Lake Nyos, Cameroon

From its churning, sometimes stormy atmosphere to its shifting tectonic plates, Earth can be a dangerous place. Earthquakes, floods and other natural disasters killed more than 780,000 people between 2009 and 2009, according to the UN International Strategy for Disaster Reduction Secretariat. Millions more were injured or displaced. No one knows how the next decade will shape out, but some areas have more reason to worry than others.

A silent killer lurks beneath the surface of this West African lake. A pocket of magma deep below the lake bed leaks carbon dioxide into the lake above. Under the pressure of 650 feet (200 meters) of water, this carbon dioxide stays dissolved, much like the carbonation in a bottle of soda. But on the night of August 21, 1986, the water in the lake abruptly turned over, and the now-depressurized carbon dioxide exploded upward like a shaken soft drink. The resulting carbon dioxide cloud rushed downhill, asphyxiating 1,700 people and thousands more animals. In the 15 miles (24 kilometers) of valleys below the lake, almost nothing survived. Today, pipes are used to siphon carbon dioxide-rich water from the bottom of Lake Nyos. The pipes prevent carbon dioxide buildup, but that doesn't make Lake Nyos entirely safe, said George Kling, a University of Michigan geochemist who was on the team that originally investigated the 1986 disaster. "We're keeping ahead of the game, but we're not drawing the gas down very quickly," Kling said. "That means that it still is a very dangerous lake."