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Major explosions and paroxysms, respectively, have been the most powerful explosive phenomena at Stromboli in recent centuries. These two categories of explosions, although not sharply separable in terms of eruptive mechanisms and hazards, can produce ballistic projectiles affecting trails and observation sites in the summit area (both major explosions and paroxysms) as well as lower elevation areas of the volcano, down to the coast (paroxysms only). Time series analysis of reconstructed activity since the end of the XIXth Century highlights that such unordinary explosions are strongly non-homogeneous in time and often show notable temporal clustering. We perform a critical review of the volcanic catalogs produced by the Italian volcanological observatories in the last ~40 years. In this review, we evaluate the effect of uncertainties on the characterization of such major explosions, in contrast to intense ‘ordinary’ Strombolian explosions that do not eject large ballistic projectiles outside the Craters Terrace and the upper portion of Sciara del Fuoco. Where sufficient information is available for major explosions, we devise an analytical summary and explore comparative mapping of field data related to the dispersal areas of ballistic projectiles, taking into account relevant uncertainties. Using Monte Carlo simulations, we propose preliminary probabilistic hazard maps for areas potentially exposed to future events of this kind, varying the radius and angle-size of the circular sectors affected. We also evaluate lateral hazard modulation in terms of the density variability of ballistic projectiles per square meter of ground, based on literature review and spatial statistics of newly collected UAV data from the ballistic deposits of the 3rd July 2019 paroxysm on the slopes above Ginostra village. These new hazard maps, once combined with vulnerability and exposure data, allow preliminary quantitative estimates of individual risk exposure levels for guides, volcanologists, and tourists spending time in areas exposed to these unordinary events. Through a retrospective counterfactual analysis of the July 2019 eruption, we demonstrate how, in a future Strombolian paroxysm at another time of day, these risk rates might result in major casualty numbers.

We use PyBox, a new numerical implementation of the box-model approach, to reproduce pyroclastic density current (PDC) deposits from the Somma–Vesuvius volcano (Italy). Our simplified model assumes inertial flow front dynamics and mass deposition equations and axisymmetric conditions inside circular sectors. Tephra volume and density and total grain size distribution of EU3pf and EU4b/c, two well-studied PDC units from different phases of the 79 CE Pompeii eruption, are used as input parameters. Such units correspond to the deposits from variably dilute, turbulent PDCs. We perform a quantitative comparison and uncertainty quantification of numerical model outputs with respect to the observed data of unit thickness, inundation areas and grain size distribution as a function of the radial distance to the source. The simulations consider (i) polydisperse conditions, given by the total grain size distribution of the deposit, or monodisperse conditions, given by the mean Sauter diameter of the deposit; (ii) axisymmetric collapses either covering the whole 360∘ (round angle) or divided into two circular sectors. We obtain a range of plausible initial volume concentrations of solid particles from 2.5 % to 6 %, depending on the unit and the circular sector. Optimal modelling results of flow extent and deposit thickness are reached on the EU4b/c unit in a polydisperse and sectorialized situation, indicating that using total grain size distribution and particle densities as close as possible to the real conditions significantly improves the performance of the PyBox code. The study findings suggest that the simplified box-model approach has promise for applications in constraining the plausible range of the input parameters of more computationally expensive models. This could be done due to the relatively fast computational time of the PyBox code, which allows the exploration of the physical space of the input parameters.

Les écoulements pyroclastiques, EPs (ou courants de densité pyroclastiques), mélanges de gaz et de particules solides qui s'écoulent sous l’effet de la gravité, représentent l’un des phénomènes volcaniques parmi les plus dangereux. Leur étude est menée à différentes échelles durant et après les éruptions. De nombreuses approches sont développées pour étudier les caractéristiques et les mécanismes des EPs. Ce chapitre fait le point sur les techniques actuelles et en développement pour l'étude et la surveillance des EPs.

