http://www.pbs.org/wnet/savageplanet/01volcano/01/indexmid.html
See
Related Links At Bottom of this Article
[ See
photograph of gas-driven fountain in Lake Nyos, Cameroon...
]
Degassing Lake
Nyos, Cameroon, Africa
Some 1,700 people living
in the valley below Lake Nyos in
northwestern Cameroon mysteriously died on the evening of
August 26, 1986. Word of the disaster spread, and scientists
arrived from around the world. What they discovered was 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.
The disaster, however
odd, wasn't unique. Two years earlier,
Lake Monoun, 60 miles to the southeast, released a heavy cloud
of toxic gas, killing 37 people. A third lake, Lake Kivu,
on the Congo-Rwanda border in Central Africa, is also known
to act as a reservoir of carbon dioxide and methane,
a valuable natural gas that is gathered from the lake
and used locally.
These three lakes are
the only ones in the world known
to contain high concentrations of carbon dioxide in their
waters. More typically, the gas is released into the
atmosphere in harmlessly bubbling soda springs, which
can be found around the world.
Gas Under Pressure
The science behind
the disaster is fairly simple. Lake Nyos
is a deep pool of water sitting in the throat of a dormant
volcano. The real culprit is a pool of hot magma, laying
almost 50 miles below the lake. The magma 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. The amount of gas that can be dissolved in the
water is dependent on water temperature and pressure.
The greater the pressure, the more gas can be trapped.
None of this would be particularly hazardous if the water
at the bottom of the lake were to regularly rise to the
surface, where the gas could be safely released.
The problem is that the waters of Lake Nyos, like many
tropical lakes, are steady and still, with little annual
mixing of the water layers.
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, creating a foaming column of carbonated
water. This eruption, or release, can be triggered even
before saturation is reached by a landslide, earthquake,
violent storm, or other disturbance of the waters.
The eruption itself
isn't dangerous, but the suddenly
released gas cloud can be fatal. 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.
Carbon dioxide normally makes up 0.03% of air, and
concentrations of more than 10% can be fatal. The
unfortunate villagers around Lake Nyos literally
suffocated under the heavy poisonous cloud of gas.
Degassing
the Lake
Today, both Lake Nyos
and Lake Monoun contain more gas
than was released during the last disasters. At the very
greatest depths, Lake Nyos is about 60% saturated with
carbon dioxide, and the waters of Lake Monoun are
83% saturated. Recent scientific studies show that
the gas concentrations in both lakes is increasing
rapidly, and that another lethal gas release is inevitable.
Currently, there is
funding to place one pipe in Lake Monoun,
which will slowly remove the gas stored in the lake over
the next five years. A pipe will also be placed in
Lake Nyos, which should be sufficient to prevent the
further build up of carbon dioxide, but since this lake
is considerably bigger than Monoun, six to ten pipes
will eventually be needed to remove all the gas stored
in the lake.
The vent pipes should
be placed in September 2000, just
after the next rainy season. Since this plan is novel,
and results a little uncertain, the scientists installing
the pipes will evacuate everyone from the area while
the work is underway.
-- By Micah Fink
Related Links:
http://www.biology.lsa.umich.edu/~gwk/research/nyos.html
Degassing Lake Nyos and Monoun
http://volcano.und.nodak.edu/vwdocs/volc_images/africa/nyos.html
Landsat Imagery of Lake Nyos, Oku Volcanic field, Cameroon
http://perso.wanadoo.fr/mhalb/nyos/index.htm
Lake Nyos Degassing Project
http://perso.wanadoo.fr/mhalb/nyos/webcam.htm
Real-Time Webcam at Lake Nyos, Cameroon
http://perso.wanadoo.fr/mhalb/nyos/project/1995galery.htm
Gallery of 1995 pictures showing successful degassing project
http://perso.club-internet.fr/richon/richon/Webcam_nyos/History_Image_webcam/Image_archives.htm
See archive of webcam images for spectacular 50 meter high fountain
http://www.naturalworldtours.co.uk/articles2003/march/march0103c.htm
Lake Kivu could power all of Rwanda
