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Anatomy of A Cataclysm: Science of The Tsunami

By Neely Tucker
Washington Post Staff Writer
Tuesday, March 29, 2005; Page C01

It caused the planet to wobble and the day to shorten.

True, there are more precise scientific facts woven into "Wave That Shook the World," the "Nova" special airing on PBS tonight at 8 about the Dec. 26 Indian Ocean tsunami.

The tsunami's aftermath on Thailand's Phi Phi Island: What started as a ripple grew exponentially higher. (Luis Enrique Ascui -- Reuters)

But one of the most catastrophic natural disasters of our lifetime has always seemed more apocalyptic than mere science can describe, something on the verge of the biblical in its range and devastation. (The powerful aftershock yesterday was reported to have killed hundreds, but triggered no tsunami.)

In contrast, the December tsunami killed as many as 280,000 and made millions homeless in 11 countries separated by millions of square miles of open water. As a NASA scientist describes it tonight, the force of the tsunami was so great it made the Earth spin the tiniest bit faster and caused the entire planet to shake in orbit.

That has a certain end-of-the-world quality that is difficult to describe.

But for a very edifying 60 minutes tonight, a range of experts eschew the grand scale of history and instead reconstruct exactly what happened on the seabed 155 miles west of the Indonesian island of Sumatra at 7:59 a.m. on Dec. 26, 2004.

The show, with its emphasis on science rather than the loss of life, is at its best when explaining what made this quake trigger the waves that it did, putting the power of the wave in perspective and telling how the offshore seabed determined the waves' impact on land.

The footage does include some of waves coming ashore, the most disturbing of which briefly shows people being swept into the onrushing water, but there is nothing too graphic for family viewing. And that might be my one complaint -- watching this, you really don't get the full horror, the grief and sorrow, triggered by the destruction.

That said, you can see plenty of that about the tsunami elsewhere, and in tonight's show an array of scientists tell us that on Dec. 26 two tectonic plates far under the Indian Ocean collided. One section was forced partially beneath the other by 30 or 50 feet over the course of about four minutes.

The rupture was massive -- at 720 miles long, the initial earthquake was the largest in the past 40 years and one of the largest in recorded history.

Worse, the rupture happened only 10 or 15 miles beneath the ocean floor. Geologically speaking, that's an inch. It allowed the force of the quake to rocket to the ocean floor with a force equal to about 23,000 Hiroshima-size atomic bombs.

The water above the rupture doesn't just shoot straight up in a geyser, however. It rockets outward at speeds up to 600 miles an hour, as fast as a passenger jet. In deep water, the surface of the ocean does little more than ripple.

But as the wave roils into shallow water, it slows down and grows exponentially higher.

"It slows down to 400, 300, 200 miles an hour," British oceanographer Simon Boxall says on the show. "The back of the wave is still going at 500 miles an hour and the back of the wave catches up with the first, and then you get this big buildup of water."

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