Abstract Volcanic unrest associated with increased hydrothermal activity is often difficult to interpret, yet it may culminate in hazardous steam-driven explosions or slope failures without magma intrusion. At La Fossa Caldera (Vulcano Island, Italy), recently affected by the 2021–ongoing unrest episode, we identify a porous scoriaceous horizon at ~ 615–655 m depth that is consistent with the inferred hydrothermal reservoir and confined by mechanically competent lava units.
