This file was created by the TYPO3 extension publications --- Timezone: CEST Creation date: 2026-04-23 Creation time: 21:06:36 --- Number of references 14 article Prudencio20201677 Unrest at Long Valley caldera (California) during the past few decades has been attributed to the ascent of hydrothermal fluids or magma recharge. The difference is critical for assessing volcanic hazard. To better constrain subsurface structures in the upper crust and to help distinguish between these two competing hypotheses for the origin of unrest, we model the 3-D seismic attenuation structure because attenuation is particularly sensitive to the presence of melt. We analyse more than 47 000 vertical component waveforms recorded from January 2000 through November 2016 obtained from the Northern California Earthquake Data Center. We then inverted the S-to-coda energy ratios using the coda normalization method and obtained an average Q of 250. Low attenuation anomalies are imaged in the fluid-rich western and eastern areas of the caldera, one of which corresponds to the location of an earthquake swarm that occurred in 2014. From a comparison with other geophysical images (magnetotellurics, seismic tomography) we attribute the high attenuation anomalies to hydrothermal systems. Average to high attenuation values are also observed at Mammoth Mountain (southwest of the caldera), and may also have a hydrothermal origin. A large high attenuation anomaly within the caldera extends from the surface to the depths we can resolve at 9 km. Shallow rocks here are cold and this is where earthquakes occur. Together, these observations imply that the high attenuation region is not imaging a large magma body at shallow depths nor do we image any isolated high attenuation bodies in the upper ≈8 km that would be clear-cut evidence for partially molten bodies such as sills or other magma bodies. © 2019 The Author(s). Published by Oxford University Press on behalf of The Royal Astronomical Society. 2020 English 0956540X 10.1093/gji/ggz543 Geophysical Journal International 220 Oxford University Press 1677-1686 Department of Theoretical Physics and Cosmos Physics of the Earth Area, University of Granada, Profesor Clavera 12, Granada, 18071, Spain; Instituto Andaluz de Geofisica, University of Granada, Campus de Cartuja, Granada, Spain; Department of Earth and Planetary Science, University of California at Berkeley, 307 McCone Hall, Berkeley, CA 94720, United States; Berkeley Seismological Laboratory, University of California-Berkeley, 215 McCone Hall, Berkeley, CA 94720, United States 3 Landforms, Coda normalization method; Hydrothermal fluids; Hydrothermal system; Long valley caldera; Seismic attenuation; Seismic tomography; Subsurface structures; Vertical component, Earthquakes, caldera; crustal structure; earthquake event; earthquake magnitude; magma; seismic attenuation; seismic data; seismic source; seismicity; seismology; three-dimensional modeling; waveform analysis, California; Long Valley Caldera; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-85086011570&doi=10.1093%2fgji%2fggz543&partnerID=40&md5=fa91cac2cf82241fc7e2dcd81b931fef cited By 8 J. Prudencio M. Manga article Hurwitz2010233 Long Valley Caldera in eastern California formed 0.76Ma ago in a cataclysmic eruption that resulted in the deposition of 600km3 of Bishop Tuff. The total current heat flow from the caldera floor is estimated to be ~290MW, and a geothermal power plant in Casa Diablo on the flanks of the resurgent dome (RD) generates ~40MWe. The RD in the center of the caldera was uplifted by ~80cm between 1980 and 1999 and was explained by most models as a response to magma intrusion into the shallow crust. This unrest has led to extensive research on geothermal resources and volcanic hazards in the caldera. Here we present results from precise, high-resolution, temperature-depth profiles in five deep boreholes (327-1,158m) on the RD to assess its thermal state, and more specifically 1) to provide bounds on the advective heat transport as a guide for future geothermal exploration, 2) to provide constraints on the occurrence of magma at shallow crustal depths, and 3) to provide a baseline for future transient thermal phenomena in response to large earthquakes, volcanic activity, or geothermal production. The temperature profiles display substantial non-linearity within each profile and variability between the different profiles. All profiles display significant temperature reversals with depth and temperature gradients &lt;50°C/km at their bottom. The maximum temperature in the individual boreholes ranges between 124.7°C and 129.5°C and bottom hole temperatures range between 99.4°C and 129.5°C. The high-temperature units in the three Fumarole Valley boreholes are at the