Geometry and dynamics of two lobe-shaped rock glaciers in the permafrost of Svalbard

Photogrammetric measurements of geometry, thickness changes and horizontal movements over time periods of more than 20 years were performed for two rock glaciers in western Svalbard. The results for Brøggerbreen rock glacier revealed no significant thickness changes (i.e. <1 cm a -1 ) and horizontal velocities in the range of a few cm a -1 . No significant horizontal or vertical changes over the observation period were detected for a rock glacier at Nordenskiöldkysten. A number of observations, however, indicate slow deformation and advance of the body. Under this assumption, the age of the rock glacier can be estimated in the order of 50 ka, which implies potential impact on the rock glacier by (de-)glaciations and sea level changes. While rock glaciers on Svalbard represent creep of cold and continuous polar permafrost, those in the European Alps are an expression of warm and discontinuous mountain permafrost creep. From inter-comparison of the above results with two rock glaciers in the Swiss Alps, we conclude that the observed differences in creep speed and surface micro-topography could, to a large extent, be explained by the substantial differences in ground thermal regime.