GLACIAL LANDFORMS, EROSIONAL FEATURES: Micro- to Macroscale Forms

Some of the most familiar products of glaciation are examined in this article, including striae, friction cracks, p-forms, and roches moutonnées, which are all formed by the subglacial processes of abrasion and quarrying. Abrasion is the process by which glaciers erode and smooth their bed by indentation fracture and plowing of clasts and polishing by shearing of fine sediment across bedrock. Quarrying of bedrock through fracturing and plucking is the dominant erosional process in the subglacial environment and provides material for the abrasion process. The role of water pressure fluctuations and subcritical crack growth is of major importance in both abrasion and quarrying. Products of abrasion include striae, friction cracks, and p-forms, which are all streamlined negative-relief features, whereas crag and tail, rock drumlins, and whalebacks are streamlined positive-relief features. Roches moutonnées are formed by quarrying and abrasion, and they form a partially streamlined positive-relief feature. All these forms may be used to reconstruct former ice-flow directions.