WorldKey points of the Cumbre Vieja volcano: why did this eruption occur...

Key points of the Cumbre Vieja volcano: why did this eruption occur in Spain? How long can it last?

Less than a week has passed since the beginning of this seismic crisis, until it finally came to an end with the eruptive phenomenon on the island of La Palma, off the northwest coast of Africa. As has been recalled in recent days, the Canary Islands archipelago is of volcanic origin, and the activity is still alive under its islands. So it’s natural to expect its inhabitants to experience an eruption like today’s on a regular basis.

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Why was an eruption expected?

On September 11, a series of earthquakes began in the southwest of the island of La Palma. Scientists linked it with the possibility that there was magma pushing the surface, which could eventually trigger an eruption. This swarm seismic, as this temporary concentration of small earthquakes in a single area is called, was getting closer and closer to the surface. The shocks, previously recorded at a depth of 20 kilometers, started to be noticed at around 100 meters in the last two days. With this behavior of the phenomenon, it was suspected that it was the magma generating ruptures on its way to the outside world. In addition, the island had swelled up to 6 inches this morning, another sign of magma.

Why did it happen now?

In October 1971, 50 years ago, there was the last eruption in La Palma, with the Teneguía volcano, which was also the last terrestrial eruption in Spain. Since then, the earthquake-volcanic activity has been quiet. Until a reactivation occurred in 2017, with several swarms seismic in later years, but not as energetic as this week’s. All this telluric force, together with the sudden deformation of the terrain, heralded the eruption.

How many earthquakes preceded the eruption?

According to the National Geographic Institute (IGN), in this swarm seismic, it was possible to record almost 7,000 tremors, of little magnitude and intensity, until this Sunday morning. The current seismic phenomenon was “very energetic”. In just a few days, it released more energy than what caused the underwater eruption of El Hierro in 2011 over two months, as explained by the director of the IGN in the Canary Islands, María José Blanco.

Why did it happen in this region?

The island of La Palma is very young geologically, only about two million years old – although it began to form under the sea four million years ago. But the island has two clearly differentiated parts: the northern one, older and more solid; and the southern one, younger and still in formation. Magma continues to widen the island in the southern part. In fact, all the volcanoes that have emerged in recent centuries have occurred in this area, such as San Juan, in 1949, and Teneguía.

Why isn’t there a single volcano?

Eruptions in the Canary Islands are usually fissures, that is, they erupt as a fissure with different points through which lava, gases and other materials emanate. David Calvo, from the Volcanological Institute of the Canaries (Involcan), explains that these eruptions occur in groups. “We’ve counted eight so far, but more may appear in the next few hours, while others are fading away,” he says. The normal is that more eruptive mouths appear, generally aligned. But as they enter a mature phase of eruption, some of these fissures will lose energy and will be covered, concentrating all of the lava’s emission force at one point. “That’s what happened with the Teneguía, which first opened several eruptive mouths and then concentrated on just one, which even covered others,” says Calvo. Something similar also occurred in the underwater eruption El Hierro, where measurements and submarines could show a row with at least three cones from which the materials emanated.

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Why did scientists know that the eruption would occur at this point?

The scientific community has had several stations installed at the site for years, from organizations such as the IGN, the Geological and Mining Institute (IGME), Canary Universities and Involcan. All these means allowed to perfectly locate the phenomenon, which focused on this point: both the swarm as the deformation of the terrain. In addition, in recent days a team with more scientists, instruments and devices had mobilized. The terrain deformation, for example, was calculated thanks to fixed stations, but also thanks to observations made by the Copernicus program with European Union satellites. On the other hand, a plane requested by the Government of the Canary Islands to the Ministry for the Ecological Transition of Spain had traveled to the region to monitor the volcanic activity. The IGME sent drones, and an Involcan helicopter was studying the tremors.

How long can the rash last?

It is not possible to know for sure. The historical background and volcanology of the area indicate that the eruptive phenomenon could last for several days, including weeks, as happened with the recent volcanoes at Tagoro, El Hierro and Teneguía. However, it is too early to know the dynamics of this eruption, the energy that could be released by the various fissures in the ground, and the number of cubic meters of magma pressing the surface towards the outside.

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