Abstract
Mammoth Mountain, a rhyolite to dacite volcanic dome complex on the southwestern rim of the Long Valley Caldera in eastern-central California, has shown signs of renewed volcanic unrest since the early 1980s. High concentrations of ambient temperature volcanogenic carbon dioxide ( CO2) are being emitted from the flanks of the mountain, and this magmatic gas is responsible for large areas of dead vegetation around the mountain since 1990. Shallow magmatic intrusions, inferred from seismic activity, ground deformation, and changes in fumarolic gas composition on and around Mammoth Mountain began in 1989 and have been interpreted as the source ofthe CO2 gas. Airborne and satellite-based digital remote sensing image data for the field area, collected using multi- and hyperspectral [NS00l (TMS), MASTER, ASTER and AVIRIS] aircraft sensors, are evaluated using the ENVI© Image Processing software to map the spatial and temporal variation in the distribution of magmatic CO2-induced tree kills between 1991 and 2004. Field spectral measurements have been incorporated into the remote sensing evaluation to establish the reflectance characteristics of the field area. These provide ground truth spectral endmembers and improve the quality of the remote sensing analyses. Areas of CO2-induced vegetation death were mapped using standard image processing techniques and the Mixture Tuned Matched Filtering algorithm. All image data sets and their associated tree-kill mapping results were geo-registered to a common base map. The results of the temporal remote sensing assessment are integrated into a geographic information system (GIS) with a detailed geologic map (1 :20,000 scale) of the field area. The GIS process highlights relationships between surface geology and areas oftree mortality. The CO2-induced tree kill areas identified here closely match previous study results documenting high CO2 soil gas concentrations and areas of high CO2 flux emanating from the soil. The GIS evaluation of remote sensing results and the corresponding geologic features identified structural controls for the CO2-induced tree kill areas. The remotely-sensed tree kills correlate with mapped faults and contacts of lava domes and flows, and are aligned with previously unmapped, covered and/or obscured faults and geologic contacts. Areas of elevated CO2 venting and the resultant dead vegetation allow interpretation of the subsurface structural control for magmatic gas migration.