Answer
The two main external factors that can promote the formation of highly incisive channels in a landscape are tectonic uplift and a change in base level. Tectonic uplift can create steeper gradients in rivers, leading to increased erosion and incision of channels. A change in base level, such as a drop in sea level or a change in the level of a lake, can also result in increased erosion and downcutting of rivers as they adjust to the new lower base level. Tectonic uplift primarily promotes the formation of highly incisive channels through the first external factor, which is the creation of steeper gradients.
The resulting valley from the combined influence of tectonic uplift and a change in base level would have a V-shaped cross-section. The steep slopes along the valley sides are a consequence of increased downcutting by the river, and the overall shape resembles the letter "V" when viewed from the side. The valley floor would be relatively narrow, as the river actively erodes downward in response to the uplift and base level changes.
Work Step by Step
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