ALBERT

Description: In this study we present a new effort to improve the uncertainty quantification (UQ) of pyroclastic density current dynamics in the Campi Flegrei caldera, thanks to the implementation of a new 2D depth-averaged granular flow model in the Monte Carlo simulation of keycontrolling variables. Campi Flegrei caldera is an active and densely populated volcanic area in the urban neighborhood of Napoli, characterized by the presence of many dispersed cones and craters, and by a caldera wall more than one hundred meters high, towards East. Basic mapping of pyroclastic density currents (PDC) hazard at Campi Flegrei has been already reported in previous studies: some related to field reconstruction and numerical modeling of specific past eruptions or individual scenarios, while others endeavored to produce specific or integrated PDC hazard maps in which the variability of important parameters of the volcanic system was explicitly accounted for. In particular, [4, 2] obtained quantitative estimates of probabilistic PDC hazard, based on the implementation of a simplified kinematic invasion model able to represent main topographic effects. This model, called box model, was extensively run thousands of times in the Monte Carlo simulation varying vent location, eruptive scale, and time frequency of the future activity. In this study we build our effort upon the previous research started in [7, 5], and utilize the physical modeling approach of [6], with the effcient numerical solution of depth-averaged equations for the flow mass and momentum, considering the effects of basal and internal, velocity dependent, friction forces. The model describes the gas-particle mixture as a homogeneous flow, assuming a mechanism of particle deposition consistent with that previously implemented in the box model. UQ is performed by assuming three different components in the input space: (i) rheology parameters, (ii)volume scale, (iii) source location. Our statistical analysis focuses on the first two components, considering a relatively small number of source locations or an uncertain source location inside a subregion of the caldera. This is a first step before the exploration of the full spatial variability of the source location. The statistical inversion of box model equations, varying the vent location (x; y) and the value of inundated area A, can provide us with initial probability estimates for the volume scale of the PDC flow, either in terms of runout distance or volume extent of the multiphase mixture. Our depth averaged model relies on these estimates for setting up the volume scale of past flows. The calibration of rheology parameters is performed according to that. Thus, the rheology and volume components of the input space are conjointly explored by means of Latin Hypercube sampling, attempting a hierarchical conditioning on feasible inputs and plausible outputs [3]. [1] A. Bevilacqua, F. Flandoli, A. Neri, R. Isaia, S. Vitale, “Temporal models for the episodic volcanism of Campi Flegrei caldera (Italy) with uncertainty quantification," Journal of Geophysical Research: Solid Earth 121, 11 (2016). [2] A. Bevilacqua, A. Neri, M. Bisson, T. Esposti Ongaro, F. Flandoli, R. Isaia, M. Rosi, S. Vitale, “The e ects of vent location, event scale, and time forecasts on pyroclastic density current hazard maps at Campi Flegrei caldera (Italy)," Frontiers in Earth Science 5, 72 (2017). [3] A. Bevilacqua, A.K. Patra, M.I. Bursik, E.B. Pitman, J.L. Macías, R. Saucedo, D. Hyman, “Probabilistic forecasting of plausible debris flows from Nevado de Colima (Mexico) using data from the Atenquique debris flow, 1955," Natural Hazards Earth System Science 19, 791-820 (2019). [4] A. Neri, A. Bevilacqua, T. Esposti Ongaro, R. Isaia, W.P. Aspinall, M. Bisson, F. Flandoli et al., “Quantifying volcanic hazard at Campi Flegrei caldera (Italy) with uncertainty assessment: 2. Pyroclastic density current invasion maps," Journal of Geophysical Research: Solid Earth 120, 2330-2349 (2015). [5] T. Esposti Ongaro, S. Orsucci and F. Cornolti, “A fast, calibrated model for pyroclastic density currents kinematics and hazard," Journal of Volcanology and Geothermal Research 327, 257 - 272 (2016). [6] M. de’ Michieli Vitturi, T. Esposti Ongaro, G. Lari, and A. Aravena, “IMEXSfloW2D 1.0: a depth-averaged numerical flow model for pyroclastic avalanches," Geoscientific Model Development, 12, 581-595 (2019). [7] M. Todesco, A. Neri, T. Esposti Ongaro, P. Papale, and M. Rosi, “Pyroclastic flow dynamics and hazard in a caldera setting: Application to Phlegrean Fields (Italy)," Geochemistry Geophysics Geosystems, 7, Q11003 (2006).

