I fenomeni legati all'attività vulcanica sono generalmente complessi e governati da una varietà di processi di importanza simile: ciò rende intrinsecamente impossibile prevedere in modo deterministico e con grande accuratezza l'evoluzione di questi fenomeni nel tempo. Il gruppo di ricerca sulla modellistica dell'INGV-Bologna studia tali processi attraverso due approcci complementari:
Modellazione numerica di sistemi vulcanici ed eventi correlati
Questa ricerca applica modelli numerici sull'evoluzione dello stato di un vulcano risolvendo equazioni matematiche deterministiche con l'obiettivo di caratterizzare determinati "scenari", cioè eventi concettuali ben definiti in termini di condizioni iniziali e "al contorno" (come ad esempio una nota eruzione vulcanica nel passato). In particolare, all'INGV-Bologna sviluppiamo modelli numerici sui processi di trasporto di massa nel sottosuolo, nel suolo e nell'atmosfera, e sui processi di genesi dei maremoti:
- trasporto di fluidi di origine magmatica e meteorica in un mezzo poroso (TOUGH2),
- trasporto di magma da un serbatoio profondo al vent,
- valanghe secche di frammenti di roccia e flussi piroclastici densi lungo le valli in aree montuose e sui vulcani,
- validazione delle simulazioni numeriche mediante esperimenti di laboratorio analogici in scala,
- trasporto, dispersione e deposizione di ceneri vulcaniche dalla colonna eruttiva sotto l'effetto delle condizioni atmosferiche e della gravità,
- dispersione di gas vulcanici nell'atmosfera e vicino al suolo, e
- la genesi di tsunami in seguito all'ingresso di densi flussi piroclastici in mare o nei laghi.
Modellazione probabilistica degli eventi vulcanici e stima della loro pericolosità
Superando il concetto di scenario predeterminato, questa ricerca si concentra piuttosto sulle incertezze intrinseche (legate all'imprevedibilità intrinseca dei fenomeni complessi) o epistemiche (dovute alle nostre carenze nella conoscenza e nella capacità di osservare e misurare questi fenomeni). In questi studi viene adottata una modellazione probabilistica degli eventi vulcanici, oppure vengono combinati diversi scenari ritenuti possibili, ciascuno con una propria probabilità stimata di accadimento. Tra le modellazioni probabilistiche adottate all'INGV-Bologna per i processi vulcanici vi sono studi su
- l'occorrenza e la ricorrenza delle eruzioni vulcaniche,
- i legami tra l'occorrenza delle eruzioni, le dimensioni e la localizzazione della bocca eruttiva,
- la relazione tra misure di sismicità, deformazione e degassamento in aree vulcaniche e la probabilità di occorrenza di diversi eventi vulcanici. Il risultato della modellazione probabilistica offre un mezzo di comunicazione ai decisori che gestiscono situazioni di pericolo.
Articoli su Riviste Scientifiche:
26/11/2024Quantification of volcanic degassing and analysis of uncertainties using numerical modeling: the case of Stephanos crater (Nisyros Island, Greece)Nisyros Island (Greece) is affected by widespread gas emissions from fumarolic fields located at the bottom of hydrother- mal craters in the southern part of its caldera. This morphology and the current low gas fluxes make Nisyros an ideal site for testing the limits of physics-based gas dispersal models in confined and low-emission conditions. Here, we focused our attention on the local scale volcanic gas dispersion from the Stephanos hydrothermal crater. In April 2023, a 1-week survey was carried out to measure weather data, CO2 and H2S gas fluxes, air concentrations from portable gas stations, and chemical composition of fumarolic gases and to acquire thermal images of the crater floor. These data were used as inputs and boundary conditions for numerical simulations using a DISGAS-2.6.0 model in order to quantify the present-day volcanic degassing and its associated uncertainties, accounting for the meteorological variability. Model results are provided in terms of H2S probabilistic exceedance and persistence maps, showing gas concentrations within the crater that fall below the thresholds indicated for the occurrence of serious respiratory problems. Since DISGAS-2.6.0 does not account for chemical reactions, this study represents a good opportunity to discuss the methodological limits of simulating the dispersion of H2S which is challenging due to its rapid degradation and dilution in the atmosphere. In this regard, we also provided an empirical law of the H2S depletion in low-emission conditions that takes into account the uncertainties related to the field measurements.
