To determine the volcanic danger of a territory it is necessary to take into account several factors. The first of these is the probability of an eruption occurring in a certain time. On the other hand, the type of eruption is important, that is, if it is explosive, Vulcan or otherwise. The possibility of derivative effects, such as landslides, tsunamis or lahars, is also considered. Finally, the topography of the terrain where the lava flows will slide is evaluated.
Once the dangerousness of a specific area has been assessed, it can be determined whether it is convenient for there to be a population living where the danger is highest. Let us remember that the danger cannot be reduced, as it is inherent to the phenomenon. But risk can be mitigated by reducing vulnerability and exposure.
To reduce the risk, for example, in the case of earthquakes, an earthquake-resistant design must be made according to the level of danger in the area in question, which means reducing vulnerability. In other words, buildings must be designed to withstand the expected movements during their useful life.
As risk is the product of danger from exposure and from vulnerability, by reducing vulnerability, we are mitigating risk. On the other hand, you can also reduce exposure in high-danger areas, avoiding building or locating a population in those areas.
In the case of volcanoes, something similar happens: in areas of high volcanic danger we must reduce exposure. The problem is that there are many populations settled on the slopes of volcanoes around the world, among other things, because volcanic lands are very fertile.
The volcano always warns before erupting
The positive part of a volcanic eruption is that it almost always gives a warning. In other words, on La Palma, for example, it had been planned a few days in advance. This has made it possible to evacuate the population and avoid loss of human life. However, it has not been possible to prevent the lava that has emanated from destroying everything it has found in its path.
To reduce the impact of eruptions, simulation models can be made to find out where the lava flows will flow. This requires recognizing the type of volcano, the composition of the magma that will emanate in the form of lava, the topography of the area where the lava flows and other climatic factors. However, in areas of greatest danger it would be desirable to reduce exposure.
In the case of the La Palma volcano, given that there was already a population installed in the area, continuous monitoring of the volcano has been carried out, monitoring various indicators, essentially seismic activity, crust deformation and gas emanation. , such as helium-3 and CO₂. When these emissions are triggered, you must begin to evacuate.
When all these factors come together, the imminent danger of an eruption is perceived. This is what happened to the La Palma volcano. There they have acted appropriately because there was a well-coordinated scientific committee with specialists in the different subjects related to indicators.
The risk of living near a volcano
Taking the above into account, it is worth wondering if it would not be convenient to avoid settlements in areas such as those now exposed on the island of La Palma. To answer this question, several factors should be taken into account.
The first is that the volcanoes of the Canary Islands are fundamentally fissile, so there is uncertainty about the exact place where the lava can emanate. The volcanic chimney is not vertical, associated with a defined volcanic cone, but is linear and the lava runs horizontally. This causes it to escape to the outside, breaking anywhere.
When the volcano has a defined crater, we know where the lava is going to emanate from, which allows us to better understand the danger and reduce exposure in the areas where it is greatest. But on the island of La Palma, given that volcanism is fissure, it is not easy to determine which are the areas where it would be advisable to avoid population settlements.
The rash is a rare event
Despite the damage that the volcano is causing in the Canary archipelago, it must be taken into account that eruptions are not frequent events. Since the 15th century, 18 eruptions have occurred throughout the archipelago, 8 of them on the island of La Palma, which is the one with the highest activity.
In this context, moving people from one place to another does not make much sense. The only alternative is to continuously monitor the activity, as has been done so far, in order to make a short-term prediction and issue an evacuation order at the right time.
Thus, the fundamental objective has been achieved: the safeguarding of human lives. It is true that houses have been lost, but they can be rebuilt again. However, the human losses would not have been repairable.
Finally, let us remember that once the eruption has occurred, the probability of another in the short term decreases considerably. Surely, another similar event will not happen again on La Palma for dozens of years.
María Belén Benito Oterino, Professor in the area of Mechanics of Continuous Media and Theory of Structures at the ETSI Topography, Geodesy and Cartography, Polytechnic University of Madrid (UPM)
This article is republished from The Conversation under a Creative Commons license. Read the original article.