Description: Published

Description: Pisa

Description: 5V. Processi eruttivi e post-eruttivi

Description: The development of long-term hazard maps for pyroclastic density currents (PDC) at Campi Flegrei (CF) caldera is a challenging problem. The probability distributions for the spatial location of the next event producing a PDC, the size of the flow, and the temporal estimate for such an event in the future must be convolved to achieve the necessary assessments. This task is additionally complicated by the remarkable epistemic uncertainty on the eruptive record, affecting the time of past events, the location of vents as well as the PDCs areal extent estimates. As a consequence, with the aim of quantifying some of the main sources of uncertainty, we provided mean and percentile maps of PDC hazard levels. The hazard maps were produced combining a vent-opening probability map, statistical estimates concerning the eruptive scales and a Cox-type temporal model including self-excitement effects, based on the eruptive record of the last 15 ka. The results were obtained by using a Monte Carlo approach and adopting a simplified inundation model based on the “box model” integral approximation and tested with 2D transient numerical simulations of flow dynamics. Remarkable differences can be observed between the past activity in the eastern and western sectors of the caldera: the dependence between PDC scales and the caldera sector was implemented in the hazard maps. Conditional maps concerning PDC originating inside limited zones of the caldera, or PDC with a limited range of scales were also produced with the aim of providing hazard assessments for particular scenarios. Finally, the effect of assuming different time windows for the hazard estimates was explored, including also the possibility of the occurrence of multiple events in the same time window. The analysis allowed us to identify areas with elevated probabilities of flow invasion as a function of the time window considered.

Description: Published

Description: Puerto Varas (Chile)

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

Description: 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.

Description: Published

Description: 2309-2329

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

Description: JCR Journal

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

Description: Published

Description: Vienna (Austria)

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

Description: Lo studio Bevilacqua et al. (2017) ha ottenuto diversi risultati sulle stime di pericolosità da PDC: 1) la statistica della scala eruttiva negli ultimi 15 ka indica che in passato sia stata significativamente maggiore nel settore orientale della caldera (a est di E14°12'). Questo ha effetti significativi sulla pericolosità da PDC, con una riduzione ad ovest, ed un aumento ad est. Mappe basate su scenari fissi sono pure disponibili, ma rappresentano una semplificazione rispetto alle stime di pericolosità complete. Gli scenari a scale eruttive fissate possono infatti corrispondere ad eventi poco probabili. Il 95% della scala eruttiva è pari a ~39±11 km2 nel settore occidentale e ~169±18 km2 in quello orientale. Grazie allo studio Bevilacqua et al. (2016) sono disponibili delle stime temporali, basate sulla statistica del record passato. Le stime tengono conto degli effetti di clustering nei dati, che sono significativi. La frequenza eruttiva è diversa fra i due settori, con una maggiore frequenza nel settore orientale. L'interpretazione di Monte Nuovo con inizio di una epoca eruttiva ha effetti significativi sulla pericolosità da PDC a 10 anni, con una riduzione sostanziale nel caso contrario. Stime di pericolosità a 50 anni sono pure disponibili, anche considerando l'effetto di eruzioni multiple. Mappe che assumono il punto di origine del PDC in una specifica porzione della caldera sono disponibili. Esse costituiscono scenari con probabilità anche significativa. Le mappe localizzate permettono di testare rapidamente vincoli sulla posizione ottenibili coi dati di monitoraggio. Le stime sulla posizione della bocca eruttiva, i.e. il punto di origine dei PDC dovrebbero essere migliorate, includendo gli effetti di precursori sismici e deformazione. In particolare: 1) sono disponibili nuovi dati sulla storia della deformazione negli ultimi 15 ka che possono permettere di indagare maggiormente il legame fra deformazione e posizione delle bocche passate (i.e. Bevilacqua et al. 2017). 2) è in studio un meccanismo di aggiornamento short-term delle mappe in seguito all'osservazione di nuovi dati sismici, che combini: - un modello fisico sulla distanza fra epicentro e potenziale nuova bocca eruttiva, - la stima della probabilità che uno sciame sia un precursore eruttivo - la sensibilità delle stime rispetto alla memoria del sistema dei dati osservati in precedenza. 3) La portabilità ed il confronto delle mappe probabilistiche e dell'incertezza ad esse associata potrebbe essere aumentata, formalizzandone una rappresentazione comune tramite campi Gaussiani. Questo richiede uno studio ulteriore delle proprietà di correlazione spaziale fra punti diversi della caldera, e può facilitare la formulazione di un meccanismo robusto di aggiornamento short-term.

