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The 21 August 1986 Lake Nyos gas disaster, Cameroon; final report of the United States scientific team to the Office of U.S. Foreign Disaster Assistance of the Agency for International Development

1987; United States Department of the Interior; Linguagem: Inglês

10.3133/ofr8797

2332-4899

Michele L. Tuttle, Morgan Clark, H.R. Compson, Joe Devine, William C. Evans, A.M. Humphrey, Gerhard Kling, E.J. Koenigsberg, J.P. Lockwood, Gudrun Wagner,

Disaster Management and Resilience

The sudden catastrophic release of gas from Lake Nyos on 21 August 1986 caused the deaths of at least 1700 people in the northwest area of Cameroon.An eleven-person multidisciplinary team was sent for three weeks to investigate the cause and to recommend steps to mitigate future hazards of this nature.The results of the field and laboratory investigations are:* Lake Nyos occupies a volcanic crater that was formed by a violent explosion only a few hundred years ago.Underlying the lake is a volcanic pipe that serves as a conduit for the gradual upward migration of carbon dioxide (CO 2 ) from deep within the earth.Over a long period of time, gas dissolved in groundwater has been accumulating in the bottom water of the lake r creating a potential hazard.* Chemical, isotope, and geologic evidence supports the hypothesis that the CO2 was derived from deep-seated magmatic sources, but that no direct volcanic activity was involved in the disaster.* An undetermined mechanism triggered a catastrophic release of CO2 from the lake, which created a lethal cloud that flowed downhill into populated areas.* The victims exposed to the cloud rapidly lost consciousness due to displacement of oxygen in the air and high levels of CO2 .Death was due to asphyxiation.Skin lesions on many survivors are thought to be pressure sores due to long periods of unconsciousness and immobility.* High concentrations of CO2 remain dissolved in Lake Nyos, representing a potential hazard until they can be safely lowered.The possibility of a failure of the weak natural dam at the lake outlet poses an additional hazard.* Other lakes in northwest Cameroon may also have the potential for catastrophic release of lethal quantities of CO2 .Field investigations are required to identify those lakes.* A method is proposed to reduce or eliminate the gas hazard at Lake Nyos and at other potentially dangerous lakes that may be revealed by future field investigations.