Lakes Nyos and Monoun Gas Disasters (Cameroon)—Limnic Eruptions Caused by Excessive Accumulation of Magmatic CO 2 in Crater Lakes

Abstract

This is a review paper on the Lakes Nyos and Monoun gas disasters that took place in the mid-1980s in Cameroon, and on their related geochemistry. The paper describes: (i) the gas disasters (the event and testimonies); (ii) the unusual geochemical characters of the lakes, i.e., strong stratification with high concentrations of dissolved CO2; (iii) the evolu- tion of the CO2 content in the lakes during pre- and syn-degassing; (iv) the noble gas signatures and their implications; (v) a review of models of a limnic eruption; (vi) a revision of a spontaneous eruption hypothesis that explains the cyclic nature of a limnic eruption (Kusakabe 2015); (vii) a brief review of the origin of the Cameroon Volcanic Line (CVL) and the geochemistry of CVL magmas; (viii) a brief review of other CO2- rich lakes in the world; and (ix) concluding remarks. Degassing of the two lakes has been successful. Most of the dissolved CO2 has been removed from Lake Monoun, resulting in the stoppage of the degassing system. How- ever, the CO2 content in the lake started to increase in recent years due to the continuing supply of gas from the underlying magma, indicating the necessity of the continuous removal of gas from the lake. Lake Nyos will attain the same situation in several years when degassing will stop. Thus, a continuation of scientific monitoring of the lakes is essential. Since the transfer to Cameroonian scientists of monitoring techniques, includ- ing analytical equipment necessary for the monitoring, has been effected through the SATREPS project (Japan’s Official Development Aid), the responsibility is now theirs, and it is strongly hoped that the lake monitoring, the rehabilitation of displaced people, and the setting up of an infrastructure for them, etc., will be carried out by the Cameroonian Government and local scientists.