Cambridge Syllabus Notes

Hazardous Environments – Natural Hazards (Cambridge International AS & A Level Geography 9696)

1. Syllabus Overview

The paper requires you to know the distribution, causes, impacts and management of four major natural hazards, applying the systems approach (Inputs → Processes → Stores → Outputs) and evaluating each hazard against the risk‑assessment framework (likelihood, vulnerability, exposure, impact).

2. Wildfire Hazards

2.1 Distribution of Wildfires

Region	Typical Climate	Dominant Vegetation	Fire Season (Months)
North America (Western USA, Canada)	Mediterranean & semi‑arid	Coniferous forests, chaparral	June – October
South America (Amazon fringe)	Tropical dry season	Savanna, dry forest	July – September
Africa (Mediterranean North, South Africa)	Mediterranean & semi‑arid	Fynbos, savanna	May – August
Australia (Eastern & Southern coasts)	Mediterranean & temperate	Eucalyptus forests, heathland	December – March
Europe (Southern Europe, Portugal, Spain)	Mediterranean	Maquis, pine forests	June – September

2.2 Systems Approach

Inputs: ignition sources (lightning, human activities), weather (high temperature, low humidity, strong wind), fuel load (dead wood, leaf litter).

Processes: fire spread, heat transfer, convection, ember generation.

Stores: combustible biomass, atmospheric moisture, topsoil organic matter.

Outputs: heat, smoke, ash, carbon emissions, altered land‑cover.

2.3 Causes (Inputs)

Natural ignition: lightning, volcanic heat, spontaneous peat combustion.
Human ignition: agricultural burning, campfires, discarded cigarettes, arson, power‑line failures.
Fuel availability (store): accumulated dead wood, leaf litter, dense understory.
Weather conditions (process): high temperature, low humidity, strong winds, prolonged drought.

The interaction of these inputs is expressed by the Fire Danger Index (FDI):

$$\text{FDI}=f(T,\;H,\;W,\;F)$$ where T = temperature (°C), H = relative humidity (%), W = wind speed (km h⁻¹), F = fuel moisture content (%).

2.4 Impacts (Outputs)

Environmental
- Loss of biodiversity – especially fire‑sensitive flora and fauna.
- Soil erosion, loss of organic matter, reduced fertility.
- Release of CO₂, CH₄ and other greenhouse gases.
- Altered hydrology – increased runoff, flash flooding.
Social
- Fatalities, injuries, displacement of communities.
- Respiratory problems from smoke inhalation.
- Destruction of cultural heritage sites.
Economic
- Damage to homes, infrastructure, timber and tourism assets.
- Cost of fire‑fighting operations and post‑fire rehabilitation.

2.5 Management (Mitigation & Adaptation)

Fuel management
- Prescribed (controlled) burning.
- Mechanical removal of dead vegetation.
- Firebreaks and buffer zones.
Land‑use planning
- Restrict development in high‑risk fire zones.
- Fire‑resistant building codes (non‑combustible roofing, ember‑proof vents).
Early warning & monitoring
- Satellite & aerial hot‑spot detection (MODIS, Sentinel‑2).
- Community fire‑watch groups and real‑time fire‑danger ratings.
Fire‑fighting resources
- Ground crews, water bombers, aerial retardant drops.
- Incident Command System for rapid coordination.
Post‑fire rehabilitation
- Re‑vegetation with native, fire‑resistant species.
- Soil stabilisation (mulching, contour bunds).
- Long‑term monitoring of ecosystem recovery.

2.6 Rate of Fire Spread (Process Equation)

An approximate relationship for fire spread is:

$$R=\frac{I}{\rho\,c}$$ where R = rate of spread (m s⁻¹), I = fire intensity (kW m⁻¹), ρ = fuel density (kg m⁻³), c = specific heat capacity of the fuel (kJ kg⁻¹ K⁻¹).

2.7 Hazard Mapping & Prediction Tools

GIS overlay of fuel‑load maps, topography, climate data → colour‑coded fire‑risk zones.
Fire‑danger rating systems (e.g., Australian FWI, US National Fire Danger Rating System).
Predictive models: FARSITE and Prometheus fire‑behaviour simulators.

