Explanation:

Abrasion and hydraulic action erode the soft rock so the hard rock is left as an overhang.Attrition breaks down the river's load.Erosion involves the wearing away of rock and soil found along the river bed and banks.Erosion also involves the breaking down of the rock particles being carried downstream by the river.The four main forms of river erosion:-
Hydraulic action - the force of the river against the banks can cause air to be trapped in cracks and crevices. The pressure weakens the banks and gradually wears it away.
Abrasion - rocks carried along by the river wear down the river bed and banks.
Attrition - rocks being carried by the river smash together and break into smaller, smoother and rounder particles.
Solution - soluble particles are dissolved into the river.