Cioni, Raffaello

Volcanic hazards associated with lava flows advancing on snow cover are often underrated, although sudden explosions related to different processes of lava-snow/ice contact can occur rapidly and are only preceded by small, easily underrated precursors. On 16 March 2017, during a mildly effusive and explosive eruption at Mount Etna, Italy, a slowly advancing lava lobe interacted with the snow cover to produce a sudden, brief sequence of explosions. White vapor, brown ash, and coarse material were suddenly ejected, and the products struck a group of people, injuring some of them. The proximal deposit formed a continuous mantle of ash, lapilli, and decimeter-sized bombs, while the ballistic material travelled up to 200 m from the lava edge. The deposit was estimated to have a mass of 7.1 ± 0.8 × 104 kg, which corresponds to a volume of 32.0 ± 3.6 m3 of lava being removed by the explosion. Data related to the texture and morphology of the ejected clasts were used to constrain a model of lava-snow interaction. The results suggest that the mechanism causing the explosions was the progressive build-up of pressure due to vapor accumulation under the lava flow, while no evidence was found for the occurrence of fuel-coolant interaction processes. Although these low-intensity explosions are not particularly frequent, the data set collected provides, for the first time, quantitative information about the processes involved and the associated hazard and suggests that mitigation measures should be established to prevent potentially dramatic accidents at worldwide volcanoes frequented by tourists and with fairly easy access, such as Etna.

The peninsular and insular Italy are punctuated by Quaternary volcanoes and their rocks constitute an important aliquot of the Italian Quaternary sedimentary successions. Also away from volcanoes itself, volcanic ash layers are a common and frequent feature of the Quaternary records, which provide us with potential relevant stratigraphic and chronological markers at service of a wide array of the Quaternary science issues. In this paper, a broad representation of the Italian volcanological community has joined to provide an updated comprehensive state of art of the Italian Quaternary volcanism. The eruptive history, style and dynamics and, in some cases, the hazard assessment of about thirty Quaternary volcanoes, from the northernmost Mt. Amiata, in Tuscany, to the southernmost Pantelleria, in Sicily Channel, are here reviewed in the light of the substantial improving of the conceptual models, methodological approaches and the overall knowledge made in the last decades in the volcanological field study. We hope that the prest review can represent an useful and agile document summarising the knowledege on the Italian volcanism at the service of the Quaternary community operating in central Mediterranean area.

We present a scenario-based, probabilistic hazard assessment for the San Salvador volcanic complex (SSVC), a volcanic field located in the vicinity of San Salvador that includes the El Boquer´on stratovolcano and 25 monogenetic vents. We define a set of likely eruption scenarios for tephra fallout and pyroclastic density currents (PDCs). The eruption scenarios range from violent Strombolian eruptions with a significant uncertainty in source position to sub-Plinian and Plinian activity fed from the central cone. The adopted methodology is mainly based on numerical modeling using Tephra2 (adopting the software TephraProb) to study tephra fallout and the branching box model and the branching energy cone model (adopting the programs BoxMapProb 2.0 and ECMapProb 2.0) to describe inertial and frictional PDCs, respectively. Despite the dominant W-WSW-trending winds, numerical results show that Plinian eruptions at El Boquer´on volcano are able to deposit thick tephra layers in the metropolitan area of San Salvador city, likely reaching mass loads of the order of 100 kg/m2 (conditional probability of 50%). The simulated sub-Plinian events highlight the seasonal influence of wind patterns. In fact, the conditional probability of significant tephra sedimentation in San Salvador city is strongly reduced when eruptions occur during the rainy season. Numerical modeling of violent Strombolian eruptions is performed considering uncertainty in vent position. Results show that the conditional probability of depositing tephra mass loads higher than 10 kg/m2 at a given point reaches a maximum value of ~7% on the NW flank of the volcano, at about 8 km from the central crater. On the other hand, very low conditional probabilities (<1%) are obtained for San Salvador city for any relevant threshold (10 kg/m2 or more) of tephra mass load during violent Strombolian events. Regarding PDCs, results show that those produced during large-scale Plinian eruptions are able to invade significant areas of the volcano surroundings, including San Salvador city. PDCs generated from the partial collapse of a sub-Plinian eruption column exhibit maximum inundation probabilities on the N, W and S flanks of the volcano. Cerro El Picacho exerts a significant shield effect on the propagation of these PDCs, with low inundation probabilities for San Salvador city (<3%). Finally, coupling published vent opening probability maps and numerical modeling of small-scale PDCs yields maximum inundation probabilities on the NW flank of the volcano, reaching maximum conditional probabilities of the order of ~10% and values of about 5% near the village of Nuevo Sitio del Nino.

