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At least 685 records · Page 38Linked to original sources
USGS2004

Mercury and Methylmercury concentrations and loads in Cache Creek Basin, California, January 2000 through May 2001

Concentrations and mass loads of total mercury and methylmercury in streams draining abandoned mercury mines and near geothermal discharge in Cache Creek Basin, California, were measured during a 17-month period from January 2000 through May 2001. Rainfall and runoff averages during the study period were lower than long-term averages. Mass loads of mercury and methylmercury from upstream sources to downstream receiving waters, such as San Francisco Bay, were generally the highest during or after winter rainfall events. During the study period, mass loads of mercury and methylmercury from geothermal sources tended to be greater than those from abandoned mining areas because of a lack of large precipitation events capable of mobilizing significant amounts of either mercury-laden sediment or dissolved mercury and methylmercury from mine waste. Streambed sediments of Cache Creek are a source of mercury and methylmercury to downstream receiving bodies of water such as the Delta of the San Joaquin and Sacramento Rivers. Much of the mercury in these sediments was deposited over the last 150 years by erosion and stream discharge from abandoned mines or by continuous discharges from geothermal areas. Several geochemical constituents were useful as natural tracers for mining and geothermal areas. These constituents included aqueous concentrations of boron, chloride, lithium, and sulfate, and the stable isotopes of hydrogen and oxygen in water. Stable isotopes of water in areas draining geothermal discharges were enriched with more oxygen-18 relative to oxygen-16 than meteoric waters, whereas the enrichment by stable isotopes of water from much of the runoff from abandoned mines was similar to that of meteoric water. Geochemical signatures from stable isotopes and trace-element concentrations may be useful as tracers of total mercury or methylmercury from specific locations; however, mercury and methylmercury are not conservatively transported. A distinct mixing trend of trace elements and stable isotopes of hydrogen and oxygen from geothermal waters was apparent in Sulphur Creek and lower Bear Creek (tributaries to Cache Creek), but the signals are lost upon mixing with Cache Creek because of dilution.

Scientific Investigations Report↗
USGS2014

Hydrogeologic framework and occurrence, movement, and chemical characterization of groundwater in Dixie Valley, west-central Nevada

