Integrating Multidisciplinary Approaches and Thermal Anomaly Indices to Advance Volcanic and Geothermal Insights on Lipari Island (Italy)

Lipari Island, the largest of the Aeolian Archipelago in the southern Tyrrhenian Sea, is a natural laboratory for investigating the intricate interactions between active volcanism, extensional tectonics, and hydrothermal processes. Spanning over 270,000 years of volcanic history, the island's evolution has been strongly influenced by the Tindari-Letojanni Fault System (TLFS), a major strike-slip fault that controls the emplacement of volcanic centers and the migration of hydrothermal fluids. Geological and geophysical studies, including ambient noise tomography (ANT) and high-resolution magnetic anomaly surveys, have revealed the complex subsurface structure of Lipari. High shear wave velocity (Vs) anomalies correlate with older volcanic buildings and active hydrothermal systems (e.g., San Calogero). At the same time, low Vs regions align with N-S trending faults, younger rhyolitic conduits, and ongoing volcanic processes. These findings highlight the crucial role of tectonics in shaping the island's geothermal and volcanic dynamics. Geochemical analyses further emphasize the influence of fluids in driving Lipari's hydrothermal systems. Elevated CO₂ fluxes, exceeding 2000 g/m²/day at key fault intersections, and distinctive isotopic signatures (e.g., helium and carbon) indicate a mantle-derived magmatic contribution to the hydrothermal activity. Sites such as Cave di Caolino and San Calogero demonstrate advanced argillic alteration, characterized by silica- and sulfate-rich minerals, driven by acidic steam condensates. This alteration reflects ongoing fluid-rock interactions and provides critical insights into the geothermal reservoirs' chemical and thermal conditions. Leveraging Sentinel-2 multispectral imagery, this study utilizes the Thermal Anomaly Index (TAI) to detect and quantify thermal anomalies across Lipari Island, overcoming the limitations of a dedicated thermal band. The TAI integrates Near Infrared (NIR) and Shortwave Infrared (SWIR) bands to identify moderate and extreme thermal variations associated with volcanic and geothermal activity. The SWIR 1 band is effective in detecting moderate heat anomalies, while the SWIR 2 band excels in capturing extreme thermal events, such as fumarolic activity and hydrothermal alteration zones. Enhanced Thermal Anomaly Indices (TAIE) further refine this analysis, enabling precise identification of active volcanic zones and areas under thermal stress, such as those prone to drought or water scarcity. Combining TAI-based thermal insights with geophysical and geochemical data identifies shallow basaltic intrusions as primary heat sources fueling Lipari's geothermal systems. These systems exhibit characteristics consistent with low-to intermediate-enthalpy geothermal reservoirs, with temperatures estimated between 170°C and 200°C. The TLFS is a primary conduit for fluid migration, facilitating geothermal fluid circulation and heat transfer. Such integrated findings underline Lipari's substantial potential for sustainable geothermal energy exploitation. This research advances our understanding of volcanic island processes by linking lithospheric-scale tectonics, hydrothermal circulation, and remote sensing methodologies. The insights gained hold significant implications for managing volcanic hazards and optimizing renewable energy resources, offering a robust framework for continuous monitoring and sustainable development.