Volcano-Triggered 'Mega Tsunamis' Won't Obliterate U.S. East Coast

May 23rd, 2012
By Dave Mosher

A tsunami triggered by landslides on the volcanic Canary Island of La Palma could crush the eastern U.S. seaboard — or not, according to the latest computer simulations.

An active volcano called Cumbre Vieja dominates La Palma's southern flank, and someday a gargantuan chunk of it may slough into the Atlantic Ocean. Resulting waves could demolish Canary Island coasts, parts of Europe and Africa's west coast. Then, in a cinematic twist redolent of disaster flicks like 2012, giant waves would crush the U.S. East Coast.

A group of researchers in 2001 floated the possibility that 80-foot waves from La Palma's collapse could scour New York City, Washington D.C. and other coastal areas. Most scientists remain skeptical of this worst-case scenario and they have focused on exploring it instead of smaller and, perhaps, more likely tsunami scenarios.

Mega tsunami

To take a fresh look at the impact of these smaller events — and give old results a reality check — a different research group created and ran the most detailed computer simulations to date for the volcano.

"This has remained unexplored territory," said Stéphan Grilli, a University of Rhode Island ocean engineer and co-author of the new tsunami study, published March 30 in Journal of Geophysical Research. "Our hunch now is that the East Coast would see no more than a hurricane storm surge of 10 to 15 feet."

The possibility of a Cumbra Vieja tsunami came to public attention late in 2000, when geologists appeared on BBC television to make a shocking claim: The volcano might erupt and shake 120 cubic miles of rock and topsoil — a volume 15 times greater than Hoover Dam's Lake Mead — into the sea. While destroying nearby coasts with waves hundreds of feet high, the mega tsunami would also cross the Atlantic Ocean within 8 hours and pummel the United States' eastern seaboard.

Some researchers cried foul, writing that the threat was "greatly overstated." Others picked apart the published study of the mega tsunami, authored by geologist Simon Day and geophysicist Steven Ward.

In their investigations of the threat, skeptical researchers estimated that a Cumbra Vieja explosion won't cause massive collapse for at least 10,000 years. That's when the volcano will be a half-mile taller, steeper and more prone to landslides. Even if a worst-case scenario is extremely unlikely, however, the possibility that a Cumbre Vieja eruption could cause smaller-scale landslides in the present can't be discounted.

Smaller collapse

To study those consequences, Grilli and colleagues modeled a smaller, 19-cubic-mile landslide (a volume of about 2.5 Lake Meads), which Grilli said is "much more likely to occur" than the landslide in Ward and Simon's original model.

The new computer models of the 19-cubic-mile landslide suggest a tsunami that would be less than 5 feet tall by the time it reached New York City. By contrast, Hurricane Irene in 2011 delivered a mostly harmless 4-foot-tall storm surge to parts of the metropolis.

Florida, previously thought to be especially vulnerable, might see waves less than 3 feet tall. Even a landslide five times larger might send waves less than 16 feet tall to New York and less than 11 feet tall to Florida.

Regions closer to La Palma, however, would see great destruction. "The larger 19-cubic-mile event would certainly be a disaster for all of the Canary Islands and the west coast of Africa," Grilli said. "Portugal and Spain could also see 15- to 50-foot waves."

Submerged shores

The simulations are an improvement over previous versions, Grilli noted, because they consider smaller 5- and 10-cubic-mile landslides, use better maps of the ocean floor and rely on more precise modeling of fluid motion.

Although the team's simulations describe potential impacts to the U.S. East Coast, they aren't very high-resolution. Each pixel in the new simulation images is about one-third of a mile on each side.

Grilli hopes to enhance the detail down to a few feet, but his team first needs more precise 3-D maps of submerged shores, which can soak up vast amounts of energy before a tsunami hits land and drastically change its behavior.

"I don't think we'll find anything near what Ward and Day predicted for the East Coast," Grilli said. "That's not to say what they did wasn't great. They raised the level of attention about this issue. It was the first time anyone had really pointed out this risk."

Ward, now at the University of California, Santa Cruz, said the new simulation seems a bit complex and may overestimate the friction that would sap energy from the tsunami and limit its impact, but "it's a fine idea to put smaller landslides in, stir up the water and see what you get."

The team plans to release more detailed East Coast tsunami inundation maps at a conference in June as part of work funded by the federal National Oceanic and Atmospheric Administration.

Top image: A screen grab from BBC "End Day." Courtesy BBC

Dave Mosher is a contributor to Wired and a freelance science journalist who writes for National Geographic News, Popular Mechanics, Scientific American and other outlets. His last piece for Txchnologist explored nanoscopic transportation.

http://www.txchnologist.com/2012/volcano-triggered-mega-tsunamis-wont-obliterate-u-s-east-coast