Contribution of methane to total gas pressure in deep waters at lakes Nyos and Monoun (Cameroon, West Africa)

Abstract

Copyright © 2013 by The Geochemical Society of Japan. tions could be cyclic (Evans et al., 1994; Kusakabe et al., 2000; Halbwachs and Sabroux, 2001), given the high gas accumulation rate observed soon after the disasters. To avert a repetition of catastrophes in the future, a controlled piping of gas-rich bottom water was initiated in 2001 (Halbwachs and Sabroux, 2001; Halbwachs et al., 2004). Follow up studies demonstrated that gas removal worked well (Halbwachs et al., 2004; Kling et al., 2005; Issa, 2008; Kusakabe et al., 2008): regular monitoring of the lakes during degassing operation has indicated that carbon dioxide (CO2) concentrations have been drastically lowered (Kling et al., 2005; Kusakabe et al., 2008). Meantime, it has been noted that CH4 concentrations in the lakes were steadily increasing instead (Kling et al., 2005). The causes of the gas blast still a matter of debate; several causes such as meteorological forces and rockfalls (Kling et al., 1987; Sigurdsson et al., 1987), gradual gas accumulation (Kusakabe et al., 2008) and volcanic activities (Tazieff et al., 1987; Chevrier, 1990) have been proposed as potential triggering mechanisms. Nevertheless, irrespective of the trigger, it is apparent that the total gas pressure played a key role in the magnitude of the Contribution of methane to total gas pressure in deep waters at lakes Nyos and Monoun (Cameroon, West Africa)