approximate same elevation as the high-temperature unit in borehole M-1 in Casa Diablo indicating lateral or sub-lateral hydrothermal flow through the resurgent dome. Small differences in temperature between measurements in consecutive years in three of the wells suggest slow cooling of the shallow hydrothermal flow system. By matching theoretical curves to segments of the measured temperature profiles, we calculate horizontal groundwater velocities in the hydrothermal flow unit under the RD that range from 1.9 to 2.8m/yr, which corresponds to a maximum power flowing through the RD of 3-4MW. The relatively low temperatures and large isothermal segments at the bottom of the temperature profiles are inconsistent with the presence of magma at shallow crustal levels. © 2010. 2010 English 03770273 10.1016/j.jvolgeores.2010.08.023 Journal of Volcanology and Geothermal Research 198 233-240 U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA, United States; U.S. Geological Survey, PO 1360, Carnelian Bay, CA, United States 1-2 Caldera; Geothermal; Heat flows; Hydrothermal; Long Valley; Resurgent dome; Temperature log, Boreholes; Domes; Geothermal energy; Geothermal fields; Geothermal logging; Geothermal power plants; Geothermal prospecting; Groundwater; Heat transfer; Temperature control; Volcanoes; Wells, Thermal logging, caldera; crust; dome; geothermal power; groundwater flow; heat flow; hydrothermal system; igneous intrusion; temperature profile; thermal regime; uplift, California; Long Valley Caldera; United States, Calluna vulgaris https://www.scopus.com/inward/record.uri?eid=2-s2.0-78650076069&doi=10.1016%2fj.jvolgeores.2010.08.023&partnerID=40&md5=aa555a6c79fc3b917dfbdab4f78d7c3a cited By 12 S. Hurwitz C.D. Farrar C.F. Williams article Ellsworth200784 2007 English 18168957 10.2204/iodp.sd.s01.04.2007 Scientific Drilling 84-87 U.S. Geological Survey (USGS), 3A-109, 345 Middlefield Road Mail Stop 977, Menlo Park, Calif. 94025, United States; Old Chemistry, Duke University, Box 90227, Durham, N.C. 27708, United States; Geological Survey of Japan, Institute of Geology and Geoinformation (AIST), Tsukuba Central 7, 1-1-1 Higashi, Japan; Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Science Center 1S06, Troy, N.Y. 12180, United States; Berkeley Seismological Lab, University of California Berkeley, 207 McCone Hall, Calif. 94720-4760, United States; Norwegian Seismic Array (NORSAR), P.O. Box 53, N-2027 Kjeller, Norway; Department of Geology and Geophysics, University of Wisconsin, 1215 West Dayton Street, Madison, Wis. 53706, United States; LDEO-Seismology Geology and Tectonophysics, 210 Seismology, 61 Route 9W - P.O. Box 1000, Palisades, N.Y. 10964, United States; Energy Technology Centers (ETC), San Ramon, Calif. 94583, United States; USGS, 345 Middlefield Road, Menlo Park, Calif. 94025, United States; Department of Geophysics, Stanford University, Mitchell Bldg., Stanford, Calif. 94305, United States 1 SUPPL. 1 https://www.scopus.com/inward/record.uri?eid=2-s2.0-72049098074&doi=10.2204%2fiodp.sd.s01.04.2007&partnerID=40&md5=9a2477b3c6dc316811d75fa8f600f1ad cited By 13 W.L. Ellsworth K. Imanishi R. Nadeau V. Oye F. Waldhauser N.L. Boness S.H. Hickman M.D. Zoback article Chang2005402 We conducted laboratory rock strength experiments in two ultra-fine-grained brittle rocks, hornfels and metapelite, which together are the major constituent of the Long Valley Caldera (California, USA) basement in the 2025-2996 m depth range. Both rocks are banded, and have very low porosity. Uniaxial compression tests at different orientations with respect to banding planes reveal that while the hornfels compressive strength is nearly isotropic, the metapelite possesses distinct anisotropy. Conventional triaxial tests in these rocks reveal that their respective strengths in a specific orientation increase approximately linearly with confining pressure. True triaxial compression experiments in specimens oriented at a consistent angle to banding, in which the magnitudes of the least (σ3) and the intermediate (σ2) principal stresses are different but kept constant during testing while the maximum principal stress is increased until failure, exhibit a behavior unlike that previously observed in other rocks under similar testing conditions. For a given magnitude of σ3, compressive strength σ1 does not vary significantly in both Long Valley rock types, regardless of the applied σ2, suggesting little or no intermediate principal stress effect. Strains measured in all three principal directions during loading were used to obtain plots of σ1 versus volumetric strain. These are consistently linear almost to the point of rock failure, suggesting no dilatancy. The phenomenon was corroborated by SEM inspection of failed specimens that showed no microcrack development prior to the emergence of one through-going shear failure plane steeply dipping in the σ3 direction. The strong dependency of compressive strength on the intermediate principal stress in other crystalline rocks was found to be related to microcrack initiation upon dilatancy onset, which rises with increased σ2 and retards the failure process. We infer that strength independence of σ2 in the Long Valley rocks derives directly from their non-dilatant deformation. © 2005 Elsevier Ltd. All rights reserved. 