Volcanic Eruptions and Management

GCSE Geography · The Challenge of Natural Hazards

How Volcanoes Form

Volcanoes occur primarily at destructive and constructive plate boundaries, and at hotspots.

At destructive boundaries, oceanic crust subducts beneath continental crust. The oceanic plate melts in the mantle, forming magma that rises through weaknesses in the crust. This produces composite (stratovolcanoes) — steep-sided, explosive, with viscous lava (e.g. Mount St Helens, Mount Pinatubo).
At constructive boundaries, magma rises to fill the gap as plates diverge. This produces shield volcanoes — gentle slopes, less explosive, with runny basaltic lava (e.g. Mauna Loa, Hawaii; Eyjafjallajokull, Iceland).

Lava flows — streams of molten rock; usually slow enough to evacuate from, but destroy everything in their path
Pyroclastic flows — superheated clouds of gas, ash, and rock travelling at 700+ km/h and up to 1,000°C; the deadliest volcanic hazard
Ash clouds — can collapse roofs, contaminate water, disrupt aviation, and cause respiratory problems
Lahars — volcanic mudflows formed when ash mixes with rainwater or melting snow; can travel at 60 km/h and bury entire towns
Volcanic gases — sulphur dioxide, carbon dioxide, and hydrogen fluoride can poison air, water, and soils

Type: Stratovolcano beneath a glacier | Boundary: Constructive (Mid-Atlantic Ridge)

Meltwater from the glacier caused flooding (jökulhlaups) — 800 people evacuated
Ash cloud reached 11 km altitude, carried southeast by winds across Europe
Over 100,000 flights cancelled across European airspace for 6 days
An estimated $1.7 billion lost by airlines; millions of passengers stranded
Local farming — ash fall contaminated grazing land; fluoride poisoning risk to livestock
Tourism initially disrupted but later increased as people visited to see the volcano

Icelandic authorities evacuated nearby farms within hours using pre-planned routes
European aviation authorities imposed the no-fly zone using satellite monitoring
Farmers kept livestock indoors and were compensated by the Icelandic government
Long-term: improved ash-detection systems and revised aviation safety protocols (now aircraft can fly through low-density ash)

Strategy	Details
Monitoring	Seismometers detect tremors beneath the volcano; tiltmeters measure ground swelling; gas sensors detect rising SO₂ levels; satellite thermal imaging
Prediction	More successful than for earthquakes — warning signs often appear days to weeks before eruption (increased seismic activity, ground deformation, gas emissions)
Planning	Exclusion zones, hazard maps, evacuation routes, emergency drills, stockpiling supplies
Protection	Lava diversion channels (used in Etna, Sicily); reinforced roofs to withstand ash loading; barriers to redirect lahars

The impact depends on:

Type of eruption — explosive vs effusive
Population density near the volcano
Level of development — wealthier countries have better monitoring, infrastructure, and emergency services
Preparedness — countries like Japan and Iceland with frequent eruptions have well-practised evacuation plans
Warning time — some eruptions give days of warning, others are sudden

Exam tip: Always link your answer back to whether the country is an HIC or LIC and how that affects the ability to prepare, respond, and recover.