January 22, 2022 6:12 pm

A more explosive and stronger volcano than expected

This volcano has been stronger than expected since for years it was perceived that the historical eruptions of the Canary Islands were much quieter. However, recent studies have already shown other more explosive than those collected in chronicles, such as that of the Chinyero in Tenerife over 100 years ago. The deposits from this eruption indicated very energetic pulses in the early phases.

The first week of this new La Palma eruption it was the most variable. As scientists have already warned, the beginnings of a volcano are the most volatile and we encounter moments of uncertainty. The magma originating from the shallow intrusion (7 to 11 km) had a high gas content that increased its explosiveness. Once the pause occurred on September 27, it has continued its activity, remaining relatively stable, with a magma that this time came directly from the mantle.

At times there have been more explosive moments, with emission of large amount of ash, or more effusive, with quite fluid casting emission. New emission points near the eruptive point have been produced and will continue to be produced, either through pre-existing mouths, such as the southern zone where phreatomagmatic explosions were emitted on the first day; or areas of emission of lava flows, such as the one we saw at the beginning of October 600 m from the main cone. This is within the expectation of this type of eruption.

Perhaps the greatest concern in the population is the possible appearance of a new eruptive center far from the current one.

Perhaps the greatest concern in the population is the possible appearance of a new eruptive center far from the current one. Although the probability is not zero, it is true that today we do not find any sign that indicates that this may happen.

Right now they exist earthquakes in two specific areas: the first at the base of the island, between 11 and 15 km, and in the area where the magmatic intrusion began to hit under the island on September 12. This activity began on the day of the stoppage and seems to be related to the contribution of new magma from the mantle.

The second seismic zone is between 30 and 40 km away and appears to be where magma was stored under the island for years or decades. This seismicity may be related to the “emptying” of magma. Nevertheless, no evolution is observed in this seismicity nor in the deformation or any other parameter that indicates the presence of a new intrusion that could generate a new volcanic eruption far from the first one.

The most normal thing is that the eruption continues to emit pyroclasts and lava flows from the already active emission centers.

The most normal thing is that the eruption continues to emit pyroclasts and lava flows from the already active emission centers, with strombolian activity (ash and other pyroclasts) and Hawaiian (lava flows), and with increases and decreases in explosiveness within the range already lived for the past three weeks.

Same danger, more vulnerable

Another unknown that this volcano has thrown refers to the increasing eruptive seismic activity, with maximum magnitudes that were exceeded every few days. The earthquakes in volcanic areas such as the Canary Islands they tend to behave differently from the better known tectonic regions.

On tectonic regime, the temporal evolution of seismicity usually follows three possible patterns: a large earthquake followed by aftershocks that decrease with time, a large earthquake preceded by increasing seismicity and followed by aftershocks that decrease with time, or a series of earthquakes that increase and they taper off without a major characteristic earthquake.

However, in volcanic regions we find a fourth type of temporal distribution with a gradual increase in activity, with earthquakes of increasing magnitude until a sharp decline occurs. We live this type of evolution in El Hierro in 2011, before and during the eruption. A possible mechanism to explain this behavior is the existence of a continuous pressure due to presence of magma or to eruptive changes. This pressure is applied over a certain region continuously and releases the energy first in the form of small earthquakes. However, there are areas capable of “storing” energy from this pressure and releasing it later in the form of larger earthquakes. The more time passes, the greater the probability of the occurrence of these earthquakes.

Everything experienced falls within a volcanic eruption of known parameters, what changes is that we are facing a volcanic eruption in modern times

Everything experienced this last month falls within a volcanic eruption of known parameters, but what changes is that we are faced with a volcanic eruption in modern times. The danger of the eruptions in the Canary Islands has not changed, but our vulnerability to them (more population and more infrastructure), something that increases the volcanic risk.

As part of mitigating this risk, the volcanic watch, the work of the National Geographic Institute, which saves lives, although it can do little with material goods. Another important point is the communication of scientific information, something in which it has been improved if we compare with the eruption of El Hierro of 10 years ago. It must be done openly, admitting when the future behavior of the eruption is not known for sure, but without ceasing to do a service to the population and responding to their concerns when possible.

To have a well-informed and educated population in the phenomenon can reduce the risk. The panic that can be generated by hoaxes or interpretations from unofficial sources must be mitigated and can only be done by informing. The palm trees understand the volcanic phenomenon and its vocabulary better than ever, and they understand the risks better and better. Yes, it should be emphasized, outside the island, the security that exists in the areas not affected by the eruption, which is 95% of La Palma. The important is that so far there have been no victimsBut the eruption could still last for months and we all have to be prepared for it.

Itahiza Domínguez Sardinia, seismologist National Geographic Institute

Source: SINC

Rights: Creative Commons.


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