Plate tectonics and the causes of tectonic hazards, their impacts, and strategies to manage and reduce risk.

What this dot point is asking

WJEC wants you to explain plate tectonics and why tectonic hazards occur, analyse their impacts and why those impacts vary, and evaluate strategies to manage and reduce risk, with case studies.

The answer

Plate tectonics and hazard causes

At constructive (divergent) boundaries plates move apart and magma rises, as along the Mid-Atlantic Ridge in Iceland; at destructive (convergent) boundaries oceanic plate subducts, causing deep earthquakes and explosive volcanoes, as around the Pacific Ring of Fire; conservative (transform) boundaries slide past, causing earthquakes, as on the San Andreas Fault in California; and collision zones build fold mountains such as the Himalayas. Hotspots create volcanoes away from boundaries, as in Hawaii.

Hazards and their impacts

Primary hazards are ground shaking and volcanic eruptions; secondary hazards include tsunami, landslides, liquefaction and ash, and often cause most deaths. Impacts are social (deaths, injury, displacement), economic (damage, lost output) and environmental, and vary with magnitude, depth, timing, population density and preparedness. The contrast between Haiti in 2010 (a magnitude $7.0$ shallow quake that killed an estimated $200{,}000$ to $300{,}000$ people in a low-income, poorly built city) and Tohoku, Japan in 2011 (a magnitude $9.0$ quake where most of the roughly $18{,}000$ deaths came from the tsunami, not the well-engineered buildings) shows that development and vulnerability, not magnitude alone, drive the death toll.

Managing and reducing risk

Management follows the hazard-management cycle: mitigation (land-use planning, building codes), preparedness (education, drills, warning systems), response (rescue, aid) and recovery (rebuilding, insurance). For earthquakes, aseismic building design (flexible frames, base isolation, counterweights) and early-warning systems save lives; for volcanoes, monitoring (seismicity, gas, ground deformation) supports evacuation, as before Mount Pinatubo in the Philippines in 1991, where evacuation saved thousands. The Park model shows how the curve of quality of life dips and recovers differently between countries depending on response and resources.

Examples in context

Example 1. Tohoku earthquake and tsunami, Japan (2011). A magnitude $9.0$ undersea quake off north-east Japan generated a tsunami over $10$ m high that overwhelmed coastal defences, killed around $18{,}000$ people and triggered the Fukushima nuclear accident. Despite the enormous magnitude, Japan's aseismic buildings, drills and early-warning system meant the shaking itself caused relatively few deaths, illustrating that a high-income country can manage the primary hazard well yet still be overwhelmed by a secondary one. Economic losses, however, exceeded $200$ billion US dollars, the costliest natural disaster on record at the time.

Example 2. Haiti earthquake (2010). A magnitude $7.0$ shallow quake struck near the densely populated capital Port-au-Prince in one of the world's poorest countries. Weak buildings collapsed, killing an estimated $200{,}000$ to $300{,}000$ people, and weak governance plus limited emergency capacity left the country dependent on slow, uneven international aid, with cholera and displacement persisting for years. The Haiti and Tohoku pairing is the classic WJEC contrast: a smaller quake causing vastly higher loss of life because of low development, high vulnerability and low capacity to cope.

Try this

Q1. Name the three main types of plate boundary that generate earthquakes. [2 marks]

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

Q2. Explain why two earthquakes of similar magnitude can have very different impacts. [3 marks]

• Cue. Risk equals hazard times vulnerability divided by capacity to cope, so building quality, population density, warning systems and emergency capacity, set by development, determine the toll.