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HydrographBaseflow = the normal dayto day discharge of the riverThe result of groundwaterseeping into the riverchannel.The rising limb of thehydrograph = the rapidincrease in dischargeresulting from rainfallcausing surface runoff andthen later throughflowThe time difference between the peak of therain event and the peak discharge is known asthe lag time or basin lagThe falling limb (=recession limb) is whendischarge decreases andthe river’s level falls. It ismainly throughflowwhich is making up theriver water.Peak discharge occurs when the river reachesits highest level
2010Q5c(i) 3 marks5c(ii) suggest why the hydrographs are different (4 marks)
Which part of thehydrological cycle is shownhere?Where is the soil able toabsorb most rainfall? Why?
What causes flooding?Impermeable rockdeforestationArable farmingBuilding on floodplainsHeavy rainfallLots of tributariesMarshy areas Verywet soilHard dry soilsteep slopes
Physical causes offloodsCause .... Because..... So....In steep valleys Water runs down steep slopesquickly because water flowfaster on steeper slopesIncreases discharge quicklywhich causes floodHeavy rain falling over along period of timeSoil becomes saturated Water table rises, no morerain can infiltrate, causesmore run off to rivers whichfill and overflow their banksHeavy rain falling over ashort period of timeIf intense rain falls on hard,baked ground then water flowsquickly to riversCauses flash floods as riverlevels rise rapidlySnow melt in spring Lots of water going into river inshort timeIncreases discharge is toomuch for it to holdImpermeable rocks Water cannot percolatethrough the rocksSoils quickly becomesaturated and this increasesoverland flow
Human causes of floods ....Cause .... Because .... So....Urban area Tarmac and concrete isimpermeableIncreases surfacerun off so morewater flows into theriverDeforestation If trees are removedthere is nothing tobreak the rain hittingthe ground which maycause soil erosionEroded soil iswashed into channelcausing flooding
Flood protection*Damshold back floodwaters*reservoirsstore floodwater*straightenchannelsIncreases speed offlow*DredgingMakes channel deeper socan hold more water*levees and embankmentsPrevents river fromoverflowing*land use zoningRestricts development touses unaffected by flooding*afforestationIncreasesinterceptionetc, reduces run off
Study Figure 9, which shows a plan for flood plainzoningFlood plain zoning is a ‘soft management strategy’.What does this mean? (1mark)Using Figure 9, describe the flood plain zoning and explain why strategies suchas this are sustainable. (6marks)AQA A 2005
Strategy How does it work? Advantages disadvantagesDams hold back floodwatersRiver flow can becontrolledReservoirs used forHEP or leisureCostlyunsightlyStraighteningchannelIncreases speed offlowFlooding riskpasseddownstreamBuild levees Prevents river fromoverflowingEffectivelyincreases channelcapacity beforeoverflowingCan providewalkways, leisureroutesCostlyunsightlyHard engineering strategies summary
With the aid of diagram (s)Explain the formation of waterfalls (6)• Alternating bands of hard and soft rock• Rapids• River erodes the softer, less resistant bands of rock• Hard rock undercut• Soft rock worn away through processes of hydraulic action(force of running water, compresses air in cracks in rock andleads to rock weakening and crumbling) and abrasion (actionof running water and it’s load, wearing away at channel sides)• Plunge pool is formed at base of waterfall• Overhang eventually collapses providing more material forriver to further deepen plunge pool• Process continues repeating, eventually river erodes furtherback upstream, leading to the formation of a gorgedownstream
Meander bendA BA cross section through a meanderCONVEX CONCAVESlow SPEED OF FLOW FastShallow DEPTH DeepDeposition PROCESS ErosionSlip off slope FEATURE River Cliff
2007 Q2 (b) Explain why the meander cross-section has this shapeThe meander cross section is asymmetrical.The river cliff is formed on the outer bend of the meander. This iswhere the water is deeper and moves more quickly.Hydraulic action and abrasion wear away at the side of thechannel, undercutting the river bank to form a river cliff.The slip-off slope is formed on the inside bend by deposition ofalluvium.Because the water is shallow and moving more slowly at thispoint the river load gets deposited to form a gentle slope.
