Volcanic Gas Hazard
Mammoth Mountain, Calif.
Erupting volcanoes emit vast amounts of gases, particularly carbon dioxide and sulfur compounds, that are toxic to humans. Dormant volcanoes can also release potentially toxic gases; such non- eruptive gas has been responsible for nearly 2000 deaths world-wide in the past decade or so. USGS personnel have investigated this type of gas hazard throughout the world for many years. Mammoth Mountain, in eastern California, is dormant but lies in a region characterized by frequent and occasionally catastrophic volcanic activity. Recently there have been reports of trees dying and dizziness in confined spaces (including at a large ski resort leasing slopes from the U.S. Forest Service). USGS scientists demonstrated that diffuse seepage of odorless carbon dioxide up through the soil zone was suffocating the tree roots and producing lethal concentrations in poorly ventilated structures and showed that the area affected by gas flow through the soil is much larger than the present-day area of tree kill. Future efforts of USGS personnel will focus on better defining the hazards associated with the gas buildup. Important questions to be addressed are: Where is there possible gas poisoning risk to the public? Is dissolved gas reaching problem levels in any of the lakes near the mountains? (More than 1500 people were killed in the 1980s in Cameroon when dissolved carbon dioxide that had accumulated in high concentrations at the bottom of two lakes was suddenly released into the atmosphere -- another study that USGS scientists were asked to investigate.) Does the high flow rate signify dangerous gas pressure buildup within the mountain? What should be the response to a sudden increase or decrease in the flow rate?
Farrar, C.D., Sorey, M.L., Evans, W.C., Howle, J.F., Kerr, B.D., Kennedy, B.M., King, C-Y, and Southon, J.R., 1995, Forest-killing diffuse CO2 emission at Mammoth Mountain as a sign of magmatic unrest: Nature, v. 376, p.675-678.
For additional information, see the project, Hydrogeochemical and Biogeochemical Studies of Volcanic, Geothermal, and Selenium-Impacted Systems or contact:
William C. Evans
U.S. Geological Survey, 345 Middlefield Rd, MS434, Menlo Park, CA 94025