Glacial Sliding on Volcanic Bedrock: Effect of Rock Surface Roughness on Ice-on-Rock Friction and Healing

The controls on glacial movement are attributed in part to frictional properties at the glacial bed. Previous laboratory experiments have constrained the roles of temperature, debris content, and velocity on ice-on-rock friction. However, there are limited experiments that investigate the frictional behavior of ice on a non-crystalline, permeable rock. Here, as part of the RORD REU, we used a vitric welded tuff member of the Pleistocene Bishop Tuff to investigate the ice-rock frictional behavior and explore the role of rock surface roughness. We ran experiments with two different rock surface roughnesses of Ra = 6.5 ± 3 μm and Ra = 11.0 ± 4 μm. Polycrystalline ice samples were created using the "standard ice" method, with an average grain size of 1.95 mm. A cryogenic biaxial friction apparatus was used, with horizontal pistons applying a normal stress and a vertical piston applying a velocity-controlled program to slide the ice sample through two stationary rock samples. Following an initial run in at 10 μm/s, a number of velocity steps and slide-hold-slides were employed, with a range in sliding velocity from 0-100 μm/s and a range in hold steps from 1-1000 s. We use the MATLAB based GUI RSFit3000 to analyze the velocity steps for the relevant rate-state friction parameters. Preliminary experimental results suggest that the steady-state friction of ice on the welded tuff is higher than that of ice-granitic rock interfaces at the same temperature (-6 °C) and normal stress (100 kPa). The ice sliding on roughened tuff showed higher steady-state friction and frictional relaxation than on the smoother tuff but lower healing, with both tuff types having greater magnitude of frictional healing and relaxation compared to granitic rocks. Our results suggest that the basal sliding of glaciers on volcanic rocks differs significantly from crystalline basement rocks, and the surface roughness of rocks at the ice-rock interface may change how glaciers slide on rock surfaces.