Manuscript with tracked changes Click here to access/download;Miscellaneous;Manuscript_tc.docx Th... more Manuscript with tracked changes Click here to access/download;Miscellaneous;Manuscript_tc.docx This research was financed by the French government IDEX-ISITE initiative 16-IDEX-0001 (CAP 20-25), the French Research Institute for Sustainable Development (IRD) in the context of the Laboratoire Mixte International "Séismes et Volcans dans les Andes du Nord", and the CNRS Tellus program. This work was also partly funded by the ClerVolc project-Program 1 "Detection and characterization of volcanic plumes and ash clouds" funded by the French government 'Laboratory of Excellence' initiative. This is ClerVolc contribution n°477.
We introduce a doubly stochastic method for performing material failure theory based forecasts of... more We introduce a doubly stochastic method for performing material failure theory based forecasts of volcanic eruptions. The method enhances the well known Failure Forecast Method equation, introducing a new formulation similar to the Hull-White model in financial mathematics. In particular, we incorporate a stochastic noise term in the original equation, and systematically characterize the uncertainty. The model is a stochastic differential equation with mean reverting paths, where the traditional ordinary differential equation defines the mean solution. Our implementation allows the model to make excursions from the classical solutions, by including uncertainty in the estimation. The doubly stochastic formulation is particularly powerful, in that it provides a complete posterior probability distribution, allowing users to determine a worst case scenario with a specified level of confidence. We apply the new method on historical datasets of precursory signals, across a wide range of possible values of convexity in the solutions and amounts of scattering in the observations. The results show the increased forecasting skill of the doubly stochastic formulation of the equations if compared to statistical regression.
The dynamics of effusive events is controlled by the interplay between conduit geometry and sourc... more The dynamics of effusive events is controlled by the interplay between conduit geometry and source conditions. Dyke-like geometries have been traditionally assumed for describing conduits during effusive eruptions, but their depth-dependent and temporal modifications are largely unknown. We present a novel model which describes the evolution of conduit geometry during effusive eruptions by using a quasi steady state approach based on a 1-D conduit model and appropriate criteria for describing fluid shear stress and elastic deformation. This approach provides time-dependent trends for effusion rate, conduit geometry, exit velocity, and gas flow. Fluid shear stress leads to upward widening conduits, whereas elastic deformation becomes relevant only during final phases of effusive eruptions. Simulations can reproduce different trends of effusion rate, showing the effect of magma source conditions and country rock properties on the eruptive dynamics. This model can be potentially applied for data inversion in order to study specific case studies. Plain Language Summary The dynamics of effusive eruptions is controlled by the interplay between the feeding conduit geometry and magma chamber conditions. Dyke-like geometries have been traditionally assumed for describing conduits of effusive eruptions, but their depth-dependent and temporal modifications are largely unknown. Conduit geometry is controlled by fluid shear stress and pressure-driven elastic deformation, which depend on magma and host rock properties. Here we present a novel model for studying the temporal evolution of effusive eruptions, using a steady-state conduit model and appropriate criteria for describing the temporal evolution of conduit geometry. Model inputs are related to host rock properties, magma source conditions, and some additional equations for describing the ascending magma behavior. The model provides time-dependent trends for effusion rate, conduit geometry, exit velocity, and gas flow. Because of the typical magma viscosity and velocity profiles along the conduit, they tend to produce higher erosion rates near the vent, giving place to upward widening conduits. Simulations are compatible with the erosion rates estimated for natural cases and are able to reproduce different curves of effusion rate. This model can be potentially applied for data inversion in order to study magma reservoir dynamics and conduit geometry evolution during specific case studies.
Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy, 1999
ABSTRACT The net effect of liquid magma composition and water content on the behavior of explosiv... more ABSTRACT The net effect of liquid magma composition and water content on the behavior of explosive volcanic eruptions was investigated by the use of numerical simulation. The two-phase flow models employed allow description of the eruptive process from the conduit entrance at the top of the magma chamber up to the pyroclastic dispersion processes in the atmosphere. Results indicate a strong influence of magma composition on eruption intensity, whereas the eruptive style appears to be mainly controlled by the total water content.
