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USGS - science for a changing world


Andrew G Hunt

Research Geologist

Geology, Geophysics, and Geochemistry Science Center

Office Phone: 303-236-4931
Fax: 303-236-4930
ORCID: 0000-0002-3810-8610

Building 95
P.O. Box 25585, Denver Federal Center, Mail Stop 963
Lakewood , CO 80225-0585

Supervisor: Warren C Day
Degassing thermal features at Yellowstone National Park include spectacular geysers, roiling hot springs, bubbling mud pots, fumaroles, frying pans, and areas of passive degassing characterized by steaming ground. Most of these features are readily identified by visible clouds of steam that are occasionally accompanied by a strong “rotten egg” odor from emissions of hydrogen sulfide gas. Gas compositions typically are greater than 90% carbon dioxide with lesser amounts of helium, hydrogen, hydrogen sulfide, methane, nitrogen and other trace components. The composition of the gas and relative amounts of gas and steam relate both to the type of feature as well as the geographic location within the park. In 2003 we...
Mammoth Mountain is a dacitic dome complex located on the southwestern rim of Long Valley Caldera, California. Mammoth Mountain has exhibited unrest over the past ~30 years, characterized by seismicity over a broad range of depths, elevated 3He/4He ratios in fumarolic gas and large-scale diffuse CO2 emissions. Monitoring of this unrest has included collection of fumarole gas samples for geochemical analysis and tree cores for radiocarbon analysis of annual growth rings. This report updates the long-term geochemical record at Mammoth Mountain, compiling the chemical and isotopic (d13C-CO2, 3He/4He) compositions of 59 gas samples collected from Mammoth Mountain fumarole from 1998 to 2016. In addition, we report radiocarbon...
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