Measuring volcanic gases: continuous on-site gas monitoring
Continuous gas-monitoring site,
Kilauea Volcano
Photograph by J.D. Griggs on June 11, 1991
Continuous gas-monitoring stations have the advantage of being able to detect both short-lived degassing events that occur in time periods lasting minutes to hours as well as long-term changes that occur over days to years. A station can be tailored to monitor fumarole gases, the air, or soil gases depending on the goals of the specific volcano monitoring strategy. Data are typically taken from the sensor(s) every few minutes and sent by radio, satellite, or telephone line to a receiving site.
The descriptions below highlight the continuous gas monitoring stations
currently used by USGS scientists to monitor activity at Kilauea Volcano, Hawai`i
and Long Valley Caldera, California.
Gas studies at the USGS Hawaiian Volcano Observatory (HVO) are conducted in
order to assess current eruptive activity and hazards of Kilauea and Mauna
Loa volcanoes and to improve our understanding of how these and other
volcanoes work. Hawaiian volcanoes, because of their accessibility and
effusive nature, serve as an ideal test sites for developing new techniques
for volcanic gas studies. Among these techniques is continuous gas
monitoring. Station near Pu`u `O`o A small computer at this gas monitoring site, located on Kilauea's east
rift zone, controls instrumentation which periodically samples the air near
the Pu`u `O`o vent (cone in background). Chemically-selective sensors for SO2 and CO2
measure gas concentrations and a wind sensor measures wind speed and
direction. Data from this solar-powered station are transmitted to HVO every
10 minutes, providing near real time data on degassing from Pu`u `O`o.
Air-quality Instruments An ambient air quality monitoring station located at the summit of Kilauea
is operated cooperatively by the National Park Service and the USGS. The
station measures concentrations of SO2 gas down to the part per
billion (ppb) level in order to provide information about the impact of volcanic
emissions on air quality. Data from this site help confirm the importance of
wind speed and direction on the geographic distribution and concentration of
volcanic air pollution. This station is part of a nationwide network of air
monitoring sites that operate within National Parks.
During specific wind regimes, emissions from the main degassing sources
of Kilauea impact the populated summit area. Data from this site show that
federal health standards for SO2 (145 ppb) have been exceeded on
more than 80 occasions during the past 13 years. An alert system using the
data from this station informs staff of the Hawai`i Volcanoes National Park
of the presence of potentially unhealthy concentrations of SO2
gas during episodes of very poor air quality.
Continuous gas monitoring at Kilauea Volcano, Hawai`i
Continuous gas monitoring near vents
Air quality monitoring in Hawai`i Volcanoes National Park
monitoring station
inside trailer
Continuous gas monitoring at Long Valley caldera, California
A network of gas-monitoring stations is currently tracking CO2 concentrations in the shallow soils at several locations around Mammoth Mountain volcano and nearby areas. Each station collects data from its sensors at least every hour and transmits the stored data every three hours to a GOES geostationary satellite. The data are evaluated by scientists at the USGS Cascades Volcano Observatory.
Scientists from Pensylvannia State University, in cooperation with the USGS, operate 1-2 monitoring stations that measure carbon dioxide soil efflux for part of the year.
CO2 degassing event captured by continuous monitoring
CO2 (percent) in soil and earthquakes
in Long Valley caldera,
Sept. 1997 - Jan. 1998
The CO2 monitoring stations around Mammoth Mountain recorded a large degassing event in the fall of 1997. The event lasted about two months. The elevated CO2 concentration correlated well to a period of intense seismic activity in the south-central part of Long Valley caldera. The earthquakes occurred in response to the intrusion of magma beneath the caldera and right-lateral faulting in the south moat seismic zone.
Programming GOES satellite transmitter
Long Valley caldera
USGS scientist programs a GOES satellite transmitter at a carbon dioxide monitoring site near Mammoth Lakes, California. Satellite telemetry offers the advantage of being able to locate monitoring stations without regard to access to telephone lines or short-distance radio links.
References
McGee, K.A., Sutton, A.J., and Sato, Motoaki, 1987, Use of satellite telemetry for monitoring active volcanoes, with a case study of a gas-emission event at Kilauea Volcano, December 1982, in Decker, R.W., Wright, T.L., and Stauffer, P.H., eds., Volcanism in Hawaii: U.S. Geological Survey Professional Paper 1350, p. 821-825.McGee, K.A., and Sutton, A.J., 1994, Eruptive activity at Mount St. Helens, Washington, USA, 1984-1988: a gas geochemistry perspective: Bulletin of Volcanology, v. 56, n. 6-7, p. 435-446.
McGee, K.A. , Gerlach, T.M., Kessler, R., and Doukas, M.P., 2000, Geochemical evidence for a magmatic CO2 degassing event at Mammoth Mountain, California, September-December 1997: Journal of Geophysical Research, v. 105, n. B4, p. 8447-8456.
McGee, K.A., and Gerlach, T.M., 1998, Annual cycle of magmatic CO2 in a tree kill soil at Mammoth Mountain: Implications for soil acidification: Geology, v. 26, n. 5, p. 463-466.
