Question map
Statement I : Portions of glacial troughs may exhibit remarkably flat floors. Statement I : The flat floor in a glacial trough is produced by uniform glacial erosion.
Explanation
Statement I is true as glacial troughs, or U-shaped valleys, are characterized by steep sides and remarkably flat, broad floors [4]. These troughs are formed when valley glaciers modify pre-existing stream-cut valleys [2]. However, Statement II is false because the flat floor is not produced by uniform glacial erosion. While one source suggests erosional activity can be uniform due to the heavy mass of ice [1], geomorphological evidence clarifies that the flat appearance is often the result of post-glacial processes. These include the deposition of ground moraines (irregular sheets of till) [3], the accumulation of glacio-fluvial sediments, or the filling of overdeepened rock basins with water or debris [4]. Glacial erosion itself is often non-uniform, leading to 'overdeepening' and stepped profiles rather than a perfectly flat rock floor [5].
Sources
- [2] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 6: Landforms and their Evolution > Glacial Valleys/Troughs > p. 55
- [4] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 6: Landforms of Glaciation > Landforms of Highland Glaciation > p. 62
- [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 17: Major Landforms and Cycle of Erosion > Glacial Trough > p. 231
- [3] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 6: Landforms and their Evolution > Moraines > p. 56
- [5] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 17: Major Landforms and Cycle of Erosion > Maturity > p. 233