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Zusammenfassung

The variability of eruptive dynamics in an active volcano is related to several factors, also including the magma input rate from depth and the influence of volcano-tectonic events. Such elements are also able to impact on the trigger mechanisms of eruptions which, in an extreme synthesis, could be related to bottom-to-top and top-to-bottom dynamics in function of the area of the feeding system whose modification is able to activate magma ascent. A new detailed and stratigraphically-constrained study of the Petrazza eruptive cycle of the PaleoStromboli I eruptive epoch (85-75 ka) has highlighted a period of unusual high-energetic explosive eruptions, likely to be associated to (partially/totally) closed conduit dynamics. A multi-disciplinary approach embracing whole rock, mineral compositional and textural studies and geobarometry confirm initial conditions of closed conduit system, allowing an extensive differentiation of magmas and the crystallization of amphibole. High-intensity explosions are then triggered by the input of hotter and more mafic magma, which partially and gradually substituted the residing one in the intermediate/shallow portions of the feeding system, leading to “classical” open-conduit eruptive dynamics. At the end of the sequence an event of extreme decompression of the magma feeding system, here related to a structural collapse of the volcanic edifice whose deposits are still visible within the sequence, triggered a rapid magma ascent at water undersaturated conditions and an high-energetic explosive eruption, assumed as the larger for the Stromboli volcanic system.