A tsunami /suːˈnɑːmi/ also called a tsunami wave train,and at one time referred to as a tidal wave, is a series of water waves caused by the displacement of a large volume of a body of water, usually in the ocean, though it can occur in large lakes. Owing to the immense volumes of water and the high energy involved, tsunamis can devastate coastal regions.

Tsunami generated by seismicitya tsunami can be generated when thrust faults associated with convergent or destructive plate boundaries move abruptly, resulting in water displacement, owing to the vertical component of movement involved. Movement on normal faults will also cause displacement of the seabed, but the size of the largest of such events is normally too small to give rise to a significant tsunami.

When the wave enters shallow water, it slows down and its amplitude (height) increases.

DrawbackIf the first part of a tsunami to reach land is a trough—called a drawback—rather than a wave crest, the water along the shoreline recedes dramatically, exposing normally submerged areas.A drawback occurs because the water propagates outwards with the trough of the wave at its front. Drawback begins before the wave arrives at an interval equal to half of the wave's period. Drawback can exceed hundreds of metres, and people unaware of the danger sometimes remain near the shore to satisfy their curiosity or to collect fish from the exposed seabed.

斯 里 兰 卡 Kalutara 海 滩 海 啸

前 ， 2004-1-1 摄

斯 里 兰 卡 Kalutara 海 滩 海 啸

时 海 浪 退 水 ， 2004-12-26 摄

更多信息详见http://en.wikipedia.org/wiki/Tsunami 维基百科 – 海啸http://baike.baidu.com/view/9425.htm百度百科 – 海啸