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:
The most obvious sign of a tsunami is the coastal water retreats just before the waves reach the shore. This is actually the trough of the wave following behind.
Tsunami can eventually crash onto the shoreline. The effects on a community can be devastating.
The main impact a tsunami has is flooding. The waters are also able to erode the foundations of coastal structures. The effects of the tsunami range from destruction and damage, death, injury, disease, environmental and financial cost, and long lasting psychological problems for the inhabitants of the region.
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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.
|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.|