of ice by planktonic communities dominated by filamentous diatoms sampled from the ice-covered Laurentian Great Lakes. We hypothesize that ice formation promotes attachment of these non-motile phytoplankton to overlying ice, thereby maintaining a favorable position for the diatoms in the photic zone. However, it is unclear whether the diatoms themselves are responsible for ice nucleation. Scanning electron microscopy revealed associations of bacterial epiphytes with the dominant diatoms of the phytoplankton assemblage, and bacteria isolated from the phytoplankton showed elevated temperatures of crystallization (Tc) as high as −3 °C. Ice nucleation-active bacteria were identified as belonging to the genus Pseudomonas, but we could not demonstrate that they were sufficiently abundant to incite the observed freezing. Regardless of the source of ice nucleation activity, the resulting production of frazil ice may provide a means for the diatoms to be recruited to the overlying lake ice, thereby increasing their fitness. Bacterial epiphytes are likewise expected to benefit from their association with the diatoms as recipients of organic carbon excreted by their hosts. This novel mechanism illuminates a previously undescribed stage of the life cycle of the meroplanktonic diatoms that bloom in Lake Erie and other Great Lakes during winter and offers a model relevant to aquatic ecosystems having seasonal ice cover around the world. PMID:23552624

  1. Structure and spatial patterns of macrobenthic community in Tai Lake, a large shallow lake, China

    USGS Publications Warehouse

    Di Li,; Erickson, Richard A.; Song Tang,; Xuwen Li,; Niu, Zhichun; Xia Wang,; Hongling Liu,; Hongxia Yu,

    2016-01-01

    Tai Lake (Chinese: Taihu), the third-largest freshwater lake in China, suffers from harmful cyanobacteria blooms that are caused by economic development and population growth near the lake. Several studies have focused on phytoplankton in Tai Lake after a drinking water crisis in 2007; however, these studies primarily focused on microcystin bioaccumulation and toxicity to individual species without examining the effects of microcystin on macrobenthic community diversity. In this study, we conducted a survey of the lake to examine the effects of microcystine and other pollutants on marcobenthic community diversity. A totally of forty-nine species of macroinvertebrates were found in Tai Lake. Limnodrilus hoffmeisteri and Corbicula fluminea were the most abundant species. Cluster-analysis and one-way analysis of similarity (ANOSIM) identified three significantly different macrobenthic communities among the sample sites. More specifically, sites in the eastern bays, where aquatic macrophytes were abundant, had the highest diversity of macrobenthic communities, which were dominated by Bellamya aeruginosa, Bellamya purificata, L. hoffmeisteri, and Alocinma longicornis. Sites in Zhushan Bay contained relatively diverse communities, mainly composed of L. hoffmeisteri, C. fluminea, L. claparederanus, R. sinicus, and Cythura sp. Sites in the western region, Meiliang Bay and Wuli Bay had the lowest diversity, mainly composed ofL. hoffmeisteri, C. fluminea, Branchiura sowerbyi, and Rhyacodrilus sinicus. In addition, the relationships between macrobenthic metrics (Shannon–Wiener, Margalef, and Pielou) and environmental variables showed that community structure and spatial patterns of macrobenthos in Tai Lake were significantly influenced by chemical oxygen demand (CODCr), biochemical oxygen demand (BOD5), lead (Pb), and microcystin-LR (L for leucine and R for arginine). Our findings provide critical information that could help managers and policymakers

  2. New 40Ar/39Ar isotopic dates from Miocene volcanic rocks in the Lake Mead area and southern Las Vegas Range, Nevada

    USGS Publications Warehouse

    Harlan, S.S.; Duebendorfer, E.M.; Deibert, J.E.

    1998-01-01

    New 40Ar/39Ar dates on volcanic rocks interlayered with synextensional Miocene sedimentary rocks in the western Lake Mead area and southern end of the Las Vegas Range provide tight constraints on magmatism, basin formation, and extensional deformation in the Basin and Range province of southern Nevada. Vertical axis rotations associated with movement along the Las Vegas Valley shear zone occurred after 15.67??0.10 Ma (2??), based on a 40Ar/39Ar date from a tuff in the Gass Peak formation in the southern Las Vegas Range. Basaltic magmatism in the western Lake Mead area began as early as 13.28??0.09 Ma, based on a date from a basalt flow in the Lovell Wash Member of the Horse Spring Formation. Isotopic dating of a basalt from the volcanic rocks of Callville Mesa indicates that these rocks are as old as 11.41??0.14 Ma, suggesting that volcanic activity began shortly after formation of the Boulder basin, the extensional basin in which the informally named red sandstone unit was deposited. The red sandstone unit is at least as old as 11.70??0.08 Ma and contains megabreccia deposits younger than 12.93??0.10 Ma. This results shows that formation of the Boulder basin was associated with development of topographic relief that was probably generated by movement along the Saddle Island low-angle normal fault. Stratal tilting associated with extension occurred both prior to and after 11.5 Ma.

  3. Idealized Large-Eddy Simulations of Sea and Lake Breezes: Sensitivity to Lake Diameter, Heat Flux and Stability

    NASA Astrophysics Data System (ADS)

    Crosman, Erik T.; Horel, John D.

    2012-09-01

    Idealized large-eddy simulations of lake and sea breezes are conducted to determine the sensitivity of these thermally-driven circulations to variations in the land-surface sensible heat flux and initial atmospheric stability. The lake-breeze and sea-breeze metrics of horizontal wind speed, horizontal extent, and depth are assessed. Modelled asymmetries about the coastline in the horizontal extent of the low-level onshore flow are found to vary as a function of the heat flux and stability. Small lake breezes develop similarly to sea breezes in the morning, but have a significantly weaker horizontal wind-speed component and a smaller horizontal extent than sea breezes in the afternoon.

  4. Selective transfer of polyunsaturated fatty acids from phytoplankton to planktivorous fish in large boreal lakes.

    PubMed

    Strandberg, Ursula; Hiltunen, Minna; Jelkänen, Elli; Taipale, Sami J; Kainz, Martin J; Brett, Michael T; Kankaala, Paula

    2015-12-01

    Lake size influences various hydrological parameters, such as water retention time, circulation patterns and thermal stratification that can consequently affect the plankton community composition, benthic-pelagic coupling and the function of aquatic food webs. Although the socio-economical (particularly commercial fisheries) and ecological importance of large lakes has been widely acknowledged, little is known about the availability and trophic transfer of polyunsaturated fatty (PUFA) in large lakes. The objective of this study was to investigate trophic trajectories of PUFA in the pelagic food web (seston, zooplankton, and planktivorous fish) of six large boreal lakes in the Finnish Lake District. Docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) and α-linolenic acid (ALA) were the most abundant PUFA in pelagic organisms, particularly in the zooplanktivorous fish. Our results show that PUFA from the n-3 family (PUFAn-3), often associated with marine food webs, are also abundant in large lakes. The proportion of DHA increased from ~4±3% in seston to ~32±6% in vendace (Coregonus albula) and smelt (Osmerus eperlanus), whereas ALA showed the opposite trophic transfer pattern with the highest values observed in seston (~11±2%) and the lowest in the opossum shrimp (Mysis relicta) and fish (~2±1%). The dominance of diatoms and cryptophytes at the base of the food web in the study lakes accounted for the high amount of PUFAn-3 in the planktonic consumers. Furthermore, the abundance of copepods in the large lakes explains the effective transfer of DHA to planktivorous fish. The plankton community composition in these lakes supports a fishery resource (vendace) that is very high nutritional quality (in terms of EPA and DHA contents) to humans.

  5. Large rock-slope failures impacting on lakes - Reconstruction of events and deciphering mobility processes at Lake Oeschinen (CH) and Lake Eibsee (D)

    NASA Astrophysics Data System (ADS)

    Knapp, Sibylle; Anselmetti, Flavio; Gilli, Adrian; Krautblatter, Michael; Hajdas, Irka

    2017-04-01

    Among single event landslide disasters large rock-slope failures account for 75% of disasters with more than 1000 casualties. The precise determination of recurrence rates and failure volumes combined with an improved understanding of mobility processes are essential to better constrain runout models and establish early warning systems. Here we present the data sets from the two alpine regions Lake Oeschinen (CH) and Lake Eibsee (D) to show how lake studies can help to decipher the multistage character of rock-slope failures and to improve the understanding of the processes related to rock avalanche runout dynamics. We focus on such that impacted on a (paleo-) lake for two main reasons. First, the lake background sedimentation acts as a natural chronometer, which enables the stratigraphic positioning of events and helps to reconstruct the event history. This way it becomes possible to (i) decipher the multistage character of the failure of a certain rock slope and maybe detect progressive failure, (ii) determine the recurrence rates of failures at that certain rock slope, and (iii) consider energies based on estimated failure volumes, fall heights and deposition patterns. Hence, the interactions between a rock-slope failure, the water reservoir and the altered rock-slope are better understood. Second, picturing a rock avalanche running through and beyond a lake, we assume the entrainment of water and slurry to be crucial for the subsequent flow dynamics. The entrainment consumes a large share of the total energy, and orchestrates the mobility leading to fluidization, a much higher flow velocity and a longer runout-path length than expected. At Lake Oeschinen (CH) we used lake sediment cores and reflection seismic profiles in order to reconstruct the 2.5 kyrs spanning rock-slope failure history including 10 events, six of which detached from the same mountain flank, and correlated them with (pre-) historical data. The Lake Eibsee records provide insights into the

  6. Lake Peipsi's eutrophication issue: new insights into large scale water quality modeling

    NASA Astrophysics Data System (ADS)

    Fink, Gabriel; Flörke, Martina

    2017-04-01

    The large and shallow European Lake Peipsi was polluted with phosphorus loadings from different point and diffuse sources over decades. The lake's trophic state changed from mesotrophic to eutrophic and hypertrophic. In the 1990s phosphorus pollution dropped significantly. However, more than twenty years later the lake is still eutrophic (L. Peipsi s.s.) and hypertrophic (L. Pihkva). It has been determined that internal loadings from a large nutrient pool in the lake's sediments play an important role in the actual phosphorus balance. For a pursuing and comprehensive understanding, there is a need for detailed and integrated water quality data. This is necessary to assess the current state as well as the younger lake nutrient history. However, in-situ data are scarce and difficult to access. To overcome this data sparse situation the global integrated modeling framework WaterGAP3 was applied (i) to test the applicability of a global scale (5 arc minutes resolution) water quality model in a local scale eutrophication study, and (ii) to provide a detailed local analysis of the eutrophication issue for Lake Peipsi. In this setting WaterGAP3 provides a detailed description of phosphorus sources, loadings and concentrations. Furthermore the newly implemented two box eutrophication module provides a long term description of total phosphorus (TP) concentrations in lakes, the consequent potential for toxic algae blooms, and the TP balance components such as the sediment storage. The WaterGAP3 global results such as river discharge, TP loads from different sectors, TP concentration in the lake and in the catchments river system cover a period of 1990-2010. Our model results indicate that the agricultural sector (diffuse source) is the primary source of TP pollution in the Lake Peipsi catchment (45%) followed by background sources (diffuse sources) such as atmospheric deposition and weathering (33%), and domestic point sources (19%). The model results confirm the reported

  7. 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.

  8. Deposits of large volcanic debris avalanches at Mount St. Helens and Mount Shasta volcanoes

    SciTech Connect

    Glicken, H.

    1985-01-01

    Large volcanic debris avalanches are among the world's largest mass movements. The rockslide-debris avalanche of the May 18, 1980, eruption of Mount St. Helens produced a 2.8 km/sup 3/ deposit and is the largest historic mass movement. A Pleistocene debris avalanche at Mount Shasta produced a 26 km/sup 3/ deposit that may be the largest Quaternary mass movement. The hummocky deposits at both volcanoes consist of rubble divided into (1) block facies that comprises unconsolidated pieces of the old edifice transported relatively intact, and (2) matrix facies that comprises a mixture of rocks from the old mountain and material picked up from the surrounding terrain. At Mount St. Helens, the juvenile dacite is found in the matrix facies, indicating that matrix facies formed from explosions of the erupting magma as well as from disaggregation and mixing of blocks. The block facies forms both hummocks and interhummock areas in the proximal part of the St. Helens avalanche deposit. At Mount St. Helens, the density of the old cone is 21% greater than the density of the avalanche deposit. Block size decreases with distance. Clast size, measured in the field and by sieving, coverages about a mean with distance, which suggests that blocks disaggregated and mixed together during transport.

  9. Radiative and climate impacts of a large volcanic eruption during stratospheric sulfur geoengineering

    NASA Astrophysics Data System (ADS)

    Laakso, A.; Kokkola, H.; Partanen, A.-I.; Niemeier, U.; Timmreck, C.; Lehtinen, K. E. J.; Hakkarainen, H.; Korhonen, H.

    2016-01-01

    first year after the eruption and again a clearly faster recovery in the concurrent eruption and SRM scenario, which is suspended after the eruption. We also found that an explosive eruption could lead to significantly different regional climate responses depending on whether it takes place during geoengineering or into an unperturbed background atmosphere. Our results imply that observations from previous large eruptions, such as Mount Pinatubo in 1991, are not directly applicable when estimating the potential consequences of a volcanic eruption during stratospheric geoengineering.

  10. Primary multiple sulfur isotopic compositions of pyrite in 2.7 Ga shales from the Joy Lake sequence (Superior Province) show felsic volcanic array-like signature

    NASA Astrophysics Data System (ADS)

    Li, Jianghanyang; Zhang, Zhe; Stern, Richard A.; Hannah, Judith L.; Stein, Holly J.; Yang, Gang; Li, Long

    2017-04-01

    Multiple sulfur isotopes provide a powerful tool to study photochemical and biological processes controlling the Archean sulfur cycle and infer related atmospheric and marine environments. However, our understanding of early Earth's environment remains limited by the availability of well-preserved geological samples, as most Archean sedimentary rocks have experienced some degree of metamorphic alteration. To evaluate sulfur isotopic behavior during post-depositional processes and elucidate the sulfur cycle at 2.7 Ga, we use high-resolution in situ analytical techniques (EPMA and SIMS) to determine elemental compositions and multiple sulfur isotopic compositions of large diagenetic pyrite nodules and fine-grained secondary pyrite disseminated in quartz veins (formed during a lower greenschist metamorphic event) in shales from the 2.7 Ga Joy Lake sequence in the southwest Superior Province. Results show that trace metals and sulfur in the secondary pyrite were derived from both metamorphic fluid and pre-existing diagenetic pyrite. Diagenetic pyrite nodules could have been partially dissolved by metamorphic fluid. But the surviving nodules show elemental and isotopic features different from those of the deduced metamorphic fluid endmember, suggesting the nodules were not geochemically altered by metamorphism, and thus preserve primary isotopic signatures acquired during diagenesis. The sulfur isotopic ratios of pyrite nodules show strong variations, with decreasing δ34S values and increasing Δ33S values from cores to rims. This negative Δ33S-δ34S relationship is different from the commonly observed 'Archean reference line' defined by most Archean pyrite data, but similar to the 'felsic volcanic array'. Our observation provides a first possible case from 2.7 Ga, the age of peak crustal growth in the Archean, to support the hypothesis that photochemical pathways could be different under conditions of intense volcanic emission. This study also shows that high

  11. Subsurface structures of large volcanic complexes on the nearside of the Moon: A view from GRAIL gravity

    NASA Astrophysics Data System (ADS)

    Huang, Qian; Xiao, Zhiyong; Xiao, Long

    2014-11-01

    The lunar nearside large volcanic complexes, such as the Rümker Hills, Aristarchus Plateau, and Marius Hills are likely sites of intense and sustained magmatic activity. These volcanic complexes, recently proposed to be shield volcanoes, are generally located at regionally high elevations and some feature relatively well-localized positive gravity anomalies. Applying localized spectral analyses on high-resolution gravity data obtained from the Gravity Recovery and Interior Laboratory (GRAIL) mission and topography data returned from the Lunar Reconnaissance Orbiter (LRO) spacecraft, we study the subsurface structures of these volcanic complexes. The gravity signal is predicted using a thin elastic lithospheric model that considers both surface and subsurface loads. Best-fit crustal and load densities show that the topographic highs of Rümker Hills, Marius Hills, Gardner and Kepler are mainly composed of material that has a density of more than 2850 kg m-3, which is consistent with that of emplaced igneous rocks. Both the Aristarchus Plateau and Hortensius have relatively lower crustal and surface load densities, with mean values around 2550 kg m-3, which are well consistent with the average bulk density of the lunar highland crust. These results, together with evidence of multiple volcanic edifices on the surface, suggest that the shallow crusts of the Rümker Hills, Marius Hills, Gardner and Kepler are mainly composed of dense intrusive/extrusive magmatic units, and those of the Aristarchus Plateau and Hortensius are mainly composed of low density materials with only small amounts of superimposed volcanic material. To further constrain the subsurface structures beneath these volcanic complexes, we analyze the Bouguer gravity anomalies for these regions. Results show that dense materials that might be solidified intrusions exist beneath Rümker Hills, Marius Hills, Gardner and Prinz, but no substantial dense materials have been detected beneath the Aristarchus

  12. The Whitsunday Volcanic Province, Central Queensland, Australia: lithological and stratigraphic investigations of a silicic-dominated large igneous province

    NASA Astrophysics Data System (ADS)

    Bryan, S. E.; Ewart, A.; Stephens, C. J.; Parianos, J.; Downes, P. J.

    2000-06-01

    Contrary to general belief, not all large igneous provinces (LIPs) are characterised by rocks of basaltic composition. Silicic-dominated LIPs, such as the Whitsunday Volcanic Province of NE Australia, are being increasingly recognised in the rock record. These silicic LIPs are consistent in being: (1) volumetrically dominated by ignimbrite; (2) active over prolonged periods (40-50 m.y.), based on available age data; and (3) spatially and temporally associated with plate break-up. This silicic-dominated LIP, related to the break-up of eastern continental Gondwana, is also significant for being the source of >1.4×10 6 km3 of coeval volcanogenic sediment preserved in adjacent sedimentary basins of eastern Australia. The Whitsunday Volcanic Province is volumetrically dominated by medium- to high-grade, dacitic to rhyolitic lithic ignimbrites. Individual ignimbrite units are commonly between 10 and 100 m thick, and the ignimbrite-dominated sequences exceed 1 km in thickness. Coarse lithic lag breccias containing clasts up to 6 m diameter are associated with the ignimbrites in proximal sections. Pyroclastic surge and fallout deposits, subordinate basaltic to rhyolitic lavas, phreatomagmatic deposits, and locally significant thicknesses of coarse-grained volcanogenic conglomerate and sandstone are interbedded with the ignimbrites. The volcanic sequences are intruded by gabbro/dolerite to rhyolite dykes (up to 50 m in width), sills and comagmatic granite. Dyke orientations are primarily from NW to NNE. The volcanic sequences are characterised by the interstratification of proximal/near-vent lithofacies such as rhyolite domes and lavas, and basaltic agglomerate, with medial to distal facies of ignimbrite. The burial of these near-vent lithofacies by ignimbrites, coupled with the paucity of mass wastage products such as debris-flow deposits indicates a low-relief depositional environment. Furthermore, the volcanic succession records a temporal change in: (1) eruptive styles

  13. Chronology and dynamics of a large silicic magmatic system. Central Taupo volcanic zone, New Zealand

    SciTech Connect

    Houghton, B.F.; Wilson, C.J.N. ); McWilliams, M.O. ); Lanphere, M.A.; Pringle, M.S. ); Weaver, S.D. ); Briggs, R.M. )

    1995-01-01

    The central Taupo Volcanic Zone in New Zealand is a region of intense Quaternary silicic volcanism accompanying rapid extension of continental crust. At least 34 caldera-forming ignimbrite eruptions have produced a complex sequence of relatively short-lived, nested, and/or overlapping volcanic centers over 1.6 m.y. Silicic volcanism at Taupo is similar to the Yellowstone system in size, longevity, thermal flux, and magma output rate. However, Taupo contrasts with Yellowstone in the exceptionally high frequency, but small size, of caldera-forming eruptions. This contrast reflects the thin, rifted nature of the crust, which precludes the development of long-term magmatic cycles at Taupo. 11 refs., 4 figs., 1 tab.

  14. Assessing Resiliency in a Large Lake Receiving Mine Tailings Waste: Impacts of Major Environmental Disturbance.

    NASA Astrophysics Data System (ADS)

    Petticrew, Ellen; Owens, Philip; Albers, Sam

    2016-04-01

    On 4th August 2014, the tailings impoundment of the Mount Polley copper and gold mine in British Columbia failed. Material from the impoundment (surface area = 2.7 km2) flowed into nearby Polley Lake and Hazeltine Creek, before discharging into Quesnel Lake, a large (ca. 100 km long, >500 m deep), relatively pristine lake. Initial estimates suggest that approximately 25 Mm3 of tailings (water and solids) and eroded soils and surficial materials from Hazeltine Creek were delivered to Quesnel Lake, raising the lake by 7.7 cm. Much of this material was deposited at the bottom of Quesnel Lake but a plume of fine-grained sediment (D50 of ca. 1 μm) remained suspended in the water column. The impact of the distribution of this sediment was monitored over the next 15 months using water column profiling for temperature, conductivity, fluorescence and turbidity with depth. The plume movement was regulated by natural processes associated with the physical limnology of this large fjord lake, specifically, seiche events which transferred suspended particles both up-lake, against the flow regime, and down-lake into the Quesnel River. Samples of lake water and bottom sediment taken from the impacted area show elevated levels of total metals and other elements, which may have important ecosystem implications in this watershed. Indeed, the breach occurred at a time when a peak run of sockeye salmon were returning to their natal streams in the Quesnel basin. Zooplankton sampling for metals was initiated in fall 2014 to determine up take of metals into the food web. This poster describes the failure of the impoundment dam and presents results of sampling the aquatic environment over the first fifteen months of impact.

  15. Frequency of large volcanic eruptions over the past 200,000 years

    NASA Astrophysics Data System (ADS)

    Wolff, Eric; Mahony, Sue; Sparks, Steven; Fujita, Shuji; Parrenin, Frédéric; Severi, Mirko; Udisti, Roberto

    2017-04-01

    Volcanic eruptions play an important role in climate forcing, and over longer periods they are an essential component of the budget of carbon dioxide in the atmosphere. Eruptions of different magnitudes pose hazards at different scales to society and ecosystems. However, establishing the past frequency of eruptions of various magnitudes is challenging. Antarctic ice cores, through their record of episodic sulfate deposition, offer the opportunity to establish such frequencies, at least in those cases where sulfur is injected into the stratosphere and deposited globally. A number of difficulties have to be overcome however. Here, we build on recent work that has used large eruption spikes to synchronise records back to 200,000 years, in particular between the East Antarctic sites of Dome C, Dome Fuji and Vostok. In each record, and for each volcano, we can estimate the amount of sulfate deposited above the background across the years following an eruption; in some cases we will use electrical conductivity data as a surrogate for sulfate. By using the three records together we can place uncertainty estimates on the amount of sulfate deposited for each eruption. We will then test methods for assessing the frequency of eruptions above a given magnitude (in terms of sulfate deposition). We will check these methods using synthetic records which can be applied on top of different backgrounds and snowfall rates, and after appropriate diffusion, to confirm that our methods are robust against such differences through 200,000 years. We will finally establish the frequency of large eruptions through two glacial cycles to assess the validity of suggestions that the rate is higher during periods of deglaciation.

  16. The discovery of stromatolites developing at 3570 m above sea level in a high-altitude volcanic lake Socompa, Argentinean Andes.

    PubMed

    Farías, María E; Rascovan, Nicolás; Toneatti, Diego M; Albarracín, Virginia H; Flores, María R; Poiré, Daniel G; Collavino, Mónica M; Aguilar, O Mario; Vazquez, Martin P; Polerecky, Lubos

    2013-01-01

    We describe stromatolites forming at an altitude of 3570 m at the shore of a volcanic lake Socompa, Argentinean Andes. The water at the site of stromatolites formation is alkaline, hypersaline, rich in inorganic nutrients, very rich in arsenic, and warm (20-24°C) due to a hydrothermal input. The stromatolites do not lithify, but form broad, rounded and low-domed bioherms dominated by diatom frustules and aragonite micro-crystals agglutinated by extracellular substances. In comparison to other modern stromatolites, they harbour an atypical microbial community characterized by highly abundant representatives of Deinococcus-Thermus, Rhodobacteraceae, Desulfobacterales and Spirochaetes. Additionally, a high proportion of the sequences that could not be classified at phylum level showed less than 80% identity to the best hit in the NCBI database, suggesting the presence of novel distant lineages. The primary production in the stromatolites is generally high and likely dominated by Microcoleus sp. Through negative phototaxis, the location of these cyanobacteria in the stromatolites is controlled by UV light, which greatly influences their photosynthetic activity. Diatoms, dominated by Amphora sp., are abundant in the anoxic, sulfidic and essentially dark parts of the stromatolites. Although their origin in the stromatolites is unclear, they are possibly an important source of anaerobically degraded organic matter that induces in situ aragonite precipitation. To the best of our knowledge, this is so far the highest altitude with documented actively forming stromatolites. Their generally rich, diverse and to a large extent novel microbial community likely harbours valuable genetic and proteomic reserves, and thus deserves active protection. Furthermore, since the stromatolites flourish in an environment characterized by a multitude of extremes, including high exposure to UV radiation, they can be an excellent model system for studying microbial adaptations under

  17. The Discovery of Stromatolites Developing at 3570 m above Sea Level in a High-Altitude Volcanic Lake Socompa, Argentinean Andes

    PubMed Central

    Farías, María E.; Rascovan, Nicolás; Toneatti, Diego M.; Albarracín, Virginia H.; Flores, María R.; Poiré, Daniel G.; Collavino, Mónica M.; Aguilar, O. Mario; Vazquez, Martin P.; Polerecky, Lubos

    2013-01-01

    We describe stromatolites forming at an altitude of 3570 m at the shore of a volcanic lake Socompa, Argentinean Andes. The water at the site of stromatolites formation is alkaline, hypersaline, rich in inorganic nutrients, very rich in arsenic, and warm (20–24°C) due to a hydrothermal input. The stromatolites do not lithify, but form broad, rounded and low-domed bioherms dominated by diatom frustules and aragonite micro-crystals agglutinated by extracellular substances. In comparison to other modern stromatolites, they harbour an atypical microbial community characterized by highly abundant representatives of Deinococcus-Thermus, Rhodobacteraceae, Desulfobacterales and Spirochaetes. Additionally, a high proportion of the sequences that could not be classified at phylum level showed less than 80% identity to the best hit in the NCBI database, suggesting the presence of novel distant lineages. The primary production in the stromatolites is generally high and likely dominated by Microcoleus sp. Through negative phototaxis, the location of these cyanobacteria in the stromatolites is controlled by UV light, which greatly influences their photosynthetic activity. Diatoms, dominated by Amphora sp., are abundant in the anoxic, sulfidic and essentially dark parts of the stromatolites. Although their origin in the stromatolites is unclear, they are possibly an important source of anaerobically degraded organic matter that induces in situ aragonite precipitation. To the best of our knowledge, this is so far the highest altitude with documented actively forming stromatolites. Their generally rich, diverse and to a large extent novel microbial community likely harbours valuable genetic and proteomic reserves, and thus deserves active protection. Furthermore, since the stromatolites flourish in an environment characterized by a multitude of extremes, including high exposure to UV radiation, they can be an excellent model system for studying microbial adaptations under

  18. High-frequency remote monitoring of large lakes with MODIS 500 m imagery

    USGS Publications Warehouse

    McCullough, Ian M.; Loftin, Cynthia S.; Sader, Steven A.

    2012-01-01

    Satellite-based remote monitoring programs of regional lake water quality largely have relied on Landsat Thematic Mapper (TM) owing to its long image archive, moderate spatial resolution (30 m), and wide sensitivity in the visible portion of the electromagnetic spectrum, despite some notable limitations such as temporal resolution (i.e., 16 days), data pre-processing requirements to improve data quality, and aging satellites. Moderate-Resolution Imaging Spectroradiometer (MODIS) sensors on Aqua/Terra platforms compensate for these shortcomings, although at the expense of spatial resolution. We developed and evaluated a remote monitoring protocol for water clarity of large lakes using MODIS 500 m data and compared MODIS utility to Landsat-based methods. MODIS images captured during May–September 2001, 2004 and 2010 were analyzed with linear regression to identify the relationship between lake water clarity and satellite-measured surface reflectance. Correlations were strong (R² = 0.72–0.94) throughout the study period; however, they were the most consistent in August, reflecting seasonally unstable lake conditions and inter-annual differences in algal productivity during the other months. The utility of MODIS data in remote water quality estimation lies in intra-annual monitoring of lake water clarity in inaccessible, large lakes, whereas Landsat is more appropriate for inter-annual, regional trend analyses of lakes ≥ 8 ha. Model accuracy is improved when ancillary variables are included to reflect seasonal lake dynamics and weather patterns that influence lake clarity. The identification of landscape-scale drivers of regional water quality is a useful way to supplement satellite-based remote monitoring programs relying on spectral data alone.

  19. Large volcanic eruptions affect climate in many more ways than just cooling (Invited)

    NASA Astrophysics Data System (ADS)

    Ward, P. L.

    2009-12-01

    . Each of the largest sulfur-emitting eruptions since 1600 (Huaynaputina, Laki, Tambora, Krakatau, Santa Maria, Novarupta, Pinatubo) were in the same year as moderate to strong El Niños but were typically followed by very strong El Niños within 6 to 8 years (Data: Bradley and Jones, 1992). During El Niños, warm water heats the tropical Pacific atmosphere. Many ocean currents are affected over short time scales by atmospheric teleconnections but then affect atmospheric conditions over longer time scales. The sum of these processes with different time constants varies when the rate of volcanic activity changes by orders of magnitude. Ward (2009, doi:10.1016/j.tsf.2009.01.005) presents data suggesting large eruptions occurring on average once per century (current rate) provide only short-term changes in climate, but when they occur every few decades, they supplement Milanković cycles and increment the world into ice ages, and when they occur as often as once per year, they cause rapid global warming. Volcanic-like sulfate deposited in Greenland from man burning fossil fuels between 1930 and 1980 was as high as the highest levels of sulfate deposited during rapid warming at the end of the last ice age. Man did not eject sulfur into the stratosphere, but it remained in the atmosphere long enough to be deposited in Greenland. Understanding how volcanoes caused abrupt warming in the past would help us understand how man is causing abrupt warming today.

  20. Shifts between ammonia-oxidizing bacteria and archaea in relation to nitrification potential across trophic gradients in two large Chinese lakes (Lake Taihu and Lake Chaohu).

    PubMed

    Hou, Jie; Song, Chunlei; Cao, Xiuyun; Zhou, Yiyong

    2013-05-01

    Ammonia oxidation plays a pivotal role in the cycling and removal of nitrogen in aquatic ecosystems. Recent findings have expanded the known ammonia-oxidizing prokaryotes from Bacteria to Archaea. However, the relative importance of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) in nitrification is still debated. Here we showed that, in two large eutrophic lakes in China (Lake Taihu and Lake Chaohu), the abundance of AOA and AOB varied in opposite patterns according to the trophic state, although both AOA and AOB were abundant. In detail, from mesotrophic to eutrophic sites, the AOA abundance decreased, while the AOB increased in abundance and outnumbered the AOA at hypertrophic sites. In parallel, the nitrification rate increased along these trophic gradients and was significantly correlated with both the AOB abundance and the numerical ratio of AOB to AOA. Phylogenetic analysis of bacterial amoA sequences showed that Nitrosomonas oligotropha- and Nitrosospira-affiliated AOB dominated in both lakes, while Nitrosomonas communis-related AOB were only detected at the eutrophic sites. The diversity of AOB increased from mesotrophic to eutrophic sites and was positively correlated with the nitrification rate. Overall, this study enhances our understanding of the ecology of ammonia-oxidizing prokaryotes by elucidating conditions that AOB may numerically predominated over AOA, and indicated that AOA may play a less important role than AOB in the nitrification process of eutrophic lakes.

  1. Magmatic gas emissions at Holocene volcanic features near Mono Lake, California, and their relation to regional magmatism

    USGS Publications Warehouse

    Bergfeld, D.; Evans, William C.; Howle, James F.; Hunt, Andrew G.

    2015-01-01

    Silicic lavas have erupted repeatedly in the Mono Basin over the past few thousand years, forming the massive domes and coulees of the Mono Craters chain and the smaller island vents in Mono Lake. We report here on the first systematic study of magmatic CO2 emissions from these features, conducted during 2007–2010. Most notably, a known locus of weak steam venting on the summit of North Coulee is actually enclosed in a large area (~ 0.25 km2) of diffuse gas discharge that emits 10–14 t/d of CO2, mostly at ambient temperature. Subsurface gases sampled here are heavily air-contaminated, but after standard corrections are applied, show average δ13C-CO2 of − 4.72‰, 3He/4He of 5.89RA, and CO2/3He of 0.77 × 1010, very similar to the values in fumarolic gas from Mammoth Mountain and the Long Valley Caldera immediately to the south of the basin. If these values also characterize the magmatic gas source at Mono Lake, where CO2 is captured by the alkaline lake water, a magmatic CO2 upflow beneath the lake of ~ 4 t/d can be inferred. Groundwater discharge from the Mono Craters area transports ~ 13 t/d of 14C-dead CO2 as free gas and dissolved carbonate species, and adding in this component brings the estimated total magmatic CO2 output to 29 t/d for the two silicic systems in the Mono Basin. If these emissions reflect intrusion and degassing of underlying basalt with 0.5 wt.% CO2, a modest intrusion rate of 0.00075 km3/yr is indicated. Much higher intrusion rates are required to account for CO2 emissions from Mammoth Mountain and the West Moat of the Long Valley Caldera.

  2. Large Water Management Projects and Schistosomiasis Control, Dongting Lake Region, China

    PubMed Central

    Li, Yue-Sheng; Zhao, Zheng-Yuan; He, Yong-Kang; Ellis, Magda K.; McManus, Donald P.

