Glaciers shape landscapes by means of erosion – the removal of rocks and sediment through processes such as abrasion/scouring and plucking.
Glaciation refers to processes that produce grooves on bedrock surfaces. Erosion rates caused by glaciation can vary considerably, depending on factors like basal sliding velocity and rock type. It is hard to obtain an exact measure of erosion rates due to glaciation as each case depends on different variables.
Plucking
Glaciers’ weight and slow movement can reshape mountains, alter coastlines, and erode valley floors – this process of change is known as plucking.
Glaciers often erode rock surfaces that contain cracks that were already present prior to their formation, creating fractures which may entrain material. Furthermore, movement from glacier movement may fracture bedrock further and abrasion may separate rocks apart further.
Glacial erosion is responsible for some of the world’s iconic landforms, including fjords and U-shaped valleys, as well as creating alpine landscapes with distinctive striations patterns and rock steps.
Physical erosion alters the shape and size of rocks without altering their chemical makeup, producing large volumes of clastic sediments which are transported far from their place of origin, often triggering landslides or mass waste events.
Abrasion
Glaciers are immensely powerful forces, and one way they cause erosion is through scraping underlying rock. This process, known as abrasion, uses frozen sediments and rocks as scrapers against bedrock they move across, leaving long scratches or grooves called striations marks.
Striations is a characteristic of landscapes formed by glacial erosion. Striations indicates the direction in which glaciers were moving, so can help identify former glacial valleys.
Not only can glaciers cause erosion through abrasion, but they can also do it through other means, including plucking and freeze-thaw weathering, which in turn create a variety of landforms such as sharp points (aretes), truncated spurs, ribbon lakes and hanging valleys. Valley glaciers in particular excel at this task – creating rugged mountainous landscapes as we know them today as well as sharp knife-edge ridges (aretes) and bowl-shaped depressions called cirques.
Quarrying
A quarry is a location where rock, crushed stone, sand and gravel are extracted from the earth for use in construction projects. Aggregate sourced from these quarries serves as a major component in road pavement and sidewalk surfacing materials.
Glaciatively eroded bedrock often displays striations patterns called striations that appear as long parallel lines scratched into its surface. These grooves vary in depth and width to give geologists insight into where glacial movement occurred.
Glacial ripping is an evolving and expansive process sequence that loosens, entrains, and transports large rock fragments (also called mega-clasts) over wide areas near the surface, disrupting low rock hills and mountain ridges while disintegrating them partially. It differs from plucking in its extent and volume of produced erratics – sometimes creating boulder spreads as large as 4-4m2 to disintegrate and destroy topographies with stoss-and-lee topographies.
Overdeepening
Overdeepenings have attracted considerable interest both from an engineering (i.e. aquifer) and geohazard assessment perspective (Frey et al. 2010). Stoss-and-lee topography often results from glacial movement causing erosion; this involves both abrasion and quarrying processes.
An important topographical control on overdeepening location and size may lie with changes in valley cross-sectional area (CSA) that influence ice velocity and erosion. When an increase in valley CSA leads to decreased ice flow velocity and erosion increases as continuity requirements force acceleration, leading to further deepening.
Studies have revealed that overdeepenings often co-localize with glacial valley confluences where the fastest ice velocity speedup occurs, although this correlation could be obscured by other controls operating over larger spatial scales (e.g. bedrock mass strength variation and flux pattern) as well as by multiple overdeepening types (Lloyd 2015). Further investigation should take place into how these controls influence overdeepening locations and sizes from regional to continental scales.