For more general information on tsunamis and what to do during a tsunami warning, please visit sites sponsored by DHS, the International Tsunami Information Center, state agencies, NOAA, and the USGS. If you hear a tsunami warning or if you feel strong shaking at the coast or very unusual wave activity (e.g., the sea withdrawing far from shore), it is important to move to high ground and stay away from the coast until wave activity has subsided (usually several hours to days). As with many natural phenomena, tsunamis can range in size from micro-tsunamis detectable only by sensitive instruments on the ocean floor to mega-tsunamis that can affect the coastlines of entire oceans, as with the Indian Ocean tsunami of 2004. Because of complex interactions with the coast, tsunami waves can persist for many hours.

Even 'small' tsunamis (for example, 6 feet in height) are associated with extremely strong currents, capable of knocking someone off their feet. Most tsunamis do not 'break' like the curling, wind-generated waves popular with surfers. A rule of thumb is that if you see the tsunami, it is too late to out run it. When tsunamis approach shore, the behave like a very fast moving tide that extends far inland. Tsunami waves are unlike typical ocean waves generated by wind and storms. Scientists do not use the term 'tidal wave' because these waves are not caused by tides. Tsunamis are ocean waves caused by large earthquakes and landslides that occur near or under the ocean.

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