New study says U.S. East Coast faces variety of tsunami threats

NEW YORK – Although the risk is small, tsunamis are possible on the East Coast of the United States from a variety of sources, according to new research. And as Hurricane Sandy showed, the region is completely unprepared for a major influx of water, said U.S. Geological Survey researcher Uri ten Brink. The most likely source for an East Coast tsunami would be an underwater avalanche along the continental slope, according to research presented by ten Brink and others earlier this month at the annual meeting of the Geological Society of America in Charlotte, N.C. Ten Brink also outlined several other possible sources of tsunamis, including earthquakes and even collapsing volcanoes. An offshore earthquake of magnitude 4.5 or above could cause submarine avalanches and create dangerous tsunamis with waves higher than 26 feet (8 meters), ten Brink told OurAmazingPlanet. Underwater canyons and bays could focus these waves and make them even bigger. A 7.2-magnitude earthquake off the southern coast of Newfoundland in 1929 caused a large underwater landslide, creating a large wave that rushed ashore and killed 28 people on the island, ten Brink said. The waves were up to 26 feet high until some reached narrow inlets, where they grew to 43 feet (13 m), he said. While the tsunami was catastrophic for Newfoundland, it created only small waves for most of the U.S. coast and didn’t cause any fatalities there. That’s typical of tsunamis from submarine landslides: They tend to be large for nearby areas but quickly taper off, ten Brink said. While this is the only example of a tsunami near the East Coast in recorded history, there are plenty of areas along the continental slope — where the North American continent ends and drops into the Atlantic Ocean basin — at risk for these landslides, ten Brink said. Another possible source for East Coast tsunamis is the Azores-Gibraltar Transform Fault, off the coast of Portugal. One massive earthquake along this fault in 1755 destroyed most of Lisbon and created a tsunami recorded as far away as Brazil. It was barely noticed on the East Coast, however, ten Brink said. His group has created computer models that suggest underwater mountains west of Portugal helped reduce the impact of this tsunami by slowing the waves and  disrupting their movement— and they could do the same thing in the future. The nearby Canary Islands, off the coast of Morocco, also present a possible hazard. One large volcano on the island of La Palma, called Cumbre Vieja, could erupt, collapse and create a large tsunami capable of reaching the East Coast. A 2001 study suggested this series of events could send a 70-foot (21 m) wave crashing into the East Coast. But ten Brink said that study hasn’t held up to subsequent review, and that the wave would be unlikely to exceed several feet in height by the time it reached North America. “I don’t see it as a credible threat,” he said. The last possible tsunami source is a slow-moving fault north of Cuba, which has caused earthquakes in the past and possibly could create a tsunami that affected Florida and the Gulf Coast. Due to the current political situation, neither Cuban nor American researchers can conduct research in the area, he said. –MNN

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