The Cabeza de Vaca volcano, during its eruption this Monday.Kike Rincon / Europa Press
The La Palma volcano coordination team works with all possible scenarios: from the most destructive to the least harmful.
However, current behavior and the history of the area indicate that the most likely is a continued non-explosive eruption that will last for weeks.
The longest known was in 1585 and lasted 84 days;
the shortest, 1971, lasted 25 days.
In any case, the return to normality for the more than 5,500 evicted residents will not be immediate after the interruption of the expulsion of lava.
We will have to wait for the affected land to cool down and stabilize, analyze the damage to infrastructure, the risks of recurrence, the levels of toxic gases and accumulated ash, among other parameters.
The seven dangers of the La Palma volcano eruption
Raúl Pérez, geologist, seismologist and researcher at the Geological Mining Institute of Spain (IGME) who is part of the monitoring team for the Cabeza de Vaca eruption on La Palma, assesses that the speed of the lava on its way to the sea has decreased and that the opening of a new eruptive mouth in the vicinity of the town of Tacande, in El Paso, has followed the same trend as the previous ones: with the same eruptive style: lava continues to come out, flowing down the slope and without explosive eruptions ”.
This behavior is similar to that recorded between October 26 and November 18, 1971 in Teneguía, where only one person died from exposure to toxic gases after bypassing the security cordon.
On that occasion, the lava did not seriously affect populated areas and reached the sea, where it generated a new area of two million square meters.
We are finding characteristics that are quite convergent with the historical ones in the Cumbre Vieja area: the coladas (lava beds) come out in favor of the ridge and the magma uses the invoicing of the terrain to find an easier escape route
Raúl Pérez, geologist, seismologist and researcher at the Geological Mining Institute of Spain
In this sense, the IGME expert on geological hazards explains: “In theory, any volcanologist would say that no eruption is similar and all have their particularity. However, we are finding characteristics that are quite convergent with the historical ones in the Cumbre Vieja area: the coladas [lava beds] come out in favor of the ridge and the magma uses the fracturing of the terrain to find an easier escape route. This, in some way, can help the explosions not be more violent because, if you already have a path made with extensional fractures, it is more likely that, when the lava comes out, it will behave less violently ”.
Ana Crespo Blanc, Professor of Geodynamics at the University of Granada, agrees with Pérez that the volcanism in the area allows us to think that the described scenario is the most likely: last centuries: eruptions that last from a month and a half to two or three months and then, when the pressure has dropped in the magmatic chamber, it will be over ”.
Knowing that key element will take some time.
Geochemical control is essential to know the pressure inside the magma chamber, which pushes the magma outwards.
But Crespo, a geologist trained at the University of Lausanne (Switzerland) and Seville, insists that, taking into account the previous eruptions in the area, “it is most likely that there will be an accumulation of lava that reaches the sea, where it it will cool and may even expand the size of the island. "
Discarded the most catastrophic scenarios
Scientists reject the most catastrophic scenarios, such as the one advocated by Steven Ward of the University of California and Simon Day of the University College London 20 years ago in
Geophysical Research Letters
Geological evidence suggests that during a future eruption, the Cumbre Vieja volcano on the island of La Palma may experience a catastrophic failure of its west flank, dropping 150 to 500 cubic kilometers of rock into the sea.
Using a geologically reasonable estimate of the movement of the landslide, we modeled the tsunami waves produced by the landslide.
The waves generated by the execution of a sliding block of between 500 and 150 cubic kilometers at 100 meters per second could travel throughout the Atlantic basin and reach the coasts of the Americas with a height of up to 25 meters ”.
It is convenient not to alarm people.
The worst case scenario would be for the magma chamber to completely empty and collapse, but this is not the case on La Palma
Ana Crespo Blanc, Professor of Geodynamics at the University of Granada
Crespo Blanc undoubtedly rejects this scenario and warns: “I think it is convenient not to alarm people.
The worst case scenario would be for the magma chamber to completely empty and collapse, but this is not the case on La Palma.
It would be a very large eruption involving the entire island and this is obviously not the case here.
It would be necessary to foresee that, once the activity that has arisen right now has elapsed, everything would return to normal ”.
The geologist Raúl Pérez also discards the scenario described by Ward and Day: “The eruption is not accompanied by phenomena of high violence. Within what is volcanism, the phenomenon that is occurring is small. For there to be a collapse of the caldera, the volumes that would have to be involved would be enormous and this is not the case. This scenario is not being contemplated because there are no indicators that it may occur, neither because of the volumes that are being estimated nor because of the eruptive characteristics ”.
In this sense, due to similar eruptions, one can think of a scenario where the expulsion of lava lasts longer than expected, but according to Pérez, "such special conditions would have to be given that they are not foreseen."
“It does take into account”, according to the geologist, “the possibility that a small interaction of magma with water could produce an explosion”.
Back to normal
The forecast indicates that the end of the eruptions would mark the possible beginning of the return to normality.
But this will not be immediate and it is not known when it will occur.
In this sense, the IGME geologist points out: “Although there is no lava, for us, the phenomenon continues.
It can continue to accumulate, even if it does not have a surface outlet ”.
To evaluate which areas are out of risk, maps of lava movement and its forecast are monitored until it completes its journey, according to data from the National Geographic Institute. Raúl Pérez adds: “Then we will have to see what infrastructures are cut off and the composition of the lava and ash fields, which can include toxic elements that have fallen on crops and aquifers. We are preparing an impact study. And the lava field has to cool and stabilize, we have to know if volcanic tubes are forming underneath and if the affected terrain is stable. It will last a long time, I can't say how long, but the return to normality will not be immediate ”.
The hazard maps, which will mark the possibilities of returning to their homes of the 6,500 evicted, review the risk posed by lava flows, ash, pyroclastic flows, gas emanations, lahars or mud flows, slopesides and tsunamis.
To prepare them, seismic activity, ground deformation, concentrations of carbon dioxide and sulfur and temperatures are also taken into account in order to anticipate other eruptions or new eruptive centers.
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