Airborne detection of diffuse carbon dioxide gas at Mammoth Mountain, California

View of Mammoth Mountain toward the south

View of Mammoth Mountain
toward the south.

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.

Graph of carbon dioxide concentrations (ppm) in air around Mammoth Mountain on 13 November 1998.

This "lampshade" contour map of CO2 concentration (parts per million above background) in air around Mammoth Mountain volcano, California, was generated with data collected on 13 November 1998 using the LI-COR infrared analyzer. Scientists made eleven complete traverses around Mammoth Mountain at various altitudes; each traverse had a diameter of about 6-7 km. Thus, the eleven orbit survey defined a cylindrical "lampshade" around Mammoth Mountain (photograph, right). Only part of the "lampshade" is shown in the contour map.

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.

Reference

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