Dixie Valley, a primarily undeveloped basin in west-central Nevada, is being considered for groundwater exportation. Proposed pumping would occur from the basin-fill aquifer. In response to proposed exportation, the U.S. Geological Survey, in cooperation with the Bureau of Reclamation and Churchill County, conducted a study to improve the understanding of groundwater resources in Dixie Valley. The objective of this report is to characterize the hydrogeologic framework, the occurrence and movement of groundwater, the general water quality of the basin-fill aquifer, and the potential mixing between basin-fill and geothermal aquifers in Dixie Valley. Various types of geologic, hydrologic, and geochemical data were compiled from previous studies and collected in support of this study. Hydrogeologic units in Dixie Valley were defined to characterize rocks and sediments with similar lithologies and hydraulic properties influencing groundwater flow. Hydraulic properties of the basin-fill deposits were characterized by transmissivity estimated from aquifer tests and specific-capacity tests. Groundwater-level measurements and hydrogeologic-unit data were combined to create a potentiometric surface map and to characterize groundwater occurrence and movement. Subsurface inflow from adjacent valleys into Dixie Valley through the basin-fill aquifer was evaluated using hydraulic gradients and Darcy flux computations. The chemical signature and groundwater quality of the Dixie Valley basin-fill aquifer, and potential mixing between basin-fill and geothermal aquifers, were evaluated using chemical data collected from wells and springs during the current study and from previous investigations. Dixie Valley is the terminus of the Dixie Valley flow system, which includes Pleasant, Jersey, Fairview, Stingaree, Cowkick, and Eastgate Valleys. The freshwater aquifer in the study area is composed of unconsolidated basin-fill deposits of Quaternary age. The basin-fill hydrogeologic unit can be several orders of magnitude more transmissive than surrounding and underlying consolidated rocks and Dixie Valley playa deposits. Transmissivity estimates in the basin fill throughout Dixie Valley ranged from 30 to 45,500 feet squared per day; however, a single transmissivity value of 0.1 foot squared per day was estimated for playa deposits. Groundwater generally flows from the mountain range uplands toward the central valley lowlands and eventually discharges near the playa edge. Potentiometric contours east and west of the playa indicate that groundwater is moving eastward from the Stillwater Range and westward from the Clan Alpine Mountains toward the playa. Similarly, groundwater flows from the southern and northern basin boundaries toward the basin center. Subsurface groundwater flow likely enters Dixie Valley from Fairview and Stingaree Valleys in the south and from Jersey and Pleasant Valleys in the north, but groundwater connections through basin-fill deposits were present only across the Fairview and Jersey Valley divides. Annual subsurface inflow from Fairview and Jersey Valleys ranges from 700 to 1,300 acre-feet per year and from 1,800 to 2,300 acre-feet per year, respectively. Groundwater flow between Dixie, Stingaree, and Pleasant Valleys could occur through less transmissive consolidated rocks, but only flow through basin fill was estimated in this study. Groundwater in the playa is distinct from the freshwater, basin-fill aquifer. Groundwater mixing between basin-fill and playa groundwater systems is physically limited by transmissivity contrasts of about four orders of magnitude. Total dissolved solids in playa deposit groundwater are nearly 440 times greater than total dissolved solids in the basin-fill groundwater. These distinctive physical and chemical flow restrictions indicate that groundwater interaction between the basin fill and playa sediments was minimal during this study period (water years 2009–11). Groundwater in Dixie Valley generally can be characterized as a sodium bicarbonate type, with greater proportions of chloride north of the Dixie Valley playa, and greater proportions of sulfate south of the playa. Analysis of major ion water chemistry data sampled during the study period indicates that groundwater north and south of Township 22N differ chemically. Dixie Valley groundwater quality is marginal when compared with national primary and secondary drinking-water standards. Arsenic and fluoride concentrations exceed primary drinking water standards, and total dissolved solids and manganese concentrations exceed secondary drinking water standards in samples collected during this study. High concentrations of boron and tungsten also were observed. Chemical comparisons between basin-fill and geothermal aquifer water indicate that most basin-fill groundwater sampled could contain 10–20 percent geothermal water. Geothermal indicators such as high temperature, lithium, boron, chloride, and silica suggest that mixing occurs in many wells that tap the basin-fill aquifer, particularly on the north, south, and west sides of the basin. Magnesium-lithium geothermometers indicate that some basin-fill aquifer water sampled for the current study likely originates from water that was heated above background mountain-block recharge temperatures (between 3 and 15 degrees Celsius), highlighting the influence of mixing with warm water that was possibly derived from geothermal sources.

Nevada↗
USGS2005

Anatahan, Northern Mariana Islands: Reconnaissance geological observations during and after the volcanic crisis of spring 1990, and monitoring prior to the May 2003 eruption

Anatahan island is 9.5 km east–west by 3.5 km north–south and truncated by an elongate caldera 5 km east–west by 2.5 km north–south. A steep-walled pit crater ∼1 km across and ∼200 m deep occupies the eastern part of the caldera. The island is the summit region of a mostly submarine stratovolcano. The oldest subaerial rocks (stage 1) are exposed low on the outer flanks and in the caldera walls. These include thick (∼10 m) and thin (2–3 m) lava flows, well-indurated tuffs, and scoria units that make up the bulk of the island. Rock compositions range from basaltic andesite to dacite, and most are plagioclase-phyric. On the steep north and south flanks of the volcano, these rocks are cut by numerous east–west-oriented, few-hundred-m-long lineaments of undetermined origin. Indurated breccias unconformably overlie scarps cut into stage 1 units low on the south flank. Intermediate-age eruptive units (stage 2) include caldera-filling lava flows and pyroclastic deposits and, on the outer flanks, vents and valley-filling lava flows. The youngest pre-2003 volcanic unit on Anatahan (stage 3) is a hydromagmatic surge and fall deposit rich in accretionary lapilli. Prior to 2003, this unit was found over almost the entire island, and in many places original depositional surfaces and outcrops could be found in high-energy environments along the coast, indicating a young (but undetermined) age. During reconnaissance visits in 1990, 1992, 1994, and 2001, geothermal activity (fumaroles as well as pits with boiling, sediment-laden pools) was observed in the southern part of the pit crater. In March and April 1990, increased local seismicity, a large regional earthquake, and reported increased fumarolic activity in the pit crater prompted evacuation of Anatahan village, at the west end of the island. Our first field investigation took place in late April 1990 to assess the level of volcanic unrest, conduct reconnaissance geological observations, collect rock and geothermal water samples, and set up a geophysical monitoring network. Results at this time were inconclusive with respect to determining whether the activity was anomalous. Water in some of the geothermal pits within the pit crater was boiling, and pH values as low as 0.7 were recorded in the field. An electronic distance measurement (EDM) network was installed, and over a ∼1-week period, up to 9 cm of extension occurred across some lines but not others. Seismicity was characterized by intermittent local earthquakes but no sustained swarms or tremor. A brief visit in June 1990 revealed that the shallow lake near the boiling pits was gone, but activity in the pits themselves was similar to that of April 1990. Only minor extension had occurred along a single EDM line since the previous visit, and no earthquakes >M2.5 occurred during the visit. Subsequent 1- to 2-day visits occurred in October 1990, May 1992, May 1994, and June 2001. Activity within the geothermal pits was relatively constant during every visit, although during this 11-year period the level of the water in each pit decreased. In June 2001, a ∼50-m-wide region of mud pots and steaming ground in the central part of the geothermal area had developed. No geologic evidence, however, suggested that an eruption would occur < 2 years afterward. Most of the EDM lines showed slight extension between late 1990 and 1992, followed by very gradual contraction from 1992 to 2001. A more extensive seismic-monitoring system was installed on the Northern Mariana Islands during these visits, and it recorded a small seismic swarm at Anatahan from May to July 1993. The telemetry component of the seismic equipment broke prior to 2001 and had not been repaired by the time of the May 2003 eruption, so no precursory seismic data were recorded to indicate pre-eruption unrest.

