Ice erodes rock and sediment, transporting it across its path. This erosion produces characteristic landforms like striations lines, hanging valleys, horns and moraines – as well as creating new ones in unexpected places!
Measuring glacier erosion can be challenging; to do so requires closely watching its long-term progression and taking measurements on rock and sediment deposits at close intervals.
Abrasion
Rock debris found within glaciers acts like sandpaper against bedrock, gouging and scraping it. This process becomes much more effective when the glacier moves rapidly. Additionally, this depends on factors like hardness of rocks as well as pressure exerted by ice.
Glacial erosion relies heavily on this abrasive action to produce landforms such as striations lines, U-shaped valleys and moraines.
Different glacier types will experience different rates of abrasion depending on their temperature and bedrock conditions. Temperate glaciers at or near pressure melting points tend to move by both basal sliding and abrasion1, while polar glaciers with low temperatures and little meltwater lubrication often see little or no abrasion1.
Plucking
Glacial erosion often involves the plucking or removal of large fragments of rock from their foundation by glacial meltwater seeping through cracks in bedrock before freezing, releasing enough pressure for fragments to be plucked off by flowing glacier ice and lifted away.
Plucking occurs most frequently in valley glaciers. It plays a critical role in creating streamlined landforms found throughout alpine regions, including glacially abraded surfaces like striations lines and fjords.
Glaciers may move slowly across Earth’s surface, yet their impacts on its surface are immense. Glaciers polish bedrock, push soil around, grind up rocks into dust and break apart larger chunks. Erosion can be an incredible force of nature; however, harmful agricultural practices and human development practices can amplify it, leading to land degradation, air and water pollution, as well as other environmental concerns.
Excavation
As glaciers move across valley walls, mechanical weathering loosens rocks on valley walls which then fall into the glacier as debris, eventually being deposited at its bottom as sediment known as glacial till. Melting glaciers then combine and erode this material, producing features such as rocks with distinct forms (known as “faceted clasts”) formed from being dragged across other rocks (called “faceted clasts”) as well as striations grooves rock flour or even pavement-like landscape features called glacial pavements.
Stoss-and-lee topography is an asymmetrical landscape consisting of hillocks of bedrock spanning a few meters to several hundred meters in plan view, created through glacial quarrying and abrasion processes that depend on jointing patterns in rock formation and the strength of ice for development. Its development depends on both glacial quarrying and abrasion forces; erosion rates are controlled by jointing patterns while strength of ice limits how far its reach stretches outward.
When multiple glaciers erode a single rock at different times, their erosion may shape it into an abrupt mountain peak known as a “horn”.
Deposition
Glaciers can be powerful agents of erosion, particularly where their edges have not frozen to their bases and can slide over bedrock or sediments. While the ice itself does not do much of the erosive work itself, the rock fragments embedded within its depths that get pushed downward onto surfaces beneath exerts much greater force in erosion than does just having an unfrozen base causing it.
Continental glaciation generally tends to flatten landscapes if their bedrock is uniform in strength and free from recent tectonic activity, and also tends to erode softer rocks more effectively than harder ones, as evidenced by mountain tops with pointed shapes called horns.
Erosion rates can be difficult to assess on 104-5 year timescales due to glacier flow variability. Furthermore, climate impacts the way glaciers erode as ice-sheet volume and dynamic activity responds to snow accumulation; abrupt switching occurs as soon as external warming takes effect. An indirect measure of erosion rates could include measuring cosmogenic nuclides found in rock samples collected along glaciated valleys although this method is limited due to their shallow depth of formation in underlying rock strata.