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WELSH JOINT EDUCATION COMMITTEE
CYD-BWYLLGOR ADDYSG CYMRU
General Certificate of Education
Tystysgrif Addysg Gyffredinol
MARKING SCHEMES
JANUARY 2007
AS/Advanced
GEOLOGY
INTRODUCTION
The marking schemes which follow were those used by the WJEC for the January 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)
(b)
(i)
Increasing temperature with depth (1)
Credit any precise correct point,
but not just 1 reading off the graph.
E.g:
Quote range (4900 °C)
or max/min temperatures 0 - 4900 °C (1)
Quote change in rate of temp increase
e.g. rapid rate over first 200km then slower (1)
(2 of these)
[2]
(ii)
correct concept of temp change / distance (1)
or
(4300- 2500)=1800 /2000 = 0.9 °C/km (2)
Accept within the range 0.8 - 0.95
[2]
(iii)
Solid (1)
[1]
(i)
Current/flow (1)
Heating/lower density/ causes rising (1)
Cooling/ raises density/ causes sinking (1)
(2 of these)
[2]
(ii)
Conduction (1)
Lithosphere is solid/cannot flow (1)
[2]
(c)
Geotherm close to temp at which rocks become molten R (1)
Asthenosphere is partially molten/plastic (1)
Reduction in rigidity/stiffness (1)
[3]
(d)
(i)
Drawing of 2 S-waves which clip the core (1)
Centre wave extended to core but not entering the core (1)
[2]
(ii)
Drawn on opposite side of Earth from focus (1)
[1]
(iii)
Geotherm/temperatures greater than
melting point in outer core/2900-5155 km R (1)
Velocity zero in outer core/ at 2900 km R (1)
Outer Core molten (1)
S waves cannot pass through outer core (1)
S waves cannot pass through a liquid (1)
Rigidity is zero (1)
[3]
18 marks
1
2.
(a)
(b)
(i)
P = stipe (1)
Q = theca (1)
[2]
(ii)
Fragile graptolite skeleton (1)
Shale low energy deposition so preserves whole fossil (1)
Sandstone high energy deposition so fragments graptolite (1)
Shale may be deposited in anaerobic conditions (1)
[2]
(i)
Older bed X below younger Y (1)
[1]
(ii)
Reduction in stipe number in shale X (A) (1)
Pendent to horizontal to scandent in shale X (A) (1)
More complex thecae in shale X (A) (1)
[3]
(iii)
Load cast or flame structure R (1)
Supports interpretation 2 because:
Sand slumps down into mud (1)
Mud squeezes up into sand (1)
Sed struc is upsidedown (1)
Because rock sequence is overturned R (1)
Law of superposition does not apply (1)
[4]
12 marks
2
3.
(a)
(b)
(c)
(i)
Reverse (1)
Footwall block moved down or hanging wall block moved up
or fault plane dips to upthrow side
[2]
(ii)
Columnar joints (1)
Cooling (1)
Contraction (1)
(2 of these)
[2]
(i)
Porphyritic (1)
[1]
(ii)
2 stage cooling (1)
Coarse crystals/phenocrysts slow cooling (1)
Fine crystals/groundmass rapid cooling (1)
Variation of depth of crystallisation (1)
Order of crystallisation or ref to crystallisation temperatures (1)
(3 of these)
[3]
(iii)
Agree that it is basalt because:
Fine grained rock/groundmass (1)
Presence of olivine/pyroxene suggests mafic/basic (1)
[2]
(i)
Breccia older/fault younger because fault cuts the breccia (1)
[1]
(ii)
Sill (1)
because
Concordant (1)
Not displaced by the fault (1)
Making it younger than all the sedimentary rocks (1)
[4]
15 marks
3
4.
(a)
(b)
(i)
Sedimentary
because: contains fossils
or is granular (1)
[1]
(ii)
Crystalline (1)
Equigranular/equicrystalline (1)
Coarse or stated crystal size (1)
“Mosaic” (1)
[2]
(iii)
Marble (1)
[1]
D in the limestone on the map (not in aureole) (1)
D is a limestone because (sedimentary and) high % CaCO3 (1)
[6]
E in the limestone area within the metamorphic aureole (1)
E is metamorphosed limestone (marble) (1)
F in the pluton except within 1mm of margin (1)
F is igneous or some stated indication of igneous
e.g. porphyritic, granite, gabbro (1)
(c)
Quality of drawing of an unconformity (1)
Labels/written explanation of meaning of unconformity
egg time gap (1)
Scale (1)
Actual example of unconformity (1)
Evidence of knowledge of meaning of included fragments (1)
Use of included fragments in determining age above
and below the unconformity (1)
[5]
Total 15 marks
4
GL3
1.
(a)
(i)
(ii)
(iii)
(b)
(i)
(ii)
Pyroclastic flows – Hot/fast (1)
Ash – Thick/choking/heavy etc (1)
(2 max)
[2]
No pyroclastic flows in S. Cruz
Less ash falls at S. Cruz (Res)
4-2 m of ash compared with >10
(2 max)
[2]
Topography – to predict pathways of flows (1)
Thickness of previous deposits – potential scale (1)
Chemical analysis of deposits - type of eruption (1)
Wind direction – ash deposits
Recorded reports of previous eruptions
(max when explained 3)
[3]
Landslide induced by volcanic activity (1)
Related to offshore debris material (1) (R)
Other relevant explanations (1)
(2 max)
[2]
Tsunamis explained (1 res)
origin/wavelength/amplitude, speed,
effect of shallowing, little energy reduction (1)
(Holistic max 3 marks)
[3]
Total 12 marks
5
2.