River features: Ox – bow lakes• With the aid of diagrams, explain theformation of an oxbow lake (6 marks)(AQAA04)•Form from a meander•erosion on outside bend especially by hydraulicpower•deposition on inside bends where water isshallower and lower velocity•neck narrows, breaks through in time of flood•deposition seals ox bow lake•eventual loss of lake to form meander scar
Formation of a floodplainThe floodplain is the wide, flat area of land either side of the river inits lower course.Floodplains contain sediments, often accumulations ofsand, gravel, loam, silt, and/or clay. Features of a floodplain include:meanders, ox-bow lakes & levees.
How does a floodplain form?The floodplain is formed by both erosion and deposition.1. Lateral erosion is caused by meanders and the slowmigration downstream to widen the floodplain.2. The river carries large quantities of suspended load.3. The deposition on the slip off slopes providessediment to build up the valley floor.4. As the water floods onto the floodplain it losesenergy, there is greater friction, the water isshallow and the rivers velocity falls so deposition ofits suspended load occurs. Regular flooding results inthe building up of layers of nutrient rich alluviumwhich forms a flat and fertile floodplain5. Over thousands of years the deposits build up toform great thicknesses of alluvium which is whyfloodplains have fertile soil for farming.
The Physical Causes of the Floods• Most of the country is less than 1 metre above sealevel• Snowmelt from the Himalayas• Bangladesh experiences heavy monsoon rains,• Tropical storms (= cyclones) bring heavy rains andcoastal flooding• The main cause was the above average & long periodof heavy rain which caused all 3 rivers to have theirpeak flow at the same time!!!
The Human Causes of the Floods1. Deforestation in Nepal and the Himalayas increasesrun off and soil erosion which adds to deposition andflooding downstream2. Urbanisation of the flood plain has increasedmagnitude & frequency of floods3. Global warming is blamed for sea level rise, increasedsnow melt & increased rainfall in the region4. Poorly maintained embankments (levees) leak &collapse
floods occurred July to SeptJuly 2004 - 40% Dhaka was underwater60% of country was flooded600 reported deaths20 million homeless100,000 in Dhaka suffered fromdiarrhoea as floodlwaters left mudand sewage35cm of rain fell in 1 day on 13thSeptDeath toll rose to 750Airport, roads and railwaysfloodedBridges destroyed$7billion damageRice crop destroyed along withfood supplies – vegetablesCash crops – jute and sugarTextbookpage 115
Short Term Responses• Boats to rescue people• Emergency supplies for food, water, tents and medicines• Fodder for livestock• Repair houses, as well as services such as sewage etc• Aid from other countriesLong Term Responses• Reduce deforestation in Nepal & Himalayas• Build 7 large dams in Bangladesh to store excess water $30-$40million and 40 yrs to complete• Build 5000 flood shelters to accommodate all the population• Build 350km of embankment - 7 metres high at a cost of $6billion to reduce flooding along the main river channels• Create flood water storage areas• Develop an effective Flood Warning Scheme
2006 Q 7c Kielder Case study• Many urban areas get their water from upland reservoirs.• Using an example of an upland reservoir that you have studied, explainthe physical and human advantages of its location.Detailed elaborated or linked statements with precise reference to case studyexemplar. Must cover both physical and human advantages of the location.Kielder Water is in the relatively narrow valley of the River North Tyne sothe (linked statement) size and cost of building the dam was relativelysmall (physical). The local geology is shale, which is impermeable so the(linked statement) water does not drain away. (physical)The high rainfall of over 1000mm meant that there (linked statement) wasan ample supply of water.(physical) The area was sparsely populated sowhen (linked statement) the valley was flooded there was not too muchdisruption to the local population.(human) The water could be used in thedensely populated industrial areas of North East England which are nearby.(human) The population of the north east could also use the reservoirfor leisure pursuits such as fishing(human). (6 marks)
Recap – what is the driving mechanism for platemovement?
