Rising from the Atlantic ocean, hundreds of miles off the coast of West Africa, there’s a volcano with a 73,000-year-old scar swiped across its face. This is the mark of an ancient catastrophe, etched into the rock when a huge chunk of the volcano’s eastern flank rushed all at once into the sea.
That particular flank collapse displaced enough water to generate a powerful tsunami—one that, new evidence shows, might have been much, much bigger than geologists previously believed. “Our work provides evidence that the well-known collapse at Fogo volcano produced a very large tsunami that impacted the nearby island of Santiago,” said Ricardo Ramalho, an Earth-sciences research fellow at the University of Bristol.
“Very large,” even by tsunami standards, seems like an understatement here.
Ramalho and his colleagues identified giant boulders almost half a mile inland, hundreds of feet above sea level, that they believe were transported by a mega-tsunami. Based on what they found, the scientists believe the tsunami swelled to a height of about 560 feet, tall as the Washington Monument, before inundating the island. “These characteristics make this event one of the largest mega-tsunamis preserved in the geological record,” Ramalho and his colleagues wrote in a paper about their findings.
Flank collapses like the one that decimated what is now Santiago are rare, but not unheard of. Hawaii has its own history of mega-tsunamis, most recently about 100,000 years ago. “One block of rock that slid off Oahu is the size of Manhattan,” wrote Becky Oskin in Live Science.