The Asian tsunami was caused by an earthquake measuring 9.3 on the richer scale - the second largest ever known in the history of Earth. Itstarted 30 kilometres under the Indian Ocean and 160 kilometres west of Sumatra, one of the island of Indonesia. Just before 8 o'clock on the morning of 26 december,the earthquake sent waves through the Indian Ocean. At first those waves were not very big, so no warning was given that they would develop into a tsunami. In fact, there was a delay of several hours before the waves hit the coast. In many places, the waves were 20 metres high and they travelled at speeds of 800 kilometres per hour.