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Last Updated: Friday, 29 October, 2004, 11:08 GMT 12:08 UK
Tidal wave threat 'over-hyped'
By Ali Ayres
in Southampton

Freak wave, BBC
The researchers behind the original claim are sticking to their guns
The risk of a landslide in the Canary Islands causing a tidal wave (tsunami) able to devastate America's east coast is vastly overstated.

That is the view of marine geologists studying ancient landslides in the area.

In typical Canary Island landslides, chunks of land break off in bits, not in one dramatic plunge, they argue.

This contradicts previous warnings that an Isle of Man-sized chunk of land could fall off the island of La Palma into the sea, causing a mega-tsunami.

However, the researchers behind the original claim are sticking to their guns, pointing to evidence of catastrophic past events in the region.

'Worst-case scenario'

Back in 1999, scientists at University College London published a paper about a volcano on the island of La Palma. They predicted that, if it erupted, the volcano could cause a landslide in which a massive chunk of land fell into the ocean.

They then proposed that a landslide this big would generate a mighty tsunami big enough to cross the Atlantic, devastating the Caribbean and the eastern seaboard of the US.

If you break [a brick] up into 10 pieces and drop them in one by one you're going to get 10 much smaller splashes
Russell Wynn, Southampton Oceanography Centre
With talk of a possible wall of water 50m high, their predictions were jumped on by the world's media.

But researchers taking part in a three-week research cruise aboard Southampton Oceanography Centre's research ship, the RRS Charles Darwin, say the threat is far lower than previous warnings would suggest.

Doug Masson, who has been researching Canary Islands landslides for 20 years, says the models are a worst-case scenario.

Coring equipment is being used to collect samples of rock sediment deposited by underwater avalanches that were in turn caused by previous landslides on La Palma.

RRS Charles Darwin, Southampton Oceanography Centre
Researchers on board the RRS Charles Darwin say the threat is far lower than previous warnings would suggest
By looking at layering in the sediments, the scientists can work out whether the debris landed on the ocean floor in one big lump or in several smaller stages. And the Southampton researchers say that other samples from the Canaries suggest their "bit-by-bit" scenario is common, if not ubiquitous to these landslides.

Russell Wynn, who is leading the research cruise, says it means there is a lot less to worry about if a landslide is triggered.

"If you take a brick and drop it in a bath you're going to generate quite a big splash.

"But if you break the brick up into 10 pieces and drop them in one by one you're going to get 10 much smaller splashes".

Melting rock

None of this impresses the team that proposed the original mega-tsunami theory. Bill McGuire is director of the Benfield Hazard Research Centre at University College London. He argues that evidence on the surface of the Canary Islands shows that previous landslides have been catastrophic.

On the island of El Hierro, a semi-circular escarpment of rock left behind after a landslide is covered in melted rock. Conclusive evidence, says Bill McGuire, of a dramatic event.

"This thing moved so quickly that it heated the rock through friction and melted it. That is a catastrophic event," he said.

Other evidence that Canary Islands landslides have had a colossal impact has come from the Bahamas themselves where boulders of rock have been discovered 20m above sea-level.

How they got there was a mystery until the timing of their deposition was linked to a past landslide - in the Canaries. Many scientists now believe that landslides in the past have triggered deadly mega-tsunamis.

So Bill McGuire is sticking to the predictions his team have made. Making no apology for backing a worst-case model, he says: "There's no question of hiding things. If you're planning for any future disaster you're not going to consider the least disastrous scenario, you're going to consider the most."

When Southampton's marine geologists return to the UK, they hope to bring with them evidence that landslides in the Canary Islands are more gradual events.




SEE ALSO:
Expert slams wave threat inertia
10 Aug 04  |  Science/Nature
Giant wave could threaten US
04 Oct 00  |  Science/Nature


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