Four Processes of Erosion
Hydraulic Action - Sheer force of the water breaks rock particles away from the river channel.
Abrasion - Eroded rocks picked up by the river scrape and rub against the channel, wearing it away. Most erosion happens by abrasion.
Attrition - Eroded rocks picked up by the river smash into each other and break into smaller fragments. Their edges also get rounded off as they rub together.
Solution - River water dissolves some types of rock, e.g chalk and limestone.
(The faster a river's flowing, the more erosion happens)
Transportation is the movement of eroded material
Traction - large particles like boulders are pushed along the river bed by the force of the water.
Saltation - pebble-sized particles are bounced along the river bed by the force of water.
Suspension - small particles like silt and clay are carried along by the water.
Solution - soluble materials dissolve in the water and are carried along.
Deposition is when a river drops eroded material
1. Deposition is when a river drops the eroded material its transporting.
2. It happens when a river slows down (loses velocity)
3. There are a few reasons why rivers slow down and deposit material:
- The volume of water in the river falls
- The amount of eroded material in the water increases
- The water is shallower, e.g. on the inside of a bend
- The river reaches its mouth