Beaches and coastal houses can be swept away by the water. Coastal flooding can also be produced by sea waves called tsunamis, giant tidal waves that are created by volcanoes or earthquakes in the ocean. When storms appear in these areas, the rain water cuts into the dry, dusty soil creating a small, fast-moving river. Flash flooding in an arroyo can occur in less than a minute, with enough power to wash away sections of pavement. River Flood - Flooding along rivers is a natural event.
Some floods occur seasonally when winter snows melt and combine with spring rains.
Water fills river basins too quickly, and the river will overflow its banks. Often the land around a river will be covered by water for miles around. Urban Flood - As undeveloped land is paved for parking lots, it loses its ability to absorb rainfall. Rain water can not be absorbed into the ground and becomes runoff, filling parking lots, making roads into rivers, and flooding basements and businesses.