Wednesday, 20 March 2013


The movement of the waves that generate tsunami

How are tsunamis generated?

  • Tsunamis are generated by any large, impulsive displacement of the sea bed level.
  • Earthquake generate tsunamis by vertical movement of the sea floor. if the sea floor movement is horizontal, a tsunami is not generated. Earthquake of M > 6.5 are critical for tsunami generation.
  • Tsunamis are also triggered by landslides into or under the water surface, and can be generated by volcanic activity and meteorite impacts.

tsunami starts during earthquake

How often do tsunamis occur?

  • On the average, there are two tsunamis per year somewhere in the world which cause damage near the source.
  • approximately every 15 years a destructive, Pacific- wide tsunami occurs.
  • The destructive tsunami on Dec 26th, 2004 on the Indian Coast seems to have occoured for the first time in the history.

tsunami on Indian Coast

How fast does a tsunami travel?

  • Tsunamis travel approximately 700 kmph in 4000 m depth of the sea water.
  • Tsunamis range in size from centimeters to over 30 m height. Most tsunamis are less than 3 m in height.
  • Tsunamis height can vary greatly along a coast. the waves are amplified by certain shoreline and bathymetric (sea floor) features.
  • a large tsunami can flood land up to more than 1.5 km from the coast. 

a large tsunami bashing land

What does a tsunami look like when it reaches shore?

  • Normally, a tsunami appears as a rapidly advancing or receding tide.
  • In some cases, a bore (wall of water) or series of breaking waves may form.
  • Sometimes a tsunami causes the water near the shore to recede, exposing the ocean floor, then the wave crest comes with a high speed.

huge waves of tsunami frightened people


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