January 21, 2022 5:34 pm

Live on a volcano

When the volcanologists guarding the dangerous volcano Colima FireIn Mexico, they asked the peasants in the area what they most feared about the volcano, they found an unexpected answer: “They are the scientists, the greatest danger …”. It was the result of several evacuations that had resulted in false alarms.

The price to pay is high: to always live exposed to a precipitous flight from the fire of the interior of the Earth, and this if the volcano is kind enough to warn politely

And it is that living on a volcano is not easy. The soil is fertile because volcanic rocks are rich in football, iron and magnesium, and release these nutrients as they break down. But the price to pay is high: living always exposed to a headlong flight of the fire from the interior of the Earth, and that if the volcano is kind enough to warn politely.

In many cases (the island of The Palm is one of them) eruptions have relatively short eruptive intervals, so that memory of previous crises serves as a behavioral guide. Many palm trees experienced the short and harmless eruption of the Teneguía in 1971; the very old may have memory of the San Juan in 1949. Historical records point to others in 1712, 1677, 1646, 1585 and, perhaps, 1492. A calm rhythm, an eruption every 70 years.

All of them have occurred in the south of the island, the area called Old Summit, which is, however, its most recent part. Cumbre Vieja is what volcanologists call a volcanic building, a large rocky construction formed by successive eruptions related to each other, each of which left a trace of a volcanic cone. The Cumbre Vieja building has taken advantage of a large north-south fracture that runs through the southern part of the island.

Volcanic map

La Palma volcanic map

Why do volcanoes love fractures?

They have two good reasons for this. The first is very evident: the same one by which the fire of a hearth requires a fireplace. It must be taken into account that a rock, when melting to become magma, increases its volume and decreases its density, which tends to rise. The fractures (faults, in geological slang) facilitate that climb.

Both El Hierro and Tenerife and Lanzarote have also suffered historical eruptions. So why on La Palma and not on another island?

The second is that the faults reduce the pressure in the deep areas (as happens when puncturing a balloon), and this decompression facilitates the increase of volume, and with it the production of magma. In volcanology they are called fissure buildings which, like Cumbre Vieja, take advantage of fractures. The most famous fissure building in the world is the crochet, in Iceland, which shares its enlarged plant and its profile in a gabled roof.

All that said, let’s face a more general question: Why has this eruption occurred in the here and now? Can it be considered a surprise? Both El Hierro and Tenerife and Lanzarote have also suffered historical eruptions. So why on La Palma and not on another island?

Canary Islands map

How the Canary archipelago was formed

The answer to these questions is not simple, because it affects ideas about the origin of the Canary archipelago, an unfinished debate. For some scientists, the Canaries are the tip of the iceberg of a great plume of hot rock that rises from the depths of the planet, and that at this moment reaches the surface in the western part of the archipelago, under El Hierro and La Palma.

But that idea leaves unexplained the historical volcanism of the central (Tenerife) and eastern (Lanzarote) Canary Islands. Another school proposes, on the contrary, that the Canaries are located on fractures (as if together they were a huge fissure building) and that the magma arises in the areas where the fractures distend, lowering the pressure in depth. This theory links the islands with the faults and volcanoes of North Africa, but it is not a perfect theory either: it does not explain, for example, why there are islands, like La Gomera, inactive for millions of years.

Whatever the origin of the archipelago, what is indisputable is that under the Cumbre Vieja building there is installed a magmatic chamber nurtured from a deep magmatic deposit. We must imagine this chamber as a turbulent mixture of magma and partially molten rock, agitated by a movement similar to that which animates the lava lamps.

What is indisputable is that under the Cumbre Vieja building there is installed a magma chamber fed from a deep magmatic deposit

Its highest parts contain many gases, and therefore are the least dense and with a greater tendency to rise. A few weeks ago, these gases they found a good fracture and forced their way through it, breaking the rock and dragging the rest of the chamber’s materials behind them. There the swelling of the land and seismic movements began that put the population and scientists on alert.

One last question the layman might ask. All that lava that comes out, does it leave a deep vacuum? Or is this one filled in some way? It’s a smart question, one that Earth Sciences have only been able to answer in the last half century. In many regions of the globe, the bottom of the oceans sinks to the very core of the planet (almost 3,000 km!).

This entry into depth is compensated by the rise of hot material (the core is about 5,000 ºC) that feeds the terrestrial volcanoes. So when we see lava rising from those beautiful jets, we have to remember that in other parts of the planet this rise is offset by a slow but steady plunge of rocks towards the mountains. depths.

Like in a lava lamp.

Lava lamp

Francisco Anguita He is a geologist and retired professor at the Faculty of Geology at the Complutense University of Madrid.

Source: SINC

Rights: Creative Commons.


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