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Geography > River Landscapes - Paper 1 > Flashcards

River Landscapes - Paper 1 Flashcards

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1
Q

Define fluvial erosion:

A

The process by which a river wears away the land. Erosion takes place in 4 ways; attrition, abrasion, hydraulic action and solution.

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2
Q

What is hydraulic action?

A

When the sheer force of fast-flowing water hits the river banks and beds and forces water into cracks. Repeated changes in air pressure weaken the channel.

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3
Q

Where is hydraulic action responsible for making vertical erosion happen?

A

The upper course of the river.

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4
Q

Where is hydraulic action responsible for making lateral erosion happen?

A

The lower course of the river, especially when fast flowing water hits the outside bends of a meander.

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5
Q

What is lateral erosion partly responsible for?

A

The migration of meanders across the flood plain.

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6
Q

What is abrasion?

A

Small boulders and stones may scratch and scrape the river banks and bed as they are transported, wearing them down.

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7
Q

What is another name for abrasion?

A

Corrasion.

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8
Q

What is ongoing abrasion responsible for?

A

Ongoing abrasion is responsible for both vertical and lateral erosion.

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9
Q

What is an effective tool in abrasion?

A

Recently fallen stones into the channel but will be angular and have sharp, jagged edges.

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10
Q

What is solution?

A

Solution refers to the dissolving of rock such as chalk or limestone. Rivers travelling over these rocks will erode them this way.

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11
Q

What is another name for solution?

A

Corrosion.

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12
Q

What is attrition?

A

Attrition affects a rivers load. When stones first enter a river, they will be jagged and angular. As they are transported downstream, stones collide with each other and also with the river banks and beds. This gradually knocks off the stones’ jagged edges so they become smoother and more rounded. Some collision may cause a stone to smash into several smaller stones. These re-sized stones will also be further smoothed and rounded on their journey to the sea.

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13
Q

What is vertical erosion?

A

Vertical erosion is the deepening of the river bed.

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14
Q

What mostly causes vertical erosion?

A

Hydraulic action.

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15
Q

Where is vertical erosion most evident?

A

In the upper course of the river.

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16
Q

What is lateral erosion?

A

Lateral erosion is ‘sideways’ erosion, it wears away the banks of the river.

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17
Q

Where is lateral erosion most evident?

A

In the lower course of the river.

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18
Q

What are the 6 types of erosion?

A

-Hydraulic action
-Attrition
-Abrasion
-Solution
-Lateral erosion
-Vertical erosion

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19
Q

What are the 4 types of transportation?

A

-Traction
-Saltation
-Suspension
-Solution

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20
Q

What is solution? (in transport) And what kinds of rock does it affect?

A

Minerals are dissolved in the water. This is a chemical change affecting rocks such as limestone and chalk.

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21
Q

What is the load that is carried during solution called?

A

Solute load.

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22
Q

What is saltation?

A

Small pebbles and stones are bounced along the river bed. The load is alternatively lifted and dropped in line with a local rise and fall in the velocity of the water.

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23
Q

What is suspension?

A

Fine, light material (such as alluvium) is held up and carried with the rivers flow.

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24
Q

What is the load that is carried during suspension called?

A

Suspended load.

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25
Q

What is traction?

A

Large boulders and rocks are rolled along the river bed.

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26
Q

What is the load that is carried during traction called?

A

Bedload.

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27
Q

What is deposition?

A

The process by which a river drops its load.

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28
Q

What is another name for deposited material?

A

Sediment.

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29
Q

What keeps load moving (why do rivers deposit sediment)? So what drops first?

A

The river’s velocity keeps load moving. The bigger the load particle, the greater the velocity needed to keep it moving. When velocity falls, large boulders and therefor the first to be deposited.

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30
Q

Where do rivers deposit sediment? Give 3 examples:

A

Along its course, a river will deposit its load wherever the velocity falls. This could be at the base of a waterfall, on the inside bend of a meander, or where the river enters a sea or lake.

31
Q

What is another factor that isn’t river velocity which can cause it to deposit more of its load?

A

In a period of drought when the discharge is low.

32
Q

What are interlocking spurs?

A

Valley landforms formed by fluvial erosion. They are projections of highland that alternate from either side of a valley and project into the valley floor. There is a zip-like, interlocking nature of the hillsides, the very narrow valley floor with its winding river, and the river takes up most of the valley floor.

33
Q

Where are interlocking spurs found?

A

In the upper course of a river where rocks are hard.

34
Q

Name an example of where interlocking spurs are:

A

The Afon Dulas Valley, a tributary valley of the River Severn.

35
Q

What are 6 characteristics of interlocking spurs?

A

-A steep gradient
-Convex shape
-Project from alternate sides of the valley
-Separated by a narrow valley floor mostly taken up by the river channel.
-Sometimes wooded
-May have scree slopes

36
Q

What are rapids?

A

Fast-flowing, turbulent sections of a river where the river bed has a relatively steep gradient. They are channel landforms of the upper course.

37
Q

What does the ability of a river to erode its bed depend on?

A

The river’s energy. It also depends on the degree of hardness of the bedrock.

38
Q

What is vertical bedding and what does it do in rapids?

A

They are alternate bands of hard and soft rock across the channel. Differential erosions will occur as soft rock is more easily eroded than hard rock.

This makes the river bed uneven and the rivers flow becomes turbulent, resulting in ‘white water’ sections typical of rapids.

39
Q

What are 4 characteristics of rapids?

A

-Turbulent flow of water
-White water
-Uneven river bed
-Steep gradient.

40
Q

What are waterfalls and gorges?

A

Channel landforms found in the upper course of a river.

