Crater Gas Emissions and the Magma Feeding System of Stromboli Volcano

Abstract

Quiescent and explosive magma degassing at Stromboli volcano sustain high temperature crater gas venting and a permanent volcanic plume which constitute key sources of information on the magma supply and dynamics, the physical processes controlling the explosive activity and, more broadly, the volcano feeding system. The chemical composition and the mass output of these crater emissions (gases, trace metals, radioactive isotopes) were measured using different methodologies: within-plume airborne measurements, ground-based plume filtering and/or in situ analysis, remote UV and OP-FTIR absorption spectroscopies. The results obtained, summarized in this paper, demonstrate a primary control of the magmatic gas phase on the eruptive regime and the budget of the volcano. The large excess gas discharge, compared to the lava extrusion rate, and the source depth of slug-driven strombolian explosions evidence extensive separate gas transfer across the volcano conduits, promoted by the high gas content (vesicularity) and then permeability of the shallow basaltic magma. Combined with data for volatiles dissolved in olivine-hosted melt inclusions, the results provide updated constraints for the magma supply rate (~0.3 m3 s-1 on average), the extent of intrusive versus extrusive magma degassing (~15), and the amount of un-erupted degassed magma that should be convectively cycled back in conduits and accumulated beneath the volcano over time (~0.25 km3 in last three decades). The results also provide insight into the possible triggering mechanism of intermittent paroxysmal explosions and the geochemical signals that might allow forecasting these events in future.