Welsh Joint Education Committee s5

MS3

WELSH JOINT EDUCATION COMMITTEE

/
£3.00 / CYD-BWYLLGOR ADDYSG CYMRU

General Certificate of Education Tystysgrif Addysg Gyffredinol

Advanced Subsidiary/Advanced Uwch Gyfrannol/Uwch

MARKING SCHEMES

SUMMER 2007

GEOLOGY

INTRODUCTION

The marking schemes which follow were those used by the WJEC for the 2007 examination in GCE Geology. They were finalised after detailed discussion at examiners' conferences by all the examiners involved in the assessment. The conferences were held shortly after the papers were taken so that reference could be made to the full range of candidates' responses, with photocopied scripts forming the basis of discussion. The aim of the conferences was to ensure that the marking schemes were interpreted and applied in the same way by all examiners.

It is hoped that this information will be of assistance to centres but it is recognised at the same time that, without the benefit of participation in the examiners' conferences, teachers may have different views on certain matters of detail or interpretation.

The WJEC regrets that it cannot enter into any discussion or correspondence about these marking schemes.

GL1

1. (a) (i)

Layer of ocean crust / Rock type / Name of igneous structures
Q / Basalt / Pillow lavas
R / Dolerite / Dykes
S / Gabbro

[4]

(ii) Plagioclase feldspar

Pyroxene or Augite 2 of these

Olivine [2]

(iii) More rapid cooling causes finer crystal size (or equivalent) (1)

More rapid cooling closer to the surface (or equivalent) (1) [2]

(b) (i) Contact with seawater (1)

Rapid cooling/quenched (1)

Forms a crust/skin (1)

Inflation/pushing through the pillow or equivalent (1) [2]

(any two)

(ii) Partial melting or equivalent (1)

Of mantle/asthenosphere (1)

Of ultramafic/peridotite (1)

Lower melting temperature components melt (1)

Credit other valid point (1) e.g. pressure release [3]

(any three)

(ii) Correct relative age of crust e.g. B older than C (1)

Correct reason for relative age of crust (1)

Thicker sediment = older. (I.e explicit statement of age thickness relationship) (1)

Because longer time for sediment accumulation/ will not have had as much sediment on it (1)

Credit link to sediment derived from the continent. (1) [3]

(any three)

Total 17 marks

2. (a) (i) Age relative to something else/ older:younger (1) [1]

(ii) Intrusion is younger than Carboniferous rocks because it cuts them or equivalent (1)

Intrusion is older than Quaternary sediment because they overlie the intrusion or equivalent (1) [2]

(b) (i) Gaseous exchange between tree and atmosphere (1) [1]

(ii) Decrease in the amount of 14C. (1)

14C decays radioactively (1)

14C not replenished from the atmosphere (1) [3]

(iii)

Suitable for dating by
14C method.
Yes/No / Reason(s)
Fossil tree in Quaternary sediment / Yes / Organic matter (1)
Young enough/not too old (1)
Fossil tree in Carboniferous sedimentary rock / No / Too old (or stated age 350-275mya) so that too much 14C is lost (1)
Igneous intrusion / No / Not organic (1)

3 correct = 2 marks

2 correct = 1 marks

1 correct = 0 mark [6]

Total 13 marks

3. (a) J located in the shale outside the metamorphic aureole (1) [1]

(b) During folding (1)

Under NE-SW compression (1)

(R one of these two as a link to Fig 3b)

Regional metamorphism (1)

Low grade (1)

(heat and) pressure 1)

Of a fine grained/or named fine grained sedimentary rock (1)

Aligned grains (1) [3]

or vice versa

trend of axial plane trace NW-SE in slate

but NE-SW in shale (1) [2]

(ii) NW-SE (1) [1]

(d) Downthrow to SE because:

Younger rock on downthrow side (1)

Shale is unmetamorphosed (1) [2]

(e) specific type of fold/fault e.g. "reverse fault", "anticline" (1)

Quality of diagram/description (2)

Reference to appropriate scale (1)

Specific location of feature (1)

Correct name of stress involved (1) R

e.g. Extension/Tension for normal fault,

Compression for reverse/thrust fault or fold

Shear for tear fault [5] Total 14 marks

4. (a) (i) Trilobite (1) [1]

(ii) Glabella (1) [1]

(b) Brachiopods have:

2 different sized valves/inequivalve (1)

plane of symmetry within 1 valve/equilateral (1) 2 of these

pedicle foramen or pedicle (1)

diductor muscle scars (1)

or equivalent

Bivalves have a pallial line/sinus (1) [2]

Decay/decomposition/eaten/eroded/breakdown (1) [2]

(d) Solution of calcite (1)

Any ref to groundwater/ porewater/percolating water (1)

Quartz/silica precipitated /crystallised (1)

Replacement (atom by atom)/Impregnation/Petrifaction (1) [3]

(e) (i) Not preserved in life position (2)