Two distinct types of crustContinental Crust Characteristic Oceanic Crust35-50 km Thickness 5-12 kmGranite (light) Composition Basalt (dark)to 3.8 billion B.P. Geological age to 150,000,000 B.P.2.7 Density 3.0Ave. +1,000 m Elevation Ave. - 3,000 mNoRemelted anddestroyedYesYes Deformed No33% Current distribution 67%Rate of Plate MovementSan Andreas Fault - 5.5 cm/yrMid-Atlantic Ridge: Iceland - 1.8 cm/yr; South Atlantic (Ascension Island) -3.9 cm/yrEast Pacific Rise - off South America Most rapid movement - 17.1 cm/yr
Type of boundary Processes Feature exampleConstructive marginsSpreadingDivergentTwo plates move apartfrom each other, newoceanic crust is formedMid ocean ridges,volcanic activityMid Atlantic ridgeDestructive marginSubduction zoneThe oceanic crustmoves towards thecontinental crust andsinks beneath it due toits greater density.Deep sea trenches andisland arcs are formedVolcanic activityNazca plate sinks underthe South AmericanplateCollision zone Two continental crustscollide as neither cansink they are folded upinto fold mountainsFold mountains Indian plate collidedwith Eurasian plate toform HimalayasConservative marginsPassive marginsTransform platesTwo plates movesideways past eachother but land isneither destroyed norcreatedFault San Andreas faultCalifornia
SupervolcanoesYellowstone, USA sits on top of a hotspot where light molten magma risestowards and collects in a store beneaththe surface.When the store of magma is emptiedquickly the land collapses into theemptied chamber and leaves a caldera
How is the distribution of supervolcanoesdifferent from that of volcanoes?1. Volcanoes occur in linear belt unlikesupervolcanoes which are more scatteredand occur individually.2. Volcanoes can occur atdestructive, constructive margins and hotspots unlike supervolcanoes which can only befound along destructive boundaries and hotspots.
Describe the ways in which a supervolcano isdifferent from a volcano (Sp paper)Shape – supervolcanoes are flat and surrounded byhigher mountains unlike volcanoes which are coneshaped, either gentle or steep. Supervolcanoes form acaldera whereas volcanoes have a craterSize – supervolcanoes are much bigger than a volcanoScale of eruption – supervolcanoes are much moreviolent and emit far more material than a volcano.Impact – a volcano will affect the local area whilst asupervolcano has a global effect
2011 Describe the likely worldwide effects of a supervolcanoeruption.Effects likely to refer to impact in immediate area of an eruption – many deaths(87000 predicted), large ashcloud rising 40 – 50km into atmosphere, destruction of10000 square km of land, ash 15cm think coveringbuildings within 10000km, flights suspended, livestock and farmland affected. The UK would see the arrival ofthe as h5 days after the eruption; temperatures would fall between 12 and 15 degrees. Parts of Europe andAmerica and Asia would see constant snow cover for 3 years, cropswould fail, monsoon rains would fail, 40% ofpopulation could face starvation. (6marks)Level 1 Basic (1-4 marks) Describes effects of a supervolcano eruption.Statements are general in a random order.Lots of people will die. There will be huge amounts of ash. People will choke to death.Buildings will collapse. Crops and animals will die. People will starve. In Yellowstone,there would be no planes.Level 2 Clear (5-6 marks)Effects are clearly described, in an organised way. There is clear reference toglobal aspect. Statements are linked.One in three people will be killed within 1000km of an eruption. Buildings wouldcollapse within this area due to the weight of the ash. This would ground planes andmake road transport difficult. Livestock would die as they would choke in hot ash.UK (England) would see the arrival of the ash about 5 days later. This will circle theEarth, changing the climate. Temperatures will fall by 10 degrees and this will makeit difficult to grow food in many areas. Certain parts of northern Europe will besnow covered for 3 years, so no food will be able to be grown.
SHIELD VOLCANO COMPOSITEVOLCANOConstructiveHot spotsType of plateboundarydestructivebasic Type of magma acidRunny, fluid Sticky, viscousGentle, effusive Type of eruption explosiveGentle sides shape Steep sidesWide base Area at base Narrow baseMauna Loa, Hawaii example Mt St Helens,Montserrat
Monitoring and Predicting volcanoes1. Earthquakes2. Tiltmeters can identify small changes in slopes3. Global positioning systems (GPS) use satellites to detectmovement of as little as 1mm.4. Change in temperature of magma can be monitored.5. Escaping gases from the vent change before an eruption –increase in sulphur dioxide.6. Seismometers used to measure earthquake waves.7. Analysis of past eruptions; gap between them and patternof flows can all help with predictions.However, volcanoes can still be very unpredictable.
