Nature 379, 57 - 59 (04 January 1996); doi:10.1038/379057a0

Dynamics of CO₂-driven lake eruptions

Youxue Zhang

Department of Geological Sciences, The University of Michigan, Ann Arbor, Michigan 48109-1063, USA

ON 21 August 1986, a massive release of carbon dioxide from Lake Nyos in Cameroon killed about 1,700 people. A similar event occurred on 15 August 1984 at Lake Monoun, also in Cameroon. It was suggested^1–5 that the CO₂ released was initially dissolved in the hypolimnion (dense lower layer) of the lake, and was released by eruptive outgassing. Because of its violence, the Nyos outburst was at first thought⁶ to have been volcanic, but undisturbed sediments and other evidence indicate that no large volcanic eruption occurred^7–9. Recent experiments^10,11 have shown that decompression of CO₂-saturated water is able to power explosive eruptions. Here I analyse the dynamics of CO₂-driven lake-water eruptions by deriving an equation of state for gas-liquid mixtures and using it to integrate the Bernoulli equation, which describes the dynamics of the bubbly flow. I find that under certain conditions these eruptions can be violent: the lake-surface exit velocity of an initially gas-saturated water parcel may reach 89m s^-1 for Lake Nyos and 51m s^-1 for Lake Monoun. The dynamics are similar to those of water-driven volcanic eruptions, which are also powered by gas exsolution from a liquid.

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