The Christmas 2018 Eruption at Mount Etna: Enlightening How the Volcano Factory Works Through a Multiparametric Inspection

The 24-27 December 2018 flank eruption at Mount Etna (Southern Italy) has been investigated through a multidisciplinary approach in which olivine chemical zoning and diffusion chronometry data were integrated with models inferred by GNSS (Global Navigation Satellite System) measurements. Inspection of the olivine chemical zoning from core to rim allowed the identification of some dominant ways of transfer and interaction between magmas pertaining to different magmatic environments. Most of crystal cores are representative of crystallization at pressure of 290-230 and 160-120 MPa. Olivine rims suggest re-equilibration at shallow pressure (<= 30 MPa). Geodetic-based models indicate pressurization of near-vertical prolate spheroidal sources centered at similar to 7.2 km below sea level (bsl) between 9 June 2017 and 28 June 2018 and later at similar to 5.1 km bsl between 28 June 2018 and the eruption onset. Geodetic data also highlight a change in the inflation rate since late June 2018 and later around November 2018, which has been here related to both replenishment phases and magma uprising across the plumbing system. Timescales of magma replenishment are in agreement with prolonged recharge from deep levels upward to shallow environments started about 6 months before the eruption, with further replenishment involving the upper magmatic environments just 3-16 days before the eruption. At present, the eruptive activity at the volcano is primarily controlled by pressure imbalances affecting extensive sections of the plumbing system, with possibility to develop persistent eruptive activity at the summit versus flank eruptions depending on fortuitous interruptions of the steady magma recharge/discharge rate at shallow levels.