Dynamics of shallow hydrothermal eruptions: new insights from Vulcano’s Breccia di Commenda eruption

摘要: Understanding the dynamics and effects of hydrothermal eruptions is crucial to hazard assessment in both volcanic geothermal areas. Eruptions from centres may occur associated with magmatic phases, but also as isolated events without input, most recent examples being those Te Maari (Tongariro, New Zealand) 2012 Ontake (Japan) 2014. The caldera Island Vulcano (southern Italy) hosts its centre La Fossa cone, active since 5.5 ka now characterised by continuous fumarolic degassing. In historical times, cone has experienced several eruptions, violent event Breccia di Commenda eruption that occurred during thirteenth century ad. Based on analysis 170 stratigraphic logs, we show three main phases. After an opening, low-intensity ash emission phase (phase 1), energy climaxed 2, when a series explosions produced asymmetric shower ballistic blocks contemporaneous emplacement highly dispersed, lithic-rich, blast-like pyroclastic density currents (PDCs). tephra units emplaced ranging volume 0.2 2.7 × 105 m3, were covered turn thin fall deposits 3). intense stage 2) was investigated numerical simulations. A three-dimensional model applied, describing eruptive mixture Eulerian–Eulerian, two-phase, non-equilibrium gas-particle fluid (plus one-way coupled Lagrangian block fraction). At initial simulation time, mass about 109 kg, overpressure above 10 MPa, temperature 250 °C, suddenly ejected 200-m-long, eastward inclined, NNE–SSW trending fissure. release formed PDCs sides fissure launched eastwards. Field investigations simulations confirm at include fallout blocks, potentially travelling beyond significant fallout. impact PDC ingress, eruption, significantly larger respect Vulcanian-type Fossa.