Floods can be very dangerous, in fact flash floods are the #1 weather-related killer in the U.S. There are different causes of flooding, but the most common is the heavy rains. It rains hard and the earth is unable to absorb all of the water which begins to flow over the surface of the ground. Other times the ground may become so soaked that the rain flows down into the rivers and causes these to overflow. Sometimes floods are caused by melting snow. Another cause of floods is pollution, when people throw garbage into the rivers or waterways, not allowing the water to flow like it normally would.