Description: Unpublished

Description: Napoli

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

Description: We have used a three-dimensional, non-equilibrium multiphase flow numerical model to simulate subplinian eruption scenarios at La Soufrière de Guadeloupe (Lesser Antilles, France). Initial and boundary conditions for computer simulations were set on the basis of independent estimates of eruption source parameters (i.e. mass eruption rate, volatile content, temperature, grain size distribution) from a field reconstruction of the 1530 CE subplinian eruption. This event is here taken as a reference scenario for hazard assessment at La Soufrière de Guadeloupe. A parametric study on eruption source parameters allowed us to quantify their influence on the simulated dynamics and, in particular, the increase of the percentage of column collapse and pyroclastic density current (PDC) intensity, at constant mass eruption rate, with variable vent diameter. Numerical results enabled us to quantify the effects of the proximal morphology on distributing the collapsing mass around the volcano and into deep and long valleys and to estimate the areas invaded by PDCs, their associated temperature and dynamic pressure. Significant impact (temperature 〉 300 °C and dynamic pressure 〉 1 kPa) in the inhabited region around the volcano is expected for fully collapsing conditions and mass eruption rates 〉 2 × 107 kg/s. We thus combine this spatial distribution of temperature and dynamic pressure with an objective consideration of model-related uncertainty to produce preliminary PDC hazard maps for the reference scenario. In such a representation, we identify three areas of varying degree of susceptibility to invasion by PDCs-very likely to be invaded (and highly impacted), susceptible to invasion (and moderately impacted), and unlikely to be invaded (or marginally impacted). The study also raises some key questions about the use of deterministic scenario simulations for hazard assessment, where probability distributions and uncertainties are difficult to estimate. Use of high-performance computing techniques will in part allow us to overcome such difficulties, but the problem remains open in a scientific context where validation of numerical models is still, necessarily, an incomplete and ongoing process. Nevertheless, our findings provide an important contribution to the quantitative assessment of volcanic hazard and risk at La Soufrière de Guadeloupe particularly in the context of the current unrest of the volcano and the need to prepare for a possible future reawakening of the volcano that could culminate in a magmatic explosive eruption.

