Long-term forecast of eruption style and size at Campi Flegrei caldera (Italy)

The Campi Flegrei caldera is an active and restless volcano in the densely inhabited Neapolitan area of southern Italy. Because of the very high value (lives, properties, infrastructures, etc.) exposed to potential volcanic hazards, it is one of the areas at highest volcanic risk on Earth. In such a situation we have made an attempt to contribute to assessment of its volcanic hazards by providing a quantitative probabilistic long-term forecast of style and size of the next eruption. We have evaluated the most relevant physical parameters of the 22 explosive eruptions of the Campi Flegrei caldera over the past 5 ka. This time span has been taken as the reference period for volcanic hazards assessment on the basis of the volcanic and deformation history of the caldera. The evaluated parameters include dispersal, volume and density of the pyroclastic deposits, volume of erupted magma, total erupted mass, and eruption magnitude. The obtained results permit a size classification of the explosive eruptions, which are grouped into three sizes: small, medium, and large. On the basis of the reconstructed eruption dynamics, we have considered a type event(s) representative of each size class and hypothesized the style of the next event. An effusive eruption will likely generate a dome or very small lava flows, while an explosive event of any size very probably will produce particles fallout and flowage of pyroclastic density currents. Using a Bayesian inference procedure, we have assigned a conditional probability of occurrence to each of the eruption size classes. A small-size explosive eruption is the most likely event with a probability of about 60%; a large-size explosive eruption is the least likely event with a probability of about 4%; a medium-size explosive eruption has a probability of occurrence of about 25%; an effusive eruption has about 11% probability of occurrence. (C) 2009 Elsevier B.V. All rights reserved.