Fluid migration in volcanic environment: thermo-poroelastic modelling of Solfatara crater.

In volcanic environment, the fluids migration in the crust can affect the evolution of magmatic processes. Meteoric water can for instance infiltrate volcanic rocks developing shallow hydrothermal systems and descending meteoric water may encounter fluids rising up from deep magma feeding system. The accurate tracking of fluid storages and movements turn out to be crucial for the evaluation of the seismic and volcanic activity. Specifically, Campi Flegrei caldera is an example of fluids interaction of different nature, especially at Solfatara crater, where the complexity of this volcanic system is highlighted by diffuse degassing, high temperatures and bradyseism phenomenon.

The Solfatara crater was formed at about 4.2 ka and it consists of a sub-rectangular depression, whose geometry is controlled by N40-50W and N50E trending fault systems. Nowadays, degassing and fumarolic emissions occur at the Solfatara crater, together with a series of small uplift episodes and seismic swarms, particularly from 1984 to 2006 when the whole caldera subsided. Specifically, these earthquakes are likely to be associated with a buried cavity filled with a water-vapour mixture at poor gas-volume fractions.

In this scenario, we propose a 2D multi-physics study of Solfatara volcanic system via the integration of thermodynamic and poroelastic model results.

We start with the first model, for which we collect the available geological and geophysical information, such as the main faults, crustal parameters and the temperature distribution in the conductive regime. This information is merged into a multiphysics Finite Element Model by using COMSOL Multiphysics software: we simulate the crustal thermal regime beneath the Solfatara crater by performing a time-dependent convective thermal model in porous media. We also simulate the fluids circulation in accordance with the Darcy’s Law by considering the bi-phasic water properties (i.e., liquid and vapor states) as approximation to characterize the modelled fluid. Furthermore, the seepage of meteoric water through the high permeable volcanic rocks is also considered. At the end of the simulation, we observe the activation of a convective cell below the Solfatara crater, where the 250°C isotherm reaches ~500 m b.s.l.. The retrieved results is compared with the available data, as the resistivity model proposed by Siniscalchi et al. (2019) and the measured temperature at the CF23 well.

Within the same discretized numerical domain, we perform the second model by considering the previous fluid pore pressure modelled field; we detect the pressure source parameters better explaining the observed ground deformations of Campi Flegrei caldera. The analysed dataset consists of processed SAR images acquired by Sentinel-1A/B satellites constellation during the 2020 – 2022 time interval. We here compare the retrieved stress field within the caldera with the hypocenters distribution.

In conclusion, this study contributes to improve the knowledge about the role of fluids migration in the framework of the magmatic processes.