On the effects of bedrock protuberances upon the depositional and relief-forming processes in different marginal environments of Spitsbergen glaciers
Abstract The problem formulated in the title is considered on the basis of examples drawn from two retreating Spitsbergen glaciers Anreasbreen and Aavatsmarkbreen, which are though to be representative of two mahor types of ice marginal environmnts differing from each other in respect of the geometry and dynamic conditions of the terminal zones. These are: type A — associated with an active steep-fronted glacier snout, and type B — associated with a stagnant terminal zone. The environments of type B related the depositional and relief-forming processes to the dynamic state of ice prior to stagnation on this basis two sub-types are distinguished: B 1 — associated with a stagnant terminal zone which experienced extending or uniform flow prior to stagnation; and B 2 — associated with a stagnant terminal zone which experienced compressive flow prior to stagnation. Larger obstacles to glacier flow on the bed bring about enhanced debris supply at the glacier surface and consequently formation of ice-cored moraines equally in all of these environments, however, the processes involved in the formation of ice-cored features as well as their location are different in each. In environment of type A, ice-cored moraines are formed on the lee-side of the protuberances in associated with dump moraines, while in environments of sub-types B 1 and B 2 they tend to be located immediately on the top of the bedbrock protuberances or in close down-glacier vicinity and do not differ genetically from the overall ice-cored morphology. A particularly efficient relief-forming process in environments of type B (both B 1 and B 2 ) is thermo-erosion by supraglacial meltwater streams. There is a general tendency to smooth the pre-existing glacier bed irregularities in environment of type A and to accentuate them in environments of type B.