What is the difference between hazard, vulnerability, exposure and risk?

A hazard is a natural process that could cause harm (the earthquake, eruption or landslide). Exposure is the people and property in the area that could be affected. Vulnerability is how susceptible those people and structures are to harm (weak buildings, poverty, lack of preparedness). Risk is the likelihood of harm, combining the hazard with exposure and vulnerability. This is why two events of equal size can have very different impacts: the hazard may be similar but the vulnerability and exposure differ.

Why is a stratovolcano more dangerous than a shield volcano?

It comes down to magma type and explosivity. An andesitic stratovolcano has viscous, gas-rich magma that traps gas and erupts explosively (high Volcanic Explosivity Index), producing the deadliest hazards: pyroclastic flows, heavy ash falls, lahars and dangerous gases. A basaltic shield volcano has runny magma from which gas escapes, so it erupts gently, mainly producing lava flows that are slow enough to escape, threatening property more than life.

Why is heavy rainfall such a common landslide trigger?

Water destabilises a slope in two ways at once. It adds weight to the slope material, increasing the driving force (the downslope component of gravity). More importantly, it raises the pore water pressure between grains, which reduces the friction (effective stress) holding the material together, lowering the resisting force. With the driving force up and the resisting force down, the balance can tip so that driving forces exceed resisting forces and the slope fails.

Are volcanoes or earthquakes easier to forecast?

Volcanoes are generally more predictable. Magma moving towards the surface produces measurable precursors: increasing small earthquakes, ground inflation (swelling), rising gas emissions and thermal anomalies. Monitoring these can often forecast an eruption days to weeks ahead and allow evacuation. Earthquakes, by contrast, strike with essentially no reliable short-term warning, so the main defence is mitigation (building codes, planning, education) rather than forecasting.

What is the single most common mistake in this module?

Using hazard and risk as synonyms, and saying water only adds weight to a slope. The hazard is the process; the risk combines the hazard with exposure and vulnerability, so equal hazards can carry very different risks. For slopes, water's biggest effect is raising pore water pressure, which cuts the friction holding the material together, not just adding weight. Always link mitigation methods to the force balance or to reducing vulnerability.

EnglandGeology

OCR A-Level Geology Module 6 Geohazards: earthquakes, volcanoes and landslides overview

A deep-dive OCR A-Level Geology guide to Module 6 Geohazards. Covers earthquake hazards, risk and mitigation, volcanic hazards and monitoring, and landslides and slope stability, with the hazard-vulnerability-risk framework and the exam patterns OCR repeats.

Generated by Claude Opus 4.817 min readOCR-H414-Module-6Updated 2026-06-02

Reviewed by: AI editorial process; not yet individually human-reviewed

Jump to a section

What Module 6 actually demands
Earthquake hazards, risk and mitigation
Volcanic hazards and monitoring
Landslides and mass movement hazards
How Module 6 is examined
Check your knowledge

What Module 6 actually demands

Geohazards applies the science of tectonics and surface processes to the dangers they pose to people. The module runs through earthquake, volcanic and landslide hazards, and across all three it asks you to think in terms of hazard, vulnerability, exposure and risk, and of monitoring, prediction and mitigation. The examiners reward applying this framework to case studies and data, not just describing the hazards.

This guide walks through the three clusters of the module, then sets out the exam patterns OCR repeats. Each cluster has a matching dot-point page with practice questions; this overview ties them together.

Earthquake hazards, risk and mitigation

Earthquakes cause primary hazards (ground shaking and surface rupture) and secondary hazards (liquefaction, landslides, tsunamis and fires). The key framework is the distinction between hazard (the process), exposure (people and property present), vulnerability (susceptibility to harm) and risk (the likelihood of harm, combining all three). This explains why equal-magnitude quakes can have very different impacts. Impact depends on magnitude, depth, ground conditions, population density, building design and preparedness. Because precise prediction is not possible, mitigation (building codes, land-use planning, early warning, education) is the main defence.

