资源环境科技发展态势分析平台

Results of glacier flow models and associated estimates of future sea level rise depend sensitively on the prescribed relation between shear stress and slip velocity at the glacier bed. Using a fully three-dimensional numerical model of ice flow, we compute steady-state sliding relations for where ice slips over a rock bed with three-dimensional, periodic topography. In agreement with studies of two-dimensional beds, water-filled cavities that form down-glacier from bedforms cause basal shear stress to peak at a threshold slip velocity and decrease at higher velocities (i.e., rate-weakening drag). However, the shear stress magnitude and extent of rate-weakening drag depend systematically on lateral topographic variations not considered previously. Moreover, steep up-glacier-facing slopes of bedforms can result in shear stress that increases monotonically over a wide range of slip velocity, helping to stabilize slip. These results highlight the potential variability of sliding relations and their likely sensitivity to the morphological diversity of glacier beds.

Plain Language Summary Parts of ice sheets that flow into the oceans and affect sea level can flow unusually fast by slipping over their beds. We use a computer to solve for the first time in three dimensions the equations that describe the flow of ice as it slips over a bumpy rock bed. We include the important tendency for glaciers to separate from rock and form water-filled cavities down-glacier from bumps. These calculations indicate that resistance to slip depends sensitively on the bump shape and spacing. Cavities can cause the bed to become more slippery the faster the ice slides, with this destabilizing effect being more severe for bumps that are laterally narrow and widely spaced. However, bumps with steeply sloping up-glacier sides can reverse this effect and cause resistance to slip to increase over a wide range of increasing slip velocity. This diverse behavior highlights the need for estimates of glacier slip velocity to incorporate the actual topography of glacier beds.