In this study, using the tephra dispersal model HAZMAP, we investigate the effect of using differ... more In this study, using the tephra dispersal model HAZMAP, we investigate the effect of using different meteorological datasets and eruption source parameters on tephra fallout hazard assessment for a sub-Plinian eruption of Vesuvius, which is considered as a reference case for hazard assessment analysis. We analyze the effect of using different meteorological data, from: i) radio-sounding carried out at the meteorological station of Brindisi (Italy) between 1962 and 1976 and between 1996 and 2012, and at Pratica di Mare (Rome, Italy) between 1995 and 2013; ii) meteorological models of the National Oceanic and Atmospheric Administration (NOAA), and of the European Centre for Medium-Range Weather Forecasts (ECMWF). Furthermore, we consider the effects of perturbing reference eruptive source parameters. In particular, we vary the total mass, the total grain-size distribution, the column height, and the effective atmospheric diffusion coefficient to evaluate how these parameters affect the hazard probability maps. Moreover, the effect of the seasonal variation of the wind field and the effect of the rain on the deposit loading are considered. Results show that the parameter that mostly affects hazard maps is, as expected, the total erupted mass; furthermore, keeping constant the erupted mass, the most important control on hazard is due to the particle terminal settling velocity distribution which is a function of the total grain-size distribution, particle density and shape. Within the considered range variations, the hazard depends less on the use of different meteorological datasets, column height and effective diffusion coefficient.
Journal of Volcanology and Geothermal Research, 2016
This study compares and evaluates one-dimensional (1D) and three-28 dimensional (3D) numerical mo... more This study compares and evaluates one-dimensional (1D) and three-28 dimensional (3D) numerical models of volcanic eruption columns in a set of different 29 inter-comparison exercises. The exercises were designed as a blind test in which a set 30 of common input parameters was given for two reference eruptions, representing a 31 strong and a weak eruption column under different meteorological conditions. 32 Comparing the results of the different models allows us to evaluate their capabilities 33 and target areas for future improvement. Despite their different formulations, the 1D 34 and 3D models provide reasonably consistent predictions of some of the key global 35 descriptors of the volcanic plumes. Variability in plume height, estimated from the 36 standard deviation of model predictions, is within ~20% for the weak plume and 37 ~1 0% for the strong plume. Predictions of neutral buoyancy level are also in 38 reasonably good agreement among the different models, with a standard deviation 39 ranging from 9 to 19% (the latter for the weak plume in a windy atmosphere). 40 Overall, these discrepancies are in the range of observational uncertainty of column 41 height. However, there are important differences amongst models in terms of local 42 properties along the plume axis, particularly for the strong plume. Our analysis 43 suggests that the simplified treatment of entrainment in 1D models is adequate to 44 resolve the general behaviour of the weak plume. However, it is inadequate to capture 45 complex features of the strong plume, such as large vortices, partial column collapse, 46 or gravitational fountaining that strongly enhance entrainment in the lower 47 atmosphere. We conclude that there is a need to more accurately quantify entrainment 48 rates, improve the representation of plume radius, and incorporate the effects of 49 column instability in future versions of 1D volcanic plume models.
When a stratified pyroclastic density current (PDC) encounters a topographic barrier, its basal a... more When a stratified pyroclastic density current (PDC) encounters a topographic barrier, its basal and more concentrated portion is blocked and can decouple from the upper part, forming dense diverted lateral flows and/or back-currents. The more dilute part of the current may be able to overcome the obstacle while part of the finest material eventually lifts off forming co-ignimbrite buoyant plumes. The manner by which PDCs propagate across 3D topography affects their vertical profile, dynamic properties and their final runout distance, making its description fundamental for the assessment of volcanic hazard. We studied the interaction of pyroclastic density currents with topographic ridges by means of 3D multiphase flow numerical simulations. As an application, we analyzed the influence of topographic obstacles on the vertical structure, propagation and runout of PDCs at the Campi Flegrei caldera (Italy), whose complex morphological environment is the result of the superposition of se...
