Galena Creek rock glacier revisited - New observations on an old controversy

Galena Creek rock glacier (GCRG),northwest Wyoming,exhibits most of the cla ssic characteristics of rock glaciers. Clean ice with silty bands was found beneath a c. 1 m thick debris mantle by Potter. He inferred that the ice i s glacigenic, originating in the small snowfield in the cirque at the head of GCRG. This view was challenged by Barsch, who asserted that the ice in G CRG is of "permafrost" origin. Since then GCRG has become a lightning rod f or opponents and proponents of the glacigenic ice model for rock glaciers. We review evidence for that model here. Movement marks emplaced on GCRG in the 1960s were resurveyed in 1995 for a 30+ year record of movement. Maximum surface velocity is 45 cm/yr on gentle slopes and 80 cm/yr in a steep reach where GCRG spills out of the cirque. The less active, down-valley third of GCRG is moving at a maximum 14 cm/yr, and lobes formed between the more and less active parts have complex movem ent and are advancing down-valley over adjacent lobes at a maximum of 6.5 c m/yr. New refraction seismic profiles on GCRG were used to determine the thicknes s of the debris mantle over ice. On the up-valley, active part of GCRG,the debris mantle is a relatively uniform c. 1 m thick. On the down-valley, les s active part, the thickness of the debris mantle is much more variable,but it is generally thicker. We cannot tell, on the basis of seismic data alon e, whether the frozen material beneath the debris mantle is ice or a debris -ice mixture, but the results are not inconsistent with the glacigenic mode l for the origin of the ice. Two long-profiles in the cirque may identify b edrock at about 20-25 m depth.