RATE CONTROLLING PROCESSES IN THE CREEP OF POLAR GLACIER ICE

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 w ith g raingrowth. However, rotation of crystals by dislocation glide and strain-induced boundary migration are cmplementary and efficient mechanisms to accommodate the incompatible plastic deformation between grains of different lattice orientation. hese deformation mechanisms concern a great p art of polar ice.