Updated February 21, 2017 | Factmonster Staff

A flood occurs when a body of water rises and overflows onto normally dry land. Floods occur most commonly when water from heavy rainfall, from melting ice and snow, or from a combination of these exceeds the carrying capacity of the river system, lake, or ocean into which it runs.

  • Where: The Netherlands and England
  • When: 1099
  • A combination of high tides and storm waves on the North Sea flooded coastal areas of England and the Netherlands, killing 100,000 people.
  • Where: United States
  • When: 1889
  • The Johnstown Flood, in Pennsylvania, was considered one of the worst disasters in U.S. history. After an unusually heavy rainstorm, a dam several miles upriver from Johnstown broke. One out of every 10 people in the path of the flood died, a total of 2,000 people in less than an hour.
  • Where: Italy
  • When: 1966
  • After a heavy rainfall, the Arno River overflowed, flooding the streets of Florence. Many great works of art in the museums were damaged, as was the architecture of the city. In two days, more than 100 people died and the city was covered with half a million tons of mud, silt, and sewage.

For other floods, see Floods, Avalanches, and Tidal Waves at Infoplease.com.

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