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Co-auteur étranger ; This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.; International audience; The eruptive activity of a volcano modifies its surface topography through morphological changes generated by the deposition of emitted volcanic material and resulting gravity-driven processes, which can form accumulation of material in addition to the most common erosional phenomena. Mapping and quantifying such morphological changes allow to derive new data useful to better describe and understand the eruptive history of the volcano itself. Nowadays, one of the mostly used method to identify such morphological changes consists of comparing Digital Elevation Models (DEM) of the volcanic area before and after an eruptive event. If the eruptive event is referred to periods prior to 1980's, the only method to reproduce DEMs consists of elaborating the historical cartography that is often available only in paper format. In this work we aim to prove the reliability of this approach, presenting a study on the morphological changes (from 1876 to 1944) of the summit caldera of the Somma–Vesuvio volcano (Italy). For the first time, we compare DEMs derived from historical maps (1876, 1906 and 1929) and a DEM dated 2012 obtained by remote sensing. The four models of the caldera, digitally reproduced at the same spatial resolution, are morphologically investigated through specific maps derived from the DEMs and a set of height profiles. In addition, further morphometric analyses and accurate quantifications in volume and surface are presented and discussed for a portion of the Somma-Vesuvio summit caldera, represented by the Gran Cono edifice. Considering the different typology of the source data used in this study, it is also provided a discussion on the respective accuracies that, especially for the historical maps, represent a crucial point for obtaining DEMs able to reproduce topographies more realistic as possible. For this reason, despite data source were processed following rigours criteria, the calculations of volume, surface and distance related to the morphological changes of the volcano are associated to an accurate quantification of the error. Following this, the main results obtained in this study are: i) the identification of several past volcanic deposits and the estimation of the related thicknesses, both in good agreement with published literature; ii) the quantification of the morphological changes of the Gran Cono from 1876 to 1944 resulting in a volume and surface growth of 133 × 106 m3 (±5%) and ~0.14 km2, respectively; iii) the identification of a possible migration path of the centroid of the Gran Cono crater along the SW-NE preferential direction during the investigated period.

This paper presents a contribution to Volcanoclastic Flows hazard assessment in very densely populated volcanic areas by using a multidisciplinary study applied to the Torre del Greco area, a municipality close to the active Somma-Vesuvius volcano, in Italy. This study integrates and combines in a GIS environment several types of data: i) information on Volcanoclastic Flows recorded during the years 1906–2010, derived from historical chronicles and local reports; ii) rainfall data relative to the investigated period; iii) summary of the recent activity of Somma-Vesuvius (AD 1631–AD 1944) deriving from the scientific literature; iv) morphological and morphometric analyses derived from a very high resolution Digital Elevation Model developed in the years 2009–2012. The historical analysis of the spatial and temporal distribution of the Volcanoclastic Flows recorded in the Vesuvian area during the last 104 years indicates that the zone mostly affected by such phenomena is the south-western sector of Somma-Vesuvius, and in particular the Torre del Greco municipality, for which a specific database on paths and directions of the historical Volcanoclastic Flows was implemented. The analysis and comparison of all available data allowed us to: i) recognize that the source zone of Volcanoclastic Flows occurred in Torre del Greco was a funnel-shaped area located immediately SW of the Somma-Vesuvius caldera boundary and just above the most urbanized area of the town; ii) individuate the key morphometric parameters (slope and curvature) necessary for the potential triggering of Volcanoclastic Flows; and iii) investigate possible relationships between the fallout deposits of the Somma-Vesuvius main recent eruptions and the historical Volcanoclastic Flows of Torre del Greco. Although this approach represents only a starting point for studies aimed at the assessment and mitigation of Volcanoclastic Flows hazard, it can be applied in other volcanic zones having similar characteristics to the Somma-Vesuvius area. Moreover, it can be used not only during a period of volcanic quiescence when heavy and/or persistent rains are able to remobilize loose pyroclastic deposits, but also in syn-eruptive conditions.

In this study, we combine reconstructions of volcanological data sets and inputs from a structured expert judgment to produce a first long-term probability map for vent opening location for the next Plinian or sub-Plinian eruption of Somma-Vesuvio. In the past, the volcano has exhibited significant spatial variability in vent location; this can exert a significant control on where hazards materialize (particularly of pyroclastic density currents). The new vent opening probability mapping has been performed through (i) development of spatial probability density maps with Gaussian kernel functions for different data sets and (ii) weighted linear combination of these spatial density maps. The epistemic uncertainties affecting these data sets were quantified explicitly with expert judgments and implemented following a doubly stochastic approach. Various elicitation pooling metrics and subgroupings of experts and target questions were tested to evaluate the robustness of outcomes. Our findings indicate that (a) Somma-Vesuvio vent opening probabilities are distributed inside the whole caldera, with a peak corresponding to the area of the present crater, but with more than 50% probability that the next vent could open elsewhere within the caldera; (b) there is a mean probability of about 30% that the next vent will open west of the present edifice; (c) there is a mean probability of about 9.5% that the next medium-large eruption will enlarge the present Somma-Vesuvio caldera, and (d) there is a nonnegligible probability (mean value of 6–10%) that the next Plinian or sub-Plinian eruption will have its initial vent opening outside the present Somma-Vesuvio caldera.

