Academic literature on the topic 'Volcanologie expérimentale'
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Journal articles on the topic "Volcanologie expérimentale":
Le Losq, Charles, and Matthieu Micoulaut. "Simuler le verre." Reflets de la physique, no. 74 (December 2022): 34–38. http://dx.doi.org/10.1051/refdp/202274034.
Dissertations / Theses on the topic "Volcanologie expérimentale":
Chédeville-Monzo, Corentin. "Mécanismes d'auto-fluidisation des écoulements pyroclastiques : approche expérimentale." Thesis, Clermont-Ferrand 2, 2016. http://www.theses.fr/2016CLF22684/document.
Pyroclastic flows are hot mixtures of gas and particles that can propagate over large distances. This high “mobility” is often attributed to their ability to be fluidized, that is, to generate and retain high gas pore pressure that reduces internal friction forces. The main objective of this thesis is to understand how irregularities of substrates on which pyroclastic flows propagate can enhance their fluidization. A first set of laboratory experiments consisted of the generation of fine-grained flows (diameter of 45-90 μm) on substrate of various roughness. Results show that the flow runout distance increases with the substrate roughness, and is up to twice the runout on a smooth substrate. High speed video analyses and air pore pressure measurements at the flow base show that the flow head propagating over a rough substrate can auto-fluidize because of particles sedimentation into the substrate interstices, which forces the air to escape upward and percolate through the flow. This auto-fluidization mechanism is efficient at all inclinations investigated (0-30°), suggesting that it could occur during the whole emplacement of a pyroclastic flow. A second study consisted of the vertical release of beds of particles in a static column. Results show that the granular mixture can be fully fluidized, even when collapsing from a relatively low height (20 cm). When particles are fine enough (<100 μm), pore pressure in the deposit diffuses for several seconds, the diffusion duration increasing with increasing bed thickness and decreasing particle size. The longest diffusion durations are observed for pyroclastic flow deposit materials (~30 s for 28.5 cm thick beds). These results suggest that pyroclastic flows propagating on irregular terrains can auto-fluidize and preserve low internal friction during their emplacement
Gueugneau, Valentin. "Etude de la formation et de la mise en place des déferlantes pyroclastiques par modélisations numérique et expérimentale." Thesis, Université Clermont Auvergne (2017-2020), 2018. http://www.theses.fr/2018CLFAC050/document.
Small volume pyroclastic density currents are complex volcanic flows, whose physical behaviour is still debated. They comprise two parts: the pyroclastic flow, rich in particles and blocks, overridden by the ash-cloud surge, a turbulent and dilute flow. The interactions between these two parts are not fully understood, as well as their exchanges of mass and momentum. Therefore, the thesis focuses on the investigation of ash-cloud surge formation mechanisms from the pyroclastic flow. The experiments reveal a mechanism of dilute flow formation by alternation of air incorporation into and elutriation of fine particles from a dense granular bed subjected to vibrations. The air is aspirated into the granular bed during dilatations, and expulsed during the contraction phases. A part of the particles are then sustained by the turbulent expulsed air and form a mixture of gas and particles that transforms into a gravity current. Extrapolated to a volcanic edifice, this mechanism of air incorporation and elutriation can be reproduced by a rough topography, where each obstacle generates a compaction followed by a dilatation of the pyroclastic flow. The quantification of the mechanism has been accomplished and the mass flux from the dense flow to the ash-cloud surge has been deduced.The numerical model is first used to study the pyroclastic flow rheology, which controls the velocity of the flow, and then the mass flux previously mentioned. One chapter is dedicated to the fluidization effect on the pyroclastic flow rheology. Results show that this mechanism can explain the long runout of these flows, and also the formation of levées and channel morphologies. The air ingestion in the flow during its movement could explain a part of the pyroclastic flows dynamic. Simple rheologies has also been analyzed: a Coulomb rheology, a plastic rheology, and a variable friction coefficient rheology. Results show that the plastic rheology seems to be the most adapted rheology to simulate the pyroclastic flow dynamic. Then, the numerical model has been used to test the mass flow law obtained through experiments. Applied to the 25 June 1997 dome collapse at Soufrière Hills Volcano at Montserrat, results show that the simulations reproduce accurately the extension and the thickness of the surge deposits. The simulations are also able to reproduce the surge derived pyroclastic flow, generated by remobilisation of surge deposits. The cycles of ingestion/expulsion of air in the pyroclastic flow by interactions with the topography could explain both the great fluidity of these flows and the formation of ash-cloud surge. These results highlight a new mechanism that could be a key process in pyroclastic flow dynamic, which could improve significantly the hazard and risk assessment using numerical model
Brugier, Yann-Aurélien. "Magmatologie du Piton de la Fournaise (Ile de la Réunion) : approche volcanologique, pétrologique et expérimentale." Thesis, Orléans, 2016. http://www.theses.fr/2016ORLE2007/document.
