c-axis fabrics in ice sheets provide a record of deformational history and control the rate of current deformation. Fabrics are developed by grain rotation at low strain-rates and temperatures, and by recrystallization at higher strain-rates and temperatures. In ice sheets characterized by longitudinal extension and vertical compression, basal shear, parallel flow, and divergent flow cause c-axes to rotate toward the vertical axis; rotation is faster parallel to flow than transverse to flow in basal shear and parallel flow, but it is independent of azimuth in divergent flow. Convergent flow causes c-axes to rotate toward a vertical plane transverse to flow. Cumulative strain, ice hardness, and stress state can be estimated from measured fabric patterns. Alternatively, fabric patterns can be predicted from observed surface strain-rates. Such predictions are confirmed by fabrics determined seismically on Ice Stream B, Antarctica, as well as by comparison with directly measured fabrics from other sites.
A paper reporting much of this work has been published in Science (Alley, 1988).