A one-dimensional numerical model has been applied to simulate the evolution of the temperature and CO2 stratification in Lake Nyos since the 1986 disaster. It incorporates a second-moment turbulence closure scheme for mixing and heating and cooling in the upper layers of the lake. The effects of inflowing stream water and input of the CO2, heat, and dissolved solids at the bottom of the lake are taken into account. The model is initialized by conditions observed immediately after the disastrous outgassing event in 1986 and integrated forward for 10 years, forced by seasonally modulated diurnal heating and nocturnal cooling and heavy summer time precipitation at the surface. Four possible conditions are investigated. The first simulation considers the normal seasonal heating/cooling cycle and steady input of heat, dissolved solids, and CO2 at the bottom. It shows that the upper layers of the lake are quite stable under normal seasonal forcing but the bottom layers reach high CO2 concentrations in less than a decade. The second simulation considers a brief introduction at the bottom of the lake of cooler waters that contain less CO2 and temporarily destabilize the bottom layers. The third and fourth simulations consider anomalous surface forcing conditions that can produce anomalous mixed layer deepening during the cooling seasons, capable of releasing the CO2 stored immediately below the normal mixed layer. These results suggest that a destabilization of the bottom layers is more likely to lead to massive and catastrophic degassing. The results also demonstrate the utility of a numerical model in investigations of caldera/crater lakes such as Lake Nyos. ¿ American Geophysical Union 1996