Degradation of talus-derived rock glaciers in the Upper Engadin, Swiss Alps

Active and inactive rock glaciers differ from relict rock glaciers in the presence of subsurface permafrost, as indicated by high seismic velocity, high DC resistivity and low bottom temperature of the winter snow cover. The lack of vegetation on the frontal slope and negative mean annual surface temperatures (MAST) distinguish active rock glaciers from inactive rock glaciers. Increasing MAST induces melting of ice-rich permafrost, which is followed by the subsidence of rock glaciers. As a result, convex-up transverse profiles are replaced by flat or depressed profiles. Permafrost degradation inactivates rock glaciers by decreasing shear stress, within or at the base of the deforming ice/rock mixture, causing stabilization and declination of the frontal slope. Relict rock glaciers are usually associated with soil development over the surficial clasts, which is responsible for further declination of the frontal slope and a more rounded topography. Copyright (C) 2002 John Wiley Sons, Ltd.