2005 English 13651609 10.1016/j.ijrmms.2005.01.002 International Journal of Rock Mechanics and Mining Sciences 42 Elsevier BV 402-414 Dept. of Mat. Science/Engineering, Geological Engineering Program, University of Wisconsin, 1509 University Avenue, Madison, WI 53706-1595, United States; Department of Geology, Chungnam National University, Daejeon, South Korea 3 Compressive strength; Crack initiation; Deformation; Failure analysis; Porosity; Strain; Strength of materials; Volumetric analysis, Brittle rocks; Metapelite; Rock strength; Volumetric strain, Rocks, deformation; triaxial test; volcanic rock, California; Long Valley; North America; United States; Western Hemisphere; World https://www.scopus.com/inward/record.uri?eid=2-s2.0-15544377807&doi=10.1016%2fj.ijrmms.2005.01.002&partnerID=40&md5=cc720f419660d49934a2e782ebfc6f5c cited By 61 C. Chang B. Haimson article Foulger200445 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. 2004 English 03770273 10.1016/S0377-0273(03)00420-7 Journal of Volcanology and Geothermal Research 132 45-71 U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States; Division of Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Durham, NC 27708-0235, United States 1 Crack initiation; Elastic moduli; Flow of water; Hydraulic fracturing; Stream flow; Stress analysis, Shear faulting; Tensile failure, Earthquakes, earthquake mechanism; faulting; focal mechanism; hydraulic fracture; microearthquake; moment tensor; seismicity; volcanic earthquake, California; Long Valley Caldera; North America; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-1642487285&doi=10.1016%2fS0377-0273%2803%2900420-7&partnerID=40&md5=13cb6623ddcf9e60690fd7d318c38526 cited By 120 G.R. Foulger B.R. Julian D.P. Hill A.M. Pitt E. Shalev article Pribnow2003329 Temperatures of 100°C are measured at 3 km depth in a well located on the resurgent dome in the center of Long Valley Caldera, California, despite an assumed &gt;800°C magma chamber at 6-8 km depth. Local downflow of cold meteoric water as a process for cooling the resurgent dome is ruled out by a Peclét-number analysis of temperature logs. These analyses reveal zones with fluid circulation at the upper and lower boundaries of the Bishop Tuff, and an upflow zone in the metasedimentary rocks. Vertical Darcy velocities range from 10 to 70 cm a-1. A 21-km-long geoelectrical profile across the caldera provides resistivity values to the order of 100 to &gt;103 Ωm down to a depth of 6 km, as well as variations of self-potential. Interpretation of the electrical data with respect to hydrothermal fluid movement confirms that there is no downflow beneath the resurgent dome. To explain the unexpectedly low temperatures in the resurgent dome, we challenge the common view that the caldera as a whole is a regime of high temperatures and the resurgent dome is a local cold anomaly. Instead, we suggest that the caldera was cooled to normal thermal conditions by vigorous hydrothermal activity in the past, and that a present-day hot water flow system is responsible for local hot anomalies, such as Hot Creek and the area of the Casa Diablo geothermal power plant. The source of hot water has been associated with recent shallow intrusions into the West Moat. The focus of planning for future power plants should be to locate this present-day flow system instead of relying on heat from the old magma chamber. © 2003 Elsevier B.V. All rights reserved. 2003 English 03770273 10.1016/S0377-0273(03)00175-6 Journal of Volcanology and Geothermal Research 127 Elsevier 329-345 Inst.Geowiss.Gemeinschaftsaufgaben, Hannover, Germany; Universität Leipzig, Leipzig, Germany; GeoForschungsZentrum Potsdam, Potsdam, Germany; US Geological Survey, Flagstaff, AZ, United States 3-4 Cooling; High temperature effects; Sediment transport; Water, Magma chambers, Geothermal fields, caldera; electrical resistivity; fluid flow; geochemistry; hydrothermal fluid; thermal regime, California; Long Valley Caldera; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-0141959632&doi=10.1016%2fS0377-0273%2803%2900175-6&partnerID=40&md5=0e1803be06a8d4310e81ccc0baebc24c cited By 34 D.F.C. Pribnow C. Schütze S.J. Hurter C. Flechsig J.H. Sass article Farrar2003305 Quaternary volcanic unrest