Model Studies on Ice-Stream Surging

Abstract

A self-surging glacier model (Budd and McInnes, 1974; Budd, 1975), in which basal sliding is parameterized in terms of energy per unit area dissipated by basal friction, TbVb, has been extended to model the steady-state and time-dependent behaviour of eight Antarctic ice streams. Their basic characteristics were established with the working hypothesis of steady-state mass balance for the ice sheet as a whole, using a 20 km grid digitization of the surface and bedrock-elevation contours in Antarctica: glaciological and geophysical folio (Drewry, 1983). When the viscosity of the ice is lowered to values that are somewhat unrealistic for the present Antarctic ice, all the model ice streams enter a pulsating fast-sliding mode of flow in which the velocity reaches several km/year for periods ranging from fractions οf a year to tens of years. Except for one ice stream (Slessor Glacier), no substantial surge-like advances were found, and even in that case no periodic surging regime developed. The pulses are tentatively attributed to processes at the grounding line, with the converging width-parameterization scheme in the surging velocity calculation as another complexity that is still being investigated. For the cyclic surging Medvezhi Glacier model (Budd and Mclnnes, 1978), it has been found that the model surges change to shorter pulses as the width-convergence rate is increased. It is concluded that the special regime and topography of ice streams — net accumulation increasing along the strongly converging flow and removal of the ice by calving rather than ablation — impede the onset of periodic surging. However, more sophisticated parameterizations of the basal hydraulics now in development may well show that ice-stream surges after all are possible.