Whether it is lateral or vertical erosion, they are four ways a river is eroded.

1. Solution/corrosion: The river water acts as a solvent and dissolves soluble minerals such as limestone. The presence of carbon dioxide would help to dissolve limestone (calcium carbonate) faster due to the chemical reaction between them.

2. Attrition: Materials carried away by the river become smaller, rounder and smoother after colliding with one another during transportation.

3. Hydraulic action: The power of fast-moving water breaks and loosens materials after hitting the river banks and bed. As the water enters the lines of weakness in the rocks, it exerts a great force to break the rocks into fragments.

4. Abrasion/corrasion: The load of a river grinds against the sides and bed of the river channel, removing materials, thus widening and deepening the channel. Abrasion is especially effective when the river has a large load.

Erosional Features

Vertical erosion is more common in the upper stream of the river, especially in heavy rains when the volume of the river water is greatly increased.

However, lateral erosion usually takes place in the middle section of the river, where the gradient of the channel is gentler. Due to erosion by the river, different features are formed.

1. Potholes

Potholes are holes of different sizes, formed by abrasion (corrasion). Pebbles in the water are swirled around on river bed by the water, forming potholes.

Over time, the holes are enlarged and deepened after repeated drilling by the pebbles. A few potholes may join together to form bigger potholes, and with more potholes, the entire river bed is deepened.

2. Rapids

Rapids are a series of fast and short falls. They are found in areas with alternating bands of resistant and less resistant rocks, as the river flows over the area, the less resistant rocks are eroded more rapidly. Thus, the river flows rapidly as it flows over the outcrops of the resistant rock.