has provided heat for episodic hydrothermal circulation in the Long Valley caldera, including the present-day hydrothermal system, which has been active over the past 40 kyr. The most recent period of crustal unrest in this region of east-central California began around 1980 and has included periods of intense seismicity and ground deformation. Uplift totaling more than 0.7 m has been centered on the caldera's resurgent dome, and is best modeled by a near-vertical ellipsoidal source centered at depths of 6-7 km. Modeling of both deformation and microgravity data now suggests that (1) there are two inflation sources beneath the caldera, a shallower source 7-10 km beneath the resurgent dome and a deeper source ∼15 km beneath the caldera's south moat and (2) the shallower source may contain components of magmatic brine and gas. The Long Valley Exploration Well (LVEW), completed in 1998 on the resurgent dome, penetrates to a depth of 3 km directly above this shallower source, but bottoms in a zone of 100°C fluid with zero vertical thermal gradient. Although these results preclude extrapolations of temperatures at depths below 3 km, other information obtained from flow tests and fluid sampling at this well indicates the presence of magmatic volatiles and fault-related permeability within the metamorphic basement rocks underlying the volcanic fill. In this paper, we present recently acquired data from LVEW and compare them with information from other drill holes and thermal springs in Long Valley to delineate the likely flow paths and fluid system properties under the resurgent dome. Additional information from mineralogical assemblages in core obtained from fracture zones in LVEW documents a previous period of more vigorous and energetic fluid circulation beneath the resurgent dome. Although this system apparently died off as a result of mineral deposition and cooling (and/or deepening) of magmatic heat sources, flow testing and tidal analyses of LVEW water level data show that relatively high permeability and strain sensitivity still exist in the steeply dipping principal fracture zone penetrated at a depth of 2.6 km. The hydraulic properties of this zone would allow a pressure change induced at distances of several kilometers below the well to be observable within a matter of days. This indicates that continuous fluid pressure monitoring in the well could provide direct evidence of future intrusions of magma or high-temperature fluids at depths of 5-7 km. © 2003 Elsevier B.V. All rights reserved. 2003 English 03770273 10.1016/S0377-0273(03)00174-4 Journal of Volcanology and Geothermal Research 127 Elsevier 305-328 U.S. Geological Survey, 5229 North Lake Blvd, Carnelian Bay, CA 96140, United States; U.S. Geological Survey, Vancouver, WA, United States; U.S. Geological Survey, Sacramento, CA, United States; Sandia National Laboratory, Albuquerque, NM, United States 3-4 Geochemistry; Metamorphic rocks; Mineral resources; Seismology, Hydrothermal circulation, Volcanoes, caldera; fluid flow; geochemistry; hydraulic property; hydrology; hydrothermal system; volcanism; well testing, California; Long Valley Caldera; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-0141974819&doi=10.1016%2fS0377-0273%2803%2900174-4&partnerID=40&md5=fd40ef322f4bdbcc79eb9dceb27da79f cited By 14 C.D. Farrar M.L. Sorey E. Roeloffs D.L. Galloway J.F. Howle R. Jacobson article FISCHER2003347 Long Valley Exploratory Well, drilled into the Resurgent Dome at Long Valley Caldera (California) to explore the potential of geothermal power in an active magmatic system, achieved temperatures of only ca. 100°C at 2500–3000 m depth, well below the range expected atop an active magma chamber. Open fissures encountered at 2600 m depth are coated by mm-sized idiomorphic quartz crystals with first- and second-order growth discontinuities. Specific growth defects indicating rapid crystallization reflect sudden changes in SiO2 supersaturation. Fluid inclusions contain low salinity (0–5 wt% NaCl) and low CO2 (<3 mole%) aqueous fluids, with V–L homogenization temperatures of 300–350°C, indicating trapping at more than 200°C above the ambient temperatures measured within the borehole today. Fluid composition and inclusion density varies between and within the growth zones, reflecting progressive changes in the hydrothermal system during crystallization. Episodic crystallization from supersaturated fluids is interpreted to reflect sudden changes in the convection pattern, presumably induced by seismic activity, with a more recent and dramatic reorganization resulting in convective cooling. The quartz crystals are sensitive recorders of the earlier higher temperature history, unaffected by the present-day situation. 