Marine Glossary

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tsunami

Also spelled tunami. A long-period sea wave, potentially catastrophic, produced by a submarine earthquake or volcanic eruption. It may travel unnoticed across the ocean for thousands of miles from its point of origin and then build up to great heights over shoal water. At sea tsunamis have wave heights of only 1 to 2 feet and wavelengths of 50 to 250 miles.

The Pacific ocean basin accounts for about 85% of all tsunamis, with about 100 minor events and 10 major events per century. Only a dozen or so have occurred in the Atlantic in the past 250 years. These are a major concern in coastal areas where elaborate detection and warning systems are in place, but they are not a concern at sea. Also called seismic sea wave, or (erroneously) tidal wave.