Glacier Sliding, Seismicity and Sediment Entrainment

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

Ice sheet stability depends on the resistance to ice sliding provided by the subglacial ice--sediment interface. Glacier basal seismicity due to small-scale stick-slip motion provides a window into sliding processes. Stick-slip motion requires an interface with reduced resistance under increased sliding or sliding rate, a property called rate-weakening friction. Experimental studies of ice slip over glacial materials, however, often exhibit rate-strengthening friction. Here, we argue that this apparent paradox may be resolved by invoking rate-weakening rock-on-rock friction between sediments frozen to the bottom of the glacier and the underlying water-saturated sediments. We present laboratory experiments and numerical simulations using a simplified viscoelastic model of small-scale stick-slip motion. We find that sediment freeze-on and stick-slip both require high effective normal stress. Sediment entrainment therefore provides a mechanism by which rock-on-rock friction may occur at glacier beds and produce small-scale stick-slip motion. At extremely high effective normal stress, however, seismicity is suppressed in favor of viscous flow. Stick-slip motion and stagnation at the Whillans Ice Stream, Antarctica may be caused by sediment entrainment due to increasing effective normal stress. Our results suggest that glacier bed seismicity due to stick-slip motion may be used to infer subglacial geomorphic activity.

Presenting Author: Bradley P. Lipovsky

Authors