Glacial erosion alters the landscape by carving and scraping away features, leaving moraines, eskers, drumlins and kettle lakes as landforms sculpted by this force of nature.
Erosion occurs when material wears away and brings the broken bits with it, gradually wearing away landforms such as corries, aretes, pyramidal peaks, U-shaped valleys and ribbon lakes in its wake. Ice can be an especially potent agent of erosion which leads to such features as corries, aretes, pyramidal peaks, U-shaped valleys and ribbon lakes.
Plucking
Glaciers are nature’s bulldozers, carving and shaping landscapes with immense force. They create features such as fjords, U-shaped valleys, pyramidal peaks and ribbon lakes; furthermore, ice flows erode and deposit sediment that leaves unique landforms such as ribbon lakes, moutonnee rocks, crag and tail formations and striations patterns behind.
Plucking is one form of glacial erosion and its rate is directly proportional to how fast the ice moves. A faster flow rate drags more abrading clasts over a bedrock region in an hour, increasing erosion rates as well as quarrying rates.
As mentioned previously, rock composition plays a large part in plucking. Some rocks are harder for ice to erode than others and as the ice passes over harder rocks it plucks them off on the lee side (also referred to as the stoss side), leaving behind interesting rock formations called stoss-and-lee topography that provides clues as to which direction the ice was moving and sometimes even gives us clues regarding its age.
Abrasion
As glaciers move down mountain slopes, rocks of various shapes and sizes strike against the earth below in a process called abrasion, producing long grooves called glacial striations in bedrock – one of the most noticeable features produced by glaciers on landscape.
Glacial erosion rates depend on both movement rate and surface properties; for instance, an increase in basal debris leads to greater abrasion but reduces basal sliding rates overall.
Erosion rates also depend on whether the rock underneath is harder or softer than other surfaces; soft rock tends to erode more quickly than more resistant varieties, and rates tend to be highest where recent tectonic activity has taken place.
Freeze-thaw weathering
Glaciated environments constrain sediment transport in several ways. Abrasion only becomes effective after deforming till has lowered the bed, as this reduces friction and dampens water-pressure fluctuations that otherwise might stimulate erosion.
Another factor limiting erosion is the speed at which glaciers move. Abrasion becomes ineffective if glacier movements are slow and ineffectual, although their speed depends heavily on other variables.
Freeze-thaw weathering (also called frost shattering) occurs when water seeps into cracks and pores of rocks and soil particles and freezes, then expands when it thaws, pushing apart these elements of rock and soil particles. Repeated cycles of freezing and thawing accelerate this process and can cause fragments of rock to fracture into fragments that break off, eventually breaking apart entirely – important processes in the preservation of fossilized plant and animal remains as well as why rocks exposed by glacial moraines feature distinctive shapes like this.
Movement
Glacial erosion rates depend on various factors. One is how fast ice moves across bedrock surfaces. Another factor is the amount of rock easily eroded by glacial movement. Together these elements come together to form various landforms like corries, aretes and pyramidal peaks.
Modern glaciers erode bedrock at rates far beyond their long-term averages, yet these erosion rates vary considerably from their long-term averages. Erosion rates tend to be maximised in the ablation zone where seasonal surface melt forms subglacial channels that flush sediment while simultaneously stimulating diurnally high basal water pressures that increase sliding velocities25,27.
Till can also serve to mitigate erosion in proglacial zones by decreasing stress concentrations, damping water-pressure fluctuations, and spreading deformation across an extended depth range.