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Sample records for caldera eastern transbaikalia

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

    SciTech Connect

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

    1993-03-01

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

  2. Geochemical and Sr-Pb-Nd isotopic characteristics of the Shakhtama porphyry Mo-Cu system (Eastern Transbaikalia, Russia)

    NASA Astrophysics Data System (ADS)

    Berzina, A. P.; Berzina, A. N.; Gimon, V. O.

    2014-01-01

    The Shakhtama Mo-Cu porphyry deposit is located within the eastern segment of the Central Asian Orogenic Belt, bordering the southern margin of the Mongol-Okhotsk suture zone. The deposit includes rocks of two magmatic complexes: the precursor plutonic (J2) and ore-bearing porphyry (J3) complexes. The plutonic complex was emplaced at the final stages of the collisional regime in the region; the formation of the porphyry complex may have overlapped with a transition to extension. The Shakhtama rocks are predominantly metaluminous, I-type high K calc-alkaline to shoshonitic in composition, with relatively high Mg#, Ni, Cr and V. They are characterized by crustal-like ISr (0.70741-0.70782), relatively radiogenic Pb isotopic compositions, ɛNd(T) values close to CHUR (-2.7 to +2.1) and Nd model ages from 0.8 to 1.2 Ga. Both complexes are composed of rocks with K-adakitic features and rocks without adakite trace element signatures. The regional geological setting together with geochemical and isotopic data indicate that both juvenile and old continental crust contributed to their origin. High-Mg# K-adakitic Shakhtama magmas were most likely generated by partial melting of thickened lower crust during delamination and interaction with mantle material, while magmas lacking adakite-like signatures were probably generated at shallower levels of lower crust. The derivation of melts, related to the formation of plutonic and porphyry complexes involved variable amounts of old Precambrian lower crust and juvenile Phanerozoic crust. Isotopic data imply stronger contribution of juvenile mantle-derived material to the fertile magmas of the porphyry complex. Juvenile crust is proposed as an important source of fluids and metals for the Shakhtama ore-magmatic system.

  3. Seismic velocity structure and earthquake relocation for the magmatic system beneath Long Valley Caldera, eastern California

    NASA Astrophysics Data System (ADS)

    Lin, Guoqing

    2015-04-01

    A new three-dimensional (3-D) seismic velocity model and high-precision location catalog for earthquakes between 1984 and 2014 are presented for Long Valley Caldera and its adjacent fault zones in eastern California. The simul2000 tomography algorithm is applied to derive the 3-D Vp and Vp/Vs models using first-arrivals of 1004 composite earthquakes obtained from the original seismic data at the Northern California Earthquake Data Center. The resulting Vp model reflects geological structures and agrees with previous local tomographic studies. The simultaneously resolved Vp/Vs model is a major contribution of this study providing an important complement to the Vp model for the interpretation of structural heterogeneities and physical properties in the study area. The caldera is dominated by low Vp anomalies at shallow depths due to postcaldera fill. High Vp and low Vp/Vs values are resolved from the surface to ~ 3.4 km depth beneath the center of the caldera, corresponding to the structural uplift of the Resurgent Dome. An aseismic body with low Vp and high Vp/Vs anomalies at 4.2-6.2 km depth below the surface is consistent with the location of partial melt suggested by previous studies based on Vp models only and the inflation source locations based on geodetic modeling. The Sierran crystalline rocks outside the caldera are generally characterized with high Vp and low Vp/Vs values. The newly resolved velocity model improves absolute location accuracy for the seismicity in the study area and ultimately provides the basis for a high-precision earthquake catalog based on similar-event cluster analysis and waveform cross-correlation data. The fine-scale velocity structure and precise earthquake relocations are useful for investigating magma sources, seismicity and stress interaction and other seismological studies in Long Valley.

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

    USGS Publications Warehouse

    Savage, J.C.

    1988-01-01

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

  5. Pre-caldera collapse of the Tastau volcanoplutonic ring complex (Eastern Kazakhstan)

    NASA Astrophysics Data System (ADS)

    Dokukina, K.

    2009-04-01

    Tastau volcanoplutonic ring complex belongs to the Zaisan Magmatic Province of Eastern Kazakhstan. ZMP consists of voluminous volcanic and plutonic rocks emplaced during regional extension affecting the Zaisan orogen. Extension affected crust previously thickened by the Late Carboniferous - Permian collision of the Kazakhstan with the Siberian craton (Buslov et al., 2004). Coeval mafic-felsic magmatism in the ZMP mostly consists of anatectic acidic magmas (Ermolov et al., 1983; Titov et al., 2001) with associated mantle-derived magmas having high-K calc-alkaline. Age of the Zaisan magmatism is Permian - Early Triassic (248 - 293 Ma) (Shcherba et al., 1998, Lyons et al., 2002). The hypabyssal Tastau volcanoplutonic ring complex 248 ± 34 Ma is the largest multiphase intrusive bodies which represent a volcanic root system. The complex intruded low-grade sedimentary rocks, which comprises sandstone and siltstone of a greywacke composition. The folded sedimentary complex was metamorphosed at a greenschist facies and up to hornblende hornfels facies during the intrusion of the complex. The volcanoplutonic complex has a form of an ellipse (13?18 km). Arc-shaped belts of composition dykes are intrude in the host rocks. A wide variety of magmatic rocks is represented within the Tastau volcanoplutonic complex: leucogranite, granite, granosyenite, gabbronorite and gabbro-diorite and calcium basite. Tastau magmatic rocks represent the continued calc-alkaline series and they are characterized by variations in chemical compositions (46 < SiO2 < 78 wt. %). Unhybrid gabbronorite have the most magnesia content (#Mg=0.50 - 0.55). Synplutonic mafic dikes and enclave are a subalcaline gabbro, a monzonite, a syenite and a quartz syenite (SiO2 = 46.2 - 62.8, Al2O3 = 15.8 - 19.6, TiO2 = 0.75 - 2.22, FeOtot = 4.7 - 11.5, MgO = 1.8 - 5.4, CaO = 2 - 7 wt.%) and high content of alkalines (Na2O+K2O = 5.2 - 9.3 wt.%). Mafic enclaves are depleted relatively the Maxut gabbro in Sr, Ca; and rich

  6. 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

  7. Spasmodic tremor and possible magma injection in long valley caldera, eastern california.

    PubMed

    Ryall, A; Ryall, F

    1983-03-25

    Intensive microearthquake swarms with the appearance of volcanic tremor have been observed in the southwest part of Long Valley caldera, southeastern California. This activity, possibly associated with magma injection, began 6 weeks after several strong (magnitude 6+) earthquakes in an area south of the caldera and has continued sporadically to the present time. The earthquake sequence and magmatic activity are part of a broad increase in tectonic activity in a 15,000-square-kilometer region surrounding the "White Mountains seismic gap," an area with high potential for the next major earthquake in the western Great Basin. PMID:17735195

  8. Stress-time context of fault permeability at the Krasnokamensk Area SE Transbaikalia

    NASA Astrophysics Data System (ADS)

    Petrov, V. A.; Lespinasse, M.; Poluektov, V. V.; Cuney, M.; Nasimov, R. M.; Hammer, J.; Schukin, S. I.

    2013-03-01

    The main aim of the contribution is to combine data on the consecutive stages of deformation, inflow and migration of palaeofluids and accumulation of mineral filling with uranium traces within the faulted-fractured environment at the Krasnokamensk Area, SE Transbaikalia, Russia. Object of examination is a framework of fault zones transecting the Proterozoic-Paleozoic granitic unit to the extent of northwestern part of uranium-bearing Streltsovskaya caldera of Mesozoic age. Considerations of stress- and permeability-time relationships in faulted-fractured zones were taken with account of stress and strain dependencies within fluid saturated rock massifs at crustal seismogenic level. Stress-time consecution of fault zone permeability was developed using set of fieldwork and lab tests including structural-geological survey, fault slip data analysis, mineral-chemical diagnostics, microstructural observations, and radiographic studies. Practical applications of obtained data for solving uranium mining and environmental issues are indicated in conclusion.

  9. Crustal deformation at long Valley Caldera, eastern California, 1992-1996 inferred from satellite radar interferometry

    USGS Publications Warehouse

    Thatcher, W.; Massonnet, D.

    1997-01-01

    Satellite radar interferometric images of Long Valley caldera show a pattern of surface deformation that resembles that expected from analysis of an extensive suite of ground-based geodetic data. Images from 2 and 4 year intervals respectively, are consistent with uniform movement rates determined from leveling surveys. Synthetic interferograms generated from ellipsoidal-inclusion source models based on inversion of the ground-based data show generally good agreement with the observed images. Two interferograms show evidence for a magmatic source southwest of the caldera in a region not covered by ground measurements. Poorer image quality in the 4 year interferogram indicates that temporal decorrelation of surface radar reflectors is progressively degrading the fringe pattern in the Long Valley region. Copyright 1997 by the American Geophysical Union.

  10. Active tectonic and magmatic processes beneath Long Valley Caldera, eastern California: an overview ( USA).

    USGS Publications Warehouse

    Hill, D.P.; Bailey, R.A.; Ryall, A.S.

    1985-01-01

    Geological, chronological, and structural studies of the Long Valley-Mono/Inyo Craters area document a long history of related volcanic eruptions and earthquakes controlled by regional extensional tectonics of the Basin and Range province. This activity has persisted for hundreds of thousands of years and is likely to continue. The Long Valley magma chamber had a volume approaching 3000 km3 prior to its climatic caldera-forming eruption 0.7 ma but has been reduced to less than a third of this volume by cooling, eruption, and crystallization. Although current unrest is concentrated in the S moat of Long Valley caldera, the Inyo/Mono Craters probably hold a greater potential for producing an eruption in the foreseeable future. The Inyo/Mono Craters have erupted at 500-year intervals over the past 2000-3000 years, whereas the Long Valley magma chamber has erupted at about 200,000-year intervals over the past 700,000 years. In either case, a major earthquake near the caldera could strongly influence the course of volcanic activity.-from Authors

  11. An episode of reinflation of the Long Valley Caldera, eastern California: 1989-1991

    USGS Publications Warehouse

    Langbein, J.; Hill, D.P.; Parker, T.N.; Wilkinson, S.K.

    1993-01-01

    Following the episodes of inflation of the resurgent dome associated with the May 1980 earthquake sequence (four M 6 earthquakes) and the January 1983 earthquake swarm (two M 5.2 events), 7 years of frequently repeated two-color geodimeter measurements spanning the Long Valley caldera document gradually decreasing extensional strain rates from 5 ppm/yr in mid-1983, when the measurements began, to near zero in mid-1989. Early October 1989 marked a change in activity when measurements of the two-color geodimeter network showed a significant increase in extensional strain rate (9 ppm/yr) across the caldera. The seismic activity began exceeding 10 M ??? 1..2 per week in early December 1989 and rapidly increased to a sustained level of tens of M ??? 1.2 per week with bursts having hundreds of events per day. The episode of inflation can be modeled by a single Mogi point source located about 7 km beneath the center of the resurgent dome. -from Authors

  12. Monitoring the Thermal Regime at Hot Creek and Vicinity, Long Valley Caldera, Eastern California

    NASA Astrophysics Data System (ADS)

    Clor, L. E.; Hurwitz, S.; Howle, J.

    2015-12-01

    Hot Creek Gorge contains the most obvious surface expression of the hydrothermal system in Long Valley Caldera, California, discharging 200-300 L/s of thermal water according to USGS measurements made since 1988. Formerly, Hot Creek was a popular public swimming area, but it was closed in 2006 due to unpredictable temperature fluctuations and sporadic geysering of thermal water within the creek (Farrar et al. USGS Fact Sheet2007-3045). The USGS has monitored the thermal regime in the area since the mid-1980s, including a long-term series of studies 0.6 km away at well CH-10b. Temperature measurements in the ~100 m deep well, which have been performed on an intermittent basis since it was drilled in 1983, reveal a complex temperature profile. Temperatures increase with depth to a maximum at about 45 meters below the ground surface, and then decrease steadily to the bottom of the well. The depth of the temperature maximum in the well (~45 m) corresponds to an elevation of ~2,120 m, roughly equivalent to the elevation of Hot Creek, and appears to sample the same hydrothermal flow system that supplies thermal features at the surface in the gorge. Starting in the early 1990s, the maximum temperature in CH-10b rose from 93.4°C to its peak in 2007 at 101.0°C. A cooling trend was observed beginning in 2009 and continues to present (99.3°C in June 2015). As the input into CH-10b is at the elevation of the creek, it exhibits the potential for response to thermal events at Hot Creek, and could provide a useful tool for monitoring future hazards. On short timescales, CH-10b also responds to large global earthquakes, greater than ~M7. These responses are captured with continuously logged high-frequency data (5s), and are usually characterized by a co-seismic water level drop of up to ten centimeters. Water levels tend to recover to pre-earthquake levels within a few hours to days.

  13. Distribution and diversity of microbial communities in meromictic soda Lake Doroninskoe (Transbaikalia, Russia) during winter

    NASA Astrophysics Data System (ADS)

    Matyugina, Evgeniya; Belkova, Natalia

    2015-11-01

    Meromictic soda and saline lakes are unique ecosystems characterized by the stability of physical, chemical and biological parameters, and they are distributed all over the world. Lakes located in regions with average annual negative air temperature are of particular interest because of the presence of two periods with intensive and dynamic processes: the so-called biological summer and the long ice season with the biological spring. Soda Lake Doroninskoe is located in Eastern Transbaikalia (51°14'N, 112°14'E) in the permafrost zone in an extreme continental climate, and is covered by ice for seven months per year. The structure and diversity of the microbial communities throughout the water column of the lake was studied by 16S rRNA gene amplicon metasequencing. Different species with specific functions were found to dominate at different depths. Metabolically flexible bacteria with a capacity to switch between anoxygenic photosynthesis and aerobic chemotrophic metabolism dominate in soda Lake Doroninskoe.

  14. Extensive glaciation in Transbaikalia, Siberia, at the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Margold, Martin; Jansen, John D.; Gurinov, Artem L.; Codilean, Alexandru T.; Fink, David; Preusser, Frank; Reznichenko, Natalya V.; Mifsud, Charles

    2016-01-01

    Successively smaller glacial extents have been proposed for continental Eurasia during the stadials of the last glacial period leading up to the Last Glacial Maximum (LGM). At the same time the large mountainous region east of Lake Baikal, Transbaikalia, has remained unexplored in terms of glacial chronology despite clear geomorphological evidence of substantial past glaciations. We have applied cosmogenic 10Be exposure dating and optically stimulated luminescence to establish the first quantitative glacial chronology for this region. Based on eighteen exposure ages from five moraine complexes, we propose that large mountain ice fields existed in the Kodar and Udokan mountains during Oxygen Isotope Stage 2, commensurate with the global LGM. These ice fields fed valley glaciers (>100 km in length) reaching down to the Chara Depression between the Kodar and Udokan mountains and to the valley of the Vitim River northwest of the Kodar Mountains. Two of the investigated moraines date to the Late Glacial, but indications of incomplete exposure among some of the sampled boulders obscure the specific details of the post-LGM glacial history. In addition to the LGM ice fields in the highest mountains of Transbaikalia, we report geomorphological evidence of a much more extensive, ice-cap type glaciation at a time that is yet to be firmly resolved.

  15. Long Valley caldera GIS Database

    NASA Astrophysics Data System (ADS)

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

    2002-12-01

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

  16. Carbon dioxide emissions from vegetation-kill zones around the resurgent dome of Long Valley caldera, eastern California, USA

    USGS Publications Warehouse

    Bergfeld, Deborah; Evans, William C.; Howle, James F.; Farrar, Christopher D.

    2006-01-01

    A survey of diffuse CO2 efflux, soil temperature and soil-gas chemistry over areas of localized vegetation-kill on and around the resurgent dome of Long Valley caldera California was performed to evaluate the premise that gaseous and thermal anomalies are related to renewed intrusion of magma. Some kill sites are long-lived features and others have developed in the past few years. Total anomalous CO2 emissions from the thirteen areas average around 8.7 t per day; but the majority of the emissions come from four sites west of the Casa Diablo geothermal power plant. Geochemical analyses of the soil-gases from locations west and east of the plant revealed the presence of isobutane related to plant operations. The δ13C values of diffuse CO2 range from − 5.7‰ to − 3.4‰, similar to values previously reported for CO2 from hot springs and thermal wells around Long Valley.At many of the vegetation-kill sites soil temperatures reach boiling at depths ≤ 20 cm. Soil temperature/depth profiles at two of the high-emissions areas indicate that the conductive thermal gradient in the center of the areas is around 320 °C m− 1. We estimate total heat loss from the two areas to be about 6.1 and 2.3 MW. Given current thinking on the rate of hydrothermal fluid flow across the caldera and using the CO2 concentration in the thermal fluids, the heat and CO2 loss from the kill areas is easily provided by the shallow hydrothermal system, which is sourced to the west of the resurgent dome. We find no evidence that the development of new areas of vegetation kill across the resurgent dome are related to new input of magma or magmatic fluids from beneath the resurgent dome. Our findings indicate that the areas have developed as a response to changes in the shallow hydrologic system. Some of the changes are likely related to fluid production at the power plant, but at distal sites the changes are more likely related to seismicity and uplift of the dome.

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

    NASA Astrophysics Data System (ADS)

    Walker, G. P. L.

    1984-09-01

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

  18. Assessment of chemical element migration in soil-plant complex of Urov endemic localities of East Transbaikalia

    NASA Astrophysics Data System (ADS)

    Vadim V., Ermakov; Valentina, Danilova; Sabsbakhor, Khushvakhtova; Aklexander, Degtyarev; Sergey, Tyutikov; Victor, Berezkin; Elena, Karpova

    2014-05-01

    - Salicaceae) and selenium (needles of larch - Larix sibirica L.) were found among the plants. References 1. Ermakov V., Jovanovic L. Characteristics of selenium migration in soil-plant system of East Meshchera and Transbaikalia// J. Geochem. Explor., 2010. Vol. 107, 200-205. 2. Ermakov Vadim, Jovanovic Larisa, Berezkin Victor, Tyutikov Sergey, Danilogorskaya Anastasiya, Danilova Valentina, Krechetova Elena, Degtyarev Alexander, Khushvakhtova Sabsbakhor. Chemical assessment of soil and water of Urov biogeochemical provinces of Eastern Transbaikalia// Ecologica, 2012. Vol. 19, 69, 5-9. 3. Ermakov V.V., Tuytikov S.F. Khushvakhtova S.D., Danilova V.N. Boev V.A., Barabanschikova R.N., Chudinova E.A. Peculiarities of quantitative determination of selenium in biological materials// Bulletin of the Tyumen State University Press, 2010, 3, 206-214. Supported by the Russian Foundation for Basic Research, grant number 12-05-00141a.

  19. Deformation near the Casa Diablo geothermal well field and related processes Long Valley caldera, Eastern California, 1993-2000

    USGS Publications Warehouse

    Howle, J.F.; Langbein, J.O.; Farrar, C.D.; Wilkinson, S.K.

    2003-01-01

    Regional first-order leveling lines, which extend from Lee Vining, CA, to Tom's Place, CA, have been surveyed periodically since 1957 by the U.S. Geological Survey (USGS), the National Geodetic Survey (NGS), and Caltrans. Two of the regional survey lines, or leveling networks, intersect at the Casa Diablo geothermal well field. These leveling networks, referenced to a distant bench mark (C916) near Lee Vining, provide time-series vertical control data of land-surface deformation that began around 1980. These data are also useful for delineating localized subsidence at Casa Diablo related to reservoir pressure and temperature changes owing to geothermal development that began in 1985. A comparison of differences in bench-mark elevations for five time periods between 1983 and 1997 shows the development and expansion of a subsidence bowl at Casa Diablo. The subsidence coincides spatially with the geothermal well field and temporally with the increased production rates and the deepening of injection wells in 1991, which resulted in an increase in the rate of pressure decline. The subsidence, superimposed on a broad area of uplift, totaled about 310 mm by 1997. The USGS established orthogonal tilt arrays in 1983 to better monitor deformation across the caldera. One tilt array (DBR) was established near what would later become the Casa Diablo geothermal well field. This array responded to magmatic intrusions prior to geothermal development, tilting away from the well field. With the start of geothermal fluid extraction in 1985, tilt at the DBR array reversed direction and began tilting into the well field. In 1991, geothermal power production was increased by a factor of four, and reservoir pressures began a period of steep decline. These changes caused a temporary three-fold increase in the tilt rate. The tilt rate became stable in 1993 and was about 40% lower than that measured in 1991-1992, but still greater than the rates measured during 1985-1990. Data from the

  20. Salting the landscapes in Transbaikalia: natural and technogenic factors

    NASA Astrophysics Data System (ADS)

    Peryazeva, E. G.; Plyusnin, A. M.; Chinavlev, A. M.

    2010-05-01

    Salting the soils, surface and subsurface waters is widespread in Transbaikalia. Hearths of salting occur within intermountain depressions of the Mesozoic and Cenozoic age both in the steppe arid and forest humid landscapes. Total water mineralization reaches 80 g/dm3 in lakes and 4-5 g/dm3 in subsurface waters. The waters belong to hydrocarbonate sodium and sulfate sodium types by chemical composition. The soda type of waters is widely spread through the whole area. Sulfate waters are found in several hearths of salting. Deposition of salts takes place in some lakes. Mirabilite and soda depositions are most commonly observed in muds of salt lakes. Deposition of salts occurs both as a result of evaporative concentrating and during freezing out the solvent. In the winter period, efflorescences of salts, where decawater soda is main mineral, are observed on ice surface. Solonchaks are spread in areas of shallow ground waters (1-2m). Soil salting is most intense in the lower parts of depressions, where surface of ground waters is at depth 0.5-1.0m. In soil cover of solonchaks, salt horizon is of various thicknesses, and it has various morphological forms of occurrence, i.e. as thick deposits of salts on soil surface and salting the surficial horizons. The soil has low alkaline reaction of medium and is characterized by high content of exchangeable bases with significant content of exchangeable sodium in the absorbing complex. Total amount of salts varies from 0.7 to 1.3%. Their maximal quantity (3.1%) is confined to the surficial layer. Sulfate-sodium type of salting is noted in the solonchak upper horizons and sulfate-magnesium-calcium one in the lower ones (Ubugunov et al, 2009). Formation of salting hearths is associated with natural and technogenic conditions. The Mesozoic depressions of Transbaikalia are characterized by intense volcanism. Covers of alkaline and moderately alkaline basalts that are enriched in potassium, sodium, carbon dioxide, fluorine, chlorine

  1. Paleomagnetism of Mesozoic Magmatic Rocks in the West Transbaikalia

    NASA Astrophysics Data System (ADS)

    Fedyukin, I.; Shatsillo, A.

    2015-12-01

    Gudzhir intrusive complex is widely spread within West Transbaikalia. The complex is presented by dykes of rocks of various composition and granite stocks within Proterozoic metamorphic rocks and Late Proterozoic granites of Angaro-Vitim batholite. Several grabens are located within the area. The grabens are filled by effusive analogues of Gudzhir complex covered by Late Jurassic-Aptian continental sedimentary rocks of Gusinoozersk series. The age of Gudzhir complex and its effusive analogues is uncertain. According to the location within sedimentary section it cannot be younger than Late Jurassic. At the same time according to the geochronological analysis (Ar-Ar method) the age of the complex is 120-100 mil.years - the end of Early Cretaceous. In the river Vitim valley (between entries of rivers Karenga and Kalar) 32 dykes of Gudzhir complex have been studied. Laboratory palaeomagnetic studies of the samples was carried out. According to the Zyidelveld diagrams within the middle- high temperature spectrum two types of magnetization components are present: high temperature components (were not used) and "transitional" magnetization component of normal polarity. The latest was considered as secondary (metachronic). Similar direction was obtained previously for the Permian-Triassic volcanites within Southern Buriatia. Obtained pole location is the same as for Middle Cretaceous samples (within SW and NE margins of Siberian platform). According to these results the rocks of Gudzhir complex were remagnetized in Cretaceous time after crustal folding. Cretaceous age of the metachronic component was obtained from the total demonstration of magnetization of primary polarity which corresponds to the Dzhalal superchrone (124-84 mil. years). According to the obtained results: 1. Post Cretaceous tectonic processes did not lead to significant movements of blocks; 2. The location of the obtained pole and its similarity to the even-aged poles of Siberia and East European platform

  2. Caldera demonstration model

    USGS Publications Warehouse

    Venezky, Dina; Wessells, Stephen

    2010-01-01

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

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

    SciTech Connect

    Goff, F.; Nielson, D.L.

    1986-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  5. Western Transbaikalia (South East Siberia): desertification from the past towards present

    NASA Astrophysics Data System (ADS)

    Alexeeva, Nadezhda; Erbajeva, Margarita A.; Khenzykhenova, Fedora I.

    2010-05-01

    Desertification is recognized as one of the most serious environmental problem in Asia, in particular in the Baikalian region including Transbaikalia and Prebaikalia. The Baikal Rift zone is a natural border between two biogeographical provinces: Siberian (north forests, taiga - Prebaikalia) and Central-Asian (arid steppes, semi-deserts and deserts - Transbaiklia). At present time southern Transbaikal area is semi-arid region, in contrast to it, Prebaikalia is characterized by more humid environment. In the past, during Neogene paleoenvironment and biogeocoenosis of these two areas were close and they included similar faunal assemblages. However the formation of a series of south Siberian ranges and uplift of surrounding the Lake Baikal mountains have became as the main orographic barrier. As a result the West Transbaikalia has been isolated from the influence of West humid Atlantic cyclone. This evidence is considered to be the main reason of the onset the climate aridisation in the region. Moreover the influence of gradually global change of the climate change towards cool and dry was rather high too. The most important sources of information on past climate change are derived from paleoclimatic records such as terrestrial archives - deposits, paleoflora and paleofauna of the Pliocene, Pleistocene and Holocene. The mammal associations and pollen flora evidenced that during the Pliocene the landscapes with predominance of forest inhabitants were replaced by savanna like areas and to the end of Pliocene the region was occupied by mammal assemblages inhabited the open landscapes. The dominant forms in the fauna were ground squirrels (Spermophilus). At that time the evidence of the first appearance of desert dweller animals - the genus Allactaga occurred. The further aridisation and cooling strengthened during the Early Pleistocene when the mammal faunas are characterized by the predominance of ochotonids, high frequency of progressive type Borsodia chinensis

  6. The Black-tailed Antechinus, Antechinus arktos sp. nov.: a new species of carnivorous marsupial from montane regions of the Tweed Volcano caldera, eastern Australia.

    PubMed

    Baker, Andrew M; Mutton, Thomas Y; Hines, Harry B; Dyck, Steve Van

    2014-01-01

    We describe a new species of dasyurid marsupial within the genus Antechinus that was previously known as a northern outlier of Dusky Antechinus (A. swainsonii). The Black-tailed Antechinus, Antechinus arktos sp. nov., is known only from areas of high altitude and high rainfall on the Tweed Volcano caldera of far south-east Queensland and north-east New South Wales, Australia. Antechinus arktos formerly sheltered under the taxonomic umbrella of A. swainsonii mimetes, the widespread mainland form of Dusky Antechinus. With the benefit of genetic hindsight, some striking morphological differences are herein resolved: A. s. mimetes is more uniformly deep brown-black to grizzled grey-brown from head to rump, with brownish (clove brown-raw umber) hair on the upper surface of the hindfoot and tail, whereas A. arktos is more vibrantly coloured, with a marked change from greyish-brown head to orange-brown rump, fuscous black on the upper surface of the hindfoot and dense, short fur on the evenly black tail. Further, A. arktos has marked orange-brown fur on the upper and lower eyelid, cheek and in front of the ear and very long guard hairs all over the body; these characters are more subtle in A. s. mimetes. There are striking genetic differences between the two species: at mtDNA, A. s. mimetes from north-east New South Wales is 10% divergent to A. arktos from its type locality at Springbrook NP, Queensland. In contrast, the Ebor A. s. mimetes clades closely with conspecifics from ACT and Victoria. A. arktos skulls are strikingly different to all subspecies of A. swainsonii. A. arktos are markedly larger than A. s. mimetes and A. s. swainsonii (Tasmania) for a range of craniodental measures. Antechinus arktos were historically found at a few proximate mountainous sites in south-east Queensland, and have only recently been recorded from or near the type locality. Even there, the species is likely in low abundance. The Black-tailed Antechinus has plausibly been detrimentally

  7. PREFACE: Collapse Calderas Workshop

    NASA Astrophysics Data System (ADS)

    Gottsmann, Jo; Aguirre-Diaz, Gerardo

    2008-10-01

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

  8. The Klyuchevskoe gold ore deposit (Eastern Transbaikalia): Formation conditions and petrogeochemical features of rocks and ores

    NASA Astrophysics Data System (ADS)

    Abramov, B. N.

    2015-09-01

    It was found that the magma chambers in the Amudzhikan complex (J3) were characterized by close degrees of their differentiation and occurred at depths corresponding to the lower continental crust. The formation of explosive breccias proceeded during each period of the ore-forming process. The magma chambers of early breccias occurred at great depths. The late breccias contain carbonate cement and are characterized by an increased REE content.

  9. The Long Valley Caldera GIS database

    USGS Publications Warehouse

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

    2003-01-01

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

  10. Emi Koussi Caldera

    NASA Technical Reports Server (NTRS)

    2002-01-01

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

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

    SciTech Connect

    Gambill, D.T.

    1981-03-01

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

  12. Pavonis Mons Caldera

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

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

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

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

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  14. Petrological cycles and caldera-forming events

    NASA Astrophysics Data System (ADS)

    Bachmann, O.; Deering, C. D.

    2012-12-01

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

  15. Pavonis Mons Summit Caldera

    NASA Technical Reports Server (NTRS)

    2002-01-01

    [figure removed for brevity, see original site]

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

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

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

  16. Formation of composite dykes by contact remelting and magma mingling: The Shaluta pluton, Transbaikalia (Russia)

    NASA Astrophysics Data System (ADS)

    Litvinovsky, B. A.; Zanvilevich, A. N.; Katzir, Y.

    2012-10-01

    A unique opportunity to study the source areas, from which composite dykes were injected, occurs in the Shaluta pluton, Transbaikalia, Russia. The major quartz syenite pluton was intruded by several synplutonic gabbro bodies of various sizes. Investigations of the contact zones between gabbro and host syenite showed that liquid basalt magma intruded the incompletely crystallized coarse-grained quartz syenite with T = 700-720 °C and caused contact remelting of the silicic rock at about 900-950 °C. Mechanical interaction between newly formed silicic melt and partially crystallized mafic magma resulted in extensive magma mingling. Chemical interaction was exhibited by migration of MgO, CaO, FeO∗, Sr, H2O and Cl from the basalt magma, whereas silica, alkalis, Rb and Ba migrated from the silicic refusion zone into the crystallized gabbro. Presence of melt inclusions with homogenization temperature ranging from 640 to 790 °C in quartz and attaining 850-900 °C in late clinopyroxene indicates that at least part of newly formed minerals crystallized from the hybrid melt. Mingled magmatic material was squeezed out inwards, into the host solid quartz syenite pluton and formed dyke-like apophyses that can be traced for a distance of 60-70 m from the contact zone. Apophyses have the same dimensions, structure and composition as typical composite dykes that are common in the roof pendant over the gabbro bodies and nearby the gabbro exposures.

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

    USGS Publications Warehouse

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  19. Arsia Mons Caldera Rim

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

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

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

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

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    30 km trend that then arcs NE into the caldera. These anomalies reflect near surface rhyolite intrusions that underlie the caldera-fill sediments that have been altered to K-feldpar and clay minerals. K gamma ray anomalies also delineate this zone of alteration. The last phase of volcanism occurs in the central part of the caldera and is associated with a broad aeromagnetic high with individual high-amplitude aeromagnetic highs coincident with three large volcanic vents. No hydrothermal alteration is associated with this last phase of volcanism. On the SW side of the McDermitt volcanic field a 10 km wide, 60 km long, NNW-trending zone of late Miocene normal faults developed after cessation of volcanism and prior to Basin and Range faulting. We propose that this extensional fault zone is the eastern continuation of the NW trending Brothers Fault Zone, but changes to a NNW trend where it is deflected by the plutons that underlies the McDermitt volcanic field. Plutons that underlie all three of these Mid Miocene volcanic fields have minimized post-caldera extensional faulting. Thus only caldera ring fracture faults were available for the development of hydrothermal systems in areas where post caldera intrusive activity was localized.

  1. Evolution of the 120 ka caldera-forming eruption of Kutcharo volcano, eastern Hokkaido, Japan: Geologic and petrologic evidence for multiple vent systems and rapid generation of pyroclastic flow

    NASA Astrophysics Data System (ADS)

    Hasegawa, Takeshi; Matsumoto, Akiko; Nakagawa, Mitsuhiro

    2016-07-01

    We investigated the eruptive sequence and temporal evolution of juvenile materials during the 120 ka Kutcharo pumice flow IV (Kp IV) eruption, which was the most voluminous (175 km3: bulk volume) caldera-forming eruption of Kutcharo volcano. The eruptive deposits are divided into four units in ascending order. Unit 1 is widely dispersed and consists of silt-sized, cohesive ash. Unit 2 is a thin, moderately sorted pumice fall deposit with a restricted distribution and small volume (< 0.2 km3). Unit 3, consisting of widely distributed ignimbrite, is the most voluminous. Unit 4 is also composed of pyroclastic flow deposits, but its distribution is limited to the northwest side of the caldera. Juvenile materials consist mainly of rhyolite pumice (74%-78% SiO2) associated with a minor amount of scoria (52%-73% SiO2) that are found only northwest of the caldera in Unit 3 and Unit 4. These scoriae can be classified on the basis of the P2O5 contents of their matrix glass into low-P, medium-P, and high-P types, which are almost entirely restricted to the lower part of Unit 3, Unit 4, and the upper part of Unit 3, respectively. These three types display distinct mixing trends with the rhyolitic compositions in SiO2-P2O5 variation diagrams. This evidence indicates that three distinct mafic magmas were independently and intermittently injected into the main body of silicic magma to erupt from the northwestern part of the magma system. Mafic injections did not occur in the southern part of the magma system. This petrologic evidence implies that the northwestern and southeastern flows of Unit 3 are heterotopic, contemporaneous products derived from multiple vent systems. Although Unit 2 was derived from an eruptive column, its volume is very small compared to Plinian fall deposits of typical caldera-forming eruptions. In our interpretation, the activity of the Kp IV eruption reached its climax rapidly, depositing Unit 3, without first producing a stable Plinian column. The

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  3. A comprehensive classification of collapse calderas

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  4. Recent crustal subsidence at Yellowstone Caldera, Wyoming

    USGS Publications Warehouse

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

    1990-01-01

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

  5. Venus - Sag Caldera 'Sachs Patera

    NASA Technical Reports Server (NTRS)

    1991-01-01

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

  6. A GEOLOGICAL AND GEOPHYSICAL STUDY OF THE BACA GEOTHERMAL FIELD, VALLES CALDERA, NEW MEXICO

    SciTech Connect

    Wilt, M.; Haar, S.V.

    1982-03-01

    The Baca location {number_sign}1 geothermal field is located in north-central New Mexico within the western half of the Plio-Pleistocene valles Caldera. Steam and hot water are produced primarily from the northeast-trending Redondo Creek graben, where downhole temperatures exceed 500 F. Stratigraphically the reservoir region can be described as a five-layer sequence that includes (1) caldera fill and the upper units of the Bandelier ash flow tuff, (2) the lower members of this tuff, which comprise the main reservoir rock at Baca, (3) the Pliocene Paliza Canyon volcanics, (4) Tertiary sands and Paleozoic sedimentary rocks, and (5) Precambrian granitic basement. Production is controlled by fractures and faults that are ultimately related to activity in the Rio Grande Rift system. Geophysically, the caldera is characterized by a gravity minimum and a resistivity low. A 40-mgal gravity minimum over the caldera is due mostly to the relatively low-density volcanics and sediments that fill the caldera and probably bears no relation to deep-seated magmatic sources. Two-dimensional gravity modeling indicates that the depth to Precambrian basement in Redondo Canyon is probably at least 3 km and may exceed 5 km in eastern parts of the caldera. Telluric and magnetotelluric surveys have shown that the reservoir region is associated with low resistivity and that a deep low-resistivity zone correlates well with the depth of the primary reservoir inferred from well data.

  7. The Reporoa Caldera, Taupo Volcanic Zone: source of the Kaingaroa Ignimbrites

    USGS Publications Warehouse

    Nairn, I.A.; Wood, C.P.; Bailey, R.A.

    1994-01-01

    The Reporoa Caldera occupies the northern end of the Reporoa Depression, previously described as a tectonic fault-angle depression. Earlier confirmation of the topographic basin as a caldera had been hindered by the lack of an associated young pyroclastic flow deposit of large enough volume to have caused caldera collapse. New exposures on the eastern margin of the Reporoa basin reveal thick lithic lag breccias (>30 m) interbedded within the 0.24 Ma Kaingaroa Ignimbrites. These ignimbrites were previously attributed to the adjacent Okataina Volcanic Centre. Lag breccia thicknesses and maximum clast sizes decrease rapidly outward from the caldera rim, and discrete breccias are absent from ignimbrite sections more than 3 km from the rim. The lithic lag breccias, together with structural and geophysical evidence, confirm Reporoa Caldera as the source of the c. 100 km3 Kaingaroa Ignimbrites, adding another major rhyolitic volcanic centre to the seven previously recognized in the Taupo Volcanic Zone. Other, older, calderas may also be present in the Reporoa Depression. ?? 1994 Springer-Verlag.

  8. Reanalysis of S-to-P amplitude ratios for gross attenuation structure, Long Valley caldera, California

    SciTech Connect

    Sanders, C.O.

    1993-12-01

    Because of the strong interest in the magmatism and volcanism at Long Valley caldera, eastern California, and because of recent sifnigicant improvements in our knowledge of the caldera velocity structure and earthquake locations, I have reanalyzed the local-earthquake S-to-P amplitude-ratio data of Sanders (1984) for the gross three-dimensional attenuation structure of the upper 10 km of Long Valley caldera. The primary goals of the analysis are to provide more accurate constraints on the depths of the attenuation anomalies using improved knowledge of the ray locations and an objective inversion procedure. The new image of the high S wave attenuation anomaly in the west-central cadlera suggests that the top of the principal anomaly is at 7-km depth, which is 2 km deeper than previously determined. Because of poor resolution in much of the region, some of the data remain unsatisfied by the final attenuation model. This unmodeled data may imply unresolved attenuation anomalies, perhaps small anomalies in the kilometer or two just above the central-caldera anomaly and perhaps a larger anomaly at about 7-km depth in the northwest caldera or somewhere beneath the Mono Craters. The central-caldera S wave attenuation anomaly has a location similar to mapped regions of low teleseismic P wave velocity, crustal inflation, reduced density, and aseismicity, strongly suggesting magmatic association.

  9. Investigation of the groundwater system at Masaya Caldera, Nicaragua, using transient electromagnetics and numerical simulation

    USGS Publications Warehouse

    MacNeil, R.E.; Sanford, W.E.; Connor, C.B.; Sandberg, S.K.; Diez, M.

    2007-01-01

    The distribution of groundwater beneath Masaya Volcano, in Nicaragua, and its surrounding caldera was characterized using the transient electromagnetic method (TEM). Multiple soundings were conducted at 30 sites. Models of the TEM data consistently indicate a resistive layer that is underlain by one or more conductive layers. These two layers represent the unsaturated and saturated zones, respectively, with the boundary between them indicating the water-table elevation. A map of the TEM data shows that the water table in the caldera is a subdued replica of the topography, with higher elevations beneath the edifice in the south-central caldera and lower elevations in the eastern caldera, coinciding with the elevation of Laguna de Masaya. These TEM data, combined with regional hydrologic data, indicate that the caldera in hydrologically isolated from the surrounding region, with as much as 60??m of difference in elevation of the groundwater table across caldera-bounding faults. The water-table information and estimates of fluxes of water through the system were used to constrain a numerical simulation of groundwater flow. The simulation results indicate that basalt flows in the outer parts of the caldera have a relatively high transmissivity, whereas the central edifice has a substantially lower transmissivity. A layer of relatively high transmissivity must be present at depth within the edifice in order to deliver the observed flux of water and steam to the active vent. This hydrologic information about the caldera provides a baseline for assessing the response of this isolated groundwater system to future changes in magmatic activity. ?? 2007.

  10. Age, duration of formation, and geotectonic position of the Zavitaya lithium granite-pegmatite system, Eastern Transbaikalia

    NASA Astrophysics Data System (ADS)

    Zagorsky, V. Ye.; Shokalsky, S. P.; Sergeev, S. A.

    2015-01-01

    The Zavitaya granite-pegmatite system with a lithium deposit is localized in the northern marginal part of the Onon terrane (Aginskii massif) and ajoins to the Ingoda-Shilka branch of the Mongol-Okhotsk suture in the south. This paper presents the first U-Pb (SHRIMP) age of granites and barren and spodumene pegmatites of the Zavitaya field. The Zavitaya polychronous granite-pegmatite system evolved through 40 million years: porphyritic biotite granites (169.0 ± 3 Ma), two mica granites-leucogranites (147.5 ± 3.1 Ma), muscovite leucogranites (140.0 ± 3.0 Ma), barren pegmatites (139.6 ± 3.1 Ma), and lithium spodumem pegmatites (129.6 ± 2.7 Ma). The formation of the system coincides with the change in geodynamic regimes of the region at the Middle Jurassic-Early Cretaceous boundary: the age of the early granites of the system and spodumene pegmatites corresponds to the termination of collision and to the beginning of the Early Cretaceous rifting, respectively.

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

    PubMed

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

    2006-03-01

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

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

    USGS Publications Warehouse

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

    2006-01-01

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

  13. New light on caldera evolution - Askja, Iceland

    SciTech Connect

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

    1991-04-01

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

  14. Caldera in Sippar Sulcus, Ganymede

    NASA Technical Reports Server (NTRS)

    2001-01-01

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

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

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

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

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

  15. Nonstatistical dynamics on the caldera.

    PubMed

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

    2014-07-21

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

  16. Nonstatistical dynamics on the caldera

    SciTech Connect

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

    2014-07-21

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

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

    NASA Astrophysics Data System (ADS)

    Geyer, Adelina; Marti, Joan

    2015-04-01

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

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

    USGS Publications Warehouse

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

    1990-01-01

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

  19. [Features of the B chromosome in Korean wood mice Apodemus peninsulae (Thomas, 1906) from Transbaikalia and the Far East identified by the FISH method].

    PubMed

    Rubtsov, N B; Kartavtseva, I V; Roslik, G V; Karamysheva, T V; Pavlenko, M V; Iwasa, M A; Koh, H S

    2015-03-01

    Korean field mice (Apodemus peninsulae) are widely distributed throughout northeastern Asia, including the Russian Far East, northern China, the Korean peninsula, Sakhalin, and Hokkaido. This mouse species is characterized by a high frequency of animals with B chromosomes differing in their number, morphology, and DNA composition in different geographical regions. For the first time a comparative analysis of DNA probes from B chromosomes with metaphase chromosomes of mice from Transbaikalia, the Far East (including the Russian Far East), Japan, and South Korea was conducted by in situ hybridization. B chromosomes in mice from the Russian Far East were shown to exhibit low variability in DNA content; however, the DNA composition of B chromosomes in species from Transbaikalia and Japan were highly variable. B chromosomes in A. peninsulae from the South Korean population demonstrate minor differences from those from the Russian Far East. We discuss the origin of B chromosomes in the studied region in comparison with previously obtained data for mice from Siberia and the Baikal region, as well as the dispersal routes of the Korean field mouse. PMID:26027373

  20. The High Rock caldera complex, NW Nevada: Geologic mapping, volcanology, geochemistry, and ultra-high precision 40Ar/39Ar dating of early Yellowstone hotspot magmatism

    NASA Astrophysics Data System (ADS)

    Hausback, B.; Smith, J.; Henry, C. D.; Hilton, R. P.; McIntosh, W. C.; Heizler, M. T.; Noble, D. C.

    2012-12-01

    Our new work reveals a complex evolution of the High Rock caldera, one of the oldest calderas related to initiation of the Yellowstone hotspot. The caldera formed at 16.43±0.01 Ma (n=2, Fish Canyon sanidine = 28.201 Ma; all ages reported here agree with stratigraphy) during eruption of the zoned (metaluminous, high-silica dacite to slightly peralkaline, low-silica rhyolite), abundantly porphyritic Summit Lake Tuff. The only exposed precaldera rocks are a suite of intermediate lavas along the western margin. They are undated but compositionally similar to 30 Ma rocks in the region, so probably unrelated to the caldera. The caldera margin is entirely buried by moat domes and post-collapse lavas and tuff. Sparsely porphyritic rhyolite lavas erupted at 16.30±0.01 Ma (n=1) north of the caldera, possibly along the ring fracture. A large suite of petrographically and compositionally nearly indistinguishable, abundantly porphyritic, peralkaline rhyolite lavas and tuffs, the Soldier Meadow (SM) rock type, erupted from vents around the entire caldera margin in two pulses at 16.14±0.01 and 16.09±0.01 Ma (n=6 and 3). The first pulse includes lavas along the western and eastern margin; the Soldier Meadow Tuff (SMT, a moderately peralkaline, crystal-rich welded ignimbrite that is thinly-layered with coarse lag breccias in the proximal area and massive in distal locations), which erupted along the eastern caldera margin; and accidental blocks (up to 3m) of SMT brought up in the interior of the caldera by later eruptions. The second pulse includes several more lavas and associated small-volume flow, fall, and surge(?) tuffs along the northeastern and southwestern margin. Distribution of the SM rock type suggests that its magma chamber underlay the entire caldera. Rocks of the second pulse are distinguished only by higher incompatible element concentrations (Rb, Zr, Nb, Th), which suggests the magma body continued to differentiate between pulses. The tuffs of Alkali Flat and

  1. Surveying Dead Trees and CO(sub 2)-Induced Stressed Trees Using AVIRIS in the long Valley Caldera

    NASA Technical Reports Server (NTRS)

    De Jong, Steven M.

    1996-01-01

    None given. Reports on dying trees in the long Valley Caldera, in the eastern Sierra Nevada (California) Mammoth Mountains. Reports on several large areas of dying trees, and causes for their dying off, including most importantly, elevated CO(sub 2) levels.

  2. Bonanza, an "Extreme" Resurgent Ignimbrite-Caldera Cycle in the San Juan Mountains, Colorado

    NASA Astrophysics Data System (ADS)

    Lipman, P. W.; McIntosh, W. C.; Zimmerer, M. J.

    2012-12-01

    -composition volcanics, and overlain by caldera-filling andesite to rhyolite lavas. Caldera-fill ignimbrite has been largely stripped from the southern and eastern flank of the dome, exposing large area of caldera-floor as a structurally coherent domed plate, bounded by ring faults with locations that are geometrically closely constrained even though largely concealed beneath valleys. Floor rocks are intensely shattered within ~100 m of ring faults, and upper levels of the floor are locally penetrated by dike-like crack fills of intracaldera ignimbrite.

  3. Evolution of the Olympus Mons Caldera, Mars

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

  4. Tectonophysics of hydrothermal ore formation: an example of the Antei Mo-U deposit, Transbaikalia

    NASA Astrophysics Data System (ADS)

    Petrov, V. A.; Rebetsky, Yu. L.; Poluektov, V. V.; Burmistrov, A. A.

    2015-07-01

    The Antei deposit of the southeastern Transbaikalian region is one of the largest uranium mines in Russia. It is hosted by the Late Paleozoic granitic basement of the Streltsovskaya caldera and was formed as a result of Late Mesozoic tectonothermal activity. Vein and stockwork-disseminated molybdenum-uranium mineralization at this deposit is controlled by zones of intense hydrothermal alteration, cataclasis, brecciation, and intense fracturing along steeply dipping faults, which acted as conduits for mineralizing fluids and hosts to the ore bodies. The upper edge of the ore-bearing zone is located at a depth of 400 m, and its lower edge was intersected at a depth of 1300 m from the day surface. The conditions of ore localization were determined using structural-geological and petrophysical studies coupled with numerical modeling of the effects of gravitational body forces at purely elastic and postcritical elastoplastic deformational stages. The dynamics of the tectonic stress field in the rock massif was reconstructed using the results of mapping of morphogenetic and kinematic characteristics of fault and fracture systems, as well as data on petrography and mineralogy of rocks and vein-filling material. It was shown that the fault framework of the deposit was formed in four tectonic stages, three of which took place in the geologic past and one of which reflects recent geologic history. Each tectonic stage was characterized by different parameters of the tectonic stress-strain field, fault kinematics, and conditions of mineral formation. The following types of metasomatic rocks are recognized within the deposit: high-temperature K-feldspar rocks and albitites (formed during the Late Paleozoic as the primary structural elements of a granitic massif) and Late Mesozoic low-temperature preore (hydromicatized rocks), synore (hematite, albite, chlorite, and quartz) and postore (kaolinite-smectite) rocks. The following petrophysical parameters were determined for all

  5. The mechanism of intrusion of the Inyo Dike, Long Valley Caldera, California

    NASA Technical Reports Server (NTRS)

    Reches, Zeev; Fink, Jonathan

    1988-01-01

    The dike geometry of the 11-km-long Inyo Dike at the margins of the Long Valley calderas in eastern California is explained here in terms of the interaction between tectonic stresses and local variations in host rock rheology. Relationships between tectonic and magmatic stresses are evaluated, and the magnitude of magmatic pressure at the depth necessary to get the dike to the surface is estimated. The application of the model to other volcanoes is also discussed.

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

    SciTech Connect

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

    1981-01-01

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

  7. Research Spotlight: Extraordinary uplift of Yellowstone caldera

    NASA Astrophysics Data System (ADS)

    Tretkoff, Ernie

    2011-02-01

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

  8. Caldera Formation on the Vance Seamounts

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

  9. Intracaldera volcanism and sedimentation - Creede Caldera, Colorado

    SciTech Connect

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

    1997-06-01

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

  10. Reconstruction of the most recent volcanic eruptions from the Valles caldera, New Mexico

    NASA Astrophysics Data System (ADS)

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

    2011-01-01

    Products of the latest eruptions from the Valles caldera, New Mexico, consist of the El Cajete Pyroclastic Beds and Battleship Rock Ignimbrite, a sequence of pyroclastic fall and density current deposits erupted at ~ 55 ka, capped by the later Banco Bonito Flow erupted at ~ 40 ka, and collectively named the East Fork Member of the Valles Rhyolite. The stratigraphy of the East Fork Member has been the subject of conflicting interpretations in the past; a long-running investigation of short-lived exposures over a period of many years enables us to present a more complete event stratigraphy for these eruptions than has hitherto been possible. The volume of rhyolitic magma erupted during the 55 ka event may have been more than 10 km 3, and for the 40 ka event can be estimated with rather more confidence at 4 km 3. During the earlier event, plinian eruptions dispersed fallout pumice over much of the Valles caldera, the southern Jemez Mountains, and the Rio Grande rift. We infer a fallout thickness of several decimeters at the site of the city of Santa Fe, and significant ash fall in eastern New Mexico. In contrast, pyroclastic density currents were channeled within the caldera moat and southwestward into the head of Cañon de San Diego, the principal drainage from the caldera. Simultaneous (or rapidly alternating) pyroclastic fallout and density current activity characterized the ~ 55 ka event, with density currents becoming more frequent as the eruption progressed through two distinct stages separated by a brief hiatus. One early pyroclastic surge razed a forest in the southern caldera moat, in a similar manner to the initial blast of the May 18, 1980 eruption of Mt. St. Helens. Ignimbrite outflow from the caldera through the drainage notch may have been restricted in runout distance due to steep, rugged topography in this vicinity promoting mixing between flows and air, and the formation of phoenix clouds. Lavas erupted during both the ~ 55 and ~ 40 ka events were

  11. Deep-sea Vector Magnetic Anomalies over the Bayonnaise Knoll Caldera (Izu-Ogasawara Arc) (Invited)

    NASA Astrophysics Data System (ADS)

    Honsho, C.; Ura, T.; Kim, K.