Autori: Silvia Massaro · Giancarlo Tamburello · Giulio Bini · Antonio Costa · Manuel Stocchi · Franco Tassi · Rebecca Biagi · Orlando Vaselli · Giovanni Chiodini · Fabio Dioguardi · Jacopo Selva · Laura Sandri · Giovanni Macedonio · Stefano Caliro· Georges VougioukalakisArticolo PDF
DOI09/12/2024Where will the next flank eruption at Etna occur? An updated spatial probabilistic assessmentThe assessment of the spatial probability of future vent opening is one of the key factors in quantifying volcanic hazard, especially for active volcanoes where eruptions can occur at different locations and altitudes over distributed areas. Mount Etna (Italy), one of the most active volcanoes in the world, exhibits such variability, and its flank eruptions can harm people, properties and services over the volcano's slopes. In this paper, we quantify the spatial probability of future vent opening for Etna's flank eruptions, adopting a kernel analysis and testing different functions (exponential, Cauchy, uniform and Gaussian). Starting from the assumption that the location of past fissures is indicative of where future events will occur, we consider the flank eruptions of the last 4000 years, thus accounting for a much longer and complete record than in previous studies. The large dataset of eruptive fissures enables splitting the data into training and testing subsets. This allows selecting the best kernel model, testing the completeness of the fissure dataset and investigating a possible migration through time in fissure location. The results show that neither under-recording nor possible migration over time significantly affects the informative value of previous flank fissures in forecasting the location of future ones. The resulting map highlights that the most likely opening area follows a northeast-to-south trend, corresponding to the location of the most active rifts. It also shows that the southern flank of the volcano, which is the most urbanized one, sits downhill of the largest cumulated probability area for flank eruption. We also run sensitivity analyses to test the effect of (i) restricting the data to the most recent 400 years and (ii) including the information on the stress induced on the mapped fissures by sources of deformation proposed in the literature for recent eruptions of Etna. The sensitivity analyses confirm the main features of the proposed map and add information on the epistemic uncertainty attached to it.
Autori: Sandri, L., Garcia, A., Proietti, C., Branca, S., Ganci, G., and Cappello, A.Articolo PDF
DOI02/10/2011A Brownian model for recurrent volcanic eruptions: an application to Miyakejima volcano (Japan)The definition of probabilistic models as mathematical structures to describe the response of a volcanic system is a plausible approach to character- ize the temporal behavior of volcanic eruptions and constitutes a tool for long-term eruption forecasting. This kind of approach is motivated by the fact that volcanoes are complex systems in which a completely deterministic description of the processes preceding eruptions is practically impossible. To describe recur- rent eruptive activity, we apply a physically motivated probabilistic model based on the characteristics of the Brownian passage-time (BPT) distribution; the phys- ical process defining this model can be described by the steady rise of a state variable from a ground state to a failure threshold; adding Brownian perturbations to the steady loading produces a stochastic load-state process (a Brownian relaxation oscillator) in which an eruption relaxes the load state to begin a new eruptive cycle. The Brownian relaxation oscillator and Brown- ian passage-time distribution connect together physical notions of unobservable loading and failure processes of a point process with observable response statistics. The Brownian passage-time model is parameterized by the mean rate of event occurrence, μ, and the ape- riodicity about the mean, α. We apply this model to analyze the eruptive history of Miyakejima volcano, Japan, finding a value of 44.2 (±6.5 years) for the μ parameter and 0.51 (±0.01) for the (dimensionless) α parameter. The comparison with other models often used in volcanological literature shows that this phys- ically motivated model may be a good descriptor of volcanic systems that produce eruptions with a char- acteristic size. BPT is clearly superior to the Exponen- tial distribution, and the fit to the data is comparable to other two-parameters models. Nonetheless, being a physically motivated model, it provides an insight into the macro-mechanical processes driving the system.
Autori: Alexander Garcia-Aristizabal, Warner Marzocchi, Eisuke FujitaArticolo PDF
DOI16/01/2013Integration of stochastic models for long-term eruption forecasting into a Bayesian event tree scheme: a basis method to estimate the probability of volcanic unrestEruption forecasting refers, in general, to the assessment of the occurrence probability of a given eruptive event, whereas volcanic hazards are normally associated with the analysis of superficial and evident phenomena that usually accompany eruptions (e.g., lava, pyroclastic flows, tephra fall, lahars, etc.). Nevertheless, several hazards of volcanic origin may occur in noneruptive phases during unrest episodes. Among others, remarkable examples are gas emissions, phreatic explosions, ground deformation, and seismic swarms. Many of such events may lead to significant damages, and for this reason, the “risk” associated to unrest episodes could not be negligible with respect to eruption-related phenomena. Our main objective in this paper is to provide a quantitative framework to calculate probabilities of volcanic unrest. The mathematical framework proposed is based on the integration of stochastic models based on the analysis of eruption occurrence catalogs into a Bayesian event tree scheme for eruption forecasting and volcanic hazard assessment. Indeed, such models are based on long-term eruption catalogs and in many cases allow a more consistent analysis of long-term temporal modulations of volcanic activity. The main result of this approach is twofold: first, it allows to make inferences about the probability of volcanic unrest; second, it allows to project the results of stochastic modeling of the eruptive history of a volcano toward the probabilistic assessment of volcanic hazards. To illustrate the performance of the proposed approach, we apply it to determine probabilities of unrest at Miyakejima volcano, Japan.
Autori: Alexander Garcia-Aristizabal, Jacopo Selva, Eisuke FujitaArticolo PDF
DOI26/09/2016Suitability of energy cone for probabilistic volcanic hazard assessment: validation tests at Somma-Vesuvius and Campi Flegrei (Italy)Pyroclastic density currents (PDCs) are gravity- driven hot mixtures of gas and volcanic particles which can propagate at high speed and cover distances up to several tens of kilometers around a given volcano. Therefore, they pose a severe hazard to the surroundings of explosive volcanoes able to produce such phenomena. Despite this threat, probabilistic volcanic hazard assessment (PVHA) of PDCs is still in an early stage of development. PVHA is rooted in the quantifi- cation of the large uncertainties (aleatory and epistemic) which characterize volcanic hazard analyses. This quantifica- tion typically requires a big dataset of hazard footprints ob- tained from numerical simulations of the physical process. For PDCs, numerical models range from very sophisticated (not useful for PVHA because of their very long runtimes) to very simple models (criticized because of their highly simplified physics). We present here a systematic and robust validation testing of a simple PDC model, the energy cone (EC), to unravel whether it can be applied to PVHA of PDCs. Using past PDC deposits at Somma-Vesuvius and Campi Flegrei (Italy), we assess the ability of EC to capture the values and variability in some relevant variables for hazard assessment, i.e., area of PDC invasion and maximum runout. In terms of area of invasion, the highest Jaccard coefficients range from 0.33 to 0.86 which indicates an equal or better performance compared to other volcanic mass-flow models. The p values for the observed maximum runouts vary from 0.003 to 0.44. Finally, the frequencies of PDC arrival computed from the EC are similar to those determined from the spatial distribution of past PDC deposits, with high PDC-arrival frequencies over an ∼8-km radius from the crater area at Somma-Vesuvius and around the Astroni crater at Campi Flegrei. The insights de- rived from our validation tests seem to indicate that the EC is a suitable candidate to compute PVHA of PDCs.
Autori: Pablo Tierz, Laura Sandri, Antonio Costa, Lucia Zaccarelli, Mauro Antonio Di Vito, Roberto Sulpizio, Warner MarzocchiArticolo PDF
DOI17/06/2021Integrative Post-event Impact Assessment Framework for Volcanic Eruptions: A Disaster Forensic Investigation of the 2011–2012 Eruption of the Cordón Caulle Volcano (Chile)Understanding the complexity of future volcanic impacts that can be potentially induced by the large variability of volcanic hazards and the multiple dimensions of vulnerability of the increasingly interdependent and interconnected societies, requires an in-depth analysis of past events. A structured and inclusive post-event impact assessment framework is proposed and applied for the evaluation of damage and disruption on critical infrastructures caused by the eruption of the Cordón Caulle volcano (Chile) in 2011–2012. This framework is built on the forensic analysis of disasters combined with the techniques of the root cause analysis that converge in a bow-tie tool. It consists of a fault tree connected to subsequent event trees to describe the causal order of impacts. Considering the physical and systemic dimensions of vulnerability, four orders of impact have been identified: i) the first order refers to the physical damage or the primary impact on a component of the critical infrastructure; ii) the second order refers to the loss of functionality in the system due to a physical damage on key components of the system; iii) the third order refers to the systemic impact due to the interdependency and connectivity among different critical infrastructures; and iv) a higher order is related to the consequences on the main economic sectors and to social disruption that can activate an overall damage to the economy of the country or countries affected. Our study in the Argentinian Patagonia shows that the long-lasting impact of the 2011–2012 Cordón Caulle eruption is mostly due to a secondary hazard (i.e., wind remobilisation of ash), which exacerbated the primary impact affecting significantly larger areas and for longer time with respect to primary tephra deposition. In addition, systemic vulnerability, particularly the intrinsic dependencies within and among systems, played a major role in the cascading impact of the analysed communities.
Autori: Lucia Dominguez, Costanza Bonadonna, Corine Frischknecht, Scira Menoni, Alexander GarciaArticolo PDF
DOI26/04/2021Stress level effect on mobility of dry granular flows of angular rock fragmentsGranular flows of angular rock fragments such as rock ava- lanches and dense pyroclastic flows are simulated numerically by means of the discrete element method. Since large-scale flows generate stresses that are larger than those generated by small-scale flows, the purpose of these simulations is to understand the effect that the stress level has on flow mobility. The results show that granular flows that slide en mass have a flow mobility that is not influenced by the stress level. On the contrary, the stress level governs flow mobility when granular flow dynamics is affected by clast agitation and collisions. This second case occurs on a relatively rougher subsurface where an increase of the stress level causes an increase of flow mobility. The results show also that as the stress level increases, the effect that an increase of flow volume has on flow mobility switches sign from causing a decrease of mobility at low stress level to causing an increase of mobility at high stress level. This latter volume effect corresponds to the famous Heim’s mobility increase with the increase of the volume of large rock avalanches detected so far only in the field and for this reason considered inexplicable without resorting to extraordinary mechanisms. Granular flow dynamics is described in terms of dimensionless scaling parameters in three different granular flow regimes. This paper illustrates for each regime the func- tional relationship of flow mobility with stress level, flow volume, grain size, channel width, and basal friction.
Autori: Bruno CagnoliArticolo PDF
DOI21/01/2020Multisource Bayesian Probabilistic Tsunami Hazard Analysis for the Gulf of Naples (Italy)A methodology for a comprehensive probabilistic tsunami hazard analysis is presented for the major sources of tsunamis (seismic events, landslides, and volcanic activity) and preliminarily applied in the Gulf of Naples (Italy). The methodology uses both a modular procedure to evaluate the tsunami hazard and a Bayesian analysis to include the historical information of the past tsunami events. In the Source Module the submarine earthquakes and the submarine mass failures are initially identified in a gridded domain and defined by a set of parameters, producing the sea floor deformations and the corresponding initial tsunami waves. Differently volcanic tsunamis generate sea surface waves caused by pyroclastic density currents from Somma-Vesuvius. In the Propagation Module the tsunami waves are simulated and propagated in the deep sea by a numerical model that solves the shallow water equations. In the Impact Module the tsunami wave heights are estimated at the coast using the Green's amplification law. The selected tsunami intensity is the wave height. In the Ba𝑦esian Module the probabilistic tsunami analysis computes the long-term comprehensive Bayesian probabilistic tsunami hazard analysis. In the prior analysis the probabilities from the scenarios in which the tsunami parameter overcomes the selected threshold levels are combined with the spatial, temporal, and frequency-size probabilities of occurrence of the tsunamigenic sources. The prior probability density functions are integrated with the likelihood derived from the historical information based on past tsunami data. The posterior probability density functions are evaluated to produce the hazard curves in selected sites of the Gulf of Naples.
Autori: Anita Grezio, Francesca Romana Cinti, Antonio Costa, Paolo Perfetti, Simona Pierdominici, Silvia Pondrelli, Pablo Tierz, Roberto Tonini, Jacopo SelvaArticolo PDF
DOI30/05/2024Eruption plumes extended more than 30 km in altitude in both phases of the Millennium eruption of Paektu (Changbaishan) volcanoThe Millennium Eruption of Paektu volcano, on the border of China and North Korea, gen- erated tephra deposits that extend >1000 km from the vent, making it one of the largest eruptions in historical times. Based on observed thicknesses and compositions of the deposits, the widespread tephra dispersal is attributed to two eruption phases fuelled by chemically distinct magmas that produced both pyroclastic flows and fallout deposits. We used an ensemble-based method with a dual step inversion, in combination with the FALL3D atmospheric tephra transport model, to constrain these two different phases. The volume of the two distinct phases has been calculated. The results indicate that about 3-16 km3 (with a best estimate of 7.2 km3) and 4-20 km3 (with a best estimate of 9.3 km3) of magma were erupted during the comendite and trachyte phases of the eruption, respectively. Eruption rates of up to 4 × 108 kg/s generated plumes that extended 30-40 km up into the strato- sphere during each phase.
