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William Evans

Research Chemist

Contact Info


Short Biography

USGS employee since 1974.

Specializing in the geochemistry of fluids in volcanic and geothermal areas.





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SELECTED PUBLICATIONS


For full bibliographic list, click on CV link above.

For pdfs of publications below, click: http://wwwrcamnl.wr.usgs.gov/hydrotherm/Evans.htm

Evans, W. C., Sorey, M. L., Kennedy, B. M., Stonestrom, D. A., Rogie, J. D., and Shuster, D. L., 2001, High CO2 emissions through porous media: transport mechanisms and implications for flux measurement and fractionation: Chemical Geology, v. 177, p. 15-29.

Evans, W. C., Sorey, M. L., Cook, A. C., Kennedy, B. M., Shuster, D. L., Colvard, E. L., White, L. D., and Huebner, M. A., 2002, Tracing and quantifying magmatic carbon discharge in cold groundwaters: Lessons learned from Mammoth Mountain, USA: Journal of Volcanology and Geothermal Research, v. 114, p. 291-312.

Evans, W. C., van Soest, M. C., Mariner, R. H., Hurwitz, S., Ingebritsen, S. E., Wicks, C. W. Jr., and Schmidt, M. E., 2004, Magmatic intrusion west of Three Sisters, central Oregon, USA: The perspective from spring geochemistry: Geology, v. 32, p. 69-72.

Evans, W. C., Bergfeld, D., van Soest, M. C., Huebner, M. A., Fitzpatrick J, and Revesz, K. M., 2006, Geochemistry of low-temperature springs northwest of Yellowstone caldera: seeking the link between seismicity, deformation, and fluid flow: Journal of Volcanology and Geothermal Research, v. 154, p. 169-180.

Evans, W.C., Bergfeld, D., McGimsey, R.G., and Hunt, A.G., 2009, Diffuse gas emissions at the Ukinrek Maars, Alaska: Implications for magmatic degassing and volcanic monitoring: Applied Geochemistry, v. 24, p. 527-535.

Evans, W. C., Bergfeld, D., McGeehin, J. P., King, J. C., and H. Heasler, 2010, Tree-ring 14C links seismic swarm to CO2 spike at Yellowstone: Geology, v. 38, p. 1075-1078.

Bergfeld, D., and Evans, W. C., 2011, Monitoring CO2 emissions in tree kill areas near the resurgent dome at Long Valley Caldera, California: U.S. Geological Survey Scientific Investigations Report 2011-5038, 22 p.




                           

My Science Topics


Science Topic
Subtopic
Natural Hazardshazards
Natural Hazardsvolcanic activity
Natural Hazardsvolcanic eruption prediction
Natural Hazardsvolcanic gas emission
Natural Resourcesgeothermal resources
Natural Resourcesresource exploration
Natural Resourcesresource extraction
Natural Resourceswater resources
Techniques and Methodsfield methods
Techniques and Methodsisotopic analysis
Techniques and Methodslaboratory methods
Techniques and Methodstree ring analysis
Water Resourcesground-water quality



My USGS Science Strategy Areas

Energy & Minerals for America's Future

A National Hazard, Risk, and Resilience Assessment Program

Geochemistry of magmatic and geothermal fluids

Image of Current Focus for Geochemistry of magmatic and geothermal fluids

One of my major research goals is to relate the surface discharge and composition of magmatic gases to the state of unrest at hazardous volcanoes, with the thought that signs of reawakening might show up in gas emissions long before they are seen by other techniques such as deformation or seismic monitoring.  Sampling targets include fumarolic vents or bubbling hot springs, but these features often tell only part of the story.  At many volcanoes, a large fraction of magmatic volatiles become dissolved and transported in low-temperature groundwater.  Recent studies that explicitly considered the effect of groundwater on gas emissions led us to conclude that precursory emissions likely preceded eruption by decades.  The challenge ahead may lie more in interpreting, rather than detecting, such long-term precursory periods of enhanced emissions.


I also study the waters that contain magmatic gases, as their geochemistry provides information about subsurface temperatures and pressures.  Such information is useful in deriving estimates of geothermal energy potential as well as in constraining volcanic hazards.  Over the course of my career, fluids studied include high-temperature vent fluids from seafloor spreading ridges (e.g., black smokers), hot spring waters from geothermal fields, waters from deep boreholes in crystalline rock, natural soda springs, and the lake waters in the dangerous gassy lakes of Cameroon.


I’m currently leading a multi-disciplinary isotopic study of tree-rings in areas of gas discharge to look back at CO2 emission rates through past seismic swarms and cycles of deformation.  This study relies on 14C analyses in growth rings to provide an annual record of gas emission strength.  The study looks for a correlation between emission strength and seismicity or deformation, with the goal of understanding the role of gas migration on both processes.
 


Carbon Dioxide "Eruptions"

Image of Carbon Dioxide "Eruptions"

Carbon dioxide (CO2) is the most abundant gas released from erupting magma, but not all magma that rises up into the shallow crust erupts.  Magmas that stall below ground release their CO2 over time, and in certain circumstances, this CO2 can be trapped in subsurface gas reservoirs or redissolved in the bottom waters of deep, stratified lakes.  Large amounts of CO2 can be trapped in this way where it can cool to normal temperatures but build up to high pressures.  If some process destabilizes the trap, the CO2 can escape to the surface where it can be toxic to to both people and plants.  Top picture above shows Lake Nyos in Cameroon, where a cloud of CO2 released from the bottom waters asphyxiated 1700 people in 1986.  Middle picture shows thousands of trees killed at Mammoth Mtn. CA in the early 1990s when CO2 from a subsurface reservoir began to leak through the soil and poison the roots.  Bottom picture shows the effect of a CO2 outburst at Shrub Mud Volcano AK, where gas and saline mud blew out suddenly in the early 2000s.  My study of these and other similar events shows that such carbon dioxide "eruptions" are not as rare as previously thought.


Contact Information

William Evans
Bldg 15, McKelvey Building, 345 Middlefield Road
Menlo Park, CA 94025-3561
wcevans@usgs.gov
650-329-4514
650-329-5590 - Fax
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