As glaciers erode, they gather rocks and sediments from bedrock for transport by glacial flow; this process is known as entrainment, while rocks collected this way are known as erratics.
These erratics form distinctive landforms, such as glacial striation, ribbon lakes and truncated spurs.
Landforms formed through erosional processes such as abrasion, plucking and freeze-thaw weathering have long been visible features of landscape. So why is it so hard to spot such erosional features today?
1. The ice is too thick
Glacial erosion transforms landscapes through glacial processes known as abrasion and plucking, leaving behind features like striations lines and grooves, drumlins, eskers, moraines shaped by landforms called drumlins.
Abrasion occurs when rock fragments embedded within a moving glacier rub against bedrock, similar to when you rub paper against wood, creating smooth surfaces and lines and grooves. Abrasion also erodes underlying rock, producing distinctive features such as ribbon lakes, corries and aretes.
Glacial erosion relies heavily on abrasion; however, other weathering processes also play a vital role. If water gets into cracks in rock and freezes to create pressure within them which widens cracks or detaches rocks altogether – known as freeze-thaw weathering this process is particularly effective near glaciers.
2. The ice is too thin
Glaciers use rocks and minerals (both large and small particles) as tools to abrade bedrock surfaces as they pass over it, leading to frictional wear that wears away at it gradually; evidence for such erosion can be seen through glacial striations patterns.
Other erosional processes may also take place. Ice can sometimes form around loose or weak sections of bedrock and pull them away – this process is known as plucking. Although plucking may appear simple enough on its face, its full effects often involve pressure melting at the base of a glacier followed by subsequent refreezing of disintegrating rock; which makes its interpretation difficult from just looking at striations patterns alone.
Glaciers also sculpt the landscape by carving out hanging valleys or truncated spurs from land that protrudes above their glacier, known as hanging valleys or truncated spurs. Furthermore, glaciers create U-shaped valleys with flat floors and steep sides – often culminating in glacial lakes at their head.
3. The ice is too fast
Glaciers moving over rock surfaces can leave behind various erosional landforms. Abrasion occurs when the glacier grinds against rocks as it travels, leaving behind parallel scratches called glacial striations on bedrock; plucking occurs when ice freezes around loose or weak sections of rock and separates them from their surroundings using pressure from underneath.
Both processes can create unique glacial landforms such as corries (elongated depressions with notches on one side) and aretes (diamond-shaped features), as well as moraines containing boulders, cobbles, gravel, sand and clay deposits.
However, glacial erosion today can be more difficult to observe than during previous ice ages due to humans emitting greenhouse gases into the atmosphere (most notably carbon dioxide), warming it and leading to faster melting glaciers resulting in rising sea levels and consequently melting glaciers around the world.
4. The ice is too cold
Glaciers create breathtaking landscapes, yet also cause serious erosion of land. Glaciers erode through various mechanisms – one being abrasion: rock and mineral particles from beneath the glacier scraping against bedrock to wear away at its surface layer piecemeal, leaving behind visible glacial striations or rock flour deposits on it’s surface.
Glaciers also erode by plucking, pulling small rocks out of the ground and transporting them in their flow into moraines, often depositing them there afterwards.
Unluckily, it can sometimes be challenging to observe either of these processes in action. Glacial erosion takes more time to produce visible effects due to cold conditions causing its glaciers to freeze to the bed instead of flowing freely and thus inhibiting glacial flow and erosion; warming climates speed this up so we can witness it firsthand.