Glacial erosion involves cutting and harvesting rocks from valley beds using basal sliding, assisted by melt water. Quarrying operations are most effective where meltwater acts as an efficient lubricant to facilitate basal sliding.
Recent research indicates that melting ice typically speeds up subglacial erosion rates over long-term averages, although its causes remain elusive.
Abrasion
As glaciers move across bedrock they scrape the surface using a process known as abrasion, creating distinctive smooth and polished bedrock surfaces characteristic of glaciated areas. Abrasion also helps form other glacial landforms such as striations which is created when glaciers move over bedrock creating long straight lines etched into it by their movement.
Abrasion depends on several factors, including hardness and concentration of debris in a glacier, as well as force exerted by it against bedrock. Furthermore, its rate also depends on fragment size and frictional force between fragments.
Erosion by melt water is another essential aspect of glacial erosion, though its rate is slower due to the lesser erosive power of melting water than that of ice or rock. Still, melting water can still break down or dissolve sand and clay deposits to expose harder rocks underneath them.
Melt Water
Glacial melt water has an immense influence on erosion. It forms unique landforms in glacial landscapes such as trench-like spillway systems such as Channeled Scabland, residual hills with smooth surfaces and longitudinal grooves known as glacial striations grooves. Furthermore, moulins (cylindrical shafts) at the surface form as well as subglacial drainage networks to different extents depending on discharge rates.
Melt water plays a critical role in various mechanical processes, including erosion and plucking. Since melt water flows fast with both bedload and suspended load, it is particularly effective at producing an abrasive erosion effect.
As glaciers retreat they often leave behind layers of gravel, sand and rocks known as till. Till is produced when streams of meltwater seep beneath a retreating glacier to deposit sediments as it recedes – creating landforms such as eskers, drumlins and kettle lakes as well as characteristic features associated with glaciation such as fjords, glaciated valleys and horns.
Subglacial Streams
Subglacial erosion often produces incised channels carved through sediments and bedrock, usually by abrasion but occasionally quarrying occurs when exploiting preexisting weaknesses in the bedrock itself. Abrasion alone cannot explain these features fully as quarrying often happens at preexisting weak points of rock structures that abrasion cannot reach.
An erosional weakness can be created either through ice deformation (cracking) or water pressure fluctuations (quarrying), with latter often happening when glaciers stretch over high points on their beds and generate less than their weight of ice (flotation), creating water pressure fluctuations that allow quarrying.
Pressure-driven processes produce the characteristic marks of glacial erosion on bedrock known as “striae.” Emerging data also suggests that quarrying may also play an integral part in erosion rates of glacial trough floors (i.e. inner gorges) from quarrying operations – potentially raising erosion rates beyond previous estimates; especially true in environments dominated by glaciated and debris-charged bedrock (e.g. fjords and deep glacial valleys) where glaciers can act as effective erosion agents. This process depends on altitude limits within which mountain glaciers can become effective erosion agents in terms of producing effective erosion rates from glacier action being self-limited due to effective glaciers being effective erosion agents from effectively being effective erosion agents due to mountain glaciers being capable of being effective erosive agents at operating effectively being effective erosion agents themselves being limited by mountain glaciers being capable of being effective erosion agents in being effective erosion agents within that system itself; such environments being self-limited by altitude limits at which mountain glaciers can effectively act as effective erosion agents capable of being effective agents capable of being effective erosion agents acting effectively enough.
Till
Till is an unsorted deposit left behind by glacial ice, composed primarily of clay and rock fragments of intermediate size (see Figure below). Due to their close encounter with grinding glacier ice, fragments often develop facets and striated patterns from grinding during melting processes. Till deposits may also be organized according to direction of movement of ice as shown by winding ridges called eskers or wide areas with stratified drift that follow where glaciers flowed in or out (for instance eskers point in or out).
Cirques, rock basins and fjords are other large-scale forms of glacial erosion found across kilometric scales that feature deep troughs as well as ridges, walls and cliffs. Cirques can often be found in areas once covered by glacier ice; their formation often makes the Arctic landscapes appear more distinct than elsewhere.