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GGe

Geography

AQA · 8035 · Paper 1 · Living with the physical environment

Paper 1 · 88 marks · 1 hour 30 minutes. Answer every question in Section A (Hazards, 33 marks including 3 for SPaG) and Section B (Living World, 25 marks). In Section C, answer two of the three: if you studied coasts and rivers, answer Q3 Coasts and Q4 Rivers and skip Q5 Glaciers.
ATc

Tectonic hazards

Natural hazards and risk

  • Natural hazard: an extreme natural event that could harm people or damage property. It's only a hazard if people live there. A natural disaster is one that has already happened.
  • Three types: atmospheric (weather), geological (land moving), flooding (water).
  • Hazard risk = the chance of being affected. It depends on location, wealth (HICs afford protection and monitoring but have more valuable property), education (e.g. earthquake drills in Japanese schools), urbanisation (more people and tall buildings close together) and climate change (more sea above 26 °C).

Plate tectonics

  • Earth: core (hottest), mantle (magma), crust (solid rock), split into tectonic plates. Continental plates are thicker and less dense; oceanic plates are thinner and denser.
  • Plates move because of convection currents in the mantle: magma near the core heats, rises, spreads under the crust, cools and sinks. Higher grades: also ridge push and slab pull (gravity).
  • Earthquakes and volcanoes are in belts along plate margins, e.g. the Pacific Ring of Fire and the Mid-Atlantic Ridge. Some aren't, like Hawaii.
MarginMovementWhat happensHazards
ConstructiveTwo plates move apartMagma rises through gaps, cools to form new crustGentle eruptions; small earthquakes
DestructiveOceanic and continental move togetherDenser oceanic plate subducts and melts; magma rises violently. Friction builds pressure, then the plates slipExplosive eruptions; strong earthquakes; tsunamis
ConservativePlates slide past each otherFriction builds pressure, then a sudden slipStrong earthquakes; no volcanoes

Effects and responses

  • Primary effects are caused by the hazard itself (ground shaking: deaths, collapsed buildings). Secondary effects are caused by the primary effects (tsunami, landslides, fires, homelessness, disease).
  • Immediate responses: hours to weeks, temporary (rescue, aid, shelters). Long-term responses: months to years, permanent (rebuilding, new laws, warning systems).

Why people live with the risk

  • Geothermal energy is cheap (65% of Iceland's energy).
  • Fertile volcanic soil for farming (olives around Mt Vesuvius).
  • Minerals to mine (copper at Mt St Helens).
  • Tourism (Hawaii's tourism worth over $15 billion).
  • Family and friends, lack of money to move, or the risk feels managed.

Reducing the risk: monitoring, prediction, planning, protection

EarthquakesVolcanoes
MonitoringSeismometers detect foreshocksTiltmeters detect the ground bulging as magma rises
PredictionCan't predict when, only where (plate margins)Satellite thermal maps show the volcano heating up
PlanningEvacuation routes, drills, survival kits, stored emergency supplies
ProtectionWide-base buildings, shock absorbers in foundations, counterweightsSloped roofs so ash slides off; trenches to divert lava

In depth: how volcanoes form

At a destructive margin (e.g. the Nazca and South American plates, the Andes):

  1. A dense oceanic plate moves towards a less dense continental plate.
  2. The oceanic plate is forced down into the mantle: this is subduction. The area where it sinks is the subduction zone.
  3. Friction and the heat of the mantle make the subducting plate melt into magma. Water carried down with the plate lowers the melting point.
  4. The new magma is less dense than the rock around it, so it rises through cracks in the continental crust.
  5. Pressure builds in a magma chamber under the surface. The magma is thick and sticky (viscous) and full of gas.
  6. When the pressure is too great, it erupts explosively, forming a steep-sided composite volcano made of layers of ash and lava.

Hazards: pyroclastic flows (fast, very hot clouds of gas and rock), ash falls, lahars (mudflows of ash and water), lava bombs and toxic gases.

At a constructive margin (e.g. Iceland on the Mid-Atlantic Ridge):

  1. Two plates move apart, pulled by convection currents (and slab pull elsewhere on the plates).
  2. The pressure drops in the gap, so mantle rock melts and magma rises to fill it.
  3. The magma is runny (low viscosity) with little gas, so eruptions are gentle and effusive.
  4. Lava flows a long way before cooling, building wide, gently sloping shield volcanoes and new oceanic crust.

