Tectonic hazards: plate boundaries, earthquakes and volcanoes
OCR J383 Paper 2 tests tectonic hazards with case-study questions. You MUST learn one earthquake case study and one volcanic case study, and be able to compare responses in HICs (High Income Countries) and LICs/NEEs (Low/Newly Emerging Economies).
Plate tectonics
The Earth's crust is divided into tectonic plates that move on the semi-molten mantle due to convection currents. Movement is a few centimetres per year.
Types of plate boundary
| Boundary | Direction of movement | Example | Hazards |
|---|---|---|---|
| Destructive (convergent) | Plates move together; denser oceanic plate subducts under continental | Andes; Pacific Ring of Fire | Earthquakes (deep); composite/stratovolcanoes |
| Constructive (divergent) | Plates move apart; magma rises to fill gap | Mid-Atlantic Ridge; Iceland | Earthquakes (shallow, less severe); shield volcanoes |
| Conservative (transform) | Plates slide past each other horizontally | San Andreas Fault (California) | Earthquakes (shallow, potentially severe); NO volcanoes |
| Collision | Two continental plates collide; neither subducts | Himalayas; Alps | Fold mountains; earthquakes; NO volcanoes |
Earthquakes
Caused when built-up stress along a fault is suddenly released, sending seismic waves through the Earth.
- Focus (hypocentre): the point where the earthquake originates underground.
- Epicentre: the point on the surface directly above the focus.
- Primary effects: shaking → building collapse, ground movement, infrastructure damage.
- Secondary effects: tsunami (if undersea), fires (broken gas pipes), disease (contaminated water), landslides.
- Richter scale: measures magnitude (logarithmic — each step = 10× more energy).
Volcanoes
Types of eruption and volcano depend on plate boundary:
| Type | Viscosity | Gas | Eruption | Shape |
|---|---|---|---|---|
| Shield | Low (basaltic) | Low | Gentle, frequent | Broad, gentle slopes |
| Composite/Stratovolcano | High (rhyolitic) | High | Violent, infrequent | Steep cone |
Case studies
Haiti earthquake (2010) — LIC
- Magnitude 7.0; shallow focus (13 km); conservative boundary.
- Causes of devastation: poorly constructed buildings (unreinforced concrete); dense urban population (Port-au-Prince); lack of emergency services; weak governance; poverty.
- Effects: ~230,000 deaths; 1.5 million displaced; 80% infrastructure destroyed.
- Response: slow and disorganised initially; international aid essential; NGOs (Médecins Sans Frontières) provided medical care; long-term reconstruction problems.
Japan earthquake and tsunami (2011) — HIC
- Magnitude 9.0; destructive boundary (Pacific plate subducts under North American plate); generated massive tsunami.
- Effects: 15,000+ deaths; Fukushima nuclear plant meltdown; $300 billion damage.
- Response: advanced early warning system gave minutes of warning; strict building codes (base isolation); military deployed immediately; well-funded recovery.
Comparing HIC vs LIC responses
| Factor | HIC (Japan) | LIC (Haiti) |
|---|---|---|
| Building quality | High (earthquake-resistant) | Poor (unreinforced) |
| Emergency services | Well-trained, well-equipped | Overwhelmed; inadequate |
| Warning systems | Advanced | Minimal |
| Recovery | Fast, well-funded | Slow; depends on international aid |
| Death toll relative to magnitude | Lower | Much higher |
Common OCR exam mistakes
- Saying "HICs cope better because they are richer" without specifying how money improves response (building codes, warning systems, emergency services).
- Confusing primary and secondary effects — an earthquake killing people directly = primary; the tsunami it triggers = secondary.
- Forgetting that conservative boundaries do NOT produce volcanoes (no magma at the surface).
- Not using case-study specifics — "a country was affected" scores nothing; "Haiti 2010, magnitude 7.0, 230,000 deaths" scores marks.
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