ALBERT

Beschreibung: 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).

Beschreibung: Published

Beschreibung: Pisa

Beschreibung: 5V. Processi eruttivi e post-eruttivi

Beschreibung: Lagrangian particle dispersal models are commonly used for tracking ash particles emitted from volcanic plumes and transported under the action of atmospheric wind fields. In this work, we adopted a Lagrangian particle model to carry out an uncertainty quantification analysis of volcanic ash dispersal in the atmosphere focused on the uncertainties affecting particle source conditions. To this aim the Eulerian fully compressible mesoscale non-hydrostatic model WRF was used to generate the driving wind field. The Lagrangian particle model LPAC (de’Michieli Vitturi et al., JGR 2010) was then used to simulate the transport of mass particles under the action of atmospheric conditions. The particle motion equations were derived by expressing the Lagrangian particle acceleration as the sum of the forces acting along its trajectory, with drag forces calculated as a function of particle diameter, density, shape and Reynolds number. The simulations were representative of weak plume events of Mt. Etna and aimed to quantify the effect on the dispersal process of the uncertainty in the mean and variance of a Gaussian density function describing the grain-size distribution of the mixture and in the particle sphericity. In order to analyze the sensitivity of particle dispersal to these uncertain parameters with a reasonable number of simulations, and therefore with affordable computational costs, response surfaces in the parameter space were built by using the generalized polynomial chaos technique. The uncertainty analysis allowed to quantify the most probable values, as well as their pdf, of the number of particles as well as of the mean and variance of the grain size distribution at various distances from the source, both in air and on the ground. In particular, results highlighted the strong reduction of the uncertainty ranges of the mean and variance of the grain-size distribution with increasing distance from source and the significant control of particle sphericity on the dispersal process.

Beschreibung: Published

Beschreibung: San Francisco (CA)

Beschreibung: 5V. Processi eruttivi e post-eruttivi

Beschreibung: A new code to simulate lava flow spread, MrLavaLoba, is presented. In the code, erupted lava is itemized in parcels having an elliptical shape and prescribed volume. New parcels bud from existing ones according to a probabilistic law influenced by the local steepest slope direction and by tunable input settings. MrLavaLoba must be accounted among the probabilistic codes for the simulation of lava flows, because it is not intended to mimic the actual process of flowing or to provide directly the progression with time of the flow field, but rather to guess the most probable inundated area and final thickness of the lava deposit. The code's flexibility allows it to produce variable lava flow spread and emplacement according to different dynamics (e.g. pahoehoe or channelized-‘a‘ā). For a given scenario, it is shown that model outputs converge, in probabilistic terms, towards a single solution. The code is applied to real cases in Hawaii and Mt. Etna, and the obtained maps are shown.

Beschreibung: Published

Beschreibung: 323-334

Beschreibung: 5V. Processi eruttivi e post-eruttivi

Beschreibung: JCR Journal

Beschreibung: Magma permeability is the most important factor controlling the transition between effusive and explosive styles during magma ascent at active volcanoes. When magma permeability is low, gas bubbles in the melt expand as the pressure decreases; above a critical gas volume fraction threshold, magma fragments, generating an explosive eruption. On the contrary, if magma is sufficiently permeable, gas ascends through the conduit towards the surface faster than the magma ascent speed, producing decoupling of gas and magma and reducing the maximum vesicularity. This decoupled flow inhibits fragmentation and leads to either an effusive eruption or quiescent degassing. Accurate modelling of permeability behaviour is therefore fundamental when simulating magma ascent processes. In this work, we compare different permeability models for low viscosity magmas using a 1D steady-state model. We use, as a test case, the 2007 effusive eruption at Stromboli volcano, Italy. We compare the numerical solutions computed using the linear Darcy's law with those obtained using the non-linear Forchheimer relation. Our numerical results show that, using Darcy's law and appropriate permeability models, it is possible to obtain an effusive eruption in agreement with observations. However, we found that, in the shallow conduit, the limit of applicability of Darcy's law (that is the modified Reynolds number Rem 〈 10) is exceeded due to high gas flow rates. Furthermore, we show that using Forchheimer's law and some parametric expressions for viscous and inertial permeabilities, results can be compatible with an effusive eruption, once appropriate values are chosen. However, one of the parameters required to obtain an effusive eruption, the friction coefficient between gas and melt, is several orders of magnitude lower than that determined from measurements of solid erupted samples. This result requires further experimental verification. We propose that our novel permeability modelling regime is suitable for basaltic volcanism. We highlight that permeabilities derived from studying solid samples are not representative of the actual permeability of a molten magma, at least in the case of low viscosity basaltic magmas. These findings have fundamental implications for the quantification of permeability, modelling of volcanic processes and volcanic eruption dynamics, and the forecasting of volcanic eruptions.

