What process leads to the formation of a V-shaped valley?

The formation of a V-shaped valley is primarily the result of downcutting by fast-moving water. This process occurs in river systems where flowing water erodes the bedrock and surrounding materials more intensely due to its velocity, especially in steep or mountainous terrains. As water moves quickly, it exerts significant energy on the landscape, carving out the valley walls and deepening the channel over time. This typically leads to characteristic V-shaped profiles in cross-section because the erosion occurs more rapidly vertically than laterally, creating steep sides.

In contrast, other processes described in the options do not primarily lead to the formation of V-shaped valleys. Rapid erosion by meandering streams tends to create wide, flat valleys with gently sloping sides rather than a narrow V shape. Depositional processes of sand and gravel lead to the buildup of riverbanks and floodplains, not to the carving of valleys. Lastly, the formation of floodplains occurs as sediment is deposited by slow-moving water, which again contributes to flat, wide areas rather than V-shaped valleys. Thus, the formation of V-shaped valleys is best attributed to the aggressive downcutting action of fast-moving water.