17. Africa has exploding lakes.
We’ve heard of killer bees, but killer lakes? Nyos, Monoun, and Kivu are all water bodies formed in the craters of active volcanoes, but these aren’t your average hot springs. Magma in the Earth’s mantle has been putting pressure on the lake beds, causing carbon dioxide from the mantle to seep into the waters. There, it turns into carbonic acid, which can explode and kill any passerby. Usually, the gases would just bubble out, but Lake Kivu is so deep at 1,500 feet that the pressure underwater dissolves the gas before it can escape. The mixture of liquefied gas and saltier water increases the water’s density in the lake, creating layers of different thicknesses that don’t mix. The CO2 methane that is trapped in the deep layers worries scientists, mostly because of what happened with Lake Nyos.

Lake Nyos, which is located in Cameroon, was the site of the only known natural event that caused large-scale asphyxiation. In August 1986, a landslide was suspected of causing the lake to emit a large cloud of carbon dioxide that caused an estimated 1800 nearby villagers to suffocate. Events like this are called limnic eruptions, and scientists are worried that Kivu is a disaster waiting to happen, mainly because of its size. In fact, scientists have discovered evidence of one previous limnic event at Kivu between 3,500 and 5,000 years ago. Since the Lake Nyos incident, degassing tubes have been placed inside the lake to keep the carbon dioxide levels checked.