In other places, there is danger from great tsunamis which come up suddenly and unexpectedly. After the great flood of 1900, Galveston, Texas, built a sea wall. But the storms of 1913 went over the wall. Earthquakes and volcanoes also produce tsunamis. During the Good Friday earthquake in Alaska in 1964, tsunamis struck the Kodiak Islands and the southern coast of Alaska.
Some seacoast floods result from abnormally high tides.
Storms and high winds also cause floods along lakeshores. Some floods occur when the water of a lake moves suddenly from side to side in rhythm. Such a movement is called a seiche. The failure of artificial structures, such as dams, has caused a number of floods. In 1889, a dam near Johnstown, Pa., burst.