Moved/ transported (1)

after death or before preservation (1) [2]

(ii) Valves fragmented/disarticulated/separated (1)

damaged

Due to transport/current etc (1)

Not in life position(1) [2]

(iii) 1 for statement of environment (1)

e.g. high energy bed 1/low energy bed 2/fast deposition bed 2

1 for evidence (1)

e.g. fragmented in bed 1/whole in bed 2/well preserved bed 2/flipped in bed 1

at least 1 for cause of change (1 R)

e.g. – may indicate deepening water over time (1)

– may indicate sudden high energy current event during bed 1 deposition (1) ) [3]

Credit other relevant answers

Total 16 marks

GL2a

SPECIMENS

A = granite (for use in Q1)

B = calcite (for use in Q2)

C = schist (for use in Q3)

1. / (a)
(b) / (i)
(ii)
(iii) / (texture only)
crystalline
porphyritic
cooling and crystallisation of a magma
2-stages (larger phenocrysts first)
TWINNING or CLEAVAGE is the only property which can gain the following marks:
description (e.g. use hand lense to see any regular breakage/twinning)
none seen in grey mineral (accept fracture)
present in pink/white mineral
Photo 1
either (D) chilled margin
(E) finer crystals than in Specimen A due to rapid cooling against cold country rock
or (D) dyke/vein
(E) a melt intruding weaknesses in cold, brittle country rock
Photo 2
(D) random chiastolite/andalusite crystals
(E) contact metamorphism of cold country rock as hot melt cools
Map 1
(D) radial dip
(E) forceful intrusion domes country rock / 1
1
1
1
1
1
1
1
1
1
1
1
1
1
1 / 2
2
3
6
(13)
2. / (a)
(b)
(c)
(d) / (i)
(ii)
(i)
(ii) / scaled drawing
shape of ooliths
structure of ooliths
pore spaces
positive acid test or rhombic cleavage
Calcite
non-frilled, showing lobes and saddles
(e.g. "zig-zag", "angular", "rounded")
Upper Palaeozoic
Goniatitic (or similar e.g. early type of suture evolution)
(No mark for evaluation only; mark reason only if evaluation is correct)
Photo 3
False
limestones/ooliths form in shallow marine environments
Photo 4
Correct
fossil group (cephalopod/ammonoid/goniatite)
uniformitarianism (nautiloids) R / 1
1
1
1
1
1
1
1
1
1
1
1
1 / 4
1
1
2
2
3
(13)
3. / (a)
(b)
(c) / (i)
(ii)
(i)
(ii)
(iii)
(iv)
(v) / e.g. freeze-thaw
water expands in cracks as it freezes
cyclic process
Textural – foliation/aligned crystals
Mineralogical – micas or garnets
b/a = 0.80 c/b = 0.12 or 0.13
plot and label the answer from part (i)
foliation causes "thin" fragments when physically weathered
spheres
plutons/granites have cooling joints
3-D spacing produces “cubic” fragments / 1
1
1
1
1
1
1
1
1
1
1 / 1
2
2
1
1
1
1
2
(11)
4. / (a)
(b)
(c) / (i)
(ii)
(i)
(ii)
(iii) / horizontal rock overlies folded rock units/ cross-cutting
e.g. weathered surface beneath Rock Unit
e.g. included fragments of older rocks (C, E, F) in Rock Unit B
NE-SW line within Rock Unit C, but not cutting through the unconformity
25m
F1 downthrows to the southeast
F1 is normal
F2 is vertical (straight line of outcrop)
Dowthrows to northwest, but is this the hanging or footwall? / 1
1
1
1
1
1
1
1
1 / 1
1
1
1
2
2
(8)
5. / (a)
(b) / see section
see table / 10
5 / 10
5
(15)

GL3

1. (a) Arrow (1R)

Glacial till impermeable – sandstone permeable (1)

– water forced to the surface.(1)

(2 max)

[2]

(b) Rotational slip plane in tip debris. [1]

angle of slope (not dip), vibration, other (any 2) [2]

(ii) Geological factor explained [2]

(d) Monitored for creep, strain, groundwater pressure,

Mapped for spring presence.

Slope stabilisation, methods – drainage, diversion etc

(3 max holistic) [3]

(e) Stability of rock faces, rock falls, ground subsidence,

gas explosions, flooding, surface/groundwater pollution

(2 max) [2]

Total 12 marks

2. (a) As Richter scale increases

energy increases (1) and frequency decreases (1)

Credit use of numbers

(2 max) [2]

(b) (i) 32 million [1]

(ii) Rare for energy to build up so high before slipping

build up if strain takes time .

(2 max) [2]

Name / Distance (km) / S-P lag time (seconds) / Amplitude
(mm) / Richter
Magnitude
Earthquake A / ~50 / 6 / 0.2 / 2
Earthquake B / ~225 / (25-27)
25 / 20 / 5
Aftershock C / 2 / 4

Care with follow on [3]

(ii) 1. 32

2. 10 [2]

(d) Increase/decrease in background rate of minor quakes

Seismic Gap.

