Key term
OCR A-Level Geography H481
Coastal Landscapes
Topic overviewThe coastal system: inputs, outputs and flows of energy and materialSediment cells, the sediment budget and the sources of coastal sedimentWinds, fetch and the generation of wavesConstructive and destructive waves, and how waves breakTides, tidal range and ocean currentsLithology, geological structure and the plan of the coastWeathering and mass movement on the coastMarine erosion, transport and depositionBays, headlands, cliffs and shore platformsGeos, blow holes, caves, arches, stacks and stumpsBeaches and the changing beach profileSpits, bars, tombolos and salt marshesHigh and low energy coastlines as characteristic landscapesEmergent coasts: raised beaches, marine terraces and abandoned cliffsSubmergent coasts: rias, fjords and shingle beachesCoastal management and its effect on the sediment budgetPorts, tourism and unintended change at the coast
Glaciated Landscapes
Topic overviewThe glacier system: inputs, stores, flows and outputsGlacier mass balance and the equilibrium lineClimate, latitude and altitude as controls on glaciationGeology, relief and aspect in glaciated landscapesFirn, glacier ice, valley glaciers and ice sheetsWarm-based and cold-based ice, and the mechanisms of glacier movementWeathering, mass movement and nivation in cold environmentsGlacial erosion and the marks it leaves on rockEntrainment, transport and deposition of glacial sedimentCorries, arêtes and pyramidal peaksGlacial troughs, hanging valleys and ribbon lakesMoraines, erratics, drumlins and till sheetsCharacteristic glaciated landscapes and how they change over timeGlacio-fluvial landforms of deglaciation: kames, eskers and outwash plainsPermafrost, patterned ground and pingosPeople in periglacial landscapes: resource extraction and thermokarstPeople in glaciated landscapes: dams, reservoirs and valley change
Dryland Landscapes
Topic overviewDryland landscape systems: inputs, stores, flows and outputsAridity, the water balance and the UNEP aridity indexRainfall, pressure belts and the global pattern of aridityRock type and structure in dryland landscapesRelief, aspect and desert microclimatesSediment supply and the dryland sediment budgetPolar drylands and the cold desertsHot deserts of the low and mid latitudesSemi-arid environments and the desert marginsWeathering and mass movement in dryland landscapesFluvial and aeolian processes in the desertWadis, canyons, pedestal rocks, ventifacts and desert pavementsBarchans, linear dunes, star dunes, alluvial fans and bajadasThe Mojave and the Sahara as desert landscape systemsInselbergs, pediments and relict landforms of past pluvialsFrost-shattered debris, nivation hollows and solifluction depositsWater supply, dams and landscape changeTourism, off-road vehicles and landscape change
Earth’s Life Support Systems
Topic overviewWater and carbon as the foundations of life on EarthOpen and closed systems, and the major global stores of water and carbonInputs and outputs of the water cycle: precipitation, snowmelt and evapotranspirationInputs and outputs of the carbon cycle, and the forms of chemical weatheringEvaporation, transpiration, condensation and the causes of rainfallInterception, runoff and catchment hydrologyPhotosynthesis, respiration, decomposition and combustion as carbon flowsNatural sequestration in oceans, vegetation, sediments and rockStores, flows and physical controls in the tropical rainforestDeforestation, farming and forest management in an Amazon drainage basinStores, flows and seasonal change in the Arctic tundraOil and gas development in the Arctic tundra, and its managementDynamic equilibrium, land use change and water extractionFossil fuel combustion, carbon sequestration and feedback loopsChange over time in the cycles, and the monitoring that records itLinks and interdependence between the water and carbon cyclesGlobal strategies to protect the carbon and water cycles
Changing Spaces; Making Places
Topic overviewThe characteristics that shape a place profileContrasting place profiles: Chelsea and BlackpoolPast and present connections, and the scales that embed a placeShifting flows of people, resources, money and ideasSpace, place and the effects of time-space compressionPerception, identity and emotional attachment to placeInformal representations of place in media and the artsFormal and statistical representations of placeMeasuring social inequality and its spatial patternsDeindustrialisation, globalisation and structural economic changeRecession, austerity and the government's role in inequalityLiving with inequality: Sparkbrook and Sutton ColdfieldPlayers driving economic change at different scalesThe Ruhr: a region reshaped by structural economic changePlacemaking and the marketing of places to investorsDesign, mixed use and community-led placemakingRebranding through reimaging and regenerationSalford Quays: from docks to MediaCityUK
Trade in the Contemporary World
Topic overviewMerchandise, services and capital flowsGlobal trade patterns: inter-regional and intra-regional flowsTrade, export value and human developmentTrade as a driver of growth, stability and developmentTrade inequalities, conflict and injusticeTransport, technology and the global supply chainMultinationals, outsourcing and the new international division of labourRegional trading blocs and the European UnionSouth–south trade and the growth of traded servicesIndia: trade patterns of an emerging economyThe United States: a core economy shaping world tradeEthiopia: trade on the periphery of the global system
