Lake Nyos Cameroon Lake Monoun Lake Nyos In

Lake Nyos, Cameroon • • Lake Monoun Lake Nyos

In August, 1986, 1, 700 to 1, 800 people living in the valley below Lake Nyos died mysteriously, along with about 3, 000 cattle, at distances as great as 27 km from the lake. In August, 1984, 37 people died mysteriously near Lake Monoun. Both disasters occurred at night.

What happened? • Biogenic action in lakes can produce toxic gases (e. g. , H 2 S, also CH 4, CO 2). • Reports of loud noise from the lake; flashes of light? • Lake turned reddish after event; shores disturbed by waves, wind. • Lake sits atop an extinct volcano. • Symptoms among survivors consistent with CO 2 poisoning. Six days afterwards, a U. S. team of scientists traveled to Lake Nyos to investigate. Their findings appeared in "Science" in April of 1987.

Sources of Gas in a Lake • Biogenic Anaerobic digestion of organic matter produces gases, which build up until a disturbance causes a sudden release. The predominant gas dissolved in the lake was found to be CO 2. Radiocarbon dating showed it to be >35, 000 years old, much older than the lake, estimated to be a few centuries old. • Volcanic Hot gases are injected into the lake, along with lava, during a volcanic eruption. A volcanic eruption would raise the temperature of the lake significantly. There was no such observed temperature rise. • Magmatic Volcanic activity under the earth’s surface produces CO 2, which seeps through the rock and sediments at the lake bottom and bubbles out in warm springs. The most likely candidate!

Interesting Lakes Besides Lakes Monoun and Nyos, only one other lake in the world is known to collect CO 2. It is Lake Kivu, on the Congo-Rwanda border. This lake also collects CH 4, which the locals gather and use. Usually, the carbon dioxide bubbles harmlessly into the atmosphere, as in soda springs, which exist all over the world.

What caused the Lake Nyos disaster? • Carbon dioxide produced by volcanic activity seeps into bottom of lake. • Bottom of lake is cold, under high pressure; water there can hold high concentration of CO 2 in solution. • Temperature profile of lake is such that the lake is stratified. • One or more CO 2 bubbles form at the bottom of the lake, either spontaneously (on some surface at the bottom) or via a disturbance (such as something falling into the lake). As they rise, they pull other bubbles with them, soon causing a sudden turnover of the lake. Water from the bottom, with high concentrations of CO 2, is now under much lower pressure, and the CO 2 now bubbles out suddenly and violently.

Can Something be Done? NYOS-MONOUN DEGASSING PROJECT January 2001 Lake Nyos Pipe Installation Cameroonian-French-Japanese-USA Team