Volcanic plume height is one the most important features of explosive activity; thus, it is a parameter of interest for volcanic monitoring that can be retrieved using different remote sensing techniques. Among them, calibrated visible cameras have demonstrated to be a promising alternative during daylight hours, mainly due to their low cost and low uncertainty in the results. However, currently these measurements are generally not fully automatic. In this paper, we present a new, interactive, open-source MATLAB tool, named ‘Plume Height Analyzer’ (PHA), which is able to analyze images and videos of explosive eruptions derived from visible cameras, with the objective of automatically identifying the temporal evolution of eruption columns. PHA is a self-customizing tool, i.e., before operational use, the user must perform an iterative calibration procedure based on the analysis of images of previous eruptions of the volcanic system of interest, under different eruptive, atmospheric and illumination conditions. The images used for the calibration step allow the computation of ad hoc expressions to set the model parameters used to recognize the volcanic plume in new images, which are controlled by their individual characteristics. Thereby, the number of frames used in the calibration procedure will control the goodness of the model to analyze new videos/images and the range of eruption, atmospheric, and illumination conditions for which the program will return reliable results. This also allows improvement of the performance of the program as new data become available for the calibration, for which PHA includes ad hoc routines. PHA has been tested on a wide set of videos from recent explosive activity at Mt. Etna, in Italy, and may represent a first approximation toward a real-time analysis of column height using visible cameras on erupting volcanoes.

The availability of computer tools able to describe the behavior of pyroclastic density currents (PDCs) with uncertainty quantification is of primary importance for the assessment of volcanic hazard. A common strategy to assess the intrinsic variability of these phenomena is based on the analysis of large sets of numerical simulations with variable input parameters. The use of models fast enough to allow for a large number of simulations, such as the so-called kinetic energy models, is thus advantageous. Due to the sensitivity of kinetic energy models to poorly constrained input parameters, the definition of their variation ranges is a critical step in the construction of hazard maps and a numerical calibration becomes necessary. We present a set of reproducible and structured calibration procedures of numerical models based either on a reference deposit or on the distribution of runout distance or inundation area of documented PDCs. In the first case, various metrics can be adopted to compare the model results with the reference PDC deposit (root mean square distance, Hausdorff distance, and Jaccard index), facilitating the development of scenario-based hazard assessments. Calibrations based on the distribution of runout distance or inundation area allow the construction of probabilistic hazard maps that are not conditioned on the occurrence of a specific scenario, but rather reflect the variability of the documented PDCs during the time window considered. Importantly, our calibration strategies allow one to set the input parameters considering their potential statistical dependence. These procedures have been implemented on the user-friendly versions of two kinetic energy models: ECMapProb 2.0 and BoxMapProb 2.0, whose functionalities are presented for the first time in this paper. The different calibration strategies and the functionalities of the two programs are illustrated by considering three case studies: El Misti (Peru), Merapi (Indonesia), and Campi Flegrei (Italy).

Low-intensity emission of volcanic ash represents the most frequent eruptive activity worldwide, spanning the whole range of magma compositions, from basalts to rhyolites. The associated ash component is typically characterized by heterogeneous texture and chemical composition, leading to misinterpretation of the role of syn-eruptive processes, such as cooling and degassing during magma ascent or even magma fragmentation. Despite their low intensity, the ash emission eruptions can be continuous for enough time to create problems to health and life networks of the communities all around the volcano. The lack of geophysical and/or geochemical precursor signals makes the petrological monitoring of the emitted ash the only instrument we have to understand the leading mechanisms and their evolution. Formation of low-level plumes related to ash-rich emissions has increasingly become a common eruptive scenario at Mt. Etna (Italy). In January–February 2019, an eruptive cycle of ash-rich emissions started. The onset of this activity was preceded on 24 December 2018 by a powerful Strombolian-like eruption from a fissure opened at the base of the New Southeast Crater. A lava flow from the same fissure and an ash-rich plume, 8–9 km high a.s.l., from the crater Bocca Nuova occurred concurrently. After about 4 weeks of intra-crater strombolian-like activity and strong vent degassing at summit craters, starting from 23 January 2019, at least four episodes of ash rich emissions were recorded, mainly issued from the Northeast Crater. The episodes were spaced in time every 4–13 days, each lasting about 3–4 days, with the most intense phases of few hours. They formed weak plumes, up to 1 km high above the crater, that were rapidly dispersed toward different directions by dominant winds and recorded up to a distance of 30 km from the vent. By combining observations on the deposits with data on textural and chemical features of the ash components, we were able to discriminate between clasts originated from different crater sources and suggest an interpretive model for syn-eruptive processes and their evolution. Data indicate the occurrence of scarce (<10 vol.%) fresh juvenile material, including at least four groups of clasts with marked differences in microlite content and number density, and matrix glasses and minerals Moreover, a large amount of non-juvenile clasts has been recognized, particularly abundant at the beginning of each episode. We propose that the low amount of juvenile ash results from episodic fast ascent of small magma batches from shallow reservoirs, traveling within a slow rising magma column subjected to cooling, degassing, and crystallization. The large number of non-juvenile clasts deriving from the thick crater infill of variably sealed or thermally altered material at the top of the magma column is suggested to contribute to the ash generation. The presence of a massive, granular crater infilling accumulating in the vent area may contribute to buffer the different geophysical signals associated with the active magma fragmentation process during the low-energy ash eruptions, as already evidenced at other volcanoes.

