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Geography > Rivers 1 > Flashcards

Rivers 1 Flashcards

Fluvial processes and landforms

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1
Q

Drainage basin

A

Any area of land where precipitation collects and is drained by a common outlet (such as a river).

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2
Q

Watershed

A

This marks the invisible boundary of high ground that separates one drainage basin from another.

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3
Q

Confluence

A

The location where two rivers combine together to form one larger river in a single channel of water.

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4
Q

Meander

A

One of a series of regular sinuous curves, bends, loops, or windings in the channel of a river (exaggerated).

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5
Q

Mouth

A

This is where the river has stopped flowing on land and meets the sea.

If the river has a delta, it might have several mouths.

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6
Q

Source

A

The farthest place in a river or stream from its estuary or mouth.

Sometimes called the headwaters

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7
Q

Tributary

A

A smaller stream or river that flows into a larger stream, main stem river, or lake. It cannot flow into the sea.

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8
Q

Delta

A

A landform created by deposition of a sediment that is carried by a river as the flow leaves its mouth.

Not all rivers have these.

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9
Q

River channel

A

The channel or groove where the river flows.

It is often u-shaped with banks either side.

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10
Q

Drainage density

A

The total number of streams in a drainage basin.

The more streams in an area, the higher the drainage density is.

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11
Q

What are the two main fluvial processes?

A

Erosion
Transportation

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12
Q

What are the processes of erosion (river)

A

Hydraulic action
Abrasion
Attrition
Solution

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13
Q

Vertical erosion

A

Vertical erosion is most prevalent in a river’s upper course, and occurs downwards, making the river channel deeper.

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14
Q

Hydraulic action (rivers)

A

The force of water colliding with the river’s bed and banks breaks rock particles away from the river channel.

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15
Q

Abrasion (rivers)

A

Rocks carried by the river repeatedly hit, scrape, and rub against the river channel, wearing it away and dislodging more rock particles into the flow of the river.

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16
Q

Attrition (rivers)

A

Rocks carried by the river knock against each other and break into smaller fragments, becoming smoother and rounder.

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17
Q

Why does particle size decrease from a river’s source to its mouth?

A

The further material travels, the more it is eroded.

Attrition causes particle size to decrease.

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18
Q

Solution (rivers)

A

Rock such as chalk and limestone is slowly dissolved, as these rocks are soluble in the slightly acidic river water.

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19
Q

How are V-shaped valleys formed?

A

Where vertical erosion occurs, the river channel deepens, with unsupported sides.

When the sides collapse this leaves a V-shaped valley.

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20
Q

When are rivers in a highly erosive state?

A

When it has lots of energy. Then, the river can carry large amounts of sediment (brown water, silt).

It is often only after heavy rainfall that a river has enough energy to erode its bed and banks.

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21
Q

Transportation

A

The movement of eroded material.

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22
Q

What does the way in which material is transported depend on?

A

-Velocity of the water (how much energy)

-Size of the particles

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23
Q

What are the four processes of transportation?

A

Traction
Saltation
Suspension
Solution

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24
Q

Traction (rivers)

A

Large particles such as boulders are dragged or rolled along the river bed by the force of the water.

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25
Q

Saltation

A

Smaller (pebble-sized) particles are bounced along the river bed by the force of the water, as they are too heavy to be suspended.

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26
Q

Suspension

A

The finest particles like silt and clay are carried along suspended in the water

(this is increased in turbulent flow).

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27
Q

Solution

A

Soluble materials, (e.g. chalk, limestone), which have dissolved in the water, are carried along.

(this is not visible).

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28
Q

Deposition

A

When a river drops the eroded material it was carrying.

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29
Q

When does deposition occur?

A

When a river loses velocity and energy.

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30
Q

Why might a river slow down (and so deposit material)?

A

-the volume of water falls

-the amount of eroded material increases

-the water is shallower e.g. on the inside of a meander

-the river reaches its mouth

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31
Q

Why are smaller particles deposited at the river’s mouth?

A

Smaller particles are transported further as the river deposits the heaviest material first when it loses energy.

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32
Q

Differential erosion (rivers)

A

Used to describe when erosion is occurring at different rates, often caused by either geology or available energy.

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33
Q

A river will flow over a variety of what from source to mouth?