Campi Flegrei is a densely populated widespread caldera located near the city of Naples. Current ... more Campi Flegrei is a densely populated widespread caldera located near the city of Naples. Current evaluation of volcanic hazard include the probable generation of pyroclastic density currents (PDC) produced by explosive events of variable size and uncertain vent location. In this study we investigate the dynamics and hazard of PDC produced by the partial collapse of the volcanic column by using the 3D transient multiphase flow model PDAC (Esposti Ongaro et al., Parallel Computing, 2007). The model allows to describe the temporal and spatial evolution of the stratified PDC by accounting for the multiparticle nature of the flow and the complex topography of the caldera. Employed eruptive intensity and pyroclast properties are representative of magmatic phases of the Agnano Monte Spina (AMS, 4100 BP) Plinian eruption, the largest explosive event of the last cycle of activity of the caldera. Eruptive centers are supposed to be located in the north-eastern part of the caldera, the area wi...
Numerical modeling of explosive volcanic eruptions has been widely applied, during the last decad... more Numerical modeling of explosive volcanic eruptions has been widely applied, during the last decades, to study pyroclastic flows dispersion along volcano's flanks and to evaluate their impact on urban areas. Results from these transient multi-phase and multi-component simulations are often reproduced in form of computer animations, representing the spatial and temporal evolution of relevant flow variables (such as temperature, or
Mapping of pyroclastic density current (PDC) hazard is particularly challenging due to the comple... more Mapping of pyroclastic density current (PDC) hazard is particularly challenging due to the complex dynamics of the flow and the uncertain nature of future events. Such a task is even more difficult in a caldera setting due to the large uncertainty on vent location and the complex topography affecting the flow propagation. Nevertheless, probabilistic mapping of PDC invasion, able to account for the significant intrinsic uncertainties affecting the system, is needed for both long- and short-term hazard assessment. Campi Flegrei is an example of active and densely urbanized caldera with a very high risk associated with the occurrence of PDC produced by explosive events of variable scale and vent location. In this study we present preliminary results of literature review, field and laboratory work, and statistical analysis of past eruptive activity aimed at producing long-term probabilistic PDC hazard maps at Campi Flegrei. Particular attention was given to the analysis of the volcanic ...
Supplementary Information accompanies the paper on Nature's website (http://www.nature.com). Ackn... more Supplementary Information accompanies the paper on Nature's website (http://www.nature.com). Acknowledgements We thank B. Hedman and K. O. Hodgson for support and facilities at SSRL, L. Go Èthe for technical assistance, and B. Lundvall at the Vasa Museum for core sampling and information.
Journal of Volcanology and Geothermal Research, 2005
The temporal evolution of fundamental flow conditions in the magma chamber plus conduit system–su... more The temporal evolution of fundamental flow conditions in the magma chamber plus conduit system–such as pressure, velocity, mass flow-rate, erupted mass, etc.–during sustained magmatic explosive eruptions was investigated. To this aim, simplified one-dimensional and isothermal models of magma chamber emptying and conduit flow were developed and coupled together. The chamber model assumed an homogeneous composition of magma and a vertical
Journal of Volcanology and Geothermal Research, 2006
Dissemination of scientific results to the general public has become increasingly important in ou... more Dissemination of scientific results to the general public has become increasingly important in our society. When science deals with natural hazards, public outreach is even more important: on the one hand, it contributes to hazard perception and it is a necessary step toward preparedness and risk mitigation; on the other hand, it contributes to establish a positive link of mutual confidence between scientific community and the population living at risk. The existence of such a link plays a relevant role in hazard communication, which in turn is essential to mitigate the risk. In this work, we present a tool that we have developed to illustrate our scientific results on pyroclastic flow propagation at Vesuvius. This tool, a CD-ROM that we developed joining scientific data with appropriate knowledge in communication sciences is meant to be a first prototype that will be used to test the validity of this approach to public outreach. The multimedia guide contains figures, images of real volcanoes and computer animations obtained through numerical modeling of pyroclastic density currents. Explanatory text, kept as short and simple as possible, illustrates both the process and the methodology applied to study this very dangerous natural phenomenon. In this first version, the CD-ROM will be distributed among selected categories of end-users together with a short questionnaire that we have drawn to test its readability. Future releases will include feedback from the users, further advancement of scientific results as well as a higher degree of interactivity.
