What is the primary effect of vertical erosion produced by a river?

The primary effect of vertical erosion produced by a river is deepening the river's bed. Vertical erosion occurs mainly in the upper course of a river, where the river cuts downwards into its own channel. This type of erosion is driven by the force of the flowing water, which is concentrated as it flows over steeper gradients, resulting in the removal of material from the riverbed.

As the river deepens its channel, the area can also become more defined, leading to a more pronounced valley shape. This process contributes significantly to the overall landscape, particularly in mountainous or hilly regions where rivers originate. The other options reflect different processes associated with river activity, but they do not directly relate to the specific action of vertical erosion as accurately as the deepening of the river's bed does.