A

rock types

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34
Q

Formation of a waterfall (step 1)

A
  1. Waterfalls form when a river flows over an area of more resistant rock followed by an area of less resistant rock.
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35
Q

formation of a waterfall (step 3)

A
  1. Over time, water flowing over the step will erode more if the less resistant rock, creating a steep drop (a waterfall).
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36
Q

Example of a waterfall in the UK

A

High Force waterfall on the river Tees, County Durham.

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37
Q

Formation of a gorge (step 1)

A
  1. More resistant rock at the top of a waterfall is eventually undercut by erosion, becomes unsupported, and collapses.
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38
Q

Formation of a gorge (step 2)

A
  1. The collapsed rocks are swirled around at the foot of the waterfall by the turbulent water, eroding the less resistant rock by abrasion.

This creates a deep plunge pool.

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39
Q

Formation of a gorge (step 3)

A
  1. Over time, the undercutting of the less resistant rock causes more collapses of the harder rock ‘overhangs’.

This means that the waterfall retreats upstream.

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40
Q

Formation of a gorge (step 4)

A
  1. As this process happens continually, a steep-sided gorge is formed downstream of the waterfall.
41
Q

Gorge

A

A narrow, steep sided valley that is usually found downstream of a waterfall.

42
Q

Outline how a gorge is formed (2)

A

By the continual collapsing and retreating of a waterfall.

43
Q

Name 2 ways a gorge can be formed other than by a retreating waterfall.

A

-Releases of meltwater after the last glaciation (e.g. cheddar gorge)

-The collapse of cave systems in limestone areas.

44
Q

Interlocking spurs

A

The hillsides that interlock with each other as the river winds around them.

45
Q

Describe the formation of interlocking spurs. (step 1)

A
  1. In the upper course of a river, most of the erosion is vertical, which creates steep sided V-shaped valleys
46
Q

Erosional (only) landforms

A

-waterfalls
-gorges
-interlocking spurs

47
Q

Erosional and depositional landforms

A

-meanders
-oxbow lakes

48
Q

Meanders

A

Wide (exaggerated) bends in a river formed in mainly lowland areas. (they are constantly changing shape).

49
Q

Formation of meanders (step 1 )

A
  1. Where a river channel is deeper on the outside of a bend, the current is faster.

This means that there is less friction to slow the water down.

50
Q

Formation of meanders (step 2)

A
  1. Which means that more erosion occurs here, (by hydraulic action and abrasion) forming river cliffs.
51
Q

Formation of meanders (step 3)

A
  1. The current is slower on the inside of the bend because there is more friction to slow the water down.
52
Q

Formation of meanders (step 4)

A
  1. So, eroded material is deposited on the inside of the bend, forming a slip-off slope.
53
Q

Thalweg

A

The line of deepest water and fastest flow in a river channel. (not in spec but for understanding)

54
Q

Outside of bend =

A

erosion

55
Q

Inside of bend =

A

deposition

56
Q

ox-bow lake

A

feature of a meander

57
Q

Formation of ox-bow lakes (step 1)

A
  1. On each meander, processes of erosion (such as abrasion) are occurring on the outside of bends.

This is due to Thalweg, the line of fastest flow in a river (which has more energy meaning more erosion).

58
Q

Formation of ox-bow lakes (step 2)

A
  1. This erosion causes the outside bends of the meander to get closer, so its neck gets narrower.
59
Q

Formation of ox-bow lakes (step 3)

A
  1. Eventually, the river will break through this neck (usually during a flood, where the river has lots of energy for lots of erosion).

The river will then flow along the shortest course.

60
Q

Formation of ox-bow lakes (step 4)

A
  1. Deposition will eventually cut off the meander forming an ox-bow lake.
61
Q

To make an answer clear…

A

draw ANNOTATED diagrams

62
Q

What does ‘fluvial’ mean?

A

River

63
Q

Depositional landforms

A

-levées
-flood plains
-estuaries

64
Q

Alluvium

A

A very fertile soil that is deposited by a river during flood events. (a sediment)

65
Q

Levées

A

Natural embankments along the edges of a river channel.

-prone to flooding
-found in lower course

66
Q

Formation of levées (step 1)

A
  1. During a flood, eroded material (alluvium) is deposited over a whole floodplain.
67
Q

Formation of levées (step 2)

A
  1. The heaviest, largest material is deposited closest to the river channel, because it gets dropped first when the water slows down and loses energy.
68
Q

Formation of levées (step 3)

A

3 Smaller material is carried further in suspension.

Fine salt adds to the alluvium on the floodplain.

