Linking surface Observables to sub-Volcanic plumbing-system:a multidisciplinary approach for Eruption forecasting at Campi Flegrei caldera (Italy).

The Campi Flegrei caldera (Italy) is one of the most dangerous volcanoes in Europe and is in a new phase of an unrest that has persisted intermittently for several decades. The geophysical and geochemical changes accompanying the unrest stimulated a number of scientific investigations that resulted in a remarkable production of articles over the last decade. However, large uncertainties still persist on the architecture of the caldera plumbing system and on the nature of the subsurface processes driving the current (and previous) unrest. LOVE-CF is a 4-years project started in October 2020 and funded by INGV, with the aim of improving our ability to forecast the behaviour of the restless Campi Flegrei caldera, through a multi-disciplinary approach based on a combination of volcanological, petrological, geochemical, seismological and geodetic observations, as well as experiments and numerical models. We aim at reconstructing a comprehensive view of the architecture and the dynamics of the plumbing system, through the investigation of representative past events, as a framework to interpret geochemical and geophysical changes observed during past and current unrests. This will allow us to better evaluate the source of the current volcanic unrest (magmatic or not magmatic) and to forecast its possible evolution towards an eruption. Merged petrological and geochemical results show the existence of a multi-depth magmatic system constituted by a shallow (150–200 MPa, corresponding to 6–8 km) felsic (trachyte-phonolite) storage area, recharged by a mafic (trachybasalt-shoshonite) deeper (>200 MPa, > 8 km) source. Model simulations of magma degassing show that the measured (N₂-He-CO₂) geochemical changes at the fumaroles of Solfatara hydrothermal site in the last decades are the result of massive (about 3 km³) magma degassing in the deep portion (≥200 MPa, >8 km of depth) of the plumbing system. This degassing mechanism would be able to flood the overlying hydrothermal system with hot magmatic fluids, thus heating and fracturing the upper crust inducing the shallow seismicity and deformation measured at the caldera.  Moreover, numerical simulations have been applied to model the actual deformation time series as well as those obtained by archeological data regarding quote variation since 35 BC until the last 1538 AD Monte Nuovo eruption. Results show that the combined activity of the magmatic fluids sources recognized at different depths can justify the ground deformation observed during the whole caldera history.