Journal of Volcanology and Geothermal Research, 1998
The role of anhydrous magma composition, water content, and crystal content on the dynamics of ex... more The role of anhydrous magma composition, water content, and crystal content on the dynamics of explosive eruptions is investigated by modeling the ascent of magma along volcanic conduits and the subsequent pyroclastic dispersion in the w atmosphere, described in a companion paper Neri, A., Papale, P., Macedonio, G., 1998. The role of magma composition x and water content in explosive eruptions: 2. Pyroclastic dispersion dynamics. J. Volcanol. Geotherm. Res., 87, 95-115.. The conduit model used is based on the solution of the fundamental transport equations assuming steady-state and isothermal flow conditions, and includes a composition-based description of magma properties and their variations along the conduit. This study stems from the well-documented vertical compositional variation of many pyroclastic deposits, often associated with reconstructed variations in initial water content. The results of the modeling show complex and sometimes non-intuitive dependence of the distribution of the flow variables on magma composition, crystal and water contents. In general, a water content decrease is expected to produce a decrease in mass flow-rate, decrease in pressure and velocity along the conduit, an increase in the exit gas volume fraction, and a decrease in velocity, pressure, and mixture density at the conduit exit. Reverse variations are expected to occur by decreasing the degree of chemical evolution of the liquid at a constant water content, apart from exit velocities which show more complex variations. The overall effect of increasing crystals is in general similar to that of increasing the degree of chemical evolution of the liquid, or decreasing the water content. The above results are to a large extent interpreted in terms of variations in magma viscosity, which is recognized as the critical magma property besides water content in the dynamics of magma ascent. The common compositional trend of explosive eruptions characterized by chemically evolved, water-richer and crystal-poorer magma erupted first is predicted to be associated with variations in the evolution of the eruption dynamics, depending on the relative magnitude of the changes. However, the exit velocity always decreases in the above trend, and the mass flow-rate increases in most relevant cases, comparing well with the results of chemical and stratigraphic studies of the deposits from explosive eruptions.
Journal of Volcanology and Geothermal Research, 2008
Numerical simulations of column collapse and pyroclastic density current (PDC) scenarios at Vesuv... more Numerical simulations of column collapse and pyroclastic density current (PDC) scenarios at Vesuvius were carried out using a transient 3D flow model based on multiphase transport laws. The model describes the dynamics of the collapse as well as the effects of the 3D topography of the volcano on PDC propagation. Source conditions refer to a medium-scale sub-Plinian event and consider a pressure-balanced jet. Simulation results provide new insights into the complex dynamics of these phenomena. In particular: 1) column collapse can be characterized by different regimes, from incipient collapse to partial or nearly total collapse, thus confirming the possibility of a transitional field of behaviour of the column characterized by the contemporaneous and/or intermittent occurrence of ash fallout and PDCs; 2) the collapse regime can be characterized by its fraction of eruptive mass reaching the ground and generating PDCs; 3) within the range of the investigated source conditions, the propagation and hazard potential of PDCs appear to be directly correlated with the flow-rate of the mass collapsing to the ground, rather than to the collapse height of the column (this finding is in contrast with predictions based on the energy-line concept, which simply correlates the PDC runout and kinetic energy with the collapse height of the column); 4) first-order values of hazard variables associated with PDCs (i.e., dynamic pressure, temperature, airborne ash concentration) can be derived from simulation results, thereby providing initial estimates for the quantification of damage scenarios; 5) for scenarios assuming a location of the central vent coinciding with that of the present Gran Cono, Mount Somma significantly influences the propagation of PDCs, largely reducing their propagation in the northern sector, and diverting mass toward the west and southeast, accentuating runouts and hazard variables for these sectors; 6) the 2D modelling approximation can force an artificial radial propagation of the PDCs since it ignores azimuthal flows produced by real topographies that therefore need to be simulated in fully 3D conditions.
