Describe the shape of a barchan.

A barchan is crescent-shaped, with a gentle convex windward slope, a steep concave slip face on the lee side, and two horns extending downwind.

Why do the horns of a barchan point downwind?

The sand is thinner at the edges of the dune, so those parts are driven forward faster than the thicker, higher centre and become trailing horns.

State the typical angle of a dune slip face.

A slip face typically stands at about 32 to 34°, the angle of repose of dry sand.

How does a barchan migrate?

Sand saltates up the gentle windward slope to the crest and then avalanches down the lee slip face, so the whole dune advances downwind while keeping its shape.

Why do smaller barchans migrate faster than larger ones?

A small barchan contains far less sand, so the same rate of transfer across its crest shifts the whole dune further; small barchans may advance tens of metres a year while large ones move only a few.

OCR A-Level Geography H481

Coastal Landscapes

Topic overview The coastal system: inputs, outputs and flows of energy and material Sediment cells, the sediment budget and the sources of coastal sediment Winds, fetch and the generation of waves Constructive and destructive waves, and how waves break Tides, tidal range and ocean currents Lithology, geological structure and the plan of the coast Weathering and mass movement on the coast Marine erosion, transport and deposition Bays, headlands, cliffs and shore platforms Geos, blow holes, caves, arches, stacks and stumps Beaches and the changing beach profile Spits, bars, tombolos and salt marshes High and low energy coastlines as characteristic landscapes Emergent coasts: raised beaches, marine terraces and abandoned cliffs Submergent coasts: rias, fjords and shingle beaches Coastal management and its effect on the sediment budget Ports, tourism and unintended change at the coast

Glaciated Landscapes

Topic overview The glacier system: inputs, stores, flows and outputs Glacier mass balance and the equilibrium line Climate, latitude and altitude as controls on glaciation Geology, relief and aspect in glaciated landscapes Firn, glacier ice, valley glaciers and ice sheets Warm-based and cold-based ice, and the mechanisms of glacier movement Weathering, mass movement and nivation in cold environments Glacial erosion and the marks it leaves on rock Entrainment, transport and deposition of glacial sediment Corries, arêtes and pyramidal peaks Glacial troughs, hanging valleys and ribbon lakes Moraines, erratics, drumlins and till sheets Characteristic glaciated landscapes and how they change over time Glacio-fluvial landforms of deglaciation: kames, eskers and outwash plains Permafrost, patterned ground and pingos People in periglacial landscapes: resource extraction and thermokarst People in glaciated landscapes: dams, reservoirs and valley change

Dryland Landscapes

Topic overview Dryland landscape systems: inputs, stores, flows and outputs Aridity, the water balance and the UNEP aridity index Rainfall, pressure belts and the global pattern of aridity Rock type and structure in dryland landscapes Relief, aspect and desert microclimates Sediment supply and the dryland sediment budget Polar drylands and the cold deserts Hot deserts of the low and mid latitudes Semi-arid environments and the desert margins Weathering and mass movement in dryland landscapes Fluvial and aeolian processes in the desert Wadis, canyons, pedestal rocks, ventifacts and desert pavements Barchans, linear dunes, star dunes, alluvial fans and bajadas The Mojave and the Sahara as desert landscape systems Inselbergs, pediments and relict landforms of past pluvials Frost-shattered debris, nivation hollows and solifluction deposits Water supply, dams and landscape change Tourism, off-road vehicles and landscape change

Earth’s Life Support Systems

Topic overview Water and carbon as the foundations of life on Earth Open and closed systems, and the major global stores of water and carbon Inputs and outputs of the water cycle: precipitation, snowmelt and evapotranspiration Inputs and outputs of the carbon cycle, and the forms of chemical weathering Evaporation, transpiration, condensation and the causes of rainfall Interception, runoff and catchment hydrology Photosynthesis, respiration, decomposition and combustion as carbon flows Natural sequestration in oceans, vegetation, sediments and rock Stores, flows and physical controls in the tropical rainforest Deforestation, farming and forest management in an Amazon drainage basin Stores, flows and seasonal change in the Arctic tundra Oil and gas development in the Arctic tundra, and its management Dynamic equilibrium, land use change and water extraction Fossil fuel combustion, carbon sequestration and feedback loops Change over time in the cycles, and the monitoring that records it Links and interdependence between the water and carbon cycles Global strategies to protect the carbon and water cycles

Changing Spaces; Making Places

Topic overview The characteristics that shape a place profile Contrasting place profiles: Chelsea and Blackpool Past and present connections, and the scales that embed a place Shifting flows of people, resources, money and ideas Space, place and the effects of time-space compression Perception, identity and emotional attachment to place Informal representations of place in media and the arts Formal and statistical representations of place Measuring social inequality and its spatial patterns Deindustrialisation, globalisation and structural economic change Recession, austerity and the government's role in inequality Living with inequality: Sparkbrook and Sutton Coldfield Players driving economic change at different scales The Ruhr: a region reshaped by structural economic change Placemaking and the marketing of places to investors Design, mixed use and community-led placemaking Rebranding through reimaging and regeneration Salford Quays: from docks to MediaCityUK

