Geography — UK A-Level
Comprehensive UK A-Level Geography flashcards (AQA/Edexcel/OCR) covering physical geography (water and carbon cycles, coasts, glaciation, hazards, ecosystems) and human geography (globalisation, changing places, urban environments, population, resources, development, superpowers), plus geographical skills and statistical methods.
Ämne: Geografi · Nivå: Gymnasium (16–19) · 400 kort
Innehåll
- A system is a set of interrelated components working together. An OPEN system (like a drainage basin) has both energy AND matter crossing its boundaries; a CLOSED system (like the global water cycle) has only energy crossing its boundaries, not matter.
- A drainage basin is an OPEN system. Inputs = precipitation. Outputs = evaporation, transpiration (combined as evapotranspiration), river discharge to the sea, and percolation to deep groundwater. Stores and flows operate within the system boundary (the watershed).
- The watershed is the boundary of a drainage basin — the imaginary line of high ground (ridge) separating one drainage basin from an adjacent one. Precipitation falling on either side flows into different basins.
- Interception is the capture of precipitation by vegetation before it reaches the ground. Interception loss is the water that evaporates from leaf surfaces without ever reaching the soil. It is greatest in dense forests and at the start of a rainfall event.
- Infiltration is the movement of water from the surface into the soil. Infiltration capacity is the maximum rate at which soil can absorb water. When rainfall intensity exceeds infiltration capacity, the excess flows over the surface as overland flow (surface runoff).
- Percolation is the downward movement of water from the soil into the underlying permeable rock (bedrock), recharging groundwater. It is generally slower than infiltration and depends on rock porosity and permeability.
- Throughflow is the lateral (sideways) movement of water through the soil downslope towards a river channel. Groundwater flow (baseflow) is the very slow movement of water through permeable rock; it sustains river flow during dry periods.
- The water table is the upper surface of the zone of saturation, where all pore spaces in rock/soil are filled with water. It rises after prolonged rainfall and falls during droughts. Springs form where the water table intersects the ground surface.
- Global water store distribution: oceans hold ~97% of all water. Of the ~3% freshwater, most is locked in ice caps and glaciers (~69% of freshwater) and groundwater (~30%); rivers, lakes and the atmosphere together hold less than 1% of freshwater.
- Residence time is the average time a water molecule spends in a particular store. It ranges from about 9 days in the atmosphere, to weeks in rivers, to thousands of years in deep groundwater and tens of thousands of years in ice sheets and the deep ocean.
- Cryospheric water is water held as ice: sea ice, ice sheets, ice caps, alpine glaciers and permafrost. Cryospheric stores were largest during glacial periods (Pleistocene), when sea levels were ~120 m lower because so much water was locked up as ice.
- Evaporation is the change of state of water from liquid to gas, requiring energy (latent heat). It depends on temperature, wind speed, humidity and the amount of available water. Transpiration is water loss through stomata in plant leaves. Together they form evapotranspiration.
- Three types of precipitation by uplift mechanism: convectional (sun heats ground, air rises, common in tropics and UK summer storms), orographic/relief (air forced up over hills/mountains), and frontal/cyclonic (warm air rises over cold air at a weather front).
- Dynamic equilibrium describes a system in balance where inputs equal outputs over time, so stores remain roughly constant despite continuous flows. Short-term disruptions (e.g. a storm, deforestation) are countered by negative feedback that restores balance.
- Negative feedback dampens change and restores equilibrium (self-regulating). Positive feedback amplifies change, pushing the system further from its original state. Example of positive feedback: ice-albedo — melting ice exposes dark surfaces that absorb more heat, causing more melting.
- The four main carbon stores are: the lithosphere (largest — carbon in sedimentary rocks like limestone, plus fossil fuels), the hydrosphere (oceans, the largest active store), the atmosphere (CO₂ and methane), and the biosphere (living organisms, soil and dead organic matter).
- The slow (geological) carbon cycle operates over millions of years and moves carbon between rocks, oceans and atmosphere via weathering, sedimentation, burial and volcanic outgassing. It cycles roughly 10–100 million tonnes of carbon per year.
- The fast (biological) carbon cycle operates over days to thousands of years via photosynthesis, respiration, decomposition and combustion, exchanging carbon between the atmosphere, biosphere and oceans. It moves far more carbon per year than the slow cycle.
- Photosynthesis transfers carbon from the atmosphere (CO₂) into the biosphere, fixing it as glucose/biomass using sunlight. Respiration and decomposition return carbon to the atmosphere as CO₂. Combustion (burning biomass or fossil fuels) also releases stored carbon.
- The oceanic carbon pump: the physical (solubility) pump dissolves CO₂ in cold polar surface water that sinks to the deep ocean; the biological pump fixes carbon via phytoplankton photosynthesis, which sinks as dead organic matter (the 'marine snow') to the seabed.
- Carbon sequestration in rocks: marine organisms (e.g. corals, shellfish, foraminifera) build calcium carbonate (CaCO₃) shells. When they die, shells sink and accumulate, eventually forming limestone — locking carbon away in the lithosphere for millions of years.
- Tropical rainforests are vital carbon stores, holding around 25% of terrestrial carbon. Deforestation reduces this store by releasing carbon through burning/decay and removing future photosynthetic uptake — a key human disruption to the carbon cycle.
- Atmospheric CO₂ has risen from ~280 ppm pre-industrial (1750) to over 420 ppm today, driven by fossil fuel combustion, deforestation and cement production. This intensifies the natural greenhouse effect and drives global warming.
- The terrestrial carbon pump links the water and carbon cycles: plants take up CO₂ and release water vapour via transpiration. Warmer climates can increase plant growth (carbon uptake) but also raise respiration and decomposition rates, complicating the net effect.
- Permafrost is a major frozen carbon store. As Arctic temperatures rise, permafrost thaws and microbial decomposition of stored organic matter releases CO₂ and methane (CH₄) — a positive feedback that accelerates warming.
- A coast can be viewed as a system with inputs (energy from waves, wind, tides, currents; sediment), processes (erosion, transport, deposition, weathering, mass movement), and outputs (sediment lost to the sea or deposited beyond the system). The littoral zone is the area of interaction between land and sea.
- A sediment cell (littoral cell) is a largely self-contained stretch of coastline where sediment movement is mostly enclosed, with boundaries often at major headlands. England and Wales are divided into 11 sediment cells, used as the basis for Shoreline Management Plans.
- Sediment budget is the balance between sediment inputs (sources) and outputs (sinks) within a sediment cell. A positive budget means net accretion (the coast builds out); a negative budget means net erosion (the coast retreats).
- Constructive waves have a strong swash and weak backwash, low height and long wavelength, with a low frequency (6–8 per minute). They deposit sediment and build up beaches. Destructive waves have weak swash, strong backwash, are tall and steep with high frequency (10–14 per minute), and erode beaches.
- Swash is the movement of water up the beach after a wave breaks; backwash is the return of water down the beach under gravity. The balance between swash and backwash determines whether a wave is constructive (net deposition) or destructive (net erosion).
- The four marine erosion processes: hydraulic action (force of water/air compressed in cracks), abrasion/corrasion (waves hurl sediment at the cliff), attrition (rocks knock together and become smaller and rounder), and solution/corrosion (chemical dissolving of soluble rock like limestone).
- The four marine transport processes: traction (large boulders rolled along the seabed), saltation (smaller pebbles bounced along), suspension (fine sediment carried within the water), and solution (dissolved material carried chemically).
- Longshore drift moves sediment along a coast. Waves approach the beach at an angle (driven by prevailing wind) so swash carries sediment up the beach obliquely; backwash returns it straight down under gravity. Repeated, this produces a net zigzag movement of sediment along the shore.
- Erosional landforms on a discordant coast: a headland (resistant rock) erodes through cracks to form a cave, then a wave-cut arch, which collapses to leave a stack, which is undercut to form a lower stump. Classic UK example: Old Harry Rocks (chalk), Dorset.