Describe the distribution ofvolcanoes1. Not found everywhere –largely found in certainlinear belts2. Located on plate boundaries – found on destructive(Pacific Rim) and constructive plate boundaries (MidAtlantic Ridge)3. Destructive plate boundary e.g. Mt St Helens, N.America4. Constructive plate boundary – Heimaey, Iceland, MidAtlantic Ridge5. A few volcanoes are located away from plateboundaries e.g. Mauna Loa in Hawaii – hot spots,plumes of magma caused by radio active heat withinthe mantle
Q1a (ii) Explain why volcanoes are found at destructive plateboundaries (3 marks)At a destructive boundary an oceanic plate and a continentalplate are moving towards each other due to convectioncurrents in the mantleThe denser oceanic crust is subducted below the lightercontinental crust.Pressure is exerted as the plates grind past each other andfriction causes the oceanic plate to melt along withsediments.The lighter magma then gets pushed up to the surface via cracksuntil it erupts.
Volcano case studyPrimary impacts Secondary impactsImmediate responses Long term responses
Volcano Mt St Helens pg 19Primary impacts Secondary impacts57 diedTrees uprootedLogging campsdestroyedRiver temperaturesraisedSediment and mudchoked channelLoss of wildlifeFarming crops ruinedDeath of fish in riversFlood waters washedaway road and railwaybridges car enginesaffected by ashElectricity suppliesinterruptedTelephone wires cutPlanes grounded
Volcano Mt St Helens pg 19Immediate responses Long term responsesMobilised helicopters tosearch for survivorsFinding shelter for strandedtouristsEmergency medicaltreatmentProviding citizens with facemasksClearing ash from roads toallow traffic to flowBuildings and bridgesneed rebuildingDrainage needed to bemonitored to ensure noflooding occurred as aresult of debrisForest neededreplanting
Formation of fold mountainsDestructive boundary (subduction = oceanic crust meets continentalcrust)1. Sediment brought down by rivers collects in a geosyncline, which is adepression under the sea; this is often near a subduction zone, along adestructive plate margin.2. As more sediment collects on top, the sediment is compressed andturns into rock.3. Plate movement, caused by convection currents in the mantle, causescompression of the rocks, which leads to folding, which causes foldmountains. Eg. Rockies,Collision boundary (continental crust meets continental crust)• Himalayas (which are formed along a collision zone).
How do people adapt to fold mtnsFarming:Valley floors – flat, deep fertile soils, shelteredTranshumance – seasonal movement of cattle upmountainside allowing hay and fodder to be grownon valley floorMilk butter cheesePlastic tubes carry milk down mountainsideNew roads, quad bikes and cable cars give easier accessto upland pasturesFarms are on south facing sides which is warmerCrops: hay, cereals, sugar been, vines and fruits
tourism• Chamonix – skiing• Important industry• Vast amounts of money spent on roads, railways tunnelsavalanche shelters cable cars houses and restaurants• Tourist facilities benefit locals as well as providing jobs• Skiers, climbers, walkers, scenery• Glaciated mountains, snow capped peaks and forests• Lakes• Winter sports resorts• Alps – close to affluent parts of Europe• Alpine climate has good snowfall, crisp clear days for wintersports and warm summers
HEPSteep slopes, high perecipitation and summermelting of glaciers produce fast flowing riversthat are ideal for generating HEPNarrow valleys are easy to damLakes in which to store waterElectricity an be used by industries that uselarge amounts of electricity – saw mills,electro chemicals, aluminium smelting
forestry• Trees grow up to 1800m• Timber industry• Soft wood felled and used as fuel, for buildingand in the manufacture of wood pulp andpaper• Switzerland – craft industries – wood carving,cuckoo clocks
problems• High altitude and steep slopes mean it is hard tobuild houses, industries and communications• Roads and railways need expensivetunnels, passes, shelters and bends• Little flat land for farming, hard to use machinery• Cold wet climate – short growing season• Avalanches and rockfalls block roads• Need avalanche protection
Any 3 facts from Figure 1e.g. earthquakes occur in linear clusters (1), many occur on plateboundaries (1) especially destructive and/or conservative plateboundaries(1); with example (1). Clustering around edge of Pacificplate (1).Maximum 1 for negative
