River Erosion 

How does a river erode?

Erosion refers to the removal of weathered material by agents such as wind, water and ice.

1) Hydraulic action: This refers to the force of the water itself. Water splashes against river banks and forces it way into cracks and openings.  This is when the sheer power of the river forces air into small pockets on the river bank and bed, causing them to break apart over time. As the water smashes against the river banks, it slowly breaks it down over time. 

2) Solution: Some minerals in rocks and soil are soluble. They are slowly dissolved by river water as it comes into contact with them.  This can happen to rocks such as limestone, which reacts with small amounts of carbonic acid in the water. 

3) Corrasion/ Abrasion: As the river flows it grinds its load against its bed and banks. This is when small rocks and pebbles are pushed along the bed of a river by the speed and intensity of the current. Over time, this has a sandpapering effect on the river bed, as rocks grinding over the surface eventually wear it down. 

4) Attrition: This refers to the process by which material being carried by the river, such as rocks and stones, collide with each other. When the rocks that rivers are carrying bash against each other in the current, and eventually break each other apart. The smaller fragments are then carried along by the river, and these eventually become smaller and more rounded.