Lake Nyos, Cameroon

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Lake Nyos, Cameroon
Lake Nyos
Lake Monoun
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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.
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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.
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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. Magmati
c Volcanic activity under the earths 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 gt35,000 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!
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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.
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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. Temperatu
re 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.
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Can Something be Done?
NYOS-MONOUN DEGASSING PROJECT January 2001 Lake
Nyos Pipe Installation Cameroonian-French-Japanes
e-USA Team
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