Creep of Alpine permafrost, investigated on the Murtèl Rock Glacier

Abstract

Borehole and surface deformation measurements from an active rock glacier in the eastern Swiss Alps are presented and analysed. Borehole deformation was measured by slope indicator and magnetic rings. Analysis of these measurements reveal two layers which behave quite differently. The upper, highly supersaturated (i.e. ice) layer undergoes steady-state creep (corresponds to a surface velocity of 5.5 to 6.0 cm/yr), overriding a non-deforming lower layer of saturated (structured) permafrost. Seventy-five per cent of the deformation takes place in a weak transitional zone, in the middle of the permafrost. Geodetic surveying shows, in contrast to the borehole measurements, a velocity variation in time by a factor of two. A constitutive law (Glen's flow law) was applied and the viscosity ratio between the upper ice layer and the weak transition zone was determined.