The rheology of snow in large chute flows

The velocity profile and basal shear force were measured for snow flowing down a chute 34 m long and 2.5 m wide. The flows were approximately steady by the end of the chute where measurements were taken and the angle was 32degrees. Measurements of the basal shear stress confirm approximate dynamic balance. The velocity profile was measured using optoelectronic sensors and showed a large slip velocity at the base, a shear layer of around 50 mm and an overlying plug-like flow of about 350 mm. The velocity profile is compatible with both a Herschel-Bulkley rheological model, which combines a constant critical stress with a power law dependence on the mean shear rate, and a Cross model where the effective viscosity varies between two limits. Estimates of the Reynolds number suggest that the flow is not turbulent. The measurements are used to estimate the distribution of energy dissipation and to show that its concentration near the base may locally melt the snow, and thus serve as an explanation for icy melt surfaces observed at the base of flowing avalanche tracks. (C) 2004 Elsevier B.V. All rights reserved.