Natural hazards: definitions, types and risk factors

A natural hazard is a natural process or event with the potential to cause loss of life, injury or property damage. The same event in an unpopulated area is just a natural process — it only becomes a hazard when it threatens people. When a hazard actually occurs and causes serious damage, it becomes a natural disaster.

The three families of natural hazards

Examiners expect you to distinguish three categories:

1. Tectonic hazards — driven by plate movement: earthquakes, volcanic eruptions, tsunamis.
2. Atmospheric (weather/climatic) hazards — driven by the atmosphere: tropical storms, droughts, extreme cold, floods caused by rainfall.
3. Geomorphological hazards — driven by surface processes: landslides, mass movement (often a secondary hazard triggered by an earthquake or heavy rain).

Some events sit across categories. A volcanic eruption (tectonic) can trigger a lahar (geomorphological) and ash clouds that disrupt aviation (atmospheric impact). Always identify the primary trigger.

Hazard risk

Hazard risk = the probability that people will be harmed by a natural hazard. Risk is not just about the hazard itself; it depends on exposure and vulnerability. The standard formula examiners reward is:

Risk = (frequency or magnitude of hazard) × (vulnerability of population) ÷ (capacity to cope)

Factors that increase hazard risk

• Urbanisation. Megacities concentrate millions of people in a small area. When Mexico City (in a tectonic zone) or Dhaka (on a low-lying flood-prone delta) experience a hazard, the population at risk is enormous.
• Poverty. Lower-income people often live in the most hazardous areas (steep slopes, floodplains, marginal land) because cheaper land is unsafe land. Their housing is less hazard-resistant. After the 2010 Haiti earthquake, weak concrete-block houses collapsed catastrophically; richer neighbourhoods with reinforced construction fared better.
• Climate change. A warmer atmosphere holds more moisture, intensifying tropical storms; sea-level rise enlarges storm-surge zones; extreme heat events (UK 2022 reaching 40 °C) become more frequent.
• Farming on marginal land. Drought-prone regions of the Sahel are farmed because better land has been claimed; failed harvests turn drought into famine.
• Plate margins and active volcanoes. Living in Tokyo, Naples or Reykjavík puts millions of people next to known tectonic risks.

Factors that decrease hazard risk

• Wealth. HICs invest in monitoring (seismometers, satellite weather), early-warning systems, building codes, evacuation infrastructure and insurance.
• Education and preparedness. Japanese schoolchildren rehearse earthquake drills monthly; Bangladesh trained 70 000 cyclone volunteers after the 1970 Bhola disaster killed an estimated 500 000.
• Effective governance. Strong planning law, enforced building codes, organised emergency services and political stability all reduce vulnerability.

Examiner tips

• Always link your answer back to people. A 7.0 magnitude earthquake in remote Antarctica is a process, not a hazard.
• Use the trio physical / social / economic to structure answers about why one country suffers more than another.
• When asked about "factors that increase risk", give both a physical factor (e.g. proximity to a plate boundary) and a human factor (e.g. poverty, urbanisation). Most marks reward this combination.
• Climate change is examinable as a risk multiplier — it doesn't usually create hazards but it does intensify existing ones.