What does T1 of WJEC A-Level Geology cover?

T1, Geohazards, is one of the two compulsory Geological Themes at A2. It applies the tectonic and structural content to natural hazards: how earthquakes are generated and the waves, magnitude, intensity and primary and secondary hazards they produce; how magma composition controls volcanic style and the volcanic hazards and the methods used to monitor volcanoes; and the types of mass movement, the controls on slope stability and the causes of ground subsidence, together with the prediction and mitigation of each hazard.

What is the difference between earthquake magnitude and intensity?

Magnitude measures the energy released at the source on a logarithmic scale (such as the moment magnitude scale), so it is a single number for the whole earthquake. Intensity measures the shaking and effects felt at a particular place (such as the Mercalli scale), so it varies with distance from the epicentre, the ground conditions and the quality of construction, and one earthquake therefore has many intensity values but only one magnitude.

How does magma composition control volcanic hazards?

Magma composition controls viscosity and gas retention. Low-silica basaltic magma is runny and lets gas escape, so it erupts effusively as lava flows with low explosivity. High-silica andesitic and rhyolitic magma is viscous and traps gas, so pressure builds and it erupts explosively, producing the deadliest hazards: pyroclastic flows, ash falls and, with water, lahars. Eruptive style and hazard are therefore predictable from composition and tectonic setting.

How are volcanoes monitored?

By combining methods that detect rising magma: seismometers record earthquakes and harmonic tremor as magma moves and fractures rock; tiltmeters, GPS and satellite radar detect swelling as the magma chamber inflates; gas sensors detect rising sulphur dioxide and carbon dioxide; and thermal and infrared surveys detect heating. Together these signals let scientists raise alert levels and order evacuation, making eruptions more predictable than earthquakes.

What controls whether a slope fails?

A slope fails when the downslope driving force exceeds the resisting strength. The controls are the slope angle (steeper is less stable), the rock type and structure (weak rocks and beds or joints dipping out of the slope provide slip surfaces), water (rain adds weight and raises pore-water pressure, the commonest trigger), vegetation (roots bind soil and remove water) and undercutting at the base by erosion or excavation, which removes support.

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WJEC A-Level Geology T1 Geohazards: a deep dive on earthquakes, volcanoes and mass movement

A deep-dive WJEC and Eduqas A-Level Geology guide to T1, Geohazards. Covers earthquake generation, seismic waves, magnitude and intensity and seismic hazards, the control of magma composition on volcanic style and the volcanic hazards and monitoring, and mass movement and ground subsidence, with the prediction and mitigation of each, and exam-style worked questions.

Generated by Claude Opus 4.814 min readWJECUpdated 2026-06-16

Reviewed by: AI editorial process; not yet individually human-reviewed

Jump to a section

What T1 actually demands
Earthquakes
Volcanoes
Mass movement and ground hazards
Check your knowledge

What T1 actually demands

T1 is applied tectonics. Examiners want you to connect the science (faults, plate boundaries, magma composition, weathering) to the hazards people face, and to give realistic, named mitigation. The recurring skill is reading a scenario, identifying the dominant hazards from the geology, and proposing prediction and management measures.

Each hazard has a dot-point page with worked questions; this overview connects them.

Earthquakes

Earthquakes release stored elastic strain by elastic rebound when rocks slip on a fault, rupturing at the focus below the surface epicentre, and send P, S and surface waves. Magnitude measures energy at the source; intensity measures effects at a place. The primary hazard is ground shaking, with liquefaction, landslides, tsunami and fire as secondary hazards. Earthquakes cannot be reliably predicted, so risk is reduced by resistant design, codes, planning, education and early warning.

Volcanoes

Magma composition controls eruptive style: basaltic magma erupts effusively as lava flows, while silicic magma erupts explosively, producing pyroclastic flows, ash and lahars. Volcanoes are monitored by seismicity, ground deformation, gas and thermal methods, making eruptions more predictable, and risk is managed by hazard maps, exclusion zones and evacuation.

Mass movement and ground hazards

Mass movement (rockfall, slide, slump, flow) is controlled by slope angle, rock type and structure, water, vegetation and undercutting. Subsidence follows the collapse of mine voids and the dissolution of soluble rock. Both are reduced by mapping, stabilisation, grouting and monitoring.

Check your knowledge

Attempt these under timed conditions, then check against the solutions.

Distinguish the focus from the epicentre of an earthquake. (2 marks)
Explain the difference between magnitude and intensity. (2 marks)
Explain why a high-silica magma erupts explosively. (2 marks)
Name the deadliest volcanic hazard. (1 mark)
State three factors that control slope stability. (3 marks)
State two causes of ground subsidence. (2 marks)

Sources & how we know this

WJEC Eduqas A-level Geology specification — WJEC Eduqas (2017)