tsunami is usually caused by strong earthquakes that happen in oceans.great sea waves will be pushed towards the shores with great speed.if the people along the shores don't know tsunami is coming,they will suffer great damage.for example,the tusnami,which happened in the indian ocean on december 26,2004,killed more than 150,000 people in indonesia,sir lanka,india,thailand and other countries.millions of people were injured and became homeless.

　　tsunami is a natural disaster.we should set up more advanced warning systems along the shores,on the islands and in man-made staellites.besides,we should protect our oceans further instead of destroying them.