Imagine this premise for a Hollywood disaster movie: A giant volcano on an island collapses during an eruption, generating a massive landslide that in turn causes an absolute Godzilla of a tsunami, an 840-foot-tall wave that travels for 30 miles and engulfs anything in its path.
Around 73,000 years ago, the towering predecessor of the Fogo volcano – one of the most active in the world– collapsed. As a result, a unbelievably massive tsunami rippled across the Atlantic Ocean, washing its destructive force over Santiago Island that now boast over 250,000 human residents. Experts now wonder if such a disaster is more common than we’d like.
Nowadays, it towers 2,829 meters (9,300 feet) above sea level, and erupts about every 20 years
We have all read about the damage and devastation that tsunamis can bring about, but the recent tsunamis are nothing compared to evidence recently unearthed by scientists working off West Africa in the Cape Verde Islands..
The tsunami, which engulfed an island 30 miles away, raises questions over whether such a collapse poses a threat to people living on volcanic islands today. By comparison, waves from biggest tsunami in modern times – the 2004 Indian Ocean tsunami – were 100 feet tall.
Santiago Island lies 55 kilometers (34 miles) from Fogo. Several years ago, Ramalho and colleagues were working on Santiago when they spotted unusual boulders lying as far as 2,000 feet inland and nearly 650 feet above sea level. Some are as big as delivery vans, and they are utterly unlike the young volcanic terrain on which they lie. Rather, they match marine-type rocks that ring the island’s shoreline: limestones, conglomerates and submarine basalts. Some weigh up to 770 tons.
The only realistic explanation the scientists could come up with: A gigantic wave must have ripped them from the shoreline and lofted them up. They derived the size of the wave by calculating the energy it would have taken to accomplish this feat.
In the early 2000s, other researchers started publishing evidence that the Cape Verdes could generate large tsunamis. Others have argued that Spain’s Canary Islands have already done so. Simon Day, a senior researcher at University College London has sparked repeated controversy by warning that any future eruption of the Canary Islands’ active Cumbre Vieja volcano could set off a flank collapse that might form an initial wave 3,000 feet high. This, he says, could erase more than nearby islands. Such a wave might still be 300 feet high when it reached west Africa an hour or so later he says, and would still be 150 feet high along the coasts of North and South America.
In 1792, part of Japan’s Mount Unzen collapsed, hitting a series of nearby bays with waves as high as 300 feet, and killing some 15,000 people. On July 9, 1958, an earthquake shook 90 million tons of rock into Alaska’s isolated Lituya Bay; this created an astounding 1,724-foot-high wave, the largest ever recorded. Two fishermen who happened to be in their boat that day were carried clear over a nearby forest; miraculously, they survived.
These events, however, occurred in confined spaces. In the open ocean, waves created by landslides are generally thought to lose energy quickly, and thus to pose mainly a regional hazard.
Several studies proved that 80 percent of tsunamis happen within the Pacific Ocean’s “Ring of Fire,” a geologically active area where tectonic shifts make volcanoes and earthquakes common.
One of the tell-tale of signs of tsunami is a vacuum effect of coastal water that exposes harbor and sea floors.
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