Flooding results when more water enters an environment than can be easily absorbed into the soil or drained away in rivers and streams. Flooding is usually caused by intense rainfalls that dump many inches of water onto an area over a short period of time, or they can also be caused by ocean swells and storm surges initiated by hurricanes and tropical storms. Tsunamis, naturally, also cause flooding. The 2004 tsunamis that resulted in an undersea earthquake in the Indian Ocean, for instance, killed about 238,000 people in 11 surrounding countries. Most of these people died from the initial landfall of the waves and resulting floods. In addition, floods can be caused artificially, such as when a dam or levee breaks.
Severe floods are a regular threat to many people living near rivers, oceans, and lakes.