In depth: how earthquakes happen

  1. Plates try to move past, towards or away from each other, but friction makes them stick.
  2. Stress (pressure) builds up in the rocks over years or centuries.
  3. Eventually the stress is greater than the friction and the rocks suddenly slip.
  4. Energy is released at the focus (the point underground) and travels out as seismic waves.
  5. The epicentre is the point on the surface directly above the focus, where shaking is usually strongest.

Strength is measured on the moment magnitude scale; each whole number is about 32 times more energy. Shallow-focus earthquakes cause more damage than deep ones.

Tsunamis form at destructive margins: the sea bed suddenly lifts as the plates slip, pushing up the water above. The wave travels fast across the ocean and grows tall as it reaches shallow water near the coast (e.g. Japan 2011).

In depth: why effects differ between places

  • Wealth: HICs can afford earthquake-proof buildings, warning systems and fast rescue (Japan 2011: ~16 000 deaths from a 9.0 earthquake and tsunami). LICs often can't (Nepal 2015: ~9 000 deaths from a 7.8 earthquake).
  • Building quality and enforcing building codes.
  • Preparedness: drills, education, emergency supplies.
  • Physical factors: magnitude, depth of the focus, distance from the epicentre, ground type, time of day, remoteness (Nepal's mountain villages were cut off by landslides).
  • Population density: more people near the epicentre means more people affected.
9-mark plan: "To what extent do the effects of earthquakes depend on a country's level of development?"
  1. Point 1, development matters: compare Japan (HIC) and Nepal (LIC) with deaths and how fast each responded.
  2. Point 2, why: building codes, warning systems, money for rebuilding.
  3. Point 3, but other factors matter: Japan still had huge losses from the tsunami (secondary effect) and the Fukushima disaster; magnitude, depth and terrain also count.
  4. Judgement: "Development is the most important factor because…, although physical factors decide how big the event is in the first place."
AWt

Weather hazards

Global atmospheric circulation

  • Warm air rises → low pressure (e.g. the Equator). Cool air sinks → high pressure (e.g. the poles, 30° N and S).
  • Wind blows from high to low pressure (trade winds blow from 30° to the Equator). Winds curve because of Earth's rotation: the Coriolis effect.
  • Rain: warm water evaporates, air rises, cools, water vapour condenses into clouds, precipitation falls. Wet places are in low pressure belts (the UK, about 55° N); dry places in high pressure belts (hot deserts, 15–30° N and S).

Tropical storms

  • Large, spinning, very low pressure storms. Called hurricanes (Atlantic, NE Pacific), typhoons (NW Pacific), cyclones (Indian Ocean, S Pacific).
  • Form 5–15° north and south of the Equator. Never at the Equator: the Coriolis effect is too weak there.
  • Need: sea at 26 °C or warmer, very low pressure, enough Coriolis effect to spin, low wind shear to stay upright.
  1. Warm sea water (26 °C+) evaporates and rises quickly.
  2. It cools and condenses into tall cumulonimbus clouds.
  3. Storms join into one 480–650 km wide and up to 8 km tall.
  4. The Coriolis effect spins it. Winds of 75 mph or more; over 100 mph at the eye wall.
  5. Cool air sinks in the centre, making the calm, cloudless eye.
  6. The prevailing wind moves it. Over land it loses energy (friction, no warm water).

Climate change could change distribution (further from the Equator), frequency (more often) and intensity (faster winds, more rain), because more sea is above 26 °C for longer. The evidence is mixed.

Reducing risk: satellite thermal maps and tracking (monitoring and prediction; cones of uncertainty), evacuation routes, warnings and survival kits (planning), storm shelters on stilts with shutters, made of concrete (protection).

Extreme weather in the UK

  • Extreme weather is unseasonal (snow in July), unexpected (drought in Cambridge) and severe (heatwaves causing deaths).
  • It's getting more frequent: Met Office extreme events went from 3 in 2000 to 12 in 2020.
  • It's getting more severe: the high temperature record from 1911 lasted 79 years, 1990's lasted 13 years, 2019's only 3 years.

