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Undersea Landslide Could be US, Europe Threat

The East Coast of the United States could be hit by giant ocean waves if a dormant volcano on the other side of the Atlantic erupts. An eruption of the Cumbre Vieja volcano in the Canary Islands could cause a massive landslide that would generate massive waves that would sweep across the Atlantic, inundating coastal areas from Maine to Florida.

The energy released by the collapse would be equal to the electricity consumption of the entire United States in half a year. Waves as high as 330 feet would race across the Atlantic. The tsunami would be capable of traveling up to 500 miles an hour and would strike parts of the Eastern Seaboard within nine hours.

According to geophysicists Steven N. Ward of the University of California at Santa Cruz and Simon Day of University College, London, an eruption could send a wave nearly 70-feet high crashing into Florida, while giant waves could also slam Africa, the west Sahara bearing the worst of the wave?s energy. The Caribbean and northeast South America would also be hit. Waves hitting Europe would be smaller, but would slam the coasts of Britain, Spain, Portugal and France.

Ward and Day describe the worst case results of a potential collapse in their paper published in the Sept. 1st issue of Geophysical Research Letters. They note that the rift across Cumbre Vieja runs north to south, with the potential for collapse on the western side of the volcano facing the Americas. Within five minutes of the collapse, a wave 1,500 feet high would head 30 miles out to sea; after 10 minutes it would go down to 900 feet and slam into nearby islands; ater 15 minutes to 60 minutes the series of waves would move outward, with 150-foot crests arriving at the African coast. Spain and England would experience waves of 15 feet to 20 feet because the island of La Palma blocks most of the waves in that direction.

After six or more hours, waves of 30 feet or so would arrive at Newfoundland and 45-foot to 60-foot waves would strike the northeast coast of South America. After about nine hours the East Coast of the United States would experience waves ranging from 30 feet to 70 feet tall.

The Cumbre Vieja last erupted in 1949 and has not shown any recent indications of activity. The volcano is on the island of La Palma, off Africa?s northwest coast. Such an event is an unlikely worst-case scenario, Ward says. ?Let?s not scare people. Certainly there is no indication that this will happen anytime soon.?

?Even when there is an eruption, the probability of collapse is low,? Day adds. ?Eruptions of Cumbre Vieja occur at intervals of decades to a century or so and there may be a number of eruptions before its collapse.?

The most recent tsunami on the East Coast occurred in 1929 when a landslide off Newfoundland created a large wave that killed 30 people in Nova Scotia, Day says.

Unlike surface waves, tsunamis reach all the way to the ocean floor. In mid-ocean they may hardly be noticeable, but as they approach shore, the ocean floor rises and so do the waves above it.

Peter Lipman, a volcanologist with the U.S. Geological Survey in Menlo Park, California, agrees that the threat exists and he is also 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 says. ?Volcanoes try to keep on adding lava to a steep slope and eventually they get the slope so loaded that it fails. I don?t see this as something that is likely to happen very often at La Palma, but it had a failure like this half a million years ago and will again in the future.?

Volcanologist Tom Simkin of the Smithsonian?s National Museum of Natural History agrees that the threat, though small, does exist. ?We all know that big landslides do happen. It doesn?t happen very often, but often enough that we ought to be paying attention to it,? he says.

To read the Geological Society's October, 2000 warning to the UK government on this issue, click here.

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