Welsh Joint Education Committee s1

WELSH JOINT EDUCATION COMMITTEE CYD-BWYLLGOR ADDYSG CYMRU

General Certificate of Education Tystysgrif Addysg Gyffredinol Advanced Subsidiary/Advanced Uwch Gyfrannol/Uwch

MARKING SCHEMES

JANUARY 2002

GEOLOGY

INTRODUCTION

The marking schemes which follow were those used by the WJEC for the 2001 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

Question 1

(a) (i) X - Biotite Mica. (1) Y - Orthoclase Feldspar. (1) [2]

(ii) Crystalline/porphyritic (1) [1]

(iii) Two stages/rate of cooling(1) Larger phenocrysts cool slowly/early/room to grow (1) Finer groundmass cools quicker/later/growth impeded (1) Magma intruded from larger/deeper to a smaller shallower body (1) (3 max) [3]

(iv) Granite (1) [1]

(b) Any three appropriate from the following list: Weathering (or detail e.g. hydrolysis) Erosion (or detail e.g. abrasion) Transport (or detail e.g. saltation) Deposition (or detail e.g. settling) Diagenesis /lithification (or detail e.g. compaction) (3 max) [3]

(c) Alignment of minerals related to directed stress/foliation (1)(RES) Regional Metamorphism (1) Pressure and Temperature (both) (1) Recrystallisation (clay to mica/quartz to quartz )/mosaic texture(1) (3 max) [3]

(d) Sedimentary - bedding, cross-bedding, graded bedding, desiccation cracks, sole structures etc

(i) Diagram(s) observation quality - (0-1-2) Scale (1) (ii) Labels/conclusions/field or other examples - (0-1-2-3)

Sedimentary texture/non sedimentary structure = 0 (5 max) [5]

Total 18 marks

1 Question 2

(a) (i) Dolerite (1) [1]

(ii) Dyke (1) Discordant (1) [2]

(b) Complete graph - 2 max Correct grain size (1 .5 mm) in middle (1) Finer grained at the chilled margin (1)

Explain - 2 max Faster cooling towards the edge/small crystals(1) Chilled margin in contact with cold country rock (1) (Visa versa with centre of dyke- crystal size/slow cooling/insulation) [4]

(c) Higher nearer to edge - Harder/more resistant to weathering/erosion (1) Contact metamorphism/recrystallisation of sandstone/baked margin (1) [2]

(d) Sketch to illustrate (or labels to indicate) max 1mm size grains (drawn to scale) (1) Well sorted(1) Well rounded (1) Red haematite coating/cement (RES1)

(4 max - no labels 3 max) [4]

Total 13 marks

2 Question 3

(a) (i) Q - Cephalopod/Ammonoid (not ammonite)/Goniatite (1) P - Graptolite (1) [2]

(ii) Q - Simple (goniatitic) suture/more complex with evolution (1) P - Single (mongraptus) stipe/scandent/older forms had more stipes(1) [2]

(c) Limestone deposited on top of shale/superposition (1) Limestone unfolded/shale tilted/unconformable relationship (1) Monograptus Silurian/Goniatite is Carboniferous (1) Silurian older than Carboniferous (1) (3 max ) [3]

(d) (i) Marine (1) Tropical/warm (21 - 29 degrees) (1) Shallow (20 m max)/high energy (1) Well oxygenated (1) Clear - sediment free (1) (3 max for list) (1) Reserved - Reason referring to Coral (or brachiopods) - coral/brachiopods only found in marine environ - optimum temp for coral - brachiopods ribbing/corals strength (etc) - organisms require oxygen - photosynthesis of algae/symbiosis with coral Uniformitarianism [4]

(ii) Coral and Brachiopod are sessile/in situ/life assemblage (1) Corals survive in a restricted ecological niche (1) Cephalopod is a swimmer/found in other environments/ death (?) assemblage (1) Corals Brachiopods are alive today - uniformitarianism (1) Goniatites are extinct (1)

(2 max) [2]

Total 13 marks

3 Question 4

(a) (i) Asthenosphere (1) [1] (ii) weaker/partial melting/ductile (1) [1]

(b) (i) [3]

Location Distribution of earthquake foci Explanation

 Shallow(1)  Faulting and volcanic activity at a A Concentrated below ridge.  Constructive plate margin. (1)

 Shallow focus at the trench  Descending plate (1) descending to greater Subduction zone/Benioff (1) B depths along a plane at 45o Destructive plate margin (1) beneath the island arc.

(ii) From Mid-ocean ridge - parallel with Benioff zone (1) East of Island arc (1) [2]

(c) (i) Mirror image (1 res) As plates move away from MOR /Sea Floor spreading (1) Plates lose heat as they move from rising convection cell (1) (2 max) [2]

(ii) A - Highest >3 (3.5 microcal/cm2/s) (1 res) Rising magma /volcanic activity (1) Upward moving convection current/Constructive margin (1) Thin lithosphere (1) (3 max)

B - Above average (2.5 microcal/cm2/s) (1 res) Rising magma/volcanic activity (1) Partial melting of subducted plate/destructive margin (1) (3 max) [6]

(iii) Oldest/furthest from ridge (1) Thick sediment blanket - insulation (1) Increased lithosphere thickness (1) [1] NB: water depth/temperature is not valid

Total 16 marks

Question 1

(a) (i) Credit : roughly semi-circular almost continuous band or zone maximum 8km long between 1-2km wide parallel to coast/within bay centred on island (2 max) [2]

