Tsunamis

Tsunamis are huge ocean waves generated by undersea earthquakes. Over the last 50 years, tsunamis have killed more people than the earthquakes that caused them.

Japanese boat on top of house The fishing boat No. 13 Good Luck was washed by a tsunami onto a house in Japan. 1960.

Jet-speed waves

Because 80% of the world’s earthquakes occur along the Pacific Rim, most tsunamis are generated in the Pacific Ocean. Underwater earthquakes cause sudden changes in the sea floor, sending waves racing through the water. Tsunami waves have been measured at speeds up to 800 km (500 miles) per hour. When tsunamis reach shallow water near the coast, the water gathers itself as waves up to 65 m (200 ft) high. Wave after wave floods the shore.

With nothing in the way, tsunamis can travel all the way across the Pacific Ocean and still be dangerous when they reach land on the other side. In 1960, the east coast of Japan was devastated by tsunami waves that had traveled from Chile— 10,000 miles in 22 hours. These same waves caused destruction all along the west coast of North America and around the Hawaiian Islands.

Hilo parking meters twisted Hilo, on the island of Hawai’i, was devastated by the same tsunami caused by the 1960 quake in Chile. The wave traveled 14 hours to hit Hawai’i.

Preventing disasters

We cannot predict earthquakes, but once there has been a large underwater earthquake, we can predict that there will be a tsunami. An international tsunami early-warning system for the entire Pacific Rim was set up in Hawai’i. Whenever a strong earthquake occurs, instruments detect whether a tsunami was generated. A warning is sent out to evacuate people from low-lying areas.

Experts are helping coastal communities in Oregon, Washington, and British Columbia plan for tsunamis. For example, researchers are mapping those areas likely to be flooded by tsunami waves. This kind of information alerts residents to potential dangers, and helps in planning the best evacuation routes. Such detailed maps also show engineers where they must build to withstand wave forces, or where they must select higher ground.

Tsunami hazard map of mouth of the Columbia River (Warrenton, Oregon). Red indicates areas of extreme tsunami danger.