FLOW IN POLYCRYSTALLINE ICE

By Chris Wilson and Brett Marmo

List of figures

Figure 1.1.1: Quartz crystal showing location of main crystal faces and principal crystallographic axes.

Figure 1.1.2: Schematic representation of the basal glide plane (0001) in ice in relation to non-basal glide planes and glide directions.

Figure 1.1.3: The flattening of a single crystal that accommodates the shortening by shearing on its basal plane in which the initial critical resolved shear-stress will be high as it lies approximately 45° to the compression direction.

Figure 1.2.1: A Pure shear deformation

Figure 1.2.2: Two dimensional representation of four undeformed polygonal grains with basal planes (0001) oriented at high-angle to the viewing plane.

Figure 1.2.3: A pure-shear deformation with 20% bulk shortening and showing the relationship to the finite strain ellipse.

Figure 1.2.4: Principal-stress distribution

Figure 1.4.1: Polycrystalline aggregate showing undeformed grains and deformed grains.

Figure 1.4.2: Stereographic projections that contrast the random c-axis preferred-orientation in undeformed verses strong fabric in deformed sample.

Figure 1.4.3: The c-axis distributions in pure shear versus a simple shear regime.

Figure 1.6.1: Flow lines in an outlet glacier in the Framnes Mountains, Antarctica (Marmo & Wilson 1998).

Figure 1.6.2: Longitudinal section parallel to the flow lines in the Framnes Mountains glacier.

Figure 1.6.3: Divergent, parallel and convergent flow regimes and observed c-axes fabric associated with each.

Figure 2.1.1: In-situ simple shear deformation apparatus.

Figure 2.1.2: Plan view of in-situ pure shear deformation apparatus.

Figure 2.2.1: Simulated fabric development in flow lines from an outlet glacier in the Framnes Mountains, Antarctica.

Figure 2.3.1: The crystal structure of ice Ih, showing the arrangement of molecules projected onto the plane.

Figure 2.3.2: The propagation of a dislocation through the basal plane of an ice lattice.

Figure 2.5.1: A Frank-Read source for the multiple initiation of dislocation loops.

Figure 2.6.1: The Ice Ih lattice.

Figure 2.8.1: When a cantilever is applied to a single crystal of ice the deformation style is dependent on the orientation of the basal plane relative to the load.

Figure 2.9.1: Creep curves in ice.

Figure 2.9.2: A schematic sketch of stress-time curve for deformation in a single crystal of ice at -10°C.

Figure 2.10.1: Two separated portions of a crystal showing a model for calculating the resolved shear stress in a single-crystal specimen.

Figure 2.11.1: Data for glide on basal and non-basal systems, and in isotropic polycrystalline ice compiled by Duval et al, (1983).

Figure 2.14.1: Schematic creep curve for polycrystalline ice under constant load.

Figure 2.15.1: Plots of strain rate as a function of strain for creep of granular polycrystalline ice in uniaxial compression under various stresses.

Figure 2.15.2: The minimum strain rate is uniaxial creep tests on granular polycrystalline ice as functions of stress at various temperatures.

Figure 2.17.1: Deformation mechanism maps for isotropic polycrystalline ice by Goodman et al. (1981).

Figure 2.19.1: Grain size reduction occurs in a shear zone developed in coarse ice deformed at -2°C.