Airborne detection of diffuse carbon dioxide gas at Mammoth Mountain, California
Since 1994, scientists have measured the emission of CO2
from around Mammoth Mountain volcano in California by conducting numerous
soil efflux surveys. Because such surveys take several days to complete,
they may not be practical or safe at times of increasing volcanic unrest
when more frequent measurements are needed. Airborne surveys of carbon
dioxide are much faster (taking 1-2 hours), but there was reason to doubt
whether the LI-COR infrared analyzer could detect the diffuse degassing
of cold CO2 known to occur in a volcanic area like Mammoth
Mountain. An experiment in 1998 to test the capability of the LI-COR,
however, clearly demonstrated that low emission rates of CO2
can be measured. Airborne traverses were made around Mammoth Mountain to measure CO2.
The cylindrical "lampshade" around the volcano in the image
shows the areas of the traverses.
Wind direction during the survey was toward the south-southwest (in the same general direction of the photograph, above right).
The contour map clearly shows a region of high CO2 downwind from the mountain at 6-7 km horizontal distance along the lampshade and at an altitude of 2,900-3,200 m. This area of peak concentration corresponds to areas of dead trees on the south side of Mammoth Mountain. The trees were killed by high concentrations of carbon dioxide gas in soil that began to appear in 1990 after an earthquake swarm during the last half of 1989. The earthquake swarm was associated with an intrusion of magma beneath Mammoth Mountain, and this shallow magma body is the most likely source of the CO2 now leaking to the surface.
The high CO2 concentration shown on the contour map represents an emission rate of about 250 tonnes/day of carbon dioxide.
Gerlach, T.M., Doukas, M.P., McGee, K.A., and Kessler, R., 1999, Airborne detection of diffuse carbon dioxide emissions at Mammoth Mountain, California: Geophysical research letters, vol. 26, n. 24, p. 3661-3664.
Methods of monitoring volcanic gases
- Measuring gas-emission rates in volcanic plumes
- Direct gas sampling and laboratory analysis
- Continuous on-site gas monitoring
- Soil-efflux measurements