1986: A deadly cloud of carbon dioxide sweeps down the slopes of an African volcano, smothering more than 1,700 people. Volcanoes can kill in many ways, but this one is pretty weird. A volcanic lake in the West African nation of Cameroon degassed violently (you could say it burped, or worse) in the middle of the night. Carbon dioxide is odorless and heavier than air. Most of the victims died in their sleep. Lake Nyos sits in the crater of a volcano that hadn't erupted in centuries ... and probably didn't actually erupt the night of Aug. 21, 1986. Magma deep underneath the lake releases carbon dioxide into its depths. Lake Nyos is 690-feet deep, enough for the water pressure to keep the CO2 dissolved in the lake water, rather than letting it bubble up and escape to the surface. And the crater rim towers above the lake, blocking winds which could otherwise stir the surface and create convection currents that would circulate the deep, CO2-saturated water upward to areas of lower pressure. The lack of seasonal variation less than seven degrees north of the equator also contributes to the lake's placidity.