Chapter 3
Glacial erosion
For a long time, the capacity of ice to substantially modify the preexisting relief has been
well known. Knowledge about its action, in spite of the large number of publications on
this issue, is not very extensive and this arises from the difficulty of studying the action of
the ice on its bed, because the more effective erosive mechanisms take place under a thick
ice cover. Some investigations directed to this aim by means of tunnel perforations have
taken place, mainly in cirques. To this observation difficulty must be added the deficiency
of knowledge on the preglacial relief, which can prevent a suitable quantitative estimation
of the glacial erosion. Glaciations have also been superposed in the course of time in many
areas, so that interpretations are more difficult (Price, 1973).
Glacial erosive action appears at the ice-rock (or ice-glacial deposits) interface. We
know that erosive effects of ice without either movement or rocky material (clean ice) are
practically negligible. For the same kind of ice in movement, if it affects fresh and little
jointed rocks, the erosive power will be null or very small, although if the bottom material
is loose it can substantially modify its morphology. The greater erosive effects occur under
the action of thick temperate glaciers causing the extraction of glacier bed fragments and
mobilizing and transporting them to a more-or-less distant place, being able in its transport
to erode the rocky or loose material at the interface.
1. Erosive processes
We have already indicated that knowledge of glacial erosion is not very extensive.
Normally we deduce processes by indirect methods by means of experimentation in a
laboratory or by applying the most common deductive method of the Earth sciences, in
which from the effects we try to classify the processes that were produced, in this case
glacial erosional landforms (Goudie, 2004a).
Many factors affect the intensity of glacial erosive processes. They can be subdivided
into three great groups: the ones inherent to the glacial system, those concerning the
lithological and structural characteristics of the rocky substratum, and the ones relative to
the geometry of the substrate (Sugden and John, 1976; Drewry, 1986).
The importance of the glacial system is given, on the one hand, by the basal ice
temperature. When the temperature is close to the melting point the erosive effects are
without a doubt much more important; in the case of glaciers with low basal temperature,
the erosive action is only effective if debris is present at the interface. In addition to the
influence of temperature, another factor of great significance is the basal speed of the ice
mass that affects the transported amount of debris and, therefore, their erosive action and
Glacial erosion
For a long time, the capacity of ice to substantially modify the preexisting relief has been
well known. Knowledge about its action, in spite of the large number of publications on
this issue, is not very extensive and this arises from the difficulty of studying the action of
the ice on its bed, because the more effective erosive mechanisms take place under a thick
ice cover. Some investigations directed to this aim by means of tunnel perforations have
taken place, mainly in cirques. To this observation difficulty must be added the deficiency
of knowledge on the preglacial relief, which can prevent a suitable quantitative estimation
of the glacial erosion. Glaciations have also been superposed in the course of time in many
areas, so that interpretations are more difficult (Price, 1973).
Glacial erosive action appears at the ice-rock (or ice-glacial deposits) interface. We
know that erosive effects of ice without either movement or rocky material (clean ice) are
practically negligible. For the same kind of ice in movement, if it affects fresh and little
jointed rocks, the erosive power will be null or very small, although if the bottom material
is loose it can substantially modify its morphology. The greater erosive effects occur under
the action of thick temperate glaciers causing the extraction of glacier bed fragments and
mobilizing and transporting them to a more-or-less distant place, being able in its transport
to erode the rocky or loose material at the interface.
1. Erosive processes
We have already indicated that knowledge of glacial erosion is not very extensive.
Normally we deduce processes by indirect methods by means of experimentation in a
laboratory or by applying the most common deductive method of the Earth sciences, in
which from the effects we try to classify the processes that were produced, in this case
glacial erosional landforms (Goudie, 2004a).
Many factors affect the intensity of glacial erosive processes. They can be subdivided
into three great groups: the ones inherent to the glacial system, those concerning the
lithological and structural characteristics of the rocky substratum, and the ones relative to
the geometry of the substrate (Sugden and John, 1976; Drewry, 1986).
The importance of the glacial system is given, on the one hand, by the basal ice
temperature. When the temperature is close to the melting point the erosive effects are
without a doubt much more important; in the case of glaciers with low basal temperature,
the erosive action is only effective if debris is present at the interface. In addition to the
influence of temperature, another factor of great significance is the basal speed of the ice
mass that affects the transported amount of debris and, therefore, their erosive action and