Simulations of magma ascent and pyroclast dispersal at Vulcano (Aeolian Islands, Italy)

Abstract

Two-phase flow models of magma ascent in volcanic conduits and pyroclast dispersal in the pressure- and temperature-stratified atmosphere were employed to study the consistency of the Palizzi pumice fall eruption phase and the last eruption of Vulcano with modeling predictions. The input data for magma ascent modeling were constrained by the limited availability of petrological, volcanological and geophysical data, and consisted of magma composition, crystal content, conduit geometry, and pressure and temperature of magma in the magma chamber. The magma ascent model was used to establish the locations of magma exsolution and fragmentation levels, gas and pyroclast velocities, pressure, and pyroclast volumetric fractions at the exits of conduits of different diameters and lengths. The vent exit conditions of gas and pyroclasts corresponding to different magma compositions and conduit geometry were employed in the pyroclastic dispersion modeling to establish the distribution of gas and pyroclasts in the atmosphere and along the slopes of the volcano during the first few minutes of the eruptions in order to determine the volcanic column and flow behavior along the slopes of the volcano. The results from simulations showed that the Palizzi pumice fall eruption phase and the last eruption of Vulcano which produced bread-crust bombs are consistent with magma ascent and pyroclastic dispersion models. Using the available volcanological, petrological and geophysical data as well as the modeling results, an eruptive scenario of each cycle of Vulcano was hypothesized where the chemical characteristics of new magma supply into the volcanic system and magma remaining in the system after preceding eruptions, mechanical characteristics of the magma ascent pathways, and the conditions of aquifers surrounding these pathways determine the duration of phreatic, phreatomagmatic, magmatic, and lava flow activities within each cycle. The modeling results also suggested that the Palizzi pumice fall eruption phase ejected magma with a dissolved water content of about 2 wt.% from a vent diameter of about 30 m, and that the dissolved water content in magma during the last eruption of Vulcano ranged between 1 and 2 wt.%. Detailed modeling of various eruptive phases and adequate volcanic hazard assessment at Vulcano not only requires the development of magma-water interaction and hydrothermal circulation models, but also the collection of modeling oriented volcanological, petrological, and geophysical data.