By United States Geological Survey – United States Geological Survey, Public Domain, Link
Lake Nyos, locally known as the “Bad Lake”, is a crater lake in the Northwest Region of Cameroon. A pocket of magma lies beneath the lake and leaks carbon dioxide into the water, changing it into carbonic acid. In 1986, possibly as the result of a landslide, Lake Nyos suddenly emitted a large cloud of carbon dioxide, which suffocated 1,746 people and 3,500 livestock in nearby towns and villages. 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 to the top, allowing the carbon dioxide to leak in safe quantities, was installed in 2001. 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.
info source: wikipedia
By Jack Lockwood, USGS – http://www.volcano.si.edu/world/volcano.cfm?vnum=0204-03-&volpage=photos&photo=002064, Public Domain, Link
Artificial carbon dioxide vent in Lake Nyos – By Photographer: Bill Evans, USGS – http://gallery.usgs.gov/photos/02_06_2012_qvm8PCb54J_02_06_2012_0#.Uun_0ffTnrd, Public Domain, Link
Cattle suffocated by carbon dioxide from Lake Nyos – By Photo by Jack Lockwood of the US Geological Survey. – http://volcano.und.nodak.edu/vwdocs/volc_images/africa/nyos.html, Public Domain, Link
Public Domain, Link