ACTIVE LAYER THERMAL REGIME AT 3 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 o ne is glacier-derived. The thermal characteristics of the very coarse- grained active layer on the rock glaciers are described and compared w ith the thermal characteristics of other types of active layer. No sig nificant differences between the active layer on talus-derived rock gl aciers and the analogue surface layer on glacier-derived rock glaciers were found. Conductive as well as non-conductive heat transfer proces ses appear to be important in the active layer on both rock glacier ty pes. In particular, phenomena such as wind pumping and refreezing of p ercolating surface melt water may temporarily provide conditions for r apid, nonconductive heat transfer processes. Different surface roughne sses, such as represented by the typical rock fragment size, could fur ther contribute towards different degrees of active layer ventilation. The calculated apparent diffusivity varies considerably during the ye ar, apparently on a seasonal basis. Meteorological controls on this va riation are discussed, and thus the environmental controls on rock gla cier formation. In general, it appears that the coarse surface layer o n rock glaciers acts as a thermal filter, protecting the permanently f rozen rock glacier core when snow cover is absent or thin, and convers ely when thick snow coa er is present. This may explain why rock glaci ers tend to be especially frequent in dry, continental areas, and less so in humid areas. (C) 1997 John Wiley & Sons. Ltd.