Development of transverse ridges on rock glaciers:: Field measurements and laboratory experiments

Very high-resolution photogrammetric and geodetic measurements about the deformation of transverse ridges on Murtel, Muragl and Suvretta rock glaciers in the Swiss Alps are discussed. The ridges are advected downstreams with a speed that equals the overall speed of the creeping permafrost within the significance level of the applied techniques. Any process of ridge formation is, thus, overlain on the mass creep. In fact, measurements yield local speed maxima on top of the ridges that can be explained by differential movement due to ridge growth through bulging under compressive flow. This hypothesis is consistent with results from laboratory experiments that were performed on a model ramp employing mixtures of Xanthan Gum, sand and gravel. Indications were also found that overthrusting is involved in the development of transverse ridges on rock glaciers. Copyright (C) 2004 John Wiley Sons, Ltd.