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Lake Nyos
Lake Nyos is a crater lake in the Northwest Region of Cameroon, located about northwest of Yaoundé. Nyos is a deep lake high on the flank of an inactive volcano in the Oku volcanic plain along the Cameroon line of volcanic activity. A volcanic dam impounds the lake waters.
A pocket of magma lies beneath the lake and leaks carbon dioxide (CO2) into the water, changing it into carbonic acid. Nyos is one of only three known exploding lakes to be saturated with carbon dioxide in this way, the others being Lake Monoun, also in Cameroon, and Lake Kivu in Democratic Republic of Congo. On August 21, 1986, possibly as the result of a landslide, Lake Nyos suddenly emitted a large cloud of CO2, which suffocated 1,700 people and 3,500 livestock in nearby towns and villages.〔New York Times, "Trying to Tame the Roar of Deadly Lakes", February 27, 2001. ().〕 Though not completely unprecedented, it was the first known large-scale asphyxiation caused by a natural event. To prevent a recurrence, a degassing tube that siphons water from the bottom layers of water to the top allowing the carbon dioxide to leak in safe quantities was installed in 2001, and two additional tubes were installed in 2011.
Today, the lake also poses a threat because its natural wall is weakening. A geological tremor could cause this natural levée to give way, allowing water to rush into downstream villages all the way into Nigeria and allowing large amounts of carbon dioxide to escape.
==Geography==
Lake Nyos lies within the Oku Volcanic Field, located near the northern boundary of the Cameroon Volcanic Line, a zone of volcanoes and other tectonic activity that extends southwest to the Mt. Cameroon stratovolcano. The field consists of volcanic maars and basaltic scoria cones.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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