Evidence of glacial erosion can be observed in various ways, such as U-shaped valleys, horns (flank cliffs of mountains separated by aretes), glacial polish and striations patterns.
These features are formed through two of the primary forms of glacial erosion – plucking and abrasion. Both processes result in incredible landscape features.
Plucking
While glacier erosion is commonly perceived as an abrasive process that produces drumlin-shaped bedforms, it also ploughs. Ploughing increases shear stresses on fewer particles which increases particle abrasion and disintegration (Reference Iverson 1999). Evidence for ploughing can be seen both past and present glacial environments.
Ploughing and abrasion occur beneath cold glaciers at relatively low rates; generally limited to areas with thin ice. However, because subglacial sediments exhibit variable deformation rates due to heterogeneity differences among them, different rates of deformation could result in rapid subglacial landform formation, including drumlins.
Subglacial erosion by ploughing can contribute to the formation of long, elongated bedrock features known as striations. Striations is most frequently found on fine-grained rocks like carbonates and sandstone, while it may occur less frequently on coarse-grained but fractured rocks like granite and sandstone; its rate depends on abrasion/abrading rates.
Abrasion
Glacial erosion occurs when rocks are ground down into talc powder by being ground against each other under the enormous weight of a glacier, leading to its ultimate destruction and creating distinct features of a glaciated landscape. This form of erosion plays a key role in creating many distinctive features within it.
To gauge the rate of this erosion, one common strategy for measuring it is searching for toolmarks or glacial striations on rocks and glaciers. Although this method works, there can be complications associated with using it to estimate rates of erosion. Bedrock erosion is greatly influenced by subglacial till, which acts as a lubricant and speeds up erosion rates. As well, the rate of abrasion can be affected by fluctuations in subglacial water systems and loading around cavities in beds (Hallet, Reference Hallet1979). Due to these influences, basal sliding velocity estimation becomes difficult – the primary factor controlling erosion. Thus, for accurate assessment of abrasion assessments one needs long-term records with frequently spaced measurements.
Freeze-thaw weathering
Freeze-thaw weathering forms periglacial landscapes through physical (mechanical) weathering and erosion. This process occurs in porous or permeable rocks and soils that experience frequent diurnal cycles of freezing and thawing, with water expanding 9% when frozen within rock pores or cracks when it expands, exerting pressure upon the rock that could ultimately cause it to fracture.
Freezing and thawing release minerals and nutrients stored in rocks that become available for plant uptake, helping create soil formation and cycling of nutrients, as well as shaping valleys, canyons, gorges and other landscape features.
Glaciers are powerful tools for shaping the landscape as they melt, transport and deposit rock fragments and sediment. As a result, glaciers create distinct glacial landforms such as corries, aretes, pyramidal peaks, U-shaped valleys ribbon lakes and roche moutonnee. These landscapes are stunning to look at while serving an essential purpose within ecosystems on Earth. Freeze-thaw weathering helps break rocks down into fine particles that end up enriching soil health through freer development and vitality.
Geomorphic structures
Glacial erosion creates distinct features in the landscape that are easily identifiable as landforms; examples include lakes, ridges, or even subtler features like aretes.
Geologists examine these structures from three angles: descriptive/geometric, kinematic and dynamic. Descriptive/geometric analysis concerns itself with positions, orientations and sizes of rocks; while kinematic analysis investigates what moved where and the force exerted upon it.
Glacial erosion can be difficult to spot in most settings; its effects rely heavily on abrasion which only works when moving ice is moving; glacial flow usually does not generate enough of this type of friction, while till can often help limit bedrock erosion by smoothing stress concentrations and dampening water-pressure fluctuations (Cuffey and Alley 1996). Therefore, it’s essential that landscapes be checked for telltale signs of glacial erosion (reference Cuffey and Alley 1996). This is why it is vital that landscapes be carefully examined in search of telltale signs of glacial erosion (reference Cuffey and Alley 1996). This is why looking out for telltale signs is essential.