tidal wave, term properly applied to the crest of a tide as it moves around the earth. The wavelike upstream rush of water caused by the incoming tide in some locations is known as a tidal bore. In popular usage the term tidal wave also is often applied to any destructive wave or to high water not related to tidal phenomena. These latter waves are of two types: tsunamis, which are waves caused by earthquakes, and storm surges (see under storm).

or seismic sea wave or tidal wave

Catastrophic ocean wave, usually caused by a submarine earthquake. Underwater or coastal landslides or volcanic eruptions also may cause tsunamis. The term tsunami is Japanese for “harbour wave.” The term tidal wave is a misnomer, because the wave has no connection with the tides. Perhaps the most destructive tsunami ever occurred in 2004 in the Indian Ocean, after an earthquake struck the seafloor off the Indonesian island of Sumatra. More than 200,000 people were killed in Indonesia, Thailand, India, Sri Lanka and other countries as far away as Somalia on the Horn of Africa.

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