The work of the Benfield Hazard Research Centre has established that much of La Palma, the most volcanically active of the Canary Islands, is now inherently unstable.
In 1994 the southern volcano on the island erupted. During the eruption an enormous crack appeared across one side of the volcano, as the western half slipped a few meters towards the Atlantic before stopping in its tracks. Another eruption could cause half of the island to simply fall away and crash into the ocean. A huge section of southern La Palma, weighing 500 thousand million tonnes, will fall into the Atlantic ocean. The resulting impact would generate a giant wave big enough to sweep westwards across the Atlantic and devastate the entire Eastern Seaboard of the United States.
Dr Simon Day of the (Benfield Hazard Research Centre UCL) began mapping La Palma in 1994. All of the evidence he found pointed to one startling conclusion - that the western half of the volcano, known as Cumbre Vieja, is gradually separating itself from the eastern half. Another important realisation was the influence of water within the rock. When this is heated by magma rising to the surface it expands and adds to the pressure on the island to fragment.
Dr Day believes the process of global warming could also contribute to the heating of water and create the set of conditions necessary for a landslide more likely.
There is evidence that shows collapses the size of La Palma create mega-tsunami that really can cross whole oceans and devastate distant continents. Scientists know that one of the last volcanic landslides in the Canaries happened here on a neighbouring island to La Palma. When a section of the island collapsed around 120,000 years ago it launched a mega-tsunami which would have swept across the Atlantic towards the Americas. Dr. Simon Day believes that evidence for its destructive power can be seen thousands of miles away in the Bahamas. He believes the huge wave reshaped some of these islands, blasting chevron ridges up to 10 kilometres long across parts of the Bahamian coastline. The wave also ripped vast boulders from the ocean floor, some over 1,000 tons in weight and dumped them high above sea-level.
‘When we started analysing the information that we gained by mapping the Cumbre Vieja we found that a change had taken place in the vents of the volcano. The north/south line of vents had extended further to the north with new vents appearing each younger further to the south. This meant that the western side of the volcano was becoming deeply unstable. The whole of this flank was moving towards the sea as a single block.’
Swiss scientists have calculated what would happen. They built a model to estimate the size of the mega-tsunami this event would create. The Cumbre Vieja landslide would be thousands of times larger than any that the scientists have studied before. Because of this, their experiments could only give an approximate figure for the dimensions of the wave.
Hermann Fritz (Swiss Federal Institute of Technology):
‘Of course there’s a huge difference in scale between the Cumbre Vieja collapse and its physical model in the laboratory. We’ve tried to err on the side of caution when we made our calculations using conservative assumptions, but nevertheless what we found when we ran the model was very disturbing. If Cumbre Vieja were to collapse as one single block it would create a giant mega-tsunami with an initial height of 650 metres and a wavelength of 18-25 miles travelling westwards across the Atlantic with speeds approximately 450 miles an hour towards America.’
George Maul, a professor of oceanography at the Florida Institute of Technology, said “We may get fewer tsunamis in the Atlantic than in the Pacific, but the population density in Western Europe, the Caribbean and the eastern United States raises the spectre of a much greater loss of life.”