41
Q

What are the characteristics of a waterfall?

A

Typically fast-flowing water plummets over a vertical cliff - often a considerable drop - into a deep plunge pool below

42
Q

Does the Riven Severn have a waterfall?

A

No. Although the Water -Break-its-Neck waterfall on one of the tributaries is sometimes referred to as the River Severn Waterfall.

43
Q

What is a gorge?

A

A gorge is a narrow, steep sided valley, with bare, rocky walls.

44
Q

What is a gorge of recession?

A

A gorge found immediately downstream of a waterfall.

45
Q

What 2 things can gorges be classed as?

A

Either a channel or valley landform.

46
Q

Why can’t the gorge at Ironbridge in the River Severn be classified as a gorge?

A

It was primarily formed as a glacial overflow channel, so can not be used an example of fluvial erosion.

47
Q

What are 7 characteristics of a gorge?

A

-Very narrow valley
-Very steep, high valley sides
-Located immediately downstream of a waterfall
-River channel takes up most, if not all of the valley floor
-Turbulent, fast-flowing white water
-Many areas of bare rock on valley sides
-Boulders litter the river bed

48
Q

How does a waterfall create a gorge?

A

By the end of stage 3 in the formation of a waterfall (once it is well established), the scene is set for a gorge to be formed. As the waterfall retreats upstream it leaves a steep-sided valley downstream which is called a gorge. Every time the overhanging cap rock breaks off, the gorge retreats and grows longer.

49
Q

How is a meander formed?

A

In the early stages of meander formation, water flows slowly over shallow areas (riffles) and faster over deep areas (pools). This eventually sets in motion a helicoidal flow that corkscrews across form one bank to another. This starts the rosion and deposition processes which continuosly shape a meander.

50
Q

In the first stage of a meander, what does fast-flowing water do?

A

It causes lateral erosion on the outside bank through abrasion and hydraulic action, which undercuts the bank and forms a river cliff.

51
Q

What is helicoidal flow and what does it do to meanders?

A

A corkscrew movement of water in a meander. The top part of the flow hits the outside bank and erodes it. The flow then ‘corkscrews’ down to the next inside bend, where it deposits its load as friction slows the flow.

52
Q

What deepens the river bed in a meander?

What would its cross profile look like after?

A

Fast flow causes vertical erosion on the outside bend, this deepend the river-bed, forming an asymmetrical cross profile.

53
Q

How does a slip-off slope in a meander form?

A

Sand and pebbles are deposited on the inside bank where the current is slower, forming a gentle slip-off slope.

54
Q

What is a sinuous river?

A

One with many meanders.

55
Q

What are the characteristics of an oxbow lake?

A

An oxbow lake is a small, horse-show shaped lake that is located several metres from a fairly straight stretch of river in its middle and lower courses.

56
Q

What are levées?

A

Naturally raised river banks found on either or both sides of a river channel that is prone to flooding. The lower course of River Severn has many levées.

57
Q

What are 5 characteristics of levées?

A

-Raised river banks (about 2-8 metres high in the UK)
-Composed of gravel, stones and alluvium
-Grading of sediments with the coarsest closest to the river channel.
-Steep-sided, but steeper on the channel side than on the land side.
-Fairly flat top, naturally covered by grass often used as a foot path (eg the Severn Way)

58
Q

Explain simply how levées are formed:

A

When a river bursts its banks, heaviest sediment is deopsited closest to the river and the size of sediment becomes increasingly smaller with distance from the channel. With each successive flood, banks are built up higher

59
Q

Why don’t levées reduce the chance of flooding?

A

Overtime the river bed develops a thicker layer of sediment (bedload deposits), which raises the river in its channel.

60
Q

What is a flood plain?

A

A large area of flat land either side a river that is prone to flooding.

61
Q

What decides the width of a flood plain?

A

The width of a flood plain is due to meander migration, where the outside bends erode laterally into the edges of the valley. Their position is also gradually moving downstream. Eventually, this cuts a wide valley.

62
Q

What happens to flood plains when floods have receded?

A

They are slightly higher and more fertile due to the deposits of silt and alluvium caused by river flooding.

63
Q

What do alluvial deposits infill in flood plains?

A

Meander scars.

64
Q

What is an estuary?

A

The tidal part of a river where the channel broadens out as it reaches the sea, where fresh water from the river merges with salt water from the sea.

65
Q

What are 4 characteristics of an estuary?

A

-High tidal range
-May be very wide
-Mudflats
-Tidal bores, which are huge waves which funnel up the river.

66
Q

How did the Ice Age help develop estuaries?

A

After the Ice Age, melting ice caused a rise in sea level. This caused low-lying valley sides of the river to become flooded.

67
Q

What does the original channel of the river in the newer estuary provide?

A

A deep channel for shipping.

68
Q

How are mudflats formed?

A

In estuaries, mudflats form where tidal water flows slowly. Where fresh river water meets salty sea water, velocity is reduced which causes deposition. This builds up layers of mud called mudflats.

69
Q

What do mudflats consist of?

A

Sand and marine salt from the sea with alluvium from the river.

70
Q

When are mudflats visible?

A

At low tide they’re exposed, and covered at high tide.

71
Q

What are there within mudflats?

A

Many small streams called creeks.

72
Q

What are riffles in meanders?

A

Shallow areas associated with the straighter sections of rivers causing the beginning of meanders. They usually have rocky beds and turbulent flow due to friction with the river bed. Sediment is deposited here whicih begins to the helicoidal flow of water.

73
Q

What are pools in meanders?

A

Deeper areas associated with meander bends. They usually have finer sediment and less turbulent flow due to the smoother river bed.

Geography (59 decks)

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