ALBERT

Description: In this study we combine detailed reconstructions of volcanological datasets and inputs from structured expert judgement (SEJ) to produce a first background (i.e. long-term or base-rate) probability map for vent opening location in the next Plinian or Sub-Plinian eruption of Somma-Vesuvius (SV). The SV volcano has, over its history, exhibited large variability in eruptive styles, and moderate spatial variability in vent locations. In particular, the vent positions associated with large explosive eruptions, i.e. Plinian and Sub-Plinian, have shown shifts within the present SV caldera. Notwithstanding this moderate shift, the location of a new active vent will have a major effect on the run-out and dispersal of pyroclastic density currents mainly due to the presence of the Mt Somma barrier, as also evidenced by past deposit patterns and illustrated by numerical simulations, and therefore will have important implications for hazard mitigation. Thus far, we have focused on three main objectives: i) the collection and critical review of key volcanological features (position of past vents, distribution of faults, etc.) that could influence the spatial distribution of future vent locations; ii) developing spatial probability density maps with Gaussian kernel function modelling to use with our different volcanological and geophysical datasets, and iii) the production of a background probability map for vent opening position, using weighted linear combination of spatial density maps for the identified volcanological and geophysical parameters, with uncertainties explicitly included from structured expert elicitation. Preliminary outcomes obtained by a first elicitation session involving about 17 experts are reported for three expert judgement weighting and pooling models: (a) the Classical Model (CM) of Cooke (1991); (b) the Expected Relative Frequency (ERF) model of Flandoli et al. (2011), and (c) an Equal Weights (EW) combination. The results of combining expert judgements with our spatial modelling illustrate the influence of uncertainties in the various variables on the spatial probability content of the final maps, depicting areas at higher and lower probability of vent opening; second order effects of alternative methods for pooling judgements for quantifying uncertainty sources are discussed.

Description: Published

Description: Firenze

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: The Somma-Vesuvius (SV) volcano has shown in its history a large variability of eruptive styles associated with a significant spatial variability of vent locations. In particular, the vent position of large explosive eruptions showed a shift within the present SV caldera. Numerical simulations of explosive eruptions with varying vent location inside the caldera indicate a major effect on the runout and dispersal of pyroclastic density currents produced by column collapse. This work summarizes the activities that have been put forward with the aim of producing a first background (also named long-term or basal) vent opening probability map for the area of the SV caldera. These activities have been focused on three main objectives: i) the collection and critical review of key volcanological features (location of past vents, distribution of faults, etc.) that can influence the spatial distribution of future vents; ii) the development of probability density maps through the use of Gaussian kernel functions on the different volcanological datasets and iii) the weighted linear combination of the density maps of the volcanological variables to produce a background vent opening probability map where uncertainties are explicitly accounted for through expert elicitation methods. Results illustrate the different influence of the volcanological variables on the final maps, the areas at higher and lower probability of vent opening and the effects of the different elicitation methods adopted to quantify the uncertainty sources. The map represents the first step to the production of maps of the probability distribution of pyroclastic flow invasion or of ash fallout for the different eruptive scenarios to be considered in the case of a next reactivation at SV.

Description: Published

Description: Prague (CZ)

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: Numerical models of pyroclastic currents are widely used for fundamental research and for hazard and risk modeling that supports decision-making and crisis management. Because of their potential high impact, the credibility and adequacy of models and simulations needs to be assessed by means of an established, consensual validation process. To define a general validation framework for pyroclastic current models, we propose to follow a similar terminology and the same methodology that was put forward by Oberkampf and Trucano (Prog Aerosp Sci, 38, 2002) for the validation of computational fluid dynamics (CFD) codes designed to simulate complex engineering systems. In this framework, the term validation is distinguished from verification (i.e., the assessment of numerical solution quality), and it is used to indicate a continuous process, in which the credibility of a model with respect to its intended use(s) is progressively improved by comparisons with a suite of ad hoc experiments. The method- ology is based on a hierarchical process of comparing computational solutions with experimental datasets at different levels of complexity, from unit problems (well-known, simple CFD problems), through benchmark cases (complex setups having well constrained initial and boundary conditions) and subsystems (decoupled processes at the full scale), up to the fully coupled natural system. Among validation tests, we also further distinguish between confirmation (comparison of model results with a single, well-constrained dataset) and benchmarking (inter-comparison among different models of complex experimental cases). The latter is of particular interest in volcanology, where different modeling approaches and approximations can be adopted to deal with the large epistemic uncertainty of the natural system.

