River Processes: Erosion & DepositionThis is a featured page

Erosion

The process of erosion is when a river uses the transported material, known as load, to erode its banks and bed. As the velocity of a river increases, so does the load it carries and the rate at which it can erode at. There are four processes of erosion: attrition, hydraulic action, corrasion, and corrosion.

The four processes of Erosion

  1. Attrition is when boulders and other material, which are being transported along the bed of a river, collide and break into smaller pieces. Over time, they eventually reduce to small, finer particles known as silt.This mostly occurs when rivers are in still flowing in their upper course.
  2. Hydraulic Action is when the force of a river knocks loose the particles from a river's banks and bed. This can happen while a river is in its upper and middle course or in the outer bends of a meander.
  3. Corrasion occurs when smaller material rubs against the banks of a river while being carried in suspension. This is most likely to happen in a rivers middle or lower course. This type of erosion can also be called abrasion because of its sand-papering action.
  4. Corrosion is when acids in the river dissolve rocks, which form in the banks and bed, and carries them away in solution. This can occur at any point of a river's course.

Click here to view an example of a river erosion.

Deposition

River deposition can be thought as the opposite of erosion. Deposition quite simply is the process where the river drops sediment and any other material it carries. The load of a river can be all sorts of different things, such as boulders, silt, stones, mud and much more. Deposition occurs when the river loses its energy to carry the load. Thus the load is "deposited".

Where does river deposition occur?

River deposition usually occurs on the inside bends of meanders. Here the force of the river is weakest and any sediment here is dumped. This is why the river is most shallow at the inside bend because of the deposited material left there. Evidence of river deposition is easily findable. Any area of rocks, pebbles, boulders that are not moving can be counted as a product of deposition. Products of deposition are called alluvium.

Material and deposition

Bigger materials would need more energy to move and therefore smaller materials would take less energy. As the rivers energy decreases the first materials to be deposited would be the large boulders followed by the smaller material. This can be observed during periods of flooding where the river deposits its heaviest material closer to the river. Example: When a volcano explodes heavy particles are closer to the mouth of the volcano.



Click here to watch how sediments are deposited.



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marshalldy
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