To better understand magmatic processes associated with the evolution of La Réunion magmas, we have carried out a multi-approach study aimed at (1) simulating experimentally the feeding system of the Piton de la Fournaise volcano, using a Steady State Basalt starting material and P-T-fO2-Volatiles (H2O, CO2) conditions compatible with the natural system; (2) determining crystallization sequences representative of La Réunion plutonic rocks for comparison with the experimental results and (3) constructing a volcanological, petrological and geochemical database for lavas of the Abnormal Group, to confirm the existence of Abnormal melts in the feeding system of the volcano. The discovery of glasses having chemical characteristics similar to the Abnormal Group establishes the implication of Abnormal melts in eruptive processes. However, plutonic rocks record crystallization sequences that for the most part indicate a low pressure magmatic evolution. Experiments in the pressure range 0.1 to 50 MPa satisfactorily reproduce conditions in the shallow magmatic systems and lead to petrological models and magma storage depths in agreement with geophysical data. Experiments at higher pressures demonstrate transitions in magma fractionation mechanisms in the feeding system that can explain the range of erupted compositions, but call into question the compositions of parental magmas
Weit, Anne. "Etude expérimentale de la concentration de particules solides dans les écoulements volcaniques biphasés turbulents." Thesis, Université Clermont Auvergne (2017-2020), 2018. http://www.theses.fr/2018CLFAC060.
Mixtures consisting of gas and particles can be found in various geophysical environments. Hot mixtures are generated by explosive volcanic eruptions and include conduit flows, jets and buoyant plumes, and pyroclastic density currents. The particle concentration within these volcanic mixtures can vary highly, from high concentrations (>50 vol. %) in dense fluidized flows to very low concentrations in dilute suspensions in which the particles are suspended by the turbulent gas phase. A concentration limit of less than ~1 vol. % in dilute suspensions was suggested by recent studies, as higher concentrations would require excessive turbulent kinetic energy. The main objective of this thesis was to investigate experimentally the behavior of a turbulent air flow in a pipe with increasing particle concentrations, for different Reynolds numbers and using different types of particles. The Reynolds numbers of the gas-particle mixtures in the experiments were up to ~106. A first set of experiments was conducted with glass beads of varying sizes from 75-80 μm up to 2 mm, for eight particle size ranges in total. Above a bulk concentration threshold of ~0.5-3 vol. %, which increased with the Reynolds number, the flow behavior changed from a homogeneous suspension of particles (below the maximum concentration) to a separation into a dense basal part and an upper dilute part carrying the maximum concentration of particles. This concentration threshold was detected with pressure measurements and a method that involved a ball of a slightly lower density than the bulk density of the particles, which could thus float over the dense basal part, if present. High-speed videos revealed that the occurrence of the maximum particle concentration coincided with the emergence of particle clusters in the dilute turbulent part. In a second part of the thesis, the experiments were repeated for five ceramic particle size ranges and they yielded the same general behavior as for the glass beads. For both types of particles, a maximum concentration could be detected for almost all particle size ranges and showed an increase with the mixture Reynolds number to the power 1/5 (glass beads) or 0.4 (ceramic beads). Considering the particle Reynolds number the maximum particle concentration then increase to the power 1/6 for both ceramic and glass particles. These results give new insights about the structure of volcanic gas-particle mixtures and they also provide constraints for input and output data of numerical simulations and for geophysical observations
Penlou, Baptiste. "Étude expérimentale des écoulements gaz-particules en contexte de fontaine pyroclastique." Electronic Thesis or Diss., Université Clermont Auvergne (2021-...), 2023. http://www.theses.fr/2023UCFA0159.
