Erosion and Deposition by Running Water, Ice, Wind and Wave Action

These include river erosion, transportation, and deposition.

Erosion of a river operates in three ways: headward, vertical, and lateral erosion.

1. Headward erosion: This is the cutting back of the river at its source, increasing the river's length.
2. Vertical erosion: This is erosion by which a river deepens its channel.
3. Lateral erosion: This is the wearing away of the sides of a river by water and its load, responsible for the widening of a river valley.

<img alt="River erosion diagram" src="https://geo.libretexts.org/@api/deki/files/14655/9.8.png?revision=1&amp;size=bestfit&amp;width=291&amp;height="233" width="291" height="233"/>

River erosion processes

River erosion involves four related processes: abrasion (corrasion), attrition, corrosion (solution), and hydraulic action.

1. Hydraulic action: The process whereby the force of moving water plucks and sweeps away loose materials (e.g., silt, gravel, and pebbles). Materials plucked by hydraulic action are responsible for bank caving and slumping.
2. Corrosion (abrasion): Occurs when the river's load rubs against the bed and sides of the river channel, causing wear and tear on the sides and bed of the river.
3. Attrition: The process in which rock fragments in the river's load collide with one another, breaking into smaller fragments as the load is carried downstream.
4. Corrosion (solution): River water dissolves certain minerals, leading to the dissolution and disappearance of rocks such as limestone, rock salt, and chalk.

1. River transport involves carrying away weathered and eroded materials from one place to another. The materials carried by the river are called the load.
2. River transports its load in four ways:
   • Saltation: Small pieces of rock fragments are carried by the river while bouncing on the riverbed.
   • Traction: Large boulders, such as pebbles, are dragged or rolled along the riverbed.
   • Suspension: Fine or light materials like silt and mud are carried in suspension. This occurs when the river flow is strong.
   • Solution: Materials that dissolve in water are carried in solution form.

A river deposits its load when its volume and speed decreases.

A river's volume decreases when:

1. It enters an arid region, especially a hot desert.
2. It crosses a region composed of porous rocks (e.g., sand and limestone).
3. During dry seasons or periods of drought.

A river's speed decreases when:

1. It enters a lake or sea.
2. It enters a flat or gently sloping plain, such as a valley bottom.

The long profile of a river is the line that follows the course of the river from its source to its mouth.

Three courses or sections of a river can be distinguished:

1. The upper course
2. The middle course
3. The lower course

The first stage of a river, often referred to as the youth or torrent course.

Characteristics of the upper course:

1. It is the source of the river.
2. The speed of the river is high.
3. Most of the work done by the river involves vertical erosion.
4. The cross-section of the river valley is V-shaped.
5. The slope of the profile is very steep.
6. It is sometimes used for hydroelectric power (H.E.P) generation.

Erosional and depositional features:

The main features in the upper course are:

1. Deep and narrow V-shaped valley
2. Steep gradient
3. Potholes on the riverbed
4. Interlocking spurs
5. Waterfalls and rapids, often with plunge pools

V-shaped valley

1. A deep, narrow valley found in the youth or first stage of a river.
2. Formed primarily through vertical erosion.
3. The valley has a V shape due to the intense downcutting of the river into the bedrock.
4. The sides of the valley are often steep and can be prone to erosion.
5. Common in the upper course of a river, where water velocity is high and erosion is more pronounced.

Potholes

1. These are circular depressions on the riverbed.
2. They are formed when pebbles carried by the swirling water cut circular depressions in the river's bed.

Interlocking spurs

1. An interlocking spur, also known as an overlapping spur, is one of any number of projecting ridges.
2. These ridges extend alternately from the opposite sides of the wall of a young, V-shaped valley.
3. A river with a winding course flows down these valleys.

Waterfall

1. A waterfall is a place where water flows over a vertical drop in the course of a stream or river.

Rapids

1. These are sections of a river where the riverbed has a relatively steep gradient.
2. The steep gradient causes an increase in water velocity and turbulence.

Plunge pool

1. This is a large depression formed at the base of a waterfall.

Gorge

1. It is a steep, narrow, and elongated valley.
2. A gorge is often formed when a waterfall retreats upstream (e.g., a gorge found in Victoria Falls).

1. This is the second stage of a river.
2. The main features of this section are bluffs, waterfalls, and rapids.

The characteristic features of the middle course of a river valley:

The speed of a river is low.

1. Most of the work of a river is transportation.
2. The cross-section of a valley in this section is open.
3. The slope of the relief is gentle.
4. The volume of the river increases.
5. Lateral erosion predominates.

Features associated with the middle course of a river valley:

• Bluffs: These are steep slopes of the truncated spurs in the middle course where interlocking spurs turn into bluffs.

Waterfalls and rapids:

1. Waterfalls and rapids can also be found in the middle stage of the river valley.
2. This is mainly caused by river rejuvenation, which increases erosive activity and transportation, hence the development of waterfalls.

1. This is the third stage of a river.
2. The main features of the lower section of a river valley are:
   • Flood plain
   • Braided river
   • Ox-bow lake
   • Levee and deferred tributary
   • Delta

Characteristics of lower stage

It is the river mouth.

1. Always there are gradient falls or slope falls.
2. The main work of a river is deposition.
3. The cross section of a valley is a U-shaped valley.
4. The speed of a river is decreased.
5. The river valley is very wide.

1. Loess form very fertile soil in desert land.
2. Waterfalls attract tourists; headlands in coastal areas are natural ports.
3. Coastal features form breeding places for fish.
4. Coral reefs are used as building materials and for settlement.