An estimate of CO2 flux in Lake Nyos, Cameroon

Abstract

An outburst of lethal gas from Lake Nyos, Cameroon, killed more than 1,700 people on 21 August 1986. The surveys carried out so far indicate that a considerable portion of the CO2 dissolved in the lake was released to the atmosphere and asphyxiated the people. We revisited the lake in December 1988. The conductivity‐temperature‐depth profiler (CTD) measurements and chemical analysis of the lake water revealed that temperature, total dissolved solids (TDS), and CO2 content of the bottom water increased in parallel fashion, especially in the bottom layer, during the preceding 25 months. The result supports the view that CO, is being supplied to the lake bottom in the form of warm, CO2‐charged, mineralized water. From the increments of temperature and CO2, during the period, fluxes of heat and CO2, were estimated to be 0.43 MW and 1.0 Mmol yr−1. The CO2 flux is large enough to saturate the lake’s hypolimnion within ∼30 yr. In the 1988 survey, the very bottom layer of the lake was estimated to be close to saturation with CO2. Using the CO2‐TDS‐Si relationship and temperature dependence of the solubility of amorphous silica, we estimated the chemical composition of the warm, mineralized water; these estimates suggest the existence of a CO2‐saturated fluid below the sedimentary cover.