Glacial erosion produces characteristic features of glaciated landscapes, such as quarrying and abrasion (responsible for creating clast-sized sediment) as well as subglacial fluvial action (which entrains substrate rocks and sediment).
Erosion leaves behind grooves and facets on rocks carried by glaciers, rock flour, or glacial pavements, contributing to overdeepenings of cirque- and trunk-valley floors, fjords and confluence-type hanging valleys.
Landforms
Glacial erosion creates many landforms. When glaciers retreat from valley bottoms they leave behind U-shaped depressions known as moraines that contain rocks, dirt and other materials deposited by them; lakes or glacial drumlins (ridges of loose rock and coarse sediment deposited by glaciers) sometimes also appear within a valley.
Glacier rock debris comes in all sizes, so when the glacier scrapes against a mountainside it scrapes against, its particles scratch or gouge into the surrounding rock surface much like pieces of sandpaper being run across wooden tables. When this occurs it produces tool marks which create patterns known as “stoss-and-lee topography”.
Glacial basin erosion rates tend to be higher than nonglacial basins with comparable watershed areas, yet its causes remain obscure. One possible factor may be dependent upon glacial hydrology phenomena affecting erosion mechanisms (for instance see Herman et al. (2011) for further discussion).
Abrasion
Abrasion is the process that forms rocks as glaciers move over them, and has created many distinctive features such as smoothed off rock surfaces (known as “clasts”) by being pulled against other rocks (called “facets”), striations and grooves in rocks, glacial pavements and glacial polish.
Other erosional processes, like quarrying, are equally crucial. These depend on differential stresses created in rocks by ice being forced around bedrock obstacles; these high tensile stresses can pull apart preexisting joints and crack systems and open them up for removal by ice flowing above.
Erosion rates on subglaciers can be difficult to assess because direct access is usually difficult, yet multiple indicators point towards the greater influence of abrasion than quarrying in terms of erosion rates. One such indicator is glacier sliding velocity: faster moving ice flows drag more abrading particles per unit time which leads to greater erosion rates.
Plucking
Warm ice-bed interfaces enable subglacial water to percolate through and act as a lubricant, aiding glacial erosion. But too much water at the bed causes glaciers to move so quickly they become incapable of erosion.
Glaciers use glacial erosion to erode rock, leaving behind fragments known as clasts that can then be deposited on moraines for eventual deposit by glaciers themselves (known as “plucking”). Sometimes these larger pieces are even moved by them itself – this process is known as plucking.
Glacier National Park is home to a massive volume of glaciers moving with rock particles that rub against and shape rock surfaces as they travel. This erosion process creates unique landforms like narrow V-shaped valleys becoming wide U-shaped canyons with amazing verticality and long, deep lakes like Bowman and McDonald; saw-toothed aretes (rock peaks) with jagged horns like Garden Wall and Flinsch Peak have also been created through glacial action.
Deposition
Deposition of sediment occurs within zones within the glacier that expand and contract throughout its cycle, as erosion increases towards the ice divide before decreasing back down towards zero by its terminus. This pattern indicates how glacial erosion depends upon ice sheet flow and subglacial hydrology.
Tills are deposits created by glaciers that contain clay, sand and gravel deposits that have been mixed together by glacial meltwater to form stratified drift deposits. Symmetrical hills of till which point in the same direction as glacier movement are known as drumlins; when found together they create drumlin fields.
Glacial erosion also leaves behind features known as rock marks. This includes features like faceted clasts, striations and grooves in rocks and glacial pavements which cause valleys to be smoothed out and flattened.