Both coasts may be in danger from deadly waves

WASHINGTON -- The giant waves called tsunamis, long known as a danger in the Pacific Ocean, may also pose a danger to the U.S. East Coast.

While stressing that there is no indication it could happen soon, a pair of scientists is warning that a slumbering volcano on the island of La Palma, off the coast of Africa, could one day give way in a massive landslide, sending waves up to 70 feet high crashing into Florida and other coastal states.

The volcano, Cumbre Vieja, last erupted in 1949. It has not shown any recent activity.

But one day a new eruption could cause an existing rift across the volcano to split open, sending a landslide crashing into the ocean, say geophysicists Steven N. Ward of the University of California at Santa Cruz and Simon Day of University College, London.

Won't happen soon

Ward stressed that a wave that size is unlikely, and that smaller landslides would produce waves one-fourth to half that height.

"Even when there is an eruption, the probability of collapse is low," Day said. "There may be many eruptions before the volcano is finally weak enough to collapse."

Peter Lipman, a volcanologist with the U.S. Geological Survey in Menlo Park, Calif., agreed that the threat exists from the volcano. He, too, was cautious about when such a disaster might occur.

"These oceanic island volcanoes are, in geologic time, very subject to exactly the kind of process they describe," he said. "Volcanoes try to keep on adding lava to a steep slope and eventually they get the slope so loaded that it fails."

Ward and Day's findings are reported in the Sept. 1 issue of Geophysical Research Letters.

Reaches ocean floor

Tsunamis (soo-NAHM-ee), long have been known as a danger around the Pacific Ocean, where warning centers monitor the sea and alert coastal residents. They are often generated by earthquakes or landslides under the sea. Occasionally, t;hey are referred to as tidal waves.

The waves have not received much attention as a hazard in the Atlantic. The most recent tsunami on the East Coast was in 1929 when a landslide off Newfoundland created a large wave that killed 30 people in Nova Scotia, Day said.

Unlike surface waves, tsunamis reach all the way to the sea floor. In mid-ocean they may hardly be noticeable, but as they approach shore the sea floor rises and so does the wave above it, potentially rising to giant status. And they travel very fast.

The worst scenario runs like this: Within five minutes of the collapse, a wave 1,500 feet high has zoomed 30 miles out to sea; at 10 minutes, it is down to 900 feet and slams into nearby islands. After six or more hours, waves of 30 feet or so arrive at Newfoundland and at about nine hours, the East Coast of the United States is hit by waves ranging from 30 feet to 70 feet.