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RESEARCH PRODUCT

Magmatic gas leakage at Mount Etna (Sicily, Italy): Relationships with the volcano-tectonic structures, the hydrological pattern and the eruptive activity.

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In this paper we provide a review of chemical and isotopic data gathered over the last three decades on Etna volcano's fluid emissions and we present a synthetic framework of their spatial and temporal relationships with the volcano-tectonic structures, groundwater circulation and eruptive activity. We show that the chemistry, intensity and spatial distribution of gas exhalations are strongly controlled by the main volcano-tectonic fault systems. The emission of mantle-derived magmatic volatiles, supplied by deep to shallow degassing of alkali-hawaiitic basalts, persistently occurs through the central conduits, producing a huge volcanic plume. The magmatic derivation of the hot gases is verified by their He, C and S isotopic ratios. Colder but widespread emanations of magma-derived CO 2 and He also occur through the flanks of the volcano and through aquifers, mainly concentrated within two sectors of the south-southwest (Paterno-Belpasso) and eastern (Zafferana) flanks. In these two peripheral areas, characterized by intense local seismicity and gravity highs, magma-derived CO 2 and helium are variably diluted by shallower crustal-derived fluids (organically-derived carbon, radiogenic helium). Thermal and geochemical anomalies recorded in groundwaters and soil gases within these two areas prior to the 1991-1993 eruption are consistent with an input of hot fluids released by ascending magma. Magmatic fluids interacted with the shallow aquifers, modifying their physico-chemical conditions, and led to strong variations of the soil CO 2 flux. In combination with routine survey of the crater plume emissions, geochemical monitoring of remote soil gases and groundwaters thus contributes to forecasting Etna's eruptions.