Tsunami risk along the Atlantic coast

Anak Krakatau volcano collapse, tsunami generation explained by URI modeling

Dave Lavallee

A University of Rhode Island professor and his team of researchers, some based at the British Geological Survey in the United Kingdom, have shown that modeling can accurately forecast tsunamis from volcanic events and lead to early-warning systems that could save lives and prevent catastrophic property damage.

Stephan Grilli, distinguished URI professor and chair of the Department of Ocean Engineering, and his team of 10 researchers write in the August edition of Nature Scientific Reports that their study of the Dec. 22, 2018, collapse of the Anak Krakatau volcano and subsequent tsunami validates the models they have developed to predict tsunamis. 

Steven Carey, URI professor emeritus of oceanography, and Annette R. Grilli, associate research professor of ocean engineering, are part of the URI research team.

Grilli and his colleagues are working to develop models that could lead to early-warning systems that could benefit the East Coast of the United States and other coastal regions. In fact, Grilli is now using the models to assess damage that could result along the U.S. East Coast if a tsunami were to originate from the Canary Islands. 

Located off northwestern Africa, the Spanish archipelago is home to several active volcanoes, including Cumbre Vieja, which scientists believe could be the site of a major volcanic collapse and resulting tsunami.

The lessons of Anak Krakatau, which is located in Indonesia, and its subsequent tsunami, which killed at least 437 people, are critical for future tsunami monitoring and early-warning systems. The Anak Krakatau tsunami resulted in the highest death toll from a volcanically induced tsunami since the eruption of Krakatau in 1883 and the sector collapse of Ritter Island in 1888.

As members of Grilli’s team surveyed the area in January and February 2019, and again this August, they were among the first in more than 100 years to study a volcanically generated tsunami. The tsunami was caused when two-thirds of Anak Krakatau, which had been erupting since June 2018, slid into the ocean.

In their research paper, the scientists report that their models successfully reproduced observed tsunami characteristics from post-event Anak Krakatau field survey results, tide gauge records, and eyewitness reports, suggesting that the scientists’ landslide volume range and assumed collapse scenario are accurate.

“Our successful simulations demonstrate that current numerical models can accurately forecast tsunami hazards from these events,” they write. “In cases such as Anak Krakatau’s, the absence of precursory warning signals, together with the short travel time following tsunami initiation presents a major challenge for mitigating tsunami coastal impact.”

“A large volcanic collapse can cause a large tsunami, and we know there is a risk of collapse at the Cumbre Vieja volcano in the Canary Islands, as collapses occurred in the distant past,” Grilli said.

He added that there are 29,000 miles of exposed coastline along 14 eastern U.S. states that are at risk from a tsunami, particularly from the Canary Islands. There is currently no early-warning system for non-seismic tsunamis for most of this region.

Based on his research, Grilli said a worst-case scenario volcano collapse in the Canary Islands could push a wall of water up to 27 feet high toward Atlantic City and give residents only 7 to 10 hours to react depending on where they live on the East Coast.

“If a 10,000-foot-tall piece of Cumbre Vieja were to slide into the ocean, it would create a tsunami that would cover all of Atlantic City,” Grilli said “but the chance of that happening is fortunately very low.”

And Atlantic City is not the only place on the East Coast where there is potential for major loss of life and property as a result of tsunamis. 

Under the auspice of the National Tsunami Hazard Mitigation Program (National Weather Service) Grilli is studying areas off Montauk, New York, and Cape Fear in North Carolina that show potential for underwater landslides and subsequent tsunami activity that would threaten the nearby coasts.

“We have three dozen maps that show inundation zones,” Grilli said. “With technology, we are working to cut the warning time down from several hours to 10 minutes.”