Increasing earthquakes, more lava and a delta devouring the sea: the perfect storm on La Palma

The magma from the Cumbre Vieja volcano is transforming La Palma. The continuous seismic swarms keep the eruption vibrant, while the deformation of the terrain remains at 30 centimeters and the lava creates a new landscape. There are already more than 700 buildings buried in the more than 470 hectares that have been razed. And although all eyes are on the arrival of the lava to the sea, under the island, earthquakes stir the guts of the volcano with increasing intensity.

In the last hours, seismicity has increased in municipalities like Fuencaliente and at least six have exceeded the magnitude of three. That is, it is a sufficient intensity for the vibrations to be felt while standing. So much so that they have come to be represented in red. It must be remembered that the eruption developed after several days of seismic swarms in which the earthquakes, little by little, were reaching less depth.

At the moment, these more intense episodes that are being lived under the island in the last hours pose no imminent danger, but they do give an idea of ​​how the situation is. As José Luis Barrera, a geologist at the Illustrious Official College of Geologists (ICOG) assures, “the magma is pushing hard” and “new fissures could open.”

The unknown remains when. It is the great question of the scientists who work on the ground and who, they repeat, are at the command of the volcano. The possibilities are on the table, but, for the moment, they rule out the possibility of opening new mouths or new emission points in the short term. However, they recall the importance of tracking the seismicity of the volcano because it is the aspect that, together with the deformation of the ground, will give information on the evolution of the eruption.

David Calvo, spokesperson for Involcan, assures EL ESPAÑOL that earthquakes are occurring in the south of the island and that, it may happen, that some are masked by the volcanic tremor, that signal continues as a roar emitted by the erupting volcano. “We continue to think that it is a recharge of the system or simply a readjustment of the island. In the short term we do not see danger,” he points out.

The seismicity detected is located in the same area “where it all began,” says Manuel Regueiro, president of the Illustrious Official College of Geologists, and although the magnitude of the earthquakes has increased, “the key is depth”. For now, these new earthquakes reported by Involcan are occurring at depths of 15 kilometers. Above 10 kilometers they would already require special attention. However, “what is worrying”, he assures, “would be to find very shallow earthquakes, 1 or 2 kilometers deep”, because that would indicate not only the opening of a new emission point, but also the area where it would take place.

For non-experts in volcanology a question may arise and it is why the magma continues to cause earthquakes in the area of ​​the seismic anomaly if it has already found an outlet conduit. But it is that it is a usual behavior of magma that, due to the energy it reaches, keeps breaking the lower part of the crust in the form of earthquakes. “There is a continuous push of lava from the magmatic chambers,” explains Regueiro.

If those earthquakes were breaking the crust and were increasingly shallow, we would be facing another scenario that experts point out as possible, but also far away. The magma would find new escape routes and open fissures within a radius of 14 kilometers from where the lava emissions are currently being produced.

Thus, the volcano, for the moment, is still in an effusive phase, with continuous emission of fluid lava through the second fissure, and expulsion of pyroclasts and ash through the main cone. “We have the feeling that we are in the stability phase,” says Calvo. In other words, the lava, although faster and more fluid than that observed a few days ago, follows its emission channel down the slope, surrounds the mountain of Tazacorte and reaches the sea by a cliff about 50 meters high in the Los Guirres beach area.

It is expected that the journey that the lava flows follow is the one that has opened this material that scientists describe as type Hawaiian for its fluidity and higher temperature. If new fissures or new emission points were to open, they could take different paths, but, as Calvo points out, the lava “has already made its track, and is heading straight for the ocean”.

The delta that will change the island

“The island is not going to be the same anymore.” The speaker is Gemma Ercilla, a marine geologist at the Institute of Marine Sciences of the CSIC in Barcelona. As Ercilla explains, the arrival of the lava to the sea will not only modify the seabed of the ‘pretty island’, but it will change all the orography of the area. “It will be necessary to map again both what is on land and what is in the sea. The coastline will substantially modify its profile”, explains the expert.

The presence of the oceanographic vessel Ramón Margalef in the Canary Islands, in fact, not only has to do with what may happen on the island’s seabed. The team of geologists, marine biologists and specialists from different branches that are in its interior will monitor a whole series of processes related to the subaerial part that, a posteriori, can affect the underwater part through fractures, gas vents or bulges of the submarine bottom.

What to expect from the evolution of the lava delta is one of the big questions currently on the table. At the moment, it is estimated that it has a front half a kilometer wide and has occupied around ten hectares since it began its fall from the cliff. But not even the experts who work on the area know exactly how much it will expand in its conical shape or grow in height.

The evolution will depend on several factors. The first of them is the orography of the coastline itself, which in the case of the area where it is deposited so far is not very deep. Experts call it the low island. This delta advances out to sea and laterally because it loses speed. Magma begins to settle as a result of this cooling. “If it had the same speed and the same fluidity, it would continue. But with the thermal contrast it solidifies”, says Ercilla. Hence it expands laterally.

However, there are more factors that will intervene in the evolution of the delta. One of them is the volume of lava that the Cumbre Vieja volcano continues to supply from the area of ​​origin; the other, the topography of the seabed. That is, the depth of the Guirres beach area. “The width of the continental shelf where the lava delta is forming is narrow,” explains José Luis Barrera. “When you reach your limit, it will fall to the seabed and form distinct reliefs“, Add.

One of the greatest dangers that the formation of the delta entails is that experts have to control what geologists call as “deltaic front”. A fan is currently being built, but this fan can be several meters high based on the accumulated lava. “As a consequence of the slopes and the rapid solidification we find unstable structures, which fracture and break“, explains Gemma Ercilla.

These instability processes can create, according to the marine geologist, “small tsunamis” that some researchers have documented through models. Ercilla herself participated in an investigation which was published a few months ago in which it is detailed how the Andalusian coast is also at risk of suffering a tsunami at some point as a result of the activity of the faults that fracture it. “One of the risk factors that these delta lavas may have are those instabilities that can occur at the front,” he details. “Within the magnitude of this front, it will be one of the aspects to be controlled“, it ends.



Reference-www.elespanol.com

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