geography revision on natural hazards

to help learn about narural hazards

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Tsunamis

A tsunami is a huge wave, usually caused by volcanic or earthquake activity under the ocean, which can eventually crash onto the shoreline. The effects on a community can be devastating.

What causes a tsunami?

When an earthquake, volcano or landslide happens on the ocean floor, water is displaced. This water forms the start of the tsunami.

When the waves reach shallower water:

  • their height can increase by several metres
  • the shallow water slows the wave
  • the waves get closer together

It is hard to see that a tsunami is approaching. The most obvious sign is the coastal water retreats just before the waves reach the shore. This is actually the trough of the wave following behind.

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Case study: Boxing Day Tsunami, 2004

On 26 December 2004 a tsunami occurred in the Indian Ocean. It was the result of the Indio-Australian Plate subducting below the Eurasian Plate. It was caused by an earthquake measuring more than magnitude 9. The earthquake caused the seafloor to uplift, displacing the seawater above.

  • In open ocean the tsunami measured less than 1 metre high.
  • The tsunami travelled at speeds up to 800km per hour.
  • When the Tsunami reached the shores, the height of the wave increased to 15 metres in some areas.
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Main impacts

  • A quarter of a million people died.
  • Two million people were made homeless.
  • People were swept away in the waters, which arrived rapidly and with little warning.
  • Thirteen countries were affected, the worst being Indonesia.
  • Indonesia was hit by the tsunami first. Fourty-five minutes later the tsunami reached Thailand.
  • Mangrove swamps helped to act as a barrier to reduce the energy of the water in some areas.
  • Short-term aid, such as water purification tablets, temporary housing and medical supplies were given from international countries.
  • Islands reliant on tourism and fishing, such as the Maldives, had to rebuild their industries.
  • An early warning system between countries surrounding the Indian Ocean has been set up.
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Comments

Abbie

copied and pasted off of bitesize by any chance?

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