    2007-01-01

    Construction of the Three Gorges Dam across the Yangtze River will substantially change the ecology of the Dongting Lake in southern China. In addition, the Central and Hunan Provinces’ governmental authorities have instigated a Return Land to Lake Program that will extend the Dongting Lake surface area from the current 2,681 km2 to 4,350 km2.The previous construction of embankments and the large silt deposits made by the Yangtze River and other connecting rivers have contributed to frequent disastrous flooding. As a consequence of the 2 water projects, >2 million persons and their domestic animals are being resettled. This article provides an overview of the historical background of these 2 large water management projects, the associated population movement, and their impact on future transmission and control of schistosomiasis in the Dongting Lake area. The dam will likely substantially extend the range of the snail habitats and increase schistosome transmission and schistosomiasis cases. PMID:18214167

  3. The climatic effects of the direct injection of water vapour into the stratosphere by large volcanic eruptions

    NASA Astrophysics Data System (ADS)

    Joshi, M. M.; Jones, G. S.

    2009-03-01

    We describe a novel mechanism that can significantly lower the amplitude of the climatic response to certain large volcanic eruptions. The proximity of oceans to some volcanoes can cause significant entrainment of water into coignimbrite clouds during the eruption. If sufficiently large amounts of this entrained water vapour enter the stratosphere, a climatically significant amount of water vapour can be left over in the lower stratosphere after the eruption, even after sulphate aerosol formation. This excess stratospheric humidity warms the climate, and acts to balance the climatic cooling induced by the volcanic aerosol, especially because the humidity anomaly lasts for a period that is longer that the residence time of aerosol in the stratosphere. In particular, Northern Hemisphere cooling is reduced in magnitude. We discuss this mechanism in the context of the discrepancy between the observed and modelled cooling following the Krakatau eruption in 1883.

  4. Effects of wind wave turbulence on the phytoplankton community composition in large, shallow Lake Taihu.

    PubMed

    Zhou, Jian; Qin, Boqiang; Casenave, Céline; Han, Xiaoxia; Yang, Guijun; Wu, Tingfeng; Wu, Pan; Ma, Jianrong

    2015-08-01

    Wind waves are responsible for some of the spatio-temporal gradients observed in the biotic and abiotic variables in large shallow lakes. However, their effects on the phytoplankton community composition are still largely unexplored especially in freshwater systems such as lakes. In this paper, using field observations and mesocosm bioassay experiments, we investigated the impact of turbulence generated by wind waves on the phytoplankton community composition (especially on harmful cyanobacteria) in Lake Taihu, a large, shallow eutrophic lake in China. The composition of the phytoplankton community varied with the intensity of wind waves in the different areas of the lake. During summer, when wind waves were strong in the central lake, diatoms and green algae seemed to dominate while harmful cyanobacteria dominated in the weakly influenced Meiliang Bay. Turbulence bioassays also showed that diatoms and green algae were favoured by turbulent mixing. The critical time for the shift of the phytoplankton community composition was approximately 10 days under turbulent conditions. However, short-term (6 days) turbulence is rather beneficial for the dominance of cyanobacteria. This study suggests that the duration of wind events and their associated hydrodynamics are key factors to understanding the temporal and spatial changes of phytoplankton communities.

  5. Recruitment of Total Phytoplankton, Chlorophytes and Cyanobacteria from Lake Sediments Recorded by Photosynthetic Pigments in a Large, Shallow Lake (Lake Taihu, China)

    NASA Astrophysics Data System (ADS)

    Cao, Huan-Sheng; Kong, Fan-Xiang; Tan, Jian-Kang; Zhang, Xiao-Feng; Tao, Yi; Yang, Zhou

    2005-08-01

    Recruitment of total phytoplankton, chlorophytes and cyanobacteria from lake sediments to the water column was studied using photosynthetic pigments at one site (1.5 m) in Lake Taihu, a large shallow lake in China. Samples were taken weekly from the migration traps installed on the bottom from March to May 2004. Abundance of total phytoplankton, chlorophytes and cyanobacteria were represented by Chlorophyll (Chl) a, b, and phycocyanin (PC), respectively. Over the three months, total phytoplankton, chlorophytes, and cyanobacteria corresponding to 48.9%, 68.9% and 316.2% of their initial concentrations in surface sediments were recruited in Lake Taihu. However, compared with their increase in pelagic abundance over the same period, the recruitment accounted for a rather small inoculum. Accompanying the recruitment, total phytoplankton and chlorophytes declined and cyanobacteria increased in the upper 0-2 cm sediments; colonies of Microcystis aeruginosa in the water column enlarged from small size with several cells to large colonies with hundreds of cells. Thus, overwintering and subsequent growth renewal of pelagic phytoplankton merits further study and comparison with benthic survival and recruitment.

  6. Oxygen isotope evolution of the Lake Owyhee volcanic field, Oregon, and implications for low-δ18O magmas of the Snake River Plain - Yellowstone hotspot

    NASA Astrophysics Data System (ADS)

    Blum, T.; Kitajima, K.; Nakashima, D.; Valley, J. W.

    2013-12-01

    The Snake River Plain - Yellowstone (SRP-Y) hotspot trend is one of the largest known low-δ18O magmatic provinces, yet the timing and distribution of hydrothermal alteration relative to hotspot magmatism remains incompletely understood. Existing models for SRP-Y low-δ18O magma genesis differ regarding the timing of protolith alteration (e.g. Eocene vs. present), depth at which alteration occurs (e.g. 15 km vs. <5 km), and physical controls on the extent of alteration (e.g. caldera collapse, crustal scale fluid flow, etc.). We expand the existing oxygen isotope data set for zircon in the Lake Owyhee volcanic field (LOVF) of east central Oregon to further identify magmatic oxygen isotope trends within the field. These data offer insight into the timing of alteration and the extent of the greater SRP-Y low-δ18O province, as well as the conditions that generate large low-δ18O provinces. 16-14 Ma silicic volcanism in the LOVF is linked to the pre-14 Ma SRP-Y hotspot, with volcanism partially overlapping extension in the north-south trending Oregon-Idaho Graben (OIG). Ion microprobe analyses of zircons from 16 LOVF silicic lavas and tuffs reveal homogeneous zircons on both the single grain and hand sample scales: individual samples have 2 S.D. for δ18O ranging from 0.27 to 0.96‰ (SMOW), and sample averages ranging from 1.8 to 6.0‰, excluding texturally chaotic and/or porous zircons which have δ18O values as low as 0.0‰. All low-δ18O LOVF magmas, including the caldera-forming Tuff of Leslie Gulch and Tuff of Spring Creek, are confined to the OIG, although not all zircons from within the OIG have low δ18O values. The presence and sequence of low-δ18O magmas in the LOVF and adjacent central Snake River Plain (CSRP) cannot be explained by existing caldera subsidence or pre-hotspot source models. These data, however, combined with volumetrically limited low-δ18O material in the adjacent Idaho Batholith and Basin and Range, are consistent with low-δ18O magmas

  7. Response to comments on "Large volcanic aerosol load in the stratosphere linked to Asian monsoon transport".

    PubMed

    Bourassa, Adam E; Robock, Alan; Randel, William J; Deshler, Terry; Rieger, Landon A; Lloyd, Nicholas D; Llewellyn, E J; Degenstein, Douglas A

    2013-02-08

    Fromm et al. and Vernier et al. suggest that their analyses of satellite measurements indicate that the main part of the Nabro volcanic plume from the eruption on 13 June 2011 was directly injected into the stratosphere. We address these analyses and, in addition, show that both wind trajectories and height-resolved profiles of sulfur dioxide indicate that although the eruption column may have extended higher than the Smithsonian report we highlighted, it was overwhelmingly tropospheric. Additionally, the height-resolved sulfur dioxide profiles provide further convincing evidence for convective transport of volcanic gas to the stratosphere from deep convection associated with the Asian monsoon.

  8. Comment on "Large volcanic aerosol load in the stratosphere linked to Asian monsoon transport".

    PubMed

    Vernier, J-P; Thomason, L W; Fairlie, T D; Minnis, P; Palikonda, R; Bedka, K M

    2013-02-08

    Bourassa et al. (Reports, 6 July 2012, p. 78) have suggested that deep convection associated with the Asian monsoon played a critical role in transporting sulfur dioxide associated with the Nabro volcanic eruption (13 June 2011) from the upper troposphere (9 to 14 kilometers) into the lower stratosphere. An analysis of the CALIPSO lidar data indicates, however, that the main part of the Nabro volcanic plume was injected directly into the lower stratosphere during the initial eruption well before reaching the Asian monsoon deep convective region.

  9. Volcanism on Venus: Large shields and major accumulations of small domes

    NASA Technical Reports Server (NTRS)

    Schaber, Gerald G.; Kozak, Richard C.

    1989-01-01

    The outer layers of the Venusian lithosphere appear to dissipate heat from the interior through mantle-driven thermal anomalies (hot spots, swells). As a result, Venus exhibits diverse forms of thin-skin tectonism and magmatic transfer to and extrusion from countless numbers of volcanic centers (e.g., shields, paterae, domes) and volcano-tectonic complexes (e.g., coronae, arachnoids). What is known about the distribution and morphologies of major Venusian shields is summarized, and the evidence for possible structural control of major accumulations as long as 5000 km of small volcanic domes is described.

  10. Acoustic telemetry reveals large-scale migration patterns of walleye in Lake Huron

    USGS Publications Warehouse

    Hayden, Todd A.; Holbrook, Christopher; Fielder, David G.; Vandergoot, Christopher S.; Bergstedt, Roger A.; Dettmers, John M.; Krueger, Charles C.; Cooke, Steven J.

    2014-01-01

    Fish migration in large freshwater lacustrine systems such as the Laurentian Great Lakes is not well understood. The walleye (Sander vitreus) is an economically and ecologically important native fish species throughout the Great Lakes. In Lake Huron walleye has recently undergone a population expansion as a result of recovery of the primary stock, stemming from changing food web dynamics. During 2011 and 2012, we used acoustic telemetry to document the timing and spatial scale of walleye migration in Lake Huron and Saginaw Bay. Spawning walleye (n = 199) collected from a tributary of Saginaw Bay were implanted with acoustic tags and their migrations were documented using acoustic receivers (n = 140) deployed throughout U.S. nearshore waters of Lake Huron. Three migration pathways were described using multistate mark-recapture models. Models were evaluated using the Akaike Information Criterion. Fish sex did not influence migratory behavior but did affect migration rate and walleye were detected on all acoustic receiver lines. Most (95%) tagged fish migrated downstream from the riverine tagging and release location to Saginaw Bay, and 37% of these fish emigrated from Saginaw Bay into Lake Huron. Remarkably, 8% of walleye that emigrated from Saginaw Bay were detected at the acoustic receiver line located farthest from the release location more than 350 km away. Most (64%) walleye returned to the Saginaw River in 2012, presumably for spawning. Our findings reveal that fish from this stock use virtually the entirety of U.S. nearshore waters of Lake Huron.

  11. Acoustic Telemetry Reveals Large-Scale Migration Patterns of Walleye in Lake Huron

    PubMed Central

    Hayden, Todd A.; Holbrook, Christopher M.; Fielder, David G.; Vandergoot, Christopher S.; Bergstedt, Roger A.; Dettmers, John M.; Krueger, Charles C.; Cooke, Steven J.

    2014-01-01

    Fish migration in large freshwater lacustrine systems such as the Laurentian Great Lakes is not well understood. The walleye (Sander vitreus) is an economically and ecologically important native fish species throughout the Great Lakes. In Lake Huron walleye has recently undergone a population expansion as a result of recovery of the primary stock, stemming from changing food web dynamics. During 2011 and 2012, we used acoustic telemetry to document the timing and spatial scale of walleye migration in Lake Huron and Saginaw Bay. Spawning walleye (n = 199) collected from a tributary of Saginaw Bay were implanted with acoustic tags and their migrations were documented using acoustic receivers (n = 140) deployed throughout U.S. nearshore waters of Lake Huron. Three migration pathways were described using multistate mark-recapture models. Models were evaluated using the Akaike Information Criterion. Fish sex did not influence migratory behavior but did affect migration rate and walleye were detected on all acoustic receiver lines. Most (95%) tagged fish migrated downstream from the riverine tagging and release location to Saginaw Bay, and 37% of these fish emigrated from Saginaw Bay into Lake Huron. Remarkably, 8% of walleye that emigrated from Saginaw Bay were detected at the acoustic receiver line located farthest from the release location more than 350 km away. Most (64%) walleye returned to the Saginaw River in 2012, presumably for spawning. Our findings reveal that fish from this stock use virtually the entirety of U.S. nearshore waters of Lake Huron. PMID:25506913

  12. Planktic Tychonema (Cyanobacteria) in the large lakes south of the Alps: phylogenetic assessment and toxigenic potential.

    PubMed

    Salmaso, Nico; Cerasino, Leonardo; Boscaini, Adriano; Capelli, Camilla

    2016-10-01

    This work allowed assessing a widespread occurrence of Tychonema bourrellyi in the largest lakes south of the Alps (Garda, Iseo, Como and Maggiore). The taxonomy of the species was confirmed adopting a polyphasic approach, which included microscopic examinations, molecular (16S rRNA and rbcLX sequences) and (Lake Garda) ecological characterisations. Over 70% of the 36 isolates of Tychonema sampled from the four lakes tested positive for the presence of genes implicated in the biosynthesis of anatoxins (anaF and/or anaC) and for the production of anatoxin-a (ATX) and homoanatoxin-a (HTX). A detailed analysis carried out in Lake Garda showed strong ongoing changes in the cyanobacterial community, with populations of Tychonema developing with higher biovolumes compared to the microcystins (MCs) producer Planktothrix rubescens Moreover, the time × depth distribution of Tychonema was paralleled by a comparable distribution of ATX and HTX. The increasing importance of Tychonema in Lake Garda was also suggested by the opposite trends of ATX and MCs observed since 2009. These results suggest that radical changes are occurring in the largest lakes south of the Alps. Their verification and implications will require to be assessed by extending a complete experimental work to the other large perialpine lakes. © FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  13. Biogeochemical processes involving dissolved CO2 and CH4 at Albano, Averno, and Monticchio meromictic volcanic lakes (Central-Southern Italy)

    NASA Astrophysics Data System (ADS)

    Cabassi, Jacopo; Tassi, Franco; Vaselli, Orlando; Fiebig, Jens; Nocentini, Matteo; Capecchiacci, Francesco; Rouwet, Dmitri; Bicocchi, Gabriele

    2013-01-01

    This paper focuses on the chemical and isotopic features of dissolved gases (CH4 and CO2) from four meromictic lakes hosted in volcanic systems of Central-Southern Italy: Lake Albano (Alban Hills), Lake Averno (Phlegrean Fields), and Monticchio Grande and Piccolo lakes (Mt. Vulture). Deep waters in these lakes are characterized by the presence of a significant reservoir of extra-atmospheric dissolved gases mainly consisting of CH4 and CO2. The δ13C-CH4 and δD-CH4 values of dissolved gas samples from the maximum depths of the investigated lakes (from -66.8 to -55.6 ‰ V-PDB and from -279 to -195 ‰ V-SMOW, respectively) suggest that CH4 is mainly produced by microbial activity. The δ13C-CO2 values of Lake Grande, Lake Piccolo, and Lake Albano (ranging from -5.8 to -0.4 ‰ V-PDB) indicate a significant CO2 contribution from sublacustrine vents originating from (1) mantle degassing and (2) thermometamorphic reactions involving limestone, i.e., the same CO2 source feeding the regional thermal and cold CO2-rich fluid emissions. In contrast, the relatively low δ13C-CO2 values (from -13.4 to -8.2 ‰ V-PDB) of Lake Averno indicate a prevalent organic CO2. Chemical and isotopic compositions of dissolved CO2 and CH4 at different depths are mainly depending on (1) CO2 inputs from external sources (hydrothermal and/or anthropogenic); (2) CO2-CH4 isotopic exchange; and (3) methanogenic and methanotrophic activity. In the epilimnion, vertical water mixing, free oxygen availability, and photosynthesis cause the dramatic decrease of both CO2 and CH4 concentrations. In the hypolimnion, where the δ13C-CO2 values progressively increase with depth and the δ13C-CH4 values show an opposite trend, biogenic CO2 production from CH4 using different electron donor species, such as sulfate, tend to counteract the methanogenesis process whose efficiency achieves its climax at the water-bottom sediment interface. Theoretical values, calculated on the basis of δ13C-CO2 values, and

  14. Advances in estimating the climate sensibility of a large lake using scenario simulations

    NASA Astrophysics Data System (ADS)

    Eder, M. M.; Schlabing, D.; Frassl, M. A.; Rinke, K.; Bárdossy, A.

    2012-04-01

    The vertical mixing behaviour of large deep lakes as e.g. Lake Constance is reflecting the long-term meteorological conditions and therefore is likely to be sensible to climate change. Today, Lake Constance does not mix completely every year, but only once in 2-3 years, which leads to the typical saw-tooth pattern in the deep water temperature. Whether complete mixing does occur is not only depending on the meteorological conditions in the respective winter period, but also on the thermal conditions in the lake and hence on the meteorological conditions in the preceding years. The lake's response to climate change thus depends on the temperature increase itself as well as on its gradient and on the inter-annual variability of the meteorological variables. Last year we showed first steps towards a model system to evaluate possible effects of climate change on Lake Constance: The Vector-Autoregressive Weathergenerator VG produces time series of meteorological data, which are used as boundary conditions for the 3D hydrodynamic lake model ELCOM (Centre of Water Research, University of Western Australia). As VG gives the opportunity to change mean and variability of selected variables, "What if?" - scenarios for process understanding can be performed. The time scales of variability turned out to be a critical point in the artificial time series for modelling the hydrodynamics of Lake Constance, as the big water body integrates over time and thus the hydrodynamics overlook the variability of air temperature on short time scales. Therefore, VG was developed further, especially with respect to the time scales of variability. While for heat input, the time scale of several days to weeks seems to be more important, wind and, when biology is modelled, short-wave radiation should be given at a sub-daily timestep. Besides producing user-defined scenario time-series, VG can also be used to stochastical downscale output of global climate model IPCC scenarios for lake modelling

  15. Large increases in carbon burial in northern lakes during the Anthropocene

    PubMed Central

    Heathcote, Adam J.; Anderson, N. John; Prairie, Yves T.; Engstrom, Daniel R.; del Giorgio, Paul A.

    2015-01-01

    Northern forests are important ecosystems for carbon (C) cycling and lakes within them process and bury large amounts of organic-C. Current burial estimates are poorly constrained and may discount other shifts in organic-C burial driven by global change. Here we analyse a suite of northern lakes to determine trends in organic-C burial throughout the Anthropocene. We found burial rates increased significantly over the last century and are up to five times greater than previous estimates. Despite a correlation with temperature, warming alone did not explain the increase in burial, suggesting the importance of other drivers including atmospherically deposited reactive nitrogen. Upscaling mean lake burial rates for each time period to global northern forests yields up to 4.5 Pg C accumulated in the last 100 years—20% of the total burial over the Holocene. Our results indicate that lakes will become increasingly important for C burial under future global change scenarios. PMID:26607672

  16. Large increases in carbon burial in northern lakes during the Anthropocene.

    PubMed

    Heathcote, Adam J; Anderson, N John; Prairie, Yves T; Engstrom, Daniel R; del Giorgio, Paul A

    2015-11-26

    Northern forests are important ecosystems for carbon (C) cycling and lakes within them process and bury large amounts of organic-C. Current burial estimates are poorly constrained and may discount other shifts in organic-C burial driven by global change. Here we analyse a suite of northern lakes to determine trends in organic-C burial throughout the Anthropocene. We found burial rates increased significantly over the last century and are up to five times greater than previous estimates. Despite a correlation with temperature, warming alone did not explain the increase in burial, suggesting the importance of other drivers including atmospherically deposited reactive nitrogen. Upscaling mean lake burial rates for each time period to global northern forests yields up to 4.5 Pg C accumulated in the last 100 years--20% of the total burial over the Holocene. Our results indicate that lakes will become increasingly important for C burial under future global change scenarios.

  17. Long-term development of hypolimnetic oxygen depletion rates in the large Lake Constance.

    PubMed

    Rhodes, Justin; Hetzenauer, Harald; Frassl, Marieke A; Rothhaupt, Karl-Otto; Rinke, Karsten

    2017-01-30

    This study investigates over 30 years of dissolved oxygen dynamics in the deep interior of Lake Constance (max. depth: 250 m). This lake supplies approximately four million people with drinking water and has undergone strong re-oligotrophication over the past decades. We calculated depth-specific annual oxygen depletion rates (ODRs) during the period of stratification and found that 50% of the observed variability in ODR was already explained by a simple separation into a sediment- and volume-related oxygen consumption. Adding a linear factor for water depth further improved the model indicating that oxygen depletion increased substantially along the depth. Two other factors turned out to significantly influence ODR: total phosphorus as a proxy for the lake's trophic state and mean oxygen concentration in the respective depth layer. Our analysis points to the importance of nutrient reductions as effective management measures to improve and protect the oxygen status of such large and deep lakes.

  18. An approach to simulation of large lake-aquifer-systems: Semi-arid Nebraska Sandhills, USA

    NASA Astrophysics Data System (ADS)

    Zlotnik, Vitaly; Rossman, Nathan; Rowe, Clinton

    2017-04-01

    In many regions of the world, large systems of shallow water bodies include hundreds and thousands of lakes and wetlands, integrated with climate- and human-controlled groundwater. In some cases, like in China and Mongolia, a dramatic reduction of areas and numbers of such lakes is observed. Disparity between spatial-temporal scales of each surface-water body and the entire system presents grand challenge to their modeling, and practical approaches are needed. We explore feasibility of modeling for the Nebraska Sand Hills (48,000 sq. km), a large, grass-stabilized dune region containing thousands of small closed-basin lakes and wetlands in hydraulic connection with the Northern High Plains aquifer. Groundwater recharge (GR), critical to the existence of lakes and wetlands in the semi-arid climate, was assessed using projected changes in decadal averages of the difference between precipitation and evapotranspiration under the 21st century GR scenarios. Sixteen downscaled Global Circulation Models (ran through the Variable Infiltration Capacity Land Surface Model) and three greenhouse emission scenarios produced median, wet, and dry GR scenarios, accounting for uncertainty in forecasts. Instead of tracking lakes individually, we propose to identify lakes as areas where the simulated regional water table exceeds land surface elevation DEM, and wetlands as areas where the water table is within 3 m from the land surface. Baseflow, the area, and numbers of lakes and wetlands were simulated using a calibrated groundwater flow model. Results indicate mild increase of lake and wetland numbers and total areas for median GR scenario by the end of century. More dramatic changes can be expected, if wet or dry GR scenarios will be realized. At intermediate times, some inversions between different scenarios are possible. Results are consistent with studies of the future GR in the High Plains and indicate feasibility of the proposed approach.

  19. Ground-water, large-lake interactions in Saginaw Bay, Lake Huron: A geochemical and isotopic approach

    USGS Publications Warehouse

    Kolak, J.J.; Long, D.T.; Matty, J.M.; Larson, G.J.; Sibley, D.F.; Councell, T.B.

    1999-01-01

    Delineating the nature and extent of ground-water inputs is necessary to understand the hydrochemistry of large lakes. Characterizing the interaction between ground water and large lakes (e.g., the Great Lakes) is facilitated by the use of geochemical and isotopic data. In this study, pore waters were extracted from sediment cores collected from Saginaw Bay and the surrounding Saginaw lowland area; the geochemistry and stable isotope signature of these pore waters were used to identify sources for the water and solutes. Cores from Saginaw Bay and the Saginaw lowland area yielded strong vertical gradients in chloride concentrations, suggesting that a high-chloride source is present at depth. The spatial distribution of cores with elevated chloride concentrations corresponds to the regional distribution of chloride in ground water. Most of the Saginaw lowland area cores contain water with significantly lower ??18O values than modern meteoric water, suggesting that the water had been recharged during a much cooler climate. The ??18O values measured in pore waters (from Saginaw Bay cores) containing high chloride concentrations are similar to modern meteoric water; however, values lighter than modern meteoric water are encountered at depth. Chloride:bromide ratios, used to distinguish between different chloride sources, identify formation brine as the likely source for chloride. Transport models indicate that a combination of advection and diffusion is responsible for the observed Saginaw lowland area pore-water profiles. Pore-water profiles in Saginaw Bay sediments are produced primarily by diffusion and require significantly less time to evolve. An upward flux of solutes derived from formation brine could occur elsewhere within the Great Lakes region and significantly affect the geochemical cycling of chloride and other contaminants (e.g., trace metals).

  20. The first second of volcanic eruptions from the Erebus volcano lava lake, Antarctica—Energies, pressures, seismology, and infrasound

    NASA Astrophysics Data System (ADS)

    Gerst, A.; Hort, M.; Aster, R. C.; Johnson, J. B.; Kyle, P. R.

    2013-07-01

    We describe a multiparameter experiment at Erebus volcano, Antarctica, employing Doppler radar, video, acoustic, and seismic observations to estimate the detailed energy budget of large (up to 40 m-diameter) bubble bursts from a persistent phonolite lava lake. These explosions are readily studied from the crater rim at ranges of less than 500 m and present an ideal opportunity to constrain the dynamics and mechanism of magmatic bubble bursts that can drive Strombolian and Hawaiian eruptions. We estimate the energy budget of the first second of a typical Erebus explosion as a function of time and energy type. We constrain gas pressures and forces using an analytic model for the expansion of a gas bubble above a conduit that incorporates conduit geometry and magma and gas parameters. The model, consistent with video and radar observations, invokes a spherical bulging surface with a base diameter equal to that of the lava lake. The model has no ad hoc free parameters, and geometrical calculations predict zenith height, velocity, and acceleration during shell expansion. During explosions, the energy contained in hot overpressured gas bubbles is freed and partitioned into other energy types, where by far the greatest nonthermal energy component is the kinetic and gravitational potential energy of the accelerated magma shell (>109 J). Seismic source energy created by explosions is estimated from radar measurements and is consistent with source energy determined from seismic observations. For the generation of the infrasonic signal, a dual mechanism incorporating a terminally disrupted slug is proposed, which clarifies previous models and provides good fits to observed infrasonic pressures. A new and straightforward method is presented for determining gas volumes from slug explosions at volcanoes from remote infrasound recordings.

  1. Volcanic activity before and after large tectonic earthquakes: Observations and statistical significance

    NASA Astrophysics Data System (ADS)

    Eggert, S.; Walter, T. R.

    2009-04-01

    The study of volcanic triggering and coupling to the tectonic surroundings has received special attention in recent years, using both direct field observations and historical descriptions of eruptions and earthquake activity. Repeated reports of volcano-earthquake interactions in, e.g., Europe and Japan, may imply that clustered occurrence is important in some regions. However, the regions likely to suffer clustered eruption-earthquake activity have not been systematically identified, and the processes responsible for the observed interaction are debated. We first review previous works about the correlation of volcanic eruptions and earthquakes, and describe selected local clustered events. Following an overview of previous statistical studies, we further elaborate the databases of correlated eruptions and earthquakes from a global perspective. Since we can confirm a relationship between volcanic eruptions and earthquakes on the global scale, we then perform a statistical study on the regional level, showing that time and distance between events follow a linear relationship. In the time before an earthquake, a period of volcanic silence often occurs, whereas in the time after, an increase in volcanic activity is evident. Our statistical tests imply that certain regions are especially predisposed to concurrent eruption-earthquake pairs, e.g., Japan, whereas such pairing is statistically less significant in other regions, such as Europe. Based on this study, we argue that individual and selected observations may bias the perceptible weight of coupling. Volcanoes located in the predisposed regions (e.g., Japan, Indonesia, Melanesia), however, indeed often have unexpectedly changed in association with either an imminent or a past earthquake.

  2. High-levels of microplastic pollution in a large, remote, mountain lake.

    PubMed

    Free, Christopher M; Jensen, Olaf P; Mason, Sherri A; Eriksen, Marcus; Williamson, Nicholas J; Boldgiv, Bazartseren

    2014-08-15

    Despite the large and growing literature on microplastics in the ocean, little information exists on microplastics in freshwater systems. This study is the first to evaluate the abundance, distribution, and composition of pelagic microplastic pollution in a large, remote, mountain lake. We quantified pelagic microplastics and shoreline anthropogenic debris in Lake Hovsgol, Mongolia. With an average microplastic density of 20,264 particles km(-2), Lake Hovsgol is more heavily polluted with microplastics than the more developed Lakes Huron and Superior in the Laurentian Great Lakes. Fragments and films were the most abundant microplastic types; no plastic microbeads and few pellets were observed. Household plastics dominated the shoreline debris and were comprised largely of plastic bottles, fishing gear, and bags. Microplastic density decreased with distance from the southwestern shore, the most populated and accessible section of the park, and was distributed by the prevailing winds. These results demonstrate that without proper waste management, low-density populations can heavily pollute freshwater systems with consumer plastics. Copyright © 2014 Elsevier Ltd. All rights reserved.

  3. The Large Lake Effect on Mackenzie River Flow: an Isotopic Perspective

    NASA Astrophysics Data System (ADS)

    Gibson, J. J.

    2004-05-01

    The Mackenzie Basin (1.7 million sq. km) incorporates a diverse range of geographic source regions, including eight of the fifteen ecoclimatic regions identified in Canada. The basin is mountainous in the west and relatively flat-lying in the east with strong north-south climatic gradients, and generally cold, dry climate conditions compared to other large river basins in the world. As a major contributor of freshwater discharge to the Arctic Ocean, the river is distinct due to the occurrence of several large lakes (Lake Athabasca, Great Slave Lake, Great Bear Lake) which act as flow, sedimentation, and biogeochemical regulators along its main drainage network. A detailed water sampling network was established in 2002 to support isotope hydrology studies in the basin by Environment Canada, as well as modelling efforts conducted in association with the Mackenzie GEWEX Study and the IAEA Coordinated Research Project on Rivers. Results from this survey reveal the complex evolution of the isotopic composition of river discharge from the headwaters of the Mackenzie River to the mouth, particularly the mixing of tributary inflows and the buffering effect of the large lakes. Spatially, the most depleted isotope signatures are observed for tributaries of the Western Cordillera, especially the Mackenzie Mountains, which are characterized by higher-altitude precipitation, greater snowfall, and higher runoff/precipitation ratios than other parts of the basin. In contrast, shield-dominated eastern areas and the central boreal-taiga plains tend to have enriched isotopic signatures reflecting lower altitude precipitation as well as significant contributions from evaporated lake and wetland sources. Here, rivers commonly traverse extensive string-of-lakes and bog-fen drainage networks. In addition, seasonality of the riverine isotopic signals is often pronounced, reflecting varying proportions of flow derived from snowmelt, groundwater, and surface waters during the ice

  4. Methanotrophy within the water column of a large meromictic tropical lake (Lake Kivu, East Africa)

    NASA Astrophysics Data System (ADS)

    Morana, C.; Borges, A. V.; Roland, F. A. E.; Darchambeau, F.; Descy, J.-P.; Bouillon, S.

    2015-04-01

    The permanently stratified Lake Kivu is one of the largest freshwater reservoirs of dissolved methane (CH4) on Earth. Yet CH4 emissions from its surface to the atmosphere have been estimated to be 2 orders of magnitude lower than the CH4 upward flux to the mixed layer, suggesting that microbial CH4 oxidation is an important process within the water column. A combination of natural abundance stable carbon isotope analysis (δ13C) of several carbon pools and 13CH4-labelling experiments was carried out during the rainy and dry season to quantify (i) the contribution of CH4-derived carbon to the biomass, (ii) methanotrophic bacterial production (MBP), and (iii) methanotrophic bacterial growth efficiency (MBGE), defined as the ratio between MBP and gross CH4 oxidation. We also investigated the distribution and the δ13C of specific phospholipid fatty acids (PLFAs), used as biomarkers for aerobic methanotrophs. Maximal MBP rates were measured in the oxycline, suggesting that CH4 oxidation was mainly driven by oxic processes. Moreover, our data revealed that methanotrophic organisms in the water column oxidized most of the upward flux of CH4, and that a significant amount of CH4-derived carbon was incorporated into the microbial biomass in the oxycline. The MBGE was variable (2-50%) and negatively related to CH4 : O2 molar ratios. Thus, a comparatively smaller fraction of CH4-derived carbon was incorporated into the cellular biomass in deeper waters, at the bottom of the oxycline where oxygen was scarce. The aerobic methanotrophic community was clearly dominated by type I methanotrophs and no evidence was found for an active involvement of type II methanotrophs in CH4 oxidation in Lake Kivu, based on fatty acids analyses. Vertically integrated over the water column, the MBP was equivalent to 16-60% of the average phytoplankton particulate primary production. This relatively high magnitude of MBP, and the substantial contribution of CH4-derived carbon to the overall

  5. Methanotrophy within the water column of a large meromictic tropical lake (Lake Kivu, East Africa)

    NASA Astrophysics Data System (ADS)

    Morana, C.; Borges, A. V.; Roland, F. A. E.; Darchambeau, F.; Descy, J.-P.; Bouillon, S.

    2014-11-01

    The permanently stratified Lake Kivu is one of the largest freshwater reservoirs of dissolved methane (CH4) on Earth. Yet CH4 emissions from its surface to the atmosphere has been estimated to be 2 orders of magnitude lower than the CH4 upward flux to the mixed layer, showing that microbial CH4 oxidation is an important process within the water column. A combination of natural abundance carbon stable isotope analysis (δ13C) of several inorganic and organic carbon pools and 13CH4-labelling experiments was carried out during rainy and dry season to quantify (i) the contribution of CH4-derived carbon to the biomass, (ii) methanotrophic bacterial production (MBP), and (iii) methanotrophic bacterial growth efficiency (MBGE), defined as the ratio between MBP and gross CH4 oxidation. We also investigated the distribution and the δ13C of specific phospholipid fatty acids (PLFA), used as biomarkers for aerobic methanotrophs. Data revealed that methanotrophic organisms oxidized within the water column most of the upward flux of CH4 to the mixed layer and a significant amount of CH4-derived carbon was incorporated into the microbial biomass in the oxycline. Maximal MBP rates were measured in the oxycline, suggesting that CH4 oxidation was mainly driven by oxic processes. The MBGE was variable (2-50%) and negatively related to CH4 : O2 molar ratios. Thus, a comparatively smaller fraction of CH4-derived carbon was incorporated into the cellular biomass in deeper waters, at the bottom of the oxycline where oxygen was scarce. The aerobic methanotrophic community was clearly dominated by type I methanotrophs and no evidence was found for an active involvement of type II methanotrophs in CH4 oxidation in Lake Kivu. Vertically integrated over the water column, the MBP was equivalent to 16-58% of the average phytoplankton primary production. This relatively high magnitude of MBP, and the substantial contribution of CH4-derived carbon to the overall biomass in the oxycline, suggest

  6. California's potential volcanic hazards

    USGS Publications Warehouse

    Jorgenson, P.

