Monitoring:  | Gas | Ground Deformation | Hydrologic | Remote Sensing | Seismicity |

Measuring volcanic CO₂ gas from the air
with an infrared analyzer (LI-COR)

Multiple traverses made through a volcanic plume

Sketch by M. Doukas

Sketch shows an airplane traversing through a volcanic plume at several different altitudes downwind from an active volcano to measure the concentration of carbon dioxide gas with a LI-COR infrared analyzer. The aircraft flies through the plume several times at right angles to the path of the plume between 100 and 200 m apart. Each traverse begins and ends in air outside the plume and is referenced to one or more vertical GPS posts established in the plane of the plume cross section.

Because plume velocity is assumed to equal wind speed, scientists and the pilot must estimate wind speed by one or more methods. For example, wind speeds can be calculated by GPS or by comparing true air speed, flying with and against the wind (along axis of of the plume), with true ground speed. Wind speed is usually the chief variable that determines the precision of CO2 gas measurements.

References

Gerlach, T.M., McGee, K.A., Sutton, A.J., and Elias, T., 1998, Rates of volcanic CO₂ degassing from airborne determinations of SO₂ rates and plume CO₂/SO₂: Test study at Pu`u `O`o cone, Kilauea Volcano, Hawaii: Geophysical Research Letters, v. 25, n. 14, p. 2675-2678.

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