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GEO1020 > Fluvial Forms > Flashcards

Fluvial Forms Flashcards

1
Q

List 5 fluvial bedforms

A 
Ripples
Dunes
Plane bed
Antidunes
Obstacle marks
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2
Q

What are fluvial bedforms similar to?

A

Aeolian bedforms

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3
Q

What is the medium for fluvial bedforms?

A

Water

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4
Q

What is the medium for aeolian bedforms?

A

Air

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5
Q

What does larger material require to be moved?

A

Higher stream power

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6
Q

What does the presence of fluvial bedforms depend on?

A

Grain size

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7
Q

What are horizontal bedplanes indicative of?

A

Lower stage plane beds

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8
Q

In which direction do ripples migrate overtime?

A

Down flow

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9
Q

Which side do ripples erode?

A

Upstream side

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10
Q

Which side do ripples deposit?

A

Downstream side

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11
Q

Give a place where ripples can be seen?

A

The beach

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12
Q

What is meant by transient?

A

Adjust quickly to change

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13
Q

Are ripples transient?

A

Yes

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14
Q

What energy conditions are required for ripples to form?

A

Lower energy conditions

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15
Q

What transportation process allows ripples to form?

A

Suspension

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16
Q

What do ripples have a high rate of?

A

Aggradation

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17
Q

Are dunes visible?

A

Yes, they poke out of the water to a greater extent

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18
Q

What do dunes cause?

A

Surface waves that are out of phase with the water bed.

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19
Q

Is the amplitude of dunes higher or lower than that of ripples?

A

Higher

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20
Q

What can the amplitude of dunes reach?

A

10s of cm to 10s of m

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21
Q

What shows migration in dunes?

A

Cross stratification

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22
Q

In which direction do dunes migrate?

A

Downflow

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23
Q

How do dunes migrate?

A

By accretion of the lee side

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24
Q

Why are dunes in dynamic equilibrium?

A

The stoss side is eroding and the lee side is depositing

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25
Q

What are two important features of the upper stage plane bed?

A

Coarser material than lower stage

Some rocks

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26
Q

In what plane bed would you find ripples?

A

Lower stage plane bed

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27
Q

In what plane bed would you find dunes?

A

Lower stage plane bed

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28
Q

What are antidunes?

A

The opposite of dunes

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29
Q

What type of feature are antidunes?

A

Erosional

30
Q

In which direction do antidunes migrate?

A

Upflow

31
Q

What waves are antidunes associated with?

A

Breaking waves

32
Q

What is the water flow like around antidunes?

A

Shallow but fast

33
Q

In which way do antidune beds dip?

A

Upflow

34
Q

Why is the stoss side of antidunes preserved?

A

Due to the dip

35
Q

Which side of the antidune is eroded?

A

Lee side

36
Q

Which side of the antidune moves upward?

A

Crest side

37
Q

How long are antidunes preserved for?

A

They are very rarely preserved

38
Q

What are two features of cluster bedforms?

A

Rocks dip into the flow

Coarser material

39
Q

List 4 obstacle marks

A

Ice blocks
Secondary bedforms
Vegetation
Anthropogenic sources

40
Q

What flow can ice blocks create?

A

Horse shoe flow

41
Q

What can ice blocks cause?

A

Scouring due to horse show flow

42
Q

What changes overtime in rivers?

A

Discharge

43
Q

What two things do bars require?

A

Cohesionless sediment

Bedload

44
Q

Why are bars difficult to define?

A

They depend upon flow depth and discharge

45
Q

What are bars?

A

Attachments to channel margins

46
Q

Where can bars be found?

A

Mid channel

47
Q

What are bar types often associated with?

A

Channel morphological type

48
Q

What transportation process causes bars?

A

Suspended load

49
Q

Are bars formed in low or high energy environments?

A

Low energy

50
Q

What bars can braided rivers have?

A

1st, 2nd and 3rd order bars

51
Q

In what environments do braided rivers occur?

A

In a number of enviroments

52
Q

Where are braided rivers usually found?

A

Where there is a lot of sediment

53
Q

Give two examples of wondering gravel bed rivers

A

River Coquet, Northumberland

Fraser River, British Columbia

54
Q

What can be done to find the age of island bars?

A

Tree coring

55
Q

What can affect the location of erosion/ deposition?

A

Positioning of flow cells

56
Q

What happens as the river channel widens? (3)

A

Flow reduces
Sediment transport reduces
Change in the type of material transported

57
Q

What are the main features of Anastomosing rivers?

A

Parallel channels

Aligned by natural levees with flood basins inbetween

58
Q

Define Anastomsing river

A

“A type of river channel with multiple interconnected, coexisting channel belts on alluvial flood plains, which most often form under low energy conditions near a local base level” Makaske 2001

59
Q

When do braided rivers occur?

A

When erodibility of bank particles is more than their transportability

60
Q

When do meandering rivers occur?

A

When erodibility and transportability of bank particles are equal

61
Q

When do straight rivers occur?

A

When transportability of bank particles is higher than erodibility

62
Q

What is the spacing like for pools and riffles?

A

It is regular

63
Q

What property changes in pools and riffles can occur and why?

A

Major changes in hydraulic properties depending upon flow stage

64
Q

What hypothesis is associated with pools and riffles?

A

Velocity reversal hypothesis

65
Q

What is the velocity reversal hypothesis?

A

Velocities in pools increase at a higher rate than in riffles

66
Q

Can rivers be damned by their own levees?

A

Yes

67
Q

When do river terraces form?

A

After glaciers melt

68
Q

Why do river terraces form after glaciers melt?

A

There is less discharge

69
Q

What do river terraces reflect a change in?

A

River channel change in water and sediment flux

70
Q

Briefly explain the magnitude and frequency concept

A

Argument over whether frequency of floods is more important than intensity. Medium magnitude floods occurring over intermediate timescales achieve most work in terms of sediment transport.

71
Q

What is avulsion?

A

Rapid channel change

72
Q

What is river terrace formation an example of?

A

Complex response

GEO1020 (16 decks)

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