National Weather Service United States Department of Commerce

Introduction to the Tsunamis

Communities along the coasts of all the world's oceans are at risk from tsunamis. Tsunamis are one of nature's most powerful and destructive forces.

Two large events in the early twenty-first century demonstrated the devastating impacts of a tsunami. Although they occur relatively infrequently, and most are small and nondestructive, tsunamis are a serious threat to life and property. Since 1850, tsunamis have claimed hundreds of thousands of lives and caused hundreds of billions of dollars in damage around the world.

A tsunami is a series of long waves generated by a large and sudden displacement of the ocean. Large earthquakes below or near the ocean floor are the most common cause, but landslides, volcanic activity, certain types of weather, and near earth objects (e.g., asteroids, comets) can also cause a tsunami.

The often heard term "tidal wave" is very misleading. Tsunamis are not related to tides, so tsunamis are not tidal waves.

Tsunamis radiate outward in all directions from their source and can move across entire ocean basins. When they reach the coast, they can cause dangerous coastal flooding and powerful currents that can last for several hours or days.

Modeled wave height (colors) and travel times (lines) of the 2004 Indian Ocean tsunami. Enlarged tsunami travel time map.

A tsunami can strike any ocean coast at any time. There is no season for tsunamis. This is quite evident when we look at some records of past tsunamis.

Fast Facts

The word "tsunami," pronounced (soo-NAH-mee) comes from the Japanese characters meaning "harbor wave."