The threat from a collapsing mountain in the Atlantic Ocean could unleash deadly
tidal waves on a similar scale to the Asian tsunami, a scientist warned today.
Hundreds of millions of people could die in a disaster affecting Britain and the eastern United States.
Professor Bill McGuire called for an early warning system to be installed to counter the potential danger.
Researchers have discovered that a chunk of volcano in the Canary Islands the size of the Isle of Man is on the brink of falling into the sea.
Scientists believe it could break away when the Cumbre Vieja volcano in La Palma next erupts.
If that happened a giant tsunami, or massive wave, reaching heights of more than 500 feet would be sent racing across the Atlantic at the speed of a passenger jet.
Around nine hours later it would hit the Caribbean islands and the east coasts of Canada and the US.
After travelling 4,000 miles the wave would be lower and wider but still around 20 metres – 50 metres (66ft – 164ft) high.
Stretching for many miles, it would home in on estuaries and harbours and sweep up to 20 miles inland, destroying everything in its path.
Boston, New York, Washington DC and Miami would be virtually wiped off the map and tens of millions of people killed.
Meanwhile the size of the waves reaching Britain would be half as high as those hitting America but this would still be on the same scale as those seen in the disaster in the Indian Ocean.
Prof McGuire, director of the Benfield Hazard Research Centre at University College London, said monitoring might at best give two weeks warning.
But although the danger had been known about since the 1990s, no-one was keeping a proper watch on the mountain.
He said that a chunk of the mountain had been teetering on the brink of collapse since the last volcanic eruption of Cumbre Vieja in 1949.
Prof McGuire said: “We expect during a future eruption that whole mass to collapse into the North Atlantic.
“You are dealing with a similar situation to the Indian Ocean only on a much more devastating scale.”
The areas affected would include the entire North Atlantic rim including north west Africa and southern Europe.
Prof McGuire said it was “certain” this would happen at some stage although whether the next eruption would be the one to cause the collapse was not known.
The next eruption could be between 20 and 200 years away.
He said the problem had been known about since the Spanish government funded a study in the 1990s but authorities had then chosen to ignore it.
Radar satellite image technology was now needed to find out how much the unstable mass has been moving.
He added: “It is an issue people are aware of but hopefully the Indian Ocean business will focus people’s minds a bit more.”
There was no warning system for tsunamis in the Atlantic and although the ocean was only affected by 2% of those in the world, their impact could be devastating.
Earthquakes such as one that hit Lisbon in 1755 could also trigger the giant waves, as they have done in the recent disaster.
The 18th century tremor produced massive waves that caused thousands of deaths and affected people as far away as the Caribbean.
“My point of view is not that everybody should be worrying about this but if you know that these things are going to happen you either sit back and just wait for it to happen or you do something about it,” Prof McGuire said.
