Monday, October 25

Ten years after the El Hierro eruption, the scientific community takes stock on La Palma

This Sunday marked the 10th anniversary of the beginning of the underwater volcanic eruption of El Hierro and also three weeks of the beginning of the eruptive process of La Palma. The main difference between the two is that in El Hierro the eruptive fissure occurred under the sea, while the one that now shocks the Canary Islands has been subaerial. This has been explained by the head of Seismology of the National Geographic Institute (IGN), Itahiza Domínguez, to Canarias Now. Despite this, the 2011 eruption has offered the scientific committee that manages the emergency on La Palma experience and knowledge to better manage this crisis and guarantee people’s safety.

La Palma faces another night of roars and tremors as one of the lava flows from the volcano approaches the sea

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The dating of the El Hierro volcano was more complex than that of the La Palma volcano, as it is an underwater phenomenon. That it occurred under the ocean was an added complexity to scientific analysis, so there is debate among experts about when to signal its beginning. The scientist member of the IGN’s terrain deformation surveillance group Laura García Cañada affirms that “on October 10, 2011 was when the volcanic tremor was registered”, a parameter that is normally used to determine the beginning of an eruptive process. For its part, for the Volcanological Institute of the Canary Islands (Involcan), the beginning took place two days later, on October 12, 2011, when a spot was located in the sea.

The Cumbre Vieja volcano, still without a formal name, has entered a more explosive phase in the last two weeks. Along these lines, Itahiza Domínguez points out that this is another of the main differences between the El Hierro and La Palma processes. The Volcanic Explosivity Index is a scale of up to 8 degrees that is used by volcanologists to measure the magnitude of the eruption. Thus, Domínguez points out that in El Hierro, being underwater and deep, it did not generate a level of explosiveness like that of La Palma, right now in grade two.

“When the underwater volcano erupted, it was feared that new mouths would open closer to the coast and the town, but in the end it was not, so it was much easier to manage than the current one,” explains seismologist Itahiza Domínguez . In the case of La Palma, professionals have always prioritized people’s lives, the only controllable parameter within the chaos. At this point, Domínguez affirms that little could be done to save the infrastructures, although the advance of lava flows is constantly being studied on the ground.

The precursors to both eruptions were the same, according to Domínguez, but the work was more complex to carry out on the marine eruption. In El Hierro, the work of the Oceanographic Institute was fundamental to be able to analyze the formation of the main cone, now this organism monitors the arrival of lava flows into the ocean from the coasts of La Palma.

The ten-year difference between the two eruptions is also noticeable in technological advance. The technologies of then were not as advanced as the current ones to work in the field. At this point, the director of the National Geographic Institute in the Canary Islands, María José Blanco, maintains that the technological advances of the time have been added to the work of the experts in this new eruption. Drone flights have been directed from the Emergency Military Unit (UME), sometimes even with thermal detectors to know the progress of the flows and the buildings and infrastructures affected.

Parameters to determine the possibility of eruption

Experts use three parameters to determine the likelihood of a volcano erupting. The first of them is seismicity. Several intermittent seismic swarms were detected on La Palma between 2017 and 2020, but the most frequent occurred in the week before the eruption, says García Cañada. Secondly, the deformations of the terrain, Cañada’s area of ​​specialization, are analyzed. At this point since seismic movements on the island increased on September 11, Involcán also reported a “significant” deformation of the land. Third, the presence of gases is also studied. IGN workers carry out these searches throughout the Archipelago. In recent weeks they have added new points on La Palma, especially in the Cumbre Vieja area, after the increase in land movements.

The work of tracking these three values ​​has served the scientists to rule out “for the moment” the possibility of an opening of a new lava-emitting center in other parts of the island away from the main one. From the National Geographic Institute, daily reports are presented by the director in the Canary Islands, María José Blanco, and the director of the Central Geophysical Observatory, Carmen López, which are presented to the scientific committee. In turn, another report comes out of this scientific committee and is presented to the steering committee. After that, a press conference takes place to explain the daily progress to the public. In the afternoon it is about doing field work and finally organizing the next day’s work. The rest of the staff maintain the control stations.

The hot spot theory

The historical eruptions produced in the western islands are explained through the hot spot theory, points out Itahiza Domínguez. However, the Greek geologist of the National Geographic Institute, Stavros Meletlidis, affirms that the creation of the Canary Islands is not explained only through this theory, but that some variants must be added. According to this hypothesis, the Canary Islands would have been formed by the existence of a point that emanates more heat from the Earth’s mantle than usual. The gases emitted from that part of the Earth’s interior would reach the base of the lithosphere forming a volcanic plume, that is, a mixture of gases that emerge towards the outside. The magma is formed in its interior of a compound of gases that when reaching the surface collides

According to this theory, the westernmost islands would always be the youngest and the eastern ones the oldest. This pattern is not met in the Archipelago since Fuerteventura is older than Lanzarote and yet it is located further west. But it does explain the constant seismic swarm on La Palma and El Hierro, protagonists of four eruptions in the last 100 years. For Stavros Meletlidis, the Canary Islands obey the general theory of hot spots, but there are things like subsidence that do not seem to be clear in the Archipelago. Subsidence is the process by which the oldest islands would disappear after thousands of years due to erosion until they became a tower of corals. The geologist affirms that Fuerteventura has existed for 20 million years, but nevertheless the island has not yet disappeared.

The volcanic islands have a formation process that is usually very fast, then they slow down, explains Itahiza Domínguez. The eruptive process of the Canary Islands is still alive and proof of this is the new volcano on La Palma. Although the island is the protagonist of the majority of eruptions in recent centuries, the volcanic systems of El Hierro and Tenerife are also still active. Thus, while La Gomera is in a moment of pause that can last for millions of years, “Tenerife is in the next step.” “It already had a stop and now it has a volcanic process again active,” Domínguez highlights. At this point, experts say that the probability of an eruption occurring in Gran Canaria, Fuerteventura and Lanzarote is much lower than in the rest of the islands.

María José Blanco recalls that “science is not a branch of certainties, but of probabilities”. In this way, the probability and the analysis of the historical eruptions that the Canary Islands have experienced shows that the Archipelago will continue to experience new volcanic processes such as that of La Palma, but it is unknown when this eruption will end and when the following may occur. At this point, the scientific coordinator of the Volcanological Institute of the Canary Islands, Nemesio Pérez, a few days ago advised the palm trees and the Canarian people not to see the volcanoes as enemies, “because they are what have made it possible for the Canary Islands to exist.”

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