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A 1,000ft high tsunami triggered by a volcano collapse 73,000 years ago could happen again, warn scientists

A tsunami of biblical proportions caused by the sudden collapse of a volcano generated a wave nearly 1,000ft (305m) high, scientists have discovered.

The event happened 73,000 years ago in the Cape Verde Islands off west Africa, long before there were any coastal cities that might have been flattened by the deluge.

But some experts fear a similar giant collapse could present a real threat today, especially around volcanic islands.

Lead scientist Dr Ricardo Ramalho, from Columbia University in New York, said: "Our point is that flank collapses can happen extremely fast and catastrophically, and therefore are capable of triggering giant tsunamis.

"They probably don't happen very often. But we need to take this into account when we think about the hazard potential of these kinds of volcanic features."

The ancient collapse occurred at Fogo, one of the world's largest and most active island volcanoes that today towers more than 9,000ft (2,743m) above sea level.

An estimated 40 cubic miles (167 cubic metres) of rock fell into the ocean in one go, resulting in an 800ft (244m) high tsunami wave that engulfed an island more than 30 miles away (48km).

By comparison, the largest known recent tsunamis, which devastated Indian ocean coasts in 2004 and eastern Japan in 2011, attained maximum heights of around 100ft (30m).

These tsunamis were triggered by undersea earthquakes rather than volcanic collapses.

Clues left by the megatsunami included boulders the size of delivery vans that had been carried up to 2,000 feet inland and nearly 650 feet above sea level on Santiago Island, 34 miles (55km) from Fogo.

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.

By calculating the energy needed to hurl the boulders so far, the scientists were able to estimate the size of the wave. Their findings are reported in the journal Science Advances.

Tsunami expert Professor Bill McGuire, from University College London, believes such megatsunami events occur only once every 10,000 years.

He added: "Nevertheless, the scale of such events, as the Fogo study testifies, and their potentially devastating impact, makes them a clear and serious hazard in ocean basins that host active volcanoes."

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