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Florida's (unlikely) tsunami scenario
Could a wall of water sweep suddenly from the east, crushing its way inland? Well ...
By THOMAS C. TOBIN
Published December 28, 2004
It's not something anyone could control. And it may never happen in your lifetime. (Though it could.)
But some scientists have developed a scenario in which a titanic landslide off the western coast of Africa could trigger a tsunami that would race across the Atlantic Ocean in nine hours and slam into Florida's east coast.
A computer model has it hitting Cape Canaveral harder than any hurricane - with a speeding wall of water 82 feet high, more than twice as tall as the 40-foot tsunami waves that devastated coastal areas Sunday across South and Southeast Asia, killing thousands.
The good news: Floridians and others on the U.S. East Coast likely would have days, even weeks, of warning.
The Florida scenario, made public in 2001 by a team of scientists in London and California, isn't one that creates much urgency at the National Oceanic and Atmospheric Administration. That agency and others concentrate their efforts in the Pacific basin, where tsunamis caused by earthquakes occur with relative frequency.
So common are earthquakes in that region that officials worry about false alarms.
The nation's Tsunami Hazard Mitigation Implementation Plan focuses on protecting coastal residents in California, Washington, Oregon, Hawaii and Alaska.
But could a tsunami threaten a certain low-lying state at the other end of the country? One surrounded on three sides by water? One already plagued by hurricanes, wildfires and drought?
"That's a good question," said Harold Mofjeld, a senior scientist at NOAA's Tsunami Research Program in Seattle.
What about a tsunami from the Gulf of Mexico?
"Unknown," Mofjeld said. Scientists are only now engaging in basic research about the gulf's continental slope, he said.
As for the Atlantic Ocean: "That's the next step."
Mofjeld said NOAA's responsibilities include notifying Americans about tsunamis from the east. But preparations are nowhere near the level of preparedness in the Pacific, with its impressive system of stations and buoys monitoring seismic and wave activity thousands of miles from U.S. shores.
Plans are under way for a warning center based in Puerto Rico that would warn of tsunamis generated by earthquakes in the Caribbean. The Atlantic, however, is not as prone to earthquakes as the Caribbean or the Pacific, Mofjeld said.
He said it doesn't have the same "subduction zones," where plates of the earth's crust overlap and grind, eventually giving way to the pressure.
Researchers, he said, are still tackling the question of how landslides cause tsunamis - the phenomenon that gives rise to the Florida scenario.
"How probable it is I don't think anybody has any idea right now," Mofjeld said. "It would have to be a very big event to begin with."
A "very big event" is exactly what scientists Simon Day and Steven N. Ward envision with the potential collapse of the Cumbre Vieja volcano in the Canary Island chain off the western coast of Africa.
Day works at the Benfield Greig Hazard Research Centre at University College in London. The center says it provides "cutting-edge" risk research for business, government and international agencies. Ward, a research geophysicist at the University of California at Santa Cruz, applied Day's theories about the Cumbre Vieja volcano to a computer model.
Based on evidence of a dozen major volcanic collapses in the Canary Islands over millions of years, the scientists say the western flank of Cumbre Vieja is due to give way during a future volcanic eruption. The last three eruptions were in 1971, 1949 and 1712.
In an interview Monday, Ward compared the vast layers of volcanic ash collecting on the mountain to roof shingles being piled high.
"They're not very stable," he said.
The scientists say the next eruption or two - or three or four - could trigger a massive collapse of the mountain's western flank. They estimate the falling chunk could be the size of a small island, perhaps 9 miles long and 9 miles wide.
They say it would drop almost vertically from the Cumbre Vieja's especially steep slope and straight into waters measuring 4,000 feet deep. Ward likened it to dropping a vast quarry into the ocean from several hundred feet. The energy released would be equal to all the electricity consumed in the United States over six months.
From there, the scenario plays out like a Hollywood disaster film.
Within two minutes, a massive splash or "water dome" reaches 3,000 high. Within an hour, waves up to 300 feet sweep through the islands and crash along the African mainland. In three to six hours a tsunami 300 miles long arcs across the Atlantic, hitting Spain and England with small waves. The north end of the arc brushes Newfoundland with 32 foot waves; the south end hits South America with 65 foot waves.
"At nine hours," the scientists' paper says, "Florida faces a tsunami, now parading in a dozen cycles or more."
It likely would go several miles inland and result in trillions of dollars of damage, the paper says.
Not wanting to scare the public, the scientists add several caveats: The volcanic eruption would happen gradually, affording time to prepare; the model envisions the mountainside collapsing in one piece; and there's no telling how many eruptions it would take to bring about the collapse.
Day could not be reached Monday for comment but has said that the "short-term and medium-term" risks of a collapse are "negligible."
However, at a news conference Monday in London, Benfield Greig scientists told reporters that the U.S. should take the threat at Cumbre Vieja more seriously.
"The important message here is we want to keep a little closer eye on (Cumbre Vieja) perhaps," Ward said in an interview. As for a tsunami monitoring system in the Atlantic, he said, "It wouldn't hurt."
- Information from Reuters was used in this report.
[Last modified December 28, 2004, 04:28:17]
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