Unravelling the Stratigraphy and Eruptive Dynamics of the Pietre Cotte and the 1888–90 eruptions activities, Vulcano (Italy)

The recent evolution (last 700 years) of La Fossa cone (Vulcano island) has long intrigued scientists and sparked debates regarding the origin and timing of products belonging to its various eruptive units. Although very recent, the stratigraphy of these products, the timing of the main eruptions and their characters, and the identification of the source area(s) still remain partly unclear. In the present work, we aim (i) to reconstruct in detail the stratigraphy of Pietre Cotte pyroclastic succession, representing the result of the activities from the XIV century up to the latest AD 1888-90 eruptive cycle, (ii) to define the processes that control the opening phases of explosive eruptions in intermediate–sialic systems characterized by closed conduits and intense interaction with active hydrothermal systems, and (iii) to understand the mechanisms responsible for variations in eruptive style during the eruptions. Stratigraphic fieldwork, lithofacies analysis and volcanological interpretation have been carried out, together with laboratory analyses of representative sample components, volcanic-glass geochemistry, thin-section petrography, and morphoscopic SEM analyses. EPMA glass analyses define two distinct compositional domains (trachytic and rhyolitic), with the gap bridged by the products of the 1888–90 eruptive cycle, indicating effective mixing/mingling processes within the shallow magmatic system. Juvenile fragment morphologies are consistent with phreatomagmatic fragmentation and magmatic degassing, with localized hydrothermal alteration. These studies have led to the definition of an updated volcanic succession result of recurring hydromagmatic to magmatic eruptions, with vent-opening phreatic phases, that produced multiple depositional units from fallout and pyroclastic density currents. The Pietre Cotte succession includes distinctive pumice-fallout layers and the well-known rhyolitic lava flow, reflecting a complex eruptive evolution. Based on our stratigraphic data and the re-interpretation of the available historical reports, combined with the available paleomagnetic ages, the rhyolitic lava flow is most likely dated to AD 1739, whereas the pumice fallout layers were likely emitted slightly after in AD 1771. Constraining the precise timing of the main explosive and effusive events is crucial to better understand the dynamics of La Fossa’s shallow magmatic–hydrothermal system and the evolution of its most recent eruptive activity, thus providing key insights for volcanic hazard assessment on Vulcano Island.