co-auteur étranger; International audience; Tephra fallout hazard assessment is undertaken with probabilistic maps that rely on numerical models. Regarding maps production, the input parameters of the model (including atmospheric conditions), the physical approximations of the numerical simulations, and the probabilities of occurrence of different eruption types in specific time frames are among the most critical sources of uncertainty. We therefore present a tephra fallout hazard assessment study for two active volcanoes (Cotopaxi and Guagua Pichincha) in Ecuador. We utilize PLUME-MoM/HYSPLIT models, and a procedure for uncertainty quantification where: i) the uncertainty on eruptive source parameters and eruption type occurrence is quantified through expert elicitation; ii) we implement a new procedure for correlations between the different parameters, and iii) we use correction coeffients to take into account the uncertainty of the numerical model. Maps of exceedance probability given a deposit thickness threshold, and thickness maps given a robability of exceedence, are produced 1) for two eruptive scenarios (sub-plinian and Plinian) and 2) as a combination of these scenarios in case the next eruption will be sub-Plinian or Plinian. These maps are described according to the uncertainty distribution of eruption type occurrence probabilities, considering their 5th percentile, mean, and 95th percentile values. We finally present hazard curves describing exceeding probabilities in 10 sensitive sites within the city of Quito. Additional information includes the areal extent and the population potentially affected by different isolines of tephra accumulation. This work indicates that full uncertainty quantification helps in providing more robust scientific information, improving the hazard assessment reliability.

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Co-auteur étranger; International audience; Future occurrence of explosive eruptive activity at Cotopaxi and Guagua Pichincha volcanoes, Ecuador, is assessed probabilistically, utilizing expert elicitation. Eight eruption types were considered for each volcano. Type event probabilities were evaluated for the next eruption at each volcano and for at least one of each type within the next 100 years. For each type, we elicited relevant eruption source parameters (duration, average plume height, and total tephra mass). We investigated the robustness of these elicited evaluations by deriving probability uncertainties using three expert scoring methods. For Cotopaxi, we considered both rhyolitic and andesitic magmas. Elicitation findings indicate that the most probable next eruption type is an andesitic hydrovolcanic/ash-emission (~ 26–44% median probability), which has also the highest median probability of recurring over the next 100 years. However, for the next eruption at Cotopaxi, the average joint probabilities for sub-Plinian or Plinian type eruption is of order 30–40%—a significant chance of a violent explosive event. It is inferred that any Cotopaxi rhyolitic eruption could involve a longer duration and greater erupted mass than an andesitic event, likely producing a prolonged emergency. For Guagua Pichincha, future eruption types are expected to be andesitic/dacitic, and a vulcanian event is judged most probable for the next eruption (median probability ~40–55%); this type is expected to be most frequent over the next 100 years, too. However, there is a substantial probability (possibly >40% in average) that the next eruption could be sub-Plinian or Plinian, with all that implies for hazard levels.

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.

In this study we use PyBox, a new numerical implementation of the box-model approach, to reproduce pyroclastic density current (PDC) deposits from the Somma-Vesuvius volcano (Italy). Our simplified model assumes inertial flow front dynamics and mass deposition equations, and axisymmetric conditions inside circular sectors. Tephra volume and density, and Total Grain Size Distribution of EU3pf and EU4b/c, two well-studied PDC units from different phases of the AD 79 Pompeii eruption of Somma-Vesuvius (Italy) are used as input parameters. Such units correspond to the deposits from variably dilute, turbulent PDCs. We perform a quantitative comparison and uncertainty quantification of numerical model outputs with respect to the observed data of unit thickness, inundation areas, and grain size distribution as a function of the radial distance to the source. The simulations that we performed with PyBox were done considering: (i) polydisperse conditions, given by the total grain size distribution of the deposit, or monodisperse conditions, given by the mean Sauter diameter of the deposit; (ii) round-angle axisymmetrical collapses or divided in two circular sectors. We obtain a range of plausible initial volume concentrations of solid particles from 2.5 % to 6 %, depending on the unit and the circular sector. Optimal modelling results of flow extent and deposit thickness are reached on the EU4b/c unit in a polydisperse and sectorialized situation, indicating that using total grain size distribution and particle densities as close as possible to the real conditions significantly improve the performance of the PyBox code. The study findings suggest that the box model simplified approaches adopted have promising applications in constraining the plausible range of the input parameters of more computationally expensive models.

International audience; The quantification of the maximum runout, invaded area, volume, and total grain-size distribution (TGSD) of pyroclastic density currents (PDC) is a critically important task because such parameters represent the needed necessary input quantities for physical modeling and hazard assessment of PDCs. In this work, new and well-established methods for the quantification of these parameters are applied to a large stratigraphic dataset of three PDC units from two eruptions of Somma-Vesuvius (the AD 79 Pompeii and the AD 472 Pollena eruptions), representative of a large spectrum of transport and depositional processes. Maximum runout and invaded area are defined on the basis of the available volcanological and topographical constraints. The related uncertainties are evaluated with an expert judgment procedure, which considersed the different sectors of the volcano separately. Quite large uncertainty estimates of dispersal area (20–40%) may have important implications in terms of hazard assessment. The testing of different methods for estimating the volume (and mass) of a PDC deposit suggests that integration, over the invaded area, of thickness (and deposit density) data using the triangulated irregular network method can minimize and localize data extrapolation. Such calculations, however, bear an intrinsic additional uncertainty (at least 10% of the total PDC deposit) related to loss or new formation of fine material during transport (at least 10% of the total PDC deposit). Different interpolation methods for TGSD produce multimodal distributions, likely reflecting the different response of each grain size class to transport and deposition processes. These data, when integrated with information on the related co-ignimbrite deposits, can give a more accurate picture of the pyroclastic mixture feeding the current.

