November 22nd, 2012 by Tim Tyler
New studies conducted by researchers at the U.S. Geological Survey have found that tsunamis pose a risk to the East Coast of the United States. Researcher Uri ten Brink noted that, “although the risk is small,” a variety of sources could actually trigger a tsunami on the East Coast.
Brink also stated: “Hurricane Sandy showed [that] the region is completely unprepared for a major influx of water.” Many parts of the East Coast, of course, received devastating flooding from the storm.
According to the findings, an underwater avalanche along the continental slope would be the most likely scenario for an East Coast tsunami. Presented at the annual meeting of the Geological Society of America in Charlotte, N.C., other possible sources discussed that could trigger an East Coast tsunami were earthquakes and even collapsing volcanoes.
With underwater avalanches posing the greatest risk, Brink said: “An offshore earthquake of magnitude 4.5 or above could cause submarine avalanches and create dangerous tsunamis with waves higher than 26 feet.” Along the East Coast there are many underwater canyons and bays that could make the tsunami bigger by focusing the waves as they come to shore.
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.
Core samples are being taken of the sediment from the submarine canyons along the continental slope to determine evidence of past landslides and their frequency. More than five years of data have been collected to map these submarine canyons with sonar in order to highlight areas most at risk of landslides, Brink added.
The Puerto Rico Trench
“The movement of tectonic plates beneath the ocean can create waves that travel much farther than those caused by submarine landslides, because they involve the movement of a much larger volume of water, with longer waves that don’t quickly dissipate,” according to Brink. When one plate dives below another at the subduction zone, it can create the most dangerous type of earthquake.
While the most infamous subduction zones are found around the Pacific Ring of Fire — such as the one that set off the massive 2011 Japan tsunami — there is indeed a subduction zone capable of creating tsunamis near the East Coast. In the northeast Caribbean, the area called the Puerto Rico trench features a subduction zone.
When the 2004 Indian Ocean tsunami hit, ten Brinks’ group received funding from the U.S. government to study the tsunami potential of the Puerto Rico trench. Although its work is still ongoing, his group has found that much of the fault doesn’t appear capable of creating an earthquake and tsunami large enough to cause big problems for the East Coast. But a tsunami originating there could cause significant destruction in the Caribbean.
A researcher from the University of Puerto Rico said, “one quake in this region in 1918 created a tsunami that killed 116 people on Puerto Rico.” The researcher, Zamara Fuentes, has been studying sediment cores around the Caribbean searching for evidence of past tsunamis. According to USGS historical records, a total of 27 tsunamis in the Caribbean have caused fatalities and extensive damage since the 16th century.
Risks Across the Atlantic
The Canary Islands also pose a potential threat. The small island La Palma, which is part of the Canary Islands, is home to the large volcano Cumbre Vieja. This large volcano could erupt and pose a threat of collapsing into the sea, which would 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, in Brink’s research, he felt that it wasn’t a “credible threat” to the East Coast.
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.
To get a good idea of how often tsunamis from this or any source are likely to strike the East Coast in the future, ten Brink and others are trying to peer back in time — but much remains to be discovered. “There are more questions than answers at this point,” ten Brink said.
While the odds of a tsunami scenario striking the East Coast are relatively low. It seems researchers are doing a lengthy study to find out exactly what the odds are. Lets hope the odds stay low.
Photo Credit: Jaimito Cartero
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