Arrange the following geomorphic stages in the correct sequential order describing the evolution of a pre-glacial river valley into a steep-sided glacial trough (U-shaped valley).
- 1A pre-glacial stream carves a V-shaped valley with interlocking spurs along a steep gradient.
- 2Climatic cooling causes snow accumulation, feeding a valley glacier that occupies and flows through the river channel.
- 3Basal plucking and active lateral abrasion truncate the interlocking spurs and steepen the valley walls.
- 4Glacial retreat exposes a wide, flat-floored U-shaped trough flanked by truncated spurs and hanging tributary valleys.
Answer
The correct sequential order of landform development is: 1. A pre-glacial stream carves a V-shaped valley with interlocking spurs -> 2. Climatic cooling causes snow accumulation, feeding a valley glacier that occupies the river channel -> 3. Basal plucking and active lateral abrasion truncate the interlocking spurs -> 4. Glacial retreat exposes a wide, flat-floored U-shaped trough flanked by truncated spurs and hanging tributary valleys.
The correct order begins with pre-existing fluvial landforms (V-shaped valley with interlocking spurs), followed by valley glacier occupation, active glacial modification (truncation of spurs and wall steepening via abrasion and plucking), and culminates in the post-glacial exposure of a flat-bottomed U-shaped trough with hanging tributary valleys.
Step-by-Step Solution
Key Concept
Glacial Trough Evolution
Estimated Time:2m 0s