The creep of polycrystalline ice

Polycrystalline blocks of ice have been tested under compressive stresses in the range from 1 to 10 bars at temperatures from —13°C to the melting-point. Under these conditions ice creeps in a manner similar to that shown by metals at high temperatures; there is a transient creep component and also a continuing or quasi-viscous component. The relation between the minimum observed flow rate έ, the applied stress σ and the absolute temperature T is έ = B exp ( -Q/RT) σn, where R is the gas constant, and B, n and Q are constants; the value of n is about 3.2, that of Q is 32 kcal/mole, and that of B is 7 x 1024 if the stress is measured in bars and the strain rate in years-1. At the higher stresses a third, accelerating stage of creep was observed; on the basis of the appearance and behaviour of sections cut from the specimens, this acceleration was attributed to recrystallization. The effect of changing the load during a test has also been studied; for large reductions creep recovery was observed. The results of these tests are discussed in connexion with previous work on metals and ice, and also with measurements of glacier flow.