Glaciers shape and transform landscapes through erosion, the breaking down of rocks. There are two primary forms of glacial erosion: abrasion and plucking.
Abrasion occurs when rock fragments in the basal ice scrape against underlying bedrock like sandpaper would, leaving long scratches known as striations scars behind them and giving way to unique landforms such as ribbon lakes, U-shaped valleys, horns and moraine formation.
Cirque Stairways
Glacial erosion has transformed the landscape through two main processes: plucking and abrasion. Abrasion plays a particularly vital role in warming-based glaciers with basal slip, breaking up rocks of various sizes before leaving behind fine-grained material known as rock flour in streams for transport downstream.
Cold-based glaciers may not experience as much abrasion due to being more “glued” to bedrock than having loose bases; nonetheless, abrasion remains an integral process in many regions.
Hillslopes depend on both erosion and plucking for their form, with glaciated valleys having steep sidewalls and rounded bottoms; nonglaciated valleys found in mountainous regions often having more of a V-shape profile.
U-Shaped Valleys
Glaciers move slowly over land surfaces, slowly carving away at them with their weight distributed more evenly across its surface and leaving behind various landforms such as U-shaped valleys, corries, aretes, and rock drumlins. Their erosional power far surpasses that of rivers due to having wider bases and being distributed more evenly across their area of operation.
Glaciers transform V-shaped valleys into U-shaped valleys through various processes, such as basal slipping, glacial plucking and abrasion. During the last Ice Age, glaciers served as giant bulldozers to shape these distinctive U-shaped valleys.
These features are typically found in areas that were once glaciated, like the Alps. Valleys tend to be long and slope in one direction. Their bottom is often filled by rivers or streams, with time giving these valleys their unique shapes through natural processes like erosion. Glaciers deposit rocks ranging from boulders to silt in unsorted deposits called glacial till on bedrock beneath.
Aretes
Glacial erosion has produced many fascinating landforms, including cirques, horns and pyramidal peaks.
Glacial erosion is driven by two primary processes: plucking and abrasion. Plucking involves glacial ice pulling on rocks and debris to tear it apart or dislodge it altogether; while its mass of sand and rock debris acts like sandpaper against bedrock surfaces to produce distinctive surface textures known as scouring.
Striations marks are characteristic of this process. Additionally, glaciers can polish rock surfaces for an elegant appearance known as glacial polish.
Pyramidal Peaks
As glaciers erode, they leave behind many materials – from rock particles to moraine (residual rock that was either pushed by or embedded within the glacier ice).
Like rivers, glaciers also contain tributaries which may feature hanging valleys due to erosion by glacial movements downstream. Glacial erosion also leaves behind ridges or spurs extending into valleys called truncated spurs which become destabilized over time and left behind when glacier retreat occurs.
Horns, aretes and corries are other notable glacial landforms. A cirque is an armchair-shaped hollow in a mountainside created by glacial erosion through rotational slip and freeze thaw weathering; an arete forms at the back of each cirque in which two or more are joined to form two contiguous hollows which overlap. When two cirques meet on one mountain then glacial erosion creates a saddle or pass over its summit known as a col whereas when three or more collate together then the resultant pyramidal peak is known as horn