(ii) Coastal location (1) Low lying (1) Undersea earthquakes (1) Shape of coastline – funnel/channelled (1) Underwater eruption/collapse (1) (2 max) [2]

(b) (i) 40 +/- 5 [1] (ii) radial tilt from centre of caldera (1) greatest tilt along the northern rim(1) Use of numbers in description (1) (2 max) [2]

(c) (i) tilt- ground inflation/bulge/displacement faulting (1) associated with rising magma/filling of magma chamber (1) causing seismic activity – movement of magma & fracturing(1) floundering of caldera –seismic (1) associated with active volcanic vents to the north (1) (3max) [3]

(ii) One from: Gravity Thermals anomalies Named gas (S02, etc) emissions/COSPEC Electronic measuring/laser Magnetism Other sensible - related to earthquake (animal behaviour etc) Described (1) [2]

Total 12 marks

5 Question 2

(a) (i) Line linking lake level and wells. (1) [1]

(ii) Natural depression at base of escarpment (1) Underlain by impermeable shale (1) Water table forced to surface (1) Perched water table (1) (2 max) [2]

(b) (i) Boreholes drilled around quarry (1) Over pumping of groundwater (greater than recharge) (1) Creating a cone of exhaustion.( (or drawn/annotated on Figure 2) (other appropriate - e.g. providing sump at bottom of quarry) (1) (2 max) [2]

(ii) Lowering of WT may cause wells (springs feeding lake) may dry up (1) lake may disappear/evaporate if WT does not reach surface (1) instability/subsidence owing to reduced pore pressure. (1) other - e.g. extra surface runoff from pumped water (1) (3 max) [3]

(c) (i) Accept general answer or specific to Figure 2. One from any TWO of the following:  Leachate pollution - as limestone permeable - groundwater flow to water supply (to the lake (SSSI))  Methane gas production - migrates through permeable rock - methane gas is explosive  Subsidence/instability - as waste decomposes and surface collapses (2 max. No geological explanation (simple list) 1 max) [2]

(ii) Contained site - Impermeable HDP lining (1) Leachate management system (1) Boreholes around to monitor (1) Boreholes to vent methane(1) Burning off/using gas as a fuel (1) Sealing top to reduce leaching (1) Cells within to separate/confine reactive materials (1) (3 max) [3]

Total 13 marks

6 Q.3 (a) Describe how the foundations of large structures can be affected by:

 unstable patterns of geological structures (e.g. bedding, jointing, faulting, cleavage); and

 depth to the water table and rockhead. [15]

(b) Account for the presence of high concentrations of radon gas in some buildings. [10]

(a)  Unstable patterns of geological structures (e.g. bedding, jointing, faulting, cleavage);

Effect of dip of beds/cleavage. Slope faces daylight. Stable friction angles. Fracturing of fault planes. Density of joints. Lubrication by water. Case studies.

 Depth to the water table and rockhead. Affect of water on stability - porosity v permeability. Pore pressure, rock type, lubrication, liquification in earthquake prone areas. Effect of fluctuating water tables e.g. London. Rockhead depth - defined. Nature of the drift material on stability. Need for high foundation strength. Case studies. (15 marks holistic)

(b) Radon defined. Natural release from radioactive decay. Sources and pathways. Granite - high risk areas (SW England). Radon dissolves in water and transported in groundwater. Released when pressure drops/near surface. Trapped by some rock types (clay) but released to atmosphere to be trapped by poorly ventilated/well insulated buildings (cellars, attics, roof and floor voids). (10 marks)

Total 25marks

7 Q.4 (a) Briefly describe the differences between the Richter and modified Mercalli scales of earthquake measurement. [5]

(b) Describe the factors that affect the level recorded on the modified Mercalli scale at a given distance from an epicentre. [8]

(c) Describe and explain the effect of a major earthquake(s) you have studied on built structures. [12]

(a) Richter Magnitude, energy released/strength, Logarithmic scale, (no limit) Scale explained (30 times energy/10 times amplitude per point) Mercalli Intensity scale, based on observations (I - XII), Example. (Max 5 marks)

(b) Earthquake size on Richter scale, depth, distance, local ground conditions, building standards, LEDC/MEDC, level of preparedness. Case studies. (Max 8 marks)

(c) Named case study(ies). Possible comparison between countries of different economic development. Collapse of bridges/buildings/pipes/tunnels etc Liquefaction, shaking, fracturing, resonance. Tsunami effects. Nature of buildings, earthquake proof effects. Depth v breadth. (Max 12 marks)

Total 25 marks

8 Q.5 (a) Describe how sites of potential slope failure can be monitored. [10]

(b) Describe, with reference to a case study(ies), how attempts are made to manage and control the destructive effects of mass movements. [15]

(a) Mechanics of mapping, air photossatelite imagery, surveying, measurement of creep, strain, groundwater pressures described. Instruments used. Accept volcanic slope monitoring (Mt St Helens). (Max 10 marks)

(b) Case study(ies) - Aberfan, Vaiont Dam, Mam Tor etc. Also accept Mt St Helens and avalanches.. Discussion of the extent to which they can be predicted using examples. Disasters occur when not predicted or acted upon. Quality of the case study material and argument.- No case study max 10 Expect: Rock bolts/grouting/gabions/netting/walls Drainage/vegetation Toe protection/ coastal protection Reduction of slope angle to stable angle.

(Holistic) (Max 15 marks)

Total 25 marks

GCE M/S Geology (Jan 2002)/JD

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