Beschreibung: Published

Beschreibung: 279-290

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

Beschreibung: JCR Journal

Beschreibung: INGV

Beschreibung: Published

Beschreibung: 5V. Processi eruttivi e post-eruttivi

Beschreibung: EUROVOLC Virtual Accesses offer the opportunity to anyone with a web access to use online tools related to volcanological research. The Volcano Dynamics Computational Center at INGV in Pisa offers the access to a suite of fast-performing numerical codes aimed at modeling different aspects of volcano dynamics: solwcad: Fortran code that computes the fully non-ideal, multi-component, compositional-dependent saturation surface of H2O+CO2 in silicate melts over P-T-composition conditions relevant to magmatism and volcanism. Calculations allow to either 1) determine the partition of H2O and CO2 between the melt and gas phase, or 2) determine the entrapment pressure and corresponding gas phase composition from dissolved amounts; MAMMA: FORTRAN90 code designed to solve a conservative model for magma ascent in a volcanic conduit, described as a compressible multi-component two-phase flow. The system of conservation equations considers the effects of the main processes that magmas experience during ascent, such as crystallization, rheological changes, fragmentation, physical interaction with conduit walls, out-gassing and degassing. The model is capable of describing conduits with elliptical cross sections and depth-dependent dimensions; PyBOX: Python/Fortran90 code that solves the so-called “box model” equations describing the kinematics of a pyroclastic density current over a flat surface and in a steady atmosphere. The model integrates a procedure to account for blockage of PDCs by a rugged topography imported as a ASCII file, by adopting the so-called “energy-conoid” approach. Virtual Access will include an interface to import the DEM file and input parameters and to visualize georeferenced maps of invasion and plots of decaying dynamic pressure.

Beschreibung: Unpublished

Beschreibung: Catania

Beschreibung: 5V. Processi eruttivi e post-eruttivi

Beschreibung: The dichotomy between explosive volcanic eruptions, which produce pyroclasts, and effusive eruptions, which produce lava, is defined by the presence or absence of fragmentation during magma ascent. For lava fountains the distinction is unclear, since the liquid phase in the rising magma may remain continuous to the vent, fragment in the fountain, then re-weld on deposition to feed rheomorphic lava flows. Here we use a numerical model to constrain the controls on basaltic eruption style, using Kilauea and Etna as case studies. Based on our results, we propose that lava fountaining is a distinct style, separate from effusive and explosive eruption styles, that is produced when magma ascends rapidly and fragments above the vent, rather than within the conduit. Sensitivity analyses of Kilauea and Etna case studies show that high lava fountains (〉50 m high) occur when the Reynolds number of the bubbly magma is greater than ∼0.1, the bulk viscosity is less than 10^6, and the gas is well-coupled to the melt. Explosive eruptions (Plinian and sub-Plinian) are predicted over a wide region of parameter space for higher viscosity basalts, typical of Etna, but over a much narrower region of parameter space for lower viscosity basalts, typical of Kilauea. Numerical results show also that the magma that feeds high lava fountains ascends more rapidly than the magma that feeds explosive eruptions, owing to its lower viscosity. For the Kilauea case study, waning ascent velocity is predicted to produce a progressive evolution from high to weak fountaining, to ultimate effusion; whereas for the Etna case study, small changes in parameter values lead to transitions to and from explosive activity, suggesting that eruption transitions may occur with little warning.