    2013-12-01

    The Bayonnaise Knoll caldera is located on the eastern margin of the backarc rift zone of the Izu-Ogasawara island arc. The caldera rim is ~3 km in diameter and 100-200 m high from the caldera floor 840-920 m deep. A large active hydrothermal field associated with sulfide deposit, called the Hakurei site, has been found at the foot of the southeastern caldera wall. We conducted deep-sea magnetic measurements using autonomous underwater vehicles to map ~75 % of an area 3 km by 4 km in the caldera. The magnetic vector field data were collected at 40-150 m altitude along the survey lines spaced 80-200 m apart. We improved the conventional correction method applied for removing the effect of vehicle magnetization, which greatly enhanced the precision of the resulting vector anomalies and allowed us to use the vector anomaly instead of the total intensity anomaly for inversion analysis. The magnetization distribution obtained using the vector anomaly was significantly different from the one obtained using the total intensity anomaly, especially in areas where the survey tracks were widely spaced. The aliasing effect appears in areas of sparse data distribution, and the magnetic field is more correctly calculated from the vector anomaly than the total intensity anomaly. The magnetization distribution in the caldera has two major features: a ~1.5-km wide belt of high magnetization, trending NNW-SSE through the caldera, and a clear low magnetization zone, ~300 m x ~500 m wide, extending over the Hakurei site. The high magnetization belt is considered to reflect basaltic volcanism associated with the backarc rifting that occurred after the formation of the Bayonnaise Knoll. The low magnetization zone is interpreted as the alteration zone resulting from the hydrothermal activity. Several zones of localized high magnetization are recognized within the high magnetization belt, some of them in the caldera wall adjacent to the low magnetization zone of the Hakurei site. We

  12. Stress evolution during caldera collapse

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

  13. Caldera formation at Tendurek, East Turkey

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  14. Geologic map of the Crystal Peak Caldera, west-central Utah

    SciTech Connect

    Steven, T.A.

    1989-01-01

    In early Oligocene time, an area 16 by 10 km across near Crystal Peak was suddenly converted from a dissected plateau to a steep-sided topographic basin; this was coincident with eruption of the Tunnel Spring tuff. Subsidence was complex; the western part of the basin seems underlain by an oval-shaped block (caldera) bounded by steep walls; whereas, the eastern part of the basin is less deeply subsided and contains thinner and more irregularly distributed fill. A gravity low closely mirrors the subsided area. In middle Oligocene time, two major ash-flow formations of the Needles Range Group invaded the caldera where they formed coherent sheets interlayered with locally derived gravels.

  15. The Chacana caldera complex in Ecuador

    NASA Astrophysics Data System (ADS)

    Hall, Minard L.; Mothes, Patricia A.

    2008-10-01

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

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

    USGS Publications Warehouse

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

    1990-01-01

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

  17. A geological and geophysical appraisal of the Baca geothermal field, Valles Caldera, New Mexico

    NASA Astrophysics Data System (ADS)

    Wilt, Michael; Vonder Haar, Stephen

    1986-03-01

    The Baca location #1 geothermal field is located in north-central New Mexico within the western half of the Plio-Pleistocene Valles Caldera. Steam and hot water are produced primarily from the northeast-trending Redondo Creek graben, where downhole temperatures exceed 260°C at depths of less than 2 km. Stratigraphically the reservoir region can be described as a five-layer sequence that includes Tertiary and Quaternary volcanic rocks, and Mesozoic and Tertiary sediments overlying Precambrian granitic basement. Production is mainly controlled by fractures and faults that are ultimately related to activity in the Rio Grande Rift system. Geophysically, the caldera is characterized by a gravity minimum and a resistivity low in its western half. A 40-mgal gravity minimum over the caldera is due mostly to the relatively low-density volcanics and sediments that fill the caldera and probably bears no relation to deep-seated magmatic sources. Two-dimensional gravity modeling indicates that the depth to Precambrian basement in Redondo Canyon is probably at least 3 km and may exceed 5 km in eastern parts of the caldera. Telluric and magnetotelluric surveys have shown that the reservoir region is associated with low resistivity and that a deep low-resistivity zone correlates well with the depth of the primary reservoir inferred from well data. Telluric and magnetotelluric data have also identified possible fault zones in the eastern and western sections of the production region that may form boundaries to the Redondo Creek reservoir. These data also suggest that the reservoir region is located at the intersection of lineaments that trend north-south and northeast-southwest. Magnetotelluric results indicate deep low resistivity at the western edge of the caldera which may be associated with deep hot fluids. On the basis of geophysical and well data, we make three estimates of reservoir dimensions. The estimates of the areal extent of the reservoir range from 10 to 30 km 2

  18. A Comparison of Historic Caldera-Forming Events

    NASA Astrophysics Data System (ADS)

    Stix, J.

    2002-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  20. The hydrothermal system of Long Valley Caldera, California

    USGS Publications Warehouse

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

    1978-01-01

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

  1. Renewed Geodetic Unrest at Santorini Caldera, Greece

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  2. Imaging hydrothermal systems at Furnas caldera (Azores, Portugal): Insights from Audio-Magnetotelluric data

    NASA Astrophysics Data System (ADS)

    Hogg, Colin; Kiyan, Duygu; Rath, Volker; Byrdina, Svetlana; Vandemeulebrouck, Jean; Silva, Catarina; Viveiros, Maria FB; Ferreira, Teresa

    2016-04-01

    The Furnas volcano is the eastern-most of the three active central volcanoes of Sao Miguel Island. The main caldera formed about 30 ka BP, followed by a younger eruption at 10-12 ka BP, which forms the steep topography of more than 200 m in the measuring area. It contains several very young eruptive centers, and a shallow caldera lake. Tectonic features of varying directions have been identified in the Caldera and its vicinity. In the northern part of the caldera, containing the fumarole field of Caldeiras das Furnas, a detailed map of surface CO2 emissions was recently made available. In 2015, a pilot survey of 13 AudioMagnetoTelluric soundings (AMT) and Electrical Resistivity Tomography (ERT) data were collected along two profiles in the eastern part of Furnas caldera in order to image the electrical conductivity of the subsurface. The data quality achieved by both techniques is extraordinary and first results indicate a general correlation between regions of elevated conductivity and the mapped surface CO2 emissions, suggesting that they may both be caused by the presence hydrothermal fluids. Tensor decomposition analysis using the Groom-Bailey approach produce a generalised geo-electric strike direction, 72deg East of North, for the AMT data compared to the surface geological strike derived from the major mapped fault crossing the profiles of 105deg. An analysis of the real induction arrows at certain frequencies (at depths greater than 350 m) infer that an extended conductor at depth does not exactly correspond to the degassing structures at the surface and extends outside the area of investigation. The geometry of the most conductive regions with electrical conductivities less then1 Ώm found at various depths differ from what was expected from earlier geologic and tectonic studies and possibly may not be directly related to the mapped fault systems at the surface. On the eastern profile, which seemed to be more appropriate for 2-D modelling with 72deg strike

  3. A geophysical and geological study of Laguna de Ayarza, a Guatemalan caldera lake

    USGS Publications Warehouse

    Poppe, L.J.; Paull, C.K.; Newhall, C.G.; Bradbury, J.P.; Ziagos, J.

    1985-01-01

    Geologic and geophysical data from Laguna de Ayarza, a figure-8-shaped doublecaldera lake in the Guatemalan highlands, show no evidence of postcaldera eruptive tectonic activity. The bathymetry of the lake has evolved as a result of sedimentary infilling. The western caldera is steep-sided and contains a large flat-floored central basin 240 m deep. The smaller, older, eastern caldera is mostly filled by coalescing delta fans and is connected with the larger caldera by means of a deep channel. Seismicreflection data indicate that at least 170 m of flat-lying unfaulted sediments partly fill the central basin and that the strata of the pre-eruption edifice have collapsed partly along inward-dipping ring faults and partly by more chaotic collapses. These sediments have accumulated in the last 23,000 years at a minimum average sedimentation rate of 7 m/103 yr. The upper 9 m of these sediments is composed of > 50% turbidites, interbedded with laminated clayey silts containing separate diatom and ash layers. The bottom sediments have >1% organic material, an average of 4% pyrite, and abundant biogenic gas, all of which demonstrate that the bottom sediments are anoxic. Although thin (<0.5 cm) ash horizons are common, only one thick (7-16 cm) primary ash horizon could be identified in piston cores. Alterations in the mineralogy and variations in the diatom assemblage suggest magnesium-rich hydrothermal activity. ?? 1985.

  4. Surface Deformation of Los Humeros Caldera, Mexico, Estimated by Interferometric Synthetic Aperture Radar (InSAR).

    NASA Astrophysics Data System (ADS)

    Santos Basurto, R.; Lopez Quiroz, P.; Carrasco Nuñez, G.; Doin, M. P.

    2014-12-01

    Los Humeros caldera is located in the eastern part of the Trans-Mexican Volcanic Belt, to the north of the state of Puebla and bordering the west side of the state of Veracruz. The study of the caldera, is of great interest because there is a geothermal field currently working inside of it. In fact, Los Humeros, is the third more important geothermal field in Mexico. In this work, we used InSAR to estimate the surface deformation on the caldera, aiming to contribute to its modeling and to help preventing subsidence related hazards on the geothermal field and surroundings. On this study, we calculated 34 interferograms from 21 SAR images of the ENVISAT European Space Agency Mission. The analysis of the interferograms, allow us to detect, decorrelation of the interferometric signal increased, when time spans were greater than 70 days. Also, for those with good signal correlation, the atmospheric signal dominated the interferogram, masking completely the deformation. Moreover, residual orbital ramps were detected, in some of the calculated interferograms. An algorithm capable to remove all the interferogram signal contributions but the deformation related, has been implemented. Resulting deformation and its correlation with several variables like the geology, the hydrogeology and the seismic records, were analysed through its integration in a Geographic Information System.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    SciTech Connect

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

    1987-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  8. I. An /sup 18/O//sup 16/O investigation of the Lake City caldera, San Juan Mountains, Colorado. II. /sup 18/O//sup 16/O relationships in tertiary ash-flow tuffs from complex caldera structures in central Nevada and the San Juan Mountains, Colorado

    SciTech Connect

    Larson, P.B.

    1984-01-01

    /sup 18/O//sup 16/O analyses were made on 355 samples in and around the 11 by 14 km Lake City calders, which formed 23 m.y. ago in response to the eruption of the rhyolitic Sunshine Peak Tuff. All of the major lithologies and hydrothermal alteration facies were analyzed, and a detailed delta/sup 18/O map was made of the caldera and its surroundings. The delta/sup 18/O values within the Lake City caldera are controlled by elevation, proximity to permeable zones, and proxmity to the resurgent intrusive rocks. delta/sup 18/O values decrease systematically with stratigraphic depth within the caldera. Mineralogic alteration facies within the caldera show complementary patterns. These data show that the resurgent intrusion was the heat engine that drove the Lake City hydrothermal system. Alteration in and near the intrusion occurred at high temperatures and intermediate water/rock ratios. Away from the resurgent intrusion, water-rock interaction in the permeable zones occurred at lower temperatures and high water/rock ratios. The regional eastward tilting has raised low-/sup 18/O rocks in the western part of the caldera to higher elevations than stratigraphically equivalent rocks in the eastern part of the caldera. Mineralogical alteration patterns are also similarly displaced.

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

    USGS Publications Warehouse

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

    2014-01-01

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

  10. Buried caldera of mauna kea volcano, hawaii.

    PubMed

    Porter, S C

    1972-03-31

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Marti, J.; Gudmundsson, A.

    2000-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  17. A preliminary study of older hot spring alteration in Sevenmile Hole, Grand Canyon of the Yellowstone River, Yellowstone Caldera, Wyoming

    USGS Publications Warehouse

    Larson, P.B.; Phillips, A.; John, D.; Cosca, M.; Pritchard, C.; Andersen, A.; Manion, J.

    2009-01-01

    Erosion in the Grand Canyon of the Yellowstone River, Yellowstone Caldera (640??ka), Wyoming, has exposed a cross section of older hydrothermal alteration in the canyon walls. The altered outcrops of the post-collapse tuff of Sulphur Creek (480??ka) extend from the canyon rim to more than 300??m beneath it. The hydrothermal minerals are zoned, with an advanced argillic alteration consisting of an association of quartz (opal) + kaolinite ?? alunite ?? dickite, and an argillic or potassic alteration association with quartz + illite ?? adularia. Disseminated fine-grained pyrite or marcasite is ubiquitous in both alteration types. These alteration associations are characteristic products of shallow volcanic epithermal environments. The contact between the two alteration types is about 100??m beneath the rim. By analogy to other active geothermal systems including active hydrothermal springs in the Yellowstone Caldera, the transition from kaolinite to illite occurred at temperatures in the range 150 to 170????C. An 40Ar/39Ar age on alunite of 154,000 ?? 16,000??years suggests that hydrothermal activity has been ongoing since at least that time. A northwest-trending linear array of extinct and active hot spring centers in the Sevenmile Hole area implies a deeper structural control for the upflowing hydrothermal fluids. We interpret this deeper structure to be the Yellowstone Caldera ring fault that is covered by the younger tuff of Sulphur Creek. The Sevenmile Hole altered area lies at the eastern end of a band of hydrothermal centers that may mark the buried extension of the Yellowstone Caldera ring fault across the northern part of the Caldera. ?? 2009 Elsevier B.V.

  18. A preliminary study of older hot spring alteration in Sevenmile Hole, Grand Canyon of the Yellowstone River, Yellowstone Caldera, Wyoming

    NASA Astrophysics Data System (ADS)

    Larson, Peter B.; Phillips, Allison; John, David; Cosca, Michael; Pritchard, Chad; Andersen, Allen; Manion, Jennifer

    2009-11-01

    Erosion in the Grand Canyon of the Yellowstone River, Yellowstone Caldera (640 ka), Wyoming, has exposed a cross section of older hydrothermal alteration in the canyon walls. The altered outcrops of the post-collapse tuff of Sulphur Creek (480 ka) extend from the canyon rim to more than 300 m beneath it. The hydrothermal minerals are zoned, with an advanced argillic alteration consisting of an association of quartz (opal) + kaolinite ± alunite ± dickite, and an argillic or potassic alteration association with quartz + illite ± adularia. Disseminated fine-grained pyrite or marcasite is ubiquitous in both alteration types. These alteration associations are characteristic products of shallow volcanic epithermal environments. The contact between the two alteration types is about 100 m beneath the rim. By analogy to other active geothermal systems including active hydrothermal springs in the Yellowstone Caldera, the transition from kaolinite to illite occurred at temperatures in the range 150 to 170 °C. An 40Ar/ 39Ar age on alunite of 154,000 ± 16,000 years suggests that hydrothermal activity has been ongoing since at least that time. A northwest-trending linear array of extinct and active hot spring centers in the Sevenmile Hole area implies a deeper structural control for the upflowing hydrothermal fluids. We interpret this deeper structure to be the Yellowstone Caldera ring fault that is covered by the younger tuff of Sulphur Creek. The Sevenmile Hole altered area lies at the eastern end of a band of hydrothermal centers that may mark the buried extension of the Yellowstone Caldera ring fault across the northern part of the Caldera.

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

    SciTech Connect

    Intemann, P.R.

    1981-01-01

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

  20. Elongate summit calderas as Neogene paleostress indicators in Antarctica

    USGS Publications Warehouse

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

    2007-01-01

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

  1. The graben caldera of Guanajuato, Mexico

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

  2. Elysium Mons Volcano - Detail of Southern Caldera Wall and Floor

    NASA Technical Reports Server (NTRS)

    1998-01-01

    On July 4, 1998--the first anniversary of the Mars Pathfinder landing--Mars Global Surveyor's latest images were radioed to Earth with little fanfare. The images received on July 4, 1998, however, were very exciting because they included a rare crossing of the summit caldera of a major martian volcano. Elysium Mons is located at 25oN, 213oW, in the martian eastern hemisphere. Elysium Mons is one of three large volcanoes that occur on the Elysium Rise-- the others are Hecates Tholus (northeast of Elysium Mons) and Albor Tholus (southeast of Elysium Mons). The volcano rises about 12.5 kilometers (7.8 miles) above the surrounding plain, or about 16 kilometers (9.9 miles) above the martian datum-- the 'zero' elevation defined by average martian atmospheric pressure and the planet's radius.

    Elysium Mons was discovered by Mariner 9 in 1972. It differs in a number of ways from the familiar Olympus Mons and other large volcanoes in the Tharsis region. In particular, there are no obvious lava flows visible on the volcano's flanks. The lack of lava flows was apparent from the Mariner 9 images, but the new MOC high resolution image--obtained at 5.24 meters (17.2 feet) per pixel--illustrates that this is true even when viewed at higher spatial resolution.

    Elysium Mons has many craters on its surface. Some of these probably formed by meteor impact, but many show no ejecta pattern characteristic of meteor impact. Some of the craters are aligned in linear patterns that are radial to the summit caldera--these most likely formed by collapse as lava was withdrawn from beneath the surface, rather than by meteor impact. Other craters may have formed by explosive volcanism. Evidence for explosive volcanism on Mars has been very difficult to identify from previous Mars spacecraft images. This and other MOC data are being examined closely to better understand the nature and origin of volcanic features on Mars.

    The three MOC images, 40301 (red wide angle), 40302 (blue wide angle

  3. Asymmetrically multi-collapsed structure of Kikai caldera in southern off Kyushu Island, Japan: A reconstruction from seismic reflection images

    NASA Astrophysics Data System (ADS)

    Ikegami, F.; Kiyokawa, S.; Oiwane, H.; Nakamura, Y.; Kameo, K.; Minowa, Y.; Kuratomi, T.

    2012-12-01

    Kikai caldera (Matsumoto, 1943) is a mostly submerged highly active caldera complex located in the southern Japan 40 km off Kyushu Island. The caldera has bathymetrically two rims partially that are previously considered as older-outer and newer-inner ones (Yokoyama et al., 1966). The caldera is believed to be the source of Akahoya tephra (Machida and Arai, 1978) which date was determined as 7300 cal. BP (Fukusawa, 1995) which is the most recent VEI-7 class eruption in the eastern margin of Asia. Intense earthquakes (Naruo and Kobayashi, 2002), low-aspect ratio Koya ignimbrite (Maeno and Taniguchi, 2007) and tsunami (Geshi, 2009) are presumed to have taken place at the climax of the eruption. There are at least two other series of giant eruption deposits that are considered to have originated from the Kikai caldera (Ono et al., 1986) and this indicates that it has been serving as an eruptive center for the past 150,000 years. We conducted seismic reflection observations in two survey cruises (KT-10-18 and KT-11-11) in 2010 and 2011 using a research vessel Tansei-maru of JAMSTEC (Japan Agency for Marine-Earth Science and Technology). The sound source was a 150 cubic inches G-I gun with 10 seconds of shot interval, and a 48-channled streamer cable was used for acquisition. Totally 24 profiles were obtained with the speed of 4 knots. First, the absence of large fault in northern and western caldera rim indicates Kikai likely had an asymmetric "trapdoor" style collapse (Lipman, 1995) rather than the ideal "piston" type one. Inner and outer topographic rims at the east to south do correspond with large faults, however the both of them may have worked in 7300 BP eruption because they reach to the seafloor. Such asymmetric multi-collapse would provide some characteristics to the climactic pyroclastic flow in 7300 BP. Second, the bathymetric rise at the center of the caldera consists of high-amplitude surface and chaotic thick facies outwardly collapsed by intense normal

  4. Central San Juan caldera cluster: regional volcanic framework

    USGS Publications Warehouse

    Lipman, Peter W.

    2000-01-01

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

  5. Seismic imaging of the Medicine Lake Caldera

    SciTech Connect

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

    1987-04-01

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

  6. Arcuate Fractures in Olympus Mons Caldera

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

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

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

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

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

  7. Title: Long Valley Caldera 2003 through 2012: Overview of low level unrest in the last decade Authors: Stuart Wilkinson, David Hill, Michael Lisowski, Deborah Bergfeld, Margaret Mangan

    NASA Astrophysics Data System (ADS)

    Wilkinson, S. K.; Hill, D. P.; Lisowski, M.; Bergfeld, D.; Mangan, M.

    2012-12-01

    Long Valley Caldera is located in central California along the eastern escarpment of the Sierra Nevada and at the western edge of the Basin and Range. The caldera formed 0.76 Ma ago during the eruption of 600 cubic kilometers the Bishop Tuff that resulted in the collapse of the partially evacuated magma chamber. Since at least late 1978, Long Valley Caldera has experienced recurring earthquake swarms and ground uplift, suggesting future eruptions are possible. Unrest in Long Valley Caldera during the 1980s to early 2000s is well documented in the literature. Episodes of inflation centered on the resurgent dome in the western part of the caldera occurred in 1979-1980, 1983, 1989-1990, 1997-1998, and 2002-2003, accumulating ~ 80 cm of uplift. Earthquakes of M ≥ 3.0 were numerous in the caldera and in the Sierra Nevada block to the south of the caldera from 1980 through 1983 (800 events including four M~ 6 earthquakes in 1980); in the caldera from 1997 through mid-1998 (150 events); and in the Sierra Nevada block from mid-1998 through 1999 (~160 events) and more modestly from 2002 through 2003 (7 events). In this presentation, we summarize the low-levels of caldera unrest during the last decade. The number of earthquakes in Sierra Nevada block and the caldera has gradually diminished over the last decade. Fifty Sierra Nevada earthquakes had magnitudes 3.0≤M≤4.6. In the caldera, only six earthquakes had magnitudes 3.0≤M≤3.8. A three-month swarm of minor earthquakes (235 events with 0.5≤M≤3.8; most below 2.0) occurred in the caldera in mid-2010. Analysis of continuous GPS data over the last year shows an inflationary pattern within the caldera centered on the resurgent dome, with a maximum uplift rate of ~ 2-3 cm/yr. The rate of deformation is comparable to that of 2002-2003, and well below ~ 70 cm/yr rates observed during the peak of inflation in the late 1990s. Steaming ground and diffuse CO2 discharge has long been a feature of Long Valley Caldera

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

    NASA Astrophysics Data System (ADS)

    Acocella, Valerio

    2006-10-01

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

  9. Historical unrest at large calderas of the world

    SciTech Connect

    Newhall, C.A.; Dzurisin, D.

    1989-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  11. AmeriFlux US-Vcp Valles Caldera Ponderosa Pine

    DOE Data Explorer

    Litvak, Marcy [University of New Mexico

    2016-01-01

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

  12. Imaging radar observations of Askja Caldera, Iceland

    NASA Technical Reports Server (NTRS)

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

    1978-01-01

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

  13. Magma storage in a strike-slip caldera

    PubMed Central

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

    2016-01-01

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

  14. Magma storage in a strike-slip caldera

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  15. Magma storage in a strike-slip caldera.

    PubMed

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  17. Geological and Geobotanical Studies of Long Valley Caldera, CA, USA Utilizing New 5m Hyperspectral Imagery

    SciTech Connect

    Martini, B.A.; Silver, E.A.; Potts, D.C.; Pickles, W.L.

    2000-07-25

    In May of 1989, a six month-long small magnitude earthquake swarm began beneath the Pleistocene-aged dacitic cumulovolcano Mammoth Mountain. The following year, increased mortality of trees in the Horseshoe Lake region was observed. Their deaths were initially attributed to the Sierran drought of the 1980's. In 1994 however, soil gas measurements made by the USGS confirmed that the kills were due to asphyxiation of the vegetation via the presence of 30-96 % CO{sub 2} in ground around the volcano[1]. Physiological changes in vegetation due to negative inputs into the ecological system such as anomalously high levels of magmatic CO{sub 2}, can be seen spectrally. With this phenomena in mind, as well as many other unanswered geological and geobotanical questions, seven lines of hyperspectral 5-meter HyMap data were flown over Long Valley Caldera located in eastern California on September 7, 1999. HyMap imagery provides the impetus to address geobotanical questions such as where the treekills are currently located at Mammoth and other locales around the caldera as well as whether incipient kills can be identified. The study site of the Horseshoe Lake treekills serves as a focus to the initial analyses of this extensive HyMap dataset due to both the treekill's geologically compelling origins and its status as a serious volcanic geohazard.

  18. Evidence for dyke intrusion earthquake mechanisms near long valley caldera, California

    USGS Publications Warehouse

    Julian, B.R.

    1983-01-01

    A re-analysis of the magnitude 6 earthquakes that occurred near Long Valley caldera in eastern California on 25 and 27 May 1980, suggests that at least two of them, including the largest, were probably caused by fluid injection along nearly vertical surfaces and not by slip on faults. Several investigators 1,2 have reported difficulty in explaining both the long-period surface-wave amplitudes and phases and the locally recorded short-period body-wave first motions from these events, using conventional double-couple (shear fault) source models. They attributed this difficulty to: (1) complex sources, not representable by single-fault models; (2) artefacts of the analysis methods used; or (3) effects of wave propagation through hypothetical structures beneath the caldera. We show here that the data agree well with the predictions for a compensated linear-vector dipole (CLVD) equivalent-force system3 with its principal extensional axis horizontal and trending N 55-65?? E. Such a mechanism is what would be expected for fluid injection into dykes striking N 25-35?? W, which is the approximate strike of numerous normal faults in the area. ?? 1983 Nature Publishing Group.

  19. Intracaldera volcanism and sedimentation-Creede caldera, Colorado

    SciTech Connect

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

    1994-12-31

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Technical Reports Server (NTRS)

    Evans, D. L.

    1978-01-01

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

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

    SciTech Connect

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

    1987-07-01

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

  3. High-resolution aeromagnetic survey of the Mono Basin-Long Valley Caldera region, California

    NASA Astrophysics Data System (ADS)

    Ponce, D. A.; Mangan, M.; McPhee, D.

    2013-12-01

    A new high-resolution aeromagnetic survey of the Mono Basin-Long Valley Caldera region greatly enhances previous magnetic interpretations that were based on older, low-resolution, and regional aeromagnetic data sets and provides new insights into volcano-tectonic processes. The surveyed area covers a 8,750 km2 NNW-trending swath situated between the Sierra Nevada to the west and the Basin and Range Province to the east. The surveyed area includes the volcanic centers of Mono Lake, Mono-Inyo Craters, Mammoth Mountain, Devils Postpile, and Long Valley Caldera. The NW-trending eastern Sierra frontal fault zone crosses through the study area, including the active Mono Lake, Silver Lake, Hartley Springs, Laurel Creek, and Hilton Creek faults. Over 6,000 line-kilometers of aeromagnetic data were collected at a constant terrain clearance of 150 m, a flight-line spacing of 400 m, and a tie-line spacing of 4 km. Data were collected via helicopter with an attached stinger housing a magnetic sensor using a Scintrex CS-3 cesium magnetometer. In the northern part of the survey area, data improve the magnetic resolution of the individual domes and coulees along Mono Craters and a circular shaped magnetic anomaly that coincides with a poorly defined ring fracture mapped by Kistler (1966). Here, aeromagnetic data combined with other geophysical data suggests that Mono Craters may have preferentially followed a pre-existing plutonic basement feature that may have controlled the sickle shape of the volcanic chain. In the northeastern part of the survey, aeromagnetic data reveal a linear magnetic anomaly that correlates with and extends a mapped fault. In the southern part of the survey, in the Sierra Nevada block just south of Long Valley Caldera, aeromagnetic anomalies correlate with NNW-trending Sierran frontal faults rather than to linear NNE-trends observed in recent seismicity over the last 30 years. These data provide an important framework for the further analysis of the

  4. An unusual syn-eruptive bimodal eruption: The Holocene Cuicuiltic Member at Los Humeros caldera, Mexico

    NASA Astrophysics Data System (ADS)

    Dávila-Harris, Pablo; Carrasco-Núñez, Gerardo

    2014-02-01

    The Cuicuiltic Member (CM) at Los Humeros Caldera, eastern Mexican Volcanic Belt is a Holocene (6.4 ka B.P.) succession of alternated fallout deposits of contrasting composition (trachydacite pumice and basaltic andesite scoria). The CM covers approximately 250 km2 on its proximal facies and its thickness ranges from 1.5 m to 8.0 m. It postdates two caldera-forming ignimbrites (Xaltipan and Zaragoza) and numerous Plinian successions. It is subdivided in 9 units (C1 to C9) according to its textural and chemical characteristics. Sub-horizontal, topography-draping layers of trachydacite pumice lapilli, andesitic pumice lapilli and basaltic-andesite scoria lapilli with sporadic one-meter blocks are common lithofacies. The base is formed by coarse trachydacite pumice lapilli (C1 and C2), overlain by a layer with banded pumice (C3). Thin layers of ash and ash-tuff are intermittent on lower units, whilst continuous at the base of C4. The middle units, C4 and C6 are basaltic-andesite pumice, and scoria lapilli to blocks; C5 is in-between the two mafic units and it is represented by a layer of pale grey pumice lapilli. Units C7 and C8 are a mixture of white trachydacite pumice, scoria lapilli and banded pumice. The uppermost layer, C9, is a brown to grey andesitic pumice lapilli. Extensive fieldwork allowed a close and reliable correlation of layers that helps to understand the complexity of stratigraphic relations and sources for those layers. The distribution of these units is varied across the caldera, with the trachydacite layers dispersal from the centre towards the NW, whilst the andesitic units have maximum thicknesses over the SE and NE sectors of the caldera. Isopach and isopleth maps, combined with detailed mapping of near-vent spatter facies, orientation of local bomb sags and variation of mean clasts size for some layers were very useful to determine the vent location, particularly for the andesitic-basaltic layers.

  5. Radon Outgassing in the Casa Diablo Region, Long Valley Caldera, California

    NASA Astrophysics Data System (ADS)

    Adarkwah, N.; Cuff, K.

    2003-12-01

    A radon outgassing survey has been conducted in the Casa Diablo region of the Long Valley Caldera. The Long Valley Caldera (LVC) is an active volcanic system situated along the eastern front of the Sierra Nevada mountain range in east-central California. The survey was centered in an area .4 km northwest of the Casa Diablo geothermal power plant, located along the southwestern-most rim of the caldera?s resurgent dome. Results from previous radon emission studies in LVC indicate that high degrees of outgassing occur in association with relatively narrow networks of unsealed fractures (Cuff, et al., 2000 and Hoyos, et al., 2001). These fracture networks act as pathways for radon and other gases generated at depth as they migrate toward the surface. The purpose of the present study was to determine whether or not a relationship exists between radon emissions in the current survey area and that in a previously surveyed area approximately .8 km west of the geothermal plant. To accomplish this, we measured radon concentration in soil-gas at 35 separate sites. These sites were located within a 140 by 100 meter grid, with 20 meter spacing between each sample site. A radon outgassing map was then created using measured concentration values along with longitude and latitude values for each sample location. Geologic maps of the area were also analyzed and compared with radon outgassing maps. Analysis of these maps indicates that radon outgassing occurs through a set of crisscrossing fractures, trending southwest-northeast and northwest-southeast respectively. The northwest trending fractures are related to mapped normal faults in the area, while those with a southwest-northeast orientation are associated with an unmapped zone of faulting that is roughly perpendicular to the other faults. The latter set of fractures has a trend similar to that discovered in the previously surveyed area to the west. In both areas the highest readings were in excess of three times background

  6. A seismological perspective of the shallow magma and hydrothermal systems under Kilauea Caldera

    NASA Astrophysics Data System (ADS)

    Chouet, B. A.; Dawson, P. B.

    2011-12-01

    The past 20 years have seen great strides in our understanding of Kilauea Volcano, in large part due to technological developments and improvements in seismological instrumentation, which now allow the surface effects of subterranean volcanic processes to be imaged in unprecedented detail. High-resolution tomography provided an image of 3D velocity anomalies down to a scale of a few hundred meters, providing indirect evidence for the presence of reservoirs under the summit region of Kilauea. A sharper image of a shallow hydrothermal reservoir under Kilauea Caldera was obtained from frequency-slowness analyses of long-period (LP) seismicity recorded on three small-aperture seismic antennas deployed in the summit caldera. Located within the top 500 m below the caldera floor and extending ~0.6 km and ~1 km in the east-west and north-south directions, this hydrothermal reservoir broadly overlaps the east wall of the Halemaumau pit crater. Further evidence of hydrothermal processes within this zone was obtained from a study of a well-recorded LP event, indicating a source mechanism consistent with the resonance of a horizontal steam-filled crack at a depth of ~150 m near the eastern rim of Halemaumau. Recurring very-long-period (VLP) signals originating in the repeated activation of a compact source region near sea level immediately beneath this hydrothermal reservoir have allowed a gradually emerging view of the shallowest segment of the magma transport pathway under the caldera. Further elaboration of our image of the magma pathway structure, made possible through detailed modeling of VLP signals accompanying degassing activity at a new vent formed in Halemaumau in March 2008, points to a dominant dike segment in the form of a nearly vertical east-trending dike. The inferred dike features a ~20° clockwise rotation in strike under the east edge of Halemaumau, where it intersects a sub-vertical north-striking dike. The triple junction made by the intersection of the

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

    NASA Astrophysics Data System (ADS)

    Nieto-Obregón, Jorge; Aguirre-Díaz, Gerardo

    2008-10-01

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

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

    NASA Astrophysics Data System (ADS)

    Afanasyev, Andrey; Costa, Antonio; Chiodini, Giovanni

    2015-04-01

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

  9. New evidence on the hydrothermal system in Long Valley caldera, California, from wells, fluid sampling, electrical geophysics, and age determinations of hot-spring deposits

    USGS Publications Warehouse

    Sorey, M.L.; Suemnicht, G.A.; Sturchio, N.C.; Nordquist, G.A.

    1991-01-01

    Data collected since 1985 from test drilling, fluid sampling, and geologic and geophysical investigations provide a clearer definition of the hydrothermal system in Long Valley caldera than was previously available. This information confirms the existence of high-temperature (> 200??C) reservoirs within the volcanic fill in parts of the west moat. These reservoirs contain fluids which are chemically similar to thermal fluids encountered in the central and eastern parts of the caldera. The roots of the present-day hydrothermal system (the source reservoir, principal zones of upflow, and the magmatic heat source) most likely occur within metamorphic basement rocks beneath the western part of the caldera. Geothermometer-temperature estimates for the source reservoir range from 214 to 248??C. Zones of upflow of hot water could exist beneath the plateau of moat rhyolite located west of the resurgent dome or beneath Mammoth Mountain. Lateral flow of thermal water away from such upflow zones through reservoirs in the Bishop Tuff and early rhyolite accounts for temperature reversals encountered in most existing wells. Dating of hot-spring deposits from active and inactive thermal areas confirms previous interpretations of the evolution of hydrothermal activity that suggest two periods of extensive hot-spring discharge, one peaking about 300 ka and another extending from about 40 ka to the present. The onset of hydrothermal activity around 40 ka coincides with the initiation of rhyolitic volcanism along the Mono-Inyo Craters volcanic chain that extends beneath the caldera's west moat. ?? 1991.

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

    USGS Publications Warehouse

    Rytuba, J.J.

    1994-01-01

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

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

    SciTech Connect

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

    1985-12-31

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

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

    NASA Astrophysics Data System (ADS)

    Steinmann, Lena; Spiess, Volkhard; Sacchi, Marco

    2015-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  14. Origin and evolution of overlapping calc-alkaline and alkaline magmas: The Late Palaeozoic post-collisional igneous province of Transbaikalia (Russia)

    NASA Astrophysics Data System (ADS)

    Litvinovsky, B. A.; Tsygankov, A. A.; Jahn, B. M.; Katzir, Y.; Be'eri-Shlevin, Y.

    2011-08-01

    The Late Palaeozoic voluminous magmatism in Transbaikalia, Russia (a territory of > 600,000 km 2 to the east of Lake Baikal) is highly diverse and complex. Of special interest are (1) the significant overlap in time between magmatic suites commonly ascribed to post-collisional and within-plate settings and (2) the provenance of the coeval, but distinct, granitoid magmas that are closely spaced within a large region. Magmatic activity lasted almost continuously from ~ 330 Ma to ~ 275 Ma and included five igneous suites occupying a total area of ~ 200,000 km 2: (1) the Barguzin suite of high-K calc-alkaline granite (330-310 Ma); (2 and 3) the coeval Chivyrkui suite of low-silica calc-alkaline granitoids and the Zaza suite of high-K calc-alkaline to alkaline granite and quartz syenite which were emplaced between 305 and 285 Ma; and (4 and 5) the partially overlapped in time Lower-Selenga monzonite-syenite suite (285-278 Ma) and the Early-Kunalei suite of alkali-feldspar and peralkaline quartz syenite and granite (281-275 Ma). The overall increase in alkalinity of the granitoids with time reflects the progress from post-collisional to within-plate settings. However, a ~ 20 m.y. long transitional period during which both calc-alkaline and alkaline granitoids were emplaced indicates the coexistence of thickened (batholiths) and thinned (rift) crustal tracts. Sr-Nd-O isotope and elemental geochemical data suggest that the relative contribution of mantle-derived components to the generation of silicic magmas progressively increased with time. The high-K calc-alkaline granite magmas that formed the Angara-Vitim batholith were generated by high degree melting of supracrustal metamorphic rocks [ɛNd(t) = - 5.7 to - 7.7; δ 18O(Qtz) = 12‰], with minor contribution of H 2O and K from the underplated mafic magma (the convective diffusion model). The coeval calc-alkaline Chivyrkui suite and the transitional to alkaline Zaza suite formed as a result of mixing of crustal silicic

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

    SciTech Connect

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

    1995-05-01

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

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

    SciTech Connect

    1993-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  18. Science guide for the Long Valley Caldera deep hole

    SciTech Connect

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

    1989-05-01

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

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

    SciTech Connect

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

    1994-03-10

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

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

    SciTech Connect

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

    1988-01-01

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

  1. Tilted lake shorelines record the onset of motion along the Hilton Creek fault adjacent to Long Valley caldera, CA, USA

    NASA Astrophysics Data System (ADS)

    Perkins, J. P.; Finnegan, N. J.; Cervelli, P. F.; Langbein, J. O.

    2010-12-01

    Prominent normal faults occur within and around Long Valley caldera, in the eastern Sierra Nevada of California. However, their relationship to both the magmatic and tectonic evolution of the caldera since the 760 ka eruption of the Bishop Tuff remains poorly understood. In particular, in the Mono-Inyo Craters north of Long Valley, extensional faulting appears to be replaced by dike intrusion where magma is available in the crust. However, it is unclear whether extensional faults in Long Valley caldera have been active since the eruption of the Bishop Tuff (when the current topography was established) or are a relatively young phenomenon owing to the cooling and crystallization of the Long Valley magma reservoir. Here we use GPS geodesy and geomorphology to investigate the evolution of the Hilton Creek fault, the primary range-front fault bounding Long Valley caldera to the southwest. Our primary goals are to determine how long the Hilton Creek fault has been active and whether slip rates have been constant over that time interval. To characterize the modern deformation field, we capitalize on recently (July, 2010) reoccupied GPS benchmarks first established in 1999-2000. These fixed-array GPS data show no discernible evidence for recent slip on the Hilton Creek fault, which further highlights the need for longer-term constraints on fault motion. To establish a fault slip history, we rely on a suite of five prominent shorelines from Pleistocene Long Valley Lake whose ages are well constrained based on field relationships to dated lavas, and that are tilted southward toward the Hilton Creek fault. A preliminary analysis of shoreline orientations using GPS surveys and a 5-m-resolution Topographic Synthetic Aperture Radar (TOPSAR) digital elevation model shows that lake shorelines tilt towards the Hilton Creek fault at roughly parallel gradients (~ 0.6%). The measured shorelines range in inferred age from 100 ka to 500 ka, which constrain recent slip on the Hilton

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

    PubMed Central

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

    2013-01-01

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

  3. Stable Isotopes of Tilted Ignimbrite Calderas in Nevada

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2003-04-01

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

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

    PubMed

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

    2013-01-01

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

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

    SciTech Connect

    Starguist, V.L.

    1988-01-01

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

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

    SciTech Connect

    Bender-Lamb, S.

    1991-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1985-11-01

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

  10. Erosionally Exhumed Fill and Floor of a Ring-Fault-Bounded Plate-Subsidence Caldera: 33.2-Ma Bonanza, Southwest Colorado

    NASA Astrophysics Data System (ADS)

    Lipman, P. W.; McIntosh, W. C.

    2009-12-01

    The Bonanza caldera (NE San Juan Mountains, Southern Rocky Mountain Volcanic Field), source of a compositionally complex regional ignimbrite sheet erupted at 33.19±0.04 Ma*, is a subequant resurgently domed structure of much larger size (~20 km diameter), subsidence depth (>3 km), and eruptive volume (>1,000 km3) than previously recognized. In the western outflow Bonanza Tuff, crystal-rich dacite (62-65% SiO2) is areally and volumetrically dominant, but grades upward into minor “upper rhyolite” in proximal sections. To the east, earlier-erupted crystal-poor rhyolite (73-74% SiO2), zoned upward into dacite, then back to rhyolite, was formerly described as a separate ignimbrite (“Gribbles Park Tuff”). Preliminary petrologic study indicates that dacitic Bonanza Tuff is at least in part a mechanical mixture of rhyolitic and andesitic magma that fragmented during pyroclastic eruption. Although some near-original caldera morphology remains expressed by present-day landforms (topographic rim, resurgent core, ring-fault valley), deep levels of erosion and tilting by penecontemporaneous and postvolcanic faults of the early Rio Grande rift system provide exceptional three-dimensional exposures of caldera-fill deposits, caldera-floor rocks, subsidence features, and resurgent structures. The western flank of the resurgent dome dips 40-50o, exposing an ~3-km-thick section of complexly compositionally zoned intracaldera ignimbrite (up to 9 alternations of rhyolite and dacite), with interleaved collapse-breccia lenses), underlain by caldera-floor intermediate-composition volcanics, and overlain by caldera-filling andesite to rhyolite lavas. Postcollapse rhyolite and a resurgent intrusion of aplitic granite have yielded 40Ar/39Ar single-crystal sanidine ages (respectively 33.13±0.06, 33.28±0.06 Ma), indistinguishable within uncertainties from that of Bonanza Tuff. Intracaldera ignimbrite has been largely eroded from the eastern two-thirds of the subsidence basin

  11. Workshop on recent research in the Valles caldera

    SciTech Connect

    Heiken, G.

    1985-02-01

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

  12. AmeriFlux US-Vcm Valles Caldera Mixed Conifer

    DOE Data Explorer

    Litvak, Marcy [University of New Mexico

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Geshi, Nobuo; Ruch, Joel; Acocella, Valerio

    2014-06-01

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

  14. Bibliography of literature pertaining to Long Valley Caldera and associated volcanic fields

    USGS Publications Warehouse

    Ewert, John W.; Harpel, Christopher J.; Brooks, Suzanna K.; Marcaida, Mae

    2011-01-01

    On May 25-27, 1980, Long Valley caldera was rocked by four M=6 earthquakes that heralded the onset of a wave of seismic activity within the caldera which has continued through the present. Unrest has taken the form of seismic swarms, uplift of the resurgent dome, and areas of vegetation killed by increased CO2 emissions, all interpreted as resulting from magma injection into different levels beneath the caldera, as well as beneath Mammoth Mountain along the southwest rim of the caldera. Continuing economic development in the Mammoth Lakes area has swelled the local population, increasing the risk to people and property if an eruption were to occur. The U.S. Geological Survey (USGS) has been monitoring geophysical activity in the Long Valley area since the mid-1970s and continues to track the unrest in real time with a sophisticated network of geophysical sensors. Hazards information obtained by this monitoring is provided to local, State, and Federal officials and to the public through the Long Valley Observatory. The Long Valley area also was scientifically important before the onset of current unrest. Lying at the eastern foot of the Sierra Nevada, the deposits from this active volcanic system have provided fertile ground for research into Neogene tectonics, Quaternary geology and geomorphology, regional stratigraphy, and volcanology. In the early 1970s, intensive studies of the area began through the USGS Geothermal Investigations Program, owing to the presence of a large young silicic volcanic system. The paroxysmal eruption of Long Valley caldera about 760,000 years ago produced the Bishop Tuff and associated Bishop ash. The Bishop Tuff is a well-preserved ignimbrite deposit that has continued to provide new and developing insights into the dynamics of ignimbrite-forming eruptions. Another extremely important aspect of the Bishop Tuff is that it is the oldest known normally magnetized unit of the Brunhes Chron. Thus, the age of the Bishop Tuff is used to

  15. The combined use of InSAR and GPS Time-Series to Infer the Deformation Signals at the Yellowstone Caldera

    NASA Astrophysics Data System (ADS)

    Pepe, A.; Tizzani, P.; Battaglia, M.; Castaldo, R.; Lanari, R.; Zeni, G.

    2015-12-01

    We investigate the Yellowstone caldera geological unrest between 1977 and 2010 by analyzing temporal changes in differential Interferometric Synthetic Aperture Radar (InSAR), precise spirit leveling andgravity measurements. The analysis of the 1992-2010 displacement time series has been retrieved by applying an "improved" version of the Small Baseline Subset (SBAS) InSAR technique which complements a novel multi-temporal noise filtering approach with a suitable identification of the network of small baseline pairs. As a result, we have identified three areas of deformation: (i) the Mallard Lake (ML) and Sour Creek (SC) resurgent domes, (ii) a region close to the Northern Caldera Rim (NCR), and (iii) the eastern Snake River Plain (SRP). While the eastern SRP shows a signal related to tectonic deformation, the other two regions are influenced by the caldera unrest. We removed the tectonic signal from the InSAR displacements, and we modeled the InSAR, leveling, and gravity measurements to retrieve the best fitting source parameters. Our findings confirmed the existence of different distinct sources, beneath the brittle-ductile transition zone, which have been intermittently active during the last three decades. Moreover, we interpreted our results in the light of existing seismic tomography studies. Concerning the SC dome, we highlighted the role of hydrothermal fluids as the driving force behind the 1977-1983 uplift; since 1983-1993 the deformation source transformed into a deeper one with a higher magmatic component. Furthermore, our results support the magmatic nature of the deformation source beneath ML dome for the overall investigated period. Finally, the uplift at NCR is interpreted as magma accumulation, while its subsidence could either be the result of fluids migration outside the caldera or the gravitational adjustment of the source from a spherical to a sill-like geometry.

  16. Magma and fluid migration at Yellowstone Caldera in the last three decades inferred from InSAR, leveling, and gravity measurements

    NASA Astrophysics Data System (ADS)

    Tizzani, P.; Battaglia, M.; Castaldo, R.; Pepe, A.; Zeni, G.; Lanari, R.

    2015-04-01

    We studied the Yellowstone caldera geological unrest between 1977 and 2010 by investigating temporal changes in differential Interferometric Synthetic Aperture Radar (InSAR), precise spirit leveling and gravity measurements. The analysis of the 1992-2010 displacement time series, retrieved by applying the SBAS InSAR technique, allowed the identification of three areas of deformation: (i) the Mallard Lake (ML) and Sour Creek (SC) resurgent domes, (ii) a region close to the Northern Caldera Rim (NCR), and (iii) the eastern Snake River Plain (SRP). While the eastern SRP shows a signal related to tectonic deformation, the other two regions are influenced by the caldera unrest. We removed the tectonic signal from the InSAR displacements, and we modeled the InSAR, leveling, and gravity measurements to retrieve the best fitting source parameters. Our findings confirmed the existence of different distinct sources, beneath the brittle-ductile transition zone, which have been intermittently active during the last three decades. Moreover, we interpreted our results in the light of existing seismic tomography studies. Concerning the SC dome, we highlighted the role of hydrothermal fluids as the driving force behind the 1977-1983 uplift; since 1983-1993 the deformation source transformed into a deeper one with a higher magmatic component. Furthermore, our results support the magmatic nature of the deformation source beneath ML dome for the overall investigated period. Finally, the uplift at NCR is interpreted as magma accumulation, while its subsidence could either be the result of fluids migration outside the caldera or the gravitational adjustment of the source from a spherical to a sill-like geometry.

  17. Effect of petrophysical properties and deformation on vertical zoning of metasomatic rocks in U-bearing volcanic structures: A case of the Strel'tsovka caldera, Transbaikal region

    NASA Astrophysics Data System (ADS)

    Petrov, V. A.; Andreeva, O. V.; Poluektov, V. V.

    2014-03-01

    The development of vertical zoning of wall-rock metasomatic alteration is considered with the Mesozoic Strel'tsovka caldera as an example. This caldera hosts Russia's largest uranium ore field. Metasomatic rocks with the participation of various phyllosilicates, carbonates, albite, and zeolites are widespread in the ore field. In the eastern block of the caldera, where the main uranium reserves are accommodated, hydromica metasomatic alteration gives way to beresitization with depth. Argillic alteration, which is typical of the western block, is replaced with hydromica and beresite alteration only at a significant depth. Postore argillic alteration is superposed on beresitized rocks in the lower part of the section. Two styles of vertical metasomatic zoning are caused by different modes of deformation in the western and eastern parts of the caldera. Variations of the most important petrophysical properties of host rocks—density, apparent porosity, velocities of P- and S-waves, dynamic Young's modulus, and Poisson coefficient—have been determined by sonic testing of samples taken from different depths. It is suggested that downward migration of the brittle-ductile transition zone could have been a factor controlling facies diversity of metasomatic rocks. Such a migration was caused by a new phase of tectonothermal impact accompanied by an increase in the strain rate or by emplacement of a new portion of heated fluid. Transient subsidence of the brittle-ductile boundary increases the depth of the hydrodynamically open zone related to the Earth's surface and accelerates percolation of cold meteoric water to a greater depth. As a result, the temperature of the hydrothermal solution falls down, increasing the vertical extent of argillic alteration. High-grade uranium mineralization is also localized more deeply than elsewhere.

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

    USGS Publications Warehouse

    Kellogg, K.S.

    1985-01-01

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

  19. Surveying Dead Trees and CO2-Induced Stressed Trees Using AVIRIS in the Long Valley Caldera

    NASA Technical Reports Server (NTRS)

    deJong, Steven M.

    1996-01-01

    Since 1980 the Long Valley Caldera in the eastern Sierra Nevada (California) has shown signs of renewed volcanic activity. Frequent earthquakes, a re-inflation of the caldera, hydrothermal activity and gas emissions are the outer symptoms of this renewed activity. In 1990 and 1991 several areas of dying trees were found around Mammoth Mountain. The cause of the die off of the trees was first sought in the persistent drought in the preceding years. However, the trees died regardless of age and species. Farrar et al. (1995) started a soil-gas survey in 1994 in the dead-tree areas and found carbon dioxide concentrations ranging from 30 to 96% at soil depths between 30 and 60 cm. CO2 concentrations in the atmosphere are usually around 0.03% and in the soil profile CO2 levels do commonly not exceed 4 to 5%. Although not much is known about the effect of high levels of carbon dioxide in the soil profile on roots, it is most likely that the trees are dying due to oxygen deprivation: the CO2 drives the oxygen out of the soil. So far, four sites of dead trees have been mapped around Mammoth Mountain. The two largest dying trees sites are located near Horseshoe Lake and near Mammoth Mountain Main Lodge covering approximately an area of 10 and 8 ha respectively. Analysis of the gas composition regarding the He-3/He-4 ratio and the percentage biogenic carbon reveals the source of the gas: the magma body beneath the Long Valley Caldera. Until recently it was not known that volcanoes release abundant carbon dioxide from their flanks as diffuse soil emanations. As a result of the magma gas emission around Mammoth Mountain there is an excellent sequence of dead trees, stressed trees, healthy trees and bare soil surfaces. This research site provides excellent opportunities to: (1) Study the capabilities of imaging spectrometry to map stressed (and dead) pine and fir species; (2) Study methods to separate the vivid vegetation, stressed vegetation and dead vegetation from the soil

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

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

    USGS Publications Warehouse

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

    1997-01-01

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

  2. Imaging the magmatic and hydrothermal systems of Long Valley Caldera, California with magnetotellurics

    NASA Astrophysics Data System (ADS)

    Peacock, J.; Mangan, M.; McPhee, D.; Ponce, D. A.

    2015-12-01

    Long Valley Caldera (LVC) in Eastern California contains active hydrothermal systems, areas of episodic seismicity, and areas of elevated gas emissions, all of which are related to a deeper magmatic system that is not well characterized. To better image the Long Valley magmatic system, 60 full-tensor broadband magnetotelluric (MT) stations were collected in LVC and modeled in three-dimensions to constrain the subsurface electrical resistivity structure down to 30 km. Three conductive zones are imaged in the preferred resistivity model. The most prominent conductive zone (<7 Ohm-m) is located 5 km beneath the resurgent dome (near the center of Long Valley Caldera), where it elongates in a north-south direction, and has westward connection to the surface close to well 44-16 near Deer Mountan. This conductive zone is interpreted to be an accumulation zone of hydrothermal fluids originating from a deeper magmatic source. The shape of the conductive body suggests that the fluids pool under the resurgent dome and migrate westward, upwelling just south of well 44-16 to feed the near surface geothermal system. A second conductive zone (<10 Ohm-m) is 4 km southeast of the resurgent dome and 5 km deep and coincident with the seismic swarm of 2014. This is another zone of fluid accumulation, where the source could be the fluid accumulation zone to the west or an independent deeper source. The third conductive anomaly (<10 Ohm-m) is a few kilometers south of the resurgent dome below a depth of 15 km, and collocated with a low p- and s-wave velocity zone, and directly beneath a GPS inflation area, all of which advocate for a magma mush zone of as much as 30% interstitial melt. The preferred resistivity model suggests an accumulation of hydrothermal fluids 5 km below the resurgent dome that originates from a deeper magmatic source at 15 km depth.

