Etna's paroxysmal activity in 2021: A deflation episode revealed by joint DInSAR and GNSS ground deformation analysis

In the final months of 2020, the summit craters of Mount Etna displayed intense Strombolian-type activity as well as an increase in seismicity. In December 2020, a period of paroxysms with powerful, brief bursts of lava fountaining began, which intensified in February 2021 and lasted until April. We used both ascending and descending Sentinel-1 SAR images along with daily GNSS solutions at 21 stations to evaluate the surface deformation at Mount Etna in order to understand the dynamics of the shallow plumbing system, which is probably related with the feeding of the observed paroxysmal activity. According to the InSAR and GNSS time series, the volcano edifice entered a period of intense and continuous deflation for almost three months, matching the prolonged paroxysmal activity characterized by the occurrence of 17 lava fountain episodes. To integrate the two data sets, we have applied the 3D SISTEM algorithm, which allows to estimate 3D ground displacements by combining GNSS measurements of deformation and differential Interferometric Synthetic Aperture Radar (DInSAR) maps of surface displacement. We have used analytical models to constrain the sources of the paroxysmal activity and to evaluate the deflating source parameters by inverting the displacement obtained with the 3D SISTEM algorithm. Preliminary results reveal a centripetal deformation pattern that might be linked to a shallow source below the summit craters area. However, a detailed analysis of the deformation pattern indicates the presence of contributions that are not related to the magmatic source, but are probably attributable to tectonic or geomorphologic processes. The aim of this work is therefore twofold. First, to infer the shape and dynamics of the magmatic feeding system of Mount Etna and its magma discharging regime. Second, given the complexity of the deformation signals at Mount Etna, to analyze how to deal with their different contributions including volcanic‐, tectonic-, geomorphological processes, and atmospheric noise.