Earth's layered structure and convection; the three plate boundary types and hotspots; contrasting volcanic and earthquake (and tsunami) hazards; and the impacts and management of tectonic hazards in a developed and a developing or emerging country.

What this dot point is asking

This is Edexcel GCSE Geography B (1GB0) Paper 1, Section A (Topic 1, Hazardous Earth). Edexcel expects you to describe Earth's layered structure (including the asthenosphere) and explain how heat from the core drives convection that moves the plates; describe the three plate boundary types (conservative, convergent and divergent) and hotspots; explain the contrasting volcanic and earthquake hazards, including tsunami; and compare the impacts and management of a tectonic hazard in a developed and a developing or emerging country. A cross-section of the Earth or a plate-boundary map often appears.

Earth's structure and plate movement

The Earth is made of concentric layers with different composition and physical state.

The plates move because heat from radioactive decay in the core warms the mantle. Hot, less dense rock rises, cools near the surface, becomes denser and sinks, setting up convection currents that drag the plates above them. Slab pull, where a dense subducting plate sinks and pulls the rest of the plate with it, is now thought to be the dominant driver at convergent boundaries.

Plate boundaries and hotspots

There are three types of plate boundary, each with characteristic hazards.

Hazard differs by boundary because of the magma: convergent boundaries produce thick, gas-rich (viscous) magma that traps pressure and erupts explosively, while divergent boundaries and hotspots produce thin, runny (basaltic) lava that flows gently. Tsunami form when an undersea earthquake at a convergent boundary suddenly displaces a column of water, sending fast, low waves that rise into destructive surges near the coast.

Impacts and management

The effects of a tectonic event, and how well it is managed, depend strongly on a country's wealth.

Primary impacts happen instantly (buildings collapsing, deaths and injuries from shaking, lava and ash); secondary impacts follow on (fires, landslides, tsunami, disease, homelessness, economic losses). In a developed country (for example Japan), management is more effective: money funds aseismic (earthquake-resistant) building design, monitoring and early-warning systems, well-rehearsed evacuation, and trained, funded emergency services. In a developing or emerging country (for example Nepal in 2015, where about 9,000 people died, or Haiti in 2010), weak buildings collapse, rescue is slow, and the country often depends on international aid, so death tolls and long-term disruption are much higher.

Management is usually split into short-term relief (shelter, food, water and medical aid in the days after) and long-term planning (rebuilding to safer standards, training emergency services, land-use planning), alongside preparation (warnings, evacuation drills, building codes) and prediction (monitoring gas, ground deformation and seismic activity, more successful for volcanoes than earthquakes).

Try this

Q1. Explain why earthquakes occur at conservative plate boundaries. [4 marks]

• Cue. Plates slide past each other, friction locks them, stress builds, and the sudden release of that stored stress produces the earthquake.

Q2. Explain one reason a developed country may suffer fewer deaths in an earthquake than a developing country. [2 marks]

• Cue. Money for earthquake-resistant building design and well-funded, trained emergency services means buildings are less likely to collapse and rescue is faster.