Thousands of years ago before people built towns and planted crops, rivers cut deep canyons and molded the continents. Often these rivers overflowed their banks and flooded the surrounding areas, depositing mineral rich silt and soil in the surrounding plains and valleys. Because of the way floods enrich soil some of the first cities were built along rivers. The most important ones grew along the Indus River in Pakistan; the Nile in Egypt; the Yellow River in China; and the Tigris and Euphrates in the Middle East. These rivers floodplains are called the “cradles of civilization”. (Michael Burgan &Robin Doak)Even though floods happen everywhere, there are only four types of floods. River floods occur along rivers and usually happen because of heavy rain over a large area. This can also be caused by melting snow and ice jams and can last for weeks. In most parts of the world dams and levees help keep rivers from flooding by blocking off water and storing it in lakes and reservoirs. Sometimes a dam will break causing another kind of flood. Dam failure floods happen when dams or other manmade structures are neglected, poorly designed, or damaged. These floods are very dangerous because a huge amount of water is released suddenly and with no warning. Flash floods happen when a large amount of rain falls very quickly. Flash floods generally occur in mountainous areas and are so deadly because they happen with little or no warning. Coastal floods occur along the shores of oceans and seas and are often caused by hurricanes and strong storms. Earthquakes that happen under the ocean or on a coast also cause them the winds produced by these winds whip up huge ocean waves that are together known as a storm surge. These earthquakes cause tsunamis, which are huge waves. Tsunamis travel long distances across the ocean before reaching land where they flood the coasts, drown people...
