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A photograph of the 2004 tsunami in Ao Nang, Krabi Province, Thailand. (Public domain)

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.

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News & Insights

Can seismic data mules protect us from the next big one?

Ocean scientists leverage game-changing technologies to improve our understanding of the global ocean’s most dangerous earthquake faults and enable more advanced warnings for seismic risk.

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News Releases

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WHOI in the News

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From Oceanus Magazine

Can seismic data mules protect us from the next big one?

Researchers look to new seafloor earthquake detection systems for better detection and warning of seismic risk

A New Tsunami-Warning System

After successfully testing a long-range underwater communications system that worked under Arctic Ocean ice, an engineering team at Woods Hole Oceanographic Institution (WHOI) adapted it for a very different environment—the tropics—and for a different purpose—to provide warnings of impending tsunamis. While the Arctic sound-signaling system lets researchers communicate with robotic vehicles operating beneath sea ice,…

Lessons from the 2011 Japan Quake

When the ground in Japan started shaking on March 11, 2011, the Japanese, who are well accustomed to earthquakes, knew this time was different. They weren’t surprised—the fault that ruptured has a long record of activity. But this time the trembling continued for six minutes. When it finished, many turned their eyes to the sea…

How to Survive a Tsunami

In the aftermath of the 2004 tsunami in the Indian Ocean that devastated villages and cost 230,000 lives, WHOI geophysicist Jian Lin saw a need for an easy-to-use Web resource to inform large numbers of people about tsunamis. “Tsunamis can neither be prevented nor precisely predicted yet,” said Lin, a senior scientist at Woods Hole…

Morss Colloquia Focus on Science and Society

Woods Hole Oceanographic Institution launched a new program, hosting three “Morss Colloquia” since October 2006. Enabled by a generous grant from Elisabeth and Henry Morss Jr., the public colloquia concerned “issues of global importance that are con-nected to human society and involve some aspect of science.” In October, hazard management officials, scientists, and coastal managers…