WASHINGTON—Based on the historical record, there's a serious risk of a devastating tsunami in the Caribbean Sea off the coasts of Puerto Rico, Haiti and the Dominican Republic, a team of scientists reported Wednesday.
An earthquake in that region could generate waves up to 40 feet high and threaten the lives of up to 35.5 million people living in coastal areas, they said. Smaller waves could reach Florida, the Gulf of Mexico and as far north as New Jersey.
Ten destructive tsunamis have been generated in the past 500 years by undersea earth movements along the boundary between the Caribbean and the North American tectonic plates—two of the great, moving slabs of rock that cover the ocean floor.
That's an average of one significant tsunami every 50 years. The most recent occurred in 1946—59 years ago—when a magnitude 8.1 earthquake in the Dominican Republican triggered a giant wave that killed 1,800 people.
The dates imply that another tsunami is already overdue, but experts say they can't predict when it might happen.
The scientists—Nancy Grindlay and Meghan Hearne of the University of North Carolina, Wilmington, and Paul Mann of the University of Texas, Austin—will publish their report in the March 22 issue of Eos, the newspaper of the American Geophysical Union.
"The rapid increase in population in the northern Caribbean to its present level of 35.5 million people means that future tsunamis will be much more destructive than the historical ones," they predicted.
In all, 88 tsunamis—most of them moderate—have been reported in the earthquake-prone, volcano-ringed Caribbean area since 1489, according to George Pararas-Carayannis, former director of the International Tsunami Information Center in Honolulu, Hawaii.
"Several of these were generated by volcanic eruptions and by collateral volcanic flank failure, debris avalanches and landslides," he wrote last year in the Science of Tsunami Hazards, a professional journal.
At least six Caribbean tsunamis are known to have killed people: in 1692, 1781, 1842, 1867, 1918 and 1946. The total death toll is unknown but at least 2,000 persons perished.
According to the Eos report, "the northern Caribbean is capable of generating tsunamis of at least up to 12 meters (40 feet) high." The effects of past tsunamis have extended up to1320 miles, it said.
"More sobering than the historical record of tsunamis is the presence of large scale underwater landslide features that may have produced immense, prehistoric (before 1400 AD) tsunamis along the northern margin of Puerto Rico that were much larger than any of those known from 500 years of historical records," the report said.
Underwater landslides cause tsunamis by displacing large volumes of water, forcing it to surge upward in a powerful wave.
"This is serious," Martitia Tuttle, a tsunami expert in Georgetown, Maine, who is not part of the Eos team, said in a telephone interview.
"Because it has happened in the historic period, certainly it's likely to happen in the future, but at this point we can't predict when," she said.
Tuttle noted that there's evidence of a major earthquake along the Caribbean plate boundary about 800 years ago.
"Strain has been accumulating on that fault since then," she said. "Enough strain has accumulated to generate a quite large—7 to 8 magnitude—earthquake, but when we can't say."
In addition to past earthquakes, marine geologists have reported many small underwater landslides and cracks, 20 miles or more long, existing in the sea floor off the coast of Puerto Rico, near where the 1918 tsunami originated.
"Cracking indicates that these areas are close to failure," the Eos report said.
For a primer on tsunamis, go to http://en.wikipedia.org/wiki/Tsunami.
TSUNAMIS IN THE CARIBBEAN
At least six lethal tsunamis have occurred in the Caribbean since historical records began with the arrival of Christopher Columbus in 1492, according to a paper to be published by the American Geophysical Society.
1692: An earthquake that destroyed Port Royal, Jamaica, caused a tsunami that inundated the south coast of the island. About 2,000 people died.
1781: A 10-foot high sea wave swept away houses and killed 10 people on the south coast of Jamaica after an earthquake that occurred during a hurricane.
1842: An earthquake generated a wave from 10 to 16 feet high along the northern coasts of the Dominican Republic, Haiti and the Virgin Islands. Several hundred fatalities were recorded at the time, but it's not clear how many were tsunami-related.
1867: A magnitude 7.5 earthquake off the coast of Puerto Rico caused a wave up to 40 feet high in the U.S. Virgin Islands. Only 17 lives were lost.
1918: Another 7.5 magnitude earthquake in the Mona Passage, between Puerto Rico and Haiti, produced a 20-foot wave on the west coast of Puerto Rico. There were 116 fatalities, 40 of them directly from the tsunami. Two-inch waves were recorded at Atlantic City, N.J.
1946: A magnitude 8.1 earthquake off the northeast coast of the Dominican Republic triggered a tsunami that killed about 1,800. The wave was also recorded at Daytona Beach, Fla., and Atlantic City.
(c) 2005, Knight Ridder/Tribune Information Services.
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