This is the sheer power of the water as it smashes against the river banks. air becomes trapped in the cracks of the river bank and bed, and causes the rock to break apart.
Abrasion
When pebbles grind along the river bank and bed in a sand-papering effect.
Attrition
When rocks that the river is carrying knock against each other. They break apart to become smaller and more rounded.
Solution
When the water dissolves certain types of rock eg. limestone.
