Numerical modelling of mechanical interactions between magma and host rocks : application to magma storage zone and conduit flow.

• Main Author: Albino, Fabien
• Other Authors: Institut des Sciences de la Terre (ISTerre), Université Joseph Fourier - Grenoble 1 (UJF)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement IRD : UR219-PRES Université de Grenoble-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS), Université de Grenoble, Philippe Lesage
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2011
• Subjects: Volcanology; Mechanical models; Numerical solutions; Magma storage; Stability of magma reservoirs; Icelandic subglacial volcanoes; Magma flow; Volcanic conduit; Volcanologie; Modèles mécaniques; Solutions numériques; Stockage du magma; Stabilité des réservoirs magmatiques; Volcans sous-glaciaires islandais; Transport de magma; Conduit volcanique; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Iceland; Katla; Mýrdalsjökull
• Online Access: https://theses.hal.science/tel-00622537; https://theses.hal.science/tel-00622537/document; https://theses.hal.science/tel-00622537/file/Albino_fabien_2011_archivage.pdf

Through two different applications, we focus on the mechanical coupling between magma and host rocks, using numerical method. First, we study the influence of stress perturbations on shallow magma chambers, with the exemple of two subglacial volcanoes (Iceland). A variation in the stress field acts to modify the magma pressure within the reservoir as well as the failure conditions to initiate an intrusion at the reservoir wall. At Grímsvötn volcano, subglacial lake discharges (so-called "jökulhlaup") often occur in relation to eruptions. Our models show that jökulhlaup promote the failure of the magma reservoir and thus trigger eruptions, as observed for 2004 eruption. The triggering effect is small, so magmatic system must be already pressurized and close to failure before the discharge of the lake occurs. At Katla volcano, our models indicate that reservoir failure is highest in summer period when the ice load at Mýrdalsjökull icecap is reduced. Coulomb stress calculation predicts also an increase of earthquake occurrence at the caldera rim at the same time. A seasonal modulation of volcanic and seismic activity at Katla related to the loading/unloading of the icecap can exist. Secondly, we focus on magma conduit flow for andesitic volcanoes. Improving our knowledge of magma dynamic during ascent is a challenge, because processes occurring in the conduit seem to govern the temporal evolution of eruptive activity. Previous models showed that magma viscosity increases during flow in the upper part of the conduit, which causes the emplacement of a viscous plug. But the relationship between the plug emplacement and precursors signals, such as ground deformation or seismicity, is not yet fully described. From our plug flow model, we find that surface deformation is mainly controlled by the geometry of the conduit, the ratio between the plug length and the total conduit length and the viscosity contrast between the plug and the magma column. We show that the evolution of the plug size is a possible explanation for ...