Plate tectonic theory, the processes at plate margins, the causes and impacts of earthquakes and volcanoes, and the management of tectonic hazards.

What this dot point is asking

CCEA wants you to explain plate tectonic theory and the evidence for it, describe the processes at the three main plate margins, account for the causes and impacts of earthquakes and volcanic eruptions, and evaluate how tectonic hazards are managed, using located examples such as the 2010 Haiti earthquake and the 2010 Eyjafjallajokull eruption.

Plate tectonic theory

The lithosphere is divided into rigid plates that move over the partly molten asthenosphere. Movement is driven by convection currents in the mantle, aided by ridge push at constructive margins and slab pull as a subducting slab drags the plate down. Evidence includes the fit of the continents (South America and Africa), matching fossils such as Mesosaurus and matching rock sequences across oceans, palaeomagnetic striping recording reversals symmetrically about ridges, and the age of sea-floor crust increasing away from ridges (sea-floor spreading).

Processes at plate margins

Causes and impacts of hazards

Earthquakes result from the sudden release of built-up stress along faults; the energy radiates from the focus, with the epicentre directly above. Their impacts include ground shaking, liquefaction of saturated sediment, landslides and tsunamis. Volcanoes at destructive margins erupt viscous, gas-rich andesitic lava explosively (pyroclastic flows, ash, lahars), while those at constructive margins or hotspots (Hawaii, Iceland) produce gentler, effusive basaltic eruptions.

Primary impacts occur immediately and directly (building collapse, ground rupture); secondary impacts develop afterwards (fire, disease, tsunami, economic disruption). Impacts are usually far worse in lower-income countries because of weaker buildings, denser informal settlement and limited emergency capacity.

Managing tectonic hazards

Management spans prediction and monitoring (seismometers, gas emission and ground-bulge measurement at volcanoes), building design (aseismic structures, cross-bracing, base isolation), land-use planning, education and drills, and well-resourced emergency response and aid. The Park model shows how an area moves through the relief, rehabilitation and reconstruction phases after an event, with the curve dipping less and recovering faster where preparedness is high.

Examples in context

Example 1. The 2010 Haiti earthquake (high vulnerability). A magnitude $7.0$ earthquake struck near Port-au-Prince on a conservative margin on 12 January 2010 at a shallow focus of about $13 \text{ km}$. Around $220{,}000$ people died and $1.5$ million were made homeless. Weak unreinforced buildings, dense informal settlement, extreme poverty and a government with little response capacity turned a moderate-magnitude event into a catastrophe, with cholera spreading in the aftermath. It illustrates how development and vulnerability govern impact.

Example 2. The 2010 Eyjafjallajokull eruption, Iceland (constructive margin and hotspot). This eruption on the Mid-Atlantic Ridge produced an ash plume that, because the ice cap chilled and fragmented the magma, was fine and high-reaching. European airspace closed for around six days, grounding over $100{,}000$ flights and costing airlines an estimated billions of euros. With few local deaths but huge global economic and transport impacts, it shows that effusive and constructive settings can still produce far-reaching secondary impacts.

Try this

Q1. Name the three main types of plate margin. [3 marks]

• Cue. Constructive (divergent), destructive (convergent) and conservative (transform).

Q2. Explain why earthquake impacts are often greater in lower-income countries. [4 marks]

• Cue. Weaker buildings, dense informal settlement, limited prediction, and a slower, under-resourced emergency response increase vulnerability.

Q3. With reference to a located example, explain how one method is used to manage a tectonic hazard. [6 marks]

• Cue. Aseismic building design, monitoring, land-use planning, education or response; link the method to reducing primary or secondary impacts.