Scientists Say: Tsunami

This word describes a series of giant ocean waves triggered by an undersea earthquake or eruption

a photo of a tsunami hazard zone sign on a wooden fence near the shoreline

Tsunami waves can strike suddenly. Coastal areas may post warning signs to alert people of the risk. Sometimes before a tsunami occurs, the water level drops and exposes the ocean floor. That can be a sign that it’s time to move to higher ground.

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Tsunami (noun, “soo-NAAM-ee”)

This word describes a series of ocean waves triggered by an underwater earthquake, landslide or volcanic eruption. The word tsunami means “harbor wave” in Japanese. At shore, these strong waves can reach up to 30 meters (98 feet) tall. Those waves would be about as tall as a 10-story building. These waves are not the same as the waves you might see if you visit a beach on the ocean. Those waves, called tidal waves, are created by the gravitational pull of the sun or moon.

Tsunamis start small on the open ocean. When an earthquake rumbles or a volcano erupts undersea, it can cause small waves on the water’s surface. In the deep ocean, these waves may be only up to 60 centimeters (2 feet) tall. But they move fast — up to 800 kilometers (498 miles) per hour. That’s as fast as some airplanes. As the waves travel toward land, friction with the sea floor slows them down. And as the ocean becomes shallower, the waves can grow in height. When they reach the coast, tsunamis can cause enormous devastation. Their powerful surges of water can uproot trees, topple buildings, carry boats inland and wash away beaches.

About four out of every five tsunamis happen in the Ring of Fire. That area of the Pacific Ocean has a lot of earthquake and volcanic activity.

In a sentence

The asteroid that crashed to Earth on the dinosaurs’ last day would have caused tsunami waves.

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Carolyn Wilke is a former staff writer at Science News Explores. She has a Ph.D. in environmental engineering. Carolyn enjoys writing about chemistry, microbes and the environment. She also loves playing with her cat.

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