Manuscript with tracked changes Click here to access/download;Miscellaneous;Manuscript_tc.docx Th... more Manuscript with tracked changes Click here to access/download;Miscellaneous;Manuscript_tc.docx This research was financed by the French government IDEX-ISITE initiative 16-IDEX-0001 (CAP 20-25), the French Research Institute for Sustainable Development (IRD) in the context of the Laboratoire Mixte International "Séismes et Volcans dans les Andes du Nord", and the CNRS Tellus program. This work was also partly funded by the ClerVolc project-Program 1 "Detection and characterization of volcanic plumes and ash clouds" funded by the French government 'Laboratory of Excellence' initiative. This is ClerVolc contribution n°477.
We introduce a doubly stochastic method for performing material failure theory based forecasts of... more We introduce a doubly stochastic method for performing material failure theory based forecasts of volcanic eruptions. The method enhances the well known Failure Forecast Method equation, introducing a new formulation similar to the Hull-White model in financial mathematics. In particular, we incorporate a stochastic noise term in the original equation, and systematically characterize the uncertainty. The model is a stochastic differential equation with mean reverting paths, where the traditional ordinary differential equation defines the mean solution. Our implementation allows the model to make excursions from the classical solutions, by including uncertainty in the estimation. The doubly stochastic formulation is particularly powerful, in that it provides a complete posterior probability distribution, allowing users to determine a worst case scenario with a specified level of confidence. We apply the new method on historical datasets of precursory signals, across a wide range of possible values of convexity in the solutions and amounts of scattering in the observations. The results show the increased forecasting skill of the doubly stochastic formulation of the equations if compared to statistical regression.
The dynamics of effusive events is controlled by the interplay between conduit geometry and sourc... more The dynamics of effusive events is controlled by the interplay between conduit geometry and source conditions. Dyke-like geometries have been traditionally assumed for describing conduits during effusive eruptions, but their depth-dependent and temporal modifications are largely unknown. We present a novel model which describes the evolution of conduit geometry during effusive eruptions by using a quasi steady state approach based on a 1-D conduit model and appropriate criteria for describing fluid shear stress and elastic deformation. This approach provides time-dependent trends for effusion rate, conduit geometry, exit velocity, and gas flow. Fluid shear stress leads to upward widening conduits, whereas elastic deformation becomes relevant only during final phases of effusive eruptions. Simulations can reproduce different trends of effusion rate, showing the effect of magma source conditions and country rock properties on the eruptive dynamics. This model can be potentially applied for data inversion in order to study specific case studies. Plain Language Summary The dynamics of effusive eruptions is controlled by the interplay between the feeding conduit geometry and magma chamber conditions. Dyke-like geometries have been traditionally assumed for describing conduits of effusive eruptions, but their depth-dependent and temporal modifications are largely unknown. Conduit geometry is controlled by fluid shear stress and pressure-driven elastic deformation, which depend on magma and host rock properties. Here we present a novel model for studying the temporal evolution of effusive eruptions, using a steady-state conduit model and appropriate criteria for describing the temporal evolution of conduit geometry. Model inputs are related to host rock properties, magma source conditions, and some additional equations for describing the ascending magma behavior. The model provides time-dependent trends for effusion rate, conduit geometry, exit velocity, and gas flow. Because of the typical magma viscosity and velocity profiles along the conduit, they tend to produce higher erosion rates near the vent, giving place to upward widening conduits. Simulations are compatible with the erosion rates estimated for natural cases and are able to reproduce different curves of effusion rate. This model can be potentially applied for data inversion in order to study magma reservoir dynamics and conduit geometry evolution during specific case studies.
Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy, 1999
ABSTRACT The net effect of liquid magma composition and water content on the behavior of explosiv... more ABSTRACT The net effect of liquid magma composition and water content on the behavior of explosive volcanic eruptions was investigated by the use of numerical simulation. The two-phase flow models employed allow description of the eruptive process from the conduit entrance at the top of the magma chamber up to the pyroclastic dispersion processes in the atmosphere. Results indicate a strong influence of magma composition on eruption intensity, whereas the eruptive style appears to be mainly controlled by the total water content.
