Edexcel A-Level Geography: Tectonic Processes and Hazards Revision Guide

Tectonic Processes and Hazards is the opening topic of Edexcel A-Level Geography, examined as Topic 1 on Paper 1. It is compulsory, so every candidate sits it, and it carries significant weight in the exam. The ideas about risk, vulnerability and resilience that you develop here also reappear in Paper 3 synoptic questions.

This guide covers the full specification content for tectonic hazards, the models and frameworks you need to reference, the case studies examiners expect, and how to write high-scoring 20-mark essays.

The Enquiry Questions

The Edexcel specification structures every topic around enquiry questions, and your revision should be built around them. Tectonic Processes and Hazards has three.

EQ1 -- Why are some locations more at risk from tectonic hazards? This is about distribution and the physical processes behind it: why earthquakes, volcanoes and tsunamis cluster where they do, and why their characteristics vary from place to place.

EQ2 -- Why do some tectonic hazards develop into disasters? This is the crucial step from physical event to human catastrophe. A hazard only becomes a disaster when it affects a vulnerable population that lacks the capacity to cope -- this is where governance, development and inequality enter the topic.

EQ3 -- How successful is the management of tectonic hazards? Here you evaluate the strategies, models and approaches used to reduce risk and respond to events, from prediction and preparation to relief and reconstruction. The topic is, in effect, a journey from physical geography (why hazards happen and where) to human geography (why they kill and how we respond), and strong answers hold both halves together.

The Structure of the Earth and Plate Tectonics

The Earth is layered into the inner core (solid iron-nickel), the outer core (liquid), the mantle, and the crust. The crust and rigid uppermost mantle together form the lithosphere, broken into tectonic plates, beneath which lies the asthenosphere, a partially molten, ductile layer over which the plates move. Oceanic crust is thin (around 6-10 km), dense and basaltic, and is continually created and destroyed; continental crust is thick (typically 30-70 km), less dense, granitic, and far older because it is not subducted.

The mechanism that drives plate movement is debated. Mantle convection -- convection currents driven by heat from radioactive decay -- is the traditional model. More recent thinking emphasises slab pull, the gravitational sinking of dense subducting oceanic plates, and ridge push, the gravitational sliding of plates away from elevated mid-ocean ridges. Most geologists now regard slab pull as the dominant force.

Plate Boundaries

The type of plate boundary controls the hazards a location experiences.

Constructive (divergent) boundaries occur where plates move apart, as at the Mid-Atlantic Ridge or the East African Rift. Magma rises to fill the gap and create new crust; volcanic activity is effusive with runny basaltic lava, and earthquakes are shallow and low magnitude.

Destructive (convergent) boundaries occur where plates move towards each other. Where oceanic crust meets continental crust the denser oceanic plate subducts, as along the Pacific coast of South America, producing deep trenches, explosive andesitic volcanoes and powerful, deep earthquakes; where two oceanic plates converge, island arcs form (Japan); where two continental plates collide, crust is buckled into fold mountains (the Himalayas), producing major earthquakes but little volcanic activity.

Conservative (transform) boundaries occur where plates slide past one another, as along the San Andreas Fault. There is no creation or destruction of crust and no volcanic activity, but the sudden release of strain generates significant earthquakes.

You should also know about intra-plate activity and hot spots -- localised plumes of rising magma that produce volcanoes far from any plate margin, the Hawaiian chain being the classic example and a useful exception to the "hazards happen at plate boundaries" rule.

For lesson-by-lesson coverage of plate tectonics and boundary types, work through our Tectonic Processes and Hazards course.

Earthquakes, Volcanoes and Tsunamis

Earthquakes result from the sudden release of strain energy along faults, radiating seismic waves from the focus (the point of rupture at depth) to the epicentre (the point directly above it). Focus depth matters: shallow-focus earthquakes do far more surface damage than deep-focus ones of equivalent magnitude. Magnitude is measured on the moment magnitude scale (Mw), which has superseded the Richter scale for large events, while felt intensity is described by the Modified Mercalli scale. Secondary hazards are often the deadliest aspect: liquefaction, where saturated soils lose strength and behave like a liquid, and landslides triggered by ground shaking.

Volcanoes vary enormously. At constructive margins and hot spots, basaltic lava produces gentle, effusive eruptions and shield volcanoes; at destructive margins, viscous andesitic magma traps gas and produces violently explosive eruptions and steep stratovolcanoes. Volcanic hazards include lava flows, pyroclastic flows (fast-moving currents of hot gas and ash, the most lethal volcanic hazard), tephra and ash fall, lahars (volcanic mudflows), and gas emissions, with explosivity described by the Volcanic Explosivity Index (VEI).

