Since Sunday, September 19, a volcanic eruption on La Palma has kept us in suspense. From a few days before, on September 11, hundreds of earthquakes were telling us that there was magma rising. This ascension could be fast or slow, and it could either stay inside or surface, as it has happened. In the case of the last underwater volcanic eruption of El Hierro in 2011, it took a long time from earthquakes to eruption. Therefore, there were calmer voices thinking that it could take weeks or months, or even not occur.
In 2017, 2018, 2019 and 2020 there had already been similar earthquakes, but deeper. There have been seismic crises in the same area of La Palma, El Hierro or Tenerife that came to nothing and did not even make the news.
What has changed this time?
These last days the earthquakes were increasingly superficial, the magma was rising and it seemed that it could end in eruption. Magma in the Canary Islands frequently moves and causes earthquakes. It depends on how much magma there is and if that magma finds a way to the surface because if it doesn’t, it ends up cooling inside.
What materials does the volcano expel?
Although it is still early days and there are no samples collected, due to the temperature at which the lava comes out (1,075 degrees), the type of eruption and the historical eruptions that have occurred in the Canary Islands, the magma appears to be a basaltic composition. A basaltic magma can come out in two ways: with and without explosions. In the first case, it is fragmented into pyroclasts, pieces of all sizes: ash if it is less than 2 mm, lapilli between 2 and 64 mm and a volcanic bomb greater than 64 mm . The magma that rises to the surface in a calmer form generates the lava flows. But in all of them the material is the same, and in this case it seems to be basalt.
How long will this rash last?
You have no idea. There is speculation according to the cubic meters of magma that is rising. As they seem to be less than those of the Teneguía in its day, it seems that it will last less than this (25 days). It is possible, but even if we know the volume of magma, we cannot control the speed at which it comes out well. The average duration of the historical eruptions of La Palma is 53 days. The shortest was 1971, 25 days; that of 1949 was 38 days, that of 1585 of 84 days and those of 1646 and 1677, 80 and 66 days respectively. Probably a few weeks.
The effects on the fauna and vegetation of the area
Animals are capable of escaping by themselves and, as for plants, the advantage of the native Canarian flora is that over millions of years they have adapted to volcanic eruptions. For example, the Canary Island pine supports them and sprouts again. Plants that cannot withstand eruptions are now extinct. At the level of forest destruction, a fire is much worse than this eruption. In addition, there is luck because there is no wind.
What has changed in volcanology in the last 50 years
Everything has changed. In 1971 there was no technical means to foresee it. Now it has been possible with seismograms or satellites, among others, which did not exist then. The way to approach it was for the island’s countrymen to notice the earthquakes.
At that time, part of the Geological Sciences faculty at the UCM monitored the Teneguía eruption in 1971, but in a traditional way and based on observation. Something could be foreseen because there was a North American station to check if Soviet submarines were passing by and they gave warnings a few days before the earthquakes.
Another difference is that there were no technical means of monitoring or emergency plans, there was no General Directorate of Civil Protection and Emergencies. From an artisanal medium it has gone to the latest cry of science at this time. It will also be noted in the damage, in 1971 some people died asphyxiated by the gases when approaching, now access is more restricted.
Eumenio Ancochea, Professor of Petrology and Geochemistry and director of the Department of Mineralogy and Petrology, Complutense University of Madrid and María Milan García, Researcher of the project “Scientific Communication and Disclosure in the Transfer of Knowledge at the University”, Complutense University of Madrid
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