TY - JOUR
T1 - Glacial erosional landforms: origins and significance for palaeoglaciology
AU - Glasser, Neil F.
AU - Bennett, Matthew R.
N1 - Glasser, N. F., Bennett, M. R. (2004). Glacial erosional landforms: origins and significance for palaeoglaciology. Progress in Physical Geography 28, 1, pp. 43–75
PY - 2004
Y1 - 2004
N2 - 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 are low sliding velocities.
Consequently, landforms dominated by glacial abrasion are created when there is no ice–bed
separation. Landforms of glacial meltwater erosion include both subglacial and ice-marginal
meltwater channels. Investigations of the relationship between glacial meltwater channels and
other aspects of the subglacial drainage system, such as areas of ice–bed contact, areas of ice–bed separation and precipitate-filled depressions, enable inferences to be made concerning former
subglacial water pressure-drainage relationships, effective pressures and glacier velocities.
Meltwater palaeovelocity and palaeodischarge can also be calculated from measurements of
channel shape, channel width and the size of material transported within former glacial
meltwater channels. We surmize that glacial erosional landforms offer insight into former glaciological
conditions at both the landform- and landscape-scale within palaeoglaciology. Exposureage
dating techniques, including cosmogenic isotope dating of bedrock surfaces, will be
important in increasing our understanding of the age and chronological significance of
landforms of glacial erosion. We conclude that landforms of glacial erosion are of great value in
ice mass reconstruction and speculate that these landforms will achieve greater recognition
within palaeoglaciology in line with improvements in exposure-age dating techniques.
AB - 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 are low sliding velocities.
Consequently, landforms dominated by glacial abrasion are created when there is no ice–bed
separation. Landforms of glacial meltwater erosion include both subglacial and ice-marginal
meltwater channels. Investigations of the relationship between glacial meltwater channels and
other aspects of the subglacial drainage system, such as areas of ice–bed contact, areas of ice–bed separation and precipitate-filled depressions, enable inferences to be made concerning former
subglacial water pressure-drainage relationships, effective pressures and glacier velocities.
Meltwater palaeovelocity and palaeodischarge can also be calculated from measurements of
channel shape, channel width and the size of material transported within former glacial
meltwater channels. We surmize that glacial erosional landforms offer insight into former glaciological
conditions at both the landform- and landscape-scale within palaeoglaciology. Exposureage
dating techniques, including cosmogenic isotope dating of bedrock surfaces, will be
important in increasing our understanding of the age and chronological significance of
landforms of glacial erosion. We conclude that landforms of glacial erosion are of great value in
ice mass reconstruction and speculate that these landforms will achieve greater recognition
within palaeoglaciology in line with improvements in exposure-age dating techniques.
KW - exposure-age dating
KW - glacial erosional landforms
KW - glacial erosional processes
KW - palaeoglaciology
U2 - 10.1191/0309133304pp401ra
DO - 10.1191/0309133304pp401ra
M3 - Article
SN - 0309-1333
VL - 28
SP - 43
JO - Progress in Physical Geography
JF - Progress in Physical Geography
IS - 1
ER -