Geology topics

William Evans

Publications and source records attributed to William Evans.

3 recordsLinked to original sources

USGS2016

The chemistry and isotopic composition of waters in the low-enthalpy geothermal system of Cimino-Vico Volcanic District, Italy

Geothermal energy exploration is based in part on interpretation of the chemistry, temperature, and discharge rate of thermal springs. Here we present the major element chemistry and the δD, δ 18 O, 87 Sr/ 86 Sr and δ 11 B isotopic ratio of groundwater from the low-enthalpy geothermal system near the city of Viterbo in the Cimino-Vico volcanic district of west-Central Italy. The geothermal system hosts many thermal springs and gas vents, but the resource is still unexploited. Water chemistry is controlled by mixing between low salinity,HCO 3 -rich fresh waters (<24.2°C) flowing in shallow volcanic rocks and SO 4 -rich thermal waters (25.3°C to 62.2°C) ascending from deep, high permeability Mesozoic limestones. The (equivalent) SO 4 /Cl (0.01–0.02), Na/Cl (2.82–5.83) and B/Cl ratios (0.02–0.38) of thermal waters differs from the ratios in other geothermal systems from Central Italy, probably implying a lack of hydraulic continuity across the region. The δ 18 O (−6.6‰ to −5.9‰) and δD (−40.60‰ to −36.30‰) isotopic composition of spring water suggest that the recharge area for the geothermal system is the summit region of Mount Cimino. The strontium isotope ratios ( 87 Sr/ 86 Sr) of thermal waters (0.70797–0.70805) are consistent with dissolution of the Mesozoic evaporite-carbonate units that constitute the reservoir, and the ratios of cold fresh waters mainly reflect shallow circulation through the volcanic cover and some minor admixture (<10%) of thermal water as well. The boron isotopic composition (δ 11 B) of fresh waters (−5.00 and 6.12‰) is similar to that of the volcanic cover, but the δ 11 B of thermal waters (−8.37‰ to −4.12‰) is a mismatch for the Mesozoic reservoir rocks and instead reflects dissolution of secondary boron minerals during fluid ascent through flysch units that overlie the reservoir. A slow and tortuous ascent enhances extraction of boron but also promotes conductive cooling, partially masking the heat present in the reservoir. Overall data from this study is consistent with previous studies that concluded that the geothermal system has a large energy potential.

Journal of Volcanology and Geothermal Research↗

USGS2011

Gas and isotope chemistry of thermal features in Yellowstone National Park, Wyoming

This report presents 130 gas analyses and 31 related water analyses on samples collected from thermal features at Yellowstone between 2003 and 2009. An overview of previous studies of gas emissions at Yellowstone is also given. The analytical results from the present study include bulk chemistry of gases and waters and isotope values for water and steam (delta18O, dealtaD), carbon dioxide (delta13C only), methane (delta13C only), helium, neon, and argon. We include appendixes containing photos of sample sites, geographic information system (GIS) files including shape and kml formats, and analytical results in spreadsheets. In addition, we provide a lengthy discussion of previous work on gas chemistry at Yellowstone and a general discussion of the implications of our results. We demonstrate that gases collected from different thermal areas often have distinct chemical signatures, and that differences across the thermal areas are not a simple function of surface temperatures or the type of feature. Instead, gas chemistry and isotopic composition are linked to subsurface lithologies and varying contributions from magmatic, crustal, and meteoric sources.

Wyoming↗

USGS1990

Origins of water and solutes in and north of the Norris-Mammoth Corridor, Yellowstone National Park

This study was initiated to investigate the impacts of geothermal development in the Corwin Springs Known Geothermal Resources Area (KGRA) on the hydrothermal features of Yellowstone National Park. To determine possible hydrogeochemical connections, we used the diagnostic stable and radioactive isotopes of several elements, and the chemical and gas compositions of thermal and cold waters from the Norris-Mammoth Corridor and areas north of the Park. The investigations were particularly comprehensive in the Mammoth Hot Springs area, Corwin Springs KGRA, and Chico Hot Springs. The geochemical tools used are still subject to uncertainties of 1 - 5%. Preliminary interpretation of the data, especially the ??D and ??18O values of water, 87Sr/86Sr ratios, ??11B values, composition and isotopes of noble gases and several conservative chemical species would indicate that the waters from Mammoth Hot Springs and La Duke Spring area have evolved chemically and isotopically by reactions with different rock types, and are probably not directly connected. These data indicate that a component (<20%) of water in Bear Creek Springs may be derived from the Mammoth system.

Conference Paper↗