FLOW IN POLYCRYSTALLINE ICE

Part 2 - Background information

By Chris Wilson and Brett Marmo

2.11 Non-basal glide

When a load is applied to an ice crystal such that there is no resolved shear stress on the basal plane, the rate of deformation is so slow that it is extremely difficult to detect. The propagation of dislocations through non-basal systems is not well understood, however deformation experiment on monocrystals by Nakaya (1958), Wakahama (1966), and Higashi (1966) indicate that non-basal systems require at least two orders of magnitude more stress to initiate glide that basal systems (Fig. 2.11.1). Hutchison (1977) suggests that glide may occur on both prismatic {} and pyramidal {} <> slip systems (Fig. 1.1.2). Weertman (1973) estimates that non-basal glide is 100 - 1000 time more difficult that basal systems, while Castelnau et al. (1996) suggests that the prismatic slip system requires 20 times more resolved shear stress to initiate glide than the basal systems and the pyramidal systems require 200 time more resolved shear stress than basal systems (Fig. 1.1.2).

Figure 2.11.1: Data for glide on basal and non-basal systems, and in isotropic polycrystalline ice compiled by Duval et al. (1983). Non-basal glide data shows the low boundary for stress giving rise to deformation and may not represent the true stress required for the observed strain rates.