    1989-01-01

    This is a summary of "Potential Hazards from Future Volcanic Eruptions in California' (USGS Bulletin No. 1847: price $4.75). The chief areas of danger are Lassen Peak, Mount Shasta and Medicine Lake Highland in the north; Clear Lake, Mono Lake and Long Valley in the centre; and Owen's River-Death Valley, Amboy Crater and the Saltan Butter in the south of the State. -A.Scarth

  7. Applying the three-dimensional model ATHAM to volcanic plumes: Dynamic of large co-ignimbrite eruptions and associated injection heights for volcanic gases

    NASA Astrophysics Data System (ADS)

    Herzog, Michael; Graf, Hans-F.

    2010-10-01

    Many of the past large volcanic eruptions like Tambora in 1815, Krakatau in 1835, and Pinatubo in 1991 were secondary so called co-ignimbrite eruptions that were forced over a large area instead of a point source as in the Plinian case. Previous modeling studies were based on one-dimensional plume models. We used the fully three-dimensional plume model ATHAM (Active Tracer High-Resolution Atmospheric Model) to investigate the dynamics and the resulting plume heights of co-ignimbrite eruptions in an idealized setup. Ash particles as well as a sulfur dioxide (SO2) tracer are included in the model. In the analysis we focus on the behavior of SO2 since the neutral buoyancy height is an ill-defined parameter for gravitationally settling particles. In contrast to Plinian plumes the co-ignimbrite plumes develop from multiple updrafts resulting in significantly reduced neutral buoyancy heights. At least a two-dimensional modeling framework is necessary to capture the relevant dynamical features.

  8. Comment on "Large volcanic aerosol load in the stratosphere linked to Asian monsoon transport".

    PubMed

    Fromm, Michael; Nedoluha, Gerald; Charvát, Zdenek

    2013-02-08

    Bourassa et al. (Reports, 6 July 2012, p. 78) report on the 13 June 2011 eruption of the Nabro volcano and satellite observations of stratospheric aerosol that they attribute to troposphere to stratosphere ascent via the Asian monsoon. They claim (citing another source) that the 13 June top injection height was well below the tropopause. We will show that the 13 June Nabro eruption plume was clearly stratospheric and contained both volcanic gases and aerosols. Moreover, we will show height-resolved stratospheric sulfur dioxide and volcanic aerosol enhancements 1 to 3 days old, unaffected by the Asian monsoon, precisely connected to the volcano. The observed stratospheric aerosols and gases are fully explained by the 13 June eruption and do not require a monsoon vehicle.

  9. Comment on "Large Volcanic Aerosol Load in the Stratosphere Linked to Asian Monsoon Transport"

    NASA Astrophysics Data System (ADS)

    Fromm, Michael; Nedoluha, Gerald; Charvát, Zdenek

    2013-02-01

    Bourassa et al. (Reports, 6 July 2012, p. 78) report on the 13 June 2011 eruption of the Nabro volcano and satellite observations of stratospheric aerosol that they attribute to troposphere to stratosphere ascent via the Asian monsoon. They claim (citing another source) that the 13 June top injection height was well below the tropopause. We will show that the 13 June Nabro eruption plume was clearly stratospheric and contained both volcanic gases and aerosols. Moreover, we will show height-resolved stratospheric sulfur dioxide and volcanic aerosol enhancements 1 to 3 days old, unaffected by the Asian monsoon, precisely connected to the volcano. The observed stratospheric aerosols and gases are fully explained by the 13 June eruption and do not require a monsoon vehicle.

  10. Spatial variations of methane emission in a large shallow eutrophic lake in subtropical climate

    NASA Astrophysics Data System (ADS)

    Xiao, Qitao; Zhang, Mi; Hu, Zhenghua; Gao, Yunqiu; Hu, Cheng; Liu, Cheng; Liu, Shoudong; Zhang, Zhen; Zhao, Jiayu; Xiao, Wei; Lee, X.

    2017-07-01

    Subtropical lakes are important source of atmospheric methane (CH4). This study aims to investigate spatial variations of CH4 flux in Lake Taihu, a large (area 2400 km2) and shallow (mean depth 1.9 m) eutrophic lake in Eastern China. The lake exhibited high spatial variations in pollution level, macrophyte vegetation abundance, and algal growth. We measured the diffusion CH4 flux via the transfer coefficient method across the whole lake. In addition, data obtained with the flux gradient and the eddy covariance methods were used in conjunction with the data on the diffusion flux to estimate the contribution by ebullition. Results from 3 years' measurements indicated high spatial variabilities in the diffusion CH4 flux. The spatial pattern of the diffusion CH4 emission was correlated with water clarity, dissolved oxygen concentration, and the spatial distributions of algal and submerged vegetation. In comparison to the transfer coefficient method, the eddy covariance and the flux gradient method observed a lake CH4 flux that was 3.39 ± 0.58 (mean ± 1 standard deviation) and 1.95 ± 0.36 times higher in an open-water eutrophic zone and in a habitat of submerged macrophytes, respectively. The result implied an average of 71% and 49% ebullition contribution to the total CH4 flux in the two zones. The annual mean diffusion CH4 flux of the whole lake was 0.54 ± 0.30 g m-2 yr-1. Our CH4 emission data suggest that the average CH4 emission reported previously for lakes in Eastern China was overestimated.

  11. High-resolution sulfur isotopes in ice cores identify large stratospheric volcanic eruptions

    NASA Astrophysics Data System (ADS)

    Burke, Andrea; Sigl, Michael; Adkins, Jess; Paris, Guillaume; McConnell, Joe

    2016-04-01

    The record of the volcanic forcing of climate over the past 2500 years is reconstructed primarily from sulfate concentrations in ice cores. Of particular interest are stratospheric eruptions, as these afford sulfate aerosols the longest residence time and largest dispersion in the atmosphere, and thus the greatest impact on radiative forcing. Identification of stratospheric eruptions currently relies on the successful matching of the same volcanic sulphate peak in ice cores from both the Northern and Southern hemispheres (a "bipolar event"). These are interpreted to reflect the global distribution of sulfur aerosols by the stratospheric winds. Despite its recent success, this method relies on precise and accurate dating of ice cores, in order to distinguish between a true 'bipolar event' and two separate eruptions that occurred in close temporal succession. Sulfur isotopes can been used to distinguish between these two scenarios since stratospheric sulfur aerosols are exposed to UV radiation which imparts a mass independent fractionation (Baroni et al., 2007). Mass independent fractionation of sulfate in ice cores thus offers a novel method of fingerprinting stratospheric eruptions, and thus refining the historic record of explosive volcanism and its forcing of climate. Here we present new high-resolution (sub-annual) sulfur isotope data from the Tunu Ice core in Greenland over seven eruptions. Sulfur isotopes were measured by MC-ICP-MS, which substantially reduces sample size requirements and allows high temporal resolution from a single ice core. We demonstrate the efficacy of the method on recent, well-known eruptions (including Pinatubo and Katmai/Novarupta), and then apply it to unidentified sulfate peaks, allowing us to identify new stratospheric eruptions. Baroni, M., Thiemens, M. H., Delmas, R. J., & Savarino, J. (2007). Mass-independent sulfur isotopic compositions in stratospheric volcanic eruptions. Science, 315(5808), 84-87. http://doi.org/10

  12. Volcanic activity before and after large tectonic earthquakes: Observations and statistical significance

    NASA Astrophysics Data System (ADS)

    Eggert, Silke; Walter, Thomas R.

    2009-06-01

    The study of volcanic triggering and interaction with the tectonic surroundings has received special attention in recent years, using both direct field observations and historical descriptions of eruptions and earthquake activity. Repeated reports of clustered eruptions and earthquakes may imply that interaction is important in some subregions. However, the subregions likely to suffer such clusters have not been systematically identified, and the processes responsible for the observed interaction remain unclear. We first review previous works about the clustered occurrence of eruptions and earthquakes, and describe selected events. We further elaborate available databases and confirm a statistically significant relationship between volcanic eruptions and earthquakes on the global scale. Moreover, our study implies that closed volcanic systems in particular tend to be activated in association with a tectonic earthquake trigger. We then perform a statistical study at the subregional level, showing that certain subregions are especially predisposed to concurrent eruption-earthquake sequences, whereas such clustering is statistically less significant in other subregions. Based on this study, we argue that individual and selected observations may bias the perceptible weight of coupling. The activity at volcanoes located in the predisposed subregions (e.g., Japan, Indonesia, Melanesia), however, often unexpectedly changes in association with either an imminent or a past earthquake.

  13. Volume-Time Relations in Large Silicic Volcanic Fields - Clues to a Thermomechanical Control on Eruption Frequency and Mechanism

    NASA Astrophysics Data System (ADS)

    de Silva, S. L.

    2005-05-01

    In assessing the hazard associated with large calderas it is crucial that the broader context of the formation, evolution, and eruption of these systems be factored into any assessment. The existing paradigm is that as large volumes of intermediate to silicic magma accumulate and evolve at high-level, a pressure build-up during second boiling results in overpressures of 20 - 25 MPa that result in the fracture of the magma chamber roof and consequent eruption. This may not be the case for the largest ignimbrite eruptions. These are typically associated with a regional ignimbrite flare-up and we should consider a more holistic approach that takes into account the spatiotemporal and volume-time evolution of the entire flare-up in understanding the operation of these systems. I illustrate this with a case study of the Altiplano-Puna Volcanic Complex of the Central Andes (APVC). The timing, pattern, and volumes of ignimbrite volcanism in the APVC reveal: 1) Pulsing of the ignimbrite eruptions with an approximate two million year period; 2) A trend to larger volume eruptions climaxing at about 4 Ma; 3) Migration and focusing of activity toward the central part of the APVC with time; and 4) Markedly diminished activity since 4 Ma. These observations suggest that the ignimbrite flare-up is result of progressive thermal (and mechanical) maturation of the crustal column due to intrusion and batholith formation and attendant effects on lithosphere strength. The progressive erosion of crustal strength results in failure of the crust and catastrophic eruption. Examination of available data from other large silicic volcanic provinces through space and time reveal a general pattern similar to that shown by the APVC. This suggests a consistency of process consisting of thermal preparation, catastrophic response, and relaxation in the development of these large volcanic fields. The possibility that the largest ignimbrite eruptions (>1000 km3) are triggered by mechanical failure of

  14. Estimation of ice thickness on large lakes from passive microwave and radar altimeter data

    NASA Astrophysics Data System (ADS)

    Duguay, Claude; Kang, Kyung-Kuk; Kouraev, Alexei; Mercier, Franck

    2010-05-01

    Lake ice grows steadily between the end of freeze-up period and the onset of break-up period as a result of the thermodynamics of freezing water as well as dynamic ice motion on the surface. In thermodynamic thickening, the conductive heat flow controls the ice growth rate and the ice thickness, and the ice thickens downward as a result of heat loss at the top of the ice cover. There has been some demonstration of the potential of brightness temperature from passive microwave airborne radiometers to estimate ice thickness. The value of passive microwave and radar altimeter data from current satellite missions merits to be examined in this respect. The major objective of this study was estimate ice thickness from brightness temperature (TB) at 10.65 and 18.70 GHz from AMSR-E channels and the 19.35 GHz frequency channel from SSM/I on large lakes of the Northern Hemisphere (e.g. Great Bear Lake, Great Slave Lake, Lake Baikal). The evolution of horizontally and vertically polarized TB derived from AMSR-E level 2A raw brightness temperature and EASE Grid Level-3 SSM/I products was compared with ice thicknesses obtained with a previously validated thermodynamic lake ice model and in situ observations over the course of seven winter seasons (2002 and 2009), as well as with recent estimates from the Jason-2 Ku-band radar altimeter data (since 2008). Results show that both passive microwave and radar altimeter data acquired in the 10-19 GHz frequency range offer a promising means for estimating ice thickness from large northern lakes.

  15. Effects of large volcanic eruptions on Eurasian climate and societies: unravelling past evidence to predict future impacts

    NASA Astrophysics Data System (ADS)

    Churakova Sidorova, Olga; Guillet, Sébastien; Corona, Christophe; Khodri, Myriam; Vaganov, Eugene; Siegwolf, Rolf; Bryukhanova, Marina; Naumova, Oksana; Kirdyanov, Aleksander; Myglan, Vladimir; Sviderskaya, Irina; Pyzhev, Anton; Grachev, Alexei; Saurer, Matthias; Beniston, Martin; Stoffel, Markus

    2016-04-01

    Substantial evidence exists for the sulphur deposition in ice cores of Greenland and Antarctica after major volcanic eruptions but their impacts have not been documented with sufficient detail so far. This is true for temperature, of which the cooling induced by eruptions has been vividly debated in recent years, but even more so for precipitation. In the Era.Net RUS Plus ELVECS, we are currently quantifying climate disturbance induced by major Common Era eruptions, the persistence of changes and their impact on short- to mid-term temperature and precipitation anomalies by using an unprecedented dataset of tree-ring records across Eurasia and a large body of recently unearthed historical archives. We will compile a comprehensive database of tree-ring proxies and historical archives; quantify temperature and precipitation impacts of large eruptions; simulate on a case-by-case basis volcanic microphysical processes and radiative forcing induced by the eruptions as well as evaluate results against tree-ring records; quantify impacts of large volcanic eruptions on atmospheric and oceanic circulations and feedbacks; and assess impacts of possible future eruptions. The new and diversified proxy data sources and more sophisticated modelling are expected to reduce discrepancies and uncertainties related to climatic responses to some of the largest eruptions. We expect to capture persistence of anomalies correctly by climate models, even more so if they are evaluated against highly resolved proxy data of past events. This will increase our confidence in the overall reliability of climate models and help to correctly capture, and therefore predict, the cooling and precipitation anomalies of possible future, large eruptions. These predictions of climatic anomalies will then be used to quantify their likely impacts on major economy and society, including food security, migration and air traffic. Acknowledgements: Era.Net RUS Plus ELVECS project № 122

  16. Recent increases in the large glacial-relict calanoid Limnocalanus macrurus in Lake Michigan

    USGS Publications Warehouse

    Barbiero, R.P.; Bunnell, D.B.; Rockwell, D.C.; Tuchman, M.L.

    2009-01-01

    Since 2004, population density of the large hypolimnetic calanoid Limnocalanus macrurus Sars. has increased dramatically in Lake Michigan. The average summer biomass of this species between 2004 and 2006 was roughly three times that of the period 1984–2003, and at levels unprecedented in our 22-year dataset, making L. macrurus the dominant zooplankter in the lake in terms of biomass. These increases have been accentuated by coincident population declines of the main daphnid, Daphnia mendotae, in the lake with the result that in 2006, L. macrurus accounted for 75% and 50% of the large (> 0.9 mm) crustacean biomass in the northern and southern basins of Lake Michigan, respectively. The increases in L. macrurus populations have closely coincided with equally dramatic increases in summer water clarity. Recent extinction coefficients are among the lowest recorded for the lake, and deepening light penetration has permitted increases in the size of the deep chlorophyll layer. In addition, planktivorous fish populations have declined coincidently with the increases in L. macrurus. It seems likely that an increase in sub-epilimnetic production has resulted in increased food resources for the deep-living L. macrurus, while low planktivore abundances have reduced predation loss, permitting L. macrurus to respond to these increases in sub-epilimnetic production.

  17. Natural trophic variability in a large, oligotrophic, near-pristine lake

    USGS Publications Warehouse

    Young, Talia; Jensen, Olaf P.; Weidel, Brian C.; Chandra, Sudeep

    2015-01-01

    Conclusions drawn from stable isotope data can be limited by an incomplete understanding of natural isotopic variability over time and space. We quantified spatial and temporal variability in fish carbon and nitrogen stable isotopes in Lake Hövsgöl, Mongolia, a large, remote, oligotrophic lake with an unusually species-poor fish community. The fish community demonstrated a high degree of trophic level overlap. Variability in δ13C was inversely related to littoral-benthic dependence, with pelagic species demonstrating more δ13C variability than littoral-benthic species. A mixed effects model suggested that space (sampling location) had a greater impact than time (collection year) on both δ13C and δ15N variability. The observed variability in Lake Hövsgöl was generally greater than isotopic variability documented in other large, oligotrophic lakes, similar to isotopic shifts attributed to introduced species, and less than isotopic shifts attributed to anthropogenic chemical changes such as eutrophication. This work complements studies on isotopic variability and changes in other lakes around the world.

  18. Gish Bar Patera, Io: Geology and Volcanic Activity, 1996-2001

    NASA Technical Reports Server (NTRS)

    Perry, Jason; Radebaugh, Jani; Lopes, Rosaly; McEwen, Alfred; Keszthelyi, Laszlo

    2003-01-01

    Since the two Voyagers passed by Jupiter in 1979, it has been known that volcanic activity is ubiquitous on the surface of Io. With over 400 volcanic centers, Io is even more volcanically active than the earth with massive flood basalt-style eruptions and komatitite lavas a common occurrence. Additionally, some volcanoes appear to be giant lava lakes, with violent activity churning the crust of the lake for periods of 20 years or more. Finally, sulfur is believed to play a large role in Io's volcanism, be it as a primary lava or as a secondary product of large, high-temperature eruptions. By studying one volcano in particular, Gish Bar Patera, one can observe many of these characteristics in one volcanic center.

  19. Gish Bar Patera, Io: Geology and Volcanic Activity, 1996-2001

    NASA Technical Reports Server (NTRS)

    Perry, Jason; Radebaugh, Jani; Lopes, Rosaly; McEwen, Alfred; Keszthelyi, Laszlo

    2003-01-01

    Since the two Voyagers passed by Jupiter in 1979, it has been known that volcanic activity is ubiquitous on the surface of Io. With over 400 volcanic centers, Io is even more volcanically active than the earth with massive flood basalt-style eruptions and komatitite lavas a common occurrence. Additionally, some volcanoes appear to be giant lava lakes, with violent activity churning the crust of the lake for periods of 20 years or more. Finally, sulfur is believed to play a large role in Io's volcanism, be it as a primary lava or as a secondary product of large, high-temperature eruptions. By studying one volcano in particular, Gish Bar Patera, one can observe many of these characteristics in one volcanic center.

  20. Lake

    ERIC Educational Resources Information Center

    Wien, Carol Anne

    2008-01-01

    The lake is blue black and deep. It is a glaciated finger lake, clawed out of rock when ice retracted across Nova Scotia in a northerly direction during the last ice age. The lake is narrow, a little over a mile long, and deep, 90 to 190 feet in places according to local lore, off the charts in others. The author loves to swim there, with a sense…

  1. Inverse transport modeling of volcanic sulfur dioxide emissions using large-scale simulations

    NASA Astrophysics Data System (ADS)

    Heng, Yi; Hoffmann, Lars; Griessbach, Sabine; Rößler, Thomas; Stein, Olaf

    2016-05-01

    An inverse transport modeling approach based on the concepts of sequential importance resampling and parallel computing is presented to reconstruct altitude-resolved time series of volcanic emissions, which often cannot be obtained directly with current measurement techniques. A new inverse modeling and simulation system, which implements the inversion approach with the Lagrangian transport model Massive-Parallel Trajectory Calculations (MPTRAC) is developed to provide reliable transport simulations of volcanic sulfur dioxide (SO2). In the inverse modeling system MPTRAC is used to perform two types of simulations, i.e., unit simulations for the reconstruction of volcanic emissions and final forward simulations. Both types of transport simulations are based on wind fields of the ERA-Interim meteorological reanalysis of the European Centre for Medium Range Weather Forecasts. The reconstruction of altitude-dependent SO2 emission time series is also based on Atmospheric InfraRed Sounder (AIRS) satellite observations. A case study for the eruption of the Nabro volcano, Eritrea, in June 2011, with complex emission patterns, is considered for method validation. Meteosat Visible and InfraRed Imager (MVIRI) near-real-time imagery data are used to validate the temporal development of the reconstructed emissions. Furthermore, the altitude distributions of the emission time series are compared with top and bottom altitude measurements of aerosol layers obtained by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) satellite instruments. The final forward simulations provide detailed spatial and temporal information on the SO2 distributions of the Nabro eruption. By using the critical success index (CSI), the simulation results are evaluated with the AIRS observations. Compared to the results with an assumption of a constant flux of SO2 emissions, our inversion approach leads to an improvement

  2. Primary production in a tropical large lake: the role of phytoplankton composition.

    PubMed

    Darchambeau, F; Sarmento, H; Descy, J-P

    2014-03-01

    Phytoplankton biomass and primary production in tropical large lakes vary at different time scales, from seasons to centuries. We provide a dataset made of 7 consecutive years of phytoplankton biomass and production in Lake Kivu (Eastern Africa). From 2002 to 2008, bi-weekly samplings were performed in a pelagic site in order to quantify phytoplankton composition and biomass, using marker pigments determined by HPLC. Primary production rates were estimated by 96 in situ (14)C incubations. A principal component analysis showed that the main environmental gradient was linked to a seasonal variation of the phytoplankton assemblage, with a clear separation between diatoms during the dry season and cyanobacteria during the rainy season. A rather wide range of the maximum specific photosynthetic rate (PBm) was found, ranging between 1.15 and 7.21 g carbong(-1)chlorophyll ah(-1), and was best predicted by a regression model using phytoplankton composition as an explanatory variable. The irradiance at the onset of light saturation (Ik) ranged between 91 and 752 μE m(-2)s(-1) and was linearly correlated with the mean irradiance in the mixed layer. The inter-annual variability of phytoplankton biomass and production was high, ranging from 53 to 100 mg chlorophyll am(-2) (annual mean) and from 143 to 278 g carbon m(-2)y(-1), respectively. The degree of seasonal mixing determined annual production, demonstrating the sensitivity of tropical lakes to climate variability. A review of primary production of other African great lakes allows situating Lake Kivu productivity in the same range as that of lakes Tanganyika and Malawi, even if mean phytoplankton biomass was higher in Lake Kivu.

  3. Hydrologic budget and dynamics of a large oligotrophic lake related to hydro-meteorological inputs

    NASA Astrophysics Data System (ADS)

    Sahoo, G. B.; Schladow, S. G.; Reuter, J. E.

    2013-09-01

    A turbulent diffusion transfer model was developed and coupled to a developed Dynamic Lake Model with Water Quality (DLM-WQ) with the goal of correctly estimating the hydrologic budget of Lake Tahoe (California-Nevada). Isohyetal lines were created using PRISM gridded monthly precipitation data during 1990-2011 to estimate the precipitation distribution directly on the lake. The US Environmental Protection Agency supported watershed model, Loading Simulation Program in C++ (LSPC), was used to generate the stream flows and pollutants loading of 64 streams. The exchange coefficients for latent heat, sensible heat and wind drag (CEN, CHN, and CDN, respectively) and precipitation inputs were calibrated using coefficient of determination (R2) as the objective function and comparing visually the estimated values to those of measured record of 1994 to 2008. CEN, CHN, and CDN were found to be optimum at 1.82 × 10-6, 3.00 × 10-6 and 1.3 × 10-3, respectively for Lake Tahoe. CEN variation results in a greater change in lake water level compared to CHN and CDN. The annual precipitation contour lines indicate a reduction of approximately 35% of Tahoe City precipitation. DLM-WQ estimated 36% reduction of Tahoe City precipitation. Although latent heat loss (17%) is small compared to combined shortwave radiation and longwave radiation (77%) the effect on water balance due to inaccurate estimates of evaporative loss is very large because the ratio of watershed to lake surface area is low at 1.64. Evaporation (32%) is the largest contributor in the hydrologic budget and its accurate estimation is therefore critical and important for sustainable water management. The DLM-WQ estimated water surface temperatures and lake water level were in excellent agreement with those of measured records for the period 1994-2008 with R2 equal to 0.97 and 0.99, respectively.

  4. Nitrogen removal from Lake Caohai, a typical ultra-eutrophic lake in China with large scale confined growth of Eichhornia crassipes.

    PubMed

    Wang, Zhi; Zhang, Zhiyong; Zhang, Yingying; Zhang, Junqian; Yan, Shaohua; Guo, Junyao

    2013-06-01

    An ecological engineering project, with large-scale utilization of Eichhornia crassipes (coverage area ∼4.3km(2)) for pollution control in an open ultra-eutrophic lake, Lake Caohai, was first implemented in 2011. In this study, the efficiency of N removal using E. crassipes in the lake was evaluated. After E. crassipes was planted in May, the concentrations of TN and NH4(+) in Waicaohai, the main part of Lake Caohai, were significantly decreased within a month, and then, remained stable from June to November, 2011, although the lake had received waste water continuously from river inlets. The average concentrations of TN, NH4(+)-N and NO3(-)-N in water of Xi Yuan Channel (outlet) were reduced to 3.3, 0.02 and 0.8mgL(-1) from 13.8, 4.7 and 5.8mgL(-1) in river inlets, respectively. The DO levels in 2011 were not decreased, but concentrations of TN and NH4(+) were significantly reduced when compared with the historical data from 2007 in the lake. Assimilation by E. crassipes was the main pathway to remove N in Lake Caohai, accounted for 52% of the total N influent (936t), or 64% of the removed N (761t). These results indicated that large scale utilization of E. crassipes for removal of N in the eutrophic lake is practicable.

  5. The climatic effects of the direct injection of water vapour into the stratosphere by large volcanic eruptions

    NASA Astrophysics Data System (ADS)

    Joshi, M. M.; Jones, G. S.

    2009-08-01

    We describe a novel mechanism that can significantly lower the amplitude of the climatic response to certain large volcanic eruptions and examine its impact with a coupled ocean-atmosphere climate model. If sufficiently large amounts of water vapour enter the stratosphere, a climatically significant amount of water vapour can be left over in the lower stratosphere after the eruption, even after sulphate aerosol formation. This excess stratospheric humidity warms the tropospheric climate, and acts to balance the climatic cooling induced by the volcanic aerosol, especially because the humidity anomaly lasts for a period that is longer than the residence time of aerosol in the stratosphere. In particular, northern hemisphere high latitude cooling is reduced in magnitude. We discuss this mechanism in the context of the discrepancy between the observed and modelled cooling following the Krakatau eruption in 1883. We hypothesize that moist coignimbrite plumes caused by pyroclastic flows travelling over ocean rather than land, resulting from an eruption close enough to the ocean, might provide the additional source of stratospheric water vapour.

  6. Global relationships between volcanic vents and fractures radial to large impact basins on Mars

    NASA Technical Reports Server (NTRS)

    Schneid, Byron D.; Greeley, Ronald

    1991-01-01

    The relation of volcanic vents on Mars to impact basins has been previously studied. It has been asserted that the concentric fractures around impact basins extend into the crust and might localize some features, including volcanoes. Herein, the possibility is assessed of radial fractures inferred to be associated with impact basins as an additional control on the location of volcanoes on Mars. Geologic mapping at 1:2 million scale enabled 250 central vents and fissure vents to be identified. Pattern of vent distribution superimposed on a globe show that most are located on three distinct circles. In addition, there are two more possible great circles which may be superimposed onto the Martian globe. These five Martian circles are briefly examined for their geological relationship to volcanoes.

  7. Methanotrophy and chemoautotrophy within the redox gradient of a large and deep tropical lake (Lake Kivu, East Africa)

    NASA Astrophysics Data System (ADS)

    Morana, Cedric; Borges, Alberto V.; Darchambeau, François; Roland, Fleur; Montante, Laetitia; Descy, Jean-Pierre; Bouillon, Steven

    2014-05-01

    Lake Kivu (East Africa) is a large (2370 km2) and deep (maximum depth of 485 m) meromictic lake. Its vertical structure consists of an oxic and nutrient-poor mixed layer down to 70 m maximum, and a permanently anoxic monimolimnion rich in dissolved gases (methane and carbon dioxide) and inorganic nutrients. Seasonal variation of the vertical position of the oxic-anoxic interface is driven by contrasting precipitation and wind speed regimes between rainy (October-May) and dry (June-September) season, the latter being characterized by a deepening of the oxic zone, and an increased input of dissolved gases and inorganic nutrients. Our work aimed at quantifying methanotrophic and chemoautotrophic production within the redox gradient of Lake Kivu and identifying the micro-organisms involved in these processes using phospholipid-derived fatty acid markers and their carbon stable isotope composition. Our approach combined both natural stable isotope abundance analysis and 13C-labelling (13C-DIC ; 13C-CH4) experiments. Sampling was carried out at two stations in Lake Kivu during rainy (February 2012) and dry (September 2012) season conditions. Methanotrophic bacterial production rates were highly variable (from 0.1 to 7.0 μmol C L-1 d-1), but maximum values were always observed at the oxic-anoxic interface when the CH4:O2 ratio varied between 0.1 and 10, suggesting that the majority of methane was oxidized aerobically. Furthermore, strong stable isotope labelling of monounsaturated C16 fatty acids indicate that active methane oxidizers were related to the group of type I aerobic methanotrophs (gammaproteobacteria). Despite the dominance of aerobic methane oxidation, significant methanotrophic bacterial production rates were found below the oxic-anoxic interface during the rainy season, indicating that at least a fraction of the upcoming methane may be oxidized anaerobically. This observation was further confirmed by the strong labelling at these depths of the 10Me16

  8. Mineral cycling and pH gradient related with biological activity under transient anoxic-oxic conditions: effect on P mobility in volcanic lake sediments.

    PubMed

    Ribeiro, D C; Martins, G; Nogueira, R; Brito, A G

    2014-08-19

    Phosphorus (P) mobility from the sediments to the water column is a complex phenomenon that is generally assumed to be mainly redox sensitive and promoted by anoxic conditions. Thus, artificial aeration of the hypolimnium has been used as a remediation technique in eutrophic water bodies but several times with unexpected disappointing results. To optimize lake restoration strategies, the aim of the present study is to assess the P flux from the sediments under transient anoxic-conditions and to identify the relevant drivers. P sequential extraction, microprofiling (of pH, O2 and H2S), and bacterial community identification were performed on a sediment microcosm approach. The results demonstrated that the overall P release from sediments to the water column during transient phase was higher during the oxic phase, mainly from pH sensitive matrixes. The microprofiles signature suggests that the observed pH gradient during the oxic phase can be a result of H2S oxidation in suboxic layers spatially separated and pared to O2 reduction in top layers, through an electroactive bacterial network. These findings point to an additional driver to be considered when assessing P mobility under transient anoxic-oxic conditions, which would derive from pH gradients, built on the microbial electrical activity in sediments from freshwaters volcanic lakes.

  9. Monitoring unrest in a large silicic caldera, the long Valley-inyo craters volcanic complex in east-central California

    USGS Publications Warehouse

    Hill, D.P.

    1984-01-01

    Recent patterns of geologic unrest in long Valley caldera in east-central California emphasize that this large, silicic volcanic system and the adjacent, geologically youthful Inyo-Mono Craters volcanic chain are still active and capable of producing locally hazardous volcanic eruptions. A series of four magnitude -6 earthquakes in May 1980 called attention to this current episode of unrest, and subsequent activity has included numerous earthquake swarms in the south moat of the caldera accompanied by inflation of the resurgent dome by more than 50 cm over the last five years. The seismicity associated with this unrest is currently monitored by a network of 31 telemetered seismic stations with an automatic processing system that yelds hypocentral locations and earthquake magnitudes in near-real time. Deformation of the ground is monitored by a) a series of overlapping trilateration networks that provide coverage ranging from annual measurements of regional deformation to daily measurements of deformation local to the active, southern section of the caldera, b) a regional network of level lines surveyed annually, c) a regional network of precise gravity stations occupied annually, d) local, L-shaped level figures surveyed every few months, and e) a network of fourteen borehole tiltmeter clusters (two instruments in each cluster) and a borehole dilatometer, the telemetered signals from which provide continuous data on deformation rates. Additional telemetered data provide continuous information on fluctuations in the local magnetic field, hydrogen gas emission rates at three sites, and water level and temperatures in three wells. Continuous data on disharge rates and temperatures from hot springs and fumaroles are collected by several on-site recorders within the caldera, and samples for liquid and gas chemistry are collected several times per year from selected hot springs and fumaroles. ?? 1984 Intern. Association of Volcanology and Chemistry of the Earth

  10. Groundwater flow in a closed basin with a saline shallow lake in a volcanic area: Laguna Tuyajto, northern Chilean Altiplano of the Andes.

    PubMed

    Herrera, Christian; Custodio, Emilio; Chong, Guillermo; Lambán, Luis Javier; Riquelme, Rodrigo; Wilke, Hans; Jódar, Jorge; Urrutia, Javier; Urqueta, Harry; Sarmiento, Alvaro; Gamboa, Carolina; Lictevout, Elisabeth

    2016-01-15

    Laguna Tuyajto is a small, shallow saline water lake in the Andean Altiplano of northern Chile. In the eastern side it is fed by springs that discharge groundwater of the nearby volcanic aquifers. The area is arid: rainfall does not exceed 200mm/year in the rainiest parts. The stable isotopic content of spring water shows that the recharge is originated mainly from winter rain, snow melt, and to a lesser extent from some short and intense sporadic rainfall events. Most of the spring water outflowing in the northern side of Laguna Tuyajto is recharged in the Tuyajto volcano. Most of the spring water in the eastern side and groundwater are recharged at higher elevations, in the rims of the nearby endorheic basins of Pampa Colorada and Pampa Las Tecas to the East. The presence of tritium in some deep wells in Pampa Colorada and Pampa Las Tecas indicates recent recharge. Gas emission in recent volcanoes increase the sulfate content of atmospheric deposition and this is reflected in local groundwater. The chemical composition and concentration of spring waters are the result of meteoric water evapo-concentration, water-rock interaction, and mainly the dissolution of old and buried evaporitic deposits. Groundwater flow is mostly shallow due to a low permeability ignimbrite layer of regional extent, which also hinders brine spreading below and around the lake. High deep temperatures near the recent Tuyajto volcano explain the high dissolved silica contents and the δ(18)O shift to heavier values found in some of the spring waters. Laguna Tuyajto is a terminal lake where salts cumulate, mostly halite, but some brine transfer to the Salar de Aguas Calientes-3 cannot be excluded. The hydrogeological behavior of Laguna Tuyajto constitutes a model to understand the functioning of many other similar basins in other areas in the Andean Altiplano.

