Fluvial Landforms (AQA GCSE Geography)
Revision Note
Written by: Bridgette Barrett
Reviewed by: Jenna Quinn
Erosion 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
These are landforms created through erosion
Waterfalls and gorges
Waterfalls form where there is a drop in the river bed from one level to another
This drop is often due to changes in the hardness of the 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
Study Figure 1, a photograph showing some features of a river in the Lake District
Explain how the landforms shown in Figure 1 are created by physical processes
[6 marks]
The command word in this question is 'Explain'
You need to outline the physical processes ensuring that you mention at least two landforms
It is not enough to say 'erosion' you need to give the type of erosion and where it occurs
This is a levelled answer, so marks are awarded for the answer overall rather than for individual points
In a level 2 and 3 answer you are expected to use geographical terms and include examples of at least two landforms - waterfall and gorge
An example of an answer for each level can be seen below
These are just examples and there are many others which can be found in the mark scheme- see topic question 10
Answer:
Level | Marks | Exemplar Answer |
|---|---|---|
1 (Basic) | 1-2 | There are layers of soft and hard rock. The soft rock erodes more easily than the hard rock which then falls into the plunge pool at the bottom. The process is repeated and the waterfall moves backwards. |
2 (Clear) | 3-4 | The waterfall may have formed where there is hard rock on top of soft rock. The soft rock erodes more quickly than the hard rock leaving the hard rock unsupported. The hard rock breaks off and falls to the bottom of the waterfall into the plunge pool leading to more erosion. This process repeats over and over again causing the waterfall to retreat upstream. |
3 (Detailed) | 5-6 | Figure 1 shows a waterfall, plunge pool and gorge. The waterfall may have formed where a river flows over hard rock with soft rock underneath, The softer rock is eroded more rapidly than the harder rock by the processes of hydraulic action and abrasion leading to undercutting of the hard rock and the formation of a plunge pool were the water hits the bottom of the waterfall with force. The hard rock is no longer supported and breaks off falling into the plunge pool which then increases abrasion and further deepens the pool. This process is repeated causing the waterfall to gradually retreat upstream leaving behind a steep sided gorge. |
Landforms of Erosion & Deposition
Some landforms are created through a combination of erosion and deposition including:
Meanders
Ox-bow lakes
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 riverbank forming a river cliff
The riverbank 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 the 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
Oxbow lake formation
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.
Worked Example
Explain the formation of an ox-bow lake.
[4 marks]
The command word in this question is 'Explain'
You need to outline the physical processes ensuring that you mention all the stages of ox-bow lake formation
It is not enough to say 'erosion' you need to give the type of erosion and where it occurs
Diagrams would be given marks as long as they were clearly annotated
Answer:
A meander is a winding curve or bend in a river. Over time, because of erosion and deposition, meanders gradually change [1]
The neck of the meander narrows due to lateral erosion on opposite sides of the meander bend [1]
During high flow (flood) conditions, the meander neck is broken through. The river now adopts the shorter (steeper) route, by-passing the old meander [1]
Deposition occurs at the edges of the new straight section, effectively cutting off the old meander [1]
The old meander now forms an ox-bow lake, separated from the main river [1]
Gradually the ox-bow lake silts up to form marshland [1]
Depositional Landforms
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
Estuaries
An estuary is where the river meets the sea
Large deposits of sediment form mudflats and salt marshes
These are the result of the interaction between the river and tides
Incoming tides bring in sediment which mixes with the sediment being carried by the river
When the incoming tide of salt water meets the freshwater of the river, the river velocity drops and deposition occurs
The deposited sediment builds up in layers to form mudflats which rise above the water surface, particularly at low tide
Eventually the vegetation starts to grow on the mudflats and form salt marshes
Worked Example
Explain how river levées are formed.
[4 marks]
The command word in this question is 'Explain'
You need to outline the physical processes ensuring that you are clear about when levées form and how
It is not enough to say 'deposition' you need to explain why the deposition happens
Answer:
Levées are long narrow ridges or raised embankments alongside the river [1] Composed of gravel, stones and alluvium/ Steeper on channel side than land side [1]
Levées occur in the lower course of a river when there is an increase in the volume of water flowing downstream and flooding occurs [1]
Sediment that has been eroded further upstream is transported downstream [1]
When the river floods, the sediment spreads out across the floodplain. Friction with the land reduces velocity and causes deposition [1]
When a flood occurs, the river loses energy. The largest material (sand and gravel) is deposited first on the sides of the river banks and smaller material (finer silt and mud) further away [1]
After many floods, the sediment builds up to increase the height of the river banks, so the levées become higher than the surrounding floodplain [1]
If a severe flood event occurs, levées may burst and cause serious damage to surrounding land [1]
Case Study: River Tees
The River Tees is located in north-east England
It is 85 miles from source to mouth
It flows eastwards from the source in the Pennines to the mouth where it flows into the North Sea
Landforms of erosion
High Force waterfall is the highest waterfall in England
High Force formed where dolerite, a hard igneous rock (known locally as 'whinstone') lays over a softer sedimentary rock, limestone
The water erodes the limestone more rapidly, undercutting the hard dolerite
Eventually the dolerite falls because it is unsupported and the process starts again
The retreat of the waterfall upstream as a result of this process has left behind a steep sided gorge
Landforms of erosion and deposition
In the middle and lower sections of the River Tees the river flows over flat, low-lying land
Meanders form such as in the area to the south-east of Darlington
Landforms of deposition
In the middle and lower sections floodplains and levées also form as a result of repeated flooding of the areas
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