Debris-Bed Friction of Hard-Bedded Glaciers

• Main Authors: Cohen, Denis, Iverson, Neal R., Hooyer, T. S., Fischer, U. H., Jackson, M., Moore, Peter Lindsay
• Format: Text
• Language: English
• Published: Iowa State University Digital Repository 2005
• Subjects: glacier; friction; sliding; measurement; model; rheology; Geophysics and Seismology; Glaciology; Natural Resources Management and Policy; Engabreen; Norway; Northern Norway
• Online Access: https://lib.dr.iastate.edu/nrem_pubs/71; https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1072&context=nrem_pubs

Field measurements of debris-bed friction on a smooth rock tablet at the bed of Engabreen, a hard-bedded, temperate glacier in northern Norway, indicated that basal ice containing 10% debris by volume exerted local shear traction of up to 500 kPa. The corresponding bulk friction coefficient between the dirty basal ice and the tablet was between 0.05 and 0.08. A model of friction in which nonrotating spherical rock particles are held in frictional contact with the bed by bed-normal ice flow can account for these measurements if the power law exponent for ice flowing past large clasts is 1. A small exponent (n < 2) is likely because stresses in ice are small and flow is transient. Numerical calculations of the bed-normal drag force on a sphere in contact with a flat bed using n = 1 show that this force can reach values several hundred times that on a sphere isolated from the bed, thus drastically increasing frictional resistance. Various estimates of basal friction are obtained from this model. For example, the shear traction at the bed of a glacier sliding at 20 m a−1 with a geothermally induced melt rate of 0.006 m a−1 and an effective pressure of 300 kPa can exceed 100 kPa. Debris-bed friction can therefore be a major component of sliding resistance, contradicting the common assumption that debris-bed friction is negligible.