New insights into the relationship between mass eruption rate and volcanic column height based on the IVESPA data set

Rapid and simple estimation of the mass eruption rate (MER) from column height is essential for real-time volcanic hazard management and reconstruction of past explosive eruptions. Using 134 eruptive events from the new Independent Volcanic Eruption Source Parameter Archive (IVESPA, v1.0), we explore empirical MER-height relationships for four measures of column height: spreading level, sulfur dioxide height, and top height from direct observations and as reconstructed from deposits. These relationships show significant differences and highlight limitations of empirical models currently used in operational and research applications. The roles of atmospheric stratification, wind, and humidity remain challenging to detect across the wide range of eruptive conditions spanned in IVESPA, ultimately resulting in empirical relationships outperforming analytical models that account for atmospheric conditions. This finding highlights challenges in constraining the MER-height relation using heterogeneous observations and empirical models, which reinforces the need for improved eruption source parameter data sets and physics-based models

New Insights Into the Relationship Between Mass Eruption Rate and Volcanic Column Height Based On the IVESPA Data Set

Rapid and simple estimation of the mass eruption rate (MER) from column height is essential for real-time volcanic hazard management and reconstruction of past explosive eruptions. Using 134 eruptive events from the new Independent Volcanic Eruption Source Parameter Archive (IVESPA, v1.0), we explore empirical MER-height relationships for four measures of column height: spreading level, sulfur dioxide height, and top height from direct observations and as reconstructed from deposits. These relationships show significant differences and highlight limitations of empirical models currently used in operational and research applications. The roles of atmospheric stratification, wind, and humidity remain challenging to detect across the wide range of eruptive conditions spanned in IVESPA, ultimately resulting in empirical relationships outperforming analytical models that account for atmospheric conditions. This finding highlights challenges in constraining the MER-height relation using heterogeneous observations and empirical models, which reinforces the need for improved eruption source parameter data sets and physics-based models

The effect of total grain-size distribution on the dynamics of turbulent volcanic plumes

The impact of explosive volcanic plumes on climate and on air traffic strongly depends on the concentration and grain-size distribution (GSD) of pyroclastic fragments injected into the atmosphere. Accurate and robust modelling of the evolution of GSD during pyroclast transport from the vent to the ash cloud is therefore crucial for the assessment of major volcanic hazards. Analysis of field deposits from various recent Plinian eruptions shows that their total GSD is well described by a power law, as expected from the physics of magma fragmentation, with an exponent (D) ranging from 3.0 to 3.9. By incorporating these measured GSD into the initial conditions of a steady-state 1D model of explosive eruption columns, we show that they have a first-order impact on the dynamical behaviour of explosive eruption columns. Starting from an initial value of D, the model tracks the evolution of GSD in the column and calculates the dynamical consequences of particle sedimentation. The maximum height reached by the column, one of the first-order results relevant to aircraft safety, changes by 30% for mass fluxes of 107 kgs-1 or larger, and by 45–85% for mass fluxes between 105 and 107 kgs-1, depending on exponent D. We compare our predictions to a specially assembled set of geologic field data and remote sensing observations from 10 Plinian eruptions for which maximum column height and mass flux are known independently. The incorporation of realistic power-law GSD in the model greatly improves the predictions, which opens new perspectives for estimation of ash load and GSD in volcanic clouds from near real-time measurements available from satellite payloads. Our results also contribute to the improvement of volcanic source term characterization that is required input for meteorological dispersion models

The contribution of experimental volcanology to the study of the physics of eruptive processes, and related scaling issues: A review

International audienceThe experimental approach has become a major tool increasingly used by volcanologists in recent decades to investigate the physics of eruptive processes in complement to field and theoretical works. Researchers have developed various methodologies to study volcanic phenomena at reduced length scale. The works involve natural or analogue materials and their types range from first-order tests, to identify fundamental processes and make qualitative comparison with field observations, to more sophisticated experiments in which precise data obtained in a controlled environment can be used to validate outputs of theoretical models. Scaling is a central issue to ensure dynamic similarity between the small-scale experiments and the large-scale volcanic phenomena when natural conditions cannot be simulated due to inherent length scale difference and/or technical limitations. In this respect, dimensionless numbers are used to map physical regimes and to define scaling laws, which allow experimental results to be extrapolated to natural scale. This review presents the variety of experimental studies conducted to investigate subterraneous and aerial volcanic phenomena involving in particular fluid-particle mixtures. We focus on the major scaling issues and the physical regimes investigated, and we also highlight in a historical perspective some of the major advances achieved through experimental studies. Finally we conclude on some perspectives for future works