Tsunamis are series of waves usually generated by submarine earthquakes at subduction zones, where vertical displacement of the seabed displaces the water column. They travel fast across the open ocean with a low wave height, then slow and build dramatically in height as they reach shallow coastal water. They can also be triggered by submarine landslides and volcanic activity.

Hazard Profiles

A hazard profile is a technique for comparing hazards across a set of physical criteria in a structured way. Typical criteria include:

• Magnitude -- the size or intensity of the event
• Speed of onset -- how quickly it arrives, from the near-instant shaking of an earthquake to the slow build of some volcanic eruptions
• Duration -- how long the event lasts
• Areal extent -- the size of the area affected
• Spatial predictability -- how well we can forecast where it will occur
• Frequency -- how often events of a given size recur

Hazard profiles are valuable because they show why two events of similar magnitude can have very different consequences, and why management must be tailored to a hazard's specific characteristics: a volcanic eruption with a slow onset and good spatial predictability can be managed by evacuation, whereas an earthquake with near-zero onset time and poor predictability cannot.

Frameworks for Understanding Risk and Disaster

These frameworks are the conceptual heart of the topic and the part that separates top answers from competent ones.

The Risk Equation

Degg's risk equation expresses the relationship between the physical event and its human consequences:

Risk = (Hazard x Vulnerability) / Capacity to cope

The insight is that the size of a disaster is not determined by the physical hazard alone. The same magnitude earthquake produces a far greater disaster where vulnerability is high (dense population, poor-quality buildings, weak governance) and capacity to cope is low (limited emergency services, little money, poor infrastructure). This is why disasters are described as "socially constructed": the hazard is natural, but the disaster is shaped by human factors.

Park's Disaster-Response Curve

The Park model (the disaster-response curve) plots quality of life, or level of social and economic functioning, against time through a hazard event. It identifies stages: a normal pre-disaster state; a sharp deterioration as the hazard strikes; a relief phase (immediate emergency response); a rehabilitation phase (restoring services and temporary infrastructure); and a reconstruction phase (rebuilding to the same or a better state). The shape and depth of the curve vary with the hazard and the place: a well-prepared, wealthy society shows a shallower dip and faster recovery, and may even "build back better" and end above its starting line, whereas a poorly prepared, low-capacity society shows a deeper dip and a slower, flatter recovery -- making the model a powerful tool for comparing recovery trajectories.

The Pressure and Release (PAR) Model

The Pressure and Release model, developed by Wisner, Blaikie, Cannon and Davis, explains disasters as the intersection of a natural hazard and a "progression of vulnerability". The pressure builds through three linked stages: root causes (limited access to power and resources) produce dynamic pressures (rapid urbanisation, lack of training, population growth, deforestation), which generate unsafe conditions (people living in dangerous locations in fragile buildings with no protection). The disaster occurs where this progression meets the hazard; the "release" is the idea that reducing the pressure -- by addressing the underlying causes of vulnerability -- reduces risk. PAR is the model to reach for when a question asks why hazards become disasters, because it pushes the explanation back to political and economic root causes.

The Hazard-Management Cycle

The hazard-management cycle frames management as a continuous, four-stage loop -- mitigation, preparedness, response and recovery -- with recovery from one event feeding into mitigation and preparedness for the next.

Case Studies

Examiners expect specific, located case study evidence with real figures. These well-attested events allow powerful comparison between high-income and lower-income contexts.

Tōhoku, Japan, 2011

A magnitude 9.0-9.1 earthquake off the Pacific coast of Tōhoku on 11 March 2011 -- the most powerful ever recorded in Japan -- triggered a devastating tsunami with run-up heights reaching tens of metres in places. Around 18,000-20,000 people died or went missing, the vast majority drowned by the tsunami rather than killed by the shaking, demonstrating the lethality of secondary hazards; the tsunami also overtopped sea defences and caused the Fukushima Daiichi nuclear accident. Japan's rigorous building codes, world-leading early-warning system and well-drilled population limited deaths from the shaking, yet the scale of the tsunami overwhelmed even its preparations. Tōhoku shows that high capacity reduces but cannot eliminate disaster, and illustrates the difference between primary and secondary hazards.

Haiti, 2010

A magnitude 7.0 earthquake struck near Port-au-Prince on 12 January 2010. Although far smaller in magnitude than Tōhoku, it was catastrophic: death-toll estimates vary widely but run into the hundreds of thousands, with millions displaced. Haiti was the poorest country in the Western Hemisphere, with extreme vulnerability and very low capacity to cope -- a shallow focus close to a densely populated capital, widespread informal housing with no seismic design, weak governance and almost no emergency infrastructure. It is the textbook illustration of the risk equation: a moderate hazard produced an extreme disaster because vulnerability was high and capacity minimal, and the slow, aid-dependent recovery maps neatly onto a deep, flat Park curve.

