What is the primary type of erosion responsible for cliff formations in upper river courses?

The primary type of erosion responsible for cliff formations in upper river courses is vertical erosion. This process occurs when the river cuts downward into the bedrock, deepening its channel. As the river flows with high energy in the upper course, it predominantly erodes the riverbed vertically, allowing it to carve steep, often rugged cliffs along the banks.

Vertical erosion is particularly effective in these upper reaches due to the steep gradient and fast-moving water, which gives it the power to remove materials directly from the bed, leading to the development of V-shaped valleys and pronounced cliff faces. This is in contrast to other forms of erosion, which may not significantly contribute to cliff formation in these areas. For example, lateral erosion mainly occurs in the middle and lower parts of the river, affecting the riverbanks rather than the cliff edges. Therefore, vertical erosion is essential for understanding the landscape shaping seen in the upper courses of rivers.