Erosion occurs when Earth’s surface becomes exposed and vulnerable. Glaciers play a major role in erosion through plundering and abrading the land they traverse, leaving behind scars.
These processes generate unique glacial landscapes, including corries, aretes, cirques and pyramidal peaks. Furthermore, they leave behind U-shaped valleys called glacial troughs as well as long grooves in bedrock known as glacial striations etching.
Glacier melt creates debris streams which impact bedrock differently depending on their discharge, with different degrees of impact depending on discharge rate. Erosion occurs through mechanical and chemical processes; mechanical ones include abrasion, quarrying, plucking and cavitation processes.
Abrasion causes surface scratching and gouging on the rock beneath a glacier, creating a ridged bedsurface known as a moraine. Additionally, this process creates many different landforms including horns and craters.
Plucking and quarrying are the two primary processes responsible for the removal of large chunks of rock from bedrock by valley glaciers, then transported downstream where they form distinctive features called crags or tails. Another form of quarrying known as freeze-thaw weathering which forms parallel lines on rocks’ surfaces known as striations lines that tell geologists more about its history than can otherwise.
Glacial movement erodes the ground, shaping it into dramatic landforms such as the Finger Lakes in eastern New York and Norway’s fjords along its coastline.
Erosion occurs through natural forces such as wind and water. Moving water erodes sedimentary rock into streams and rivers, as well as creating canyon gullies and valleys like those found at Grand Canyon.
Wind erosion can occur quickly when winds blast across flat landscapes. Therefore, farmers and engineers must use techniques known as erosion control to stop it transporting dirt and rocks towards buildings, roads and highways. One such erosion control strategy involves placing structures such as gabions (huge wireframes that hold boulders in place) near cliffs in order to manage erosion.
Glacial erosion occurs through quarrying, abrasion and melt water erosion processes. They are most effective when the ice melts, providing lubrication that promotes basal sliding and traps clasts in its path.
While glacial erosion produces many of the striking landforms we see today, its subglacial components can be more challenging to observe. Most studies of subglacial erosion assume that glacier ice rests upon bedrock beneath temperate glaciers – but observations from under these glaciers indicate this may not always be true.
Subglacial erosion includes abrading, which involves the score-and-polish action of larger rock fragments transported at glacier bases on surface rocks. Abrading occurs most commonly on warm-based glaciers where pressure melting point exists continuously and basal sliding occurs; abrading may also account for longitudinally lineated surfaces characteristic of glacially eroded bedrock surfaces.
Abrading may also contribute to the formation of aretes and the triangle-shaped surfaces found within cirques; however, abrasion may be significantly less effective than sliding or basal shear stresses due to removing material only from the surface layer, while shear forces can cause cracking and disintegration beneath its ice surface.
Glaciers leaving characteristic depositional landforms when they melt; including moraines, eskers and kames compiled of unsorted rock fragments carried along by the glacier as it moved.
Glacial erosion rates vary considerably and depend on a range of factors, including the rate at which till deforms, sediment transport capacity and surface slope. In glaciated basins with adverse bed slopes (i.e. bed slopes larger than their respective surface slope magnitude), stream incision rates may be dramatically decreased, leading to extremely low basin-averaged rates of erosion.
As mountain glaciers travel downhill, they come into contact with rocks with different resistances to erosion; weaker rocks may be reduced while stronger ones covered, creating staircase lakes such as those found in the Alps. As they do so, this erosion process leaves behind grooves and indentation on rocks that demonstrate where they moved across Earth’s surface – leaving behind U-shaped valleys filled with sea water known as fjords as evidence of glacial activity.