Trade in the Contemporary World

Topic overview Merchandise, services and capital flows Global trade patterns: inter-regional and intra-regional flows Trade, export value and human development Trade as a driver of growth, stability and development Trade inequalities, conflict and injustice Transport, technology and the global supply chain Multinationals, outsourcing and the new international division of labour Regional trading blocs and the European Union South–south trade and the growth of traded services India: trade patterns of an emerging economy The United States: a core economy shaping world trade Ethiopia: trade on the periphery of the global system

Global Migration

Topic overview The global migrant population: size, composition and direction of flow Inter-regional and intra-regional flows, and the world's major migration corridors Remittances, the Human Development Index and the migration-development link Migration as a driver of stability, growth and development Inequality, conflict and injustice in the global migration system Economic globalisation and the emergence of new source and host areas Young workers, women migrants and the growth of South-South movement Conflict, persecution and the world's refugee movements National immigration and emigration policy, and how it is changing Mexico: an emerging economy shaped by a migration corridor The United Kingdom: an advanced country driving change in the migration system Nepal: a low-income country with little leverage over its migration

Human Rights

Topic overview The idea of human rights and its legal foundations Norms, intervention and geopolitics Forced labour and modern slavery Maternal mortality and access to safe childbirth Capital punishment and where it persists Patterns of gender inequality: schooling, reproductive health and work Women's rights in India Human rights abuse as a cause and a consequence of conflict Institutions, treaties and laws that protect human rights Global governance of human rights in eastern DR Congo Short-term relief and long-term change in DR Congo

Power and Borders

Topic overview States, nations and the sovereign control of territory Norms, intervention and geopolitics Contested borders and the legacy of colonial boundaries Transnational corporations and economic sovereignty Trading blocs, supranational institutions and pooled sovereignty Ethnic dominance, minority marginalisation and separatism Ukraine: sovereignty and territorial integrity under challenge Resources, conflict and the causes of geopolitical instability Global institutions, international law and the flows that carry intervention South Sudan: governing a conflict from global to local Short-term and long-term outcomes of intervention for people and places The Democratic Republic of the Congo: global governance in an LIDC

Climate Change

Topic overview Reconstructing past climates from natural archives Icehouse and greenhouse Earth, from Cenozoic cooling to the Holocene Continental drift and volcanic activity as drivers of climate Milankovitch cycles and changes in solar output The natural greenhouse effect and the atmosphere's greenhouse gases Warming of the surface, atmosphere and oceans since the late 19th century Retreating ice, shrinking snow cover and rising sea level Why greenhouse gas emissions have risen since the pre-industrial era The changing global balance of emissions, from an AC to an EDC The enhanced greenhouse effect and the global energy balance The evolution of the global warming debate Governments, international organisations and the media in the climate debate Climate models, the carbon cycle and feedback Future emission scenarios and projected temperature and sea level rise Impacts on ecosystems, health and extreme weather The vulnerability of people and environments to climate change Mitigation through energy efficiency, fuel shifts and low-carbon energy Carbon capture and storage, forestry strategies and geoengineering Retreat, accommodation and protection as adaptation Adapted homes, cities, transport and economies Contrasting countries: impacts, opportunities and the challenges of responding The IPCC, international agreements and policy from global to local

Disease Dilemmas

Topic overview Ways of classifying disease, and the epidemic to pandemic scale Mapping the burden of malaria, HIV, tuberculosis, diabetes and heart disease Disease diffusion, the Hägerstrand model and the barriers that slow it Temperature, rainfall, relief and water supply as controls on disease Mosquitoes, vectors and the seasonal rhythm of outbreaks Climate change, emerging infections and diseases that jump from animals Cholera in Haiti after the 2010 earthquake Rising living standards and the epidemiological transition Diseases of poverty and diseases of affluence Air pollution and lung cancer in China Malaria in Nigeria: from causes to control Cardiovascular disease in the United Kingdom The World Health Organization and the surveillance of global outbreaks Médecins Sans Frontières and the West African Ebola epidemic Physical barriers to treatment and the fight against HIV and AIDS Medicinal plants, their growing conditions and the trade that threatens them Pharmaceutical transnationals and the global flow of medicines Eradication campaigns, grassroots education and the role of women

Exploring Oceans

Topic overview The size and spread of the world's oceans The shape of the sea floor, from shelf to trench Salinity and temperature through the water column Surface currents and the great ocean gyres The North Atlantic conveyor, from Gulf Stream to deep return flow Light, warmth and nutrients as limits on ocean life Food webs in the inter-tidal zone and the deep sea Harvesting Southern Ocean krill Whaling, stakeholder conflict and resource thresholds Ocean energy: oil, gas, waves and tides Mining the deep sea bed for metals The global commons, maritime zones and ocean governance The major sources of marine pollution The Deepwater Horizon oil spill and its aftermath Drifting plastic and the North Pacific garbage patch Ocean acidification, warming seas and coral bleaching Rising sea level and low-lying island communities Sea ice, the albedo feedback and irreversible thresholds The changing Arctic: peoples, politics and new sea routes Shipping lanes, container ships and seaborne trade Naval power and contested seas Piracy and migration by sea

