There's a lake with a history of this: https://en.wikipedia.org/wiki/Lake_Nyos#1986_disaster https://en.wikipedia.org/wiki/Lake_Nyos#1986_disaster Apparently,

There's a lake with a history of this: https://en.wikipedia.org/wiki/Lake_Nyos#1986_disaster https://en.wikipedia.org/wiki/Lake_Nyos#1986_disaster Apparently, it was known (or believed) by the locals to house an evil spirit.