  11. Aerosol generation and circulation in the shore zone of a Large Alpine lake - 2 - Aerosol distributions over Lake Tahoe, CA

    NASA Astrophysics Data System (ADS)

    VanCuren, R.; Pederson, J.; Lashgari, A.; Dolislager, L.; McCauley, E.

    2012-01-01

    The temporal, spatial, and size-distribution patterns of particles in ambient air over the surface of Lake Tahoe (Nevada and California) were studied as part of the 2003-2004 Lake Tahoe atmospheric deposition study (LTADS). The concentration of population along the shoreline of Lake Tahoe makes accurate characterization of local aerosol generation and transport especially important in estimation of annual particle flux to the surface of the lake. Measurements taken while cruising on the lake show that aerosol concentrations in near shore areas are primarily controlled by a combination of diurnal cycling of land- and lake- breezes and particle emissions driven by cycles of human activity near the shore. These effects were observed to be highly localized. Highest concentrations were found just offshore from urbanized areas, especially shoreline centers of activity; lowest concentrations were found along undeveloped shoreline; low-to-intermediate concentrations were measured over the middle areas of the lake. The on-lake data reported here indicate that aerosols over the lake, and thus dry deposition to the lake, are dominated by the same processes that control onshore emissions, and that the impact is strongest in the near shore areas of the lake.

  12. Fault propagation folds induced by gravitational failure and slumping of the Central Costa Rica volcanic range - Implications for large terrestrial and Martian volcanic edifices

    NASA Technical Reports Server (NTRS)

    Borgia, Andrea; Burr, Jeremiah; Montero, Walter; Morales, Luis Diego; Alvarado, Guillermo E.

    1990-01-01

    Maps are presented that describe the compressional tectonic structures found at the base of the Central Costa Rica volcanic range (CCRVR), which comprise thrust faults and related fault propagation folds, only partly covered by syntectonic and posttectonic volcanoclastic deposits. Evidence is presented that these structures formed by gravitational failure and lumping of the flanks of the volcanic range. It is suggested that similar structures may be found at the toe of the southern flank of Kilauea volcano, Hawaii, and along the perimeter scarp of the Olympus Mons volcano on Mars.

  13. Potential for large-bodied zooplankton and dreissenids to alter the productivity and autotrophic structure of lakes.

    PubMed

    Higgins, Scott N; Althouse, B; Devlin, S P; Vadeboncoeur, Y; Vander Zanden, M J

    2014-08-01

    While limnological studies have emphasized the importance of grazers on algal biomass and primary production in pelagic habitats, few studies have examined their potential role in altering total ecosystem primary production and it's partitioning between pelagic and benthic habitats. We modified an existing ecosystem production model to include biotic feedbacks associated with two groups of large-bodied grazers of phytoplankton (large-bodied zooplankton and dreissenid mussels) and estimated their effects on total ecosystem production (TEP), and the partitioning of TEP between phytoplankton and periphyton (autotrophic structure) across large gradients in lake size and total phosphorus (TP) concentration. Model results indicated that these filter feeders were capable of reducing whole-lake phytoplankton production by 20-70%, and increasing whole-lake benthic production between 0% and 600%. Grazer effects on TEP were constrained by lake size, trophic status, and potential feedbacks between grazing and maximum rates of benthic photosynthesis (BP(MAX)). In small (mean depth Z < 10 m) oligotrophic and mesotrophic (TP < 100 mg P/m2) lakes, both large-bodied zooplankton and dreissenids were capable of increasing the benthic fraction (Bf) by 10-50% of TEP. Small lakes were also the only systems where TEP had the potential to increase in the presence of large-bodied grazers, but such increases only occurred if grazer-induced changes in water clarity, macrophyte coverage, or nutrient availability stimulated specific growth rates of periphyton. In other scenarios, TEP declined by a maximum of 50%. In very large lakes (Z > 100 m), Bf was minor (< 10%) in the presence or absence of grazers, but increases in littoral habitat and the stimulation of benthic production in these ecosystems could be of ecological relevance because littoral zones in large lakes contain a relatively high proportion of within-lake biodiversity and are important for whole-lake food webs.

  14. Volcanic ash ingestion by a large gas turbine aeroengine: fan-particle interaction

    NASA Astrophysics Data System (ADS)

    Vogel, Andreas; Clarkson, Rory; Durant, Adam; Cassiani, Massimo; Stohl, Andreas

    2016-04-01

    Airborne particles from explosive volcanic eruptions are a major safety threat for aviation operations. The fine fraction of the emitted particles (<63 microns diameter) may remain in the atmosphere for days, or even weeks, and can affect commercial air traffic routes. Over the past century, there have been a considerable number of aircraft encounters with drifting volcanic ash clouds. Particles ingested into the engine cause erosion of upstream surfaces of compressor fan blades and rotor-path components, and can also cause contamination or blockage of electrical systems and the fuel system such as fuel nozzles and air bleed filters. Ash particles that enter the hot-section of the engine (combustor and turbine stages; temperature between 1400-1800°C) are rapidly heated above the glass transition temperature (about 650-1000°C) and become soft (or form a melt) and can stick as re-solidified deposits on nozzle guide vanes. The glass deposits change the internal aerodynamic airflow in the engine and can affect the cooling capability of the different components by clogging the cooling inlets/outlets, which can lead to a loss of power or flame-out. The nature of volcanic ash ingestion is primarily influenced by the fan at the front of the engine which produces the thrust that drives the aircraft. The ingested air is split between the core (compressor/combustor/turbine) and bypass (thrust) at a ratio of typically between, 1:5-10 on modern engines. Consequently, the ash particles are fractionated between the core and bypass by the geometry and dynamics of the fan blades. This study uses computational fluid dynamics (CFD) simulations of particle-laden airflows into a turbofan engine under different atmospheric and engine operation conditions. The main aim was to investigate the possible centrifugal effect of the fan blades as a function of particle size, and to relate this to the core intake concentration. We generated a generic 3D axial high-bypass turbofan engine using

  15. Palaeoenvironmental and palaeoclimatic implications of the Late-Quaternary sediment record of Vico volcanic lake (central Italy)

    NASA Astrophysics Data System (ADS)

    Narcisi, Biancamaria

    2001-03-01

    A 15-m-long sediment core recovered from the Lago di Vico caldera lake in central Italy has been the subject of macrofacies description and sedimentological (organic carbon content, grain size and mineralogy) investigation. The results have been integrated with the pollen data from the same core in order to provide a regional climatic and environmental history, with inferences on past lake levels and on moisture and temperature regimes. Radiometric (14C and 40Ar/39Ar) dating, biostratigraphical considerations and tephra analyses provide a chronological framework and indicate that the sequence spans the last 90 000 yr. Several moist periods have been identified that were characterised by enhanced weathering by hydrolysis of the catchment rocks. These alternated with relatively dry phases associated with lowering of lake-levels. The lowest hydrolysis efficiency of the whole record, accompanied by notable aeolian deposition, was attained during the last glacial phase but moisture conditions were such that the lake-level did not decrease, probably owing to reduced temperatures. Evidence for cool climate also emerges for the early Pleniglacial. The highest available moisture was achieved within the Holocene at 5 kyr BP. The Late Holocene does not show either increase of aridity or degradation of the vegetation cover, until at least Roman times.

  16. Chronology of tectonic, geomorphic, and volcanic interactions and the tempo of fault slip near Little Lake, California

    USGS Publications Warehouse

    Amos, Colin B.; Brownlee, Sarah J.; Rood, Sylan H.; Fisher, G. Burch; Burgmann, Roland; Renne, Paul R.; Jayko, Angela S.

    2013-01-01

    New geochronologic and geomorphic constraints on the Little Lake fault in the Eastern California shear zone reveal steady, modest rates of dextral slip during and since the mid-to-late Pleistocene. We focus on a suite of offset fluvial landforms in the Pleistocene Owens River channel that formed in response to periodic interaction with nearby basalt flows, thereby recording displacement over multiple time intervals. Overlap between 40Ar/39Ar ages for the youngest intracanyon basalt flow and 10Be surface exposure dating of downstream terrace surfaces suggests widespread channel incision during a prominent outburst flood through the Little Lake channel at ca. 64 ka. Older basalt flows flanking the upper and lower canyon margins indicate localization of the Owens River in its current position between 212 ± 14 and 197 ± 11 ka. Coupled with terrestrial light detection and ranging (lidar) and digital topographic measurements of dextral offset, the revised Little Lake chronology indicates average dextral slip rates of at least ∼0.6–0.7 mm/yr and 4 to 105 yr. Despite previous geodetic observations of relatively rapid interseismic strain along the Little Lake fault, we find no evidence for sustained temporal fluctuations in slip rates over multiple earthquake cycles. Instead, our results indicate that accelerated fault loading may be transient over much shorter periods (∼101 yr) and perhaps indicative of time-dependent seismic hazard associated with Eastern California shear zone faults.

  17. Constitutive presence of antibiotic resistance genes within the bacterial community of a large subalpine lake.

    PubMed

    Di Cesare, Andrea; Eckert, Ester M; Teruggi, Alessia; Fontaneto, Diego; Bertoni, Roberto; Callieri, Cristiana; Corno, Gianluca

    2015-08-01

    The fate of antibiotic resistance genes (ARGs) in environmental microbial communities is of primary concern as prodromal of a potential transfer to pathogenic bacteria. Although of diverse origin, the persistence of ARGs in aquatic environments is highly influenced by anthropic activities, allowing potential control actions in well-studied environments. However, knowledge of abundance and space-time distribution of ARGs in ecosystems is still scarce. Using quantitative real-time PCR, we investigated the presence and the abundance of twelve ARGs (against tetracyclines, β-lactams, aminoglycosides, quinolones and sulphonamides) at different sampling sites, depths and seasons, in Lake Maggiore, a large subalpine lake, and in the area of its watershed. We then evaluated the correlation between each ARG and a number of ecological parameters in the water column in the deepest part of the lake. Our results suggest the constitutive presence of at least four ARGs within the bacterial community with a high proportion of bacteria potentially resistant to tetracyclines and sulphonamides. The presence of these ARGs was independent of the total bacterial density and temperature. The dynamics of tet(A) and sulII genes were, however, positively correlated with dissolved oxygen and negatively to chlorophyll a, suggesting that the resistant microbes inhabit specific niches. These observations indicate that the lake is a reservoir of antibiotic resistances, highlighting the need of a deeper understanding of the sources of ARGs and the factors allowing their persistence in waters.

  18. Very large release of mostly volcanic carbon during the Palaeocene-Eocene Thermal Maximum.

    PubMed

    Gutjahr, Marcus; Ridgwell, Andy; Sexton, Philip F; Anagnostou, Eleni; Pearson, Paul N; Pälike, Heiko; Norris, Richard D; Thomas, Ellen; Foster, Gavin L

    2017-08-30

    The Palaeocene-Eocene Thermal Maximum (PETM) was a global warming event that occurred about 56 million years ago, and is commonly thought to have been driven primarily by the destabilization of carbon from surface sedimentary reservoirs such as methane hydrates. However, it remains controversial whether such reservoirs were indeed the source of the carbon that drove the warming. Resolving this issue is key to understanding the proximal cause of the warming, and to quantifying the roles of triggers versus feedbacks. Here we present boron isotope data-a proxy for seawater pH-that show that the ocean surface pH was persistently low during the PETM. We combine our pH data with a paired carbon isotope record in an Earth system model in order to reconstruct the unfolding carbon-cycle dynamics during the event. We find strong evidence for a much larger (more than 10,000 petagrams)-and, on average, isotopically heavier-carbon source than considered previously. This leads us to identify volcanism associated with the North Atlantic Igneous Province, rather than carbon from a surface reservoir, as the main driver of the PETM. This finding implies that climate-driven amplification of organic carbon feedbacks probably played only a minor part in driving the event. However, we find that enhanced burial of organic matter seems to have been important in eventually sequestering the released carbon and accelerating the recovery of the Earth system.

  19. Very large release of mostly volcanic carbon during the Palaeocene-Eocene Thermal Maximum

    NASA Astrophysics Data System (ADS)

    Gutjahr, Marcus; Ridgwell, Andy; Sexton, Philip F.; Anagnostou, Eleni; Pearson, Paul N.; Pälike, Heiko; Norris, Richard D.; Thomas, Ellen; Foster, Gavin L.

    2017-08-01

    The Palaeocene-Eocene Thermal Maximum (PETM) was a global warming event that occurred about 56 million years ago, and is commonly thought to have been driven primarily by the destabilization of carbon from surface sedimentary reservoirs such as methane hydrates. However, it remains controversial whether such reservoirs were indeed the source of the carbon that drove the warming. Resolving this issue is key to understanding the proximal cause of the warming, and to quantifying the roles of triggers versus feedbacks. Here we present boron isotope data—a proxy for seawater pH—that show that the ocean surface pH was persistently low during the PETM. We combine our pH data with a paired carbon isotope record in an Earth system model in order to reconstruct the unfolding carbon-cycle dynamics during the event. We find strong evidence for a much larger (more than 10,000 petagrams)—and, on average, isotopically heavier—carbon source than considered previously. This leads us to identify volcanism associated with the North Atlantic Igneous Province, rather than carbon from a surface reservoir, as the main driver of the PETM. This finding implies that climate-driven amplification of organic carbon feedbacks probably played only a minor part in driving the event. However, we find that enhanced burial of organic matter seems to have been important in eventually sequestering the released carbon and accelerating the recovery of the Earth system.

  20. The mechanism of polar vortex strengthening after large tropical volcanic eruptions as simulated in the MPI-ESM

    NASA Astrophysics Data System (ADS)

    Bittner, Matthias; Timmreck, Claudia; Schmidt, Hauke; Toohey, Matthew; Krueger, Kirstin

    2016-04-01

    State-of-the-art climate models that have participated in the recent CMIP5 model intercomparison activity do, on average, not produce the strengthened northern hemispheric (NH) polar vortex after historical large tropical volcanic eruptions as suggested by observations. Here, we study the impact of volcanic eruptions of different strength on the NH winter stratosphere in the MPI-ESM Earth system model. We compare the dynamical impact in ensemble simulations of a very large Tambora eruption in 1815 with the response to the two largest eruptions of the CMIP5 historical simulations (Krakatau, 1883; and Mt. Pinatubo, 1991). The mechanism, of the strengthening of the vortex can clearly be identified in the simulations for the Tambora eruption. An increased meridional stratospheric temperature gradient is often assumed to be the cause of the vortex strengthening. The position of the maximum temperature anomaly gradient is located, however, at approximately 30°N, far away from the polar vortex . Hence, the vortex strengthening is caused only indirectly by the changed temperature gradient which first produces a subtropical wind anomaly in early winter. This leads planetary waves propagating more equatorward causing finally the vortex strengthening. The simulated response to the weaker eruptions of Krakatau and Pinatubo is also a slight average strengthening of the polar vortex, but individual ensemble members differ strongly indicating that internal variability can mask the impact on the polar vortex in the NH post-eruption winter under such moderate eruption strengths. The large forcing of the Tambora eruption does not only cause a mean vortex strengthening but also a reduction of the ensemble variability of the vortex.

  1. Limnogeology in Brazil's "forgotten wilderness": a synthesis from the large floodplain lakes of the Pantanal

    USGS Publications Warehouse

    McGlue, Michael M.; Silva, Aguinaldo; Corradini, Fabricio A.; Zani, Hiran; Trees, Mark A.; Ellis, Geoffrey S.; Parolin, Mauro; Swarzenski, Peter W.; Cohen, Andrew S.; Assine, Mario L.

    2011-01-01

    Sediment records from floodplain lakes have a large and commonly untapped potential for inferring wetland response to global change. The Brazilian Pantanal is a vast, seasonally inundated savanna floodplain system controlled by the flood pulse of the Upper Paraguay River. Little is known, however, about how floodplain lakes within the Pantanal act as sedimentary basins, or what influence hydroclimatic variables exert on limnogeological processes. This knowledge gap was addressed through an actualistic analysis of three large, shallow (2- > Si4+ > Ca2+), mildly alkaline, freshwater systems, the chemistries and morphometrics of which evolve with seasonal flooding. Lake sills are bathymetric shoals marked by siliciclastic fans and marsh vegetation. Flows at the sills likely undergo seasonal reversals with the changing stage of the Upper Paraguay River. Deposition in deeper waters, typically encountered in proximity to margin-coincident topography, is dominated by reduced silty-clays with abundant siliceous microfossils and organic matter. Stable isotopes of carbon and nitrogen, plus hydrogen index measured on bulk organic matter, suggest that contributions from algae (including cyanobacteria) and other C3-vegetation dominate in these environments. The presence of lotic sponge spicules, together with patterns of terrigenous sand deposition and geochemical indicators of productivity, points to the importance of the flood pulse for sediment and nutrient delivery to the lakes. Flood-pulse plumes, waves and bioturbation likewise affect the continuity of sedimentation. Short-lived radioisotopes indicate rates of 0.11-0.24 cm year-1 at sites of uninterrupted deposition. A conceptual facies model, developed from insights gained from modern seasonal processes, can be used to predict limnogeological change when the lakes become isolated on the floodplain or during intervals associated with a strengthened flood pulse. Amplification of the seasonal cycle over longer time scales

  2. Air pollution in the shore zone of a Large Alpine Lake - 1 - Road dust and urban aerosols at Lake Tahoe, California-Nevada

    NASA Astrophysics Data System (ADS)

    VanCuren, R.; Pederson, J.; Lashgari, A.; Dolislager, L.; McCauley, E.

    2012-01-01

    Concentrated human activity and limited atmospheric mixing create a high potential for airborne pollutant impacts to alpine lakes developed as mountain resorts. Lake Tahoe is a major alpine resort straddling the California-Nevada border, receiving more than two million visitors each year. The lake's clarity has declined substantially since the inception of intense development in the Tahoe basin in the 1970s. The 2002-2004 Lake Tahoe Atmospheric Deposition Study (LTADS) was conducted as part of a multi-agency effort to develop a water quality management plan for the lake. Estimating aerosol deposition to the lake requires detailed knowledge of the spatial and temporal patterns of aerosol concentration, size distribution, and chemical composition over the entire basin - and developing a management plan requires also that the sources of the aerosols be known with considerable specificity. In lieu of the intensive measurement network implied by this level of detail, we hypothesized that a set of measurements to characterized the temporal, spatial, and size distribution patterns of particles in ambient air and in local emissions in the vicinity of Lake Tahoe could be used to extrapolate long time series of simple measurements to an annual aerosol deposition computation. Here we report the results of our detailed aerosol measurement campaign. Our results show that there are strong systematic and repeating gradients in aerosol loading that occur as functions of location, land use, traffic activity, and time of day, and that road dust is a major source of aerosols around the lake. In addition, we observed strong consistency of particle size distributions as a function of source type, largely independent of particle concentrations. Finally, we demonstrated the use of particle counters to directly observe downwind dispersion and deposition of particles. Together, these findings support the use of imputed location- and time-specific size distributions in annual aerosol

  3. Lake deposits record evidence of large post-1505 AD earthquakes in western Nepal

    NASA Astrophysics Data System (ADS)

    Ghazoui, Z.; Bertrand, S.; Vanneste, K.; Yokoyama, Y.; Van Der Beek, P.; Nomade, J.; Gajurel, A.

    2016-12-01

    According to historical records, the last large earthquake that ruptured the Main Frontal Thrust (MFT) in western Nepal occurred in 1505 AD. Since then, no evidence of other large earthquakes has been found in historical records or geological archives. In view of the catastrophic consequences to millions of inhabitants of Nepal and northern India, intense efforts currently focus on improving our understanding of past earthquake activity and complement the historical data on Himalayan earthquakes. Here we report a new record, based on earthquake-triggered turbidites in lakes. We use lake sediment records from Lake Rara, western Nepal, to reconstruct the occurrence of seismic events. The sediment cores were studied using a multi-proxy approach combining radiocarbon and 210Pb chronologies, physical properties (X-ray computerized axial tomography scan, Geotek multi-sensor core logger), high-resolution grain size, inorganic geochemistry (major elements by ITRAX XRF core scanning) and bulk organic geochemistry (C, N concentrations and stable isotopes). We identified several sequences of dense and layered fine sand mainly composed of mica, which we interpret as earthquake-triggered turbidites. Our results suggest the presence of a synchronous event between the two lake sites correlated with the well-known 1505 AD earthquake. In addition, our sediment records reveal five earthquake-triggered turbidites younger than the 1505 AD event. By comparison with historical archives, we relate one of those to the 1833 AD MFT rupture. The others may reflect successive ruptures of the Western Nepal Fault System. Our study sheds light on events that have not been recorded in historical chronicles. Those five MMI>7 earthquakes permit addressing the problem of missing slip on the MFT in western Nepal and reevaluating the risk of a large earthquake affecting western Nepal and North India.

  4. Were Holocene large slumps in Lake Geneva off the city of Lausanne caused by fault activity?

    NASA Astrophysics Data System (ADS)

    Correia Demand, Jehanne; Marillier, François; Kremer, Katrina; Girardclos, Stéphanie

    2014-05-01

    Lake Geneva is set in an area where glacier advances and retreats have carved Tertiary Molasse rocks in front of the Alpine units. Glacial and lacustrine sediments have accumulated in the lake on top of the Molasse. Within Holocene sedimentary layers, seismic studies in the central part of Lake Geneva ("Grand-Lac") have shown the presence of several mass transport deposits (MTD). A large one, MTD A, is observed off the city of Lausanne. The depth of the associated failure scars (100 m water depth), its volume (~ 0.13 km3), and the occurrence of other smaller MTDs that were possibly co-deposited with MTD A point to the occurrence of a major slide event in the lake, most likely associated with an earthquake. Based on 14C dating, the sediment age model for MTD A gives an age interval of 1865-1608 BC (Kremer et al. 2014). To resolve the details of the MTDs off Lausanne, and to better understand its geological context different seismic systems were used. These were a 3.5 KHz pinger with a theoretical vertical resolution of 0.15 m and a multichannel system with water-gun or air-gun seismic sources with vertical resolution of 0.6 m and 1.1 m, respectively. After a first pass processing, the multi-channel data were reprocessed in order to take into account the shape of the streamer in the water and to enhance the results of migration. In addition to typical seismic images of MTDs observed in other alpine lakes such as chaotic or transparent seismic character between well-organized reflections, two intriguing positive water-bottom topographic features associated with apparent sub-vertical offsets are revealed by the seismic data. They are located in the near vicinity of the depot centers of the MTDs and conspicuously located near faults in the Tertiary Molasse. These are thrust faults that are offset by small strike-slip faults, and we suggest that the positive topographic features are linked to a compressive component within the sediments due to displacements along these

  5. Human Impact on the Geomorphological Evolution of the Opak River Following the 2010 Large Volcanic Event of the Merapi (Indonesia)

    NASA Astrophysics Data System (ADS)

    Gob, F.; Gautier, E.; Virmoux, C.; Grancher, D.; Tamisier, V.; Primanda, K. W.; Wibowo, S. B.

    2016-12-01

    During large eruptions, active volcanos may introduce very large quantities of sediment to the drainage system through tephra falls and pyroclastic flows, thus modifying the river system. Once remobilized, the sediment inputs propagate downstream as a sediment wave modifying the channel geometry of the river and reloading the sediment cascade of the catchments. Considering the extreme nature of the volcanic events, the parameters that control the post-eruption evolution of the river system are generally only described as natural and the role played by human activities seems negligible. Communities that live on the volcano slopes and foothills are rather considered to suffer from natural disasters associated with the eruption and its consequences (lahars, etc.) or take advantage of the benefits of the volcanic environment (rich soil, mining and geothermal resources, etc.). This study examines the impact of human influence on the fluvial readjustment of a Javanese river impacted by a major eruption of the Merapi volcano (Indonesia) in October/November 2010. The basin of the Opak River was subject to substantial sediment input related to massive pyroclastic deposits that were remobilized by numerous lahars during the year after the eruption. Two study sites were equipped in order to evaluate the morphodynamic evolution of the riverbed of the Opak River. Topographic surveys, bedload particle marking and suspended sediment sampling revealed an important sediment mobilization during efficient flash-floods. Surprisingly, no bed aggradation related to the progradation of a sediment wave was observed. Two years after the eruptive event, marked bed incision was observed. The Opak River readjustment differs from that of other fluvial systems affected by massive eruptions in two ways. Firstly, the local population massively extracted the sand and blocks injected by the eruption as they represent a valuable economic resource. Secondly, several dams trapped the major part of the

  6. Eruptive history and tectonic setting of Medicine Lake Volcano, a large rear-arc volcano in the southern Cascades

    USGS Publications Warehouse

    Donnelly-Nolan, J. M.; Grove, T.L.; Lanphere, M.A.; Champion, D.E.; Ramsey, D.W.

    2008-01-01

    Medicine Lake Volcano (MLV), located in the southern Cascades ??? 55??km east-northeast of contemporaneous Mount Shasta, has been found by exploratory geothermal drilling to have a surprisingly silicic core mantled by mafic lavas. This unexpected result is very different from the long-held view derived from previous mapping of exposed geology that MLV is a dominantly basaltic shield volcano. Detailed mapping shows that < 6% of the ??? 2000??km2 of mapped MLV lavas on this southern Cascade Range shield-shaped edifice are rhyolitic and dacitic, but drill holes on the edifice penetrated more than 30% silicic lava. Argon dating yields ages in the range ??? 475 to 300??ka for early rhyolites. Dates on the stratigraphically lowest mafic lavas at MLV fall into this time frame as well, indicating that volcanism at MLV began about half a million years ago. Mafic compositions apparently did not dominate until ??? 300??ka. Rhyolite eruptions were scarce post-300??ka until late Holocene time. However, a dacite episode at ??? 200 to ??? 180??ka included the volcano's only ash-flow tuff, which was erupted from within the summit caldera. At ??? 100??ka, compositionally distinctive high-Na andesite and minor dacite built most of the present caldera rim. Eruption of these lavas was followed soon after by several large basalt flows, such that the combined area covered by eruptions between 100??ka and postglacial time amounts to nearly two-thirds of the volcano's area. Postglacial eruptive activity was strongly episodic and also covered a disproportionate amount of area. The volcano has erupted 9 times in the past 5200??years, one of the highest rates of late Holocene eruptive activity in the Cascades. Estimated volume of MLV is ??? 600??km3, giving an overall effusion rate of ??? 1.2??km3 per thousand years, although the rate for the past 100??kyr may be only half that. During much of the volcano's history, both dry HAOT (high-alumina olivine tholeiite) and hydrous calcalkaline

  7. Eruptive history and tectonic setting of Medicine Lake Volcano, a large rear-arc volcano in the southern Cascades

    NASA Astrophysics Data System (ADS)

    Donnelly-Nolan, Julie M.; Grove, Timothy L.; Lanphere, Marvin A.; Champion, Duane E.; Ramsey, David W.

    2008-10-01

    Medicine Lake Volcano (MLV), located in the southern Cascades ˜ 55 km east-northeast of contemporaneous Mount Shasta, has been found by exploratory geothermal drilling to have a surprisingly silicic core mantled by mafic lavas. This unexpected result is very different from the long-held view derived from previous mapping of exposed geology that MLV is a dominantly basaltic shield volcano. Detailed mapping shows that < 6% of the ˜ 2000 km 2 of mapped MLV lavas on this southern Cascade Range shield-shaped edifice are rhyolitic and dacitic, but drill holes on the edifice penetrated more than 30% silicic lava. Argon dating yields ages in the range ˜ 475 to 300 ka for early rhyolites. Dates on the stratigraphically lowest mafic lavas at MLV fall into this time frame as well, indicating that volcanism at MLV began about half a million years ago. Mafic compositions apparently did not dominate until ˜ 300 ka. Rhyolite eruptions were scarce post-300 ka until late Holocene time. However, a dacite episode at ˜ 200 to ˜ 180 ka included the volcano's only ash-flow tuff, which was erupted from within the summit caldera. At ˜ 100 ka, compositionally distinctive high-Na andesite and minor dacite built most of the present caldera rim. Eruption of these lavas was followed soon after by several large basalt flows, such that the combined area covered by eruptions between 100 ka and postglacial time amounts to nearly two-thirds of the volcano's area. Postglacial eruptive activity was strongly episodic and also covered a disproportionate amount of area. The volcano has erupted 9 times in the past 5200 years, one of the highest rates of late Holocene eruptive activity in the Cascades. Estimated volume of MLV is ˜ 600 km 3, giving an overall effusion rate of ˜ 1.2 km 3 per thousand years, although the rate for the past 100 kyr may be only half that. During much of the volcano's history, both dry HAOT (high-alumina olivine tholeiite) and hydrous calcalkaline basalts erupted

  8. Large-eddy simulations of a Salt Lake Valley cold-air pool

    NASA Astrophysics Data System (ADS)

    Crosman, Erik T.; Horel, John D.

    2017-09-01

    Persistent cold-air pools are often poorly forecast by mesoscale numerical weather prediction models, in part due to inadequate parameterization of planetary boundary-layer physics in stable atmospheric conditions, and also because of errors in the initialization and treatment of the model surface state. In this study, an improved numerical simulation of the 27-30 January 2011 cold-air pool in Utah's Great Salt Lake Basin is obtained using a large-eddy simulation with more realistic surface state characterization. Compared to a Weather Research and Forecasting model configuration run as a mesoscale model with a planetary boundary-layer scheme where turbulence is highly parameterized, the large-eddy simulation more accurately captured turbulent interactions between the stable boundary-layer and flow aloft. The simulations were also found to be sensitive to variations in the Great Salt Lake temperature and Salt Lake Valley snow cover, illustrating the importance of land surface state in modelling cold-air pools.

  9. Long-term impacts of invasive species on a native top predator in a large lake system

    USGS Publications Warehouse

    Rush, Scott A.; Paterson, Gordon; Johnson, Tim B.; Drouillard, Ken G.; Haffner, Gordon D.; Hebert, Craig E.; Arts, Michael T.; McGoldrick, Daryl J.; Backus, Sean M.; Lantry, Brian F.; Lantry, Jana R.; Schaner, Ted; Fisk, Aaron T.

    2012-01-01

    1. Declining abundances of forage fish and the introduction and establishment of non-indigenous species have the potential to substantially alter resource and habitat exploitation by top predators in large lakes. 2. We measured stable isotopes of carbon (δ13C) and nitrogen (δ15N) in field-collected and archived samples of Lake Ontario lake trout (Salvelinus namaycush) and five species of prey fish and compared current trophic relationships of this top predator with historical samples. 3. Relationships between δ15N and lake trout age were temporally consistent throughout Lake Ontario and confirmed the role of lake trout as a top predator in this food web. However, δ13C values for age classes of lake trout collected in 2008 ranged from 1.0 to 3.9‰ higher than those reported for the population sampled in 1992. 4. Isotope mixing models predicted that these changes in resource assimilation were owing to the replacement of rainbow smelt (Osmerus mordax) by round goby (Neogobius melanostomus) in lake trout diet and increased reliance on carbon resources derived from nearshore production. This contrasts with the historical situation in Lake Ontario where δ13C values of the lake trout population were dominated by a reliance on offshore carbon production. 5. These results indicate a reduced capacity of the Lake Ontario offshore food web to support the energetic requirements of lake trout and that this top predator has become increasingly reliant on prey resources that are derived from nearshore carbon pathways.

  10. Large offset normal faults, ridge obliquity, and the distribution of volcanism at a melt-poor ultra-slow spreading ridge

    NASA Astrophysics Data System (ADS)

    Cannat, M.; Sauter, D.; Mendel, V.; Escartin, J.

    2006-12-01

    We report on an extensive set of off-axis bathymetry, gravity, and magnetic data, providing a 26 myrs-long record of axial tectonic and magmatic processes over a 660 km-long, and very melt-poor portion of the ultra- slow Southwest Indian Ridge (SWIR). 37% of the total mapped area, both on and off-axis, has a smooth seafloor morphology, and appears to have formed with no, or very little axial volcanism. This smooth seafloor terrane is inferred to expose large expanses of mantle-derived peridotites, with minor gabbros and diabases. It locally transitions into corrugated terranes (4% of mapped area). Volcanic seafloor, with numerous volcanic cones and tight, spreading-perpendicular fault scarps, covers the remaining 59% of the mapped area. In this talk, we focus on the transition from smooth to volcanic terranes, showing that while the smooth seafloor forms at minimal melt supply to the ridge, gravity anomalies suggest that the volcanic seafloor forms over a range of crustal thickness and melt supply: from very reduced as in smooth terranes, to about twice the average for this region of the SWIR. Crustal magnetization in volcanic terranes appears to correlate with gravity-derived crustal thickness, and is locally as low as in smooth terranes. Finally, the analysis of seafloor morphology suggests that major ridge-parallel normal faults in smooth terranes also controlled the accretion of adjacent volcanic seafloor. These observations lead us to propose that there is no clearcut change in accretion processes between the two types of seafloor, but rather that beneath the upper volcanic layer, volcanic terranes of the SWIR may display a range of intermediate and lower crust compositions, from dominantly ultramafic, to dominantly basaltic. Ridge obliquity in our study area varies along-axis from more than 30, to less than 10 degrees. In oblique regions, we observe that volcanic terranes are systematically associated with a reorientation of major faults, from oblique to

  11. Putative Large and Small Volcanic Edifices in Valles Marineris, Mars, and Evidence of Ground Water/Ice

    NASA Astrophysics Data System (ADS)

    Chapman, M. G.; Smellie, J. L.

