Morelli, Rebecca Sveva (2025) Investigating Hydrothermal Dynamics in active calderas: onshore and offshore multidisciplinary approaches at Campi Flegrei caldera (Italy) and Fogo volcano (Azores, Portugal). [Tesi di dottorato]

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Abstract

Hydrothermal systems are fundamental components of active calderas, controlling the circulation of heat and fluids between magmatic reservoirs and the surface. By mediating the transfer of thermal and volatile energy, they generate a wide spectrum of geophysical and geochemical signals, seismicity, acoustic, deformation and degassing, that may precede, accompany, or mimic magmatic unrest. These processes operate on various temporal and spatial scales, from transient pore-pressure fluctuations to long-term alteration of the volcanic edifice. Over repeated cycles, hydrothermal pressurization and mineral deposition can progressively weaken host rocks, creating conditions favourable to renewed eruptive activity. Yet, interpreting unrest remains complex because the same signals may originate from magmatic inputs, hydrothermal dynamics, or external factors such as rainfall, sea-level variations, or tectonic stress. This study explores the interactions between magmatic and hydrothermal systems in two calderas characterized by both onshore and offshore activity: Campi Flegrei caldera (Italy) and Fogo volcano (Azores). A multidisciplinary approach was adopted, integrating seafloor geodesy, seismo-acoustics, and geochemical analyses. Bottom Pressure Recorders deployed offshore in the Gulf of Pozzuoli, detected centimetric-scale uplift consistent with hydrothermal reservoir pressurization. At Pisciarelli, the most active onshore site, continuous seismo-acoustic monitoring revealed shallow degassing processes modulated by rainfall and vapor condensation, demonstrating the sensitivity of hydrothermal systems to environmental forcing. At Fogo caldera, submarine fluid sampling and CO₂ flux mapping quantified significant volatile and heat emissions, highlighting the contribution of submarine degassing to the overall energy budget. The integration of these methods shows that hydrothermal systems can produce measurable unrest signals, whether magma is present or not. Combining geophysical, geodetic, and geochemical data across onshore and offshore sectors provides a comprehensive framework to interpret caldera dynamics. Such multiparametric approaches are essential for improving early detection, reducing interpretative ambiguity, and strengthening volcanic hazard assessment in densely inhabited coastal regions.

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