Glacial erosion refers to the process by which glaciers sculpt land by way of two key processes: Abrasion and Plucking.
Glaciers’ erosion leaves behind classic landscape features such as U-shaped valleys, drumlins, aretes, horns, roche moutonees, hanging valleys and striations – but what best describes its rate?
Freeze-thaw weathering is a physical process that breaks apart rocks by the repetitive freezing and thawing of water, usually found in cold climates, where liquid seeps into cracks in rocks during the day and then freezes overnight, weakening and eventually dissolving them over time. Over time this cycle repeats itself until eventually weakening or breaking apart the rock completely occurs.
This process can produce breathtaking geological features, including cirques and hanging valleys, as well as striations-and-troughed rock surfaces found on mountain slopes – which provide ideal habitats for plants, invertebrates and birds alike.
Freeze-thaw weathering can wreak havoc in human-built structures like buildings and roads. Repeated freezing and thawing cycles can break down surface coatings and paint layers, exposing building materials to harsh weather conditions that reduce their lifespan over time and require costly repairs or replacements.
Glaciers erode bedrock by scraping and polishing it – this process is known as abrasion. Abraded rocks often exhibit patterns of grooves on their surfaces caused by rocks and sediment entrapped within the base of a glacier as it moves across bedrock; boulders may be particularly detrimental.
Abrasion can also create knobs and tails. As glaciers move across mountains, their erosion wears away harder areas of rock which become protruding knobs protecting softer rock on their lee side; when further worn away by further erosion these knobs may form tails pointing toward their glacier’s margins.
Abrasion can also result in the creation of U-shaped valleys, horns and moraines formed from rocks deposited by glaciers; these features contribute to shaping the landscape as visible markers that can be easily observed by hikers.
Pluckeding can account for many erosional features produced by glaciers. This occurs when rock fragments embedded in ice of a moving glacier rub against surfaces below, creating friction which causes shear forces that separate clasts from bedrock by shearing force, before being carried off by the glacier itself.
Glacial movement creates U-shaped valleys, cirques, aretes, moutonees roche moutonees rock steps and grooves known as glacial striae. When two glaciers move in opposite directions on an mountain side, an arete forms between them that becomes sharp-sided ridge known as an arete.
Pure ice is not particularly effective at erosion due to its low shear strength; however, temperate glaciers possess a basal debris zone several centimeters to several meters thick that acts as an effective abrasive. The action of this zone is enhanced by hard rock fragments adhering to it; in effect it’s like rubbing paper against sandpaper with embedded pieces of garnet embedded into it.
Glaciers erode rocks using two primary mechanisms: abrasion and plucking. Abrasion leads to erosional features like striations and polished areas, while plucking occurs as the result of frozen ice moving away from rocks, creating tension which pulls away pieces; this process typically occurs at the headwall of a cirque and produces irregular fragments known as scree.
As glaciers move, freeze-thaw weathering occurs as well. This process occurs when ice freezes during the daytime and thaws out at nighttime, allowing water to seep into cracks and joints of rocks and eventually weaken and cause them to break apart when the ice eventually thaws and melts again.
Rotational slip erosion is another effective erosive process, whereby slump blocks move downslope on concave-upward slip surfaces with rotation around an axis running parallel to the slope, thus altering its original gradient while creating a trimline between old and new landforms – often called trimlines.