You’d do well to avoid Lake Nyos, which sits in a crater on the flank of a Cameroonian volcano. In 1986, like a shaken soft drink can, it suddenly released 80 million cubic meters of carbon dioxide, which rushed down nearby valleys and suffocated 1,800 people and 3,500 livestock where they stood.

It’s not known what caused the eruption, but it turned the lake a deep red.