Glaciers shape breathtaking landscapes and have an enormous influence on climate. However, glacial erosion often occurs so slowly that it is hard to observe in action.
Their enormous weight erodes bedrock into distinctive landforms like ribbon lakes, corries and pyramidal peaks – but why is it hard to detect?
1. It takes a long time
Glacial erosion happens at an extremely slow pace; most glaciers only move half a meter annually. Yet glaciers still create distinct landforms, including periglacial trim lines that show how high the ice was during erosion; crevasses and flow stripes which indicate rotational movement patterns; and glacially abraded bedrock known as striations patterns.
Striations is created when tools (rock and mineral particles, large and small) embedded within a glacier rub against its rock surface, wearing away at it particle by particle, producing distinctive glacial landforms like ribbon lakes and pyramidal peaks. To create these features, the base must be moving and exhibit basal slip; cold-based glaciers tend not to engage in this type of erosion.
2. It’s in a remote location
Glaciers create landscape changes through two means of erosion: plucking (when rock debris is pulled away by moving glaciers) and abrasion (the movement of the ice gouging into and scraping against the ground below it). Each movement affects different types of rocks differently, leading to features like striation lines or grooves known as aretes forming over time.
These features can be seen across various scales from millimeters to kilometers, yet observing glacial erosion features requires ground surveys in order to examine details up close and create high resolution maps of erosion – both processes which take many man hours of work to complete.
Glaciers are pervasive geological agents that shape remarkable landscapes; yet their long-term efficacy and controls remain poorly understood across Polar continental shields1. Although tectonics, lithology, climate and other natural factors all have some degree of an effect, it’s difficult to isolate one factor over the others and quantify it in real time in a natural setting. Furthermore, glaciers erode at significantly slower rates than fluvial erosion leaving an impressive footprint2. This fact speaks volumes for their limited mobility compared to their impact as pervasiveness in shaping extraordinary landscapes compared to fluvial erosion leaving an immobilised imprint on its course over time2.
3. It’s in a mountain
Glaciers are powerful geological agents capable of creating incredible landscapes and shaping our climate, yet despite this power they remain hard to spot due to glacial erosion taking place at such a slow rate that most glaciers move less than half a meter per year.
Due to glacial erosion’s slow rate, its characteristics – such as striations lines, grooves and glacial polish (rocks smoothed by erosion between debris carried by ice and bedrock) can be hard to spot.
However, when you come across these distinct landforms they are captivating to observe. Examples include cirques, aretes, pyramidal peaks and U-shaped valleys as well as drumlins (streamlined elongated features) and ribbon lakes. Furthermore, glaciers may erode away bedrock surface deposits creating a “glacial polish”. Other processes related to glacial erosion include plucking, abrasion and freeze-thaw weathering processes that cause them.
4. It’s in a valley
As glaciers move downhill they encounter rocks which they erode away as they travel, leaving behind incredible landforms like striations grooves and glacial pavements – still visible today in landscapes worldwide.
When non-glaciated rivers erode mountain landscapes, they typically create V-shaped valleys. When glaciers take over these V-shaped valleys, however, they often widen, steepen, and deepen them into U-shaped ones due to the sheer force of ice’s sheer force causing plucking effects.
Glaciers transport rocks of various sizes and origins as they move through, from giant boulders to silt. Because glaciers move so swiftly, they carry bits from various sources that come together like tools. Giant boulders dropped by glaciers are known as glacial erratics while any smaller pieces they carry are termed glacial till. Glaciers use these tools to form geomorphic features like drumlins, cirques and aretes using this process.