Pyroclastic columns form during explosive volcanic eruptions in which a mixture of gases and particles is ejected at high speed from a vent and can lead to the formation of convective plumes. The stability of these columns depends on various parameters that can vary over time and cause partial or total collapse of the pyroclastic mixture. These collapses give rise to eruptive fountains, forming density currents called pyroclastic density currents (PDCs). The objective of this thesis is twofold: to study (1) the mechanisms of particle sedimentation in the plume and the dilute part of PDCs, and (2) the mechanisms of PDC emergence in the impact zones of the fountains. The chosen method is the experimental approach.A first series of experiments involves suspending particles ranging in size from 49 to 467.5 µm in a cylindrical device and measuring the local particle concentration for each mixture. For this purpose, two independent approaches were used and provided similar results: an acoustic method and the use of pressure sensors. These experiments highlight two mechanisms of particle sedimentation: enhanced sedimentation and delayed sedimentation. In suspensions of small particles (78 µm), the sedimentation rate increases with the local particle concentration due to the formation of « clusters » that fall at a speed four times higher than the terminal settling velocity of individual particles (enhanced sedimentation). However, in suspensions of larger particles (467.5 µm), the sedimentation rate decreases with increasing particle concentration, despite the presence of « clusters » and it is 30 % lower than the settling speed of individual particles (delayed sedimentation). These results suggest that the sedimentation mechanisms in the presence of « clusters » occurring in plumes or the dilute part of PDC should be considered in models used to simulate these volcanic phenomena to better predict deposit characteristics.A second series of experiments simulates a pyroclastic fountain by releasing particles of sizes ranging from 29 and 269 µm into a channel at a height of 3.27 meters. The results show that dilute mixtures (1.6 - 4.4 vol.%) in free fall accumulate in the impact zone to form concentrated granular flows (~ 45 - 48 vol.%) whose interstitial fluid pressure nearly compensates for the weight of particles for sizes < 76 µm. Furthermore, the maximum fluid pressure measured at the impact, the flow travel distance, and the horizontal stretching of deposits increase with decreasing particle size. Considering the experiment dimensions, these results indicate that a high interstitial fluid pressure can be generated in the impact zone of collapsing pyroclastic fountains. The small particle size, causing low permeability and a long pressure diffusion time, may be one of the main factors leading to the long runout distances covered by the flows
Poussineau, Stéphane. "Dynamique des magmas andésitiques : approche expérimentale et pétrostructurale ; application à la Soufrière de Guadeloupe et à la Montagne Pelée." Phd thesis, Université d'Orléans, 2005. http://tel.archives-ouvertes.fr/tel-00010122.
Le premier aspect repose sur l'étude d'une éruption particulière de la Soufrière de Guadeloupe (1440 AD). La stratégie d'étude a été de coupler une étude pétrographique des produits émis avec une étude expérimentale. Cette approche nous a permis de contraindre avec précision les conditions pré-éruptives ainsi que la dynamique de la chambre magmatique qui s'est avérée être zonée thermiquement et chimiquement.
Le second aspect a consisté en l'acquisition des données naturelles et expérimentales sur les produits des éruptions historiques de la Montagne Pelée afin d'apporter des éléments nouveaux pour la compréhension du dynamisme des magmas andésitiques dégazés. La nature des produits a nécessité de coupler différentes approches (étude texturale des produits naturels, teneur en eau des verres résiduels, anisotropie de susceptibilité magnétiques sur les produits de dômes, expériences de décompressions contrôlées et acquisition de données expérimentales à basse pression).