A tsunami is a series of enormous ocean waves caused by a sudden, massive disturbance underwater, usually an earthquake on the ocean floor. When the seafloor suddenly shifts or drops during an earthquake, it displaces huge amounts of water above it, like stomping in a bathtub but on a scale thousands of times larger. These waves race across the ocean at speeds up to 500 miles per hour, as fast as a jet airplane.

In deep water, tsunami waves might only be a few feet high and pass under ships unnoticed. But as they approach shallow coastal waters, something dramatic happens: the waves slow down and grow taller, sometimes reaching heights of 100 feet or more. Unlike regular waves that crash and retreat in seconds, a tsunami can flood inland for several minutes, sweeping away everything in its path.

The word comes from Japanese: tsu means harbor and nami means wave. Japan has experienced many tsunamis throughout its history, so the Japanese language had a specific word for this phenomenon long before English did. Scientists now use tsunami worldwide because it precisely describes these rare but devastating waves.

Coastal communities in tsunami-prone areas install warning systems and plan evacuation routes to help people reach higher ground quickly when danger approaches.