The eruption of a voclano on the Canary Island of La Palma resurrects the “mega-tsunami” theory, but is it possible? Rob Kiteley takes a look at what the experts say.
The volcanic eruption on La Palma has revived a theory that has been circulating for more than 20 years: that a major landslide emanating from the slopes of the Cumbre Vieja volcano could result in a catastrophic landslide that could wreak carnage not just on the Canary Islands, but on Western Europe more widely, the Caribbean and even on the eastern coast of the United States.
This theory has persisted despite denials by the Instituto Vulcanológico de Canarias and geologists from the National Geographical Institute who insist there is no data to support the theory.
The much debated hypothesis is based on a single research paper published in 2001 by Simon Day, of the Benfield Greig Hazard Research Centre, University of London and Steven Ward, a professor at the Institute of Geophysics and Planetary Physics at the University of California.
Their research theorizes that an erupting volcano on La Palma could become unstable, and if it were to collapse, between 150 and 500 cubic kilometers of volcanic rock could be sent hurtling into the sea, triggering a devastating tsunami.
According to the research “the waves could be up to 25 meters high, and would even cause damage to the south of England further north and then to the west they would reach the North American coast, as well as “destroy the West African coast with waves of up to 100 meters”.
But authorities and experts maintain that there is no evidence to support the claim. Volcanologist Robin George Andrews, argues that whilst there are precedents of such an event, there is no indication that the possibility exists at the moment.
He argues that even if huge rock loads fell into the sea, the effects would not be significant enough to cause a ‘megatsunami ‘.
However there is precedent for such an occurrence.
A volcanic eruption north of La Palma 560,000 years ago dumped 200 km3 of volcanic material into the sea and is thought to have caused an enormously damaging tsunami.
But could history really repeat itself?
Dave Petley, an avalanche expert at Sheffield University, visited the Cumbre Vieja volcano in person in 2017 to test the theory.
He found “no evidence” that a part of the volcano could be unstable.
Petley points out that after the eruption of the Teneguía volcano in 1971, there were no signs of risk of collapse.
Although he does stress that it cannot be ruled entirely, and part of the slope could in theory detach and fall into the sea, but it wouldn’t result in the scale of disaster that Ward and Day suggest in their research.
Andrews argues that “For the Cumbre Vieja flank to meet conditions close to instability, an exceptionally high-magnitude earthquake and a large-scale explosive volcanic eruption would have to occur simultaneously, or the current volcanic building should reach at least 1,000 in its natural growth – meters more than the current maximum elevation . To reach this height, more than 40,000 years would have to pass, taking as a reference the average growth rate of the island in the last million years “.
The consensus therefore seems to be that whilst theoretically possible at some point in the future (tens-of-thousands of years at least), there is no evidence to suggest the volcano is unstable or in imminent danger of collapsing at the moment.
What’s more, if it were to happen, there is no evidence to suggest the consequences of rock spewing into the sea would be anywhere near as catastrophic as the theory suggests.
It is safe to say that the mega-tsunami theory can be consigned to history.
The last time a volcano erupted on La Palma was almost exactly 50 years ago, in October 1971, when the Teneguía volcano spewed lava for more than three weeks.
Subsequently no significant seismic activity was detected again until 2017, which marked the start of a series of tremors (known as earthquake swarms) which would occur periodically and culminate in this weeks’ volcanic eruption.