Active layer thermal regime at three rock glaciers in Greenland

Active layer temperature measurements are described from three active rock glaciers in Greenland: two in central‐west Greenland, and one in north‐east Greenland. Two of the rock glaciers are talus‐derived and one is glacier‐derived. The thermal characteristics of the very coarse‐grained active layer on the rock glaciers are described and compared with the thermal characteristics of other types of active layer. No significant differences between the active layer on talus‐derived rock glaciers and the analogue surface layer on glacier‐derived rock glaciers were found. Conductive as well as non‐conductive heat transfer processes appear to be important in the active layer on both rock glacier types. In particular, phenomena such as wind pumping and refreezing of percolating surface melt water may temporarily provide conditions for rapid, non‐conductive heat transfer processes. Different surface roughnesses, such as represented by the typical rock fragment size, could further contribute towards different degrees of active layer ventilation. The calculated apparent diffusivity varies considerably during the year, apparently on a seasonal basis. Meteorological controls on this variation are discussed, and thus the environmental controls on rock glacier formation. In general, it appears that the coarse surface layer on rock glaciers acts as a thermal filter, protecting the permanently frozen rock glacier core when snow cover is absent or thin, and conversely when thick snow cover is present. This may explain why rock glaciers tend to be especially frequent in dry, continental areas, and less so in humid areas. © 1997 John Wiley & Sons, Ltd.