In depth: global atmospheric circulation

  1. The Sun heats the equator most. Warm air rises, creating low pressure and lots of rain (rainforests).
  2. The air cools, spreads north and south, and sinks at about 30°, creating high pressure: dry, clear skies (hot deserts).
  3. Surface winds blow from high to low pressure: the trade winds back to the equator and the westerlies towards 60°.
  4. At about 60° warm and cold air meet and rise (low pressure, wet: the UK). At the poles cold air sinks (high pressure, dry).
  5. These loops are the Hadley, Ferrel and Polar cells. They explain where deserts, rainforests and tropical storms are found.

In depth: how a tropical storm forms

  1. The sea is at least 26–27 °C, in late summer and autumn, between about 5° and 30° from the equator.
  2. Warm, moist air rises quickly, creating an area of very low pressure at the surface.
  3. As the air rises it cools and condenses into towering cumulonimbus clouds. Condensation releases heat, which powers the storm.
  4. Air rushes in at the surface to replace the rising air. The Coriolis effect (Earth's spin) makes it spin, anticlockwise in the northern hemisphere. This is why storms don't form right on the equator.
  5. Cool, dry air sinks in the centre, forming the calm, clear eye. The eye wall around it has the strongest winds and heaviest rain.
  6. The storm moves with the prevailing winds, growing over warm sea. It weakens over land or cold water because it loses its supply of warm, moist air.

Hazards: winds over 119 km/h, storm surges (the sea pushed onto land by wind and low pressure; Haiyan's was over 5 m), heavy rain, flooding and landslides.

Climate change: warmer seas could mean storms are more intense and found further from the equator. The number of storms may not rise.

6-mark plan: "Explain how tropical storms form."
  1. Conditions: sea above 26 °C, 5–30° latitude.
  2. Rising warm, moist air leads to low pressure.
  3. Condensation releases heat and powers the storm.
  4. The Coriolis effect makes it spin; the eye and eye wall form.
  5. It weakens over land because it loses its energy source. Use cause-and-effect words throughout: "this causes…", "as a result…".
ACl

Climate change

From the AQA specification.

Evidence

  • Ice cores: air bubbles show past CO₂ and temperature, going back 800 000 years.
  • Tree rings: wider rings in warm, wet years.
  • Temperature records since about 1850 show warming of around 1 °C.
  • Shrinking glaciers and sea ice; rising sea level.

Causes

  • Natural: changes in Earth's orbit (Milankovitch cycles), volcanic eruptions (ash blocks the sun, so cooling), sunspots (more sunspots, more solar energy).
  • Greenhouse effect: greenhouse gases trap heat that would escape into space. The enhanced greenhouse effect is when humans add more of these gases.
  • Human: burning fossil fuels (CO₂), agriculture (methane from cattle and rice paddies), deforestation (fewer trees absorbing CO₂, plus CO₂ released when trees are burned).

Effects

  • People: coastal flooding from sea level rise, more extreme weather, crop failures, water shortages, more disease in warmer areas.
  • Environment: melting ice, coral bleaching, species losing habitats.

Managing it

  • Mitigation (reduce the causes): alternative energy (wind, solar), carbon capture and storage, planting trees, international agreements (Paris Agreement, 2015).
  • Adaptation (live with the effects): drought-resistant crops, managing water supply (reservoirs, hosepipe bans), coastal defences against sea level rise.

In depth: the greenhouse effect, step by step

  1. Short-wave radiation from the Sun passes through the atmosphere and heats the Earth's surface.
  2. The Earth gives off heat as long-wave radiation.
  3. Greenhouse gases (carbon dioxide, methane, nitrous oxide, water vapour) absorb some of it and send it back to Earth, keeping the planet warm. This natural effect makes life possible.
  4. Humans add more greenhouse gases, so more heat is trapped: the enhanced greenhouse effect, which causes global warming.

In depth: causes

Natural causesHuman causes
Orbital changes (Milankovitch cycles): changes in Earth's orbit and tilt change how much sunlight we get, over thousands of years.
Solar output: sunspots mean more energy from the Sun.
Volcanic eruptions: ash blocks sunlight and cools the planet for a year or two.		Burning fossil fuels for energy, transport and industry releases CO₂.
Agriculture: cattle and rice paddies give off methane; fertilisers give off nitrous oxide.
Deforestation: fewer trees absorb CO₂, and burning them releases it.

