Ischia is a rare case of a well-exposed caldera system that has experienced rapid recent resurgence, which call be used to dissect the anatomy of an otherwise inaccessible active hydrothermal system developed in a caldera-forming environment. Integrated analyses of melt and fluid inclusions, mineralogy and stable isotopic compositions of pumices, tuffs and syenitic xenoliths of the Ischia volcanic system provide strong physico-chemical constraints oil the shallow magmatic reservoir and the hydrothermal system. The hydrothermal system has been exposed by the rapid uplift of the Mt. Epomeo resurgent block. The engine of the hydrothemal system of Ischia can be identified in the shallow magmatic system (at around 2 km depth) that hosts hot (c. 1000 degrees C) trachytic magma. The hydrothermal system developed principally within thick intracaldera ignimbrite deposits, and extended to a depth of at least 1 km, defining a series of facies characterized by associations of alteration mineral assemblages typical of a seawater-dominated high-temperature geothermal system.

Melt inclusion data indicate that Vesuvius feeding system active after 1631 eruption consists of a shallow reservoir (P < 100 MPa) and a vertically extended volume of crust (probably carbonate rocks) containing interconnected cracks filled by magma, at pressures >200 MPa. This work demonstrates that input of volatile-rich magma blobs causes the recent violent strombolian and subplinian eruptions at Vesuvius. Volatile-rich mafic magmas and associated exsolved gas bubbles rising from this deep storage system could trigger composite effusive-explosive eruptions and govern the transition from lava effusion to lava fountain phases. The results of this work highlight the role of magmatic volatiles and of the deep system in the explosive dynamics of the eruptions during this period of activity.

Mt. Vesuvius has experienced a period of semipersistent volcanic activity over the last three centuries, producing mainly lava effusions and some mixed effusive‐explosive eruptions of higher magnitude. We present a systematic study on major and volatile elements of melt inclusions trapped in olivine crystals peculiar to lapilli fallout emplaced during the more intense episodes of explosive activity. Based on these data, we propose that the deep feeding system active during this period was formed by a vertically extended volume of crust containing interconnected cracks filled by magma, at pressures >200 MPa. The rise of deep CO2‐H2O‐rich magma blobs from this system triggered the high Volcanic Explosivity Index (VEI 2–3) eruptions, provoking the emission of intense lava effusions of degassed magmas and abrupt transition to intense lava fountains and sustained columns.