ABSTRACT. Uniaxial compression creep tests were p erformed on a rtificial and natural polycrystalline ices at tempera tures near -7°C . The grain-size range investigated was from I to 10 mm. C ontrary to previous results, the p ermanent creep-ra te was not found to in crease with crystal size. Only the transien' t creep appears to b e sensitive to variations in crystal size.R EsuME . L a vitesse du j1uage stationnaire de la glace poiyeristalline erolt elle avee la taille des eristaux? Des experiences d e fluage en compression uniaxial e o nt ete realisees sur d es glaces polycristallines artificielles et naturell es aux temperatures voisines de -7°C. L a taille des grains va ria it entre I et 10 mm. A I'oppose des resultats recemment publies, il est montre que la vitesse du fluage sta tionnaire ne croit p a s a vec la taille des crista ux. Seulement le flu age tra nsitoire appa ra it etre influence pa r d es variations de la taille des cristaux.

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.

ABSTRACT. Uniaxial compression creep tests were p erformed on a rtificial and natural polycrystalline ices at tempera tures near -7°C . The grain-size range investigated was from I to 10 mm. C ontrary to previous results, the p ermanent creep-ra te was not found to in crease with crystal size. Only the transien' t creep appears to b e sensitive to variations in crystal size.R EsuME . L a vitesse du j1uage stationnaire de la glace poiyeristalline erolt elle avee la taille des eristaux? Des experiences d e fluage en compression uniaxial e o nt ete realisees sur d es glaces polycristallines artificielles et naturell es aux temperatures voisines de -7°C. L a taille des grains va ria it entre I et 10 mm. A I'oppose des resultats recemment publies, il est montre que la vitesse du fluage sta tionnaire ne croit p a s a vec la taille des crista ux. Seulement le flu age tra nsitoire appa ra it etre influence pa r d es variations de la taille des cristaux.

No 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.