• tsunami
    (Courtesy U.S. Navy)

What is a Tsunami?

A tsunami is a massive, fast-moving wave created by an underwater earthquake or landslide. The large volume of water displaced by a sudden movement of the seafloor creates a pulse in the ocean that races out from its source at speeds of up to 500 miles per hour and extends thousands of feet below the surface.

In deep water, a tsunami might be only a few inches high, but when it nears shore and shallow water, it builds to reveal its true size. Japanese for "harbor wave," a tsunami can be dozens of feet high and hundreds of feet wide when it crashes into the coast.

Although rare, tsunamis like those that occurred in March 2011 in Japan and December 2004 around the Indian Ocean were tragic reminders of the destructive power of the ocean. Tsunamis can also reach far from their deep-sea source, spreading from one side of an ocean basin to another.

As a result, governments of countries surrounding the Pacific and Indian Oceans, with help from scientists from around the world, continuously monitor the ocean bottom for possible tsunami-producing seismic activity and the fast-moving signs of tsunamis in the open ocean. Even a few minutes' warning can mean the difference between wide scale catastrophe and saving hundreds or thousands of lives.