Modélisation de l'écoulement de la glace dans les calottes polaires : prise en compte d'une loi de comportement anisotrope

The ice flows by plastic deformation under gravity, and by sliding over the bedrock, when local temperature is close to the melting point. Mechanical test in laboratory and in-situ deformation measurements have shown the strong viscoplastic annisotropy of deep polar ices. To study the influence of t...

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Bibliographic Details
Main Author: Mangeney, Anne
Other Authors: Laboratoire de glaciologie et géophysique de l'environnement (LGGE), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Université Pierre et Marie Curie - Paris VI, Catherine Ritz
Format: Doctoral or Postdoctoral Thesis
Language:French
Published: HAL CCSD 1996
Subjects:
Online Access:https://theses.hal.science/tel-00781625
https://theses.hal.science/tel-00781625/document
https://theses.hal.science/tel-00781625/file/These-Mangeney-1996.pdf
Description
Summary:The ice flows by plastic deformation under gravity, and by sliding over the bedrock, when local temperature is close to the melting point. Mechanical test in laboratory and in-situ deformation measurements have shown the strong viscoplastic annisotropy of deep polar ices. To study the influence of this anisotropy on the flow, we have developped an original and robust numerical model, solving the complet set of mechanical equations. The results show that the anisotropic behaviour of the ice change significantly the flow in polar ice sheets and the datation of ice cores. For isothermal "ice sheets", the surface obtained in the anisotropic case is more flat than in the isotropic case, and shear strain rates are higher and more concentrated at the base of the glacier. The other important result is that the anisotropic ice flow is less sensitive to variations of bedrock topography. The ice is accelerated over bump and is more stagnant in the holes of the relief. In the holes the age of the ice is underestimated by a factor 2 when the anisotropy is not taken into account. Parallel to the complete mode!, we have developped a model based on the shallow ice approximation, that we have formulated for the first time, in the anisotropic case. Comparing the results ofthis model with those obtained with the complete model, we show that the approximation well represents the ice flow over a flat bedrock in the isotropic and anisotropic case, but is not able to de scribe accurately the anisotropic flow over an very irregular bedrock. La glace s'écoule par déformation plastique sous l'effet de la gravité, ainsi que par glissement sur le lit rocheux lorsque la température locale est proche du point de fusion. Les essais mécaniques en laboratoire et les mesures de déformation in-situ ont mis en évidence la forte anisotropie viscoplastique des glaces polaires profondes. Pour étudier l'influence de cette anisotropie sur l'écoulement, nous avons développé un modèle numérique original et robuste résolvant le système complet des ...