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.

Map of countries affected by 2004 tsunami and the nearby tectonic plate boundaries

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

A tsunami forms when energy from an earthquake jolts the seabed up by several metres, displacing hundreds of cubic kilometres of water.

Earthquake occurs and a tsunami forms

  • Convection currents in the mantle move the plates towards each other. 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.