什麼是海嘯？
Tsunamis are giant waves caused by earthquakes or volcanic eruptions under the sea. Out in the deep ocean, tsunami waves are not very tall. But as they travel toward land and the water becomes shallower, they build up to greater and greater heights.
The speed of a tsunami depends on the depth of the ocean, not on how far it is from where it started. In deep water, tsunami waves can travel as fast as a jet plane, and they only slow down when they reach shallow water.
Tsunamis are often called "tidal waves", but oceanographers discourage this name, because tides have very little to do with these giant waves.
In September 2009, for example, a large earthquake in the southern Pacific Ocean caused a tsunami that brought serious damage and loss of life to Samoa, American Samoa and Tonga.
海嘯是海底地震或火山爆發所引起的巨浪。在深海裡，海嘯的浪並不太高；可是當它們往陸地推進、海水越來越淺時，浪就會變得越來越高。
海嘯的速度取決於海水的深度，而不是離發源地有多遠。在深海中，海嘯可以跑得和噴射機一樣快，只有到了淺水區才會慢下來。
海嘯常常被叫做「潮汐波」（tidal wave），但海洋學家不贊成這個叫法，因為潮汐和這種巨浪幾乎沒有關係。
例如，2009 年 9 月，南太平洋發生一場大地震，引發的海嘯讓薩摩亞、美屬薩摩亞和東加受到嚴重的破壞，也造成了人員傷亡。