Evidence: global temperatures up about 1.2 °C since 1880, ice cores (bubbles of old air show past CO₂ and temperature), shrinking glaciers and sea ice, sea level rising about 20 cm since 1900, and tree rings.

Managing it: mitigation reduces the causes (renewable energy, carbon capture, planting trees, international agreements like the Paris Agreement). Adaptation copes with the effects (drought-resistant crops, flood defences, managing water supply).

9-mark plan: "Evaluate the view that human activity is the main cause of recent climate change."
  1. The case for humans, with evidence: CO₂ rising fast since the Industrial Revolution, linked to fossil fuels, farming and deforestation.
  2. Natural causes exist (orbit, solar, volcanoes), but they act slowly or briefly and don't match the fast recent rise.
  3. Judgement: "Human activity is the main cause because the warming since 1950 is too fast and too large to be explained by natural causes."
BEc

Ecosystems

  • Ecosystem: the links between plants, animals, climate and the land. Global scale (hot desert) or small scale (a pond, a woodland).
  • Biotic = living (trees, fish). Abiotic = non-living (soil, light, water).
  • Producers (plants) photosynthesise; consumers eat them or other consumers; decomposers (bacteria, fungi, worms) break down dead material.
  • Food chains and webs show energy moving from producers to consumers. Arrows point to the eater.
  • Pyramid of biomass: biomass falls at each level because energy is used for movement, respiration and so on, not just growth.
  • Nutrient cycle: soil → biomass (plants absorb) → litter (they die) → soil (decomposition). Stores are Soil, Biomass, Litter.
  • Interdependence: change one part (e.g. fewer beetles) and it affects the rest (fewer woodpeckers, then fewer owls).
  • Biome: a global-scale ecosystem, e.g. tropical rainforest, hot desert, tundra.

In depth: how an ecosystem works

  • Producers (plants) turn sunlight into energy. Consumers eat them (primary), and are eaten in turn (secondary, tertiary). Decomposers (fungi, bacteria) break down dead matter.
  • Food webs show how many food chains link together, so a change to one species affects others.
  • Nutrient cycling: nutrients pass from the soil to the biomass (living things) and the litter (dead leaves), then back to the soil as things decompose.

Example of change: if ponds in a woodland are drained, plants that need water die, so the insects and frogs that eat them decline, then the birds that eat those decline. Each change ripples through the food web.

6-mark plan: "Explain how a change to one part of an ecosystem affects other parts." Name the change, follow it through the food web step by step (producer, then consumer, then predator), and include the effect on nutrient cycling. Use a real example such as British woodland.
BRf

Tropical rainforests

Characteristics

  • Between the tropics of Cancer and Capricorn (Amazon, Malaysia). The sun hits directly, so it's hot (about 27 °C all year). A low pressure belt makes it wet (over 2 000 mm rain a year). So biodiversity is very high.
  • Layers: emergent (tallest trees, e.g. tualang), canopy (a roof that blocks light; most animals live here), under canopy (saplings wait for gaps), shrub layer (dark; ferns with large leaves).
  • Nutrient cycle: most nutrients are in the biomass. Few in the soil (fast uptake, heavy rain leaches them) and few in the litter (it decomposes quickly).

Adaptations

  • Drip tips (weeping fig): rain runs off so leaves don't break.
  • Buttress roots (tualang): support tall trees.
  • Lianas and climbers (vanilla orchid): reach the light in the canopy while rooted in soil.
  • Epiphytes (bromeliads): grow on branches and collect water in overlapping leaves.
  • Large leaves (giant taro): absorb more light in the dark shrub layer.

Deforestation

  • Causes: logging (clear-felling hardwoods like teak), subsistence farming (slash and burn), commercial farming (plantations), mineral extraction (open-cast mines), energy (HEP dams flood land), settlements and population growth, road building (opens up more forest).
  • Impacts: soil erosion (no roots to bind the soil; nutrients leached), local climate change (less transpiration, so drier), global climate change (less CO₂ absorbed), but also economic development (jobs, exports, tax).