Description: Published

Description: 76

Description: 5V. Processi eruttivi e post-eruttivi

Description: JCR Journal

Description: Understanding the dynamics and effects of hydrothermal eruptions is crucial to the hazard assessment in both volcanic and geothermal areas. Eruptions from hydrothermal centres may occur associated with magmatic phases, but also as isolated events without magmatic input, with the most recent examples being those of Te Maari (Tongariro, New Zealand) in 2012 and Ontake (Japan) in 2014. The most recent caldera of the Island of Vulcano (southern Italy) hosts in its centre the La Fossa cone, active since 5.5 ka and now characterised by continuous fumarolic degassing. In historical times, La Fossa cone has experienced several hydrothermal eruptions, with the most violent event being the Breccia di Commenda eruption that occurred during the thirteenth century ad. Based on analysis of 170 stratigraphic logs, we show that the Breccia di Commenda eruption occurred in three main phases. After an opening, low-intensity ash emission phase (phase 1), the eruption energy climaxed during phase 2, when a series of violent explosions produced an asymmetric shower of ballistic blocks and the contemporaneous emplacement of highly dispersed, lithic-rich, blast-like pyroclastic density currents (PDCs). The tephra units emplaced during phase 2, ranging in volume from 0.2 to 2.7 × 10^5 m3, were covered in turn by thin ash fall deposits (phase 3). The dynamics of the most violent and intense stage of the eruption (phase 2) was investigated by numerical simulations. A three-dimensional numerical model was applied, describing the eruptive mixture as a Eulerian–Eulerian, two-phase, non-equilibrium gas-particle fluid (plus a one-way coupled Lagrangian ballistic block fraction). At the initial simulation time, a mass of about 10^9 kg, with initial overpressure above 10 MPa, and a temperature of 250 °C, was suddenly ejected from a 200-m-long, eastward inclined, NNE–SSW trending fissure. The mass release formed blast-like PDCs on both sides of the fissure and launched ballistic blocks eastwards. Field investigations and numerical simulations confirm that hydrothermal explosions at La Fossa cone include intense ballistic fallout of blocks, emission of PDCs potentially travelling beyond the La Fossa caldera and significant ash fallout. The hazard associated with both ballistic impact and PDC ingress, as associated with hydrothermal eruption, is significantly larger with respect to that associated with Vulcanian-type events of La Fossa.

Description: Published

Description: id 83

Description: 5V. Processi eruttivi e post-eruttivi

Description: JCR Journal

Description: Pyroclastic avalanches are a type of granular flow generated at active volcanoes by different mechanisms, including the collapse of steep pyroclastic deposits (e.g., scoria and ash cones), fountaining during moderately explosive eruptions, and crumbling and gravitational collapse of lava domes. They represent end-members of gravity-driven pyroclastic flows characterized by relatively small volumes (less than about 1 Mm3) and relatively thin (1–10 m) layers at high particle concentration (10–50 vol %), manifesting strong topographic control. The simulation of their dynamics and mapping of their hazards pose several different problems to researchers and practitioners, mostly due to the complex and still poorly understood rheology of the polydisperse granular mixture and to the interaction with the complex natural three-dimensional topography, which often causes rapid rheological changes. In this paper, we present IMEX_SfloW2D, a depth-averaged flow model describing the granular mixture as a single-phase granular fluid. The model is formulated in absolute Cartesian coordinates (whereby the fluid flow equations are integrated along the direction of gravity) and can be solved over a topography described by a digital elevation model. The numerical discretization and solution algorithms are formulated to allow for a robust description of wet–dry conditions (thus allowing us to accurately track the front propagation) and an implicit solution to the nonlinear friction terms. Owing to these features, the model is able to reproduce steady solutions, such as the triggering and stopping phases of the flow, without the need for empirical conditions. Benchmark cases are discussed to verify the numerical code implementation and to demonstrate the main features of the new model. A preliminary application to the simulation of the 11 February pyroclastic avalanche at the Etna volcano (Italy) is finally presented. In the present formulation, a simple semi-empirical friction model (Voellmy–Salm rheology) is implemented. However, the modular structure of the code facilitates the implementation of more specific and calibrated rheological models for pyroclastic avalanches.

Description: Italian Department of Civil Protection, INGV-DPC agreement B2 2016, task D1

Description: Published

Description: 581-595

Description: 5V. Dinamica dei processi eruttivi e post-eruttivi

Description: JCR Journal