January 24, 2022 1:33 pm

“We are going to learn how this eruption came about, but we cannot predict when it will end”

A few days ago the volcano apparently stopped its eruptive activity for a few hours. A common behavior in this type of phenomenon, according to scientists. The team that works on La Palma, led by the National Geographic Institute (IGN), is in charge of monitoring these changes in the eruption to protect safety for the population.

The IGN works together with the members of the Volcanic Emergency Plan of the Canary Islands (Pevolca), the Volcanological Institute of the Canary Islands (INVOLCAN) and other local institutions. The team is joined by the security forces, the island council and various political representatives. Likewise, other institutions have also asked to collaborate in the field of research and have had their support. The University of Granada has been one of them and has transferred a group of seismologists, with extensive experience in volcanoes, to work on the ground for a few days.

How did you manage to participate in the study of the volcano in situ?

The IGN has authorized us to go and they have supported us together with INVOLCAN. They have left us from an SUV to be able to access the area, to contact with people who know the terrain and have guided us. Now that the team is back, they are the ones in charge of the maintenance of the instruments.

How many people make up the team?

We were four people from the University of Granada. We installed the station in the first two days and the three people who stayed later verify that everything works to transmit the data.

What is the complexity of installing meters in an active volcano to know its evolution?

It is a task that can be more or less complex. The first two days I already realized, for example, that the solar panels that we install to power it must be taken care of because they become covered with ash and stop working. That alone means that someone goes there with a brush and cleans it from time to time. It is difficult for us because we are far away and we have no staff. The support of these local groups, which is essential to maintain it, also the Military Emergency Unit (UME) and the Civil Guard have collaborated with us. There is a very large team of people on La Palma that is allowing scientists to do our work.

There is a very large team of people on La Palma that is allowing scientists to do our work

Are there other institutions that are there right now?

Yes, there are other additional groups, especially from universities, because they are not usually part of the political structure of crisis management, it is not their objective. We go there punctually and each one contributes what they have more experience with. In our case it is a seismic antenna, which is a particular arrangement of seismometers that allows the weakest or most difficult signals to be detected, with the same principle as a communications antenna. Only that applied to the seismic wave.

What do you record with these seismometers?

We monitor volcanic sources in more detail, such as volcanic tremor. This is the name given to the vibrations that accompany volcanic eruptions. All the movements of the magma, the emission of gases or the explosive outflow of lava produce vibrations in the ground. They are not only external, when the phenomenon is observed on the surface, but also exist inside when fluids move through the ducts. It is analogous to when someone turns on a faucet on an old pipe and it starts ringing and rumbling. We apply the same principle in volcanic conduits. We record the vibrations and with this instrument we can analyze them.

The UGR team on La Palma preparing the station.  / Photo courtesy of the researcher

The UGR team on La Palma preparing the station. / Photo courtesy of the researcher

Doesn’t the seismic network act the same?

With a traditional seismic network it is very difficult, because it is a continuous signal in which the arrival times cannot be determined. The analysis is a bit more complex.

Where have you placed them?

Instead of around the source at great distances from each other, they are placed in a cluster dense to correlate what a sensor registers with that of the neighbor. Our goal was to put them as close to the volcanic eruption as possible to have higher resolution, but as long as it is safe. We have chosen an area that is to the east, on the other side of the ridge, so that the lava flows will not go in that direction, they go down the slope. We have put them 3 km apart. The danger is the gases and the ashes that, sometimes, depending on how the wind is going, fall on it.

We have placed the seismometers 3 km apart. The danger is the gases and ashes, which sometimes, depending on how the wind goes, fall on top

What do these vibrations from the ground tell you?

They originate in the volcanic ducts, we record them and what we receive is the raw data of the vibrations of very close points, since they are placed one from another at about 100 meters. The normal thing in a seismic network is that they are 5 or 10 km between them. What it allows is to reconstruct how the band fronts propagate and see where they come from. Not only the individual earthquakes that can occur, but also the background noise that the volcano produces. In many cases these are more intense than the earthquakes themselves.

Does it allow you to give clues to know how the volcano is progressing?

We study how the eruption behaves in real time. If the activity continues, if it has stopped. And all we want is to learn how it develops, what are the processes that occur and apply that knowledge in the next eruption. Learn as much as possible for the future.

The UGR team on La Palma preparing the station.  / Photo courtesy of the researcher

The UGR team on La Palma preparing the station. / Photo courtesy of the researcher

You also use the knowledge of previous eruptions, right?

What research has been done in the past is accumulating knowledge about how volcanoes work, thus allowing us to better interpret it. The data that we are obtaining right now, on the geometry of the ducts or the proximity of the source, are things that have already happened. We are going to learn how this eruption occurred and its dynamics, but we cannot predict when it will end. It’s about being more prepared.

We study how the eruption behaves in real time

A few days ago the activity of the volcano stopped for a few hours. Is it usual in this type of eruption?

Eruptions are very chaotic processes, with a lot of variability. It does not have to come out all the lava or all the gases at once. They accumulate and when the pressure rises above the threshold, external phenomena occur. But in all eruptions there are ups and downs. The duration, depending on the volcano, is too. It can be from a few weeks to months or even years. Temporarily stopping an eruption is not uncommon. For example, Kīlauea in Hawaii erupted from 1983 to 2010, but intermittently, with small lava flows, then more explosive processes and more massive emissions that ceased. It is precisely what we intend to study right now, to know if the magma is being depleted or was it a temporary stop until the magma chamber recharges.

When did you start making measurements in the volcanoes of the Canary Islands?

We started with seismic antennas on Teide in the 90s, with instruments in the Las Cañadas caldera. We also conducted a similar experiment in 2004, when there was a seismic reactivation. It was the event that gave rise to the organization of PEVOLCA. Then we had another seismic antenna working during the El Hierro eruption, which allowed us to detect the position of the eruptive center and whether or not there were more eruptions, in addition to the main one. Being underwater it is not so easy to identify. Besides, we have done other types of studies with seismic networks in Gran Canaria and Lanzarote, in the Timanfaya area. Although there the level of seismicity was much lower.

In La Palma the precursor earthquakes occurred in the previous week and were decreasing in depth. We were practically seeing the position of the magma front

You were also in the most recent in El Hierro

On that occasion there were precursor and large earthquakes, thousands in the months before the eruption. But curiously, the earthquakes were deep, northwest of El Hierro and the eruption was to the south. This is telling us something about what the volcano is like inside. That there is an area that is difficult for magma to traverse.

However, on La Palma the precursor earthquakes occurred in the previous week and were decreasing in depth. We were practically seeing the position of the magma front. It is a different behavior and can give us an idea that the internal structure of the two volcanic buildings is not the same. It is very interesting to compare it with eruptions like that of Teneguia, which also had precursor earthquakes during the previous week. It is a behavior that is repeated. The problem is usually that there is little data from the point of view of seismology because it is a young science, it has barely been active for a century.

In addition to this archipelago, your work has taken you to remote places like Antarctica.

Yes, we have worked on Italian volcanoes like Etna, or in Hawaii on Kīlauea, but also for many years on Deception Island, which is a volcano in Antarctica where Spain has a scientific base. In this place the interest to determine the volcanic activity is essential for the safety of the researchers who are working. If an eruption is difficult in a civilized area, imagine where there are no resources.


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