Glacial Erosion Processes
There are two types of glacial erosion:
Abrasion
Occurs when rocks and stones become embedded in the base and sides of the glacier. These are then rubbed against the bedrock (at the bottom of the glacier) and rock faces (at the sides of the glacier) as the glacier moves. This causes the wearing away of the landscape as the glacier behaves like sandpaper.
Plucking
Occurs when rocks and stones become frozen to the base or sides of the glacier and are plucked from the ground or rock face as the glacier moves. It leaves behind a jagged landscape.
There are two associated processes:
– Meltwater erosion and the role of meltwater in entrainment.
– Freeze-thaw weathering breaks up rock on valley sides, which then falls onto a glacier and can later become entrained.
Glacial Transportation
There are three type of ways in which a glacier can transport material:
1. Supraglacial: mainly weathered material, carried on the top of a glacier.
2. Englacial: formally supraglacial material, but now buried by fresh snowfall and carried within the ice.
3. Subglacial: material carried below the ice, which is dragged and pulverised by the overlying glacier.
Glacial Landform Environments
Periglacial – Exist at the edges of glaciers and can be extensive in scale. As these areas are so large, the landforms here often occur at a macro-scale.
Glacial – Within the actual physical mass of glacier ice, forming the glacier system, which includes the processes of flow, erosion and deposition.
Marginal – At the sides or end of a glacier. Weathering and deposition operate here to create landforms such as moraines.
Proglacial – In front of, at, or immediately beyond the margin of a glacier. Fluvioglacial processes operate here, creating outwash plains, meltwater channels and proglacial lakes.
Scale of these Landforms or Environments
Macro-Scale Ice-sheet eroded knock and lochan landscapes, cirques, arêtes and pyramidal peaks, glacial troughs, ribbon lakes, till plains, terminal moraines, sandurs.
Meso-Scale Crag and tail, roches moutonneés, drumlins, kames, eskers and kame terraces, kettle holes.
Micro-Scale Striations, glacial grooves and chatter marks, erratics
Glacial Deposition:
This is the settling of sediments left behind by a moving glacier.
– The collective name for all the sediments and debris deposited under glacial conditions is Glacial Drift.
– Sediments that were deposited by melting ice or by glacial streams are Fluvio-Glacial.
– Material deposited directly by the glacier, such as moraine and intra-glacial material dropped ‘in situ’ by retreating ice, is known as till.
-Piles of till deposited along the edges of past glaciers are called moraines.
The Scale of Environments and Landforms
It is important to be able to comment on the scale of the physicial environment as this is AO2, when making a judgment on the impact of different processes on the landscape:
Macro-Scale
Ice-sheet eroded knock and lochan landscapes, cirques, arêtes and pyramidal peaks, glacial troughs, ribbon lakes, till plains, terminal moraines, sandurs.
Meso-Scale
Crag and tail, roches moutonneés, drumlins, kames, eskers and kame terraces, kettle holes.
Micro-Scale
Striations, glacial grooves and chatter marks, erratics