BASAL-FLOW CHARACTERISTICS OF A NONLINEAR FLOW SLIDING FRICTIONLESS OVER STRONGLY UNDULATING BEDROCK

The flow field of a medium sliding without friction over a strongly un dulating surface is calculated numerically. The results are used to el ucidate the basal-flow characteristics of glacier flow and the are dis cussed with reference to known analytical solutions. Extrusion flow is found to become increasingly pronounced as the value of n, where n is a parameter in Glen's flow law, becomes larger. For sinusoidal bedroc k undulations, a flow separation occurs if the amplitude-to-wavelength ratio exceeds a critical value of about 0.28. The main flow then sets up a secondary flow circulation within the trough, and the ice partic ipating in this circular motion theoretically never leaves it. The sli ding velocity is calculated numerically as a function of the mean basa l shear stress, the amplitude-to-wavelength ratio and the flow paramet er n. For moderate and high slope fluctuations, the sliding velocity i s significantly different from what would be expected from results bas ed on the small-slope approximation.