Volcanic Case Studies

AQA A-Level Geography requires detailed knowledge of volcanic events at different levels of development. This lesson examines three key eruptions — Mount Pinatubo (1991), Eyjafjallajökull (2010), and Soufrière Hills, Montserrat (1995–present) — and explores monitoring and prediction techniques.

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Mount Pinatubo, Philippines (June 1991)

Context

• Located on the island of Luzon, approximately 90 km north-west of Manila
• Situated on a destructive plate boundary where the Philippine Sea Plate subducts beneath the Eurasian Plate
• The volcano had been dormant for over 600 years before the 1991 eruption
• VEI 6 — the largest eruption of the 20th century (second half)

The Eruption

• An initial magnitude 7.7 earthquake on 16 July 1990 may have triggered the reawakening
• From April 1991, increasing seismicity and steam emissions provided warning
• The climactic eruption on 15 June 1991 ejected approximately 10 km³ of material, producing an ash column reaching 35 km into the stratosphere
• Coincided with Typhoon Yunya, which brought heavy rainfall, turning ash into deadly lahars

Impacts

Category	Details
Deaths	~847 (mostly from lahar-related roof collapses and disease in evacuation centres)
Displacement	Over 200,000 people evacuated; ~20,000 indigenous Aeta people permanently displaced
Infrastructure	Clark Air Base (US military) destroyed; 8,000+ houses demolished; agricultural land buried
Economic	Estimated $700 million in damage; lost harvests; long-term livelihood destruction
Global climate	~17 million tonnes of SO₂ injected into the stratosphere; global temperatures fell by ~0.5 °C for 1–2 years; enhanced ozone depletion

Response and Management

• PHIVOLCS (Philippine Institute of Volcanology and Seismology) and USGS scientists successfully predicted the eruption
• A 40 km exclusion zone was established; mass evacuation saved an estimated 20,000 lives
• Post-eruption lahars continued for over a decade during monsoon seasons, requiring ongoing engineering solutions (lahar channels, sediment dams)

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Eyjafjallajökull, Iceland (April–May 2010)

Context

• Located in southern Iceland on the Mid-Atlantic Ridge — a constructive plate boundary where the North American and Eurasian plates diverge
• Relatively small eruption: VEI 4
• The volcano sits beneath a glacier (ice cap ~200 m thick), which amplified the hazard

The Eruption

• An initial flank eruption began on 20 March 2010 (effusive, basaltic)
• The main eruption from the summit began on 14 April 2010 — meltwater interacting with magma caused phreatomagmatic explosions, fragmenting lava into extremely fine ash
• The ash plume reached 9 km altitude and was carried south-east across Europe by prevailing winds

Impacts