In this study, using the tephra dispersal model HAZMAP, we investigate the effect of using differ... more In this study, using the tephra dispersal model HAZMAP, we investigate the effect of using different meteorological datasets and eruption source parameters on tephra fallout hazard assessment for a sub-Plinian eruption of Vesuvius, which is considered as a reference case for hazard assessment analysis. We analyze the effect of using different meteorological data, from: i) radio-sounding carried out at the meteorological station of Brindisi (Italy) between 1962 and 1976 and between 1996 and 2012, and at Pratica di Mare (Rome, Italy) between 1995 and 2013; ii) meteorological models of the National Oceanic and Atmospheric Administration (NOAA), and of the European Centre for Medium-Range Weather Forecasts (ECMWF). Furthermore, we consider the effects of perturbing reference eruptive source parameters. In particular, we vary the total mass, the total grain-size distribution, the column height, and the effective atmospheric diffusion coefficient to evaluate how these parameters affect the hazard probability maps. Moreover, the effect of the seasonal variation of the wind field and the effect of the rain on the deposit loading are considered. Results show that the parameter that mostly affects hazard maps is, as expected, the total erupted mass; furthermore, keeping constant the erupted mass, the most important control on hazard is due to the particle terminal settling velocity distribution which is a function of the total grain-size distribution, particle density and shape. Within the considered range variations, the hazard depends less on the use of different meteorological datasets, column height and effective diffusion coefficient.
Journal of Volcanology and Geothermal Research, 2016
This study compares and evaluates one-dimensional (1D) and three-28 dimensional (3D) numerical mo... more This study compares and evaluates one-dimensional (1D) and three-28 dimensional (3D) numerical models of volcanic eruption columns in a set of different 29 inter-comparison exercises. The exercises were designed as a blind test in which a set 30 of common input parameters was given for two reference eruptions, representing a 31 strong and a weak eruption column under different meteorological conditions. 32 Comparing the results of the different models allows us to evaluate their capabilities 33 and target areas for future improvement. Despite their different formulations, the 1D 34 and 3D models provide reasonably consistent predictions of some of the key global 35 descriptors of the volcanic plumes. Variability in plume height, estimated from the 36 standard deviation of model predictions, is within ~20% for the weak plume and 37 ~1 0% for the strong plume. Predictions of neutral buoyancy level are also in 38 reasonably good agreement among the different models, with a standard deviation 39 ranging from 9 to 19% (the latter for the weak plume in a windy atmosphere). 40 Overall, these discrepancies are in the range of observational uncertainty of column 41 height. However, there are important differences amongst models in terms of local 42 properties along the plume axis, particularly for the strong plume. Our analysis 43 suggests that the simplified treatment of entrainment in 1D models is adequate to 44 resolve the general behaviour of the weak plume. However, it is inadequate to capture 45 complex features of the strong plume, such as large vortices, partial column collapse, 46 or gravitational fountaining that strongly enhance entrainment in the lower 47 atmosphere. We conclude that there is a need to more accurately quantify entrainment 48 rates, improve the representation of plume radius, and incorporate the effects of 49 column instability in future versions of 1D volcanic plume models.
When a stratified pyroclastic density current (PDC) encounters a topographic barrier, its basal a... more When a stratified pyroclastic density current (PDC) encounters a topographic barrier, its basal and more concentrated portion is blocked and can decouple from the upper part, forming dense diverted lateral flows and/or back-currents. The more dilute part of the current may be able to overcome the obstacle while part of the finest material eventually lifts off forming co-ignimbrite buoyant plumes. The manner by which PDCs propagate across 3D topography affects their vertical profile, dynamic properties and their final runout distance, making its description fundamental for the assessment of volcanic hazard. We studied the interaction of pyroclastic density currents with topographic ridges by means of 3D multiphase flow numerical simulations. As an application, we analyzed the influence of topographic obstacles on the vertical structure, propagation and runout of PDCs at the Campi Flegrei caldera (Italy), whose complex morphological environment is the result of the superposition of se...
