Eduqas A-level Geology · T2

Geological map applications

Exam-style questions with answers for T2 Geological map applications in Eduqas A-level Geology (spec A480QS). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below.

All questions and answers

Question 1 · Spec T2, Key Idea 1 · Map keys
State three things to check in a map key before interpreting outcrop patterns. [3 marks]
Answer:
Any three from: ages of units (1); lithologies (1); symbols for structures (1); scale (1); whether superficial deposits are shown (1).
Question 2 · Spec T2, Key Idea 1 · Superficial deposits
Explain why superficial deposits make bedrock geology harder to interpret. [2 marks]
Answer:
They cover the bedrock (1); so the bedrock contacts beneath them must be inferred (1).
Question 3 · Spec T2, Key Idea 1 · Map scale
On a 1:25 000 map, two contacts are 4 cm apart. Calculate the ground distance. [2 marks]
Answer:
4 × 25 000 = 100 000 cm (1); = 1 km (1).
Question 4 · Spec T2, Key Idea 1 · Grid references
A point has an easting of 12 400 m and a northing of 34 600 m. Write its six-figure grid reference. [1 mark]
Answer:
124346.
Question 5 · Spec T2, Key Idea 1 · Outcrop patterns
Describe how the outcrop of horizontal beds relates to topographic contours. [1 mark]
Answer:
The contacts follow (are parallel to) the topographic contours.
Question 6 · Spec T2, Key Idea 1 · Outcrop patterns
A contact crosses hills and valleys as a straight line. State the dip of the contact. [1 mark]
Answer:
Vertical (or very steep).
Question 7 · Spec T2, Key Idea 1 · Outcrop patterns
Explain why dipping beds form V-shapes where they cross valleys. [2 marks]
Answer:
The contact meets the valley sides at different heights (1); so its outcrop bends to form a V that depends on dip and valley slope (1).
Question 8 · Spec T2, Key Idea 1 · V-rule
Explain why the V-rule does not always show dip direction. [2 marks]
Answer:
The shape depends on both the dip and the gradient of the valley (1); beds dipping downstream at a lower angle than the valley floor give a V pointing upstream (1).
Question 9 · Spec T2, Key Idea 1 · Structure contours
Define a structure contour. [1 mark]
Answer:
A line joining points of equal height on a geological surface.
Question 10 · Spec T2, Key Idea 1 · Structure contours
Explain how structure contours show dip direction. [2 marks]
Answer:
The bed dips from higher to lower structure contours (1); at right angles to the trend of the contours (strike) (1).
Question 11 · Spec T2, Key Idea 1 · Structure contours
Structure contours 50 m apart in height are 100 m apart horizontally. Calculate the dip. [2 marks]
Answer:
tan(dip) = 50 ÷ 100 = 0.5 (1); dip = 26.6° (1).
Question 12 · Spec T2, Key Idea 1 · Three-point problem
Explain how three points on a bed can be used to find its strike and dip. [2 marks]
Answer:
Interpolate between the points to find points of equal height and join them as structure contours (strike lines) (1); dip is found from the spacing and height difference of the contours (1).
Question 13 · Spec T2, Key Idea 1 · Cross-sections
Describe the first steps in drawing a geological cross-section. [2 marks]
Answer:
Draw a topographic profile along the section line to scale (1); transfer the positions of contacts, faults and dip measurements onto it (1).
Question 14 · Spec T2, Key Idea 1 · Cross-sections
A section has a horizontal scale of 1:10 000 and a vertical scale of 1:2000. Calculate the vertical exaggeration and state its effect. [2 marks]
Answer:
10 000 ÷ 2000 = ×5 (1); dips appear steeper than they really are (1).
Question 15 · Spec T2, Key Idea 1 · Apparent dip
Explain why apparent dip is used when a section line is oblique to strike. [1 mark]
Answer:
Only sections perpendicular to strike show true dip; oblique sections show a smaller apparent dip.
Question 16 · Spec T2, Key Idea 1 · True thickness
A bed dips 30° under flat ground. Its outcrop width perpendicular to strike is 200 m. Calculate its true thickness. [2 marks]
Answer:
True thickness = 200 × sin 30° (1); = 100 m (1).
Question 17 · Spec T2, Key Idea 1 · Boreholes
A contact is 80 m below a borehole top at 350 m above sea level. Calculate the height of the contact. [1 mark]
Answer:
350 − 80 = 270 m above sea level.
Question 18 · Spec T2, Key Idea 1 · Boreholes
Explain why borehole rocks should not be correlated by colour alone. [2 marks]
Answer:
Similar colours occur in different units (1); so lithology, fossils and stratigraphic position are needed (1).
Question 19 · Spec T2, Key Idea 1 · Folds
Beds get younger towards the centre of an upright fold. Name the fold. [1 mark]
Answer:
A syncline.
Question 20 · Spec T2, Key Idea 1 · Folds
A fold has the oldest beds in its centre. Name the fold. [1 mark]
Answer:
An anticline.
Question 21 · Spec T2, Key Idea 1 · Plunging folds
State the information needed to interpret a fold whose outcrops close at one end. [2 marks]
Answer:
The dip directions and ages of the beds, to show whether it is an anticline or syncline (1); and the direction of plunge of the fold axis (1).
Question 22 · Spec T2, Key Idea 1 · Faults
Explain why the displacement of a contact on a map may not show the full slip of a fault. [2 marks]
Answer:
The offset seen on the map depends on the dip of the beds and the topography (1); and may combine vertical and horizontal movement (1).
Question 23 · Spec T2, Key Idea 1 · Faults
The hanging wall of a fault has moved down relative to the footwall. Name the fault. [1 mark]
Answer:
A normal fault.
Question 24 · Spec T2, Key Idea 1 · Unconformities
Describe the map evidence for an angular unconformity. [2 marks]
Answer:
Younger beds overlie and cut across the outcrops of several older units (1); the older beds have a different dip and strike (1).
Question 25 · Spec T2, Key Idea 1 · Geological history
A dyke cuts folded beds but ends at an unconformity below flat younger beds. State the order of events. [3 marks]
Answer:
Deposition then folding of the older beds (1); intrusion of the dyke (1); uplift and erosion, then deposition of the younger beds (1).
Question 26 · Spec T2, Key Idea 1 · Intrusions
State three pieces of evidence that a body is an intrusion. [3 marks]
Answer:
Any three from: cross-cutting contacts (1); chilled margins (1); baked country rock (metamorphic aureole) (1); xenoliths of country rock (1).
Question 27 · Spec T2, Key Idea 1 · Metamorphic aureoles
Explain why rock properties may be different near an intrusion. [2 marks]
Answer:
Contact metamorphism changes minerals and texture in the aureole (1); altering strength and permeability (1).
Question 28 · Spec T2, Key Idea 1 · Sills and lava flows
A concordant igneous body has a vesicular top and unbaked rock above it. Identify it. [1 mark]
Answer:
A lava flow.
Question 29 · Spec T2, Key Idea 1 · Faults
Explain how faulting can repeat a sequence of beds in a cross-section. [2 marks]
Answer:
Movement on the fault moves part of the sequence (1); so the same beds appear twice across the section (1).
Question 30 · Spec T2, Key Idea 1 · Geological history
Explain why structures are projected above the land surface in a cross-section. [2 marks]
Answer:
To show where rocks were before erosion removed them (1); helping to work out the geological history (1).
Question 31 · Spec T2, Key Idea 2 · Springs
Explain why springs occur where sandstone overlies mudstone. [2 marks]
Answer:
Water moves down through the permeable sandstone until it reaches the impermeable mudstone (1); it flows sideways and emerges where the contact meets the surface (1).
Question 32 · Spec T2, Key Idea 2 · Artesian wells
State the information needed to predict whether a well into a confined aquifer will flow at the surface. [1 mark]
Answer:
Whether the potentiometric surface is above the ground level at the well.
Question 33 · Spec T2, Key Idea 2 · Pollution
Explain why a well down-gradient of a waste site in the same aquifer is at risk. [2 marks]
Answer:
Groundwater flows from the waste site towards the well (1); carrying leachate through the connected aquifer (1).
Question 34 · Spec T2, Key Idea 2 · Reserves
State four pieces of information needed to estimate the reserves of a coal seam. [4 marks]
Answer:
Any four from: area of the seam (1); true thickness (1); dip (1); depth (1); faults that displace it (1); density (1).
Question 35 · Spec T2, Key Idea 2 · Reserves
Explain why using map area × thickness underestimates the volume of a dipping seam. [2 marks]