69
Q

Formation of levées (Step 4)

A

4.Over time, the deposited material builds up, creating levées along the edges of the channel (layers of successive deposits thickens the alluvium).

Levées add to the river’s capacity.

70
Q

Flood plain

A

A wide, flat area on marshy land, either side of a river.

Found in the middle and lower courses of a river

71
Q

How are flood plains built up?

A

-Fertile layers of alluvium is deposited when a river floods, building up the flood plain.

-Migrating meanders widen a floodplain as they move across it laterally, and downstream over time. (lateral erosion).

-The deposition that happens on the slip-off slopes of meanders also builds up the floodplain

72
Q

Estuaries

A

Tidal areas where a river meets the sea.

73
Q

Describe an estuary

A

-found at the mouth of a river

-land is close to sea level

-river valley is at its widest

-water here is tidal

74
Q

Mudflat formation (steps 1 and 2)

A
  1. When water floods over the banks of a river, it carries silt and sand onto the valley floor.
  2. As high tide is reached, the water has little energy so moves more and deposits this sediment. (the water at estuaries is tidal)
75
Q

Example of a mudflat.

A

The Severn Estuary, Gloustershire has a mudflat

76
Q

Lateral erosion

A

Lateral erosion is most prevalent in the middle to lower courses of a river and occurs side to side, widening the river channel.

77
Q

Formation of a waterfall (step 2)

A
  1. The less resistant rock is eroded by the processes of hydraulic action and abrasion more quickly than the more resistant rock, creating a ‘step’ in the river.
78
Q

Erosion at High Force waterfall, River Tees

A

Less resistant carboniferous limestone is being eroded away more quickly than than the resistant band of dolerite above.

79
Q

Describe the formation of interlocking spurs (step 2)

A
  1. The river lacks the power to erode laterally, so has to wind around the high hillsides that stick out into their paths on either side.
80
Q

Why does deposition occur to form oxbow lakes?

A

Current either no longer flows, or flows more slowly at the neck.

Because the river flows along the shortest course. (the straight path).

81
Q

Mudflat formation (steps 3 and 4)

A

3.Over time, more mud builds up, creating large mudflats.

4.At low tide, the wide, muddy banks are exposed.

82
Q

What is the name of the path of a river as it flows downhill?

A

Its course

83
Q

What does the long profile of a river show you?

A

How the gradient changes.

84
Q

Course of a river- overview:

A

Rivers have:

-A steep upper course (nearer the source)
-A gently sloping middle course
-An almost flat lower course (nearer the mouth)

85
Q

What do rivers form as they flow downhill?

A

-Channels
-Valleys

86
Q

What do rivers (basically) do?

A

-Erode the landscape

-Transport eroded material to somewhere further along the coast where is it deposited

-Upland area e.g. mountains to a lowland body of water e.g. the sea or a lake.

87
Q

What does the shape of the river valley and channel depend on? (these change shape).

A

Whether erosion or deposition is the dominant process.

88
Q

What does a river’s cross profile show you?

A

What a cross- section of a river looks like.

89
Q

Upper course of a river

A

-Steep gradient
-V-shaped valley with steep sides
–Narrow, shallow channel

90
Q

Middle course of a river

A

-Medium gradient
-Gently sloping valley sides
-Wider, deeper channel

91
Q

Lower course of a river

A

-Gentle gradient
-Very wide, almost flat valley
-Very wide, deep channel

92
Q

What changes the cross-profile of a river?

A

Vertical and lateral erosion.

93
Q

Where are most of the UK’s upland areas located?

A

The north and west

94
Q

Where are most of the UK’s lowland areas located?

A

The south and east

95
Q

What types of rock are highland areas made of in the UK?

A

-hard
-igneous (e.g. granite)
-metamorphic (e.g. slate)
-resistant to erosion

96
Q

Give examples of UK highland areas.

A

-The Scottish Highlands
-northern Wakes

97
Q

What types of rock are lowland areas made of in the UK?

A

-softer
-sedimentary (e.g. chalk and clays)
-erode more easily

98
Q

Where are most UK cities located?

A

In lowland areas and often on the UK’s main rivers.

For example, London (on the Thames), Liverpool (on the Mersey), and Cardiff (on the Severn Estuary).

Geography (18 decks)

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