What are Tsunamis?

Tsunami (soo-NAH-mee) is a Japanese word meaning "harbor wave." It is a series of ocean waves created by a sudden displacement of seawater.

A local tsunami is the result of an earthquake, or other water displacing event, occurring just offshore. People in affected areas may only have minutes to act.

Tele-tsunamis are waves that travel from the source across the open ocean. These may take several hours to reach affected populations. There can be five to 60 minutes between the wave crests. The first wave may not be the largest. The second wave is often deadlier, as it carries more debris.

Most tsunamis are generated by undersea earthquakes, but they can be caused by other sudden displacements of seawater - such as submarine landslides, volcanic eruptions and, in very rare instances, meteor strikes.

Tele-tsunamis travel quickly across oceans...more than 500 mph (about the speed of an airplane) in deep water. In the open ocean, wave height is nearly undetectable (typically less than three feet) except by sophisticated instruments, but increases as the wave nears the shore. Damage from tsunamis results from the force of the waves, the debris they carry, and resulting flooding, fires and other impacts.