Glacial erosion creates dramatic landscapes, such as cirques, troughs, rock basins and fjords. Furthermore, glacial erosion may leave behind pyramidal peaks, nunatuks or rock drumlins as landforms.
“Abrasion” is a complex process where rocks of various sizes embedded in an icy base rub against each other and wear away at the underlying rock layer, leaving striations-shaped surfaces behind.
1. The Ice is Very Slow
Flowing glaciers erode the land through both abrasion (wearing away surfaces) and plucking (collecting rocks for transport). As they progress across their path they leave features such as faceted clasts, striations grooves, rock flour and glacial pavements in their wake; U-shaped valleys, ribbon lakes, cirques and horns may also form. When moving they expel different kinds of rock than are commonly found nearby and deposit it at their bases or moraines as till.
But glacier erosion can be hard to observe due to glaciers moving so slowly – often less than half a meter per year! Thus making direct observation difficult; therefore remote sensing or modeling provide the only reliable solutions.
2. The Ice is Deep
Glacier erosion occurs when glaciers move across land surfaces, wearing away and carrying away bits of rock with it. It’s a slow process; sometimes taking thousands of years for glaciers to traverse an entire landscape.
Glaciers use two key processes to erode land: abrasion and plucking. Abrasion occurs when rocks of all shapes and sizes are pushed by moving glaciers onto bedrock, scraping against it to scrape away bits of rock — leaving behind grooves known as striations in its wake.
Pulling is another form of glacier erosion. When pulling on land, glaciers create grooves in its surface called strikemarks which show us where and how a glacier moved through a landscape; yet these characteristics are difficult to measure accurately.
3. The Ice is High
Glaciers scrape against rocks and erode sediment, carrying it away with their flow. This abrasive action produces landforms such as faceted clasts, striations grooves, rock flour and rock flour as well as U-shaped valleys, ribbon lakes and truncated spurs.
Though glacial erosion may seem invisible, its processes are difficult to witness in real time – most glaciers move less than half a meter annually – therefore geologists use various techniques to reconstruct its processes.
Geologists use landscape measurements to determine how fast and where glacial ice was moving, as well as materials deposited by glaciers such as rock drumlins and moraine, to reconstruct erosional processes at work in glaciers, which helps them understand glacial formations such as aretes or aretes-keels (or bummocks) or how cirques were transformed into bowl-like shapes by their steep cliff sides eroding into bowls; similarly fjords become filled with sea water over time.
4. The Ice is Cold
Flowing ice is an immensely powerful force capable of dramatically altering landscapes and producing stunning landforms. This occurs through plucking and abrasion – two different methods used by glaciers to erode rocks – creating amazing landforms such as truncated spurs, ribbon lakes, corries, aretes, crag and tails, pyramidal peaks and many others.
Glacial erosion depends on the pressure exerted by an ice sheet against a rock bed underneath it, which in turn depends on temperature and volume of ice-sheet; its effectiveness however relies heavily on how healthy that rock bed itself is, something which is difficult to observe.
When glaciers scrape against rocks they carry, they create long parallel lines known as striations marks on bedrock surface that indicate which direction and point the glacier was traveling at any particular moment in its movement through landscape. Geologists use this evidence as part of understanding glacial processes.