The Most Intense Deflation of the Last Two Decades at Mt. Etna: The 2019–2021 Evolution of Ground Deformation and Modeled Pressure Sources

We analyze Global Navigation Satellite System (GNSS) and tilt data from the permanent monitoring networks of Etna volcano starting just after the 24 December 2018 eruption to an unusual two-month period of deflation in February–March, 2021, which coincided with the occurrence of 17 lava fountain episodes. Based on changes in slope in the GNSS displacement time series, we divide the period starting 7 months after the eruption into five phases, spanning the continued inflation of the edifice punctuated by short periods of effusive and strombolian activity (four phases) and a 2-month phase of intensive deflation. Our model indicates a progressive deepening of the internal pressure sources followed by a fast ascending source starting two-months before the first 2021 paroxysms. We explain these results in light of a recent volcanological model on the nature and behavior of magma ascending through the Etnean feeding system.