  3. Lithium in the McDermitt caldera, Nevada and Oregon

    USGS Publications Warehouse

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

    1978-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2001-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  7. Cu-Ni-PGE fertility of the Yoko-Dovyren layered massif (northern Transbaikalia, Russia): thermodynamic modeling of sulfide compositions in low mineralized dunite based on quantitative sulfide mineralogy

    NASA Astrophysics Data System (ADS)

    Ariskin, Alexey A.; Kislov, Evgeny V.; Danyushevsky, Leonid V.; Nikolaev, Georgy S.; Fiorentini, Marco L.; Gilbert, Sarah; Goemann, Karsten; Malyshev, Alexey

    2016-06-01

    The geology and major types of sulfide mineralization in the Yoko-Dovyren layered massif (northern Transbaikalia, Russia) are presented. This study focuses on the structure, mineralogy, and geochemistry of poorly mineralized plagiodunite and dunite in the lower part of the intrusion. Assuming these rocks contain key information on the timing of sulfide immiscibility in the original cumulate pile, we apply a novel approach which combines estimates of the average sulfide compositions in each particular rock with thermodynamic modeling of the geochemistry of the original sulfide liquid. To approach the goal, an updated sulfide version of the COMAGMAT-5 model was used. Results of simulations of sulfide immiscibility in initially S-undersaturated olivine cumulates demonstrate a strong effect of the decreasing fraction of the silicate melt, due to crystallization of silicate and oxide minerals, on the composition of the intercumulus sulfide liquid. Comparison of the observed and modeled sulfide compositions indicates that the proposed modeling reproduces well the average concentrations of Cu, Cd, Ag, and Pd in natural sulfides. This suggests the sulfide control on the distribution of these elements in the rocks. Conversely, data for Pt and Au suggest that a significant portion of these elements could present in a native form, thus depleting the intercumulus sulfide melt at an early stage of crystallization.

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

    SciTech Connect

    Goff, F.

    1983-03-01

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

  9. Investigations of volcanic and earthquake-related deformation: Observations and models from Long Valley Caldera, northwestern Peloponnese, and northwestern Costa Rica

    NASA Astrophysics Data System (ADS)

    Feng, Lujia

    2011-12-01

    The advent of Global Positioning System (GPS) has revolutionized geodesy with high accuracy, fast speed, simple use, and low cost. This dissertation investigates three topics on volcano and earthquake-related deformation using GPS measurements and models to demonstrate the power of the new generation of geodetic methods. The three topics include the 2002-2003 continued episodic inflation at Long Valley Caldera in eastern California, the coseismic and postseismic response of the energetic 2008 MW 6.4 Achaia-Elia Earthquake in northwest Peloponnese, Greece, and the interseismic megathrust coupling and forearc sliver transport near the Nicoya Peninsula in northwest Costa Rica.

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

    NASA Astrophysics Data System (ADS)

    Shitashima, K.; Maeda, Y.

    2002-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Long, Carl L.

    1985-11-01

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

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

    SciTech Connect

    Williams, S.N.

    1983-01-01

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

  13. Historical activity at Campi Flegrei caldera, southern Italy

    USGS Publications Warehouse

    Dvorak, J.; Gasparini, P.

    1990-01-01

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

  14. On the formation of calderas during ignimbrite eruptions

    USGS Publications Warehouse

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

    1984-01-01

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

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

    SciTech Connect

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

    1986-12-01

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

  16. The earliest low and high δ18O caldera-forming eruptions of the Yellowstone plume: Implications for the 30-40 Ma Oregon calderas and speculations on plume-triggered delaminations

    NASA Astrophysics Data System (ADS)

    Seligman, Angela; Bindeman, Ilya; McClaughry, Jason; Stern, Richard; Fisher, Chris

    2014-11-01

    We present new isotopic and trace element data for four eruptive centers in Oregon: Wildcat Mountain (40 Ma), Crooked River (32-28 Ma), Tower Mountain (32 Ma), and Mohawk River (32 Ma). The first three calderas are located too far east to be sourced through renewed subduction of the Farallon slab following accretion of the Yellowstone-produced Siletzia terrane at ~50 Ma. Basalts of the three eastern eruptive centers yield high Nb/Yb and Th/Yb ratios, indicating an enriched sublithospheric mantle source, while Mohawk River yields trace element and isotopic (δ18O and ɛHf) values that correlate with its location above a subduction zone. The voluminous rhyolitic tuffs and lavas of Crooked River (41 x 27 km) have δ18Ozircon values that include seven low δ18Ozircon units (1.8-4.5 ‰), one high δ18Ozircon unit (7.4-8.8 ‰), and two units with heterogeneous zircons (2.0-9.0 ‰), similar to younger Yellowstone-Snake River Plain rhyolites. In order to produce these low δ18O values, a large heat source, widespread hydrothermal circulation, and repeated remelting are all required. In contrast, Wildcat Mountain and Tower Mountain rocks yield high δ18Ozircon values (6.4-7.9 ‰) and normal to low ɛHfi values (5.2-12.6), indicating crustal melting of high-δ18O supracrustal rocks. We propose that these calderas were produced by the first appearance of the Yellowstone plume east of the Cascadia subduction zone, which is supported by plate reconstructions that put the Yellowstone plume under Crooked River at 32-28 Ma. Given the eastern location of these calderas along the suture of the accreted Siletzia terrane and North America, we suggest that the Yellowstone hotspot is directly responsible for magmatism at Crooked River, and for plume-assisted delamination of portions of the edge of the Blue Mountains that produced the Tower Mountain magmas, while the older Wildcat Mountain magmas are related to suture zone instabilities that were created following accretion of the

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

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

    USGS Publications Warehouse

    Bacon, Charles R.

    2008-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-01-01

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

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

    USGS Publications Warehouse

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

    2011-01-01

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

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

    SciTech Connect

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

    1992-01-01

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

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

    PubMed Central

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

    2016-01-01

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

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

    USGS Publications Warehouse

    Kwoun, Oh-Ig; Lu, Zhiming

    2004-01-01

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

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

    PubMed

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  8. Deformation of the Long Valley Caldera, California: Inferences from measurements from 1988 to 2001

    USGS Publications Warehouse

    Langbein, J.O.

    2003-01-01

    Two periods of volcanic unrest occurred between 1989 and 1998 in the Long Valley Caldera, eastern California. Numerous earthquakes were recorded, and these periods of unrest were documented with high-precision geodetic measurements. The first round of unrest started rapidly in late 1989 and slowly decreased in rate through the early 1990s. For this interval there are both leveling and two-color electronic distance meter (EDM) measurements. The second round of unrest started slowly in mid-1997, climaxed in late 1997, and rapidly returned to quiescence by mid-1998. Deformation was recorded by both the two-color EDM and continuous GPS. Both episodes require inflation at 6-7 km beneath the resurgent dome, and both episodes had roughly 0.1 m extension across the resurgent dome. In addition, the data presented here suggest that there is a deeper, 10-20 km, inflation source beneath the south moat of the caldera. For both episodes, the better-resolved inflation beneath the resurgent dome is a near-vertical, prolate spheroid rather than an isotropic source, which suggests that magma came up through vertical cracks. However, the modeling suggests that the location changed with the depth from 6.0 to 6.7 km for the later episode. In contrast to the earlier episode, the 1997-1998 episode has additional deformation in the south moat, where the simplest model is that of a right-lateral slip on a steeply dipping plane that is defined by the location of earthquakes in the south moat. Models of the time-dependent behavior suggest that slip on this fault occurred from late November through December 1997, corresponding to the time of greatest moment release by the earthquake swarm in the south moat. Confounding the interpretation of these data is an active geothermal field near the center of the EDM network and adjacent to the south moat and resurgent dome. Additional modeling of leveling and EDM data within the geothermal field during a period of low rate of inflation of the dome

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

    NASA Astrophysics Data System (ADS)

    Green, J.

    2007-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2003-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  13. Insight into vent opening probability in volcanic calderas

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  14. Thermal history of caldera-forming magmatic systems

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

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

    USGS Publications Warehouse

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

    1985-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Jousset, P. G.; Rohmer, J.

    2012-12-01

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

  18. Dilational processes accompanying earthquakes in the Long Valley Caldera

    USGS Publications Warehouse

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

    2000-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

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

    NASA Astrophysics Data System (ADS)

    Browning, John; Gudmundsson, Agust; Thordarson, Thorvaldur

    2015-04-01

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

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

    SciTech Connect

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

    1986-02-10

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  3. 3D modelling of the Tejeda Caldera cone-sheet swarm, Gran Canaria, Canary Islands, Spain

    NASA Astrophysics Data System (ADS)

    Samrock, Lisa K.; Jensen, Max J.; Burchardt, Steffi; Troll, Valentin R.; Mattsson, Tobias; Geiger, Harri

    2015-04-01

    . 2011, and references therein), and we discuss the implications of this architecture for the feeding system of the Tejeda volcano and the associated temporal variations of cone-sheet emplacement. References: Burchardt, S., Tanner, D.C., Troll, V.R., Krumbholz, M., Gustafsson, L.E. (2011) Three-dimensional geometry of concentric intrusive sheet swarms in the Geitafell and the Dyrfjöll volcanoes, eastern Iceland. Geochemistry, Geophysics, Geosystems 12(7): Q0AB09. Burchardt, S., Troll, V.R., Mathieu, L., Emeleus, H.C., Donaldson, C.H. (2013) Ardnamruchan 3D cone-sheet architecture explained by a single elongate magma chamber. Scientific Reports 3:2891. Schirnick, C. (1996) Formation of an intracaldera cone sheet dike swarm (Tejeda Caldera, Gran Canaria) (Dissertation). Christian-Albrechts-Universität, Kiel, Germany. Schirnick, C., van den Bogaard, P., Schmincke, H.-U. (1999) Cone-sheet formation and intrusive growth of an oceanic island - The Miocene Tejeda complex on Gran Canaria (Canary Islands). Geology, 27: 207-210.

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

    SciTech Connect

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

    1993-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

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

    SciTech Connect

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

    1993-04-01

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

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

    USGS Publications Warehouse

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

    2015-01-01

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

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

    USGS Publications Warehouse

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

    2015-01-01

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

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

    SciTech Connect

    Chesner, C.A.

    1985-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1984-03-01

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

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

    SciTech Connect

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

    1987-04-01

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

  12. A New Model for Episodic Caldera Deformation at Yellowstone

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  13. The 1996-2009 borehole dilatometer installations, operation, and maintenance at sites in Long Valley Caldera, CA

    USGS Publications Warehouse

    Myren, Glenn; Johnston, Malcolm; Mueller, Robert

    2011-01-01

    High seismicity levels with accelerating uplift (under the resurgent dome) in Long Valley caldera in the eastern Sierra Nevada from 1989 to 1997, triggered upgrades to dilational strainmeters and other instrumentation installed in the early 1980's following a series of magnitude 6 earthquakes. This included two additional high-resolution borehole strainmeters and replacement of the failed strainmeter at Devil's Postpile. The purpose of the borehole-monitoring network is to monitor crustal deformation and other geophysical parameters associated with volcanic intrusions and earthquakes in the Long Valley Caldera. Additional instrumentation was added at these sites to improve the capability of providing continuous monitoring of the magma source under the resurgent dome. Sites were selected in regions of hard crystalline rock, where the expected signals from magmatic activity were calculated to be a maximum and the probability of an earthquake of magnitude 4 or greater is large. For the most part, the dilatometers were installed near existing arrays of surface tiltmeters, seismometers, level line, and GPS arrays. At each site, attempts are made to separate tectonic and volcanic signals from known noise sources in each instrument type. Each of these sites was planned to be a multi-parameter monitoring site, which included measurements of 3-component seismic velocity and acceleration, borehole strain, tilt, pore pressure and magnetic field. Using seismicity, geophysical knowledge, geologic and topographic maps, and geologists recommendations, lists of preliminary sites were chosen. Additional requirements were access, and telemetry constraints. When the final site choice was made, a permit was obtained from the U.S. Forest Service. Following this selection process, two new borehole sites were installed on the north and south side of the Long Valley Caldera in June of 1999. One site was located near Big Spring Campground to the east of Crestview. The second site was

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

    SciTech Connect

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

    1988-01-01

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

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

    SciTech Connect

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

    1985-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

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

    USGS Publications Warehouse

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

    1991-01-01

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

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

    SciTech Connect

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

    1992-02-01

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

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

    SciTech Connect

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

    1983-01-01

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

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

    SciTech Connect

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

    1982-04-10

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

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

    NASA Astrophysics Data System (ADS)

    Schmitt, A. K.

    2004-12-01

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

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

    SciTech Connect

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

    1985-01-01

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

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

    SciTech Connect

    Reimer, G.M.

    1986-11-10

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

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

    USGS Publications Warehouse

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

    1984-01-01

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

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

    USGS Publications Warehouse

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

    2007-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Hildyard, R.; Kokelaar, P.

    2006-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  9. Non-double-couple microearthquakes at Long Valley caldera, California, provide evidence for hydraulic fracturing

    USGS Publications Warehouse

    Foulger, G.R.; Julian, B.R.; Hill, D.P.; Pitt, A.M.; Malin, P.E.; Shalev, E.

    2004-01-01

    Most of 26 small (0.4??? M ???3.1) microearthquakes at Long Valley caldera in mid-1997, analyzed using data from a dense temporary network of 69 digital three-component seismometers, have significantly non-double-couple focal mechanisms, inconsistent with simple shear faulting. We determined their mechanisms by inverting P - and S -wave polarities and amplitude ratios using linear-programming methods, and tracing rays through a three-dimensional Earth model derived using tomography. More than 80% of the mechanisms have positive (volume increase) isotropic components and most have compensated linear-vector dipole components with outward-directed major dipoles. The simplest interpretation of these mechanisms is combined shear and extensional faulting with a volume-compensating process, such as rapid flow of water, steam, or CO2 into opening tensile cracks. Source orientations of earthquakes in the south moat suggest extensional faulting on ESE-striking subvertical planes, an orientation consistent with planes defined by earthquake hypocenters. The focal mechanisms show that clearly defined hypocentral planes in different locations result from different source processes. One such plane in the eastern south moat is consistent with extensional faulting, while one near Casa Diablo Hot Springs reflects en echelon right-lateral shear faulting. Source orientations at Mammoth Mountain vary systematically with location, indicating that the volcano influences the local stress field. Events in a 'spasmodic burst' at Mammoth Mountain have practically identical mechanisms that indicate nearly pure compensated tensile failure and high fluid mobility. Five earthquakes had mechanisms involving small volume decreases, but these may not be significant. No mechanisms have volumetric moment fractions larger than that of a force dipole, but the reason for this fact is unknown. Published by Elsevier B.V.

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

    NASA Astrophysics Data System (ADS)

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

    1995-08-01

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

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

    USGS Publications Warehouse

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

    1993-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1993-03-01

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

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

    PubMed

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

    2014-10-31

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

  14. Caldera collapse in the Galápagos Islands, 1968

    USGS Publications Warehouse

    Simkin, T.; Howard, K.A.

    1970-01-01

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

  15. Localized Temporal Gravity Investigations at Long Valley Caldera

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Ferreira, Teresa; Oskarsson, Niels

    1999-09-01

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

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

    SciTech Connect

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

    1983-12-01

    This field trip guide has been compiled from extensive field trips led at Los Alamos National Laboratory during the past six years. The original version of this guide was designed to augment a workshop on the Valles Caldera for the Continental Scientific Drilling Program (CSDP). This workshop was held at Los Alamos, New Mexico, 5-7 October 1982. More stops were added to this guide to display the volcanic and geothermal features at the Valles Caldera. The trip covers about 90 miles (one way) and takes two days to complete; however, those who wish to compress the trip into one day are advised to use the designated stops listed in the Introduction. Valles Caldera and vicinity comprise both one of the most exciting geothermal areas in the United States and one of the best preserved Quaternary caldera complexes in the world.

  18. Maars to calderas: end-members on a spectrum of explosive volcanic depressions

    NASA Astrophysics Data System (ADS)

    Palladino, Danilo; Valentine, Greg; Sottili, Gianluca; Taddeucci, Jacopo

    2015-07-01

    We discuss maar-diatremes and calderas as end-members on a spectrum of negative volcanic landforms (depressions) produced by explosive eruptions (note - we focus on calderas formed during explosive eruptions, recognizing that some caldera types are not related to such activity). The former are dominated by ejection of material during numerous discrete phreatomagmatic explosions, brecciation, and subsidence of diatreme fill, while the latter are dominated by subsidence over a partly evacuated magma chamber during sustained, magmatic volatile-driven discharge. Many examples share characteristics of both, including landforms that are identified as maars but preserve deposits from non-phreatomagmatic explosive activity, and ambiguous structures that appear to be coalesced maars but that also produced sustained explosive eruptions with likely magma reservoir subsidence. A convergence of research directions on issues related to magma-water interaction and shallow reservoir mechanics is an important avenue toward developing a unified picture of the maar-diatreme-caldera spectrum.

  19. Temporal gravity and height changes of the Yellowstone caldera, 1977 - 1994

    USGS Publications Warehouse

    Arnet, F.; Kahle, H.-G.; Klingele, E.; Smith, R.B.; Meertens, Charles M.; Dzurisin, D.

    1997-01-01

    This paper describes the longest record of gravity measurements in the area of the Yellowstone caldera, Wyoming. The temporal gravity changes, at the ??12 ??Gal (10-8 ms-2) precision level, are compared with changes in heights from leveling and GPS. The gravity field decreased across the caldera from 1977 to 1983 during the uplift and attained a maximum decrease of up to -60 ?? 12 ??Gal along the Caldera axis. The gravity field then reversed polarity to increasing values, of up to 60 ?? 12 ??Gal between 1986 and 1993. The ratio between height and gravity changes varied during the entire time, but converged over the latter period following the free-air gravity gradient. General ground deformation deduced from leveling showed caldera-wide uplift of ???15 mm/a during the period of gravity decrease, then from leveling and GPS, subsidence of ??? 25 mm/a during the gravity increase. Copyright 1997 by the American Geophysical Union.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    Calderas are among the most spectacular, dangerous and active volcanoes on the Earth. Seismicity, surface deformation and degassing are commonly observed at many calderas, denoting unrest. The unrest can be intermittent, lasting for months to years, or persistent, over decades to centuries. Although most caldera unrest episodes do not lead to an eruption, the possibility of an impending eruption warrants detailed monitoring and study. To better understand caldera unrest and forecast any possible eruption, we built a database from all available publications and reports on the recent unrest episodes at calderas in the world and then carried out a statistical analysis. We focused on the unrest episodes from the last 25 years, being complementary to Newhall and Dzurisin (1988). We considered the monitoring data from 42 unresting calderas, totaling 166 unrest episodes, of which 110 eruptive and 56 failed (unrest without eruption). Attention has been given to unrest duration, seismicity, deformation and gas variations, along with their possible interaction. First, we analyzed the unrest duration through the Kolmogorov-Smirnov two-sample test to find any significant variation between different classes of unrest: unrest duration of the eruptive vs failed unrest episodes, unrest duration at mafic vs felsic calderas, unrest duration at mafic calderas with eruptive vs failed unrest and unrest duration at felsic calderas with eruptive vs failed unrest. Subsequently, we analyzed the inter-event time between two eruptions, searching any relationship between time and the VEI of the preceding or following eruption, according to time and size predictable models. We then used the Fisher Discriminant Analysis to find any linear combination of features which maximizes the separation between two (or more) classes of objects. Finally, we used the binary decision tree to classify the unrest through several input variables. The statistical analysis of the database confirms that all

  1. Inner structure of La Pacana Caldera (Central Andes, Chile) using gravimetry data

    NASA Astrophysics Data System (ADS)

    Delgado, F.; Pavez Alvarado, A.

    2010-12-01

    La Pacana caldera is located in the Altiplano Puna Volcanic Complex in the Chilean Andes and is a 60 by 35 km NS elongated body. It is one of the largest resurgent calderas in the world, comparable to the supervolcanoes of La Garita, Toba and Yellowstone. It has been described as being formed 4 My ago during an eruption with a VEI of 8,7, which makes it the fifth largest eruption ever in the geological record. This eruption was followed by a subsidence of 0,9 up to 2 km according to previous studies. Different models for this caldera formation were proposed but with a lack of sub surface information. We hence carried a gravimetry study to investigate its inner structure and to better off constrains on these proposed models. The residual Bouguer anomaly (figure 1) is asymetric with multiple high and low gravity, with an average amplitude of -14 mGal, which reaches -24 mGal near the resurgent dome, interpreted as the deepest part of the caldera. Based on this, we propose that the main collapse zone is not related to the topographic border, but to resurgent dome edges. This is compatible with a piecemeal collapse geometry. There are several gravity highs below strato-volcanoes and postcaldera domes within La Pacana caldera, which are interpreted as magmatic reservoirs. Our data combined with previous geological studies allowed us to separate La Pacana in two nested calderas and to trace its NNW, N and NNE borders, previously unrecognized features. The 2,5 D forward modelling cross sections constrained with geological data showed that the maximum caldera depth is 1,3 km with a minimum of 0,6 km in its southern part. We finally suggest that caldera rims are surrounded by paleozoic basement uplifted by thrust fault systems. La Pacana's residual Bouguer anomaly is small (1/2) when compared with the ones associated to other supervolcanoes (Toba, Yellowstone). La Pacana caldera constitutes then an anomaly for supervolcanoes internal structure due to its interpreted low

  2. Recent geologic history of lake Atitlán, a caldera lake in western Guatemala

    USGS Publications Warehouse

    Newhall, C.G.; Paull, C.K.; Bradbury, J.P.; Higuera-Gundy, A.; Poppe, L.J.; Self, S.; Bonar, Sharpless N.; Ziagos, J.

    1987-01-01

    Heat-flow measurements inside and just outside the caldera are high (290 and 230 mW m−2), suggesting hydrothermal convection and a shallow heat source. High heat flow, a geological record of post-caldera silicic eruptions, and unexplained fluctuations of lake level (episodic tumescence ofthe lake floor?) suggest that magma remains beneath Lake Atitlán and that future eruptions are possible.

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

    NASA Astrophysics Data System (ADS)

    Corbi, Fabio; Rivalta, Eleonora; Pinel, Virginie; Maccaferri, Francesco; Bagnardi, Marco; Acocella, Valerio

    2016-04-01

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

  4. The Denham Caldera on Raoul Volcano: dacitic volcanism in the Tonga Kermadec arc

    NASA Astrophysics Data System (ADS)

    Worthington, Tim J.; Gregory, Murray R.; Bondarenko, Vladislav

    1999-05-01

    Denham Caldera, on Raoul Volcano in the Tonga-Kermadec arc, is a simple collapse structure. It is 6.5×4 km 2 across, >0.3 km deep, represents an erupted magma volume of 8-16 km 3, and is considerably larger than previously estimated. Caldera formation was contemporaneous with an eruption of homogeneous dacitic magma at 2.2 ka. Tephra from this event is preserved as a pumice fall and pyroclastic flow sequence up to 120 m thick on Raoul Island. Offshore, this sequence forms a submarine deposit diminishing in thickness from 120 m near the northern caldera rim to 80 m at a distance of 3.5 km, where it rests upon an erosional planation surface of 17-20 ka age incised into older volcaniclastic rocks. Both the caldera volume and ejecta distribution of the 2.2 ka eruption are comparable to the caldera volume and ejecta distribution of the 1883 Krakatau eruption. Resurgent volcanism has built at least six submarine pyroclastic cones along a north-northeast trending lineament crossing Denham Caldera. Redistribution of pumiceous dacite from these cones, including ephemeral islands that emerged during the 1814 and 1870 eruptions, has contributed to recent shoaling in Denham Bay. A smaller eruption occurred in 1964-65, and hydrothermal activity persists at several sites along the lineament. Voluminous felsic volcanism at intra-oceanic arcs is usually associated with crustal extension, and was unexpected in the Tonga-Kermadec arc. However, because the tectonic fabric within the active back-arc Havre Trough is oblique to the Kermadec arc, rifts within the trough apparently propagate to the volcanic front and transfer extensional strain to the arc, thereby promoting the ascent of felsic magma. The orientation of Denham Caldera, as well as that of Macauley Caldera 110 km further south, thus reflect the stress field of the Havre Trough and not the predominant field of the arc.

  5. Tephrostratigraphy and eruptive history of post-caldera stage of Toya Volcano, Hokkaido, northern Japan

    NASA Astrophysics Data System (ADS)

    Miyabuchi, Yasuo; Okuno, Mitsuru; Torii, Masayuki; Yoshimoto, Mitsuhiro; Kobayashi, Tetsuo

    2014-06-01

    A detailed tephrostratigraphy of Toya Volcano in Hokkaido, northern Japan has been constructed to evaluate the post-caldera eruptive history of the volcano. The tephrostratigraphic sequence preserved above the Toya ignimbrite reaches a total thickness of 8 m southeast of the caldera. After the caldera formation (115-112 ka), there was a long quiescent period of more than 60 ka years. The first post-caldera activity started with Nakajima Osarugawa pumice-fall deposit (Nj-Os) inside the caldera at 48 ka. Eruptive activity at Nakajima Volcano resumed at 30 ka with Nakajima Sekinai pumice-fall deposit (Nj-Sk), and was followed by continuous emission of fine ash including abundant accretionary lapilli. Soon after the Nakajima pyroclastic eruption Usu Volcano began its activity with discharges of basaltic ash and scoria (forming the Usu prehistoric tephra) and extrusion of homogeneous lavas namely Usu somma lava, resulting in the formation of the initial volcanic edifice. Subsequently, a large sector collapse occurred between 30 and 20 ka that emplaced the Zenkoji debris avalanche with little break after the formation of the initial Usu volcanic edifice. After the sector collapse, the volcano remained dormant for about 20-30 ka years. Eruptive activity at Usu Volcano resumed in 1663 AD with the most explosive plinian eruption in the post-caldera stage of Toya Volcano. Since then, seven eruptions have been recorded in 1769, 1822, 1853, 1910, 1943-1945, 1977-1978 and 2000 at multi-decadal interval. Total tephra volume during the post-caldera stage is estimated at about 0.9 km3 (dense rock equivalent: DRE), whereas total lava volume is calculated at about 2.3 km3. Therefore, the average magma discharge rate during the post-caldera stage of Toya Volcano is estimated at about 0.03 km3/ky, which is one or two order smaller than those of other Quaternary volcanoes in Japan.

  6. Proceedings of the second workshop on hydrologic and geochemical monitoring in the Long Valley Caldera

    SciTech Connect

    Sorey, M.L.; Farrar, C.D.; Wollenberg, H.A.

    1986-12-01

    A workshop was held to review the results of hydrologic and geochemical monitoring and scientific drilling in the Long Valley caldera. Such monitoring is being done to detect changes in the hydrothermal system induced by ongoing magmatic and techonic processes. Data from a 2400-ft deep core hole completed in June 1986 were presented at the 1986 workshop and participants discussed the need and rationale for siting locations for future scientific drilling in the caldera.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  8. Three-dimensional gravity modeling of the geologic structure of Long Valley caldera

    SciTech Connect

    Carle, S.F.

    1988-11-10

    A 48-mGal gravity low coincides with Long Valley caldera and is mainly attributed to low-density caldera fill. Gravity measurements by Unocal Geothermal have been integrated with U.S. Geological Survey data, vastly improving gravity station coverage throughout the caldera. A strong regional gravity trend is mainly attributed to isostasy. A ''best fitting'' (based on regional control of basement densities) Airy-Heiskanen isostatic model was used for the regional correction. A three-dimensional, multiple-unit gravity modeling program with iterative capabilities was developed to model the residual gravity. The density structure of Long Valley caldera and vicinity was modeled with 22 discrete density units, most of which were based on geologic units. Information from drill hole lithologies, surface geology, and structural geology interpretations constrain the model. Some important points revealed by the three-dimensional gravity modeling are that (1) the volume of ejected magma associated with the Bishop Tuff eruption is greater than previously thought, (2) the caldera structure is strongly influenced by precaldera topography and the extensions of major, active faults, (3) the main west ring fracture is coincident with the Inyo Domes--Mono Craters fracture system, (4) a relatively low-density region probably underlies the caldera, and (5) a silicic magma chamber may underlie Devils Postpile. copyright American Geophysical Union 1988

  9. Catastrophic isotopic modification of rhyolitic magma at times of caldera subsidence, Yellowstone plateau volcanic field.

    USGS Publications Warehouse

    Hildreth, W.; Christiansen, R.L.; O'Neil, J.R.

    1984-01-01

    This Wyoming volcanic field has undergone repeated eruption of rhyolitic magma strongly depleted in 18O. Large calderas subsided 2.0, 1.3 and 0.6 m.y. ago on eruption of ash-flow sheets. More than 60 other rhyolite lavas and tuffs permit reconstruction of the long-term chemical and isotopic evolution of the silicic system. Narrow delta 18O ranges in the ash-flow sheets contrast with wide delta 18O variation in post-caldera lavas. The earliest post-collapse lavas are 3-6per mille lighter than the preceding ash-flow sheets. The 18O depletions were short-lived events that immediately followed caldera subsidence and sequences of post-caldera lavas record partial recovery toward pre-caldera delta 18O values. Contemporaneous extra-caldera rhyolites show no effects of the repeated depletions. Although some contamination by foundering roof rocks seems to be required, water was probably the predominant contaminant.-W.H.B.

  10. Exploration of Geothermal Natural Resources from Menengai Caldera at Naruku, Kenya

    NASA Astrophysics Data System (ADS)

    Patlan, E.; Wamalwa, A.; Thompson, L. E.; Kaip, G.; Velasco, A. A.

    2011-12-01

    The Menengai Caldera, a large, dormant volcano, lies near the city of Naruku, Kenya (0.20°S, 36.07°E) and presents a significant natural geothermal energy resource that will benefit local communities. Kenya continues to explore and exploit its only major energy resource: geothermal energy. The Geothermal Development Company (GDC) of Kenya and University of Texas at El Paso (UTEP) have initially deployed seven seismic stations to address the volcanic hazards and associated processes that occurs through the analysis of data collection from seismic sensors that record ground motion. Seven more sensors are planned to be deployed in Aug. 2011. In general, the internal state and activity of the caldera is an important component to the understanding of porosity of the fault system, which is derived from the magma movement of the hot spot, and for the exploitation of geothermal energy. We analyze data from March to May 2011 to investigate the role of earthquakes and faults in controlling the caldera processes, and we find 15 events occurred within the caldera. We will utilize the double difference earthquake location algorithm (HypoDD) to analyze the local events in order to find active faulting of the caldera and the possible location of the magma chamber. For future work, we will combine the exiting data with the new seismic station to image the location of the caldera magma chamber.

  11. The Silent Canyon Caldera Complex--A three-dimensional model based on drill-hole stratigraphy and gravity inversion

    SciTech Connect

    Sawyer, D.A.; Anderson, M.L.; Hildenbrand, T.G; McKee, E.H.; Rowley, P.R.

    1999-12-13

    The structural framework of Pahute Mesa, nevada, is dominated by the Silent Canyon caldera complex, a buried, multiple collapse caldera complex. Using the boundary surface between low density Tertiary volcanogenic rocks and denser granitic and weakly metamorphosed sedimentary rocks (basement) as the outer faults surfaces for the modeled collapse caldera complex, it is postulated that the caldera complex collapsed on steeply dipping arcuate faults two, possibly three, times following eruption of at least two major ash-flow tuffs. The caldera and most if its eruptive products are now deeply buried below the surface of Pahute Mesa. Relatively low-density rocks in the caldera complex produce one of the largest gravity lows in the western conterminous United States.

  12. Relation of mercury, uranium, and lithium deposits to the McDermitt caldera complex, Nevada-Oregon

    USGS Publications Warehouse

    Rytuba, James J.; Glanzman, Richard K.

    1979-01-01

    The McDermitt caldera complex, located along the Nevada-Oregon border, is a Miocene collapse structure 45 km in diameter. Large-volume rhyolitic and peralkaline ash-flow tufts were erupted from 17.9-15.8 m.y. ago, leading to the formation of overlapping and nested calderas. Emplacement of rhyolitic ring domes, located primarily along the western margin of the calderas, represents the last phase of volcanic activity.

  13. Building and interpreting a database to understand recent caldera unrest from monitoring data

    NASA Astrophysics Data System (ADS)

    Di Lorenzo, Riccardo; Acocella, Valerio; Scandone, Roberto; Geshi, Nobuo

    2014-05-01

    Calderas are among the most spectacular, dangerous and active volcanoes on the Earth. Activation of seismicity, surface deformation and anomalous degassing are commonly observed at many calderas, denoting unrest. The unrest can be intermittent, lasting for months to years, or persistent, over decades to centuries. Although most caldera unrest episodes do not lead to an eruption, the possibility of an impending eruption warrants detailed monitoring and study. To better understand caldera unrest, we built a database from all available publications and reports on the recent unrest episodes at calderas in the world. We focused our attention on the unrest episodes which have occurred in the last 25 years, being complementary to Newhall and Dzurisin (1988). We considered the monitoring data from more than 45 unresting calderas, 35 of which characterized by eruptions. Attention has been given to seismicity, deformation and gas variations, along with their possible interaction. The database consists of an excel sheet containing the: (a) caldera descriptive parameters (caldera name, UTM coordinates, maximum and minimum diameter, area, date of last eruption, magma composition); (b) seismic data (width, maximum and minimum depth of area undergoing seismicity, frequency and duration and maximum magnitude; (c) geodetic data (location and width of deformed area, intensity and duration of the deformation); (d) geochemical data (location of anomalies, changes in maximum temperature, variations in chemical composition, duration of the anomaly, pH changes); (e) presence of eruptions and their characterization. The preliminary analysis of the database confirms that all eruptions are preceded by an unrest episode, but not all unrest episodes culminate in an eruption; this suggests that these indicators are a necessary condition to establish the state of unrest, which may anticipate an impending eruption; however, the indicators are not always adequate to determine the occurrence of

  14. Seismic and gravity signature of the Ischia Island Caldera (Italy)

    NASA Astrophysics Data System (ADS)

    Capuano, P.; de Matteis, R.; Russo, G.

    2009-04-01

    The Campania (Italy) coasts are characterized by the presence of several volcanoes. The island of Ischia, located at the northwestern end of the Gulf of Naples, belongs to the Neapolitan Volcanic District together with Phlegrean Fields and Vesuvius, having all these Pleistocene volcanoes erupted in historical times, and it is characterized by diffuse hydrothermal phenomena The island represents the emergent part of a more extensive volcanic area developed mainly westward of the island, with underwater volcanoes aligned along regional fault patterns. The activity of Ischia volcano is testified by the occurrence of eruptions in historical times, the presence of intense hydrothermal phenomena, and by seismic activity (e.g. the 1883 Casamicciola earthquake). Ischia is populated by about 50,000 inhabitants increasing, mainly in the summer, due to thriving tourism business, partially due to its active volcanic state. Hazard assessment at active, densely populated volcanoes is critically based on knowledge of the volcanoes past behavior and the definition of its present state. As a contribution to the definition of the present state of the Ischia island volcano, we obtain a model of the shallow crust using geophysical observables through seismic tomography and 3D gravity inversion. In particular we use travel times collected during the Serapis experiment on the island and its surroundings and free air anomaly. A new 3D gravity inversion procedure has been developed to take better into account the shape and the effects of topography approximating it by a triangular mesh. Below each triangle, a sequence of triangular prisms is built, the uppermost prism having the upper face coincident with the triangle following the topography. The inversion is performed searching for a regularized solution using the minimum norm stabilizer. The main results inferable from the 3D seismic and gravity images are the definition of the caldera rims hypothesize by many authors along the

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

    NASA Astrophysics Data System (ADS)

    Lehman, Jay A.; Smith, Robert B.; Schilly, Michael M.; Braile, Lawrence W.

    1982-04-01

    The 1978 Yellowstone-Snake River Plain seismic experiment provided detailed refraction data that were recorded across a two-dimensional array of seismographs in Yellowstone National Park. A delay time analysis was applied to 173 crystalline basement Pg arrivals from these data to determine the three-dimensional distribution of velocities and the layer configuration of the upper crust beneath the Yellowstone caldera. The P wave velocity structure of the caldera is characterized by a surface layer of combined sediments and rhyolite flows, averaging 2.8 km/s, that range in thickness from 1.5 to 2.0 km. Adjacent to the caldera, the crystalline upper crustal layer has a velocity of 6.05±0.01 km/s, but this layer decreases by 6% to 5.70 km/s beneath the caldera and extends northeast 15 km beyond the caldera. Smaller zones of very low P velocity, 4.0 km/s, a 30% velocity reduction compared to the 6.05 km/s layer, occur in the upper crust beneath the northeastern caldera rim and beneath the southwest caldera in the vicinity of the Upper and Midway Geyser basins. A three-dimensional gravity interpretation based upon densities derived from the seismic model suggests that the regional gravity low of -60 mGal over the caldera correlates directly with (1) the surface layer of combined sediments and rhyolite flows, (2) the low-velocity, 5.7-km/s, upper crustal layer, and (3) the 4.0-km/s low-velocity zone beneath the northeastern caldera rim. An interpretation of the seismic velocities and densities, based on experimental data and theoretical models, suggests that the 6.05-km/s (ρ = 2.70 g/cm3) regional Pg velocity is characteristic of crystalline basement rocks such as the Precambrian granitic gneisses that are exposed north and south of the Yellowstone caldera. The 5.7-km/s velocity layer (ρ = 2.65 g/cm3) is interpreted to be a 10-km-thick hot body of granitic composition. The 4.0-km/s low-velocity body (ρ = 2.40 g/cm3) beneath the northeastern caldera rim is associated

  16. Possible tectonomagnetic effect observed from mid-1989, to mid-1990, in Long Valley caldera, California

    SciTech Connect

    Mueller, R.J.; Johnston, M.J.S.; Langbein, J.O. )

    1991-04-01

    Precise measurements of local magnetic fields have been obtained with a differentially connected array of three proton magnetometers in the Long Valley caldera region since 1984. Two magnetometers are located inside the caldera with a third reference magnetometer located 26 km southeast of the caldera. After correction for secular variation, it is apparent that an anomalous 2 nT decrease in the magnetic field occurred from mid-1989 to mid-1990 at the magnetometer located closest to the center of the resurgent dome inside the caldera. During this period a significant increase in geodetic strain rate of 8.5 ppm/yr was observed on the two-color geodimeter network within the caldera from October, 1989, to mid-1990 and a dramatic increase in seismic activity occurred from December, 1989 to July, 1990. A simple dilatational point-source model with pressure increasing by 52 Mpa from October 1989 to August 1990 at a depth of about 7 km beneath the center of the resurgent dome can be fit to the strain data. If this same model is used to calculate piezomagnetic fields in the caldera, the results obtained agree with the observed local magnetic field data provided the Curie point isotherm is at a depth of {le}5 km. Taken together, these magnetic, seismic and geodetic data suggest that an episode of active magmatic intrusion occurred from late 1989 to mid-1990 at a depth of about 7-8 km beneath the resurgent dome within the Long Valley caldera. Other indications of this intrusion should be evident in measurements of leveling, local gravity, and seismic imaging data.

  17. Geologic map of the Cochetopa Park and North Pass Calderas, northeastern San Juan Mountains, Colorado

    USGS Publications Warehouse

    Lipman, Peter W.

    2012-01-01

    The San Juan Mountains in southwestern Colorado have long been known as a site of exceptionally voluminous mid-Tertiary volcanism, including at least 22 major ignimbrite sheets (each 150-5,000 km3) and associated caldera structures active at 33-23 Ma. Recent volcanologic and petrologic studies in the San Juan region have focused mainly on several ignimbrite-caldera systems: the southeastern area (Platoro complex), western calderas (Uncompahgre-Silverton-Lake City), and the central cluster (La Garita-Creede calderas). Far less studied has been the northeastern San Juan region, which occupies a transition between earlier volcanism in central Colorado and large-volume younger ignimbrite-caldera foci farther south and west. The present map is based on new field coverage of volcanic rocks in seventeen 7.5' quadrangles in northeastern parts of the volcanic field, high-resolution age determinations for 120 new sites, and petrologic studies involving several hundred new chemical analyses. This mapping and the accompanying lab results (1) document volcanic evolution of the previously unrecognized North Pass caldera and the morphologically beautifully preserved but enigmatic Cochetopa basin, including unique features not previously described from ignimbrite calderas elsewhere; (2) provide evidence for a more rapid recurrence of large ignimbrite eruptions than previously known elsewhere; (3) quantify the regional time-space-volume progression from the earlier Sawatch magmatic trend southward into the San Juan region; and (4) permit more rigorous comparison between the broad mid-Tertiary magmatic belt in the western U.S. Cordillera and the type continental-margin arc volcanism in the central Andes.

  18. Qualitative and Quantitative Assessment of Naturals Hazards in the Caldera of Mount Bambouto (West Cameroon)

    NASA Astrophysics Data System (ADS)

    Zangmo Tefogoum, G.; Kagou Dongmo, A.; Nkouathio, D. G.; Wandji, P.

    2009-04-01

    Mount Bambouto is polygenic stratovolcano of the Cameroon Volcanic Line, build between 21 Ma and 4,5Ma (Nkouathio et al., 2008). It is situated at about 200 km NE of mount Cameroon, at 09°55' and 10°15' East and, 05°25' and 05°50' Nord. This volcano covers an area of 500 Km2 and culminates at 2740 m at Meletan hill and bears a collapse caldera (13 x 8 km). Fissural, extrusive and explosive dynamism are responsible of the construction in three main stages this volcano including the edification of a sommital large rim caldera. Mount Bambouto structure gives rise to different natural hazards, of volcanological origin and meteorological origin. In the past time, landslides, floodings, firebush, blocks collapse took place in this area with catastrophic impact on the population. New research program had been carried out in the caldera concerning qualitative and quantitative evaluation of natural risks and catastrophes. The main factors of instability are rain, structure of the basement, slopes, lithology and anthropic activities; particularly, the occurrence of exceptional rainfall due to global change are relevant; this gives opportunity to draw landslides hazards zonation map of the Bambouto caldera which is the main risk in this area. We evaluate the financial potential of the caldera base on the average income of breeding, farming, school fees and the cost of houses and equipments for each family. The method of calculation revealed that, the yearly economy of the mounts Bambouto caldera represents about 2 billions FCFA. Some recommendations have been made in order to prevent and reduced the potential losses and the number of victims in particular by better land use planning. These help us to estimate the importance of destruction of the environment and biodiversity in case of catastrophes. We conclude that in the Bambouto caldera there is moderate to high probability that destructive phenomena due to landslides occurs within the upcoming years with enormous

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  20. The Tala Tuff, La Primavera caldera Mexico. Pre-eruptive conditions and magma processes before eruption

    NASA Astrophysics Data System (ADS)

    Sosa-Ceballos, G.

    2015-12-01

    La Primavera caldera, Jalisco Mexico, is a Pleistocenic volcanic structure formed by dome complexes and multiple pyroclastic flows and fall deposits. It is located at the intersection of the Chapala, Colima, and Tepic grabens in western Mexico. The first volcanic activity associated to La Primavera started ~0.1 Ma with the emission of pre-caldera lavas. The caldera collapse occurred 95 ka and is associated to the eruption of ~20 km3of pumice flows known as the Tala tuff (Mahood 1980). The border of the caldera was replaced by a series of domes dated in 75-30 ky, which partially filled the inner depression of the caldera with pyroclastic flows and falls. For more than a decade the Federal Commission of Electricity in Mexico (CFE) has prospected and evaluated the geothermal potential of the Cerritos Colorados project at La Primavera caldera. In order to better understand the plumbing system that tapped the Tala tuff and to investigate its relation with the potential geothermal field at La Primavera we performed a series of hydrothermal experiments and studied melt inclusions hosted in quartz phenocrysts by Fourier Infra red stectroscopy (FTIR). Although some post caldera products at La Primavera contain fayalite and quartz (suggesting QFM conditions) the Tala tuff does not contain fayalite and we ran experiments under NNO conditions. The absence of titanomagnetite does not allowed us to calculate pre-eruptive temperature. However, the stability of quartz and plagioclase, which are natural phases, suggest that temperature should be less than 750 °C at a pressure of 200 MPa. The analyses of H2O and CO2 dissolved in melt inclusions yielded concentrations of 2-5 wt.% and 50-100 ppm respectively. This data confirm that the pre-eruptive pressure of the Tala tuff is ~200 MPa and in addition to major elements compositions suggest that the Tala tuff is either, compositionally zoned or mixed with other magma just prior to eruption.

  1. MGS-TES thermal inertia study of the Arsia Mons Caldera

    USGS Publications Warehouse

    Cushing, G.E.; Titus, T.N.

    2008-01-01

    Temperatures of the Arsia Mons caldera floor and two nearby control areas were obtained by the Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES). These observations revealed that the Arsia Mons caldera floor exhibits thermal behavior different from the surrounding Tharsis region when compared with thermal models. Our technique compares modeled and observed data to determine best fit values of thermal inertia, layer depth, and albedo. Best fit modeled values are accurate in the two control regions, but those in the Arsia Mons' caldera are consistently either up to 15 K warmer than afternoon observations, or have albedo values that are more than two standard deviations higher than the observed mean. Models of both homogeneous and layered (such as dust over bedrock) cases were compared, with layered-cases indicating a surface layer at least thick enough to insulate itself from diurnal effects of an underlying substrate material. Because best fit models of the caldera floor poorly match observations, it is likely that the caldera floor experiences some physical process not incorporated into our thermal model. Even on Mars, Arsia Mons is an extreme environment where CO2 condenses upon the caldera floor every night, diurnal temperatures range each day by a factor of nearly 2, and annual average atmospheric pressure is only around one millibar. Here, we explore several possibilities that may explain the poor modeled fits to caldera floor and conclude that temperature dependent thermal conductivity may cause thermal inertia to vary diurnally, and this effect may be exaggerated by presence of water-ice clouds, which occur frequently above Arsia Mons. Copyright 2008 by the American Geophysical Union.

  2. Near real-time monitoring of volcanic surface deformation from GPS measurements at Long Valley Caldera, California

    NASA Astrophysics Data System (ADS)

    Ji, Kang Hyeun; Herring, Thomas A.; Llenos, Andrea L.

    2013-03-01

    Long Valley Caldera in eastern California is an active volcanic area and has shown continued unrest in the last three decades. We have monitored surface deformation from Global Positioning System (GPS) data by using a projection method that we call Targeted Projection Operator (TPO). TPO projects residual time series with secular rates and periodic terms removed onto a predefined spatial pattern. We used the 2009-2010 slow deflation as a target spatial pattern. The resulting TPO time series shows a detailed deformation history including the 2007-2009 inflation, the 2009-2010 deflation, and a recent inflation that started in late-2011 and is continuing at the present time (November 2012). The recent inflation event is about four times faster than the previous 2007-2009 event. A Mogi source of the recent event is located beneath the resurgent dome at about 6.6 km depth at a rate of 0.009 km3/yr volume change. TPO is simple and fast and can provide a near real-time continuous monitoring tool without directly looking at all the data from many GPS sites in this potentially eruptive volcanic system.

  3. Lower Pliensbachian caldera volcanism in high-obliquity rift systems in the western North Patagonian Massif, Argentina

    NASA Astrophysics Data System (ADS)

    Benedini, Leonardo; Gregori, Daniel; Strazzere, Leonardo; Falco, Juan I.; Dristas, Jorge A.

    2014-12-01

    In the Cerro Carro Quebrado and Cerro Catri Cura area, located at the border between the Neuquén Basin and the North Patagonian Massif, the Garamilla Formation is composed of four volcanic stages: 1) andesitic lava-flows related to the beginning of the volcanic system; 2) basal massive lithic breccias that represent the caldera collapse; 3) voluminous, coarse-crystal rich massive lava-like ignimbrites related to multiple, steady eruptions that represent the principal infill of the system; and, finally 4) domes, dykes, lava flows, and lava domes of rhyolitic composition indicative of a post-collapse stage. The analysis of the regional and local structures, as well as, the architectures of the volcanic facies, indicates the existence of a highly oblique rift, with its principal extensional strain in an NNE-SSW direction (˜N10°). The analyzed rocks are mainly high-potassium dacites and rhyolites with trace and RE elements contents of an intraplate signature. The age of these rocks (189 ± 0.76 Ma) agree well with other volcanic sequences of the western North Patagonian Massif, as well as, the Neuquén Basin, indicating that Pliensbachian magmatism was widespread in both regions. The age is also coincident with phase 1 of volcanism of the eastern North Patagonia Massif (188-178 Ma) represented by ignimbrites, domes, and pyroclastic rocks of the Marifil Complex, related to intraplate magmatism.

  4. Near real-time monitoring of volcanic surface deformation from GPS measurements at Long Valley Caldera, California

    USGS Publications Warehouse

    Ji, Kang Hyeun; Herring, Thomas A.; Llenos, Andrea L.

    2013-01-01

    Long Valley Caldera in eastern California is an active volcanic area and has shown continued unrest in the last three decades. We have monitored surface deformation from Global Positioning System (GPS) data by using a projection method that we call Targeted Projection Operator (TPO). TPO projects residual time series with secular rates and periodic terms removed onto a predefined spatial pattern. We used the 2009–2010 slow deflation as a target spatial pattern. The resulting TPO time series shows a detailed deformation history including the 2007–2009 inflation, the 2009–2010 deflation, and a recent inflation that started in late-2011 and is continuing at the present time (November 2012). The recent inflation event is about four times faster than the previous 2007–2009 event. A Mogi source of the recent event is located beneath the resurgent dome at about 6.6 km depth at a rate of 0.009 km3/yr volume change. TPO is simple and fast and can provide a near real-time continuous monitoring tool without directly looking at all the data from many GPS sites in this potentially eruptive volcanic system.

  5. Variation of Fracturing Pressures with Depth Near the Valles Caldera

    SciTech Connect

    Dash, Zora; Murphy, Hugh

    1983-12-15

    Hydraulic Fracturing at the Fenton Hill Hot Dry Rock Geothermal site near the Valles Caldera has yielded fracturing pressures from 14 to 81 MPa (2030 to 11,750 psi) at depths ranging from 0.7 to 4.4 km (2250 to 14,400 ft). This data can be fit to a fracture gradient of 19 MPa/km (0.84 psi/ft), except for an anomalous region between 2.6 to 3.2 km where fracturing pressures are about 20 MPa lower than estiamted using the above gradient. This anomaly coincides with a biotite granodiorite intrusive emplaced into a heterogeneous jointed metamorphic complex comprised of gneisses, schists and metavolcanic rocks. Microseismic events detected with sensitive downhole geophones suggest that shear failure is an important process during hydraulic fracturing of such jointed rock. Consequently the usual relation between minimum earth stress and fracture opening pressure, based upon classic tensile failure, cannot be used apriori; fracture opening pressure is instead a complex function of joint orientation and all three components of principal earth stress.

  6. Scientific core hole VC-2A, Valles Caldera, New Mexico

    SciTech Connect

    Musgrave, J.; Goff, S. ); Turner, T. , Salt Lake City, UT )

    1990-10-01

    This report details the remedial action activities that were necessary to complete scientific core hole Valles caldera {number sign}2A (VC-2A) before it was relinquished to the landowners. Sandia National Laboratories, acting as the Geoscience Research Drilling Office (GRDO), managed the coring operations. Los Alamos National Laboratory (Los Alamos) obtained the proper drilling permits with the New Mexico State Engineers Office (SEO). A legal agreement between Los Alamos and the landowners states that the Laboratory will give the landowners the completed core hold with casing, well head, and other hardware at the end of May 1991, or earlier if scientific investigations were completed. By May 1988, the Science Team completed the planned scientific investigations in the VC-2A core hole. Upon the insistence of the GRDO, the New Mexico Oil Conservation Division (OCD) inspected the core hole, declared jurisdiction, and required that the 11.43- by 11.43-cm annular cement job be repaired to comply with OCD regulations. These regulations state that there must be a return to surface of cement in all cementing operations. We successfully completed a squeeze cementing operation and relinquished the core hold to the landowners in November 1988 to the satisfaction of the OCD, SEO, the landowners, and Los Alamos. 7 refs., 4 figs., 1 tab.

