Lake Nyos

The Lake Nyos (actually Lake Lwi , become popular under the name of Lake Nyos ; Nyos being the name of the village which shelters this Lake) is a lake of crater located in the province of the North-West of the Cameroun, with the coordinates. The lake Nyos is a lake of altitude, on the side of a inactive Volcan close to the Mont Oku, along the Cameronian Ceinture of active volcanos. A natural Stopping of volcanic rocks trap water of the lake.

The tragedy of August 21st, 1986

The August 21st 1986, in the evening, the lake Nyos, in the North-West of the Cameroun, exploded and released approximately a cubic kilometer of carbonic gas CO₂ causing the death of more than 1700 people as well as many animals.

According to one of the theses suggested to explain this atypical eruption, the carbonic gas, of mantellic origin, would be gradually stored in deep water of the lake and would escape from it under the effect of a " renversement" lake, caused by a Seism or a Landslide.

The process of ex-solution started and developed in the whole of water of the lake by a chain reaction. A gas explosion projected in the airs a column of water to a height exceeding 80 Mr. The enormous quantity of released carbonic gas, being denser than the air, has then " run " in the neighbouring valleys by asphyxiating any form of life up to 30 km of the lake.

The thesis of the reversal of water of the lake was and remains formally contradicted by French and Italian scientists. Their analyzes establish the permanence of the stratification of water of the lake, including during new explosions observed later on. For these teams, the analyzes of the chemistry of the gazs and that of water show all that the assumption of a consecutive degasification of deep water to an inversion of the lower and higher layers of the lake, cannot give an account of the phenomenon. Among the many remarks, the appearance in the central part of the lake of a circle of red color constant of approximately 75 meters of ray, reinforces with as much the assumption of a phreatic eruption that the analyzes of the content CO2 of water of the lake carried out each day of at the end of August at the end of September 1986 establish that very little dissolved CO2 was released at the time of the catastrophe. Degasification created an unequal wave (1 meter in north, 80 meters in the center and 20 meters in the south) which can interpéter only by a relatively powerful water jaillissemnt. The granite of the edges of the lake was pickled on a narrowly localized tape, which can also be explained only by the repercussion of an important water mass, since a height from 100 to 200 meters above affected surface. The assumption of an eruptive process (phreatic eruption) only makes it possible to give of it an account, as it could give an account of the catastrophe of Diëng, in Indonesia.

The controversy which divides the scientists is obviously crucial as regards prevention of the risks for the surrounding populations. The degasification of water of lakes of maars thus does not achieve the unanimity of the researchers.

Film of Mr. and K. Kraft on this tragedy.

Organ of Nyos

Since January 2001, a French team directed by professor Michel Halbwachs leads an operation of degasification of the CO₂ trapped to the bottom it lake in order to prevent that the catastrophe of 1986 does not reproduce. The operation, called the Organ of Nyos uses a vertical pipe in Polyéthylène connecting deep water of the lake saturated with CO₂ to surface.

Pumping is carried out by car-siphon: A mechanical pump aspires water at the head column. The liquid taken in deep water of the lake (rich in gas dissolves) rises in the column. Its pressure decreases and water approaches the limit of saturation. When this one is reached, of the bubbles start to be formed which rise naturally in the column. New bubbles appear which involve the liquid. Once the started process, the action of the pump is useless and this one can be stopped. A carbonic gas and water jet spouts out with the opening of the column and the carbonic gas is dissipated in inoffensive quantity in the atmosphere. The jet formed with the lake Nyos rises to 50 m above the lake. The system is designed to function several years in order to éradiquer the risk of a limnic news eruption.

Nyos is not only

After several research carried out on the African lakes by the scientists, it proves that the lake Nyos is not the only lake concerned with possible a limnic eruption. The Lac Monoun is him also potentially dangerous, it contains in its water 10 million m ³ of CO₂ to be compared with the 300 million m ³ contained in the lake Nyos. In 1984, an eruption occurred and killed more than 37 people. An operation of degasification is also carried out on the Lac Monoun since 2003.

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