Explain the four processes of erosion in rivers.

Hydraulic action: This process involves air particles finding their way into the cracks of rocks. This then causes air particles to compress which adds pressure, causing rocks to break away and erode. Abrasion/ Corasion: Sediment transported by the river is sometimes dragged along the river bed, causing the erosion of the bed. Attrition: The velocity of the river causes rocks to collide and break fragments off one another. This causes rocks to become smoother and more rounded. You will find smaller more rounded rocks further downstream as velocity increases. Corrosion/Solution: This is particulalry common with carbonate rocks such as limestone and chalk. These dissolve in the river to form a weak acid by a chemical process. 

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