Chapter 6: Landforms of Glaciation
This chapter details how glaciers (moving masses of ice) shape the landscape in high latitudes and high altitudes. Glaciation is a powerful agent of erosion, transportation, and deposition.
1. The Nature of Glaciers
- Snowline: The height above which snow remains on the ground all year.
- Glacier Movement: Glaciers move under the force of gravity. Movement is faster in the center and top, and slower at the sides and bottom due to friction.
- Processes of Glacial Erosion:
- Plucking: The glacier freezes onto rocks and “plucks” them away as it moves.
- Abrasion: The ice uses embedded rocks like sandpaper to grind and polish the valley floor.
2. Glacial Erosional Landforms (Highlands)
- Corrie (Cirque/Cwm): A horseshoe-shaped depression carved into a mountain. When the ice melts, the circular lake left behind is called a Tarn.
- Arête: A sharp, knife-like ridge formed between two adjacent corries.
- Pyramidal Peak (Horn): A pointed mountain peak formed when several corries cut back into the same mountain (e.g., Matterhorn in the Alps).
- U-Shaped Valley (Glacial Trough): Glaciers widen and deepen V-shaped river valleys into broad, flat-bottomed U-shapes.
- Hanging Valley: A tributary valley that “hangs” above the main U-shaped valley, often resulting in waterfalls.
- Fjord: A deep, water-filled glacial valley that has been submerged by the sea.
3. Glacial Depositional Landforms (Lowlands)
Material transported by a glacier is called Moraine or Glacial Drift.
- Terminal Moraine: A ridge of debris deposited at the furthest point reached by the glacier.
- Lateral Moraine: Debris deposited along the sides of the glacier.
- Drumlins: Smooth, oval-shaped hills of glacial till that look like “half-buried eggs.”
- Eskers: Long, winding ridges of sand and gravel deposited by meltwater streams running under the ice.
- Erratic: Large boulders stranded far from their original location after the ice melts.
4. Quick Revision: Key Terms
- Roche Moutonnée: A rock hill smoothed on the “up-ice” side and jagged on the “down-ice” side.
- Crag and Tail: A mass of hard rock (crag) protecting a slope of softer rock (tail) behind it.
- Outwash Plain: A flat area of gravel and sand deposited by meltwater beyond the terminal moraine.
| Feature | Type | Distinctive Character |
|---|---|---|
| Corrie | Erosion | Armchair-shaped hollow |
| Arête | Erosion | Sharp ridge |
| Drumlin | Deposition | “Basket of eggs” topography |
| Moraine | Deposition | Unsorted glacial debris |