This study presents new and revised data sets about the spatial distribution of past volcanic vents, eruptive fissures, and regional/local structures of the Somma-Vesuvio volcanic system (Italy). The innovative features of the study are the identification and quantification of important sources of uncertainty affecting interpretations of the data sets. In this regard, the spatial uncertainty of each feature is modeled by an uncertainty area, i.e., a geometric element typically represented by a polygon drawn around points or lines. The new data sets have been assembled as an updatable geodatabase that integrates and complements existing databases for Somma-Vesuvio. The data are organized into 4 data sets and stored as 11 feature classes (points and lines for feature locations and polygons for the associated uncertainty areas), totaling more than 1700 elements. More specifically, volcanic vent and eruptive fissure elements are subdivided into feature classes according to their associated eruptive styles: (i) Plinian and sub-Plinian eruptions (i.e., large- or medium-scale explosive activity); (ii) violent Strombolian and continuous ash emission eruptions (i.e., small-scale explosive activity); and (iii) effusive eruptions (including eruptions from both parasitic vents and eruptive fissures). Regional and local structures (i.e., deep faults) are represented as linear feature classes. To support interpretation of the eruption data, additional data sets are provided for Somma-Vesuvio geological units and caldera morphological features. In the companion paper, the data presented here, and the associated uncertainties, are used to develop a first vent opening probability map for the Somma-Vesuvio caldera, with specific attention focused on large or medium explosive events.

Volcanic islands pose several major types of natural hazards, often interconnected and concentrated in relatively small areas. The quantification of these hazards must be framed from a multi-hazard perspective whilst building on existing single-hazard analyses. Ischia is a densely inhabited volcanic island with a long eruptive history lasting more than 150 ka (last in 1302 AD) characterized by the significant asymmetric resurgence of a caldera block. Here, we review the state-of-art of the natural hazards of Ischia, aiming at building a solid base for future holistic multi-hazard quantifications. We frame our analysis in three steps: i) review of geological, historical and current activity; ii) review of available hazard models and analyses; iii) development of an interpretative framework for the interdependent hazards. The results highlight that volcanic activity has been quite intense and many volcano-related hazardous phenomena have affected the island including in very recent times, both for eruptive (phreatic or magmatic eruptions) and non-eruptive (earthquakes, landslides, and tsunamis) phenomena. The effects of some of them (e.g. tsunamis, tephra) are also relevant beyond the island territory. Quantitative hazard assessments are almost absent and should be developed in the future considering the evident interconnections between hazards. To this end, we propose a conceptual interpretative multi-hazard framework that highlights the fundamental role played by the resurgent block in controlling and connecting the different hazards, in terms of both spatial distribution of the sources and temporal clustering.

We present the results of a meso-scale systematic structural analysis of fractures, faults and dykes exposed at the Somma-Vesuvius volcano (southern Italy). Observed fractures include: (i) radial and tangential (with respect the caldera axis), sub-metric to metric joints associated with the edifice load and volcano-tectonic activity (i.e. inflation, deflation and caldera collapse stages) and (ii) decameter-scale fractures related to volcano flank instabilities. For the Somma-Vesuvius volcano, preexisting radial joints were commonly reactivated as transfer faults during the caldera formation, allowing different blocks to move toward the center of the collapsing area. Dykes occur with different geometries, including en-echelon structures bounding structural depressions. The orientation analysis of all structures indicates that they are preferentially oriented. Furthermore, we provide a morphological lineament analysis using high-resolution Digital Terrain Models of Somma-Vesuvius. Azimuth and spatial distribution of dykes and morphological lineaments were analyzed for comparison with the old Somma Crater and Gran Cono axes, respectively. Results highlight the overprinting of radial and clustered strain patterns recorded in different volcano-tectonic evolution stages. We suggest a possible deformation evolution model in which structures develop along either radial or preferential trends, highlighting different volcanic conditions: (i) where radial patterns occur, the structures developed during volcanic inflation cycles with a closed magmatic conduit condition whereas (ii) clustered patterns are probably associated with a regional strain field that overcomes the local deformation field, a situation typical in the case of open-conduit activity.

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.

