- Created by: Darren
- Created on: 28-05-13 19:00
Upper course of a river
In the upper course of a river gradients are steep and river channels are narrow. Vertical erosion is greatest in the upper course of a river. As the result of this typical features include steep valley sides, interlocking spurs, rapids, gorges and waterfalls.
When a river runs over alternating layers of hard and soft rock, rapids and waterfalls may form.
Waterfalls commonly form where water rushes down steep hillsides in upland areas and quickly erodes the rocks. The height and number of waterfalls along a stream or river depends upon the type of rocks that are being eroded by the water. Some types of rocks (shale, for example) wear away more easily than others (such as sandstone or limestone).
As the river or stream wears away the weak rocks, they travel across the surface of stronger rocks. These more resistant rocks become the capstones to waterfalls. The number and thickness of these stronger rock units in a vertical sequence of rocks controls how many water falls there are and how much vertical drop there is on each waterfall.
Rivers erode in four ways:
Abrasion or corrasion - This is when large pieces of bedload material wear away the river banks and bed.
Attrition - This is when the bed load itself is eroded when sediment particles knock against the bed or each other and break, becoming more rounded and smaller.
Hydraulic Action - This is when the force of water erodes softer rock.
Solution or corrosion - This is when acidic water erodes rock.
Rivers transport material in four ways:
- Solution - minerals are dissolved in the water and carried along in solution.
- Suspension - fine light material is carried along in the water.
- Saltation - small pebbles and stones are bounced along the river bed.
- Traction - large boulders and rocks are rolled along the river bed.
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