Geography — Core Revision Notes

1. Natural Hazards

A natural hazard is a naturally occurring event that threatens people or property. A natural disaster occurs when a natural hazard causes significant loss of life or economic damage. Tectonic hazards (earthquakes and volcanoes) occur mainly at plate boundaries. Earthquakes result from the sudden release of energy as tectonic plates move — focus is the point of origin underground; epicentre is the point on the surface directly above. The Richter scale measures earthquake magnitude (logarithmic — each step is 10× more powerful). Volcanoes occur at destructive (subduction) boundaries where oceanic plate melts and rises as magma, and at constructive boundaries where plates move apart. Shield volcanoes (gentle slopes, runny lava, mild eruptions) differ from composite volcanoes (steep sides, viscous lava, violent explosive eruptions).

Plate boundary types and their hazards

• Destructive (convergent): oceanic plate subducts under continental — violent earthquakes, composite volcanoes, tsunami (Japan, Andes)
• Constructive (divergent): plates move apart — less violent earthquakes, shield volcanoes, rift valleys (Mid-Atlantic Ridge, Iceland)
• Conservative (transform): plates slide past each other — powerful earthquakes, NO volcanoes (San Andreas Fault, California)
• Collision: two continental plates converge — fold mountains, intense earthquakes, no volcanoes (Himalayas)
• Hot spots: mantle plume creates volcanoes in the middle of plates (Hawaii)
• Tsunami: underwater earthquake or volcanic eruption displaces seawater; waves travel at 800 km/h, increase in height as they approach shore

2. Population

Population is studied in terms of distribution (where people live), density (people per km²), and change over time. Birth rate = live births per 1000 people per year. Death rate = deaths per 1000 people per year. Natural increase = birth rate − death rate. The Demographic Transition Model (DTM) has 5 stages: Stage 1 — high BR, high DR, stable (pre-industrial); Stage 2 — high BR, falling DR, rapid growth (improved sanitation/medicine); Stage 3 — falling BR, low DR, slower growth; Stage 4 — low BR, low DR, stable (developed); Stage 5 — very low BR, slightly rising DR, population decline or negative growth. LEDCs (Less Economically Developed Countries) are in stages 2–3; MEDCs are in stages 4–5. Population pyramids show age-sex structure: broad base = youthful population (stage 2); narrow base = ageing population (stage 4/5).

Population policies and migration

• Anti-natalist policy (reduce birth rate): China's one-child policy (1979–2015) — fines for extra children; caused gender imbalance (preference for boys) and ageing population
• Pro-natalist policy (encourage more births): France, Sweden — financial incentives, paid parental leave, free childcare
• Migration: movement of people between places. Push factors drive people away (poverty, conflict, drought). Pull factors attract people (jobs, safety, services).
• Rural-urban migration: movement from countryside to cities — increases urban population rapidly in LEDCs
• International migration: economic migrants, refugees, asylum seekers
• Ageing population challenges: increased demand for pensions, healthcare, care homes; smaller working population to pay taxes
• Youthful population challenges: need for more schools, maternity services; high dependency ratio

3. Rivers & Flooding

A river system begins in upland areas (source) and flows to the sea (mouth). The drainage basin is the land that drains into a river. The watershed is the ridge of high land dividing drainage basins. In the upper course: high energy, steep gradient, V-shaped valley, waterfalls, interlocking spurs — erosion dominates. In the middle course: meanders, ox-bow lakes, flood plains beginning to form. In the lower course: wide flood plain, meanders, levées, estuary — deposition dominates. River processes: erosion (hydraulic action, abrasion, attrition, solution), transportation (traction, saltation, suspension, solution), deposition (as velocity decreases). Flooding is caused by prolonged heavy rain, snowmelt, impermeable ground, deforestation, and urbanisation.

Flood management strategies

• Hard engineering: dams (store water but flood upstream habitats), levées/embankments (protect banks but may increase flood risk downstream), channel straightening (moves water away faster), flood walls
• Soft engineering: flood plain zoning (no building on the flood plain), afforestation (trees intercept rainfall and increase infiltration), restoring meanders (slows water flow), warning systems, insurance incentives
• Sustainable management: works with natural processes, low environmental impact, acceptable cost, maintains river ecosystems
• In LICs: less money for engineering; community-based early warning systems, flood-resistant building designs, mangrove conservation in coastal areas
• Meander formation: fast water on the outer bank erodes (river cliff); slow water on inner bank deposits (slip-off slope); loop grows until neck is cut off → ox-bow lake

4. Coasts

Coastal processes: erosion (hydraulic action, abrasion, corrosion/solution, attrition), transportation (longshore drift — swash moves sediment along coast diagonally; backwash pulls directly back), deposition. Erosion landforms: headlands and bays (differential erosion of hard/soft rock), wave-cut platforms, cliffs, caves, arches, stacks, stumps (formed in sequence). Deposition landforms: beaches, spits (extend from a headland into open water and curve at end due to wind direction change), bars (spits that seal a bay), tombolos (link an island to mainland), sand dunes. Sea level change: eustatic (global change in sea level — glacial melt raises sea level); isostatic (local land level change — e.g. post-glacial rebound). Rising sea levels threaten low-lying coasts (Bangladesh, Maldives, Thames Estuary).

Coastal management strategies

• Sea wall: reflects wave energy; expensive (£2,000–10,000 per metre); may cause scour at base
• Groynes: wooden/rock structures perpendicular to shore; trap sediment and build beach
• Rock armour (rip-rap): large boulders absorb wave energy; cheaper than sea wall; natural-looking
• Beach nourishment: add sand/shingle; cheap, natural-looking; must be repeated regularly
• Managed retreat: allow land to flood naturally; compensate landowners; creates salt marsh (natural flood buffer and habitat)
• Do nothing: cost-benefit analysis — if land value < management cost, let coast retreat
• Integrated Coastal Zone Management (ICZM): holistic planning of entire coastline rather than individual sections

5. Climate, Ecosystems & Sustainability

The climate describes the average weather conditions for a region over 30+ years. Biomes are large-scale ecosystems defined by climate and vegetation type. Tropical rainforests (TRF): near the equator; high temperature (~27°C) year-round; high rainfall (>2,000mm/yr); four layers (emergent, canopy, understorey, forest floor); high biodiversity; rapid nutrient cycling in thin soils. Deforestation threats: habitat loss, climate change (CO₂ release), soil erosion, disruption of water cycle. Hot deserts: high daytime temperatures (>40°C), cold nights, rainfall <250mm/yr; plants adapted by deep roots, water storage (succulents), or very short life cycles (ephemerals); animals nocturnal to avoid heat. Temperate deciduous forests: four seasons, deciduous trees shed leaves in winter; soils are deep and fertile.

6. Urban Geography

Urbanisation is the increase in the proportion of people living in towns and cities. In LICs it is driven by rural-to-urban migration and natural increase. Megacities have populations > 10 million (e.g. Lagos, Mumbai, Mexico City, Tokyo). Urban land use models: Burgess concentric zone model (CBD at centre, then inner city, suburbs, rural-urban fringe); Hoyt sector model (wedge-shaped zones following transport routes). Problems in LIC cities: squatter settlements (shanty towns / favelas / slums) — lack clean water, sanitation, electricity, security; overcrowding; traffic congestion; air and water pollution. Solutions: site-and-service schemes, self-help housing programmes, microfinance, improving infrastructure. In HIC cities: deindustrialisation (old industrial zones become derelict), counter-urbanisation (people move to rural areas), urban regeneration schemes.