What is a common reason for the formation of terraces along a river?

The formation of terraces along a river is commonly associated with a drop in base level. When the base level of a river system decreases, it indicates that the river has more energy and can cut vertically into its riverbed. This erosion can create a stair-step landscape where the remnants of the former floodplain are left behind as terraces.

These terraces represent previous levels of the river as it once flowed at a higher elevation before the base level change occurred. When this drop happens, the river cuts downwards into its sediment and rock layers, leading to the formation of these distinct landforms.

Other options reflect processes that generally do not lead to terrace formation. An increase in sediment load may lead to sediment deposition rather than vertical erosion, while a decrease in water flow tends to stabilize riverbanks rather than promote erosion. Consistent rainfall is more about hydrological cycles and might not impact the vertical cutting of the river. Therefore, the correct connection here is the alteration of base level, which enables the river to carve out those terraces.