Erosion occurs when rocks are broken apart and carried away by water, wind or ice, creating landforms like U-shaped valleys, horns or moraines.
Glaciers erode rocks through two processes: abrasion and plucking. Picture using sandpaper over rocks to leave scratches behind: that’s an example of abrasion.
Freeze-thaw weathering breaks down rocks through repeated cycles of freezing and thawing, weakening mineral grains so they’re easier to dislodge from rock mass and form scree slopes, talus piles and boulder fields. Furthermore, this process releases minerals and nutrients stored within rocks; which aid in their cycling processes critical for ecological health.
This process typically occurs in areas with continental climates that are very cold, where water seeps into cracks in rock during warmer days and freezes at night, creating pressure that fractures rocks mechanically rather than chemically, though chemical processes such as subglacial water seepage and dissolution can have an influence. Fragmented rock debris provides habitat and niches for plants and small invertebrates alike, offering essential resources that allow species to thrive even under such extreme circumstances.
Glaciers wear away at the land they travel over, leaving behind distinctive erosional features known as erosional landforms that include striations lines, grooves and clefts as well as creating cirques, hanging valleys and ribbon lakes. These features are formed through both glacial erosion processes such as abrasion and plucking as well as freeze-thaw weathering processes.
This process occurs as rocks buried below a glacier’s surface move slowly underneath it, being scraped by its moving ice as it descends, which scrapes across them abrasively like using sandpaper on wood, wearing away at them to form long parallel scratches called glacial striations.
Glacier erosion tends to favor protrusions of hard rock in bedrock that protrude through softer rocks, which then are preferentially eroded, creating knobs of rock that protrude out from beneath the glacier’s path. Over time these protrusions will be pulled along and may eventually break off and form tails – these features are known as knob-and-tail erosion.
Plucking or quarrying
An accumulation and transport of rock debris by glaciers can create numerous iconic landscape features, including striations lines, ribbon lakes, corries, aretes, U-shaped valleys, roches moutonnee and crag and tail formations and hanging valleys.
Plucking or quarrying takes place when a glacier encounters hard, brittle rock surfaces that are difficult to erode. As it rubs against them, crescentic gouges or lunate fractures form along their length, often parallel with each other and often pointed upward or downward as evidence of where their movement occurred. These sickles represent how far or fast it moved across its target area.
Ice can also scour away at mountain slopes, widening and steepening them as it creates U-shaped valleys. When flowing through river valleys, glaciers scour rocks away from canyon walls creating rock step profiles as they flow downstream – leaving behind long parallel grooves called glacial striations in their wake.
Glaciers leave behind many distinctive landforms when they move rocks and sediments across their paths, such as U-shaped valleys, cirques, aretes, rock steps, fjords and striations patterns.
These features were formed through glacial erosion’s abrasion and plucking processes as well as freeze-thaw weathering processes. Freeze-thaw weathering occurs when liquid water seeps into cracks in rocks beneath and freezes, expanding them as it freezes, eventually breaking off bits of rock as it expands them further and then expanding again, cracking apart more pieces from underneath and creating long scratches called “striations.”
Glacier abrasion is the primary form of glacier erosion. This process happens when glacier ice rubs against bedrock and cuts into it like a piece of sandpaper, leaving behind scratches known as striations on it that typically follow its course, although sometimes they may cross to show changes in directionality of movement.