The nature of vulcanicity and its relation to plate tectonics; forms of volcanic hazard; the primary and secondary impacts; and prediction, prevention, protection and adaptation responses.

What this dot point is asking

AQA section 3.1.5 wants you to explain the nature of vulcanicity and its link to plate tectonics, identify the forms of volcanic hazard, set out the primary and secondary impacts (environmental, social, economic, political; short and long term), and evaluate the management responses of prediction, prevention, protection and adaptation. Magma chemistry, set by the plate-margin context, controls everything that follows.

The nature of vulcanicity

Vulcanicity is controlled by magma chemistry, which is set by the plate-tectonic context.

At constructive margins and hot spots, hot basaltic magma is fluid and low in gas, so it erupts gently as lava flows. At destructive margins, subduction generates cooler, silica-rich magma that traps gas; pressure builds until it erupts explosively, producing pyroclastic flows and ash.

Forms of volcanic hazard

• Lava flows: destroy property but usually move slowly enough to escape (basaltic flows).
• Pyroclastic flows: fast, superheated clouds of gas, ash and rock; the most lethal hazard.
• Ash (tephra) falls: bury crops, collapse roofs, contaminate water and ground aircraft (the 2010 Eyjafjallajokull ash cloud grounded European flights).
• Volcanic gases: $CO_2$, sulphur dioxide and others can suffocate and poison.
• Lahars: volcanic mudflows of ash and water (rain or melted ice) that race down valleys.
• Jokulhlaups: sudden glacial outburst floods when an eruption melts overlying ice.

Impacts

Impacts also scale with development and governance: wealthier, better-governed places monitor, evacuate and rebuild more effectively, so the same eruption can be far deadlier in a poorer country.

Management responses

• Prediction: the most effective tool. Monitoring seismicity, ground deformation (tiltmeters, GPS, satellite InSAR) and gas emissions gives warning, enabling evacuation. Forecasting and timely evacuation saved thousands at Pinatubo (1991).
• Prevention: essentially impossible; an eruption cannot be stopped.
• Protection: limited success, for example diverting or chilling lava flows and reinforcing roofs against ash.
• Adaptation and preparedness: hazard mapping, land-use zoning to keep settlement away from valleys, building codes, education and evacuation drills reduce long-term exposure.

Try this

Q1. Name four forms of volcanic hazard. [4 marks]

• Cue. Lava flows, pyroclastic flows, ash (tephra) falls, gases, lahars or jokulhlaups (any four).

Q2. Explain why composite volcanoes erupt more explosively than shield volcanoes. [3 marks]

• Cue. Composite volcanoes form from viscous, silica-rich, gas-charged magma at destructive margins; trapped gas builds pressure until it erupts explosively, unlike fluid basaltic lava.

Q3. Explain why prediction is the most effective volcanic management strategy. [3 marks]

• Cue. Monitoring seismicity, deformation and gas gives advance warning to evacuate, saving lives where the eruption itself cannot be prevented.