Geology profs explain source of tsunamis

07 January 2005 | 11:36 Code : 4614 Geoscience events
On the morning of Dec. 26, a 30-foot tsunami crashed into the coasts of Indonesia, Thailand, Sri Lanka and southern India at the speed of a jet plane.

On the morning of Dec. 26, a 30-foot tsunami crashed into the coasts of Indonesia, Thailand, Sri Lanka and southern India at the speed of a jet plane.But what caused the deadly waves? Northwestern geology professors are making sure students understand the science behind the tragedy.Geology Prof. Emile Okal is hosting a lecture, titled "The Sumatra Disaster: Questions and Answers with a Tsunami Scientist" Saturday at 5 p.m. in Harris Hall.

"I feel it's part of my duty as a professor to share my knowledge and expertise with the Northwestern community at large," Okal said. Okal said he hopes to tell students a few stories about how being educated about natural disasters can help save lives and then open the floor to questions.Geology Prof. Seth Stein included a lecture on what caused the Indian Ocean tsunami in his "Geology 202" class on Monday. Stein explained to students what caused the tsunami and why it was so deadly.

Stein said tsunamis are caused by earthquakes on the ocean floor, which in turn are caused by a shift in Earth's tectonic plates along fault lines. The Indian Ocean earthquake that caused the December tsunami occurred along the Sunda trench, between the India tectonic plate and the Burma tectonic plate. Stein said although the plates usually move only about 50 millimeters every year, about 200 years of accumulated motion along the fault line caused it to move by 30 feet.

"Think of taking a 700-mile-long stretch of sea floor and pushing it 30 feet," Stein said. The drastic move caused the ocean floor to collapse in some places and rise in others, displacing a large amount of water and generating waves, or tsunamis, Stein said.

"The thing travels at about the speed of a jet plane across the ocean, but in the deep ocean, its amplitude is small," Stein said. "If you were in a boat you would never even notice it, but as the wave approaches shore, it slows up, and its amplitude builds up to conserve energy."Stein said the nature of the tsunami gave it several destructive qualities. He said most people probably drowned when they were swept up by the powerful wave, but others were killed by debris. He also said the tsunami flooded coastal water wells with salt water, depleting stores of fresh water. Finally, the cesspools created by the stagnant salt water will become mosquito breeding grounds and bring the threat of water- and insect-borne diseases. Stein also addressed one of the questions that has victims most distressed: "Why wasn't anyone warned?"He said other areas of the world track tsunamis by evaluating seismic waves, which travel much faster than the tsunami and can serve as warnings. But because tsunamis in the Indian Ocean are rare, neighboring countries failed to produce a warning system.

"This was just an organizational failure," Stein said. "The idea of creating an Indian Ocean tsunami system had been floating around for a while, but in never reached the top of any country's priority list."Both Stein and Okal agree that increased education about tsunamis may help prevent future disasters.

"When people for one reason or another are more aware of the nature of such dangers, lives are saved," said Okal.


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