Flooding

Floods are probably the strongest and most dangerous form of natural disaster on Earth. In fact, one study looked at all of the people killed in natural disasters in the 20-year period ending in 1967. During this time, over 173,000 people were killed as a direct result of river floods. At the same time, about 270,000 people were killed from 18 other categories of natural disasters, including hurricanes, earthquakes, and tornadoes.

Water, when unleashed, is virtually impossible to stop. The reason behind this is twofold: water is heavy and can move with significant speed. For instance, while a single gallon of water weighs 8.5 lb (3.2 kg), the weight of high volumes of impounded water really adds up. Hoover Dam alone holds back the waters of Lake Mead, which is about 15 mi (24 km) long and contains around 10.5 trillion gal (33.6 trillion kg) of water; multiplication shows that this water weighs almost 90 trillion lb (33.6 trillion kg). Added to its weight is the fact that water can travel up to 20 mi (32 km) per hour. As it picks up speed, it also picks up incredible strength. In fact, moving under certain conditions, 1 in (2.54 cm) of rain can have the same energy potential as 60,000 tons (54,400 metric tons) of TNT.