Measurement of P and S velocities passing through fault zone.

Reduction indicates influx of water into rock as micro-fractures open.

On returning to normal, pore pressure rises = quake.

Duration of anomaly = predicted magnitude of quake.

Holistic (3 max) [3]

Total 13 marks
Section B

3. (a) Describe the properties of rock that control porosity and permeability in aquifers.

Aquifer, permeability, porosity (specific yield) defined.

High POROSITY depends upon gaps between grains large/interconnected

Primary and secondary porosity depends upon

Packing of grains – cubic v rhombic

Fracture/joint spacing

Shape/orientation of grains – angular v rounded

Sorting of grains – small fit in between larger.

Cementation

PERMEABILITY depends upon

Connectivity of pores

Size of pores

Joints and fractures

Interconnected joints, faults, fractures, solution cavities

Examples – Limestone, sandstone, fractured/jointed igneous and met rock

Credit structures if related to permeability (artesian basins/confined/unconfined aquifer). Good aquifer depends upon good permeability/specific retention.

Case studies given credit. [10]

(b) Explain how geologically related problems may result from interference with the hydrological system.

Holistic – may include:

1. Local exhaustion of water table – cones of depression.

Extraction exceeds recharge.

Reduction of flow from springs/wells – dry wells and valleys – loss of wetland habitat/domestic supply in arid region.

Loss of artesian effect.

Flooding if hydrological system is blocked/throughflow restricted.

2. Reduction in pore pressure causing surface subsidence.

3. Contamination as pollutants are drawn in – pollutants identified.

Sea water contamination in coastal areas

Examples (e.g. London) and diagrams credited.

Acid Mine Drainage – mining

4. Reference to interference with coastal processes – longshore drift, coastal erosion/deposition.

5. Pumping water into faults – earthquake reactivation – Denver, building reservoirs increases pore pressure and instability – Vaiont dam [15]

Total 25 marks

4. (a) Using one or more case studies, describe how one of the following volcanic phenomena can be hazardous:

(i} lahars

(ii) volcanic gas

(iii) blast/explosion

lahar

Reworked ash from volcano. Melted snow and torrential rain.

Hot, liquid. Consistency of concrete – fast flowing.

Suffocation/drowning/burial.

Difficult to predict. Lasts for years.

E.G. Armero(Columbia)/Pinatobo etc.

volcanic gases

Variety – CO2, H2S, CO, SO2 etc – contain fluorine, sulphur, chlorine – noxious

Hot (1000C) – Suffocation/drowning/burial/burning/respiratory problems

Effect on vegetation. – Not affecting buildings but kill people – silent killer

E.G. Lake overturn – Lake Nyos – Cameroon.

blast/explosion

Explosive index – Types – Hawaiian – Ultra Plinian.

Lateral blast – e.g. Mt St. Helens – Heat, speed, force, distance travelled.

Vertical blast – e.g. Pinatubo, Krakatoa

Secondary effects – trees levelled, rivers blocked by debris, effect of bombs/ash etc. tsunamis

(Max 10 – No case study – max 7)

(b) Explain how the risk to life and property associated with a major volcanic event largely depends upon the extent to which an eruption can be predicted or its effect minimised.

Holistic approach

Volcanic hazard defined – i.e. Risk of the harmful effect to human life or property of an unavoidable volcanic event.

Minimising volcanic hazards and efficient/effective prediction reduces the risk and scale of the potential hazard.

Minimising may involve – evacuation, hazard mapping, diversion/blocks, dropping-spraying with water, explosion of flow margin.

Case studies credited – Iceland, Etna.

Prediction may include – monitoring ground deformation, gravity and thermal anolalies, gas emissions and seismic activity (harmonic tremors).

Effectiveness discussed and case studies given credit – Pinatubo.

Ultimately always risk of hazard if people choose to live near volcanoes.

(Max 15 to include evaluation – 12 max if none)

Total 25 marks

5. (a) Compare the changes in radon gas emissions before and after an earthquake with the changes in groundwater levels (identified in wells) over the same period of time. Explain your answer.

During build-up of elastic strain prior to earthquake (dilation) cracks open – radon released and increase recorded. Water levels fall.

Radon gas emissions stabilise in diffusion stage where no new cracks open. Water levels rise as water infills cracks. (Credit also – Radon gas increase also associated with the movement of groundwater into the micro-cracks as it is soluble in water.)

Fall to background levels after quake when micro-cracks close. Water levels rise further.

(Max 10 marks)

(b) Account for the presence of high radon gas concentrations in some buildings located in particular areas of the British Isles.

You should consider

the sources, and pathways of the gas to the surface,

the surface geology in high risk areas and

the risk involved in high concentrations.

Radon defined. A dangerous (when in high concentrations) inert gas from decay of uranium rich rock.