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Physical Geog = Coasts and Rivers > Rivers - KQ1 (river processes and fluvial landforms) > Flashcards

Rivers - KQ1 (river processes and fluvial landforms) Flashcards

1
Q

What is a catchment area/drainage basin?

A

A land area drained by a river, providing the water source for the main river and tributaries

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2
Q

What are sub-aerial processes?

A

A combination of weathering and mass movement processes operating on river slopes

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3
Q

What processes occur on river valley slopes?

A
  • Mass movements
  • Flows of water
  • Erosion
  • Weathering
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4
Q

What are the mass movements occurring on river valley slopes?

A
  • Soil creep
  • Slides
  • Falls
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5
Q

What is soil creep?

A

Type of mass movement

  • Individual soil particles are pushed to the surface by wetting, heating or freezing of water.
  • Move at right angles to the surface as there is least resistance there
  • Fall under the influence of gravity after particles dry, cool or the water has thawed
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6
Q

What are slides?

A

Type of mass movement

- Sliding material maintains its shape until it impacts at the bottom of a slope and leads to large, slumped terraces

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7
Q

What are falls?

A

Type of mass movement

  • Occur on steep slopes, often due to weathering (freeze thaw = erosion prising open cracks)
  • Once rocks are detached they fall under influence of gravity
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8
Q

What are the flows of water on river valley slopes?

A
  • Surface wash
  • Sheet wash
  • Through flow
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9
Q

What is surface wash?

A

Type of flow of water

  • Occurs when soil’s infiltration capacity is exceeded and gullies may form
  • Could occur when water drains across saturated or frozen ground, following previous heavy rainfall
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10
Q

What is sheet wash?

A

Type of flow of water

  • Unchannelled flow of water over a soil surface
  • Material dislodged by rain-slash can be transported
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11
Q

What is through flow?

A

Type of flow on water

  • Water moving down through the soil
  • Channelled into natural pipes in the soil, giving it enough energy to transport material (= amounts to a considerable volume)
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12
Q

What are the types of weathering occurring on a river valley slope?

A
  • Freeze thaw
  • Carbonation
  • Oxidation
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13
Q

What is freeze thaw?

A

Type of weathering

  • Occurs when water in joints and cracks freeze at 0*C and expands by 10% and then exerts pressure
  • Makes rocks crack and break away
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14
Q

What is carbonation?

A

Type of weathering

  • Occurs on rocks with calcium carbonate (eg chalk and limestone)
  • Rainfall and dissolved carbon dioxide forms a weak carbonic acid
  • Calcium carbonate reacts with the acid water and forms calcium bicarbonate which is soluble and removed by percolating water
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15
Q

What is oxidation?

A

Type of weathering

- Occurs when iron compounds react with oxygen to produce a reddish brown coating

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16
Q

What are the factors affecting slope processes?

A
  • Sea level change
  • Weathering rate
  • Rock type (hard and soft rock)
  • Climate (temperate environments have rounder slopes due to chemical weathering)
  • Rock structure
  • Aspect (north-facing slopes remain in the shade and temperatures rarely rise above freezing, however south-facing slopes experience freeze-thaw)
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17
Q

What are factors affecting the rate of mass movement?

A
  • Slope angle
  • Amount of regolith (loose material created by weathering)
  • Amount of water present
  • Amount of vegetation
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18
Q

What are the processes of fluvial erosion?

A
  • Abrasion
  • Attrition
  • Hydraulic action
  • Corrosion/solution
  • Cavitation
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19
Q

What is abrasion?

A

Sediment scours the channel, undermining the banks and valley slopes

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20
Q

What is attrition?

A

Sediment collides with other sediment and erodes

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21
Q

What is corrosion/attrition?

A

Chemical action of stream water, which dissolves carbonate rocks such as chalk and limestone

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22
Q

What is hydraulic action?

A

Occurs when tiny bubbles of air implode in fissures and cracks in channel banks
- Tiny shock waves that result weaken the banks and eventually lead to collapsing

23
Q

What is fluvial erosion?

A

Erosion = a particle becomes part of the streams load when it is in motion (entrained)

  • Sediment eroded by the stream is acquired in vertical, lateral and headward erosion
  • Erosion decreases downstream as the gradient is shallower downstream
24
Q

What is vertical erosion?

A

When the channel is deepened

25
Q

What is lateral erosion?

A

When the channel is widened

26
Q

What is headward erosion?

A

When the channel length increases

27
Q

What factors affect the rate of fluvial erosion?

A
  • Rock type = strength of bonded particles and presence of joints and bedding planes. Weak rocks such as sand and gravel are more easily eroded than consolidated rocks
  • Rock structure = orientation of beds, faults and weaknesses
  • River velocity = Greater the discharge, the greater the potential for erosion
  • Rainfall regime = seasonal rains on the Nile
  • Sea level change = downcutting results when seal level falls or land undergoes uplift
  • Bed roughness = Rougher bed = more friction = more energy lost from river flow = less energy for erosion
  • Channel shape = a more semi-circular river bed = less friction so more energy for erosion
  • pH = rates of solution increase when water is more acidic = more carbonation can take place
28
Q

How are fluvial deposits transported?

A
  • Stream carries sediment as its sediment load
  • Suspension
  • Solution
  • Traction
  • Saltation
29
Q

What is the name of the size of the particles of a load?

A

Callibre of the load

30
Q

What is suspension?

A

The smallest particles (silts and clays) are carried in suspension as the suspended load

31
Q

What is solution?

A

In areas of calcareous rock, material is carried in solution as the dissolved load

32
Q

What is traction?

A

Pebbles are rolled along the bed

33
Q

What is saltation?