Autori: Antonio Costa, Leonardo Mingari, Victoria C. Smith, Giovanni Macedonio, Danielle McLean, Arnau Folch, Jeonghyun Lee, Sung-Hyo YunArticolo PDF
DOI18/01/2021Stochastic Modeling of Explosive Eruptive Events at Galeras Volcano, ColombiaA statistical analysis of explosive eruptive events can give important clues on the behavior of a volcano for both the time- and size-domains, producing crucial information for hazards assessment. In this paper, we analyze in these domains an up-to-date catalog of eruptive events at Galeras volcano, collating data from the Colombian Geological Survey and from the Smithsonian Institution. The dataset appears to be complete, stationary and consisting of independent events since 1820, for events of magnitude ≥2.6. In the time-domain, Inter- Event Times are fitted by various renewal models to describe the observed repose times. On the basis of the Akaike Information Criterion, the preferred model is the Lognormal, with a characteristic time scale of ∼1.6 years. However, a tendency for the events to cluster in time into “eruptive cycles” is observed. Therefore, we perform a cluster analysis, to objectively identify clusters of events: we find three plausible partitions into 6, 8 and 11 clusters of events with magnitude ≥ 2.6 the 6-cluster partition being the preferred. The Inter-Event Times between cluster onsets (inter-cluster) and between events belonging to the same cluster (intra-cluster) are also modeled by renewal models. For inter-cluster data, the preferred model is the Brownian Passage Time, describing a periodical occurrence (mean return time ∼36 years) perturbed by a Gaussian noise. For the intra-cluster explosions, the preferred model is the Lognormal, with a characteristic time scale of ∼0.9 years. In the size-domain, we analyze only single events, due to the low number of clusters. Considering two independent parts of the catalog, we cannot reject the null hypothesis of the erupted mass being described by a power law, implying no characteristic eruption size. Finally, looking for time- and size-predictability, we find a significant inverse linear relationship between the logarithm of the erupted mass during a cycle and the time to the subsequent one. These results suggest that, presently, Galeras is still in the eruption cycle started in 2007; a new eruptive cycle may be expected in a few decades, unless the present cluster resumes to activity with magnitude ≥2.6.
Autori: Laura Sandri, Alexander Garcia, Antonio Costa, Alejandra Guerrero Lopez, Gustavo CordobaArticolo PDF
DOI24/02/2023A New Radar-Based Statistical Model to Quantify Mass Eruption Rate of Volcanic PlumesAccurate forecasting of volcanic particle (tephra) dispersal and fallout requires a reliable estimation of key Eruption Source Parameters (ESPs) such as the Mass Eruption Rate (QM). QM is usually estimated from the Top Plume Height (H ) using empirical and analytical models. For the first time, we TP combine estimates of HTP and QM derived from the same sensor (radar) with mean wind velocity values (vW) for lava-fountain fed tephra plumes associated with 32 paroxysms of Mt. Etna (Italy) to develop a new statistical model based on a Markov Chain Monte Carlo approach for model parameter estimation. This model is especially designed for application to radar data to quickly infer QM from observed HTP and vW, and estimate the associated uncertainty. It can be easily applied and adjusted to data retrieved by radars worldwide, improving our capacity to quickly estimate QM and related uncertainties required for the tephra dispersal hazard.
Autori: L. Mereu, S. Scollo, A. Garcia, L. Sandri , C. Bonadonna ,F. S. MarzanoArticolo PDF
DOI19/01/2023Slope-Break Collisions: Comment on “Insight Into Granular Flow Dynamics Relying on Basal Stress Measurements: From Experimental Flume Tests” by K. Li et al.Numerical simulations show that the positive correlation observed in laboratory experiments by Li et al. (2022, https://doi.org/10.1029/2021jb022905) between an increase of grain size and particle agitation, on the one hand, and an increase of granular flow mobility, on the other hand, is not a valid cause-and-effect relationship. In other words, their mobility differential is not caused by a different energy dissipation rate that results from a different grain size content. Instead, the flows stop because of a head-on collision with the horizontal flume at the bottom of a steep 40° incline. Essentially, the slope-break jams the granular movement. Indeed, a combination of laboratory experiments and numerical simulations demonstrated that the mobility of unhindered dense granular flows increases as grain size and clast agitation decrease. Consequently, there is no evidence that the high mobility of large natural rock avalanches is due to an increase of particle agitation.
Autori: Bruno CagnoliArticolo PDF
DOI08/07/2022Quantifying the influence of cooling and shear rate on the disequilibrium rheology of a trachybasaltic melt from Mt. EtnaMagmas often experience severe disequilibrium conditions during their migration through the Earth’s crust and the subsequent emplacement on its surface. During their transport, magmas are subjected to a wide range of cooling (q) and deformation rates (γ ̇), generating physico-chemical perturbations in the magmatic system able to inhibit or promote crystallization processes. Quantifying the magnitude and timescale of kinetic effects is essential to correctly constrain the rheological evolution of magmas and their ability to flow. Here we present a suite of cooling deformation experiments (CDE) conducted on a basalt from Mt. Etna (Sicily, Italy) to disentangle and model the concurrent effects of q (from 1 to 10◦C/min) and γ ̇ (from 1 to 10 s−1) on the rheology of the system. The analysis of the temporal evolution of viscosity indicates that both q and γ ̇ strongly affect the onset of crystallization and achievement of a rheological cut-off over time, which represents the steep viscosity increase responsible for inhibiting magma flow. Both these rheological thresholds occur at lower T and earlier in time with increasing q, as well as at higher T and earlier in time with increasing γ ̇. To reproduce the observed effects of crystallization on the apparent viscosity, we adopt a stretched exponential function that identifies two main crystallization regimes: i) a first shear-induced crystallization regime, characterized by a gentle viscosity increase and ii) a second cooling-dominated regime, marked by a steeper viscosity increase. The relative extent of these crystallization regimes strictly depends on the interplay between q and γ ̇ on the crystallization kinetics and suggest a first order control of q and a subordinate role of γ ̇.
