Study Tracks Path of Indian Ocean Tsunami

Since December's Indian Ocean tsunami, scientists have tried to retrace the path of the giant waves to learn how and why the water moved in unexpected directions. Researchers who say they have mapped the tsunami's route note their findings in the journal Science.

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Six months ago, a giant earthquake and tsunami hit the Indian Ocean. The disaster ranks as one of modern history's most lethal, killing as many as 300,000 people. Survivors described what happened when the waves hit the shore and photos and homemade videos captured moments of terror. Now scientists have had time to take careful measure of just how big and powerful those waves were. NPR's Christopher Joyce reports on some of their findings.


Jose Borrero spent his own money to fly to Sumatra after he heard about the tsunami. He arrived in the hardest hit city, Banda Aceh, amid chaos and despair. As a tsunami expert, he came to measure this freakish act of nature before its marks disappeared. Banda Aceh was built on a coastal plain and was largely gone. To find out how high up the water reached, Borrero looked for water marks or rack lines of debris on cliffs or mountainsides along Sumatra's west coast. It was like looking for a giant bathtub ring.

Mr. JOSE BORRERO (University of Southern California): The water came rushing up the side and actually stripped away all of the trees, all of the topsoil, all the vegetation and was down to almost bare rock up to an elevation of, you know, 20, 25 meters. Then if you would climb a little bit above that into the green of the jungle that survived, you would find some of the debris that was pushed up even higher.

JOYCE: At places along the west coast, the water reached 31 meters, about a hundred feet high, or the height of about a 10-story building. Borrero also confirmed that the ocean penetrated far inland. He could tell exactly how far by comparing his own on-the-scenes observations with satellite images.

Mr. BORRERO: When 10 to 15 meters of sea level rise happens, it just goes as far inland as it wants to, basically to the base of the mountains which in some places was, you know, four or five kilometers.

JOYCE: Something else the tsunami did was turn a corner. The waves originated in the open ocean to the west of Sumatra. Banda Aceh is protected from the sea by a peninsula of land. When the waves hit, they changed direction. They bent around the peninsula and charged straight down into the city. But that wasn't all. The city was actually pinned between two wave fronts.

Mr. BORRERO: Some witnesses said that the water came from both directions, meaning from the west and also from the north, and at first, I was, like, `That's impossible,' until I kept driving--this was on my way out to go look at the west coast for the first time and then I realized that this tsunami damage didn't stop and then it just got worse until I got to the beach on the other side of Sumatra.

JOYCE: What happened was the western wave front traveled more than a mile over land and smashed into the waves coming down from the north with Banda Aceh caught in the middle. Borrero, who does research at the University of Southern California, described his findings in this week's issue of the journal Science.

Another team writing in the journal reports on the tsunami's direct hit on Sri Lanka, an island off the southern tip of India. Philip Liu of Cornell University says witnesses agreed there were three waves, the second was the highest. Using the same measurement techniques that Borrero used in Sumatra, Liu says that wave reached 30 feet high in some places. Shorelines where barrier sand dunes or coral reefs had been removed were often hit the hardest. Although the tsunami came from the southeast, Liu heard puzzling stories about big waves hitting the west coast of Sri Lanka several hours later. He says the explanation lies with the Maldive Islands, hundreds of miles to the west of Sri Lanka.

Mr. PHILIP LIU (Cornell University): Part of this wave reflected back from Maldive. Maldive serves like a vertical barrier of these islands.

JOYCE: Liu and Borrero say their measurements and those of other scientists will help refine computer models of tsunamis. They say satellite observations cannot only direct rescuers where they'll be needed the most, but also indicate where people shouldn't build in the future, and their computer models will help scientists predict how big waves will behave. Christopher Joyce, NPR News.

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