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Lake Nyos


SomeLake Nyos Sidebar 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.



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. House in the village of Nyos.

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.



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.

Lake NyosIn an effort to side-step another catastrophe, an international team of scientists, supported by the U.S. Office of Foreign Disaster Assistance, have developed a plan to try to remove the gas from the lakes. The plan is to place large pipes in Lakes Nyos and Monoun. These pipes, each about five inches in diameter, will be placed on a floating platform and sent down to the lowest layers of water, creating a vent to the surface. Water will be pumped from the bottom of the lake, and the gas-water fountain that results releases the carbon dioxide harmlessly into the atmosphere.

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


 

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