Download Lake Nyos - UCSB Physics

Lake Nyos, Cameroon
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Lake 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.
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.
•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 CO2, 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
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