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Causes and consequences of the La Palma volcano eruption

The volcanic eruption that began yesterday Sunday at 15.

on the island of La Palma is one more of the historical eruptions that have taken place in this volcanic archipelago and which will undoubtedly continue to exist in the coming years . As with the El Hierro eruption, now 10 years ago, this new eruption has very similar characteristics to all the historical eruptions that have occurred on these islands. That is, it is a strombolian-type eruption, initiated through a fracture and with the emission of lavas, pyroclasts and gases, and whose duration can vary, generally, from a few weeks to a few months.

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We must look for the cause of the eruption in the accumulation of magma (molten rock) at the base of the volcanic building on La Palma (between 6 and 8 kilometers deep), magma that comes from the earth’s mantle, generated in an area that we call the asthenosphere and that is located a few tens of kilometers deep . In this area, the pressure and temperature conditions make it possible for the rock found there to partially melt, thus generating magma. This silicate composition liquid, which will contain remains of rock, suspended crystals and dissolved gases, has a lower density than the rock in its surroundings. Given the difference in density with the enclosing rock, when magma accumulates in sufficient quantity, it tends to rise (due to buoyancy) towards more superficial areas, taking advantage of fractures already present in the rock or that the magma itself can create. In this way, it will rise to lower pressure and temperature levels, and may even accumulate at intermediate levels in contact areas between rocks of different properties.

When magma accumulates in sufficient quantity, it tends to rise towards more superficial areas, taking advantage of fractures already present in the rock

These accumulation zones, which we call magmatic reservoirs or magmatic chambers, allow deep magma to accumulate closer to the surface, which will generate an overpressure that will deform and break the rocks around it. This will translate into an increase in seismicity and soil deformation as measured by volcanic monitoring equipment. In the same way, when fractures open, gases are also released from the magma and will also be recorded by these same teams. This is how we can know that the volcano is preparing for a new eruption. In fact, in the case of this eruption of La Palma, this pre-eruptive process began on the day 11 of September with a very notable increase in seismicity and soil deformation, as well as in the emission of magmatic gases, which has been maintained to this day. This has made it possible to anticipate the eruption and take the necessary measures for its prevention and the reduction of possible associated risks.

(LA PALMA), 19/09/2021.- Una erupción volcánica ha comenzado esta tarde de domingo en los alrededores de Las Manchas, en El Paso (La Palma), después de que el complejo de la Cumbre Vieja acumulara miles de terremotos en la última semana, conforme el magma iba presionando el subsuelo en su ascenso. Las autoridades habían comenzado horas antes evacuar a las personas con problemas de movilidad en cuatro municipios. Arturo Rodriguez

The eruption that is developing It should not involve risks other than those related to the location of the lava flows, which are totally controlled by the topography, and the accumulation of pyroclasts around the emission mouth, which will end up forming the corresponding volcanic building. Volcanic gases, such as those derived from sulfur or CO₂ itself, are also present and must be taken into account due to the danger they represent, although they are restricted in the same areas as the previous products.

The duration of the eruption will depend on the amount of magma available to be expelled to the outside, which determines the excess pressure that is exerted from the magmatic chamber, ceasing this when the overpressure returns to balance with its environment. Previous eruptions similar to the current one have lasted from a few weeks to a few months.

Joan Martí Molist is director of Geosciences Barcelona, ​​CSIC

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