The progressive development of inhomogeneous shear and crystallographic fabric in glacial ice

Zones of shear, a few centimeters thick, in otherwise weakly deformed superimposed ice at the margin of the Barnes Ice Cap, are marked by decrease in plunge of elongate air bubbles, increase in degree of preferred crystallographic orientation, increase in grain size, and the development of a weakly sutured texture. The shear zone boundaries are parallel to bedrock and a direction of maximum shearing strain rate. In the interiors, shear strain attains values exceeding γ = 10, and the c-axes are tightly grouped in a cluster normal to the shear zone boundaries. With increase in overall deformation, the ice attains a high and apparently uniform shear strain by growth and coalescence of shear zones, leaving relict lenses of lower strain, or 'less-deformed zones', with characters opposite to those of the shear zones themselves.