Northern Mariana Islands↗
USGS1997

Hydrologic investigations in the Mammoth Corridor, Yellowstone National Park and vicinity, U.S.A.

The Mammoth Corridor in and adjacent to Yellowstone National Park encompasses a N-S alignment of geothermal features that extends from the Norris Geyser Basin adjacent to the Yellowstone caldera through Mammoth Hot Springs to the Corwin Springs Known Geothermal Resources Area (KGRA). Thermal springs in this region discharge water that ranges from NaKCl, silica-depositing type to CaNaHC0 3 SO 4 , travertine-depositing type. Although only a few relatively shallow wells have been drilled in the corridor, the region is of special interest because of the environmental issues associated with potential geothermal development adjacent to Yellowstone National Park. The U.S. Geological Survey conducted an intensive hydrogeologic study of this region during 1988–1990 and continued to collect hydrologic and geophysical data until 1994. The results of these investigations document the rates of discharge of thermal water and heat within the corridor, evidence for a magmatic heat source beneath the Mammoth Hot Springs area, and evidence for separate geothermal systems associated with Mammoth Hot Springs and with thermal waters discharging in the KGRA in the vicinity of La Duke Hot Springs. These investigations also indicate that limited development of the 70°C geothermal resource in the La Duke area would not affect thermal springs in Yellowstone National Park.

Geothermics↗
USGS2001

Naturalized salmonid populations occur in the presence of elevated trace element concentrations and temperatures in the firehole river, Yellowstone National Park, Wyoming, USA

We investigated the effects of geothermally influenced waters on the distribution of rainbow trout, Oncorhynchus mykiss , and brown trout, Salmo trutta , in the Firehole River and its tributaries in Yellowstone National Park (WY, USA) from June 1997 to June 1998. Geothermal features in the Firehole River basin elevate mineral content and temperature in portions of the river and its tributaries. We found concentrations of boron and arsenic to be elevated in geothermally influenced areas compared with upstream sites. Boron concentrations occasionally exceeded 1,000 μg/L, a proposed limit for the protection of aquatic organisms. Arsenic concentrations occasionally exceeded 190 μg/L, the chronic ambient water quality criterion. Temperatures in geothermally influenced sites ranged up to 30°C and were consistently 5 to 10°C higher than upstream sites unaffected by geothermal inputs. Rainbow trout occurred at sites with elevated concentrations of boron, arsenic, and other trace elements and elevated water temperatures. Rainbow trout inhabited and spawned at sites with the most elevated trace element concentrations and temperatures; however, brown trout were absent from these sites. Water temperature may be the major factor determining brown trout distributions, but we cannot exclude the possibility that brown trout are more sensitive than rainbow trout to boron, arsenic, or other trace elements. Further investigations are needed to determine species-specific tolerances of boron, arsenic, and other trace elements among salmonids.

