A tsunami is a sequence of ocean waves that sends surges of water, sometimes reaching heights of over 100 feet onto land. These walls of water can cause extensive destruction when they crash aground. Tsunamis may also be caused by underwater landslides or volcanic eruptions. They may even be launched, as they frequently were in Earth’s ancient past, by the impact of a large meteorite plunging into an ocean.
Tsunamis race across the sea at up to 500 miles an hour about as fast as a jet airplane. A tsunami’s trough, the low point beneath the wave’s crest, often reaches shore first. When it does, it produces a vacuum effect that sucks coastal water seaward and exposes harbor and sea floors. In Deep Ocean, tsunami waves may appear only a foot or so high. But as they approach shoreline and enter shallower water they slow down and begin to grow in energy and height.
The best resistance against any tsunami is early warning that allows people to look for higher ground. The Pacific Tsunami caution System, a union of 26 nations headquartered in Hawaii, maintains a web of seismic equipment and water level gauges to recognize tsunamis at sea. Similar systems are proposed to protect coastal areas worldwide.