HR: 10:35h
AN: T12B-02 INVITED    [Abstracts]
TI: Anisotropic ice in Glaciers and Polar ice Sheets: Experimental Results and Modelling
AU: * Duval, P
EM: duval@lgge.obs.ujf-grenoble.fr
AF: Duval, LGGE/CNRS BP 96, St. Martin d'Heres, 38402, France
AU: Lebensohn, R
EM: lebenso@lanl.gov
AF: Lebensohn, Los Alamos National Laboratory, Los Alamos, NM 87545, United States
AU: Montagnat, M
EM: montagnat@lgge.obs.ujf-grenoble.fr
AF: Duval, LGGE/CNRS BP 96, St. Martin d'Heres, 38402, France
AB: The slow motion of polar ice sheets is governed by the viscous deformation of anisotropic ices. Strain rates are typically between 10-9 and 10-13 s-1 and temperature above -57°C. At such low strain rates, the stress exponent can be lower than 2. But, basal slip is still the dominant deformation mode. At the both scales of the ice crystal and the polycrystal, the deformation is highly heterogeneous. This behavior is associated with the anisotropy of the ice crystal and the mismatch of slip at grain boundaries for the polycrystal. Due to the low lattice friction, dislocations glide cooperatively and long-range internal stresses develop, which are accommodated by excess dislocations, in contrast to statistical dislocations associated with short-range interactions between dislocations. The viscoplastic deformation induces the development of lattice preferred orientation (textures) giving a non- random orientation of the c-axes in the largest part of ice sheets. Initially isotropic ice formed after the transformation of snow into ice becomes anisotropic as textures develop. Depending on textures, the directional viscosity can be 10 times lower or 10 times higher than that for isotropic ice. Then, both the ice crystal and textured ices are characterized by an exceptional plastic anisotropy. Dynamic recrystallization can produce stress- controlled textures. In this case, ice must be considered as isotropic. The computation of the mechanical behaviour of anisotropic polycrystalline ice using self-consistent approaches is nowadays a standard approach. These models consist in regarding each crystal of the polycrystal as an inclusion embedded in an infinite homogeneous equivalent medium whose the behavior represents that of the polycrystal. Predictions of the mechanical response obtained with the second-order self-consistent approach are compared with full-field solutions. A good prediction of the mechanical behaviour of anisotropic ices is obtained on condition that stress and strain rates fluctuations within grains are introduced.
DE: 0726 Ice sheets
DE: 0738 Ice (1863)
DE: 0776 Glaciology (1621, 1827, 1863)
DE: 3902 Creep and deformation
DE: 8160 Rheology: general (1236, 8032)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting