Scientists warn that similar event to collapse of volcano on Cape Verdean island of Fogo 73,000 years ago poses major threat to nearby islands

This article is more than 4 years old

This article is more than 4 years old

The sudden collapse of a volcano caused a tsunami that created waves up to 240 metres (800ft) high 73,000 years ago, scientists have discovered.

The mega-tsunami took place near the Cape Verde islands off west Africa when the slopes of the volcano gave way – a process known as a “flank collapse” – and some experts fear a similar collapse could present a real threat today, especially around volcanic islands.

The lead scientist, Dr Ricardo Ramalho, now at Bristol University, and his team at 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.”

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The ancient collapse occurred at the Cape Verdean island of Fogo, one of the world’s largest and most active island volcanoes, which towers 2,743 metres above sea level.

An estimated 167 cubic km (40 cubic miles) of rock fell into the ocean, resulting in a wave that engulfed an island more than 30 miles away.

By comparison, the largest known recent tsunamis, which devastated Indian Ocean coasts in 2004 and eastern Japan in 2011, attained maximum heights of about 30 metres. These tsunamis were triggered by undersea earthquakes rather than volcanic collapses.

Clues left by the mega-tsunami include boulders the size of lorries that had been carried up to 600 metres inland and nearly 200 metres above sea level on Santiago island, 34 miles from Fogo.

Facebook Twitter Pinterest A huge boulder found on Santiago island carried more than 30 miles by the tsunami. Photograph: Ricardo Ramalho/Columbia University/PA

The boulders, weighing up to 770 tonnes, matched marine-type rocks ringing the island’s shores and were quite unlike the volcanic terrain on which they were found.

By calculating the energy needed to hurl the boulders such a distance, the scientists were able to estimate the size of the wave. Their findings are reported in the journal Science Advances. Prof Bill McGuire, a tsunami expert from University College London, believes such mega-tsunami events occur once every 10,000 years.

He said: “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.”