2.8 Risk‑Assessment Matrix (Wildfire)

Likelihood	Vulnerability	Exposure	Overall Risk
High (annual fire‑danger days >150)	High (poor‑quality housing, elderly)	High (dense settlement in fire‑prone bush)	Very High
Medium	Medium	Medium	Medium
Low	Low	Low	Low

2.9 Case Study – 2019‑2020 Australian “Black Summer”

Date & Location: Nov 2019 – Mar 2020; NSW, Victoria, SA.
Scale: > 46 million ha burnt; > 3 000 structures destroyed; 34 deaths.
Physical Causes: Extreme heatwave (T > 40 °C), prolonged drought, strong east‑southerly winds.
Human Factors: Accumulated fuel from decades of fire‑suppression, limited prescribed burns.
Impacts:
- Environmental – > 3 billion animals killed, ~ 770 Mt CO₂ emitted.
- Social – 3 000 people displaced, significant mental‑health effects.
- Economic – AUS $4.4 billion direct costs; tourism decline.
Management Evaluation:
- Successes: rapid aerial suppression, strong community fire‑watch networks.
- Failures: insufficient fuel‑reduction in high‑risk zones; fragmented inter‑state coordination.
- Recommendations: increase prescribed burning, improve cross‑state incident command, invest in predictive fire‑danger modelling.

3. Earthquake Hazards

3.1 Global Distribution & Tectonic Setting

Region	Tectonic Setting	Typical Magnitude Range
Pacific “Ring of Fire” (Japan, Chile, Indonesia)	Convergent plate boundaries (subduction)	6.0 – 9.5
Alpide Belt (Turkey, Iran, Himalaya)	Continental collision & transform faults	5.5 – 8.0
Intraplate zones (e.g., New Madrid, USA)	Ancient fault re‑activation	5.0 – 7.0

3.2 Systems Approach

Inputs: tectonic stress accumulation, lithospheric rigidity.

Processes: fault slip, seismic wave propagation, ground shaking.

Stores: elastic strain energy stored in rocks, fault zone material.

Outputs: shaking intensity, surface rupture, secondary hazards (landslides, liquefaction, tsunamis).

3.3 Causes (Inputs)

Stress build‑up along faults due to relative plate motions.
Release of elastic strain energy when shear stress exceeds rock strength.

3.4 Impacts (Outputs)

Ground shaking → building collapse, infrastructure damage.
Secondary hazards: landslides, liquefaction, tsunamis, fire, disease outbreaks.
Economic loss from disruption of services, reconstruction costs.
Social impacts: loss of life, displacement, long‑term trauma.

3.5 Management

Seismic‑resistant design: base isolation, ductile detailing, reinforced concrete frames.
Land‑use zoning: avoid construction on active fault traces and soft sediments.
Early‑warning systems: Japan’s J‑Alert, USGS ShakeAlert – provide seconds to minutes of warning.
Public education: regular earthquake drills, “Drop‑Cover‑Hold” campaigns.

3.6 Hazard Mapping & Prediction Tools

Seismicity maps (historical earthquake epicentres) overlaid with fault‑line GIS data.
Probabilistic Seismic Hazard Analysis (PSHA) – estimates ground‑motion exceedance probabilities.
Real‑time monitoring networks (broadband seismometers, GPS geodesy) for strain accumulation.

3.7 Risk‑Assessment Matrix (Earthquake)

Likelihood	Vulnerability	Exposure	Overall Risk
High (M ≥ 7 expected within 50 yr)	High (poor‑quality unreinforced masonry)	High (dense urban centre on soft alluvium)	Very High
Medium	Medium	Medium	Medium
Low	Low	Low	Low

3.8 Case Study – 2023 Turkey‑Syria Earthquake (M 7.8)

Date & Location: 6 Feb 2023; southern Turkey & north‑west Syria.
Tectonic Cause: Strike‑slip motion on the East Anatolian Fault (continental transform).
Impacts:
- ≈ 50 000 deaths, > 100 000 injuries.
- Widespread building collapse; over 1 million people displaced.
- Secondary landslides in mountainous areas; severe winter‑weather complications.
- Economic loss estimated at US $30 billion.
Management Evaluation:
- Success: rapid international humanitarian response, use of mobile field hospitals.
- Failures: inadequate enforcement of seismic building codes, poor retrofitting of older structures.
- Recommendations: stricter code enforcement, systematic retrofitting programme, expansion of early‑warning network.

