Cambridge International A Level Geography (9696): Topic 9 – Hazardous environments – Study Guide

This guide covers topic 9, Hazardous environments (sections 9.1-9.4), of the Cambridge International AS & A Level Geography (9696) syllabus for examination in 2025 and 2026. Hazardous environments is one of four Advanced Physical Geography Options assessed in Paper 3. A Level candidates study two of the four physical options.

Use the revision notes for this unit and the practice questions for this unit. The 9696 geography hub and the 9696 checklist show where this option fits. Plate margins are taught in the Core Physical Geography study guide.

Coverage table

Syllabus reference	What you must know or be able to do (from the document)	Where assessed
9.1	Global distribution of earthquakes and volcanoes related to plate tectonics	Paper 3
9.1	Earthquake hazards (shaking, landslides, soil liquefaction, tsunami); eruption types and products (nuées ardentes, lava flows, lahars, volcanic landslides, pyroclastic flows, ash fallout)	Paper 3
9.1	Primary and secondary impacts; prediction, hazard mapping, preparedness, monitoring and perception of risk	Paper 3
9.2	Mass movements and their hazards: nature, causes, impacts; prediction, hazard mapping, preparedness, monitoring and perception of risk	Paper 3
9.3	Distribution of areas most at risk from tropical cyclones and tornadoes; their formation and development	Paper 3
9.3	Large-scale hazards (storm surge, coastal flooding, intense rain leading to river floods and mass movement, high winds); small-scale hazards (rain and hail, high winds, pressure imbalances)	Paper 3
9.3	Primary and secondary impacts; prediction, preparedness, monitoring and perception of risk	Paper 3
9.4	Case study: problems of sustainable management of a hazardous environment; evaluate attempted or possible solutions	Paper 3

How Paper 3 sets this option

The syllabus states that Paper 3 lasts 1 hour 30 minutes, is worth 60 marks and is 25% of the A Level. You answer on two optional topics. Each topic has a compulsory 10-mark structured question and a choice of one from two 20-mark essays. AO4 (evaluation) carries 40% of Paper 3, so judgement matters as much as knowledge. The syllabus asks for real case studies, ideally from 1980 onwards; only 9.4 names a compulsory one.

9.1 Global distribution of tectonic hazards

Most earthquakes and volcanoes lie along plate margins. The Pacific “Ring of Fire” has most subduction zones, so it has many explosive volcanoes and most very large earthquakes. Conservative margins have earthquakes but no volcanoes. Collision zones, such as the Himalaya, have large earthquakes over a wide belt.

Key terms

• Hazard: a natural event that threatens life and property.
• Disaster: a hazard event that overwhelms a community’s ability to cope.
• Vulnerability: how easily people or property are harmed.
• Risk: the likelihood of harm (hazard x vulnerability).

9.1 Earthquake hazards

Moment magnitude measures energy released. Intensity (for example Modified Mercalli) measures shaking and damage at a place.

• Shaking: damage rises with shallow focus, closeness to the epicentre, soft sediments that amplify waves, and poor construction.
• Landslides: shaking loosens steep slopes. After the Gorkha, Nepal earthquake of 25 April 2015 (Mw 7.8, nearly 9,000 deaths), an avalanche and landslide in the Langtang valley left over 300 people missing.
• Soil liquefaction: shaking raises pore-water pressure in saturated sand or silt, so it behaves like a liquid. In Christchurch, New Zealand (22 February 2011, Mw 6.2, 185 deaths), liquefaction in the eastern suburbs brought around 400,000 tonnes of silt to the surface. Over 8,000 homes in the residential “red zone” were later bought out and removed.
• Tsunami: sudden uplift of the sea floor at a subduction zone displaces the water column. The Tohoku, Japan earthquake (11 March 2011, Mw 9.0-9.1) caused a 38.9 m run-up at Miyako and 19,759 deaths. It also caused meltdowns at the Fukushima Daiichi nuclear plant.

Evaluation. Christchurch shows a moderate, shallow earthquake near a city can be deadly. Tohoku shows a prepared country can be overwhelmed by an event larger than planned for.

9.1 Volcanic hazards: eruption types and products

Eruption style depends on magma viscosity and gas content. Runny basaltic magma lets gas escape, so eruptions are effusive. Viscous, high-silica magma traps gas and erupts explosively (Vulcanian, Peléan, Plinian). The Volcanic Explosivity Index (VEI) ranks eruptions from 0 to 8.