Global Migration
Topic overviewThe global migrant population: size, composition and direction of flowInter-regional and intra-regional flows, and the world's major migration corridorsRemittances, the Human Development Index and the migration-development linkMigration as a driver of stability, growth and developmentInequality, conflict and injustice in the global migration systemEconomic globalisation and the emergence of new source and host areasYoung workers, women migrants and the growth of South-South movementConflict, persecution and the world's refugee movementsNational immigration and emigration policy, and how it is changingMexico: an emerging economy shaped by a migration corridorThe United Kingdom: an advanced country driving change in the migration systemNepal: a low-income country with little leverage over its migration
Human Rights
Topic overviewThe idea of human rights and its legal foundationsNorms, intervention and geopoliticsForced labour and modern slaveryMaternal mortality and access to safe childbirthCapital punishment and where it persistsPatterns of gender inequality: schooling, reproductive health and workWomen's rights in IndiaHuman rights abuse as a cause and a consequence of conflictInstitutions, treaties and laws that protect human rightsGlobal governance of human rights in eastern DR CongoShort-term relief and long-term change in DR Congo
Power and Borders
Topic overviewStates, nations and the sovereign control of territoryNorms, intervention and geopoliticsContested borders and the legacy of colonial boundariesTransnational corporations and economic sovereigntyTrading blocs, supranational institutions and pooled sovereigntyEthnic dominance, minority marginalisation and separatismUkraine: sovereignty and territorial integrity under challengeResources, conflict and the causes of geopolitical instabilityGlobal institutions, international law and the flows that carry interventionSouth Sudan: governing a conflict from global to localShort-term and long-term outcomes of intervention for people and placesThe Democratic Republic of the Congo: global governance in an LIDC
Climate Change
Topic overviewReconstructing past climates from natural archivesIcehouse and greenhouse Earth, from Cenozoic cooling to the HoloceneContinental drift and volcanic activity as drivers of climateMilankovitch cycles and changes in solar outputThe natural greenhouse effect and the atmosphere's greenhouse gasesWarming of the surface, atmosphere and oceans since the late 19th centuryRetreating ice, shrinking snow cover and rising sea levelWhy greenhouse gas emissions have risen since the pre-industrial eraThe changing global balance of emissions, from an AC to an EDCThe enhanced greenhouse effect and the global energy balanceThe evolution of the global warming debateGovernments, international organisations and the media in the climate debateClimate models, the carbon cycle and feedbackFuture emission scenarios and projected temperature and sea level riseImpacts on ecosystems, health and extreme weatherThe vulnerability of people and environments to climate changeMitigation through energy efficiency, fuel shifts and low-carbon energyCarbon capture and storage, forestry strategies and geoengineeringRetreat, accommodation and protection as adaptationAdapted homes, cities, transport and economiesContrasting countries: impacts, opportunities and the challenges of respondingThe IPCC, international agreements and policy from global to local
Disease Dilemmas
Topic overviewWays of classifying disease, and the epidemic to pandemic scaleMapping the burden of malaria, HIV, tuberculosis, diabetes and heart diseaseDisease diffusion, the Hägerstrand model and the barriers that slow itTemperature, rainfall, relief and water supply as controls on diseaseMosquitoes, vectors and the seasonal rhythm of outbreaksClimate change, emerging infections and diseases that jump from animalsCholera in Haiti after the 2010 earthquakeRising living standards and the epidemiological transitionDiseases of poverty and diseases of affluenceAir pollution and lung cancer in ChinaMalaria in Nigeria: from causes to controlCardiovascular disease in the United KingdomThe World Health Organization and the surveillance of global outbreaksMédecins Sans Frontières and the West African Ebola epidemicPhysical barriers to treatment and the fight against HIV and AIDSMedicinal plants, their growing conditions and the trade that threatens themPharmaceutical transnationals and the global flow of medicinesEradication campaigns, grassroots education and the role of women
Exploring Oceans
