1. An earthquake occurs when at the surface of the Earth the plates suddenly move against each other, causing a sudden release of energy in the Earth's crust - this creates seismic waves
2. On December 26th, 2004 an earthquake was caused between the Eurasian and Australian plates in the Indian Ocean - measuring 9.0 on the moment magnitude scale, the largest earthquake in 40 years
3. This earthquake lasted several minutes and triggered a tsunami at 00:58 UTC, a series of huge waves, which spread thousands of kilometres over the Indian ocean over several hours
4. The tsunami formed due to the energy from the earthquake jolting the seabed vertically by several metres, causing the displacement of hundreds of cubic kilometres of water
5. Large waves began to move through the Indian Ocean, away from the epicentre
6. In the ocean's deep water the tsunami moved at staggering speeds of up to 800km/h (500mph), but when it reached shallower water near coastal areas it slowed down, and increased in height
7. Some areas, such as the Sri Lankan tourist resort of Kalutara, had almost no warning of the approaching tsunami; the first warning they had was moments before the tsunami struck, when the waterline suddenly retreated and hundreds of metres of beach and seabed became exposed
8. The waves of the tsunami hit land at intervals varying between 5 and 40 minutes
The earthquake that triggered the 2004 Asian tsunami measured 9.0 on the moment magnitude scale, the biggest earthquake to have occurred in 40 years.
Since 1900, there have been only 3 other earthquakes recorded with a greater magnitude:
Also, in 1952 another earthquake of magnitude 9.0 was recorded off the coast of Kamchatka.
Each of these huge earthquakes also triggered tsunamis (in the Pacific Ocean), but the death toll was significantly lower than that of the Asian tsunami - ranging from zero to a few thousand.
