What is a tsunami?
A tsunami is a series of huge ocean waves usually caused by an undersea earthquake. In deep water, the waves travel as fast as a jet plane, then grow taller as they reach shallow coastlines.
When a large earthquake suddenly lifts or drops the seafloor, it pushes up the entire column of water above it, creating waves. Landslides, volcanic eruptions and, rarely, meteorite impacts can also cause tsunamis. In the open ocean, tsunami waves may be less than a meter high but travel at about 800 kilometers per hour.
As the waves approach land and the water gets shallower, they slow down and grow much taller, sometimes reaching more than 10 meters. Often, the sea first pulls back from the shore, exposing the seabed, before the wave arrives. This is a natural warning sign to move to high ground immediately.
Major tsunamis
The 2004 Indian Ocean tsunami killed about 230,000 people in 14 countries. The 2011 tsunami in Japan caused the Fukushima nuclear disaster. Today, warning systems using ocean sensors and seismic data alert coastal areas around the Pacific and Indian Oceans.
Did You Know?
The word tsunami comes from Japanese, meaning harbor wave. Tsunamis are sometimes wrongly called tidal waves, but they have nothing to do with tides.