River Landscapes (Edexcel IGCSE Geography)
Revision Note
Written by: Bridgette Barrett
Reviewed by: Jenna Quinn
Upland Landforms
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
Upland:
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:
The soft rock erodes quicker, undercutting the hard 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
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 leads to material from the valley sides collapsing into the river forming a steep 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
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
Lowland:
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 slip-off slope
Deposition on one side and erosion on the other leads to the meander migrating across the valley
Oxbow lakes
With distance downstream the size of the meanders increase
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 be slower, leading to deposition
The meander becomes cut off from the main river channel, forming an oxbow lake
Examiner Tips and Tricks
Remember when describing the formation of oxbow 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
The migration of meanders leads to the formation of the floodplain
High discharge may cause the river to overflow the banks
More of the water is in contact with the land surface as the water spreads across the floodplain
Increased friction 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
Examiner Tips and Tricks
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.
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