Precautions against earthquakesIndividuals Authorities Long term planningEmergency pack –water, food, blankets,first aid kit, radio andtorchMonitor hazard sopeople can be warnedEnsure road andrailways are built toreduce effects ofearthquakesShelter under table orbedHave emergencysupplies readyEnsure new buildingsare earthquake proofTurn off gas andelectricityMake plans for shelter,food and water suppliesand for emergencyservicesProvide education andadvertising so peopleknow what to do.After earthquake –move to open groundPlan to broadcastinformation for peopleaffected
1. Computer controlled movable roof weights to counter the shockwaves2. Steel frames that can sway during earth movements. Building needsto be stiff vertically but flexible horizontally3. ‘Birdcage’ interlocking steel frame, cross bracing to give addedstrength and prevent twisting4. Automatic window shutters to prevent falling glass5. Sheer core of reinforced concrete and tensioned cables around liftshaft6. Fire resistant building materials7. Outer panels flexibly attached to steel structure8. Automatic sprinkler system and gas shut off to prevent fires9. Strengthened steel and reinforced concrete road supports10. Foundations set deep into the ground11. Rubber shock absorbers to absorb earth tremors, foundation pilesmade out of alternative layers of steel and rubber to make buildingflexible12. Open areas where people can assemble if evacuated
Impact of earthquake• Depends on magnitude of earthquakeand density of the population in an area• Wealth - People and authorities inricher areas are generally moreprepared than those in poorer areas• Wealth means they are able to develop– Earthquake proof buildings– More effective emergency services– Speedier response
Tsunamis are caused by earthquakes at sea.Earthquakes happen when the plates that make up the Earths surface suddenlymove against each other.A tsunami forms when energy from an earthquakevertically jolts the seabed by several metres,displacing hundreds of cubic kilometres of water.Large waves begin moving through the ocean, awayfrom the earthquakes epicentre.In deep water, the tsunami moves at great speeds.When it reaches shallow water near coastal areas, thetsunami slows but increases in height.
Cause Effect Response9.1 Richter Scaleearthquakecaused by thesubduction of theIndo-Australian platebeneath the Eurasianplate.The sudden movementof the plate under thesea caused the giantwave 5-40 metreshigh, which first hitSumatra, then SriLanka and Thailand.Primary effects•>220,000 people died•650,000 seriously injured•2 million homeless•Many buildings were sweptaway by the waves as theywere made of wood•Roads, bridges and utilitiesdestroyedSecondary effects•Spread of diseases such ascholera, dysentery•Loss of coastal fishingindustries•Loss of tourism revenue fromareas such as Thailand•Many orphans left due tochildren surviving withoutparentsImmediate response:•Panic in the first instance; scale ofdisaster meant rescue services and couldnot cope.•Injured people were untreated for days.•Bodies left to rot in streets.•Immediate response from internationalaid agencies and governments, providingUS$7billion.•160 aid organisations and UN agencieshelped to provide food, shelter andmedical help•Provided water purification tablets, food,sheeting and tents.Longer term response•Governments struggled to spend all ofmoney donated, but progress made.•Banda Aceh in Sumatra rebuilt, althoughstill 60,000 Indonesians still living intents.•Indian Ocean Tsunami Warning systemwas set up June 2006 to try and givewarning of tsunamis with 39 tsunami buoys•289 hospitals been rebuilt orrehabilitated
Weathering and erosion work together.Weathering breaks up and weakens thesurface of rocks but leaves debris in situErosion wears away and removes theloosened material.
Mass movement: movement of materialdownhill due to the force of gravity. Can bevery slow eg soil creep, or fast eg mud-slide orrock fall or rotational slip causing slumping.Mass movement is increased if there is presenceof water to lubricate; also if there is novegetation holding slope in place.
Why are soft coastlines vulnerable torapid erosion?•Many parts of the UK have coastlines of softerrocks such as clay which is very susceptible toerosion and weathering.•These rocks do not have a strong structure andbecome unstable when wet•A combination of heavy rainfall soaking throughthe rock and wave attack at the base of thecliff may trigger slumping and landslides
June 2010Mass movement is a process affecting the coastal zone.Describe this process.(3 marks)Mass movement occurs when loose material on the landsurface (1) moves downslope (1) due to gravity (1)sliding and slumping (1).This is often fast and sudden (1) as with landslides (1)when the base of the cliff has been eroded, makingthe cliff unstable (1).With a landslide, the whole column of material moves inone go (1), slumping is similar, but this involves acurved movement (1).