Cambridge International A Level Geography (9696): Topic 9 – Hazardous environments – Revision Notes

Read the Hazardous environments study guide first; these notes condense it for revision.

These notes cover 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. It is one of four Advanced Physical Geography Options in Paper 3, where you answer on two options. For each option you answer a compulsory 10-mark structured question and one 20-mark essay from a choice of two.

Test yourself afterwards with the practice questions for this unit. The 9696 geography hub and the 9696 checklist show how this option fits with the rest of the course. For plate margins and basic slope processes, see the Core Physical Geography revision notes. The Sundarbans as coastal protection is covered in the coastal environments unit, and another Paper 3 option is set out in the coastal environments guide.

What the syllabus lists

Section	Content as printed
9.1 Tectonic hazards	Distribution of earthquakes and volcanoes related to plate tectonics; earthquake hazards (shaking, landslides, soil liquefaction, tsunami); eruption types and products (nuées ardentes, lava flows, lahars, volcanic landslides, pyroclastic flows, ash fallout); primary and secondary impacts; prediction, hazard mapping, preparedness, monitoring, perception of risk
9.2 Mass movements	Nature and causes; impacts on lives and property; prediction, hazard mapping, preparedness, monitoring, perception of risk
9.3 Atmospheric disturbances	Areas most at risk from cyclones, hurricanes, typhoons and tornadoes; their formation; 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); impacts; prediction, preparedness, monitoring, perception of risk
9.4 Sustainable management	Case study of the problems of sustainably managing a hazardous environment, evaluating attempted or possible solutions

Key terms

Term	Definition
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; often summarised as hazard x vulnerability
Moment magnitude	A measure of the energy released by an earthquake
Intensity	The strength of shaking and damage at a particular place
Soil liquefaction	Saturated sand or silt loses strength during shaking and behaves like a liquid
Tsunami	Sea waves caused by sudden displacement of the water column, often by sea-floor uplift
Nuée ardente	A glowing cloud of hot gas and ash moving rapidly downslope
Pyroclastic flow	A fast, ground-hugging current of hot gas, ash and rock
Lahar	A volcanic mudflow of ash and water
Volcanic landslide	The collapse of an unstable volcano flank
VEI	Volcanic Explosivity Index, from 0 to 8
Shear stress / shear strength	Forces pushing material downslope / resistance from friction and cohesion
Pore-water pressure	Pressure of water in the spaces in soil; when high, it reduces shear strength
Storm surge	A rise in sea level caused by low pressure and onshore winds
Mesocyclone	A rotating updraught inside a supercell thunderstorm
Primary / secondary impact	Caused directly by the event / caused by the primary impacts
Hazard mapping	Zoning land by level of danger to guide planning and evacuation

Case studies at a glance

9.1 Tectonic

Case	What	Key facts	One evaluation point
Tohoku, Japan, 11 March 2011	Mw 9.0-9.1 earthquake and tsunami	Run-up of 38.9 m at Miyako; 19,759 deaths; Fukushima Daiichi meltdowns	A prepared, wealthy country was overwhelmed by an event larger than planned for
Christchurch, NZ, 22 February 2011	Mw 6.2 earthquake	185 deaths; around 400,000 tonnes of liquefied silt; over 8,000 red-zone homes removed	Moderate magnitude, high impact: shallow focus close to a city
Gorkha, Nepal, 25 April 2015	Mw 7.8 earthquake	Nearly 9,000 deaths; Langtang avalanche and landslide left over 300 missing	Shows earthquake-triggered mass movement in mountains
Mont Pelée, Martinique, 8 May 1902	Nuée ardente	About 28,000 deaths in Saint-Pierre	Older than 1980, but the event that defined the term
Nevado del Ruiz, Colombia, 13 November 1985	Lahars	Over 20,000 deaths in Armero; a newspaper version of the hazard map had no key	Failure of communication, not of science
Mount St Helens, USA, 18 May 1980	Volcanic landslide and lateral blast	Largest landslide on land in recorded history; about 57 deaths; flank bulged 1.5-1.8 m a day	Monitoring led to a “red zone” before the eruption
Pinatubo, Philippines, 15 June 1991	VEI 6 eruption	About 60,000 evacuated; 847 deaths, mostly from roofs under wet ash during Typhoon Yunya	Credited with saving tens of thousands of lives

9.2 Mass movements

Case	What	Key facts	One evaluation point
Freetown, Sierra Leone, 14 August 2017	Mudslides	1,141 dead or missing; about 1,000 mm of rain since 1 July	Deforestation and informal housing turned heavy rain into disaster
Oso, USA, 22 March 2014	Landslide	43 deaths; 49 homes and structures destroyed; earlier slide in 2006	Risk was known but under-perceived

