A new study found that ancient Fogo, which is an active island volcano in Africa, was devoured by a megatsunami that reached up to about 800 feet high. The oceanic volcanoes were said to have been swallowed by high waves, which resulted from a disastrous collapse 73,000 years ago.
Massive disintegration of steep volcanic islands is believed to have the ability to initiate high-impact megatsunamis. However, proofs pointing to the actual production and the effects of such events, as well as its increased run-ups continue to be limited or regarded as controversial. With this, scientists persist to have second thoughts on whether or not island flank collapses can truly produce highly significant natural fluctuations that can trigger great tsunamis.
In a new study performed by an international scientific team, the researchers discovered unique boulders that measured up to about 25 feet in width and 770 tons in weight on Santiago, which is the largest island on Cape Verde and lies about 34 miles from Fogo. The giant chunks were found lying as far as 2,000 feet within the land and approximately 9,300 feet above sea level.
Ricardo Ramalho, lead author and geologist at the University of Bristol, said that the team was initially baffled as to why such boulders, which looked different from the volcanic terrain that holds it, were situated there. When they realized that the only possible explanation for the structures' origin was a great tsunami impact, they got excited.
The researchers used a computer model to help quantify the size of the wave that must have propelled the rocks to Santiago.
Next, the researchers estimated when the theorized megatsunami occurred. To do this, the helium isotope content of the large rocks, which were consistent of limestone and other rocks surrounding the shoreline, was analyzed. The embedded isotopes represent the length of time that the boulders have been lying on the island, exposed to cosmic rays.
The findings of the investigations, published in the journal Science Advances on Friday, Oct. 2, showed that the megatsunami occurred some 73,000 years ago, following a landslide on Fogo that was theorized to have triggered up to about 38 cubic miles of rocks blasting into the ocean.
"Our work shows that we need to be vigilant and that we should not underestimate the threat posed by flank collapses and the tsunamis they trigger," said Ramalho. He iterated, however, that the volcanic collapses do not typically result in catastrophe and that it does not necessarily trigger megatsunamis. He also advised that each volcano must be tracked and studied individually and comprehensively.
In the future, the team would want to study whether Fogo or other volcanoes may topple down and potentially initiate large tsunamis.
"There is a growing awareness that extreme geohazards such as these will eventually, one day happen, so we might as well coolly and realistically see what can be done to mitigate their effects," Ramalho closed.
