Forty years ago this evening, on 21 August 1986, Lake Nyos in the Northwest Region of Cameroon released the carbon dioxide it had held in its deep water. The gas moved downhill, heavier than air, and filled the valleys below. It suffocated 1,746 people and roughly 3,500 head of livestock.
Nyos, Cha, Subum and Fang lost most of their people. The cattle lay where they had been grazing, in the…