Influence of permeability on the hydrothermal system at Vulcano Island (Italy): inferences from numerical simulations

Abstract

Volcano-hydrothermal systems are governed by complex interactions between fluid transport, and geochemical and mechanical processes. Evidence of this close interplay has been testified by distinct spatial and temporal correlations in geochemical and geophysical observations at Vulcano Island (Italy). To understand the interaction between fluid circulation and the geochemical and geophysical manifestations, we perform a parametric study to explore different scenarios by implementing a hydro-geophysical model based on the equations for heat and mass transfer in a porous medium and thermo-poroelastic theory. Numerical simulations allow us to define the controlling role of permeability distribution on the different modeled parameters as well as on the geophysical observables. Changes in the permeability within the highly fractured crater area could be responsible for the fluctuations in gas emission and temperature recorded during the crisis periods, which are accompanied by shallow volcano-seismicity in the absence of significant deformation and gravity variations. Despite the general medium permeability of the volcanic edifice, the presence of more highly permeable pathways, which allow the gas to rapidly escape, as testified by the presence of a well-developed fumarolic field, prevents the pressure buildup at shallow depths. Graphic abstract

Multiphysics Modeling of Volcanic Unrest at Mt. Ruapehu (New Zealand)

“…We find similarities in the spatial displacement patterns from HTU simulations to findings reported in Stissi et al. (2021) and Currenti et al. (2017).…”

“…We find similarities in the spatial displacement patterns from HTU simulations to findings reported in Stissi et al (2021) and . Here, highest vertical displacements correlate with largest pore pressure and temperature variations (Figure 5).…”

“…This might result from a wider injection area and a longer-lasting injection period compared to the study of Christenson et al (2010). Unlike the linear pore pressure evolution in other studies (e.g., Christenson et al, 2010;Stissi et al, 2021), we simulate elevated initial pore pressures around the HTS and its proximity after protracted background injection. As a result pore pressures reach ∼10 MPa around the injection area and are similar to the pore pressure parameterization in Coco, Gottsmann, et al (2016).…”

Evidence of poro-elastic inflation at the onset of the 2021 Vulcano Island (Italy) unrest

“…The crude simplification of the investigated models (i.e., simple geometries, constant strain changes within the source, and homogeneous medium parameters) is challenging in thermo-poro-elastic processes where the spatial distributions of pore-pressure and temperature changes are generally more complex than those described by simple spherical or cylindrical homogeneous distributions. Usually, pore-pressure and temperature changes are very sensitive to rock permeability, which strongly governs the fluid circulation in hydrothermal systems (Stissi et al, 2021). The presence of narrow permeable pathways (e.g., fractures and weak zones) may locally perturb the fluid circulation and, hence, may induce local pore-pressure or temperature changes.…”

“…In order to verify the results and check the accuracy of the numerical integration, solutions from Formulas 16, 17 were compared with the numerical thermo-poro-elastic results (Supplementary Material) calculated using COMSOL Multiphysics software (COMSOL, 2012), which solves Eqs 1-3 with a finite-element (FE) discretization Stissi et al, 2021).…”