River processes and pressure

Question 1

Hydraulic action

Answer 1

The force of the water on the bed and banks of the river removes material

Question 2

Attrition

Answer 2

The load that is carried by the river bumps together and wears down into smaller, smoother pieces

Question 3

Abrasion

Answer 3

Material carried by the river rubs against the bed and banks and wears them away

Question 4

Solution

Answer 4

Some rock minerals dissolve in river water (e.g. calcium carbonate in limestone)

Question 5

Traction

Answer 5

Large boulders roll along the river bed

Question 6

Saltation

Answer 6

Smaller pebbles are bounced along the river bed, picked up and then dropped as the flow of the river changes

Question 7

Suspension

Answer 7

Finer sand and silt particles are carried along in the flow, giving the river a brown appearance

Question 8

Solution

Answer 8

Minerals from rocks such as limestone and chalk, are dissolved in the water and carried along in the flow, although they cannot be seen

Question 9

Deposition

Answer 9

When the river loses energy (slows down) it may drop some of its load

Question 10

How are waterfalls formed (upper course feature)?

Answer 10

1- Band of more resistant rock lies over less resistant rocks
2- Less resistant rock is eroded more quickly, leaving a ‘step’ - the waterfall
3- More resistant rock is undercut, forming an overhang
4- Overhang can no longer be supported, blocks of rock fall down
5- Powerful fall of water erodes plunge pool using fallen rocks
6- Waterfall retreats upstream

Question 11

How are interlocking spurs formed (upper course feature)?

Answer 11

• The river at its source is small and has limited energy. - It flows naturally from side to side, around ridges in the valley sides, called spurs
• The spurs become interlocking with those on the other side of the valley

Question 12

How are meanders formed (lower course feature)?

Answer 12

• they are bends in the river’s course
• in the lower course, the river uses up surplus energy by swinging one way to the other, causing lateral erosion on the outside of bends and deposition on the inside

Question 13

How are do bow lakes formed (lower course feature)?

Answer 13

• forms when a river creates a meander, due to the river’s eroding bank
• after a long period of time, the meander becomes very curved, and eventually the neck of the meander becomes narrower
• the river cuts through the neck during a flood, cutting off the meander and forming an oxbow lake

Question 14

Explain how erosion and deposition form floodplains (lower course feature) (4)?

Answer 14

• as a river meanders in its lower course, lateral erosion erodes away the valley sides, making the valley flatter
• the meanders migrate downstream
• at the same time, deposition occurs as every time the river floods, fine particles of silt are deposited onto the valley sides, forming the floodplain over thousands of years

Question 15

How are levées formed (lower course feature)?

Answer 15

• as the river floods over its bank, the water slows down
• the water can’t carry the biggest + heaviest silt particles and thyme are dropped straight away on the bank forming flood plains
• increased deposition on the river bed when the river is low gradually raises the river bed upwards
• after many floods, the deposits on the bank build up, forming levées

Question 16

How are deltas formed (lower course feature)?

Answer 16

• the speed of a river decreases as it approaches the sea and it deposits most of the material it has been carrying
• over time sediment builds up to create an almost flat area of new land, which is the delta
• as the river is now flowing very slowly over the almost flat gradient, it’s channel fills up with sediment and the river splits and spreads out into many different streams

Question 17

How does the erosion rate impact the river landscapes and sediment load?

Answer 17

• the erosion rate is greater where discharge and energy of river are greater
• so rivers in wet climates erode more material than those in dry climates, impacting on the shape of the river valley and amount of sediment

Question 18

Discharge of river

Answer 18

Volume of water flowing through river channel in a given time