Society 23/09/2021

La Palma volcano will not cause a giant tsunami

The most catastrophic forecasts about the effects of the Cumbre Vieja eruption are based on false or biased data

3 min
The lava flow, advancing through the streets of Todoque, La Palma.

BarcelonaThis is not Krakatoa. This is not even Mount Teide, Mount Etna or Mount Vesuvius. At Cumbre Vieja, on the island of La Palma, what we have is a volcanic edifice in the making, about which there is still more uncertainty than certainty. However, if we take into account the geological history of the island, what science says and what the models predict, it is hardly possible to speak of such a catastrophic outcome as those that have been circulating these last few days on social networks, most of them without any scientific basis. There will not be a giant tsunami that will reach New York nor a toxic cloud that will cause a nuclear winter on the European continent. The catastrophists will have to wait for another event.

The devastation on La Palma is not negligible. The lava flow from the Cumbre Vieja slope towards the sea is a disaster in every sense of the word, but on a local scale. The total area covered by the lava flows, despite the more than justified drama of the affected population, is very limited. And, as spectacular as the images are, the effects of the toxic gases can be relatively easily avoided for the time being. If this were not the case, the evacuation of the entire island would have already been activated.

"We are witnessing a volcano in formation", sums up volcanologist Joan Martí, from the CSIC Centre de Geociències Barcelona. This means that we are still at an early stage of the formation of what is known as a volcanic edifice, conical in shape and crowned by the characteristic crater. The composition of the magma means that the rivers of lava advance slowly and that layers of incandescent rock are deposited one on top of the other as they advance down the slope with a surface temperature of over a thousand degrees. Now, if you look at the arrangement of the volcanoes that have formed over the last five hundred years, all with similar characteristics, you will see that they are aligned along the southern chalk line of the island of La Palma.

The director of the Benfield Grieg Hazard Research Centre at University College London, Bill McGuire, wrote in 2001 that this vast area of at least 24 km in length would eventually erupt on the western side and fall in a hasty manner into the Atlantic. According to his calculations, modelled by researchers Steven Ward and Simon Day of the same university, around 500 cubic kilometres of rock would break off at once and fall into the ocean, causing a huge wave of rock to burst into the sea triggering a huge tidal wave that would take nine hours to reach New York. The waves could reach 150 meters and travel at 100 meters per second.

The hypothesis, which was the subject of a BBC documentary, was soon discredited. The authors were accused of using biased, erroneous or false data, as well as poor mathematical models. The most widespread theory accepted by the scientific community proposes the existence of large amounts of magma at least 10 km deep that presses from time to time, but without any known period, to come out. This is what would have happened in the last half millennium with the eight documented eruptions, nine with the current one. Even so, the New York City Council included the possibility of a tsunami in 2018 on the list of possible natural disasters.

On the other hand, the possibility of toxic clouds and acid rain precipitation, although feasible, will in no case affect human or environmental health beyond the island of La Palma. What is being observed is what was expected: columns of water vapour, above all, and of sulphur dioxide and carbon dioxide, as well as ash and rocks. The forecast is that the winds will dissipate these gases into the atmosphere. The possibility of acid rain is real but not of great magnitude. The possibility of a tsunami or nuclear winter is non-existent. That the island will change its physiognomy or even its surface is certain.