Glacial erosional landforms: origins and significance for palaeoglaciology

• Published in: Progress in Physical Geography: Earth and Environment
• Main Authors: Glasser, Neil F., Bennett, Matthew R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: SAGE Publications 2004
• Subjects: General Earth and Planetary Sciences; Earth and Planetary Sciences (miscellaneous); Geography, Planning and Development; Ice Sheet
• Online Access: http://dx.doi.org/10.1191/0309133304pp401ra; http://journals.sagepub.com/doi/pdf/10.1191/0309133304pp401ra

Glacial inversion modelling of continental-scale palaeo-ice sheets is now recognized as an important tool in palaeoglaciology. Existing palaeoglaciological reconstructions of the dimensions, geometry and dynamics of former ice sheets are based mainly on glacial depositional, as opposed to glacial erosional, landforms. Part of the reason for this is a lack of detailed understanding of the origin and significance of glacial erosional landforms. Here we review recent developments in our understanding of the processes and landforms of glacial erosion and consider their value in palaeoglaciology. Glacial erosion involves the removal and transport of bedrock and/or sediment by glacial quarrying, glacial abrasion and glacial meltwater. These processes combine to create a suite of landforms that are frequently observed in areas formerly occupied by ice sheets and glaciers, and which can be used in palaeoglaciological reconstructions. For example, all landforms of glacial erosion provide evidence for the release of subglacial meltwater and the existence of warm-based ice. Landforms of glacial quarrying such as roches moutonnées, rock basins and zones of areal scouring are created when cavities form between an ice sheet and its bed and therefore are indicative of low effective basal pressures (0.1-1 MPa) and high sliding velocities that are necessary for ice-bed separation. Fluctuations in basal water pressure also play an important role in the formation of glacially quarried landforms. Landforms of glacial abrasion include streamlined bedrock features (‘whalebacks’), some ‘p-forms’, striae, grooves, micro-crag and tails, bedrock gouges and cracks. Abrasion can be achieved by bodies of subglacial sediment sliding over bedrock or by individual clasts contained within ice. Although abrasion models depend critically on whether clasts are treated as dependent or independent of subglacial water pressure, it appears that abrasion is favoured in situations where effective basal pressures are greater than 1 MPa and where there ...