Tsunamis

Tsunami is a Japanese word which means 'harbour wave'. A tsunami is a large sea wave caused by the displacement of a large volume of water. They can be caused by earthquakes triggered by moving sections of the Earth's crust under the ocean.

In the last decade there have been a number of devastating tsunamis. Two large ones caused particularly extensive devastation: the Indian Ocean tsunami (26 December 2004) and the Japanese tsunami (11 March 2011).

The Indian Ocean tsunami of 2004 was caused by plates moving and slipping under the ocean.

Tsunami formation

Earthquake occurs and a tsunami forms

Water is displaced and waves move through the ocean at speed

Tsunami slows as water reaches the shore, but waves increase in height

• The plates move towards each other and pressure builds up as the denser Indo-Australian plate is forced under the overriding Burma plate.
• An earthquake occurs.
• Water is displaced, creating a wave which spreads out.
• As the wave approaches the shore, the wave height increases and the wave length shortens.