Wyoming↗
USGS2004

Mercury and methylmercury concentrations and loads in the Cache Creek watershed, California

Concentrations and loads of total mercury and methylmercury were measured in streams draining abandoned mercury mines and in the proximity of geothermal discharge in the Cache Creek watershed of California during a 17-month period from January 2000 through May 2001. Rainfall and runoff were lower than long-term averages during the study period. The greatest loading of mercury and methylmercury from upstream sources to downstream receiving waters, such as San Francisco Bay, generally occurred during or after winter rainfall events. During the study period, loads of mercury and methylmercury from geothermal sources tended to be greater than those from abandoned mining areas, a pattern attributable to the lack of large precipitation events capable of mobilizing significant amounts of either mercury-laden sediment or dissolved mercury and methylmercury from mine waste. Streambed sediments of Cache Creek are a significant source of mercury and methylmercury to downstream receiving bodies of water. Much of the mercury in these sediments is the result of deposition over the last 100-150 years by either storm-water runoff, from abandoned mines, or continuous discharges from geothermal areas. Several geochemical constituents were useful as natural tracers for mining and geothermal areas, including the aqueous concentrations of boron, chloride, lithium and sulfate, and the stable isotopes of hydrogen and oxygen in water. Stable isotopes of water in areas draining geothermal discharges showed a distinct trend toward enrichment of 18O compared with meteoric waters, whereas much of the runoff from abandoned mines indicated a stable isotopic pattern more consistent with local meteoric water. ?? 2004 Elsevier B.V. All rights reserved.

Science of the Total Environment↗
USGS2008

Living in Yellowstone's Caldera: A geochemical trophic cascade in elk

Though the geology of earth's rare geothermal environments and their associated microbial communities are intensely studied, less scientific attention has focused on their potential effects through the plant-herbivore-carnivore trophic chain. The west-central portion of Yellowstone National Park contains a 2000-km 2 volcanic caldera with 2- to 60-million-year-old, predominantly rhyolitic, rocks that produce relatively infertile soils. The caldera area contains one of the largest concentrations of active geothermal features in the world, including thousands of geysers, fumaroles , hot springs, and mud pots. In many other chapters of this book, we address the ecological impacts of this unique geology to the ecology of the large mammals that live within the caldera, primarily through the effects of geothermal heat on snow pack. In this chapter, we explore the unique geochemistry of the geothermal environments and the consequences of this geochemistry to elk and perhaps other herbivores that reside within the caldera. These studies were prompted by behavioral and demographic observations of elk during the initial years of our studies that we could not explain and, in turn, led us to formulate hypotheses about potential geochemical influences on elk ecology. Specifically, we contrast the concentrations of fluoride (F) and silica (SiO 2 ) found in the Madison headwaters area with areas on Yellowstone's northern range located approximately 50 km to the northwest, where geothermal features are rare or absent. We then trace the consequences of geochemical differences through abiotic and biotic linkages in the ecosystem.

Book↗
USGS1998

Three-dimensional seismic structure and moment tensors of non-double-couple earthquakes at the Hengill-Grensdalur volcanic complex, Iceland

The volcanic and geothermal areas of Iceland are rich sources of non-double-couple (non-DC) earthquakes. A state-of-the-art digital seismometer network deployed at the Hengill–Grensdalur volcanic complex in 1991 recorded 4000 small earthquakes. We used the best recorded of these to determine 3-D V P and V P /V S structure tomographically and accurate earthquake moment tensors. The V P field is dominated by high seismic wave speed bodies interpreted as solidified intrusions. A widespread negative (−4 per cent) V P /V S anomaly in the upper 4km correlates with the geothermal field, but is too strong to be caused solely by the effect of temperature upon liquid water or the presence of vapour, and requires in addition mineralogical or lithological differences between the geothermal reservoir and its surroundings. These may be caused by geothermal alteration. Well-constrained moment tensors were obtained for 70 of the best-recorded events by applying linear programming methods to P - and S -wave polarities and amplitude ratios. About 25 per cent of the mechanisms are, within observational error, consistent with DC mechanisms consistent with shear faulting. The other 75 per cent have significantly non-DC mechanisms. Many have substantial explosive components, one has a substantial implosive component, and the deviatoric component of many is strongly non-DC. Many of the non-DC mechanisms are consistent, within observational error, with simultaneous tensile and shear faulting. However, the mechanisms occupy a continuum in source-type parameter space and probably at least one additional source process is occurring. This may be fluid flow into newly formed cracks, causing partial compensation of the volumetric component. Studying non-shear earthquakes such as these has great potential for improving our understanding of geothermal processes and earthquake source processes in general.

