|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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