Assessing future vent opening locations at the Somma-Vesuvio volcanic complex: 2. Probability maps of the caldera for a future Plinian/sub-Plinian event with uncertainty quantification

In this study, we combine reconstructions of volcanological data sets and inputs from a Structured Expert Judgement to produce a first long-term probability map for vent opening location for the next Plinian or sub-Plinian eruption of Somma-Vesuvio. In the past, the volcano has exhibited significant spatial variability in vent location; this can exert a significant control on where hazards materialise (particularly of pyroclastic density currents). The new vent opening probability mapping has been performed through: i) development of spatial probability density maps with Gaussian kernel functions for different data sets, and ii) weighted linear combination of these spatial density maps. The epistemic uncertainties affecting these datasets were quantified explicitly with expert judgements, and implemented following a doubly stochastic approach. Various elicitation pooling metrics, and sub-groupings of experts and target questions were tested to evaluate the robustness of outcomes. Our findings indicate that: a) Somma-Vesuvio vent opening probabilities are distributed inside the whole caldera, with a peak corresponding to the area of the present crater, but with more than 50% probability that the next vent could open elsewhere within the caldera; b) there is a mean probability of about 30% that the next vent will open west of the present edifice; c) there is a mean probability of about 9.5% that the next medium-large eruption will enlarge the present SV caldera, and d) there is a non-negligible probability (mean value of 6-10%) that the next Plinian or sub-Plinian eruption will have its initial vent opening outside the present Somma-Vesuvio caldera.