The ground shakes. The tide goes into reverse. A thunderous roar fills the air.
And then it strikes. Wave after wave of crashing, crushing water. And when it is over, nothing is left.
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 across the edges of 4 tectonic plates, where most earthquakes -- the principal cause of tsunamis – are born.
When two tectonic plates push together, the resulting earthquake sends an enormous burst of energy up through the ocean, displacing enormous quantities of water.
A series of waves expands in all directions. In deep water, 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 10 story building.
Unlike ordinary waves, a tsunami wave doesn’t crest and break. Instead, it advances like a wall of water that crashes over the coastline and everything in its way, reaching even as far as a mile inland.
The initial impact is only the first blow. More damage is caused when the wave recedes, dragging everything in it back underwater.
And most tsunamis have multiple waves, each arriving anywhere from 10 to 60 minutes after the first strike, just when survivors think the danger is over.
The deadliest tsunami ever recorded occurred in December of 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.