    2001-12-01

    Large mounds and mesas of interior layered deposits (ILDs) in Valles Marineris Chasmata have been suggested to be sub-ice volcanoes based on MGS and Viking data [1,2,3]. Similar to terrestrial sub-ice volcanoes, spectral investigation indicates the bright mounds are hydrothermally altered, palagonitic rocks [4]. These putative edifices are associated with outcrops of dark materials that have each been interpreted previously as young, volcanic ash deposits of mafic composition [5,6]. Spectral investigation also indicates that the dark materials are less water-altered and mafic in composition [4]. TES-detected concentrations of crystalline hematite have been noted to occur in these dark materials [7]. Mars Observer Camera (MOC) images indicate that the dark materials locally blanket chasmata floors and embay ILDs and are associated with small volcanic vents. These apparent vents may have emitted some of the ash-like deposits. The vent features appear very young, lacking impact craters and having non-eroded rims. Where they embay the ILDs, the vents have low rims similar to terrrestrial maar or tuff cones, which possibly indicates interaction with groundwater or ice. In support of ground-ice within the ILDs, MOC data show (1) channels that occur on the flanks of the bright mounds, and (2) theatre-headed gullies are eroded into caprock of the ILDs and the heads of valleys, formerly interpreted by Viking data to be wind flutes on ILD flanks. Both features may be related to spring sapping. MOC images also show that dark materials on the floor of many chasmata and Aram Chaos are associated with small fissures or cone-shaped mounds with central depressions that do not appear to have interacted with ground-ice. Perhaps late-stage water/ice circulated or was stored within the interior mounds after removal of large ponds of surface ice elsewhere. Young, dark, volcanic ash in the chasmata could be a product of both "dry" volcanism and water/magma interactions, which may have

  12. Mantle Heterogeneities and Crustal Processes of the Cascade Arc Represented by Basalts of the Poison Lake Chain, Lassen Volcanic Center, California

    NASA Astrophysics Data System (ADS)

    Wenner, J. M.; Teasdale, R.; Hiebing, M. S.; Lenz, Q. A.; Kroeninger, K.

    2013-12-01

    Basalts in the Poison Lake chain (PLC) include eight chemically distinct groups of primitive calc-alkaline basalts (defined by major element geochemistry and mineralogy). Located east of the Lassen Volcanic Center, PLC primitive basalts span the range of basalt compositions exposed throughout the entire Cascade arc (e.g. Ba: 100-1000 ppm; (Sr/P)n: 1.3 - 3.8; La/Yb: 4-26). PLC groups have trace-element and isotope ratios that show little evidence of direct genetic relationships among groups or a common source. Major, trace element and isotope ratios show evidence of contributions from multiple mantle sources including MORB, fluid rich subduction component and subduction-related sediment. Some groups record compositional variations from multiple mantle sources with minimal crustal processing. Similarly, preliminary probe data for olivine-spinel pairs suggest that some PLC groups are derived from heterogeneous mantle sources. Geochemical evidence indicates that other groups have petrogenetic histories that include crustal processes such as fractional crystallization, mixing or crustal contamination. Isotope ratios, major and trace element compositions and crystal compositions provide insights into the extent of source heterogeneities versus the degree of crustal processing. The broad range of compositional variations in basalts of PLC provides the opportunity to examine the extent of mantle heterogeneities and crustal processing in a small geographic area (50km2) for rocks that are nearly the same age (100-110 ka). The diverse primitive compositions erupted in the constrained time and space of the Poison Lake chain and the lack of genetic relationship among groups make it the ideal place to investigate the small scale nature of mantle domains and the roles of subduction and modification processes in the generation of basaltic compositions in arcs such as the Cascades, Mexico, Japan.

  13. Volcanic hazard management in dispersed volcanism areas

    NASA Astrophysics Data System (ADS)

    Marrero, Jose Manuel; Garcia, Alicia; Ortiz, Ramon

    2014-05-01

    Traditional volcanic hazard methodologies were developed mainly to deal with the big stratovolcanoes. In such type of volcanoes, the hazard map is an important tool for decision-makers not only during a volcanic crisis but also for territorial planning. According to the past and recent eruptions of a volcano, all possible volcanic hazards are modelled and included in the hazard map. Combining the hazard map with the Event Tree the impact area can be zoned and defining the likely eruptive scenarios that will be used during a real volcanic crisis. But in areas of disperse volcanism is very complex to apply the same volcanic hazard methodologies. The event tree do not take into account unknown vents, because the spatial concepts included in it are only related with the distance reached by volcanic hazards. The volcanic hazard simulation is also difficult because the vent scatter modifies the results. The volcanic susceptibility try to solve this problem, calculating the most likely areas to have an eruption, but the differences between low and large values obtained are often very small. In these conditions the traditional hazard map effectiveness could be questioned, making necessary a change in the concept of hazard map. Instead to delimit the potential impact areas, the hazard map should show the expected behaviour of the volcanic activity and how the differences in the landscape and internal geo-structures could condition such behaviour. This approach has been carried out in La Palma (Canary Islands), combining the concept of long-term hazard map with the short-term volcanic scenario to show the expected volcanic activity behaviour. The objective is the decision-makers understand how a volcanic crisis could be and what kind of mitigation measurement and strategy could be used.

  14. Effect of wave-current interactions on sediment resuspension in large shallow Lake Taihu, China.

    PubMed

    Li, Yiping; Tang, Chunyan; Wang, Jianwei; Acharya, Kumud; Du, Wei; Gao, Xiaomeng; Luo, Liancong; Li, Huiyun; Dai, Shujun; Mercy, Jepkirui; Yu, Zhongbo; Pan, Baozhu

    2017-02-01

    The disturbance of the water-sediment interface by wind-driven currents and waves plays a critical role in sediment resuspension and internal nutrient release in large, shallow lakes. This study analyzed the effects of the interactions between wind-induced currents an1d waves on the driving mechanism of sediment resuspension in Lake Taihu, the third largest freshwater lake in China, using acoustic and optic techniques to collect long-term, high-frequency, synchronous in situ measurements of wind, currents, waves, and suspended solid concentrations (SSCs). The results suggested that water turbidity started to increase at wind speeds of approximately 4 m/s and significantly increased when wind speeds exceeded 6 m/s. In most cases, wind-induced waves were the main energy source for changes in turbidity. Wave-generated shear stress contributed more than 95% to sediment resuspension and that only in weak wind conditions (<4 m/s) did the lake bottom shear stresses generated by currents and waves contributed equally. The relationship between SSC and bottom shear stress generated by wave was established by fitting the observed results. The processes of sediment dynamics were divided into four stages (A through D) according to three shear-stress thresholds. In stage A, SSC remained stable (about 45 mg/L) and τw was less than 0.02 N/m(2). In stage B, the sediment bed was starting to be activated (SSC 45∼60 mg/L) and τw was in the range of 0.02∼0.07 N/m(2). In stage C, a medium amount of sediment was suspended (SSC 60∼150 mg/L) and τw ranged from 0.07 to 0.3 N/m(2). In stage D, large amount of sediment was suspended (SSC 150∼300 mg/L) and τw was larger than 0.3 N/m(2). The findings of this paper reveal the driving mechanism of sediment resuspension, which may further help to evaluate internal nutrient release in large shallow Lake Taihu.

  15. Large fractionations of C and H isotopes related to methane oxidation in Arctic lakes

    NASA Astrophysics Data System (ADS)

    Cadieux, Sarah B.; White, Jeffrey R.; Sauer, Peter E.; Peng, Yongbo; Goldman, Amy E.; Pratt, Lisa M.

    2016-08-01

    Microbial oxidation of methane (CH4) plays a central role in carbon cycling in Arctic lakes, reducing potential CH4 emissions associated with warming. Isotopic signatures of CH4 (δ13C and δ2H) are indicators of microbial oxidation, wherein the process strongly enriches 13C and 2H in residual CH4. We present δ13C and δ2H measurements obtained from sampling the water column and sediment for dissolved CH4 from three, small Arctic lakes in western Greenland under both open-water and ice-covered conditions from 2013 to 2014. Despite substantial variations in aquatic chemistry among the lakes, δ13C and δ2H of CH4 suggested that CH4 was produced predominantly by acetoclastic methanogenesis in the littoral sediments and hydrogenotrophic methanogenesis in the profundal sediments in all of the lakes. Surprisingly large variations for both δ13C and δ2H of CH4 were observed, with δ13C extending from -72‰ to +7.4‰ and δ2H from -390‰ to +250‰. The CH4 isotopic values reported here were significantly more enriched (p < 0.0001) in both 13C and 2H than values reported from other Arctic freshwater environments. As is characteristic of methanotrophy, the enrichment in 13C and 2H was associated with low CH4 concentrations. We suggest that the CH4 most enriched in 13C and 2H may reflect unusually efficient methanotrophic communities in Arctic ice-margin lakes. This study provides the first measurement of δ2H for CH4 in an Arctic freshwater environment at concentrations <10 μM. The extreme enrichment of 13C and 2H of CH4 from Arctic methanotrophy has significant implications for interpreting sources and sinks of CH4. Without knowledge of local geology, stable isotope values of CH4 higher than -30‰ for δ13C and -150‰ for δ2H could be misinterpreted as thermogenic, geothermal, or abiogenic origins. Given crystalline bedrock and the strong positive correlation between δ13C and δ2H throughout the water columns in three Arctic lakes confirms that CH4 heavily

  16. Local to regional scale industrial heavy metal pollution recorded in sediments of large freshwater lakes in central Europe (lakes Geneva and Lucerne) over the last centuries.

    PubMed

    Thevenon, Florian; Graham, Neil D; Chiaradia, Massimo; Arpagaus, Philippe; Wildi, Walter; Poté, John

    2011-12-15

    This research first focuses on the spatial and temporal patterns of heavy metals from contrasting environments (highly polluted to deepwater sites) of Lake Geneva. The mercury (Hg) and lead (Pb) records from two deepwater sites show that the heavy metal variations before the industrial period are primarily linked to natural weathering input of trace elements. By opposition, the discharge of industrial treated wastewaters into Vidy Bay of Lake Geneva during the second part of the 20th century, involved the sedimentation of highly metal-contaminated sediments in the area surrounding the WWTP outlet pipe discharge. Eventually, a new Pb isotope record of sediments from Lake Lucerne identifies the long-term increasing anthropogenic lead pollution after ca. 1500, probably due to the development of metallurgical activities during the High Middle Ages. These data furthermore allows to compare the recent anthropogenic sources of water pollution from three of the largest freshwater lakes of Western Europe (lakes Geneva, Lucerne, and Constance). High increases in Pb and Hg highlight the regional impact of industrial pollution after ca. 1750-1850, and the decrease of metal pollution in the 1980s due to the effects of remediation strategies such as the implementation of wastewater treatment plants (WWTPs). However, at all the studied sites, the recent metal concentrations remain higher than pre-industrial levels. Moreover, the local scale pollution data reveal two highly contaminated sites (>100 μg Pb/g dry weight sediment) by industrial activities, during the late-19th and early-20th centuries (Lake Lucerne) and during the second part of the 20th century (Vidy Bay of Lake Geneva). Overall, the regional scale pollution history inferred from the three large and deep perialpine lakes points out at the pollution of water systems by heavy metals during the last two centuries due to the discharge of industrial effluents. Copyright © 2011 Elsevier B.V. All rights reserved.

  17. Peralkaline felsic magmatism at the Nemrut volcano, Turkey: impact of volcanism on the evolution of Lake Van (Anatolia) IV

    NASA Astrophysics Data System (ADS)

    Macdonald, Ray; Sumita, Mari; Schmincke, Hans-Ulrich; Bagiński, Bogusław; White, John C.; Ilnicki, Sławomir S.

    2015-04-01

    Nemrut volcano, adjacent to Lake Van (Turkey), is one of the most important peralkaline silicic centres in the world, where magmatism for ~570,000 years has been dominated by peralkaline trachytes and rhyolites. Using onshore and Lake Van drill site tephra samples, we document the phenocryst and glass matrix compositions, confirming a complete spectrum from very rare mafic to dominantly silicic magmas. Magma mixing has been common and, along with the multi-lineage nature of the magmas, indicates that Nemrut has been a very open system where, nevertheless, compositionally zoned caps developed during periods of relative eruptive quiescence. Geothermometry suggests that the intermediate-silicic magmas evolved in an upper crustal magma reservoir at temperatures between 1100 and 750 °C, at fO2 close to the FMQ buffer. The silicic magmas either were halogen poor or exsolved a halogen-rich phase prior to or during eruption. An unusual Pb-rich phase, with up to 98.78 wt% PbO, is interpreted as having exsolved from the intermediate-rhyolitic magmas.

  18. Rock magnetic studies on sediments from Erlongwan maar lake, Long Gang Volcanic Field, Jilin province, NE China

    NASA Astrophysics Data System (ADS)

    Frank, Ute

    2007-01-01

    Detailed rock magnetic investigations were carried out on two 23-m-long sediment cores from Erlongwan maar lake, NE China. The completely laminated sediment sequence of the lake is interrupted by 410 graded layers with thicknesses between 0.1 and 150 cm. Magnetite of PSD-size was identified as the main magnetic carrier mineral by temperature-dependent measurements of the saturation magnetization and determination of hysteresis parameters. The minerogenic components in the laminated sediments and the graded layers are nearly identical, and their rock magnetic characteristics reflect the prevailing conditions, anoxic or oxic, during deposition. The most reliable criteria for estimating the availability of oxygen is whether an increase in minerogenic influx is linked to a shift in the magnetic grain size spectrum to coarser (oxic) or finer (anoxic) grains. Comparison of different rock magnetic parameters indicative for magnetic grain size and coercitivity revealed, that the S-ratio which is known to reflect the presence of high coercive minerals, is grain size indicative in sediments with a monomineralic magnetic composition.

  19. LakeMIP Kivu: Evaluating the representation of a large, deep tropical lake by a set of 1-dimensional lake models

    NASA Astrophysics Data System (ADS)

    Thiery, Wim; Stepanenko, Viktor; Darchambeau, François; Joehnk, Klaus; Martynov, Andrey; Mironov, Dmitrii; Perroud, Marjorie; van Lipzig, Nicole

    2013-04-01

    The African great lakes are of utmost importance for the local economy (fishing), as well as being essential to the survival of the local people. During the last decades, these lakes experienced fast changes in ecosystem structure and functioning and their future evolution is a major concern. In this study, for the first time a set of one-dimensional lake models are evaluated over East-Africa, in particular over Lake Kivu (2.28 °S; 28.98 °E). The unique limnology of meromictic Lake Kivu, with the importance of salinity and geothermal springs in a tropical high-altitude climate, presents a worthy challenge to the 1D-lake models currently involved in the Lake Model Intercomparison Project (LakeMIP). Furthermore, this experiment will serve as the basis for a future, more complex intercomparison, coupling lake models with atmospheric circulation models to analyse climate change effects on the lake. Meteorological observations from two automatic weather stations, one at Kamembe airport (Rwanda, 2003-2008), the other at ISP Bukavu (DRC, 2003-2011), are used to drive each of these models. For the evaluation, a unique dataset is used which contains over 150 temperature profiles recorded since 2002. The standard LakeMIP protocol is adapted to mirror the limnological conditions in Lake Kivu and to unify model parameters as far as possible. Since some lake models do not account for salinity and its effect upon lake stratification, two sets of simulations are performed with each model: one for the freshwater layer only (60 m) and one for the average lake depth (240 m) including salinity. Therewith, on the one hand it is investigated whether each model is able to reproduce the correct mixing regime in Lake Kivu and captures the controlling of this seasonality by the relative humidity, which constrains evaporation except during summer (JJA). On the other hand, the ability of different models to simulate salinity- and geothermal-induced effects upon deep water stratification is

  20. The Rungwe Volcanic Province, Tanzania - A volcanological review

    NASA Astrophysics Data System (ADS)

    Fontijn, Karen; Williamson, David; Mbede, Evelyne; Ernst, Gerald G. J.

    2012-02-01

    The Rungwe Volcanic Province in SW Tanzania is a densely populated area that is considered volcanically active. As part of the East African Rift System, a significant control of tectonic activity seems to exist on the location and also potential destabilization of volcanic edifices. Three large volcanoes, Ngozi, Rungwe, and Kyejo, dominate the landscape and all show contrasting eruptive behaviour in the recent geological past. Kyejo volcano is a flow-dominated volcano that had a historic lava flow eruption. Lake sediment cores, drilled in Lakes Malawi, Masoko, Rukwa, and Tanganyika, provide a record of frequent explosive eruptions in the last few tens of thousands of years. In combination with on-land stratigraphic observations, they constrain the minimum eruptive frequency of especially Rungwe and Ngozi volcanoes. Both volcanoes had Plinian-style eruptions in the Holocene. The most striking documented Rungwe eruption, the ca. 4 ka Rungwe Pumice, is a rare case of a Plinian eruption in near-wind-free conditions. Furthermore, the Rungwe Pumice, just like any other Rungwe tephra deposit, does not show any evidence of pyroclastic density current deposits. Apart from explosive eruptions at a range of scales happening every few hundred years at Rungwe, the volcano also experienced at least two sector collapse events generating debris avalanches. All existing evidence shows that the Rungwe Volcanic Province is prone to future significant explosive eruptions. To further assess, quantify and mitigate volcanic hazard risks, extensive and systematic multidisciplinary geological research, and both volcanic and tectonic monitoring are needed.

  1. Discovery of a Large Volcanic Eruption in 1761 From Pre-Venus-Transit and Other Proxy Data, Using Benjamin Franklin's Method of Linking the 1783-1784 Cold Weather to the Laki Eruption

    NASA Astrophysics Data System (ADS)

    Pang, K. D.

    2006-12-01

    , Nature 307, 121, 1984]. Annual weather reviews in imperial, provincial and county histories in China have been examined. Unseasonable cold are classified by their degree of severity: (1) Late (April-June) or early (July-Sept.) killing frosts; (2) Bitter cold/heavy snowfall; and (3) Heavy sustained snowfall, bitter cold with frozen wells, lakes and rivers. The latter cases were often widespread and multi-year, with the coast icebound also. The weather of 1761-1762 was a "3." Heavy sustained snow fell over many sites from the Tropic of Cancer to the Yellow River. In the north wells and rivers froze. Taihu (Great Lake near Shanghai) and nearby rivers froze over and were not navigable. Innumerable trees, birds and livestock perished, etc. Whereas all three of Benjamin Franklin's conditions have been met I conclude that a very large volcanic eruption early in 1761 had a major impact on the Earth's climate. Its location is unknown, but was probably low- or mid-latitude, as sulfuric acid from the volcanic cloud settled onto both poles. Finally Benjamin Franklin's criteria for a climate-altering volcanic eruption are still universally used (the appearance of brilliant red twilight displays have since been added). Moreover his legacy continues to inspire climate researchers. See, for example, "Climatic Impact of the mid-15th-Century Kuwae Caldera Formation...," Pang, Eos 74, No. 43, 106, 1993; and as cited in "Earth in Balance," Al Gore, p. 379, Penguin, 1993. See also "Constantinople's Volcanic Twilight," Lynn Simarski, Aramco World 47, No. 6, 8-13, 1996.

  2. Volcanism on Io

    NASA Astrophysics Data System (ADS)

    Davies, Ashley Gerard

    2014-03-01

    Preface; Introduction; Part I. Io, 1610 to 1995: Galileo to Galileo: 1. Io, 1610-1979; 2. Between Voyager and Galileo: 1979-95; 3. Galileo at Io; Part II. Planetary Volcanism: Evolution and Composition: 4. Io and Earth: formation, evolution, and interior structure; 5. Magmas and volatiles; Part III. Observing and Modeling Volcanic Activity: 6. Observations: thermal remote sensing of volcanic activity; 7. Models of effusive eruption processes; 8. Thermal evolution of volcanic eruptions; Part IV. Galileo at Io: the Volcanic Bestiary: 9. The view from Galileo; 10. The lava lake at Pele; 11. Pillan and Tvashtar: lava fountains and flows; 12. Prometheus and Amirani: Effusive activity and insulated flows; 13. Loki Patera: Io's powerhouse; 14. Other volcanoes and eruptions; Part V. Volcanism on Io: The Global View: 15. Geomorphology: paterae, shields, flows and mountains; 16. Volcanic plumes; 17. Hot spots; Part VI. Io after Galileo: 18. Volcanism on Io: a post-Galileo view; 19. The future of Io observations; Appendix 1; Appendix 2; References; Index.

  3. Volcanism on Io

    NASA Astrophysics Data System (ADS)

    Davies, Ashley Gerard

    2007-08-01

    Preface; Introduction; Part I. Io, 1610 to 1995: Galileo to Galileo: 1. Io, 1610-1979; 2. Between Voyager and Galileo: 1979-1995; 3. Galileo at Io; Part II. Planetary Volcanism: Evolution and Composition: 4. Io and Earth: formation, evolution, and interior structure; 5. Magmas and volatiles; Part III. Observing and Modeling Volcanic Activity: 6. Observations: thermal remote sensing of volcanic activity; 7. Models of effusive eruption processes; 8. Thermal evolution of volcanic eruptions; Part IV. Galileo at Io: the Volcanic Bestiary: 9. The view from Galileo; 10. The lava lake at Pele; 11. Pillan and Tvashtar: lava fountains and flows; 12. Prometheus and Amirani: Effusive activity and insulated flows; 13. Loki Patera: Io's powerhouse; 14. Other volcanoes and eruptions; Part V. Volcanism on Io: The Global View: 15. Geomorphology: paterae, shields, flows and mountains; 16. Volcanic plumes; 17. Hot spots; Part VI. Io after Galileo: 18. Volcanism on Io: a post-Galileo view; 19. The future of Io observations; Appendix 1; Appendix 2; References; Index.

  4. The Influence of Macrophytes on Sediment Resuspension and the Effect of Associated Nutrients in a Shallow and Large Lake (Lake Taihu, China)

    PubMed Central

    Zhu, Mengyuan; Zhu, Guangwei; Nurminen, Leena; Wu, Tingfeng; Deng, Jianming; Zhang, Yunlin; Qin, Boqiang; Ventelä, Anne-Mari

    2015-01-01

    A yearlong campaign to examine sediment resuspension was conducted in large, shallow and eutrophic Lake Taihu, China, to investigate the influence of vegetation on sediment resuspension and its nutrient effects. The study was conducted at 6 sites located in both phytoplankton-dominated zone and macrophyte-dominated zone of the lake, lasting for a total of 13 months, with collections made at two-week intervals. Sediment resuspension in Taihu, with a two-week high average rate of 1771 g·m-2·d-1 and a yearly average rate of 377 g·m-2·d-1, is much stronger than in many other lakes worldwide, as Taihu is quite shallow and contains a long fetch. The occurrence of macrophytes, however, provided quite strong abatement of sediment resuspension, which may reduce the sediment resuspension rate up to 29-fold. The contribution of nitrogen and phosphorus to the water column from sediment resuspension was estimated as 0.34 mg·L-1 and 0.051 mg·L-1 in the phytoplankton-dominated zone. Sediment resuspension also largely reduced transparency and then stimulated phytoplankton growth. Therefore, sediment resuspension may be one of the most important factors delaying the recovery of eutrophic Lake Taihu, and the influence of sediment resuspension on water quality must also be taken into account by the lake managers when they determine the restoration target. PMID:26030094

  5. Large-scale patterns in summer diffusive CH4 fluxes across boreal lakes, and contribution to diffusive C emissions.

    PubMed

    Rasilo, Terhi; Prairie, Yves T; Del Giorgio, Paul A

    2015-03-01

    Lakes are a major component of boreal landscapes, and whereas lake CO2 emissions are recognized as a major component of regional C budgets, there is still much uncertainty associated to lake CH4 fluxes. Here, we present a large-scale study of the magnitude and regulation of boreal lake summer diffusive CH4 fluxes, and their contribution to total lake carbon (C) emissions, based on in situ measurements of concentration and fluxes of CH4 and CO2 in 224 lakes across a wide range of lake type and environmental gradients in Québec. The diffusive CH4 flux was highly variable (mean 11.6 ± 26.4 SD mg m(-2)  d(-1) ), and it was positively correlated with temperature and lake nutrient status, and negatively correlated with lake area and colored dissolved organic matter (CDOM). The relationship between CH4 and CO2 concentrations fluxes was weak, suggesting major differences in their respective sources and/or regulation. For example, increasing water temperature leads to higher CH4 flux but does not significantly affect CO2 flux, whereas increasing CDOM concentration leads to higher CO2 flux but lower CH4 flux. CH4 contributed to 8 ± 23% to the total lake C emissions (CH4  + CO2 ), but 18 ± 25% to the total flux in terms of atmospheric warming potential, expressed as CO2 -equivalents. The incorporation of ebullition and plant-mediated CH4 fluxes would further increase the importance of lake CH4 . The average Q10 of CH4 flux was 3.7, once other covarying factors were accounted for, but this apparent Q10 varied with lake morphometry and was higher for shallow lakes. We conclude that global climate change and the resulting shifts in temperature will strongly influence lake CH4 fluxes across the boreal biome, but these climate effects may be altered by regional patterns in lake morphometry, nutrient status, and browning. © 2014 John Wiley & Sons Ltd.

  6. Water level and ice monitoring of large and middle-sized lakes of Russia

    NASA Astrophysics Data System (ADS)

    Rybushkina, Galina; Troitskaya, Yuliya; Soustova, Irina

    2014-05-01

    Studying of water level and ice cover of large and medium sized lakes are of interest because they represent natural reservoirs of fresh water and are associated with human economic activity. Moreover, the water level variations and ice cover duration are important indicators of climate changes. In addition to in situ observations satellite methods of monitoring have certain advantages connected with the global coverage, instantaneous observations of large water areas and relatively low cost. However, the use of satellite methods for inland waters is often difficult because of their spatial resolution comparable to or greater than the size of water reservoirs. Remote sensing with high spatial resolution is often associated with a large repeat period of data (ICESat), or with a significant dependence of the quality of data on weather conditions (Landsat). In this regard, the use of Jason -2 satellite equipped with dual-frequency (13.6 GHz and 5 GHz) radar altimeters and passive three-frequency (18, 21 and 37 GHz) microwave radiometers is of interest, because the footprint diameter of their altimeters in Ku-band is about 10 km and the repeat period of observations is ten days, that make it suitable for observations of large and medium-sized inland waters. In this work we use the data of three mentioned above satellites to determine the water level variations and ice-cover régime of 8 lakes in Russia, water areas of which are intersected by the tracks of these satellites. Variations in water level is calculated on the base of retracking method [1] taking into account the fact that the waveforms of altimetry pulses of satellites Jason-2 and ICESat are distorted due to the influence of land. Satellite data are compared with available in situ observations and the correlation coefficient with in situ observations is calculated. The ice regime of lakes is determined using a new method [2] based on the analysis of the difference between the brightness temperatures of land

  7. Surface subsidence caused by mantle plumes and volcanic loading in large igneous provinces

    NASA Astrophysics Data System (ADS)

    Leng, Wei; Zhong, Shijie

    2010-03-01

    Large igneous provinces form with massive flood basalts being erupted over a large region within a few million years. A prevailing model for their formation is a mantle plume model in which a plume head originates from the core-mantle boundary, ascends through the mantle, and produces topographic uplift and eventually massive melting at the surface. However, many geological observations indicate surface subsidence in the central region before or during flood basalt eruptions. In this study, we demonstrate that a plume head temporarily ponding below the 660-km phase change boundary causes significant subsidence at the Earth's surface over an extended period before the eruption, and that the loading from erupted basalts causes surface subsidence at the periphery of the eruption area that affects the environment for subsequent episodes of basalt eruptions. Our studies therefore demonstrate that the observed subsidence history in many flood basalt provinces is characteristic of the dynamics of mantle plumes and may be used as diagnostics for identifying plume-induced flood basalt events.

  8. Transport and emplacement mechanisms of large volcanic debris avalanches: evidence from the northwest sector of Cantal Volcano (France)

    NASA Astrophysics Data System (ADS)

    Schneider, Jean-Luc; Fisher, Richard V.

    1998-07-01

    Large volcanic debris avalanche (VDA) deposits of Miocene age occur within the stratigraphic sequence of Cantal stratovolcano (central France). The VDA of Cantal volcano were initiated by sector collapse of a cone of high elevation (up to 4500 m. a.s.l.). Two distinct superimposed VDA deposit units (Breccias I and II) resulted from at least two successive large-scale collapse events during the evolution of the volcanic complex. Breccia I, the oldest one, is very thick (up to 200 m) and heterolithologic. It is overlain by Breccia II, which is thinner (up to 50 m) and contains more heterometric clasts ranging from hectometer- to millimeter-size. The VDA deposits are poorly sorted. Clasts are angular and highly fractured at different scales, often with jigsaw fit. In Breccia II, jigsaw megaclasts have usually subspheric shapes with size decreasing distally. Basal deposits commonly display thin inversely graded layers, reorientated clasts along ramp structures, and cataclasis of the substratum. Some units have a distal fabric in the form of a poorly developed clast imbrication. The clasts are commonly sub-rounded thereby indicating abrasion during viscous flow. Anisotropy of magnetic susceptibility (A.M.S.) measurements indicate absence of a preferentially oriented matrix fabric. Magnetic foliation parallel to the bedding suggests that the depositional process is dominated by particle settling. The magnetic fabric is better organized in distal deposits where magnetic carriers are imbricated. Moreover, the fragmented clasts and megaclasts are not abraded, rather inflation led to isotropic spherical dispersion of clastic material (=Isotropic Dispersive Inflation) which fed the interclast matrix. This is also confirmed by the lack of rotation at the individual crystal level. All these data strongly suggest transport of VDA by liquified non-turbulent granular flows. Distally, imbricated deposits suggest more turbulent flow. Emplacement of the VDA results from progressive

  9. The storage and release of water from a large glacier-dammed lake; Russell Lake near Yakutat, Alaska, 1986

    USGS Publications Warehouse

    Seitz, H.R.; Thomas, D.S.; Tomlinson, Bud

    1986-01-01

    In May 1986, the entrance to Russell Fiord, Alaska, was blocked by the advancing Hubbard Glacier, forming a 34-mile long ice-dammed lake. Runoff to the lake, mainly runoff from melting snow and glacier ice, filled the lake to an elevation of 83 feet above sea level by October 8, when the ice dam failed. The lake level rose at an average rate of 0.6 ft/day, and average daily inflow to the lake was calculated to be 16,500 cu ft/sec. After failure of the ice dam, the water level fell to the former high tide level of Russell Fiord within 24 hours. Average discharge through the breach in the ice dam during a 4-hr period of maximum water level decline is estimated to have been 3.8 million cu ft/sec. The formation and breakout of the lake is expected to be repeated as the Hubbard Glacier continues to advance, though the timing of the phenomenon cannot be predicted with certainty. (USGS)

  10. Fremont Lake, Wyoming - Preliminary survey of a large mountain lake: A section in Geological Survey research 1972, Chapter D

    USGS Publications Warehouse

    Rickert, David A.; Leopold, Luna Bergere

    1972-01-01

    Fremont Lake, at an altitude of 2,261 m, has an area of 20.61 km2 and a volume of 1.69 km3. The maximum depth is 185 m, which makes it the seventh deepest natural lake in the conterminous United States. Theoretical renewal time is 11.1 years. Temperature data for 1971 indicate that vernal circulation extended to a depth of less than 90 m. The summer heat income was 19,450 cal/cm2. The dissolved-oxygen curve is orthograde, with a slight metalimnetic maximum, and a tendency toward decreasing concentrations at depth. At 180 m, oxygen was at 80 percent of saturation in late July 1970. The lake has a remarkably low dissolved-solids content of 12.8 mg/l, making it one of the most dilute medium-sized lakes in the world. Detailed chemical data are given for the water column at three sites in the lake and for the influent and effluent streams. Net plankton included representatives of seven genera of phytoplankters and three genera of zooplankters. A reconnaissance indicated substantially no bacteriological contamination in the lake, but there was an appreciable amount in two minor streams in the vicinity of a summer-home colony.

  11. Planetary volcanism

    SciTech Connect

    Cattermole, P.

    1989-01-01

    This book presents studies of the volcanic features of individual planets. Bring together the most recently acquired data on selected regions of individual planets and discusses in detail the volcanic processes at work. Begins with a discussion of theoretical considerations and a survey of volcanism on earth. Continues with a comparative approach to planetary volcanism, looking at the volcanic features of different planets. Draws conclusions about planetary development based on the characteristic volcanic features of the different planets.

  12. A mechanism of large volcanic eruptions and the interaction between Katla and Eyjafjallajokull

    NASA Astrophysics Data System (ADS)

    Gudmundsson, Agust

    2010-05-01

    The volume of eruptive materials may vary widely between successive eruptions in a single volcano, as well as between similar-sized volcanoes of the same type and tectonic environment. The likely maximum volume that can be issued in a single eruption from a particular volcano or a rift-zone segment has major implications for the risks associated with that volcano. There may be several reasons for the difference in the volume issued in successive eruptions. These include changes in (1) tectonic conditions, (2) magma composition and gas content, (3) size, shape, and magma content of the source chamber. In many basaltic eruptions, however, factors 1-3 are unlikely to change much between eruptions, or between similar volcanoes, suggesting a different explanation for the abrupt variations in eruptive volume. Poroelastic models indicate that the volume of magma that flows out of a magma chamber during its rupture V f, is normally a very small fraction of the total volume of magma in the chamber, V t. The magma chamber is then assumed to rupture and eject magma (though a dyke or a sheet) when its excess pressure (magmatic pressure in excess of the minimum principal compressive stress in the host rock) reaches the in situ tensile strength of the host rock. These models have been used for many years to account for the volume of magma (intrusive and extrusive) flowing out of a chamber during an eruption and/or dyke injection. While useful, these models do not explain how similar-sized magma chambers and volcanoes in a given tectonic regime, and with similar types of magma or the same magma chamber, can erupt widely different volumes. In particular, they do not explain the mechanical conditions for comparatively large eruptions in a particular volcano. Focusing on basaltic eruptions, I propose that the energy available for a large eruption depends partly on the mechanical behaviour of the layered rocks of the associated volcano or rift zone. For a certain host-rock behaviour

  13. Carbon dioxide and energy fluxes over a large shallow lake in China

    NASA Astrophysics Data System (ADS)

    Zhao, Xiaosong

    2017-04-01

    The turbulent exchange of carbon dioxide and energy between water and atmosphere over lakes differ from those over vegetated surfaces due to high heat capacity of water and different water ecological environment. For a shallow lake, the underlying surface generally changes between water covered and land covered with water level fluctuation, which significantly influences carbon dioxide and energy fluxes. Continuous measurement of the carbon dioxide (CO2), latent (LE) and sensible (H) heat fluxes was made using the eddy covariance method over the Poyang Lake, the largest fresh lake in China, from August 2013 to December 2015. Results indicated that the surface energy budget has a strong seasonal pattern, with peaks in LE and H observed in early August and September. There was 10 days delay between the net radiation and the latent heat flux. More net radiation (Rn) was allocated to the LE rather than H through the year, with monthly mean LE/Rn of 0.65 and H/Rn of 0.11, which caused Bowen ratio was 0.15 in water-covered period, lower than that in land-covered period. The water heat storage experienced shifting from heat storage to heat release, with maximum heat storage in July and maximum heat release in September. The water heat advection was account for 4% to 10% of Rn and peaked in June. The annual evaporation is 875 mm, 893 mm and 1019 mm in 2013 (from August 2013 to July 2014), 2014 and 2015, which was account for approximately 57% of precipitation in the three years. The large lake acted as a CO2 source in inundating period and a CO2 sink in exposure period. The energy fluxes were controlled by environmental factors with timescale dependence. On daily scale, the LE and H were highly correlated with product of wind speed and vapor pressure deficit (UVPD) or wind speed (U) in the water-covered period, and with Rn in the land-covered period. Monthly LE, H and annual H were controlled by Rn, while annual LE was primarily dependent on water depth. Annual CO2 budget

  14. Hafnium isotopic variations in volcanic rocks from the Caribbean Large Igneous Province and Galápagos hot spot tracks

    NASA Astrophysics Data System (ADS)

    Geldmacher, J.; Hanan, B. B.; Blichert-Toft, J.; Harpp, K.; Hoernle, K.; Hauff, F.; Werner, R.; Kerr, A. C.

