Non-isothermal momentum transfer and ground displacements rate at Campi Flegrei caldera (Southern Italy)

We propose a thermo-fluid-dynamics model to study some recent uplift episodes occurred in the period 2008–2013 at Campi Flegrei caldera (Italy). Accounting for eight overpressure sources (from 5 to 40 MPa) in the hydrothermal system, our model solves for heat and momentum balances to obtain fluid velocities responsible for the observed ground displacement. For a validation of the model we use a dataset from seven continuous GNSS stations of the Neapolitan Volcanoes Continuous GPS network (NeVoCGPS), belonging to a geodetic monitoring system covering the Neapolitan volcanic area, and operated by the Istituto Nazionale di Geofisica e Vulcanologia. We compare the observed and modelled vertical displacements to assess “threshold” values for the vertical ground accelerations below which ground displacements could be described with the classic fluid-dynamics equations applied to the hydrothermal system without invoking a direct magmatic contribution. We find out that below 280 mm/yr2 the observed ground acceleration can be explained as just due to the interaction between the deep magmatic and hydrothermal systems. On the contrary, for values exceeding the modelled “threshold”, the direct magmatic contribution can be likely invoked as source of the ground deformations. Through this study, we target to contribute to the debate on the origin of the observed ground deformation, mainly to separate the effects of hydrothermal perturbations, caused by the injection of deep magmatic fluids into the aquifer, from the direct magma intrusion.