Campi Flegrei (CF) is an example of an active caldera containing densely populated settlements at very high risk of pyroclastic density currents (PDCs). We present here an innovative method for assessing background spatial PDC hazard in a caldera setting with probabilistic invasion maps conditional on the occurrence of an explosive event. The method encompasses the probabilistic assessment of potential vent opening positions, derived in the companion paper, combined with inferences about the spatial density distribution of PDC invasion areas from a simplified flow model, informed by reconstruction of deposits from eruptions in the last 15 ka. The flow model describes the PDC kinematics and accounts for main effects of topography on flow propagation. Structured expert elicitation is used to incorporate certain sources of epistemic uncertainty, and a Monte Carlo approach is adopted to produce a set of probabilistic hazard maps for the whole CF area. Our findings show that, in case of eruption, almost the entire caldera is exposed to invasion with a mean probability of at least 5%, with peaks greater than 50% in some central areas. Some areas outside the caldera are also exposed to this danger, with mean probabilities of invasion of the order of 5–10%. Our analysis suggests that these probability estimates have location-specific uncertainties which can be substantial. The results prove to be robust with respect to alternative elicitation models and allow the influence on hazard mapping of different sources of uncertainty, and of theoretical and numerical assumptions, to be quantified.

This study presents a new method for producing long-term hazard maps for pyroclastic density currents (PDC) originating at Campi Flegrei caldera. Such method is based on a doubly stochastic approach and is able to combine the uncertainty assessments on the spatial location of the volcanic vent, the size of the flow and the expected time of such an event. The results are obtained by using a Monte Carlo approach and adopting a simplified invasion model based on the box model integral approximation. Temporal assessments are modelled through a Cox-type process including self-excitement effects, based on the eruptive record of the last 15 kyr. Mean and percentile maps of PDC invasion probability are produced, exploring their sensitivity to some sources of uncertainty and to the effects of the dependence between PDC scales and the caldera sector where they originated. Conditional maps representative of PDC originating inside limited zones of the caldera, or of PDC with a limited range of scales are also produced. Finally, the effect of assuming different time windows for the hazard estimates is explored, also including the potential occurrence of a sequence of multiple events. Assuming that the last eruption of Monte Nuovo (A.D. 1538) marked the beginning of a new epoch of activity similar to the previous ones, results of the statistical analysis indicate a mean probability of PDC invasion above 5% in the next 50 years on almost the entire caldera (with a probability peak of ~25% in the central part of the caldera). In contrast, probability values reduce by a factor of about 3 if the entire eruptive record is considered over the last 15 kyr, i.e. including both eruptive epochs and quiescent periods.

Naples is a large city located between two active volcanic areas: Campi Flegrei to the W and Vesuvius to the SE. The Solfatara crater, inside the caldera of the Campi Flegrei and nearest to the western quarters of the city, is a prodigious source of natural CO 2 with a mean emission rate of 1067 ton/d, i.e. seven times higher than that of Vesuvius (151 ton/d). This study shows that the area around the Solfatara and part of the urban area of Naples are affected by the volcanic plume when atmospheric circulatory patterns are dominated by the locally frequent sea breezes. Under these conditions the CO 2 content in the air increases above normal values, reaching more than 1000 ppm in proximity to the Solfatara crater to a few tens of ppm several kilometres from the source. Although these values do not indicate a health risk even under the most unfavourable atmospheric conditions, the volcanic source contributes to the total CO 2 burden from all urban emissions and hence to overall air quality. An emission rate ten times higher than the present one would lead to an air CO 2 concentration in excess of recommended health protection thresholds.

Campi Flegrei (CF) is an example of an active caldera containing densely populated settlements at very high risk of pyroclastic density currents (PDCs). We present here an innovative method for assessing background spatial PDC hazard in a caldera setting with probabilistic invasion maps conditional on the occurrence of an explosive event. The method encompasses the probabilistic assessment of potential vent opening positions, derived in the companion paper, combined with inferences about the spatial density distribution of PDC invasion areas from a simplified flow model, informed by reconstruction of deposits from eruptions in the last 15 ka. The flow model describes the PDC kinematics and accounts for main effects of topography on flow propagation. Structured expert elicitation is used to incorporate certain sources of epistemic uncertainty, and a Monte Carlo approach is adopted to produce a set of probabilistic hazard maps for the whole CF area. Our findings show that, in case of eruption, almost the entire caldera is exposed to invasion with a mean probability of at least 5%, with peaks greater than 50% in some central areas. Some areas outside the caldera are also exposed to this danger, with mean probabilities of invasion of the order of 5-10%. Our analysis suggests that these probability estimates have location-specific uncertainties which can be substantial. The results prove to be robust with respect to alternative elicitation models and allow the influence on hazard mapping of different sources of uncertainty, and of theoretical and numerical assumptions, to be quantified.

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.