Analogue modeling of flank instability at Mount Etna: Understanding the driving factors

Mount Etna is characterized by significant flank instability, whose triggering factors are still a matter of debate. We use analog models to investigate the role of different factors. In the models, a cone and base of granular material simulate the volcanic edifice and its basement. The asymmetric geometry of the basement simulates the topographic gradient around the volcano. Injections of silicone (sets A and B) and low-viscosity vegetable oil (set C) simulate the pressurization of plutonic complex, deep reservoirs, and the emplacement of dikes, respectively. Other experiments (set D) reproduce regional extensional tectonics in the last 10(5) years, within layers with different cohesion simulating strength differences in the basement. Laser scanner and control points allow the tracking of surface deformation with submillimeter precision. The asymmetric topography enhances flank instability on the side with the weakest confinement (i.e., seaside), providing the preparing factor for instability. In sets A and B, any type of pressurized reservoir enhances, up to 10 times, the amount of flank instability toward the seaside with respect to the other flanks of the volcano. In set C, dike emplacement enhances seaside flank instability up to 8 times. Regional tectonics and crustal layering in set D enhance flank instability up to 2 and 1.3 times, respectively. Considering the duration and frequency of the simulated processes in nature, we propose a semiquantitative evaluation and hierarchy of the factors controlling flank instability at Etna. Magmatic activity (point-like source inflation and dike emplacement) provides the most important triggering factor. Extensional tectonics, in the last 10(5) years, and crustal layering are more than 10 times less effective. This study shows the importance of differential buttressing at the volcano base for flank instability. This condition is an important indication to expect asymmetric activity in any volcano (flank eruptions and deformation).