What is a natural hazard?

A natural hazard is a natural process that threatens people or property — a natural event only becomes a hazard when it puts people at risk.

• Tectonic hazards — caused by the movement of tectonic plates, e.g. earthquakes and volcanic eruptions.
• Atmospheric (climatic) hazards — caused by weather and climate, e.g. tropical storms, floods and droughts.

Hazard risk is the chance of being affected by a natural hazard. Factors that affect risk include:

• Vulnerability — more people living in a hazardous area means more people at risk.
• Capacity to cope — wealthier (HIC) areas can prepare, protect and respond better than poorer (LIC) areas.
• Nature of the hazard — its type, frequency and magnitude (how strong it is).

When is it a hazard?

Plate tectonics theory

The Earth's crust is broken into large tectonic plates that float on the semi-molten mantle below. Slow-moving convection currents in the mantle drag these plates around.

• Continental crust — thicker, less dense, cannot sink.
• Oceanic crust — thinner, denser, can sink (subduct).

Where plates meet is called a plate margin (boundary). Almost all earthquakes and volcanoes happen along plate margins — for example, around the edge of the Pacific Ocean (the "Ring of Fire").

The three plate margins

Where hazards occur: volcanoes form at destructive and constructive margins; earthquakes occur at all three types of margin (destructive, constructive and conservative).

Match the term to its meaning

Tap a term on the left, then tap its correct description on the right.

Which margin?

Effects and responses to hazards

When you describe the impact of a tectonic hazard, split it two ways:

• Primary effects — the immediate, direct impacts of the shaking or eruption, e.g. buildings collapse, people killed or injured, roads destroyed.
• Secondary effects — the knock-on impacts that follow, e.g. fires from broken gas pipes, tsunamis, disease from dirty water, unemployment.

Responses are also split by time:

• Immediate responses — in the hours and days after: rescue survivors, treat the injured, provide food, water and shelter.
• Long-term responses — over months and years: rebuild homes, repair infrastructure, improve building codes, boost the economy.

Primary or secondary effect?

Tap the correct type of effect for each earthquake impact.

Contrasting earthquakes: HIC vs LIC/NEE

AQA expects two contrasting earthquakes to show that effects and responses differ with wealth. A common textbook pairing:

• L'Aquila, Italy (2009) — HIC. Magnitude 6.3. Around 309 people died and thousands were made homeless. As a wealthier country, Italy had search-and-rescue teams, hospitals and money to rebuild, and later improved building regulations.
• Gorkha, Nepal (2015) — LIC/NEE. Magnitude 7.8. Around 9,000 people died and hundreds of thousands of buildings were destroyed. As a poorer country, Nepal had weaker buildings, poor infrastructure and relied heavily on international aid.

The key idea: Nepal's earthquake was far stronger, but the huge difference in deaths and damage is largely down to wealth — poorer countries have weaker buildings and less capacity to prepare and respond.

Why the difference?

Living with, and managing, tectonic hazards

Despite the danger, people still live in hazardous areas because:

• Fertile soils — volcanic ash weathers into rich farmland.
• Resources & tourism — geothermal energy, minerals and visitors bring jobs and money.
• Family & roots — it is home; some cannot afford to move, or believe the risk is small.

Risk can be reduced by the "three Ps":

• Monitoring & Prediction — instruments track volcanoes; earthquakes cannot be reliably predicted, but risk zones are known.
• Protection — earthquake-resistant buildings and sea walls against tsunamis.
• Planning — hazard maps, evacuation drills and emergency supplies.

Your turn — why live in hazardous areas?

Tropical storms: where and how they form

Tropical storms are called hurricanes (Atlantic/east Pacific), cyclones (Indian Ocean) or typhoons (west Pacific). They form over warm tropical oceans and need:

• Sea temperature above about 27°C, and deep warm water, to provide energy from evaporation.
• Latitudes of about 5°–30° north and south — far enough from the equator for the Coriolis effect to make the storm spin (but not right on it).

Structure: the calm centre is the eye; the ring of towering cloud around it, the eyewall, has the fiercest winds and heaviest rain.

Measuring storms & a warming world

Tropical storm strength is measured on the Saffir–Simpson scale, from Category 1 (weakest) to Category 5 (most intense), based mainly on wind speed.

Climate change may affect tropical storms:

• Distribution — warmer seas could let storms form in a wider band of ocean.
• Frequency — the total number each year may change (evidence is uncertain).
• Intensity — warmer oceans give storms more energy, so the most powerful storms may become stronger, with heavier rainfall.

Case study: Typhoon Haiyan, Philippines 2013

Typhoon Haiyan struck the Philippines in November 2013 as one of the strongest tropical storms ever to make landfall (a Category 5 storm).

• Primary effects: around 6,000+ people killed; strong winds and a storm surge (over 5 m in places) destroyed buildings, especially in the city of Tacloban.
• Secondary effects: flooding, contaminated water spreading disease, power cuts, and destroyed crops causing food shortages and lost livelihoods.
• Immediate responses: international aid, emergency shelter, food and water; evacuations before the storm helped reduce deaths.
• Long-term responses: rebuilding homes and infrastructure, replanting mangroves, and improving early-warning and evacuation plans.

Exam tip: a strong answer names the place and date, gives facts/figures, and clearly separates primary vs secondary effects and immediate vs long-term responses.

Conditions for formation

Extreme weather in the UK

The UK experiences a range of extreme weather: heavy rain and flooding, strong winds and storms, heavy snow and cold snaps, heatwaves and droughts.

Example — Somerset Levels floods, winter 2013–14. Weeks of heavy rain and the wettest January on record left large areas of low-lying Somerset flooded for weeks.

• Effects: around 600 homes flooded, over 14,000 hectares of farmland under water, roads cut off and villages isolated.
• Responses: pumps removed floodwater, and afterwards rivers were dredged and flood defences improved.

Is UK weather getting more extreme? Evidence such as record-breaking rainfall, more frequent flooding and record high temperatures suggests UK extreme weather events are becoming more common and severe.

Climate change: evidence and causes

Over the Quaternary period (the last ~2.6 million years), the climate has swung between cold glacial and warmer interglacial periods. Recent evidence of change includes ice cores, tree rings, retreating glaciers, shrinking sea ice and rising sea levels and temperatures.

Possible natural causes:

• Orbital (Milankovitch) changes — cycles in the Earth's orbit and tilt alter how much solar energy we receive.
• Solar output — variations in the Sun's energy (sunspot activity).
• Volcanic activity — large eruptions release ash and gases that can cool the climate for a while.

Human causes — burning fossil fuels, agriculture (methane from livestock and rice) and deforestation release greenhouse gases, boosting the enhanced greenhouse effect and warming the planet.

Natural or human cause?

Mitigation vs adaptation

There are two broad ways to manage climate change:

• Mitigation — reducing the causes: switching to renewable energy, carbon capture, planting trees to absorb CO₂ and international agreements to cut emissions.
• Adaptation — coping with the effects: changing crops to suit new conditions, managing water supply, and building coastal and flood defences.

Mitigation or adaptation?

Tap a strategy, then tap the box it belongs in.

Your turn — mitigation vs adaptation

The key ideas to know

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