What are Tsunamis?
Tsunamis are ocean waves triggered by large earthquakes that occur near or under the ocean, volcanic eruptions, submarine landslides, and by onshore landslides in which large volumes of debris fall into the water. Scientists do not use the term "tidal wave" because these waves are not caused by tides. Tsunami waves are unlike typical ocean waves generated by wind and storms, and most tsunamis do not "break" like the curling, wind-generated waves popular with surfers. Tsunamis typically consists of multiple waves that rush ashore like a fast-rising tide with powerful currents. Tsunami waves can travel much farther inland than normal waves. When tsunamis approach shore, they behave like a very fast moving tide that extends far inland. If a tsunami-causing disturbance occurs close to the coastline, a resulting tsunami can reach coastal communities within minutes. A rule of thumb is that if you see the tsunami, it is too late to outrun it. Even small tsunamis (for example, 6 feet in height) are associated with extremely strong currents, capable of knocking someone off their feet. Because of complex interactions with the coast, tsunami waves can persist for many hours.
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. 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).
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What is it about an earthquake that causes a tsunami?
Although earthquake magnitude is one factor that affects tsunami generation, there are other important factors to consider. The earthquake must be a shallow marine event that displaces the seafloor. Thrust earthquakes (as opposed to strike slip) are far more likely to generate tsunamis, but small tsunamis have occurred in a
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What is the difference between a tsunami and a tidal wave?
Although both are sea waves, a tsunami and a tidal wave are two different and unrelated phenomena. A tidal wave is a shallow water wave caused by the gravitational interactions between the Sun, Moon, and Earth. ("Tidal wave" was used in earlier times to describe what we now call a tsunami.) A tsunamis is an ocean wave
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Is there a system to warn populations of an imminent occurrence of a tsunami?
NOAA maintains the U.S. Tsunami Warning Centers, which work in conjunction with USGS seismic networks to help determine when and where to issue tsunami warnings. If an earthquake meets certain criteria for potentially generating a tsunami, the pop-up window and the event page for that
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Could a large tsunami happen in the United States?
Large tsunamis have occurred in the United States and will undoubtedly occur again.
Significant earthquakes around the Pacific rim have generated tsunamis that struck Hawaii, Alaska, and the U.S. west coast. One of the largest and most devastating tsunamis that Hawaii has experienced was in 1946 from an earthquake
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Extensive damage to buildings and roads, and large boats washed far ashore, provide valuable information to tsunami researchers. Here, in Natori, Japan, south of Sendai, the height of damage indicates that the water flow from the tsunami wave was about 10 meters (33 feet).