National Research Program


Volcanic Gas Hazards

Mammoth Mountain, Calif. and Cameroon

CO2 kills trees on Mammoth Mountain, California[An area of Mammoth Mountain where carbon dioxide was found to have suffocated tree roots.]

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. Reports of trees dying and dizziness in confined spaces (including at a large ski resort leasing slopes from the U.S. Forest Service) led to investigations by USGS. They found 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. Continued monitoring is critical since carbon dioxide gas is heavier than air and thus potentially dangerous to people in depressions, and poorly ventilated enclosures, such as cabins.

Another situation of carbon dioxide release occurred in the 1980's in Cameroon. More than 1500 people were killed when dissolved carbon dioxide that had accumulated in high concentrations at the bottom of two lakes was suddenly released into the atmosphere. USGS scientists were asked to help with the investigation of the Cameroon lakes and have been involved in efforts to avoid another catastrophe through controlled degassing of the lakes.

For additional information about the potential hazard at Mammoth Mountain, see the USGS fact sheet, Invisible CO2 gas killing trees at Mammoth Mountain, California; for information about efforts controlled degassing in Cameroon see Kling, G. W., Evans, W.C., Tanyileke, G., Kusakabe, M., Ohba, T., Yoshida, Y., and Hell, J. V., 2005, Degassing Lakes Nyos and Monoun – Defusing certain disaster: Proceedings of the National Academy of Sciences USA, v. 102, p. 14,185-14,190; or contact:

William C. Evans wcevans@usgs.gov, U.S. Geological Survey, 345 Middlefield Rd, MS439, Menlo Park, CA 94025

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