Atlantic capable of deadly tsunamis, experts say

Earthquakes, landslides, eruptions triggered waves 9 times since 18th century

December 28, 2004|By Michael Stroh | Michael Stroh,SUN STAFF

Could it happen here?

The deadly tsunamis that crushed coastlines across Southeast Asia and Africa over the weekend might seem a world away. But researchers cautioned yesterday that the Atlantic Ocean is capable of spawning similarly deadly walls of water.

"It's just a matter of time," says Harry Woodworth, a meteorologist in the Philadelphia office of the National Weather Service who studies Atlantic tsunamis.

Although tsunamis are of more concern in Asia and the Pacific Rim, Woodworth says the deadly waves can occur anywhere that water is disturbed by an earthquake or other major geological event.

The meteorologist has documented at least nine instances of giant waves striking the East Coast or Caribbean since the 18th century. The most catastrophic, in 1929 off the coast of Canada, killed up to 50 people.

Though Atlantic tsunamis have been far less deadly than their counterparts in Asia - those Sunday are estimated to have killed more than 22,0000 - scientists say the phenomenon may warrant more attention and are trying to raise awareness of the potential danger.

"We may have severely underestimated the level of the tsunami hazard along the margins of the Atlantic Ocean," concluded a report issued last year by the Benfield Hazard Research Centre of the University College London.

The term tsunami derives from the Japanese tsu (harbor) and nami (wave). Though often mistakenly referred to as tidal waves, tsunamis have nothing to do with the behavior of tides. Most are born deep under the ocean, triggered by earthquakes such as the 9.0-magnitude quake off the Indonesian island of Sumatra over the weekend.

George Maul, an oceanographer at the Florida Institute of Technology, says earthquakes caused several major Atlantic tsunamis. In 1755, a major earthquake off the coast of Portugal triggered a tsunami that swept across the Atlantic. Some Caribbean islands reported 21-foot waves.

In 1946, an earthquake off the Dominican Republic created a tsunami felt as far north as Atlantic City, N.J.

Maul says Caribbean islands are especially prone to tsunamis because they lie over a subduction zone where two of the Earth's plates grind together. Maul is attempting to help create a tsunami warning system in the Caribbean similar to the one the National Oceanic and Atmospheric Administration operates in Hawaii and Alaska to monitor the Pacific Rim.

But scientists note that tsunamis can be caused by geological events other than earthquakes. And research suggests that the most devastating Atlantic tsunamis could be created by volcanic eruptions and landslides.

In 1929, a 7.2-magnitude earthquake struck the Grand Banks, off Newfoundland, shaking sediment on the continental slope. As the sediment slid to the ocean floor at speeds exceeding 40 mph, it triggered a tsunami that killed dozens. The effects of the tsunami were felt as far south as New York City.

An earthquake or other triggering mechanism doesn't have to be near to be deadly. The tsunamis Sunday ravaged shorelines in Somalia, in East Africa, 1,000 miles west of the quake's epicenter near the Indonesian island of Sumatra. In 1960, a quake in Chile sparked a tsunami that killed people as far away as Japan.

Today, some scientists are casting a worried eye on a volcano in the Canary Islands, off the coast of Morocco. Known as Cumbre Vieja, the volcano cleaved nearly in half after its last eruption in 1949. Scientists fear that another eruption could shake loose a rock slab the size of Manhattan.

In 2001, Steven Ward of the University of California, Santa Cruz and a colleague created a computer model to find out what would happen if such a piece of Cumbre Vieja fell into the Atlantic.

The model predicted that the African coast would be pummeled by a 325-foot wave. Nine hours later, waves up to 80 feet high could crash down on the East Coast, submerging cities from New York to Miami. Damage in the United States alone could run into the trillions of dollars, experts say.

"Nobody knows when it's going to happen. It could happen next year or centuries from now," says Michael Kearney, a University of Maryland geographer who studies the impact of waves and storms on coastal systems.

Kearney says a 30-foot tsunami such as hit Southeast Asia on Sunday could devastate low-lying areas in Maryland.

While such an event is possible, he says, "I don't lose any sleep over it. The chances are infinitesimally small. We're more likely to get hit by a Category 5 hurricane."

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