Lake Nyos is located in northwestern Cameroon. Under its waters lies a pocket of volcanic magma, out of which CO₂ seeps and dissolves into the lake's water. On August 21, 1986, something—most likely a landslide, but possibly an earthquake or thunderstorm—triggered the release of a large amount of CO₂ from the lake. The gas spread up to 15 miles from the lake in a thick, suffocating cloud. Some people managed to escape, but 1,746 died, and thousands of animals were killed by a lack of oxygen. On the advice of scientists,
a pumping system was installed in the lake in 2001.
Lake Monoun is near Lake Nyos in Cameroon. On the night of August 15, 1984, people living near the lake heard a strange boom. It came from the lake, which released a CO₂ cloud that spread out and suffocated 37 people, including 10 people in a truck (according to published reports, two people sitting on the truck's roof, above the CO₂ cloud, survived). What triggered the disturbance is still unknown. Pumps were installed in 2003 to avert a repeat disaster.