- Created by: ellllllllllaa
- Created on: 19-05-19 13:29
Abrasion- fluvial erosion
- Also called corrasion.
- Small boulders and stones may scratch and scrape their way down a river during transport, thereby wearing down the river banks and bed.
- Most erosion happens by abrasion.
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Hydraulic Action- fluvial erosion
- When the sheer force of fast flowing water hits the river banks and bed and forces water into cracks.
- The force of the water and repeated changes in pressure weaken the channel and gradually, the banks and bed wear away.
- Responsible for vertical erosion in the upper course and lateral erosion in the lower course.
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Attrition- fluvial erosion
- Attrition affects a rivers load.
- When stones first enter a river, they will be jagged and angular. As they are transported downstream, the stones collide with each other and the river banks and bed.
- This gradually erodes the stones jagged edges so that they are smooth and rounded.
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Solution (Corrosion)- fluvial erosion
- Solution refers to the dissolving of rocks such as chalk and limestone.
- Rivers travelling over these rocks will erode them in this way.
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- Soluble materials (e.g. minerals) dissolve in the water and are carried along.
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- Small particles like silt and clay are carried along by the water.
- The load is fine, light material.
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- Small pebbles and stones are bounced along the river bed by the force of the water.
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- Large particles like boulders and rocks (bedload) are pushed along the river bed by the force of the water.
What is the difference between bedload and load?
- The bedload is the load on the bed of the river.
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- Deposition is when a river drops the load (sediment) it is transporting.
- It happens when a river slows down (loses velocity)
- Large boulders are the first to be deposited as they need more energy to be transported.
- The finest particles are deposited last as they require little energy.
- This is why mountain streams have boulders aong their bed, whereas close to the river's mouth, there is only fine silt.
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What causes velocity to fall?
- The river reaches its mouth.
- The river is less steep.
- The amount of eroded material (load) increases (as this increases the amount of friction).
- The volume of water in the river falls (can be caused by weather- low rainfall = low flow).
- The river is shallower (e.g. on the inside of a bend)
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