Answer:
The map shows the horizontal projection of the seam (1); the actual area of a dipping seam is larger (1).
Question 36 · Spec T2, Key Idea 2 · Hydrocarbons
An anticline has porous sandstone under shale. State two things needed to confirm an oil field. [2 marks]
Answer:
Any two from: a mature source rock and migration route (1); an effective seal (1); good reservoir porosity and permeability (1); a well proving hydrocarbons are present (1).
Question 37 · Spec T2, Key Idea 2 · Hydrocarbons
Explain why a fault through a reservoir does not always cause leakage. [2 marks]
Answer:
If the fault places the reservoir against impermeable rock, or the fault zone contains clay gouge, it seals (1); open fractures would allow leakage (1).
Question 38 · Spec T2, Key Idea 2 · Geothermal energy
State three geological factors that make a good geothermal site. [3 marks]
Answer:
Any three from: high temperatures at shallow depth (1); permeable rock or fractures (1); a supply of water (1); a large enough reservoir (1).
Question 39 · Spec T2, Key Idea 2 · Route planning
Explain why a route through strong rock may still need slope engineering. [2 marks]
Answer:
Joints, faults and bedding can make blocks unstable (1); so failure can occur along discontinuities even in strong rock (1).
Question 40 · Spec T2, Key Idea 2 · Tunnels
Explain why mapping is combined with boreholes and geophysics for a tunnel route. [2 marks]
Answer:
Surface mapping cannot show conditions at tunnel depth (1); boreholes and geophysics show faults, weak rocks and groundwater along the route (1).
Question 41 · Spec T2, Key Idea 2 · Reservoirs
Explain why a reservoir on fractured limestone needs special investigation. [2 marks]
Answer:
Water may leak through fractures and solution cavities (1); and cavities may make the foundations unstable (1).
Question 42 · Spec T2, Key Idea 2 · Foundations
Explain why both superficial clay and bedrock must be investigated on a building site. [2 marks]
Answer:
The clay controls settlement near the surface (1); changes in bedrock affect deeper support for piles (1).
Question 43 · Spec T2, Key Idea 2 · Slope stability
Weak beds dip towards a cutting at a lower angle than the cutting face. Explain the hazard. [2 marks]
Answer:
The beds daylight in the face (1); so blocks could slide along the bedding planes (planar failure) (1).
Question 44 · Spec T2, Key Idea 2 · Mining hazards
Explain why old mine plans must be checked against site investigation data. [2 marks]
Answer:
Old plans may be incomplete or inaccurate (1); and voids may have collapsed or changed since (1).
Question 45 · Spec T2, Key Idea 2 · Waste disposal
Explain why an unfractured clay site is better than a fractured aquifer for waste disposal. [2 marks]
Answer:
Clay has low permeability (1); so leachate cannot easily escape to groundwater (1).
Question 46 · Spec T2, Key Idea 2 · Pollution
Contamination lies on permeable gravel over mudstone. Predict where pollution will spread. [2 marks]
Answer:
Sideways through the gravel (1); along the top of the impermeable mudstone, following the hydraulic gradient (1).
Question 47 · Spec T2, Key Idea 1 · Map conventions
Explain why inferred contacts are shown with different symbols to observed contacts. [1 mark]
Answer:
To show they are less certain, as they are interpreted rather than seen.
Question 48 · Spec T2, Key Idea 2 · Map scale
Explain why a small-scale map is not suitable for designing foundations. [2 marks]
Answer:
It generalises boundaries (1); and may not show small faults, weathered zones or superficial deposits (1).
Question 49 · Spec T2, Key Idea 2 · Site investigation
A new borehole contradicts a mapped interpretation. State what should happen next. [2 marks]
Answer:
Check the borehole data and correlation (1); then revise the interpretation to fit all the reliable evidence (1).
Question 50 · Spec T2, Key Idea 2 · Recommendations
State three things a map-based site recommendation should include. [3 marks]
Answer:
Any three from: the preferred interpretation (1); supporting map and borehole evidence (1); uncertainties (1); further investigation needed (1).

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