Autori: Fabrizio Di Fiore, Alessandro Vona, Antonio Costa, Silvio Mollo, Claudia RomanoArticolo PDF
DOI11/05/2019Probabilistic hazard analysis for tsunamis generated by subaqueous volcanic explosions in the Campi Flegrei caldera, ItalyA probabilistic hazard analysis of tsunami generated by subaqueous volcanic explosion is applied to the Campi Flegrei caldera (Campania, Italy). An event tree is developed to quantify the tsunami hazard due to the submarine explosions by: i) defining potential size classes of explosion magnitude on the basis of past volcanic activity in the Campi Flegrei caldera and sites in the underwater part of the caldera; ii) simulating the generation and propaga- tion of the consequent tsunami waves able to reach the coasts of the Campania region for all combinations of tsunami-generating vents and sizes; and iii) quantifying the tsunami probability and relative uncertainty, condi- tional upon the occurrence of an underwater eruption at Campi Flegrei. Tsunami hazard generated by subaque- ous volcanic explosions is considered crucial because of its potential high impact on the densely populated coastal areas of the Pozzuoli Bay and Gulf of Naples even if the probability for eruptions in the submarine part of the caldera is certainly low. The tsunami hazard analysis is presented using conditional hazard curves and maps, that is calculating the probability (and relative uncertainties) of exceeding given tsunami intensity thresh- olds (wave amplitudes at the coast), given the occurrence of a subaqueous eruption. The results indicate that a significant tsunami hazard exists in many areas of the Bay of Naples.
Autori: R. Paris, M. Ulvrova, J. Selva, B. Brizuela, A. Costa, A. Grezio, S. Lorito, R. ToniniArticolo PDF
DOI05/12/2023Flow front mobility of rock avalanches as a function of flow volume, grain size, channel width, basal friction and flow scaleThe ability to predict the mobility of rock avalanches is necessary when designing strategies to mitigate the risks they pose. A popular mobility indicator of the flow front is the Heim’s apparent friction coefficient 𝜇H. In the field, 𝜇H shows a decrease in value as flow volume V increases. But this correlation has been a mystery as to whether it is due to a causal relationship between V and mobility since: (1) field data of 𝜇H do not collapse onto a single curve because typically widely scattered and (2) laboratory experiments have shown an opposite volume effect on the center of mass mobility of miniature flows. My numerical simulations confirm for the first time the existence of a functional relationship of scaling parameters where 𝜇H decreases as V increases in unsteady and nonuniform 3D flows. Data scatter is caused by 𝜇H that is affected by numerous other variables besides V. The interplay of these variables produces differ- ent granular regimes with opposite volume effects. In particular, 𝜇H decreases as V increases in the regime characterized by a relatively rough subsurface. The relationship holds for large-scale flows that, like rock avalanches, consist of a very large number of fine clasts traveling in wide channels. In these dense flows, flow front mobility increases as flow volume increases, as channel width increases, as grain size decreases, as basal friction decreases and as flow scale increases. Larger-scale flows are more mobile because they have larger Froude number values.
Autori: Bruno CagnoliArticolo PDF
DOI25/02/2025A TARGET-BASED, MULTI-HAZARD ASSESSMENT APPROACH AS A TOOL FOR SUPPORTING DECISION-MAKING IN VOLCANIC AREAS: A CASE STUDY IN MT. ETNA, ITALYMulti-hazard assessment aims at evaluating the potential impacts of various natural and humaninduced hazards in a given area of interest and time period. The analysis can include hazards of different nature – such as volcanic eruptions, earthquakes, floods, landslides, and industrial accidents – considering their interdependencies and cumulative effects. Multi-hazard assessments can provide critical insights into the potential impact of multiple hazards, enabling decision makers to adopt a wider view of the problem with respect to the approach of analyzing single hazards independently. Volcanoes are interesting targets for implementing multi-hazard analyses because they are intrinsically a multi-hazard source due to the variety of phenomena usually related to volcanic eruptions (e.g. volcano seismicity, lava flows, tephra fall, lahars, etc.). This paper presents a target-based approach for multi-hazard analysis at Etna volcano (Italy) in which the output of probabilistic single hazard assessment can be harmoniously integrated and used for assessing a wide number of scenarios. The findings underscore the advantages of adopting such a kind of approach for supporting decision makers when using the results of multiple probabilistic hazards assessments for performing tasks of planning, mitigation, or emergency preparedness. This work has been performed in the framework of the INGV project “Pianeta Dinamico” – PANACEA, a project developed for implementing multi-hazard and multi-risk assessments at Etna volcano.
