624
Climatic Geomorphology
activity of the large icecaps during the Quaternary. These interpretations must be based on
precise analogies with the actual environment. Despite the difficulties for interpretation,
nowadays there is a detailed knowledge of the principal groups of landforms, the processes
involved and the geomorphologic history of the Laurentide and Fennoscandian ice sheets.
In the last three decades, important progress on the knowledge of climate change has
been made on the basis of core records, deep sea sediments, and ice sheets. This implies a
substantial scientific advance concerning the interpretation of the landforms produced by
ice sheets (Hughes, 1992).
Erosive morphologies resulting from the activity of ice sheets are a function of a
group of basic variables. The factor of greatest effect is the temperature at the base of
the ice, because when it reaches its melting point it slides and erodes. Geology plays a
variable role; on the one hand, the erosion develops more easily in fractures, whereas on
the other hand, the presence of permeable rocks facilitates the loss of water and the
decrease of erosion. Topography controls the ice thickness, and also favours the
convergence and divergence of the ice flow (Chorley et al., 1984). Nevertheless, it is
necessary to take into account that some zones, as in Buchan, Scotland, there was not any
glacial erosion, because thick weathered profiles remain intact after having been covered
by ice (Hall, 1986). This is one of the arguments used by the followers of the hypothesis
of glacial protectionism.
Some authors have calculated the volume eroded by ice in ice sheets of intermediate
latitudes. White (1972) considered that its erosive capacity has been very high, because it
has eroded and mobilized a rock thickness of more than 1000 m in the Hudson Bay region.
The erosive action of the ice sheets is helped by the existence of thick regoliths, as in
northern Scotland where there is a regolith thicker than 50 m (Fitzpatrick, 1963). When the
front of the glacier advances, it runs into loose material, which is easily evacuated, pushed
as does a bulldozer (Bakker, 1965; Thomas, 1994). These regoliths, resulting from
preglacial chemical weathering, constitute a good reason for explaining the fine-grained
tills, in comparison to those made up of fresh rocks (Feininger, 1971).
Regional erosional landforms are marks of subglacial erosion affecting bedrock. They
consist of elongated hills, roches moutonn6e and bedrock basins. The erosion is more
intense along joints, faults and dikes. This landscape is known as a topography of hills and
lakes, so termed in Scotland by Linton (1963). Also large areas exist with this morphology
in the Canadian Shield and western Greenland. This topography is characterized by a
landscape in a variety of forms, controlled by weak substrate structures, and with widths of
no more than 100 m.
The deposits generated by the activity of glacier masses occupy 10% of the Earth's
surface. Depositional landforms, which are related to icecaps, often are difficult to interpret, because they are the result of the superposition of materials corresponding to several
glaciations, in which dates are commonly difficult to obtain.
Moraines formed by icecaps present a simpler pattern than the ones generated in valley
glaciers. At first glance, the landforms look straight but their main form is arched, as from
the Laurentide ice sheet, where this form is the result of numerous lobes on the frontal side
of the icecap (Figure 24.7). In many places, these large moraines are thrust moraines, with
hundreds kilometres of length and thicknesses of up to 400 m. Locally, they can exceed
200 m height. The interpretation is complex when deposits of different ages but similar
lithology are superimposed. The C-14 dates indicate the different ice-sheet lobes have
Climatic Geomorphology
activity of the large icecaps during the Quaternary. These interpretations must be based on
precise analogies with the actual environment. Despite the difficulties for interpretation,
nowadays there is a detailed knowledge of the principal groups of landforms, the processes
involved and the geomorphologic history of the Laurentide and Fennoscandian ice sheets.
In the last three decades, important progress on the knowledge of climate change has
been made on the basis of core records, deep sea sediments, and ice sheets. This implies a
substantial scientific advance concerning the interpretation of the landforms produced by
ice sheets (Hughes, 1992).
Erosive morphologies resulting from the activity of ice sheets are a function of a
group of basic variables. The factor of greatest effect is the temperature at the base of
the ice, because when it reaches its melting point it slides and erodes. Geology plays a
variable role; on the one hand, the erosion develops more easily in fractures, whereas on
the other hand, the presence of permeable rocks facilitates the loss of water and the
decrease of erosion. Topography controls the ice thickness, and also favours the
convergence and divergence of the ice flow (Chorley et al., 1984). Nevertheless, it is
necessary to take into account that some zones, as in Buchan, Scotland, there was not any
glacial erosion, because thick weathered profiles remain intact after having been covered
by ice (Hall, 1986). This is one of the arguments used by the followers of the hypothesis
of glacial protectionism.
Some authors have calculated the volume eroded by ice in ice sheets of intermediate
latitudes. White (1972) considered that its erosive capacity has been very high, because it
has eroded and mobilized a rock thickness of more than 1000 m in the Hudson Bay region.
The erosive action of the ice sheets is helped by the existence of thick regoliths, as in
northern Scotland where there is a regolith thicker than 50 m (Fitzpatrick, 1963). When the
front of the glacier advances, it runs into loose material, which is easily evacuated, pushed
as does a bulldozer (Bakker, 1965; Thomas, 1994). These regoliths, resulting from
preglacial chemical weathering, constitute a good reason for explaining the fine-grained
tills, in comparison to those made up of fresh rocks (Feininger, 1971).
Regional erosional landforms are marks of subglacial erosion affecting bedrock. They
consist of elongated hills, roches moutonn6e and bedrock basins. The erosion is more
intense along joints, faults and dikes. This landscape is known as a topography of hills and
lakes, so termed in Scotland by Linton (1963). Also large areas exist with this morphology
in the Canadian Shield and western Greenland. This topography is characterized by a
landscape in a variety of forms, controlled by weak substrate structures, and with widths of
no more than 100 m.
The deposits generated by the activity of glacier masses occupy 10% of the Earth's
surface. Depositional landforms, which are related to icecaps, often are difficult to interpret, because they are the result of the superposition of materials corresponding to several
glaciations, in which dates are commonly difficult to obtain.
Moraines formed by icecaps present a simpler pattern than the ones generated in valley
glaciers. At first glance, the landforms look straight but their main form is arched, as from
the Laurentide ice sheet, where this form is the result of numerous lobes on the frontal side
of the icecap (Figure 24.7). In many places, these large moraines are thrust moraines, with
hundreds kilometres of length and thicknesses of up to 400 m. Locally, they can exceed
200 m height. The interpretation is complex when deposits of different ages but similar
lithology are superimposed. The C-14 dates indicate the different ice-sheet lobes have