The morphostructural setting of Mount Etna sedimentary basement (Italy): Implications for the geometry and volume of the volcano and its flank instability

The reinterpretation of more than 2500 subsurface data, consisting of geoelectric and borehole prospecting undertaken at Mount Etna, allows reconstructing the contour map of the sedimentary basement. This reconstruction highlights a complex asymmetric topography due to the inhomogeneous long-term updoming of the region and the interrelationship between the development of the drainage network and flank instability. These different processes have produced a major morphological difference between the eastern sector, characterised by a 17 km-wide horseshoe-shaped depression, and the other flanks formed by palaeovalleys. The origin of the wide horseshoe-shaped depression can be attributed to the large-scale flank instability processes involving the entire continental margin in the Etna offshore. This depression of the Etna basement was generated by a series of coalescent landslides before the beginning of the eruptive activity of the Timpe phase more than 220 ka ago. This wide depression is the main cause of the flank instability that produced the gravitational slope failures of the Valle del Bove about 10 ka ago. Regarding Mt Etna's geometry, we have estimated a total volume of about 532 km3 that was emplaced during the past 330 ka, resulting in an average rate of volcanic output of 0.0016 km3/a. The reconstruction of the temporal variation of the average eruptive rate highlights a drastic increase of volcanism during the last 100 ka in response to the gradual stabilization of the plumbing system in the Etna region that led to the build-up of the composite stratovolcano structure. The data presented in this paper represent the state of knowledge of the sedimentary basement of Etna, which can be used for future studies aimed at developing a detailed understanding of the deep structure of the volcano's unstable flanks