Media playback is unsupported on your device

Japan's earthquake and tsunami explained

11 March 2011 Last updated at 11:50 GMT

A massive earthquake has hit the north-east of Japan, triggering a tsunami that has caused extensive damage.

Japanese television showed cars, ships and even buildings being swept away by a vast wall of water after the 8.9-magnitude earthquake.

Seismologist Dr Roger Musson explains how the enormous tsunami was triggered.