Helium isotope evidence for magmatic gases in Lake Nyos, Cameroon

Abstract

We have measured ³He/4He and 4He/20Ne ratios of gas samples collected at Lake Nyos where a toxic gas disaster occurred on August 21, 1986 and at Lake Monoun in Cameroon, West Africa. The ³He/4He ratios, corrected for air contamination, are 5.39–5.75 Ratm (where Ratm is the atmospheric ratio of 1.40 × 10−6) for Lake Nyos and 3.56 Ratm for Lake Monoun. The data suggest a significant contribution of mantle‐derived helium in these Cameroon volcanic crater lakes. The origin of CO2 gas “erupted” during Lake Nyos disaster is inferred to be of magmatic origin based on the high ³He/4He ratio. Copyright 1987 by the American Geophysical Union.