Campi Flegrei is a densely populated widespread caldera located near the city of Naples. Current ... more Campi Flegrei is a densely populated widespread caldera located near the city of Naples. Current evaluation of volcanic hazard include the probable generation of pyroclastic density currents (PDC) produced by explosive events of variable size and uncertain vent location. In this study we investigate the dynamics and hazard of PDC produced by the partial collapse of the volcanic column by using the 3D transient multiphase flow model PDAC (Esposti Ongaro et al., Parallel Computing, 2007). The model allows to describe the temporal and spatial evolution of the stratified PDC by accounting for the multiparticle nature of the flow and the complex topography of the caldera. Employed eruptive intensity and pyroclast properties are representative of magmatic phases of the Agnano Monte Spina (AMS, 4100 BP) Plinian eruption, the largest explosive event of the last cycle of activity of the caldera. Eruptive centers are supposed to be located in the north-eastern part of the caldera, the area wi...
Numerical modeling of explosive volcanic eruptions has been widely applied, during the last decad... more Numerical modeling of explosive volcanic eruptions has been widely applied, during the last decades, to study pyroclastic flows dispersion along volcano's flanks and to evaluate their impact on urban areas. Results from these transient multi-phase and multi-component simulations are often reproduced in form of computer animations, representing the spatial and temporal evolution of relevant flow variables (such as temperature, or
Mapping of pyroclastic density current (PDC) hazard is particularly challenging due to the comple... more Mapping of pyroclastic density current (PDC) hazard is particularly challenging due to the complex dynamics of the flow and the uncertain nature of future events. Such a task is even more difficult in a caldera setting due to the large uncertainty on vent location and the complex topography affecting the flow propagation. Nevertheless, probabilistic mapping of PDC invasion, able to account for the significant intrinsic uncertainties affecting the system, is needed for both long- and short-term hazard assessment. Campi Flegrei is an example of active and densely urbanized caldera with a very high risk associated with the occurrence of PDC produced by explosive events of variable scale and vent location. In this study we present preliminary results of literature review, field and laboratory work, and statistical analysis of past eruptive activity aimed at producing long-term probabilistic PDC hazard maps at Campi Flegrei. Particular attention was given to the analysis of the volcanic ...
Supplementary Information accompanies the paper on Nature's website (http://www.nature.com). Ackn... more Supplementary Information accompanies the paper on Nature's website (http://www.nature.com). Acknowledgements We thank B. Hedman and K. O. Hodgson for support and facilities at SSRL, L. Go Èthe for technical assistance, and B. Lundvall at the Vasa Museum for core sampling and information.
Journal of Volcanology and Geothermal Research, 2005
The temporal evolution of fundamental flow conditions in the magma chamber plus conduit system–su... more The temporal evolution of fundamental flow conditions in the magma chamber plus conduit system–such as pressure, velocity, mass flow-rate, erupted mass, etc.–during sustained magmatic explosive eruptions was investigated. To this aim, simplified one-dimensional and isothermal models of magma chamber emptying and conduit flow were developed and coupled together. The chamber model assumed an homogeneous composition of magma and a vertical
Journal of Volcanology and Geothermal Research, 2006
Dissemination of scientific results to the general public has become increasingly important in ou... more Dissemination of scientific results to the general public has become increasingly important in our society. When science deals with natural hazards, public outreach is even more important: on the one hand, it contributes to hazard perception and it is a necessary step toward preparedness and risk mitigation; on the other hand, it contributes to establish a positive link of mutual confidence between scientific community and the population living at risk. The existence of such a link plays a relevant role in hazard communication, which in turn is essential to mitigate the risk. In this work, we present a tool that we have developed to illustrate our scientific results on pyroclastic flow propagation at Vesuvius. This tool, a CD-ROM that we developed joining scientific data with appropriate knowledge in communication sciences is meant to be a first prototype that will be used to test the validity of this approach to public outreach. The multimedia guide contains figures, images of real volcanoes and computer animations obtained through numerical modeling of pyroclastic density currents. Explanatory text, kept as short and simple as possible, illustrates both the process and the methodology applied to study this very dangerous natural phenomenon. In this first version, the CD-ROM will be distributed among selected categories of end-users together with a short questionnaire that we have drawn to test its readability. Future releases will include feedback from the users, further advancement of scientific results as well as a higher degree of interactivity.
