Model Answer
0 min readIntroduction
Glaciers are significant agents of erosion and deposition, shaping landscapes across the globe, particularly in high-altitude and high-latitude regions. A valley glacier, also known as an alpine glacier, is a glacier that flows within a defined valley, constrained by the surrounding topography. These glaciers originate in cirques, high-altitude basins, and flow downhill due to gravity, carving and modifying the landscape through powerful erosional processes. Understanding the landforms created by valley glaciers is crucial for interpreting past glacial activity and predicting future landscape evolution. This answer will detail the major landforms produced due to glacial erosion by valley glaciers.
Valley Glaciers: A Definition
Valley glaciers are elongated masses of ice that flow down pre-existing valleys. They are typically nourished by snow accumulation in cirques and accumulate snow and ice as they move downslope. Their movement is governed by gravity, internal deformation of the ice, and the presence of a basal layer of water that lubricates the glacier's bed. The erosive power of a valley glacier is immense, stemming from the weight of the ice and the abrasive action of the entrained rock debris.
Major Landforms Produced by Glacial Erosion
1. Erosional Landforms in the Upper Valley (Cirque & Headwall)
- Cirque: A bowl-shaped depression at the head of a glacial valley, formed by glacial erosion and freeze-thaw weathering. The back wall is steep, forming a headwall.
- Headwall: The steep, often cliff-like wall at the back of a cirque. It’s formed by intense glacial plucking and frost wedging.
- Arête: A sharp, knife-edged ridge separating two adjacent cirques. Formed by the erosive action of two glaciers flowing on opposite sides of a divide.
- Horn: A pyramidal peak formed when three or more cirques erode a mountain from different sides. The Matterhorn in the Alps is a classic example.
2. Erosional Landforms in the Valley Floor & Sides
- U-Shaped Valley: The most characteristic landform created by glacial erosion. Glaciers transform V-shaped river valleys into broad, flat-bottomed U-shaped valleys through lateral erosion and vertical downcutting.
- Hanging Valley: A tributary valley that enters a main U-shaped valley at a higher elevation. Formed because the tributary glacier eroded less than the main glacier. Often features waterfalls.
- Truncated Spurs: Ridges that have been cut off by the erosive action of a glacier. They appear as triangular facets on the valley sides.
- Roches Moutonnées: Asymmetrical rock formations with a smooth, gently sloping stoss (upstream) side and a steep, plucked lee (downstream) side. Indicative of glacial flow direction.
- Striations: Scratches and grooves on bedrock surfaces caused by rocks embedded in the base of the glacier. Provide evidence of glacial movement direction.
- Glacial Polish: Smooth, polished bedrock surfaces created by the abrasive action of fine sediment in the glacier.
3. Erosional Landforms at the Valley Mouth
- Fjords: Long, narrow, deep inlets with steep sides, formed when a glacial valley is flooded by the sea after the glacier retreats. Common in Norway, New Zealand, and Chile.
- Fiords vs. Fjords: While often used interchangeably, 'fjord' is the Norwegian term, and 'fiord' is the English adaptation.
4. Processes of Glacial Erosion
Glacial erosion occurs through several key processes:
- Abrasion: The grinding and scouring of bedrock by rocks and sediment embedded in the base of the glacier.
- Plucking (Quarrying): The removal of rock fragments from the bedrock by the glacier. Occurs when meltwater penetrates cracks in the rock and freezes, wedging the rock apart.
- Freeze-Thaw Weathering: The repeated freezing and thawing of water in cracks in the rock, causing it to break apart. This process is particularly important in cirque formation.
| Landform | Erosional Process | Location |
|---|---|---|
| Cirque | Plucking, Freeze-Thaw | Head of Glacial Valley |
| U-Shaped Valley | Abrasion, Plucking | Valley Floor |
| Fjord | Abrasion, Plucking | Valley Mouth (Submerged) |
| Roches Moutonnées | Abrasion, Plucking | Valley Sides |
Conclusion
Valley glaciers are powerful agents of landscape modification, leaving behind a distinctive suite of erosional landforms. These landforms, ranging from cirques and U-shaped valleys to fjords and roches moutonnées, provide valuable insights into past glacial activity and the dynamic nature of Earth’s surface. Understanding these processes is crucial for hazard assessment in glaciated regions and for interpreting the geological history of mountainous areas. Continued glacial retreat due to climate change will further modify these landscapes, highlighting the importance of studying these processes.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.