    2003-07-01

    We report Hf isotope compositions of 79 lavas that record the early (˜5-95 Ma) history of the Galápagos plume volcanism. These include lavas from the Caribbean Large Igneous Province (CLIP; ˜95-70 Ma), the accreted Galápagos paleo-hot spot track terranes (54-65 Ma) of Costa Rica (Quepos, Osa and Burica igneous complexes), and the Galápagos hot spot tracks (<20 Ma) located on the Pacific seafloor (Cocos, Carnegie, Malpelo, and Coiba Ridges and associated seamounts). These samples have previously been well characterized in terms of major and trace elements, Sr-Nd-Pb isotopes and Ar/Ar ages. As a result of the relative immobility of the high field strength and rare earth elements during syn- and post-emplacement hydrothermal activity and low-temperature alteration, combined Lu-Hf and Sm-Nd isotope systematics, when used in conjunction with Pb isotopes, provide a particular powerful tool, for evaluating the source compositions of ancient and submarine lavas. The combined Nd-Hf isotope data suggest that three of the isotopically distinct source components found today in the Galápagos Islands (the Floreana-like southern component, the Fernandina-like central component, and the depleted Genovesa-like eastern component) were present in the CLIP already by 95-70 Ma. The fourth Pinta-like northern component is first recorded at about 83-85 Ma by volcanism taking place during the transition from the plume head/CLIP to plume tail stage and has then been present in the hot spot track continuously thereafter. The identification of the unique northern and southern Galápagos Plume Hf-Nd-Pb isotope source signatures within the CLIP and the oldest hot spot track lavas provides direct evidence that the CLIP represents the plume head stage of the Galápagos hot spot. Hafnium isotopes are consistent with the possibility that two types of sediment components may have contributed to the Hf, Nd and Pb isotope compositions of the Galápagos plume lavas. One component, characterized

  15. Initiation and Impact of Siberian Traps Volcanism

    NASA Astrophysics Data System (ADS)

    Planke, S.; Svensen, H.; Polozov, A. G.; Jerram, D.; Faleide, J. I.

    2011-12-01

    The Siberian Traps Large Igneous Province was formed during the end-Permian, about 251 million years ago. Basaltic melt was injected into the organic and salt rich Tunguska sedimentary basin, forming interconnected sill complexes and associated hydrothermal vent complexes. The initial eruptions took place in a wet environment, documented by tuff layers. The explosive eruptions were followed by effusive magmatism, forming the characteristic volcanic traps. Further away, in the southwest Barents Sea, the earliest Triassic is characterized by rapid basin subsidence and deposition of thick clastic sedimentary sequences. We have conducted field work in Siberia during 2004 to 2010 to study the formation and implications of the Siberian Traps volcanism. The massive magmatism likely triggered the end-Permian mass extinction and pertubated the global carbon cycle. Four key processes link the Siberian Traps Large Igneous Province to the end-Permian carbon cycle perturbation and mass extinction: 1) degassing of subaerially emplaces lava flows, 2) explosive volcanism and tephra eruptions, 3) phreatomagmatic pipes rooted in the evaporates of the Tunguska Basin, and 4) degassing following contact metamorphism around coal, shale, and evaporate lithologies in the Tunguska Basin. Field work in 2010 focused on the nature of explosive volcanism and tephra eruptions. Thick deposits of basaltic tuff and tephra have been reported as widespread in the lower succession of the Siberian Traps, for instance in the Maymecha region (300 meters of basal mafic tuffs), commonly taken as direct evidence for the explosive nature of the initial phase of volcanism. This is puzzling as explosive volcanism is unusual in low viscosity and volatile-poor basaltic systems. As few modern studies have documented the extent and nature of these tuff deposits, especially in the areas outside the ore-rich regions around Norilsk, this may have contributed to their enigmatic status. The field work revealed that

  16. Hazardous crater lakes studied

    NASA Astrophysics Data System (ADS)

    Kusakabe, Minoru

    Crater lakes usually sit on top of volcanic conduits and act as condensers of magmatic vapor. Studies of crater lakes can therefore provide information on both deep magmatic activity and variations in the degassing state of a shallow magmatic body. The Lake Nyos gas disaster of August 1986 and a similar event in August 1984 at Lake Monoun, both in Cameroon, resulted from the accumulation of magmatic CO2 in the bottom layers of the lakes. Geochemical monitoring of crater lakes is a promising tool for forecasting not only limnic but also volcanic eruptions. Acid-mineralized waters formed by condensation of hot magmatic volatiles in crater lakes are thought to bear some resemblance to hydrothermal fluids acting in the genesis of acid-sulfate alteration and Au-Cu-Ag mineralization of volcanic-hosted precious metal deposits.

  17. Composition, Geometry and Emplacement Dynamics of a Large Volcanic Island Landslide Offshore Martinique, Lesser Antilles: New Insights from IODP Expedition 340

    NASA Astrophysics Data System (ADS)

    Brunet, M.; Le Friant, A.; Boudon, G.; Lafuerza, S.; Talling, P. J.; Hornbach, M. J.; Ishizuka, O.; Lebas, E.; Guyard, H.

    2015-12-01

    Landslides are common features in the vicinity of volcanic islands. In this contribution, we investigate landslides emplacement and dynamics around the volcanic island of Martinique based on the first scientific drilling of such deposits. The evolution of the active Montagne Pelée volcano on Martinique has been marked by three major flank-collapses that removed much of the western flank of the volcano. Subaerial collapse volumes vary from 2 to 25 km3 and debris avalanches flowed into the Grenada Basin. High-resolution seismic data (AGUADOMAR - 1999, CARAVAL - 2002 and GWADASEIS - 2009) is combined with new drill cores that penetrate up to 430 m through the three submarine landslide deposits (Site U1399, Site U1400, Site U1401, IODP Expedition 340, Joides Resolution, March-April 2012). This combined geophysical and core data provide an improved understanding of landslide processes offshore a volcanic island. The integrated analysis shows a large submarine landslide deposit, comprising up to 300 km3 of remobilized seafloor sediment that extends for 70 km away from the coast and covers an area of 2100 km2. We propose a new model dealing with seafloor sediment failures and down-slope slide propagation mechanisms, triggered by volcanic flank-collapse events affecting Montagne Pelée volcano. Newly recognized landslide deposits occur deeper in the stratigraphy, suggesting the recurrence of large-scale mass-wasting processes offshore the island and thus, the necessity to better assess the associated tsunami hazards in the region.

  18. Volcanic Aerosol Radiative Properties

    NASA Technical Reports Server (NTRS)

    Lacis, Andrew

    2015-01-01

    Large sporadic volcanic eruptions inject large amounts of sulfur bearing gases into the stratosphere which then get photochemically converted to sulfuric acid aerosol droplets that exert a radiative cooling effect on the global climate system lasting for several years.

  19. Assessing the variability of glacier lake bathymetries and potential peak discharge based on large-scale measurements in the Cordillera Blanca, Peru

    NASA Astrophysics Data System (ADS)

    Cochachin, Alejo; Huggel, Christian; Salazar, Cesar; Haeberli, Wilfried; Frey, Holger

    2015-04-01

    Over timescales of hundreds to thousands of years ice masses in mountains produced erosion in bedrock and subglacial sediment, including the formation of overdeepenings and large moraine dams that now serve as basins for glacial lakes. Satellite based studies found a total of 8355 glacial lakes in Peru, whereof 830 lakes were observed in the Cordillera Blanca. Some of them have caused major disasters due to glacial lake outburst floods in the past decades. On the other hand, in view of shrinking glaciers, changing water resources, and formation of new lakes, glacial lakes could have a function as water reservoirs in the future. Here we present unprecedented bathymetric studies of 124 glacial lakes in the Cordillera Blanca, Huallanca, Huayhuash and Raura in the regions of Ancash, Huanuco and Lima. Measurements were carried out using a boat equipped with GPS, a total station and an echo sounder to measure the depth of the lakes. Autocad Civil 3D Land and ArcGIS were used to process the data and generate digital topographies of the lake bathymetries, and analyze parameters such as lake area, length and width, and depth and volume. Based on that, we calculated empirical equations for mean depth as related to (1) area, (2) maximum length, and (3) maximum width. We then applied these three equations to all 830 glacial lakes of the Cordillera Blanca to estimate their volumes. Eventually we used three relations from the literature to assess the peak discharge of potential lake outburst floods, based on lake volumes, resulting in 3 x 3 peak discharge estimates. In terms of lake topography and geomorphology results indicate that the maximum depth is located in the center part for bedrock lakes, and in the back part for lakes in moraine material. Best correlations are found for mean depth and maximum width, however, all three empirical relations show a large spread, reflecting the wide range of natural lake bathymetries. Volumes of the 124 lakes with bathymetries amount to 0

  20. Petrologic considerations for hot dry rock geothermal site selection in the Clear Lake Region, California

    SciTech Connect

    Stimac, J.; Goff, F. ); Hearn, B.C. Jr. )

    1992-01-01

    The Clear Lake area is well known for anomalous heat flow, thermal springs, hydrothermal mineral deposits, and Quaternary volcanism. These factors, along with the apparent lack of a large reservoir of geothermal fluid north of Collayomi fault make the Clear Lake area an attractive target for hot dry rock (HDR) geothermal development. Petrologic considerations provide some constraints on site selection for HDR development. Spatial and temporal trends in volcanism in the Coast Ranges indicate that magmatism has migrated to the north with time, paralleling passage of the Mendocino triple junction and propagation of the San Andreas fault. Volcanism in the region may have resulted from upwelling of hot asthenosphere along the southern margin of the subducted segment of the Gorda plate. Spatial and temporal trends of volcanism within the Clear Lake volcanic field are similar to larger-scale trends of Neogene volcanism in the Cost Ranges. Volcanism (especially for silicic compositions) shows a general migration to the north over the {approximately}2 Ma history of the field, with the youngest two silicic centers located at Mt. Konocti and Borax Lake. The Mt. Konocti system (active from {approximately} 0.6 to 0.3 Ma) was large and long-lived, whereas the Borax Lake system is much smaller but younger (0.09 Ma). Remnants of silicic magma bodies under Mt. Konocti may be in the latter stages of cooling, whereas a magma body centered under Borax Lake may be in the early stages of development. The existence of an upper crustal silicic magma body of under Borax Lake has yet to be demonstrated by passive geophysics, however, subsurface temperatures in the area as high (> 200{degrees}C at 2000 m) as those beneath the Mt. Konocti area. Based on petrologic considerations alone, the Mt. Konocti-Borax Lake area appears to be the most logical choice for HDR geothermal development in the region.

  1. A Killer Lake

    ERIC Educational Resources Information Center

    Horvath, Thomas

    2005-01-01

    In 1986, Lake Nyos, a volcanic lake in Cameroon, released a huge amount of carbon dioxide gas, killing over 1,700 people in the surrounding area. This case study, developed for use in a limnology or aquatic biology course, explores that event, introducing students to concepts relating to lake formation, thermal stratification, and dissolved gases.…

  2. A Killer Lake

    ERIC Educational Resources Information Center

    Horvath, Thomas

    2005-01-01

    In 1986, Lake Nyos, a volcanic lake in Cameroon, released a huge amount of carbon dioxide gas, killing over 1,700 people in the surrounding area. This case study, developed for use in a limnology or aquatic biology course, explores that event, introducing students to concepts relating to lake formation, thermal stratification, and dissolved gases.…

  3. Volcanic Seismology

    NASA Astrophysics Data System (ADS)

    McNutt, Stephen R.

    2005-01-01

    Recent developments in volcanic seismology include new techniques to improve earthquake locations that have changed clouds of earthquakes to lines (faults) for high-frequency events and small volumes for low-frequency (LF) events. Spatial mapping of the b-value shows regions of normal b and high b anomalies at depths of 3-4 and 7-10 km. Increases in b precede some eruptions. LF events and very-long-period (VLP) events have been recorded at many volcanoes, and models are becoming increasingly sophisticated. Deep long-period (LP) events are fairly common, but may represent several processes. Acoustic sensors have greatly improved the study of volcanic explosions. Volcanic tremor is stronger for fissure eruptions, phreatic eruptions, and higher gas contents. Path and site effects can be extreme at volcanoes. Seismicity at volcanoes is triggered by large earthquakes, although mechanisms are still uncertain. A number of volcanoes have significant deformation with very little seismicity. Tomography has benefited from improved techniques and better instrumental arrays.

  4. CHARACTERIZATION OF ENDOCRINE-DISRUPTION AND CLINICAL MANIFESTATIONS IN LARGE-MOUTH BASS FROM FLORIDA LAKES

    EPA Science Inventory

    Previous efforts from this laboratory, have documented altered endocrine function and sexual differentiation for alligators and turtles from Lake Apopka in Central Florida. This lake has been exposed to a variety of contaminants which are potentially endocrine-disrupting. Therefo...

  5. CHARACTERIZATION OF ENDOCRINE-DISRUPTION AND CLINICAL MANIFESTATIONS IN LARGE-MOUTH BASS FROM FLORIDA LAKES

    EPA Science Inventory

    Previous efforts from this laboratory, have documented altered endocrine function and sexual differentiation for alligators and turtles from Lake Apopka in Central Florida. This lake has been exposed to a variety of contaminants which are potentially endocrine-disrupting. Therefo...

  6. Biodiversity of Clostridium botulinum Type E Associated with a Large Outbreak of Botulism in Wildlife from Lake Erie and Lake Ontario ▿

    PubMed Central

    Hannett, George E.; Stone, Ward B.; Davis, Stephen W.; Wroblewski, Danielle

    2011-01-01

    The genetic relatedness of Clostridium botulinum type E isolates associated with an outbreak of wildlife botulism was studied using random amplification of polymorphic DNA (RAPD). Specimens were collected from November 2000 to December 2008 during a large outbreak of botulism affecting birds and fish living in and around Lake Erie and Lake Ontario. In our present study, a total of 355 wildlife samples were tested for the presence of botulinum toxin and/or organisms. Type E botulinum toxin was detected in 110 samples from birds, 12 samples from fish, and 2 samples from mammals. Sediment samples from Lake Erie were also examined for the presence of C. botulinum. Fifteen of 17 sediment samples were positive for the presence of C. botulinum type E. Eighty-one C. botulinum isolates were obtained from plants, animals, and sediments; of these isolates, 44 C. botulinum isolates produced type E toxin, as determined by mouse bioassay, while the remaining 37 isolates were not toxic for mice. All toxin-producing isolates were typed by RAPD; that analysis showed 12 different RAPD types and multiple subtypes. Our study thus demonstrates that multiple genetically distinct strains of C. botulinum were involved in the present outbreak of wildlife botulism. We found that C. botulinum type E is present in the sediments of Lake Erie and that a large range of bird and fish species is affected. PMID:21115703

  7. Integrated simulation and assessment of water quantity and quality of a large urban lake group under the water network connection project

    NASA Astrophysics Data System (ADS)

    Yang, W.; Zhang, L.; Zhang, Y.

    2016-12-01

    The water network connection project is to reestablish a hydraulic connection between lakes and rivers and to improve the water ecologysystem. Tangxun Lake, located in Wuhan, is the largest urban lake in China. With the economic development, a large group of urban lakes composed of Tangxun Lake, South Lake, Qingling Lake, Yezhi Lake, Huangjia Lake and Ye Lake have been suffering from serious water quality problems in recent years. In order to improve water quality of Tangxun Lake and determine a suitable water diversion scheme, a hydrodynamic and water quality model based on DEM grid was developed This model was designed using finite volume method for hydrodynamic and transport model dispersion, the SIMPLEC method for solving the flow field, and the pressure weighted interpolating method for the flow field modification. With the influence of point source pollution and non-point source pollution taken into consideration, indexes including CODMn, NH3-N, total nitrogen (TN) and total phosphorus (TP) were chosen to simulate the water quality variation of the lakes mentioned above, and the parameters of the model was calibrated and verified using field data. To provide an optimal diversion flow, several diversion conditions were simulated by utilizing the model. The results indicated that the proposed model can simulate the water quantity and quality of urban shallow lakes effectively, and the relative error between simulated value and observation data was less than 15%. The water network connection project can help improve water quality of lakes to some extent.

  8. Climatic, volcanic and tectonic events recorded in recent sediments of the Rukwa rift, Western Tanzania

    NASA Astrophysics Data System (ADS)

    Delvaux, D.; Mees, F.; Williamson, D.; Macheyeki, A. S.

    2009-04-01

    Lake Rukwa is now a shallow lake occupying the floor of the closed Rukwa depression in the western branch of the East African Rift System. Sediment records of the paleo-lake level show that during the Late Pleistocene to Early Holocene, Lake Rukwa reached the level of the overflow sill, 180 m higher than its present level, and was overflowing into Lake Tanganyika. Lacustrine sediments from this period are now exposed on the margin of the depression, and in particular along the Songwe River, where several large sections up to 35 meters high can be studied. Investigation of selected sections reveals a complex evolution in alternating fluvio-deltaic to lacustrine environment, punctuated by episodic inflow of volcanic material from the nearby Rungwe Volcanic Province. Macroscopic description of the sedimentary packages and their geometry, combined with C14 dating, diatom analysis, and optical microscopy allow to propose a preliminary evolution scheme in which climatically induced lake level change, volcanic input and tectonic influence can be reconstructed. In particular, correlations between sections at different altitudes allow to better constrain the lake level fluctuation than previous estimates based on drill core analysis.

  9. Characterization of the sub-continental lithospheric mantle beneath the Cameroon volcanic line inferred from alkaline basalt hosted peridotite xenoliths from Barombi Mbo and Nyos Lakes

    NASA Astrophysics Data System (ADS)

    Pintér, Zsanett; Patkó, Levente; Tene Djoukam, Joëlle Flore; Kovács, István; Tchouankoue, Jean Pierre; Falus, György; Konc, Zoltán; Tommasi, Andréa; Barou, Fabrice; Mihály, Judith; Németh, Csaba; Jeffries, Teresa

    2015-11-01

    We carried out detailed petrographic, major and trace element geochemical, microstructural and FTIR analyses on eight characteristic ultramafic xenoliths from Nyos and Barombi Mbo Lakes in the continental sector of the Cameroon Volcanic Line (CVL). The studied xenoliths are spinel lherzolites showing lithologies similar to the other xenoliths reported previously along the CVL. They have protogranular and porphyroclastic textures. One of the Barombi xenolith contains amphibole, which had not been previously reported in this locality. Amphibole is common in the Nyos xenoliths suite. Peridotite xenoliths from both localities show some chemical heterogeneity, but Barombi xenoliths generally are less depleted in basaltic elements with respect to Nyos xenoliths. Trace element compositions of Nyos spinel lherzolites show a moderately depleted initial (premetasomatic) composition and variable enrichment in REE. Evidence for both modal and cryptic metasomatism is present in Nyos xenoliths. Rare earth element patterns of clinopyroxene suggest that interaction between mafic melts and the upper mantle occurred beneath the Nyos locality. Barombi Mbo xenoliths, on the other hand, record a small degree of partial melting. The Barombi Mbo xenoliths have weak, dominantly orthorhombic olivine crystal preferred orientations, whereas Nyos ones have strong axial-[010] patterns, which may have formed in response to transpression. Nominally anhydrous mantle minerals (NAMs) of the Barombi Mbo xenoliths show generally higher bulk concentrations of 'water' (70-127 ppm) than Nyos xenoliths (32-81 ppm). The Barombi Mbo xenoliths could originate from a juvenile segment of the lithospheric mantle, which had been originally part of the asthenosphere. It became a part of the lithosphere in response to thermal relaxation following the extension, forming a weakly deformed lower lithospheric mantle region along the CVL. The Nyos xenoliths, however, represent a shallow lithospheric mantle bearing

  10. Large differences in potential denitrification and sediment microbial communities across the Laurentian great lakes

    USDA-ARS?s Scientific Manuscript database

    Lakes can be important sites for removal of reactive nitrogen (N) through denitrification, but spatial heterogeneity in denitrification rates can be high, and our understanding of factors controlling the capacity of lakes to remove excess N is incomplete. In oligotrophic Lake Superior, a century-lon...

  11. Relationships between testate amoeba communities and water quality in Lake Donghu, a large alkaline lake in Wuhan, China

    NASA Astrophysics Data System (ADS)

    Qin, Yangmin; Fournier, Bertrand; Lara, Enrique; Gu, Yansheng; Wang, Hongmei; Cui, Yongde; Zhang, Xiaoke; Mitchell, Edward A. D.

    2013-06-01

    The middle Yangtze Reach is one of the most developed regions of China. As a result, most lakes in this area have suffered from eutrophication and serious environmental pollution during recent decades. The aquatic biodiversity in the lakes of the area is thus currently under significant threat from continuous human activities. Testate amoebae (TA) are benthic (rarely planktonic) microorganisms characterized by an agglutinated or autogenous shell. Owing to their high abundance, preservation potential in lacustrine sediments, and distinct response to environmental stress, they are increasingly used as indicators for monitoring water quality and reconstructing palaeoenvironmental changes. However this approach has not yet been developed in China. This study presents an initial assessment of benthic TA assemblages in eight lakes of Lake Donghu in the region of Wuhan, China. Testate amoeba community structure was most strongly correlated to water pH. In more alkaline conditions, communities were dominated by Centropyxis aculeata, Difflugia oblonga, Pontigulasia compressa, Pon. elisa and Lesquereusia modesta. These results are consistent with previous studies and show that TA could be useful for reconstructing past water pH fluctuations in China. To achieve this, the next step will be to expand the database and build transfer function models.

  12. Large-scale changes in bloater growth and condition in Lake Huron

    USGS Publications Warehouse

    Prichard, Carson G.; Roseman, Edward F.; Keeler, Kevin M.; O'Brien, Timothy P.; Riley, Stephen C.

    2016-01-01

    Native Bloaters Coregonus hoyi have exhibited multiple strong year-classes since 2005 and now are the most abundant benthopelagic offshore prey fish in Lake Huron, following the crash of nonnative AlewivesAlosa pseudoharengus and substantial declines in nonnative Rainbow Smelt Osmerus mordax. Despite recent recoveries in Bloater abundance, marketable-size (>229 mm) Bloaters remain scarce. We used annual survey data to assess temporal and spatial dynamics of Bloater body condition and lengths at age in the main basin of Lake Huron from 1973 to 2014. Basinwide lengths at age were modeled by cohort for the 1973–2003 year-classes using a von Bertalanffy growth model with time-varying Brody growth coefficient (k) and asymptotic length () parameters. Median Bloater weights at selected lengths were estimated to assess changes in condition by modeling weight–length relations with an allometric growth model that allowed growth parameters to vary spatially and temporally. Estimated Bloater lengths at age declined 14–24% among ages 4–8 for all year-classes between 1973 and 2004. Estimates of  declined from a peak of 394 mm (1973 year-class) to a minimum of 238 mm (1998 year-class). Observed mean lengths at age in 2014 were at all-time lows, suggesting that year-classes comprising the current Bloater population would have to follow growth trajectories unlike those characterizing the 1973–2003 year-classes to attain marketable size. Furthermore, estimated weights of 250-mm Bloaters (i.e., a large, commercially valuable size-class) declined 17% among all regions from 1976 to 2007. Decreases in body condition of large Bloaters are associated with lower lipid content and may be linked to marked declines in abundance of the amphipodsDiporeia spp. in Lake Huron. We hypothesize that since at least 1976, large Bloaters have become more negatively buoyant and may have incurred an increasingly greater metabolic cost performing diel vertical migrations to prey upon the opossum

  13. Volcanic Stratigraphy of the Quaternary Rhyolite Plateau in Yellowstone National Park

    USGS Publications Warehouse

    Christiansen, Robert L.; Blank, H. Richard

    1972-01-01

    The volcanic sequence of the Quaternary Yellowstone plateau consists of rhyolites and basalts representing three volcanic cycles. The major events of each cycle were eruption of a voluminous ash-flow sheet and formation of a large collapse caldera. Lesser events of each cycle were eruption of precaldera and postcaldera rhyolitic lava flows and marginal basaltic lavas. The three major ash-flow sheets are named and designated in this report as formations within the Yellowstone Group. The lavas are assigned to newly named formations organized around the three ash-flow sheets of the Yellowstone Group to represent the volcanic cycles. Rocks of the first volcanic cycle comprise the precaldera Junction Butte Basalt and rhyolite of Broad Creek; the Huckleberry Ridge Tuff of the Yellowstone Group; and the postcaldera Lewis Canyon Rhyolite and basalt of The Narrows. Rocks of the second volcanic cycle do not crop out within Yellowstone National Park, and only the major unit, the Mesa Falls Tuff of the Yellowstone Group, is named here. The third volcanic cycle is represented by the precaldera Mount Jackson Rhyolite and Undine Falls Basalt; the Lava Creek Tuff of the Yellowstone Group; and the postcaldera Plateau Rhyolite and five post-Lava Creek basaltic sequences. Collapse to form the compound and resurgent Yellowstone caldera was related to eruption of the Lava Creek Tuff. The Plateau Rhyolite is divided into six members - the Mallard Lake, Upper Basin, Obsidian Creek, Central Plateau, Shoshone Lake Tuff, and Roaring Mountain Members; all but the Mallard Lake postdate resurgent doming of the caldera. The basalts are divided into the Swan Lake Flat Basalt, Falls River Basalt, basalt of Mariposa Lake, Madison River Basalt, and Osprey Basalt. Sediments are intercalated in the volcanic section below the Huckleberry Ridge and Mesa Falls Tuffs and within the Junction Butte Basalt, sediments and basalts of The Narrows, Undine Falls Basalt, Plateau Rhyolite, and Osprey Basalt.

  14. New homogenized daily lake surface water temperature data of three decades from multiple sensors confirm warming of large sub-alpine lake Garda

    NASA Astrophysics Data System (ADS)

    Pareeth, Sajid; Salmaso, Nico; Adrian, Rita; Neteler, Markus

    2016-04-01

    Availability of remotely sensed multi-spectral images from the early eighties covering three decades of voluminous data could help researchers to study the change dynamics in bio-physical characteristics of land and water. However it is very important to homogenize these data originating from multiple sources which follow different standards and quality. In this study, we explored the thermal dynamics of a large sub-alpine lake Garda over last twentyeight years (1986 - 2014) using Lake Surface Water Temperature (LSWT) derived from the thermal bands of moderate resolution sensors - AVHRR/2, AVHRR/3, ATSR1, ATSR2, A(A)TSR and MODIS aboard multiple satellites. We developed a homogenized daily LSWT dataset (12:00 P.M) at 1km spatial resolution combining the data from these sensors using split window technique and performing an acquisition time correction. The gaps in the temporal database due to clouds were filled by applying Harmonic ANalysis of Time Series (HANTS). The results show high correlation (R2 > 90) between satellite derived LSWT (taken into account both individual sensors and the combined data) and the in-situ data. The time correction enable us to perform a trend analysis on unified datasets corrected for its acquisition times. The trend analysis using non-parametric tests shows significant warming in annual trend at the rate of 0.01K yr-1 (p<0.05), while in summer the increasing trend is 0.02K yr-1(p<0.1). The results are in line with similar findings on warming of Alpine lakes. Moreover, the advantage of the spatial coverage at 1 km resolution we are able to characterize the thermal dynamics of the lake Garda at multiple locations of this large lake.

  15. Reconciling the opposing effects of warming on phytoplankton biomass in 188 large lakes.

    PubMed

    Kraemer, Benjamin M; Mehner, Thomas; Adrian, Rita

    2017-09-07

    Lake ecosystems are deeply integrated into local and regional economies through recreation, tourism, and as sources of food and drinking water. Shifts in lake phytoplankton biomass, which are mediated by climate warming will alter these benefits with potential cascading effects on human well-being. The metabolic theory of ecology suggests that warming reduces lake phytoplankton biomass as basal metabolic costs increase, but this hypothesis has not been tested at the global scale. We use satellite-based estimates of lake surface temperature (LST) and lake surface chlorophyll-a concentration (chl-a; as a proxy for phytoplankton biomass) in 188 of the world's largest lakes from 2002-2016 to test for interannual associations between chl-a and LST. In contrast to predictions from metabolic ecology, we found that LST and chl-a were positively correlated in 46% of lakes (p < 0.05). The associations between LST and chl-a depended on lake trophic state; warming tended to increase chl-a in phytoplankton-rich lakes and decrease chl-a in phytoplankton-poor lakes. We attribute the opposing responses of chl-a to LST to the effects of temperature on trophic interactions, and the availability of resources to phytoplankton. These patterns provide insights into how climate warming alters lake ecosystems on which millions of people depend for their livelihoods.

  16. Imaging the midcontinent rift beneath Lake Superior using large aperture seismic data

    USGS Publications Warehouse

    Trehu, Anne M.; Morel-a-l'Huissier, Patrick; Meyer, R.; Hajnal, Z.; Karl, J.; Mereu, R. F.; Sexton, J.; Shay, J.; Chan, W. K.; Epili, D.; Jefferson, T.; Shih, X. R.; Wendling, S.; Milkereit, B.; Green, A.; Hutchinson, Deborah R.

    1991-01-01

    We present a detailed velocity model across the 1.1 billion year old Midcontinent Rift System (MRS) in central Lake Superior. The model was derived primarily from onshore-offshore large-aperture seismic and gravity data. High velocities obtained within a highly reflective half-graben that was imaged on coincident seismic reflection data demonstrate the dominantly mafic composition of the graben fill and constrain its total thickness to be at least 30km. Strong wide-angle reflections are observed from the lower crust and Moho, indicating that the crust is thickest (55–60km) beneath the axis of the graben. The total crustal thickness decreases rapidly to about 40 km beneath the south shore of the lake and decreases more gradually to the north. Above the Moho is a high-velocity lower crust interpreted to result from syn-rift basaltic intrusion into and/or underplating beneath the Archean lower crust. The lower crust is thickest beneath the axis of the main rift half-graben. A second region of thick lower crust is found approximately 100km north of the axis of the rift beneath a smaller half graben that is interpreted to reflect an earlier stage of rifting. The crustal model presented here resembles recent models of some passive continental margins and is in marked contrast to many models of both active and extinct Phanerozoic continental rift zones. It demonstrates that the Moho is a dynamic feature, since the pre-rift Moho is probably within or above the high-velocity lower crust, whereas the post-rift Moho is defined as the base of this layer. In the absence of major tectonic activity, however, the Moho is very stable, since the large, abrupt variations in crustal thickness beneath the MRS have been preserved for at least a billion years.

  17. Investigation of the complexity of streamflow fluctuations in a large heterogeneous lake catchment in China

    NASA Astrophysics Data System (ADS)

    Ye, Xuchun; Xu, Chong-Yu; Li, Xianghu; Zhang, Qi

    2017-04-01

    The occurrence of flood and drought frequency is highly correlated with the temporal fluctuations of streamflow series; understanding of these fluctuations is essential for the improved modeling and statistical prediction of extreme changes in river basins. In this study, the complexity of daily streamflow fluctuations was investigated by using multifractal detrended fluctuation analysis (MF-DFA) in a large heterogeneous lake basin, the Poyang Lake basin in China, and the potential impacts of human activities were also explored. Major results indicate that the multifractality of streamflow fluctuations shows significant regional characteristics. In the study catchment, all the daily streamflow series present a strong long-range correlation with Hurst exponents bigger than 0.8. The q-order Hurst exponent h(q) of all the hydrostations can be characterized well by only two parameters: a (0.354 ≤ a ≤ 0.384) and b (0.627 ≤ b ≤ 0.677), with no pronounced differences. Singularity spectrum analysis pointed out that small fluctuations play a dominant role in all daily streamflow series. Our research also revealed that both the correlation properties and the broad probability density function (PDF) of hydrological series can be responsible for the multifractality of streamflow series that depends on watershed areas. In addition, we emphasized the relationship between watershed area and the estimated multifractal parameters, such as the Hurst exponent and fitted parameters a and b from the q-order Hurst exponent h(q). However, the relationship between the width of the singularity spectrum (Δα) and watershed area is not clear. Further investigation revealed that increasing forest coverage and reservoir storage can effectively enhance the persistence of daily streamflow, decrease the hydrological complexity of large fluctuations, and increase the small fluctuations.

  18. The mount st. Helens volcanic eruption of 18 may 1980: large short-term surface temperature effects.

    PubMed

    Robock, A; Mass, C

    1982-05-07

    The surface temperature effects of the 18 May 1980 eruption of Mount St. Helens Volcano were examinedfor 1 day immediately after the eruption; 24-hour temperature differences and Model Output Statistics errors as well as the detailed temporal evolution of surface temperature at selected stations were used. During the daytime hours immediately after the eruption, the temperature was suppressed by the volcanic plume by as much as 8 degrees C. That night, low-level volcanic dust produced temperature enhancements of up to 8 degrees C. These effects quickly diminished the next day as the volcanic dust cloud dissipated and moved toward the east. The net local effect of the eruption appears to be warming, in contrast to cooling which might be expected over climatic time scales.