Topic overviewThe size and spread of the world's oceansThe shape of the sea floor, from shelf to trenchSalinity and temperature through the water columnSurface currents and the great ocean gyresThe North Atlantic conveyor, from Gulf Stream to deep return flowLight, warmth and nutrients as limits on ocean lifeFood webs in the inter-tidal zone and the deep seaHarvesting Southern Ocean krillWhaling, stakeholder conflict and resource thresholdsOcean energy: oil, gas, waves and tidesMining the deep sea bed for metalsThe global commons, maritime zones and ocean governanceThe major sources of marine pollutionThe Deepwater Horizon oil spill and its aftermathDrifting plastic and the North Pacific garbage patchOcean acidification, warming seas and coral bleachingRising sea level and low-lying island communitiesSea ice, the albedo feedback and irreversible thresholdsThe changing Arctic: peoples, politics and new sea routesShipping lanes, container ships and seaborne tradeNaval power and contested seasPiracy and migration by sea
Future of Food
Topic overviewFood security and its three pillarsMeasuring hunger: undernourishment data and food security indicesShifting patterns of food security between and within countriesClimate, soil, water and relief as controls on where food can be grownThe journey of food from farm to plate, and the waste it leavesTypes of farming: intensive, extensive, subsistence and commercialGlobalisation, rising demand and global tastesThe issues and opportunities of a globalised food industryLand ownership, competition and land grabbingMalthus, Boserup and the population–resource debateYemen: conflict, aridity and the collapse of food accessVulnerable people and the pinchpoints in global food distributionDesertification and the drylands of the SahelExtreme weather, water scarcity and tectonic shocks to food productionInuit hunting and food security in the ArcticSalinisation, deforestation and agrochemical pollution from farmingThe Aral Sea: a landscape remade by irrigationHealth effects of hunger, over-nutrition and agrochemical exposureMalawi and the United States: contrasting experiences of food insecurityTrade policy, the World Trade Organization and appropriate aidAgribusiness, food TNCs, supermarkets and fair tradeFrom emergency relief to capacity building and system redesign
Hazardous Earth
Topic overviewThe Earth's internal structure and the global pattern of platesContinental drift and the evidence from fossils, rocks and ancient glaciationsSea-floor spreading, palaeomagnetism and the age of the ocean floorDivergent boundaries and the landforms of the mid-ocean ridgesSubduction at oceanic-continental and oceanic-oceanic boundariesContinental collision and conservative boundariesMagma chemistry, viscosity and explosive volcanism at subduction zonesEffusive eruptions, shield volcanoes and hot-spot volcanismVolcano size and shape, super-volcanoes and the Volcanic Explosivity IndexLava flows, pyroclastic flows and volcanic gasesTephra, ashfall, lahars and volcanic tsunamisEarthquake focus, depth and the seismic waves releasedMeasuring earthquakes: Richter, moment magnitude and Mercalli intensityFault scarps, rift valleys and the landscapes faulting createsGround shaking, ground displacement and liquefactionEarthquake-triggered landslides, avalanches and floodingTsunamis from sea-bed uplift and underwater landslidesWhy people choose to live in tectonically active placesThe impacts of volcanic eruptions in countries at contrasting levels of developmentThe impacts of earthquakes in countries at contrasting levels of developmentPredicting, monitoring and managing volcanic hazardsLand-use zoning, building design and managing earthquake riskChanging risk over time and the disaster risk equationThe Park model of disaster response
Geographical Skills
Topic overviewGeographical data, its types and the ethics of using itCollecting data: sampling, measurement error and digital devicesQualitative methods, sources and drawing conclusionsMeasures of central tendency and dispersionCorrelation, lines of best fit and Spearman's rankSignificance tests: chi-squared, Mann-Whitney U and the t-testClimate graphs, maps and graphical techniques
Hazardous Earth
Magma chemistry, viscosity and explosive volcanism at subduction zones
- 2 things to know
- Component 03
Overview
Recall questions on viscosity and what controls it, the silica content of basaltic, andesitic and rhyolitic magma, temperature, why viscous magma erupts explosively, water from the subducting plate, composite volcanoes, Plinian, Peléean and Strombolian eruptions, Mount St Helens in 1980, and lava domes.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
What is viscosity, and what does it control in an eruption?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is viscosity, and what does it control in an eruption?
Model answer
Viscosity is a liquid's resistance to flow, and in magma it controls how easily gas can escape and therefore how explosive the eruption will be.
- 2
Which three properties of magma determine its viscosity?
Model answer
Its silica content, its temperature and its dissolved gas content.
- 3
How does silica content affect the viscosity of magma?
Model answer
Silica molecules link into long chains that tangle together, so the more silica the magma contains the stiffer and more viscous it becomes.
- 4
State the approximate silica content of basaltic magma.
Model answer
Roughly 45 to 52%.
- 5
State the approximate silica content of rhyolitic magma.
Model answer
About 70% or more.
- 6
Which magma type is typical of subduction-zone volcanoes?
Model answer
Andesitic magma, with an intermediate silica content of roughly 57 to 63%.
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