Depth-varying constitutive properties observed in an isothermal glacier

Detailed three-dimensional in-situ measurements of deformation at depth are used to examine the rheology of a 6 × 10⁶ m³ block of temperate glacier ice. Assuming that the viscosity of this ice is primarily dependent on stress, the relationship between inferred stress and measurements of strain-rate above ∼115 m depth suggest a constitutive relationship with a stress exponent n ∼ 1. Deformation below 115 m is described by a non-linear flow law with a power exponent of approximately 3-4. A sharp transition between the two flow regimes is likely caused by a change in the dominant mechanism from superplastic flow, basal slip, and/or diffusional flow near the surface to dislocation and intragranular deformation at depth.