Long-term thermo-fluid dynamic modeling of Solfatara hydrothermal system, Campi Flegrei caldera

Abstract

Solfatara hydrothermal system lies within the active and densely populated volcanic area of the Campi Flegrei caldera; during bradyseismic crises, the Solfatara crater behaves as a deforming region with intense seismicity and gas emissions. Advancements on multiphysics modeling of this area can therefore provide insights into the relationship between the magmatic and hydrothermal systems of this high-risk caldera. In this work, we performed a 2D numerical modeling describing the long-term thermo-fluid dynamic processes arising beneath the Solfatara crater. This model is innovative since it simulates the evolution of thermal and fluid flow regimes from the system formation, i.e., 4500 yrs. ago, without a priori assumptions about the amount of deep hot CO₂-rich fluid injections. We first collect geological information to define a more refined heterogeneous model integrating well data, rocks density, porosity, permeability, heat capacity, thermal conductivity, surface emissivity parameters and structural elements. We set a steady-state conductive temperature model and use the result as the initial condition for the transient analysis. Then, we performed time-dependent studies by coupling the heat transfer with the fluid flow laws, retrieving an imaging of the hydrothermal system in terms of temperature, density and fluids migration velocity distributions. Our results highlighted the generation of a buoyancy-driven convective cell beneath the Solfatara crater, with a gas zone extending between 1000 and 500 m b.s.l. We conclude by reiterating the importance of this model, which has to be used as a starting scenario for new studies on the evolution of geochemical and geophysical indicators of the Solfatara system.