Glacial erosion produces landforms from rock fragments (clasts) and sediment carried by glaciers, such as striations lines, grooves, and pavements ranging from decimeter to kilometric scales.
Quarrying and abrasion techniques work best when the glacier contains enough melt water to facilitate basal sliding, such as is often found with warm-based glaciers.
1. Abraded Surfaces
Glacial erosion sculpts the landscape by carving away rocks, sediment and other material, leaving behind distinctive marks known as glacial striations that help scientists pinpoint locations where glaciers once flowed.
Contrasting with river channels that erode soil through chemical and physical weathering processes, glaciers erode by mechanically abrading bedrock with two processes being the dominant forces: abrasion and quarrying.
Glacier ice resembles sandpaper as it rubs against bedrock surfaces, grinding away material to produce scratches (striations) in the rock surface and producing scratches (striations) where material has been lost to erosion1. Rate of abrasion depends upon size, concentration and velocity of ice, with warm-based glaciers producing greater basal sliding which drags debris across bedrock surfaces1 while cold-based glaciers remain frozen to their beds and consequently limit abrasion1. 1
2. Stoss-and-Lee Topography
Glacial erosion’s abrading and plucking processes result in noticeable landforms that stand out in any landscape, such as pyramidal peaks (corries), U-shaped valleys (hanging valleys, truncated spurs, ribbon lakes and roche moutonnee), sandstone arches and cliffs (aretes), rock outcrops with an uneven erosion pattern called “crags and tails” or stoss-and-lee topography, among many other notable features.
These features occur at scales ranging from meters to hundreds of meters and are characterized by smooth, streamline-molded upstream sides and steep, blocky downstream sides that may contain striations lines. Models using an easy relationship between erosion and glacier basal velocity and these forms tend to predict them accurately; overdeepened cirque floors or confluence-type overdeepenings in fjords or trunk valleys might also appear, as do overdeepened cirque floors and confluence-type overdeepenings in fjords and trunk valleys; however comparing erosion patterns over a large area fails to confirm an expected correlation with snow accumulation or mass balance – suggesting bedrock control on glacial erosion is complex.
3. Quarrying
Glacial erosion leaves behind various geomorphic features that are easily recognized, such as cirques, troughs, rock basins and fjords. Smaller features may include striations lines or deposits of sand-gravel.
Quarrying (or plucking) is the process by which pressure from overlying ice causes existing bedrock fractures to expand, isolating blocks of rock from their surrounding intact bedrock and creating isolated blocks of rock that stand alone from it. Quarrying is commonly believed to cause higher rates of denudation than abrasion.
Unfortunately, it can be challenging to measure quarrying rates due to difficulties distinguishing fracture patterns from concurrent fluvial erosion. The best way of doing so would be collecting very long records with frequent observations – although such records aren’t readily available – and making closely spaced observations; but such records don’t tend to exist either. Therefore, current models of quarrying rely heavily on assumptions regarding fracture growth and exploiting preexisting discontinuities with sliding ice that don’t correspond with field evidence.
4. Abrasion
Glacial erosion alters land through two main methods: abrasion and plucking. Abrasion involves glacier ice scraping rocks like giant file shredders sandpapering their surfaces; this causes landforms such as faceted clasts, striations grooves glacial pavements as well as glacial polish and rock flour to form on them.
Plucking is an indirect result of freeze-thaw weathering at the base of a glacier. Here, ice adheres to some rocks before pulling it away from others before further eroding away at what remains, leaving behind an irregular surface with sharp angles.
Glacial erosion creates many different landforms, including corries, aretes, pyramidal mountain peaks, cirques, U-shaped valleys, hanging valleys and ribbon lakes – as well as less obvious formations such as roche moutonnee and crag and tail formations. Glacial erosion is an extremely powerful force which can produce some spectacular landforms.