Geophysical Journal International↗
USGS2003

Hydrothermal and tectonic activity in northern Yellowstone Lake, Wyoming

Yellowstone National Park is the site of one of the world's largest calderas. The abundance of geothermal and tectonic activity in and around the caldera, including historic uplift and subsidence, makes it necessary to understand active geologic processes and their associated hazards. To that end, we here use an extensive grid of high-resolution seismic reflection profiles (∼450 km) to document hydrothermal and tectonic features and deposits in northern Yellowstone Lake. Sublacustrine geothermal features in northern Yellowstone Lake include two of the largest known hydrothermal explosion craters, Mary Bay and Elliott's. Mary Bay explosion breccia is distributed uniformly around the crater, whereas Elliott's crater breccia has an asymmetric distribution and forms a distinctive, ∼2-km-long, hummocky lobe on the lake floor. Hydrothermal vents and low-relief domes are abundant on the lake floor; their greatest abundance is in and near explosion craters and along linear fissures. Domed areas on the lake floor that are relatively unbreached (by vents) are considered the most likely sites of future large hydrothermal explosions. Four submerged shoreline terraces along the margins of northern Yellowstone Lake add to the Holocene record of postglacial lake-level fluctuations attributed to “heavy breathing” of the Yellowstone magma reservoir and associated geothermal system. The Lake Hotel fault cuts through northwestern Yellowstone Lake and represents part of a 25-km-long distributed extensional deformation zone. Three postglacial ruptures indicate a slip rate of ∼0.27 to 0.34 mm/yr. The largest (3.0 m slip) and most recent event occurred in the past ∼2100 yr. Although high heat flow in the crust limits the rupture area of this fault zone, future earthquakes of magnitude ∼5.3 to 6.5 are possible. Earthquakes and hydrothermal explosions have probably triggered landslides, common features around the lake margins. Few high-resolution seismic reflection surveys have been conducted in lakes in active volcanic areas. Our data reveal active geothermal features with unprecedented resolution and provide important analogues for recognition of comparable features and potential hazards in other subaqueous geothermal environments.

Wyoming↗
USGS2010

Temperature data from wells in Long Valley Caldera, California

The 30-by-20-km Long Valley Caldera (LVC) in eastern California (fig.1) formed at 0.76 Ma in a cataclysmic eruption that resulted in the deposition of 600 km? of Bishop Tuff outside the caldera rim (Bailey, 1989). By approximately 0.6 Ma, uplift of the central part of the caldera floor and eruption of rhyolitic lava formed the resurgent dome. The most recent eruptive activity in the area occurred approximately 600 yr ago along the Mono-Inyo craters volcanic chain (Bailey, 2004; Hildreth, 2004). LVC hosts an active hydrothermal system that includes hot springs, fumaroles, mineral deposits, and an active geothermal well field and power plant at Casa Diablo along the southwestern boundary of the resurgent dome (Sorey and Lewis, 1976; Sorey and others, 1978; Sorey and others, 1991). Electric power generation began in 1985 with about 10 Mwe net capacity and was expanded to about 40 Mwe (net) in 1991 (Campbell, 2000; Suemnicht and others, 2007). Plans for further expansion are focused mainly on targets in the caldera?s western moat (Sass and Priest, 2002) where the most recent volcanic activity has occurred (Hildreth, 2004). LVC has been the site of extensive research on geothermal resources and volcanic hazards (Bailey and others, 1976; Muffler and Williams, 1976; Miller and others, 1982; Hill and others 2002). The first geothermal exploratory drilling was done in the shallow (< 200 m deep) hydrothermal system at Casa Diablo in the 1960?s (McNitt, 1963). Many more boreholes were drilled throughout the caldera in the 1970?s and 1980?s by private industry for geothermal exploration and by the U.S. Geological Survey (USGS) and Sandia National Laboratory for volcanic and geothermal research and exploration. Temperature logs were obtained in some of these wells during or immediately following drilling, before thermal equilibration was complete. Most of the temperature logs, however, were obtained weeks, months, or years after well completion and are representative of dynamic thermal equilibrium. The maximum reservoir temperature for LVC is estimated to be about 220?C on the basis of chemical geothermometers (Fournier and Truesdell, 1973) using analytical results from water samples collected from a large number of wells and springs across the caldera and around its periphery (Lewis, 1974; Mariner and Wiley, 1976; Farrar and others, 1985, 1987, 1989, White and Peterson, 1991). The deepest well in LVC (~3 km) is the Long Valley Exploratory Well (LVEW) drilled in the 1990?s with funding from the U.S. Department of Energy to investigate the potential for near-magmatic-temperature energy extraction and the occurrence of magma under the central part of the resurgent dome (Finger and Eichelberger, 1990; Finger and Jacobsen, 1999; Sackett and others, 1999). However, temperatures beneath the resurgent dome have proved disappointingly low and in LVEW reach a maximum of only 102 degrees C in a long isothermal section (2,100 to 3,000 m) in Mesozoic basement rocks (Farrar and others, 2003). Temperature data from well logs and geothermometry reveal that the highest temperatures in LVC are beneath the western moat. The hottest temperatures measured in LVC exceed 200 degrees C in two wells (44-16 and RDO-8) located in the western moat. Well 44-16 was drilled through the entire thickness of post-caldera volcanic fill and bottomed in Mesozoic basement. Well RDO-8 was drilled through post-caldera volcanic rocks and 305 m into the Bishop Tuff (Wollenberg and others, 1986). Temperatures in the hydrothermal system decrease toward the east by processes of conduction and dilution from cold groundwater recharge that occurs mostly around the caldera margin and beneath the resurgent dome. Reservoir temperatures at Casa Diablo (fig.1) are about 170?C (for example, MBP-3 and Mammoth-1), decreasing to about 100 degrees C in wells near Hot Creek Gorge (for example, MW-4 and CH-10B), and are generally less than 50?C in thermal springs near Lake