A crucial feature to manage a volcanic crisis is the ability of volcanologists to promptly detect an impending eruption. This is often affected by significant uncertainty, mainly for the difficulty in interpreting the monitoring signals in terms of the exact timing of a possible eruption. Here we contribute to this problem, focusing on the states of active volcanoes with closed conduit, as deduced from monitoring data. Four main states can be identified. In the quiescence state 1) the monitoring data lie on a baseline, suggesting the lack of shallow magma/fluid movement. The unrest state is highlighted by minor 2) to major 3) variations in the intensity and rate of monitoring data; in both cases, radial ground deformation pattern and non-migrating seismicity imply shallow magma and/or fluid accumulation. The state of impending eruption 4) is characterised by non-radial, asymmetric ground deformation pattern and migrating seismicity, which suggest that magma approaches the surface through a propagating dyke. As early recognition of this distinctive state is crucial for timely eruption forecast, monitoring activity should be aimed at its prompt detection. The application of this rationale to two types of active volcanoes in densely inhabited areas, a restless caldera (Campi Flegrei) and a quiescent stratovolcano (Vesuvio), highlights its feasibility and importance in eruption forecasting. This rationale may foster a general reference framework to be adopted in case of unrest, supporting in interpreting the monitoring data, as well as more effective: 1) operationally-oriented, monitoring system; 2) probabilistic forecast; 3) use of volcanic alert levels.

Uncertainty quantification of the model – definition of mean under/overestimation coefficientes of the model Uncertainty quantification for the probability of occurrence of different eruption types for the range of eruptive source parameters – expert elicitation session Hazard maps produced for sub-plinian and plinian eruptions considered separately and together Cotopaxi (4 eruption types) Guagua Pichincha (2 eruption types) Two map types: for a given tephra accumulation threshold and different probabilities for a given probabilité donnée et différents seuils d'accumulation de téphra Three maps (« lower », « natural » et « upper ») that quantify the different sources of uncertainty Quito : hazard curves defined for 10 sensitive sites

OBJECTIF DU PROJET Création de cartes d’aléa probabilistes des retombées de cendre pour les volcans Cotopaxi et Guagua Pichincha et réalisation d'une étude d’aléa plus détaillé pour la ville de Quito NOUVEAUTÉS Utilisation d'un modèle numérique (PLUME-MoM / HYSPLIT) jamais utilisé pour produire des cartes d’aléa probabilistes des retombées de cendre Quantification explicite des principales sources d'incertitudes 1.Du modèle numérique 2.De la probabilité d'avoir différents styles éruptifs 3.De la plage de variation des paramètres éruptifs

The San Salvador volcanic complex (El Salvador) and Nejapa-Chiltepe volcanic complex (Nicaragua) have been characterized by a significant variability in eruption style and vent location. Densely inhabited cities are built on them and their surroundings, including the metropolitan areas of San Salvador (∼2.4 million people) and Managua (∼1.4 million people), respectively. In this study we present novel vent opening probability maps for these volcanic complexes, which are based on a multi-model approach that relies on kernel density estimators. In particular, we present thematic vent opening maps, i.e., we consider different hazardous phenomena separately, including lava emission, small-scale pyroclastic density currents, ejection of ballistic projectiles, and low-intensity pyroclastic fallout. Our volcanological dataset includes: (1) the location of past vents, (2) the mapping of the main fault structures, and (3) the eruption styles of past events, obtained from critical analysis of the literature and/or inferred from volcanic deposits and morphological features observed remotely and in the field. To illustrate the effects of considering the expected eruption style in the construction of vent opening maps, we focus on the analysis of small-scale pyroclastic density currents derived from phreatomagmatic activity or from low-intensity magmatic volcanism. For the numerical simulation of these phenomena we adopted the recently developed branching energy cone model by using the program ECMapProb. Our results show that the implementation of thematic vent opening maps can produce significantly different hazard levels from those estimated with traditional, non-thematic maps.