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A tsunami (pronounced soo-nah-mee) is a wave or chain of waves generated when a large body of water is abruptly displaced. The word "tsunami" is derived from the two Japanese words 'tsu' meaning "harbor" and 'nami' meaning "wave." Underwater earthquakes, volcanoes, landslides, man-made explosions, or even meteors have the ability to cause these massive displacements of water.

Tsunamis are not the same as tidal or wind-generated waves normally seen at the beach. Whereas a wind-generated wave may have a wavelength (point between both crests of two waves) of 300 feet for a period of 10 seconds, a tsunami can have a wavelength of over sixty miles lasting for a period of over an hour. This large moving volume of water lasting for long periods of time is what causes so much catastrophic damage


Most tsunamis are formed by earthquakes greater than 7 on the Richer scale that has a focus less than 18 miles deep in the earth. These submarine earthquakes occur frequently in the Pacific Ocean where continental tectonic plates move up and over each other. This movement causes the ocean water above the surface of the seafloor to displace pushing it upward. Below is a diagram of tsunami formed from a tectonic plate generated earthquake.


  • Although tsunamis in California are rare, the entire California coastline is vulnerable to these events

  • An unusual lowering of ocean water at the beach exposing the sea floor is a warning of a tsunami or other large wave (This "draw back" of water means the water will surge back strongly)

  • Beaches, lagoons, bays, estuaries, tidal flats, and river mouths are the most dangerous places to be

  • It is rare for a tsunami to penetrate more than a mile inland

  • Tsunamis cannot be surfed as they have no face for a surfboard to dig into and are usually filled with debris

  • Tsunamis can reach heights of 20 to 50 feet along the coast

  • The first tsunami surge is usually followed with a higher, larger, and stronger surge sometimes hours later

  • It is not possible to predict the number of surges or the periods of time between each wave