Eduqas GCSE Geology · 1.5

Deformational Structures

50 revision questions with answers for 1.5 Deformational Structures in Eduqas GCSE Geology (spec C480QS). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, Five Degrees, Associations, or read every question and answer below. Not official Eduqas material.

All 50 questions and answers

Question 1
What is tectonic stress?
Answer:
A force per unit area acting on rock that may cause it to deform.
Question 2
What does compressional stress do to rocks?
Answer:
It squeezes them, commonly shortening and folding them or producing reverse faults.
Question 3
What does tensional stress do to rocks?
Answer:
It pulls them apart, commonly extending the crust and producing normal faults.
Question 4
What does shear stress do?
Answer:
It pushes adjacent parts in opposite directions, commonly producing sideways displacement.
Question 5
Why can rocks fold rather than fracture?
Answer:
Under suitable pressure, temperature and timescale, rocks can deform ductilely.
Question 6
What is strike?
Answer:
The compass direction of a horizontal line on an inclined planar surface.
Question 7
What is dip?
Answer:
The maximum angle at which a planar surface slopes from the horizontal, and the direction of that slope.
Question 8
How are strike and dip direction related?
Answer:
Dip direction is at right angles to the strike direction.
Question 9
A bed strikes north-south and dips east. What is the dip direction in degrees?
Answer:
090 degrees, measured clockwise from north.
Question 10
What instrument is used to measure dip in the field?
Answer:
A compass-clinometer.
Question 11
What does a dip of zero degrees mean?
Answer:
The measured plane is horizontal.
Question 12
Can a vertical bed have a dip angle of 90 degrees?
Answer:
Yes. A vertical plane dips at 90 degrees.
Question 13
Why may a field dip measurement be unreliable?
Answer:
The exposed surface may be uneven, weathered, too small or not the true bedding plane.
Question 14
How can you improve a dip measurement on an uneven surface?
Answer:
Find a representative bedding surface, use a flat board if appropriate, and repeat readings at several points.
Question 15
Why should a geological map show both dip direction and angle?
Answer:
The two together describe how steeply and in which direction the bed slopes.
Question 16
What is a fold?
Answer:
A bend in originally more nearly planar rock layers caused by deformation.
Question 17
What is an antiform?
Answer:
A fold that is convex upwards, with limbs dipping away from the hinge in a simple upright fold.
Question 18
What is a synform?
Answer:
A fold that is concave upwards, with limbs dipping towards the hinge in a simple upright fold.
Question 19
What is the limb of a fold?
Answer:
One side of the fold between adjacent hinges.
Question 20
What is an axial plane?
Answer:
An imaginary plane joining the hinge lines of successive folded layers.
Question 21
What is an axial plane trace on a map?
Answer:
The line where the axial plane intersects the mapped surface.
Question 22
A fold has unequal limb dips. How should it be described?
Answer:
It is asymmetrical; state the dip on each limb if measurements are given.
Question 23
Why should a field sketch preserve the number of visible beds?
Answer:
Bed number and geometry are evidence for interpreting the fold and its history.
Question 24
What should be included in a useful fold sketch?
Answer:
Accurate curved bed outlines, limb dips, a scale and labels for the relevant structures.
Question 25
Can a synform or antiform name alone tell you the age order of beds?
Answer:
No. These names describe shape; age order needs separate evidence.
Question 26
What is a fault?
Answer:
A fracture in rock along which displacement has occurred.
Question 27
What is fault displacement?
Answer:
The amount and direction of movement of markers or rock across a fault.
Question 28
What is a normal fault?
Answer:
A fault in which the hanging wall moves down relative to the footwall, commonly under tension.
Question 29
What is a reverse fault?
Answer:
A fault in which the hanging wall moves up relative to the footwall, commonly under compression.
Question 30
What is a thrust fault?
Answer:
A low-angle reverse fault in which the hanging wall has moved up relative to the footwall.
Question 31
What is a strike-slip fault?
Answer:
A fault where displacement is mainly horizontal, parallel to the fault's strike.
Question 32
Which stress commonly produces a normal fault?
Answer:
Tensional stress.
Question 33
Which stress commonly produces a reverse fault?
Answer:
Compressional stress.
Question 34
Which stress commonly produces a strike-slip fault?
Answer:
Shear stress.
Question 35
How can matching beds help identify a fault?
Answer:
A bed or contact offset across a fracture provides a marker showing displacement.
Question 36
A marker bed is offset horizontally across a fault on a map. What type is suggested?
Answer:
Strike-slip, provided the evidence shows predominantly horizontal movement.
Question 37
How do you identify the hanging wall on an inclined fault?
Answer:
It is the block above the fault plane; the footwall lies below it.
Question 38
Why is identifying the downthrown block alone not always enough to name a fault?
Answer:
The orientation of the fault plane and relative movement of hanging wall and footwall are also needed.
Question 39
A mapped contact is offset 3 cm on a 1:10,000 map. What is the real offset?
Answer:
3 cm x 10,000 = 30,000 cm = 300 m.
Question 40
What is an unconformity?
Answer:
A surface representing a gap in the geological record caused by erosion and/or non-deposition.
Question 41
What is an angular unconformity?
Answer:
A surface where younger beds overlie eroded older beds with a different orientation.
Question 42
Order events for an angular unconformity.
Answer:
Older beds deposit, deform and uplift; erosion truncates them; younger sediment is deposited above.
Question 43
What visual evidence supports an angular unconformity?
Answer:
Older inclined or folded beds are truncated beneath younger beds at a different angle.
Question 44
Why does an unconformity represent missing time?
Answer:
Some rock was eroded or no sediment accumulated during part of the sequence.
Question 45
Are younger beds below or above an undisturbed unconformity?
Answer:
Above it; the older rocks lie beneath the erosional surface.
Question 46
Why should you record a grid reference for an exposure?
Answer:
It lets the observation be accurately located on a map and revisited.
Question 47
Give two hazards to consider at a cliff exposure.
Answer:
Falling rock and rising tides; also assess ground stability and safe access.
Question 48
What should a field sketch of a fault include?
Answer:
The fault trace, matching offset beds, relative displacement, a scale and clear labels.
Question 49
Why record several structural readings rather than just one?
Answer:
Repeated readings show variation, help identify errors and strengthen the interpretation.
Question 50
How can cross-sections assist geological interpretation?
Answer:
They show an inferred vertical slice through beds and structures, linking map observations in three dimensions.

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Deformational Structures

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