formation of river land forms

Question 1

Explain the formation of interlocking spurs (2)

Answer 1

• The discharge is very small in the upper course so the river has very little energy to erode, and the rocks tend to be more resistant to erosion (igneous and metamorphic).
• So the river flows around the spurs rather than eroding them, resulting in the formation of interlocking spurs.

Question 2

Explain the formation of V-shaped valleys (2)

Answer 2

• The discharge is very small in the upper course so the river has very little energy to erode, and the rocks tend to be more resistant to erosion (igneous and metamorphic)
• The river does erode vertically due to the pull of gravity as it is an upland area. This creates v-shaped valleys.

Question 3

Explain the formation of waterfalls

Answer 3

• Waterfalls form when hard rock is above soft rock. The soft rock is eroded more quickly than the hard rock by processes such as hydraulic action and abrasion
• This leaves an overhang of hard rock which eventually collapses due to the pull of gravity, which results in the formation of the plunge pool.
• Over time, the soft rock is further eroded, so a new overhang forms and the process repeats
• The waterfall retreats resulting in the formation of a steep sided gorge

Question 4

Explain the formation of meanders (4)

Answer 4

• Meanders occur in the middle and lower course of the river
• Discharge has increased and so the river has more energy to erode laterally, resulting in the river meandering.
• The fastest flow is on the outside of the bend, where it is deepest and so where the effect of friction is less. The faster flow has more energy to erode by processes such as hydraulic action and abrasion. Eventually the eroded bank collapses, leaving a steep river cliff.
• The slower flow is on the inside bend where the water is shallower and so where friction with the river bed is greatest. The slower flow has less energy and so the river deposits its load, resulting in the formation of a point-bar.

Question 5

Explain the formation of Oxbow lakes (4)

Answer 5

• Erosion processes such as hydraulic action and abrasion cause the neck of the meander to become narrower. During times of flood the river’s velocity increases and so it has more energy to erode
• This can result in the river breaking through the neck of the meander.
• The river now flows straight and so the fastest flow which greater energy to erode is in the centre of the channel, and the slower flow is at the sides
• Deposition takes place as the sides due to the slower flow having less energy to transport load. This deposition eventually cuts off the meander, creating an oxbow lake

Question 6

Explain the formation of floodplains (4)

Answer 6

• Floodplains can be created by both migrating meanders and floods
• Migrating meanders erode the valley sides laterally by processes such as hydraulic action and abrasion, resulting in the flattening of the valley sides and so the creation of a floodplain
• When a river floods it deposits its load across the valley, which flattens the land, again creating a floodplain
• The heaviest material is deposited first as the river doesn’t have the energy to transport it, and the lighter material is deposited further across the floodplain. This is called sequential deposition

Question 7

Explain the formation of levees (4)

Answer 7

• When a river floods it deposits its load across the valley
• The heaviest material is deposited first as the river doesn’t have the energy to transport it (sequential deposition)
• This material builds up resulting in the creation of raised river banks called levees
• As the river floods more over time, the levees become larger