Formations

Question 1

Ox bow lake

Answer 1

1- Erosion of outer bank forms river cliff. Deposition inner bank forms slip off slope
2- Further hydraulic action and abrasion of outer banks, neck gets smaller
3- Erosion breaks through neck, so river takes the fastest route, redirecting flow
4- Evaporation and deposition cuts off main channel leaving an oxbow lake

Question 2

Waterfall

Answer 2

1- River flows over alternative types of rocks
2- River erodes soft rock faster creating a step
3- Further hydraulic action and abrasion form a plunge pool beneath
4- Hard rock above is undercut leaving cap rock which collapses providing more material for erosion
5- Waterfall retreats leaving steep sided gorge

Question 3

Floodplains and levees

Answer 3

When a river floods, fine silt/alluvium is deposited on the valley floor
- Closer to the river’s banks, the heavier materials build up to form natural levees

Question 4

Advantages of floodplains

Answer 4

• Nutrient rich soil makes it ideal for farming
• Flat land for building houses

Question 5

Meanders

Answer 5

• thalweg is the fastest flow of river on the outside bend
  = more energy to erode outside bend
• hydraulic action and abrasion erodes the river bed and bank
  = causes a river cliff
• inside bank has low energy
  = not enough power to erode
  = areas of deposition
  = slip off slope formed by deposition
  = sediment is dropped off and builds up due to low energy

Question 6

Levees

Answer 6

• long, narrow ridges alongside river made of gravel, stones, alluvium
• steeper on channel side than land side
• occur in lower course of river when there’s increase in water volume flowing downstream and flooding occurs
• sediment that has been eroded further upstream is transported downstream
• when river floods sediment spread out across floodplain
• friction with land reduces velocity and causes deposition
• when flood occurs river looses energy and larger materials deposited first on side of river banks
• after many floods sediment builds up to increase river bank height
  = levees become higher than surrounding floodplain