Probabilistic assessment of hazard related to pyroclastic currents at Ischia

The first step towards mitigating the risks associated with pyroclastic density currents (PDCs) consists in quantifying the probability of their occurrence through probabilistic hazard studies. The Island of Ischia constitutes the emerged portion of a large volcanic system, known as the Ischia Volcanic Field (IVF). The last eruption, which occurred in AD 1302, was preceded by centuries of intense volcanic activity, with more than 30 eruptions in the last 10,000 years. At present, the Ischia system is quiescent, but new magmatic intrusions could trigger renewed resurgence, seismic activity and slope instability, potentially culminating in volcanism. The island hosts a permanent population of approximately 60,000 inhabitants, which increases dramatically during summer. This demographic context highlights the urgency of quantitatively assessing volcanic hazards on the island, a topic still poorly addressed in the literature. The aim of this work is to quantify the hazard related to the invasion by PDC on Ischia. We adopted two alternative simplified modeling frameworks (the Energy Cone and the Box model) to study all known explosive eruptions of over the past 10 ky. For each eruption we inverted for potential source parameters and investigated their possible correlations. Vent location uncertainty was addressed adopting a kernel approach based on the spatial distribution of active vents during the past 10 ky. By integrating uncertainties in vent location with dimensional variability of currents, we quantified the hazard associated with PDCs both conditionally, given the occurrence of an eruption, and unconditionally, by estimating the probability of invasion within the next century. This analysis provides a first quantitative estimate of the probabilistic hazard associated with pyroclastic flows for Ischia and demonstrates that the highest probabilities are found in densely populated areas, especially in the area of Casamicciola Terme, Ischia Porto, and Barano. Conditional probability of PDC invasion ​​above 5% includes those areas as well as parts of the NW and SW sectors of the island, between Forio, Panza, and Lacco Ameno, including most of the main populated areas.