To investigate dislocation densities of deformed polycrystalline ice the modified Warren-Averbach and modified Williamson-Hall plots of X-ray line broadening have been applied to artificial ice with and without silica particles, which model microparticles in ice sheets. This also provides us with the dislocation velocity during creep. Creep tests were conducted at −20ºC and 2 MPa by altering the strains using the artificial ice. In the primary creep region the ice with microparticles is remarkably deformed, and the strain rate is suppressed because of high dislocation densities. At 10% strain the dislocation density shows the maximum value due to the continuous dislocation pile-ups in the silica-containing ice: the dislocation density in the pure ice remains almost constant within the maximum strain used in this study. As the strains continuously decrease, microparticles pin the grain boundaries, leading to small grain sizes. Such small grain sizes provide sinks for dislocation annihilations, resulting in decrease in the dislocation densities in the silica-containing ice.