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.

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.

Co-auteur étranger; International audience; Numerical modelling of tephradispersaland depositionis essential forevaluation of volcanichazards. Manymodels consider reasonable physical approximations in order toreducecomputational times, but this may introduce a certain degree of uncertainty in the simulation outputs.The important step of uncertainty quantification is dealt in this paper with respect to a coupled version of a plume model (PLUME-MoM) and a tephra dispersal model (HYSPLIT). The performances of this model are evaluated through simulationsoffourpasteruptions of different magnitudesand styles from three Andean volcanoes, and the uncertainty is quantified by evaluating the differences between modeled and observed data of plume height (at different time steps above the vent)as well asmass loading and grain sizeat givenstratigraphic sections.Different meteorological datasets were alsotestedand hada sensible influence on the model outputs. Other results highlight that the modeltendsto underestimate plume heights whileoverestimatingmass loading values, especially for higher magnitude eruptions.Moreover, the advective part of HYSPLIT seems to work more efficiently than the diffusive part.Finally, though the coupledPLUME-MoM/HYSPLIT model generally is less efficient inreproducing deposit grain sizes, we propose itmay be used for hazard maps production for higher magnitude eruptions (sub-Plinian or Plinian)for what concern mass loading.

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.

Monogenetic volcanic eruptions are generally assumed to last to tens of years and produce frequent, intermittent explosive activity that creates eruption columns up to ~ 10 km in elevation. Although this view fits the historically observed eruptions, few data have been collected about the range of durations and eruption sizes possible from monogenetic events. Examining other eruption deposits can help clarify the range of eruption styles and sizes possible from future explosive monogenetic eruptions. The ~ 38 ka Marcath event at Lunar Crater Volcanic Field, Nevada, produced a scoria cone, two tephra fall deposits, and a lava field. We reconstruct the activity that produced the largest tephra fall deposit. Explosive activity produced an eruption column up to ~ 7 km and a volume of about 0.018 km 3 . The Marcath tephra-forming activity was small compared to other characterized scoria cones. Post-eruptive remobilization of the deposit has occurred especially around the margins through both fluvial and eolian processes and has likely removed at least 0.001 km 3 of fine material from the distal portions of the deposit.

Volcanoes within monogenetic volcanic fields often are arranged in alignments and clusters, which are related to effects of magma source geometry in the upper mantle, principal stress orientations, and crustal structures on their magma feeding systems. We use cluster analysis with dendrogram, vent morphometric analysis, and field structural data to explore the relationships between volcanoes and tectonic features in the Plio-Pleistocene part of the Lunar Crater Volcanic Field (LCVF; Pancake Range, Nevada, USA), which includes 96 monogenetic volcanic edifices totaling 119 vents. Structural analysis identified three main sets of faults with dip-slip kinematics (mostly normal with a few examples of thrust faults), striking N-S, E-W, and NE-SW. The NE-SW set comprises dip-slip faults with a dominant normal component of movement which are consistent with the modern state of stress based upon the World Stress Map database. Spatial distribution pattern analysis suggests a clustered distribution of vents in the LCVF, and GIS-based spatial density analysis shows that these clusters trend mostly NE-SW. Morphometric study of the monogenetic cones, which provides information on feeder dike orientation where dikes are not directly exposed, suggests dominant NNE-SSW to NE-SW orientations of near-surface inferred dikes. An amount of 27 out of 31 inferred feeder dikes within the LCVF is parallel to the present orientation of the greatest principal horizontal stress (σ Hmax) as suggested by World Stress Map data derived from hydrofracturing and earthquake focal mechanisms. In some cases, dike strike is parallel with that of pre-existing Quaternary dip-slip faults. We suggest that the spatial distribution of vents is related to domains of different scales of partial melting and compositional heterogeneity in the upper mantle source, which is substantiated by geochemical data. The relationship of feeder dikes with respect to shallow tectonic structures, although somewhat ambiguous at LCVF, is consistent with behavior that is intermediate between volcanic fields with high- and low-long-term magma fluxes.