Data Series↗
USGS1995

Hydrologic data and description of a hydrologic monitoring plan for the Borax Lake area, Oregon

Borax Lake is located in southeastern Oregon, within the Alvord Valley Known Geothermal Resource Area. Borax Lake is a large hot spring; there are more than 50 smaller hot springs within about one-half mile to the north of the lake. Several geothermal exploration wells have been drilled near Borax Lake, and there is concern that development of the geothermal resources could affect the lake and nearby hot springs. A factor to consider in developing the resource is that the Borax Lake chub is an endangered species of fish that is found exclusively in Borax Lake. This study was designed to collect basic hydrologic data to develop a long-term monitoring plan. Baseline data, collected before geothermal production wells are used extensively, will provide an understanding of natural trends and will help identify change caused by development. Basic data collected during reconnaissance field visits to the area included spring temperatures, specific conductances, and discharge; field measurements in wells included water-level measurements and temperature, specific conductance, and discharge measurements in flowing wells. The study of the Borax Lake area included depth and temperature measurements in the vent area of the lake, point velocity measurements, underwater video photography, and an evaluation of methods to measure discharge from the lake. Water-quality samples were collected at Borax Lake, one hot spring, and one flowing well. Information from field visits was used to develop a monitoring plan. The plan would include monitoring Borax Lake by measuring discharge, stage, evaporation, temperature, and specific conductance; water-quality sampling and analysis; and monitoring shallow ground-water levels near Borax Lake using shallow piezometers. Minimally, one hot spring in North Borax Lake Spring Group 1 would be monitored for temperature and specific conductance and sampled for water-quality analysis. In addition, two flowing wells would be monitored for water levels, temperature, specific conductance, and discharge and sampled for water-quality analysis. The construction characteristics of these wells must be verified before long-term data collection begins. In the future, it may be helpful to monitor shallow and (or) deep observation wells drilled into the thermal aquifer to understand the possible effects of geothermal development on Borax Lake and nearby springs.

Oregon↗
USGS2011

Monitoring CO2 emissions in tree kill areas near the resurgent dome at Long Valley Caldera, California

We report results of yearly measurements of the diffuse CO 2 flux and shallow soil temperatures collected since 2006 across two sets of tree-kill areas at Long Valley Caldera, California. These data provide background information about CO 2 discharge during a period with moderate seismicity, but little to no deformation. The tree kills are located at long-recognized areas of weak thermal fluid upflow, but have expanded in recent years, possibly in response to geothermal fluid production at Casa Diablo. The amount of CO 2 discharged from the older kill area at Basalt Canyon is fairly constant and is around 3-5 tonnes of CO 2 per day from an area of about 15,000 m 2 . The presence of isobutane in gas samples from sites in and around Basalt Canyon suggests that geothermal fluid production directly effects fluid upflow in the region close to the power plant. The average fluxes at Shady Rest are lower than average fluxes at Basalt Canyon, but the area affected by fluid upflow is larger. Total CO 2 discharged from the central portion of the kill area at Shady Rest has been variable, ranging from 6 to11 tonnes per day across 61,000 m 2 . Gas collected at Shady Rest contains no detectable isobutane to link emissions chemically to geothermal fluid production, but two samples from 2009-10 have detectable H 2 S and suggest an increasing geothermal character of emitted gas. The appearance of this gas at the surface may signal increased drawdown of water levels near the geothermal productions wells.

