A team of researchers from INGV and the universities of Catania and Ferrara has revisited the data from the eruption of Etna on December 28, 2014, paving the way for new interpretative models of the eruptive activity of both the Sicilian volcano and basaltic volcanoes in general . The study was published in Scientific Reports of Nature
The eruptive activity on Etna can also occur without the arrival of magma from the depths, but only due to the effect of the continuous flow of gas which overheats the rocks of the apical part of the volcanic edifice. These conclusions were reached by a study conducted by a group of researchers from the Etna Observatory of the National Institute of Geophysics and Volcanology (INGV-OE), in collaboration with the Universities of Catania and Ferrara.
The results of the work, entitled Dome-like behavior at Mt. Etna: The case of the 28 December 2014 South East Crater paroxysm, have been posted on Scientific Reports di Nature (https://www.nature.com/articles/s41598-017-05318-9)
"In this work, the eruptive activity of Etna", highlights Mario Mattia, INGV-OE researcher, "is analyzed starting from the study of the eruption of December 28, 2014, which had caused a collapse of part of the South Crater -East and a later recall of magma due to the consequent decompression. Hence the analogy of the Sicilian volcano with explosive ones, characterized by domes semi-solid lava which, collapsing, causes violent explosions”.
To reach these conclusions, different from the previous interpretations put forward by the scientific community which assumed the intrusion of a lava body at surface levels (dike), the following were used: the ground deformation data obtained by means of the GPS receiver network (Global Positioning System) of the INGV-OE with very high precision which allow to detect even the smallest swellings of the volcanic edifice, linked to the arrival of fluids (inflation), and the deflations that follow the emission of magma and gas (deflation); the flow data of sulfur dioxide (SO2), detected thanks to the permanent network installed on Etna, called FLAME and made up of ten ultraviolet spectrometers which highlight the quantity of gas passing through the summit craters; and, finally, those relating to the chemical composition of the erupted lava and the volcanological observations made on the ground (top of the Southeast Crater), in the months preceding the eruptive event.
"The work revisits the data obtained from the monitoring of Etna and paves the way for a revision of the current interpretative models of the eruptive activity of the Sicilian volcano and of the basaltic ones in general, reducing the rigid boundary, drawn up to now, between volcanoes explosives (of the andesitic type) and volcanoes effusive (basaltic type). It is also important to re-evaluate the role of gases which, in addition to representing a primary factor in the eruptive dynamics, are proposed as real heat engine”, continues Matthias.
The gases are capable of altering the stability of the eruptive cones, independently of the ascent of magma, with all the possible effects for the analysis of volcanic hazard. In this sense, volcanic monitoring should reconsider the role of gases which, contrary to what has been accepted so far by the scientific community, are independent of the ascent of deep magma.
"In fact", concludes the researcher, it has been demonstrated that gases can, by releasing heat, trigger processes such as the eruption or landslides of gas-rich lava material and, therefore, burning avalanches, far more dangerous than common lava flows. This model, created to explain the eruption of December 28, 2014, proposes a possible revision and improvement of volcanic monitoring and surveillance activities.
Extended
On the 28 December 2014, a violent and short paroxysmal eruption occurred at the South East Crater (SEC) of Mount Etna that led to the formation of huge niches on the SW and NE flanks of the SEC edifice from which a volume of ~3 × 106 m3 of lava was erupted. Two basaltic lava flows discharged at a rate of ~370 m3/s, reaching a maximum distance of ~5 km. The seismicity during the event was scarce and the eruption was not preceded by any notable ground deformation, which instead was dramatic during and immediately after the event. The SO2 flux associated with the eruption was relatively low and even decreased a few days before. Observations suggest that the paroxysm was not related to the ascent of volatile-rich fresh magma from a deep reservoir (dyke intrusion), but instead to a collapse of a portion of SEC, similar to what happens on exogenous andesitic domes. The sudden and fast discharge eventually triggered a depressurization in the shallow volcano plumbing system that drew up fresh magma from depth. Integration of data and observations has allowed to formulate a novel interpretation of mechanism leading volcanic activity at Mt. Etna and on basaltic volcanoes worldwide.
Photo 1 - Incandescent fractures testifying that, before the eruptive activity of 28 December 2014, the cone of the southeast crater was in a state of instability due to very high (magmatic) temperatures
Photo 2 - South East crater of Etna