ambience: ocean waves
The devastating Indian Ocean tsunami was one of the greatest natural disasters in history. What makes tsunamis so powerful and so dangerous? I’m Jim Metzner, and this is the Pulse of the Planet.
“The scary thing about a tsunami is that it can travel across the ocean losing very, very little energy. “
Gerard Fryer is an associate Geophysicist and tsunami Researcher at the University of Hawaii.
“The wave length of the tsunami, the distance from one crest to the next, may be something like 100 miles or even 200 miles, but the ocean is only about three miles deep. So these are shallow water waves, and the interesting point about shallow water waves is that they always travel at the same speed. The speed is dependent only on the depth of the water, so when the waves finally get to a distant shore, theyâ€™re still carrying all their power all at once that they had when they started. Out on the open ocean the waves are only maybe six inches or so high, but as they get into shallow water, they slow down. And as they slow down, to carry the same amount of energy, they have to increase in height, and thatâ€™s what makes them dangerous. So as a tsunami approaches a coastline, it builds up in size, it slows down, and, eventually it will flood the land.”
How fast was the Indian Ocean tsunami traveling?
“It formed in deep water, and right after it formed, it wouldâ€™ve taken off at about 500 miles an hour and travels across the deep ocean at about that speed. And when it runs into land, it’s probably traveling at about 30 miles an hour. So, the old saying that you canâ€™t outrun a tsunami, actually isnâ€™t true. If you see a tsunami coming, take off, you know, because the tsunami is slowing down. Itâ€™s eventually going to stop. If you saw a car careening at you at 30 miles an hour, youâ€™d run away from it, hoping that the car would stop. Well, tsunamis eventually stop, so if you see a tsunami, run away from it.”