Defining a 3D physical model for the hydrothermal circulation at Campi Flegrei caldera (Italy)

• Published in: Journal of volcanology and geothermal research Vol. 264; pp. 172 - 182
• Main Authors: Petrillo, Z., Chiodini, G., Mangiacapra, A., Caliro, S., Capuano, P., Russo, G., Cardellini, C., Avino, R.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier B.V 15-08-2013; Elsevier
• Subjects: 3D model; Calderas; Campi Flegrei; Crystalline rocks; Density; Dynamical systems; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geothermal; Geothermal system; Igneous and metamorphic rocks petrology, volcanic processes, magmas; Physical properties; Rock physical properties; Rocks; Topography; Volcanic risk; Water table topography; Water tables; Southern Europe; Italy; Phlegraean Fields; Campania Italy; Europe; Italy, Campi Flegrei; MED, Italy, Campi Flegrei; Water table topography; 3D model; Volcanic risk; Geothermal system; Campi Flegrei; Rock physical properties; physical properties; extension; plumes; simulation; permeability; surveys; physical models; solfataras; temperature; geothermal systems; craters; onshore; inverse problem; hydrothermal circulation; outcrops; density; porosity; topography; water table; offshore; depth; bathymetry; calderas; injection
• ISSN: 0377-0273; 1872-6097
• DOI: 10.1016/j.jvolgeores.2013.08.008

Our study is aimed to develop a 3D physical model of the Campi Flegrei geothermal system, in order to achieve a more accurate and comprehensive representation of the hydrothermal processes occurring in the caldera. The new model, developed by using the TOUGH2 code simulator, accounts for the caldera rocks' physical properties, bathymetry and water table topography. In particular, the computational domain is constrained by density values obtained by tomographic inversion of gravity data collected during several surveys at CF both onshore and offshore the caldera. Empirical relations between density and porosity and between porosity and permeability, derived by published data on samples cored in deep wells or collected in outcrops, allowed us to characterize the main rocks physical parameters controlling the dynamic of the CF geothermal system. We have performed and compared several simulations investigating the effects of the injection at depth, underneath Solfatara crater, of a hot gaseous mixture rich in CO2. We show that, with respect to the available literature on 2D axisymmetric models, the effects of the water table topography together with the bathymetry and the heterogeneous distribution of the rocks' physical properties, lead to important differences in the hydrothermal circulation of fluids at CF. These constraints allow the activation of convective cells with different behaviors, which produce variable patterns of temperature inside the hydrothermal system. As a consequence, the predominant effect is again represented by a central plume below the Solfatara crater, but with a non-axisymmetric structure and a wider extension. Additionally, high temperature zones are present near the coastline and in the middle part of the submerged area of the caldera with a SE–NW alignment.
Moreover, our results indicate that, the submerged part of the CF caldera would deserve a more accurate study and survey, being affected by phenomenon of heating and degassing. This information could be very useful in terms of hazard assessment and volcanic risk mitigation in such an active and densely inhabited volcanic and geothermal area.
•We develop the first 3D physical model of the Campi Flegrei geothermal system.•We include rocks' physical properties, bathymetry and water table topography in the domain.•We use cored samples and gravity tomography to extrapolate density values at the simulation domain.•Empirical relations between density, porosity and permeability are estimated.•The simulated geothermal field agrees with measured CO2 flux and temperature in wells.