Movement of a Large Ice Mass Before Breaking off

Abstract In a two-dimensional model of an ice mass breaking off from a cliff, stresses and velocities are calculated numerically according to Glen's flow law. A tensile crack opens in the zone of maximum tensile principal stress σ1 and propagates to a depth where σ1, iɜ, zero. Ice flow then produces an overhang of the partly detached ice mass. Consequently, the stress σ1 below the tip of the crack becomes tensile again and the crack propagates for another small distance. This process goes on until the centre of gravity of the detaching ice mass has moved past the supporting edge of the bedrock. Velocities v of the ice mass calculated for different stages of the process are plotted as a function of time t. The plotted points lie in the vicinity of a curve given by (1) where vc, tA B and D are constants. The same type of function has been found for velocities measured at an ice mass breaking off the Grubengletscher.