Locations on both African and European Atlantic coastlines -- including Britain -- are also thought to be at risk.

The new research, a collaboration between Dr. Simon Day of the Benfield Greig Hazard Research Centre at University College London and Dr. Steven Ward of the University of California, reveals the extent and size of the mega-tsunami, the consequence of a giant landslide that may be triggered by a future eruption of the Cumbre Vieja volcano.

Previous research by Simon Day and colleagues predicted that a future eruption would be likely to cause a landslide on the western flank of Cumbre Vieja.

A block of rock approximately twice the volume of the Isle of Man would break off, travelling into the sea at a speed of up to 350 kilometers per hour. The disintegration of the rock, this earlier study predicted, would produce a debris avalanche deposit extending 60 kilometers from the island.

The energy released by the collapse would be equal to the electricity consumption of the entire United States in half a year.

The new model -- which provides further insights into the consequences of the collapse -- predicts that the landslide would create an exceptionally large tsunami with the capability to travel great distances and reaching speeds of up to 800 kilometers per hour.

Immediately after Cumbre Vieja's collapse, a dome of water 900 meters high and tens of kilometers wide will form, only to collapse and rebound.

As the landslide continues to move underwater, a series of wave crests and troughs are produced which soon develop into a tsumani "wave train" which fuels the waves' progress. After only 10 minutes, the model predicts, the tsunami will have moved a distance of almost 250 kilometers.

The greatest effects are predicted to occur north, west and south of the Canaries. On the West Saharan shore, waves are expected to reach heights of 100 meters from crest to trough, and on the north coast of Brazil, waves over 40 meters high are anticipated.

Florida and the Caribbean, the final destinations in the North Atlantic to be affected by the tsunami, will have to brace themselves for receiving 50 meter high waves -- higher than Nelson's column in London -- some 8 to 9 hours after the landslide.

Towards Europe, wave heights will be smaller, but substantial tsunami waves will hit the Atlantic coasts of Britain, Spain, Portugal and France.

For tsunamis striking flat-lying coastline regions such as Florida, calculating the inundation distance -- the extent to which water penetrates inland taking the form of fast-moving floods after waves break -- is crucial to assessing potential damage.

Dr. Day and his colleagues estimate inundation distances in the region of several kilometers from the coast. Accurate estimates of the scale of economic loss are yet to be made, but are thought to be in the multi-trillion-dollar range.

Placing the results of the Cumbre Vieja model in its wider context, Dr. Day, a postdoctoral Research Fellow at UCL, said, "Anyone planning a holiday to the Canary Islands and the islanders themselves need not panic. Cumbre Vieja is not erupting, so the short-term and medium-term risks are negligble."

Dr. Day continued:

"The collapse will occur during some future eruption after days or weeks of precursory deformation and earthquakes. An effective earthquake monitoring system could provide advanced warning of a likely collapse and allow early emergency management organizations a valuable window of time in which to plan and respond.

"Eruptions of Cumbre Vieja occur at intervals of decades to a century or so and there may be a number of eruptions before its collapse. Although the year-to-year probability of a collapse is therefore low, the resulting tsunami would be a major disaster with indirect effects around the world.

"Cumbre Vieja needs to be monitored closely for any signs of impending volcanic activity and for the deformation that would precede collapse."

(Reference: "Cumbre Vieja Volcano; Potential Collapse and Tsunami at La Palma, Canary Islands," Ward and Day, will be published in the September 2001 edition of Geophysical Research Letters.

31-Aug-2001