Oku Volcanic Field

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Western Africa


Lake Monoun and Nyos, Oku Volcanic field, Cameroon


Lake Nyos is the most renowned of the numerous maars and basaltic cinder cones associated with the deeply dissected Mount Oku massif. The 1.2 x 1.9 km wide lake, seen here from the south, was the site of a gas-release event on August 21, 1986 that caused at least 1700 fatalities. Wave damage stripped the peninsula at the left of vegetation. The emission of around 1 cu km of magmatic carbon dioxide has been attributed to either non-volcanic overturn of stratified lake waters, to phreatic explosions, or to injection of hot gas into the lake. 

Photo Credit: Photo by Jack Lockwood, 1986 (U.S. Geological Survey).

The Oku volcanic field is made of maars. Lake Nyos is inside the crater of one of the maars that formed about 400 years ago. The maar formed during an explosive eruption of carbon dioxide gas. The lake is about 5,900 feet (1,800 m) across and 682 feet (208 m) deep. 

map of the area
Map of the Cameroon Line and Benue Trough, after Fitton and Dunlop (1985). Volcanic rocks are shown in black.
The approximate position of lakes Monoun and Nyos are indicated by stars.

On August 21,1986, a cloud of carbon dioxide gas was released from Lake Nyos. Because carbon dioxide is more dense than air it hugged the ground and flowed down valleys. The cloud traveled as far as 15 miles (25 km) from the lake. It was moving fast enough to flatten vegetation, including a few trees. 1,700 deaths were caused by suffocation. 845 people were hospitalized. 

Sources of Information:

Fitton, J. G., 1980, The Benue Trough and Cameroon Line- a migrating rift system in West Africa: Earth and Planetary Science Letters, v. 51, p. 132-138.

Le Marechal, A., 1975a, Carte geologique de l'ouest du Cameroun et de l' Adamaoua, 1:1,000,000; ORSTOM.

Le Marechal, A., 1975b, Directions structurales de l'ouest du Cameroun et de l'Adamaoua, 1:1,000,000; ORSTOM.

Evans, W.C., Kling, G.W., Tuttle, M.L., Tanyileke, G., and White, L.D., 1993, Gas buildup in Lake Nyos, Cameroon: The recharge process and its consequences: Applied Geochemistry, v. 8, p. 207-221.

Evans, W.C., White, L.D., Tuttle, M.L., Kling, G.W., Tanyileke, G. and Michel, R.L., 1994, Six years of change at Lake Nyos, Cameroon, yield clues to the past and cautions for the future: Geochemistry, v. 28, p. 139-162.

Kling, G.W., Tuttle, M.L., and Evans, W.C., 1989, The evolution of thermal structure and water chemistry in Lake Nyos: Journal of Volcanology and Geothermal Research, v. 39, p. 151-165.

Lockwood, J.P., and Rubin, M., 1989, Origin and age of the Lake Nyos maar, Cameroon: Journal of Volcanology and Geothermal Research, v. 39, p. 117-124.

Lockwood, J.P., Costa, J.E., Tuttle, M.L., Nni, J., and Tebor, S.G., 1988, The potential for catastrophic dam failure at Lake Nyos maar, Cameroon: Bulletin of Volcanology, v. 50, p. 340-349.

Sigvaldason, G.E., 1989, International conference on Lake Nyos disaster, Yaounde, Cameroon 16-20 March, 1987: Conclusions and recommendations: Journal of Volcanology and Geothermal Research, v. 39, p. 97-109.

Simkin, T., and Siebert, L., 1994, Volcanoes of the World: Geoscience Press, Tucson, Arizona, 349 p.

Tazieff, H., 1989, Mechanisms of the Nyos carbon dioxide disaster and of so-called phreatic steam eruptions: Journal of Volcanology and Geothermal Research, v. 39, p. 109-116. 
Information Contacts: C. Twining, American Embassy, Douala; Yaoundé Domestic Radio Service.