Autori: Alexander Garcia, Laura Sandri, Vera Pessina, Fabrizio Meroni, Elisa Varini, Annalisa CappelloArticolo PDF
DOI17/03/2025Towards a probabilistic risk analysis due tovolcanic‑hazards at Mount EtnaMount Etna is the largest active volcano in Europe and is renowned for its effusive and explosive eruptions, frequently accompanied by intense seismic activity. The densely urbanized area of Eastern Sicily (Italy), situated on the flanks of Mt. Etna, has been the focus of an innovative and comprehensive research project aimed at evaluating the potential volcano hazards and subsequent risks. Hazard scenarios were generated within the research project PANACEA (Probabilistic AssessmeNt of volCanorelated multi-hazard and multi-risk at Mount EtnA) and they have been effectively employed in risk assessment for built-up areas and lifelines. The risk analyses were conducted for lava flow, tephra fall and volcanic earthquake hazards. Risk scenarios were assessed at different spatial scales, from the local one (at the resolution of the census track) to the sub-regional scale, defined as the union of some municipalities. Probabilistic damage scenarios were calculated with the aim of conducting a multi-hazard risk analysis, estimating direct losses in terms of structural damage, casualties and loss of functionality. A few examples of risk assessment are presented here to test the last step of the whole process developed in PANACEA.
Autori: Vera Pessina, Fabrizio Meroni, Elisa Varini, Marina Longoni, Laura Sandri, Alexander Garcia, Annalisa CappelloArticolo PDF
DOI21/03/2025New developments in the estimation of tephra fallout hazard at Mt. Etna, in Italy, during the PANACEA projectMount Etna, in Italy, is one the most active volcanoes in the world. Over the past two decades, its explosive activity has intensified, producing high eruptive columns that rise up to about 15 km above sea level. The particles ejected during these eruptions have caused numerous challenges for the population living on the volcano’s slope, mainly due to difficulties in removing the deposits, but also in terms of health risks and mobility disruptions. The increase in Etna’s explosive activity has led in continuous improvements in the monitoring and forecasting system adopted by the Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, since 2009, using new sensors and enhanced data collection and analysis. In this paper, we present a review of several activities carried out in the frame of the Work Package 2 (WP2) of the ‘Probabilistic AssessmeNt of volCano-related multi-hazard and multi-risk at Mount EtnA (PANACEA)’ project. While the PANACEA project aims at using accurate physics-based models and advanced probabilistic approaches to assess volcanic multi-hazards and identify at-risk zones, the WP2 objective is to improve previous studies on the tephra fallout hazards for Etna. In this context, various activities have been conducted such as: enrich the data collection of eruption source parameters by analysing previous studies and developing new methods for their quantification; improve hazard estimates using multi-model approaches; quantify the uncertainty in eruption source parameters. Additionally, progresses have been made in developing hazard maps that include ballistic impact analysis. These approaches may be extended to other active volcanoes where advanced monitoring and surveillance systems are in place
Autori: Simona Scollo, Costanza Bandanna, Alexander Garcia, Luigi Mereu, Michele Prestifilippo, Francesco Romeo, Laura Sandri, Manuel StocchiArticolo PDF
DOI13/06/2025Estimating the mass of tephra accumulated on roads to best manage the impact of volcanic eruptions: the example of Mt Etna, ItalyExplosive eruptions release significant quantities of tephra, which can spread and settle on the ground, potentially leading to various types of damage and disruption to public infrastructure, including road networks. The quantification of the tephra load is, therefore, of significant interest to evaluate and reduce environmental and socio-economic impact, as well as for managing crises. Tephra dispersal and deposition is a function of multiple factors, including the mass eruption rate (MER), tephra characteristics (size, shape, density), top plume height (HTP), grain size distribution (GSD), and local wind field. In this work, we quantified the tephra mass deposited on the main road network on the east-southeast flanks of Mt Etna (Italy) during lava fountains that occurred in 2021, which reached heights of hundreds of metres. We focused on road connections of municipali- ties significantly affected by these events such as Milo, Santa Venerina, and Zafferana Etnea. First, we analysed a sequence of 39 short-lasting and intense lava fountains detected by the X-band weather radar, applying a volcanic ash radar retrieval approach that permits us to compute the main eruption source parameters (ESPs), such MER, HTP, and GSD. When radar measurements were unavailable for a specific event, we analysed images acquired both by the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) radiometer and by the visible and/or thermal infrared camera of the Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo (Catania), to derive the main ESPs. Second, we used the computed ESPs as inputs to run two different numerical models, Tephra2 and Fall3D, and to reproduce tephra dispersal and accumulation on the road network. Finally, we produce, for the first time, geo-referenced estimates of tephra mass deposited on the whole road network of three municipalities, allowing us to identify the main roads which have been mostly impacted by tephra accumulation, as well as to estimate the total mass of primary tephra that has been removed from roads. Such in- formation represents a valuable input for planning and quick management of the short-term tephra load hazard for future explosive events on Mt Etna.