Value and sustainable management

  • Value: medicines, food, biodiversity, regulating climate (local and global), indigenous homes.
  • Selective logging: only old trees cut so the forest recovers (but slower and more expensive).
  • Replanting: seeds from primary forest grow secondary forest.
  • Conservation areas such as national parks (hard to police). Education so people buy fewer products linked to deforestation.
  • Ecotourism: small, locally owned resorts; locals keep the profit so they don't need to log or mine.
  • International hardwood agreements: only certified logs traded (International Tropical Timber Agreement, 1983; 62 countries by 2006).
  • Debt reduction: HICs cancel debt if LICs spend the money on conservation.

In depth: how the rainforest works

  • Climate: hot (about 27 °C) and wet (over 2000 mm of rain a year) all year round, because it's at the equator under low pressure.
  • Layers: emergent, canopy, under-canopy and shrub layer, competing for light.
  • Plant adaptations: drip-tip leaves shed heavy rain; buttress roots support tall trees in shallow soil; lianas climb towards the light.
  • Animal adaptations: e.g. sloths move slowly to save energy and are camouflaged with algae.
  • Fast nutrient cycle: leaves decompose quickly in the heat and damp, and plants absorb the nutrients straight away. The soil itself is poor once trees are removed, as heavy rain washes the nutrients out (leaching).

In depth: causes and effects of deforestation

  1. Causes: commercial farming (cattle, palm oil), logging, mineral extraction (Carajás iron mine), roads, energy (HEP dams), settlement and population growth (see Malaysia).
  2. Economic effects: + jobs, exports and money for development; − loss of future income from tourism and medicines.
  3. Environmental effects: soil erosion, loss of biodiversity, and less CO₂ absorbed, so more climate change. Burning releases even more CO₂.

Sustainable management: selective logging, replanting, conservation and ecotourism, education, international agreements (e.g. on hardwood), and debt reduction (debt-for-nature swaps).

9-mark plan: "To what extent do the benefits of deforestation outweigh the costs?" Use your case study: give the economic benefits with data, then the environmental and social costs, then judge whether the benefits are short-term while the costs are long-term. End with a clear conclusion.
BDs

Hot deserts

Characteristics

  • Between 15° and 30° N and S (Thar, Sahara, Atacama). Sun hits directly, so hot; a high pressure belt means air sinks and clouds rarely form, so dry (under 250 mm rain a year). Biodiversity is low.
  • High diurnal temperature range: hot days, cold nights, because there are no clouds to keep the heat in.
  • Nutrient cycle: most nutrients are in the soil. Few plants absorb them and little rain leaches them.

Adaptations

  • Camel: fatty hump (energy), wide feet (don't sink), two rows of eyelashes and thin nostrils (sand), thick fur on top only.
  • Fennec fox: nocturnal (avoids heat, loses less water), large ears (lose heat).
  • Kangaroo rat: light fur reflects heat; very concentrated urine saves water.
  • Plants: cacti store water in thick stems, have spines instead of leaves and long or wide roots. Many have waxy skins to cut water loss.

Desertification

  • Desertification: soil on the fringe of a hot desert becomes dry and degraded (loses nutrients).
  • Causes: population growth leading to over-grazing, over-cultivation and deforestation for firewood; climate change (hotter, less rain). With no plants to bind and shade it, soil dries out and its nutrients wash away.
  • Reducing the risk: planting trees (roots bind soil, leaves shade it), ponding banks and contour traps (stone lines that trap water and soil), zaï pits filled with compost.

In depth: hot deserts

  • Climate: under 250 mm of rain a year, because air sinks at about 30° (high pressure, no clouds). Very hot days but cold nights, because there are no clouds to trap heat.
  • Plant adaptations: cacti store water in their stems, have spines instead of leaves to reduce water loss, and have long or wide roots.
  • Animal adaptations: camels store fat in their humps and lose little water; many animals are nocturnal.

In depth: desertification

  1. Causes: climate change (less rain), population growth, overgrazing, over-cultivation, removing wood for fuel, and over-abstraction of water.
  2. Vegetation is lost, so roots no longer hold the soil together.
  3. Bare soil is eroded by wind and rain and loses its nutrients, so land turns to desert.

Reducing the risk: water and soil management, tree planting (the Great Green Wall in the Sahel), stone lines (magic stones) to catch run-off, and appropriate technology that local people can afford and repair.

9-mark plan: "Do the opportunities of a hot desert outweigh the challenges?" Use the Thar Desert. Opportunities: mineral extraction, energy (solar and wind), farming with irrigation (the Indira Gandhi Canal), tourism. Challenges: extreme heat, water supply, poor access. Then judge: opportunities can outweigh the challenges where investment like the canal overcomes them.
CCo

Coasts

Waves

ConstructiveDestructive
Long wavelength, low, low energyShort wavelength, tall, high energy
Gently spill up the beachPlunge onto the beach
Swash stronger than backwashBackwash stronger than swash
Add sediment (build beaches)Remove sediment

Fetch = the distance the wind blows over. Longer fetch means more powerful waves.

Processes

  • Erosion: hydraulic power (air forced into cracks), abrasion (rocks thrown at the cliff), attrition (rocks knock together and get smaller and rounder).
  • Weathering: mechanical (freeze-thaw: water freezes in cracks and expands), chemical (rainwater dissolves limestone), biological (roots and burrowing animals).
  • Mass movement: sliding, slumping (rotational, on soft wet clay), rock fall.
  • Longshore drift: waves approach at an angle of the prevailing wind; swash carries sediment up at an angle; backwash pulls it straight down; sediment zig-zags along the coast.

Landforms

  • Headlands and bays: alternating hard and soft rock. Soft rock erodes faster into bays; hard rock is left sticking out as headlands.
  • Cave → arch → stack → stump: a crack in a headland is widened by hydraulic power and abrasion into a cave; it erodes through into an arch; the roof is weathered and collapses, leaving a stack; the stack is eroded into a stump.
  • Wave-cut platform: erosion between high and low tide makes a wave-cut notch; the cliff above collapses; repeated, the cliff retreats and leaves a flat rocky platform.
  • Beaches (sand in sheltered bays, shingle on exposed coasts) and sand dunes (wind blows dry sand inland; marram grass traps it).
  • Spit: longshore drift carries sediment past a bend in the coast or a river mouth; it builds out to sea; a change in wind direction curves the end; salt marsh forms behind it.
  • Bar: a spit grows right across a bay, trapping a lagoon behind it.

Coastal management

StrategyHow it works+−
Sea wallConcrete wall reflects wavesVery effectiveVery expensive; ugly; can increase erosion of the beach
Rock armourLarge boulders absorb wave energyCheaper; fishing spotUgly; rocks can be moved in storms
GabionsWire cages of rocks absorb energyCheapUgly; wire rusts
GroynesWooden fences trap longshore driftBuilds a wider beachStarves beaches further along of sediment
Beach nourishmentAdd sand to widen the beachNatural look; good for tourismMust be repeated
Beach reprofilingReshape the beach with machinesCheapNeeds constant redoing
Dune regenerationPlant marram grass, fence off dunesCheap; habitatRestricts access
Managed retreatLet low-value land flood; build an earth embankment further backCheap; new wetland habitatLand (e.g. farms) lost

Hard engineering = built structures. Soft engineering = works with nature.

In depth: landform formation, step by step

Cave → arch → stack → stump (e.g. Old Harry Rocks, Dorset):

  1. A headland has a weakness such as a crack or joint.
  2. Hydraulic power and abrasion widen the crack into a cave.
  3. The cave erodes right through the headland to form an arch (Durdle Door).
  4. The base of the arch is eroded and weathering weakens the roof until it collapses, leaving a stack.
  5. The stack is eroded at its base until it collapses into a stump, covered at high tide.

Spit (e.g. Spurn Head, Hurst Castle):

  1. Longshore drift moves sediment along the coast in the direction of the prevailing wind.
  2. Where the coast changes direction (a bend or river mouth), the sediment is deposited out to sea.
  3. Over time it builds into a long ridge of sand or shingle attached to the land at one end.
  4. Changes in wind direction curve the end into a recurved hook.
  5. Sheltered water behind the spit becomes a salt marsh.
9-mark plan: "Evaluate a coastal management scheme you have studied." Use Lyme Regis: why it was needed (people, homes, tourism, landslides), the strategies (sea wall, beach nourishment, rock armour, slope stabilisation), the costs and benefits, and then a judgement on whether it worked, with data. Also mention any problems it caused further along the coast.
CRv

Rivers

Profiles

Upper courseMiddle courseLower course
ValleySteep, V-shapedWide, gently slopingVery wide, almost flat
ChannelNarrow, shallowWider, deeperVery wide and deep
Main processVertical erosionLateral erosion and depositionDeposition

The long profile shows the river getting less steep from source to mouth.

