Everything is measured on Etna: the tremor, the gases, the deformations of the ground, the ash that changes the color of the cars parked at the foot of the volcano. The initial question, the one regarding his birth, remained more slippery. Now a study signed by researchers from the University of Lausanne together with Anna Rosa Corsaro of the Ingv of Catania tries to bring order right there, at the point from which the story begins, and does so with a hypothesis that gives the origin of Etna a profile almost without twins in the world.
The strong idea lies entirely in this gap: the Sicilian volcano could have formed with a mechanism similar to that of the petit-spots, tiny underwater volcanoes observed and described for the first time in Japan in 2006. The leap, here, has something unsettling. Petit-spots usually give rise to small, low, almost marginal structures. Etna, on the other hand, erupts several times a year, exceeds 3,000 meters above sea level and has been carrying on its activity for approximately 500,000 years.
To understand the origin of Etna they went back half a million years
Up until now, geology has interpreted large volcanoes within three main frameworks: those that arise along the margins where the plates separate, those linked to subduction, i.e. the sinking of one plate under another, and those associated with hotspots, the deep rises of very hot mantle material, as happens in Hawaii. Etna runs away from all three with a certain obstinacy. It is close to a subduction zone, but its lavas show chemical affinities reminiscent of intraplate volcanism. Such a combination has always kept the question open.
To try to unravel this knot, the research group analyzed lava samples covering the entire history of the volcano, from the initial phase to the present. The trace that emerges has its own clarity: the composition of Etna’s magmas remained overall stable even while the tectonic framework around Sicily changed. In such a long history, such continuity weighs heavily, because it suggests a persistent deep source and a feeding mechanism that has remained consistent over time.
Here the most interesting part opens up, even for those who look at geology from afar. According to the authors, Etna would be fed by small quantities of magma already present in the upper mantle, in a band connected to the so-called Low Velocity Zone, the contact zone between the lithosphere, i.e. the rigid external part of the Earth, and the asthenosphere, more plastic and mobile. That magma is not formed at the last moment before the eruption: it remains there, accumulated in small fractions, and waits for the dynamics of the plates to open the way for it.
The study places this deep reserve about 80 kilometers below the surface. Pushing it upwards would be the tectonic movements linked to the collision between the African and Eurasian plates, with fractures and folds that function as escape routes. The researchers also use a very concrete image: a kind of squeezing, like when trapped liquid comes out of a sponge. Inside that mechanical gesture, much more than in a classic ascent from a hotspot, lies the key to understanding how this volcano was built over time.
This reading also allows us to keep together two pieces that until now were uncomfortable next to each other. On the one hand, Etna lives close to a subduction zone; on the other hand it erupts alkaline lava rich in volatiles which bear little resemblance to classical arc volcanoes and much more to other types of systems. The new model tries to give a single body to this anomaly and also broadens the discussion to the Hyblaean Plateau, i.e. to an older volcanism in eastern Sicily, which could have entered the same geodynamic story.
A fourth category of volcanoes remains a cautious trail
The authors themselves keep the conditional, as it should be when talking about Earth science and profound processes. But the change of perspective is all there. Etna could belong to a fourth family of volcanoes, still little known, linked precisely to the petit-spot mechanism. It would be a huge case, in every sense: a gigantic terrestrial volcanic system that was born with a logic observed until now mainly in small underwater buildings.
The scope of the discovery goes beyond the charm of the unique case. Better understanding where the magma comes from and on what conditions its transport to the surface depends also helps to refine the interpretation of Etna’s frequent eruptions and therefore the assessment of volcanic risk, a topic that concerns the daily life of hundreds of thousands of people in Sicily. The paper recalls that the volcano recorded more than 240 paroxysmal episodes between 1986 and 2021, with a direct impact on a heavily inhabited area of its natural periphery.
Etna remains there, as always, before everyone’s eyes. Only now the mountain appears a little less obvious. Under that dark mass of lava, snow and ash, the magma could have remained waiting for a very long time, already present in the right place, ready to rise as soon as the Earth granted it an opening. Under that mountain, apparently, the fire was already there. He was only waiting for one way.
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