Friday, November 10, 2006

Upper Course of the River: V-Shaped Valleys

V-Shaped Valleys

In the upper course of a river, water flows quickly through a narrow channel with a steep gradient; as it does so it cuts downwards. This vertical erosion results in a number of distinctive landforms including the steep sloping v-shaped valley through which the river flows in its upper course.

So how does a v-shaped valley form?

1. Vertical erosion (in the form of abrasion, hydraulic action and solution) in the river channel results in the formation of a steep sided valley
2. Over time the sides of this valley are weakened by weathering processes and continued vertical erosion at the base of the valley
3. Gradually mass movement of materials occurs down the valley sides, gradually creating the distinctive v-shape.
4. This material is then gradually transported away by the river when there is enough energy to do so.

As the river flows through the valley it is forced to swing from side to side around more resistant rock outcrops (spurs). As there is little energy for lateral erosion, the river continues to cut down vertically flowing between spurs of higher land creating interlocking spurs.

Visualising V-shaped Valley Formation

Key Term Check
V-shaped Valley - a valley which resembles a 'v' in cross section. These valleys have steep sloping sides and narrow bottoms.

Interlocking Spur - spurs are ridges of more resistant rock around which a river is forced to wind as it passes downstream in the upper course. Interlocking spurs form where the river is forced to swing from side to side around these more resistant ridges.

- collective term for the material carried by a river

Click on the diagram above to see a larger version.

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