“[The study] provides robust evidence of megatsunami formation [and] confirms that when volcanoes collapse, they can do so extremely rapidly”, said tsunami expert Bill McGuire, a professor emeritus at University College London who was not involved in the research.
Advertisement
One of the world’s largest and most active island volcanoes occurred a few 73,000 years ago at the Fogo volcano.
Fogo volcano is 9,300 feet above sea level these days and erupts after every 20 years.
In the future, the team would want to study whether Fogo or other volcanoes may topple down and potentially initiate large tsunamis. He iterated, however, that the volcanic collapses do not typically result in catastrophe and that it does not necessarily trigger megatsunamis.
But Ramalho wasn’t convinced of this theory, and the geological evidence he collected at Santiago and in the vicinity of Fogo have convinced him that there must have been a megatsunami that carried these boulders up to the very top of the island, hundreds of feet up.
The boulders, weighing up to 770 tons, matched marine-type rocks ringing the island’s shores and were quite unlike the volcanic terrain in which they were found. The only realistic explanation the scientists could come up with: A very big wave must have ripped them from the shoreline and lofted them up.
Computer models helped the researchers calculate the size of the wave that must have hurled these giant rocks onto Santiago.
To date when this mega tsunami happened, Ramalho and his colleagues analyzed isotopes of helium embedded in the boulders. Such isotopes change depending on how long a rock has been lying in the open, exposed to cosmic rays. The analyses centered around 73,000 years – well within an earlier estimate of a smaller event.
(Photo: NASA) This satellite image shows the dark scar crated by the collapse of a massive volcano between 65,000 and 124,000 years ago. As a result, they’re more likely to suddenly collapse, and that’s what Ramalho believes happens in Fogo’s case.
“But”, he added, “it’s maybe not as rare as we thought”. Others have argued that Spain’s Canary Islands have already done so.
A tsunami of biblical proportions caused by the sudden collapse of a volcano generated a wave almost 1,000ft (305m) high, scientists have discovered. This, he says, could erase more than nearby islands. He mentioned that the USA western coast and Hawaii could be prone to such apocalyptic calamity. A 2013 study of deep-sea sediments by the United Kingdom’s National Oceanography Centre suggests that the Canaries have probably mostly seen gradual collapses.
The controversy partially hangs on the physics of waves. Santiago Island, where the ancient wave allegedly pummeled, now serves as a haven for about 250,000 inhabitants. In contrast, in the open ocean, previous research suggested that waves generated by landslides generally lose energy quickly. However, this is based largely on modeling, not real-world experience, so no one really knows how fast a killer wave might decay into a harmless ripple.
The understanding that tsunamis come from undersea earthquakes stretches all the way back to Greek historian Thucydides in the late 5th century BC, who wrote the History of the Peloponnesian War. The largest-known recent tsunami that hit the Indian Ocean’s coasts in 2004 only reached a height of about 100 feet.
Advertisement
When Fogo erupted past year, Ramalho and other geologists rushed in to observe. “Right now, people in Cape Verde have a lot more to worry about, like rebuilding their livelihoods after the last eruption”, said Ramalho.