Volcanic hazards and monitoring

Volcanic hazards depend on magma type and explosivity: explosive (andesitic and rhyolitic) volcanoes produce the deadliest hazards (pyroclastic flows, heavy ash, lahars, gases, sector collapse), while basaltic volcanoes mainly produce slower lava flows. Volcanoes are monitored by seismicity, ground deformation (inflation), gas emissions and thermal anomalies, which usually give warning of an eruption. Mitigation uses hazard maps, exclusion zones and evacuation. Crucially, volcanoes are generally more predictable than earthquakes, because magma movement produces measurable precursors that allow forecasting and evacuation.

Landslides and mass movement hazards

Slope failure (rockfall, translational and rotational slides or slumps, debris flows) is governed by the balance of driving forces (downslope gravity, increased by steepness and weight) against resisting forces (friction and cohesion, plus support). Failure occurs when driving exceeds resisting. Triggers include slope angle, weak rock and out-dipping discontinuities, water (which adds weight and raises pore pressure, cutting friction), weathering, earthquakes and human activity. Warning signs include tension cracks and bulging toes. Stabilisation (drainage, regrading, retaining walls, rock bolts, vegetation) works by restoring the force balance, and drainage is often the most effective because water is so often the trigger.

How Module 6 is examined

A typical OCR profile for Geohazards:

Framework questions (Paper 2). Applying hazard, vulnerability, exposure and risk to explain why similar events have different impacts.
Hazard and mechanism questions (Paper 1). Describing secondary earthquake hazards, volcanic hazards and their link to magma type, and slope-failure types.
Monitoring and mitigation questions (Papers 1 and 2). Interpreting volcano-monitoring data, and explaining stabilisation methods through the force balance.
Level-of-response extended answers (Paper 2). Why a stratovolcano is more dangerous than a shield volcano, and how the force balance controls slope stability, are predictable extended questions.

Check your knowledge

A mix of recall and application questions covering the whole module. Attempt them under timed conditions, then check against the solutions.

Distinguish hazard, vulnerability and risk. (3 marks)
Describe two secondary hazards of an earthquake. (4 marks)
Explain why soft, water-saturated ground worsens earthquake damage. (3 marks)
Explain why an andesitic stratovolcano is more dangerous than a basaltic shield volcano. (4 marks)
Describe two methods of monitoring a volcano and what each reveals. (4 marks)
State when a slope fails, in terms of forces. (1 mark)
Explain two ways heavy rainfall reduces slope stability. (2 marks)
Describe two engineering methods to stabilise a slope, with the mechanism of each. (4 marks)

Solutions

Q1: A hazard is a natural process that could cause harm (the earthquake, eruption or landslide). Vulnerability is how susceptible people and structures are to harm. Risk is the likelihood of harm, combining the hazard with exposure and vulnerability.
Q2: Any two of: liquefaction (shaking of water-saturated sediment makes it behave like a liquid, so buildings sink or tilt); tsunami (a submarine quake displaces the sea floor and a large volume of water, flooding coasts); landslides on unstable slopes; and fires from ruptured gas and power lines.
Q3: Soft sediment amplifies the seismic waves, so shaking is stronger and longer. If loose and water-saturated, it can liquefy, losing strength so buildings sink or tilt. Both effects increase the damage compared with solid bedrock at the same distance.
Q4: An andesitic stratovolcano has viscous, gas-rich magma that erupts explosively (high VEI), producing pyroclastic flows, heavy ash, lahars and gases, which are fast, far-reaching and deadly. A basaltic shield volcano has runny magma that erupts gently as lava flows, which are slower and mainly threaten property, so it is less dangerous.
Q5: Any two of: seismicity (rising small earthquakes show magma moving and fracturing rock); ground deformation (inflation detected by tiltmeters, GPS or InSAR shows magma accumulating and pressure building); gas emissions (rising sulfur dioxide signals magma nearing the surface); and thermal anomalies (increasing heat shows magma rising).
Q6: A slope fails when the driving forces exceed the resisting forces.
Q7: Water adds weight to the slope material, increasing the driving force, and it raises the pore water pressure, which reduces the friction holding the grains together, decreasing the resisting force.
Q8: Any two of: drainage (removes water, lowering pore pressure and weight, so friction and stability rise); regrading (reduces the slope angle and so the driving force); retaining walls, rock bolts or soil nails (add support, increasing the resisting force); and vegetation (binds soil and removes water).