Abstract:
Future sea level rise will be dominated by the fast-moving (up to 3 km/yr) glacial arteries of the polar ice caps, called ice streams. As ice cannot flow at such high speeds, deformation is focused at the bed, which is largely underlain by water-saturated sediment, or till. The bed is relatively inaccessible, representing one of the largest sources of uncertainity in ice sheet models, but the growing observations of seismicity from these settings offer an opportunity to constrain and monitor evolving basal conditions and subglacial slip mechanics. Currently, there is a lack of experimental confirmation of seismic mechanisms for ice slipping on till. I will present a series of double-direct-shear experiments at controlled temperatures slightly above and below the ice melting point, focused on frictional behaviors associated with seismic instability. Utilizing the rate-and-state friction formulation, we explore the effect of a range of realistic subglacial conditions (including temperature, slip velocity, and embedded debris) on stability and healing. Our only experiments which exhibited the frictional behaviors necessary for stick-slip were at temperatures below the pressure melting point, suggesting the importance of frozen conditions in nucleating seismic slip on soft, till beds.