Product	What it is	Example
Nuée ardente	Glowing cloud of hot gas and ash moving downslope at high speed	Mont Pelée, Martinique, 8 May 1902: about 28,000 deaths in Saint-Pierre
Pyroclastic flow	Ground-hugging current of hot gas, ash and rock	Too fast to outrun
Lava flow	Molten rock moving downslope	Usually slow; destroys property more than lives
Lahar	Volcanic mudflow of ash and water	Nevado del Ruiz, Colombia, 13 November 1985: over 20,000 deaths in Armero
Volcanic landslide	Collapse of an unstable flank	Mount St Helens, USA, 18 May 1980: the largest landslide on land in recorded history; about 57 deaths
Ash fallout	Fine ash spread by wind	Pinatubo, 1991: wet ash collapsed roofs

9.1 Primary and secondary impacts

Primary impacts come directly from the event, such as collapse from shaking. Secondary impacts follow: fires, disease, lost jobs, and lahars in later rainy seasons. Mount Pinatubo, Philippines (climax 15 June 1991, VEI 6) killed 847 people, mostly when roofs collapsed under wet ash because Typhoon Yunya arrived the same day. Lahars returned with heavy rain for years afterwards.

9.1 Prediction, hazard mapping, preparedness, monitoring and perception of risk

• Prediction: earthquakes cannot be predicted to a precise time, only given long-term probabilities. Volcanoes often give warning signs.
• Monitoring: seismometers record swarms of small earthquakes as magma rises; tiltmeters, GPS and satellite radar measure swelling; gas sensors measure sulphur dioxide. Before the 1980 collapse, the north flank of Mount St Helens bulged by 1.5-1.8 m a day.
• Hazard mapping: zones from past deposits and lahar paths guide land use and evacuation.
• Preparedness: building codes, drills, education and early warning. In 2011 Japan’s system alerted millions about a minute before strong shaking reached Tokyo.
• Perception of risk: people may accept risk for fertile soils or jobs, be fatalistic, or trust officials too much.

At Pinatubo, the Philippine Institute of Volcanology and Seismology, helped by the United States Geological Survey, used a five-level alert system, and about 60,000 people were evacuated from within 30 km. At Armero, a hazard map was finished in October 1985, but it was poorly distributed. A newspaper version had no key and showed Armero in a green zone that people read as safe. On the night, residents were told to stay calm.

Worked paragraph (9.1). Monitoring reduces volcanic deaths only when warnings turn into action. At Pinatubo in 1991, monitoring led to a staged alert system and about 60,000 people left the danger zone, so deaths were limited to 847 and the evacuation is credited with saving tens of thousands of lives. At Armero in 1985, a hazard map showed the lahar risk, yet more than 20,000 people died because the map was unclear and officials gave reassuring messages. So communication matters as much as the instruments. However, Pinatubo gave a long build-up of warning signs; some volcanoes give far less.

9.2 Mass movements: nature, causes and impacts

Mass movement is the downslope movement of rock and soil under gravity. Slopes fail when shear stress exceeds shear strength (friction and cohesion). Types include falls, slides (including rotational slumps) and flows (mudflows, debris flows).

• Physical causes: steep slopes; weak or weathered rock; heavy rain, which raises pore-water pressure and adds weight; undercutting by rivers or waves; earthquakes.
• Human causes: deforestation; cutting slopes for roads; loading slopes with buildings; poor drainage.

Freetown, Sierra Leone. On 14 August 2017, mudslides left 1,141 people dead or missing. Rainfall since 1 July was about 1,000 mm, around three times the seasonal average. Deforestation, informal housing on steep slopes and poor drainage raised vulnerability.

9.2 Prediction, hazard mapping, preparedness, monitoring and perception of risk

• Monitoring: inclinometers and GPS track slow movement; piezometers measure groundwater pressure; satellite radar spots small ground changes.
• Prediction: rainfall thresholds link rain totals to past landslides and trigger warnings.
• Hazard mapping: combines slope angle, geology, past failures and drainage to zone land.
• Preparedness: drainage, retaining walls, rock bolts, replanting and evacuation plans.

Oso, USA. On 22 March 2014 a landslide near Oso, Washington killed 43 people and destroyed 49 homes and structures. The hillside had slid before, including in 2006, and a 2010 county study called it one of the county’s most dangerous. Good data did not prevent disaster because the risk was under-perceived.

Worked paragraph (9.2). Human activity often turns a slope hazard into a disaster. In Freetown in 2017, rainfall about three times the seasonal average raised pore-water pressure and triggered flows. But deforestation had removed the roots binding the soil, and informal housing on steep slopes put thousands of people in the path of the debris. The trigger explains when the mudslides happened; human factors explain why 1,141 people were dead or missing. At Oso, by contrast, the human failure was the decision to stay.

9.3 Distribution and formation of atmospheric disturbances

Tropical cyclones are called hurricanes in the Atlantic and north-east Pacific, typhoons in the north-west Pacific, and cyclones in the Indian Ocean and South Pacific. Areas most at risk include the Caribbean and US Gulf coast, the Philippines, southern China and Japan, the Bay of Bengal, Mozambique and Madagascar, and northern Australia.

A tropical cyclone needs: sea surface temperatures of at least 26.5 °C to a depth of about 50 m; a position at least about 5° from the equator, so the Coriolis force can start rotation; low vertical wind shear; moist air in the lower and middle troposphere; and a pre-existing disturbance. Rising air condenses and releases latent heat, warming the core and lowering surface pressure, so more air spirals in. An eye forms where air sinks at the centre. The storm weakens over land or cold water. Category 5 on the Saffir-Simpson scale means winds of 252 km/h or more.

