Etna: portrait of a hyperactive volcanic cone

Etna is one of the most active volcanoes on the planet, with a large majority of eruptions at the level of the summit area which, consequently, is in perpetual evolution. The last born of the four summit craters, the Southeast crater, appeared in 1971 and for more than fifty years, it has not stopped growing. So much so that last year, its summit exceeded that of the northeast crater, thus becoming the summit of Mongibello. But, sometimes, it is also partially destroyed, like last February 10…

At the beginning of XX^and centurythe top of theEtna had only one crater: the central crater. In 1911, a new cone was built to the northeast of it and in 1945 and 1970, two distinct craters formed inside the central crater, Voragine and Bocca Nuova respectively. In 1971, a small vent opened on the lower southeast flank of the central crater, without obvious activity until April 1978, when a violent eruption marked the beginning of a long series still in progress which builds the crater South East. Since that date, and even if the other summit craters are still active and sometimes show eruptive activity, the Southeast crater almost completely monopolizes the activity.

By dint of paroxysms, brief and intense phases of activity, and periods with less intense but continuous explosive activity for sometimes several months, a first volcanic cone formed between 1978 and 2007, about 250 meters high. In the summer of 2007, just as in 1971, a vent opened on the eastern flank of this volcanic cone and concentrated the eruptive activity. A cone formed around this new mouth: the new southeast crater. In just a few years, it reached the same altitude as the cone against which it was formed, which had been built in more than thirty years! These two cones ended up completely merging, so that today the distinction between the two no longer has any reason to be.

A cone that builds quickly… and destroys even faster!

Last year, the Southeast Crater produced fifty-two paroxysms, with lava fountains from 500 to 1,000 meters high whose shreds of lava, each time, fell on the cone and allowed it to be built very quickly. In six months, it thus rose by 30 meters to peak at 3,357 meters at the beginning of August 2021, thus delighting the summit of Mongibello at the North-East crater that it was for forty years! But, for each meter of height gained, there are also hundreds of thousands of m³ projections that pile up and make this cone grow! With an area at the base of about 1,000 meters in diameter, it now reaches more than 350 meters in height: higher than the Eiffel Tower!

This immense cone is not comparable to the small eruptive cones formed during the eruptions of the Piton of the Fournaise which reach between 30 and 50 meters high. On the other hand, it is a little more so of the volcanic cone than theeruption on the island of La Palma, in the Canary Islands, built last year: about 800 meters in diameter and 200 meters high. But, unlike these volcanic cones which are monogenic, that is to say built in a single eruption and definitively extinguished afterwards, the Southeast crater is a polygenic edifice, formed by numerous eruptions. It is therefore a real eruptive center. Moreover, in fifty years of activity, it is essentially paroxysms of a few hours maximum that have built it: its growth is therefore truly impressive!

If the construction of such a cone there is no doubt in time, it should also be noted some episodes of destruction during fairly sudden events in general, which reminds us that these volcanic cones are not never very strong.

the February 10, 2022the overpressure generated by the paroxysm probably forced the magma to pierce the southern flank of the Southeast crater, which destabilized it and caused its collapse. It is the thermal camera and the analysis of the deposit which make it possible to understand what happened because, at that moment, the fountains of lava more than 1,000 meters high strafed the entire area: volcanic bombs fell on the Barbagallo mountains, monogenic volcanic cones located more than a kilometer from the eruptive vents!

At 10:26 p.m., a pyroclastic flow traveled 1,600 meters to the south, covering the upstream cone of the Barbagallo mountains and stopping at an altitude of 2,750 meters, a little lower than a small hut which it modestly burned. The deposit formed is made up of materials with variable grain size, from fine ash to decametric blocks. These are therefore both old pieces of the cone that have slipped and been carried away by the flow, but also ashes from the magma and pulverized pieces. The scar formed cuts the entire Southeast crater over about 500 meters long and 100 to 200 meters wide: a real scar! Will it be covered by future activity?