Dynamics of the 1873 CE “Breccia De Fiore” phreatic eruption at Vulcano (Aeolian Islands, Italy) through historical chronicles, physical volcanology, and numerical modelling

Phreatic events may represent precursors of magmatic eruptions or occur independently as single or multiple episodes at volcanoes with hydrothermal systems. We examine the Breccia De Fiore deposit from the prolonged phreatic activity during September-October 1873 at the La Fossa cone of Vulcano (Aeolian Islands, Italy). By integrating data from historical chronicles, stratigraphy, sedimentology, physical analyses, and 3D numerical simulations, we investigate eruption dynamics. The sedimentological characteristics of the deposits, asymmetrically dispersed along the north-western flank of the cone, are interpreted as the simultaneous emplacement of pyroclastic density currents and ballistic projectiles. Numerical simulations model the eruptive mixture as an Eulerian gas-particle fluid coupled with Lagrangian ballistic particles. Results suggest the deposit originated from multiple, shallow, low-magnitude explosions (< 5 x 10(4) m(3) cumulative volume). The deposit dispersal is well reproduced by simulating explosions from an inclined vent, driven by pressure build-up (up to 5 MPa) at shallow depths (< 150 m) within the hydrothermal system. This study helps constrain critical parameters of phreatic scenarios at La Fossa volcano, including erupted mass and specific energy, emphasising the hazards posed by such small events and the crucial need for improving hazard assessment, especially given the close presence of populated, touristic sites.