Tens of thousands of people lost their lives on Christmas Day by devastating tsunami waves triggered by one of the most violent earthquakes in Indian Ocean in a century. But why the disaster comes so sudden and widespread? And what's a tsunami in the end?

A depressing proof that the mankind is still so weak and helpless when mother nature loses temper, even in an age marked by omnipotence of high-tech. But although science did nothing to forecast the disaster, it still can shed some light on this tragic event.

British geologists say the violent collision between the Indian Plate and the Eurasian Plate was the chief culprit of the disaster. Seismic monitoring network shows that the Indian Plate has been moving northward and constantly colliding with the neighboring Eurasian Plate. The turning point came when the line of over 1,000 kilometers of rocks separating the two Major Plates to the west of the Indonesian island of Sumatra could no longer bear the impact and collapsed all of a sudden. The jolt of massive quake up to 9 degree on the Richter Scale let loose a vertical movement of the seabed, shaking the whole water body from the surface to the bottom.

Zhang Xiaodong, Deputy Director of China Seismic Monitoring Network Center, said: "Why earthquake under the sea can trigger tsunami? As usual, when an undersea earthquake reaches the level of 6.5 degree on the Richter Scale, the displacement of the earth crust can jolt the deep sea violently. The seismic wave will gradually transmit to the upper layer of the sea and spread to even wider area at that level. When the seismic wave reaches the coast, it surely will cause very serious disaster. Sweeping waves can be as high as large buildings, affecting human life and constructions on land. "

The unexpected disaster at a time when everyone should be happiest has prompted a worldwide relief campaign for the affected region. But the tourism industry of the region, usually the pillar of their economy, may take years to recover.