The challenge of natural hazards.

HookChile's 2010 earthquake was 30 times stronger than Nepal's — and killed 18 times fewer people

ModelWhat turns a natural event into a hazard

A natural hazard is a natural event or process that threatens people or property. The event itself is neutral — an earthquake in an empty desert harms no one. It becomes a hazard only where it overlaps with human life, and it becomes a natural disaster when that hazard actually causes serious loss of life or damage. The specification splits hazards into two families: geological hazards driven by the Earth's internal processes (earthquakes, volcanic eruptions, landslides) and atmospheric hazards driven by the weather and climate (tropical storms, floods, droughts).

Hazard risk is the probability of being harmed by a natural hazard. Three big factors push it up or down. First, vulnerability — the more people living in an exposed place, the greater the risk, which is why floodplains and volcanic slopes keep filling up with settlement despite the danger. Second, capacity to cope — wealthier countries can afford defences, monitoring, emergency services and insurance, so the same event does less harm. Third, the nature of the hazard itself: its type, frequency (how often), magnitude (how powerful) and how much warning it gives.

Why, then, do people live in hazardous places at all? Volcanic soils are extremely fertile; coasts and floodplains offer flat land, water and trade routes; tectonic zones bring geothermal energy and tourism; and for millions there is simply no choice — the land is where family, work and community already are. Risk is always weighed against reward.

MechanismPlate tectonics — the engine under the crust

The Earth has a solid inner core, a liquid outer core, a semi-molten mantle and a thin, cracked outer crust. The crust and rigid upper mantle are broken into tectonic plates that float on the mantle below. There are two kinds: thin, dense oceanic crust and thick, less dense continental crust. The plates move a few centimetres a year — about the rate your fingernails grow — dragged by convection and by the pull of dense oceanic slabs sinking back into the mantle. Almost every earthquake and volcano on Earth sits on a plate boundary.

There are three margin types to know. At a constructive (divergent) margin plates pull apart and magma rises to form new crust — the Mid-Atlantic Ridge is splitting Iceland in two. At a destructive (convergent) margin plates move together; where dense oceanic crust meets continental crust it is forced down in a subduction zone, melting to feed explosive volcanoes and triggering powerful earthquakes — this is the setting of Chile's 2010 quake, where the Nazca Plate dives beneath the South American Plate. At a conservative (transform) margin plates slide past one another; no crust is made or destroyed, but friction locks them until they jolt free — the San Andreas Fault in California is the textbook example. Nepal sits at a fourth variation, a collision zone, where two continental plates (Indian and Eurasian) crumple upward to build the Himalayas.

CaseTwo earthquakes, two death tolls — Nepal 2015 vs Chile 2010

AQA wants a comparison of two tectonic events in areas of contrasting wealth, split into primary effects (caused directly and immediately — collapsed buildings, deaths, injuries), secondary effects (knock-on consequences — landslides, disease, economic collapse), and immediate versus long-term responses.

In Nepal (a lower-income country), the Gorkha earthquake's primary effects were devastating: around 9,000 dead, 22,000 injured, and roughly 3 million left homeless as brick and stone homes pancaked. Kathmandu's historic Dharahara tower collapsed. Secondary effects followed fast — the shaking triggered avalanches on Mount Everest that killed climbers at base camp, and buried the village of Langtang; blocked mountain roads cut off remote villages and slowed aid. Immediate responses leaned heavily on international help: search-and-rescue teams, field hospitals, tents and helicopters. Long-term recovery — rebuilding homes and temples, repairing roads — stretched on for years and depended on foreign aid.

In Chile (a higher-income country), a far larger quake did far less human damage. Strict earthquake-resistant building codes meant most modern structures survived; the roughly 500 deaths came heavily from the tsunami rather than collapse. Chile funded much of its own response, restored power and water within days, and rebuilt within a couple of years. The contrast is the exam's core lesson: preparation and wealth, not magnitude, decide the human cost.

ModelReducing tectonic risk — the four Ps

You cannot stop an earthquake, so the specification tests four ways of managing the risk. Monitoring uses instruments — seismometers for ground movement, gas and bulge sensors for swelling volcanoes — to watch for warning signs. Prediction is realistic for volcanoes (rising tremors and gas often precede an eruption) but still largely impossible for earthquakes, so hazard maps of high-risk zones matter more than forecasting the exact day.

Protection means engineering to survive the shaking: cross-bracing, deep foundations, and base isolation — rubber-and-steel bearings that let a building sway independently of the ground, used in structures from Tokyo to San Francisco. Automatic shut-off valves cut gas and power to prevent fires. Planning ties it together: land-use zoning that keeps the most vulnerable buildings off the worst ground, emergency drills, stockpiled supplies, and educated communities. Japan's annual Disaster Prevention Day drills are the standard example — a country that treats preparation as routine, not panic.

