Potentially hazardous lakes in West Africa

Abstract

Two West African volcanic lakes have, within the last few years, released toxic aerosols of water and carbon dioxide which have killed well over a thousand people. It is obviously desirable that other volcanic lakes in the area should be checked to see whether any of them contain potentially dangerous concentrations of carbon dioxide. And since there are more than 40 volcanic lakes in West Africa it is important that a list of priorities be established so that those lakes which are more likely to be hazardous are checked first.

The solubility of carbon dioxide increases with pressure and hence with depth, therefore only large deep volcanic lakes can contain potentially hazardous concentrations. In West Africa there are 15 large volcanic lakes which are known to be more than 40 metres deep and there are also at least a further 12 large volcanic lakes (9 in Cameroon and 3 on the Gulf of Guinea Islands) which are of unknown depth. Establishing the depths of all the volcanic lakes of West Africa should be a matter of high priority.

Of the 15 deep volcanic lakes in Cameroon the two which caused the recent disasters, Lakes Nyos and Monoun, still contain large amounts of dissolved gas and are therefore still hazardous. Four of the lakes have been checked and found to contain no excess carbon dioxide at depth and the temperature profiles of a further seven lakes have been checked and found to be uniform at depth. A uniform temperature profile indicates that the lake circulates and therefore does not contain excess gas at depth.

Only two deep volcanic lakes remain to be eliminated from the list of lakes which might contain excess gas at depth. One of these, Lake Enep, is set in a deep caldera so that even if it were found to contain excess gas there would be no danger since any gas released would be confined by the caldera. The other, Lake Oku, has been associated with the deaths of groups of people in the past and therefore of all the lakes in West Africa it is the one which most merits further investigation.