4. Volcanic Hazards

4.1 Global Distribution

Active volcanoes cluster along convergent plate margins (subduction zones) and continental rifts. Major belts include:

Pacific Ring of Fire (e.g., Japan, Chile, Alaska).
Mediterranean‑African Belt (e.g., Italy, Greece).
East African Rift (e.g., Tanzania, Kenya).

4.2 Systems Approach

Inputs: magma generation (partial melting), volatile enrichment, tectonic stress.

Processes: magma ascent, degassing, eruption dynamics (explosive vs. effusive).

Stores: magma chamber, volcanic gases, surrounding rock.

Outputs: lava flows, ash fall, pyroclastic density currents, lahars, volcanic gases.

4.3 Types of Eruptions & Associated Hazards

Explosive (e.g., Plinian) – ash fall, pyroclastic flows, lahars, sulphur dioxide & carbon dioxide emissions.
Effusive (e.g., Hawaiian) – lava flows, fire hazards, limited ash.

4.4 Impacts

Health: respiratory problems from ash, sulphur gases.
Agriculture: crop loss, soil acidification, water contamination.
Infrastructure: damage to roads, airports, power lines; tourism decline.
Climate: short‑term cooling from sulphate aerosols (e.g., 1991 Pinatubo).

4.5 Management

Continuous volcano monitoring – seismicity, gas emissions (SO₂, CO₂), ground deformation (InSAR, GPS).
Hazard maps showing zones of lava flow, ash fall, lahars, pyroclastic density currents.
Exclusion zones & evacuation plans based on eruption scenario modelling.
Public awareness campaigns and community drills.

4.6 Hazard Mapping & Prediction Tools

GIS overlay of historic eruption footprints, topography, population density → risk zones.
Probabilistic Volcanic Hazard Assessment (PVHA) – combines eruption frequency with exposure.
Real‑time monitoring networks: broadband seismometers, multi‑gas analyzers, satellite thermal imagery (e.g., MODIS).

4.7 Risk‑Assessment Matrix (Volcano)

Likelihood	Vulnerability	Exposure	Overall Risk
High (frequent historic eruptions)	High (unreinforced housing, limited early‑warning)	High (dense settlements on volcanic slopes)	Very High
Medium	Medium	Medium	Medium
Low	Low	Low	Low

4.8 Case Study – 2021 Hunga Tonga‑Hunga Ha'apai Eruption

Date & Location: 15‑16 Jan 2021; submarine volcano in the South Pacific.
Eruption Type: Highly explosive, generating a massive atmospheric shock wave and tsunamigenic sea‑level rise.
Impacts:
- Global atmospheric pressure wave detected worldwide.
- Local tsunami – coastal flooding on Tonga’s main islands.
- Ash fall disrupted air travel across the Pacific.
- Economic loss for Tonga estimated at US $200 million (≈ 30 % of GDP).
Management Evaluation:
- Success: rapid satellite monitoring, timely tsunami warnings issued by Pacific Tsunami Warning Centre.
- Limitations: limited local evacuation infrastructure, communication challenges on remote islands.
- Recommendations: strengthen community‑based tsunami education, improve real‑time alert dissemination.

5. Mass‑Movement Hazards – Landslides & Tsunamis

5.1 Landslides – Distribution & Causes

Geographic hotspots: Himalayan slopes, New Zealand Southern Alps, Andes, Japanese mountain ranges, California chaparral.
Pre‑disposing factors: steep slope angle, weak geology (shales, sandstones), vegetation loss, water saturation.
Triggering factors: intense rainfall, rapid snowmelt, earthquakes, volcanic activity, anthropogenic disturbance (road cuts, mining).

5.2 Systems Approach (Landslide)

Inputs: rainfall intensity, seismic shaking, volcanic heat.

Processes: slope failure, mass movement, debris flow.

Stores: unstable rock/soil mass, pore‑water pressure.

Outputs: ground displacement, sediment flux, infrastructure damage.

5.3 Landslide Impacts

Loss of life, destruction of homes and transport routes.
Sediment influx into rivers → increased flood risk, reduced water quality.
Economic disruption to agriculture, tourism, and industry.

5.4 Landslide Management

Hazard zoning using slope‑stability models (Infinite‑slope, Limit‑Equilibrium, GIS‑based susceptibility maps).
Engineering controls: retaining walls, drainage systems, re‑vegetation, terracing.
Early‑warning: rain‑fall thresholds, ground‑movement sensors (inclinometers, GPS).
Community preparedness: evacuation routes, public awareness campaigns.

5.5 Tsunami – Generation, Propagation & Impacts

Generation mechanisms: offshore megathrust earthquakes, submarine landslides, volcanic island collapse.
Propagation: long‑wavelength sea‑surface waves travel across ocean basins at 700–800 km h⁻¹.
Coastal impacts: inundation, erosion, salt‑water intrusion, loss of life and infrastructure.

5.6 Systems Approach (Tsunami)

Inputs: seismic energy, submarine mass movement, volcanic explosion.

Processes: wave generation, oceanic propagation, shoaling and run‑up.

Stores: ocean water column, coastal geomorphology.

Outputs: coastal flooding, sediment deposition, damage to built environment.

5.7 Tsunami Management

International and regional early‑warning systems (e.g., DART buoys, NOAA Tsunami Warning Center).
Coastal hazard mapping – inundation zones, evacuation routes, vertical evacuation structures.
Public education – regular tsunami drills, signage, community response plans.
Land‑use planning – restrict critical infrastructure in low‑lying coastal zones.

5.8 Hazard Mapping & Prediction Tools (Landslide & Tsunami)

Landslide susceptibility maps: GIS overlay of slope, lithology, land‑cover, rainfall intensity.
Probabilistic landslide forecasting using rainfall‑threshold models (e.g., McCarthy & Hearn).
Tsunami inundation modelling (e.g., MOST, COMCOT) combined with coastal DEMs.
DART buoy network provides real‑time sea‑level data for rapid tsunami alerts.

5.9 Risk‑Assessment Matrices

Hazard	Likelihood	Vulnerability	Exposure	Overall Risk
Landslide	High (rainfall >200 mm day⁻¹ frequent)	High (poorly engineered slopes, low‑income housing)	High (dense rural settlements on steep terrain)	Very High
Tsunami	Medium (megathrust events ≈ 100 yr)	High (low‑rise coastal communities, inadequate evacuation routes)	High (coastal cities with >1 million inhabitants)	High

5.10 Case Study – 2004 Indian Ocean Tsunami

Date & Origin: 26 Dec 2004; Mw 9.1–9.3 megathrust earthquake off Sumatra (Indonesia).
Propagation: Waves travelled across the Indian Ocean, reaching Africa and the Americas.
Impacts:
- ≈ 230 000 deaths across 14 countries.
- Massive coastal destruction – > 2 million homes damaged or destroyed.
- Economic loss estimated at US $10 billion.
Management Evaluation:
- Success: post‑event establishment of the Indian Ocean Tsunami Warning System.
- Shortcomings: lack of pre‑event warning infrastructure, limited public awareness.
- Recommendations: maintain and regularly test regional warning buoys, integrate community‑based evacuation drills.

6. Hazard Mapping, Prediction & Risk Assessment (AO3)

6.1 General Hazard‑Mapping Techniques

GIS‑based overlay of physical hazard layers (faults, volcanoes, slope, rainfall, vegetation) with exposure layers (population, infrastructure, economic value).
Remote‑sensing imagery (Landsat, Sentinel‑2, MODIS) for vegetation health, burn‑scar detection, lava‑flow mapping.
Colour‑coded hazard zones (e.g., low/medium/high fire‑risk, seismic intensity, landslide susceptibility).

6.2 Prediction & Early‑Warning by Hazard

Hazard	Key Predictive Indicators	Monitoring Tools
Wildfire	Fuel load, drought index, wind forecasts, FDI	Satellite hot‑spot detection (MODIS, VIIRS), weather stations, fire‑danger rating systems
Earthquake	Seismic swarms, strain accumulation, GPS‑measured crustal deformation	Broadband seismometer networks, GPS/geodetic stations, early‑warning alerts (ShakeAlert)
Volcano	Increased seismicity, gas fluxes (SO₂, CO₂), ground uplift	Seismographs, multi‑gas analysers, InSAR, thermal satellite imagery
Landslide	Rainfall intensity/duration, pore‑water pressure, slope movement	Rain gauges, inclinometer networks, satellite interferometry, GIS susceptibility models
Tsunami	Offshore seismic magnitude, sea‑level anomalies	DART buoys, tide‑gauge networks, seismic monitoring, real‑time modelling (e.g., SIFT)

6.3 Risk‑Assessment Framework (AO3)

Likelihood – based on historical frequency and current triggers.
Vulnerability – social (age, poverty), economic (value of assets), physical (building quality, land‑use).
Exposure – number of people, infrastructure, and ecosystems located in the hazard zone.
Impact – estimated loss of life, economic cost, environmental damage.

Overall risk is qualitatively expressed as:

$$\text{Risk}= \text{Likelihood} \times \text{Vulnerability} \times \text{Exposure}$$

In examinations, a matrix (low, medium, high) is used for each component.

6.4 Evaluation of Management Strategies (AO3)

Effectiveness – degree to which risk or loss of life is reduced.
Cost‑benefit – financial outlay versus avoided damage.
Social acceptability – community support, equity, cultural considerations.
Environmental sustainability – impact of mitigation measures on ecosystems (e.g., effects of large‑scale prescribed burning).

7. Summary Table – Hazard‑Specific Key Points

Hazard	Typical Distribution	Main Causes (Inputs)	Key Impacts	Principal Management Measures
Wildfire	Mediterranean, semi‑arid, tropical dry‑season regions	Lightning, human ignition, fuel load, hot/dry windy weather	Loss of biodiversity, soil erosion, smoke‑related health problems, property damage	Fuel reduction (prescribed burns, firebreaks), land‑use planning, early‑warning, rapid fire‑fighting, post‑fire rehab
Earthquake	Plate‑boundary zones (subduction, transform, collision) and intraplate faults	Stress accumulation on faults, sudden release of elastic strain	Building collapse, landslides, liquefaction, tsunamis, economic disruption	Seismic‑resistant design, zoning, early‑warning systems, public drills
Volcano	Convergent margins, continental rifts, hotspots	Magma generation, volatile exsolution, tectonic stress	Ash fall, pyroclastic flows, lahars, gas emissions, climate effects	Monitoring (seismic, gas, deformation), hazard maps, exclusion zones, evacuation plans
Landslide / Tsunami	Steep, high‑rainfall terrains; coastal zones adjacent to subduction zones	Rainfall, earthquakes, volcanic activity, human disturbance (for landslides); offshore megathrust earthquakes, submarine landslides (for tsunamis)	Fatalities, infrastructure loss, sedimentation, coastal inundation	Slope‑stability modelling, engineering controls, early‑warning (rain gauges, DART buoys), land‑use planning, community preparedness

8. References (Suggested Revision Sources)

Cambridge International AS & A Level Geography (9696) – syllabus and past‑paper exemplars.
UNEP & WMO – “Global Climate and Wildfire Report”.
USGS – Earthquake Hazards Program and ShakeAlert.
Global Volcanism Program (Smithsonian Institution) – volcano case studies.
International Tsunami Information Center – DART buoy data and modelling tools.
FAO & UNEP – Landslide susceptibility mapping guidelines.

Wildfire hazards: distribution, causes, impacts, management