River Landscapes (Edexcel IGCSE Geography)

Upland Landforms

Spec point — 4GE1-S3.042

River landscape characteristics

• The changes in river channel characteristics, lead to changes in the river landscape

• The upland and lowland areas of rivers have distinctive landforms

• In upland areas, the common landforms include:

  • waterfalls
  • gorges
  • v-shaped valleys
  • interlocking spurs

Waterfalls and gorges

• Waterfalls form when there is a drop in the river bed from one level to another

  • This drop is often due to changes in the hardness of rock, where hard rock overlies soft rock

• Hydraulic action and abrasion are the main erosional processes in waterfall formation

• The softer rock erodes quicker, undercutting the harder rock and creating a plunge pool

• This leads to the development of an overhang of hard rock which eventually over time, collapses

• The overhang falls into the plunge pool increasing abrasion and making the plunge pool deeper

• The process then begins again and the waterfall retreats upstream leaving a steep-sided gorge

Diagram showing waterfall and gorge formation

V-shaped valleys

• Vertical erosion is dominant in the upper course of the river
• This cuts down into the river bed and deepens the river channel
• Weathering and mass movement lead to material from the valley sides collapsing into the river forming a steep v-shaped valley

Diagram showing the formation of a v-shaped valley

Interlocking spurs

• In the upper course of the river, the channel starts to meander
• Erosion happens on the outside of the bend
• In the upland areas this forms interlocking spurs

Diagram showing interlocking spurs

Worked Example **Explain the formation of a waterfall. (4)

• Identify the command word
• The command word is 'explain'
• Your focus is on 'waterfall'

-** Answer: **(you should include 4 points from the following)

• Waterfalls occur where there is a step in the landscape often where hard rock such as dolerite overlays soft rock such as limestone (1)
• The soft rock erodes due to hydraulic action, at a faster rate than the hard rock**(1) leading to undercutting and the formation of a plunge pool (1)
• This leaves an overhang of hard rock which eventually collapses due to gravity (1)
• The process is then repeated causing the waterfall to retreat upstream leaving a steep side gorge (1)

Lowland Landforms

Spec point — 4GE1-S3.042

• Landforms found in lowland areas of the river include:

  • meanders
  • ox-bow lakes
  • floodplains
  • levees

Meanders

• In lowland areas lateral erosion is dominant

• Meanders increase in size

• The fastest water flow (thalweg) is on the outside of the river bends, leading to erosion:

  • The erosion undercuts the river bank forming a river cliff
  • The river bank collapses and the edge of the meander moves further out

• The slowest flow is on the inside of the river bends, leading to deposition:

  • The deposits form a gentle slope known as a slip-off slope

• Deposition on one side and erosion on the other leads to the meander migrating across the valley

  • This forms a wide, flat floodplain on either side of the river

Cross-section of a meander

Ox-bow lakes

• With distance downstream, the size of the meanders increases
• The erosion on outside bends can eventually lead to the formation of a meander neck
• At a time of flood, the river may cut through the neck of the meander, forming a straighter course for the water
• The flow of water at entry and exit from the meander will then be slower, leading to deposition
• The meander becomes cut off from the main river channel, forming an ox-bow lake

Oxbow Lake Formation

Exam Hint Remember when describing the formation of ox-bow lakes it is important to state that the river will break through the neck of the meander during a flood. At other times the river does not have enough power to break through.

Floodplains and levees

• Floodplains are flat expanses of land on either side of the river

  • They are formed by the migration of meanders across the valley
  • Material is then added to the floodplain during times of flood

• High discharge may cause the river to overflow the banks (flooding)

• More of the water is in contact with the land surface as the water spreads across the floodplain

• Increased friction caused by this contact reduces velocity and material is deposited across the floodplain gradually increasing the floodplain height

• The heaviest material is deposited first nearest to the river channel forming natural embankments called levees

Diagram showing floodplain and levee formation

Exam Hint When describing landform formation it is helpful to write the formation down as a sequence of steps. This will make the process easier to remember.