Cause and effect of the Japanese tsunami

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Cause and effect of the Japanese tsunami

The word tsunami is Japanese for "harbor wave". They often happen in Japan and about 195 have been recorded. Tsunamis can devastate coastal regions. They are often referred to as ‘tidal waves’, but have nothing to do with tides.

The 2011 Tōhoku earthquake with its resulting tsunami and flooding were caused by a 9.0-   off the coast of  that happened on Friday, 11 March 2011. It has been named the ‘Great Eastern Japan Earthquake’. The  was approximately 45 miles east of the  of , with the  at an underwater depth of approximately 20 miles. This earthquake triggered extremely destructive  waves of up to 30m that struck Japan minutes after the quake, in some cases traveling up to 6 miles inland, with smaller waves reaching many other countries after several hours. The flooding caused huge damage.

What causes a tsunami?

Tsunamis, also called seismic sea waves, are usually caused by earthquakes, less commonly by submarine landslides, infrequently by submarine volcanic eruptions and very rarely by a large meteorite impact in the ocean. Undersea volcanic eruptions can produce truly terrible tsunami waves. The Great Krakatau Volcanic Eruption of 1883 caused giant waves reaching heights of 125 feet above sea-level, killing thousands of people and wiping out numerous coastal villages.

To form tsunamis, earthquakes must occur underneath or near the ocean, be large and create movements in the sea floor. All ocean regions of the world can experience tsunamis, but in the Pacific Ocean there is are much more frequent large, destructive tsunamis because of the many large earthquakes along the margins of the Pacific Ocean.

Tectonic earthquakes are a particular kind of earthquake that are associated with a deformation of the Earth's crust. When these earthquakes happen beneath the sea, the water above the deformed area is displaced. More specifically, a tsunami can be generated when  move abruptly, resulting in the water being displaced. Movement on normal faults will also cause displacement of the seabed, but the size is normally too small to cause a tsunami.

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Most tsunamis are caused by earthquakes generated in a , an area where an oceanic plate is being forced down in to the mantle by  forces. The friction between the subducting plate and the overriding plate is enormous. This friction prevents a slow and steady rate of subduction and instead the two plates become "stuck".

As the stuck plate continues to push into the mantle the movement causes a slow distortion of the overriding plate. The result is a build up of energy very similar to the energy stored in a compressed spring. This energy can build up in ...

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