California↗
USGS2017

Geologic setting of the proposed West Flank Forge Site, California: Suitability for EGS research and development

The proposed West Flank FORGE site is within the China Lake Naval Air Weapons Station (NAWS), China Lake, CA. The West Flank is west of the Coso geothermal field, an area of China Lake NAWS dominated by the Quaternary Coso volcanic field largely comprised of rhyolite domes and their volcaniclastic and epiclastic horizons. The largest dome flow complex, Sugarloaf Mountain, marks the northwestern margin of the geothermal field. The West Flank is situated due west of Sugarloaf. The geologic setting of the West Flank was determined from one deep well (83-11) drilled as a potential production hole in 2009. The bottom-hole temperature (BHT) of well 83-11 approaches 600 oF (315˚C), but flow tests demonstrate very low, non-commercial permeabilities. With the exception of the upper 600 feet of volcaniclastic alluvium, well 83-11 is completed in granitic basement. The West Flank possesses the primary attributes of a FORGE site: non-commercial permeability ( <10 -16 m 2 ), a 175˚ to 225˚C temperature range in crystalline rocks, and a location outside an existing geothermal field The Coso Mountains host the Coso volcanic field and are within a right-releasing stepover between the dextral Airport Lake (ALF) and Little Lake fault zones (LLFZ) and the Wild Horse Mesa and Owens Valley faults. Two distinct fault populations have been identified at Coso: WNW-trending and antithetical, NE-trending strike-slip faults and N- to NNE-trending normal faults. These faults are both high permeability drilling targets at depth within the main (productive) geothermal field and they locally segment the field into distinct hydrothermal regimes. The West Flank may be segmented from the rest of the field by one such northerly trending fault. The overall minimum principal stress orientation in the main geothermal field varies from 103˚ to 108˚; however, the minimum horizontal principal stress in 83-11 is rotated to 081˚.

California↗
USGS2025

Evolution of permeability and strength recovery of shear fracture under hydrothermal conditions

Geothermal energy is a clean and renewable resource that depends on the ability to move water through hot rock. In many locations, the ability to move water through rock requires the presence of extensive natural or human-made systems of fractures. However, these fracture systems are influenced by a variety of complex processes that occur at the temperature and pressure conditions found in geothermal reservoirs. To make geothermal systems more efficient, it is important to understand how these fractures evolve over time in response to these processes. This study explored how fractures in rock change under high-temperature and pressure conditions, like those found in geothermal reservoirs, through laboratory experiments and numerical simulations. In general fractures, tend to close due to pressure from the surrounding rock preventing the flow of water. One set of laboratory experiments revealed that fractures in granitic rock can weaken over time at elevated temperatures. These weak fractures can then slip slowly potentially keeping the fracture open for a longer period. This study also showed that at the highest temperature examined (250 °C) large differences between the chemical composition of the rock and the fluid moving through it could improve water flow temporarily likely due to the water dissolving parts of the rock. Flow rate predicted by models shows overall good agreement with the flow rate measured in our experiments but with some long time-scale variations that may be due to mechanical wear of the fracture surface. A second set of experiments found that, over the temperature range examined, the closure of fractures was caused by brittle failure driven by high stresses at points where fracture surfaces were in contact. This result suggests that fracture closure in geothermal reservoirs could be counteracted by maintaining high pore pressures. Additionally, we also tested a new method using electrical resistance to measure fracture closure in controlled systems with high precision.

Final Technical Report↗
USGS2010

The thermal regime in the resurgent dome of Long Valley Caldera, California: Inferences from precision temperature logs in deep wells

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 <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.

