IGCSE Geography Lesson: River Processes

Lesson Outcomes

By the end of this lesson you will know: 

  • The processes involved in the formation of river features including weathering and mass movement, erosion and deposition
  • The factors affecting these processes such as stream velocity, slope and geology.

River Processes

rivers

Running water has a significant influence on the features in our landscape. These features are formed through the following processes:

  • Erosion
  • Transportation
  • Deposition

The above processes work in partnership with 2 other processes:

  • Weathering
  • Mass movement
Weathering

This is when elements of the weather (mainly precipitation and temperature) affect and change the landscape. There are 3 types of weathering:

  1. Physical weathering
  2. Biological weathering
  3. Chemical weathering

Physical Weathering

This breaks rock into smaller pieces. Examples of physical weathering include:

weathering

Biological Weathering

This is the action of plants on rock. Tree roots can grow and crack or even split rocks. Other plants such as lichens release acids that can eat away at rock over time.

tree root damage

Chemical Weathering

Slightly acidic rainfall chemically erodes rock - this is especially important in alkaline rock such as limestone.

chemical weathering

Once rocks have been broken down by the processes of weathering, the broken rock starts to move down the slope under the force of gravity, this can take several forms but is known collectively as a mass movement.

soil creep

landslide

Mass movements vary with regards to size and speed. On gentle slopes soil creep can occur whereas steeper slopes create much faster movements such as mudslides and landslides.


River Erosion

Erosion is the wearing away of the land. There are several ways that a river can erode the channel and valley.

1. Hydraulic Action

This is the sheer force of the water crashing against the banks and bed, breaking away pieces of rock.

2. Abrasion (corrasion)

Material carried by the river (load) wears away the banks and bed much like the action of sandpaper on wood.

3. Solution (corrosion)

The rock in the banks and bed can be chemically eroded by the slightly acidic river water.


River Transportation

The river load can be transported in different ways.

transportation


River Deposition

Deposition is the laying down of material. River load will be deposited when the water no longer has the energy to carry it. This means that as the river slows down the larger material will be deposited first and the smallest particles (silt) will be deposited last.


Use the Internet!

Check out these clips on river processes:

http://www.bbc.co.uk/education/clips/ztktsbk

http://www.bbc.co.uk/education/clips/zpdpyrd


Activity

Write an extended answer describing and explaining the processes of erosion, transportation and deposition.

  • Handy hint: in your exam you will be awarded a mark for every valid point you make e.g. Hydraulic action is the sheer force of the water breaking pieces of rock away.

End of Lesson Check

Do you know...

  • The processes involved in the formation of river features including weathering and mass movement, erosion and deposition?
  • The factors affecting these processes such as stream velocity, slope and geology?

Last modified: Wednesday, 6 September 2017, 11:59 PM