Granular mixture deflation and generation of pore fluid pressure at the impact zone of a pyroclastic fountain: Experimental insights

International audienceWe present the results of analogue laboratory experiments on pyroclastic fountain collapse. Mixtures of air and glass beads ranging in size around 75 ± 15 μm, with Stokes number of ~10−3−101 and representative of 0.1–1 mm sized particles in nature, were released from a hopper at heights of 0.45–2.95 m above the base of a horizontal channel. Free fall caused continuous dilation of the granular material and led to mean particle concentrations of ~9–36 vol%, with concentration inversely proportional to drop height, before the particles impacted the channel base. Decoupling between the particles and the ambient air upon impact caused deflation of the mixture, which then propagated laterally as a dense granular flowoverridden by a dilute suspension. Measurements at the impingement surface revealed that pore fluid pressure, generated through high air-particle relative velocity during deflation, counterbalanced up to ~50% of theweight of theemerging granular flow. The runout distance of the dense flow increased linearly with the fall height, similar to published results on unidirectional flows generated from collapse of packed granular columns. This suggests that the runout of flows resulting from release of granular material is controlled essentially by conversion of potential to kinetic energy and that the initial particle concentration is a second order parameter.We conclude that fountaining of pyroclastic material containing largeamounts of particles with Stokes numbers of the order 10−3−101 can generate dense pyroclastic flows with some degree of pore fluid pressure

The route to self-similarity in turbulent jets and plumes

International audienceThe description of entrainment in turbulent free jets is at the heart of physical models of some major flows in environmental science, from volcanic plumes to the dispersal of pollutant wastes. The classical approach relies on the assumption of complete self-similarity in the flows, which allows a simple parameterization of the dynamical variables in terms of constant scaling factors, but this hypothesis remains under debate. We use in this paper an original parameterization of entrainment and an extensive review of published experimental data to interpret the discrepancy between laboratory results in terms of the systematic evolution of the dynamic similarity of the flow as a function of downstream distance from the source. We show that both jets and plumes show a variety of local states of partial self-similarity in accordance with the theoretical analysis of George (1989), but that their global evolution tends to complete self-similarity via a universal route. Plumes reach this asymptotic regime faster than jets which suggests that buoyancy plays a role in more efficiently exciting large-scale modes of turbulence

Volcanic hazard assessment for tephra fallout in Martinique

International audienceMount Pelée (Martinique) is one of the most active volcanoes in the Lesser Antilles arc with more than 34 magmatic events in the last 24,000 years, including the deadliest eruption of the 20 th century. The current volcanic hazard map used in the civil security plan puts the emphasis on the volcanic hazard close to the volcano. This map is however based on an incomplete eruptive history and does not take into account the variability of the expected source conditions (mass eruption rate, total erupted mass, and grain-size distribution) or the wind effect on ash dispersal. We propose here to refine the volcanic hazard map for tephra fallout by using the 2-D model of ash dispersal HAZMAP. We first simulate the maximum expected eruptive scenario at Mount Pelée (i.e., the P3 eruption) using a seasonal wind profile. Building upon the good agreement with field data, we compute probability maps based on this maximum expected scenario, which show that tephra fallout hazard could threaten not only areas close to the volcano but also the southern part of Martinique. We then use a comprehensive approach based on 16 eruptive scenarios that include new field constraints obtained in the recent years on the past Plinian eruptions of Mount Pelée volcano. Each eruptive scenario considers different values of total erupted mass and mass eruption rate, and is characterized by a given probability of occurrence estimated from the refined eruptive history of the volcano. The 1979-2019 meteorological ERA-5 database is used to further take into account the daily variability of winds. These new probability maps show that the area of probable total destruction is wider when considering the 16 scenarios compared to the maximum expected scenario. The southern part of Martinique, although less threatened than when considering the maximum expected scenario, would still be impacted both by tephra fallout and by its high dependence on the water and electrical network carried from the northern part of the island. Finally, we show that key infrastructures in Martinique (such as the international airport) have a non-negligible probability of being impacted by a future Plinian eruption of the Mount Pelée. These results provide strong arguments for and will support significant and timely reconceiving of the emergency procedures as the local authorities have now placed Mount Pelée volcano on alert level yellow (vigilance) based on increased seismicity and tremor-type signals

