Glacial erosion refers to the process of altering bedrock directly caused by glacial movement. It includes processes like quarrying, abrasion and plucking.
Features produced include faceted rocks known as clasts, striations grooves and glacial polish. Other results are chattermarks eskers drumlin fields and moraine.
Melting glaciers leave behind all of the rocks they’ve carried in a pile known as glacial till. Stratified drift is composed of sedimentary particles separated by space.
1. Freeze-thaw
Freeze-thaw weathering occurs when water seeps into rock cracks or pores and freezes when temperatures decrease, expanding cracks as its presence causes cracking to expand further and the process repeats itself until eventually rock fractures.
Cracked and porous materials weaken over time as the expansion and contraction of freezing and thawing water expands and contracts, exerting strain in cracks, fissures, and pores that lead to stress cracking, fissures, pores, weakening material from within over time – this phenomenon being an essential element in rock breakdown. Freeze-thaw events also contribute to diverse landscape formation, soil development and fertility, ecosystem processes as well as geological record formation. They pose hazards to human-made structures by cracking spalling and structural degradation leading to increased maintenance costs but proper design as well as drainage systems can mitigate their effect to an extent.
2. Basal slip
Glacial erosion produces many different forms of debris: faceted clasts; striations and grooves; glacial pavements; rock flour; and chatter cracks, the latter appearing similar to tool lines on machines due to stick-slip friction between faster ice flow and slower bedrock layers.
Abrasion is more prevalent under warm-based ice because it can drag bits of rock across bedrock; under cold-based ice, however, fast-moving ice becomes “glued” to bedrock and can only scrape or push away bits (see below).
At first glance, glacial movement may be difficult to identify; however, when an examination of horizontal streamwise cross sections through valley glaciers takes place the motion can often be divided up into basal slippage and internal deformation.
3. Abrasion
Glaciers create spectacular landscapes by eroding rocks and producing dramatic landscapes. As they scrape and grind rocks, erode sediment, and gouge out basins, glaciers create striking landforms such as aretes, horns, drumlins and cirques.
Abrasion is the term most often used to refer to glacial erosion. Ice grinding against rock creates striations patterns on its surface, producing glacial runoff.
As is true of any process, for abrasion to continue there must be an uninterrupted source of new abrasive material – this could come in the form of rock debris transported downward from above or washed in via raindrops from below.
4. Plucking
Glaciers erode the land they traverse through plucking and abrasion, producing unique glacially sculptured landforms as they pass.
Eskers are winding ridges of sand and gravel deposited by glaciers; drumlins are asymmetrical hills of sand and gravel that point in the direction the ice moved; wide areas with uniform deposits from glaciers are known as stratified drift.
An erosion process known as glacial abrasion breaks off rocks from their bedrock, with these fragments then “plucked” off by a glacier and carried away (Figure below). This process works best when there are large, preexisting cracks in the bedrock which allow this plucking process to work its magic, leaving long parallel grooves called glacial striations grooves behind (Figure below).
5. Crevasse
Glacial erosion rates depend heavily on its environment. When occurring in cold environments, glacial erosion progresses more slowly; while in warm ones it may occur much quicker.
Crevasses are large cracks spanning from several meters to kilometers found in glaciers or ice sheets that form when huge pieces of ice separate, leaving an opening which poses dangers to mountain climbers and skiers.
Glacier crevasses can often be caused by drag along valley walls or turning corners, but can also be caused by different sliding speeds of layers in a glacier – in particular the lower, more rigid layer moving slower than its more flexible upper part – leading to new cracks forming which cross with existing ones and form new crevasses.