The word “tsunami” comprises the Japanese word ‘Tsu” (meaning harbour) and “Nami” (meaning wave). A tsunami is a series of enormous waves created by an underwater disturbance usually associated with earthquakes occurring below or near the ocean.


Tsunamis are caused by violent seafloor movement associated with earthquakes, landslides, lava entering the sea, seamount collapse, or meteorite impact. The most common cause is earthquakes.

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  • Plate movement & earthquake: Most strong earthquakes occur in subduction zones where an ocean plate slides under a continental plate or another younger ocean plate. Earthquake on ocean floor can result in sudden rise or fall of the earth’s crust. This movement can cause water to rise and fall, creating tsunami waves.
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Landslides: They can happen on seafloor, just like on land. Areas of the seafloor that are steep and loaded with sediment, such as the edge of the continental slope, are more prone to undersea landslides. When an undersea landslide occurs (perhaps after a nearby earthquake) a large mass of sand, mud and gravel can move down the slope. This movement will draw the water down and may cause a tsunami that will travel across the ocean.

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Volcanic eruptions: They occur in several ways:

  • destructive collapse of coastal, island and underwater volcanoes which result in massive landslides.
  • pyroclastic flows, which are dense mixtures of hot blocks, pumice, ash and gas, plunging down volcanic slopes into the ocean and pushing water outwards.
  • a caldera volcano collapsing after an eruption causing overlying water to drop suddenly.
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  • Extra-terrestrial impacts: scientists realize that if these celestial bodies should strike the ocean, a large volume of water would undoubtedly be displaced to cause a tsunami. Scientists have calculated that if a moderately large asteroid, 5-6 km in diameter, should strike the middle of the large ocean basin such as the Atlantic Ocean, it would produce a tsunami that would travel all the way to the Appalachian Mountains in the upper two-thirds of the United States.
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