Vertical erosion involves the wearing away and deepening of the river bed. This is mostly by hydraulic action. It is most common in the upper course of the river.

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Hydraulic action

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Attrition is when sediment particles knock against the bed or each other and break, becoming more rounded and smaller as you move down the river.

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Hydraulic action is when the force of fast-flowing water hits the bed and banks and forces water and air into cracks in the bedrock. The repeated changes in air pressure cause the river bed to weaken.

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Solution (or corrosion) is when acidic water dissolves rocks such as chalk or limestone.

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