Description: Published

Description: 51

Description: 5V. Processi eruttivi e post-eruttivi

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: JCR Journal

Description: Quantifying uncertainty is crucial for producing hazard assessments which civil protection authorities use to mitigate the associated risks. In this study we combine detailed reconstructions of volcanological datasets and inputs from Structured Expert Judgment (SEJ) to produce a first background (i.e. longterm or base-rate) probability map for vent opening location in the next Plinian or Sub-Plinian eruption of Somma-Vesuvius (SV). The SV volcano has, over its history, exhibited a large variability in eruptive styles, and a moderate but significant spatial variability in vent locations. In particular, the vent positions associated with large explosive eruptions, i.e. Plinian and Sub-Plinian, have shown shifts within the present SV caldera. Notwithstanding this moderate shift, the location of a new vent could have a major effect on the run-out and dispersal of pyroclastic density currents mainly due to the presence of the Mt. Somma barrier, as also evidenced by past deposit patterns and illustrated by 3D numerical simulations, and therefore will have important implications for hazard mitigation. Thus far, we have focused on three main objectives: i) the collection and critical review of key volcanological features (position of past vents, distribution of faults, etc.) that could influence the spatial distribution of future vent locations, organized in a specific geo-database where epistemic uncertainties related to feature spatial distributions have been quantified; ii) developing spatial probability density maps with Gaussian kernel function modelling to use with our different volcanological and geophysical datasets, and iii) the production of a background probability map for vent opening position, using weighted linear combination of spatial density maps for the identified volcanological and geophysical parameters, with uncertainties (related to both epistemic and aleatoric uncertainties) explicitly included by using SEJ. Outcomes obtained during two elicitation sessions involving about 15 experts are reported for three expert judgment weighting and pooling models: (a) the Classical Model (CM) of Cooke (1991); (b) the Expected Relative Frequency (ERF) model of Flandoli et al. (2011), and (c) the Equal Weights (EW) combination. The results of combining expert judgements with our spatial modeling of the identified variables illustrate that: a) vent opening probabilities are evenly distributed around the caldera with a peak in correspondence with the area of the present crater but with about 50% mean probability that the vent will open in other areas of the caldera; b) there is a mean cumulative probability of about 30% that the next vent will open west of the present edifice in the so-called “Piano delle Ginestre” area; c) there is a mean probability of more than 20% that next Plinian eruption will enlarge the present SV caldera and a not negligible probability (of almost 10%) that the next Plinian or sub-Plinian eruption will have its initial vent opening outside the present outline of the SV caldera. Robustness of results have been tested by considering the effects of alternative pooling methods, subgroups of experts with different backgrounds and experiences and sub-groups of volcanological datasets. Uncertainty analysis also allowed identification of the most controversial issues and to have a first estimate of the associated ranges, which will be the focus of specific investigation to improve our basic knowledge to reduce uncertainty

Description: Published

Description: Buffalo (NY)

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: Blasting experiments were performed that investigate multiple explosions that occur in quick succession in unconsolidated ground and their effects on host material and atmosphere. Such processes are known to occur during phreatomagmatic eruptions at various depths, lateral locations, and energies. The experiments follow a multi-instrument approach in order to observe phenomena in the atmosphere and in the ground, and measure the respective energy partitioning. The experiments show significant coupling of atmospheric (acoustic)- and ground (seismic) signal over a large range of (scaled) distances (30–330 m, 1–10 m J −1/3). The distribution of ejected material strongly depends on the sequence of how the explosions occur. The overall crater sizes are in the expected range of a maximum size for many explosions and a minimum for one explosion at a given lateral location. As previous research showed before, peak atmospheric over-pressure decays exponentially with scaled depth. An exponential decay r𝐴𝐴ate of 𝑑𝑑̄0 = 6.47 × 10−4 mJ−1∕3 was measured. At a scaled explosion depth of 4 × 10 −3 m J −1/3 ca. 1% of the blast energy is responsible for the formation of the atmospheric pressure pulse; at a more shallow scaled depth of 2.75 × 10 −3 m J −1/3 this ratio lies at ca. 5.5%–7.5%. A first order consideration of seismic energy estimates the sum of radiated airborne and seismic energy to be up to 20% of blast energy. Finally, the transient cavity formation during a blast leads to an effectively reduced explosion depth that was determined. Depth reductions of up to 65% were measured.

Description: Published

Description: e2022JB023952

Description: 5V. Processi eruttivi e post-eruttivi

Description: JCR Journal