GCSE Geography AQA - Rocks

Igneous:

• formed by cooling of molten rock, either underground or on surface
• Intrusive - magma rises to surface but doesn't break through, solidifies
• Extrusive - magma erupts on surface as lava, solidifies
• Characteristics - interlocking crystals - crystalline; intrusive - cools slower, crystals larger; extrusive - cools faster, crystals smaller; hard, resistant to erosion, form upland areas e.g. Granite (intrusive) & Basalt (extrusive)

Sedimentary:

• compaction of sediments, deposited in sea
• Organic - chalk, limestone; skeletions of sea creatures made of calcium carbonate
• Inorganic - acculumation & compression of other sediments, e.g. mud & sand
• Characterisitics - layers called strata, fossils, weaker than igneous, some soluble e.g. chalk, limestone & clay

Metamorphic:

• alternation of pre-existing igneous, sedimentary or metamorphic rocks by heat/pressure
• Characteristics - crystalline, very hard, resistant to erosion e.g. slate & marble

Distribution of rocks in Britain:

Granite - widespread over Cornwall/Devon, Ireland & Scotland

Chalk - long bands forming North & South Downs, Chiltern Hills - south-east England

Clay - long bands forming London Basic etc - south-east England

Carboniferous Limestone - much of Ireland & North England

Freeze-thaw weathering:

• water fills cracks/joints in rock
• water freezes & cracks expand
• repeated cycles increase size, until block of rock breaks off
• loose rocks called scree
• needs plenty of water, fluctuating temperatures,  repeated cycles

Exfoliation:

• happens on boulders, outer layer expands in the heat
• contracts at night, causes cracks at right angles on surface
• slabs fall off
• needs fluctuating temps like in deserts, repeated cycles
• onion-skin

Solution - dissolving rocks/minerals by rainwater

Carbonation:

• weathering of limestone/chalk by acidic rainwater
• some minerals dissolved in rainwater & removed by solution
• pure water little effect on limestone, rainwater absorbs CO2, & forms weak carbonic acid
• calcium carbonate in limestone dissolves & forms calcium bicarbonate
• forms cracks - grikes & clints - limestone pavement

Biological weathering:

• roots expand & grow in cracks - move them apart
• animals burrow into weaker rocks - undermine structure
• organic acids released by vegetatiom & speed up biological weathering

Granite - 

Characteristics - minerals are grey-coloured quartz, black mica, pink feldspar (subsequent to chemical weathering); vertical joints formed when it cools & contracted; horizontal joints formed by pressure release as overlying rocks are removed by erosion; joints make granite vulnerable to freeze-thaw & some exfoliation

Tors - formed by weaker overlying rocks being eroded & all that is left is a granite outcrop

Chalk - harder; permeable; escarpments of 200m+; dry valleys; thin, infertile soil; economic uses - horseracing, quarries, sheep rearing; land use - horseracing, paragliding, sheep rearing etc

Clay - weaker, impermeable, clay vales, wet & marshy, fertile soil, economic uses - brick laying, pottery; land use - clay pits, cattle farming, arable farming

Surface features: 

• Limestone pavements - exposed limestone, grikes & clints, carbonation
• Swallow holes - streams dissolve limestone, joints become enlarged by carbonation & river erosion
• Dry valleys - old river valleys in Ice Age, ground frozen & ground saturated
• Gorges - roof of cave system collapses, steep sided, rock outcrops
• Resurgence - streams disappear down swallow hole, flow underground, water meets impermeable rock, flows over till it reaches surface - resurgence stream

Underground features:

• Underground caverns - water flows underground & dissolves limestone
• Stalactites - water drips from roof, evaporates leaving hard minerals
• Stalagmites - water drips on floor, water evaporates
• Pillars - when stalactite & stalagmites join - rare
• Curtain - water flows over a surface, many stalactites joined

Environmental Damage:

• loss of habitats
• eye sore - ugly
• pollution to rivers
• loss of farmland
• methane from waste tips
• CO2
• noise & dust
• Damage to village roads

Uses of exhausted quarries:

• restored to farmland by top soil replaced
• motorcross/mountain biking
• waste tips used as dry ski slopes
• lakes - wildlife reserves, fishing, water sports

Devon, south-west England; granite upland; rises to 612m; rugged moorlands; tors; marshes; rainfall high & granite impermeable

Land use: population density low; sheep farming on rough pasture; forestry; quarrying; reservoirs - impermeable nature & high rainfall; outdoor activities

How farmers help to conserve Dartmoor: Environmental Sensitive Area, farmers agreed to certain managements; reduce no. of livestock grazing sensitive areas, restrict use of fertilisers & pesticides; paid to maintain stone walls & hedgerows

Farmer's problems: cost of fuel, food & bedding for animals gone up; some farmers diversified into other areas, some can't; changes to payments from EU mean farmers get less money

Strategies: Dartmoor Hill Farm Project - support for farmers selling livestock directly to public; organises specialist sheep sales; set up apprenticeship scheme for hill farming

• Chalk & clay landscapes, formed in bands, clay very common in UK

• Clay vales - undulating lowland between 20 - 60m; many surface streams; farms

• Dip slope of chalk escarpment - land slopes to south between 200m - 50m; lack of surface drainage; lack of settlements or communications

• Chalk ridge - escarpment

• Scarp slope of chalk escarpment - land rises steeply from north to south between 60 - 200m

Landuse: settlements limited due to lack of water; thin soils & steep slopes - hill sheep farming; quarrying of limestone for buildings & chemical industry

Tourism: increasing importance, National parks, Area of Outstanding Natural Beauty (AONB) in limestone areas, nature tourism - birds, wildflowers, walking etc

Benefits of tourism - brings money £478mn a year; employment opportunities for local people; 13% work of pop. work in tourism; local craft industries & farms benefit from tourists

Costs of tourism - traffic, pollution, litter, harm wildlife; farm gates left open; demand for holiday homes; footpath erosion; more efficient sewage system needed; loss of peace & solitude

Advantages:

Economic - employment for rural areas; increase income; multiplier effect; Hope Quarry provides 182 jobs, don't need to commute; Hope Quarry Cement Works recieve 2mn tonnes of limestone from it, 1.3mn tonnes of cement a year; cheaper way of getting limestone

Environmental - modern technology minimises impacts, may be restored afterwards; Hope Quarry estimated enough resources for 30-50 more working years; if quarrying is in one area, effects are conc. on one area

Disadvantages:

Social - extracting & treating rock creates noise & dust; heavy lorry traffic; high transport cost

Environmental - habitats lost, agriculture impossible, Hope Quarry is a huge hole in the ground - visual effect on landscape; many associated buildings & waste tips; Hope Quarry produces 1mn tonnes of CO2 a year

Southeast of Chichester, West Sussex; original landuse - intensive arable farming & ecological surveys; Mineral Planning Authority & Tarmac plc agreed to restoration scheme; 30 ha; sand & gravel extraction

Restoration scheme - freshwater lake of 11.5 ha; reedbeds; shallow & deep ponds; gravel beachs & islands; 2.5ha of grassland - wetlands, scapes & shallow ponds; 1ha of woodland & scrub; tern rafts, bird nesting boxs & bat boxes

The lake - main feature, for wildlife - invertebrates, birds, plants etc, reedbeds planted on 20% of it, archeological interest

Grassland - mosaic of microhabitats - bare ground, short sward etc

Woodland - native trees - oak, ash etc

Aftercare period - 10 years, Tarmac plc to hold annual meetings, Mineral Planning Authority to inspect & review

Wildlife - black poplar, chaser dragonfly, great crested newt, song thrush, reed bunting, water vole, pipistrielle bat, otter