Future of Food

Topic overview Food security and its three pillars Measuring hunger: undernourishment data and food security indices Shifting patterns of food security between and within countries Climate, soil, water and relief as controls on where food can be grown The journey of food from farm to plate, and the waste it leaves Types of farming: intensive, extensive, subsistence and commercial Globalisation, rising demand and global tastes The issues and opportunities of a globalised food industry Land ownership, competition and land grabbing Malthus, Boserup and the population–resource debate Yemen: conflict, aridity and the collapse of food access Vulnerable people and the pinchpoints in global food distribution Desertification and the drylands of the Sahel Extreme weather, water scarcity and tectonic shocks to food production Inuit hunting and food security in the Arctic Salinisation, deforestation and agrochemical pollution from farming The Aral Sea: a landscape remade by irrigation Health effects of hunger, over-nutrition and agrochemical exposure Malawi and the United States: contrasting experiences of food insecurity Trade policy, the World Trade Organization and appropriate aid Agribusiness, food TNCs, supermarkets and fair trade From emergency relief to capacity building and system redesign

Hazardous Earth

Topic overview The Earth's internal structure and the global pattern of plates Continental drift and the evidence from fossils, rocks and ancient glaciations Sea-floor spreading, palaeomagnetism and the age of the ocean floor Divergent boundaries and the landforms of the mid-ocean ridges Subduction at oceanic-continental and oceanic-oceanic boundaries Continental collision and conservative boundaries Magma chemistry, viscosity and explosive volcanism at subduction zones Effusive eruptions, shield volcanoes and hot-spot volcanism Volcano size and shape, super-volcanoes and the Volcanic Explosivity Index Lava flows, pyroclastic flows and volcanic gases Tephra, ashfall, lahars and volcanic tsunamis Earthquake focus, depth and the seismic waves released Measuring earthquakes: Richter, moment magnitude and Mercalli intensity Fault scarps, rift valleys and the landscapes faulting creates Ground shaking, ground displacement and liquefaction Earthquake-triggered landslides, avalanches and flooding Tsunamis from sea-bed uplift and underwater landslides Why people choose to live in tectonically active places The impacts of volcanic eruptions in countries at contrasting levels of development The impacts of earthquakes in countries at contrasting levels of development Predicting, monitoring and managing volcanic hazards Land-use zoning, building design and managing earthquake risk Changing risk over time and the disaster risk equation The Park model of disaster response

Geographical Skills

Topic overview Geographical data, its types and the ethics of using it Collecting data: sampling, measurement error and digital devices Qualitative methods, sources and drawing conclusions Measures of central tendency and dispersion Correlation, lines of best fit and Spearman's rank Significance tests: chi-squared, Mann-Whitney U and the t-test Climate graphs, maps and graphical techniques

Dryland Landscapes

Barchans, linear dunes, star dunes, alluvial fans and bajadas

2 things to know
Component 01

Overview

Recall questions on the conditions, shape and migration of barchans, slip faces, linear dunes and star dunes, alluvial fans and their sorting, bajadas, and fieldwork methods for measuring dune shape, barchan migration, fan sorting and geo-spatial mapping.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Describe the form of a linear dune.

Key term

What conditions produce a barchan dune?

Questions from this subtopic

Each one with the model answer underneath.

1
What conditions produce a barchan dune?
Model answer
A limited supply of sand lying on a firm, flat surface, combined with winds blowing consistently from a single direction, produces barchans.
2
Describe the shape of a barchan.
Model answer
A barchan is crescent-shaped, with a gentle convex windward slope, a steep concave slip face on the lee side, and two horns extending downwind.
3
Why do the horns of a barchan point downwind?
Model answer
The sand is thinner at the edges of the dune, so those parts are driven forward faster than the thicker, higher centre and become trailing horns.
4
State the typical angle of a dune slip face.
Model answer
A slip face typically stands at about 32 to 34°, the angle of repose of dry sand.
5
How does a barchan migrate?
Model answer
Sand saltates up the gentle windward slope to the crest and then avalanches down the lee slip face, so the whole dune advances downwind while keeping its shape.
6
Why do smaller barchans migrate faster than larger ones?
Model answer
A small barchan contains far less sand, so the same rate of transfer across its crest shifts the whole dune further; small barchans may advance tens of metres a year while large ones move only a few.

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Coastal Landscapes

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Earth’s Life Support Systems

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Hotter magma is .

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AThe lower quartile is the 2nd value, 11 cm.

BThe upper quartile is the 6th value, 16 cm.

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