Herman Farbrot

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.

Composition and internal structures of a rock glacier on the strandflat of western Spitsbergen, Svalbard

This article presents data on composition and internal structures of a large lobe-shaped rock glacier at Nordenskiöldkysten, western Spitsbergen, based on Ground Penetrating Radar (GPR) and direct current (DC) resistivity tomography measurements. This rock glacier has a more complex surface topography than most rock glaciers in Svalbard and is probably also older. The GPR data indicate a quite chaotic structural pattern, far more complicated than for other investigated rock glaciers in Svalbard. This pattern might be due to the anticipated complex history of the rock glacier, involving glaciation and relative sea level changes. The geophysical results indicate ice-rich conditions, especially below ridges. Overall, the resistivity values are decreasing towards the front of the rock glacier, probably due to dynamic effects. Also, the resistivity results indicate that the active layer is thicker in dumps than below ridges. Considerations of ice content combined with previous velocity measurements indicate that the apparent standstill of the rock glacier is due to the low-gradient situations in which the rock glacier flows onto the strandflat.