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Eduqas GCSE Geology (9-1) > 1.5 Deformational Structures > Flashcards

1.5 Deformational Structures Flashcards

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1
Q

What law can be used to explain how rocks are deformed?

A

Hooke’s law - stress is proportional to strain

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2
Q

What is stress?

A

The force applied to a rock

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3
Q

What is strain?

A

The change in shape of a rock

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4
Q

What will the change that will take place in a rock under stress depend on?

A
  • the amount of stress applied to the rock
  • the type of stress applied to the rock
  • the time over which the stress is applied
  • the temperature at which the stress is applied
  • the type of rock stress is applied to
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5
Q

What are the 3 main types of stress?

A
  • tensional stress
  • compressional stress
  • shear stress
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6
Q

What is tensional stress?

A

Force when the rock is being pulled apart

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7
Q

What is compressional stress?

A

Force when the rock is being pressed together

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8
Q

What is shear stress?

A

Force when the rock is being sheared by opposing movements either side

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9
Q

Is elastic deformation common in rocks?

A

No

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10
Q

When might elastic deformation occur in rocks?

A

With a rebound effect in earthquakes

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11
Q

What is elastic deformation?

A

When an object changes shapes and then returns to its original shape

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12
Q

When does brittle deformation occur?

A

When rock is cold and cracks

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13
Q

What features can brittle deformation form?

A

Joints and faults

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14
Q

When does plastic deformation occur?

A

When the temperature of a rock is increased and can bend to form folds

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15
Q

What feature can plastic deformation form?

A

Folds

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16
Q

What are competent rocks?

A

Strong rocks

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17
Q

What are incompetent rocks?

A

Weak rocks

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18
Q

Examples of competent rocks?

A

Granite, sandstone, limestone

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19
Q

Examples of incompetent rocks?

A

Shale, mudstone

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20
Q

What are faults?

A

Fractures in the upper part of the crust, where movement has taken place

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21
Q

What type of deformation are faults a result of?

A

Brittle

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22
Q

What is the dip of a fault?

A

The angle of the fault plane measured from the horizontal

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23
Q

What is the throw or downthrow of a fault?

A

The amount of vertical movement along the fault plane

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24
Q

What is the hanging wall of a fault?

A

The block positioned over the fault

25
Q

What is the footwall of a fault?

A

The block positioned below the fault

26
Q

What is a normal fault?

A

When the hanging wall is downthrown

27
Q

What is a reverse fault?

A

When the hanging wall is upthrown

28
Q

What are the types of dip slip faults?

A

Normal and reverse

29
Q

What are the types of fault?

A

Dip slip and strike slip

30
Q

Where do folds form?

A

Where rocks are taken deeper into the crust and bent and buckled by compressive forces

31
Q

What type of deformation is involved when rocks are folded?

A

Plastic or ductile

32
Q

What is an antiform?

A

A fold in the rock that folds upwards (sad face)

33
Q

What is a synform?

A

A fold in the rock that folds downwards (happy face)

34
Q

What will happen to a fold’s axial plane when it is symmetrical?

A

The axial plane will be vertical

35
Q

What will happen to a fold’s axial plane when it is asymmetrical?

A

The axial plane will be tilted at a lower angle

36
Q

If a symmetrical fold has resulted in an antiform, where will the greatest compressive force be coming from?

A

The side with the gentlest limb

37
Q

If a symmetrical fold has resulted in a synform, where will the greatest compressive force be coming from?

A

The side with the steepest limb

38
Q

What happens when the forces creating a synform/antiform become greater?

A

It may lead to one limb being overturned - creating overfold

39
Q

How is an overfold formed?

A

When the force on an antiform/synform becomes greater and leads to one limb being overturned`

40
Q

How can the pattern of beds on the top surface a plan diagram tell you the type of fold?

A
  • narrow single band in middle → antiform

* thick single band in middle → synform

41
Q

What is a thrust fault?

A

When some folds are pushed over so much that their axial planes are almost horizontal, and may snap along the axial plane

42
Q

Why is geotechnical investigation carried out on all major construction sites?

A

To determine if the foundation material is strong enough for what is being constructed

43
Q

What should be considered when seeing if a rock is strong enough to be built on?

A
  • ground surface - signs of instability?
  • soil - high porosity?
  • weathered bedrock
  • jointing and faults
44
Q

What might foundation material be liable to?

A
  • compaction - clay affected particularly
  • swelling - expansion of clays and other materials when they absorb water
  • rotational slip or sliding - rocks prone to shearing may be affected
45
Q

Rocks susceptible to compaction, swelling and rotational slip?

A
  • mudstone, siltstone and shale - compaction
  • clay - rotational slip
  • sliding and rotational slip - glacial till/boulder clay
46
Q

Ways to make slopes more stable?

A
  • efficient drainage - increase stability
  • form loose materials into shallow slopes by planting vegetation
  • retaining walls - prevent rock slides
  • gabions - prevent rock slides
  • rock bolts to tie loose blocks into the firmer rock - prevent rock falls
47
Q

Ways to make tunnels more stable?

A
  • creating an arch or cylinder shape to tunnel - withstand pressure
  • reinforcement - prevent ground swelling from below and closing tunnel
  • support sides - e.g. rings, arches and shotcrete to prevent collapse
  • good drainage - reduce pressure of water on tunnel sides
48
Q

What is a good example of how an engineering project was carried out in difficult conditions?

A

The Channel Tunnel - crossrail in London - clay and chalk

49
Q

What are the types of dam?

A
  • embankment
  • arch
  • gravity
  • buttress
50
Q

Where are embankment dams used?

A

Where foundation is weak, but there are large volumes of material available

51
Q

How does an embankment dam resist water?

A

Sheer size of the dam resists pressure of water

52
Q

Where are arch dams constructed?

A

In narrow valleys with strong bedrock either side

53
Q

How is an arch dam kept in position against the valley walls?

A

Its curved shape

54
Q

What are gravity dams formed out of?

A

One giant concrete block

55
Q

Why is less concrete needed in a buttress dam than a gravity dam?

A

The concrete slabs are supported by the buttresses (arms projecting out of the dam) leaving a space in the centre

56
Q

What type of force are normal faults formed by?

A

Forces of tension

57
Q

What type of force are reverse faults formed by?

A

Forces of compression

58
Q

Why are normal faults more common than reverse faults?

A

Compression is more likely to cause folding than to produce (reverse) faulting

Eduqas GCSE Geology (9-1) (13 decks)

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