Many influences control the processes and patterns of glaciation, as well as the form, size, and distribution of erosional forms.
The four major factors include:
 

1.  Glaciological variables (characteristics of the ice, especially at the bed):  include basal shear and normal stress, subglacial water pressures and the local drainage system arrangement, as well as the flow direction, basal velocity, thermal regime, and the amount of debris entrained in the ice.

2.  Substratum characteristics (physical properties of the bed):  include the underlying geologic structure, lithology, fracture and joint distribution of the bedrock, the degree of previous weathering of the bedrock, thickness and composition of unconsolidated sediments, and the permeability of the underlying sediments.

3.  Topographic variables:  On a grand scale, topography may define a cachement area, influence the location of glacial ice masses, their morphology, and mass budget.  On a small scale, topography may act as a roughness element, define local flow patterns, and determine stress locations at the bed.

4.  Temporal variables: control the duration of a glaciation, as well as the changes in the above variables across time.

This diagram illustrates a dominantly streamlined erosional landscape, even though it includes trough erosion and selective linear erosion as well as areal scour.  Trough erosion is the most efficient type of glacial erosion, as it causes the most dramatic erosion and landscape modification of all.  Selective linear erosion produces streamlined landforms.  The influence of areal scour erosion by an ice sheet does the least amount of erosion and landscape modification because it polishes the existing resistant bedrock rather than carving or breaking the rocks and incorporating them into the ice.

The erosional influence of ice sheets versus alpine glaciation is evident in this diagram.  The erosive potential of ice sheets is distributed across a large area, which decreases the amount of concentrated energy locally available to influence the morphology of the landscape.  Modification by local alpine glaciation is indicated by vertical lines, where the closest line spacing represents the highest amount of landscape modification.  Horizontal lines indicate modification by ice sheets, with the closest line spacing represents the highest amount of landscape modification.  Areas which have been influenced by both types of glacial systems.

The influence of ice sheets and alpine glaciation upon landscape modification and evolution is evident in this diagram.  This figure represents (a) a preserved proglacial landscape, (b) mountain glaciation, (c) interconnected valleys of ice sheet glaciation, and (d) areal scour.

Erosional landscapes are composed of smaller-scale erosional features and landforms which demonstrate the processes and conditions at work when they are formed.  Small-scale erosional forms include striae, rat tails, chattermarks, crescentic gouges and fractures, and p-forms.  Intermediate-scale erosional forms include roches mountonnees, whalebacks and rock drumlins, crag and tails, and channels (such as nye channels, tunnel valleys, ice-marginal (lateral) channels, proglacial channels, and flood tracks).  Large-scale erosional landforms include rock basins and overdeepenings, basins in soft sediments, troughs and fiords, cirques, and strandflats.  A more complete discussion of these landforms and features may be found in the Erosional Landscapes section of our hypertext.

The landscape distribution of Antarctica is dominated by ice shelves to the left (north) around the West Antarctic Ice Sheet.  The East Antarctic Ice Sheet has some ice shelf development, as well as areal scouring and selective linear erosion.  The predominantly alpine landscapes in this region are probably a result of more coastal precipitation, as well as being at the ice sheet-mountain glacier interface.

This map of Greenland illustrates the distribution of landscape types outside of the ice sheet margin.  Warm upwelling ocean currents from Great Britain bring water-saturated air masses and lots of snow to the eastern coastline.  This results in a great deal of precipitation along the southeast coastline, but creates an arid, low precipitation climate to the west.  The dominance of areal scouring along the southwestern coastline is probably a result of this dry, cold-based climate.

Cross-cutting relationships are indicators of temporal or spatial (or both!) change at any scale.  Such relationships of landforms may represent the work of different glacial periods, or various stages of a single glaciation.  A small-scale example is the cross-cutting striae on bedrock of the Snowdon massif, Wales, or on a larger scale, the Tampere area of southwestern Finland.  Erosional landforms of these regions demonstrate cross-cutting relationships of striae, till fabric, and rock whalebacks.  A grander scale example of cross-cutting relationships would be the striae beneath the Laurentide ice sheet as described in Glaciers with Space:  Time in our hypertext.

This map is a location map of a field area in the Snowdon area of western Wales.  The large dot represents the study area, the solid arrows represent early ice sheet movement, the broken arrows represent the more recent Loch Lomond (Younger Dryas) Stadial Glacier movement, and the solid line represents the spatial limit of the Loch Lomond Stadial Glacier.

This illustration depicts the pattern of striae produced by early ice sheet flow.  The hatchured lines represent the areas from which ice sheet striations have been removed (for the most part) by Loch Lomond Stadial erosion.

This diagram demonstrates the relationship between striations, till fabric, and whalebacks formed during three successive directions of glacier movement during the same glaciation.  The bold, solid arrows represent the oldest direction of glacier movement, the bold, dashed arrows represent the direction of glacier flow during an intermediate stage, and the dashed arrows indicate the most recent motion (as interpreted by Virkkala, 1960).

This diagram shows the evolution of a trough cross-profile as modelled by (Harbor 1988). The evolution of the troughs with respect to time are shown in succession downward.  Ice discharge, surface slope and bedrock are all constants.  The varying ice velocites create a greater amount of erosion at the base of the glacier.  These velocity differences create an overdeepening leaving the side walls almost vertical and susceptible to mass-wasting.

Benn, Douglas I., and David J. A. Evans, 1998, Glaciers and Glaciation, Arnold Publishers, London, 734 p.

Flint, Richard Foster, 1971, Glacial and Quaternary Geology, John Wiley and Sons, Inc., Canada, 892 p.

Harbor, Jonathan M., Hallet, Bernard, and Charles F. Raymond, 1988, "A numerical model of landform development by     glacial erosion", Nature, vol. 333, p. 347-349.

Harbor, Jonathan M., 1992, "Application of a general sliding law to simulating flow in a glacier cross-section", Journal of Glaciology, vol. 38, no. 128, p. 182-190.

Sugden, David E., and Brian S. John, 1976, Glaciers and Landscape:  A geomorphological approach, Halsted Press, John Wiley and Sons, New York, 376 p.
 
 

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