The causes of tectonic hazards, why some develop into disasters, the impact of tectonic processes on people and places, and how risk can be managed through prediction, mitigation and the disaster cycle.

What this dot point is asking

Edexcel wants you to explain plate tectonic theory and the causes of earthquakes, volcanoes and tsunamis, explain why some tectonic hazards become disasters using the hazard, risk and vulnerability framework, and evaluate how risk can be managed through prediction, mitigation and the disaster cycle.

Plate tectonic theory and the causes of hazards

Earthquakes result from the sudden release of stress along faults; their magnitude is measured on the moment magnitude scale. Volcanoes form where magma reaches the surface. Tsunamis are usually triggered by submarine earthquakes at subduction zones that displace the water column.

The strength and behaviour of a margin help explain magnitude and recurrence. The 2011 Tohoku earthquake ($M_w\,9.0$) ruptured the Japan Trench subduction zone, where the Pacific plate descends beneath the Eurasian plate, and lifted the seabed enough to launch a tsunami over 10 m high. Magnitude is logarithmic: each whole step on the moment magnitude scale represents roughly $32\times$ more energy released, so a $M_w\,9.0$ event releases far more energy than the $M_w\,7.0$ that struck Haiti in 2010.

Why some hazards become disasters

A disaster is the realisation of a hazard that seriously disrupts a community beyond its own resources. The risk equation is often written as

The Pressure and Release (PAR) model traces a disaster back to root causes (such as limited access to power and resources), dynamic pressures (such as rapid urbanisation and weak institutions) and unsafe conditions (such as poor housing on unstable ground) that meet the hazard.

The contrast between Haiti 2010 and Tohoku 2011 is the classic comparison. Haiti, a low-income country, was struck by a moderate $M_w\,7.0$ quake with a shallow focus near the dense, poorly built capital Port-au-Prince. Around $230{,}000$ people died, largely because of pancaking unreinforced concrete buildings, a weak state and no warning. Japan, a high-income country, absorbed a far larger $M_w\,9.0$ event with aseismic engineering, drills and an early-warning system; most of the roughly $18{,}000$ deaths came from the tsunami, not building collapse, and the Fukushima Daiichi nuclear meltdown showed how secondary hazards compound a disaster. Development shaped vulnerability and capacity to cope, while physical factors (focus depth, the tsunami) shaped the hazard.

Managing tectonic risk

The Park (disaster response) model plots quality of life over time through deterioration, relief, rehabilitation and reconstruction, and the curve varies with hazard type and management. A well-prepared HIC like Japan shows a shallower dip and faster recovery than a LIC like Haiti, whose curve fell further and rose slowly. The hazard management cycle covers mitigation, preparedness, response and recovery. Strategies include prediction and monitoring (seismometers, gas and ground-deformation sensors for volcanoes), aseismic building design, land-use zoning, education and early-warning systems. Earthquakes cannot reliably be predicted; volcanic eruptions often can be.

This connects synoptically to wider geopolitics. Players differ in power: national governments set building codes, NGOs and the UN deliver relief, and insurers shape recovery. Attitudes to risk vary: fatalistic acceptance in some communities versus active mitigation in others. Futures matter because urbanisation in megacities such as Tokyo, Manila and Istanbul concentrates exposure, so managing tectonic risk is increasingly about reducing vulnerability before the event, not just responding after it.

Examples in context

Example 1: Eyjafjallajokull, Iceland (2010). This constructive-margin eruption was modest in volume but its ash plume grounded European aviation for six days, costing airlines around \1.7$ billion. It shows that a low-magnitude hazard in a connected, globalised world can have outsized economic and social impacts far from the source, a synoptic link to globalisation and interdependence.

Example 2: Nepal earthquake (2015). A $M_w\,7.8$ quake on the India-Eurasia collision margin killed around $9{,}000$ people and destroyed heritage sites in Kathmandu. As a low-income, mountainous country, Nepal faced landslides as a secondary hazard, blocked roads slowing relief, and heavy dependence on international aid, illustrating the PAR model's dynamic pressures (rapid, unplanned urban growth) and unsafe conditions (weak masonry housing).

Try this

Q1. Explain why tsunamis are most associated with destructive plate margins. [4 marks]

• Cue. Subduction generates large submarine earthquakes that vertically displace the seabed and the water column above.

Q2. Using the risk equation, explain why two earthquakes of equal magnitude can produce very different death tolls. [4 marks]

• Cue. Risk depends on vulnerability and capacity to cope, not magnitude alone; development, building quality and preparedness vary.