Lake Nyos is in Northwest Cameroon. It is a crater lake on the flank or edge of an extinct volcano in the Oku volcanic field. The lake waters are held back by a volcanic dam.
Causes
About 110 million years ago South America and Africa were split apart, a consequence is that this caused West Africa to experience rifting. The rift is known as the Mbéré Rift Valley, and because the crust is stretching apart magma has reached the surface beneath Lake Nyos. Lake Nyos is also surrounded by old lava flows and pyroclastic deposits. This pocket of magma beneath the lake leaks carbon dioxide (CO2) into the water, creating a weak carbonic acid.
IMPACTS
On August 21, 1986, possibly as the result of a landslide, Lake Nyos suddenly emitted a large cloud of CO2. 1,700 people suffocated together with 3,500 livestock in nearby towns and villages (within 25kms of the lake).Many of the victims had been poisoned by a mixture of gases including hydrogen and sulfur gases. This lead to burning pains in the eyes and nose, and coughing100,000 - 300,000 tons of CO2 released in a cloud rising at nearly 100 kilometres per hourThe worst affected villages were Cha, Nyos, and Subum. People suffocated in their sleep as CO2 is 1.5 times denser than air and hugged the ground.Following the eruption, many survivors were treated at the main hospital in Yaoundé, the country's capital.
One survivor, Joseph Nkwain from Subum, described himself when he awoke after the gases had struck:
"I could not speak. I became unconscious. I could not open my mouth because then I smelled something terrible . . . I heard my daughter snoring in a terrible way; very abnormal . . . When crossing to my daughter's bed . . . I collapsed and fell. I was there till nine o'clock in the (Friday) morning . . . until a friend of mine came and knocked at my door . . . I was surprised to see that my trousers were red, had some stains like honey. I saw some . . . starchy mess on my body. My arms had some wounds . . . I didn't really know how I got these wounds . . .I opened the door . . . I wanted to speak, my breath would not come out . . . My daughter was already dead . . . I went into my daughter's bed, thinking that she was still sleeping. I slept till it was 4:30 p.m. in the afternoon . . . on Friday. (Then) I managed to go over to my neighbors' houses. They were all dead . . . I decided to leave . . . . (because) most of my family was in Wum . . . I got my motorcycle . . . A friend whose father had died left with me (for) Wum . . . As I rode . . . through Nyos I didn't see any sign of any living thing . . . (When I got to Wum), I was unable to walk, even to talk . . . my body was completely weak." From A. Scarth (1999)
