What typically causes a stream to begin downcutting in the process of forming incised meanders?

The process of downcutting in streams, which leads to the formation of incised meanders, is primarily driven by a drop in base level or an uplift of land. When the base level, which is the lowest point to which a stream can erode, decreases, the stream has increased energy and capacity to erode its channel downward. This results in deeper cuts into the landscape, leading to the characteristic vertical walls of incised meanders.

When there is a drop in base level, such as due to tectonic activities or the lowering of sea levels, the stream attempts to reach this new base level by eroding its bed. Similarly, if land is uplifted due to geological processes, the stream is also encouraged to cut deeper into its channel to adjust to the new topography.

In contrast, an increase in base level would result in less downcutting, as it raises the threshold for erosion. Stable land elevation suggests no major changes, limiting the potential for dramatic changes in stream dynamics, while a change in sediment load could affect the stream’s ability to erode but is not the primary driver for initiating downcutting. Therefore, the dynamics of base level changes and land uplift are critical in understanding the formation of incised meanders