Glacial periods cause erosion by scraping rocks of all shapes and sizes along with their terrain by the moving ice, producing classic landforms such as roches moutonees, whalebacks, rock drumlins and fjords.
But which term best defines glacial erosion? Unfortunately, the answer can be complex.
Plucking
Researchers know that glacier’s rocky bases can be hard to access, yet researchers know that rock particles and sediments exist within them that collide when glacier ice scours its surface causing “tool-marks”, from microscopic scratches to deep gouges centimetres deep that create various landforms characteristic of glaciated environments.
Once rocks get to the bottom of a glacier’s ice layer, they can break apart and be plucked off of mountainside terrain by means of “plucking,” also known as plucking. Once plucked from their original position on mountainside terrain, these fragments are carried downstream on glacial pavements or glacial pavements and rub against each other causing surface erosion that results in distinctive landforms like faceted clasts, grooves in rocks, glacial pavements or rock flour (reference Lee and Bobet for more). Furthermore it produces features like aretes connecting two valleys or nunatuks which flat top topped mountains (Reference Lee and Bobet for further reading).
Abrasion
Glaciers contain bits of rock, sediment, and debris which erode away as the glacier moves over it – this process is known as abrasion and creates long scratchy marks known as striations on bedrock surfaces that help scientists assess which way a glacier was flowing. These marks help scientists accurately pinpoint its path.
Glacier abrasion works best when there is minimal basal ice and rock beneath, and when its strength is uniform. This is due to friction caused by heavy, thick glaciers against their bed which causes basal sliding to slow down1.
Erosion caused by abrasion varies greatly across glaciated regions due to two main factors: material added and how fast that material is removed from glaciers. Therefore, erosion rates vary considerably among them.
Freeze-thaw weathering
Glaciers’ movement can dislodge rocks and sediment from the earth’s surface, leaving distinct landforms such as striations patterns or polished surfaces behind.
Freeze-thaw weathering is a key form of erosion that systematically breaks apart rocks over time. This process occurs when water seeps into cracks in rocks during the day, then freezes at night (as reported by Water Encyclopedia). As water expands by approximately 9% when frozen it enlarges existing cracks until eventually pieces of rock break off as part of this cycle.
Freeze-thaw weathering releases minerals and nutrients stored within rock that contribute to nutrient cycling, contribute to soil development and fertility, play an essential part in ecosystems and the geological record, while simultaneously acting as an environmental hazard such as rockfalls or landslides as well as potentially damage human-made structures if repeated cycles of freezing and thawing weaken materials leading to structural instability or deterioration. However, freeze-thaw weathering also poses geological hazards including rockfalls or landslides due to repeated cycles of freezing/thawing cycles weakening materials which weaken over time leading to structural instability or even total deterioration of structures built out from under these repeated cycles.
Basal slip
Glacial erosion occurs when glaciers or ice sheets wear away rocks and soil from bedrock, creating classic landscape features such as U-shaped valleys, cirques, aretes, roche moutones and hanging valleys as well as striations lines and glacial polish.
Abrasion erodes bedrock surfaces underlying glaciers by carrying tools (rock and mineral particles) carried in its movement along with it. Abrasion works best on warm-based glaciers where basal sliding occurs; in cold-based glaciers however, where their ice becomes “glued” to their beds and cannot erode away at them1.
Due to limited access, most physical processes that contribute to glacial erosion remain poorly understood. Therefore, most knowledge of subglacial erosion has come from theories3-6 or observed landforms left behind when glaciers have melted2. Recent studies on temperate and cold-based glaciers7,8 have suggested a nonlinear relationship between erosion rates and basal sliding speeds9. These results support the general notion that glacial erosion is linked with its thermal regime below.