18 YEARS AGO TODAY

Aug 21 1986
1,700 people are killed in Cameroon when Lake Nyos emits a huge cloud of fast-moving fog, quickly enveloping the villages of Nyos, Kam, Cha, and Subum and killing thousands of cattle and even more birds and wild animals. One eyewitness later describes the landscape as being "littered with human remains and animal carcasses."
Scientists discovered that the crater lake, perched inside a dormant volcano, had become laden with carbon dioxide gas. This gas had suddenly bubbled out of the lake and asphyxiated nearly every living being in the surrounding valley community.
Lake Nyos is a deep pool of water sitting in the throat of a dormant volcano. A pool of hot magma, laying almost 50 miles below the lake, releases the carbon dioxide and other gases, which travel upward through the earth. The gases gets trapped in natural spring water, which eventually rises toward the surface and feed into the crater lake.
The carbon dioxide, instead of being released harmlessly into the atmosphere, collects in the cold water at the bottom of the lake. If the water at the bottom of the lake were to regularly rise to the surface, the gas could be safely released. The problem is that the waters of Lake Nyos are steady and still.

Degassing Nyos: perso.wanadoo.fr/mhalb/ nyos/project/project.htm
Over time, the lowest levels of the lake become more and more saturated with gas. And eventually, when they reach 100% saturation, the gas can bubble spontaneously out of the lake.
Carbon dioxide is heavier than air, and when released, it pours over the rim of the crater and slides down into the surrounding low-lying valley. The unfortunate villagers around Lake Nyos literally suffocated under the heavy poisonous cloud of gas.
-Savage Planet
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