Marginally stable recent Plinian eruptions of Mt. Pelée volcano (Lesser Antilles): the P2 AD 280 eruption

International audienceMajor volcanic hazards in the Lesser Antilles arc include powerful Plinian explosive eruptions that inject ash high into the atmosphere and produce dangerous pyroclastic density currents (PDC) on the ground. Understanding the key physical processes governing the dynamics and stability of past volcanic columns is a fundamental problem in volcanology as well as being central to assessing specific hazards in this region and elsewhere. However, the number of cases for which the transition of regime between a stable and collapsing eruptive plume is described in detail remains too small to constrain fully theoretical models of volcanic plumes. Here we present a detailed reconstruction of the time evolution of the P2 AD 280 eruption at Mt. Pelee volcano in Martinique, to expand the database available to test physical models. The P2 sequence, which forced the first inhabitants to flee to other islands for decades as suggested by archaeological evidence, starts with a basal ash layer interpreted as the result of an initial violent laterally directed explosion to the NE of the volcano. Most of the deposit sequence is made of a pumice fall deposit interbedded with a low-concentration PDC deposit interpreted as the result of a partial column collapse. The upper pumice fall unit shows an inverse gradation and is overlain by a final high-concentration PDC deposit or locally by the correlative low-concentration PDC deposit. Field data on deposit dispersal, thickness, and grain-size distribution are used together with physical models to reconstruct the dynamic evolution of this eruption. Empirical models of deposit thinning suggest that the minimum volume of pyroclastic deposits is 0.67-0.88km(3) dense rock equivalent (DRE), much larger than the 0.17km(3) DRE previously estimated. We find that the mass eruption rate increased from 6x10(7) to 1.1x10(8)kgs(-1), producing an initially stable 23- to 26-km-high Plinian plume, which ultimately collapsed to form a fountain. We discuss the mechanisms leading to column collapse based on published data on magmatic water contents and our estimates of grain-size distributions and mass discharge rates. The eruption started close to the plume/fountain transition and the volcanic column ultimately collapsed mainly due to an increase in mass discharge rate. This marginally stable evolution was also inferred from analysis of the P1 AD 1300 eruption deposits, suggesting consistent behavior during the recent Plinian eruptions of Mt. Pelee volcano. In these two eruptions, the transition occurred at conditions well predicted by our theoretical model of volcanic plumes

The timing and intensity of column collapse during explosive volcanic eruptions

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New physical description of turbulence and implications for explosive volcanic flows

Les gaz et les cendres injectés dans l'atmosphère au cours d'une éruption volcanique explosive représentent une menace pour les populations, les biens et l'environnement. Cette menace est d'autant plus élevée lorsque le jet volcanique s'effondre sur lui-même et génère des écoulements pyroclastiques. L'étude des éruptions Pliniennes du volcan de la Montagne Pelée révèle que les modèles théoriques de prédiction d'effondrement de colonne souffrent d'un décalage avec les données recueillies sur le terrain. Le but de cette thèse est de comprendre quel est l'ingrédient physique qui manque aux modèles pour être en accord avec les données géologiques. Un nouveau modèle d'entraînement de fluide environnant au sein d'un jet turbulent est présenté. Celui-ci permet de remettre en cohérence de nombreuses données expérimentales sur des jets turbulents générés en laboratoire, et son application à la prédiction d'effondrement de colonnes volcaniques est tout à fait satisfaisante. L'effet nouvellement mis en lumière a une forte influence sur le comportement du jet volcanique et a des implications importantes sur les estimations de flux mis en jeu lors d'éruptions explosives. Pour aller plus loin dans l'étude de la dynamique des colonnes explosives, un dispositif expérimental inédit produisant des jets de gaz chaud chargés en particules a été élaboré. Ce dispositif permet de reproduire pour la première fois le régime d'effondrement partiel où le jet volcanique se sépare en une partie dense et une partie plus légère. Ces résultats apportent une meilleure compréhension de la dynamique d'un jet turbulent en général, et améliorent les modèles théoriques actuels de colonnes volcaniques.PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF