Quantifying volcanic hazard at Campi Flegrei caldera (Italy) with uncertainty assessment: 1. Vent opening maps

Abstract

Campi Flegrei is an active volcanic area situated in the Campanian Plain (Italy) and dominated by a resurgent caldera. The great majority of past eruptions have been explosive, variable in magnitude, intensity, and in their vent locations. In this hazard assessment study we present a probabilistic analysis using a variety of volcanological data sets to map the background spatial probability of vent opening conditional on the occurrence of an event in the foreseeable future. The analysis focuses on the reconstruction of the location of past eruptive vents in the last 15 ka, including the distribution of faults and surface fractures as being representative of areas of crustal weakness. One of our key objectives was to incorporate some of the main sources of epistemic uncertainty about the volcanic system through a structured expert elicitation, thereby quantifying uncertainties for certain important model parameters and allowing outcomes from different expert weighting models to be evaluated. Results indicate that past vent locations are the most informative factors governing the probabilities of vent opening, followed by the locations of faults and then fractures. Our vent opening probability maps highlight the presence of a sizeable region in the central eastern part of the caldera where the likelihood of new vent opening per kilometer squared is about 6 times higher than the baseline value for the whole caldera. While these probability values have substantial uncertainties associated with them, our findings provide a rational basis for hazard mapping of the next eruption at Campi Flegrei caldera.

The Effects of Vent Location, Event Scale, and Time Forecasts on Pyroclastic Density Current Hazard Maps at Campi Flegrei Caldera (Italy)

“…In this section we will briefly review the methods adopted in Bevilacqua et al (2015) and Neri et al (2015), and we will present the new procedures for convolving the spatial hazard mapping with the temporal modeling of Bevilacqua et al (2016). In particular, in the Section PDC Hazard Maps Conditional on the Occurrence of an Explosive Eruption, we will describe the methods aimed at combining the vent opening location and the invaded area estimates thus producing hazard maps conditional on the occurrence of a PDC.…”

“…Some of the epistemic uncertainty sources of the volcanological information are also considered (see Bevilacqua et al, 2015 for more details). In particular, concerning the localization of eruptive vents whose position is reconstructed from field data.…”

“…Such Monte Carlo simulation has a nested structure, configured for estimating the FIGURE 2 | (a) Probability map of new vent opening location, modified from Bevilacqua et al (2015). Contours and colors indicate the mean percentage probability of vent opening per km 2 conditional on the occurrence of an eruption originating on-land.…”

“…All the explosive eruptions possibly taking place in the selected time frame are included in the hazard mapping, and the area invaded by PDC is assumed equal to the union of the single extents in the sequence. In particular, a multivariate temporal sampling is repeated inside the Monte Carlo simulation, separately assessing the events in the different zones of the caldera partition of Bevilacqua et al (2015). The areal size sampling is repeated for each PDC.…”

“…The PDC hazard assessments presented in this paper largely rely on and further extend the recent studies of Bevilacqua et al (2015) and Neri et al (2015), which presented quantitative probabilistic PDC invasion maps, considering some of the main epistemic uncertainty effects. They were developed by using a quite articulated Monte Carlo simulation including some of the main system variables (i.e., vent location and PDC size), but not its time.…”