  19. Lake Bonneville

    USGS Publications Warehouse

    Gilbert, Grove Karl

    1890-01-01

    This volume is a contribution to the later physical history of the Great Basin. As a geographic province the Great Basin is characterized by a dry climate, changes of drainage, volcanic eruption, and crustal displacement. Lake Bonneville, the special theme of the volume, was a phenomenon of climate and drainage, but its complete history includes an account of contemporaneous eruption and displacement.

  20. Sequence and relative timing of large lakes in Gale crater (Mars) after the formation of Mount Sharp

    NASA Astrophysics Data System (ADS)

    Palucis, Marisa C.; Dietrich, William E.; Williams, Rebecca M. E.; Hayes, Alexander G.; Parker, Tim; Sumner, Dawn Y.; Mangold, Nicolas; Lewis, Kevin; Newsom, Horton

    2016-03-01

    The quantification of lake levels in Gale crater is important to define the hydrologic and climatic history experienced by the sedimentary deposits found by Curiosity. We propose that there were at least three major lake stands within Gale, each persisted >1000 years, and all occurred after Mount Sharp reached close to its current topographic form. Deltaic deposits off the southern rim of Gale, derived from incision of Farah Vallis, and corresponding deposits off the southern flank of Mount Sharp define the highest lake level, which had a mean depth of 700 m. Canyons similar in form to Farah Vallis enter into craters and/or the crustal dichotomy near Gale from the south, suggesting that the highest lake was supplied by a large-scale flow system. The next lake level, established after a period of drying and rewetting, is defined by four deltaic features, three sourced from Mount Sharp and one from the western rim of Gale, as well as the termination of gullies around the northern rim of Gale. This second lake level had a mean depth of 300 m. The presence of the gullies suggests more locally sourced water. Lake levels then rose another 100 m, as evidenced by two deltaic deposits derived from the rim of Gale and the termination of a second set of gullies. Post-lake, reduced hydrologic activity continued, evidenced by a time of fan building (including Peace Vallis). The sequence of events suggests an episodic shift through time from relatively wet regional conditions to a drier environment with local runoff.

  1. Lithospheric flexure: the key to the structural evolution of large volcanic edifices on the terrestrial planets. (Invited)

    NASA Astrophysics Data System (ADS)

    McGovern, P. J.

    2009-12-01

    Large volcanic edifices, such as the majestic Hawaiian islands, the immense Olympus Mons on Mars, and the numerous, broad, but relatively short basaltic shields of Venus, constitute enormous excess masses at the surfaces of their respective planets. The lithosphere, the mechanically strong outer layer of a planet, responds to growing edifice loads on a regional scale by flexing, in a manner similar to a loaded beam in a building. The shape of lithospheric flexure and the resulting stress state exert critical influences on the structure of the evolving edifices, which in turn feed back into the flexural response. Flexural depression of the lithosphere forms topographic moats surrounding volcanoes; these depressions are partially to completely filled by landslide debris, volcaniclastic materials, and sediments (Hawaii, Marquesas, Reunion chains, Olympus Mons), or flat aprons of volcanic flows (Venusian volcanoes, Tharsis Montes on Mars). Flexure produces a "dipole" state of stress in the lithosphere beneath the edifice: extension at the bottom, and compression at the top. The orientation of the most compressive stress,σ1, is therefore vertical in the lower lithosphere and horizontal in the upper lithosphere. The effects of this dipole were manifested physically in the Hawaiian earthquake pair of October 15, 2006 (see McGovern, GRL, 2007). By Anderson's criteria for intrusive magma ascent, the lower lithosphere stress state is conducive to magma ascent in vertical dikes, but in the upper lithosphere, ascending magma will get diverted into sub-horizontal sills. Finite element models of pressurization of magma chambers embedded in flexing lithospheres demonstrate this tendency: chambers in the upper (compressional) lithosphere fail near their middles under a stress state that favors sill formation (see Galgana et al., this volume). Thus, chambers are likely to assume oblate forms via lateral expansion, perhaps producing an extensive sill complex. Such complexes may

  2. Fluorescent components and spatial patterns of chromophoric dissolved organic matters in Lake Taihu, a large shallow eutrophic lake in China.

    PubMed

    Yao, Bo; Hu, Chunming; Liu, Qingquan

    2016-11-01

    Water samples at both surface and bottom layers were taken from 102 sites in Lake Taihu to study the fluorescent components and spatial patterns of chromophoric dissolved organic matters (CDOM). Three-dimensional excitation-emission matrix data obtained from the samples were analyzed by parallel factor approach in which four humic-like and two protein-like fluorescent components (named C1-C6) were identified. The results showed that fluorescence intensities were higher in the northern and western lake regions, and notable declines of fluorescence maxima (F max) were observed from the northwest to the center and then to the southeast of the lake. Calculated biological index (BIX) values ranged from 0.88 to 1.44 and humification index (HIX) values from 0.64 to 3.37 for all the samples. The spatial variations of BIX and HIX values suggested stronger allochthonous CDOM characteristics in Zhushan Bay and the western area and autochthonous characteristics in the southern and eastern areas. Vertically, the average F max value of the surface samples was about 6 % less than that of the bottom samples, but noticeable variations existed among different sampling sites and components. These distribution characteristics of CDOM were mainly attributed to the spatial heterogeneity of sources and wind-induced transportation process. Interestingly, the C6 component (Exmax/Emmax = 250/455 nm) seemed to be unique in samples from Zhushan Bay and probably resulted from the discharge of the Taige River. Therefore, it could be used as an indicator of point-source discharge and a tracer to study the fate of CDOM in the lake.

  3. Controlling cyanobacterial blooms by managing nutrient ratio and limitation in a large hyper-eutrophic lake: Lake Taihu, China.

    PubMed

    Ma, Jianrong; Qin, Boqiang; Wu, Pan; Zhou, Jian; Niu, Cheng; Deng, Jianming; Niu, Hailin

    2015-01-01

    Excessive nitrogen (N) and phosphorus (P) loading of aquatic ecosystems is a leading cause of eutrophication and harmful algal blooms worldwide, and reducing nutrient levels in water has been a primary management objective. To provide a rational protection strategy and predict future trends of eutrophication in eutrophic lakes, we need to understand the relationships between nutrient ratios and nutrient limitations. We conducted a set of outdoor bioassays at the shore of Lake Taihu. It showed that N only additions induced phytoplankton growth but adding only P did not. Combined N plus P additions promoted higher phytoplankton biomass than N only additions, which suggested that both N and P were deficient for maximum phytoplankton growth in this lake (TN:TP=18.9). When nutrients are present at less than 7.75-13.95 mg/L TN and 0.41-0.74 mg/L TP, the deficiency of either N or P or both limits the growth of phytoplankton. N limitation then takes place when the TN:TP ratio is less than 21.5-24.7 (TDN:TDP was 34.2-44.3), and P limitation occurs above this. Therefore, according to this ratio, controlling N when N limitation exists and controlling P when P deficiency is present will prevent algal blooms effectively in the short term. But for the long term, a persistent dual nutrient (N and P) management strategy is necessary. Copyright © 2014. Published by Elsevier B.V.

  4. Large floods and rapid deglaciation of the Lake Michigan Lobe and environs, ca. 19 to 18 ka

    NASA Astrophysics Data System (ADS)

    Curry, B.; Brown, S.; Hajic, E.; Konen, M.

    2007-12-01

    Our collective research indicates that features attributed to large floods are associated with events separated in time by about 900 years. The oldest event is interpreted from a long and narrow morainal gap floored by coarse sand and gravel outwash that likely formed by a plungepool and migration of this nickpoint via overflow of Glacial Lake Wauponsee across the Marseilles Moraine near Oswego, Illinois. The weighted mean of four AMS C-14 ages of tundra plant stems and leaves identified from the base of the overlying lake fill is 18,900 ± 35 cal yr BP (15,710 ± 35 yr BP). The age of another overflow channel across the Marseilles Moraine is not yet known, but similar channel floor elevations relative to the Oswego channel suggest that they were contemporaneous. Landforms attributed to a younger large flood are located downstream of where the Fox River breaches the Woodstock Moraine in Algonquin, Illinois. Radiocarbon ages of tundra plant fossils preserved in sediment of ice-walled and slackwater lakes associated with the Woodstock and West Chicago Moraines indicate the younger floods likely predate 18,080 cal yr BP (14,860 ± 40 yr BP; UCIAMS-26265). A statistically similar age of 18,000 cal yr BP (14,830 ± 50 yr BP; B-207031) was obtained from organics preserved in a slackwater lake deposit in the Illinois River valley near Havana. The slackwater lake basin is floored by coarse gravelly sand attributed to the latest stage of flooding. At this time, the similar C-14 ages are the only evidence that link the proglacial and distal sites (more than 150 km apart) to the same flood. Based on continuity of morainic ridges, we believe that the large floods that eroded scarps into the southern margin of the Valparaiso Moraine north and parallel to the Kankakee River in NW Indiana and NE Illinois are contemporaneous with the younger large floods discussed above. The scarp was eroded by meltwater from interlobate areas of the Lake Michigan and Huron-Erie Lobes. The rate of

  5. Cyanobacterial bloom management through integrated monitoring and forecasting in large shallow eutrophic Lake Taihu (China).

    PubMed

    Qin, Boqiang; Li, Wei; Zhu, Guangwei; Zhang, Yunlin; Wu, Tingfeng; Gao, Guang

    2015-04-28

    The large shallow eutrophic Lake Taihu in China has long suffered from eutrophication and toxic cyanobacterial blooms. Despite considerable efforts to divert effluents from the watershed, the cyanobacterial blooms still reoccur and persist throughout summer. To mitigate cyanobacterial bloom pollution risk, a large scale integrated monitoring and forecasting system was developed, and a series of emergency response measures were instigated based on early warning. This system has been in place for 2009-2012. With this integrated monitoring system, it was found that the detectable maximum and average cyanobacterial bloom area were similar to that before drinking water crisis, indicating that poor eutrophic status and cyanobacterial bloom had persisted without significant alleviation. It also revealed that cyanobacterial bloom would occur after the intense storm, which may be associated with the increase in buoyance of cyanobacterial colonies. Although the cyanobacterial blooms had persisted during the monitoring period, there had been a reduction in frequency and intensity of the cyanobacterial bloom induced black water agglomerates (a phenomenon of algal bloom death decay to release a large amount black dissolved organic matter), and there have been no further drinking water crises. This monitoring and response strategy can reduce the cyanobacterial bloom pollution risk, but cannot reduce eutrophication and cyanobacterial blooms, problems which will take decades to resolve. Copyright © 2015 Elsevier B.V. All rights reserved.

  6. Spatial variations in food web structures with alternative stable states: evidence from stable isotope analysis in a large eutrophic lake

    NASA Astrophysics Data System (ADS)

    Li, Yunkai; Zhang, Yuying; Xu, Jun; Zhang, Shuo

    2017-05-01

    Food web structures are well known to vary widely among ecosystems. Moreover, many food web studies of lakes have generally attempted to characterize the overall food web structure and have largely ignored internal spatial and environmental variations. In this study, we hypothesize that there is a high degree of spatial heterogeneity within an ecosystem and such heterogeneity may lead to strong variations in environmental conditions and resource availability, in turn resulting in different trophic pathways. Stable carbon and nitrogen isotopes were employed for the whole food web to describe the structure of the food web in different sub-basins within Taihu Lake. This lake is a large eutrophic freshwater lake that has been intensively managed and highly influenced by human activities for more than 50 years. The results show significant isotopic differences between basins with different environmental characteristics. Such differences likely result from isotopic baseline differences combining with a shift in food web structure. Both are related to local spatial heterogeneity in nutrient loading in waters. Such variation should be explicitly considered in future food web studies and ecosystem-based management in this lake ecosystem.

  7. ANALYSIS OF LOW-LEVEL PESTICIDES FROM HIGH-ELEVATION LAKE WATERS BY LARGE VOLUME INJECTION GCMS

    EPA Science Inventory

    This paper describes the method development for the determination of ultra-low level pesticides from high-elevation lake waters by large-volume injection programmable temperature vaporizer (LVI-PTV) GC/MS. This analytical method is developed as a subtask of a larger study, backgr...

  8. ANALYSIS OF LOW-LEVEL PESTICIDES FROM HIGH-ELEVATION LAKE WATERS BY LARGE VOLUME INJECTION GCMS

    EPA Science Inventory

    This paper describes the method development for the determination of ultra-low level pesticides from high-elevation lake waters by large-volume injection programmable temperature vaporizer (LVI-PTV) GC/MS. This analytical method is developed as a subtask of a larger study, backgr...

  9. Volcanism & Tectonism

    NASA Image and Video Library

    2011-07-19

    Just as on Earth, volcanism and tectonism are found together on Mars. In this image from NASA 2001 Mars Odyssey spacecraft the ridges and fractures of Claritas Fossae are affecting or perhaps hosting the volcanic flows of Solis Planum.

  10. Planation surfaces as a record of medium to large wavelength deformation: the example of the Lake Albert Rift (Uganda) on the East African Dome

    NASA Astrophysics Data System (ADS)

    Brendan, Simon; François, Guillocheau; Cécile, Robin; Jean, Braun; Olivier, Dauteuil; Massimo, Dall'Asta

    2016-04-01

    African relief is characterized by planation surfaces, some of them of continental scale. These surfaces are slightly deformed according to different wavelengths (x10 km; x100 km, x1000 km) which record both mantle dynamics (very long wavelength, x 1000 km) and lithosphere deformation (long wavelength deformation, x 100 km). Different types of these planation surfaces are recognized: - Etchplains capped by iron-duricrust which correspond to erosional nearly flat weathered surfaces resulting from the growth of laterites under warm and humid conditions. - Pediments which define mechanical erosional surfaces with concave or rectilinear profiles delimited by upslope scarps connected upstream with the upper landforms. We here focused on the Lake Albert Rift at the northern termination of the western branch of the East African Rift System of which the two branches are surimposed on the East-African Dome. Different wavelengths of deformation were characterized based on the 3D mapping of stepped planation surfaces: (1) very long wavelength deformations resulting from the uplift of the East African Dome; (2) long wavelength deformations resulting from the opening of the eastern branch and (3) medium wavelength deformations represented by the uplift of rift shoulders like the Rwenzori Mountains. The paleo-landscape reconstruction of Uganda shows the existence of four generations of landforms dated according to their geometrical relationships with volcanic rocks. A four stepped evolution of the Ugandan landforms is proposed: • 70 - 22 Ma: generation of two weathered planation surfaces (etchplain Uw and Iw). The upper one (Uw) records a very humid period culminating at time of the Early Eocene Climatic Optimum (70-45 Ma). It corresponds to the African Surface. A first uplift of the East African Dome generates a second lower planation surface (Iw) connected to the Atlantic Ocean base level; • 17-2.7 Ma: planation of large pediplains connected to the local base level induced

  11. Spaceborne Thermal Infrared Measurements of Volcanic Thermal Features

    NASA Astrophysics Data System (ADS)

    Vaughan, R. G.; Hook, S. J.; Davies, A. G.

    2006-12-01

    Thermal Infrared (TIR) remote sensing measurements of high-temperature volcanic features improve our understanding of volcanic processes and our ability to identify renewed volcanic activity, forecast eruptions, and assess hazards. We will present a time-series analysis of ASTER TIR data acquired over 3 different volcanoes that span a range of temperatures typical of volcanic features: 1) crater lake at Mount Ruapehu; 2) dacite dome at Mount St. Helens, and 3) lava lake at Mount Erebus. The goals of this study were to determine a baseline for the thermal behavior of these volcanoes by characterizing non-volcanic background temperature variations as well as identify how temporal changes in the ASTER-derived temperatures relate to dynamic volcanic processes. Also, one of the on-going and future goals of this work is to develop background thermal variation models for many volcanoes to help identify changes that may occur prior to eruptions. Measuring the temporal thermal behavior of well-monitored active volcanoes provides insights on how to interpret TIR data over other volcanoes that are more remote and less well-studied. At Mount Ruapehu, 34 nighttime ASTER-derived temperatures (integrated over 90-m pixels) from Apr 2001 to Mar 2006 ranged from 10 to 34 C, reflecting regular seasonal variations, with some thermal anomalies that possibly relate to increased fumarolic activity on the crater floor beneath the lake. At Mount St Helens, 19 nighttime ASTER-derived temperatures from Mar 2000 to Feb 2006 ranged from -10 to 96 C. They varied seasonally before the most recent eruption (Oct 2004), and tracked with dome growth after the eruption, relating to dome volume and morphology changes. At Mount Erebus, 115 nighttime ASTER-derived temperatures from Mar 2001 to July 2006 ranged from 0 to 90 C. The sub-pixel sized lava lake showed a large range of retrieved temperatures but no systematic variability, possibly due to steam frequently condensing over the lake. Currently

  12. Production of dissolved organic matter by phytoplankton and its uptake by heterotrophic prokaryotes in large tropical lakes

    NASA Astrophysics Data System (ADS)

    Morana, Cedric; Sarmento, Hugo; Descy, Jean-Pierre; Gasol, Josep M.; Borges, Alberto V.; Bouillon, Steven; Darchambeau, François

    2014-05-01

    In pelagic ecosystems, phytoplankton extracellular release (ER) can substantially subsidize the heterotrophic prokaryotic carbon demand. Factors influencing ER were never investigated in large tropical lakes. We performed time-course experiments to quantify the fraction of phytoplankton production released (PER) and the microbial uptake of freshly excreted compounds (DOCp) in 4 large tropical lakes: lakes Kivu, Edward, Victoria and Albert. In Lake Kivu, we also examined whether the major heterotrophic bacterial group were active in the uptake of freshly excreted compounds using MAR-FISH (microautoradiography coupled to fluorescent in situ hybridization). PER varied across a productivity gradient covering 2 orders of magnitude, with higher values at low productivity. Futhermore, PER was comparatively higher in oligotrophic tropical lakes than in their temperate counterparts and was positively related to the light:phosphate balance. Both observations suggest that environmental factors play a key role in the control of phytoplankton excretion. Furthermore, the standing stocks of DOCp were small and generally contributed less than 1 % to the total dissolved organic carbon as it was rapidly assimilated by prokaryotes, in other words we observed a tight coupling between the production and the heterotrophic consumption of DOCp. We found that none of the major phylogenetic bacterial groups investigated differed in their ability to take up DOCp, in contrast with earlier results reported for standard labelled single-molecule substrates (leucine, glucose, ATP). Overall, these results highlight the strong dependence of all heterotrophic prokaryotes on the labile pool of DOCp, and the importance of carbon transfer between phytoplankton and heterotrophic prokaryotes in large African lakes.

  13. Hydrological regulation drives regime shifts: evidence from paleolimnology and ecosystem modeling of a large shallow Chinese lake.

    PubMed

    Kong, Xiangzhen; He, Qishuang; Yang, Bin; He, Wei; Xu, Fuliu; Janssen, Annette B G; Kuiper, Jan J; van Gerven, Luuk P A; Qin, Ning; Jiang, Yujiao; Liu, Wenxiu; Yang, Chen; Bai, Zelin; Zhang, Min; Kong, Fanxiang; Janse, Jan H; Mooij, Wolf M

    2017-02-01

    Quantitative evidence of sudden shifts in ecological structure and function in large shallow lakes is rare, even though they provide essential benefits to society. Such 'regime shifts' can be driven by human activities which degrade ecological stability including water level control (WLC) and nutrient loading. Interactions between WLC and nutrient loading on the long-term dynamics of shallow lake ecosystems are, however, often overlooked and largely underestimated, which has hampered the effectiveness of lake management. Here, we focus on a large shallow lake (Lake Chaohu) located in one of the most densely populated areas in China, the lower Yangtze River floodplain, which has undergone both WLC and increasing nutrient loading over the last several decades. We applied a novel methodology that combines consistent evidence from both paleolimnological records and ecosystem modeling to overcome the hurdle of data insufficiency and to unravel the drivers and underlying mechanisms in ecosystem dynamics. We identified the occurrence of two regime shifts: one in 1963, characterized by the abrupt disappearance of submerged vegetation, and another around 1980, with strong algal blooms being observed thereafter. Using model scenarios, we further disentangled the roles of WLC and nutrient loading, showing that the 1963 shift was predominantly triggered by WLC, whereas the shift ca. 1980 was attributed to aggravated nutrient loading. Our analysis also shows interactions between these two stressors. Compared to the dynamics driven by nutrient loading alone, WLC reduced the critical P loading and resulted in earlier disappearance of submerged vegetation and emergence of algal blooms by approximately 26 and 10 years, respectively. Overall, our study reveals the significant role of hydrological regulation in driving shallow lake ecosystem dynamics, and it highlights the urgency of using multi-objective management criteria that includes ecological sustainability perspectives when

  14. Tephra layers from Holocene lake sediments of the Sulmona Basin, central Italy: implications for volcanic activity in Peninsular Italy and tephrostratigraphy in the central Mediterranean area

    NASA Astrophysics Data System (ADS)

    Giaccio, B.; Messina, P.; Sposato, A.; Voltaggio, M.; Zanchetta, G.; Galadini, F.; Gori, S.; Santacroce, R.

    2009-12-01

    We present a new tephrostratigraphic record from the Holocene lake sediments of the Sulmona basin, central Italy. The Holocene succession is represented by whitish calcareous mud that is divided into two units, SUL2 (ca 32 m thick) and SUL1 (ca 8 m thick), for a total thickness of ca 40 m. These units correspond to the youngest two out of six sedimentary cycles recognised in the Sulmona basin that are related to the lake sedimentation since the Middle Pleistocene. Height concordant U series age determinations and additional chronological data constrain the whole Holocene succession to between ca 8000 and 1000 yrs BP. This includes a sedimentary hiatus that separates the SUL2 and SUL1 units, which is roughly dated between <2800 and ca 2000 yrs BP. A total of 31 and 6 tephra layers were identified within the SUL2 and SUL1 units, respectively. However, only 28 tephra layers yielded fresh micro-pumices or glass shards suitable for chemical analyses using a microprobe wavelength dispersive spectrometer. Chronological and compositional constraints suggest that 27 ash layers probably derive from the Mt. Somma-Vesuvius Holocene volcanic activity, and one to the Ischia Island eruption of the Cannavale tephra (2920 ± 450 cal yrs BP). The 27 ash layers compatible with Mt. Somma-Vesuvius activity are clustered in three different time intervals: from ca 2000 to >1000; from 3600 to 3100; and from 7600 to 4700 yrs BP. The first, youngest cluster, comprises six layers and correlates with the intense explosive activity of Mt. Somma-Vesuvius that occurred after the prominent AD 79 Pompeii eruption, but only the near-Plinian event of AD 472 has been tentatively recognised. The intermediate cluster (3600-3100 yrs BP) starts with tephra that chemically and chronologically matches the products from the "Pomici di Avellino" eruption (ca 3800 ± 200 yrs BP). This is followed by eight further layers, where the glasses exhibit chemical features that are similar in composition to the

  15. Composition, geometry, and emplacement dynamics of a large volcanic island landslide offshore Martinique: From volcano flank-collapse to seafloor sediment failure?

    NASA Astrophysics Data System (ADS)

    Brunet, Morgane; Le Friant, Anne; Boudon, Georges; Lafuerza, Sara; Talling, Peter; Hornbach, Matthew; Ishizuka, Osamu; Lebas, Elodie; Guyard, Hervé

    2016-03-01

    Landslides are common features in the vicinity of volcanic islands. In this contribution, we investigate landslides emplacement and dynamics around the volcanic island of Martinique based on the first scientific drilling of such deposits. The evolution of the active Montagne Pelée volcano on this island has been marked by three major flank-collapses that removed much of the western flank of the volcano. Subaerial collapse volumes vary from 2 to 25 km3 and debris avalanches flowed into the Grenada Basin. High-resolution seismic data (AGUADOMAR-1999, CARAVAL-2002, and GWADASEIS-2009) is combined with new drill cores that penetrate up to 430 m through the three submarine landslide deposits previously associated to the aerial flank-collapses (Site U1399, Site U1400, Site U1401, IODP Expedition 340, Joides Resolution, March-April 2012). This combined geophysical and core data provide an improved understanding of landslide processes offshore a volcanic island. The integrated analysis shows a large submarine landslide deposit, without debris avalanche deposits coming from the volcano, comprising up to 300 km3 of remobilized seafloor sediment that extends for 70 km away from the coast and covers an area of 2100 km2. Our new data suggest that the aerial debris avalanche deposit enter the sea but stop at the base of submarine flank. We propose a new model dealing with seafloor sediment failures and landslide propagation mechanisms, triggered by volcanic flank-collapse events affecting Montagne Pelée volcano. Newly recognized landslide deposits occur deeper in the stratigraphy, suggesting the recurrence of large-scale mass-wasting processes offshore the island and thus, the necessity to better assess the associated tsunami hazards in the region.

  16. The Application of Methane Clumped Isotope Measurements to Determine the Source of Large Methane Seeps in Alaskan Lakes

    NASA Astrophysics Data System (ADS)

    Douglas, P. M.; Stolper, D. A.; Eiler, J. M.; Sessions, A. L.; Walter Anthony, K. M.

    2014-12-01

    Natural methane emissions from the Arctic present an important potential feedback to global warming. Arctic methane emissions may come from either active microbial sources or from deep fossil reservoirs released by the thawing of permafrost and melting of glaciers. It is often difficult to distinguish between and quantify contributions from these methane sources based on stable isotope data. Analyses of methane clumped isotopes (isotopologues with two or more rare isotopes such as 13CH3D) can complement traditional stable isotope-based classifications of methane sources. This is because clumped isotope abundances (for isotopically equilibrated systems) are a function of temperature and can be used to identify pathways of methane generation. Additionally, distinctive effects of mixing on clumped isotope abundances make this analysis valuable for determining the origins of mixed gasses. We find large variability in clumped isotope compositions of methane from seeps in several lakes, including thermokarst lakes, across Alaska. At Lake Sukok in northern Alaska we observe the emission of dominantly thermogenic methane, with a formation temperature of at least 100° C. At several other lakes we find evidence for mixing between thermogenic methane and biogenic methane that forms in low-temperature isotopic equilibrium. For example, at Eyak Lake in southeastern Alaska, analysis of three methane samples results in a distinctive isotopic mixing line between a high-temperature end-member that formed between 100-170° C, and a biogenic end-member that formed in isotopic equilibrium between 0-20° C. In this respect, biogenic methane in these lakes resembles observations from marine gas seeps, oil degradation, and sub-surface aquifers. Interestingly, at Goldstream Lake in interior Alaska, methane with strongly depleted clumped-isotope abundances, indicative of disequilibrium gas formation, is found, similar to observations from methanogen culture experiments.

  17. Effects of large-scale tephra deposition on vegetation and environment: evidence from three lakes in Northwest Iceland

    NASA Astrophysics Data System (ADS)

    Dögg Eddudóttir, Sigrún; Erlendsson, Egill; Tinganelli, Leone; Gísladóttir, Guðrún

    2016-04-01

    The environment of Iceland is one of the most dynamic in the world, shaped by complex interactions of climate and volcanic activity. The country was uninhabited until about AD 870 and therefore Icelandic paleoecological records offer a unique look at undisturbed environments for most of the Holocene. Using lake sediment records from three different environments in Northwest Iceland, from highland, lowland and oceanic settings, we examine the effects of two of the largest Holocene tephra depositions on the environment. They are the silicic Hekla 4 (c. 4200 cal. yr BP), which produced c. 9 km3 of tephra and the basaltic Saksunarvatn tephra (c. 10,300 cal. yr BP) which dispersed >15 km3 of tephra across the North Atlantic. To examine whether the tephras affected vegetation communities we examine pollen and plant macrofossils prior to, and following, both tephra falls. Lithological proxies such as magnetic susceptibility and organic matter content provide information about landscape stability prior to and after the events. Both tephra deposits affected the environment. However, the magnitude of environmental change and rate of recovery observed in the sediments is dependent on the vegetation in the vicinity of the lakes at the time of the tephra fall, climate and the characteristics of the tephra.

  18. STS-55 Earth observation of Lake Natron, Tanzania, East Africa

    NASA Technical Reports Server (NTRS)

    1993-01-01

    STS-55 Earth observation taken aboard Columbia, Orbiter Vehicle (OV) 102, shows Lake Natron in Tansania, in the 35-mile-wide East African Rift Valley. This lake is surrounded by sodium carbonate volcanoes. Through erosion, these salts of volcanic origin are transported into the rift valley lakes. The various shades of bright red reflecting from the lake result from the water chemistry and biotic blooms. The white spots in the lakebed are drying soda salts. The depth and circulation of the water in the southern end of the lake cause it to appear dark blue rather than bright red. In the repeated photographs of this lake from orbit, we have seen the extent and intensity of its colors fluctuate seasonally. In this photograph, the biotic activity appears to be at a peak. Such a large extent of red-colored water was not present in the photos taken from STS-56, just a few days before (04-10-93).

  19. STS-55 Earth observation of Lake Natron, Tanzania, East Africa

    NASA Technical Reports Server (NTRS)

    1993-01-01

    STS-55 Earth observation taken aboard Columbia, Orbiter Vehicle (OV) 102, shows Lake Natron in Tansania, in the 35-mile-wide East African Rift Valley. This lake is surrounded by sodium carbonate volcanoes. Through erosion, these salts of volcanic origin are transported into the rift valley lakes. The various shades of bright red reflecting from the lake result from the water chemistry and biotic blooms. The white spots in the lakebed are drying soda salts. The depth and circulation of the water in the southern end of the lake cause it to appear dark blue rather than bright red. In the repeated photographs of this lake from orbit, we have seen the extent and intensity of its colors fluctuate seasonally. In this photograph, the biotic activity appears to be at a peak. Such a large extent of red-colored water was not present in the photos taken from STS-56, just a few days before (04-10-93).

  20. Contamination and Risk Assessment of Heavy Metals in Lake Bed Sediment of a Large Lake Scenic Area in China

    PubMed Central

    Wan, Li; Xu, Liang; Fu, Yongsheng

    2016-01-01

    The exposure of heavy metals to lake bed sediment of scenic areas may pose risks on aquatic ecosystems and human health, however very few studies on risk assessment have been reported for scenic areas. Accordingly, this study determined concentration levels, and assessed contamination characteristics and risks, of heavy metals in lake bed sediment of National Scenic Areas Songhuahu (NSAS) in China. The concentrations of Zn, Cr, Pb, Ni, and Cu were determined in 29 bed sediment samples. Results showed that the mean values of Zn, Cr, Pb, Ni, and Cu were 92.69, 90.73, 38.29, 46.77, and 49.44 mg/kg, respectively. Pearson correlation coefficients indicated that organic matter was a major factor influencing distribution of heavy metals. The results for enrichment factors indicated that contamination rates and anthropogenic inputs of single heavy metals decreased in the order Cu > Ni > Pb > Cr > Zn; results of Nemerow integrated pollution index suggested that 72.41% of sampling sites were exposed to low to moderately integrated pollution, and 27.59% of sampling sites were exposed to strongly integrated pollution. According to results for potential ecological risk index, ecological risks of single and all the heavy metals in bed sediment from all the sampling sites were low. Human risks were assessed with hazardous quotients, and the results suggested that exposure of heavy metals to bed sediment posed no or little risk to human health, and the pathway of ingestion significantly contributed to human health risks. PMID:27455296

  1. Approaches to Integrated Assessment of Large Lakes involving New Survey Designs and Synoptic, in situ Technologies

    EPA Science Inventory

    The Laurentian Great Lakes have had, for decades, regular water quality monitoring programs to track conditions in their offshore waters, as dictated by a binational Great Lakes Water Quality Agreement between the US and Canada. Unfortunately, resources have limited monitoring t...

  2. Eutrophication monitoring for Lake Superior’s Chequamegon Bay before and after large summer storms

    EPA Science Inventory

    A priority for the Lake Superior CSMI was to identify susceptible nearshore eutrophication areas. We developed an integrated sampling design to collect baseline data for Lake Superior’s Chequamegon Bay to understand how nearshore physical processes and tributary loading rel...

  3. Approaches to Integrated Assessment of Large Lakes involving New Survey Designs and Synoptic, in situ Technologies

    EPA Science Inventory

    The Laurentian Great Lakes have had, for decades, regular water quality monitoring programs to track conditions in their offshore waters, as dictated by a binational Great Lakes Water Quality Agreement between the US and Canada. Unfortunately, resources have limited monitoring t...

  4. Capturing variations in inundation with satellite remote sensing in a morphologically complex, large lake

    NASA Astrophysics Data System (ADS)

    Wu, Guiping; Liu, Yuanbo

    2015-04-01

    Poyang Lake is the largest freshwater lake in China, with high morphological complexity from south to north. In recent years, the lake has experienced expansion and shrinkage processes over both short- and long-term scales, resulting in significant hydrological, ecological and economic problems. Exactly how and how rapidly the processes of spatial change have occurred in the lake during the expansion and shrinkage periods is unknown. Such knowledge is of great importance for policymakers as it may help with flood/drought prevention, land use planning and lake ecological conservation. In this study, we investigated the spatial-temporal distribution and changing processes of inundation in Poyang Lake based on Moderate Resolution Imaging Spectroradiometer (MODIS) Level-1B data from 2000 to 2011. A defined water variation rate (WVR) and inundation frequency (IF) indicator revealed the water surface submersion and exposure processes of lake expansion and shrinkage in different zones which were divided according to the lake's hydrological and topographic features. Regional differences and significant seasonality variability were found in the annual and monthly mean IF. The monthly mean IF increased slowly from north to south during January-August but decreased quickly from south to north during September-December. During the lake expansion period, the lake-type water body zone (Zone II) had the fastest expansion rate, with a mean monthly WVR value of 34.47% in February-March, and was followed by the channel-type water body zone (Zone I) in March-May (22.47%). However, during the lake shrinkage period, rapid shrinkage first appeared around the alluvial delta zones in August-October. The sequence of lake surface shrinkage from August to December is exactly opposite to that of lake expansion from February to July. These complex inundation characteristics and changing process were driven by the high temporal variability of the river flows, the morphological diversity of the

  5. Earthquakes and their influence on the large aquatic ecosystems (taking Lake Sevan as an example).

    NASA Astrophysics Data System (ADS)

    Gulakyan, S.; Wilkinson, I.

