The effective viscosity of ice depends upon many factors, including temperature, deviatoric stress, crystal orientation and impurities. A flow law that includes these factors and is simple to implement is a requirement for numerically efficient ice-flow models. The dominant microscale flow mechanism changes as temperature, deviatoric stress or grain-size changes. For both anisotropic and isotropic constitutive relations, this shift in dominant flow mechanism is expressed as a change in the stress exponent. We study the effects of this shift in stress exponent on ice flow using a two-term flow law for isotropic ice. Our stress-strain-rate relationship does not explicitly describe the microscale processes of ice deformation; however, it encompasses a range of deformation behaviors with a simple law.In terrestrial ice, a flow-mechanism shift may occur in low-deviatoric-stress regions near ice divides, resulting in a near-linear constitutive relationship for ice flow. Compared to a non-linear (Glen) divide, a divide dominated by a near-linear flow mechanism has verticalvelocity profiles that are similar at divide and flank sites, internal layers that do not develop a Raymond bump, and a steady-state surface profile that is more rounded near the divide.
The Journal of Glaciology is published six times per year. It accepts submissions from any discipline related to the study of snow and ice. All articles are peer reviewed. The Journal is included in the ISI Science Citation Index.