According to their controversial study, an explosion of the Cumbre Vieja volcano on the island of La Palma could send a chunk of rock twice the size of the Isle of Wight into the Atlantic at up to 350 kilometres (220 miles) an hour.

Many experts believe the risk of "mega-tsunamis" from such a massive landslide on La Palma has been hugely overstated.

But in the study's scenario, energy released would equal the electricity consumption of the United States for six months, sending gigantic tidal waves across the Atlantic at the speed of a jet plane.

Devastation in the United States would reach trillions of dollars with tens of millions of lives at risk. Spain, Portugal, Britain, France, Brazil, the Caribbean and West Africa would also be swamped by giant waves.

"It may occur in the next eruption, which could be next year, or ... it may be 10 eruptions down the line," said Bill McGuire of Britain's Benfield Hazard Research Centre.

Cumbre Vieja, which last exploded in 1971, typically erupts at intervals of between 20 and 200 years.

"We just don't know when it will happen, but are people prepared to take the risk after the Indian Ocean events?" McGuire said, calling for a programme to monitor the slide in Cumbre Vieja's flank.

"We need to get people out in advance of the collapse itself. Once the collapse has happened, the Caribbean would have 9 hours, the US 6 to 12 hours to evacuate tens of millions of people," he said.

SCAREMONGERING?

Other experts say such predictions about La Palma or the Hawaiian volcano of Kilauea are grossly exaggerated.

The Tsunami Society, an international association of experts, dismisses such theories as "scaremongering". It argues Cumbre Vieja would not collapse in a single block and the wave generated would be much smaller.

"We are talking about thousands of years in the future. Anything could happen. An asteroid could also fall on earth," George Pararas-Carayannis, founder of the Tsunami Society, said.

Many wave experts believe tsunami from abrupt landslides dissipate more quickly than those generated by powerful earthquakes, like the Dec. 26 quake off Indonesia which stretched thousands of miles along the ocean floor.

Charles Mader, editor of the Science of Tsunami Hazards journal and an expert on wave modelling, predicts that even in the event of a massive landslide on La Palma the tsunami reaching North America would be no more than 1 metre high.

But McGuire stands by the wave modelling for the La Palma tsunami, carried out by Steven Ward of the University of California.

As the world reels from the Indian Ocean disaster, which killed more than 150,000 people, oceanographers and geologists agree the threat of tsunamis has been underestimated.

"It would not surprise me at all if tomorrow we saw another tsunami like this," said Pararas-Carayannis, pointing to faults off Portugal, Puerto Rico and Peru as possible risks.

For McGuire, a warning system in the Indian Ocean could have completely prevented loss of life in Sri Lanka and India from south Asian tsunami, as in most cases people would only have had to travel 1 kilometre inland to avoid the waves.

He ranks tsunami risk as second only to global warming in the hazards facing the planet.