Processes

  • Erosion: hydraulic action (force of water), abrasion (rocks scrape the bed and banks), attrition (rocks knock together, smaller and rounder), solution (water dissolves rock). Vertical erosion deepens; lateral erosion widens.
  • Transportation: traction (large boulders rolled), saltation (pebbles bounced), suspension (fine particles carried), solution (dissolved minerals).
  • Deposition: when the river loses energy (slower, shallower, at the mouth).

Landforms

  • Interlocking spurs: in the upper course the river winds around hard rock it can't erode, leaving spurs.
  • Waterfall and gorge: hard rock lies over soft rock; the soft rock erodes faster, making an overhang and a plunge pool; the overhang collapses; the waterfall retreats upstream, leaving a steep-sided gorge.
  • Meander: the fastest flow on the outside bend erodes a river cliff; slow flow on the inside deposits a slip-off slope.
  • Ox-bow lake: erosion narrows the meander's neck; in a flood the river cuts through; deposition seals off the old loop.
  • Flood plain: flat land either side of the river, built up from silt deposited in floods.
  • Levées: in a flood the heaviest sediment is dropped first, next to the channel; repeated floods build raised banks.
  • Estuary: the tidal mouth of a river where mudflats form.

Flooding

  • A river floods when discharge (water flowing) is greater than capacity (what the channel holds).
  • Physical factors: heavy or prolonged precipitation, impermeable geology (clay, granite), steep relief. Human factor: land use (urban concrete is impermeable; deforestation means less interception).
  • Hydrograph: bars = rainfall, line = discharge. Lag time is the time from peak rainfall to peak discharge. Short lag time = high flood risk.
Hard engineeringSoft engineering
Dams and reservoirs: control discharge; expensive, flood landFlood warnings: time to move belongings; don't stop the flood
Channel straightening: water flows away faster; can flood places downstreamFlood plain zoning: no building on high-risk land; limits development
Embankments: raise the banks; can fail catastrophicallyPlanting trees: interception slows water reaching the river
Flood relief channels: extra route for water; expensiveRiver restoration: restore meanders and wetlands to store water

In depth: river landforms, step by step

Waterfall and gorge (e.g. High Force on the River Tees):

  1. The river flows over a band of hard rock lying on top of soft rock.
  2. The soft rock erodes faster (hydraulic action, abrasion), creating a step.
  3. Water falls over the step and erodes a deep plunge pool at the bottom.
  4. The soft rock under the hard rock is undercut, leaving an overhang.
  5. The overhang becomes unsupported and collapses; the rocks fall into the plunge pool and cause more abrasion.
  6. This repeats, so the waterfall retreats upstream, leaving a steep-sided gorge.

Meander to ox-bow lake:

  1. The fastest water is on the outside of a bend, causing lateral erosion and a river cliff.
  2. Slower water on the inside deposits sediment, forming a slip-off slope.
  3. The bends get bigger and the neck between them narrows.
  4. During a flood, the river cuts through the neck and takes the shortest route.
  5. Deposition seals off the old bend, leaving an ox-bow lake.

Floodplain and levées: when the river floods it slows down and drops sediment. The heaviest sediment is dropped first, right by the channel. Over many floods this builds raised banks called levées, and the fine silt spread further away builds a flat, fertile floodplain.

In depth: what makes flooding more likely

  • Physical: heavy or long rainfall, impermeable rock (e.g. clay), steep slopes, already-saturated ground.
  • Human: urbanisation (concrete is impermeable, and drains carry water quickly), deforestation (less interception), farming.
  • Hydrographs: a short lag time and high peak discharge mean a "flashy" river and more flood risk (e.g. Boscastle 2004: steep, narrow valley and extreme rain).
6-mark plan: "Explain how a waterfall forms." Follow the six steps in order with the key terms (hard/soft rock, undercutting, overhang, plunge pool, retreat, gorge). Name an example like High Force. A labelled sketch can earn marks.