Lake Nyos, Cameroon

•Lake NyosLake Nyos

Lake Monoun•

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., H2S, also CH4, CO2).

• 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 CO2 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.

•Volcanic

Hot gases are injected into the lake, along with lava, during a volcanic eruption.

•Magmatic

Volcanic activity under the earth’s surface produces CO2, which seeps through the rock and sediments at the lake bottom and bubbles out in warm springs.

The predominant gas dissolved in the lake was found to be CO2. Radiocarbon dating showed it to be >35,000 years old, much older than the lake, estimated to be a few centuries old.

A volcanic eruption would raise the temperature of the lake significantly. There was no such observed temperature rise.

The most likely candidate!

Interesting Lakes

Besides Lakes Monoun and Nyos, only one other lake in the world is known to collect CO2. It is Lake Kivu, on the Congo-Rwanda border. This lake also collects CH4, 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 CO2 in solution.

•Temperature profile of lake is such that the lake is stratified.

•One or more CO2 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 CO2, is now under much lower pressure, and the CO2 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