As if the harrowing violence of earthquakes and tsunamis wasn't enough, the Earth is also trying to sneak up on you to kill you silently and quickly. That's right, Mother Earth is trying to smother you with poisonous gas, and she'll use the cover of a friendly looking lake to disguise her intentions.
In Africa there are a number of lakes that rest in old volcano craters. Many miles below the surface, hot magma pushes gases such as carbon dioxide upward to the lake bottoms. In most geographical areas, lakes encounter enough mild day-to-day turmoil that the water and gases mix regularly, causing harmful gases to release slowly and safely into the air.
But some lakes, particularly those in the tropics, are relatively still, and the gas collects in large volumes. The unmoving water traps those gases until the pressure finally gives way in an enormous rush to the surface. As carbon dioxide gushes, it forms an invisible cloud that can travel miles from the lake, suffocating any creature its path.
In 1986, just such a cloud killed around 1,700 people in Cameroon. These kind of disasters may not be spectacular, but under the right circumstances they're as deadly and insidious as any dangers Earth wields.