  7. Volcanic calderas delineate biogeographic provinces among Yellowstone thermophiles.

    PubMed

    Takacs-Vesbach, Cristina; Mitchell, Kendra; Jackson-Weaver, Olan; Reysenbach, Anna-Louise

    2008-07-01

    It has been suggested that the distribution of microorganisms should be cosmopolitan because of their enormous capacity for dispersal. However, recent studies have revealed that geographically isolated microbial populations do exist. Geographic distance as a barrier to dispersal is most often invoked to explain these distributions. Here we show that unique and diverse sequences of the bacterial genus Sulfurihydrogenibium exist in Yellowstone thermal springs, indicating that these sites are geographically isolated. Although there was no correlation with geographic distance or the associated geochemistry of the springs, there was a strong historical signal. We found that the Yellowstone calderas, remnants of prehistoric volcanic eruptions, delineate biogeographical provinces for the Sulfurihydrogenibium within Yellowstone (chi(2): 9.7, P = 0.002). The pattern of distribution that we have detected suggests that major geological events in the past 2 million years explain more of the variation in sequence diversity in this system than do contemporary factors such as habitat or geographic distance. These findings highlight the importance of historical legacies in determining contemporary microbial distributions and suggest that the same factors that determine the biogeography of macroorganisms are also evident among bacteria. PMID:18363714

  8. Fernandina caldera collapse morphology in geometric and dynamic comparison to sandbox models, subsidence sinks over nuclear-explosion cavities, and some other calderas

    NASA Astrophysics Data System (ADS)

    Howard, K. A.

    2009-12-01

    The 1968 collapse structure of Fernandina caldera (1.5 km3 collapsed) and also the smaller Darwin Bay caldera in Galápagos each closely resembles morphologically the structural zoning of features found in depressions collapsed into nuclear-explosion cavities (“sinks” of Houser, 1969) and in coherent sandbox-collapse models. Coherent collapses characterized by faulting, folding, and organized structure contrast with spalled pit craters (and lab experiments with collapsed powder) where disorganized piles of floor rubble result from tensile failure of the roof. Subsidence in coherent mode, whether in weak sand in the lab, stronger desert alluvium for nuclear-test sinks, or in hard rock for calderas, exhibits consistent morphologic zones. Characteristically in the sandbox and the nuclear-test analogs these include a first-formed central plug that drops along annular reverse faults. This plug and a surrounding inward-tilted or monoclinal ring (hanging wall of the reverse fault) contract as the structure expands outward by normal faulting, wherein peripheral rings of distending material widen the upper part of the structure along inward-dipping normal faults and compress inner zones and help keep them intact. In Fernandina, a region between the monocline and the outer zone of normal faulting is interpreted, by comparison to the analogs, to overlie the deflation margin of an underlying magma chamber. The same zoning pattern is recognized in structures ranging from sandbox subsidence features centimeters across, to Alae lave lake and nuclear-test sinks tens to hundreds of meters across, to Fenandina’s 2x4 km-wide collapse, to Martian calderas tens of kilometers across. Simple dimensional analysis using the height of cliffs as a proxie for material strength implies that the geometric analogs are good dynamic analogs, and validates that the pattern of both reverse and normal faulting that has been reported consistently from sandbox modeling applies widely to calderas.

  9. Eruptive and noneruptive calderas, northeastern San Juan Mountains, Colorado: Where did the ignimbrites come from?

    USGS Publications Warehouse

    Lipman, P.W.; McIntosh, W.C.

    2008-01-01

    The northeastern San Juan Mountains, the least studied portion of this well-known segment of the Southern Rocky Mountains Volcanic Field are the site of several newly identified and reinterpreted ignimbrite calderas. These calderas document some unique eruptive features not described before from large volcanic systems elsewhere, as based on recent mapping, petrologic data, and a large array of newly determined high-precision, laser-fusion 40Ar/39Ar ages (140 samples). Tightly grouped sanidine ages document exceptionally brief durations of 50-100 k.y. or less for individual Oligocene caldera cycles; biotite ages are more variable and commonly as much as several hundred k.y. older than sanidine from the same volcanic unit. A previously unknown ignimbrite caldera at North Pass, along the Continental Divide in the Cochetopa Hills, was the source of the newly distinguished 32.25-Ma Saguache Creek Tuff (???400-500 km3). This regionally, distinctive crystal-poor alkalic rhyolite helps fill an apparent gap in the southwestward migration from older explosive activity, from calderas along the N-S Sawatch locus in central Colorado (youngest, Bonanza Tuff at 33.2 Ma), to the culmination of Tertiary volcanism in the San Juan region, where large-volume ignimbrite eruptions started at ca. 29.5 Ma and peaked with the enormous Fish Canyon Tuff (5000 km3) at 28.0 Ma. The entire North Pass cycle, including caldera-forming Saguache Creek Tuff, thick caldera-filling lavas, and a smaller volume late tuff sheet, is tightly bracketed at 32.25-32.17 Ma. No large ignimbrites were erupted in the interval 32-29 Ma, but a previously unmapped cluster of dacite-rhyolite lava flows and small tuffs, areally associated with a newly recognized intermediate-composition intrusion 5 ?? 10 km across (largest subvolcanic intrusion in San Juan region) centered 15 km north of the North Pass caldera, marks a near-caldera-size silicic system active at 29.8 Ma. In contrast to the completely filled North Pass

  10. Structural deformation and sedimentation in an active Caldera, Rabaul, Papua New Guinea

    USGS Publications Warehouse

    Greene, H. Gary; Tiffin, D.L.; McKee, C.O.

    1986-01-01

    Recent seismic and tectonic activity in Rabaul Caldera, Papua New Guinea, suggests that magma is accumulating at a shallow depth beneath this partially submerged structure and that a new volcano may be developing. Changes in onshore elevation since 1971 (as much as 2 m on south Matupit Island) indicate that rapid and large-scale uplifts have occurred on the seafloor near the center of the caldera. The frequency of seismic events within the caldera has also increased during this period. Earthquake locations define an elliptical ring surrounding the center of this uplift within the caldera. A marine geophysical survey in 1982 by the U.S. Geological Survey's R/V "S.P. Lee" in Rabaul Caldera shows the development of a bulge in the seafloor near the center of the caldera. High-resolution seismic reflection profiles show that this bulge consists of two domal uplifts bounded and separated by two major north-south-trending fault zones. Deformed sediments overlie these zones; a prominent slump flanks the area of the bulge. Five major acoustic units were identified in the seismic reflection profiles: an acoustic basement and four sedimentary units consisting of irregularly layered, cross-layered, contorted, and well-layered sequences. The acoustic basement is probably composed of crystalline volcanic rocks, and the layered acoustic units are probably sediments, primarily ash deposited in different environments. The cross-layered, irregularly layered, and contorted units appear to have been deposited in a dynamic environment subjected to strong currents, seismicity, and/or mass wasting, while the well-layered units were deposited in a low-energy environment. Locally, well-layered sequences interfinger with the other sedimentary units, indicating a transitional environment that alternated between high-energy and low-energy depositional processes. A submarine channel cuts most of the acoustic units and appears to be the conduit for sediment transport out of the caldera; it

  11. Inversion for sources of crustal deformation and gravity change at the Yellowstone caldera

    SciTech Connect

    Vasco, D.W.; Taylor, C.L. ); Smith, R.B. )

    1990-11-10

    The Yellowstone caldera was formed in the latest of three explosive eruptions of rhyolites and ash flow tuffs totaling 3,700 km{sup 3} at 2, 1.2, and 0.6 m.y. before present. Its youthful volcanic history, widespread hydrothermal activity, intense seismicity, and extremely high heat flow, in excess of 30 times the continental average, marks the Yellowstone volcanic system as a giant caldera at unrest. Orthometric height increases of the caldera of up to 76 cm, measured from precise leveling surveys from 1923 to 1975-1977, were inverted to determine volume expansion source models for the caldera-wide deformation. For the 1923 to 1977 uplift episode, two regions of expansion were found: (1) in the northern part of the caldera near the Sour Creek resurgent dome of {approximately}0.37 km{sub 3}, and (2) in the southern part of the caldera, near the Mallard Lake resurgent dome of {approximately}0.41 km{sub 3}. Both bodies occur in the upper crust from near-surface depths to 6.0 km, but the largest volume expansions were found in the 3.0-6.0 km depth range. The southern caldera source volume, near the Mallard Lake dome, may extend down to 9.0 km. From 1976 to 1987, nearly simultaneous measurements of elevation and gravity changes were made on a profile across the northern caldera during a period of net uplift. Models of the temporal gravity variation infer that the volume increase for the northern caldera source must lie above 9.0 km and involved a density perturbation greater than +0.002 g/cm{sup 3}. The modeled volumetric sources are in the same general locations as bodies of low P wave velocities, high seismic attenuation, and large negative Bouguer gravity anomalies. It is likely that the modeled volumetric increases were caused by migration of magmas and/or the introduction of large volumes of hydrothermal fluids into the upper crust.

  12. Under Construction: Rebuilding Kīlauea's Shallow Magma Storage System After Caldera Collapse

    NASA Astrophysics Data System (ADS)

    Swanson, D. A.; Wright, T. L.

    2015-12-01

    Draining of Kīlauea's upper level magma reservoir system in ~1500 CE led to a N-S elongate, roughly circular structural caldera ~6.5 km in diameter surrounding a prominent topographic caldera (TC) 4 x 3 km in diameter. The TC was probably at least 600 m deep with a volume of ~4-6 km3. The reservoir system has been rebuilding since then, mostly during the past 200 y of relatively high magma supply. Current reservoir locations are well defined geodetically (Poland et al., 2014) but do not match the presumed configuration of magma storage before the caldera collapse, if the common assumption holds that collapse width equals reservoir width. For example, magma does not underlie the northern 1-2 km of the TC, as judged by relatively high P-wave velocities (Dawson et al., 1999) and lack of deformation related to magma storage. The northernmost reservoir, near Halemaumau, is within the TC, but an order of magnitude more magma fills the south caldera reservoir south of the TC (Poland et al., 2014). Currently, the Halemaumau reservoir is shallower than the south caldera reservoir (1-2 km vs. 3-4 km), but in the 1960s magma was likely stored 3-3.5 km deep near Halemaumau (Wright and Klein, 2014). Many deformation centers are south of the TC and have an E-W spread of ~4 km. These observations suggest an evolving storage system that, if drained today, would not form a caldera of the size or location of the TC. Yet the TC is at the summit of the volcano, the site of an older caldera (Holcomb, 1987) and a positive Bouguer gravity anomaly (Kauahikaua et al., 2000), and is apparently the preferred location of reservoir draining and caldera collapse. We think the reservoir system will continue to evolve, expanding and centering itself below the topographic caldera, which will likely be where the next collapse takes place. Dawson et al., 1999, GRL. Holcomb, 1987, USGS PP 1350. Kauahikaua et al., 2000, Geology. Poland et al., 2014, USGS PP 1801. Wright and Klein, 2014, USGS PP 1806.

  13. Magma Storage, Recharge and the Caldera Cycle at Rabaul, Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Fabbro, G.; Bouvet de Maisonneuve, C.; Sindang, M.

    2015-12-01

    Many calderas have a history of repeated caldera-forming eruptions, interspersed with periods of more minor activity. Rabaul, for instance, has had at least 11 ignimbrite-forming eruptions over the last 200 ky. The most recent of these was the '1400 BP' eruption, which led to caldera collapse. Since then, there has been multiple smaller eruptions, including the ongoing activity from Tavurvur and Vulcan. An important question facing volcanology today is what controls the size of eruptions at calderas such as Rabaul.Detailed stratigraphic sampling of the 1400BP eruption reveals that prior to eruption, the magma reservoir below Rabaul contained a well-mixed dacite with whole-rock SiO2 contents of 65.0-66.4 wt%. The dacite contains a single phenocryst assemblage of plag (An44-52), cpx (En43-46Fs13-15Wo40-41), opx (En69-71Fs25-28Wo3) and magnetite, along with minor apatite. The homogeneity of the dacite is underscored by the narrow range of compositions of both the matrix glass and the melt inclusions (67.8-69.0 wt% SiO2). The only exception to this is at the top of the ignimbrite, representing some of the last magma to have been withdrawn. Dispersed throughout the dacitic pumices are darker, more mafic blebs. Streaks of mingled magma with a range of SiO2 contents, down to 59.9 wt% SiO2 are also found in the pumice, suggesting that a mafic recharge magma was intruded into the base of the reservoir shortly before eruption. High TiO2 contents rule out the direct involvement of basalt, and instead imply the magma that intruded into the reservoir was an andesite with at least 56 wt% SiO2. Phenocrysts related to this recharge magma are rare, and the crystals found in the dark blebs are identical in composition to those found in the dacite, indicating that the recharge was aphyric. The present-day, post-caldera recharge magma is different to the pre-1400 BP recharge magma: it is basaltic. This suggests that the plumbing system of Rabaul is different during the pre-caldera and

  14. Quiescent deformation of the Aniakchak Caldera, Alaska mapped by InSAR

    USGS Publications Warehouse

    Kwoun, Oh-Ig; Lu, Zhiming; Neal, C.; Wicks, C., Jr.

    2006-01-01

    The 10-km-wide caldera of the historically active Aniakchak volcano, Alaska, subsides ???13 mm/yr, based on data from 19 European Remote Sensing Satellite (ERS-1 and ERS-2) interferometric synthetic aperture radar (InSAR) images from 1992 through 2002. The pattern of subsidence does not reflect the distribution of pyroclastic deposits from the last eruption in 1931 and therefore is not related to compaction of fragmental debris. Weighted least-squares inversion of the deformation maps indicates a relatively constant subsidence rate. Modeling the deformation with a Mogi point source locates the source of subsidence at ???4 km below the central caldera floor, which is consistent with the inferred depth of magma storage before the 1931 eruption. Magmatic CO2 and He have been measured at a warm soda spring within the caldera, and several sub-boiling fumaroles persist elsewhere in the caldera. These observations suggest that recent subsidence can be explained by the cooling or degassing of a shallow magma body (???4 km deep), and/or the reduction of the pore-fluid pressure of a cooling hydrothermal system. Ongoing deformation of the volcano detected by InSAR, in combination with magmatic gas output from at least one warm spring, and infrequent low-level bursts of seismicity below the caldera, indicate that the volcanic system is still active and requires close attention for the timely detection of possible hazards. ?? 2006 Geological Society of America.

  15. Geologic Map of the Central San Juan Caldera Cluster, Southwestern Colorado

    USGS Publications Warehouse

    Lipman, Peter W.

    2006-01-01

    The San Juan Mountains are the largest erosional remnant of a composite volcanic field that covered much of the southern Rocky Mountains in middle Tertiary time. The San Juan field consists mainly of intermediate-composition lavas and breccias, erupted about 35-30 Ma from scattered central volcanoes (Conejos Formation) and overlain by voluminous ash-flow sheets erupted from caldera sources. In the central San Juan Mountains, eruption of at least 8,800 km3 of dacitic-rhyolitic magma as nine major ash flow sheets (individually 150-5,000 km3) was accompanied by recurrent caldera subsidence between 28.3 Ma and about 26.5 Ma. Voluminous andesitic-dacitic lavas and breccias erupted from central volcanoes prior to the ash-flow eruptions, and similar lava eruptions continued within and adjacent to the calderas during the period of more silicic explosive volcanism. Exposed calderas vary in size from 10 to 75 km in maximum dimension; the largest calderas are associated with the most voluminous eruptions.

  16. The link between circumferential dikes and eruptive fissures around calderas: insights from numerical and analog models

    NASA Astrophysics Data System (ADS)

    Corbi, Fabio; Rivalta, Eleonora; Pinel, Virginie; Maccaferri, Francesco; Acocella, Valerio

    2016-04-01

    Active calderas are seldom associated with circumferential eruptive fissures along their rim, but eroded portions of extinct magmatic complexes reveal widespread evidence of circumferential dikes. This discrepancy suggests that, while the conditions to emplace circumferential dikes below volcanoes are easily met, mechanisms must exist to arrest the dikes before they reach the surface. Here we explain this discrepancy with laboratory experiments of air injection into a gelatin medium shaped to mimic a volcanic edifice with caldera. Our models show that the ascending dikes experience a variable degree of deflection, depending on the competition between dike overpressure, Pe, and the forcing induced by the topographic load, Pl. When Pl/Pe = 4.3 - 4.5 the analog dikes proceed almost insensitive to the stress rotation and erupt within the caldera. When Pl/Pe = 4.8 - 5.3 the analog dikes closely propagate orthogonal to the least compressive stress σ3 and stall below the caldera rim in a circumferential arrangement. Progressive buoyancy increase through repeated supply of fluid is fundamental for the occurrence of circumferential fissures. Complementary numerical models explain the observed circumferential arrangement and validate the experiments. These results contribute defining the shallow magma transfer and related hazard assessment within calderas.

  17. Volcanic and tectonic processes coinciding with glaciation and crustal rebound: an early Holocene rhyolitic eruption in the Dyngjufjöll volcanic centre and the formation of the Askja caldera, north Iceland

    NASA Astrophysics Data System (ADS)

    Sigvaldason, Guðmundur

    2002-03-01

    A pronounced volcanic production maximum on the rift zones through Iceland coincided with rapid crustal rebound during and after glacier melting at the Pleistocene/Holocene boundary. At peak glaciation, ice thickness over central Iceland may have reached 1,500-2,000 m, causing 400-500-m depression of the crust. Rapid climatic improvement caused glacier melting and removal of the ice load within about 1,000 years. Low mantle viscosity resulted in rapid crustal rebound which was completed in about 1,000 years, with an average rate of uplift on the order of nearly half a metre per year over central Iceland. High volcanic production rate is documented by tephrachronological dating and volume estimates of several large-volume monogenetic lava shields and polygenetic volcanic centres along the plate boundary. A Plinian rhyolitic eruption, dated at about 10 ka within the Askja caldera in the Dyngjufjöll volcanic centre, left a pumice deposit which serves as a marker horizon during this remarkable, high-intensity period in the history of the volcano. At the time of the eruption, glaciers had retreated from the coastal areas of the country but the central, elevated parts were covered with a thinning glacier. The Plinian eruption (1-2 km3 dense rock equivalent) was triggered by pressure release caused by glacier melting and volatile supersaturation. Distal deposits of rhyolitic pumice are found in soil sections in coastal areas of eastern and northern Iceland where the pumice occurs between tephra layers from other sources which have been dated by independent methods. A few proximal deposits are preserved within the Dyngjufjöll centre. These provide age constraints on major tectonic and volcanic events during the period of crustal rebound, before and after complete glacier removal. The rhyolitic pumice is sandwiched between thick layers of phreatomagmatic basaltic tephra formed in an open melt-water lake. Sharp contacts between the deposits suggest quick succession of

  18. Near real-time monitoring of surface deformation at Long Valley Caldera, California (Invited)

    NASA Astrophysics Data System (ADS)

    Ji, K.; Llenos, A. L.; Herring, T.

    2013-12-01

    Continuous monitoring of volcanic activity enables us to detect changes from usual activity, issue alerts of impending eruptions and thereby reduce volcanic risk. We have developed a near real-time monitoring tool for surface deformation: the Targeted Projection Operator (TPO). TPO is simple, fast, and easily applied whenever new data are available. With Global Positioning System (GPS) data, we have used TPO for continuous monitoring of surface deformation in the Long Valley Caldera (LVC) region in eastern California. TPO projects GPS position time series onto a target spatial pattern and obtains the amplitude of the projection at each epoch. For this, we assume that a deformation event (i.e., an inflationary or deflationary event) has the same spatial pattern as past events but with possibly different amplitude. This assumption is reasonable for the recent quiet phase in LVC because the 2007-2009 inflation is similar to the 2009-2010 deflation with respect to the deformation pattern. We selected horizontal pattern of the 2009-2010 event along which the GPS data are projected to recover the time-varying amplitudes. Large changes in amplitude imply changes in strength of the event. An anomalous change can be detected by comparing with amplitudes during relatively quiet time periods. Growing misfits between the TPO spatial pattern and the spatial variations of the GPS pattern, indicate changes in the deformation mechanism which can then be explored to assess whether potentially new mechanisms are developing. So far this has not been the case for LVC; the current spatial patterns of deformation match the shape deduced for the 2007-2009 inflation event. TPO shows that LVC has experienced inflation since late 2011 although the rate briefly slowed down in May and October 2012 and has started to slow again since June 2013. The rate of this event is about four times faster than the 2007-2009 inflation event and is consistent with a Mogi source located beneath the resurgent

  19. FEM-based linear inverse modeling using a 3D source array to image magma chambers with free geometry. Application to InSAR data from Rabaul Caldera (PNG).

    NASA Astrophysics Data System (ADS)

    Ronchin, Erika; Masterlark, Timothy; Dawson, John; Saunders, Steve; Martí Molist, Joan

    2015-04-01

    In this study, we present a method to fully integrate a family of finite element models (FEMs) into the regularized linear inversion of InSAR data collected at Rabaul caldera (PNG) between February 2007 and December 2010. During this period the caldera experienced a long-term steady subsidence that characterized surface movement both inside the caldera and outside, on its western side. The inversion is based on an array of FEM sources in the sense that the Green's function matrix is a library of forward numerical displacement solutions generated by the sources of an array common to all FEMs. Each entry of the library is the LOS surface displacement generated by injecting a unity mass of fluid, of known density and bulk modulus, into a different source cavity of the array for each FEM. By using FEMs, we are taking advantage of their capability of including topography and heterogeneous distribution of elastic material properties. All FEMs of the family share the same mesh in which only one source is activated at the time by removing the corresponding elements and applying the unity fluid flux. The domain therefore only needs to be discretized once. This precludes remeshing for each activated source, thus reducing computational requirements, often a downside of FEM-based inversions. Without imposing an a-priori source, the method allows us to identify, from a least-squares standpoint, a complex distribution of fluid flux (or change in pressure) with a 3D free geometry within the source array, as dictated by the data. The results of applying the proposed inversion to Rabaul InSAR data show a shallow magmatic system under the caldera made of two interconnected lobes located at the two opposite sides of the caldera. These lobes could be consistent with feeding reservoirs of the ongoing Tavuvur volcano eruption of andesitic products, on the eastern side, and of the past Vulcan volcano eruptions of more evolved materials, on the western side. The interconnection and

  20. Tilted middle Tertiary ash-flow calderas and subjacent granitic plutons, southern Stillwater Range, Nevada: cross sections of an Oligocene igneous center

    USGS Publications Warehouse

    John, D.A.

    1995-01-01

    Steeply tilted late Oligocene caldera systems in the Stillwater caldera complex record a number of unusual features including extreme thickness of caldera-related deposits, lack of evidence for structural doming of the calderas and preservation of vertical compositional zoning in the plutonic rocks. The Stillwater caldera complex comprises three partly overlapping ash-flow calderas and subjacent plutonic rocks that were steeply tilted during early Miocene extension. The Job Canyon caldera, the oldest (ca. 29-28 Ma) caldera, consists of two structural blocks. The 25 to 23 Ma Poco Canyon and Elevenmile Canyon calderas and underlying Freeman Creek pluton overlap in time and space with each other. Caldera collapse occurred mostly along subvertical ring-fracture faults that penetrated to depths of >5 km and were repeatedly active during eruption of ash-flow tuffs. The calderas collapsed as large piston-like blocks, and there is no evidence for chaotic collapse. Preserved parts of caldera floors are relatively flat surfaces several kilometers across. -from Author

  1. Post-Supereruption (18-19 Ma) Magmatic Reactivation Beneath the Silver Creek Caldera, Black Mountains, AZ

    NASA Astrophysics Data System (ADS)

    Mcdowell, S.; Miller, C. F.; Ferguson, C.

    2011-12-01

    The Silver Creek caldera, southern Black Mountains, AZ, is the source of the supereruption that produced the Miocene (18.8 Ma) Peach Spring Tuff (PST), an extensive ignimbrite found throughout much of northwestern Arizona, southern Nevada, and southeastern California. The caldera's eastern margin is intruded by a slightly younger (18.5 +/- 0.5 Ma), ~30 km2 complex of epizonal, intermediate to felsic plutonic rocks. Because it is the largest known suite of intrusive rocks associated with the Peach Spring supereruption and contiguous (~19.5-17.5 Ma) volcanic activity in the Black Mountains, the Silver Creek intrusive complex provides a valuable record of processes operating in the shallow crust in the aftermath of a major eruption and during a period of intense volcanic activity. Rocks in the Silver Creek intrusive complex have historically been divided into two units, the Moss porphyry and the Times porphyry, though the complex exhibits textural and compositional complexity that belies a simple two-unit classification scheme. Field observations and geochemical analysis indicate that the northern portion of the Silver Creek suite comprises porphyries and coarse-grained rocks with ~62 to ~68 wt. % SiO2 ("Moss porphyry"). Rounded, 2-10 cm enclaves (59 wt. % SiO2) with crenulate margins are sparse overall but locally abundant in this portion of the complex. The southern part of the complex consists of leucogranitic porphyry and coarse-grained granite with >70 wt. % SiO2 ("Times porphyry"). At the east/west-trending Times/Moss contact zone along Silver Creek, the coarse-grained component of the Times contains < 0.5-2 m-diameter, fine-grained enclaves with crenulate margins and compositions similar to that of the intermediate Moss to the north. Mafic, intermediate, and felsic porphyritic dikes crosscut the entire complex. Major and trace element compositions of the Silver Creek intrusive complex define a coherent and continuous array extending from the most mafic enclaves

  2. Accelerated uplift and magmatic intrusion of the Yellowstone caldera, 2004 to 2006.

    PubMed

    Chang, Wu-Lung; Smith, Robert B; Wicks, Charles; Farrell, Jamie M; Puskas, Christine M

    2007-11-01

    The Yellowstone caldera began a rapid episode of ground uplift in mid-2004, revealed by Global Positioning System and interferometric synthetic aperture radar measurements, at rates up to 7 centimeters per year, which is over three times faster than previously observed inflation rates. Source modeling of the deformation data suggests an expanding volcanic sill of approximately 1200 square kilometers at a 10-kilometer depth beneath the caldera, coincident with the top of a seismically imaged crustal magma chamber. The modeled rate of source volume increase is 0.1 cubic kilometer per year, similar to the amount of magma intrusion required to supply the observed high heat flow of the caldera. This evidence suggests magma recharge as the main mechanism for the accelerated uplift, although pressurization of magmatic fluids cannot be ruled out. PMID:17991858

  3. A core hole into the hydrothermal system of the Long Valley caldera

    SciTech Connect

    Wollenberg, H.; White, A.; Flexser, S.; Sorey, M.; Farrar, C.

    1987-03-01

    To investigate the present-day hydrothermal system, the ''Shady Rest'' hole was continuously cored 715m into the southwestern moat of the Long Valley caldera. The hole intersected 100m of glacial till and 300m of postcaldera rhyolite before entering the welded Bishop Tuff and bottoming in that unit. A sharp temperature rise over the upper 350m, and near-isothermal conditions below reflect the presence of approx.200/sup 0/C water moving through open, calcite-lined fractures in silicified Early Rhyolite and Bishop Tuff. The depth to the Bishop is the shallowest encountered in holes in the caldera, and the temperatures measured are among the hottest observed in wells drilled within the caldera.

  4. A geochemical survey using heavy mineral concentrates in the Mount Belknap caldera vicinity, Utah

    USGS Publications Warehouse

    Tucker, R.E.; Miller, W. Roger; Motooka, J.M.

    1982-01-01

    Geochemical surveys of the rocks, heavy-mineral concentrates, and surface and spring waters in the vicinity of the Mount Belknap caldera, Tushar Mountains, west-central Utah, were conducted during the summers of 1978 and 1979. Anomalous concentrations of mostly lithophile elements, particularly niobium, beryllium, lead, yttrium, tin, zinc, manganese, and molybdenum in the magnetic and nonmagnetic fraction of heavy-mineral concentrates derived from stream sediment suggest that late stage, highly differentiated felsic rocks were involved in the eruptive history of the Mount Belknap caldera. Q-mode factor analysis was used to characterize the geochemical assemblages within the survey area, and the areal distribution of high-factor scores associated with mineralization indicates favorable target areas for future exploration. The results of these studies indicate that porphyry-type molybdenum and possible associated vein-type uranium mineralized deposits may exist in or near the Mount Belknap caldera.

  5. Geologic Model of the Baca Geothermal Reservoir, Valles Caldera, New Mexico

    SciTech Connect

    Nielson, Dennis L.; Hulen, Jeffrey B.

    1983-12-15

    The caldera environment represents a complex interaction of volcanic, structural, and often, hydrothermal processes. As a result calderas are often targets for geothermal exploration and development. From the standpoint of the reservoir engineer, such geothermal systems would be hosted by rocks that display a complex interplay of stratigrphic permeability, structural permeability, and changing permeability which results from the process of hydrothermal alteration and new fracture generation. The purpose of this paper is to present a geolgic model of the Baca geothermal reservoir which is situated in New Mexico. The geologic history of the Valles caldera is presented in Smith and Bailey (1968). The data we present is largely based on our studies of subsurface samples from Union Oil Company's Baca project area. Additional results of our work have been published previously (Hulen and Nielson, 1982, 1983; Nielson and Hulen, in press).

  6. Valles caldera region, New Mexico, and the emerging continental scientific drilling program

    SciTech Connect

    Goff, F.; Gardner, J.N.

    1988-06-10

    Valles caldera is best known in recent years as an excellent example of a resurgent caldera and as the site of a high-temperature geothermal system. However, Valles caldera and the surrounding Jemez Mountains volcanic field possess a rich history of geologic research that dates back to the late 1880s. Through the years, the research focus has changed as different economic and scientific factors have exerted their influence. Early work emphasized mining activity, while modern work has stressed volcanology and, later, geothermal development. Only in the last 5 years has it been possible to view the region as a dynamic, integrated magma-hydrothermal system having a complex evolution lasting more than 13 m.y.

  7. Hydrologic and geochemical monitoring in Long Valley caldera, Mono County, California, 1986. Water Resources Investigation

    SciTech Connect

    Farrar, C.D.; Sorey, M.L.; Sore, S.A.; Rojstaczer, S.A.; Steinemann, A.C.

    1989-01-01

    The U.S. Geological Survey continued to monitor hydrologic and geochemical conditions in the Long Valley caldera during 1986. The monitoring is directed toward detecting changes in the hydrologic system caused by tectonic or magmatic processes. Data collected during 1986 include chemical and isotopic composition of water from selected stream sites, springs, and wells; pumpage from four geothermal wells; flow rates of selected springs and stream sites; mean daily water or gas temperatures at selected sites; mean daily atmospheric pressures and water levels at selected wells, and precipitation records for two sites. Seismicity within the caldera persisted at a relatively low level compared with the more active periods of 1978-84. The most significant events of seismicity that affected hydrologic monitoring sites in Long Valley during 1986 occurred during July, in response to the Chalfant Valley earthquakes, centered about 20 miles southeast of the caldera.

  8. Graben calderas of the Sierra Madre Occidental: The case of Guanajuato, central Mexico

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    The Sierra Madre Occidental (SMO) volcanic province is characterized by voluminous silicic ignimbrites that reach an accumulated thickness of 500 to 1500 m. A single ignimbrite can reach up to 350 m thick in its outflow facies. This ignimbrite sequence formed mostly within 38-23 Ma, building up a total estimated volume of ca. 580,000 km3 making the SMO the largest ignimbrite province of the world. We have showed that several and probably most of the SMO ignimbrites were erupted from fissures associated to Basin and Range fault systems or grabens (Geology, 2003), thus naming these volcano-tectonic structures as graben calderas (Caldera Volcanism book, Elsevier, 2008). Generally, the sequence observed in graben calderas include, from oldest to youngest, alluvial fan deposits combined with lacustrine deposits, pyroclastic surge deposits and minor volume ignimbrites, a large-volume ignimbrite that could be massive or made of successive layers, and sometimes silicic lava domes and/or mafic fissural lavas both with vents aligned with the graben trend. Fallout deposits, plinian or non-plinian, are not observed in the sequence. Thus, onset of caldera collapse represented by the major ignimbrite must occur just after deposition of continental sediments within the graben domain. A similar volcano-tectonic development is observed in pull-apart grabens. Therefore, extensional or transtensional tectonics, before and during caldera collapse, and the emplacement of a subgraben shallow silicic magma chamber are the necessary conditions for the development of graben calderas. We describe here the case of the Guanajuato graben caldera, located in the central part of Mexico and in the southeastern portion of the SMO volcanic province. The caldera is part of the economically important mining district of Guanajuato, with 28 silver mines, some active since the 16th century. The caldera structure, a rectangle of 10 x 16 km, was controlled by NW and NE regional fault systems. Most ore

  9. The largest caldera-forming eruptions in Kamchatka: geochronology, definition, volumes, and petrologic and isotopic investigation

    NASA Astrophysics Data System (ADS)

    Bindeman, I. N.; Leonov, V.; Shipley, N. K.

    2012-12-01

    The continental arc of Kamchatka has the highest magma production rates in the world and arguably the largest number of calderas per unit arc length, which are in response to rapid head-on collision at a subduction angle of ~45°. Kamchatkan caldera sizes and volumes of ignimbrite eruptions some of the world's largest, but rapid volcanic and tectonic uplift and burial, rapid erosion rates, and bulldozing effects of multiple glaciations have reshaped Pleistocene and older calderas. This has left behind remnants of isolated, yet thick, often intracaldera-only ignimbrite sequences. While the contribution of Kamchatkan arc volcanism to global Pleistocene volcanism and oscillating Pleistocene climate is of prime importance, the combination of harsh climate, remoteness, poor road infrastructure, and heavy vegetation cover make fieldwork and recognition of caldera volcanics challenging. We present new results of geologic, geochronologic, geochemical and isotopic investigation of two of the largest caldera in Kamchatka - Pauzhetka (27x18km, 0.44Ma) and Karymshina (30x16km, 1.78 Ma). In both places large-volume climactic ignimbrites are represented by quartz-, zircon-, and biotite- bearing, but sanidine-free rhyolitic to high-silica rhyolitic tuffs. These compositional characteristics and evolved trace elemental ratios indicate a high degree of differentiation rarely achieved in other silicic rocks of the Kamchatka arc and worldwide. Crystallinity of ignimbrites ranges from high (35%) to relatively low (10%). Preliminary investigation of chemical and isotopic variations in pre-caldera sequences in both calderas demonstrates diverse peripheral eruptions of basaltic to dacitic compositions, with predominance of the former. The search for the precursor high-silica rhyolite continues. At Karymshina, pre-caldera magmas have a greater diversity of Sr (0,703283-0,703552) and Nd (0,513046- 0,512962) ratios, and moderately diverse and elevated δ18O values (5.5-7.5‰). In contrast

  10. The 2014-2015 slow collapse of the Bárðarbunga caldera, Iceland

    NASA Astrophysics Data System (ADS)

    Tumi Gudmundsson, Magnus; Jónsdóttir, Kristín; Roberts, Matthew; Ófeigsson, Benedikt G.; Högnadóttir, Thórdís; Magnússon, Eyjólfur; Jarosch, Alexander H.; Pálsson, Finnur; Einarsson, Páll; Sigmundsson, Freysteinn; Drouin, Vincent; Hjörleifsdóttir, Vala; Reynolds, Hannah I.; Dürig, Tobias; Vogfjörd, Kristín; Hensch, Martin; Munoz-Cobo Belart, Joaquin; Oddsson, Björn

    2015-04-01

    The Bárðarbunga caldera is located in central Iceland, under in NW corner of Vatnajökull ice cap. The caldera is about 65 km2 in area, with 500-600 m high topographic rims and is fully covered with up to 800 m thick ice. On 16 August 2014 an intense earthquake swarm started in Bárðarbunga, the beginning of a major volcano-tectonic rifting event forming a 45 km long dyke extending from the caldera to Holuhraun lava field outside the northern margin of Vatnajökull (Sigmundsson et al., 2014). A large basaltic, effusive fissure eruption began in Holuhraun on 31 August that by January had formed a lava field of volume in excess of one cubic kilometre. The collapse of the caldera is expected to have begun a few days after the onset of the earthquake swarm, probably coinciding with the first M5 earthquake. This slow caldera collapse has been monitored through repeated mapping of the gradually increasing subsidence bowl (~80 km2 in December) with airborne profiling of the ice surface, satellite mapping, an online GPS station set up in September on the glacier surface in the centre of the caldera with a strong motion sensor added in November, and indirectly through recording of seismic activity. Satellite interferograms constrain both ice movements and the rate of collapse. The rate of collapse was greatest in the first two weeks or 0.5-1 m/day in the centre, but has since gradually declined with time. The daily rate was 0.1-0.2 m/day in January, when the maximum lowering had reached about 60 m. A gradual widening of the subsidence bowl has been observed since early September. It is asymmetric, deepest in the NE part of the caldera. Downwards displacement extends outside the pre-existing topographic caldera rims, particularly on the south side where the rims have subsided by over 10 meters. Ice-flow modelling indicates that the ice is mostly passively subsiding with the caldera floor. Thus, horizontal ice flow has had little effect on the shape of the subsidence bowl

  11. Accelerated uplift and magmatic intrusion of the Yellowstone caldera, 2004 to 2006

    USGS Publications Warehouse

    Chang, W.-L.; Smith, R.B.; Wicks, C.; Farrell, J.M.; Puskas, C.M.

    2007-01-01

    The Yellowstone caldera began a rapid episode of ground uplift in mid-2004, revealed by Global Positioning System and interferometric synthetic aperture radar measurements, at rates up to 7 centimeters per year, which is over three times faster than previously observed inflation rates. Source modeling of the deformation data suggests an expanding volcanic sill of ???1200 square kilometers at a 10-kilometer depth beneath the caldera, coincident with the top of a seismically imaged crustal magma chamber. The modeled rate of source volume increase is 0.1 cubic kilometer per year, similar to the amount of magma intrusion required to supply the observed high heat flow of the caldera. This evidence suggests magma recharge as the main mechanism for the accelerated uplift, although pressurization of magmatic fluids cannot be ruled out.

  12. Aeromagnetic mapping of the structure of Pine Canyon caldera and Chisos Mountains intrusion, Big Bend National Park, Texas

    USGS Publications Warehouse

    Drenth, B.J.; Finn, C.A.

    2007-01-01

    Analysis of aeromagnetic and gravity data reveals new details of the structure, igneous geology, and temporal evolution of the prominent, enigmatic ca.32 Ma Pine Canyon caldera and the Chisos Mountains (Big Bend National Park, Texas). The main caldera-filling Pine Canyon Rhyolite, the oldest member of the South Rim Formation, is reversely magnetized, allowing it to be used as a key marker bed for determining caldera fill thickness. Modeling of gravity and magnetic anomalies indicates that the Pine Canyon Rhyolite is probably thicker in the northeastern part of the caldera. Lineaments in the magnetic data suggest the presence of buried faults beneath the caldera that may have led to increased downdrop in the northeast versus the southwest, allowing a thicker section of caldera fill to accumulate there. The Pine Canyon caldera has been interpreted as a downsag caldera because it lacks surficial faulting, so these inferred faults are the first mapped features there that could be responsible for caldera collapse. The caldera boundary correlates well with the margins of a gravity low. General features of the caldera match well with basic models of downsag calderas, meaning that the Pine Canyon caldera may be a classic example of downsagging, of which few well-described examples exist, in terms of a geophysical signature. The source of a long-wavelength magnetic high over the Chisos Mountains is interpreted as a previously unknown broad intrusion, the long axis of which trends parallel to a major crustal boundary related to the Ouachita orogeny or an even earlier Precambrian margin. This feature represents the largest intrusion (28-34 km diameter, 1-4 km thick, 700-3000 km3 in volume) in an area where relatively small laccoliths are ubiquitous. The intrusion most likely represents a long-lived (>1 m.y.) reservoir replenished by small batches of magma of varying composition, as reflected in the variation of eruptive products from the Pine Canyon and Sierra Quemada

  13. Geothermal Systems of the Yellowstone Caldera Field Trip Guide

    SciTech Connect

    Foley, Duncan; Neilson, Dennis L.; Nichols, Clayton R.

    1980-09-08

    Geothermal studies are proceedings on two fronts in the West Yellowstone area. High-temperature resources for the generation of electricity are being sought in the Island Park area, and lower temperatures resources for direct applications, primarily space heating, are being explored for near the town of West Yellowstone. Potential electric geothermal development in the Island Park area has been the subject of widespread publicity over fears of damage to thermal features in Yellowstone Park. At the time of writing this guide, companies have applied for geothermal leases in the Island Park area, but these leases have not yet been granted by the US Forest Service. The Senate is now discussing a bill that would regulate geothermal development in Island Park; outcome of this debate will determine the course of action on the lease applications. The Island Park area was the site of two cycles of caldera activity, with major eruptions at 2.0 and 1.2 million years ago. The US Geological Survey estimates that 16,850 x 10{sup 18} joules of energy may remain in the system. Geothermal resources suitable for direct applications are being sought in the West Yellowstone vicinity by the Montana Bureau of Mines and Geology, under funding from the US Department of Energy. West Yellowstone has a mean annual temperature of 1-2 C. Research thus far suggests that basement rocks in the vicinity are at a depth of about 600 m and are probably similar to the rocks exposed north of Hebgen Lake, where Precambrian, Paleozoic and Mesozoic rocks have been mapped. A few sites with anomalously warm water have been identified near the town. Work is continuing on this project.

  14. Travel Time Distribution Modeling in the Valles Caldera, New Mexico

    NASA Astrophysics Data System (ADS)

    Broxton, P. D.; Troch, P. A.; Brooks, P. D.; Lyon, S. W.; Gustafson, J. R.; Veatch, W. C.

    2007-12-01

    Modeling the transit times of catchment waters is of paramount importance in hydrology. The distribution of the time it takes for individual water molecules to move through a hydrologic system (a.k.a., the travel time distribution) is a fundamental characterization of a catchment. Travel time distributions are affected by a variety of physical characteristics of catchments (e.g., vegetation type, degree of soil development) that depend on the amount of solar energy the catchment receives. These characteristics, therefore, can be considered a function of aspect. The goal of this research is to constrain travel time distributions on a series of eight radial mountain streams having different slope aspects on Redondo Peak, a resurgent dome in the center of the Valles Caldera, near Los Alamos, New Mexico. Redondo Peak is an excellent natural laboratory for this type of experiment because all aspects are represented on different sides of the mountain while the internal geology and climate are relatively consistent. To model the transit time distributions of each catchment, variations of chemical load of the snowpack, isotopic compositions of meltwater samples, and snowcover distribution data from closely related studies are coupled with periodic stream and precipitation samples that are analyzed for stable water isotopes content. Additional information comes from a network of temperature sensors to monitor the distribution of snowmelt and headwater stream discharge as well as a series of flumes to capture the flows from the streams. The travel time distributions determined in this project provide a bottom up approach to verify catchment-scale models.

  15. Vertical collapse origin of Las Cañadas caldera (Tenerife, Canary Islands) revealed by 3-D magnetotelluric inversion

    NASA Astrophysics Data System (ADS)

    Piña-Varas, P.; Ledo, J.; Queralt, P.; Marcuello, A.; Bellmunt, F.; Ogaya, X.; Pérez, N.; Rodriguez-Losada, J. A.

    2015-03-01

    Tenerife island geology is one of the most complexes of the Canaries archipelago. This complexity is evidenced by the existing controversy regarding the lateral or vertical collapse origin of the Las Cañadas caldera. The resistivity structure of the Las Cañadas caldera has been determined by the 3-D inversion of 188 broadband magnetotelluric data. The resistivity distribution obtained in the final model shows clear evidences of the presence of a vertical structure under the Teide, associated to the buried northern wall of the caldera. Additionally, the characteristics of the main resistivity structure, a ring-shaped low-resistivity body (<10 Ω m) interpreted as a hydrothermal clay alteration cap, would point out the presence of a handwall for the Icod Valley lateral landslide located under the Teide, but not in the southern caldera wall (current wall). All these support the vertical collapse hypothesis to explain the origin of the Las Cañadas caldera.

  16. Consequences of frictional melting and catastrophic dilation along caldera superfaults: Glencoe, Scotland

    NASA Astrophysics Data System (ADS)

    Clesham, Stephen; Kokelaar, Peter; Lavallee, Yan; Faulkner, Dan

    2014-05-01

    The Glencoe Caldera records complex piecemeal caldera collapse along superfaults with slip rates in sufficient to induce frictional melting. The deeply dissected volcano exposes outer fault segments with cm-scale bands of pseudotachylyte in contact with breccias, cataclasites and magmatic fault intrusions along the fault plane. Processes of frictional melting, cataclasis and intrusion were closely associated and the various materials show evidence for fluid-state mixing. At shallow depths, where the caldera faults dip outwards, rapid subsidence of the caldera footwall led to catastrophic dilation and the formation of free surfaces at low pressures. Decompressed hydrothermal systems were explosively excavated to form irregular voids behind the original fault surfaces. In such dilatant sections of the fault, frictional melts and then magma intrusions were fragmented and explosively transformed to froths or sprays that coated newly-formed void walls. We suggest that these processes are likely to have formed the lithic breccias with hydrothermally altered and thermally spalled clasts - common in caldera-related ignimbrites. Mineralogy and clast-size distribution analysis indicate that some pseudotachylytes formed virtually in-situ, from the (Dalradian) metamorphic basement psammites and quartzites, while others were apparently sourced at considerable depths. Lithic clasts and xenoliths within the fault intrusions and pseudotachylytes imply a granitic source, probably the Rannoch Moor pluton, which in turn suggests transport of frictional melt for at least several hundreds of metres up the caldera fault, conceivably as fluidized froth. Modelling and reproduction of pseudotachylyte using laboratory friction experiments are intended to investigate the conditions that generated these rocks, and to explore their mobility as melts and fragmented products, shedding light on the processes of friction in volcanic environments.

  17. Characterizing analogue caldera collapse with computerized X-ray micro-tomography

    NASA Astrophysics Data System (ADS)

    Poppe, Sam; Holohan, Eoghan; Boone, Matthieu; Pauwels, Elin; Cnudde, Veerle; Kervyn, Matthieu

    2013-04-01

    Analogue models in the past mainly explored caldera collapse structures by documenting 2D model cross-sections. Kinematic aspects and 3D structures of caldera collapse are less well understood, although they are essential to interpret recent field and monitoring data. We applied high resolution radiography and computerized X-ray micro-tomography (µCT) to image the deformation during analogue fluid withdrawal in small-scale caldera collapse models. The models test and highlight the possibilities and limitations of µCT-scanning to qualitatively image and quantitatively analyse deformation of analogue volcano-tectonic experiments. High resolution interval radiography sequences document '2.5D' surface and internal model geometry, and subsidence kinematics of a collapsing caldera block into an emptying fluid body in an unprecedented way. During the whole drainage process, all subsidence was bound by caldera ring faults. Subsidence was associated with dilatation of the analogue granular material within the collapsing column. The temporal subsidence rate pattern within the subsiding volume comprised three phases: 1) Upward ring fault propagation, 2) Rapid subsidence with the highest subsidence rates within the uppermost subsiding volume, 3) Relatively slower subsidence rates over the whole column with intermittent subsidence rate acceleration. Such acceleration did almost never affect the whole column. By using radiography sequences it is possible in a non-destructive manner to obtain a continuous observation of fault propagation, down sag mechanisms and the subsequent development of collapse structures. Multi-angle µCT scans of the collapse result allow for a full virtual 3D reconstruction of the model. This leads to an unprecedented 3D view on fault geometries. The developed method is a step towards the quantitative documentation of volcano-tectonic models that would render data interpretations immediately comparable to monitoring data available from recent

  18. Scientific core hole Valles caldera No. 2b (VC-2b), New Mexico

    SciTech Connect

    Garner, J.N.; Hulen, J.B.; Lysne, P.; Jacobson, R.; Goff, F.; Nielson, D.L.; Pisto, L.; Criswell, C.W.; Gribble, R.; Utah Univ. Research Inst., Salt Lake City, UT; Sandia National Labs., Albuquerque, NM; Los Alamos National Lab., NM; Utah Univ. Research Inst., Salt Lake City, UT; Tonto Drilling Services, Inc., Salt Lake City, UT; Los Alamo

    1989-01-01

    Research core hole was continuously cored to 1.762 km on the western flank of the caldera's resurgent dome in 1988. Bottom hole temperature is about 295{degree}C within Precambrian (1.5 Ga) quartz monzonite, deep within the liquid-dominated portions of the Sulphur Springs hydrothermal system. VC-2b may be the deepest, hottest, continuously cored hole in North America. Core recovery was 99.2%. The only major drilling problems encountered were when temperatures at the bit exceeded 225{degree}C below depths of about 1000 m. The result of these conditions was loss of viscosity and/or lubricity in the mud, apparently caused by breakdown of the high temperature polymers. Lithologies in caldera-fill indicate the drill site may be proximal to ignimbrite vents and that an intracaldera lake with temperatures approaching boiling formed soon after the caldera itself. Structural correlations between VC-2b and the 528-m-deep companion hole VC-2a indicate the earlier Toledo caldera (1.45 Ma; Otowi Member tuffs) and even older Lower Tuffs caldera experienced no structural resurgence similar to the 1.12 million year old Valles caldera. The hydrothermal system penetrated by these bores, consists of a shallow vapor-rich cap, which has evolved from an earlier 200{degree}C liquid-dominated system, overlying stacked, liquid-dominated zones up to about 300{degree}C. Geochemistry of mud returns collected during drilling suggests chloride-rich geothermal fluids were entering the bore and mixing with the drilling fluids in the fractured lower Paleozoic and Precambrian sections. 23 refs., 5 figs., 1 tab.

  19. Recrystallization and anatexis along the plutonic-volcanic contact of the Turkey Creek caldera, Arizona

    USGS Publications Warehouse

    du Bray, E.A.; Pallister, J.S.

    1999-01-01

    Unusual geologic and geochemical relations are preserved along the contact between intracaldera tuff and a resurgent intrusion within the 26.9 Ma Turkey Creek caldera of southeast Arizona. Thick intracaldera tuff is weakly argillically altered throughout, except in zones within several hundred meters of its contact with the resurgent intrusion, where the groundmass of the tuff has been variably converted to granophyre and unaltered sanidine phenocrysts are present. Dikes of similarly granophyric material originate at the tuff-resurgent intrusion contact and intrude overlying intracaldera megabreccia and tuff. Field relations indicate that the resurgent intrusion is a laccolith and that it caused local partial melting of adjacent intracaldera tuff. Geochemical and petrographic relations indicate that small volumes of partially melted intracaldera tuff assimilated and mixed with dacite of the resurgent intrusion along their contact, resulting in rocks that have petrographic and compositional characteristics transitional between those of tuff and dacite. Some of this variably contaminated, second-generation magma coalesced, was mobilized, and was intruded into overlying intracaldera rocks. Interpretation of the resurgent intrusion in the Turkey Creek and other calderas as intracaldera laccoliths suggests that intrusions of this type may be a common, but often unrecognized, feature of calderas. Development of granophyric and anatectic features such as those described here may be equally common in other calderas. The observations and previously undocumented processes described here can be applied to identification and interpretation of similarly enigmatic relations and rocks in other caldera systems. Integration of large-scale field mapping with detailed petrographic and chemical data has resulted in an understanding of otherwise intractable but petrologically important caldera-related features.

  20. Gas Chemistry of Submarine Hydrothermal Venting at Maug Caldera, Mariana Arc

    NASA Astrophysics Data System (ADS)

    Embley, R. W.; Lupton, J. E.; Butterfield, D. A.; Lilley, M. D.; Evans, L. J.; Olson, E. J.; Resing, J. A.; Buck, N.; Larson, B. I.; Young, C.

    2014-12-01

    Maug volcano consists of 3 islands that define the perimeter of a submerged caldera that was formed by an explosive eruption. The caldera reaches a depth of ~225 meters, and has a prominent central cone or pinnacle that ascends within 20 meters of the sea surface. Our exploration of Maug began in 2003, when a single hydrocast in the caldera detected a strong suspended particle and helium plume reaching a maximum of δ3He = 250% at ~180 meters depth, clearly indicating hydrothermal activity within the caldera. In 2004 we returned armed with the ROPOS ROV, and two ROPOS dives discovered and sampled low temperature (~4 °C) diffuse venting associated with bacterial mats on the NE flank of the central pinnacle at 145 m depth. Samples collected with titanium gas tight bottles were badly diluted with ambient seawater but allowed an estimate of end-member 3He/4He of 7.3 Ra. Four vertical casts lowered into the caldera in 2004 all had a strong 3He signal (δ3He = 190%) at 150-190 meters depth. A recent expedition in 2014 focused on the shallow (~10 m) gas venting along the caldera interior. Scuba divers were able to collect samples of the gas bubbles using evacuated SS bottles fitted with plastic funnels. The gas samples had a consistent ~170 ppm He, 8 ppmNe, 60% CO2, 40%N2, and 0.8% Ar, and an end-member 3He/4He ratio of 6.9 Ra. This 3He/4He ratio falls within the range for typical arc volcanoes. The rather high atmospheric component (N2, Ar, Ne) in these samples is not contamination but appears to be derived from subsurface exchange between the ascending CO2 bubbles and air saturated seawater. A single vertical cast in 2014 had a maximum δ3He = 55% at 140 m depth, much lower than in 2003 and 2004. This decrease is possibly due to recent flushing of the caldera by a storm event, or may reflect a decrease in the deep hydrothermal activity. This area of shallow CO2 venting in Maug caldera is of particular interest as a natural laboratory for studying the effects of ocean

  1. There's more than one way to build a caldera magma chamber: Evidence from volcanic-plutonic relationships at three faulted Rio-Grande-rift calderas

    NASA Astrophysics Data System (ADS)

    Zimmerer, M. J.; McIntosh, W. C.

