6.4400°N, 10.2986°E.
Crater lake in northwestern Cameroon, 1.5 km long and up to 208 metres deep, occupying a maar of the Oku Volcanic Field. On the night of August 21, 1986, the lake released approximately 1.6 million tonnes of CO₂ in a limnic eruption — a sudden overturn of the water column that liberated gas dissolved in the deep waters under hydrostatic pressure. The CO₂ cloud, denser than air, rolled down adjacent valleys at 50 km/h and asphyxiated 1,746 people and over 3,500 livestock in surrounding villages, killing all life within 25 km. The event remains the deadliest known natural CO₂ release in human history. A degassing pipe installed in 2001 now slowly releases CO₂ to the surface continuously, preventing pressure build-up.
A volcanic lake silently exhaled enough carbon dioxide in one night to suffocate every living thing for fifteen miles in every direction.