Journal of Volcanology and Geothermal Research↗
USGS2025

Applying U-Th disequilbrium for dating siliceous sinters

Continental hydrothermal systems are critical avenues for the crustal transport of heat and mass captured for geothermal energy and mineral exploration. Thus, understanding their temporal evolution and longevity is important for resource characterization. Deposits of microlaminated siliceous sinter, common surface expressions of high temperature reservoirs (> 170 °C), have the potential to trace hydrothermal histories. Geothermal reservoirs are often located within uranium-bearing silicic volcanic rock where subsurface fluid-rock interactions extract U into hydrothermal fluids. U incorporated in the surface sinter deposit has the potential to provide a U— Th disequilibrium dating option. We focus on samples from El Tatio geyser field in the Altiplano of northern Chile, the largest geothermal system in the Andes. Our resulting 230 Th/U ages, along with the water and deposit elemental compositions, suggest concentrations of U and Th vary predictably along the sinter apron. While distal facies containing the highest U concentrations (> 50 μg/g) are least affected by detrital Th corrections, they can display suspected open-system behavior. In contrast, more medial facies, where bacterial mats and other porous textures are co mmonly concentrated, have only trace amounts of U (< 0.1 μg/g), which leads to unreliable or geologically improbable dates. Proximal facies tend to date most consistently. By comparing existing 14 C ages with 230 Th/U results, 230 Th/U ages tend to be younger than the 14 C ages, supporting the presence of a 14 C-dead carbon influence. New data confirm that the onset of geothermal activity at El Tatio goes back to the late Pleistocene.

Altiplano, El Tatio geyser field↗
USGS2023

A Bayesian multi-stage modelling framework to evaluate impacts of energy development on wildlife populations: An application to Greater Sage-Grouse (Centrocercus urophasianus)

Increased demand for domestic production of renewable energy has led to expansion of energy infrastructure across western North America. Much of the western U.S. comprises remote landscapes that are home to a variety of vegetation communities and wildlife species, including the imperiled sagebrush ecosystem and indicator species such as greater sage-grouse ( Centrocercus urophasianus ). Geothermal sources in particular have potential for continued development across the western U.S. but impacts to greater sage-grouse and other species are unknown. To address this information gap, we describe a novel two-pronged methodology that analyzes impacts of geothermal energy production on pattern and process of greater sage-grouse populations using (a) before-after control-impact (BACI) measures of population growth and lek absence rates and (b) concurrent-to-operation evaluations of demographic rates. Growth and absence rate analyses utilized 14 years of lek survey data collected prior (2005–2011) and concurrent (2012–2018) to geothermal operations at two sites in Nevada, USA. Demographic analyses utilized relocation data, restricted inference to concurrent years, and incorporated 17 additional control sites. Demographic results were applied to >100 potential geothermal sites distributed across the study region to generate spatially explicit predictions of unrealized population-level impacts.

MethodsX↗
USGS2004

Estimating tectonic history through basin simulation-enhanced seismic inversion: Geoinformatics for sedimentary basins

A data assimilation approach is demonstrated whereby seismic inversion is both automated and enhanced using a comprehensive numerical sedimentary basin simulator to study the physics and chemistry of sedimentary basin processes in response to geothermal gradient in much greater detail than previously attempted. The approach not only reduces costs by integrating the basin analysis and seismic inversion activities to understand the sedimentary basin evolution with respect to geodynamic parameters-but the technique also has the potential for serving as a geoinfomatics platform for understanding various physical and chemical processes operating at different scales within a sedimentary basin. Tectonic history has a first-order effect on the physical and chemical processes that govern the evolution of sedimentary basins. We demonstrate how such tectonic parameters may be estimated by minimizing the difference between observed seismic reflection data and synthetic ones constructed from the output of a reaction, transport, mechanical (RTM) basin model. We demonstrate the method by reconstructing the geothermal gradient. As thermal history strongly affects the rate of RTM processes operating in a sedimentary basin, variations in geothermal gradient history alter the present-day fluid pressure, effective stress, porosity, fracture statistics and hydrocarbon distribution. All these properties, in turn, affect the mechanical wave velocity and sediment density profiles for a sedimentary basin. The present-day state of the sedimentary basin is imaged by reflection seismology data to a high degree of resolution, but it does not give any indication of the processes that contributed to the evolution of the basin or causes for heterogeneities within the basin that are being imaged. Using texture and fluid properties predicted by our Basin RTM simulator, we generate synthetic seismograms. Linear correlation using power spectra as an error measure and an efficient quadratic optimization technique are found to be most effective in determining the optimal value of the tectonic parameters. Preliminary 1-D studies indicate that one can determine the geothermal gradient even in the presence of observation and numerical uncertainties. The algorithm succeeds even when the synthetic data has detailed information only in a limited depth interval and has a different dominant frequency in the synthetic and observed seismograms. The methodology presented here even works when the basin input data contains only 75 per cent of the stratigraphic layering information compared with the actual basin in a limited depth interval.

Geophysical Journal International↗