Mechanical Behaviour of Antarctic Ice

Abstract

The mechanisms of Antarctic ice deformation are discussed. Diffusional flow (Nabarro-Herring or Coble creep) seems to dominate creep f o r the f i r s t 905 m near Dome C. Formation mechanisms of single-maximum fabrics are examined. Dislocation creep does not explain the preferred c-axis o r i e n t a t i o n observed i n the Antarctic ice sheet. The quantitative effects of crystallographic o r i e n t a t i o n on s t r a i n -r a t e are given. The a c t i v a t i o n energy f o r dislocation creep was found to be 78 kJ mol" 1 between -7.2°C and -30°C. Ratel i m i t i n g mechanisms are discussed.

Precise altimetric topography in ice-sheet flow studies

“…As shown in Table I, n is found between 0.64 and 1.27, and k between 0.10 and 0. 12, which corresponds to an activation energy between 65 and 80 kJ mol-J • This value is close to the value of 75 kJ mol-J of Homer and Glen (1978) and of 80 kJ mol-J of Duval and and Le Gac (1982).…”

“…Activation energy seems to depend on temperature. Creep tests made by Duval and Le Gac ( 1982) gave a value of 78 ± 4 kJ mol-I for temperatures between -10 and -25°C . A larger value is expected for warmer temperatures.…”

Fabric development with nearest‐neighbor interaction and dynamic recrystallization

“…In ice sheets, fabric evolution has been well documented from extensive thin section measurements on ice cores [Alley et al, 1995;Gow et al, 1997;Thorsteinsson et al, 1997] and from sonic logging in boreholes and on the ice cores themselves [Kohnen and Gow, 1979;Taylor, 1982;Anandakrishnan et al, 1994;Thorsteinsson et al, 1999]. A consequence of fabric development is that bulk physical properties become anisotropic, as shown by experiments and theory [Steinemann, 1958;RussellHead and Budd, 1979;Duval, 1981;Duval and LeGac, 1982;Budd and Jacka, 1989;van der Veen and Whillans, 1990;Wenk and Christie, 1991;Alley, 1992;Anandakrishnan et al, 1994;Azuma, 1994Azuma, , 1995Azuma and Goto-Azuma, 1996;Castelnau et al, 1996a].…”

Mécanismes de la déformation plastique de la glace polycristalline

“…Les valeurs de la constante B sont typiquement de l'ordre de 0,02 bar-3 a-I à -7 oC et 0,1 bar-3 a-I à -0,1 oC (Duval et Le Gac, 1982). Des valeurs supérieures à 0,5 peuvent être atteintes pour de la glace tempérée.…”

“…Le point important qui émerge de ces résultats est que la vitesse de déformation du polycristal n'est par contrôlée par le glissment basal mais par des processus de restauration (Duval et le Gac, 1982;Duval et al, 1983). Le mécanisme proposé est la montée des dislocations dans les sous-joints de flexion composés de dislocations basales.…”