    2011-12-01

    The temporal and chemical relationships of volcanic and plutonic rocks of the Questa (NM), Mt. Aetna (CO), and Organ caldera (NM) complexes were investigated to establish the origin of these silicic magmas. Rio Grande Rift faulting at these systems has exposed both intracaldera sequences and subvolcanic plutons. Ar/Ar and U/Pb ages reveal the timing of volcanic activity and pluton emplacement and cooling. We observe a link between ignimbrite zoning patterns and the temporal-chemical relationship of volcanic and plutonic rocks. The Questa caldera erupted the high-SiO2 peralkaline Amalia Tuff (AT) at 25.4 Ma. Volumetrically minor phases of two resurgent plutons and a ring dike are compositionally similar to the AT. The age of the ring dike (25.4 Ma) is indistinguishable to AT, suggesting that the peralkaline intrusions are nonerupted AT. The remaining pluton ages are 100 ka to 6.1 Ma younger than AT and are too young to be the AT residual crystal mush. The Mt. Princeton batholith and nested Mt. Aetna caldera are interpreted to be the sources for the 37.3 Ma, low-SiO2 rhyolitic Wall Mountain Tuff (WMT) and the 34.3 Ma, dacitic Badger Creek Tuff (BCT). U/Pb and Ar/Ar ages of Mt. Princeton batholith (36.5 to 35.1 Ma) indicate that it was emplaced and rapidly cooled during the interval between the WMT and BCT eruptions, and that any WMT age intrusions are now eroded. During the eruption of the BCT, the fully crystallized Mt. Princeton batholith collapsed into the Mt. Aetna caldera. Intrusions along the margins of the Mt. Aetna caldera are compositionally identical the BCT and contain zircons 100 to 500 ka older than the tuff, suggesting that the BCT magma chamber was incrementally emplaced prior to caldera eruption. The Organ caldera complex erupted three ignimbrites: a basal high-silica 36.5 Ma rhyolite, a middle intermediate-silica 36.2 Ma rhyolite, and an upper 36.0 Ma low-silica rhyolite. The intracaldera sequence is intruded by the Organ Needle pluton. U/Pb zircon

  2. Eastern American Indian Communities.

    ERIC Educational Resources Information Center

    Thomas, Robert K.

    Identification of social and cultural commonalities among American Indians of the eastern U.S. reveal 4 geographical areas--(1) the eastern seaboard (the largest group in both number of distinct groups and population); (2) the inland area; (3) Louisiana (a combination of inland and seaboard characteristics); (4) the eastern Great Lakes area…

  3. Tensor CSAMT survey over the Sulphur Springs thermal area, Valles Caldera, New Mexico, U.S.A. Part 1: Implications for structure of the western caldera

    SciTech Connect

    Wannamaker, P.E.

    1997-03-01

    An extensive tensor controlled-source audiomagnetotelluric (CSAMT) survey has been carried out over the Sulphur Springs geothermal area, Valles Caldera, New Mexico. Forty-five sites were acquired using two crossed transmitter bipoles placed approximately 13 km south of the center of the survey. The soundings in the Sulphur Springs area were arranged in four profiles to cross major structural features. CSAMT and magnetotelluric (MT) data taken outside Valles Caldera were constrained by drill logs and imply resistive Bandelier Tuff, underlain by conductive Paleozoic sediments, and further underlain by resistive, primarily Precambrian crystalline rocks. Model cross-sections within the caldera were derived using 2-D parameterized inversion constrained by drilling, with layered-earth inversion for starting models. Southeast of the Sulphur Creek fault, the upper 200 m of the section are of relatively low resistivity and correspond to unconsolidated land-slide and debris flows. The Bandelier Tuff below exhibits higher but variable resistivities because of alteration controlled by local faulting. Beneath the Bandelier Tuff, the Paleozoic sedimentary layer is only moderately less resistive than it is outside the caldera, with the lowest values occurring northwest of Sulphur Creek. Its low resistivity per se does not necessarily represent a hydrothermal aquifer. The Sulphur Creek fault appears to be a locus of substantial change in structural relief; upthrow of stratigraphy and basement to its west appears to be about 400--500 m. A major normal fault down to the southeast is located under the topographic expression of Freelove Canyon, which is up to 1 km farther southeast than suggested by previous geologic sections. High resistivities possibly corresponding to a vapor zone in the upper 500 m near VC-2B and VC-2A are not consistent with the CSAMT data.

  4. A short review of our current understanding of the development of ring faults during collapse caldera formation

    NASA Astrophysics Data System (ADS)

    Geyer, Adelina; Marti, Joan

    2014-09-01

    The term collapse caldera refers to those volcanic depressions resulting from the sinking of the chamber roof due to the rapid withdrawal of magma during the course of an eruption. During the last three decades, collapse caldera dynamics has been the focus of attention of numerous, theoretical, numerical and experimental studies. Nonetheless, even if there is a tendency to go for a general and comprehensive caldera dynamics model, some key aspects remain unclear, controversial or completely unsolved. This is the case of ring fault nucleation points and propagation and dip direction. Since direct information on calderas’ deeper structure comes mainly from partially eroded calderas or few witnessed collapses, ring faults layout at depth remains still uncertain. This has generated a strong debate over the detailed internal fault and fracture configuration of a caldera collapse and, in more detail, how ring faults initiate and propagate. We offer here a very short description of the main results obtained by those analogue and theoretical/mathematical models applied to the study of collapse caldera formation. We place special attention on those observations related to the nucleation and propagation of the collapse-controlling ring faults. This summary is relevant to understand the current state-of-the-art of this topic and it should be taken under consideration in future works dealing with collapse caldera dynamics.

  5. The Oligocene Creede Formation, Colorado: The sedimentary record of a deep lake within a resurgent caldera

    SciTech Connect

    Larsen, D.; Smith, G.A. . Dept. of Earth and Planetary Sciences)

    1993-04-01

    The Oligocene Creede Formation is the sedimentary fill of the Creede caldera in the Tertiary San Juan volcanic field in southern Colorado. Scientific drill core and outcrop studies of Creede strata allow an evaluation of the post-collapse sedimentary environments present within a caldera. Although the Creede Formation is structurally disrupted, correlation of fallout tuffs in exposed strata to those in the cores has clarified stratigraphic relationships. Following ash-fallout from the caldera-forming eruption, up to 121 meters of coarse grained debris-flow strata and rockfall debris with interstratified basinward ephemeral lake deposits were deposited. The presence of pseudomorphs after ikaite and up-section increase in carbonate facies suggest that the lake water was somewhat alkaline and cold (near freezing), and evolved chemically with time. A late-stage drop in lake level combined with integration of basin-feeding drainages and decreased subsidence lead to basinward progradation of coarser deltaic and lacustrine fan deposits. Sedimentation patterns suggest that subsidence occurred largely in the northern half of the caldera, and decreased late in the lake's history allowing the basin to fill with sediment.

  6. Monitoring super-volcanoes: Geophysical and geochemical signals at Yellowstone and other large caldera systems

    USGS Publications Warehouse

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

    2006-01-01

    Earth's largest calderas form as the ground collapses during immense volcanic eruptions, when hundreds to thousands of cubic kilometres of magma are explosively withdrawn from the Earth's crust over a period of days to weeks. Continuing long after such great eruptions, the resulting calderas often exhibit pronounced unrest, with frequent earthquakes, alternating uplift and subsidence of the ground, and considerable heat and mass flux. Because many active and extinct calderas show evidence for repetition of large eruptions, such systems demand detailed scientific study and monitoring. Two calderas in North America, Yellowstone (Wyoming) and Long Valley (California), are in areas of youthful tectonic complexity. Scientists strive to understand the signals generated when tectonic, volcanic and hydrothermal (hot ground water) processes intersect. One obstacle to accurate forecasting of large volcanic events is humanity's lack of familiarity with the signals leading up to the largest class of volcanic eruptions. Accordingly, it may be difficult to recognize the difference between smaller and larger eruptions. To prepare ourselves and society, scientists must scrutinize a spectrum of volcanic signals and assess the many factors contributing to unrest and toward diverse modes of eruption. ?? 2006 The Royal Society.

  7. Deformation of the Wineglass Welded Tuff and the timing of caldera collapse at Crater Lake, Oregon

    USGS Publications Warehouse

    Kamata, H.; Suzuki-Kamata, K.; Bacon, C.R.

    1993-01-01

    Four types of deformation occur in the Wineglass Welded Tuff on the northeast caldera rim of Crater Lake: (a) vertical tension fractures; (b) ooze-outs of fiamme: (c) squeeze-outs of fiamme; and (d) horizontal pull-apart structures. The three types of plastic deformation (b-d) developed in the lower part of the Wineglass Welded Tuff where degree of welding and density are maximum. Deformation originated from concentric normal faulting and landsliding as the caldera collapsed. The degree of deformation of the Wineglass Welded Tuff increases toward the northeast part of the caldera, where plastic deformation occurred more easily because of a higher emplacement temperature probably due to proximity to the vent. The probable glass transition temperature of the Wineglass Welded Tuff suggests that its emplacement temperature was ???750??C where the tuff is densely welded. Calculation of the conductive cooling history of the Wineglass Welded Tuff and the preclimactic Cleetwood (lava) flow under assumptions of a initially isothermal sheet and uniform properties suggests that (a) caldera collapse occurred a maximum of 9 days after emplacement of the Wineglass Welded Tuff, and that (b) the period between effusion of the Cleetwood (lava) flow and onset of the climactic eruption was <100 years. If cooling is controlled more by precipitation during quiescent periods than by conduction, these intervals must be shorter than the calculated times. ?? 1993.

  8. Wall-rock argillic alteration and uranium mineralization of the northwestern Strel'tsovka caldera

    NASA Astrophysics Data System (ADS)

    Andreeva, O. V.; Golovin, V. A.; Petrov, V. A.

    2010-02-01

    Alteration of rocks and localization of uranium mineralization in the northwestern Strel’tsovka caldera are exemplified in the Dal’nee deposit. In the main parameters of hydrothermal mineralization (temperature, pH, pressure, and composition of solution), the Dal’nee deposit differs from the deposits of the Strel’tsovka ore field located in the central part of the caldera. The localization of high-grade stratiform orebodies are interpreted in light of kinematic relations between steeply and gently dipping faults that formed in the tectonic setting of the NE-SW-trending, long-living, right-lateral, strike-slip faulting. The wide halos of argillic alteration and the structural control of uranium mineralization are caused by the fact that the deposit is located at the margin of the geological block, which has developed since the Late Triassic in a regime of extension (pull-apart) to form a depression, which is arranged en echelon relative to the main caldera and comparable to it in area. Currently, this depression is overlapped by sediments of the Sukhoi Urulyungui Basin. Such a structure markedly increases the probability of finding hidden uranium ores associated with low-temperature argillic alteration in the volcanosedimantary rocks and granitoid basement of the northwestern Strel’tsovka caldera.

  9. Isotope geochemistry of thermal and nonthermal waters in the Valles caldera, Jemez Mountains, northern New Mexico

    SciTech Connect

    Vuataz, F.D.; Goff, F.

    1986-02-10

    Over 100 stable isotope and 45 tritium analyses from thermal and nonthermal waters of the Jemez Mountains region, New Mexico, have been used to define the hydrodynamics of the Valles caldera (Baca) geothermal system and related geothermal fluids of the region. Evaluation of 36 cold meteoric waters yields an equation for the Jemez Mountains meteoric water line of deltaD = 8delta/sup 18/O+12, while further evaluation of nine cold meteoric waters yields an equation relating recharge elevation to deuterium content of E(meters) = -44.9 (deltaD)-1154. Based on the deuterium content of five Baca well waters (223/sup 0/--294/sup 0/C), the average recharge elevation of the Valles geothermal system ranges from 2530 to 2890 m. This range of elevations falls between the elevations of the lowest point of the caldera floor (2400 m) and the summit of the resurgent dome inside the caldera (3430 m). Thus stable isotopes indicate that the caldera depression probably serves as a recharge basin for the deep geothermal system. Although cold spring waters of the Jemez Mountains region consist of meteoric water, tritium analyses show that most of them contain water between 20 and 75 years old.

  10. Structure and stratigraphy beneath a young phreatic vent: South Inyo Crater, Long Valley caldera, California

    SciTech Connect

    Eichelberger, J.C.; Vogel, T.A.; Younker, L.W.; Dan Miller, C.; Heiken, G.H.; Wohletz, K.H.

    1988-11-10

    An 861-m-long hole has been cored on a slanted trajectory that passed directly beneath South Inyo Crater in the west moat of Long valley Caldera, California. The purpose of the hole was to investigate the magmatic behavior that led to surface deformation and phreatic activity during the 600-year-old eruption of the Inyo vent chain. The hole was sited 216 m southwest of the crater, passed beneath its center at a depth of 566 m, and terminated 79 m northeast of the crater center at a depth of 810 m. Metamorphic basement was encountered at a depth of 779 m. The volcanic and sedimentary sequence consists solely of post-Bishop Tuff caldera fill, including 319 m of moat basalt and 342 m of early rhyolite, and is nearly 900 m thinner than in a Unocal Corporation well 900 m to the southeast. Apparently, a major fault lies between the two holes and forms part of the western structural boundary of the caldera, 3--4 km inboard of its topographic boundary. Breccia zones that intrude the caldera fill were intersected at 12.0--9.3 m and 1.2--0.8 m SW and 8.5--25.1 m NE of the crater center.

  11. A three-dimensional gravity model of the geologic structure of Long Valley caldera

    SciTech Connect

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

    1987-03-01

    Several attempts to define and interpret this anomaly have been made in the past using 2-D and 3-D models. None of the previous interpretations have yielded definitive results, but in fairness, the interpretation here has benefited from a larger gravity data base and more subsurface control than available to previous workers. All published 3-D models simplistically assumed constant density of fill. All 2-D models suffered from the inherent three-dimensionality of the complicated density structure of Long Valley caldera. In addition, previous interpreters have lacked access to geological data, such as well lithologies and density logs, seismic refraction interpretations, suface geology, and structural geology interpretations. The purpose of this study is to use all available gravity data and geological information to constrain a multi-unit, 3-D density model based on the geology of Long Valley caldera and its vicinity. Insights on the geologic structure of the caldera fill can help other geophysical interpretations in determining near-surface effects so that deeper structure may be resolved. With adequate control on the structure of the caldera fill, we are able to examine the gravity data for the presence of deeper density anomalies in the crust. 20 refs., 7 figs.

  12. Topographic modelling of caldera analogues using Structure from Motion - Multiview stereo-photogrammetry

    NASA Astrophysics Data System (ADS)

    Ulusoy, İnan; Aydın, Eda; Evren Çubukçu, H.

    2016-04-01

    Analogue caldera models have long been used in volcanology to investigate structural evolution of volcanoes during tumescence and collapse periods. Influence of tectonic forces on volcanic features are also in the scope of those experiments. As well as interior modelling of the caldera experiments, topographic modelling is essential for digital monitoring and quantification purposes. Topographic modelling of those sandbox models is possible using laser scanning techniques. Particle tracking using still images is another way to demonstrate and quantify the structure and movement during the experiment. The quantum leap in the digital photography and computation tools and ease of access to both, provides the use of a new modelling technique in various scales and applications in Geology. Although the roots are older, Structure from Motion - Multiview stereo-photogrammetry (SfM-MVS) is a relatively new technique for surface modelling via several high resolution photographs. We have used SfM-MVS to digitally model the elevation of the tumescence and collapse cycles in analogue caldera experiments. Several sandbox experiments have been modelled using SfM-MVS technique stage by stage during tumescence and collapse periods. It has been possible to evaluate the structural evolution of the collapse models. Additionally, using particle tracking via still images acquired during the experiments, we have modelled the superficial evolution of the caldera structure. SfM-MVS is an effective low budget method for modelling in decimetric scale down to millimetre/micrometre precision.

  13. Monitoring super-volcanoes: geophysical and geochemical signals at Yellowstone and other large caldera systems.

    PubMed

    Lowenstern, Jacob B; Smith, Robert B; Hill, David P

    2006-08-15

    Earth's largest calderas form as the ground collapses during immense volcanic eruptions, when hundreds to thousands of cubic kilometres of magma are explosively withdrawn from the Earth's crust over a period of days to weeks. Continuing long after such great eruptions, the resulting calderas often exhibit pronounced unrest, with frequent earthquakes, alternating uplift and subsidence of the ground, and considerable heat and mass flux. Because many active and extinct calderas show evidence for repetition of large eruptions, such systems demand detailed scientific study and monitoring. Two calderas in North America, Yellowstone (Wyoming) and Long Valley (California), are in areas of youthful tectonic complexity. Scientists strive to understand the signals generated when tectonic, volcanic and hydrothermal (hot ground water) processes intersect. One obstacle to accurate forecasting of large volcanic events is humanity's lack of familiarity with the signals leading up to the largest class of volcanic eruptions. Accordingly, it may be difficult to recognize the difference between smaller and larger eruptions. To prepare ourselves and society, scientists must scrutinize a spectrum of volcanic signals and assess the many factors contributing to unrest and toward diverse modes of eruption. PMID:16844648

  14. Galileo's Last Fly-Bys of Io: NIMS Observations of Loki, Tupan, and Emakong Calderas

    NASA Technical Reports Server (NTRS)

    Lopes, Rosaly M. C.; Kamp, L. W.; Davies, A. G.; Smythe, W. D.; Carlson, R. W.; Doute, S.; McEwen, A.; Turtle, E. P.; Leader, F.; Mehlman, R.

    2002-01-01

    NIMS results from the 2001 Galileo fly-bys of Io will be presented, focusing on three calderas that may contain lava lakes. Preliminary results from the January 2002 Io fly-by will be presented. Additional information is contained in the original extended abstract.

  15. Steady subsidence of a repeatedly erupting caldera through InSAR observations: Aso, Japan

    NASA Astrophysics Data System (ADS)

    Nobile, Adriano; Acocella, Valerio; Ruch, Joel; Aoki, Yosuke; Borgstrom, Sven; Siniscalchi, Valeria; Geshi, Nobuo

    2016-04-01

    The relation between unrest and eruption at calderas is still poorly understood. Aso caldera, Japan, shows minor episodic eruptions, mainly phreatic, associated with steady subsidence. We analyse the recent deformation of Aso using SAR images from 1993 to 2011 and compare this with the eruptive activity. Although the dataset suffers from limitations (e.g., atmospheric effects, coherence loss, low signal to noise ratio), we observe a steady subsidence signal from 1996 to 1998, that suggests an overall contraction of a magmatic source below the caldera centre, from 4.5 to 7 km depth. Because of the similar volumes of the contracting source and erupted material, we propose that the contraction may have been induced by the release of the magmatic fluids feeding the eruptions. If confirmed by further data, this hypothesis suggests that degassing processes play a crucial role in triggering minor eruptions within open conduit calderas, as at Aso. These features underline the importance of defining any eruptive potential also from deflating magmatic systems with open conduit.

  16. Hydrothermal fluid flow and deformation in large calderas: Inferences from numerical simulations

    USGS Publications Warehouse

    Hurwitz, S.; Christiansen, L.B.; Hsieh, P.A.

    2007-01-01

    Inflation and deflation of large calderas is traditionally interpreted as being induced by volume change of a discrete source embedded in an elastic or viscoelastic half-space, though it has also been suggested that hydrothermal fluids may play a role. To test the latter hypothesis, we carry out numerical simulations of hydrothermal fluid flow and poroelastic deformation in calderas by coupling two numerical codes: (1) TOUGH2 [Pruess et al., 1999], which simulates flow in porous or fractured media, and (2) BIOT2 [Hsieh, 1996], which simulates fluid flow and deformation in a linearly elastic porous medium. In the simulations, high-temperature water (350??C) is injected at variable rates into a cylinder (radius 50 km, height 3-5 km). A sensitivity analysis indicates that small differences in the values of permeability and its anisotropy, the depth and rate of hydrothermal injection, and the values of the shear modulus may lead to significant variations in the magnitude, rate, and geometry of ground surface displacement, or uplift. Some of the simulated uplift rates are similar to observed uplift rates in large calderas, suggesting that the injection of aqueous fluids into the shallow crust may explain some of the deformation observed in calderas.

  17. Structural controls on the emission of magmatic carbon dioxide gas, Long Valley Caldera, USA

    NASA Astrophysics Data System (ADS)

    Lucic, Gregor; Stix, John; Wing, Boswell

    2015-04-01

    We present a degassing study of Long Valley Caldera that explores the structural controls upon emissions of magmatic carbon dioxide gas. A total of 223 soil gas samples were collected and analyzed for stable carbon isotopes using a field-portable cavity ring-down spectrometer. This novel technique is flexible, accurate, and provides sampling feedback on a daily basis. Sampling sites included major and minor volcanic centers, regional throughgoing faults, caldera-related structures, zones of elevated seismicity, and zones of past and present hydrothermal activity. The classification of soil gases based on their δ13C and CO2 values reveals a mixing relationship among three end-members: atmospheric, biogenic, and magmatic. Signatures dominated by biogenic contributions (~4 vol %, -24‰) are found on the caldera floor, the interior of the resurgent dome, and areas associated with the Hilton Creek and Hartley Springs fault systems. With the introduction of the magmatic component (~100 vol %, -4.5‰), samples acquire mixing and hydrothermal signatures and are spatially associated with the central caldera and Mammoth Mountain. In particular, they are concentrated along the southern margin of the resurgent dome where the interplay between resurgence-related reverse faulting and a bend in the regional fault system has created a highly permeable fracture network, suitable for the formation of shallow hydrothermal systems. This contrasts with the south moat, where despite elevated seismicity, a thick sedimentary cover has formed an impermeable cap, inhibiting the ascent of fluids and gases to the surface.

  18. The first report of the aphids of the Valles Caldera National Preserve, New Mexico, USA

    Technology Transfer Automated Retrieval System (TEKTRAN)

    We report 50 species, belonging to 26 genera of aphids (Hemiptera: Aphididae), collected within and near the boundary of the Valles Caldera National Preserve in the Jemez Mountains of northern New Mexico, USA. Of these, 35 (70%) represent new distribution records for New Mexico. Plant genera/species...

  19. Fluid-Rock Interaction in the Miocene Tejeda Caldera, Gran Canaria, Canary Islands

    NASA Astrophysics Data System (ADS)

    Donoghue, E.; Troll, V. R.; Harris, C.; Walter, T. R.; Pérez Torrado, F. J.

    2007-12-01

    Rhyolite-trachyte tuffs deposited within the Miocene Tejeda caldera (Mogán Group 14-13.3Ma) show evidence of severe fluid-rock interaction. The altered tuffs are restricted to a peripheral zone directly inside the caldera margin, and occur at four distinct horizons within the mid-upper Mogán ignimbrite succession. Upper-Mogán tuffs display pervasive intermediate argillic alteration (smectite+illite+zeolites+adularia) and silicification (microcrystalline quartz+amorphous silica), indicative of low-temperature (≤250°C) near-neutral pH conditions. Quartz+kaolinite+muscovite+chlorite+calcite alteration of mid-Mogán tuffs and breccias may reflect boiling of higher-temperature, acidic hydrothermal fluids at depth. Si+Na+K+Pb+Sr+Rb were highly mobile during fluid-rock interaction, whereas Ti+Zr+Nb were dominantly refractory. Altered intra-caldera tuffs (n=65) have higher δ18O values than equivalent unaltered extra-caldera ignimbrites, reflecting an overall low-temperature near-surface environment in which meteoric water (δD ca.-15‰, δ18O ca.-3‰) was the dominant fluid source. A decrease in δ18O from upper- to mid- Mogán altered tuffs is consistent with an increase in fluid temperature with depth. Unaltered ignimbrites have δD values of -110 to -168‰ (n=6) and ≤0.2wt% H2O, indicative of Rayleigh-type H2O-exsolution. Altered tuffs have δD values of -52 to -117‰ (n=75) and up to 4wt% H2O, reflecting interaction with steam (δD\\ll-15‰) or an evolved low-δD fluid. Apparently unaltered ignimbrites between altered horizons (n=13), and shield basalts directly outside the caldera margin (n=6), have elevated δD and H2O values relative to equivalent unaltered rocks, indicative of minor alteration. Supported by numerical modelling, our Gran Canaria data reflect an intrusion-related, structurally controlled epithermal system, in which fluids and/or vapours migrated through intra-caldera tuffs via channelised, porous flow. This study may help to unravel the

  20. Evidence from cosmic-ray exposure dating based on 36Cl for the pre-Minoan caldera on Santorini, Greece

    NASA Astrophysics Data System (ADS)

    Athanassas, Constantin; Bourlès, Didier; Braucher, Regis; Druitt, Tim; Nomikou, Paraskevi; Léanni, Laetitia

    2016-04-01

    The physiography of Santorini prior to the Minoan (Late Bronze Age) eruption (17th century BCE) is of great archaeological interest, given the importance of Santorini as a commercial centre and port in the Minoan empire. However, the paleogeography of the pre-Minoan caldera has been a point of controversy: Heiken and McCoy (1984) advocated the existence, in the southern part of the present-day caldera, of a pre-existing caldera formed during the 172 ka Lower Pumice eruption, whereas Druitt and Francaviglia (1992), based on the presence of in situ plinian pumice from the Minoan eruption adhering to the modern cliff, conceived the pre-Minoan (22 ka) caldera as having occupied much of the northern basin of the present-day caldera. With the goal of settling the debate we performed cosmic ray exposure dating employing in situ-produced cosmogenic 36Cl to date different generations of caldera cliffs at Santorini, and hence to identify those cliffs predating the Minoan eruption. Our methodology involved the determination of the in situ-produced cosmogenic 36Cl in basaltic and andesitic rocks cropping out in the cliffs. The samples returned 36Cl CRE ages consistent with previously published field mapping of cliff populations based on geomorphological and stratigraphic arguments (Druitt and Francaviglia 1992), suggesting that much of the present cliff line of northern Santorini predated the Minoan eruption, or was superficially modified by landslips and rockfalls during that eruption. The 36Cl CRE ages enable us to better define the paleogeography of the pre-Minoan caldera. References [1] Druitt, T. H. and Francaviglia, V.1992. Caldera formation on Santorini and the physiography of the islands in the Late Bronze Age. Bulletin of Volcanology 54, 484-493. [2] Heiken G and McCoy F (1984) Caldera development during the Minoan eruption, Thira, Cyclades, Greece. Journal of Geophysical Research: 89 (B10), 8841-8862.

  1. Nonlinear teleseismic tomography at Long Valley caldera, using three-dimensional minimum travel time ray tracing

    SciTech Connect

    Weiland, C.M.; Steck, L.K.; Dawson, P.B.

    1995-10-10

    The authors explore the impact of three-dimensional minimum travel time ray tracing on nonlinear teleseismic inversion. This problem has particular significance when trying to image strongly contrasting low-velocity bodies, such as magma chambers, because strongly refracted/and/or diffracted rays may precede the direct P wave arrival traditionally used in straight-ray seismic tomography. They use a simplex-based ray tracer to compute the three-dimensional, minimum travel time ray paths and employ an interative technique to cope with nonlinearity. Results from synthetic data show that their algorithm results in better model reconstructions compared with traditional straight-ray inversions. The authors reexamine the teleseismic data collected at Long Valley caldera by the U.S. Geological Survey. The most prominent feature of their result is a 25-30% low-velocity zone centered at 11.5 km depth beneath the northwestern quandrant of the caldera. Beneath this at a depth of 24.5 km is a more diffuse 15% low-velocity zone. In general, the low velocities tend to deepen to the south and east. The authors interpret the shallow feature to be the residual Long Valley caldera magma chamber, while the deeper feature may represent basaltic magmas ponded in the midcrust. The deeper position of the prominent low-velocity region in comparison to earlier tomographic images is a result of using three-dimensional rays rather than straight rays in the ray tracing. The magnitude of the low-velocity anomaly is a factor of {approximately}3 times larger than earlier models from linear arrival time inversions and is consistent with models based on observations of ray bending at sites within the caldera. These results imply the presence of anywhere from 7 to 100% partial melt beneath the caldera. 40 refs., 1 fig., 1 tab.

  2. Crustal-scale perspective on the rapid development of Oligocene silicic calderas and related underlying plutonic systems, western Nevada USA

    NASA Astrophysics Data System (ADS)

    Colgan, J. P.; John, D. A.; Henry, C.; Watts, K. E.

    2015-12-01

    Geologic mapping, U-Pb zircon ages, and 40Ar/39Ar sanidine ages document the timing and extent of Oligocene magmatism in the southern Stillwater Range and Clan Alpine Mountains of western Nevada, where Miocene extension has exposed five nested silicic calderas and related granitic plutons to crustal depths locally ≥9 km. The ≤29.4-28.8 Ma Job Canyon caldera in the Stillwater Range is filled with ~4 km of intracaldera tuff and lava flows; the 28.4 Ma IXL pluton intrudes intracaldera tuff and extends to ≥9 km depth. The 29 Ma Deep Canyon caldera covers ~250 km2 of the Clan Alpine Mountains, but only the upper ~1 km is exposed. The ≤26.0-25.2 Ma Poco Canyon caldera in the Stillwater Range is filled with two distinct intracaldera tuffs totaling 4.5 km thick, underlain by the 24.8 Ma Freeman Creek pluton exposed to depths ≥8 km. The small 25.3 Ma Louderback Mountains caldera in the SW Clan Alpine Mountains is filled with ~600 m of intracaldera tuff deposited on Oligocene rhyolite lava flows. The 25.1 Ma Elevenmile Canyon caldera spans ~1600 km2 in the Stillwater Range, Clan Alpine Mountains, and Desatoya Mountains, where it overlaps or cross cuts older calderas. Its total volume is ≥2500 km3, mostly consisting of the 1-4 km thick tuff of Elevenmile Canyon. 24.9-25.5 Ma silicic intrusive rocks underlie the Louderback Mountains and Elevenmile Canyon calderas to depths ≥6-8 km, locally surrounding septa of basement rock and older Oligocene igneous rocks. Two magmatic pulses, each lasting ~1 m.y. and associated with the 29 and 25 Ma caldera complexes, replaced almost the entire Mesozoic upper crust with Oligocene intrusive and extrusive rock to depths ≥9 km over a 1500 km2 area (pre-extension). Magma emplacement was most likely accommodated by downward transfer of country rocks and accompanied by isostatic surface uplift. If other Great Basin calderas are similar, the dense concentration of shallowly exposed calderas in central Nevada may be underlain by a

  3. Geothermal hydrology of Valles Caldera and the southwestern Jemez Mountains, New Mexico

    USGS Publications Warehouse

    Trainer, Frank W.; Rogers, Robert J.; Sorey, M.L.

    2000-01-01

    The Jemez Mountains in north-central New Mexico are volcanic in origin and have a large central caldera known as Valles Caldera. The mountains contain the Valles geothermal system, which was investigated during 1970-82 as a source of geothermal energy. This report describes the geothermal hydrology of the Jemez Mountains and presents results of an earlier 1972-75 U.S. Geological Survey study of the area in light of more recent information. Several distinct types of thermal and nonthermal ground water are recognized in the Jemez Mountains. Two types of near-surface thermal water are in the caldera: thermal meteoric water and acid sulfate water. The principal reservoir of geothermal fluids is at depth under the central and western parts of the caldera. Nonthermal ground water in Valles Caldera occurs in diverse perched aquifers and deeper valley-fill aquifers. The geothermal reservoir is recharged by meteorically derived water that moves downward from the aquifers in the caldera fill to depths of 6,500 feet or more and at temperatures reaching about 330 degrees Celsius. The heated geothermal water rises convectively to depths of 2,000 feet or less and mixes with other ground water as it flows away from the geothermal reservoir. A vapor zone containing steam, carbon dioxide, and other gases exists above parts of the liquid-dominated geothermal zone. Two subsystems are generally recognized within the larger geothermal system: the Redondo Creek subsystem and the Sulphur Creek subsystem. The permeability in the Redondo Creek subsystem is controlled by stratigraphy and fault-related structures. Most of the permeability is in the high-angle, normal faults and associated fractures that form the Redondo Creek Graben. Faults and related fractures control the flow of thermal fluids in the subsystem, which is bounded by high-angle faults. The Redondo Creek subsystem has been more extensively studied than other parts of the system. The Sulphur Springs subsystem is not as well

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

    NASA Astrophysics Data System (ADS)

    de Natale, Giuseppe; Troise, Claudia

    2010-05-01

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

  5. Understanding the link between circumferential dikes and eruptive fissures around calderas based on numerical and analog models

    NASA Astrophysics Data System (ADS)

    Corbi, Fabio; Rivalta, Eleonora; Pinel, Virginie; Maccaferri, Francesco; Acocella, Valerio

    2016-06-01

    Active calderas are seldom associated with circumferential eruptive fissures, but eroded magmatic complexes reveal widespread circumferential dikes. This suggests that, while the conditions to emplace circumferential dikes are easily met, mechanisms must prevent them from reaching the surface. We explain this discrepancy with experiments of air injection into gelatin shaped as a volcano with caldera. Analog dikes show variable deflection, depending on the competition between overpressure, Pe, and topographic unloading, Pl; when Pl/Pe = 4.8-5.3, the dikes propagate orthogonal to the least compressive stress. Due to the unloading, they become circumferential and stall below the caldera rim; buoyancy is fundamental for the further rise and circumferential fissure development. Numerical models quantitatively constrain the stress orientation within the gelatin, explaining the observed circumferential dikes. Our results explain how dikes propagate below the rim of felsic and mafic calderas, but only in the latter they are prone to feed circumferential fissures.

  6. Geothermal data for 95 thermal and nonthermal waters of the Valles Caldera - southern Jemez Mountains region, New Mexico

    SciTech Connect

    Goff, F.; McCormick, Trujillo, P.E. Jr.; Counce, D.; Grigsby, C.O.

    1982-05-01

    Field, chemical, and isotopic data for 95 thermal and nonthermal waters of the southern Jemez Mountains, New Mexico are presented. This region includes all thermal and mineral waters associated with Valles Caldera and many of those located near the Nacimiento Uplift, near San Ysidro. Waters of the region can be categorized into five general types: (1) surface and near surface meteoric waters; (2) acid-sulfate waters (Valles Caldera); (3) thermal meteoric waters (Valles Caldera); (4) deep geothermal and derivative waters (Valles Caldera); and (5) mineralized waters near San Ysidro. Some waters display chemical and isotopic characteristics intermediate between the types listed. The object of the data is to help interpret geothermal potential of the Jemez Mountains region and to provide background data for investigating problems in hydrology, structural geology, hydrothermal alterations, and hydrothermal solution chemistry.

  7. Hydrogeochemical data for thermal and nonthermal waters and gases of the Valles Caldera- southern Jemez Mountains region, New Mexico

    SciTech Connect

    Shevenell, L.; Goff, F.; Vuataz, F.; Trujillo, P.E. Jr.; Counce, D.; Janik, C.J.; Evans, W.

    1987-03-01

    This report presents field, chemical, gas, and isotopic data for thermal and nonthermal waters of the southern Jemez Mountains, New Mexico. This region includes all thermal and mineral waters associated with Valles Caldera and many of those located near the Nacimiento Uplift, north of San Ysidro. Waters of the region can be categorized into five general types: (1) surface and near-surface meteoric waters; (2) acid-sulfate waters at Sulphur Springs (Valles Caldera); (3) thermal meteoric waters in the ring fracture zone (Valles Caldera); (4) deep geothermal waters of the Baca geothermal field and derivative waters in the Soda Dam and Jemez Springs area (Valles Caldera); and (5) mineralized waters near San Ysidro. Some waters display chemical and isotopic characteristics intermediate between the types listed. Data in this report will help in interpreting the geothermal potential of the Jemez Mountains region and will provide background for investigating problems in hydrology, structural geology, hydrothermal alterations, and hydrothermal solution chemistry.

  8. Probing the source and timing of rejuvenation and hybridization in post-caldera rhyolite magmas at Yellowstone Caldera

    NASA Astrophysics Data System (ADS)

    Till, C.; Vazquez, J. A.; Boyce, J. W.; Stelton, M. E.

    2013-12-01

    We find petrographic, isotopic and geochemical evidence for rejuvenation and recycling of subvolcanic intrusions within low δ18O intracaldera rhyolite lavas erupted following the formation of Yellowstone Caldera. In order to resolve the timing and compositional end-members involved in rejuvenation and hybridization of Yellowstone's subvolcanic magma reservoir, we have analyzed the Pb isotopic composition of clinopyroxene and sanidine phenocrysts and performed U-Pb dating of zircons from the South Biscuit Basin (SBB) and Scaup Lake (SCL) rhyolite lava flows. Both SBB and SCL erupted ca. 260 ka based on indistinguishable 40Ar/39Ar ages [1,2] and represent a renewed episode of postcaldera volcanism after a hiatus of ~200 kyr. Zoned phenocrysts of quartz, clinopyroxene, orthopyroxene, plagioclase, and sanidine and accessory zircon and Fe-Ti oxides characterize both SBB and SCL. SCL and SBB clinopyroxene have identical compositions and core-to-rim zoning patterns in Fe, Mg, and trace elements and commonly exhibit exsolution lamellae in their cores, suggesting that subsolidus conditions were attained during the early evolution of these rhyolites. The exsolution-bearing cores are mantled by a zone of relatively high Mg/Fe and low HREE & Rb, which is in turn overgrown by a rim with slightly lower Mg/Fe, and higher HREE & Rb. This zoning pattern suggests rejuvenation of subsolidus rhyolite by the influx of at least two less evolved, hotter silicic magmas. Diffusion modeling of Fe-Mg concentration profiles in clinopyroxene suggests that these events occurred on the order of 103 yrs prior to eruption. To identify the source of the rejuvenated rhyolite and delimit intra-grain variability, we analyzed the Pb-isotopic compositions of the SBB and SCL clinopyroxene zones via LA-MC-ICPMS. The different zones within SBB and SCL clinopyroxene yield indistinguishable Pb-isotope compositions with 208Pb/206Pb=2.165-2.185 and 207Pb/206Pb=0.882-0.890, which matches the Pb

  9. Conductive heat flux in VC-1 and the thermal regime of Valles Caldera, Jemez Mountains, New Mexico

    NASA Astrophysics Data System (ADS)

    Sass, J. H.; Morgan, Paul

    1988-06-01

    Over 5% of heat in the western United States is lost through Quaternary silicic volcanic centers, including the Valles caldera in north central New Mexico. These centers are the sites of major hydrothermal activity and upper crustal metamorphism, metasomatism, and mineralization, producing associated geothermal resources. We present new heat flow data from Valles caldera core hole 1 (VC-1), drilled in the southwestern margin of the Valles caldera. Thermal conductivities were measured on 55 segments of core from VC-1, waxed and wrapped to preserve fluids. These values were combined with temperature gradient data to calculate heat flow. Above 335 m, which is probably unsaturated, heat flow is 247±16 mW m-2. The only deep temperature information available is from an uncalibrated commercial log made 19 months after drilling. Gradients, derived from uncalibrated temperature logs, and conductivities are inversely correlated between 335 and 737 m, indicating a conductive thermal regime, and component heat fluxes over three depth intervals (335-539 m, 549-628 m, and 628-737 m) are in excellent agreement with each other with an average of 504±15 mW m-2. Temperature logs to 518 m depth with well-calibrated temperature sensors result in a revised heat flow of 463±15 mW m. We use shallow thermal gradient data from 75 other sites in and around the caldera to interpret the thermal regime at the VC-1 site. A critical review of published thermal conductivity data from the Valles caldera yields an average thermal conductivity of ≥1 W m-1 K-1 for the near-surface tuffaceous material, and we assume that shallow gradient values (°C km-1) are approximately numerically equal to heat flow (mW m-2). Heat loss from the caldera is asymmetrically distributed, with higher values (400 mW m-2 or higher) concentrated in the west-southwestern quadrant of the caldera. This quadrant also contains the main drainage from the caldera and the youngest volcanism associated with the caldera. We

  10. Lithic breccia and ignimbrite erupted during the collapse of Crater Lake Caldera, Oregon

    USGS Publications Warehouse

    Druitt, T.H.; Bacon, C.R.

    1986-01-01

    The climactic eruption of Mount Mazama (6845 y.B.P.) vented a total of ???50 km3 of compositionally zoned rhyodacitic to basaltic magma from: (a) a single vent as a Plinian pumice fall deposit and the overlying Wineglass Welded Tuff, and (b) ring vents as ignimbrite and coignimbrite lithic breccia accompanying the collapse of Crater Lake caldera. New field and grain-size data for the ring-vent products are presented in this report. The coarse-grained, poorly bedded, clast-supported lithic breccia extends as far as 18 km from the caldera center. Like the associated ignimbrite, the breccia is compositionally zoned both radially and vertically, and silicic, mixed, and mafic types can be recognized, based on the proportion of rhyodacitic pumice. Matrix fractions in silicic breccias are depleted of fines and are lithic- and crystal-enriched relative to silicic ignimbrite due to vigorous gas sorting during emplacement. Ignimbrite occurs as a proximal veneer deposit overlying the breccia, a medial (??? 8 to ??? 25 km from the caldera center), compositionally zoned valley fill as much as > 110 m thick, and an unzoned distal ({slanted equal to or greater-than} 20 km) facies which extends as far as 55 km from the caldera. Breccia within ??? 9 km of the caldera center is interpreted as a coignimbrite lag breccia formed within the deflation zone of the collapsing ring-vent eruption columns. Expanded pyroclastic flows of the deflation zone were probably vertically graded in both size and concentration of blocks, as recently postulated for some turbidity currents. An inflection in the rate of falloff of lithic-clast size within the lithic breccia at ??? 9 km may mark the outer edge of the deflation zone or may be an artifact of incomplete exposure. The onset of ring-vent activity at Mt. Mazama was accompanied by a marked increase in eruptive discharge. Pyroclastic flows were emplaced as a semicontinuous stream, as few ignimbrite flow-unit boundaries are evident. As eruption from

  11. Evolution of the Creede Caldera and its relation to mineralization in the Creede mining district, Colorado

    USGS Publications Warehouse

    Barton, Paul B.; Rye, Robert O.; Bethke, Philip M.

    2000-01-01

    At 25 Ma a major epithermal silver and base metal deposit formed in rhyolitic welded tuff near Creede, Colorado. Nearly 24000 metric tons of silver, appreciable lead, and small amounts of zinc, copper, and gold, have been produced from large, crustified veins under Bachelor and Bulldog Mountains north and northwest of Creede. Prior geologic, hydrologic, and stable-isotope studies showed that ore deposition was associated with the mixing and boiling of waters from diverse sources and suggester that a critical part of the ore-forming fluid may have originated within the ancient lake and sediments of the lacustrine Creede Formation that filled the Creede caldera. Two drill holes that sampled the heretofore hidden lower half of the Creede Formation are the focus of this book. The Creede caldera formed at 26.9 Ma within a high constructional plateau of silicic ashflows that covered and were sporadically interlayed with, intermediate lavas and lahars from large stratovolcanoes. The Creede caldera lake had an inflow evaporation balance that did not permit rapid filling to create a brim-full deep lake. Thus salts were evaporatively concentrated; but, with the exception of possible gypsum, no evaporite minerals preserved. Cool springs deposited travertine as mounds and contributed to limestone interlaminations within the sediment. The lake bottom was anoxic, and bacterial reduction of sulfate led to extreme sulfur isotopic fractionation in diagenetic pyrite. The caldera gradually resurged, converting the initial equant lake into an arcuate moat. Resurgent doming, alluvial fans, lacustrine sediments, ashfalls, and lava domes displaced water, lifted the lake so that it overlapped what later became the southern edge of the mineralized are, and eventually filled the basin. At 25.1 Ma an unseen pluton intruded beneath the northen part of the Creede district and created a convecting olume that drew in brine from the Creede caldera fill, meteotic water from highlands to the north

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  13. Aeromagnetic evidence for a volcanic caldera(?) complex beneath the divide of the West Antarctic Ice Sheet

    USGS Publications Warehouse

    Behrendt, John C.; Finn, C.A.; Blankenship, D.; Bell, R.E.

    1998-01-01

    A 1995-96 aeromagnetic survey over part of the Sinuous Ridge (SR) beneath the West Antarctic Ice Sheet (WAIS) divide shows a 70-km diameter circular pattern of 400-1200-nT anomalies suggesting one of the largest volcanic caldera(?) complexes on earth. Radar-ice-sounding (RIS) shows the northern part of this pattern overlies the SR, and extends south over the Bentley Subglacial Trench (BST). Modeled sources of all but one the caldera(?) anomalies are at the base of <1-2-km thick ice and their volcanic edifices have been glacially removed. The exception is a 700-m high, 15-km wide 'volcano' producing an 800-nT anomaly over the BST. 'Intrusion' of this 'volcano' beneath 3 km of ice probably resulted in pillow basalt rather than easily removed hyaloclastite erupted beneath thinner ice. The background area (-300 to -500-nT) surrounding the caldera(?) is possibly caused by a shallow Curie isotherm. We suggest uplift of the SR forced the advance of the WAIS.A 1995-96 aeromagnetic survey over part of the Sinuous Ridge (SR) beneath the West Antarctic Ice Sheet (WAIS) divide shows a 70-km diameter circular pattern of 400-1200-nT anomalies suggesting one of the largest volcanic caldera(?) complexes on earth. Radar-ice-sounding (RIS) shows the northern part of this pattern overlies the SR, and extends south over the Bentley Subglacial Trench (BST). Modeled sources of all but one the caldera(?) anomalies are at the base of < 1-2-km thick ice and their volcanic edifices have been glacially removed. The exception is a 700-m high, 15-km wide 'volcano' producing an 800-nT anomaly over the BST. 'Intrusion' of this 'volcano' beneath 3 km of ice probably resulted in pillow basalt rather than easily removed hyaloclastite erupted beneath thinner ice. The background area (-300 to -500-nT) surrounding the caldera(?) is possibly caused by a shallow Curie isotherm. We suggest uplift of the SR forced the advance of the WAIS.

  14. Dynamics of the Askja caldera landslide, July 2014, from seismic signal analysis

    NASA Astrophysics Data System (ADS)

    Schöpa, Anne; Burtin, Arnaud; Hovius, Niels; Green, Robert G.

    2016-04-01

    A voluminous landslide occurred at the Askja caldera in the Icelandic highlands on July 21st, 2014. The next day, flood marks of at least ten tsunami waves, that had reached the northern shore of the caldera lake, could be mapped out. The highest flood marks were found up to 60 m above the lake level close to famous tourist spots underlining the high hazard potential of the area. Since the landslide happened at night, no direct observations of the mass movement nor of the subsequent tsunami waves in the caldera lake were made. We present the analysis of seismic data from a network of 58 seismic stations that recorded data during the event. The seismic data give valuable information on the triggering, initiation, timing, and propagation of the landslide, with additional details on precursory signals before and oscillation waves in the caldera lake after the main landslide. From the set of seismic wave forms, characteristic features were extracted that could be used for early warning proposes. The seismic data reveals that the main slope failure along the southeastern caldera wall was a large, single event starting at 23.24 UTC. The main part of the energy was released in the first two minutes followed by smaller events, before the background noise level was re-established some 40 minutes after the main failure. Subsequent mass movements, much lower in amplitude, occurred during the following hours. About 20 minutes before the main failure, the background noise level started to rise. Ground velocities were up to three times higher that the background level with dominant frequencies between 2-4 Hz. The increase in background noise level is visible in stations up to 30 km away from the landslide area. This velocity increase is followed by a prominent velocity drop five minutes before the main failure. The spatial distribution of the velocity decrease with its centre at the detachment area of the landslide has an elliptical outline with a long axis oriented NE-SW. This

  15. Older Hydrothermal Activity along the Northern Yellowstone Caldera Margin at Sulphur Creek, Yellowstone Park, Wyoming

    NASA Astrophysics Data System (ADS)

    Manion, J. L.; Larson, P.

    2008-12-01

    The Tuff of Sulphur Creek (480 ka) is well exposed in the Seven Mile Hole area of the Grand Canyon of the Yellowstone River, Yellowstone National Park, Wyoming. The rhyolitic tuff erupted after the collapse of the Yellowstone Caldera (640 ka) and hosts more than 350 vertical meters of hydrothermal alteration. Two epithermal alteration assemblages with different mineral associations have been identified in the area: an illite-silica-pyrite phase and a kaolinite-alunite-silica-pyrite phase. Kaolinite and opal occur along the canyon rim, montmorillonite and other smectites are found at intermediate depths, and illite and sulfides (pyrite) are found deepest in the section. Our work on the north side of the Sevenmile Hole altered area has found a complex system of veining. The veins are concentrated in the eastern portion of the canyon and are less frequent to the west. Brecciated cross-cutting veins ranging from 2 to 30cm wide are found at the base of the canyon. Moving vertically up the canyons walls, the veining style becomes less complex. These veins are about 1 to 1.5cm wide and are not brecciated, occurring less frequently than the brecciated veins. The canyon walls and the canyon rim mainly contain millimeter-scale cross-cutting silica veinlets. These stockwork-like veinlets are the most abundant fracture filling that we find throughout the canyon walls. Veins at the base of the system, found in the stream bed, contain abundant sulfides (mainly pyrite). Sulfides are present in three forms: disseminated in a silica matrix, as massive pyrite in healed fractures, and encrusting clays and silica. The latter is the least common. Disseminated and massive sulfides are typically associated with the matrix in the brecciated veins. Breccias include angular clasts of altered tuff with argillized feldspar phenocrysts and fragments of earlier vein-filling opal. Sulfides are most abundant in the bottom of the canyon and in the western part of the field area. Hydrothermal

  16. Postcaldera volcanism and hydrothermal activity revealed by autonomous underwater vehicle surveys in Myojin Knoll caldera, Izu-Ogasawara arc

    NASA Astrophysics Data System (ADS)

    Honsho, Chie; Ura, Tamaki; Kim, Kangsoo; Asada, Akira

    2016-06-01

    Myojin Knoll caldera, one of the submarine silicic calderas lying on the volcanic front of the northern Izu-Ogasawara arc, has attracted increasing attention since the discovery of a large hydrothermal field called the Sunrise deposit. Although numerous submersible surveys have been conducted in Myojin Knoll caldera, they have not sufficiently explored areas to produce a complete picture of the caldera and understand the origin of the Sunrise deposit. We conducted comprehensive deep-sea surveys using an autonomous underwater vehicle and obtained high-resolution bathymetric and magnetic data and sonar images from ~70% of the caldera. The detailed bathymetric map revealed that faulting and magma eruptions, possibly associated with an inflation-deflation cycle of the magma reservoir during postcaldera volcanism, had generally occurred in the caldera wall. The main dome of the central cone was covered with lava flows and exhibits exogenous growth, which is unusual for rhyolitic domes. The magnetization distribution in the central cone indicates preferential magma intrusion along a NW-SE direction. It is presumed that magma migrated along this direction and formed a rhyolite dome at the foot of the southeastern caldera wall, where the Sunrise deposit occurs. The Sunrise deposit is composed mainly of three ridges extending in slope directions and covers ~400 × ~400 m. Magnetization reduction in the deposit area is small, indicating that the alteration zone beneath the Sunrise deposit is slanting rather than vertical. It is presumed that several slanting and near-vertical volcanic vents serve as pathways of hydrothermal fluid in Myojin Knoll caldera.

  17. Magma Evolution During a Single Caldera Cycle: Insights from Melt Inclusions of the 3.49 Ma Tara Supereruption, Guacha Caldera, SW Bolivia

    NASA Astrophysics Data System (ADS)

    Grocke, S.; de Silva, S. L.; Wallace, P. J.; Iriarte, R.

    2012-12-01

    Melt inclusions in quartz phenocrysts erupted during the 3.49 Ma Tara Ignimbrite supereruption (>800 km3 DRE) from the Guacha Caldera complex in SW Bolivia provide the rare opportunity to examine the magma evolution during a complete resurgent caldera cycle. Data from naturally glassy, crystal- and vapor-bubble free quartz-hosted melt inclusions from pumices in the climactic plinian and ignimbrite phase and lavas from the post-resurgent domes combined with data on matrix glass and whole rock compositions reveal that the three eruptive phases were genetically related and potentially derived from an andesitic magma represented by scoria in the ignimbrite. Variations in Cl, H2O, B and Li suggest the presence of a separate vapor phase in the pre-climactic Tara magma. H2O contents in the plinian pumice overlap with those in the ignimbrite pumice (2.2 to 6.0 and 2.1 to 5.4 wt.% H2O, respectively) but the ignimbrite-forming magma contains higher CO2 (<630 versus <300 ppm) suggesting a vertically arranged pre-climactic magma column from 7.5 km to 4 km. The initial plinian fall-producing eruption tapped a less-evolved, crystal-poor (~10%) roofward liquid that syneruptively mixed with the more crystalline (~45%) climactic, ignimbrite-forming magma. Melt inclusions from the highly-differentiated post-climactic magma contain no detectable CO2 and ~2% H2O in melt inclusions and connote a shallowing (<2 km) post-climactic magma system that crystallized a new generation of quartz crystals and accompanied the resurgent doming of the Guacha II caldera floor. The eruptive transition during the climactic eruption was not controlled by the volatile budget of the melt but more likely by external factors such as vent geometry and conduit evolution. Post climactic effusive volcanism reflects the degassed nature of the remnant magma.

  18. Rhyolitic calderas of the Yukon-Tanana Terrane, east central Alaska: volcanic remnants of a mid-Cretaceous magmatic arc

    USGS Publications Warehouse

    Bacon, C.R.; Foster, H.L.; Smith, James G.

    1990-01-01

    Four large but poorly exposed rhyolitic calderas are present in the Yukon-Tanana terrane (YTT) in east central Alaska. At least two are mid-Cretaceous in age (~93 Ma). Similar volcanic rocks, the South Fork Volcanics, occur northeast of the Tintina fault in Yukon Territory. Evidence for the calderas consists of thick deposits of devitrified crystal- and lithic-rich densely welded tuff, interpreted as caldera fill, associated with lava domes or shallow intrusive rocks. Coeval outflow sheets have been largely stripped by erosion. The calderas are preserved within a northeast trending depression extending across the axis of the elongate mid-Cretaceous plutonic province. Trace element abundances in andesites and rhyolites associated with the caldera structures are similar to those of volcanic and plutonic rocks of subduction-related magmatic arcs developed on continental crust and thus are suggestive of formation in such an environment. Late Cretaceous and early Tertiary igneous rocks in the YTT near the calderas are interpreted to have been emplaced in a more extensional setting when the subduction-related magmatic front was farther oceanward. -Authors

  19. 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.

  20. The Silent Canyon caldera: a three-dimensional model as part of a Pahute Mesa-Oasis Valley, Nevada, hydrogeologic model

    USGS Publications Warehouse

    McKee, Edwin H.; Phelps, Geoffery A.; Mankinen, Edward A.

    2001-01-01

    A 3-dimensional caldera model based on gravity inversion, drill-hole data, and geologic mapping offers the framework for a hydrogeologic evaluation of the Silent Canyon caldera in the central part of Pahute Mesa, Nevada. It has been recognized for several decades that the central part of Pahute Mesa is the site of a buried caldera called the Silent Canyon caldera. Conceptually, the structural framework of the Silent Canyon caldera is based on the idea of collapse of the caldera roof over a shallow magma chamber to form a structural basin following violent volcanic eruptions. Calderas are common in certain volcanic regions of the world, and most well-exposed calderas are broadly similar to each other, particularly the arcuate or circular shape of their collapse depression. There are other reasons for modeling the Silent Canyon caldera as a circular feature in addition to knowledge that calderas throughout the world are generally circular features. The Silent Canyon caldera is the site of one of the largest gravity lows in the Western United States, indicating a thick accumulation of low-density rocks such as lavas and tuffs—a fact confirmed by drilling on Pahute Mesa. This gravity low is bowl-shaped, and the uppermost volcanic units on Pahute Mesa form a circular outcrop pattern of inward-dipping tuff interpreted to be the result of their filling the upper part of the bowl-shaped depression. Together, these features are consistent with, and indicative of, a circular collapse structural model for the Silent Canyon caldera. The collapse depression of the Silent Canyon caldera, bounded by arcuate faults, is filled with as much as 6 km (19,800 ft) of volcanic and sedimentary rocks that are considerably less dense than the underlying and surrounding basement rocks. The boundary surface between less dense caldera fill and more dense basement is modeled as the caldera ring fault. Rocks in the upper part of the caldera fill are penetrated by drilling, and the drill

  1. Using InSAR to investigate long term caldera unrest: case studies from Yellowstone and Long Valley

    NASA Astrophysics Data System (ADS)

    battaglia, maurizio

    2016-04-01

    Interpreting geodetic measurements can be particularly difficult in the case of slow, years-to-decades deformation, such as that commonly observed at large Quaternary silicic calderas. For example, Yellowstone caldera has shown a complex behavior over recent decades: uplift of resurgent domes within the caldera started sometime after 1923, reaching a total of 90 cm, but in 1984 the deformation reversed to subsidence at a rate of 1-2 cm/yr until 1992. Starting in 1992, the deformation began migrating from one resurgent dome to the other, and deformation was also detected along the caldera boundary - the so-called Northern Caldera Rim - starting in the mid-1990s. Evidence from geodetic surveys suggests that magma intrusion and/or pressurization of hydrothermal fluids may both drive uplift at Yellowstone. Geodetic measurements at Long Valley caldera have also revealed multiple episodes of caldera uplift, but in contrast to Yellowstone, deformation is largely restricted to the caldera's single resurgent dome. The fact that the energy released during the resurgent dome uplift is much larger than that which can be explained by seismic activity within and around the caldera, together with the observation that the onset of accelerated deformation precedes increases in earthquake activity by several weeks, suggests that the major source of caldera unrest is probably magma intrusion beneath the resurgent dome. Here we present time series of surface deformation for Yellowstone and Long Valley retrieved by applying the SBAS InSAR technique. We estimate the average regional deformation signal by using the mean velocity values derived from coherent SAR pixels belonging to areas outside the caldera. This tectonic signal is removed from the InSAR displacement and we modeled the InSAR, leveling, and gravity measurements to retrieve the best fitting source parameters. For Yellowstone caldera, different distinct sources, either hydrothermal or magmatic, have been intermittently

  2. Eastern Europe's Silicon Rush

    ERIC Educational Resources Information Center

    Woodard, Colin

    2007-01-01

    This article presents how the fast expansion of information technology industry in eastern Slovakia is putting a strain on its labor supply. Suddenly, computer-science graduates have become one of the former Eastern Bloc's greatest assets, attracting multinational technology companies hungry for skilled programmers, technicians, and engineers.…

  3. Middle Eastern rhinoplasty.

    PubMed

    Azizzadeh, Babak; Mashkevich, Grigoriy

    2010-02-01

    The ethnic appearance of the Middle Eastern nose is defined by several unique visual features, particularly a high radix, wide overprojecting dorsum, and an amorphous hanging nasal tip. These external characteristics reflect distinct structural properties of the osseo-cartilaginous nasal framework and skin-soft tissue envelope in patients of Middle Eastern extraction. The goal, and the ultimate challenge, of rhinoplasty on Middle Eastern patients is to achieve balanced aesthetic refinement, while avoiding surgical westernization. Detailed understanding of the ethnic visual harmony in a Middle Eastern nose greatly assists in preserving native nasal-facial relationships during rhinoplasty on Middle Eastern patients. Esthetic alteration of a Middle Eastern nose follows a different set of goals and principles compared with rhinoplasties on white or other ethnic patients. This article highlights the inherent nasal features of the Middle Eastern nose and reviews pertinent concepts of rhinoplasty on Middle Eastern patients. Essential considerations in the process spanning the consultation and surgery are reviewed. Reliable operative techniques that achieve a successful aesthetic outcome are discussed in detail. PMID:20206101

  4. Gravity anomalies, caldera structure, and subsurface geology in the Rotorua area, New Zealand

    SciTech Connect

    Hunt, T.M. )

    1992-04-01

    This paper discusses a re-examination of gravity which indicates that Rotorua Caldera does not have the circular, negative gravity anomaly typical of other rhyolitic calderas. New gravity measurements and residual gravity anomalies in Rotorua City are consistent with numerous rhyolite domes and ignimbrite sheets, interbedded with a thick sequence of poorly-compacted sediments. Within the city a gravity high extends from the shore of Lake Rotorua south to Whakarewarewa and is associated with a buried ridge, formed by the coalescing of two rhyolite domes. A gravity low centered near Linton Park suggests that rhyolites are thin or absent in this area and sediments extend to a depth of about 1 km. A quantitative analysis of the residual gravity anomalies was limited by insufficient information about the density, extent, and thickness of the material underlying the rhyolites, and the uncertainty in the distribution and density of silicification within the sediments.

  5. Decrease in deformation rate observed by two-color laser ranging in Long Valley Caldera

    USGS Publications Warehouse

    Linker, M.F.; Langbein, J.O.; McGarr, A.

    1986-01-01

    After the January 1983 earthquake swarm, the last period of notable seismicity, the rapid rate of deformation of the south moat and resurgent dome of the Long Valley caldera diminished. Frequently repeated two-color laser ranging measurements made within a geodetic network in the caldera during the interval June 1983 to November 1984 reveal that, although the deformation accumulated smoothly in time, the rate of extension of many of the baselines decreased by factors of 2 to 3 from mid-1983 to mid-1984. Areal dilatation was the dominant signal during this period, with rates of extension of several baselines reaching as high as 5 parts per million per annum during the summer of 1983. Within the south moat, shear deformation also was apparent. The cumulative deformation can be modeled as the result of injection of material into two points located beneath the resurgent dome in addition to shallow right lateral slip on a vertical fault in the south moat.

  6. The structural setting of the Ischia Island Caldera (Italy): first evidence from seismic and gravity data

    NASA Astrophysics Data System (ADS)

    Capuano, Paolo; De Matteis, Raffaella; Russo, Guido

    2015-09-01

    Ischia Island is one of the active volcanoes of the Neapolitan area (Italy). Hazard assessment of active, densely populated volcano is primarily based on knowledge of the volcano's past behaviour and of its present state. As a contribution to the definition of the present structural setting of Ischia Island, we constructed a new model of the shallow crust using geophysical data: seismic wave travel times and Bouguer anomaly data. We analysed these data sets through seismic tomography and gravity data inversion. The main results inferable from the 3D seismic and gravity images are the definition of the caldera rim along the perimeter of the island, as hypothesized by many authors, and the presence of a high velocity and density area inside the caldera consistent with extension of the resurgent block that characterizes the recent deformation of the island.

  7. Late Cretaceous Middle Fork caldera and its resurgent granite porphyry intrusion, east-central Alaska

    NASA Astrophysics Data System (ADS)

    Bacon, C. R.; Dusel-Bacon, C.; Aleinikoff, J. N.; Slack, J. F.

    2012-12-01

    Named for the Middle Fork of the North Fork of the Fortymile River, the Middle Fork caldera encompasses a 10 x 20 km area of rhyolite welded tuff and granite porphyry ~100 km west of the Yukon border. Intracaldera tuff has ≤4 mm quartz and feldspar phenocrysts and cm-sized fiamme; its maximum exposed thickness is 850 m. Less densely welded tuff near the caldera margins locally contains 1-2 cm K-feldspar megacrysts and pumice clasts to 6 cm. Zircon from intracaldera tuff yields a SHRIMP-RG U-Pb age of 68.7 ± 1.1 Ma (all ages 95% confidence). Granite porphyry occupies much of an 8 x 12 km area having 650 m of relief within the western part of the caldera fill. Zircon from the porphyry gives a SHRIMP-RG U-Pb age of 68.4 ± 1.0 Ma. These ages agree with a previous 40Ar/39Ar biotite age of 69.1 ± 0.5 Ma for proximal outflow tuff. The crystal-rich intracaldera tuff contains embayed quartz, plagioclase>K-feldspar, biotite, and Fe-Ti oxide phenocrysts in a very fine-grained crystalline groundmass. The porphyry carries 40-50% of larger phenocrysts of the same phases (skeletal quartz to 1 cm; K-feldspar to 2 cm, rarely to 4 cm) in a fine-grained groundmass characterized by abundant 50-100 μm quartz. Compositions of 3 tuff and 3 porphyry samples overlap, form a limited differentiation series at 69-72% SiO2, have arc geochemical signatures, and yield subparallel chondrite-normalized rare earth element patterns with light REE enrichment, concave-upward heavy REE, and small negative Eu anomalies. Although their phenocrysts differ in size (owing to fragmentation of crystals in the tuff) and abundance, the similar mineralogy, composition (in spite of crystal concentration in the tuff), and indistinguishable ages of the tuff and porphyry indicate that the magmas were closely related. A rare magmatic enclave (54% SiO2, arc geochemical signature) in the porphyry may be similar to parental magma and provides evidence of mafic magma and thermal input. The porphyry is interpreted

  8. 3D Imaging of Brittle/Ductile transition of the crust beneath the resurgent calderas

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  9. Volatiles from the 1994 Eruptions of Rabaul: Understanding Large Caldera Systems

    PubMed

    Roggensack; Williams; Schaefer; Parnell

    1996-07-26

    The 1994 eruption of Rabaul, in Papua New Guinea, involved a small plinian eruption at Vulcan and a vulcanian eruption on the opposite side of the caldera at Tavurvur. Vulcan's ash leachates indicate seawater interaction that is consistent with earlier observations of low sulfur dioxide emissions and the presence of ice crystals in the initial plinian eruption cloud. In contrast, Tavurvur ash leachates indicate no seawater interaction, and later sulfur dioxide emissions remained high despite low-level eruptive activity. Silicic melt inclusions indicate that the andesitic melt contained about 2 weight percent water and negligible carbon dioxide. Mafic melt inclusions in Tavurvur ash have water and carbon dioxide contents that vary systematically over the course of the eruption. The mafic melt inclusions suggest that a mafic dike intruded from below the silicic chamber and provide further evidence that mafic intrusions drive caldera unrest. PMID:8662536

  10. Gradual caldera collapse at Bárdarbunga volcano, Iceland, regulated by lateral magma outflow.

    PubMed

    Gudmundsson, Magnús T; Jónsdóttir, Kristín; Hooper, Andrew; Holohan, Eoghan P; Halldórsson, Sæmundur A; Ófeigsson, Benedikt G; Cesca, Simone; Vogfjörd, Kristín S; Sigmundsson, Freysteinn; Högnadóttir, Thórdís; Einarsson, Páll; Sigmarsson, Olgeir; Jarosch, Alexander H; Jónasson, Kristján; Magnússon, Eyjólfur; Hreinsdóttir, Sigrún; Bagnardi, Marco; Parks, Michelle M; Hjörleifsdóttir, Vala; Pálsson, Finnur; Walter, Thomas R; Schöpfer, Martin P J; Heimann, Sebastian; Reynolds, Hannah I; Dumont, Stéphanie; Bali, Eniko; Gudfinnsson, Gudmundur H; Dahm, Torsten; Roberts, Matthew J; Hensch, Martin; Belart, Joaquín M C; Spaans, Karsten; Jakobsson, Sigurdur; Gudmundsson, Gunnar B; Fridriksdóttir, Hildur M; Drouin, Vincent; Dürig, Tobias; Aðalgeirsdóttir, Guðfinna; Riishuus, Morten S; Pedersen, Gro B M; van Boeckel, Tayo; Oddsson, Björn; Pfeffer, Melissa A; Barsotti, Sara; Bergsson, Baldur; Donovan, Amy; Burton, Mike R; Aiuppa, Alessandro

    2016-07-15

    Large volcanic eruptions on Earth commonly occur with a collapse of the roof of a crustal magma reservoir, forming a caldera. Only a few such collapses occur per century, and the lack of detailed observations has obscured insight into the mechanical interplay between collapse and eruption. We use multiparameter geophysical and geochemical data to show that the 110-square-kilometer and 65-meter-deep collapse of Bárdarbunga caldera in 2014-2015 was initiated through withdrawal of magma, and lateral migration through a 48-kilometers-long dike, from a 12-kilometers deep reservoir. Interaction between the pressure exerted by the subsiding reservoir roof and the physical properties of the subsurface flow path explain the gradual, near-exponential decline of both collapse rate and the intensity of the 180-day-long eruption. PMID:27418515

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

    PubMed

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

    2012-02-01

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

  12. Deep Borehole Measurements for Characterizing the Magma/Hydrothermal System at Long Valley Caldera, CA

    SciTech Connect

    Carrrigan, Charles R.

    1989-03-21

    The Magma Energy Program of the Geothermal Technology Division is scheduled to begin drilling a deep (6 km) exploration well in Long Valley Caldera, California in 1989. The drilling site is near the center of the caldera which is associated with numerous shallow (5-7 km) geophysical anomalies. This deep well will present an unparalleled opportunity to test and validate geophysical techniques for locating magma as well as a test of the theory that magma is still present at drillable depths within the central portion of the caldera. If, indeed, drilling indicates magma, the geothermal community will then be afforded the unique possibility of examining the coupling between magmatic and hydrothermal regimes in a major volcanic system. Goals of planned seismic experiments that involve the well include the investigation of local crustal structure down to depths of 10 km as well as the determination of mechanisms for local seismicity and deformation. Borehole electrical and electromagnetic surveys will increase the volume and depth of rock investigated by the well through consideration of the conductive structure of the hydrothermal and underlying regimes. Currently active processes involving magma injection will be studied through observation of changes in pore pressure and strain. Measurements of in situ stress from recovered cores and hydraulic fracture tests will be used in conjunction with uplift data to determine those models for magmatic injection and inflation that are most applicable. Finally, studies of the thermal regime will be directed toward elucidating the coupling between the magmatic source region and the more shallow hydrothermal system in the caldera fill. To achieve this will require careful logging of borehole fluid temperature and chemistry. In addition, studies of rock/fluid interactions through core and fluid samples will allow physical characterization of the transition zone between hydrothermal and magmatic regimes.

  13. Renewed uplift at the Yellowstone caldera measured by leveling surveys and satellite radar interferometry

    USGS Publications Warehouse

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

    1999-01-01

    A first-order leveling survey across the northeast part of the Yellowstone caldera in September 1998 showed that the central caldera floor near Le Hardy Rapids rose 24 ?? 5 mm relative to the caldera rim at Lake Butte since the previous survey in September 1995. Annual surveys along the same traverse from 1985 to 1995 tracked progressive subsidence near Le Hardy Rapids at an average rate of -19 ?? 1 mm/year. Earlier, less frequent surveys measured net uplift in the same area during 1923-1976 (14 ?? 1 mm/year) and 1976-1984 (22 ?? 1 mm/year). The resumption of uplift following a decade of subsidence was first detected by satellite synthetic aperture radar interferometry, which revealed approximately 15 mm of uplift in the vicinity of Le Hardy Rapids from July 1995 to June 1997. Radar interferograms show that the center of subsidence shifted from the Sour Creek resurgent dome in the northeast part of the caldera during August 1992 to June 1993 to the Mallard Lake resurgent dome in the southwest part during June 1993 to August 1995. Uplift began at the Sour Creek dome during August 1995 to September 1996 and spread to the Mallard Lake dome by June 1997. The rapidity of these changes and the spatial pattern of surface deformation suggest that ground movements are caused at least in part by accumulation and migration of fluids in two sill-like bodies at 5-10 km depth, near the interface between Yellowstone's magmatic and deep hydrothermal systems.

  14. Dynamic magmatic processes at a continental rift caldera, observed using satellite geodesy

    NASA Astrophysics Data System (ADS)

    Lloyd, Ryan; Biggs, Juliet; Birhanu, Yelebe; Wilks, Matt; Gottsmann, Jo; Kendall, Mike; Lewi, Elias

    2016-04-01

    Large silicic calderas are a key feature of developing continental rifts, such as the Main Ethiopian Rift (MER), and are often observed to be deforming. Corbetti is one such example of a Holocene caldera in the MER that is undergoing deformation. However, the cause of the unrest, and the relationship to rift processes such as magma storage, transport and extension remain poorly understood. To investigate, we use InSAR (ascending and descending Cosmo-SkyMed data) and continuous GPS to observe the temporal and spatial evolution of sustained uplift at the Corbetti Caldera. Within the caldera, which was thought to have formed ~200 ka, there is evidence for numerous periods of resurgent volcanism in the form of plinian eruptions as well as effusive obsidian flows. How the sources of these varying styles of volcanism are reconciled at depth and in time is currently poorly constrained. Previous research has shown that pre-rift structures have a significant influence on the strain field, and hence on the magmatic and hydrothermal processes which drive it. The Cosmo-SkyMed data used in this study was specifically chosen such that each ascending image has a corresponding descending image acquired as contemporaneously as possible. This is necessary, given the rate of uplift, so as to reduce the number of assumptions when constructing time-series from multiple look directions, and when incorporating GPS data. We decompose the ascending and descending line-of-site deformation signals into vertical and east-west components and use finite source modeling to constrain the depth and geometry of the source of deformation. These results are then compared to available seismic, dynamic microgravity and magnetotelluric data to better understand this system, and how it is related to the volcanic hazard and local geothermal resources.

  15. Caldera formation and varied eruption styles on North Pacific seamounts: the clastic lithofacies record

    NASA Astrophysics Data System (ADS)

    Portner, Ryan A.; Clague, Dave A.; Paduan, Jennifer B.

    2014-08-01

    Detailed examination of volcaniclastic and sedimentary rocks collected from the Taney (30 Ma), President Jackson (4 Ma), Vance (3 Ma) and Alarcon (2 Ma) near-ridge seamount chains of the North Pacific reveals seven clastic lithofacies that record various modes of eruption, magma fragmentation, and particle dispersal. Lithofacies are distinguished by differences in lithology, bedding habit, compositional heterogeneity, and relationship to volcanic landforms. Breccia lithofacies were produced through mechanical fragmentation during caldera collapse (polymict) or effusive eruptions onto steep slopes (monomict). Rare globular lapilli mudstone lithofacies contain clasts with morphologies formed by magma-sediment mingling processes (peperite). Seamount summit pyroclastic deposits include proximal lapilli tuff with vesicular pyroclasts, and more distal limu o Pele tuff lithofacies. Much finer-grained hydrothermal mudstone/tuff lithofacies occurs around caldera rims and contains greenschist minerals, hydrothermal clays and basaltic ash that record subsurface phreatomagmatic fragmentation processes. Very fine-grained ash is transported to distal regions by oceanic currents and hydrothermal plumes, and is a component of the regional pelagic sediment budget. Pyroclastic lithofacies only occur on seamount summits suggesting formation during the latter stages of seamount evolution. As a seamount drifts away from an adjacent ridge axis and associated heat source, its magma supply is reduced allowing for magmatic gas buildup and mild explosive eruptions. During this stage, the diminished melt supply under the seamount is unable to fully compensate for extension along the ridge axis and vertical seamount growth. Lateral intrusion into spreading-related structures in this stage causes magma withdrawal and caldera formation. Formation of caldera ring faults also promotes seawater ingress into subseafloor hydrothermal cells, which interact with magma conduits causing phreatomagmatic

  16. Hydrothermal outflow plume of Valles caldera, New Mexico, and a comparison with other outflow plumes

    SciTech Connect

    Goff, F.; Shevenell, L.; Gardner, J.N.; Vuataz, F.; Grigsby, C.O.

    1988-06-10

    Stratigraphic, temperature gradient, hydrogeochemical, and hydrologic data have been integrated with geologic data from previous studies to show the structural configuration of the Valles caldera hydrothermal outflow plume. Hydrologic data suggest that 25--50% of the discharge of the Valles outflow is confined to the Jemez fault zone, which predates caldera formation. Thermal gradient data from bores penetrating the plume show that shallow gradients are highest in the vicinity of the Jemez fault zone (up to 190 /sup 0/C/km). Shallow heat flow above the hydrothermal plume is as high as 500 mW m/sup -2/ near core hole VC-1 (Jemez fault zone) to 200 mW m/sup -2/ at Fenton Hill (Jemez Plateau). Chemical and isotopic data indicate that two source reservoirs within the caldera (Redondo Creek and Sulphur Springs reservoirs) are parents to mixed fluids flowing in the hydrothermal plume. However, isotopic data, borehole data, basic geology, and inverse relations between temperature and chloride content at major hot springs indicate that no single reservoir fluid and no single diluting fluid are involved in mixing. The Valles caldera hydrothermal plume is structurally dominated by lateral flow through a belt of vertical conduits (Jemez fault zone) that strike away from the source reservoir. Stratigraphically confined flow is present but dispersed over a wide area in relatively impermeable rocks. The Valles configuration is contrasted with the configuration of the hydrothermal plume at Roosevelt Hot Springs, which is dominated by lateral flow through a near-surface, widespread, permeable aquifer. Data from 12 other representative geothermal systems show that outflow plumes occur in a variety of magmatic and tectonic settings, have varying reservoir compositions, and have different flow characteristics.

  17. Characterizing magma storage at Aira caldera and Sakurajima volcano (Japan) from geodetic inversions

    NASA Astrophysics Data System (ADS)

    Hickey, J.; Gottsmann, J.; Iguchi, M.; Nakamichi, H.

    2014-12-01

    Aira caldera is located within Kagoshima Bay at the southern end of Kyushu, in Japan. Sakurajima, a post-caldera andesitic stratovolcano, sits on the calderas southern rim and is Japan's most active volcano. Historical records of activity at Sakurajima are punctuated with larger events: for example, in 1914 a major flank eruption ejected 0.52 km3 of pumice and ash, and 1.34 km3 of lava. The co-eruptive subsidence accompanying this eruption was around one metre in the vertical component, as determined from leveling surveys. Repeat surveys, and the addition of modern GPS data indicate that the present day level of ground uplift is approaching the level inferred before the 1914 eruption. This study is focused on interpreting the current deformation with integration of additional geophysical signals to constrain the subsurface magma storage conditions. Analytical geodetic models have been previously used to infer a deep spherical reservoir beneath Aira caldera and a smaller source beneath the summit craters of Sakurajima. However, subsequent geophysical explorations have shown that the assumptions inherent in these simple models may not apply. We use the Finite Element method to model the recorded deformation with an inverse least-squares approach. Our models incorporate the surrounding topography/bathymetry and three-dimensional medium heterogeneities inferred from seismic tomography. These are used to assess their respective significance when solving for the optimum source location. Subsequent forward Finite Element models quantify the importance of rheology and thermo-mechanical coupling owing to the observed high seismic attenuation and aseismic zones. The results are evaluated alongside the current volcanic activity to yield new insights into the behaviour of the Aira-Sakurajima sub-volcanic system.

  18. Reconstructing the evoluortunity to study processes related to composite volction of an eroded Miocene caldera volcano (Yamanlar volcano, İzmir, Turkey)

    NASA Astrophysics Data System (ADS)

    Karaoğlu, Özgür; Brown, Richard J.

    2016-05-01

    The Miocene Yamanlar composite volcano is located in the central part of a shear zone in western Turkey. The volcano's deeply-eroded interior provides excellent three-dimensional exposure of a faulted caldera-floor and caldera-fill rocks as well as surrounding extracaldera ignimbrites. We present a much-revised stratigraphy and geological map of Yamanlar in order to quantify the evolutionary stages of the volcano. The Yamanlar volcanic cone was composed of > 800 m of basaltic-andesite to andesite lavas and lava domes. The volcano underwent at least one phase of caldera formation associated with an explosive eruption that deposited an ignimbrite sheet within and outside the caldera. Lithofacies architecture analysis is applied to the proximal and medial exposures of the Early-Middle Yamanlar Formation, which occurs outside of the caldera. Field evidence of the succession indicates a caldera-forming eruption. Our results indicate that the formation of the Yamanlar caldera resulted from one major catastrophic eruption that generated several sustained pyroclastic density currents (PDCs) subdivided by fall deposits with sharp contacts. The ignimbrite sheet is composed of four flow units. The presence of numerous coarse-grained lithic-rich horizons within the ignimbrite sheet is consistent with caldera subsidence. Post-caldera volcanism is indicated by intrusions and lava domes erupted along the inferred caldera-bounding faults, some of which record ~ 90 m of displacement. Widespread, coarse-grained breccias that overlie the ignimbrite sheet are interpreted as debris avalanche deposits resulting from gravitational failure of the flanks of the volcano or the caldera wall during or after caldera subsidence.

  19. Deep borehole measurements for characterizing the magma/hydrothermal system at Long Valley Caldera, CA

    SciTech Connect

    Carrigan, C.R.

    1989-01-01

    The Magma Energy Program of the Geothermal Technology Division is scheduled to begin drilling a deep (6 km) exploration well in long Valley Caldera, California in 1989. The drilling site is near the center of the caldera which is associated with numerous shallow (5-7 km) geophysical anomalies. This deep well will present an unparalleled opportunity to test and validate geophysical techniques for locating magma as well as a test of the theory that magma is still present at drillable depths within the central portion of the caldera. If, indeed, drilling indicates magma, the geothermal community will then be afforded the unique possibility of examining the coupling between magmatic and hydrothermal regimes in a major volcanic system. Goals of planned seismic experiments that involve the well include the investigation of local crystal structure down to depths of 10 km as well as the determination of mechanisms for local seismicity and deformation. Borehole electrical and electromagnetic surveys will increase the volume and depth of rock investigated by the well through consideration of the conductive structure of the hydrothermal and underlying regimes. 9 refs., 5 figs.

  20. Petrologic evolution of divergent peralkaline magmas from the Silent Canyon caldera complex, southwestern Nevada volcanic field

    USGS Publications Warehouse

    Sawyer, D.A.; Sargent, K.A.

    1989-01-01

    The Silent Canyon volcanic center consists of a buried Miocene peralkaline caldera complex and outlying peralkaline lava domes. Two widespread ash flow sheets, the Tub Spring and overlying Grouse Canyon members of the Miocene Belted Range Tuff, were erupted from the caldera complex and have volumes of 60-100 km3 and 200 km3, respectively. Eruption of the ash flows was preceded by widespread extrusion of precaldera comendite domes and was followed by extrusion of postcollapse peralkaline lavas and tuffs within and outside the caldera complex. Lava flows and tuffs were also deposited between the two major ash flow sheets. Rocks of the Silent Canyon center vary significantly in silica content and peralkalinity. Weakly peralkaline silicic comendites (PI 1.0-1.1) are the most abundant precaldera lavas. Postcollapse lavas range from trachyte to silicic comendite; some have anomalous light rare earth element (LREE) enrichments. Silent Canyon rocks follow a common petrologic evolution from trachyte to low-silica comendite; above 73% SiO2, compositions of the moderately peralkaline comendites diverge from those of the weakly peralkaline silicic comendites. The development of divergent peralkaline magmas, toward both pantelleritic and weakly peralkaline compositions, is unusual in a single volcanic center. -from Authors

  1. Pre-drilling data review and synthesis for the Long Valley Caldera, California

    NASA Astrophysics Data System (ADS)

    Goldstein, N. E.

    A 2-day symposium was held at the Lawrence Berkeley Laboratory (LBL) on March 17-18, 1987, to review a large body of scientific investigations for the Long Valley Caldera and to discuss concepts and models for the present-day magmatic-hydrothermal system. Speakers at the symposium also addressed the problem of where to locate future scientific drill holes in the caldera.Deep scientific drilling projects such as those being contemplated by the U.S. Department of Energy (DOE) Geothermal Technologies Division (GTD), under the Magma Energy Program, and by the DOE Office of Basic Energy Sciences (OBES) along with the U.S. Geological Survey (USGS) and the National Science Foundation (NSF), under the Continental Scientific Drilling Program (CSDP), will be major and expensive national undertakings that will require strong support from geoscientists and engineers and from industry and government-supported laboratories. DOE/OBES is sponsoring a program of relatively shallow core holes (less than 1 km) in the caldera, and DOE/GTD is considering the start of a deep (6-km) hole for geophysical observations and sampling of the near-magmatic environment as early as fiscal year (FY) 1988.

  2. Lithology, mineralogy, and paleontology of Quaternary lake deposits in Long Valley Caldera, California

    USGS Publications Warehouse

    Fournier, R.B.

    1989-01-01

    Drill cores and cuttings from two drill holes, about 3 km apart, in Long Valley caldera, Mono County, California, were studied using x-ray diffraction and optical methods. A thick sequence of tuffs and lake sediments was encountered in LVCH-1 (1,000 ft deep) and Republic well 66-29 (6,920 ft deep), drilled in the southeast part of the Long Valley caldera. Ostracods, diatoms, and isotopic data indicate that the sediments and tuffs were deposited in a shallow caldera lake which changed in salinity over time. Conditions ranged from very saline in the older lake to fresh in the youngest. The sequence of secondary minerals from top to bottom is: clinoptilolite, mordenite, analcime, K-feldspar (and albite). In some geothermal systems, this sequence of secondary minerals is a function of temperature; however, the paleontological and isotopic data indicate that the change in secondary minerals with increasing depth is due to the older strata being deposited in a more saline environment. No mineralogical evidence of hydrothermal alteration is present, although the high lithium content of some clays and feldspars and the isotopic composition of some sulfate (gypsum) seems to require a hydrothermal source. (Lantz-PTT)

  3. Relationship between the Porco, Bolivia, Ag-Zn-Pb-Sn deposit and the Porco Caldera

    USGS Publications Warehouse

    Cunningham, C.G.

    1994-01-01

    The Porco Ag-Zn-Pb-Sn deposit, a major Ag producer in the 16th century and currently the major Zn producer in Bolivia, consists of a swarm of fissure-filling veins in the newly recognized Porco caldera. The caldera measures 5 km by 3 km and formed in response to the eruption of the 12 Ma crystal-rich dacitic Porco Tuff. The mineralization is associated with, and is probably genetically related to, the 8.6 Ma Huayna Porco stock. The Porco deposit consists of steeply dipping irregular and curvilinear veins that cut the intracaldera Porco Tuff about 1 km east of the Huayna Porco stock. Most of the veins are aligned along the structural margin (ring fracture) of the caldera. The ore deposit is zoned around the Huayna Porco stock. The primary Ag minerals are most abundant in the upper parts of the viens. Fluid inclusions in sphalerite stalactites have homogenization temperatures of about 225??C and salinities of about 8 wt% NaCl equiv. The stalactites and the presence of sparse vapor-rich inclusions suggest deposition of sphalerite under boiling conditions. -from Authors

  4. New evidence for the age of the youngest eruption in the Valles caldera, New Mexico

    SciTech Connect

    Reneau, S.L.; Gardner, J.N.; Forman, S.L.

    1996-01-01

    New geochronologic data provide evidence for an age of about 50 to 60 ka for the youngest volcanic eruptions within the Valles caldera, New Mexico - an age that is significantly younger than most previous age determinations. Thermoluminescence age estimates for buried soils beneath the El Cajete pumice, a key stratigraphic marker in the region, range from 48 to 61 ka and {sup 14}C analyses of burnt logs within volcanic surge beds near the El Cajete vent yield similar ages of 50 to >58 ka. These data conflict with fissontrack, {sup 40}Ar/{sup 39}Ar, and K-Ar ages of 130 to >200 ka, but are supported by recent analyses by electron spin resonance. The results of this study reinforce the need to apply a variety of dating methods when evaluating the age of young volcanic events and support the hypothesis that the El Cajete eruptions were part of a new cycle of volcanic activity in the Valles caldera after an exceptionally long period of quiescence of nearly 460 ka. The new age constraints also suggest a previously unrecognized link between cycles of volcanism and pulses of hydrothermal activity in the caldera, such that hydrothermal outflow appears to decrease significantly following completion of eruptive cycles. 24 refs., 3 figs., 2 tabs.

  5. Numerical models of caldera deformation: Effects of multiphase and multicomponent hydrothermal fluid flow

    USGS Publications Warehouse

    Hutnak, M.; Hurwitz, S.; Ingebritsen, S.E.; Hsieh, P.A.

    2009-01-01

    Ground surface displacement (GSD) in large calderas is often interpreted as resulting from magma intrusion at depth. Recent advances in geodetic measurements of GSD, notably interferometric synthetic aperture radar, reveal complex and multifaceted deformation patterns that often require complex source models to explain the observed GSD. Although hydrothermal fluids have been discussed as a possible deformation agent, very few quantitative studies addressing the effects of multiphase flow on crustal mechanics have been attempted. Recent increases in the power and availability of computing resources allow robust quantitative assessment of the complex time-variant thermal interplay between aqueous fluid flow and crustal deformation. We carry out numerical simulations of multiphase (liquid-gas), multicomponent (H 2O-CO2) hydrothermal fluid flow and poroelastic deformation using a range of realistic physical parameters and processes. Hydrothermal fluid injection, circulation, and gas formation can generate complex, temporally and spatially varying patterns of GSD, with deformation rates, magnitudes, and geometries (including subsidence) similar to those observed in several large calderas. The potential for both rapid and gradual deformation resulting from magma-derived fluids suggests that hydrothermal fluid circulation may help explain deformation episodes at calderas that have not culminated in magmatic eruption.

  6. Proceedings of the symposium on the Long Valley Caldera: A pre-drilling data review

    SciTech Connect

    Goldstein, N.E.

    1987-09-01

    This proceedings volume contains papers or abstracts of papers presented at a two-day symposium held at the Lawrence Berkeley Laboratory (LBL) on 17 and 18 March 1987. Speakers presented a large body of new scientific results and geologic-hydrogeoloic interpretations for the Long Valley caldera. The talks and the discussions that followed focused on concepts and models for the present-day magmatic-hydrothermal system. Speakers at the symposium also addressed the topic of where to site future scientific drill holes in the caldera. Deep scientific drilling projects such as those being contemplated by the DOE Division of Geothermal Technology (DGT), under the Magma Energy Program, and by the DOE Office of Energy Research, Division of Engineering and Geosciences (DEG), along with the USGS and NSE, under the Continental Scientific Drilling Program (CSDP), will be major and expensive national undertakings. DOE/DEG is sponsoring a program of relatively shallow coreholes in the caldera, and DOE/DGT is considering the initiation of a multiphase program to drill a deep hole for geophysical observations and sampling of the ''near magmatic'' environment as early as FY 1988, depending on the DOE budget. Separate abstracts have been prepared for the individual papers.

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

    NASA Astrophysics Data System (ADS)

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

    2003-10-01

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

  8. Time-dependent chamber and vent conditions during explosive caldera-forming eruptions

    NASA Astrophysics Data System (ADS)

    Folch, A.; Martí, J.

    2009-04-01

    We use a modified version of the CPIUC model [Macedonio, G., Neri, A., Martí, J., Folch, A., 2005. Temporal evolution of flow conditions in sustained explosive eruptions, Journal of Volcanology and Geothermal Research, 143, 153-172] to simulate chamber and vent conditions during the different phases of a piston-like caldera-forming eruption. Our idealized caldera-forming scenario assumes an initial central-vent conduit that, after critical chamber decompression, migrates to a fissure-vent peripheral conduit(s). Further decompression leads to final piston-like subsidence which stops only after the virtual destruction of the magmatic reservoir. The simulations find that the pressure at the conduit entrance drops during the decompression phases at a rate depending on the conduit geometry, chamber volatile zonation and fragmentation threshold. The higher the volume contrast between the initial central-vent and the final peripheral fissure-vent conduits, the higher the pressure drop and the jump in the mass eruption rate. Pressure increases back to lithostatic during piston subsidence while some compressible magma remains within the chamber. Finally, during the later phase, pressure experiments a gentle increase or decrease depending on the balance between deposition of intra-caldera material and decrease in the contents of volatiles as deeper chamber levels are tapped.

  9. Satellite InSAR Reveals a new Style of Deformation at Yellowstone Caldera

    NASA Astrophysics Data System (ADS)

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

    2002-12-01

    Interferograms constructed from European Space Agency ERS-2 satellite image pairs reveal a ~40 km diameter area of uplift straddling the north rim of Yellowstone caldera, just south of the Norris Geyser Basin. From 1996 to 2001, the area of peak uplift moved ~100 mm in a line-of-sight (LOS) direction toward the ERS-2 satellite, consistent with an episode of inflation. The latest interferogram of the episode is from autumn 2000 and autumn 2001 scenes, and it reveals ~30 mm of LOS movement, suggesting that the episode is ongoing. A simple point-source model of the uplift, puts an inflation source at ~10 km depth, with an associated volume increase of ~0.05 km3. In an earlier satellite interferometry study, we found deformation to be mostly restricted to the caldera floor, associated with the two main resurgent domes. However, based on limited but active deformation of the Norris-Mammoth Corridor (an active hydrothermal area from Norris Geyser Basin, northeast to Mammoth Hot Springs) we suggested in our earlier study the presence of an outlet from the caldera that feeds the hydrothermal features of the Norris-Mammoth Corridor. The area of uplift that we find in this study is centered on the proposed outlet. The inferred source depth of ~10 km seems to require a magmatic source, however, further modeling using distributed sources is needed to constrain the range of permitted source depths.

  10. The Job Canyon caldera, Stillwater Range, west-central Nevada: A steeply tilted late Oligocene igneous complex

    SciTech Connect

    John, D.A.; Pickthorn, W.J. )

    1993-04-01

    The Job Canyon caldera (JCC) and underlying IXL pluton are the oldest ([approx]29 Ma) and most well preserved parts of the Stillwater caldera complex (SCC), southern Stillwater Range (SR). SCC consists of three partly overlapping calderas JCC, Poco Canyon caldera (PCC), and Elevenmile Canyon caldera (ECC) and the underlying IXL and Freeman Creek plutons. SCC was steeply tilted to the west or east by earliest Miocene extensional faulting exposing sections of late Oligocene rocks as thick as 10 km. JCC consists of 2 structural blocks separated by an E-striking fault zone that was later reactivated to form the north margins of PCC and ECC. The north block of JCC consists of 1.1 km of dacite and andesite lavas, overlain by 2 km of rhyolitic ash-flow tuff locally interbedded with megabreccia, overlain by 2.5 km of dacite and andesite lavas. The south block of JCC is broken into 5 small fault blocks that have thinner sequences of caldera fill consisting of rhyolite ash-flow tuff underlain locally by dacite and andesite lavas. Caldera collapse was accomplished both by large-scale displacement along steep bounding faults and by small displacement along high-angle faults in the interior of the caldera. Hydrothermal alteration of caldera fill is pervasive within JCC and in the upper part of the IXL pluton and appears to predate formation of PCC and tilting of SCC. Most alteration is propylitic and intensity of alteration increases downwards within caldera fill. Preliminary whole-rock [delta][sup 18]O values indicate that hydrothermal fluids were dominated by meteoric water. These values increase upwards to +5 to [minus]3 permil near the top suggesting that there was a steep temperature gradient with temperature increasing with depth. SCC was steeply tilted at about 24--23 Ma shortly following formation of PCC and ECC at about 25--24 Ma. Late Miocene--Holocene Basin and Range faulting has uplifted the SR exposing the older extensional faults and fossil hydrothermal system.

  11. The Late Cretaceous Middle Fork caldera, its resurgent intrusion, and enduring landscape stability in east-central Alaska

    USGS Publications Warehouse

    Bacon, Charles R.; Dusel-Bacon, Cynthia; Aleinikoff, John N.; Slack, John F.

    2014-01-01

    The Middle Fork is a relatively well preserved caldera within a broad region of Paleozoic metamorphic rocks and Mesozoic plutons bounded by northeast-trending faults. In the relatively downdropped and less deeply exhumed crustal blocks, Cretaceous–Early Tertiary silicic volcanic rocks attest to long-term stability of the landscape. Within the Middle Fork caldera, the granite porphyry is interpreted to have been exposed by erosion of thick intracaldera tuff from an asymmetric resurgent dome. The Middle Fork of the North Fork of the Fortymile River incised an arcuate valley into and around the caldera fill on the west and north and may have cut down from within an original caldera moat. The 70 Ma land surface is preserved beneath proximal outflow tuff at the west margin of the caldera structure and beneath welded outflow tuff 16–23 km east-southeast of the caldera in a paleovalley. Within ∼50 km of the Middle Fork caldera are 14 examples of Late Cretaceous (?)–Tertiary felsic volcanic and hypabyssal intrusive rocks that range in area from <1 km2 to ∼100 km2. Rhyolite dome clusters north and northwest of the caldera occupy tectonic basins associated with northeast-trending faults and are relatively little eroded. Lava of a latite complex, 12–19 km northeast of the caldera, apparently flowed into the paleovalley of the Middle Fork of the North Fork of the Fortymile River. To the northwest of the Middle Fork caldera, in the Mount Harper crustal block, mid-Cretaceous plutonic rocks are widely exposed, indicating greater total exhumation. To the southeast of the Middle Fork block, the Mount Veta block has been uplifted sufficiently to expose a ca. 68–66 Ma equigranular granitic pluton. Farther to the southeast, in the Kechumstuk block, the flat-lying outflow tuff remnant in Gold Creek and a regionally extensive high terrace indicate that the landscape there has been little modified since 70 Ma other than entrenchment of tributaries in response to post–2

  12. Ages of zircons from pre-, syn- and post-caldera eruption products of the Changbaishan Volcano, indicating rapid magmatic development

    NASA Astrophysics Data System (ADS)

    Zou, H.; Fan, Q.; Zhang, H.; Schmitt, A. K.

    2013-12-01

    The Millennium Eruption of Changbaishan Volcano with its eponymous 1000 CE eruption age represents one of the two largest volcanic eruptions on Earth in the past 2000 years. In addition to this major caldera-producing eruption of comendite magma, the Changbaishan Volcano also erupted smaller-scale comendite at ~5 ka and trachyte at ~0.3 ka. Here we report U-Th disequilibrium ages of zircons from pumice and lava of the pre-caldera (~5 ka), syn-caldera (the 1 ka Millennium eruption), and post-caldera (~0.3 ka) events. The zircon isochron ages are 12.4+/-1.5 ka (2σ, n=29, MSWD=0.87) for the 5 ka eruption, and 12.2 +/- 1.7 ka (n=16, MSWD=1.0) for the 1 ka eruption which is in agreement within uncertainty with a previously reported isochron age of 10.6+/-1.6 ka (n=11, MSWD=0.61) for a different 1 ka sample (Zou et al., 2010, Lithos). The zircon storage times in the pre-eruptive magma body are thus 7 ka for the pre-caldera eruption and 11 ka for the syn-caldera eruption. Furthermore, identical zircon ages in pre-caldera and syn-caldera rocks suggest that both comenditic eruptions tapped the same magma body. In contrast to the uniform zircon ages for the 5 ka and 1 ka comenditic eruptions, zircon ages for the post-caldera 0.3 ka trachytic eruption define multimodal age populations. The youngest peak for the 0.3 ka eruption is 2.6+/-1.8 ka (n=11, MSWD=0.90), an older peak is 130+/-10 ka (n=13, MSWD=1.7), and the oldest population is ≧230 ka (near U-Th equilibrium). The youngest mode represents zircon microphenocrysts (autocrysts) that crystallized in a trachytic magma chamber in the built-up to the 0.3 ka eruption, whereas the 130 ka and ≧230 ka zircons are interpreted as antecrysts derived from earlier episodes of magmatism. If this interpretation is correct, the zircon storage time in the eruptible magma body for the 0.3 ka eruption is extremely short at 2.3+/-1.8 ka. The distinct multimodal zircon age distributions for the 0.3 ka eruption of trachytic magma

  13. Post-caldera volcanism: In situ measurement of U-Pb age and oxygen isotope ratio in Pleistocene zircons from Yellowstone caldera

    USGS Publications Warehouse

    Bindeman, I.N.; Valley, J.W.; Wooden, J.L.; Persing, H.M.

    2001-01-01

    The Yellowstone Plateau volcanic field, the site of some of the largest known silicic volcanic eruptions, is the present location of NE-migrating hotspot volcanic activity. Most volcanic rocks in the Yellowstone caldera (0.6 Ma), which formed in response to the climactic eruption of 1000 km3 of Lava Creek Tuff (LCT), have unusually low oxygen isotope ratios. Ion microprobe analysis of both U-Pb age and ??18O in zircons from these low-??18O lavas reveals evidence of complex inheritance and remelting. A majority of analyzed zircons from low-??18O lavas erupted inside the Yellowstone caldera have cores that range in age from 2.4 to 0.7 Ma, significantly older than their eruption ages (0.5-0.4 Ma). These ages and the high-??18O cores indicate that these lavas are largely derived from nearly total remelting of normal-??18O Huckleberry Ridge Tuff (HRT) and other pre-LCT volcanic rocks. A post-HRT low-??18O lava shows similar inheritance of HRT-age zircons. The recycling of volcanic rocks by shallow remelting can change the water content and eruptive potential of magma. This newly proposed mechanism of intracaldera volcanism is best studied by combining in situ analysis of oxygen and U-Pb isotope ratios of individual crystals. ?? 2001 Elsevier Science B.V. All rights reserved.

  14. Quartz and feldspar zoning in the eastern Erzgebirge volcano-plutonic complex (Germany, Czech Republic): evidence of multiple magma mixing

    NASA Astrophysics Data System (ADS)

    Müller, Axel; Breiter, Karel; Seltmann, Reimar; Pécskay, Zoltán

    2005-03-01

    Zoned quartz and feldspar phenocrysts of the Upper Carboniferous eastern Erzgebirge volcano-plutonic complex were studied by cathodoluminescence and minor and trace element profiling. The results verify the suitability of quartz and feldspar phenocrysts as recorders of differentiation trends, magma mixing and recharge events, and suggest that much heterogeneity in plutonic systems may be overlooked on a whole-rock scale. Multiple resorption surfaces and zones, element concentration steps in zoned quartz (Ti) and feldspar phenocrysts (anorthite content, Ba, Sr), and plagioclase-mantled K-feldspars etc. indicate mixing of silicic magma with a more mafic magma for several magmatic phases of the eastern Erzgebirge volcano-plutonic complex. Generally, feldspar appears to be sensitive to the physicochemical changes of the melt, whereas quartz phenocrysts are more stable and can survive a longer period of evolution and final effusion of silicic magmas. The regional distribution of mixing-compatible textures suggests that magma mingling and mixing was a major process in the evolution of these late-Variscan granites and associated volcanic rocks. Quartz phenocrysts from 14 magmatic phases of the eastern Erzgebirge volcano-plutonic complex provide information on the relative timing of different mixing processes, storage and recharge, allowing a model for the distribution of magma reservoirs in space and time. At least two levels of magma storage are envisioned: deep reservoirs between 24 and 17 km (the crystallisation level of quartz phenocrysts) and subvolcanic reservoirs between 13 and 6 km. Deflation of the shallow reservoirs during the extrusion of the Teplice rhyolites triggered the formation of the Altenberg-Teplice caldera above the eastern Erzgebirge volcano-plutonic complex. The deep magma reservoir of the Teplice rhyolite also has a genetic relationship to the younger mineralised A-type granites, as indicated by quartz phenocryst populations. The pre-caldera

  15. Compton-Belkovich Volcanic Complex (CBVC): An ash flow caldera on the Moon

    NASA Astrophysics Data System (ADS)

    Chauhan, M.; Bhattacharya, S.; Saran, S.; Chauhan, P.; Dagar, A.

    2015-06-01

    Volcanic calderas are found on Earth, Mars, Venus and Io, and are rare, but unique volcanic structures in the Solar System. Compton-Belkovich Volcanic Complex (CBVC) (60.5°N-99.5°E) on the far side of the Moon is a unique non-mare feature due to its evolved lithology, regional tectonic setting, its location being near the north pole, far from the Procellarum KREEP Terrane (PKT) and its recent association with endogenic water. High-resolution remote sensing observations of several structural features at CBVC such as ring faults, radial faults, fractures manifested by various morphological features such as domes of varied sizes and shapes and pyroclastic ash flows characterize it to be a volcanic caldera. The loading of Humboldtianum basin with basalts and subsequent development of extensional structures outside it along with high-thorium anomaly and resulting silicic volcanism at CBVC producing central collapsed caldera could be considered as an analogy to silicic calderas on Earth formed in extensional tectonic regime even though the tectonic processes involved in these two cases are entirely different, the former being impact-related, whereas the latter involves rifting or hotspot-related activities associated with extensional plate tectonics. Presence of high-reflectance feature and its extension to the east-southeast of the topographic expression and its relation with pyroclastic dispersal have been supported by radar-based Mini-RF observations and high-resolution LROC-NAC imagery. It suggests the presence of a late-stage fine pyroclastic layer within the CBVC region. The diverse volcanic features that exist at the studied site indicate a series of deformation and eruption events associated with silicic magmatism and thus, CBVC could be considered as an ash flow caldera on the Moon. Here, we present a detailed appraisal of various volcanic and structural features detected at CBVC through high-resolution optical as well as radar observations. Based on the

  16. Mechanisms of crustal uplift and subsidence at the Yellowstone caldera, Wyoming

    USGS Publications Warehouse

    Dzurisin, D.; Yamashita, K.M.; Kleinman, J.W.