Journal of Volcanology and Geothermal Research, 1998
The role of anhydrous magma composition, water content, and crystal content on the dynamics of ex... more The role of anhydrous magma composition, water content, and crystal content on the dynamics of explosive eruptions is investigated by modeling the ascent of magma along volcanic conduits and the subsequent pyroclastic dispersion in the w atmosphere, described in a companion paper Neri, A., Papale, P., Macedonio, G., 1998. The role of magma composition x and water content in explosive eruptions: 2. Pyroclastic dispersion dynamics. J. Volcanol. Geotherm. Res., 87, 95-115.. The conduit model used is based on the solution of the fundamental transport equations assuming steady-state and isothermal flow conditions, and includes a composition-based description of magma properties and their variations along the conduit. This study stems from the well-documented vertical compositional variation of many pyroclastic deposits, often associated with reconstructed variations in initial water content. The results of the modeling show complex and sometimes non-intuitive dependence of the distribution of the flow variables on magma composition, crystal and water contents. In general, a water content decrease is expected to produce a decrease in mass flow-rate, decrease in pressure and velocity along the conduit, an increase in the exit gas volume fraction, and a decrease in velocity, pressure, and mixture density at the conduit exit. Reverse variations are expected to occur by decreasing the degree of chemical evolution of the liquid at a constant water content, apart from exit velocities which show more complex variations. The overall effect of increasing crystals is in general similar to that of increasing the degree of chemical evolution of the liquid, or decreasing the water content. The above results are to a large extent interpreted in terms of variations in magma viscosity, which is recognized as the critical magma property besides water content in the dynamics of magma ascent. The common compositional trend of explosive eruptions characterized by chemically evolved, water-richer and crystal-poorer magma erupted first is predicted to be associated with variations in the evolution of the eruption dynamics, depending on the relative magnitude of the changes. However, the exit velocity always decreases in the above trend, and the mass flow-rate increases in most relevant cases, comparing well with the results of chemical and stratigraphic studies of the deposits from explosive eruptions.
Journal of Volcanology and Geothermal Research, 2008
Numerical simulations of column collapse and pyroclastic density current (PDC) scenarios at Vesuv... more Numerical simulations of column collapse and pyroclastic density current (PDC) scenarios at Vesuvius were carried out using a transient 3D flow model based on multiphase transport laws. The model describes the dynamics of the collapse as well as the effects of the 3D topography of the volcano on PDC propagation. Source conditions refer to a medium-scale sub-Plinian event and consider a pressure-balanced jet. Simulation results provide new insights into the complex dynamics of these phenomena. In particular: 1) column collapse can be characterized by different regimes, from incipient collapse to partial or nearly total collapse, thus confirming the possibility of a transitional field of behaviour of the column characterized by the contemporaneous and/or intermittent occurrence of ash fallout and PDCs; 2) the collapse regime can be characterized by its fraction of eruptive mass reaching the ground and generating PDCs; 3) within the range of the investigated source conditions, the propagation and hazard potential of PDCs appear to be directly correlated with the flow-rate of the mass collapsing to the ground, rather than to the collapse height of the column (this finding is in contrast with predictions based on the energy-line concept, which simply correlates the PDC runout and kinetic energy with the collapse height of the column); 4) first-order values of hazard variables associated with PDCs (i.e., dynamic pressure, temperature, airborne ash concentration) can be derived from simulation results, thereby providing initial estimates for the quantification of damage scenarios; 5) for scenarios assuming a location of the central vent coinciding with that of the present Gran Cono, Mount Somma significantly influences the propagation of PDCs, largely reducing their propagation in the northern sector, and diverting mass toward the west and southeast, accentuating runouts and hazard variables for these sectors; 6) the 2D modelling approximation can force an artificial radial propagation of the PDCs since it ignores azimuthal flows produced by real topographies that therefore need to be simulated in fully 3D conditions.
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Papers by Augusto Neri