Gas hydrate induced lake degassing: Lake Nyos
Fouquet, T. (1999). Gas hydrate induced lake degassing: Lake Nyos. MSc Thesis. Vrije Universiteit Brussel (VUB), Faculteit der wetenschappen: Brussel. 148 pp.
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| Available in | Author |
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Document type: Dissertation
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| Keywords |
Chemical compounds > Organic compounds > Hydrocarbons > Gas hydrates
Fresh water |
| Abstract |
On 26 August 1986 an enormous volume of CO2 was released from Lake Nyos that killed about 1700 people. Two years earlier there was a smaller release of CO2 that killed 37 people. This rare natural disaster is complex, little understood, and difficult to study. Many controversies are encountered when studying literature. Three hypotheses concerning the degassing have been discussed (limnic theory, volcanic theory and the theory concerning the gas storage in the sediments) and it can be concluded that the event was of limnic origin. Evidence for this is that the concentration of CO2 in the bottom water has been rising since the event and using pipes that reach into the bottom waters to pump up the bottom water and allow gas discharge was a success. But what scientist still do not agree on is what triggered the gas release. When the lake water was near saturation, any additional energy could have unbalanced the situation. But no concentration measurements were performed before the degassing so, stating that the concentration was near saturation is a speculation. This means that perhaps the trigger mechanism is not a detail like some scientists want to believe. Rogers was the first to propose that hydrates could have formed the basis of the degassing. Stability calculations show that H2S-rich hydrates are stable when the gas available for hydrate formation has a high concentration of H2S (up to 55.5mole%) which means that when hydrates did form, it must have been due to in situ bacterial production. Because of buoyancy, the hydrate rich sediment layer loosened from the bottom and caused the overturn of the lake water. The theory of H2S-rich hydrates can explain the mixing of the sediments to a depth of 2 m, the symptoms of the victims which are caused by sulphur containing gases and the reported smell of rotten eggs. |
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