Floods can cause untold misery. More than 3,000 people were killed and 14 million left homeless in China during the summer of 1998. The cause: the heaviest flooding of Chinas Yangtze and other rivers since 1954. In 1931 almost four million died along Chinas Huang, or Yellow River, when it surged over its banks. Heavy summer rains in the U.S. Midwest swelled the Mississippi, Missouri, and several other rivers in 1993, destroying entire towns and covering millions of acres of farmland.
But when rivers overflow their banks due to melting snow or torrential rains, floods enrich surrounding land, leaving behind organic material and minerals in the sand, silt, and debris. Ancient Egyptians planned their planting and their lives around the summer flooding of the Nile, which leaves a thin, even coating of black mud along either side when it recedes, leaving the soil so enriched that fertilizer is unnecessary.
Flash floods, which rise and fall rapidly with little or no warning, and tsunamisseismic waves caused by undersea earthquakes and volcanoesalso drown people and livestock and destroy their habitations, as does flooding due to rains associated with hurricanes.