What factor influences the formation of stair-step canyons?

The formation of stair-step canyons is primarily influenced by the presence of alternating layers of hard and soft rock. This geological phenomenon occurs when different types of rock layers are subjected to erosion at different rates. Hard rock, such as limestone or granite, tends to erode more slowly compared to softer rock, like sandstone or shale, which erodes more quickly.

As water flows through these rock layers, it wears away the softer elements, creating steps or terraces in the canyon structure. This results in the characteristic stair-step appearance, where layers alternate, creating distinct levels. This process illustrates the broader principles of differential erosion, where variations in rock composition lead to varying shapes and formations in the landscape.

The other options do not encapsulate the complexity of canyon formation as accurately. For instance, weathering of only one type of rock lacks the variability necessary to create the distinct stair-step features. Similarly, volcanic activity alone does not contribute to the layered structure typical in stair-step canyons, and glacial processes, while influential in shaping landscapes, are not the primary drivers for this specific type of canyon formation. Therefore, the interplay of hard and soft rock layers is crucial in understanding why stair-step canyons develop as they do.