A

Larger particles (sand, gravels, very small stones) are bounced along the bed

34
Q

What is the order of transportation from smallest to biggest?

A
  • Solution
  • Suspension
  • Saltation
  • Traction
35
Q

Why might sediment load on different rivers vary?

A
  • Rainfall total (climate)
  • Erodible sediments (eg loess, glacial deposits and volcanic ash)
  • Lack of vegetation
  • Deforestation
  • Uplift (leading to downcutting and more erosion)
  • Intense human activity, removing vegetation and exposing group surfaces
36
Q

What causes fluvial deposition?

A
  • Shallowing of gradient decreases velocity and energy
  • Decrease in volume of water
  • Increase in friction between water and channel
  • Human obstructions such as dams
37
Q

What factors affect the amount of deposition?

A
  • Velocity
  • Availability of sediment
  • Human intervention (eg dams and weirs)
38
Q

What are the landforms of fluvial erosion?

A
  • V-shaped valley
  • Waterfalls and rapids
  • Meanders (outward bends)
39
Q

What are the landforms of fluvial deposition?

A
  • Meanders (inside bend)
  • Oxbow lake
  • Floodplains
  • Distributaries
  • Levees and flood banks
40
Q

How are v-shaped valleys formed?

A

Fluvial erosion

  • Weathering and mass movements occur on the valley sides, while the river erodes the base of the slopes
  • V-shape depends on rate of downward erosion by the river, rock resistance, climate, location along river’s course (rivers in upper course tends to have steeper v-shaped valleys than those in lower course)
41
Q

How are waterfalls and rapids formed?

A

Fluvial erosion
- Occur on the margins of horizontally bedded rocks
- Softer rock underneath harder rock is eroded quicker = overhanging
- Eventually harder rock collapses into plunge pool = worn away by waterfall
Main process = erosion
- Hydraulic action and abrasion = plunge pool
- Kinetic energy due to change in gradient = encourages formation of plunge pool and overhanging = provides rocks to become tools for abrasion within plunge pool
- Repeated undercutting and collapsing = waterfall retreats and gorge is formed

42
Q

Give examples of waterfalls

A
  • EXAMPLE = Severn Breaks its Neck, Wales, Plynlimon Hills
  • EXAMPLE = High Force Waterfall, River Tees, near Middleton-in-Teesdale, Tees Valley, England:
    1 - at High Force river runs over whinstone (hard igneous rock) which is above carboniferous limestone (weak rock) = eroded quicker
    2 - creates overhanging of whinstone
    3 - eventually collapses into plunge pool, which is worn away by waterfall (hydraulic action, abrasion and solution)
    4 - overtime waterfall retreats as the overhanging collapses and develops again = currently formed 700m gorge in valley and waterfall is 20m high
43
Q

How are meanders formed? (outside bend)

A

Fluvial erosion
- In lower land, river goes side to side on valley floor
- Water approaches slight bend = continues to flow straight ahead on outside of rivers bend
- Flow is strong and fast and has high amount of energy = erodes bend faster
- Outer riverbank becomes undercut = collapses and retreats = small river cliff is formed
- Line of fastest flow = thawleg
Main processes = lateral erosion, transportation, deposition and evaporation

44
Q

How are meanders formed? (inside bend)

A

Fluvial deposition

  • Inside bend = current is slowest with least energy = deposition = creates gently sloping slip-off slope
  • Below slip-off slope = point bar (deposited material (sand and gravel) that accumulates inside bend)
45
Q

How are oxbow lakes formed?

A

Fluvial deposition
- Meander neck gets narrower as inside bend is eroded more and more = eventually river cuts through neck and shortens course
- Deposition occurring in old neck of old meander makes it blocked off and forms oxbow lake = dries up due to evaporation
EXAMPLE = Welshpool

46
Q

How are floodplains formed?

A

Fluvial deposition
- Valley floor between SHREWSBURY and IRONBRIDGE is often flooded by River Severn after heavy rainfall further upstream
- Fine silt and mud is deposited onto valley floor = part of valley floor is covered by river when it floods called flood plain
Main process = deposition

47
Q

How are distributaries formed?

A

Fluvial deposition

  • Form when river’s flow is blocked by deposition (branch of river that does not return to main body after leaving it)
  • Silt is deposited by each of distributaries and they spread out over wide area
  • More and more silt is deposited into sea until sufficient thickness accumulates to form new land
48
Q

How are levees and flood banks formed?

A

Fluvial deposition

  • Deposited material on rivers bed and banks builds up over time
  • Deposits of alluvium on either side of river are levees/flood banks
49
Q

What are the main factors affecting the development of fluvial landforms?

A
  • Availability of load for transport
  • Energy of river
  • Channel roughness
  • Channel shape
  • Velocity
  • Rock type
  • Rock structure
  • Beach size
  • Sea level change
  • Human intervention (eg. Aswan Dam)
50
Q

What are the types of sea level change?

A

Eustatic and isostatic

51
Q

What is eustatic sea level change?

A
  • A worldwide rise or fall in sea level due to an increase or decrease in the volume of water in the oceans
  • Caused by climate change (glacial and interglacial periods)
52
Q

What is isostatic sea level change?

A
  • Local sea level change due to rise and fall of the land due to loading and unloading
  • Caused by tectonic uplift or ice removal leading to isostatic rebound
53
Q

What are the landforms produced by sea level rise?

A

SUBMERGENCE
- Rias
EXAMPLE = Bristol Channel and Lower Severn Estuary

54
Q

What are landforms produced by sea level fall?

A

EMERGENCE
- River terraces
- Floodplains
_ Incised Meanders

Physical Geog = Coasts and Rivers (8 decks)

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