The evaluation examiners reward: protection is expensive and only richer countries can afford it at scale, while planning and education are cheaper and can save many lives in lower-income countries. Cost and wealth shape every choice — the same theme as the Nepal–Chile contrast.

MechanismWeather hazards — global circulation and tropical storms

The world's climate belts are set by global atmospheric circulation. At the equator, intense heating makes air rise, creating a belt of low pressure, heavy rain and rainforest. That air spreads out, cools and sinks at around 30° north and south, forming high pressure, clear skies and the world's hot deserts. This loop of rising and sinking air (the Hadley cell), together with the Ferrel and Polar cells, explains why rainforests and deserts sit where they do, and it drives the trade winds that steer tropical storms.

Tropical storms — called hurricanes, cyclones or typhoons depending on the ocean — form only under specific conditions: sea temperatures of at least 26.5°C, ocean depth of about 60m, latitudes between roughly 5° and 30° (so the Coriolis effect can spin them), and low wind shear. Warm, moist air rises rapidly, condenses and releases huge amounts of latent heat, which powers stronger winds in a self-feeding cycle. The result is a spinning system with a calm central eye of sinking air, a violent eyewall of the strongest winds and heaviest rain, and spiralling rain bands. The storm weakens once it hits land or cooler water and loses its warm-ocean fuel. Climate change is expected to make tropical storms more intense and shift where they occur, as warmer seas provide more energy.

Typhoon Haiyan (Philippines, 8 November 2013) is the specification's example. A Category 5 storm with winds around 314 km/h, it drove a storm surge up to five or six metres into the coastal city of Tacloban. Primary effects: roughly 6,300 dead and over a million homes damaged or destroyed. Secondary effects: flooding, contaminated water spreading disease, and a collapse of food supply and livelihoods. Immediate responses included international aid, evacuations and emergency shelter; long-term responses focused on rebuilding, mangrove replanting and improved storm defences.

CaseUK extreme weather — the Somerset Levels floods, winter 2013–14

The UK's weather is becoming more extreme, and AQA asks for one recent UK event. The Somerset Levels floods of winter 2013–14 are the standard case. The Levels are low-lying, naturally waterlogged land in the south-west; after the wettest January in England since records began in 1910, the rivers Parrett and Tone could not carry the water away, partly because they had not been dredged for years and had filled with silt.

The social and economic effects were severe: around 600 homes flooded, the village of Muchelney was cut off for weeks, roads and railways were closed, and about 14,000 hectares of farmland sat underwater for over a month, drowning crops and stranding livestock. Environmental effects included stagnant, contaminated floodwater and debris left across fields. Management responses combined immediate action — pumping, emergency shelter — with a longer-term £20 million Flood Action Plan: dredging the Parrett and Tone, raising road levels, building banks to protect vulnerable communities, and improving pumping and river maintenance.

The wider point is causation. UK flooding results from both physical factors (prolonged rainfall, saturated ground, impermeable geology) and human factors (building on floodplains, land drainage, reduced river maintenance). Naming the rivers, the dates and the response figures is what lifts an answer from a general description of 'a flood' into a genuine case study.

ModelClimate change — evidence, causes, and what we can do

Climate change is any long-term shift in the Earth's climate, and the specification wants you to separate the evidence, the causes, and the management. Evidence comes from ice cores (trapped air bubbles record atmospheric gases going back 800,000 years), tree rings, historical harvest and temperature records, retreating glaciers, shrinking Arctic sea ice, and global sea-level rise of roughly 20cm over the 20th century as ice melts and warming water expands.

Causes split into natural and human. Natural causes include orbital changes (the Milankovitch cycles — slow variations in the shape of Earth's orbit, its axial tilt and its wobble, which reshaped the ice ages), variations in solar output (fewer sunspots coincided with the cooler 'Little Ice Age'), and major volcanic eruptions, whose ash and gases briefly cool the planet by blocking sunlight. But the rapid warming since the Industrial Revolution is driven by the enhanced greenhouse effect: burning fossil fuels releases carbon dioxide, livestock and rice paddies and landfill release methane, and deforestation removes the trees that would absorb carbon. Effects include rising sea levels threatening low-lying land, more frequent extreme weather, shifting croplands and habitats, and water stress.

Management uses two strategies. Mitigation tackles the causes — switching to renewable energy, carbon capture and storage, planting trees, and international agreements such as the 2015 Paris Agreement to cap warming. Adaptation tackles the effects — building flood defences like the Thames Barrier, developing drought-resistant crops, and managing water supply more efficiently. Strong answers use both, and judge which is realistic for which country: mitigation needs global cooperation and money; adaptation is what a vulnerable country must do while it waits for the world to act.

VocabularyKey terms the mark scheme pays for

TrapsMisconceptions that cost marks

ExamWhat examiners want