January 18, 2022 10:19 pm

“The most recent eruptions on La Palma lasted between 24 and 84 days, that is the fork of what we can expect”

While the inhabitants of La Palma look with concern and sadness at the situation the island is going through, with innumerable material losses, geologists and volcanologists work to report on the evolution of the eruption. Although the origin of the archipelago is purely volcanic, few historical records are known of these phenomena in the area.

Alicia Felpeto works at the National Geographic Institute where they are giving the last hour of the seismicity, the eruption and the main keys of this natural phenomenon.

What type of rash is this? Because in the Canary Islands they are not like those we see in other areas of the world faster and with great explosiveness.

It is of the strombolian type. It has a small explosive component but it is mainly lava flows.

What differences exist with the one that occurred in Teneguía 50 years ago?

There are not many, basically the mechanism is practically the same. If I remember correctly, in Teneguía there were up to four different volcanic cones. This has had many mouths that are activated and deactivated. We do not know how many will remain at the end as more permanent examples.

And in duration?

We still cannot know that.

What indicators are valued to make an estimate? If there are …

It is very difficult to know the duration of the eruption because it depends on the amount of magma available. Sometimes there is not a single magma reservoir. In many cases there is a superficial one, about which we can know something more, and another deep one, in which in general we know something less. For this reason, the bottom one can be fed to the top one for a long time, even if the top one is relatively small. When an eruption is going to end is one of the most difficult questions to answer in volcanology.

When an eruption will end is one of the most difficult questions to answer in volcanology

How long have previous eruptions in this area lasted?

On the island of La Palma, the duration of the most recent historical eruptions – of the last six – varies between 24 and 84 days. That would be the fork of what we can expect.

Why is La Palma the Canary Island that has had the most since there are records?

Because it is one of the youngest islands in the archipelago, along with El Hierro. That is why they are more active and more powerful. In fact, in the latter, although we only have one documented eruption, which is that of 2011, many researchers suspect that there have been more in the historical period. But due to a problem of lack of documentation, due to a fire in an archive on the island, we have probably lost information related to the last 500 years.

These volcanoes make the ground rise and the Canaries exist, what would happen if there were no more volcanic activity?

There would be no Canary Islands. They have been built on the basis of underwater eruptions. A volcano grows from below and when the upper part emerges is when we call them islands, but below is the rest of the volcanic building. If there were no eruptions, they would not exist, just as we would not have Cape Verde or the Azores.

Why are they concentrated in the southern half of the island?

The north is a much older part. This caldera-like shape is erosion, with very active materials. All the modern activity on the island, geologically speaking, occurs at the Cumbre Vieja. Historic eruptions have been in that area, to one side or the other.

The washes are causing significant material losses. Can you predict the path they will take?

Up to a point, yes. Numerical simulations can be done. What is more difficult to model is when they will arrive at each point of route. There are quite complex factors involved, since lava is a viscous fluid that needs a certain height. The viscosity varies from the center of emission, with temperatures of about 1,100 or 1,200 ºC, to areas where it almost slows down at about 800 ºC. In between, the viscosity changes by up to five orders of magnitude and how the speed will evolve is very difficult to know. What we can do is measure the current speed and see if it continues to emit, until we reach the sea or another place in a while.

The temperature of emission is interesting to measure, but also the interior of the lava flow

They are working with drones on the island to measure the temperature. What clues do these variations give regarding the evolution of the eruption?

The emission temperature is interesting to measure, but also the interior of the lava flow. Because, sometimes, during their movement they begin to cool down the sides and the upper part becomes solid. This area acts as a thermal insulator for the lava inside. In this way, it does not lose temperature, maintains its viscosity and runs fast as if it were close to the center of emission. That is why it is good to keep an eye on them, because they can represent a danger if the lava inside goes much faster than if it were exposed. It is one of the important reasons for knowing the temperature.

What changes can there be in a few days?

We can hope that there are no longer as many openings of mouths and new lava fountains, as we have seen in the first hours. The normal thing is that it calms down and there are only one, two or three mouths active at the same time. Therefore, this count that is done now will lead to the fact that many of them will end up disappearing shortly. At least that is what has happened in other eruptions.

Does the moon really influence an eruption?

It could play a role if the volcano were about to explode, in the sense that the effect of the land tide could be the final push it lacked. But it is not entirely clear that this is really significant as an effect of the eruption.

This eruption is basaltic monogenetic and is not very explosive. The ashes are in small quantity

Regarding the ashes, many indications are being given about their cleaning or that they are not thrown into the water. What is the magnitude of the volcanic activity on La Palma?

They are very little ash compared to a large explosive volcanism. This is monogenetic basalt and is not very explosive. The ashes are in small quantity. Volcanoes that actually spew ashes, so to speak, are travails that are built with a differentiated magma that, compared to wine, has gone from being must to ripening and being wine. This also happens with magmas, they stay in a magmatic chamber for a long time, they lose a series of minerals and become enriched in gases and their explosive potential increases. An example is the Pinatubo in the Philippines, which in 1991 caused 40 km of ash column injected into the atmosphere, which influenced the climate of the entire planet. Ash is a serious problem in this type of eruption. Here the volume is much smaller.

How does life return to these areas through which the lava flows and what nutrients do the eruptions contribute to the soil?

Long-term volcanoes are great soil fertilizers. Lavas is a more complicated thing. Recovery depends on the climate in which they are. In Central American countries, for example, it is very fast. However, the Timanfaya area, in Lanzarote, only 15 or 20 years ago that lichens began to colonize the lavas. It is a much slower process, but in the end you will have very rich soil. If you approach the area that was covered by medium-sized pyroplasts, a few centimeters long, they are super rich areas. From there these crops come out in the shape of a cone with the vines in the background. These vines grew much better than the ones that were planted before. Everything is a ten with ten. In the eruption part there is a destructive part, obviously, but in the long term there is a positive part. Among them, if there were no volcanism, there would be no archipelago.

How do these eruptions behave on the islands? Are they clustered in time and then are there periods of rest?

Sometimes it happens. The s. XVIII was the most intense that was experienced in the Canary Islands in this sense. This is usual, whether it be in groups or clusters. I suppose it has to do with the dynamics of the upper mantle, where they are produced, and in the way in which the amount of magma input varies. Even so, the history we have in places like the Canary Islands is so concise, that making statistics with such a small time window, with only 14 eruptions, is complicated. But that same grouping in clusters it occurs in many other areas.

Long-term volcanoes are great soil fertilizers

Since when are there records?

When I speak of historical eruptions, I mean those of which we have written documents where they speak of which day began and ended. We can look back a little more and talk about those that we know were there but we do not know the date, even the year is uncertain. A well-known case is that of Christopher Columbus who saw a fire on one of the islands, but we do not know when, or in what exact place.


Comments (0)

Leave a Reply

Your email address will not be published. Required fields are marked *