The sliding velocity over a sinusoidal bed at high water pressure

Abstract

AbstractUnder idealized conditions, when pressurized water has access to all low-pressure areas at the glacier bed, a sliding instability exists at a critical pressure,pc,well below the overburden pressure,p0.The critical pressure is given by, wherelis the wave length andais the amplitude of a sinusoidal bedrock, andTis the basal shear stress. When the subglacial water pressure, pw, approaches this critical value, the area of ice-bed contact,△l,becomes very small and the pressure on the contact area becomes very large. This pressure is calculated from a force balance and the corresponding rate of compression is obtained using Glen’s flow law for ice. On the assumption that compression in the vicinity of the contact area occurs over a distance of the order of the size of this area,Δl,a deformational velocity is estimated. The resultant sliding velocity shows the expected instability at the critical water pressure. The dependency on other parameters, such as wavelengthland roughnessa/l,was found to be the same as for sliding without bed separation.