The sudden release of carbon dioxide gas, which may accumulate gradually within the stratified water bodies of a crater lake, caused two fatal disasters in Cameroon during the past decade. We model the various processes that may have led to the release by considering (1) gas injection, (2) an internal triggering mechanism, (3) propagation of a disturbance after triggering, and (4) the forces that end the outburst. We suggest that the 1986 Lake Nyos outburst was triggered at the lake bottom. The final explosive stage of the release ended quickly when a sufficiently large volume of gas bubbles prevented circulation of water eddies within the lake. A cellular automaton model is used to estimate the amount of carbon dioxide gas released and the characteristic time interval between successive outbursts. If both the gas accumulation rate and the diffusion rate of carbon dioxide through water are constant, then rapid gas release will occur at fairly regular intervals. In which case, the amount of gas released from Lake Nyos is 0.17¿0.05 km3 at standard temperature and pressure each 37¿10 years. It is possible, however, that an external event could trigger a sudden release or that the diffusion rate of carbon dioxide may change as more gas accumulates, which could shorten the release time. ¿ American Geophysical Union 1996