    1994-01-01

    Leveling surveys in 1923, 1976, and each year from 1983 to 1993 have shown that the east-central part of the Yellowstone caldera, near the base of the Sour Creek resurgent dome, rose at an average rate of 14??1 mm/year from 1923 to 1976 and 22??1 mm/year from 1976 to 1984. In contrast, no detectable movement occurred in the same area from 1984 to 1985 (-2??5 mm/year), and from 1985 to 1993 the area subsided at an average rate of 19??1 mm/year. We conclude that uplift from 1923 to 1984 was caused by: (1) pressurization of the deep hydrothermal system by fluids released from a crystallizing body of rhyolite magma beneath the caldera, then trapped beneath a self-sealed zone near the base of the hydrothermal system; and (2) aseismic intrusions of magma into the lower part of the sub-caldera magma body. Subsidence since 1985 is attributed to: (1) depressurization and fluid loss from the deep hydrothermal system, and (2) sagging of the caldera floor in response to regional crustal extension. Future intrusions might trigger renewed eruptive activity at Yellowstone, but most intrusions at large silicic calderas seem to be accommodated without eruptions. Overpressurization of the deep hydrothermal system could conceivably result in a phreatic or phreatomagmatic eruption, but this hazard is mitigated by episodic rupturing of the self-sealed zone during shallow earthquake swarms. Historical ground movements, although rapid by most geologic standards, seem to be typical of inter-eruption periods at large, mature, silicic magma systems like Yellowstone. The greatest short-term hazards posed by continuing unrest in the Yellowstone region are: (1) moderate to large earthquakes (magnitude 5.5-7.5), with a recurrence interval of a few decdes; and (2) small hydrothermal explosions, most of which affect only a small area (<0.01 km2), with a recurrence interval of a few years. ?? 1994 Springer-Verlag.

  17. Volcanic inflation measured in the caldera of Axial Seamount: Implications for magma supply and future eruptions

    NASA Astrophysics Data System (ADS)

    Nooner, Scott L.; Chadwick, William W.

    2009-02-01

    Since 2000, ambient seawater pressure has been precisely measured at five seafloor benchmarks inside the summit caldera at Axial Seamount to monitor volcanic inflation, using a remotely operated vehicle to deploy a mobile pressure recorder (MPR) in campaign-style surveys. Additionally, seawater pressure has been measured at the caldera center with multiyear deployments of continuously recording bottom pressure recorders (BPRs). These pressure data (converted to depth) are currently the only measurements of volcanic inflation at a submarine volcano. We show new data spanning 2004 to 2007 documenting steady inflation of 12.7 ± 0.4 cm/a at the caldera center. The spatial pattern of uplift is consistent with magma storage in a shallow reservoir underlying the caldera at a depth of ˜3.5 km, and the current uplift rate implies that magma is being supplied to the volcano at a rate of ˜7.5 × 106 m3/a. However, the supply rate immediately after the last eruption in 1998 was significantly higher, and the temporal pattern of uplift at Axial caldera appears to be governed by at least two processes occurring at very different time scales. We interpret the high uplift rates immediately following the 1998 eruption as either due to influx from one or more small satellite magma bodies or as the result of viscoelastic relaxation and/or poroelastic behavior of the crust surrounding the shallow magma chamber, and we present a numerical model which supports the latter interpretation. In contrast, we interpret the current lower uplift rate as due to a steady longterm magma supply from the mantle. This two component uplift pattern has not been observed on land volcanoes, suggesting that magma supply/storage processes beneath this ridge axis volcano differ from volcanoes on land (including Iceland). To reconstruct the uplift history at Axial, we fit the combined MPR and BPR data to two possible uplift scenarios, with which we forecast that the next eruption at Axial is likely to occur

  18. History of surface displacements at the Yellowstone Caldera, Wyoming, from leveling surveys and InSAR observations, 1923-2008

    USGS Publications Warehouse

    Dzurisin, Daniel; Wicks, Charles W.; Poland, Michael P.

    2012-01-01

    Modern geodetic studies of the Yellowstone caldera, Wyoming, and its extraordinary tectonic, magmatic, and hydrothermal systems date from an initial leveling survey done throughout Yellowstone National Park in 1923 by the U.S. Coast and Geodetic Survey. A repeat park-wide survey by the U.S. Geological Survey (USGS) and the University of Utah during 1975-77 revealed that the central part of the caldera floor had risen more than 700 mm since 1923, at an average rate of 14±1 mm/yr. From 1983 to 2007, the USGS conducted 15 smaller surveys of a single level line that crosses the northeast part of the caldera, including the area where the greatest uplift had occurred from 1923 to 1975-77. The 1983 and 1984 surveys showed that uplift had continued at an average rate of 22±1 mm/yr since 1975-77, but no additional uplift occurred during 1984-85 (-2±5 mm/yr), and during 1985-95 the area subsided at an average rate of 19±1 mm/yr. The change from uplift to subsidence was accompanied by an earthquake swarm, the largest ever recorded in the Yellowstone area (as of March 2012), starting in October 1985 and located near the northwest rim of the caldera. Interferometric synthetic aperture radar (InSAR) images showed that the area of greatest subsidence migrated from the northeast part of the caldera (including the Sour Creek resurgent dome) during 1992-93 to the southwest part (including the Mallard Lake resurgent dome) during 1993-95. Thereafter, uplift resumed in the northeast part of the caldera during 1995-96, while subsidence continued in the southwest part. The onset of uplift migrated southwestward, and by mid-1997, uplift was occurring throughout the entire caldera (essentially rim to rim, including both domes). Consistent with these InSAR observations, leveling surveys indicated 24±3 mm of uplift in the northeast part of the caldera during 1995-98. The beginning of uplift was coincident with or followed shortly after an earthquake swarm near the north caldera rim

  19. Nested Calderas in the Northern Kawich Range, Central Nevada: Termination of the Ignimbrite Flare-up in the Great Basin

    NASA Astrophysics Data System (ADS)

    Honn, D. K.; Smith, E. I.

    2006-05-01

    During the ignimbrite flare-up in the Great Basin of the western United States nearly 500,000 km3 of ash- flow tuff related to caldera collapse was erupted between about 40 and 23 Ma. In the central Great Basin the flare-up ended abruptly at about 23 Ma and major caldera generating eruptions did not occur again for nearly 7 Ma. To test models for the demise of this voluminous igneous event, we studied ash-flow tuffs in the northern Kawich Range, central Nevada that erupted just before the end of the ignimbrite flare-up. Five calderas were discovered in the northern Kawich Range; each filled with intracaldera rhyolite tuffs and caldera collapse breccias. Based on 40Ar / 39Ar dating of sanidine and crosscutting relations, the calderas erupted in the following order from oldest to youngest: Clifford Spring (23.67 ± 0.09 Ma), Tobe Spring (22.77 ± 0.07 Ma), Cow Canyon (22.78 ± 0.07 Ma), Bellehelen (22.87 ± 0.16 Ma), and Warm Springs. Field evidence including the occurrence of older welded tuff clasts in younger collapse breccia deposits indicates that these calderas represent separate events and not a single caldera with piecemeal collapse. The five intracaldera tuffs are chemically and chronologically similar to the widespread Pahranagat Formation (33,000 km2)and the Pyramid Spring tuff. To explain the eruption of at least seven tuffs of very similar chemistry over a short period of time (1.06 m.y), large scale partial melting (>50%) of the lower crust is required. Transfer of heat from the crust to the atmosphere during these eruptions cooled the crust may have resulted in the suppression of the ignimbrite flare-up in the Great Basin at 23 Ma.

  20. Superposed local and regional paleostresses: Fault-slip analysis of Neogene extensional faulting near coeval caldera complexes, Yucca Flat, Nevada

    SciTech Connect

    Minor, S.A.

    1995-06-10

    Numerous reduced stress tensors are computed by multiple inversions of 906 temporally and spatially partitioned fault-slip data from the Yucca Flat region in the southwest Nevada volcanic field to constrain the Neogene paleostress and faulting history and to investigate how the regional tectonic stress field was affected by local caldera magmatism. Perturbed, shallow (<400 m), pre-11 Ma paleostress configurations, determined west and northwest of present (post-11 Ma) Yucca Flat basin, existed during mild extensional faulting and are attributed to superposition of transient caldera-magmatic stresses on the regional stress field. A brief ({approximately} 0.5 m.y.) change to a strike-slip stress state occurred at about 13 Ma and was accompanied by small-offset, quasi-conjugate strike-slip faulting. This stress state was most distinct, relative to a normalslip state, near calderas where stress solutions and fault relations indicate closer affinities to a reverse-slip state. Inferred 11.6-11.45 Ma paleostress tensors indicate radial tension associated with either initial caldera collapse or local post-collapse topographic modification of the stress field. Post-11 Ma normal-slip stress tensors are associated with normal- and oblique-slip faults that accommodated subsidence and eastward extension of Yucca Flat basin away from the caldera complexes. These tensors do not indicate stress modifications due to residual caldera-related effects and thus were used to infer post-11 Ma regional stress changes. The stress field has rotated as much as 65{degrees} clockwise since 11 Ma during extensional development of Yucca Flat basin, with most of the rotation and extension occurring before about 8.5 Ma. Results suggest that shallow magmatism and caldera development can strongly alter extensional tectonic stress fields, fault patterns, and slip directions in the uppermost crust out to distances of roughly two magma chamber radii away from a magma body. 59 refs., 11 figs., 2 tabs.

  1. Crust and upper mantle P wave velocity structure beneath Valles caldera, New Mexico: Results from the Jemez teleseismic tomography experiment

    SciTech Connect

    Steck, Lee K.; Fehler, Michael C.; Roberts, Peter M.; Baldridge, W. Scott; Stafford, Darrik G.; Lutter, William J.; Sessions, Robert

    1998-10-01

    New results are presented from the teleseismic component of the Jemez Tomography Experiment conducted across Valles caldera in northern New Mexico. We invert 4872 relative {ital P} wave arrival times recorded on 50 portable stations to determine velocity structure to depths of 40 km. The three principle features of our model for Valles caldera are: (1) near-surface low velocities of {minus}17{percent} beneath the Toledo embayment and the Valle Grande, (2) midcrustal low velocities of {minus}23{percent} in an ellipsoidal volume underneath the northwest quadrant of the caldera, and (3) a broad zone of low velocities ({minus}15{percent}) in the lower crust or upper mantle. Crust shallower than 20 km is generally fast to the northwest of the caldera and slow to the southeast. Near-surface low velocities are interpreted as thick deposits of Bandelier tuff and postcaldera volcaniclastic rocks. Lateral variation in the thickness of these deposits supports increased caldera collapse to the southeast, beneath the Valle Grande. We interpret the midcrustal low-velocity zone to contain a minimum melt fraction of 10{percent}. While we cannot rule out the possibility that this zone is the remnant 1.2 Ma Bandelier magma chamber, the eruption history and geochemistry of the volcanic rocks erupted in Valles caldera following the Bandelier tuff make it more likely that magma results from a new pulse of intrusion, indicating that melt flux into the upper crust beneath Valles caldera continues. The low-velocity zone near the crust-mantle boundary is consistent with either partial melt in the lower crust or mafic rocks without partial melt in the upper mantle. In either case, this low-velocity anomaly indicates that underplating by mantle-derived melts has occurred. {copyright} 1998 American Geophysical Union

  2. Relation of Mercury, Uranium, and Lithium Deposits to the McDermitt Caldera Complex, Nevada-Oregon

    USGS Publications Warehouse

    Rytuba, James J.; Glanzman, Richard K.

    1978-01-01

    The McDermitt caldera complex, located along the Nevada-Oregon border, is a Miocene collapse structure 45 kilometer in diameter. Large-volume rhyolitic and peralkaline ash-flow tuffs were erupted from 17.9 to 15.8 m.y. ago, leading to the formation of overlapping and nested calderas. Emplacement of rhyolitic ring domes, located primarily along the western margin of the calderas, represents the last phase of volcanic activity. The complex is the site of large deposits of mercury, an are deposit and several occurrences of uranium, and widespread occurrences of lithium. Mercury deposits at Cordero, McDermitt, Bretz, Ruja, and Opalite occur along ring fractures in sedimentary rocks that fill the calderas. Near the deposits the rocks are altered to zeolites and within the ore zones to potassium feldspar and silicate minerals. Although the mercury deposits contain anomalous concentrations of uranium, the most important uranium occurrences are restricted to rhyolitic ring domes emplaced along the western margin of the calderas. Lithium occurrences are located in tuffaceous rocks that are altered to zeolites and potassium feldspar. Concentrations of lithium ranging from 0.1 to 0.68 percent are associated with the clay mineral hectorite. The rhyolitic rocks erupted from the McDermitt caldera complex are enriched in mercury, uranium, and lithium and are likely source rocks for these elements in the ore deposits. Tuffaceous caldera fill-sediment averages 0.29 ppm mercury, 22 ppm uranium, and 236 ppm lithium; large-volume ash-flow tuffs contain up to 0.26 ppm mercury, 20 ppm uranium, and 300 ppm lithium.

  3. 40Ar/39Ar dating of the eruptive history of Mount Erebus, Antarctica: Summit flows, tephra, and caldera collapse

    USGS Publications Warehouse

    Harpel, C.J.; Kyle, P.R.; Esser, R.P.; McIntosh, W.C.; Caldwell, D.A.

    2004-01-01

    Eruptive activity has occurred in the summit region of Mount Erebus over the last 95 ky, and has included numerous lava flows and small explosive eruptions, at least one plinian eruption, and at least one and probably two caldera-forming events. Furnace and laser step-heating 40Ar/39Ar ages have been determined for 16 summit lava flows and three englacial tephra layers erupted from Mount Erebus. The summit region is composed of at least one or possibly two superimposed calderas that have been filled by post-caldera lava flows ranging in age from 17 ?? 8 to 1 ?? 5 ka. Dated pre-caldera summit flows display two age populations at 95 ?? 9 to 76 ?? 4 ka and 27 ?? 3 to 21 ??4 ka of samples with tephriphonolite and phonolite compositions, respectively. A caldera-collapse event occurred between 25 and 11 ka. An older caldera-collapse event is likely to have occurred between 80 and 24 ka. Two englacial tephra layers from the flanks of Mount Erebus have been dated at 71 ?? 5 and 15 ?? 4 ka. These layers stratigraphically bracket 14 undated tephra layers, and predate 19 undated tephra layers, indicating that small-scale explosive activity has occurred throughout the late Pleistocene and Holocene eruptive history of Mount Erebus. A distal, englacial plinian-fall tephra sample has an age of 39 ?? 6 ka and may have been associated with the older of the two caldera-collapse events. A shift in magma composition from tephriphonolite to phonolite occurred at around 36 ka. ?? Springer-Verlag 2004.

  4. 40Ar/39Ar dating of the eruptive history of Mount Erebus, Antarctica: summit flows, tephra, and caldera collapse

    NASA Astrophysics Data System (ADS)

    Harpel, Christopher J.; Kyle, Philip R.; Esser, Richard P.; McIntosh, William C.; Caldwell, David A.

    2004-12-01

    Eruptive activity has occurred in the summit region of Mount Erebus over the last 95 ky, and has included numerous lava flows and small explosive eruptions, at least one plinian eruption, and at least one and probably two caldera-forming events. Furnace and laser step-heating 40Ar/39Ar ages have been determined for 16 summit lava flows and three englacial tephra layers erupted from Mount Erebus. The summit region is composed of at least one or possibly two superimposed calderas that have been filled by post-caldera lava flows ranging in age from 17 ± 8 to 1 ± 5 ka. Dated pre-caldera summit flows display two age populations at 95 ± 9 to 76 ± 4 ka and 27 ± 3 to 21 ± 4 ka of samples with tephriphonolite and phonolite compositions, respectively. A caldera-collapse event occurred between 25 and 11 ka. An older caldera-collapse event is likely to have occurred between 80 and 24 ka. Two englacial tephra layers from the flanks of Mount Erebus have been dated at 71 ± 5 and 15 ± 4 ka. These layers stratigraphically bracket 14 undated tephra layers, and predate 19 undated tephra layers, indicating that small-scale explosive activity has occurred throughout the late Pleistocene and Holocene eruptive history of Mount Erebus. A distal, englacial plinian-fall tephra sample has an age of 39 ± 6 ka and may have been associated with the older of the two caldera-collapse events. A shift in magma composition from tephriphonolite to phonolite occurred at around 36 ka.

  5. Geochemistry of low-temperature springs northwest of Yellowstone caldera: Seeking the link between seismicity, deformation, and fluid flow

    USGS Publications Warehouse

    Evans, William C.; Bergfeld, D.; van Soest, M.C.; Huebner, M.A.; Fitzpatrick, J.; Revesz, K.M.

    2006-01-01

    A comprehensive geochemical survey of springs outside the northwest margin of the Yellowstone caldera was undertaken in 2003 and 2004. This survey was designed to detect: (1) active leakage from a huge reservoir of CO2 gas recently postulated to extend from beneath the caldera into this area; and (2) lingering evidence for subsurface flow of magmatic fluids into this area during the 1985 seismic swarm and concomitant caldera subsidence. Spring temperatures are low (< 15 ??C), but two large-discharge springs contain 14C-dead carbon that can be identified as magmatic from calculated end-member values for ??13C(dead) and 3He/C(dead) of - 4??? and 1 ?? 10- 10, respectively, similar to values for intra-caldera fumarolic and hot-spring gases. However, the combined discharge of magmatic C is only 5.4 tonnes/day, < 0.1% of the total output from Yellowstone. The two springs have slightly elevated 3He/4He ratios near 1 RA and anomalous concentrations of Cl, Li, and B, and appear to represent minor leakage of gas-depleted, thermal waters out of the caldera. The small CO2 signal detected in the springs is difficult to reconcile with a large underlying reservoir of gas in faulted and seismically active terrain. When considered with analyses from previous decades, the results provide no evidence to associate the ten-year period of caldera deflation that began in 1985 with expulsion of magmatic fluids through the caldera rim in this area.

  6. Is there a geochemical link between volcanic and plutonic rocks in the Organ Mountains caldera?

    NASA Astrophysics Data System (ADS)

    Memeti, V.; Davidson, J.

    2013-12-01

    Results from separate volcanic and plutonic studies have led to inconsistent conclusions regarding the origins and thus links between volcanic and plutonic systems in continental arcs and the magmatic processes and time scales responsible for their compositional variations. Some have suggested that there is a geochemical and geochronological disconnect between volcanic and plutonic rocks and hence have questioned the existence of magma mush columns beneath active volcanoes. Investigating contemporary volcanic and plutonic rocks that are spatially connected is thus critical in exploring these issues. The ca. 36 Ma Organ Mountains caldera in New Mexico, USA, represents such a system exposing contemporaneous volcanic and plutonic rocks juxtaposed at the surface due to tilting during extensional tectonics along the Rio Grande Rift. Detailed geologic and structural mapping [1] and 40Ar/39Ar ages of both volcanics and plutons [2] demonstrate the spatial and temporal connection of both rock types with active magmatism over >2.5 myr. Three caldera-forming ignimbrites erupted within 600 kyr [2] from this system with a total erupted volume of 500-1,000 km3 as well as less voluminous pre- and post-caldera trachyte and andesite lavas. The ignimbrite sequence ranges from a crystal-poor, high-SiO2 rhyolite at the base to a more crystal-rich, low-SiO2 rhyolite at the top. Compositional zoning with quartz-monzonite at the base grading to syenite and alaskite at the top is also found in the Organ Needle pluton, the main intrusion, which is interpreted to be the source for the ignimbrites [1]. Other contemporaneous and slightly younger plutons have dioritic to leucogranitic compositions. We examined both volcanic and plutonic rocks with petrography and their textural variations with color cathodoluminescence, and used whole rock element and Sr, Nd and Pb isotope geochemistry to constrain magma compositions and origins. Electron microprobe analyses on feldspars have been completed to

  7. The ecology of xenophyophores (Protista) on eastern Pacific seamounts

    NASA Astrophysics Data System (ADS)

    Levin, Lisa A.; Thomas, Cynthia L.

    1988-12-01

    Large, agglutinating protozoans of the class Xenophyophorea are the dominant epifaunal organisms on soft and hard substrates of many bathyal seamounts in the eastern Pacific Ocean off Mexico. Observations made with the submersible Alvin and remotely towed camera sleds on 17 seamounts at 31°, 20°, 13° and 10°N revealed more than ten distinct xenophyophore test morphologies. Most of these appear to represent previously undescribed species. Reticulate forms are numerically dominant at 20°, 13° and 10°N. Xenophyophore abundances increase with decreasing latitude, being rare at 30°N, present at densities of 0.1-1.0 m -2 at 20° and 13°N and often exceeding 1.0 m -2 at 10°N, occasionally reaching 10-18 m -2. Highest concentrations are observed on caldera floors near the base of steep caldera walls, at depths between 1700 and 2500 m. Most individuals select sand-size pelagic foraminiferan tests (63-500 μm) and exclude pebble, silt and clay-size particles for test construction. Xenophyophore on seamounts modify the structure of metazoan communities and may play a role in maintenance of infaunal diversity. Twenty-seven xenophyophore tests were found to provide habitat for 16 major macrofaunal taxa (152 individuals) and three meiofaunal taxa (333 individuals). The presence of xenophyophores also enhances the abundance of isopods, tanaids, ophiuroids, nematodes and harpacticoid copepods dwelling in sediments surrounding the tests. Mobile megafauna are attracted to sediment beneath and adjacent to xenophyophores. We suggest that xenophyophores, which are abundant on many topographic features in deep water (e.g. guyots, trenches, canyons and continental slopes), are a functionally important component of deep-sea benthic communities and require further autecological and synecological investigation.

  8. Eastern Equine Encephalitis

    MedlinePlus

    ... Facebook Tweet Share Compartir Image of Culiseta melanura mosquito, photo taken by Jason Williams, reproduced by permission from the Virginia Mosquito Control Association. Eastern equine encephalitis virus (EEEV) is ...

  9. Magma plumbing system at the beginning of repeated caldera eruption: A case study on Aso-1 erupted about 270 ky ago from Aso caldera, SW Japan

    NASA Astrophysics Data System (ADS)

    Miyagi, I.; Hoshizumi, H.; Miyabuchi, Y.

    2015-12-01

    In order to understand the commencement of magma plumbing system of a polygenetic caldera, we started petrological study on the earliest eruptive product of Aso caldera, SW Japan. Aso caldera is one of the active volcano in Japan which have produced four stages (Aso-1, -2, -3, -4) of large-scale pyroclastic flow deposits 270 to 90 ky. ago. A suite of samples were collected from the bottom of Aso-1 pyroclastic flow deposit and from the underlying tephra layer (Ono et al., 1979). The tephra comprises more than 10 pumice fall units inter-layered by dark gray volcanic ash. For whole rock chemistry, coarser pumice fragments were separated. For mineral and glass chemistry, phenocrysts and glass particles were handpicked from the sieved 500-1000 um fractions under a binocular microscope. This fraction consist of plagioclase, orthopyroxene, variably vesiculated volcanic glass fragments, and clinopyroxene phenocrysts. They were analyzed using an electron micro-probe. The suite of samples are similar and major temporal change is the chemical composition of orthopyroxenes; those from upper horizon are relatively Mg rich. Anorthite content of plagioclase phenocryst is bimodal 49-53 mol. % (major) and 57-70 mol. % (minor). Silica content of matrix glass fall in a narrow range 68-70 wt. %. Temperature and oxygen fugacity were estimated to be 865-905 deg-C and FMQ+2 log unit, respectively, using ILMAT (Lepage, 2003). Pressure and water content of the magma are estimated to be 5-7 kbar and 0.5-1 wt. % H2O, respectively, using rhyolite-MELTS (Gualda et al., 2012) on the most undifferentiated tholeiitic basalt of Aso 4KC-03 (Hunter, 1998) to reproduce the observed composition of matrix glass (68-70 wt. % SiO2) and plagioclase (An 49-53 mol. %). The calcic plagioclase (An 57-70 mol. %), however, suggest that the basalt was initially hydrous and require magma degassing before the differentiation. If we assume degassing by magma convection in a conduit (Kazahaya et al., 1994), the

  10. Tephrochronology and Paleomagnetism in the Northwest Wall of Kilauea Caldera, Hawai`i, Reveal the Age of the Observatory Shield

    NASA Astrophysics Data System (ADS)

    Rose, T.; Fiske, R.; Swanson, D.; Champion, D.; McGeehin, J.

    2002-12-01

    Chemical analysis of tephra in the northwest wall of Kilauea's caldera, and paleomagnetism of associated lava flows, allow correlation to more distal tephra and flows of known C-14 age. This correlation shows that the Observatory shield-the shield that existed before the modern caldera formed about 500 ka-must be considerably younger than previously considered. We dug a pit through a mantle of scree to exhume a 2.2-m-thick section of tephra about one-third of the way up the caldera wall. A distinct color change divides the tephra section into upper and lower parts. Glassy ash and lapilli from just below the color change have unusually high TiO2 and K2O contents (3.1 and 0.75 wt. percent, respectively) recognized at more than 30 localities in the 1.3 to 1.1 ka Kulanaokuaiki tephra south, west, and north of the summit. The paleomagnetism of lava flows beneath the exhumed tephra is equivalent to that of the Kipuka Nene flows, which underlie complete sections of Kulanaokuaiki tephra southeast of the caldera. Tephra in another exposure, at the base of the caldera wall several hundred meters northeast of the pit, consists only of beds above the high Ti-K ash. That ash, and tephra below, are apparently buried beneath a flow that is interlayered with the tephra. The exposed upper part of this flow has the same paleomagnetic direction as the Hope`o (Hornet kipuka) flow, which occurs between the upper and lower Kulanaokuaiki tephra 6 km south of the summit. The flow immediately overlying the upper part of the tephra correlates magnetically with the 1.0 ka Old Kalue flows, which directly overlie complete sections of Kulanaokuaiki tephra on Kilauea's south flank. Flows making up the upper ~30 m of the caldera wall correlate magnetically with the 0.6-0.8 ka Young Kalu`e, Ahua, Lua Manu, and Observatory lava flows that blanket wide areas around the caldera, in the Koa`e fault system, and on the south flank. We conclude that the tephra in the caldera wall, considered by some as

  11. An extraordinary episode of Yellowstone caldera uplift, 2004-2010, from GPS and InSAR observations

    NASA Astrophysics Data System (ADS)

    Chang, Wu-Lung; Smith, Robert B.; Farrell, Jamie; Puskas, Christine M.

    2010-12-01

    Geodetic measurements of Yellowstone ground deformation from 2006 to June 2010 reveal deceleration of the recent uplift of the Yellowstone caldera following an unprecedented period of uplift that began in 2004. In 2006-2008 uplift rates decreased from 7 to 5 cm/yr and 4 to 2 cm/yr in the northern and southwest caldera, respectively, and in 2009 rates further reduced to 2 cm/yr and 0.5 cm/yr in the same areas. Elastic-dislocation modeling of the deformation data robustly indicates an expanding sill at ˜7-10 km depth near the top of a seismically imaged, crystallizing magma reservoir, with a 60% decrease in the volumetric expansion rate between 2006 and 2009. Reduction of hydrothermal-volcanic recharge from beneath the northeast caldera and seismic moment release of the 2008 and 2010 large earthquake swarms are plausible mechanisms for decelerating the caldera uplift and may have influenced the change in recent caldera motion from uplift to subsidence.

  12. Evidence for the contemporary magmatic system beneath Long Valley Caldera from local earthquake tomography and receiver function analysis

    USGS Publications Warehouse

    Seccia, D.; Chiarabba, C.; De Gori, P.; Bianchi, I.; Hill, D.P.

    2011-01-01

    We present a new P wave and S wave velocity model for the upper crust beneath Long Valley Caldera obtained using local earthquake tomography and receiver function analysis. We computed the tomographic model using both a graded inversion scheme and a traditional approach. We complement the tomographic I/P model with a teleseismic receiver function model based on data from broadband seismic stations (MLAC and MKV) located on the SE and SW margins of the resurgent dome inside the caldera. The inversions resolve (1) a shallow, high-velocity P wave anomaly associated with the structural uplift of a resurgent dome; (2) an elongated, WNW striking low-velocity anomaly (8%–10 % reduction in I/P) at a depth of 6 km (4 km below mean sea level) beneath the southern section of the resurgent dome; and (3) a broad, low-velocity volume (–5% reduction in I/P and as much as 40% reduction in I/S) in the depth interval 8–14 km (6–12 km below mean sea level) beneath the central section of the caldera. The two low-velocity volumes partially overlap the geodetically inferred inflation sources that drove uplift of the resurgent dome associated with caldera unrest between 1980 and 2000, and they likely reflect the ascent path for magma or magmatic fluids into the upper crust beneath the caldera.

  13. A 12,000-year record of vertical deformation across the Yellowstone caldera margin: The shorelines of Yellowstone Lake

    NASA Technical Reports Server (NTRS)

    Locke, William W.; Meyer, Grant A.

    1994-01-01

    The 600 ka Yellowstone caldera exhibits several signs of unrest, the most evident of which is historic ground deformation including both uplift and subsidence. We document deformation in the area of the southern caldera across approximately 12,000 years using the postglactic shoreline terraces of Yellowstone Lake. Raised shoreline elevations were interpreted from 230 leveling profiles surveyed across flights of terraces, with an accuracy of +/- 0.5 m. Of about 11 recognizable terraces, the five most continuous raised shorelines were correlated around the lake basin to reveal deformation patterns. Net deformation over the past approximatley 3 kyr has been dominantly up within the caldera interior and slightly down along the caldera rim, relative to the extracaldera region. This uplift is roughly similar to the historic pattern and may largely represent the effects of the most recent inflation episode. Subtraction of the total estimated magnitude of inflation in this epsiode suggests that the overall trend of postglacial deformation has been subsidence. The cause of this trend is undetermined but is most likely related to the effects of regional extension and long-term cooling within the Yellowstone caldera.

  14. A catalogue of caldera unrest at Taupo Volcanic Centre, New Zealand, using the Volcanic Unrest Index (VUI)

    NASA Astrophysics Data System (ADS)

    Potter, Sally H.; Scott, Bradley J.; Jolly, Gill E.; Johnston, David M.; Neall, Vince E.

    2015-09-01

    Caldera unrest occurs frequently at Taupo Volcanic Centre (TVC), New Zealand, occasionally resulting in deleterious socio-economic impacts. This large silicic volcano most recently erupted in 232 AD in an explosive, caldera-forming rhyolitic eruption, devastating the central North Island. Eruptions are preceded by volcanic unrest, often consisting of seismicity, deformation, degassing, and/or geothermal system changes. These phenomena may also occur due to non-magmatic processes, complicating eruption forecasting. As volcanic unrest may or may not lead to an eruption, it needs to be characterised to provide effective warnings; this is best achieved by understanding past unrest. In this research, a catalogue of caldera unrest at TVC is developed using an historical chronology methodology, spanning from 1872 to December 2011. The Volcanic Unrest Index (VUI), which is introduced by Potter et al. (2015), is estimated for the catalogue, demonstrating its use and providing a characterisation of unrest at TVC. Sixteen episodes of unrest are identified; 4 are classified as moderate unrest (VUI 3), and 12 are classified as minor unrest (VUI 2). There has been median interval of approximately 3 years between unrest episodes and a median unrest episode duration of just under 5 months. This research provides context for future caldera unrest crises at TVC and contributes to the global caldera unrest dataset.

  15. Conductive heat flux in VC-1 and the thermal regime of Valles caldera, Jemez Mountains, New Mexico ( USA).

    USGS Publications Warehouse

    Sass, J.H.; Morgan, P.

    1988-01-01

    Over 5% of heat in the western USA is lost through Quaternary silicic volcanic centers, including the Valles caldera in N central New Mexico. These centers are the sites of major hydrothermal activity and upper crustal metamorphism, metasomatism, and mineralization, producing associated geothermal resources. Presents new heat flow data from Valles caldera core hole 1 (VC-1), drilled in the SW margin of the Valles caldera. Thermal conductivities were measured on 55 segments of core from VC-1, waxed and wrapped to preserve fluids. These values were combined with temperature gradient data to calculate heat flow. Above 335 m, which is probably unsaturated, heat flow is 247 + or - 16 mW m-2. Inteprets the shallow thermal gradient data and the thermal regime at VC-1 to indicate a long-lived hydrothermal (and magmatic) system in the southwestern Valles caldera that has been maintained through the generation of shallow magma bodies during the long postcollapse history of the caldera. High heat flow at the VC-1 site is interpreted to result from hot water circulating below the base of the core hole, and we attribute the lower heat flow in the unsaturated zone is attributed to hydrologic recharge. -from Authors

  16. Eruptive history of Mount Mazama and Crater Lake Caldera, Cascade Range, U.S.A.

    NASA Astrophysics Data System (ADS)

    Bacon, Charles R.

    1983-10-01

    New investigations of the geology of Crater Lake National Park necessitate a reinterpretation of the eruptive history of Mount Mazama and of the formation of Crater Lake caldera. Mount Mazama consisted of a glaciated complex of overlapping shields and stratovolcanoes, each of which was probably active for a comparatively short interval. All the Mazama magmas apparently evolved within thermally and compositionally zoned crustal magma reservoirs, which reached their maximum volume and degree of differentiation in the climactic magma chamber ˜ 7000 yr B.P. The history displayed in the caldera walls begins with construction of the andesitic Phantom Cone ˜ 400,000 yr B.P. Subsequently, at least 6 major centers erupted combinations of mafic andesite, andesite, or dacite before initiation of the Wisconsin Glaciation ˜ 75,000 yr B.P. Eruption of andesitic and dacitic lavas from 5 or more discrete centers, as well as an episode of dacitic pyroclastic activity, occurred until ˜ 50,000 yr B.P.; by that time, intermediate lava had been erupted at several short-lived vents. Concurrently, and probably during much of the Pleistocene, basaltic to mafic andesitic monogenetic vents built cinder cones and erupted local lava flows low on the flanks of Mount Mazama. Basaltic magma from one of these vents, Forgotten Crater, intercepted the margin of the zoned intermediate to silicic magmatic system and caused eruption of commingled andesitic and dacitic lava along a radial trend sometime between ˜ 22,000 and ˜ 30,000 yr B.P. Dacitic deposits between 22,000 and 50,000 yr old appear to record emplacement of domes high on the south slope. A line of silicic domes that may be between 22,000 and 30,000 yr old, northeast of and radial to the caldera, and a single dome on the north wall were probably fed by the same developing magma chamber as the dacitic lavas of the Forgotten Crater complex. The dacitic Palisade flow on the northeast wall is ˜ 25,000 yr old. These relatively silicic

  17. Caldera Collapse in the Galapagos Islands, 1968: The largest known collapse since 1912 followed a flank eruption and explosive volcanism within the caldera.

    PubMed

    Simkin, T; Howard, K A

    1970-07-31

    The summit caldera of Isla Fernandina, a large, uninhabited basaltic shield volcano, was further enlarged by 1 to 2 km(3) in June 1968. A small quake and large vapor cloud on 11 June were followed 4 hours later by a remarkable volcanic ash cloud and, after another hour, by a major explosion recorded at infrasonic stations throughout the hemisphere. Seismic activity increased to a peak on 19 June, when more than 200 events per day were recorded by a seismograph 140 km away. Several hundred quakes were in the magnitude range 4.0 to 5.4 m(b), but few such events were recorded after 23 June. Unusual lightning accompanied the major cloud, and, during the evening of 11 June, distant observers reported red glow and flashes from the area. Fine ash fell that night and much of the next day to distances at least 350 km from the volcano. PMID:17739001

  18. Taupo in time and space: dynamics of a rhyolitic caldera volcano and its magmatic system

    NASA Astrophysics Data System (ADS)

    Wilson, C. J.; Allan, A. S.; Barker, S. J.; Morgan, D. J.; Charlier, B. L.; Baker, J. A.; Wooden, J. L.

    2012-12-01

    Traditional views see the caldera-forming event as the eruptive career pinnacle of any aspiring large silicic magma system, around which perspectives focus in 'pre-', syn-' and 'post-caldera' groupings of eruptions. Important question arising from such notions are: (1) Is the caldera-forming eruption a freak event, reflecting unusual circumstances, or does it represent a stochastic extreme on a continuously evolving record? (2) How rapidly does the melt-dominant large magma body accumulate? (3) What are the recovery/renewal processes and timings after a caldera-forming eruption? (4) What hangover from the main event is seen in behaviour of the 'post-caldera' system? The central Taupo Volcanic Zone (New Zealand) is a valuable area in which to test models for large silicic systems because of its rapid frequency of moderate to large sizes of its eruptions over the past ~1.6 Ma. Here we review the eruptive record for Taupo volcano itself over the last 50,000 years, highlighting old and new results that detail its evolution over that period, during which the 25.4 ka, ~530 cubic km Oruanui event formed the main caldera-related eruption. In the Taupo area, erupting at vents <15 km apart, there are two systems ('Oruanui', 'NE-dome') of contrasting chemical and isotopic characteristics that were active prior to 25.4 ka, erupting magma volumes which range over 3 orders of magnitude in size. Growth of the large Oruanui system did not curtail the NE-dome system: it contributed some magma by diking to the early Oruanui eruption phases and probably remains viable today. Assembly of the Oruanui melt-dominant body was accomplished over hundreds of years prior to the eruption, using components that had been assembled over tens of thousands of years. Destruction of the Oruanui melt-dominant body and its fractionation-related root (mush) zone of crystals was complete enough such that there is no magmatic resurgence, and subsequent activity involves a new, third magma system. Initial

  19. Magma Genesis of Sakurajima, the Quaternary post- Aira caldera volcano, southern Kyushu Island, Japan

    NASA Astrophysics Data System (ADS)

    Shibata, T.; Suzuki, J.; Yoshikawa, M.; Kobayashi, T.; Miki, D.; Takemura, K.

    2012-12-01

    Sakurajima volcano is the Quaternary post-caldera volcano of Aira caldera, which was caused by the eruption of huge amount of silicic pyroclastics, situated on Ryukyu arc, southern Kyushu Island, Japan. This volcano is quite active, so it can be considered that the preparation of next caldera-forming eruption with huge amount of silicic magma is proceeding. It is, therefore, expected that the investigation of magma genesis of Sakurajima volcano give us information for the mechanism generating huge amount of silicic magma, which cause the caldera formation. We analyzed major and trace elements with Sr, Nd and Pb isotopic compositions of volcanic rocks from Sakurajima volcano. We sampled (ol) - opx - cpx - pl andesite and dacite from almost all the volcanic units defined by Fukuyama and Ono (1981). In addition to Sakurajima samples, we also studied basaltic rocks erupted at pre-caldera stage of the Aira caldera to estimate the primary magma of Sakurajima volcano. Major and trace element variations generally show linear trends on the Harker diagrams, with the exception of P2O5 and TiO2. Based on the trend of P2O5 vs.SiO2, we divided studied samples low-P (P2O5 < 0.15 wt. %) and high-P (P2O5 > 0.15 wt. %) groups and these groups also display two distinct trends on TiO2-SiO2 diagram. The composition of trace elements shows typical island arc character as depletion of Nb and enrichments of Rb, K and Pb, suggesting addition of aqueous fluids to the mantle wedge. The Zr and Nb concentrations make a liner trend (Zr/Nb = 27) and this trend across from tend of MORB (Zr/Nb = 35) to that of crustal materials (Zr/Nb=17). The Sr, Nd and Pb isotopic compositions broadly plot to on the mixing curve connecting MORB-type mantle and sediments of the Philippine Sea Plate, indicating that the primary magma was generated by partial melting of MORB-type mantle wedge, which was hydrated with fluids derived from the subducted Philippine Sea sediments. But we found that our data plot apart

  20. Insights into deposition and deformation of intra-caldera ignimbrites, central Nevada

    NASA Astrophysics Data System (ADS)

    MacDonald, William D.; Palmer, H. Currie; Deino, Alan L.; Shen, Po-Yu

    2012-11-01

    Magnetic studies, together with structural and 40Ar/39Ar age analyses, were used to investigate the development and deformation of ignimbrites of the Caetano Tuff formation in central-north Nevada. Magnetic susceptibility, susceptibility anisotropy (AMS) and magnetic remanence approaches were used to decipher events accompanying emplacement and subsequent deformation of that tuff, for both intracaldera tuffs and outflow deposits. 40Ar/39Ar ages, both those presented here and previously published ages, indicate about 33.8 Ma for the age of Caetano ignimbrites, approximately at the Eocene/Oligocene boundary. Although extensive faulting associated with regional extension of the Great Basin region has dissected these deposits, the thickness of the intra-caldera ignimbrites has been estimated at 3.5 km or more. Thermal modeling for cooling of a caldera filling of 3.5 km thickness indicates acquisition of remanent magnetization can persist up to 25 ka, sufficient to average secular variation. This contrasts with rapid cooling and remanence acquisition in outflow ignimbrites typically only tens of meters thick. A 750 m thick reference section was selected for more detailed study about 10 km to the west of the type area. This reference section, fault-bounded at both base and top, represents the upper part of the formation. Its lower member includes the uppermost 250 m of the lower massive resistant unit of ignimbrites, a middle member of 375 m of well stratified pyroclastic deposits, vitrophyres and sediments, and an upper member of about 125 m of recessive ignimbrite and thin-bedded clastic and pyroclastic deposits. Structural and magnetic remanence measurements suggest 13° eastward tilting of the caldera floor occurred early during deposition of the middle member. Flow directions inferred from AMS Kmax axes in the middle member diverge about 45° relative to those in the underlying member and suggest a change in vent source accompanying the deposition of the middle

  1. Chemical-abrasion SIMS dating of zircon from the Eocene Caetano caldera, Nevada

    NASA Astrophysics Data System (ADS)

    Colgan, J.; Watts, K. E.; John, D. A.; Henry, C. D.; Coble, M. A.; Vazquez, J. A.

    2012-12-01

    The Eocene Caetano caldera in northern Nevada formed during eruption of ~1100 km3 of crystal-rich rhyolite. Miocene extension cut the caldera into a set of fault blocks that expose minor pre-caldera volcanic rocks, two units of intracaldera Caetano Tuff up to 4 km thick, ash-flow tuff feeder dikes and ring-fracture intrusions, caldera collapse breccias, and post-collapse resurgent intrusions. Single-crystal 40Ar/39Ar sanidine dates on all parts of the caldera system overlap, yielding a 34.01 ± 0.05 Ma (n=17, Fish Canyon sanidine = 28.201 Ma) age for the eruption. 40Ar/39Ar dating also documents several preceding episodes of magmatism: 35.69 ± 0.06 Ma (sanidine, n =13) rhyolite dikes in the nearby Cortez gold district, 35.21 ± 0.18 Ma (plagioclase, n=1) andesite lava underlying Caetano Tuff, and a 38.90 ± 0.11 Ma (biotite, n=1), dacite dike in the northeastern caldera wall. Extensive U-Pb SHRIMP dating of zircon from both the Cortez dikes and all phases of the Caetano system suggests continuous magmatism from 40-34 Ma. However, all samples contain at least some—sometimes many—zircons with U-Pb ages younger than the 34.0 Ma argon age. To determine if anomalously young zircon ages are due to Pb-loss, we analyzed representative samples of the upper Caetano Tuff and the Redrock Canyon resurgent pluton with and without chemical abrasion to mitigate Pb-loss. Bulk zircon separates were annealed at 850°C for 48 hours, then chemically abraded with 10:1 HF/HNO3 vapor in a Parr bomb at 225°C for 8 hours, based on protocols outlined by Mattinson (2005). Both treated and untreated zircons from the same sample were mounted in epoxy and polished to their midsections, then imaged on the SEM using BSE and CL. The SHRIMP-RG at Stanford University was used to determine U-Pb ages and trace element concentrations in single spots for ~25 to 30 individual zircons per sample, using a round-robin procedure and two zircon age standards (R33 and 080) to monitor external precision

  2. Elastomechanical methods in the exploration of the Valles Caldera, New Mexico. Final report, June 8, 1981-October 8, 1981

    SciTech Connect

    Bodvarsson, G.

    1981-01-01

    The Valles caldera in the Jemez Mountains of New Mexico is a case of an active caldera that is an object for a comprehensive ground tilt field program to map both elastic and rheic discontinuities. Based on a rather comprehensive theoretical development that is outlined in five separate Essays, estimates of the amplitudes of some of the possible ground tilt signals were obtained. Based on the results, the strongest signals of the order of 100 to 200 nanoradians would appear to result from the purely elastic response of the caldera fill to a barometric forcing. Moreover, assuming a magmatic underplate below the Valles, barometric forcing may lead to a flexure of the upper crust that could generate tilt signals of a similar magnitude. Present data material is insufficient to allow a useful estimate to be made of the possible tilt signals due to the rheic properties of a Valles pluton that may be in the state of partial fusion.

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

    USGS Publications Warehouse

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

    2006-01-01

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

  4. Analysis of two-color geodimeter measurements of deformation within the Long Valley caldera: June 1983 to October 1985.

    USGS Publications Warehouse

    Langbein, J.; Linker, M.; Tupper, D.

    1987-01-01

    Line length changes from several baselines in a trilateration network within the Long Valley caldera clearly define a decrease in strain rate from June 1983 through October 1985. The data consist of more than 1600 length measurements on 23 baselines using a two- color geodimeter, which has a precision of 0.2 ppm of the line length. A model is constructed using these observations as well as yearly observations of a trilateration network within and near the caldera. The model contains two points of inflation located at 5 and 10 km beneath the resurgent dome of the caldera plus dextral slip on a fault plane within the south moat within an elastic half-space. -from Authors

  5. Preliminary study of the potential environmental concerns associated with surface waters and geothermal development of the Valles Caldera

    SciTech Connect

    Langhorst, G.J.

    1980-06-01

    A preliminary evaluation is presented of possible and probable problems that may be associated with hydrothermal development of the Valles Caldera Known Geothermal Resource Area (KGRA), with specific reference to surface waters. Because of the history of geothermal development and its associated environmental impacts, this preliminary evaluation indicates the Valles Caldera KGRA will be subject to these concerns. Although the exact nature and size of any problem that may occur is not predictable, the baseline data accumulated so far have delineated existing conditions in the streams of the Valles Caldera KGRA. Continued monitoring will be necessary with the development of geothermal resources. Further studies are also needed to establish guidelines for geothermal effluents and emissions.

  6. Can we see the distal dyke communicate with the caldera? Examples of temporal correlation analysis using seismicity from the Bárðarbunga volcano

    NASA Astrophysics Data System (ADS)

    Jónsdóttir, Kristín; Jónasson, Kristján; Tumi Guðmundsson, Magnús; Hensch, Martin; Hooper, Andrew; Holohan, Eoghan; Sigmundsson, Freysteinn; Halldórsson, Sæmundur Ari; Vogfjörð, Kristín; Roberts, Matthew; Barsotti, Sara; Ófeigsson, Benedikt; Hjörleifsdóttir, Vala; Magnússon, Eyjólfur; Pálsson, Finnur; Parks, Michelle; Dumont, Stephanie; Einarsson, Páll; Guðmundsson, Gunnar

    2016-04-01

    The Bárðarbunga volcano is composed of a large oval caldera (7x11 km) and fissures extending tens of kilometers away from the caldera along the rift zone, which marks the divergent plate boundary across Iceland. On August 16th, 2014 an intense seismic swarm started below the Bárðarbunga caldera and in the two weeks that followed a dyke migrated some 47 km laterally in the uppermost 6-10 km of the crust along the rift. The dyke propagation terminated in lava fields just north of Vatnajökull glacier, where a major (1.5 km3) six months long eruption took place. Intense earthquake activity in the caldera started in the period August 21-24 with over 70 M5 earthquakes accompanying slow caldera collapse, as verified by various geodetic measurements. The subsidence is likely due to magma withdrawal from a reservoir at depth beneath the caldera. During a five months period, October-February, the seismic activity was separated by over 30 km in two clusters; one along the caldera rims (due to piecewise caldera subsidence) and the other at the far end of the dyke (as a result of small shear movements). Here we present statistical analysis comparing the temporal behaviour of seismicity recorded in the two clusters. By comparing the earthquake rate in the dyke in temporal bins before and after caldera subsidence earthquakes to the rate away from these bins (background rate), we show posing a statistical p-value test, that the number of dyke earthquakes was significantly higher (p <0.05) in the period 0-3 hours before a large earthquake (>M4.6) in the caldera. Increased dyke seismicity was also observed 0-3 hours following a large caldera earthquake. Elevated seismicity in the dyke before a large caldera earthquake may occur when a constriction in the dyke was reduced, followed by pressure drop in the chamber. Assuming that the large caldera earthquakes occurred when chamber pressure was lowest, the subsiding caldera piston may have caused temporary higher pressure in the

  7. The lifecycle of caldera-forming volcanoes in the Main Ethiopian Rift: insights from Aluto volcano

    NASA Astrophysics Data System (ADS)

    Mather, T. A.; Hutchison, W.; Yirgu, G.; Biggs, J.; Cohen, B. E.; Barfod, D. N.; Lewi, E.; Pyle, D. M.

    2015-12-01

    The silicic peralkaline volcanoes of the East African Rift are some of the least studied and yet potentially most dangerous volcanoes in the world. We present the first detailed account of the eruptive history of Aluto, a restless silicic volcano located in the Main Ethiopian Rift, using new constraints from fieldwork, remote sensing, 40Ar/39Ar geochronology and geochemistry. Prior to the growth of the Aluto volcanic complex (before 500 ka) the region was characterized by a significant period of fault development and mafic fissure eruptions. The earliest volcanism at Aluto built up a trachytic complex over 8 km in diameter. Aluto then underwent large-volume ignimbrite eruptions at ca. 300 ka developing a ~42 km2 collapse structure. After a hiatus of ~250 kyr, a phase of post-caldera volcanism began. Since ca. 60 ka, highly-evolved peralkaline rhyolite lavas, ignimbrites and pumice fall deposits have erupted from vents across the complex. The age of the youngest volcanism is not well known. Geochemical modelling is consistent with rhyolite genesis from protracted fractionation (>80 %) of typical 'rift basalt'. Based on the field stratigraphy and the number, style and volume of recent eruptions we suggest that silicic eruptions occur at an average rate of 1 per 1000 years, and that future eruptions of Aluto will involve explosive emplacement of localised pumice cones and effusive obsidian coulees of volumes between 1-100 × 106 m3. Comparisons with other caldera volcanoes in this section of the rift suggest that there may be parallels between Aluto's behaviour and that of other volcanic centres, both in terms of the volcanic 'lifecycle', and broad timings of caldera collapse events.

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

    USGS Publications Warehouse

    Lipman, P.W.

    1967-01-01

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

  9. Geothermal activity in the subglacial Katla caldera, Iceland, 1999-2005, studied with radar altimetry

    NASA Astrophysics Data System (ADS)

    Guđmundsson, Magnús T.; Höganadóttir, Pórdís; Kristinsson, Arnór Bergur; Guđbjörnsson, Snaebjörn

    The Katla caldera is located under the Mýrdalsjökull ice cap and is one of the most hazardous volcanoes in Iceland due to major jökulhlaups that accompany eruptions. Subglacial geothermal activity is manifested in several 10-50 m deep depressions (ice cauldrons) within and at the caldera rim and the total geothermal heat output is of the order of a few hundred megawatts. A shortlived but powerful pulse in geothermal heat output took place in 1999, probably including a minor subglacial eruption, when new ice cauldrons formed in three places and an unexpected jökulhlaup occurred. Following these events, a comprehensive monitoring program was set up for Katla, including ice surface elevation profiling from aircraft, to monitor variations in geothermal heat and detect signs of subglacial water accumulation. A radar altimeter coupled with a kinematic GPS is used, achieving an absolute elevation accuracy of 3 m and internal consistency of 1-2 m. Profiles across the caldera are flown twice a year. An annual accumulation-ablation cycle in surface elevation with amplitude of 5-10 m is observed. By removing this cycle from the data, changes due to subglacial geothermal activity are obtained. After the events in 1999, a decline in geothermal activity was observed. In 2001-03 some ice cauldrons expanded and deepened by 10-15 m, indicating renewed increase in geothermal activity. This trend is also apparent for 2003-05. The increase in geothermal poweramounts to a few tens of megawatts. It is likely that the increased thermal output is related to increased seismicity and caused by magma inflow.