Beschreibung: RCUK NERC DisEqm project

Beschreibung: Published

Beschreibung: 116658

Beschreibung: 5V. Processi eruttivi e post-eruttivi

Beschreibung: JCR Journal

Beschreibung: The use of numerical models aimed at producing probabilistic maps is becoming more and more a common practice for tephra fallout hazard assessment. However, it is important to complement such maps with a quantification of the major sources of aleatoric/epistemic uncertainties, to help stakeholders and decisionmakers in taking informed decisions. In this contribution, we present an example of uncertainty quantification applied to a tephra fallout hazard assessment. The study is related to two volcanoes (Cotopaxi and Guagua Pichincha) threatening the capital city of Ecuador, Quito. Uncertainty was quantified with respect to three aspects: 1) the numerical model itself; 2) the probability of occurrences of different eruptive styles; 3) the range of variation of three eruptive input parameters (total fallout mass, eruption duration, average plume height). For point 1), the model used (which couples the plume model PLUMEMoM and the tephra dispersal model HYSPLIT) was tested in reproducing recent eruptions from South American volcanoes. This step allowed quantifying the difference between real (observed) and modelled values of several parameters, including mass loading, from which we derived coefficients of average model overestimation and underestimation. Concerning points 2) and 3), we performed an expert judgement (elicitation) session involving 20 experts of different countries and areas of expertise. This allowed deriving detailed uncertainty ranges that we used to i) sample the eruptive input parameters at each iteration during hazard map production; ii) linearly combine maps of different eruptive magnitude/style according to their relative probability of occurrence. The final products of this study are hazard maps of different formats and hazard curves for 10 sensitive sites in the city of Quito. Each of these maps/curves is presented as a set of three maps/curves (“lower”, “mean” and “upper”) which quantify the major sources of uncertainty.

Beschreibung: Published

Beschreibung: Catania

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

Beschreibung: The temporal evolution of effusion rate is the main controlling factor of lava spreading and emplacement conditions. Therefore, it represents the most relevant parameter for characterizing the dynamics of effusive eruptions and thus for assessing the volcanic hazard associated with this type of volcanism. Since the effusion rate curves can provide important insights into the properties of the magma feeding system, several efforts have been performed for their classification and interpretation. Here, a recently published numerical model is employed for studying the effects of magma source and feeding dike properties on the main characteristics (e.g., duration, erupted mass, and effusion rate trend) of small‐volume effusive eruptions, in the absence of syn‐eruptive magma injection from deeper storages. We show that the total erupted mass is mainly controlled by magma reservoir conditions (i.e., dimensions and overpressure) prior to the eruption, whereas conduit processes along with reservoir properties can significantly affect mean effusion rate, and thus, they dramatically influence eruption duration. Simulations reproduce a wide variety of effusion rate trends, whose occurrence is controlled by the complex competition between conduit enlargement and overpressure decrease due to magma withdrawal. These effusion rate curves were classified in four groups, which were associated with the different types described in the literature. Results agree with the traditional explanation of effusion rate curves and provide new insights for interpreting them, highlighting the importance of magma reservoir size, initial overpressure, and initial width of the feeding dike in controlling the nature of the resulting effusion rate curve.

Beschreibung: Published

Beschreibung: e2019JB01930

Beschreibung: 5V. Processi eruttivi e post-eruttivi

Beschreibung: JCR Journal

Beschreibung: Kinetic energy models, also called kinetic models, are simple tools able to provide a fast estimate of the inundation area of pyroclastic density currents (PDCs). They are based on the calculation of the PDC front kinetic energy as a function of the distance from a source point. On a three‐dimensional topography, the PDC runout distance is estimated by comparing the flow kinetic energy with the potential energy associated with the topographic obstacles encountered by the PDC. Since kinetic models do not consider the occurrence of channelization processes, the modeled inundation areas can be significantly different from those observed in real deposits. To address this point, we present a new strategy that allows improving kinetic models by considering flow channelization processes, and consists in the inclusion of secondary source points in the expected channelization zones, adopting a tree branch‐like structure. This strategy is based on the redistribution of a key physical variable, such as the flow energy or mass depending on the considered kinetic model, and requires the adoption of appropriate equations for setting the characteristics of the secondary sources. Two models were modified by applying this strategy: the energy cone and the box model. We tested these branching models by comparing their results with those derived from their traditional formulations and from a two‐dimensional depth‐averaged model, considering two specific volcanoes (Chaitén and Citlaltépetl). Thereby, we show the capability of this strategy of improving the accuracy of kinetic models and considering flow channelization processes without including additional, unconstrained input parameters.

Beschreibung: Published

Beschreibung: e2019JB019271

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

Beschreibung: JCR Journal