River Landscapes

Question 1

What are Erosional landforms?

Answer 1

The processes of erosion can create different landforms. The erosional features are often found in the upper course of the river.

Question 2

How is a waterfall formed?

Answer 2

• The soft rock is eroded quicker than the hard rock and this creates a step.
• As erosion continues, the hard rock is undercut forming an overhang.
• Abrasion and hydraulic action continue to erode the soft rock to create a plunge pool (small scale landform).
• Over time this gets bigger, increasing the size of the overhang until the hard rock is no longer supported and it collapses.
• This process continues and the waterfall retreats upstream.
• A steep-sided valley is left where the waterfall once was. This is called a gorge.

Question 3

How are V-shaped valleys formed?

Answer 3

In the upper course there is more vertical erosion as the river is less powerful, so material cannot be moved in suspension and is instead moved along the river bed using traction or saltation. This erosion, together with the movement of weathered material at the sides of the river, creates the classic V-shaped valley. If there are areas of hard rock which are harder to erode, the river will bend around them.

Question 4

How are meanders formed?

Answer 4

As the river makes its way to the middle course, it gains more water and therefore more energy, so material can be carried in suspension and is used to erode the river banks. Lateral erosion starts to widen the river. When a river flows over flatter land it develops large bends called meanders.

Question 5

How are river cliffs and slip-off slopes formed?

Answer 5

• As a river goes around a bend, most of the water is pushed towards the outside. This causes increased speed due to less friction and therefore increased erosion (through hydraulic action and abrasion).
• The lateral erosion on the outside bend causes undercutting of the river bank to form a river cliff.
• There is less water on the inside bend of a meander so friction causes the water to slow down, lose energy and deposit the material the river is carrying, creating a gentle slope.
• The build-up of deposited sediment is known as a slip-off slope (small scale landform) or sometimes river beach.

Question 6

What are floodplains and how are they formed?

Answer 6

A floodplain is a landform of the lower course. It is a flat area of land which is covered in water when a river bursts its banks. They form due to both erosion and deposition. Erosion creates a wide, flat area on either side of the river. During a flood, material being carried by the river is deposited (as the river loses its speed and energy to transport material). Over time, the height of the floodplain increases as material is deposited on either side of the river.

Question 7

What are levees and how are they formed?

Answer 7

• Levees occur in the lower course of a river when there is an increase in the volume of water flowing downstream and flooding occurs.
• Sediment that has been eroded further upstream is transported downstream.
• When the river floods, the sediment spreads out across the floodplain.
• When a flood occurs, the river loses energy. The largest material is deposited first on the sides of the river banks and smaller material further away.
• After many floods, the sediment builds up to increase the height of the river banks, meaning that the channel can carry more water (a greater discharge) and flooding is less likely to occur in the future.

Question 8

What factors affect the rates of landform change?

Answer 8

Geology – such as hard and soft rocks in the formation of a waterfall.
Climate – in the UK this varies with seasons, and affects the discharge amounts in a river and the level of energy it has to erode and deposit.
Human activity – intended and unintended consequences, such as building a dam which traps sediment and controls the flow of a river.