Autori: Luigi Mereu, Manuel Stocchi, Alexander Garcia, Michele Prestifilippo, Laura Sandri, Costanza Bonadonna, and Simona ScolloArticolo PDF
DOI16/09/2025Turbulent diffusion and volcanic gas dispersion in the atmospheric surface layer: insights from La Solfatara, Campi Flegrei, ItalyNumerical models are widely used to simulate volcanic gas dispersion and estimate local emission sources. However, significant uncertainties arise from the approximations inherent in their physical formulations. Recent advances in high-performance computing (HPC) have enabled high-resolution simulations with minimal numerical diffusion, revealing previously unnoticed limitations in the Monin–Obukhov Similarity Theory used within atmospheric gas dispersion models. One key issue is the determination of the minimum vertical turbulence diffusion coefficient (Kzmin) in the atmospheric surface layer (ASL), which plays a crucial role in reducing biases in advection–diffusion models caused by inadequate turbulence representation. In this study, we refine the Eulerian passive gas transport model DISGAS (v. 2.5.1) using measured data on fumarolic and diffuse CO₂ fluxes and air concentrations, along with local wind measurements collected during an ad hoc field campaign from 4 to 10 May 2023. To account for uncertainties in gas flow rates and turbulent velocity fluctuations, we conducted a statistically robust set of simulations by varying CO₂ fluxes and Kzmin values. Model outputs were compared with in situ CO₂ concentration measurements at fixed monitoring stations. Results indicate that during stable atmospheric conditions, setting Kzmin within the range of 1.5–2 m2 s−1 significantly improves agreement with observations and reduces systematic biases in source esti- mation. These findings refine model parameterization to better represent turbulence under stable atmospheric conditions at La Solfatara crater during the May 2023 survey. Moreover, the proposed methodology can be adopted for automated data assimilation workflows aimed at constraining unknown fumarolic gas source fluxes in other volcanic settings.
Autori: Silvia Massaro, Giovanni Macedonio, Giancarlo Tamburello, Manuel Stocchi, Francesco Rufino , Stefano Caliro, Giulio Bini, Alessandro Santi, Rosario Avino, Jacopo Selva, Laura Sandri Fabio Dioguardi , Giovanni Chiodini and Antonio CostaArticolo PDF
DOI21/08/2025From Eruptive Histories to Volcano Monitoring: Probabilistic Eruption Forecasting and Volcanic Hazard Assessment at Varying Temporal and Spatial Scales, in “ Modern Volcano Monitoring”, Z. Spica and C. Caudron (eds.),, Advances in Volcanology, Springer Nature Switzerland AG 2025, https://doi.org/10.1007/978-3-031-86841-2_12In this chapter, we introduce the reader to the concepts of quantitative eruption forecasting and volcanic hazard assessment. These are two key tasks that modern volcanology increasingly tackles by means of probabilistic approaches, in order to account for the different types and sources of uncertainty that affect both volcanic processes and our knowledge of them. We detail how these two tasks are accomplished at different temporal scales from the short- to the long-term, based on different pieces of information, and using a variety of statistical models and approaches. Such models and approaches are also relevant for volcanic hazard assessments at varying spatial scales, spanning from a local, single volcano scale to more comprehensive assessments of hazard from multiple volcanoes. We describe how different factors are accounted for in the available literature, in terms of monitoring data, eruption size or style, vent location, and volcanic phenomena (such as tephra fallout, ballistic ejection, gas dispersal, pyroclastic density currents, lava flows and lahars). Future developments in the area may revolve around: (i) tackling data scarcity through creating and maintaining harmonized (global) volcanological databases, combined with the use of analogue volcanoes; (ii) further developing frameworks to test, validate and/or compare physical and statistical models in order to optimize their application to probabilistic volcanic hazard assessment and eruption forecasting; (iii) harmonization of data formats and data structures to enable scaling of hazard and risk assessments across hazardous phenomena and sectors of society.
Autori: Sandri Laura, Tierz Pablo, Loughlin SueArticolo PDF
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