A theory of a “mega-tsunami” that wipes out the East Coast was widely debunked. Yet it persists.

March 06--Some say a volcanic explosion on an island 3,500 miles away could push out a wall of water that would destroy much of the East Coast of the United States.

Sound far-fetched? It is, according to much research by geologists. But that doesn't stop the theory from creeping back into public discussion each time tsunamis are mentioned.

It happened again a month ago, when AccuWeather sent an erroneous alert that for a few tense moments made people on the East Coast think a wall of water was coming their way. Once again, predictions about La Palma, in the Canary Islands off the coast of Morocco, began to circulate.

Generally the scenario goes like this: The Cumbre Vieja volcano on La Palma falls into the ocean, sending disaster-movie-like waves throughout the Atlantic Basin. A BBC docudrama series in 2000 called "End Day" took that image mainstream, showing water rushing as far west as Richmond, destroying almost everything along the way.

"It's more like a worst, worst, worst case scenario, where the (computer) model runs were so simplified that such a disaster seemed much more likely," said Uri ten Brink of the U.S. Geological Survey. Brink helped author a 2016 technical report for the U.S. Nuclear Regulatory Commission that largely debunked the "End Day" scenario.

"It has happened before, some 100,000 to 200,000 years ago (at La Palma) because we have seen some of the landslide deposits on the sea floor. But these are not frequent events.

"One of the things we struggle with with natural disasters is that these are rare events that don't happen very often. But when they do, they are serious disasters."

Some in the scientific community put more stock in the possibility than others, like Steve Ward of the University of California at Santa Cruz and Simon Day, who formally worked there. In analysis papers written in 2001 and 2005, they said the BBC scenario was "highly possible."

Others downplay it but maintain just a touch of caution, like Larry Atkinson, an oceanography professor at Old Dominion University.

"There is some geological evidence that it could happen," Atkinson said, pointing to rocks that seem to indicate a landslide at the Fogo volcano in the Cape Verde Islands off west Africa 73,000 years ago.

"But a lot of things 'could happen.' Asteroids fly by all the time, too."

The Fogo eruption was detailed in a paper written by Ricardo Ramalho, a research fellow at the University of Bristol in England. He wrote that 700-ton boulders that sit high in the hills of an island about 35 miles away ended up there after a tsunami caused by an eruption some 73,000 years ago.

In his report, Ramalho said events like that "don't happen very often. But we need to take this into account when we think about the hazard potential of these kinds of volcanic features."

The USGS report said that while some predictions say La Palma would cause waves "hundreds of meters" high, those waves would likely be more like 10 meters. Still, that would cause plenty of damage to the East Coast.

The good news in that report is that any tsunami action caused by a La Palma landslide would take between five and six hours to reach the U.S. coast. The U.S. Tsunami Warning Center would immediately start monitoring its system of buoys and would send out alerts -- potentially giving residents enough time to head to higher ground a couple of hours to the west.

"Most researchers would say the chances of an event like the BBC scenario are very low," Brink said. "There have been lots of papers written on this subject, and all of the proper modeling show waves being drastically lower.

"An awful lot of energy would be lost by the time a tsunami got to the United States."

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