HR: 1340h
AN: V43D-1441    [Abstracts]
TI: Carbon Dioxide Emissions From Kill Zones Around the Resurgent Dome, Long Valley Caldera, CA
AU: * Bergfeld, D
EM: dbergfel@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road MS 434, Menlo Park, CA 94025 United States
AU: Evans, W C
EM: wcevans@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road MS 434, Menlo Park, CA 94025 United States
AU: Farrar, C D
EM: cdfarrar@usgs.gov
AF: U.S. Geological Survey, 5229 North Lake Blvd, Carnelian Bay, CA 96140 United States
AU: Howle, J F
EM: jfhowle@usgs.gov
AF: U.S. Geological Survey, 5229 North Lake Blvd, Carnelian Bay, CA 96140 United States
AB: An episode of seismic unrest beneath the resurgent dome at Long Valley caldera (LVC) in eastern California began in 1980 and is associated with approximately 80 cm of cumulative uplift on parts of the dome since that time. Studies of hydrologic and geochemical parameters can be useful in determining the source of uplift; and of particular relevance here, studies of diffuse soil degassing and temperature have been used to examine relations between gas emissions, uplift, and energy release. We present results from an eighteen-month investigation of soil temperature, soil-gas chemistry and CO$_{2}$ efflux from fourteen discrete areas of vegetation kill that have appeared inside the caldera over the past two decades. Compared with the tree-kill around Mammoth Mountain on the southwest rim of the caldera, dead zones we studied around the resurgent dome are small. Individually the areas cover between 800 and 36,000 m$^{2}$. All of the areas have some sites with elevated CO$_{2}$ flux and elevated soil temperature. \delta $^{13}$C values of CO$_{2}$ from sites in eight of the studied areas are between -5.7 and -3.9\permil, and are within the range of magmatic CO$_{2}$. Results from the flux measurements indicate that on average total CO$_{2}$ emissions from four of the areas sum about 10 tonnes per day. The other vegetation kill areas currently have only a few sites that exhibit anomalous soil temperatures and CO$_{2}$ flux, and CO$_{2}$ emissions from these areas are typically less than 0.3 of a tonne per day. The chemical composition of gas emissions from thermal ground in kill zones located 1.5 to 2 km northwest of the Casa Diablo geothermal power plant demonstrate a connection between some of the dead areas and perturbations related to geothermal fluid production. These results and estimates of thermal output from two of the high flux grids are used to evaluate the premise that the gaseous and thermal anomalies are related to magmatic intrusion beneath the resurgent dome.
DE: 8400 VOLCANOLOGY
DE: 8424 Hydrothermal systems (8135)
DE: 1040 Isotopic composition/chemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting