ALBERT

Description: The Somma-Vesuvius (SV) volcanic complex has shown in his history a moderate variability of eruptive styles associated with a significant spatial variability of the associated vent locations. This is proved by the presence of numerous eccentric vents which fed effusive eruptions and also by the variability of the vent area of the large explosive eruptions that showed a shift within the present multistage SV caldera. Numerical simulations of explosive eruptions with variable vent locations inside the caldera have shown that this variability, although restricted to an area a few square kilometers, can have a major effect on the associated hazard, particularly for the threat associated to the occurrence of pyroclastic density currents produced by column collapse. This work summarizes some of the activities that have been put forward with the aim of producing a first long-term vent opening probability map for the area of the Somma-Vesuvius caldera. These activities mainly consist in the recognition and collection of key volcano features that can be linked to the spatial distribution of volcanic activity as well as used for their probabilistic treatment. Key variables that have been considered so far include: a) location of Plinian and sub-Plinian volcanic vents; b) location of moderately explosive eruptions (Violent Strombolian to ash emission); c) location of parasitic vents and eruptive fissures; d) distribution of subsurface faults from DTM analysis; e) distribution of the main deep lineaments, as deduced from published geophysical inversions. Locations of Plinian and sub-Plinian volcanic vents have been represented considering their uncertainties based on the available reconstruction of deposits and expert judgment. Parasitic cone and eruptive fissure locations have been also compiled after a comparative analysis of different bibliographic sources, including geological, geomorphological and topographic maps. Distribution of faults and fractures have been finally derived by integrating data from literature studies and new analysis of different digital terrain models (DTM). All the data have been imported into a GIS-based workspace that allowed to organize, analyze and elaborate different datasets. By assuming that each dataset can contribute to the probability distribution of vent opening through the assignment of appropriate weights (e.g. based on expert elicitation), preliminary vent opening (susceptibility) maps will be produced. Results will be used in the production of more accurate hazard maps of the range of expected explosive phenomena in case of a future reactivation of Somma-Vesuvius.

Description: Published

Description: Milano

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

Description: The Campi Flegrei (CF) is an active volcanic area located in the Campanian Plain, along the Tyrrhenian margin of the Southern Appennines (Italy), dominated by the formation of a 12 km large, resurgent caldera. The nested Campi Flegrei caldera results from successive collapses related to the eruptions of the Campanian Ignimbrite (CI; 39.3±0.1 ka) and Neapolitan Yellow Tuffs (NYT; 14.9±0.4 ka). After the NYT eruption, volcanism was concentrated in three epochs of activity, alternating to periods of quiescence. The great majority of the eruptions have been explosive, variable in magnitude and also characterized by the generation of fallout, ash deposits and pyroclastic density currents (PDCs). We present here a methodology aimed at the construction of a probability map of PDC hazard of the CF area. At this stage, results are preliminary and will be improved by future research work. Nevertheless, first outcomes already provide numerous insights in the problem and contribute to define future research directions. In the study we had to cope with three different problems, related to different probability spaces: • constructing a probability map of the place of a new vent opening • giving a probability law to the area of invasion of a PDC from a fixed new vent • choosing a probability distribution for the uncertainty that affects the model itself To calculate the probabilistic simulations we used the R statistics software, and to plot the maps we used the ESRI platform.

Description: Published

Description: Vienna (Austria)

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

Description: Campi Flegrei is an active volcanic area located in the Campanian Plain, along the Tyrrhenian margin of the southern Apennines (Italy), dominated by the formation of a 12 km large, resurgent caldera. The great majority of the eruptions have been explosive, variable in magnitude and intensity and characterized by the generation of remarkable ash fallout and pyroclastic density currents deposits. In this study we present results of field work and statistical analysis of past eruptive activity aimed at producing long-term probabilistic maps of vent opening at Campi Flegrei. Field work was focused on the structural and morphological nature of the caldera and particularly on the reconstruction of the location of past eruptive vents as well as of main faults and eruptive fissures formed in the last 15 kyr of activity. The statistical analysis performed accounted for the spatial distribution of past vent locations but was flexible enough to incorporate the heterogeneous geological information available, such as the density of faults/fissures or the clue of possible past vents hidden by the more recent activity. One key objective of the analysis was to directly incorporate into the maps the main uncertainties affecting the system. This was done by adopting appropriate density distributions of the probability of vent opening of the different areas of the caldera and by relying on expert judgement. Results allowed to quantify the influence of the different theoretical assumptions and sources of uncertainty on the long-term mapping of vent opening. The distributions obtained represent the starting point for the production of long-term ash fallout and pyroclastic density hazard maps at Campi Flegrei caldera.

Description: Published

Description: Kagoshima (Japan)

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