2003 0377-0273 https://doi.org/10.1016/S0377-0273(03)00176-8 Journal of Volcanology and Geothermal Research 127 347-363 3 Long Valley Caldera, hydrothermal system, thermal history, fluid inclusions, quartz crystallization, open fissures https://www.sciencedirect.com/science/article/pii/S0377027303001768 Crustal Unrest in Long Valley Caldera, California: New interpretations from geophysical and hydrologic monitoring and deep drilling M. Fischer K. Röller M. Küster B. Stöckhert V.S. McConnell article Sorey2003165 Since 1978, volcanic unrest in the form of earthquakes and ground deformation has persisted in the Long Valley caldera and adjacent parts of the Sierra Nevada. The papers in this special volume focus on periods of accelerated seismicity and deformation in 1980, 1983, 1989-1990, and 1997-1998 to delineate relations between geologic, tectonic, and hydrologic processes. The results distinguish between earthquake sequences that result from relaxation of existing stress accumulation through brittle failure and those in which brittle failure is driven by active intrusion. They also indicate that in addition to a relatively shallow (7-10-km) source beneath the resurgent dome, there exists a deeper (∼15-km) source beneath the south moat. Analysis of microgravimety and deformation data indicates that the composition of the shallower source may involve a combination of silicic magma and hydrothermal fluid. Pressure and temperature fluctuations in wells have accompanied periods of crustal unrest, and additional pressure and temperature changes accompanying ongoing geothermal power production have resulted in land subsidence. The completion in 1998 of a 3000-m-deep drill hole on the resurgent dome has provided useful information on present and past periods of circulation of water at temperatures of 100-200°C within the crystalline basement rocks that underlie the post-caldera volcanics. The well is now being converted to a permanent geophysical monitoring station. © 2003 Elsevier B.V. All rights reserved. 2003 English 03770273 10.1016/S0377-0273(03)00168-9 Journal of Volcanology and Geothermal Research 127 Elsevier 165-173 U..Geological Survey, 161 Sausal Drive, Portola Valley, CA 94028, United States; Oregon Dept. of Geol./Mineral Rsrc., Portland, OR, United States; U.S. Geological Survey, Vancouver, WA, United States 3-4 Earthquakes; Hydrology; Pressure effects; Seismology; Thermal effects, Hydrothermal fluids, Volcanoes, borehole; caldera; geodesy; hydrothermal system; research; volcanic earthquake; volcano, California; Long Valley Caldera; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-0141974826&doi=10.1016%2fS0377-0273%2803%2900168-9&partnerID=40&md5=daeb60c711437f430b98dd3c99ff143c cited By 21 M.L. Sorey V.S. McConnell E. Roeloffs article Battaglia2003219 We model the source of inflation of Long Valley caldera by combining geodetic and micro-gravity data. Uplift from GPS and leveling, two-color EDM measurements, and residual gravity change determinations are used to estimate the intrusion geometry, assuming a vertical prolate ellipsoidal source. The U.S. Geological Survey occupied the Long Valley gravity network six times from 1980 to 1985. We reoccupied this network twice, in the summer of 1998 (33 stations), and the summer of 1999 (37 stations). Before gravity data can be used to estimate the density of the intrusion, they must be corrected for the effect of vertical deformation (the free-air effect) and changes in the water table. We use geostatistical techniques to interpolate uplift and water table changes at the gravity stations. The inflation source (a vertical prolate ellipsoid) is located 5.9 km beneath the resurgent dome with an aspect ratio equal to 0.475, a volume change from 1982 to 1999 of 0.136 km3 and a density of around 1700 kg/m3. A bootstrap method was employed to estimate 95% confidence bounds for the parameters of the inflation model. We obtained a range of 0.105-0.187 km3 for the volume change, and 1180-2330 kg/m3 for the density. Our results do not support hydrothermal fluid intrusion as the primary cause of unrest, and confirm the intrusion of silicic magma beneath Long Valley caldera. Failure to account for the ellipsoidal nature of the source biases the estimated source depth by 2.9 km (a 33% increase), the volume change by 0.019 km3 (a 14% increase) and the density by about 1200 kg/m3 (a 40% increase). © 2003 Elsevier B.V. All rights reserved. 