A frightening revelation has been made by a team of U.S. scientists. They predict that there is a serious risk of a devastating tsunami occurring in the Caribbean Sea off the coasts of Puerto Rico, Haiti and the Dominican Republic. They base their forecast on historical records.

In an article in Eos, the newspaper of the American Geophysical Union, scientists Nancy Grindlay and Meghan Hearne of the University of North Carolina, Wilmington, and Paul Mann of the University of Texas, Austin said 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.

According to their calculations, that's an average of one significant tsunami every 50 years. The most recent occurred in 1946 - sixty years ago - when a magnitude 8.1 earthquake in the Dominican Republican triggered a giant wave that killed 1,800 people.

The scientists said the dates imply that another tsunami is already overdue, but added they can't predict when it might happen.

An earthquake in that northern part of the Caribbean could generate waves up to 40 feet high and threaten the lives of up to 35.5 million people living in coastal areas. Smaller waves could reach Florida, the Gulf of Mexico and as far north as New Jersey.

They wrote: "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."

George Pararas-Carayannis, former director of the International Tsunami Information Centre in Honolulu, Hawaii said that since 1489, in all 88 tsunamis - most of them moderate - have been reported in that part of the Caribbean which is located on an earthquake fault and ringed by volcanoes.

"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.

The Eos article states that the northern Caribbean is capable of generating tsunamis of at least up to 12 meters (40 feet) high. It added that the effects of past tsunamis have extended up to 1320 miles.

"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," said Martitia Tuttle, a tsunami expert in Georgetown, Maine, who is not part of the Eos team. "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 added.

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 article stated.