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Kilauea collapse could possibly spur superwave

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    The tsunami generated by Fogo’s collapse apparently swept boulders like this one from the shoreline up into the highlands of Santiago Island. Here, a researcher chisels out a sample.
    Makauwahi sinkhole at Mahaulepu near Poipu, Kauai, has marine deposits inside as a result of the megatsunami and was discovered by David Burney.
    The Makauwahi sinkhole is about 100 yards from the beach and 24 feet up hill.

A team of scientists working in the Cape Verde Islands off of West Africa has found evidence of a massive volcanic collapse that triggered a “megatsunami” some 73,000 years ago, reigniting debate about whether such a calamitous event could happen today perhaps even in Hawaii.

The team’s findings were published in the most recent edition of the journal Science Advances.

The collapse occurred at the Fogo volcano, still one of the world’s most active. The resulting megatsunami estimated at 800 feet in height is believed to have engulfed Santiago Island, some 34 miles away.

By comparison, modern tsunamis off the Indian Ocean coasts in 2004 and eastern Japan in 2011 measured roughly 100 feet and were generated by undersea earthquakes.

The recent study from the Cape Verde Islands began several years ago when Ricardo Ramalho of Columbia University’s Lamont-Doherty Earth Observatory and other scientists discovered boulders that matched the composition of marine rocks that surround Santiago Island lying as far as 2,000 feet inland and nearly 650 feet above sea level. Some of the rocks were as big as delivery vans and weighed up to 770 tons.

The scientists concluded that only a massive wave could have moved the boulders so far ashore.

Subsequent measurements of helium isotopes near the boulders surfaces a means of measuring of how long the rocks had been out of the water led the team to determine that the wave must have occurred about 73,000 years ago, well within the same time frame as the flank collapse at Fogo volcano.

While there are several examples within the past several hundred years of volcanic flanks collapsing and producing deadly tsunamis, there is scant evidence dating from prehistoric times of sudden, massive collapses displacing the volume of water necessary to trigger a megatsunami. Many scientists theorize that the collapse of massive volcanic structures is more likely to occur gradually, thereby producing smaller tsunamis.

“Our point is that flank collapses can happen extremely fast and catastrophically, and therefore are capable of triggering giant tsunamis,” Ramalho said in a statement Friday. “They probably 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.”

There is ample evidence of such activity in the ongoing formation and maturation of the Hawaiian Islands, notably the Alika 2 landslide, which occurred an estimated 120,000 years ago.

In 2003 a team of scientists including University of Hawaii geologist Gary McMurtry and then-UH geophysicist Gerard Fryer reported on marine fossils found far above the ancient coastline of Kohala (the oldest of five volcanoes that formed the Big Island), the likely result of the nearly 220-cubic-mile landslide and resulting 500-foot megatsunami. The giant wave may even have deposited marine material 1,000 feet high on Molokai and Lanai.

And on Kauai, a sinkhole near Poipu about 100 yards inland has marine deposits in its interior from an ancient tsunami that topped its walls, scientists say.

On Oahu, the Koolau landslide, which occurred more than a million years ago, sent an area roughly the size of Manhattan tumbling into the sea, producing a tsunami that Fryer said would have been perhaps three times larger than the one produced by the Alika 2 slide.

On Molokai, one-third of the Wailau volcano is thought to have slid into the ocean some 1.4 millions years ago, generating a megatsunami 2,000 feet high, according to a study by the National Park Service.

So could another catastrophic collapse happen in Hawaii? And if so, where?

The area most frequently cited as a potential collapse hazard has been the south flank of Kilauea, which has been sliding seaward continuously for thousands of years at a rate of about 3 inches per year, hastened at various times by large earthquakes, according to the Hawaiian Volcano Observatory.

However, a 2014 article released by the observatory said that while an eruption of sufficient force could theoretically cause the flank to fall away, most evidence suggests that the flank will simply continue to sag gradually.

Fryer, senior geophysicist with the Pacific Tsunami Warning Center, who was not involved in the Fogo study, said it has prompted him to re-evaluate the likelihood of a catastrophic volcanic collapse occurring today.

Fryer had long theorized that major oceanic island landslides tend to occur at the tail end of an ice age, when low sea levels provide less support for a mountain and slow-moving tropical storms are more likely to produce heavy rain over slopes that may already be destabilized by pre-eruption inflation.

The Fogo collapse, however, occurred during a period of high sea levels.

“Should we worry about these things?” Fryer said via email. “When I was still confident of my theory, my answer was an emphatic ‘no’ since we are not currently in an ice age. I’m less sure now.

“It’s worth pointing out, however, that the last such event in the Hawaiian Islands was 18,000 years ago,” he continued. “On a human time scale, these giant landslides are very rare.”

To see a computer simulation of what a Kilauea Volcano flank collapse and resulting tsunami might look like, visit The simulation was produced by Steven Ward of the University of California at Santa Cruz.

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