2003 English 03770273 10.1016/S0377-0273(03)00171-9 Journal of Volcanology and Geothermal Research 127 Elsevier 219-245 Department of Geophysics, Stanford University, Stanford, CA 94305-2215, United States; U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, United States 3-4 Deformation; Gravitational effects; Microgravity processing, Ellipsoidal sources, Geology, caldera; geodetic datum; geometry; geostatistics; GPS; gravity; modeling; uplift, California; Long Valley Caldera; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-0037477680&doi=10.1016%2fS0377-0273%2803%2900171-9&partnerID=40&md5=8418bc5cc3ccdfcdc51c270b592bf007 cited By 113 M. Battaglia P. Segall C. Roberts article Foulger2003 A temporary network of 69 three-component seismic stations captured a major seismic sequence in Long Valley caldera in 1997. We performed a tomographic inversion for crustal structure beneath a 28 km × 16 km area encompassing part of the resurgent dome, the south moat, and Mammoth Mountain. Resolution of crustal structure beneath the center of the study volume was good down to ∼3 km below sea level (∼5 km below the surface). Relatively high wave speeds are associated with the Bishop Tuff and lower wave speeds characterize debris in the surrounding moat. A low-Vp/Vs anomaly extending from near the surface to ∼1 km below sea level beneath Mammoth Mountain may represent a CO2 reservoir that is supplying CO2-rich springs, venting at the surface, and killing trees. We investigated temporal variations in structure beneath Mammoth Mountain by differencing our results with tomographic images obtained using data from 1989/1990. Significant changes in both Vp and Vs were consistent with the migration of CO2 into the upper 2 km or so beneath Mammoth Mountain and its depletion in peripheral volumes that correlate with surface venting areas. Repeat tomography is capable of detecting the migration of gas beneath active silicic volcanoes and may thus provide a useful volcano monitoring tool. 2003 English 21699313 Journal of Geophysical Research: Solid Earth 108 Blackwell Publishing Ltd ESE 6-1 - 6-16 Volcano Hazards Team, U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States; Division of Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Durham, NC 27708-0235, United States 3 caldera; crustal structure; seismic tomography; seismic velocity; velocity structure, California; Long Valley; Mammoth Mountain; United States https://www.scopus.com/inward/record.uri?eid=2-s2.0-0038792042&partnerID=40&md5=ae44916891ad81446ed860b9050ac965 cited By 53 G.R. Foulger B.R. Julian A.M. Pitt D.P. Hill E. Shalev article sackett1999long 1999 10.3133/ofr99158 US Geological Survey US Geological Survey 99-158 378 Penelope C Sackett Vicki S McConnell Angela L Roach Susan S Priest John H Sass article Sass199843 In December 1997, the California Energy Commission (CEC) agreed to provide funding for Phase III continued drilling of the Long Valley Exploratory Well (LVEW) near Mammoth Lakes, CA, from its present depth. The CEC contribution of $1 million completes a funding package of $2 million from a variety of sources, which will allow the well to be cored continuously to a depth of between 11,500 and 12,500 feet. The core recovered from Phase III will be crucial to understanding the origin and history of the hydrothermal systems responsible for the filling of fractures in the basement rock. The borehole may penetrate the metamorphic roof of the large magmatic complex that has fed the volcanism responsible for the caldera and subsequent activity. 1998 English 01607782 Bulletin. Geothermal Resources Council 27 Geothermal Resources Council, Davis, CA, United States 43-46 U.S. Geological Survey, Denver, United States 2 Costs; Exploratory boreholes; Geothermal wells; Project management, Exploratory wells, Core drilling https://www.scopus.com/inward/record.uri?eid=2-s2.0-0032026104&partnerID=40&md5=9db2f5194509bae1a9f5d5a09629f311 cited By 0 John Sass John Finger Vicki McConnel article https://doi.org/10.1029/98EO00326 The Long Valley caldera region, located between the Sierra Nevada and the Basin and Range Province in eastern California, encompasses a large volcanic complex whose eruptive history began nearly 4 m.y.a. and continues to the present, with eruptions occurring, on average, every few hundred years. Eruptive activity in the area occurred as recently as 250 years ago with small eruptions from vents on Paoha Island in the middle of Mono Lake and 550–600 years ago from three vents at the southern end of the Inyo volcanic chain in the west moat of Long Valley caldera. The current unrest in the caldera began in 1980 and has included recurring earthquake swarms and uplift of the resurgent dome in the center of the caldera by over 70 cm [Bailey and Hill, 1990]. Long Valley caldera is one of several large calderas around the world that have shown similar signs of magmatic unrest in the last few decades. 1998 https://doi.org/10.1029/98EO00326 Eos, Transactions American Geophysical Union 79 429-432 36 https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/98EO00326 David P. Hill Michael L. Sorey William L. Ellsworth John Sass