    2003-04-01

    Lake dynamic and earthquakes. The model includes hydrothermodynamic equations and boundary conditions at the surface and on the lake bed, include configuration and depth of the lake, the temperature regime, wind velocity and direction, etc. Ground motion during an earthquake is variable, but dependent on the sediment type. Here are considered the following questions: · Earthquakes and hypolimnion, stratification . · Inertia waves, aftershocks of earthquakes and lake dynamic. · Earthquakes and ground water circulation in water ecosystems. · Earthquakes and water chemistry of an ecosystem ( phosphorous, calcium carbonate, gases and etc). · Earthquakes and benthos species. These models implemented for the data of Lake Sevan (Armenia). We acknowledge, with thanks, NATO for supporting this program through Linkage Grant No. 9-975530.

  6. Large-scale mapping and predictive modeling of submerged aquatic vegetation in a shallow eutrophic lake.

    PubMed

    Havens, Karl E; Harwell, Matthew C; Brady, Mark A; Sharfstein, Bruce; East, Therese L; Rodusky, Andrew J; Anson, Daniel; Maki, Ryan P

    2002-04-09

    A spatially intensive sampling program was developed for mapping the submerged aquatic vegetation (SAV) over an area of approximately 20,000 ha in a large, shallow lake in Florida, U.S. The sampling program integrates Geographic Information System (GIS) technology with traditional field sampling of SAV and has the capability of producing robust vegetation maps under a wide range of conditions, including high turbidity, variable depth (0 to 2 m), and variable sediment types. Based on sampling carried out in August-September 2000, we measured 1,050 to 4,300 ha of vascular SAV species and approximately 14,000 ha of the macroalga Chara spp. The results were similar to those reported in the early 1990s, when the last large-scale SAV sampling occurred. Occurrence of Chara was strongly associated with peat sediments, and maximal depths of occurrence varied between sediment types (mud, sand, rock, and peat). A simple model of Chara occurrence, based only on water depth, had an accuracy of 55%. It predicted occurrence of Chara over large areas where the plant actually was not found. A model based on sediment type and depth had an accuracy of 75% and produced a spatial map very similar to that based on observations. While this approach needs to be validated with independent data in order to test its general utility, we believe it may have application elsewhere. The simple modeling approach could serve as a coarse-scale tool for evaluating effects of water level management on Chara populations.

  7. Magnetic properties of lake sediments from Lake Chalco, central Mexico, and their palaeoenvironmental implications

    NASA Astrophysics Data System (ADS)

    Ortega Guerrero, Beatriz; Thompson, Roy; Urrutia Fucugauchi, Jaime

    2000-02-01

    Lake Chalco (99.0°W, 19.5°N) in the Basin of Mexico, was formed during the Pleistocene after the emplacement of the Chichinautzin volcanic field that closed the former drainage system. The lake sediment record has been influenced by a number of factors, including glacial-interglacial cycles, local volcanism, erosion of soils and anthropogenic disturbances. The magnetic properties of the lake sediments and the associated tephra layers of the last 16500 yr have been studied. It is found that the magnetic properties of the Lake Chalco sediments are very distinctive. Magnetic concentration varies by a factor of 1000 and magnetic stability also varies over an extremely wide range. The predominant magnetic mineral is titanomagnetite in addition to an imperfect antiferromagnetic phase, possibly goethite. An unusually large range of coercivities is found in certain of the tephras. Down-core variations in magnetic properties closely follow climatic/environmental changes previously established by other proxy methods. The late Pleistocene and late Holocene lake sediments display a higher concentration of magnetic minerals than the early-middle Holocene sediments. In the non-volcanic sediments, fluctuations in the magnetic concentration reflect changes in both the intensity of erosion, as represented by ferrimagnetic and paramagnetic minerals, and by the maturing of soils, as represented by geothite.

  8. Pelagic Ciliates in a Large Mesotrophic Lake: Seasonal Succession and Taxon-Specific Bacterivory in Lake Constance

    NASA Astrophysics Data System (ADS)

    Cleven, Ernst-Josef

    2004-07-01

    The taxonomic composition of the ciliate assemblage and their taxon-specific bacterial grazing rates in Lake Constance were investigated over the course of one year. Bacterial grazing rates were measured using natural fluorescently labelled bacteria (FLB) and compared to bacterial production. Small species such as Balanion planctonicum/Urotricha furcata and Rimostrombidium spp./Halteria sp. were the most numerous ciliates on the annual average. Larger ciliates such as Rimostrombidium lacustris and Limnostrombidium spp. contributed significantly to total ciliate biomass, but were relatively unimportant as bacterial grazers. Per capita ingestion rates ranged from 0-194 bacteria ciliate-1 h-1 and changed seasonally up to a hundredfold within a given taxon. Approximately 1% of the bacterial production were removed by the ciliate community on the annual average. (

  9. Large lake basins of the southern High Plains: Ground-water control of their origin

    SciTech Connect

    Wood, W.W.; Sanford, W.E. ); Reeves, C.C. Jr )

    1992-06-01

    The origin of the {approximately}40-50 topographically large lake basins on the southern High Plains of Texas and New Mexico has been an enigma. Previous workers have considered deflation or evaporite dissolution at depth and subsequent collapse as the most probable mechanisms. However, the eolian hypotheses have been unable to provide convincing arguments as to how the wind selectively erodes the thick, deflation-resistant calcrete 'caprock' that is persistent over much of the southern High Plains. Furthermore, recent detailed studies on some of the basins show no significant evaporite dissolution at depth, and neither mechanism offers a satisfactory explanation as to why the basins are almost universally associated with subsurface topographic highs, or why they are absent where the High Plains aquifer thickness exceeds 60 m. The authors address these latter concerns and modify the deflation hypothesis by proposing that the calcrete caprock may never have been deposited in the areas now occupied by the basins. The absence of calcrete deposition is proposed to have resulted from high water tables caused by an increase in hydraulic gradient where aquifers thinned above bedrock highs. A high water table close to an/or intersecting the surface prevents deposition of calcrete, and, thus, the uncemented surface would be more susceptible to deflation than the surrounding calcrete-covered areas after decline of the water table. The rise in water table associated with bedrock highs is documented by numerical simulation using boundary conditions and hydrologic parameters representative of the southern High Plains.

  10. Large residuals on geoidal heights determined on the Fagnano Lake, Tierra del Fuego-Argentina

    NASA Astrophysics Data System (ADS)

    Gomez, M. E.; Del Cogliano, D.; Perdomo, R.

    2013-05-01

    A new geoid model was developed in Tierra del Fuego and it was evaluated in the area of Fagnano Lake. The model was developed by means of the Equivalent Source Technique combining gravity data, levelling information measured on the province and observations of a GPS buoy on the Fagnano Lake. Those GPS buoy measurements provide information of the mean lake level surface (Del Cogliano et al., 2007). A cross validation process was realized in order to evaluate the model on the lake. What allowed determining a 6 cm geoid in the area of Fagnano Lake. Also, an evaluation of the EGM2008 (Pavlis et al., 2008) was made on the lake. Its behaviour was compared to that observed on the levelling lines. Differences of several decimetres were found when EGM2008 undulations were compared to observed geoid undulations in the lake area. In the regions where EGM2008 has included real gravimetric observations, differences between model and observations were only of a few centimetres. Such model has the particularity that includes fill-in gravity in that region. The above mentioned evaluation derived in an analysis of the effect that not representative gravity information could have on the estimation of geoid undulations in high mountainous regions. We found that this effect could be significant if there is no real information in the computing area (Gomez et al, 2012).

  11. Long-term effects of a trophic cascade in a large lake ecosystem

    PubMed Central

    Ellis, Bonnie K.; Stanford, Jack A.; Goodman, Daniel; Stafford, Craig P.; Gustafson, Daniel L.; Beauchamp, David A.; Chess, Dale W.; Craft, James A.; Deleray, Mark A.; Hansen, Barry S.

    2011-01-01

    Introductions or invasions of nonnative organisms can mediate major changes in the trophic structure of aquatic ecosystems. Here we document multitrophic level impacts in a spatially extensive system that played out over more than a century. Positive interactions among exotic vertebrate and invertebrate predators caused a substantial and abrupt shift in community composition resulting in a trophic cascade that extended to primary producers and to a nonaquatic species, the bald eagle. The opossum shrimp, Mysis diluviana, invaded Flathead Lake, Montana, the largest freshwater lake in the western United States. Lake trout had been introduced 80 y prior but remained at low densities until nonnative Mysis became established. The bottom-dwelling mysids eliminated a recruitment bottleneck for lake trout by providing a deep water source of food where little was available previously. Lake trout subsequently flourished on mysids and this voracious piscivore now dominates the lake fishery; formerly abundant kokanee were extirpated, and native bull and westslope cutthroat trout are imperiled. Predation by Mysis shifted zooplankton and phytoplankton community size structure. Bayesian change point analysis of primary productivity (27-y time series) showed a significant step increase of 55 mg C m−2 d−1 (i.e., 21% rise) concurrent with the mysid invasion, but little trend before or after despite increasing nutrient loading. Mysis facilitated predation by lake trout and indirectly caused the collapse of kokanee, redirecting energy flow through the ecosystem that would otherwise have been available to other top predators (bald eagles). PMID:21199944

  12. Long-term effects of a trophic cascade in a large lake ecosystem.

    PubMed

    Ellis, Bonnie K; Stanford, Jack A; Goodman, Daniel; Stafford, Craig P; Gustafson, Daniel L; Beauchamp, David A; Chess, Dale W; Craft, James A; Deleray, Mark A; Hansen, Barry S

    2011-01-18

    Introductions or invasions of nonnative organisms can mediate major changes in the trophic structure of aquatic ecosystems. Here we document multitrophic level impacts in a spatially extensive system that played out over more than a century. Positive interactions among exotic vertebrate and invertebrate predators caused a substantial and abrupt shift in community composition resulting in a trophic cascade that extended to primary producers and to a nonaquatic species, the bald eagle. The opossum shrimp, Mysis diluviana, invaded Flathead Lake, Montana, the largest freshwater lake in the western United States. Lake trout had been introduced 80 y prior but remained at low densities until nonnative Mysis became established. The bottom-dwelling mysids eliminated a recruitment bottleneck for lake trout by providing a deep water source of food where little was available previously. Lake trout subsequently flourished on mysids and this voracious piscivore now dominates the lake fishery; formerly abundant kokanee were extirpated, and native bull and westslope cutthroat trout are imperiled. Predation by Mysis shifted zooplankton and phytoplankton community size structure. Bayesian change point analysis of primary productivity (27-y time series) showed a significant step increase of 55 mg C m(-2) d(-1) (i.e., 21% rise) concurrent with the mysid invasion, but little trend before or after despite increasing nutrient loading. Mysis facilitated predation by lake trout and indirectly caused the collapse of kokanee, redirecting energy flow through the ecosystem that would otherwise have been available to other top predators (bald eagles).

  13. Large-scale hydrodynamic modeling of the middle Yangtze River Basin with complex river-lake interactions

    NASA Astrophysics Data System (ADS)

    Lai, Xijun; Jiang, Jiahu; Liang, Qiuhua; Huang, Qun

    2013-06-01

    The flow regime in the middle Yangtze River Basin is experiencing rapid changes due to intensive human activities and ongoing climate change. The middle reach of Yangtze River and the associated water system are extremely difficult to be reliably modeled due to highly complex interactions between the main stream and many tributaries and lakes. This paper presents a new Coupled Hydrodynamic Analysis Model (CHAM) designed for simulating the large-scale water system in the middle Yangtze River Basin, featured with complex river-lake interactions. CHAM dynamically couples a one-dimensional (1-D) unsteady flow model and a two-dimensional (2-D) hydrodynamic model using a new coupling algorithm that is particularly suitable for large-scale water systems. Numerical simulations are carried out to reproduce the flow regime in the region in 1998 when a severe flood event occurred and in 2006 when it experienced an extremely dry year. The model is able to reproduce satisfactorily the major physical processes featured with seasonal wetting and drying controlled by strong river-lake interactions. This indicates that the present model provides a promising tool for predicting complex flow regimes with remarkable seasonal changes and strong river-lake interactions.

  14. Large wood budget assessment along a gravel bed river affected by volcanic eruption: the Rio Blanco study case (Chile).

    NASA Astrophysics Data System (ADS)

    Oss-Cazzador, Daniele; Iroume, Andres; Lenzi, Mario; Picco, Lorenzo

    2016-04-01

    Wood in riverine environments exerts different functions on ecological and geomorphic settings, influencing morphological processes, and increasing risks for sensitive structures. Large wood (LW) is defined as wood material, dead or alive, larger than 10 cm in diameter and 1 m in length. Natural hazards can strongly increase the presence of LW in waterways and flood events can transport it affecting the ecosystem and landscape. This study aims to increase the knowledge of wood budget, considering the effects of two subsequent slight flood events along a sub-reach of the Rio Blanco gravel bed river , in Chilean Patagonia, strongly affected by the eruption of Chaiten volcano in 2008. The volcanic eruption affected almost 3,5 km 2 of evergreen forest on the southern (left) bank, because of primary direct effects from pyroclastic density currents and lahar-floods that caused deposition up to 8 m of reworked tephra, alluvium, and wood on floodplains and terrace along the Rio Blanco. After the eruption, there was a considerable increase of LW into the main channel: into the bankfull channel, volume exceeds 100 m 3 /ha. Field surveys were carried out in January and March 2015, before and after two slight flood events (Recurrence Intervals lower than 1 year). The pre-event phase permitted to detect and analyze the presence of LW into the study area, along a 80 m-long reach of Rio Blanco (7500 m 2 . Every LW element was manually measured and described, a numbered metal tag was installed, and the position was recorded by GPS device. In January, there was a total amount of 113 m 3 /ha, 90% accumulated in LW jams (WJ) and 10% as single logs. The LW was characterized by mean dimensions of 3,36 m height, 0,25 m diameter and 0,26 m 3 volume, respectively. The WJ are characterized by wide range of dimension: volume varies from 0,28 m 3 to 672 m 3 , length from 1,20 m to 56 m, width from 0,40 m to 8,70 m and height from 0,20 m to 3 m, respectively. After the flood events, field

  15. Thermocline deepening boosts ecosystem metabolism: evidence from a large-scale lake enclosure experiment simulating a summer storm.

    PubMed

    Giling, Darren P; Nejstgaard, Jens C; Berger, Stella A; Grossart, Hans-Peter; Kirillin, Georgiy; Penske, Armin; Lentz, Maren; Casper, Peter; Sareyka, Jörg; Gessner, Mark O

    2017-04-01

    Extreme weather events can pervasively influence ecosystems. Observations in lakes indicate that severe storms in particular can have pronounced ecosystem-scale consequences, but the underlying mechanisms have not been rigorously assessed in experiments. One major effect of storms on lakes is the redistribution of mineral resources and plankton communities as a result of abrupt thermocline deepening. We aimed at elucidating the importance of this effect by mimicking in replicated large enclosures (each 9 m in diameter, ca. 20 m deep, ca. 1300 m(3) in volume) a mixing event caused by a severe natural storm that was previously observed in a deep clear-water lake. Metabolic rates were derived from diel changes in vertical profiles of dissolved oxygen concentrations using a Bayesian modelling approach, based on high-frequency measurements. Experimental thermocline deepening stimulated daily gross primary production (GPP) in surface waters by an average of 63% for >4 weeks even though thermal stratification re-established within 5 days. Ecosystem respiration (ER) was tightly coupled to GPP, exceeding that in control enclosures by 53% over the same period. As GPP responded more strongly than ER, net ecosystem productivity (NEP) of the entire water column was also increased. These protracted increases in ecosystem metabolism and autotrophy were driven by a proliferation of inedible filamentous cyanobacteria released from light and nutrient limitation after they were entrained from below the thermocline into the surface water. Thus, thermocline deepening by a single severe storm can induce prolonged responses of lake ecosystem metabolism independent of other storm-induced effects, such as inputs of terrestrial materials by increased catchment run-off. This highlights that future shifts in frequency, severity or timing of storms are an important component of climate change, whose impacts on lake thermal structure will superimpose upon climate trends to influence algal

  16. Spatio-seasonal variability of chromophoric dissolved organic matter absorption and responses to photobleaching in a large shallow temperate lake

    NASA Astrophysics Data System (ADS)

    Encina Aulló-Maestro, María; Hunter, Peter; Spyrakos, Evangelos; Mercatoris, Pierre; Kovács, Attila; Horváth, Hajnalka; Preston, Tom; Présing, Mátyás; Torres Palenzuela, Jesús; Tyler, Andrew

    2017-03-01

    The development and validation of remote-sensing-based approaches for the retrieval of chromophoric dissolved organic matter (CDOM) concentrations requires a comprehensive understanding of the sources and magnitude of variability in the optical properties of dissolved material within lakes. In this study, spatial and seasonal variability in concentration and composition of CDOM and the origin of its variation was studied in Lake Balaton (Hungary), a large temperate shallow lake in central Europe. In addition, we investigated the effect of photobleaching on the optical properties of CDOM through in-lake incubation experiments. There was marked variability throughout the year in CDOM absorption in Lake Balaton (aCDOM(440) = 0. 06-9.01 m-1). The highest values were consistently observed at the mouth of the main inflow (Zala River), which drains humic-rich material from the adjoining Kis-Balaton wetland, but CDOM absorption decreased rapidly towards the east where it was consistently lower and less variable than in the westernmost lake basins. The spectral slope parameter for the interval of 350-500 nm (SCDOM(350-500)) was more variable with increasing distance from the inflow (observed range 0.0161-0.0181 nm-1 for the mouth of the main inflow and 0.0158-0.0300 nm-1 for waters closer to the outflow). However, spatial variation in SCDOM was more constant exhibiting a negative correlation with aCDOM(440). Dissolved organic carbon (DOC) was strongly positively correlated with aCDOM(440) and followed a similar seasonal trend but it demonstrated more variability than either aCDOM or SCDOM with distance through the system. Photobleaching resulting from a 7-day exposure to natural solar UV radiation resulted in a marked decrease in allochthonous CDOM absorption (7.04 to 3.36 m-1, 42 % decrease). Photodegradation also resulted in an increase in the spectral slope coefficient of dissolved material.

  17. Atmospheric partitioning and the air-water exchange of polycyclic aromatic hydrocarbons in a large shallow Chinese lake (Lake Chaohu).

    PubMed

    Qin, Ning; He, Wei; Kong, Xiang-Zhen; Liu, Wen-Xiu; He, Qi-Shuang; Yang, Bin; Ouyang, Hui-Ling; Wang, Qing-Mei; Xu, Fu-Liu

    2013-11-01

    The residual levels of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere and in dissolved phase from Lake Chaohu were measured by (GC-MS). The composition and seasonal variation were investigated. The diffusive air-water exchange flux was estimated by a two-film model, and the uncertainty in the flux calculations and the sensitivity of the parameters were evaluated. The following results were obtained: (1) the average residual levels of all PAHs (PAH16) in the atmosphere from Lake Chaohu were 60.85±46.17 ng m(-3) in the gaseous phase and 14.32±23.82 ng m(-3) in the particulate phase. The dissolved PAH16 level was 173.46±132.89 ng L(-1). (2) The seasonal variation of average PAH16 contents ranged from 43.09±33.20 ng m(-3) (summer) to 137.47±41.69 ng m(-3) (winter) in gaseous phase, from 6.62±2.72 ng m(-3) (summer) to 56.13±22.99 ng m(-3) (winter) in particulate phase, and 142.68±74.68 ng L(-1) (winter) to 360.00±176.60 ng L(-1) (summer) in water samples. Obvious seasonal trends of PAH16 concentrations were found in the atmosphere and water. The values of PAH16 for both the atmosphere and the water were significantly correlated with temperature. (3) The monthly diffusive air-water exchange flux of total PAH16 ranged from -1.77×10(4) ng m(-2) d(-1) to 1.11×10(5) ng m(-2) d(-1), with an average value of 3.45×10(4) ng m(-2) d(-1). (4) The results of a Monte Carlo simulation showed that the monthly average PAH fluxes ranged from -3.4×10(3) ng m(-2) d(-1) to 1.6×10(4) ng m(-2) d(-1) throughout the year, and the uncertainties for individual PAHs were compared. (5) According to the sensitivity analysis, the concentrations of dissolved and gaseous phase PAHs were the two most important factors affecting the results of the flux calculations.

  18. Large seasonal changes in hydrogen isotope fractionation between algal biomarkers and lake surface water

    NASA Astrophysics Data System (ADS)

    Ladd, N.; Dubois, N.; Schubert, C. J.

    2016-12-01

    The hydrogen isotope composition (2H/1H) of biomarkers produced by algae is strongly influenced by the 2H/1H ratio of the water in which the organism grew. 2H/1H ratios of algal biomarkers preserved in lake sediments are thus a useful tool for reconstructing past changes in lake water isotope values, which can be used to infer hydroclimate changes. However, a number of variables can influence the magnitude of hydrogen isotope fractionation between algal lipids and their source water in laboratory cultures, particularly factors relating to growth rates. Quantifying the natural extent of these changes in field settings and identifying their causes is essential for robust application of 2H/1H ratios of algal lipids as paleohydroclimate proxies, yet these remain poorly constrained. This work targets the effect of nutrient availability and variable growth rates on 2H/1H fractionation in algal biomarkers through a comparative study between two central Swiss lakes: eutrophic Lake Greifen and oligotrophic Lake Lucerne. Suspended particles from surface water were collected at six time points throughout the spring and summer of 2015, and hydrogen isotope values of short chain saturated and unsaturated fatty acids were measured. We paired these measurements with in situ incubations conducted with NaH13CO3, which were used to calculate the production rate of short chain fatty acids in lake surface water. We demonstrate that as algal productivity increased from April to June, the magnitude of 2H/1H fractionation in Lake Greifen increased by as much as 140 ‰ for individual fatty acids. Fractionation also increased with increasing productivity for fatty acids in Lake Lucerne, but the magnitude of the effect was smaller than in Lake Greifen. We attribute these changes to relatively greater contributions of highly depleted H from NADPH in photosystem I as temperature and light availability increased. Larger changes in 2H/1H fractionation in Lake Greifen than in Lake Lucerne may

  19. Accumulation of microcystins in a dominant Chironomid Larvae (Tanypus chinensis) of a large, shallow and eutrophic Chinese lake, Lake Taihu

    PubMed Central

    Xue, Qingju; Su, Xiaomei; Steinman, Alan D.; Cai, Yongjiu; Zhao, Yanyan; Xie, Liqiang

    2016-01-01

    Although there have been numerous studies on microcystin (MC) accumulation in aquatic organisms recently, the bioaccumulation of MCs in relatively small sized organisms, as well as potential influencing factors, has been rarely studied. Thus, in this study, we investigated the bioaccumulation of three MC congeners (-LR, -RR and -YR) in the chironomid larvae of Tanypus chinensis (an excellent food source for certain fishes), the potential sources of these MCs, and potentially relevant environmental parameters over the course of one year in Lake Taihu, China. MC concentrations in T. chinensis varied temporally with highest concentrations during the warmest months (except August 2013) and very low concentrations during the remaining months. Among the three potential MC sources, only intracellular MCs were significantly and positively correlated with MCs in T. chinensis. Although MC concentrations in T. chinensis significantly correlated with a series of physicochemical parameters of water column, cyanobacteria species explained the most variability of MC accumulation, with the rest primarily explained by extraMC-LR. These results indicated that ingestion of MC-producing algae of cyanobacteria accounted for most of the MC that accumulated in T. chinensis. The high MC concentrations in T. chinensis may pose a potential health threat to humans through trophic transfer. PMID:27499175

  20. Accumulation of microcystins in a dominant Chironomid Larvae (Tanypus chinensis) of a large, shallow and eutrophic Chinese lake, Lake Taihu

    NASA Astrophysics Data System (ADS)

    Xue, Qingju; Su, Xiaomei; Steinman, Alan D.; Cai, Yongjiu; Zhao, Yanyan; Xie, Liqiang

    2016-08-01

    Although there have been numerous studies on microcystin (MC) accumulation in aquatic organisms recently, the bioaccumulation of MCs in relatively small sized organisms, as well as potential influencing factors, has been rarely studied. Thus, in this study, we investigated the bioaccumulation of three MC congeners (-LR, -RR and -YR) in the chironomid larvae of Tanypus chinensis (an excellent food source for certain fishes), the potential sources of these MCs, and potentially relevant environmental parameters over the course of one year in Lake Taihu, China. MC concentrations in T. chinensis varied temporally with highest concentrations during the warmest months (except August 2013) and very low concentrations during the remaining months. Among the three potential MC sources, only intracellular MCs were significantly and positively correlated with MCs in T. chinensis. Although MC concentrations in T. chinensis significantly correlated with a series of physicochemical parameters of water column, cyanobacteria species explained the most variability of MC accumulation, with the rest primarily explained by extraMC-LR. These results indicated that ingestion of MC-producing algae of cyanobacteria accounted for most of the MC that accumulated in T. chinensis. The high MC concentrations in T. chinensis may pose a potential health threat to humans through trophic transfer.

  1. The Role of Fish Communities in Water Quality Management of a Large Shallow Lake

    NASA Astrophysics Data System (ADS)

    Tátrai, István; Paulovits, Gábor; Mátyás, Kálmán; Korponai, János

    2003-09-01

    Management measures of Lake Balaton such as wetland reconstruction at the main inflow to the lake along with the unplanned commercial fishery led to great changes in the density and biomass of fish populations. There was no significant difference in CPUE data between the two, eastern and western, basins. Biomass of total fish stock in Lake Balaton has decreased substantially, 2-3 times between 1991-1999, and ranges between 120-194 kg ha-1. Bottom-up effects are more important than the top-down effects due to the impact of internal nutrient load. Changes in the biomass and thus the activity of omnivorous fish in the lake lowered the intensity of various indirect effects and feedback mechanisms causing changes in the nutrient metabolism of the lake. Intensified fishery effort in Lake Balaton did not result in an increased stock of piscivores. The ratio of piscivores and omnivores remained at 5% during the whole study period. Despite this low piscivores to omnivores ratio, the water quality has improved in all basins.

  2. Large difference in carbon emission – burial balances between boreal and arctic lakes

    PubMed Central

    Lundin, E. J.; Klaminder, J.; Bastviken, D.; Olid, C.; Hansson, S. V.; Karlsson, J.

    2015-01-01

    Lakes play an important role in the global carbon (C) cycle by burying C in sediments and emitting CO2 and CH4 to the atmosphere. The strengths and control of these fundamentally different pathways are therefore of interest when assessing the continental C balance and its response to environmental change. In this study, based on new high-resolution estimates in combination with literature data, we show that annual emission:burial ratios are generally ten times higher in boreal compared to subarctic – arctic lakes. These results suggest major differences in lake C cycling between biomes, as lakes in warmer boreal regions emit more and store relatively less C than lakes in colder arctic regions. Such effects are of major importance for understanding climatic feedbacks on the continental C sink – source function at high latitudes. If predictions of global warming and northward expansion of the boreal biome are correct, it is likely that increasing C emissions from high latitude lakes will partly counteract the presumed increasing terrestrial C sink capacity at high latitudes. PMID:26370519

  3. Large difference in carbon emission – burial balances between boreal and arctic lakes.

    PubMed

    Lundin, E J; Klaminder, J; Bastviken, D; Olid, C; Hansson, S V; Karlsson, J

    2015-09-15

    Lakes play an important role in the global carbon (C) cycle by burying C in sediments and emitting CO2 and CH4 to the atmosphere. The strengths and control of these fundamentally different pathways are therefore of interest when assessing the continental C balance and its response to environmental change. In this study, based on new high-resolution estimates in combination with literature data, we show that annual emission:burial ratios are generally ten times higher in boreal compared to subarctic - arctic lakes. These results suggest major differences in lake C cycling between biomes, as lakes in warmer boreal regions emit more and store relatively less C than lakes in colder arctic regions. Such effects are of major importance for understanding climatic feedbacks on the continental C sink - source function at high latitudes. If predictions of global warming and northward expansion of the boreal biome are correct, it is likely that increasing C emissions from high latitude lakes will partly counteract the presumed increasing terrestrial C sink capacity at high latitudes.

  4. Modelling of seasonal and long-term trends in lake salinity in southwestern Victoria, Australia.

    PubMed

    Yihdego, Yohannes; Webb, John

    2012-12-15

    In southwestern Victoria a large number of lakes are scattered across the volcanic plains; many have problems with increasing salinity. To identify the hydrologic components behind this problem, three lakes, Burrumbeet, Linlithgow and Buninjon, were selected for detailed water and salt budget modelling using monthly values of rainfall, evaporation, surface inflow and outflow, and groundwater inflow and outflow (using the new modified difference method developed in this study). On average, rainfall begins to exceed evaporation with the onset of winter rainfall in May, so lake levels rise and lake salinities decline. The modelled lakes have become more saline over the last decade, a time of drought with below average rainfall, and all eventually dried out, their salinities rising to very high levels as they shallowed. Lake Burrumbeet is generally much less saline than Lakes Linlithgow and Buninjon, because it has substantial groundwater outflow, probably due to leakage through one or more volcanic necks. This limits the amount of time the lake water is subject to evaporation, and also allows significant salt export. The other lakes do not leak. The modelling indicates that when the lakes dry out, salt is lost from the lake-beds, probably due to wind deflation of salt crusts and leakage into the underlying groundwater. The removal of salt during drying-out phases resets the salinity of the lakes, limiting their ability to become more saline with time. Drying-out phases may therefore be essential in preventing the increased salinisation of lakes and wetland environments across the volcanic plains. Copyright © 2012 Elsevier Ltd. All rights reserved.

  5. Stratigraphic framework and lake level history of Lake Kivu, East African Rift

    NASA Astrophysics Data System (ADS)

    Wood, Douglas A.; Scholz, Christopher A.

    2017-10-01

    Sediment cores and seismic reflection data acquired from the eastern basin of Lake Kivu, Rwanda reveal extensive limnologic variations due to changes in regional climate and basin structure. The eastern basin of the lake contains a sedimentary wedge which is > 1.5 km in thickness on its western side, and basal sediments are estimated to be at least 1.5 million years old. Sediments are likely to be thicker and older than this in the northern, Congolese basin of the lake. Above the ∼300 m iosbath only a thin layer of Holocene sediments are observed indication that this may have been the lake's high stand prior to that time. There are at least three erosional unconformities interpreted as desiccation or near-desiccation events which are estimated to have occurred at ∼475 ka, ∼100 ka, and ∼20 ka; the two most recent of these low stages likely developed during the African Megadrought and Last Glacial Maximum (LGM) periods. Following the LGM, the water levels rose to form a ∼100 m deep lake with its surface ∼370 m below the current lake level. The lake remained near that level for several thousand years and during this time the Virunga Volcanic Province expanded. At ∼12.2 ka a change to wetter climate conditions rapidly filled the lake to spill out of the Bukavu Bay basin southward toward Lake Tanganyika. Tephra sampled from the cores show that there have been at least 24 large local volcanic events since the early Holocene lake transgression.

  6. Impact of an extremely large magnitude volcanic eruption on the global climate and carbon cycle estimated from ensemble Earth System Model simulations

    NASA Astrophysics Data System (ADS)

    Segschneider, J.; Beitsch, A.; Timmreck, C.; Brovkin, V.; Ilyina, T.; Jungclaus, J.; Lorenz, S. J.; Six, K. D.; Zanchettin, D.

    2012-07-01

    The response of the global climate-carbon cycle system to an extremely large Northern Hemisphere mid latitude volcanic eruption is investigated using ensemble integrations with the comprehensive Earth System Model MPI-ESM. The model includes dynamical compartments of the atmosphere and ocean and interactive modules of the terrestrial biosphere as well as ocean biogeochemistry. The MPI-ESM was forced with anomalies of aerosol optical depth and effective radius of aerosol particles corresponding to a super eruption of the Yellowstone volcanic system. The model experiment consists of an ensemble of fifteen model integrations that are started at different pre-ENSO states of a contol experiment and run for 200 yr after the volcanic eruption. The climate response to the volcanic eruption is a maximum global monthly mean surface air temperature cooling of 3.8 K for the ensemble mean and from 3.3 K to 4.3 K for individual ensemble members. Atmospheric pCO2 decreases by a maximum of 5 ppm for the ensemble mean and by 3 ppm to 7 ppm for individual ensemble members approximately 6 yr after the eruption. The atmospheric carbon content only very slowly returns to near pre-eruption level at year 200 after the eruption. The ocean takes up carbon shortly after the eruption in response to the cooling, changed wind fields, and ice cover. This physics driven uptake is weakly counteracted by a reduction of the biological export production mainly in the tropical Pacific. The land vegetation pool shows a distinct loss of carbon in the initial years after the eruption which has not been present in simulations of smaller scale eruptions. The gain of the soil carbon pool determines the amplitude of the CO2 perturbation and the long term behaviour of the overall system: an initial gain caused by reduced soil respiration is followed by a rather slow return towards pre-eruption levels. During this phase, the ocean compensates partly for the reduced atmospheric carbon content in response to

  7. Impact of an extremely large magnitude volcanic eruption on the global climate and carbon cycle estimated from ensemble Earth System Model simulations

    NASA Astrophysics Data System (ADS)

    Segschneider, J.; Beitsch, A.; Timmreck, C.; Brovkin, V.; Ilyina, T.; Jungclaus, J.; Lorenz, S. J.; Six, K. D.; Zanchettin, D.

    2013-02-01

    The response of the global climate-carbon cycle system to an extremely large Northern Hemisphere mid-latitude volcanic eruption is investigated using ensemble integrations with the comprehensive Earth System Model MPI-ESM. The model includes dynamical compartments of the atmosphere and ocean and interactive modules of the terrestrial biosphere as well as ocean biogeochemistry. The MPI-ESM was forced with anomalies of aerosol optical depth and effe