The geomorphic significance of rock glaciers: estimates of rock glacier debris volumes and headwall recession rates in West Greenland

To obtain knowledge on rockwall retreat rates at sites with rock glaciers, an inventory of about 400 individual rock glacier sites in West Greenland was carried out by means of field studies, and using aerial photographs and topographic maps. A number of sites with ice-cored moraines beyond normal glaciers were included in the analysis for comparative purposes. The estimated debris volume was compared with the size of the source headwall. The result of the inventory suggests that the presence of rock glaciers indicates extraordinary high retreat rates for rock free faces above. Especially, headwalls above glacier-derived rock glaciers are exposed to high weathering rates, and thereby presumably delimit critical ranges regarding altitude for headwall retreat rates. The relation of such a critical altitudinal range to other regional concepts, such as glaciation level (GL) and glacier equilibrium line, is discussed. From this, comments are also made on the relation between various permafrost zones and the typical regional climate within the maximum headwall weathering altitude at sites with active rock glaciers. Finally, the potential importance of this range of maximum weathering for understanding the long-term evolution of high-relief cold-climate landscapes is emphasised.