1.1.7

Tsunamis

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Cause of Tsunamis

Tsunamis are a big hazard for many places in the world. They are a secondary hazard following some earthquakes.

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Cause

  • Most tsunamis are generated by submarine earthquakes at subduction zones.
  • The sea bed is displaced vertically (up or down) - this motion displaces a large volume of water in the ocean column which then moves outwards from the point of displacement.
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Examples

  • In 2004, the Boxing Day tsunami happened in Indonesia. The epicentre took place in Banda Aceh, western Sumatra. The tsunami was so large its devastating effects reached far beyond.
  • A magnitude 9 earthquake off the coast of Tōhoku, Japan resulted in a tsunami in 2011.

Characteristics of Tsunamis

Tsunamis can be identified by their specific characteristics:

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Long wavelength at sea

  • The wavelength is the distance measured between two identical points of a wave.
    • When tsunamis are at sea, the wavelength is often over 100 km long.
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Short amplitude at sea

  • Tsunamis have very short amplitudes at sea - they are usually about 1 m in height and are barely noticeable.
    • But, when tsunamis reach land, their height can increase to over 25 m in some cases.
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Velocity

  • Tsunamis move very quickly and can reach speeds of up to 700 kph in deep water.
    • Tsunamis slow down as they reach shallow water.
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Drawback

  • One of the identifying factors before a tsunami happens is a localised drop in sea level (drawback), as water is drawn back and up for use by the approaching tsunami.
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Wave-train

  • The way that a tsunami hits a coastline is like a series of waves that we call a wave-train.

Jump to other topics

1Tectonic Processes & Hazards

2Option 2A: Glaciated Landscapes & Change

3Option 2B: Coastal Landscapes & Change

4Globalisation

5Option 4A: Regenerating Places

6Option 4B: Diverse Places

7The Water Cycle & Water Insecurity (A2 only)

8The Carbon Cycle & Energy Security (A2 only)

9Superpowers (A2 only)

10Option 8A: Health & Human Rights (A2 only)

11Option 8B: Migration & Identity (A2 only)

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