A strange event happened on August 21, 1986 in Cameroon. A resident of one of the villages in the north-west of the country, returning home at dawn, found all the villagers, as well as all the livestock dead. There was deathly silence around. Later it turned out that all living things within a radius of 23 kilometers from Lake Nyos died, which is about 1746 local residents and 155 tourists.
What happened that night? Scientists have found an explanation in Lake Nyos. It is located in the crater of a once active volcano. After the last eruption, magma corked at the bottom of the lake and continued to emit gases. Through the soil, these gases entered the groundwater and returned to the lake. In all crater lakes, water is periodically mixed, gases come to the surface and do not harm the environment. However, in Nyos, the boundaries between water layers are not violated. Gases saturate deep strata until some natural phenomenon (wind, landslide, earthquake) violates their integrity and releases gases outside. Then carbon dioxide breaks out at a tremendous speed and fills the surrounding space. Scientists have found that the strong wind was most likely the cause of the August 21 release.
After the release of gases, the water level in the lake dropped by one meter. The trees surrounding Nyos were fallen, as the gas escape looked like a violent explosion. About 35 thousand local residents were evacuated from the danger zone. Many people were severely poisoned by hydrogen and sulfur. Scientists have found that such emissions can occur once every 10-30 years. In 2011, a pipe was laid along the bottom of the lake, which brings gases to the surface and makes the lake safe for the environment.
Interestingly, in addition to Nyos, there are two more such lakes: Mamun - located 95 kilometers from Nyos, where in 1984 the same disaster occurred, in which 37 people died; Kivu - located DR Congo.