Internal structure and ice content of Reichenkar rock glacier (Stubai Alps, Austria) assessed by geophysical investigations

The Reichenkar rock glacier (Tyrol, Austria) is a typical tongue‐shaped, 1400 m long, ice‐cored active rock glacier, which connects to a debris‐free cirque glacier. Aerial photographs from 1954 and 1990 indicate its mean surface velocity to be 0.6 m/a while a photograph from 2003 and annual global positioning system (GPS) measurements since 1998 show that velocities in the past decade have increased to 3 m/a. Integration of ground‐penetrating radar (GPR), seismic and gravimetric data reveals that the Reichenkar rock glacier consists of four layers. The uppermost debris layer has an average thickness of about 5 m and is underlain by ice‐rich permafrost with an average thickness of about 25 m. A prominent reflector detected by GPR is identified as the top of an unfrozen till layer located a few metres above the bedrock. Seismic refraction data clearly indicate the boundary between till and bedrock. The geophysical interpretation shows that the ice‐rich permafrost of the rock glacier has an ice content of 45–60%, depending on assumptions concerning the air content of the ice. Creep velocities calculated from the geophysical model, ice contents and an extension of Glen's flow law are in good accordance with observed surface velocities. Copyright © 2007 John Wiley & Sons, Ltd.