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Study: Megatsunami hit Africa 73,000 years ago

"We need to be vigilant, these findings stand as a warning that the hazard potential of volcanic island lateral collapses should not be underestimated," researcher Ricardo Ramalho said.

By Brooks Hays
Researchers say massive boulders on the island of Santiago are proof of the power of a megatsunami generated by volcanic collapse in the Cape Verde Islands, some 73,000 years ago. Photo by Ricardo Ramalho/Bristol University
Researchers say massive boulders on the island of Santiago are proof of the power of a megatsunami generated by volcanic collapse in the Cape Verde Islands, some 73,000 years ago. Photo by Ricardo Ramalho/Bristol University

BRISTOL, England, Oct. 5 (UPI) -- Some 73,000 years ago, Fogo, a massive volcanic island in the Cape Verde Islands, collapsed. Scientists knew this, having studied evidence of a huge rock slide in the adjacent ocean.

But researchers have debated what effects the collapse had on the surrounding ocean. Some suggested the collapse caused a series of small to medium-sized tsunamis, with waves 45 feet high.

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But new evidence suggests the ancient volcanic collapse generated a megatsunami 300 feet in height.

In a recent paper, published in the journal Science Advances, scientists detailed the ancient effects of the wave, which traveled some 30 miles before collapsing violently on the nearby island of Santiago, off the coast of West Africa.

The evidence of the so-called megatsunami lies inland in the form of massive boulders, some weighing as much as 700 tons. Researchers used cosmogenic analysis -- the study of the changes in isotopes on rock surfaces, precipitated by lengthy exposure to cosmic rays -- to estimate how long the rocks have rested there.

Their research suggests the massive boulders, sourced from the coastal cliffs of Santiago, were deposited around the same time as Fogo's collapse -- exposed to cosmic rays for 73,000 years.

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Researchers at England's Bristol University and Columbia University, in the United States, say only a megatsunami could have generated the force needed to move such impressive rocks so far.

Fogo is now rebuilt. The potential for collapse remains alive there.

"The active volcano we see today grew on top of this collapse's scar, being almost as tall and steep as the old volcano before the collapse," Ricardo Ramalho, lead study author and researcher at Bristol's School of Earth Sciences, said in a press release. "The potential energy for a new collapse therefore exists but what we don't know if or when this is ever going to happen."

Ramalho and his colleagues say more research is needed to understand what causes a volcanic collapse, and how such a collapse might cause a megatsunami -- as opposed to a series of smaller tsunamis.

"We need to be vigilant, these findings stand as a warning that the hazard potential of volcanic island lateral collapses should not be underestimated, and consequently our society needs to do more to improve its resilience to such a threat," Ramalho added.

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