9.3 Atmospheric

Case	What	Key facts	One evaluation point
Typhoon Haiyan, Philippines, 8 November 2013	Storm surge and wind	About 5 m surge at Tacloban airport; about 6,300 deaths	Surge, not wind, drove most deaths
Cyclone Idai, Mozambique, 15 March 2019	Flooding from intense rain	About 1,600 deaths in three countries; over 4,000 cholera cases	Secondary impacts lasted weeks
Joplin, USA, 22 May 2011	EF5 tornado	158 deaths; 17 minutes’ warning	Warnings were given but many did not act
Daulatpur-Saturia, Bangladesh, 26 April 1989	Tornado	About 1,300 deaths	Tornado risk is not only a US issue

9.4 Sustainable management: coastal Bangladesh

• Cyclone Preparedness Programme set up in the early 1970s, after the 1970 cyclone, by the government and the Bangladesh Red Crescent Society.
• Deaths: 300,000-500,000 (1970), about 138,000 (1991), at least 3,447 (Sidr, 2007), when about 2 million people went to shelters.
• 139 polders built from the 1960s; the Sundarbans mangroves act as a buffer but face shrimp farming, salinity and sea-level rise.
• Evaluation: big gains in lives saved; weaker gains in livelihoods and the environment.

Must-know distinctions

• Magnitude vs intensity: one number per earthquake vs many values across places.
• Lahar vs pyroclastic flow: cold or warm water-rich mud vs hot gas and rock.
• Nuée ardente vs ash fallout: a glowing flow down the slope vs ash falling from the air over a wide area.
• Effusive vs explosive eruptions: runny basaltic magma vs viscous, gas-rich magma.
• Prediction vs forecasting: an exact time and place vs a probability over years.
• Hazard vs disaster: the event vs the event plus human vulnerability.
• Large-scale vs small-scale atmospheric disturbances: cyclones hundreds of kilometres wide lasting days vs tornadoes a few hundred metres wide lasting minutes.
• Tropical cyclone vs tornado formation: warm ocean and latent heat vs wind shear in a supercell over land.
• Primary vs secondary impacts: collapse and drowning vs disease, fire and lost income.

Mini essay plan

Question: “Assess the extent to which the impacts of tectonic hazards depend more on human factors than on physical factors.” [20]

1. Introduction. Define hazard, vulnerability and risk. State your line: physical factors set the potential scale; human factors decide how much of it becomes disaster.
2. Physical factors. Magnitude and depth (Tohoku Mw 9.0-9.1); ground conditions (Christchurch liquefaction); type of hazard (pyroclastic flows give no escape).
3. Human factors. Communication and trust (Armero’s hazard map with no key); monitoring and evacuation (Pinatubo); building quality and land use (Christchurch red zone).
4. Interaction. Pinatubo’s deaths were raised by a typhoon (physical) acting on weak roofs (human).
5. Counter-argument. At the extreme end, physical scale wins: Tohoku’s tsunami overwhelmed a wealthy, prepared country.
6. Judgement. Human factors explain most differences between places; physical factors dominate only for the very largest events.

Quick self-test

1. Name the four earthquake hazards listed in 9.1.
2. What raises pore-water pressure during liquefaction?
3. Give two differences between a lahar and a pyroclastic flow.
4. Why did roofs collapse at Pinatubo in 1991?
5. What went wrong with the Armero hazard map?
6. State two human causes of mass movement.
7. Give the sea surface temperature needed for a tropical cyclone.
8. Why do tropical cyclones not form on the equator?
9. What is a mesocyclone?
10. Name two hazards from a small-scale atmospheric disturbance.
11. How many deaths did Cyclone Sidr cause, and how many people were evacuated?
12. Give one problem with relying on embankments in coastal Bangladesh.

Answers

1. Shaking, landslides, soil liquefaction and tsunami.
2. Shaking compacts saturated grains, so water pressure between them rises and grain contact is lost.
3. Lahars are water-rich mudflows; pyroclastic flows are hot gas and rock. Lahars can happen years later with rain.
4. Wet ash from Typhoon Yunya’s rain made the ash fallout heavy.
5. It was poorly distributed, and a newspaper version had no key and showed Armero in a green zone read as safe.
6. Any two: deforestation, cutting slopes for roads, building on slopes, poor drainage.
7. At least 26.5 °C, to a depth of about 50 m.
8. The Coriolis force is too weak there to start rotation.
9. A rotating updraught within a supercell thunderstorm.
10. Any two: intense rain, hail, high winds, pressure imbalances.
11. At least 3,447 deaths; about 2 million people were evacuated to shelters.
12. Any one: costly to maintain; can be overtopped or breached; may give a false sense of safety.

Where marks are usually lost

• Listing hazards from the syllabus without explaining the process (for example, liquefaction without pore-water pressure).
• Mixing up lahars, pyroclastic flows and nuées ardentes.
• Using case studies as stories instead of as evidence for a point.
• Writing “earthquakes can be predicted” without saying only probabilities are possible.
• Giving cyclone formation conditions as a list, with no link to latent heat and falling pressure.
• Forgetting the small-scale hazards: hail and pressure imbalances are named in the syllabus.
• In 9.4, describing measures without judging them against social, economic and environmental sustainability.
• Ending an essay without a clear judgement on the question’s “extent” or “how far”.

Official syllabus

These notes follow 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 you are entered for.