The warnings are few. The signs are sudden The tide goes into reverse a thunderous roar fills the air and then... it strikes and when it is over nothing is . A tsunami The word in Japanese means "harbor wave". Japan has been hit by many tsunamis in its history as a result of its location It lies accross the edges of four tectonic plates where most earthquakes, the principal cause of tsunamis, are born When two tectonic plates push together, the resulting eathquake sends an enourmous burst of energy up through the ocean displacing enormous quantities of water A series of waves expands in all directions In deep waters, these waves travel fast up to 500 miles an hour but only reach a height of a few feet A passing ship might not even notice but as the waves enter shallow waters friction with the ocean floor lowers the waves' speed and raises their height until at landfall, they can engulf a ten-storey building Unlike ordinary waves a tsunami wave doesn’t crest and break. Instead it advances like a wall of water that crashes into the coastline and everything in its way, reaching even as far as a mile inland. More damage is caused when the wave recedes dragging everything in it back under water. And most tsunamis have multiple waves, each arriving anywhere from 10 to 16 minutes after the first strike. Just when survivors think the danger is over. The deadliest tsunami ever recorded occurred in December 2004. An earthquake off the coast of Indonesia triggered a tsunami that surged across the Indian Ocean and reached as far as the coast of Africa. Whole sections of cities were destroyed More than 200 000 people died. Most had no way of being warned. Five thousand miles away the Pacific Tsunami warning Center in Honolulu is on call twenty four hours a day to prevent a similar tragedy from happening in the United States Scientists monitor tremors and quakes from around the globe. If a quake big enough to cause a tsunami occurs, it is their job to alert the coastlines in the tsunami’s path. The advice is simple: move to higher ground, wait for news of the tsunami has passed and be ready to deal with the ruins left in its wake.