Glacier ice is an incredible force of nature; its rock debris and movement combine to form beautiful landforms such as striations lines and ribbon lakes. Additionally, glacial erosion is responsible for many other interesting landforms like corries, aretes, pyramidal peaks and more.
One of the more difficult questions to answer is which term best describes glacial erosion rates. There have been various terms used, but which is most accurate?
Freeze-thaw weathering
Freeze-thaw weathering (also referred to as frost weathering) is a highly destructive erosion process. When water seeps into cracks, fissures and pores in rocks before freezing, expanding by approximately 9% when frozen to push cracked rock apart and weaken cohesion between mineral grains; over time leading to fragmentation; then the loose rock created from this process lands as scree slopes or talus piles at the bases of cliffs and steep slopes.
Freeze-thaw weathering depends on environmental conditions such as fluctuating temperature and moisture availability, being particularly common in cold climates and high-altitude regions.
Freeze-thaw weathering forms crevices and cracks which provide niches and habitats for an array of organisms, as well as contributing to soil development, nutrient cycling, ecosystem function and balance. Furthermore, its layers of weathered rock and sediment deposit offer invaluable information about past environmental conditions and geological history; radiocarbon dating techniques allow these deposits to be accurately dated.
Abrasion
Erosion rates can differ widely due to various conditions influencing glacier erosion, such as percent glacier cover, ice speed and lithology, subglacial hydrology, accumulation/discharge rates and bedrock geometry.
Glaciers create distinctive landscapes through erosion; examples include U-shaped valleys, horns and moraine. Melting glaciers also contribute significantly to sea level rise through their erosion process.
Some abrasion features are easily discernible on bedrock surfaces as striations marks, caused by forces acting cyclically normal and tangential (similar to chatter marks in certain machining operations). Dilatation joints – long longitudinal cracks found along surfaces congruent to bedrock surfaces – are another example.
Mechanical weathering loosens rocks from glacier walls, causing them to tumble into them and be carried downstream by melting glaciers, depositing as unsorted piles known as glacial till. When these pieces melted into rivers they form glacial till. Large rocks dropped by melting glaciers are known as erratics – landforms characterized by irregular hills of bedrock with smooth upstream sides and steep, jagged downstream sides characterized by their shape and orientation.
Plucking
As they travel down mountain valleys, glaciers erode rocks and earth beneath them by plucking. When sediments and rocks frozen within its ice act like sandpaper against rock surfaces beneath, scraping away at them. Glaciers also leave behind grooves showing which way they have moved – these grooves are known as glacial striations.
Plucking can create many distinct landforms. For instance, it can transform V-shaped river valleys into U-shaped glacial valleys by taking rocks from their walls. Plucking also produces unique features like horns, aretes, and cirques.
Rain or snowfall on a glacier can also have a significant effect on its erosion. Rainwater may lubricate its surface, speeding its journey faster and increasing erosion rates. Furthermore, when plowing through soft rocks or sand deposits can accumulate as bedrock debris (moraines). This process is known as glacial quarrying.
Carving
Glacial erosion creates many landforms, including glaciated valleys and cirques – round basins which may or may not contain glaciers.
Evidence for glacial erosion includes glacial striations – long scratches left behind by moving glaciers on rock surfaces – as well as mountains formed from their debris by glaciers that created them.
Physical erosion results in rocks becoming smaller or smoother, often producing clastic sediments. Chemical weathering accelerates this process by altering atoms, ions, or molecules within rocks to make them more or less soluble. Glacial erosion also produces mass wasting events like landslides and avalanches, which erode and transport large amounts of soil reshaping coastlines and destroying communities in their path. They’re especially common downstream from glacial snouts where they quickly erode beaches. Although glacial erosion’s mechanisms may seem inexplicable at first, researchers have discovered that precipitation may play a vital role in controlling its progression – researchers believe precipitation levels play the single greatest role here.