The correct option is 1 and 3 only.
Explanation
Topography, or relief, acts as a passive control factor in soil formation. It influences soil development primarily through slope gradient, which dictates the rate of erosion, surface runoff, and water percolation. The balance between the removal of weathered material and its accumulation determines soil thickness.
Statement-wise Analysis
- Statement 1 is Correct: On steep slopes, gravity causes rapid surface runoff and mass movement. The rate of erosion often exceeds the rate of soil formation, preventing the accumulation of weathered material. Consequently, soils on steep slopes are typically shallow and thin.
- Statement 2 is Incorrect: Over flat upland areas, surface runoff is minimal, and erosion is slow. These conditions allow weathered material and organic matter to accumulate undisturbed. Therefore, soils in flat upland areas tend to be thick and deep, rather than thin.
- Statement 3 is Correct: Gentle slopes offer the most favourable conditions for soil formation. They provide a balance where erosion is slow enough to allow accumulation, yet the slope is sufficient to ensure good drainage and percolation. This results in deep, fertile soil profiles.
Key Takeaway: There is a direct correlation between slope gradient and soil depth; steep slopes result in thin soils due to high erosion, while flat or gentle slopes foster thick soil development due to accumulation and stability.