La Palma Tsunami Is a Matter of Future

Dutch scientists found the volcanic island of La Palma (in Canaries) being more stable than generally assumed.

The southwestern flank of the island isn't likely to fall into the sea (potentially causing a tsunami) for at least another 10,000 years, professor Jan Nieuwenhuis states.

The alarm had started 6 years ago, when geologists warned that the south western flank of the island could fall into the sea during a volcanic eruption in the near future. The western flank of the Cumbre Vieja would slide down westwards into the Atlantic Ocean.

Very strong earthquakes would create a large wave (mega-tsunami) that would move rapidly westwards. Most of the energy of the wave would head straight out across the Atlantic towards the United States, Bahamas and the Caribbean, but a smaller wave or waves would head in other directions too, affecting Europe and Africa. All these waves would get smaller as they cross the Atlantic.

Scientists believe that they could still be as much as 50 metres high, for example, when they reach the east coast of the United States. Cities like New York, Boston, Lisbon and Casablanca would be all but wiped from the face of the planet, according to the more pessimistic estimates.

The Dutch researchers discovered the Cumbre Vieja volcano on the island to be too small to fall apart, after simulating on models several volcanic eruptions. 'This is simply a very stable island', says team leader professor Jan Nieuwenhuis.

The team calculated that the power of 12,000 to 28,000 billion Newton is required to pull apart the volcano . That is much more than can be expected from a volcanic outburst on La Palma. Only under very extreme conditions, the flank could become unstable (an exceptionally strong magmatic outburst combined with unusually heavy rainfall). 'Based on what we know now, so many things must go wrong that a disaster seems very, very unlikely', says Janneke van Berlo.

The results show that the surest way to cause a landslide is to wait for at least another 10,000 years. The Cumbre Vieja volcano steadily grows and this causes the flanks of the volcano to become steeper and less stable. 'A combination of substantial vertical growth and eruption forces will most probably act to trigger failure. To reach substantial growth, a time span in the order of 10,000 years will be required', Van Berlo states.

La Palma doesn't look very solid even today. Parts of its flanks were lost at least twice in prehistoric times already. And during the last eruption, in 1949, a two kilometer long brake appeared at the top of Cumbre Vieja's southwestern flank.

The team said that the rip is the result of an innocent, shallow phenomenon, for example local adaptive settlements of the volcano. The ancient collapses are good evidence that La Palma is stable now: the collapses only occurred when La Palma was much higher than today, at least 3,000 meter.

Even if the volcanic slope did become critically unstable, it isn't likely it will fall. 'Of course the flank won't go in one piece, but break up first', Nieuwenhuis said. 'And it could very well slide down a little and then settle in a more stable configuration, just like our dykes in Holland often do when they go unstable.'

The plunge won't be a fast and sudden event, Nieuwenhuis stresses. ‘It will more be like a steam locomotive powering up. The first meter of movement should take several days’.

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