Nepal (Gorkha), 2015

A magnitude 7.8 earthquake struck the Gorkha district of Nepal on 25 April 2015, followed by a major aftershock. Around 9,000 people died and large parts of the Kathmandu Valley and remote mountain districts were devastated. Nepal is a lower-income, mountainous country where rugged terrain hampered the relief effort, many traditional unreinforced masonry buildings collapsed, and the quake triggered landslides and a deadly avalanche on Everest. Gorkha shows how physical geography and development level interact to shape both vulnerability and the difficulty of response.

Eyjafjallajökull, Iceland, 2010

The 2010 eruption of Eyjafjallajökull is the key example of a hazard whose impacts are economic and global rather than local and fatal. Because the volcano sits beneath an ice cap, meltwater interacting with magma produced fine, glassy ash that prevailing winds carried across European airspace. The resulting airspace closure for roughly six days grounded over 100,000 flights and stranded millions of passengers, with billions of dollars in losses to aviation, yet there were very few direct casualties. It shows that a hazard's magnitude and the scale of its consequences are not the same thing: a relatively small eruption in a remote area can have a vast, globalised economic footprint.

How to Write 20-Mark Essays on Tectonic Hazards

The 20-mark essay on Paper 1 is the most demanding question you will face on this topic. Here is how to structure your response for maximum marks.

Understand the Assessment Objectives

The 20-mark question assesses three things:

• AO1 (Knowledge and understanding) -- 5 marks for accurate, detailed knowledge
• AO2 (Application) -- 10 marks for applying that knowledge to the question, using evidence and examples
• AO3 (Evaluation) -- 5 marks for evaluating different perspectives and reaching a justified conclusion

Half the marks are for application, so use your case studies to address the question directly, not simply describe them.

Essay Structure

Introduction (2-3 minutes): Define key terms, set out your line of argument, and signpost your structure.

Main body (18-20 minutes): Write three or four paragraphs, each making a distinct, analytical point, using a PEEL structure -- Point, Evidence, Explain, Link. Anchor every point in located case study evidence and use the models as analytical tools rather than facts to be recited.

Conclusion (3-4 minutes): Do not repeat your points. Weigh the evidence and reach a substantiated judgement, using phrases such as "on balance", "the most significant factor is", or "this holds true to a large extent because".

Common Essay Questions on Tectonic Hazards

• "Assess the extent to which the impacts of a tectonic hazard are determined by levels of development." (Haiti vs. Tōhoku; deploy the risk equation)
• "Evaluate the view that vulnerability is more important than physical processes in turning a hazard into a disaster." (PAR model is central)
• "To what extent is the successful management of tectonic hazards dependent on prediction?" (predictable volcanoes vs. unpredictable earthquakes)
• "Assess the usefulness of hazard-management models in understanding responses to tectonic disasters." (Park and the management cycle)

Common Mistakes to Avoid

• Being descriptive rather than analytical. Do not just describe what happened at Tōhoku -- explain why the outcome was as it was.
• Using vague examples. "A big earthquake in a poor country" is not a case study; "the magnitude 7.0 Haiti earthquake of 2010, with a shallow focus near a densely populated capital and widespread informal housing" is.
• Reciting models without applying them. The risk equation and PAR are analytical tools -- use them to explain a real event.
• Ignoring the command word. "Assess" and "evaluate" require weighing of viewpoints; "to what extent" demands a judgement.

Key Vocabulary for Tectonic Hazards

• Lithosphere / asthenosphere -- the rigid plate layer and the ductile layer beneath it
• Slab pull / ridge push -- the gravitational forces now thought to dominate plate movement
• Focus / epicentre -- the point of rupture at depth and the point above it on the surface
• Liquefaction -- the loss of soil strength under seismic shaking
• Risk equation -- Risk = (Hazard x Vulnerability) / Capacity to cope
• Vulnerability / capacity to cope -- the human factors that turn a hazard into a disaster
• PAR model -- explains disasters through a progression of vulnerability from root causes to unsafe conditions
• Park's response curve -- the disaster-response model tracking recovery over time
• Hazard profile -- a structured comparison of hazards across physical criteria

Further Revision

For full specification coverage of tectonic processes and hazards with lesson-by-lesson content and AI-powered quizzes, work through our Tectonic Processes and Hazards course. You should also explore the related physical and synoptic topics:

• The Water Cycle and Water Insecurity -- the other compulsory physical-systems topic on Paper 1, sharing the systems and resilience thinking
• Synoptic Skills and Exam Preparation -- risk, vulnerability and resilience are recurring synoptic themes in Paper 3

Tectonic Processes and Hazards rewards candidates who move fluently between physical processes and human vulnerability. Master the models, pair them with precise case studies, and you will have a topic that lifts your performance across the whole of Paper 1.