- A wave-cut platform forms when waves erode the base of a cliff, creating a wave-cut notch. The overhang collapses and the cliff retreats landward, leaving a gently sloping rocky platform exposed at low tide where the cliff once stood.
- A concordant coast has alternating rock bands running parallel to the coastline; a discordant coast has bands running at right angles to it. Discordant coasts produce headlands and bays through differential erosion. Dorset's coast shows both (e.g. Lulworth Cove on the concordant section).
- A spit is a depositional landform: a long ridge of sand/shingle extending from the coast across a bay or estuary, formed by longshore drift. A change in wind direction can curve (recurve) the end, forming a hooked spit. Example: Spurn Head, Holderness coast.
- A tombolo is a bar of sediment connecting the mainland to an offshore island (e.g. Chesil Beach links to the Isle of Portland, Dorset). A bar forms when a spit grows across a bay, sealing off a lagoon behind it.
- Salt marshes develop in sheltered, low-energy environments (behind spits, in estuaries). Fine sediment settles, halophytic (salt-tolerant) plants like Spartina colonise and trap more sediment, raising the surface. They are important carbon sinks and natural coastal buffers.
- Sand dunes form a succession (psammosere): embryo dunes → fore dunes → yellow dunes → grey dunes → dune slacks. Marram grass is a key pioneer that stabilises sand and traps more, allowing the succession to develop landward away from the sea.
- Eustatic sea-level change is a global change in the volume of water in the oceans (e.g. from melting ice or thermal expansion). Isostatic change is a local change in land level relative to the sea (e.g. land rising after ice sheets melt — isostatic rebound).
- Emergent coastlines (from falling sea level / land rising) produce landforms such as raised beaches and relict (abandoned) cliffs. Submergent coastlines (from rising sea level / land sinking) produce rias (drowned river valleys), fjords (drowned glacial valleys) and Dalmatian coasts.
- A ria is a drowned, unglaciated river valley with a V-shaped cross-section and a winding, gradually deepening profile (e.g. Kingsbridge Estuary, Devon). A fjord is a drowned glacial valley with a U-shaped cross-section, steep walls and a shallow entrance (threshold), as in Norway.
- Hard engineering coastal defences use built structures to resist the sea: sea walls, groynes (trap longshore drift sediment), rock armour/riprap (boulders absorbing wave energy), gabions (wire cages of rock), and revetments. They are effective but expensive and can disrupt natural processes downdrift.
- Soft engineering coastal defences work with natural processes: beach nourishment (adding sediment), dune regeneration/stabilisation, marsh creation, and cliff regrading. They are cheaper and more sustainable but need ongoing maintenance and may offer less protection in extreme storms.
- Managed retreat (managed realignment) deliberately allows the sea to flood low-value land, creating new salt marsh that absorbs wave energy and protects land behind. It is a key part of Shoreline Management Plans where 'hold the line' is too costly. Example: Medmerry, West Sussex (2013).
- Shoreline Management Plans (SMPs) set policy for each coastal stretch using four options: hold the line, advance the line, managed realignment, and no active intervention (do nothing). Decisions weigh cost-benefit analysis and the value of land and assets at risk.
- The Holderness coast (East Yorkshire) is the fastest-eroding coastline in Europe, retreating ~1.8 m per year on average. The soft boulder clay (glacial till) is easily eroded, and defences at Hornsea/Mappleton starve beaches downdrift, accelerating erosion there (terminal groyne effect).
- A glacial system has inputs (snowfall in the accumulation zone), throughputs (ice movement), and outputs (melting/ablation in the ablation zone). The glacier mass balance (budget) is the difference between accumulation and ablation; a positive balance makes the glacier advance, a negative one makes it retreat.
- The equilibrium line on a glacier separates the accumulation zone (above, net gain of ice) from the ablation zone (below, net loss). It marks where annual accumulation exactly equals annual ablation. It moves up-glacier in warm years and down-glacier in cold ones.