Six years of change at Lake Nyos, Cameroon, yield clues to the past and cautions for the future.

Abstract

The catastrophic release of gas from Lake Nyos, Cameroon, in 1986 caused substantial but incomplete mixing of the stratified water column. The post-release evolution of water-column structure has been monitored through April 1992. Changes began immediately after the event as rainfall and inflow brought dilute fluid into the surface layer. Inflow and surface mixing have gradually deepened the chemocline. The Total Dissolved Solids (TDS) values in the upper 40 m of the water column have dropped from a few hundred mg/kg just after the release to <100 mg/kg. The chemocline is presently strongest at 50 m depth; 5 m below this, the TDS = 570 mg/kg. From 55 to 150 m depth is a gentle gradient in which TDS reaches 920 mg/kg. Little change in water-column chemistry has occurred in this depth interval since the release. Between 150 m depth and lake bottom at 210 m depth, a strong secondary chemocline has formed. Temperature, CO2 concentration ([C02]), and TDS have all increased in the deepest layer in response to recharge by warm, mineralized water, reaching values of 25.0C, 320 mmol/kg, and 1800 mg/kg, respec tively, 1 m above lake bottom.