Charting a Tsunami's Path

ByNED POTTER

Dec. 27, 2004 — -- A tsunami can hit without warning. It can drop 200 billion gallons of water on a shoreline in a minute. Scientists say it is one of nature's most massive killers.

"Imagine that you're standing on the beach and the ocean becomes a mountain," said Vasily Titov, co-director of the U.S. government's program for tsunami warnings. "Wherever a tsunami reaches, it creates complete destruction and it kills people very surely. It's a very determined killer."

Earthquakes and hurricanes make headlines more often, but tsunamis are often deadlier. They mostly happen around the edges of the Pacific, set off by earthquakes and volcanoes. Ninety-five percent of the world's seismic activity happens in the Pacific, which is why Sunday's devastation around the Indian Ocean was such a surprise.

The disaster began a few hundred miles off the coast of Indonesia, with a magnitude 9 earthquake. That quake was the largest recorded since one in 1960 in Chile.

If it had happened on land, it would have caused massive devastation, but the effects, most likely, would have been fairly local.

Instead, the shock wave -- spreading from beneath the ocean floor -- sent a giant bulge of water all the way to the surface, six miles above. The ripple effect quickly spread, reaching Sri Lanka in two hours, the coast of India in three hours and the easternmost parts of Africa in six.

On the open ocean, a tsunami can move at 500 miles an hour, but the waves are surprisingly small. If you are on a ship you might not even feel them as they race by.

As they get into shallow water, though, they are slowed dramatically by friction from the bottom -- and the force has nowhere to go but up.

"In the open ocean it was about 3 feet; on the coastline it's about 20 [feet] to 30 feet," said Eddie N. Bernard, director of the Pacific Marine Environmental Laboratory, part of the National Oceanic and Atmospheric Administration.

And the greatest harm is often done as the waves crash back into the ocean -- having ripped loose trees, houses and anything else in the way.

"The flow of debris that is generated by this wave is just a killer," said Titov.

The U.S. mainland has not had a major tsunami in 150 years. There are many small ones, causing nothing more than beach erosion. But in Hawaii they've been the deadliest natural hazard of the last half-century, causing 300 deaths -- more than earthquakes, typhoons or volcanic activity.

In the 1990s, the United States began formal tsunami warnings, using buoys in the Pacific to detect waves. Warnings might be sent to Hawaii, southern Alaska and, albeit rarely, the coasts of Washington, Oregon and California.

But the countries around the Indian Ocean had no warning systems. There seemed no need for a phenomenon that had not been seen on a large scale there in at least 500 years.

For more on how you can help victims of the devastating waves, go to www.usaid.gov.

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