G18: Geological Hazard Processes
Geological hazards including landslides, subsidence, flooding and their relationship to geology, plus hazard monitoring and management.
Geological Hazard Processes
Geological hazards including landslides, subsidence, flooding and their relationship to geology, plus hazard monitoring and management.
Key Fact: Geological hazards arise from Earth processes that pose risk to people and property: landslides, subsidence, earthquakes, volcanic eruptions, flooding
Key Fact: Landslides (mass movement): rockfalls, slides, flows and creep; triggered by heavy rain, earthquakes, undercutting, or human activity
Key Fact: Factors affecting slope stability: angle, geology (weak layers, joints), water content (lubricates and adds weight), vegetation (stabilises or destabilises)
Key Fact: Subsidence: ground sinking due to dissolution of limestone (sinkholes), mining, or groundwater extraction
Key Fact: Monitoring: satellite (InSAR), GPS, strain gauges, seismometers, gas monitoring, groundwater level sensors
Key Fact: Management: hazard mapping, building codes, slope stabilisation, drainage, early warning systems, evacuation planning
📋 Key Vocabulary and Concepts
For Geological Hazard Processes, you must know:
- Mass movement: The downslope movement of rock, soil or debris under gravity, including falls, slides, flows and creep
- Rockfall: A type of mass movement where fragments of rock break away from a steep cliff and fall freely under gravity
- Subsidence: The sinking of the ground surface, caused by underground cavity collapse, mineral dissolution, or fluid extraction
- Sinkhole: A surface depression formed by the collapse of a cavity in soluble rock (limestone) beneath, caused by dissolution by groundwater
- Factor of safety: The ratio of resisting forces (friction, cohesion) to driving forces (gravity) on a slope; values >1 mean the slope is stable
❓ Practice Questions
Q: What factors increase the risk of a landslide?
Q: How does water trigger landslides?
Q: What causes subsidence and sinkholes in limestone areas?
Q: Name three methods of monitoring geological hazards.
Q: How can the risk from geological hazards be reduced?
✅ Answers
- Steep slope angle, weak or fractured geology (e.g. clay layers, jointed rock), water saturation (heavy rain raises pore water pressure, lubricates failure surfaces, and adds weight), removal of vegetation (roots stabilise soil), and human activities (cutting into slopes, loading the top, mining).
- Water increases pore water pressure within the slope, reducing friction between grains. It lubricates potential slip surfaces (especially clay layers). It adds weight to the soil. It can physically erode the base of slopes. All these reduce the factor of safety below 1, causing failure.
- Rainwater (slightly acidic from dissolved CO2) percolates through joints in limestone, gradually dissolving the rock and creating underground cavities. When the cavity roof becomes too thin to support the surface, it collapses, forming a sinkhole. Lowering the water table (from pumping) can accelerate this by removing buoyant support.
- 1) Seismometers to detect earthquakes and volcanic tremor. 2) GPS and satellite radar (InSAR) to measure ground deformation. 3) Groundwater monitoring (piezometers) to detect water level changes that may trigger landslides.
- Hazard mapping and zoning (avoid building in high-risk areas), slope stabilisation (retaining walls, drainage, rock bolts), building codes for earthquake resistance, early warning systems (sensors, alarms), and emergency planning (evacuation routes, shelters).
🎯 Exam Tips
- Water is the most common landslide trigger, explain how (pore pressure, lubrication, weight)
- Factor of safety: >1 = stable, <1 = failure
- Subsidence in limestone = dissolution + cavity collapse
- Monitoring + management strategies are both examined
📝 Exam Technique
GCSE Geology Exam Tips — Geological Hazard Processes:
1. For Geological Hazard Processes questions, use correct geological terminology and classify features precisely
2. Reference specific geological time periods and processes
3. When interpreting data, consider the quality and limitations of the evidence
4. Apply your understanding of Geological Hazard Processes to fieldwork observations and map data
5. For evaluation, weigh competing geological theories with evidence
1. For Geological Hazard Processes questions, use correct geological terminology and classify features precisely
2. Reference specific geological time periods and processes
3. When interpreting data, consider the quality and limitations of the evidence
4. Apply your understanding of Geological Hazard Processes to fieldwork observations and map data
5. For evaluation, weigh competing geological theories with evidence
⚠️ Common Errors
✗ Landslides only happen on very steep slopes ✓ Landslides can occur on moderately steep slopes (15-30 degrees) if the geology and water conditions are unfavourable; even gentle clay slopes can fail when saturated
✗ Sinkholes only form in limestone ✓ While most sinkholes form in soluble rocks (limestone, gypsum, salt), they can also form from mining subsidence or collapsing drainage tunnels
✗ Human activity has no effect on landslide risk ✓ Human activities such as slope cutting, loading the top of slopes, deforestation, leaking water mains, and mining significantly increase landslide risk
✍️ Model Answer
Full-Mark Response
Explain the causes of landslides and describe how geological hazard risk can be monitored and managed. [6 marks]
Landslides occur when the driving forces (gravity, weight of material) exceed the resisting forces (friction, cohesion, vegetation root strength) on a slope, i.e. when the factor of safety drops below 1. Geological factors include steep slopes, weak rock layers (especially clay which becomes slippery when wet), jointing and fracturing that reduces rock mass strength, and unfavourable dipping of bedding planes (daylighting joints). Water is the most common trigger: heavy rainfall raises pore water pressure, reducing friction between grains; it lubricates clay layers along potential slip surfaces; and it adds weight to the slope material. Human activities exacerbate risk: cutting into slopes for roads removes support; loading the slope crest (building) increases driving forces; deforestation removes root cohesion; and leaking water mains raise groundwater levels. Monitoring uses GPS and satellite radar (InSAR) to detect ground movement, piezometers to measure groundwater levels, seismometers for earthquake monitoring, and strain gauges on rock faces. Management strategies include hazard mapping to identify high-risk zones, land-use planning to avoid development in dangerous areas, engineering solutions (retaining walls, drainage systems, rock bolts, soil nailing), early warning systems that alert populations before failure, and emergency preparedness including evacuation plans. The most effective approach combines all these strategies.
📊 AO Deep Dive
Assessment Objective Analysis
AO1 (Knowledge & Understanding): Demonstrate knowledge and understanding of geological hazard processes, including key geological concepts, observational data and theoretical models relevant to OCR J357.
AO2 (Application of Knowledge): Apply knowledge and understanding of geological hazard processes to both familiar and unfamiliar geological contexts, using field evidence and theoretical principles to explain phenomena.
AO3 (Analysis & Evaluation): Analyse geological data related to geological hazard processes, evaluate evidence from observations and investigations, and construct reasoned arguments using scientific methodology.
📝 Exam Questions by Topic
🎬 Video Resources
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