A rock glacier/debris‐covered glacier system at galena creek, absaroka mountains, wyoming

AbstractAt Galena Creek, the ice/debris system has alternated between rock glacier and debris‐covered glacier modes due to changes in the size of the accumulation area. In the rock glacier mode, coarse debris is concentrated at the base of couloirs along the lower edge of a small, steep accumulation area where it becomes part of the surface debris mantle of the rock glacier. In the debris‐covered glacier mode, debris is primarily incorporated englacially within an expanded accumulation area. Englacial debris originating on the sides of the cirque is concentrated at the margins of the glacier; debris originating from the cirque headwall is concentrated where it emerges in the ablation area and forms a debris cover. As the equilibrium line rises during warm periods, the debris‐covered glacier is transformed into a rock glacier. The marginal englacial debris is exposed progressively up‐glacier resulting in ice‐cored debris ridges which extend into the cirque and are analogous to the ice‐cored lateral moraines of many subpolar alpine glaciers. The debris‐covered terminus continues to flow as a rock glacier lobe. The debris ridges/lateral moraines record previous positions of a debris‐covered glacier margin and can be used to map past accumulation areas and to infer the position of the associated glacier terminus. At least three of these features are cross‐cut by the rock glacier. Age estimates for three glacial advances are made using reasonable surface velocities and the distance between a rock glacier lobe and the inferred position of its associated glacier terminus. The estimated ages correlate with regional alpine glacier chronologies. These observations, which are not unique to the Absaroka Range, have general utility for understanding how changes in the relative flux of ice and debris control the morphology of the resulting deposits and for placing rock glacier deposits within alpine glacier chronologies.Key words: rock glacierdebris‐coveredice‐coredAbsaroka