Glaciated landscapes feature erosion of bedrock by glaciers that gives rise to distinctive landforms. Abrasion and quarrying also play their part in shaping these distinctive features such as striations or chatter marks on rock surfaces.
Abrasion is an integral component of warm-based glacier movement and plays an integral part in creating unique glacial features, including horns and bowl-shaped depressions known as cirques.
Abrasion
Glaciers use their abrasive power on their beds to leave behind many iconic glacial landforms, such as rock striations and grooves from being pulled along, glacial polish and pavements, valley walls covered in these features, particularly cirques and U-shaped valleys.
Abrasion from water erosion can erode underlying rocks, leaving behind talus deposits at the sides of valleys or as small domes known as “roche moutonnees” at the head of some valleys.
Glacier transport of materials has an enormous effect on abrasion rates. Abrasion depends on friction between ice and rocks with which it interacts; when more material comes into contact with each rock surface, more friction ensues and more likely occurs; hence abrasion rates decline at relatively lower debris concentrations before friction-induced drag overwhelms their forces and overtake them.
Quarrying
Quarrying is undeniably an essential process that influences glacial erosion rates, with evidence for it found in rock flour, surface striations grooves, and pavements caused by dragging rocks over glacier beds; smoothed-off clasts from contact with other rocks; striated bedding planes or fractured surfaces of rock debris found within certain glaciers’ beds; as well as higher denudation rates than expected for specific glaciers.
Plucking refers to the subglacial removal of blocks of rock that have become detached from their surroundings, producing an arete or trough (Hildes et al. 2004; Riihimaki and others 2005). Recent advances in abrasion mechanics emphasize quarrying as a potential avenue for quicker glacial erosion.
Freezing on
Glaciers may erode bedrock, but they also contribute to making our landscape so visually striking – including U-shaped valleys, cirques, moraines and even striations (ice-related scrape marks) which add interest.
The erosion rate of a glacier depends on what it’s freezing on. If it’s on deformed till, its erosion rate will be much slower due to reduced stress concentrations on its bed, dampened water pressure fluctuations that might promote erosion, and an uneven distribution of deformation across an ample thickness.
Glacial erosion rates are proportional to rock uplift rates and mass balance. They become less sensitive to ELA changes when the glacier becomes steep and response times become short, due to steeper glaciers losing less mass quickly than thinner ones.
Ice Flow
As glaciers move across mountain sides, they erode rocks of all sizes. The fragmented rock fragments that result are then deposited as till, which acts to inhibit further erosion by smoothing bedrock surfaces to reduce stress concentrations, dampening water-pressure fluctuations which might contribute to bedrock erosion (e.g. in inner gorges) and spreading deformation across large volumes to limit damage from ice sheet flow (Cuffey and Alley 1996).
Rapid erosion can create distinctive depositional landforms such as eskers, kames and drumlins; while abrasion, quarrying and plucking also produce features like fjords and deeply incised valleys as well as broad areas of unsorted deposits called fluvioglacial drift – often creating distinct shapes like kettle lakes or cirques in landscapes like this one. Many of these landforms are now being studied closely to increase our knowledge of glacial geomorphic processes.