ABSTRACT

Lake Nyos released, a toxic aerosol of water and cabon dioxide, which killed an estimated 1700 people, in 1986. Since the amount of gas released represented only a small proportion of the gas which was dissolved in the lake and since the lake is currently being recharged with gas at an alarming rate, the only reliable way to avoid another disaster is to remove some of the gas. However, before this is attempted it is important to try to understand what triggered the ‘overturn’ which released gas in 1986, if we fail to do this we might find that the very process of removing gas could trigger the disaster which it is designed to prevent. There is general agreement that the best way to remove gas from Lake Nyos would be to install a pipe (or a number of pipes) with one end close to the lake bed. If gas-rich bottom water is then drawn up the pipe, by pumping water from the top, natural ‘gas-lift’ will be induced which will maintain flow within the pipe. And the gas which is released will cool the water as it rises. The practical problems are thus not ones of maintaining the flow of water within the pipe but of controlling the flow and disposing of the cold, partially degassed, water. If the water is returned onto the surface of the lake, as has been suggested, it will sink and could destabilise the lake. If it is discharged outside the lake basin, as has also been suggested, the amount of cold stream water retained by the lake may be increased and this too could destabilise the lake. Therefore it is proposed that the water should be discharged into a storage reservoir then reinjected at its level of neutral buoyancy. Once the amount of gas in the lake had been reduced to a safe level, then a pipe could be installed with one end near the lake bed and the other through the narrow natural dam in the north-west corner of the lake. Water flowing into the lake would continuously displace bottom water and any future buildup of gas in the deep water would thus be avoided.