Earthquake

An earthquake can create a large wave known as a tsunami (the Japanese term) or, seismic sea wave. A tsunami is barely detectable as it moves through deep water. Where the ocean becomes shallow near the shore, however, the fast-moving tsunami becomes a large wave that rises out of the sea and strikes the shore with unstoppable force. In a small, mountain-ringed bay, a tsunami can rush hundreds of meters up a sea-facing mountainside. A wall of water forms when a large tsunami enters a shallow bay or estuary, and it can move upriver for many miles. Sometimes tsunamis are mistakenly referred to as tidal waves, because they resemble a tide-related wave called a tidal bore.

The most destructive tsunamis in history have killed tens of thousands of people, many of them located great distances from the earthquake epicenter. The tsunami produced by a 1946 earthquake in the Aleutian Islands, Alaska, killed a total of 165 people. Of that number, 159 were in Hawaii, 5 were in Alaska, and 1 was in California. Coastal towns affected by tsunamis often have no topographic barriers between them and the sea and had no warning of the impending disaster. Building a breakwater to divert a tsunami and expend its energy is sometimes an option for otherwise unprotected coastal towns.