  10. Quaternary silicic pyroclastic deposits of Atitlán Caldera, Guatemala

    USGS Publications Warehouse

    Rose, William I., Jr.; Newhall, Christopher G.; Bornhorst, Theodore J.; Self, Stephen

    1987-01-01

    Atitlán caldera has been the site of several silicic eruptions within the last 150,000 years, following a period of basalt/andesite volcanism. The silicic volcanism began with 5–10 km3 of rhyodacites, erupted as plinian fall and pyroclastic flows, about 126,000 yr. B.P. At 85,000 yr. B.P. 270–280 km3 of compositionally distinct rhyolite was erupted in the Los Chocoyos event which produced widely dispersed, plinian fall deposits and widespread, mobile pyroclastic flows. In the latter parts of this eruption rhyodacite and minor dacite were erupted which compositionally resembled the earliest silicic magmas of the Atitlán center. As a result of this major eruption, the modern Atitlán (III) caldera formed. Following this event, rhyodacites were again erupted in smaller (5–13 km3) volumes, partly through the lake, and mafic volcanism resumed, forming three composite volcanoes within the caldera. The bimodal mafic/silicic Atitlán volcanism is similar to that which has occurred elsewhere in the Guatemalan Highlands, but is significantly more voluminous. Mafic lavas are thought to originate in the mantle, but rise, intrude and underplate the lower crust and partly escape to the surface. Eventually, silicic melts form in the crust, possibly partly derived from underplated basaltic material, rise, crystallize and erupt. The renewed mafic volcanism could reflect either regional magmato-tectonic adjustment after the large silicic eruption or the onset of a new cycle.

  11. The Owens River as a tiltmeter for Long Valley caldera, California

    SciTech Connect

    Reid, J.B. Jr )

    1992-05-01

    In the lower 11 km of its course around the resurgent dome of Long Valley caldera, the Owens River displays two parallel meander belts, comparable in meander wavelength and amplitude but unequal in age, elevation, and discharge. It appears the two belts take turns carrying the river's flow depending on whether the dome is inflating or subsiding. The inboard belt, some 200-300 m closer to the dome and now 30-60 cm higher in elevation, contains an underfit stream and is now being abandoned. The outboard channel formed in a series of avulsions apparently induced by recent uplift of the dome. In the upper 4 km of the two-channel reach, avulsion occurred between 1856 and 1878 as inferred from the original US Coast and Geodetic Survey mapping the caldera. Avulsion had already occurred by 1856 in the lower 4 km of the river, suggesting a possible migration of the center of uplift through time. More ancient meander scars at the inboard and outboard limits of the floodplain imply additional earlier episodes of inflation and subsidence. Projection of surveyed topographic profiles across the river's floodplain to the center of the dome suggests that cumulative recent uplift is on the order of 15-35 m, or about 30-70 times greater than that measured for the caldera since 1979 (Castle et al. 1984). The duration of the era of subsidence can be estimated by comparing oxbow densities in the old and new meander belts in the upper two-channel reach; the data suggest that the dome may have been in subsidence for a period of at least 500 to 1,000 yr ending about 150 yr ago. No eruptions of the Long Valley volcanic system have accompanied these inflations and subsidings.

  12. Insight into Vent Opening Probability in Volcanic Calderas in the Light of a Sill Intrusion Model

    NASA Astrophysics Data System (ADS)

    Giudicepietro, Flora; Macedonio, G.; D'Auria, L.; Martini, M.

    2016-05-01

    The aim of this paper is to discuss a novel approach to provide insights on the probability of vent opening in calderas, using a dynamic model of sill intrusion. The evolution of the stress field is the main factor that controls the vent opening processes in volcanic calderas. On the basis of previous studies, we think that the intrusion of sills is one of the most common mechanism governing caldera unrest. Therefore, we have investigated the spatial and temporal evolution of the stress field due to the emplacement of a sill at shallow depth to provide insight on vent opening probability. We carried out several numerical experiments by using a physical model, to assess the role of the magma properties (viscosity), host rock characteristics (Young's modulus and thickness), and dynamics of the intrusion process (mass flow rate) in controlling the stress field. Our experiments highlight that high magma viscosity produces larger stress values, while low magma viscosity leads to lower stresses and favors the radial spreading of the sill. Also high-rock Young's modulus gives high stress intensity, whereas low values of Young's modulus produce a dramatic reduction of the stress associated with the intrusive process. The maximum intensity of tensile stress is concentrated at the front of the sill and propagates radially with it, over time. In our simulations, we find that maximum values of tensile stress occur in ring-shaped areas with radius ranging between 350 m and 2500 m from the injection point, depending on the model parameters. The probability of vent opening is higher in these areas.

  13. Preorogenic history of the Adirondacks as an elsonian anorogenic caldera complex

    SciTech Connect

    McLelland, J.

    1985-01-01

    The Adirondack Highlands are characterized by the close association of a distinctive trinity of metaigneous rocks: (1) anorthosites, (2) mangeritic and quartz mangeritic gneisses that tend to envelop the anorthosites, and (3) alaskitic and trondjhemitic gneisses many of which represent metamorphosed volcanic material. All rocks within the province exhibit high concentrations of iron (FeO/FeO + MgO approx. 0.8), and both titaniferous and non-titaniferous iron oxide deposits occur. The mangeritic rocks are alkaline to peralkaline while the alaskitic gneisses are meta- to peraluminous. A/CNK, KN/C, as well as oxides vs SiO/sub 2/ plots yield patterns identical to those cited by J. L. Anderson (1983) as diagnostic of Proterozoic anorogenic plutonism. Within North American this plutonism corresponds to the Elsonian magmatic event with most ages falling between 1.5 - 1.3 b.y. This belt is characterized by high-level anorogenic bimodal magmatism developed in caldera complexes with zoned magma chambers and widespread rhyolitic ash-flow tuffs. Examples of this activity are found in the St. Francois Mountains, Missouri; the Wolf River batholith, Wisconsin; and the Nain Province. The Adirondacks lie along this trend and exhibit the same bulk chemistry and chemical variation as the other complexes. In addition they show enrichment in halogens (esp. F), REE, Zr, and other trace elements associated with calderas. Fayalite and ferroaugite are widely developed. These similarities strongly suggest that prior to the Grenville Orogeny, the Adirondacks consisted of bimodal caldera complexes which were part of the Elsonian anorogenic magmatism extending across North America.

  14. Analysis of gravimetric anomalies in Furnas caldera (São Miguel, Azores)

    NASA Astrophysics Data System (ADS)

    Montesinos, F. G.; Camacho, A. G.; Vieira, R.

    1999-09-01

    Furnas Volcano (São Miguel Island, Azores) is a steep-sided caldera complex resulting from several collapses. In this paper, we analyse and interpret the gravity survey carried out by the Instituto de Astronomı´a y Geodesia (Spain) and the gravity data published by the Instituto Nacional de Meteorologia e Geofisica (Portugal). The resulting Bouguer anomaly reveals the presence of a regional trend, several local features and a component of noise. In separating the regional trend we use a robust polynomial fitting. Further, a covariance analysis and a least squares prediction are applied to filter the noise and to model the local anomaly. A first signal map represents the main local anomaly, while the secondary signal map shows superficial anomalies. This distribution reveals a local main minimum close to the 1630 A.D. and Gaspar craters. Several possible alignments are shown that lead to a model, mainly with SW-NE and SE-NW orientations, of the negative anomaly, with the pattern of the low density zones showing a relationship with the volcanic features. Applying a stabilized linear method of gravimetric inversion, we obtain a density contrast distribution of the sources of the filtered local Bouguer anomaly, considering as unknowns the anomalous densities of a fixed discrete distribution of rectangular prisms which represents the subsoil volume. A mixed minimization criteria for the weighted residuals and the weighted density contrast allow us to obtain a solution as a discrete three-dimensional density contrast model. The obtained anomalous densities model shows a clear relation with the structure of the caldera complex and tectonic trends, with the principal body of negative contrast density being associated with the subsurface structure of the caldera.

  15. A fluid-driven earthquake swarm on the margin of the Yellowstone caldera

    USGS Publications Warehouse

    Shelly, David R.; Hill, David P.; Massin, Frederick; Farrell, Jamie; Smith, Robert B.; Taira, Taka'aki

    2013-01-01

    Over the past several decades, the Yellowstone caldera has experienced frequent earthquake swarms and repeated cycles of uplift and subsidence, reflecting dynamic volcanic and tectonic processes. Here, we examine the detailed spatial-temporal evolution of the 2010 Madison Plateau swarm, which occurred near the northwest boundary of the Yellowstone caldera. To fully explore the evolution of the swarm, we integrated procedures for seismic waveform-based earthquake detection with precise double-difference relative relocation. Using cross-correlation of continuous seismic data and waveform templates constructed from cataloged events, we detected and precisely located 8710 earthquakes during the three-week swarm, nearly four times the number of events included in the standard catalog. This high-resolution analysis reveals distinct migration of earthquake activity over the course of the swarm. The swarm initiated abruptly on January 17, 2010 at about 10 km depth and expanded dramatically outward (both shallower and deeper) over time, primarily along a NNW-striking, ~55º ENE-dipping structure. To explain these characteristics, we hypothesize that the swarm was triggered by the rupture of a zone of confined high-pressure aqueous fluids into a pre-existing crustal fault system, prompting release of accumulated stress. The high-pressure fluid injection may have been accommodated by hybrid shear and dilatational failure, as is commonly observed in exhumed hydrothermally affected fault zones. This process has likely occurred repeatedly in Yellowstone as aqueous fluids exsolved from magma migrate into the brittle crust, and it may be a key element in the observed cycles of caldera uplift and subsidence.

  16. Anomalous shear wave delays and surface wave velocities at Yellowstone Caldera, Wyoming

    SciTech Connect

    Daniel, R.G.; Boore, D.M.

    1982-04-10

    To investigate the effects of a geothermal area on the propagation of intermediate-period (1--30 s) teleseismic body waves and surface waves, a specially designed portable seismograph system was operated in Yellowstone Caldera, Wyoming. Travel time residuals, relative to a station outside the caldera, of up to 2 s for compressional phases are in agreement with short-period residuals for P phases measured by other investigators. Travel time delays for shear arrivals in the intermediate-period band range from 2 to 9 s and decrease with increasing dT/d..delta... Measured Rayleigh wave phase velocities are extremely low, ranging from 3.2 km/s at 27-s period to 2.0 km/s at 7-s period; the estimated uncertainty associated with these values is 15%. We propose a model for compressional and shear velocities and Poisson's ratio beneath the Yellowstone caldera which fits the teleseismic body and surface wave data: it consists of a highly anomalous crust with an average shear velocity of 3.0 km/s overlying an upper mantle with average velocity of 4.1 km/s. The high average value of Poisson's ratio in the crust (0.34) suggests the presence of fluids there; Poisson's ratio in the mantle between 40 and approximately 200 km is more nearly normal (0.29) than in the crust. A discrepancy between normal values of Poisson's ratio in the crust calculated from short-period data and high values calculated from teleseismic data can be resolved by postulating a viscoelastic crustal model with frequency-dependent shear velocity and attenuation.

  17. Mineralogical and Fluid Inclusion Studies on Seafloor Hydrothermal Vents at TA25 Caldera, Tonga Arc

    NASA Astrophysics Data System (ADS)

    Choi, S. K.; Pak, S. J.; Choi, S. H.; Lee, K. Y.; Kim, H. S.; Lee, I. K.

    2015-12-01

    The extensive hydrothermal vent field was discovered at TA25("V18s-HR" in the SO-167 cruise) caldera in the Tonga arc, southwest Pacific. The TA25 caldera is a submarine volcano of dacitic composition and hosts the NE- and NW-trending hydrothermal vent on the western caldera wall. These active hydrothermal crusters are mostly small (chimney: <0.5m in tall; sulfide mound: <3m in diameter) and immature, and emit the transparent fluids of which temperature range from 150℃ to 242℃ (average = 203℃). The hydrothermal sulfide ores, recovered by ROV and/or TV-grab, are mainly composed of sphalerite, pyrite, marcasite, galena, chalcopyrite, covellite, tennantite, enargite and sulfates such as barite, gypsum/anhydrite. It is observed that three distinct mineralogical zonation from exterior to interior of the chimneys: (1) barite-gypsum/anhydrite-pyrite-sphalerite; (2) sphalerite-pyrite-galena±chalcopyrite; (3) sphaleirte-pyrite-chalcopyrite-enargite-tennantite±galena±covellite. FeS content in sphalerite increases from chimney exterior to interior. Chalcopyrite is more abundant in the mound than in the chimney, implying fluid temperatures in mound are greater than in the chimney. The enargite assemblage (pyrite-chalcopyrite-enargite-tennantite) is indicative of high-sulfidation epithermal deposits. Fluid inclusions on barite crystals from mound samples show mono-type inclusion (two-phase liquid-rich inclusions) which is less than 20㎛ in diameter. Homogenization temperatures and salinities from fluid inclusion study range from 148℃ to 341℃ (average = 213℃) and 0.4 to 3.6 equiv. wt.% NaCl, respectively. The main mineralization temperature in mound might be greater than 200℃ since barite on fluid inclusion is early stage mineral.

  18. Initial results from VC-1, First Continental Scientific Drilling Program Core Hole in Valles Caldera, New Mexico

    NASA Astrophysics Data System (ADS)

    Goff, Fraser; Rowley, John; Gardner, Jamie N.; Hawkins, Ward; Goff, Sue; Charles, Robert; Wachs, Daniel; Maassen, Larry; Heiken, Grant

    1986-02-01

    Valles Caldera 1 (VC-1) is the first Continental Scientific Drilling Program (CSDP) core hole drilled in the Valles caldera and the first continuously cored well in the caldera region. The objectives of VC-1 were to penetrate a hydrothermal outflow plume near its source, to obtain structural and stratigraphie information near the intersection of the ring fracture zone and the precaldera Jemez fault zone, arid to core the youngest volcanic unit inside the caldera (Banco Bonito obsidian). Coring of the 856-m well took only 35 days to finish, during which all objectives were attained and core recovery exceeded 95%. VC-1 penetrates 298 m of moat volcanics and caldera fill ignimbrites, 35 m of precaldera volcaniclastic breccia, and 523 m of Paleozoic carbonates, sandstones, and shales. A previously unknown obsidian flow was encountered at 160 m depth underlying the Battleship Rock Tuff in the caldera moat zone. Hydrothermal alteration is concentrated in sheared, brecciated, and fractured zones from the volcaniclastic breccia to total depth with both the intensity and rank of alterations increasing with depth. Alteration assemblages consist primarily of clays, calcite, pyrite, quartz, and chlorite, but chalcopyrite and sphalerite have been identified as high as 450 m and molybdenite has been identified in a fractured zone at 847 m. Carbon 13 and oxygen 18 analyses of core show that the most intense zones of hydrothermal alteration occur in the Madera Limestone above 550 m and in the Madera and Sandia formations below 700 m. This corresponds with zones of most intense calcite and quartz veining. Thermal aquifers were penetrated at the 480-, 540-, and 845-m intervals. Although these intervals are associated with alteration, brecciation, and veining, they are also intervals where clastic layers occur in the Paleozoic sedimentary rocks.

  19. Initial results from VC-1, first Continental Scientific Drilling Program core hole in Valles caldera, New Mexico

    SciTech Connect

    Goff, F.; Rowley, J.; Gardner, J.N.; Hawkins, W.; Goff, S.; Charles, R.; Wachs, D.; Maassen, L.; Heiken, G.

    1986-02-10

    Valles Caldera 1 (VC-1) is the first Continental Scientific Drilling Program (CSDP) core hole drilled in the Valles caldera and the first continuously cored well in the caldera region. The objectives of VC-1 were to penetrate a hydrothermal outflow plume near its source, to obtain structural and stratigraphic information near the intersection of the ring fracture zone and the precaldera Jemez fault zone, and to core the youngest volcanic unit inside the caldera (Banco Bonito obsidian). Coring of the 856-m well took only 35 days to finish, during which all objectives were attained and core recovery exceeded 95%. VC-1 penetrates 298 m of moat volcanics and caldera fill ignimbrites, 35 m of precaldera volcaniclastic breccia, and 523 m of Paleozoic carbonates, sandstones, and shales. A previously unknown obsidian flow was encountered at 160 m depth underlying the battleship Rock Tuff in the caldera moat zone. Hydrothermal alteration is concentrated in sheared, brecciated, and fractured zones from the volcaniclastic breccia to total depth with both the intensity and rank of alterations increasing with depth. Alteration assemblages consist primarily of clays, calcite, pyrite, quartz, and chlorite, but chalcopyrite and sphalerite have been identified as high as 450 m and molybdenite has been identified in a fractured zone at 847 m. Carbon 13 and oxygen 18 analyses of core show that the most intense zones of hydrothermal alteration occur in the Madera Limestone above 550 m and in the Madera and Sandia formations below 700 m. This corresponds with zones of most intense calcite and quartz veining. Thermal aquifers were penetrated at the 480-, 540-, and 845-m intervals. Although these intervals are associated with alteration, brecciation, and veining, they are also intervals where clastic layers occur in the Paleozoic sedimentary rocks.

  20. Caldera subsidence and magma chamber depth of the Olympus Mons volcano, Mars

    NASA Technical Reports Server (NTRS)

    Zuber, M. T.; Mouginis-Mark, P. J.

    1992-01-01

    An axisymmetric finite element model is constructed to calculate elastic stresses in a volcanic edifice to examine the relationship between surface tectonism, caldera subsidence, and the physical characteristics of Olympus Mons' magmatic reservoir. Model results indicate that the surface stress state is not strongly sensitive to the aspect ratio or pressure distribution of the magma chamber, or to the contrast in stiffness between the magma chamber and surroundings, but is strongly dependent on the depth and width of the chamber. A gross similarity is suggested between the configurations of the magmatic plumbing systems of Olympus Mons and several well-studied terrestrial volcanoes such as the Hawaiian shields.

  1. Mawson Formation at Allan Hills, Antarctica: Evidence for a Large-scale Phreatomagmatic Caldera

    NASA Astrophysics Data System (ADS)

    Elliot, D. H.; Fortner, E. H.; Elliot, R. J.

    2003-12-01

    At Allan Hills, Transantarctic Mountains, Jurassic Mawson Formation pyroclastic rocks are more than 300 m thick. Previously described as unconformable on older Permian and Triassic Beacon strata, the Mawson is now known to be, at least in part, intrusive. Triassic Feather Formation country rocks at the contact display a zone of in situ brecciation. This is followed inward by a zone of megaclasts (10s of m long) derived from younger Triassic Lashly Formation strata, and then by a structureless, grey, sand-rich breccia which has increasing proportions of pyroclasts laterally and vertically. The grey breccia is overlain by units, up to 10s of m thick, of stratified tuff breccia and lapilli tuff, both of which consist of high proportions of Beacon and dolerite clasts set in a matrix of pyroclasts and sand-sized debris also derived from Beacon rocks. All but the brecciated country rocks are cut by basaltic diatremes, and by tuff-breccia and lapilli-tuff intrusive bodies. Megaclasts are mainly Lashly C strata which were a minimum of 120 m stratigraphically and topographically above any extant country rock, and demonstrate that the Mawson rocks are filling a collapse structure. The sequence of events is interpreted to be: 1) initial phreatic activity, on emplacement of a Ferrar Dolerite sill at depth, causing in situ brecciation; 2) withdrawal of magma and collapse of overlying strata to form a caldera containing megaclasts of Lashly strata; 3) renewed magma emplacement which initially caused phreatic activity but increasingly became phreatomagmatic, and formed the grey breccia by disaggregation of the collapsed Beacon strata; 4) full scale phreatomagmatism that erupted the stratified tuff breccia and lapilli tuff; 5) intrusion of basalt diatremes, bodies of tuff breccia and lapilli tuff, and dolerite plugs and dikes. Away from the mapped area, on the southern arm of Allan Hills, tuff breccia and lapilli tuff are crudely stratified and could be either outflow facies or

  2. Hydrothermal precious-metal deposits related to graben-calderas of the Sierra Madre Occidental

    NASA Astrophysics Data System (ADS)

    Aguirre-Diaz, G. J.; Labarthe-Hernandez, G.; Nieto-Obregon, J.; Tristan-Gonzalez, M.; Gonzalez-Partida, E.

    2007-05-01

    The Sierra Madre Occidental (SMO) covers the NW portion of Mexico and it is the host for several important precious metal mine operations, such as Tayoltita, Cienega, Topia, Fresnillo, Zacatecas, Guanajuato and Bolaños, just to mention a few. The southern part of the Basin and Range extension affected also NW Mexico and formed NW- to NE-trending normal faults that bound many large grabens, which are particularly long and deep in the southern SMO. Both graben formation and mid-Tertiary silicic volcanic activity coincided in space and time, particularly for the 38-23 Ma period, the Ignimbrite Flare-up event, but this activity dates back to Eocene and was as young as Miocene. This volcanism included large rhyolitic domes, too. At the southern SMO, the vents of this silicic volcanism are related to graben's master faults and we have named them graben-calderas. Evidences include large pyroclastic dikes and post-ignimbrite aligned rhyolitic domes and lava dikes. All these features were found along the graben-caldera walls or on the graben's shoulders. Some of these vents are related to gold and silver hydrothermal mineralization. In most cases a paleo-lake filled the graben-caldera for a period of time, either during the ignimbrite emplacement or after it. Some of the graben-caldera ignimbrites were deposited in subaqueous environments and post-ignimbrite rhyolitic domes and dikes were intruded in non-consolidated water-saturated tuffs or sedimentary deposits. This lacustrine environment provided the necessary water for the hydrothermal system. The combination of all these factors in space and time, grabens+volcanism+water, resulted in the development of precious-metal hydrothermal ore deposits. Bolaños mine in the Bolaños graben represent our case-study, but we have confirmed the same tectono-volcanic-lake relationship at other mine-districts along the SMO. We conclude that locating the fissural vents of the silicic ignimbrites by means of just geologic mapping is be

  3. IR Temperatures of Mauna Loa Caldera Obtained with Multispectral Thermal Imager

    SciTech Connect

    Kurzeja, R.J.

    2001-07-18

    A survey of surface temperatures of the Mauna Loa caldera during 7/14/00 and 7/15/00 was made by SRTC in conjunction with a MTI satellite image collection. The general variation of surface temperature appears quite predictable responding to solar heating. The analysis of detailed times series of temperature indicates systematic variations in temperature of 5 C corresponding to time scales of 3-5 minutes and space scales of 10-20 m. The average temperature patterns are consistent with those predicted by the Regional Atmospheric Modeling System (RAMS).

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  5. Source Modeling and Seismic-Volcano Implications of the 2004-2007 Accelerated Deformation at Yellowstone Caldera

    NASA Astrophysics Data System (ADS)

    Chang, W.; Smith, R.; Wicks, C.; Farrell, J.; Puskas, C.

    2007-12-01

    The youthful Yellowstone volcanic system is characterized by extensive earthquakes, episodes of cyclical uplift and subsidence, extraordinarily high heat flow, and widespread hydrothermal activity. In mid-2004, deformation of the 45-km-wide by 75-km-long Yellowstone caldera, measured by continuously operating GPS and InSAR, unexpectedly changed from subsidence to uplift at rates of up to 6.6 cm/yr that is three to four times faster than earlier deformation episodes. This pronounced uplift has continued to the time of this abstract submission, fall 2007, and was also accompanied by unusual subsidence of up to 4 cm/yr across the northwest caldera rim near the Norris Geyser Basin. Corresponding horizontal motions of 0.8-2.2 cm/yr and 0.7-2.0 cm/yr directed outward from the caldera and inward to the Norris area, respectively. Source modeling of the deformation data revealed an expanding sill-like structure 10 km beneath the caldera with a volumetric expansion rate of 0.11 km3/yr, consistent with the amount of magma required to supply the observed high heat flow of the caldera, and a contracting tabular body 8 km under the Norris area with a volumetric contraction rate of 0.01 km3/yr. The modeled expanding sill overlaps with the top of a tomographically imaged magma body, implying that the accelerated uplift is related to the inflation from the shallowest part of the magma chamber. The inflation of the caldera sill can furthermore induce dilatational strain in the surrounding volcanic rocks beneath the northern caldera rim, causing hydrothermal fluids to migrate into the caldera that can depressurize the Norris hydrothermal systems and cause the ground to subside. We also evaluate the elastic and viscoelastic stress evolution of this accelerated uplift to model the temporal changes of Columb failure stress on adjacent faults. The results will help us understand the interaction between the volcanic system and earthquake occurrence of the Yellowstone region.

  6. Early Miocene Kirka-Phrigian caldera, western Anatolia - an example of large volume silicic magma generation in extensional setting

    NASA Astrophysics Data System (ADS)

    Seghedi, Ioan; Helvacı, Cahit

    2014-05-01

    Large rhyolitic ignimbrite occurrences are close connected to the Early Miocene initiation of extensional processes in the central-west Anatolia along Taşvanlı-Afyon zones. Field correlations, petrographical, geochemical and geochronological data lead to a substantial reinterpretation of the ignimbrite surrounding Kırka area, known from its world-class borate deposits, as representing the climatic event of a caldera collapse, unknown up to now and newly named "Kırka-Phrigian caldera". The caldera, which is roughly oval (24 km x 15km) in shape, one of the largest in Turkey, is supposed to have been formed in a single stage collapse event, at ~19 Ma that generated huge volume extracaldera outflow ignimbrites. Transtensive/distensive tectonic stresses since 25 Ma ago resulted in the NNW-SSE elongation of the magma chamber and influenced the roughly elliptical shape of the subsided block (caldera floor) belonging to the apex of Eskişehir-Afyon-Isparta volcanic area. Intracaldera post-collapse sedimentation and volcanism (at ~ 18 Ma) was controlled through subsidence-related faults with generation of a series of volcanic structures (mainly domes) showing a large compositional range from saturated silicic rhyolites and crystal-rich trachytes to undersaturated lamproites. Such volcanic rock association is typical for lithospheric extension. In this scenario, enriched mantle components within the subcontinental lithospheric mantle will begin to melt via decompression melting during the initiation of extension. Interaction of these melts with crustal rocks, fractionation processes and crustal anatexis driven by the heat contained in the ascending mantle melts produced the silicic compositions in a large crustal reservoir. Such silicic melts generated the initial eruptions of Kırka-Phrigian caldera ignimbrites. The rock volume and geochemical evidence suggests that silicic volcanic rocks come from a long-lived magma chamber that evolved episodically; after caldera

  7. CRUSTAL REFRACTION PROFILE OF THE LONG VALLEY CALDERA, CALIFORNIA, FROM THE JANUARY 1983 MAMMOTH LAKES EARTHQUAKE SWARM.

    USGS Publications Warehouse

    Luetgert, James H.; Mooney, Walter D.

    1985-01-01

    Seismic-refraction profiles recorded north of Mammoth Lakes, California, using earthquake sources from the January 1983 swarm complement earlier explosion refraction profiles and provide velocity information from deeper in the crust in the area of the Long Valley caldera. Eight earthquakes from a depth range of 4. 9 to 8. 0 km confirm the observation of basement rocks with seismic velocities ranging from 5. 8 to 6. 4 km/sec extending at least to depths of 20 km. The data provide further evidence for the existence of a partial melt zone beneath Long Valley caldera and constrain its geometry. Refs.

  8. New geologic mapping combined with geochemical, paleomagnetic, and high-precision 40Ar/39Ar analyses reveal multiple overlapping calderas formed 16.4-15.7 Ma at High Rock caldera complex, northwestern Nevada

    NASA Astrophysics Data System (ADS)

    Coble, M. A.; Mahood, G. A.

    2012-12-01

    We present new evidence from 1:100,000- and 1:24,000-scale geologic mapping for the presence of at least four overlapping calderas, 24 to 40 km in diameter, that formed in an interval of only 0.7 m.y. during the mid-Miocene at High Rock caldera complex in northwest Nevada and southern Oregon. In total, an estimated minimum volume of ~725 km3 of rhyolitic magma erupted from the complex between 16.5 and 15.5 Ma, covering an area of ~9,000 km2. Rapid eruption of numerous units at volumetric rates as high as 3,000-4,000 km3/m.y., strong welding of lithic-poor ignimbrites, extensive vapor-phase alteration of lavas and ignimbrites alike, a limited range of phenocryst content and assemblage, silicification along faults, and a lack of well-exposed stratigraphic sections has hindered previous reconnaissance-scale mapping and identification of caldera centers. Calderas are located based on truncation of precaldera rhyolitic lavas by caldera topographic walls, by arcuate patterns of rhyolite lavas that erupted along buried caldera ring faults, and by the presence of pumiceous caldera lake sediments. We attribute formation of the Virgin Valley, Badger Mountain, Hanging Rock, and Cottonwood Creek Calderas to collapse on eruption, respectively, of the ca. 16.37 Ma Idaho Canyon Tuff, the 16.34 Ma Summit Lake Tuff, the 16.0 Ma Soldier Meadows Tuff, and the 15.7 Ma Tuff of Yellow Rock Canyon. Additional smaller-volume pyroclastic units erupted during emplacement of geochemically similar rhyolitic lavas. More than 60 new 40Ar/39Ar ages were obtained on ignimbrites, fall deposits, and rhyolitic, trachytic and basaltic lavas. Many of the eruptive units in the HRCC differ in age by less than 100 k.y., which, at ca. 16 Ma, requires precision at the 1-2‰ (2σ standard error) level to distinguish units using 40Ar/39Ar geochronology. The high-precision of the analyses of sanidine in the rhyolites, coupled with geochemical and paleomagnetic measurements, allowed us to correlate far

  9. Eastern Pacific Ocean Conference

    NASA Astrophysics Data System (ADS)

    The promotion of interaction among investigators of all oceanographic disciplines studying the eastern Pacific Ocean was the goal of the 1990 Eastern Pacific Ocean Conference (EPOC), held October 17-19 on the snow-covered slopes of Mt. Hood, Oreg. Thirty oceanographers representing all disciplines attended.Dick Barber, Duke University Marine Lab, Beaufort, N.C., chaired a session on the eastern equatorial Pacific Ocean, emphasizing issues related to biological activity. Steve Ramp of the Naval Postgraduate School in Montery, Calif., chaired a session on recent results from northern and central California experiments. On October 19, following an early morning earthquake, a business meeting and discussions regarding a collaboration in future experiments were held.

  10. Crustal-scale recycling in caldera complexes and rift zones along the Yellowstone hotspot track: O and Hf isotopic evidence in diverse zircons from voluminous rhyolites of the Picabo volcanic field, Idaho

    USGS Publications Warehouse

    Drew, Dana L.; Bindeman, Ilya N.; Watts, Kathryn E.; Schmitt, Axel K.; Fu, Bin; McCurry, Michael

    2013-01-01

    Rhyolites of the Picabo volcanic field (10.4–6.6 Ma) in eastern Idaho are preserved as thick ignimbrites and lavas along the margins of the Snake River Plain (SRP), and within a deep (>3 km) borehole near the central axis of the Yellowstone hotspot track. In this study we present new O and Hf isotope data and U–Pb geochronology for individual zircons, O isotope data for major phenocrysts (quartz, plagioclase, and pyroxene), whole rock Sr and Nd isotope ratios, and whole rock geochemistry for a suite of Picabo rhyolites. We synthesize our new datasets with published Ar–Ar geochronology to establish the eruptive framework of the Picabo volcanic field, and interpret its petrogenetic history in the context of other well-studied caldera complexes in the SRP. Caldera complex evolution at Picabo began with eruption of the 10.44±0.27 Ma (U–Pb) Tuff of Arbon Valley (TAV), a chemically zoned and normal-δ18O (δ18O magma=7.9‰) unit with high, zoned 87Sr/86Sri (0.71488–0.72520), and low-εNd(0) (−18) and εHf(0) (−28). The TAV and an associated post caldera lava flow possess the lowest εNd(0) (−23), indicating ∼40–60% derivation from the Archean upper crust. Normal-δ18O rhyolites were followed by a series of lower-δ18O eruptions with more typical (lower crustal) Sr–Nd–Hf isotope ratios and whole rock chemistry. The voluminous 8.25±0.26 Ma West Pocatello rhyolite has the lowest δ18O value (δ18Omelt=3.3‰), and we correlate it to a 1,000 m thick intracaldera tuff present in the INEL-1 borehole (with published zircon ages 8.04–8.35 Ma, and similarly low-δ18O zircon values). The significant (4–5‰) decrease in magmatic-δ18O values in Picabo rhyolites is accompanied by an increase in zircon δ18O heterogeneity from ∼1‰ variation in the TAV to >5‰ variation in the late-stage low-δ18O rhyolites, a trend similar to what is characteristic of Heise and Yellowstone, and which indicates remelting of variably hydrothermally altered tuffs

  11. Doctoring in Eastern Europe

    PubMed Central

    Wilde, Henry

    1983-01-01

    Health care in Eastern Europe has not achieved world standards nor the goals of planners of socialist societies. With luck, perseverance, bribes or good connections, it is possible to obtain good medical and surgical care in Eastern Europe for a major illness. Primary and even secondary care usually are substandard, however, and often completely unacceptable to most Western foreigners. The reasons for this are complex but mainly rooted in different attitudes of health workers towards their patients, poor physical plants, poor salary structures, inadequate advancement opportunities for health care workers, poor social status and professional recognition for nurses and almost complete isolation of the average primary care doctor from hospital medicine. PMID:6659504

  12. Tensor controlled-source audiomagnetotelluric survey over the Sulphur Springs thermal area, Valles Caldera

    SciTech Connect

    Wannamaker, P.E.

    1991-10-01

    The extensive tensor CSAMT survey of the Sulphur Springs geothermal area, Valles Caldera, New Mexico, consists of 45 high-quality soundings acquired in continuous-profiling mode and has been funded in support of CSDP drillholes VC-2A and VC-2B. Two independent transmitter bipoles were energized for tensor measurements using a 30 KW generator placed approximately 13 km south of the VC-2B wellhead. These current bipoles gave source fields over the receiver sites which were substantially independent in polarization and provided well-resolved tensor elements. The surroundings in the Sulphur Springs area were arranged in four profiles to cross major structural features. At each receiver, two orthogonal electric and three orthogonal magnetic field components were acquired in accordance with tensor principles. Derivation of model resistivity cross sections from our data and their correlation with structure and geochemistry are principal components of the OBES award. However, Sulphur Springs also can serve as a natural testbed of traditional assumptions and methods of CSAMT with quantification through rigorous model analysis. Issues here include stability and accuracy of scalar versus tensor estimates, theoretical versus observed field patterns over the survey area, and controls on near-field effects using CSAMT and natural field data both inside and outside the caldera.

  13. Geology of the Flat Swamp Mountain caldera and related rocks, Carolina slate belt, central North Carolina

    SciTech Connect

    Butler, J.R. . Dept. of Geology)

    1994-03-01

    The Flat Swamp Member (FSM) of the Cid Formation (Late Proterozoic) and related volcanogenic deposits in the Carolina slate belt of central North Carolina constitute a submarine caldera complex, mildly deformed and metamorphosed to lower greenschist facies. The intracaldera facies, including mudflow breccias, ashfall tuffs, pyroclastic flows and lava flows, are 1.2 to 1.8 km thick in the Denton area. The FSM thins abruptly near Badin, passing laterally into extracaldera facies less than 150 m thick of coarse- to fine-grained crystal-rich ashfall tuffs with an upper unit of extremely fine-grained devitrified vitric tuffs. The thickness and average grainsize decrease to the south and east, until the FSM merges with adjacent mudstones. The Morrow Mountain Rhyolite includes bodies of homogeneous rhyolite as much as several km across emplaced within the FSM and stratigraphically lower units, interpreted to be shallow intrusions and some surface-breaking lava domes, emplaced at depths from 0 to 3 km within the caldera and along the ring-fractures. The FSM has been mapped over an area of about 2,400 km[sup 2], and it forms a time-constant layer useful in elucidating slate belt stratigraphy.

  14. Late Pleistocene granodiorite beneath Crater Lake caldera, Oregon, dated by ion microprobe

    USGS Publications Warehouse

    Bacon, C.R.; Persing, H.M.; Wooden, J.L.; Ireland, T.R.

    2000-01-01

    Variably melted granodiorite blocks ejected during the Holocene caldera-forming eruption of Mount Mazama were plucked from the walls of the climactic magma chamber ~15 km depth. Ion-microprobe U-Pb dating of zircons from two unmelted granodiorite blocks with SHRIMP RG (sensitive high-resolution ion microprobe-reverse geometry) gives a nominal 238U/206Pb age of 101+78-80 ka, or 174+89-115 ka when adjusted for an initial 230Th deficit. SHRIMP RG U-Th measurements on a subset of the zircons yield a 230Th/238U isochron age of 112 ?? 24 ka, considered to be the best estimate of the time of solidification of the pluton. These results suggest that the granodiorite is related to andesite and dacite of Mount Mazama and not to magmas of the climactic eruption. The unexposed granodiorite has an area of at least 28 km2. This young, shallow pluton was emplaced in virtually the same location where a similarly large magma body accumulated and powered violent explosive eruptions ~7700 yr ago, resulting in collapse of Crater Lake caldera.

  15. Molecular analysis of the benthos microbial community in Zavarzin thermal spring (Uzon Caldera, Kamchatka, Russia)

    PubMed Central

    2014-01-01

    Background Geothermal areas are of great interest for the study of microbial communities. The results of such investigations can be used in a variety of fields (ecology, microbiology, medicine) to answer fundamental questions, as well as those with practical benefits. Uzon caldera is located in the Uzon-Geyser depression that is situated in the centre of the Karym-Semyachin region of the East Kamchatka graben-synclinorium. The microbial communities of Zavarzin spring are well studied; however, its benthic microbial mat has not been previously described. Results Pyrosequencing of the V3 region of the 16S rRNA gene was used to study the benthic microbial community of the Zavarzin thermal spring (Uzon Caldera, Kamchatka). The community is dominated by bacteria (>95% of all sequences), including thermophilic, chemoorganotrophic Caldiserica (33.0%) and Dictyoglomi (24.8%). The benthic community and the previously examined planktonic community of Zavarzin spring have qualitatively similar, but quantitatively different, compositions. Conclusions In this study, we performed a metagenomic analysis of the benthic microbial mat of Zavarzin spring. We compared this benthic community to microbial communities found in the water and of an integral probe consisting of water and bottom sediments. Various phylogenetic groups of microorganisms, including potentially new ones, represent the full-fledged trophic system of Zavarzin. A thorough geochemical study of the spring was performed. PMID:25563397

  16. Inflation model of Uzon caldera, Kamchatka, constrained by satellite radar interferometry observations

    USGS Publications Warehouse

    Lundgren, P.; Lu, Zhiming

    2006-01-01

    We analyzed RADARSAT-1 synthetic aperture radar (SAR) data to compute interferometric SAR (InSAR) images of surface deformation at Uzon caldera, Kamchatka, Russia. From 2000 to 2003 approximately 0.15 m of inflation occurred at Uzon caldera, extending beneath adjacent Kikhpinych volcano. This contrasts with InSAR data showing no significant deformation during either the 1999 to 2000, or 2003 to 2004, time periods. We performed three sets of numerical source inversions to fit InSAR data from three different swaths spanning 2000 to 2003. The preferred source model is an irregularly shaped, pressurized crack, dipping ???20?? to the NW, 4 km below the surface. The geometry of this solution is similar to the upper boundary of the geologically inferred magma chamber. Extension of the surface deformation and source to adjacent Kikhpinych volcano, without an eruption, suggests that the deformation is more likely of hydrothermal origin, possibly driven by recharge of the magma chamber. Copyright 2006 by the American Geophysical Union.

  17. Geobotanical characterization of a geothermal system using hyperspectral imagery: Long Valley Caldera, CA

    SciTech Connect

    Carter, M R; Cochran, S A; Martini, B A; Pickles, W L; Potts, D C; Priest, R E; Silver, E A; Wayne, B A; White, W T

    1998-12-01

    We have analyzed hyperspectral Airborne Visible-Infrared Imaging System (AVIRIS) imagery taken in September of 1992 in Long Valley Caldera, CA, a geothermally active region expressed surficially by hot springs and fumaroles. Geological and vegetation mapping are attempted through spectral classification of imagery. Particular hot spring areas in the caldera are targeted for analysis. The data is analyzed for unique geobotanical patterns in the vicinity of hot springs as well as gross identification of dominant plant and mineral species. Spectra used for the classifications come from a vegetation spectral library created for plant species found to be associated with geothermal processes. This library takes into account the seasonality of vegetation by including spectra for species on a monthly basis. Geological spectra are taken from JPL and USGS mineral libraries. Preliminary classifications of hot spring areas indicate some success in mineral identification and less successful vegetation species identification. The small spatial extent of individual plants demands either sub-pixel analysis or increased spatial resolution of imagery. Future work will also include preliminary analysis of a hyperspectral thermal imagery dataset and a multitemporal air photo dataset. The combination of these remotely sensed datasets for Long Valley will yield a valuable product for geothermal exploration efforts in other regions.

  18. Eruptive history of Mount Mazama and Crater Lake Caldera, Cascade Range, U.S.A.

    USGS Publications Warehouse

    Bacon, C.R.

    1983-01-01

    New investigations of the geology of Crater Lake National Park necessitate a reinterpretation of the eruptive history of Mount Mazama and of the formation of Crater Lake caldera. Mount Mazama consisted of a glaciated complex of overlapping shields and stratovolcanoes, each of which was probably active for a comparatively short interval. All the Mazama magmas apparently evolved within thermally and compositionally zoned crustal magma reservoirs, which reached their maximum volume and degree of differentiation in the climactic magma chamber ??? 7000 yr B.P. The history displayed in the caldera walls begins with construction of the andesitic Phantom Cone ??? 400,000 yr B.P. Subsequently, at least 6 major centers erupted combinations of mafic andesite, andesite, or dacite before initiation of the Wisconsin Glaciation ??? 75,000 yr B.P. Eruption of andesitic and dacitic lavas from 5 or more discrete centers, as well as an episode of dacitic pyroclastic activity, occurred until ??? 50,000 yr B.P.; by that time, intermediate lava had been erupted at several short-lived vents. Concurrently, and probably during much of the Pleistocene, basaltic to mafic andesitic monogenetic vents built cinder cones and erupted local lava flows low on the flanks of Mount Mazama. Basaltic magma from one of these vents, Forgotten Crater, intercepted the margin of the zoned intermediate to silicic magmatic system and caused eruption of commingled andesitic and dacitic lava along a radial trend sometime between ??? 22,000 and ??? 30,000 yr B.P. Dacitic deposits between 22,000 and 50,000 yr old appear to record emplacement of domes high on the south slope. A line of silicic domes that may be between 22,000 and 30,000 yr old, northeast of and radial to the caldera, and a single dome on the north wall were probably fed by the same developing magma chamber as the dacitic lavas of the Forgotten Crater complex. The dacitic Palisade flow on the northeast wall is ??? 25,000 yr old. These relatively

  19. Age discrimination among eruptives of Menengai Caldera, Kenya, using vegetation parameters from satellite imagery

    NASA Technical Reports Server (NTRS)

    Blodget, Herbert W.; Heirtzler, James R.

    1993-01-01

    Results are presented of an investigation to determine the degree to which digitally processed Landsat TM imagery can be used to discriminate among vegetated lava flows of different ages in the Menengai Caldera, Kenya. A selective series of five images, consisting of a color-coded Landsat 5 classification and four color composites, are compared with geologic maps. The most recent of more than 70 postcaldera flows within the caldera are trachytes, which are variably covered by shrubs and subsidiary grasses. Soil development evolves as a function of time, and as such supports a changing plant community. Progressively older flows exhibit the increasing dominance of grasses over bushes. The Landsat images correlated well with geologic maps, but the two mapped age classes could be further subdivided on the basis of different vegetation communities. It is concluded that field maps can be modified, and in some cases corrected by use of such imagery, and that digitally enhanced Landsat imagery can be a useful aid to field mapping in similar terrains.

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

    NASA Astrophysics Data System (ADS)

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

    2007-05-01

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

  1. Inflation of Long Valley Caldera from 1 year of continuous GPS observations

    NASA Technical Reports Server (NTRS)

    Webb, Frank H.; Bursik, Marcus; Dixon, Timothy; Farina, Frederic; Marshall, Grant; Stein, Ross S.

    1995-01-01

    A permanent Global Positioning System (GPS) receiver at Casa Diablo Hot Springs, Long Valley Caldera, California was installed in January, 1993, and has operated almost continuously since then. The data have been transmitted daily to the Jet Propulsion Laboratory (JPL) for routine analysis with data from the Fiducial Laboratories for an International Natural sciences Network (FLINN) by the JPL FLINN analysis center. Results from these analyses have been used to interpret the on going deformation at Long Valley, with data excluded from periods when the antenna was covered under 2.5 meters of snow and from some periods when Anti Spoofing was enforced on the GPS signal. The remaining time series suggests that uplift of the resurgent dome of Long Valley Caldera during 1993 has been 2.5 +/- 1.1 cm/yr and horizontal motion has been 3.0 +/- 0.7 cm/yr at S53W in a no-net-rotation global reference frame, or 1.5 +/- 0.7 cm/yr at S14W relative to the Sierra Nevada block. These rates are consistent with uplift predicted from frequent horizontal strain measurements. Spectral analysis of the observations suggests that tidal forcing of the magma chamber is not a source of the variability in the 3 dimensional station location. These results suggest that remotely operated, continuously recording GPS receivers could prove to be a reliable tool for volcanic monitoring throughout the world.

  2. Inflation of Long Valley Caldera from 1 year of continuous GPS observations

    NASA Astrophysics Data System (ADS)

    Webb, Frank H.; Bursik, Marcus; Dixon, Timothy; Farina, Frederic; Marshall, Grant; Stein, Ross S.

    1995-02-01

    A permanent Global Positioning System (GPS) receiver at Casa Diablo Hot Springs, Long Valley Caldera, California was installed in January, 1993, and has operated almost continuously since then. The data have been transmitted daily to the Jet Propulsion Laboratory (JPL) for routine analysis with data from the Fiducial Laboratories for an International Natural sciences Network (FLINN) by the JPL FLINN analysis center. Results from these analyses have been used to interpret the on going deformation at Long Valley, with data excluded from periods when the antenna was covered under 2.5 meters of snow and from some periods when Anti Spoofing was enforced on the GPS signal. The remaining time series suggests that uplift of the resurgent dome of Long Valley Caldera during 1993 has been 2.5 +/- 1.1 cm/yr and horizontal motion has been 3.0 +/- 0.7 cm/yr at S53W in a no-net-rotation global reference frame, or 1.5 +/- 0.7 cm/yr at S14W relative to the Sierra Nevada block. These rates are consistent with uplift predicted from frequent horizontal strain measurements. Spectral analysis of the observations suggests that tidal forcing of the magma chamber is not a source of the variability in the 3 dimensional station location. These results suggest that remotely operated, continuously recording GPS receivers could prove to be a reliable tool for volcanic monitoring throughout the world.

  3. Thermomechanical controls on magma supply and volcanic deformation: application to Aira caldera, Japan.

    PubMed

    Hickey, James; Gottsmann, Joachim; Nakamichi, Haruhisa; Iguchi, Masato

    2016-01-01

    Ground deformation often precedes volcanic eruptions, and results from complex interactions between source processes and the thermomechanical behaviour of surrounding rocks. Previous models aiming to constrain source processes were unable to include realistic mechanical and thermal rock properties, and the role of thermomechanical heterogeneity in magma accumulation was unclear. Here we show how spatio-temporal deformation and magma reservoir evolution are fundamentally controlled by three-dimensional thermomechanical heterogeneity. Using the example of continued inflation at Aira caldera, Japan, we demonstrate that magma is accumulating faster than it can be erupted, and the current uplift is approaching the level inferred prior to the violent 1914 Plinian eruption. Magma storage conditions coincide with estimates for the caldera-forming reservoir ~29,000 years ago, and the inferred magma supply rate indicates a ~130-year timeframe to amass enough magma to feed a future 1914-sized eruption. These new inferences are important for eruption forecasting and risk mitigation, and have significant implications for the interpretations of volcanic deformation worldwide. PMID:27619897

  4. Eastern Frequency Response Study

    SciTech Connect

    Miller, N.W.; Shao, M.; Pajic, S.; D'Aquila, R.

    2013-05-01

    This study was specifically designed to investigate the frequency response of the Eastern Interconnection that results from large loss-of-generation events of the type targeted by the North American Electric Reliability Corp. Standard BAL-003 Frequency Response and Frequency Bias Setting (NERC 2012a), under possible future system conditions with high levels of wind generation.

  5. The McDermitt Caldera, NV-OR, USA: Geologic mapping, volcanology, mineralization, and high precision 40Ar/39Ar dating of early Yellowstone hotspot magmatism

    NASA Astrophysics Data System (ADS)

    Henry, C. D.; Castor, S. B.; Starkel, W. A.; Ellis, B. S.; Wolff, J. A.; Heizler, M. T.; McIntosh, W. C.

    2012-12-01

    The irregularly keyhole-shaped, 40x30 to 22 km, McDermitt caldera formed at 16.35±0.03 Ma (n=4; Fish Canyon sanidine = 28.201 Ma) during eruption of a zoned, aphyric, mildly peralkaline rhyolite to abundantly anorthoclase-phyric, metaluminous dacite (McDermitt Tuff, MDT). Intracaldera MDT is locally strongly rheomorphic and, where MDT and caldera floor are well-exposed along the western margin, contains abundant megabreccia but is a maximum of ~450 m thick. If this thickness is representative of the caldera, intracaldera MDT has a volume of ~400 km3. Outflow MDT is currently known up to 13 km south of the caldera but only 3 km north of the caldera. Maximum outflow thickness is ~100 m, and outflow volume is probably no more than about 10% that of intracaldera MDT. The thickness and volume relations indicate collapse began very early during eruption, and most tuff ponded within the caldera. Outflow is strongly rheomorphic where draped over paleotopography. Late, undated icelandite lavas and domes are probably residual magma from the caldera chamber. Resurgence is expressed as both a broad, symmetrical dome in the north part and a fault-bound uplift in the south part of the caldera. Mineralization associated with the caldera includes Zr-rich U deposits that are indistinguishable in age with the McDermitt Tuff, Hg, Au, Ga, and Li-rich intracaldera tuffaceous sediments. Although formed during probable regional extension, the caldera is flat-lying and cut only at its west and east margins by much younger, high-angle normal faults. The caldera formed in an area of highly diverse Cenozoic volcanic rocks. The oldest are 39 and 46 Ma metaluminous dacite lavas along the northwest margin. Coarsely plagioclase-phyric to aphyric Steens Basalt lavas crop out around the west, northwest, and northeast margin. An anorthoclase-phyric, low-Si rhyolite lava (16.69±0.02 Ma) that is interbedded with probable Steens lavas northeast of the caldera and a biotite rhyolite lava dome (16.62

  6. Tensor controlled-source audiomagnetotelluric survey over the Sulphur Springs Thermal area, Valles Caldera, New Mexico, U.S.A.; Implication for structure of the western Caldera and for CSAMT methodology

    SciTech Connect

    Wannamaker, P.E.

    1994-06-01

    We have carried Out an extensive tensor CSAMT survey of the Sulphur Springs geothermal area, Valles Caldera, New Mexico. This survey, consisting of 45 high-quality sites, has been acquired by in support of Continental Scientific Drilling Program (CSDP) drillholes VC-2A and VC-2B. Two independent transmitter dipoles were energized for tensor measurements using a 30 kW generator placed approximately 13 km south of the VC-2B wellhead. The soundings in the Sulphur Springs area were arranged in four profiles to cross major structural features. The electric bipoles parallel to each profile were deployed contiguously to ensure against spatial aliasing of the impedance response corresponding to current flow across structural trends. The frequency range of acquisition was 4096 Hz down to 1 Hz for the central line, but only down to 4 Hz for most sites of the other lines. Data quality is high overall and is established by repeatability of measurements. Agreement between the CSAMT and available natural field MT data is very good over almost all the period range of overlap indicating that we are free of calibration problems and that far-field results are generally being obtained. Non plane-wave effects in the CSAMT around Sulphur Springs are apparent at 1 to 2 Hz, and perhaps slightly even at 4 Hz, however, which is near the bottom of our frequency range. CSAMT and MT data taken outside the Valles Caldera to the west were modeled in an attempt to compare resistivity structure exterior to the caldera to that within. With the availability of tensor CSAMT and MT data both inside and outside Valles Caldera, assumptions and methods of CSAMT are tested. In the Sulphur Springs area, near-coincident CSAMT and MT data near well VC -2B indicate that non-lane-wave effects in the apparent resistivity and impedance phase occure at a frequency near to that predicted from the resistivity structure local to the wester caldera.