Assessing deposit-derived pyroclastic flow hazard at Stromboli (Italy): 2. Probabilistic invasion maps

This study assesses the hazard of deposit-derived pyroclastic density currents generated by paroxysms at Stromboli (Italy). Events that occurred in 1930 and 1944 demonstrate the destructive potential of these flows and the need to assess their hazard. By developing a new probabilistic approach, this work provides first estimates of invasion probability over future decades in case of events similar to those of last century. The analysis of topographic basins, alongside the use of a numerical flow model tested with the well-documented 1930 event (Neri et al., submitted), allowed the identification of 6 main drainage basins with significant impact potential. San Bartolo, Scalo dei Balordi, and Ginostra “A” emerged as the most exposed, with estimated conditional invasion probabilities up to 28% at 50 m a.s.l.. The basins of Vallonazzo, San Vincenzo, and Ginostra “B”, showed lower but still significant probabilities. Using a new temporal model that links the frequency of paroxysms to PDC occurrence, we estimated a mean probability of at least one PDC occurrence outside Sciara del Fuoco of about 9% over the next 10 years and about 49% over 50 years. When combined with spatial estimates, mean invasion probabilities of up to 4% in inhabited areas of the three more exposed basins over the next decade were computed, which increased sevenfold over 50 years. In the other inhabited valleys considered, the invasion probabilities are about half of these values. Our findings highlight the remarkable, although uncertain, risk associated with deposit-derived PDCs outside the Sciara del Fuoco.