The surroundings of Teide, in Tenerife, suffered a few weeks ago a swarm of about 400 small earthquakes, hardly felt by the population. After the eruption of La Palma, however, any small seismic movement raises the alert among the population, which lives with the uncertainty of whether the next magma from the Canary Islands will come out of the highest peak in Spain. Itahiza Domínguez, seismologist at the National Geographic Institute (IGN) in the Canary Islands, assures that, in the short term, “there is nothing to indicate an upcoming eruption.”
-What does the seismic swarm that occurred a few weeks ago in the vicinity of Teide mean?
-The seismic activity of Friday June 17 at dawn, which produced more than 400 earthquakes, falls within the usual. In recent years, in Tenerife we have seen three similar swarms in the same area and at the same depths (10 kilometers away). They may be related to the island’s own activity. The island of Tenerife is much more active than La Palma and El Hierro in inter-eruptive periods, producing about 1,000 earthquakes a year. We believe it is related to the complex system that sleeps under the island. We have a magma chamber under Teide and probably a more intricate system throughout the island. On volcanic islands, magma can accumulate for many years before being released. In Tenerife there could be magma and that seismicity was related to the movement of gases at those depths or to the movement of material itself. Apart from the swarms, we always have a lot of seismicity in that area. The usual every week is to register between 10 and 20 earthquakes in the place and we believe that it is associated with that system.
-What do we know about this phenomenon?
-Tenerife is an island where we have not seen instrumented volcanic activity and we do not know how seismicity behaves before an eruption. But in principle they are very small earthquakes, which are very close together and of a similar magnitude. All this seems to indicate that it is not a moving magma, because if it were, it would have to generate a lot of seismicity and at different magnitudes. We have theories, although it is difficult to specify. What we do know is that if an eruption is going to happen, we should see different signals.
“The island of Tenerife is much more active than La Palma and El Hierro in inter-eruptive periods, producing about 1,000 earthquakes a year”
– Is it possible that there will be an eruption on Teide in the short term?
-There is nothing to say. This activity is small and we do not see other types of activities, such as a clear emission of gases or a deformation. And this is what we expect to find when a volcanic eruption occurs, as it happened in La Palma or El Hierro. However, it is impossible to know if an eruption will occur within a year. The odds are not that they are high, but they cannot be ruled out. There are no signs that indicate that it could be now, but it could be within a year or within 100, because that is how the eruptions in the Canary Islands are. In Tenerife, for example, we have had eruptions sometimes every 100 and sometimes every 200, and we don’t have very broad statistics. Determining when it will happen well in advance is impossible. Among other things, because we don’t know how much magma is down there. The techniques that have been applied to understand Tenerife’s subsoil are also unable to determine if it has the strength to come out. It is one of the great challenges of volcanology, both here and in the rest of the world. That said, we don’t see any forerunner signs in the short term, but we don’t have a crystal ball to know when that will happen.
-If an eruption occurs, would it be on Teide itself or could it occur elsewhere on the island?
-It is impossible to specify. As far as we know, the probability that the next eruption will occur on Teide is lower than that it will be basaltic or monogenetic, that is, in another place on the island. We know that Teide’s last eruption was relatively quiet about 1,000 years ago. 2,000 years ago there was a more explosive one. Between the two there have been some more explosive eruptions, but many others were basaltic, such as those of Chinyero, Fasnia, Arafo or Siete Fuentes. Therefore, knowing if it will be on Teide or another place is impossible. When the precursors begin to be given, it is possible that we will have information to say if it is in one place or another. There are geologists who say that there is a direct relationship between basaltic eruptions and the Teide magmatic chamber. With which, a phenomenon of recharge of the magmatic chamber can be confused with an eruption phenomenon in another place. The problem is that we have no information, because we have never recorded an eruption on Tenerife with instruments and because there are no good records of an eruption on Teide.
– How many years have there been eruptions in Tenerife?
-Historically, we have an eruption in the fifteenth century, probably that of Boca Cangrejo, which coincides with that time. Then we went 200 years without any eruption, until the period between 1704 and 1706, when four eruptions were described, although there are those who describe it as only one. Then one was produced in 1798 and the next one in 1909. On average, in the last 500 years there has been one every hundred years. That is why people might think that the next one is already here, but there have been periods of 200 years without an eruption. We would have to have more data and the dating of previous eruptions cannot be done with much precision.
“On average, in the last 500 years there has been an eruption every hundred years. That is why people might think that the next one is already here”
– What does volcanic surveillance on Teide consist of?
-It is based on three main legs. One is seismology, or what is the same, measuring earthquakes. When you have a magma that enters the crust, it is normal that seismicity is generated because that magma overpresses the crust and generates breaks in the rock. The other leg would be the deformation, because the magma deforms the terrain. Then there are gas measurement techniques. The magma that generates the eruptions is partly molten, partly crystallized, and partly gaseous. These gases are the engine of the eruptions because they give the magma excess pressure so that it comes to the surface. The diffuse gas of the soil and the Teide fumaroles are also measured.
– What values will let us know that the Teide-Pico Viejo system is awakening?
There is no specific number of anomalous values, it depends on each system. One would expect to find anomalous values of seismicity, deformation and gases. But there are not many systems in the world like the one we have here, in which two types of eruptions can occur. Therefore, it is difficult to buy it with other places.
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