The concept of hazard and risk; hazard perception and the Park model; plate tectonics and volcanic, seismic, tropical storm and wildfire hazards; their impacts; and the responses to and management of these hazards.

What this dot point is asking

AQA section 3.1.5 wants you to understand the concept of hazard and risk, explain hazard perception and management models, apply plate tectonic theory to volcanic and seismic hazards, explain the formation and impacts of tropical storms and wildfires, and assess the responses used to manage them. The synoptic thread running through the topic is that a hazard becomes a disaster only when it interacts with a vulnerable population, so impact is always a function of the physical event and human geography together.

The concept of hazard and risk

Hazard perception depends on experience, wealth, education, religion and the perceived value of a location. Three broad responses recur: fatalism (acceptance, the hazard is unavoidable), adaptation (prepare and prediction-driven adjustment) and fear (relocation away from the risk). Perception explains why people continue to live on the slopes of active volcanoes such as Etna, where fertile soils and tourism outweigh perceived risk.

Two models structure responses. The Park (disaster response) model plots quality of life against time, falling sharply during the event, then rising through relief (immediate aid), rehabilitation (temporary restoration) and reconstruction (rebuilding to the same or a better state). The depth of the dip and the speed of recovery depend on the hazard and on the level of development. The hazard management cycle is iterative: mitigation, preparedness, response and recovery feeding back into mitigation.

Plate tectonics

The lithosphere is divided into rigid plates moving over the plastic asthenosphere, driven primarily by slab pull (subducting dense crust dragging the plate) with contributions from ridge push and mantle convection. The four margin types each produce a characteristic hazard signature:

• Constructive (divergent): plates diverge, magma rises by decompression melting, building gentle shield volcanoes (Iceland on the Mid-Atlantic Ridge) and shallow, low-magnitude quakes.
• Destructive (convergent): oceanic crust subducts beneath continental or oceanic crust, releasing water that lowers the mantle's melting point and feeds viscous, gas-rich composite (strato) volcanoes prone to violent eruptions; the Benioff zone generates deep, high-magnitude earthquakes and the largest tsunamis.
• Collision: two continental plates meet, crust crumples upward (the Himalayas), producing major earthquakes but little volcanism.
• Conservative (transform): plates slide past laterally (the San Andreas Fault); friction locks the margin until stress releases as a powerful earthquake. No subduction means no magma, so no volcanoes.

Intra-plate hot spots are stationary mantle plumes; as a plate drifts over one, a chain of progressively older volcanoes forms (the Hawaiian-Emperor seamount chain).

Volcanic and seismic hazards

The relationship between magnitude and impact is non-linear. The moment magnitude scale is logarithmic, so each whole number is roughly a tenfold increase in amplitude and about 32 times the energy release. This is why a magnitude 9.0 event releases vastly more energy than a magnitude 7.0, yet a shallow magnitude 7.0 directly beneath a poorly built city can kill far more people than a deep magnitude 9.0 offshore.

Tropical storms

Tropical storms (hurricanes, cyclones, typhoons) form over oceans warmer than about $27\,^{\circ}\text{C}$ to a depth of around 70 metres, between roughly 5 and 30 degrees latitude where the Coriolis effect is strong enough to initiate rotation but the storm is not on the equator. Warm, moist air rises rapidly, condenses and releases latent heat, which powers further uplift in a self-sustaining engine, creating the calm, low-pressure eye surrounded by the towering eyewall. They bring high winds, intense rainfall, flooding and a devastating storm surge as low pressure and onshore winds pile water against the coast (the main killer in Hurricane Katrina, 2005). The Saffir-Simpson scale ranks intensity. Warming sea-surface temperatures may increase the proportion of high-category storms and raise rainfall totals.

Wildfires

Wildfires require three ingredients in the fire triangle: fuel (vegetation, drier with higher biomass), favourable weather (drought, high temperatures, low humidity and strong winds) and a source of ignition (lightning or, increasingly, human activity). Fire behaviour ranges from slow ground and surface fires to fast, destructive crown fires that leap between treetops. Management focuses on fuel reduction (controlled burns), early detection and defensible space around property.

Impacts, responses and the role of development

Impacts are primary (immediate: deaths, building collapse, severed services) and secondary (later: disease, fires from ruptured gas mains, economic loss, tsunamis). The scale reflects vulnerability and capacity to cope, which often correlate with the level of development: higher-income countries tend to suffer fewer deaths but greater absolute economic losses, while lower-income countries suffer mass casualties and slower recovery. Management combines monitoring and prediction (seismographs, satellite tracking, gas sensors), preparedness (education, building codes, evacuation drills), mitigation (land-use zoning, sea defences) and recovery.

Try this

Q1. Distinguish between a hazard and a disaster. [2 marks]

• Cue. A hazard threatens people; a disaster is the realisation that overwhelms the community's ability to cope using its own resources.

Q2. Explain why earthquakes do not occur at hot spots. [3 marks]

• Cue. Hot spots are intra-plate mantle plumes away from margins; without plate-boundary friction or subduction there is little tectonic strain, so volcanism occurs without significant seismicity.

Q3. Assess the usefulness of the Park model for understanding responses to a tectonic hazard. [9 marks]

• Cue. Strengths: shows phases (relief, rehabilitation, reconstruction) and lets you compare recovery between places. Limits: generalised curve, ignores secondary hazards and assumes a single event; recovery depends on development and aid. Reach a judgement.