RATE CONTROLLING PROCESSES IN THE CREEP OF POLAR GLACIER ICE

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Abstract
Torsion tests have been carried out on artificial ice and on samples cut from an ice core obtained at South Pole Station. Results give a stress exponent smaller than 2 for stresses lower than 0.1 MPa. Analysis of the inclinometer survey of the Dye 3 borehole yields the same result. The deformation mechanisms of polar ice at low stresses are reviewed. A Newtonian viscosity may be expected with dislocation glide accommodated by grainboundary migration linked with graingrowth. However, rotation of crystals by dislocation glide and strain-induced boundary migration are complementary and efficient mechanisms to accommodate the incompatible plastic deformation between grains of different lattice orientation. These deformation mechanisms concern a great part of polar ice

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