Tornadoes mostly form in supercell thunderstorms. Warm, moist air near the ground lies under drier air, and winds change with height (wind shear). The shear creates a horizontal rolling motion that a strong updraught tilts upright into a rotating mesocyclone; a rear-flank downdraught can bring the rotation to the ground. The United States has by far the most tornadoes, especially in “Tornado Alley”. Bangladesh also has deadly tornadoes. The Enhanced Fujita scale rates them EF0-EF5.

9.3 Hazards and impacts

Large-scale disturbances.

• Storm surge and coastal flooding: low pressure lets the sea rise and onshore winds pile water against the coast. Typhoon Haiyan reached the Philippines on 8 November 2013; a surge of about 5 m wrecked Tacloban airport terminal, and about 6,300 people died.
• Intense rainfall: causes severe river floods and mass movement. Cyclone Idai made landfall near Beira, Mozambique on 15 March 2019. About 1,600 people died across Mozambique, Zimbabwe and Malawi, and over 4,000 cholera cases followed.
• High winds: destroy buildings and crops.

Small-scale disturbances.

• Intense precipitation: downpours and large hail damage crops, vehicles and roofs.
• High winds: the strongest tornadoes exceed 300 km/h. The Joplin, Missouri tornado (22 May 2011, EF5) killed 158 people; the Daulatpur-Saturia tornado in Bangladesh (26 April 1989) killed about 1,300.
• Pressure imbalances: pressure falls sharply inside the vortex, adding to the wind’s force. Most damage comes from wind and flying debris, so opening windows does not help.

9.3 Prediction, preparedness, monitoring and perception of risk

Satellites and computer models track cyclones days ahead, within a “cone” of uncertainty. Doppler radar detects rotation in thunderstorms, so tornado warnings come only minutes ahead. At Joplin the warning came 17 minutes before touchdown, yet many residents did not act; repeated warnings can cause “warning fatigue”.

Worked paragraph (9.3). Storm surge, not wind, often causes most deaths in a tropical cyclone. During Typhoon Haiyan, a surge of about 5 m swept into Tacloban, wrecking even the airport terminal. A surge is highest where onshore winds push water into shallow, narrowing bays, so low-lying coastal settlements face the greatest danger. So the shape of the coast and where people live can matter more than wind speed. Yet wind drives the surge, so the two cannot be fully separated.

9.4 Case study: the coastal zone of Bangladesh

Coastal Bangladesh, on the Ganges-Brahmaputra-Meghna delta, suits this required case study; your teacher may choose another.

Problems. The land is low and flat, population density is very high, and poverty limits stronger housing or moving away.

Measure	Evidence	Evaluation
Cyclone Preparedness Programme (early 1970s, after the 1970 cyclone; government and Bangladesh Red Crescent Society)	Volunteers pass warnings to villages	Credited with saving thousands of lives; works only if people trust warnings
Cyclone shelters	About 2 million people evacuated to shelters for Cyclone Sidr (15 November 2007)	Sidr deaths at least 3,447, against about 138,000 in 1991 and 300,000-500,000 in 1970
Polders and embankments (139 polders, built from the 1960s)	Protect farmland from tidal flooding and salt water	Costly to maintain; a large surge can overtop or breach them, and they may give a false sense of safety
Mangroves (the Sundarbans, one of the world’s largest mangrove forests)	A natural buffer against surges	Threatened by shrimp farming, salinity and sea-level rise; badly damaged by Sidr

Is it sustainable? Deaths have fallen sharply, so the social measures work. But economic losses remain high, shrimp farmers profit from clearing mangroves that protect everyone else, and sea-level rise may outpace engineering.

Worked paragraph (9.4). Bangladesh shows that management can save lives without removing the hazard. Cyclone Sidr in 2007 caused damage that some officials described as worse than the 1991 cyclone, yet deaths fell from about 138,000 to at least 3,447 because about 2 million people reached shelters. However, the management is only partly sustainable: homes, crops and livelihoods are still lost, and mangroves that buffer surges are being cleared for shrimp farms. It has succeeded socially but not yet economically or environmentally.

Common errors

• Treating lahars and pyroclastic flows as the same: lahars are water-rich mudflows; pyroclastic flows are hot gas and rock.
• Describing liquefaction without saturated sediment and pore-water pressure.
• Saying cyclones form “on the equator”, where the Coriolis force is too weak.
• Listing impacts without saying which are primary and which secondary.
• Describing the 9.4 case study without evaluating solutions or conflicts between groups.

Where to go next

Recap plate margins with the Core Physical Geography revision notes and practice. Plan all four papers with preparing for the staged four-paper route, and see mangrove protection in the coastal environments unit.

Official syllabus

This guide follows the Cambridge International AS & A Level Geography (9696) syllabus for examination in 2025 and 2026, topic 9, sections 9.1-9.4. Your teacher will confirm which two Paper 3 options your school teaches.