(a)
(i)
(ii)
(b)
(c)
(d)
200m /133yr = 1.5 m/yr
(1)
(1)
[2]
East Bay – Starved of sediment (1)
Longshore drift reduced (1)
by breakwater trapping sed (1)
little protection from wave action (1)
or West Bay
(max 2 holistic)
[2]
(i)
~15 degrees (accept 14 – 16)
(ii)
Line (similar gradient to the left) (1)
Accuracy through 30m/35 degrees (1)
[2]
Clay below – impermeable
Sand and gravel above – permeable
Rain and groundwater forced to surface at interface
Sea-level eroding the weak clay.
Landslip/collapse/slumping/slip
(3 max holistic)
[3]
One measure explained.
Drainage, re-profiling cliff to reduce slope angle,
protection of landslide toe, barriers (rip-rap/sea wall)
Geotextiles, sand replenishment in East Bay etc.
Credit examples
(3 max)
[3]
Total 12 marks
6
Question 3
(a)
Explain why many of the world's most hazardous (explosive) volcanoes are confined
to a distinct zone around the Pacific.
[15]
Zones - Destructive (associated with subduction/partial melting of basalt
to give andesite/rhyolite)
e.g. Mt. St Helens/Katmai/Krakatoa/Taupo
Most explosive Composition (silicic/andesitic/rhyolitic)
Viscous - high silica content
Gaseous - can't readily escape
Relationship between these factors and plate tectonic context
Types and nature of hazard explained – Pyroclastic flows, blast, ash etc.
Holistic (Depth v Breadth)
(b)
Describe how the hazards associated with volcanoes and earthquakes and their
management might be similar.
[10]
Similarities (Holistic)
Hazard








Both linked to specific zones around the globe.
Seismic activity is also associated with volcanic activity – underground
magma movement
Volcanic and seismic events - often fast and violent
Both may cause fast mass movements of material. (pyroclastic flows v
landslides)
Both cause tsunami
Both produce piles of unstable, loose debris (ash etc and collapse
buildings/unstable rock waste.
Hazard in both depends upon frequency, intensity (VEI and Richter scales)
Hazard in both depends upon degree and quality of economic development
(local building standards, population density etc)
Management



Both can be partly predicted and managed to minimise risk.
Contingency plans can be drawn up for both, e.g. for fire/police/hospital
services, evacuation plans, refugee camps, etc
Hazard maps can be drawn for both.
Examples given credit.
(Max 10 marks)
Total 25 marks
7
Question 4
(a)
Describe how groundwater pollution can result from the following human activities.
(i)
(ii)
(i)
(ii)
Waste disposal
Mining
[15]
Landfill hazard of escaping leachate. Other contaminants – oil, highly toxic
and radioactive waste. Acidity – named contaminants (cadmium, lead, etc)
Reference to porosity and permeability of aquifer.
Mine drainage pollution described – Pyrite/iron oxidised in acidic mine water.
(Pyrite + Oxygen + Water  Ferrous Iron + Sulphate + Acidity) Leaching
mine waste tips – surface pollution.
Examples credited.
(Max 7 + 1 for each. Max 15 marks).
(b)
For one of the human activities in (a), explain how the problems associated with
groundwater pollution might be overcome or reduced.
[10]
Landfill liners identified (graded liners, impermeable bentonite clay, geomembranes )
and explained in association with current legislation. Waste management strategies in
landfill design and management. (covering with clay, choice of site, pumping leachate
and gas etc)
Example credited
OR
Acidity is buffered by the addition of alkaline chemicals such as calcium carbonate,
sodium hydroxide, sodium bicarbonate or anhydrous ammonia. These chemicals raise
the pH to acceptable levels and decrease the solubility of dissolved metals.
Precipitates form that settle from the solution.
Limestone - An anoxic limestone drain - buried bed of limestone constructed to
intercept subsurface mine water flows and prevent contact with atmospheric oxygen.
Diversion well - Acidic water is conveyed by a pipe to a downstream "well" which
contains crushed limestone aggregate.
Anaerobic /aerobic wetlands – passive treatment using plants and compost
(www.dep.state.pa.us/dep/deputate/minres/bamr/amd/science_of_amd.htm)
Examples credited
(Max 10 marks)
Total 25 marks
8
Question 5
(a)
Using annotated diagrams, explain how problems of ground stability may be
associated with two of the following:
[15]
(i)
dip of strata
Effect of strata dipping "into" and "out of" a rock face (daylighting) at angles
< and > the stable slope friction angle. Associated with the type of strata (shale
v sandstone). Examples.
(ii)
orientation of rock cleavage, joint and fault patterns
Joints/faults/cleavage defined. Increases weathering surface and breaks rock
up into discrete sections. Density of joints/faults controls weathering rate.
Joint/fault direction patterns. Effect of dicontinuity planes "daylighting" at
angles > stable slope angle. Examples.
(iii)
variations in the water table.
Water table defined. Water table fluctuations results in reduction and increase
in pore pressures. (seasonal). Weakens rock. Allows subsidence. Acidic
groundwater may help dissolve cement between grains. Increase on water
table may allow pore pressure to overcome friction and cause slide. (Water
lubrication) Examples.
(Max 7 +1 each Max 15) Where no diagrams – max 12.
(b)
Describe how sites of potential ground instability may be monitored.
[10]
Mechanics of mapping, air photos-satellite imagery, surveying, measurement of
creep, strain, groundwater pressures described.
Instruments used. Credit examples.
Accept volcanic slope monitoring (Mt St Helens).
(Max 10marks)
Total 25 marks
GCE Geology Marking Scheme (January 2007)/ED
9
Welsh Joint Education Committee
245 Western Avenue
Cardiff. CF5 2YX
Tel. No. 029 2026 5000
Fax. 029 2057 5994
E-mail: [email protected]
website: www.wjec.co.uk/exams.html