Integration of geophysical images and thermo-fluid dynamic modelling to understand the current dynamics of the Pisciarelli Fumarole Field (Campi Flegrei Caldera, Italy)

The Pisciarelli fumarolic-hydrothermal area, in the Campi Flegrei caldera (southern Italy), along with the adjacent Solfatara maar-diatreme, is currently considered the most concerning site due to the recent increase in volcanic activity. This ongoing activity includes very high CO2 fluxes (over 600 tons/day), continuous evolution of its morphological elements, and a large portion of the seismic events recorded in the entire caldera. Here, we present the first comprehensive interdisciplinary study aimed at reconstructing the architecture and the fluid dynamics of the Pisciarelli Fumarole Field area. Our study integrates geophysical imaging and thermo-fluid dynamic numerical modelling to understand the hydrothermal processes occurring in the shallow feeding system of Pisciarelli. The main pathways (i.e. faults and/or fracture networks) for fluid and gas migration from deep sources to the Earth’s surface have been identified by utilizing 3D electrical resistivity and time-domain induced polarization tomographies of the very shallow hydrothermal system of Pisciarelli. Also, the mapping of the spontaneous potential has been realized in the area. Based on these data, numerical modelling has been developed to understand the current system dynamics (i.e. temperature, gas pressure, gas saturation and fluid flow distributions) and the physical processes likely occurring within the system. For this purpose, the numerical simulator TOUGH2 was employed to solve the thermodynamic equation for an H2O+CO2 mixture flowing in the system of interest, considered a porous and fractured medium. An accurate 3D petrophysical model of the explored hydrothermal system was built using the geophysical tomographies. Subsequently, by imposing constraints derived from different data (i.e. volcanological and geochemical analyses available in the literature), the natural state of the system in its current conditions has been estimated. This includes reconstructing the water and CO2 pressure distribution, as well as the temperature, the CO2 flow, the gas saturation degree, and other relevant variables. The thermo-dynamical modelling provided valuable insights into the role played by the main fault system and the highly permeable channel identified by the geophysical survey in the dynamics of the hot fluid mixture rising to the surface. Furthermore, a simulated map of the CO2 flux was produced, clarifying the mechanisms at the base of the intense degassing activity of Pisciarelli. These results contribute significantly to a better understanding of the current dynamics of the Pisciarelli Fumarole Field. This knowledge provides a basis for improved hazard assessment and risk mitigation strategies in this highly active volcano-hydrothermal system.