🌋 Year 8 Geography

Tectonic Hazards

Plate Tectonics

• The Earth's crust is broken into large plates that move very slowly (a few centimetres per year) due to convection currents in the mantle
• Oceanic crust: dense, thin, made of basalt
• Continental crust: less dense, thicker, made of granite
• Plate boundaries are where plates meet; most tectonic hazards occur at boundaries

Types of Plate Boundary

• Destructive (convergent): plates move towards each other. Oceanic crust subducts (sinks) under continental crust. Creates deep ocean trenches, fold mountains, and volcanoes. e.g. Pacific Ring of Fire, Nazca plate under South American plate → Andes Mountains
• Constructive (divergent): plates move apart. Magma rises to fill the gap, forming new crust. Creates mid-ocean ridges and rift valleys. e.g. Mid-Atlantic Ridge; East African Rift Valley
• Conservative (transform): plates slide past each other horizontally. No crust created or destroyed. Creates fault lines and powerful earthquakes. e.g. San Andreas Fault (California)
• Collision: two continental plates converge. Neither subducts; rock is forced upwards forming fold mountains. e.g. Indian plate into Eurasian plate → Himalayas

Earthquakes

• Caused by sudden movement along a fault line; the focus is where the earthquake originates underground; the epicentre is the point on the surface directly above
• Seismic waves radiate outwards; primary (P) waves travel fastest; secondary (S) waves cause more damage
• Measured on the Richter scale (logarithmic — each unit is 10× more powerful) or the Moment Magnitude Scale
• Secondary hazards: liquefaction (soil behaves like liquid), tsunamis (triggered by underwater earthquakes), landslides, fires from broken gas mains

Volcanoes

• Form at destructive boundaries (where subducted plate melts) and constructive boundaries (where magma rises)
• Hot spots: some volcanoes form over hot spots in the mantle far from boundaries (e.g. Hawaii)
• Types: shield volcanoes (gentle slopes, runny lava, less violent, e.g. Hawaii), composite/strato volcanoes (steep, explosive, mix of lava and ash, e.g. Mount Fuji)
• Products: lava flows, pyroclastic flows (superheated gas and rock, 700°C+), ash clouds, lahars (volcanic mudflows), lava bombs
• Benefits of living near volcanoes: fertile volcanic soils, geothermal energy, tourism, mineral deposits

Why People Live in Hazard Zones

• Economic reasons: cannot afford to move; jobs and homes are there
• Psychological: "it won't happen to me" / unpredictable timing
• Environmental benefits: fertile soils, resources, scenic landscapes
• Long time since last eruption/quake: lower perceived risk

Tropical Storms (Hurricanes, Cyclones, Typhoons)

Formation

• Form over warm ocean water (above 26.5°C) between 5° and 20° north/south of the equator
• Warm water evaporates → warm, moist air rises rapidly → air cools and condenses → releases huge amounts of energy → creates a spiral of rising air
• The eye of the storm (calm centre, 20–40km wide) is surrounded by the eyewall (strongest winds and heaviest rain)
• Tropical storms weaken when they move over cooler water or land
• Wind speeds must exceed 119 km/h (74 mph) to be classified as a hurricane/typhoon/cyclone
• Different names: Atlantic/East Pacific = Hurricane; West Pacific = Typhoon; South Pacific/Indian Ocean = Cyclone

Effects and Responses

• Primary effects: strong winds destroy buildings, storm surges flood coastal areas, heavy rain causes flooding and landslides
• Secondary effects: loss of power and communications, disease (cholera in contaminated water), homelessness, economic damage, disruption to agriculture and trade
• Managing tropical storms: monitoring and prediction (satellites, aircraft), early warning systems, evacuation planning, building design (stilts, reinforced roofs), sea walls and flood barriers

Case Study: Typhoon Haiyan (Philippines, 2013)

• One of the strongest tropical cyclones ever recorded on landfall; wind speeds 315 km/h
• Over 6,300 people killed; 4 million displaced; Tacloban city almost completely destroyed
• Storm surge of 7m inundated coastal areas; flooding destroyed infrastructure
• International aid response; long-term rebuilding with "build back better" approaches
• The Philippines is particularly vulnerable: in the typhoon belt, poor infrastructure, and limited resources for preparedness

Tropical Rainforests

Characteristics

• Found near the equator (5°N–5°S) where temperatures average 26–28°C year-round and rainfall exceeds 2000mm/year, with no distinct dry season
• Major rainforests: Amazon (South America), Congo Basin (Central Africa), Southeast Asian islands (Borneo, Sumatra)
• The most biodiverse ecosystems on Earth — approximately 50% of all land species live in rainforests (only 6% of land area)

The Layered Structure

• Emergent layer (35–70m+): tallest trees rise above the canopy; strong winds; eagle and large birds
• Canopy (20–35m): dense layer of overlapping leaves; most animal and plant diversity; blocks 80% of sunlight
• Understory (5–20m): shade-tolerant plants; large leaves to capture limited light; jaguars, snakes
• Forest floor: very dark; little vegetation; fallen leaves decompose rapidly; nutrients cycled quickly; insects, fungi, large mammals

Adaptations

• Plants: drip tips on leaves (allow heavy rain to run off preventing fungal growth), buttress roots (shallow roots need wide base for stability in thin soil), large leaves (maximise light capture)
• Animals: camouflage, tree-dwelling lifestyle, loud calls to communicate through dense vegetation

Nutrient Cycling

• Despite lush vegetation, tropical rainforest soils are surprisingly poor in nutrients
• Nutrients are cycled very rapidly: leaf litter decomposes fast in the warm, wet conditions → nutrients absorbed by roots immediately → little stored in soil
• When forest is cleared, the nutrient cycle is broken and the soil quickly becomes infertile

Deforestation

Why Are Rainforests Being Destroyed?

• Agriculture: subsistence farming (slash and burn by local communities) and commercial farming (cattle ranching, soya for animal feed, palm oil — all for export). Soya and beef are the biggest drivers in the Amazon.
• Logging: commercial logging for timber (mahogany, teak) for furniture and construction; illegal logging is a major problem
• Mining: gold, iron ore, and other minerals. Causes direct habitat destruction and water pollution.
• Infrastructure: roads, dams (hydroelectric power), urban expansion open up remote areas

Impacts of Deforestation

• Loss of biodiversity: species extinction (many yet undiscovered)
• Contribution to climate change: trees store carbon; burning releases CO₂ (deforestation contributes approximately 10–15% of global greenhouse gas emissions)
• Disruption of the water cycle: less transpiration reduces rainfall — causing droughts and desertification
• Soil erosion: tree roots hold soil together; without them, heavy rain washes soil into rivers
• Impact on indigenous peoples: loss of homeland, culture, and resources

Solutions

• Sustainable forestry (selective logging, replanting)
• Protected national parks and reserves
• International agreements (REDD+ scheme: payments to developing countries for protecting forests)
• Consumer pressure: certification schemes (FSC for timber, Roundtable on Sustainable Palm Oil)
• Debt-for-nature swaps: rich countries cancel debts in exchange for environmental protection commitments

Urbanisation

Global Urbanisation Trends

• More than 55% of the world's population now lives in urban areas (2018); projected to reach 68% by 2050
• Urbanisation is fastest in LICs and MICs (lower and middle income countries): Sub-Saharan Africa, South Asia
• High income countries (HICs) are already heavily urbanised (UK ≈ 84%)

Reasons People Move to Cities (Push and Pull)

• Push factors (from rural areas): lack of jobs, poor healthcare and education, natural disasters/environmental degradation, conflict
• Pull factors (to cities): employment opportunities, better pay, schools, hospitals, entertainment, social networks
• Rural-urban migration is the main driver of urbanisation in LICs

Urbanisation in LICs: Squatter Settlements (Slums)

• When cities grow faster than housing supply, informal settlements (slums/favelas/shanty towns) develop
• Characteristics: self-built homes from scrap materials, no clean water or sanitation, no electricity, overcrowding, insecure land tenure, crime
• However: strong communities, economic activity, gradual improvement over time
• Case study: Dharavi, Mumbai — approximately 600,000–1 million people in 1.75 km²; diverse small industries generating $700 million/year; a thriving (if deprived) community with its own economy

Urban Issues in HICs

• Suburbanisation: people move to the city edge for space; causes commuter traffic, green belt pressure
• Urban decline in inner cities: deindustrialisation led to unemployment, deprivation, derelict buildings
• Urban regeneration: government investment in run-down areas — e.g. London Docklands, Manchester's Northern Quarter

Climate Change

The Greenhouse Effect

• The natural greenhouse effect: the Sun's shortwave radiation passes through the atmosphere; Earth's surface re-radiates longwave (infrared) radiation; greenhouse gases (CO₂, water vapour, methane, nitrous oxide) absorb some of this and re-radiate it back to Earth, keeping it warm enough for life
• Enhanced greenhouse effect: human activities increase greenhouse gas concentrations → more heat trapped → global temperatures rise

Causes of Climate Change

• Burning fossil fuels (coal, oil, natural gas) for energy and transport: the largest source of CO₂
• Deforestation: removes carbon sinks; burning releases CO₂
• Agriculture: methane from cattle and rice paddies; nitrous oxide from fertilisers
• Industry: cement production, chemical manufacturing
• Global CO₂ has risen from ~280 ppm (pre-industrial) to over 420 ppm (2024)
• Natural factors: volcanic eruptions, solar activity, Milankovitch cycles — but these cannot explain the rapid current warming

Consequences of Climate Change

• Rising temperatures: more frequent and intense heatwaves; heat-related deaths; crop failures
• Melting ice sheets and glaciers → sea level rise (threatens Bangladesh, Pacific island nations, coastal cities)
• Ocean acidification: CO₂ dissolved in seawater forms carbonic acid; threatens coral reefs and shellfish
• More extreme weather: intense storms, droughts, floods (though attribution to climate change is complex)
• Ecosystem disruption: species unable to adapt face extinction; changing migration and breeding patterns

Responses: Mitigation and Adaptation

• Mitigation (reducing the cause): switching to renewable energy, improving energy efficiency, reforestation, carbon capture and storage (CCS), changing diet (less meat), international agreements (Paris Agreement 2015: limit warming to 1.5–2°C)
• Adaptation (managing the effects): sea walls and flood defences, drought-resistant crops, early warning systems, redesigning buildings for extreme heat