From micro-scale pore networks to macro-scale volcanic hazard: characterizing the hydrothermal reservoir system via non-destructive 3D imaging

Periods of volcanic unrest, such as the 2021-2023 episode at La Fossa crater (Vulcano Island, Italy), present significant challenges for emergency management due to the inherent uncertainties of hydrothermal systems. This recent escalation, characterized by increased fumarole temperatures, ground uplift, and high gas fluxes highlighted the urgent need for physically based frameworks to interpret non-eruptive unrest. To address this, we present an integrated methodological workflow that bridges the gap between micro-scale rock properties and macro-scale volcanic behaviour. Our approach begins with a comprehensive stratigraphic reconstruction down to 1000 metres, achieved by correlating surface outcrop samples with deep "horizons" from historical geothermal well cores.

The core of our research leverages cutting-edge imaging technologies to quantify the reservoir-caprock system's internal architecture. We employ high-resolution X-ray microtomography (X-CT) to generate non-destructive 3D reconstructions with a 1µm voxel resolution, allowing for the precise mapping of pore-network connectivity and the distinction between effective and isolated porosity. This static characterization is further enhanced by dynamic 4D time-resolved imaging, where in-situ mechanical experiments—including uniaxial compression and tensile tests—are performed during CT scanning. This allows for the real-time visualization of fracture initiation and propagation within the volcanic matrix under simulated hydrothermal pressure.

By integrating these advanced imaging data with laboratory measurements of hydraulic and elastic properties, we define the geomechanical thresholds that govern fluid-driven failures. This multi-analytical methodology not only provides new insights into the tectonic and stratigraphic controls of Vulcano’s hydrothermal system but also establishes a robust, technology-driven protocol for assessing volcanic hazards in complex systems where subsurface data are sparse.