Impact of Earthquakes and Volcanoes

4.1 Negative Impacts of Earthquakes

Primary Effects

• Ground shaking — structural damage and collapse of buildings (kills most people)
• Surface rupture — fault breaks through surface; ground displacement
• Liquefaction — water-saturated sediments behave like liquid; building collapse (major cause in Bhuj 2001)
• Landslides and avalanches — triggered on slopes; Nepal 2015 earthquake triggered 4,312 landslides

Secondary Effects

• Tsunamis — submarine earthquakes displace ocean water; 2004 Indian Ocean tsunami (Mw 9.1–9.3): 227,898 deaths in 14 countries; waves up to 30 m (Banda Aceh, Indonesia)
• Fires — ruptured gas lines and downed power lines; 1906 San Francisco fire killed more than shaking
• Disease and hunger — Haiti 2010 (Mw 7.0: 316,000 deaths + cholera epidemic)

Long-term Impacts

• Economic damage (Japan 2011: $360 billion loss — most expensive natural disaster in history)
• Infrastructure destruction and population displacement
• Mental health impacts on survivors

4.2 Negative Impacts of Volcanoes

During Eruption

• Pyroclastic flows — Superheated (~800°C) mixtures of gas, ash, and rock fragments moving at 150–700 km/h; most lethal volcanic hazard; Vesuvius 79 CE → 2,000+ deaths at Pompeii
• Lava flows — slow enough to evacuate but destroy everything in path
• Ash fall — collapses roofs, contaminates water, disrupts aviation (Eyjafjallajökull 2010 shut European airspace for 6 days, costing €1.3 billion)
• Volcanic gases — SO₂ creates acid rain; CO₂ and H₂S can asphyxiate people in valleys (Lake Nyos disaster, Cameroon, 1986: CO₂ cloud from volcanic lake killed 1,746 people)
• Lahars (volcanic mudflows) — Nevado del Ruiz 1985 (Colombia) → lahar buried Armero town; 23,000 deaths

Global Effects of Large Eruptions

• Volcanic winter — Pinatubo (1991) injected 20 million tonnes SO₂ into stratosphere → global temperature dropped 0.5°C for 2 years → crop failures globally
• Tambora 1815 (Indonesia, VEI 7) — caused "Year Without a Summer" (1816); crop failures in Europe and North America; famines; 200,000+ deaths from starvation

4.3 Positive Impacts of Volcanoes

Fertile Soils

Volcanic ash weathers into mineral-rich soils. Java (Indonesia) has the world's highest rural population density (~1,000/km²) despite hosting 40+ active volcanoes — rice yields from volcanic soils are exceptional. Mt. Vesuvius region (Italy) similarly supports viticulture and agriculture.

Geothermal Energy

Iceland generates 66% of electricity and 90% of home heating from geothermal (hot springs, geysers). Also: Kenya, New Zealand, Philippines have large geothermal capacity.

Mineral Deposits

Hydrothermal vents associated with volcanism deposit gold, silver, copper, lead, zinc. Major copper deposits in Chile, Arizona are volcanic-hydrothermal. Sulphur mined from volcanic craters.

New Land Creation

Hawaiian Islands entirely created by volcanic activity. The newest island, Lō'ihi, is currently forming underwater and will emerge in ~10,000–100,000 years.

Scientific and Medical Resources

Geothermal water used in health spas (Iceland's Blue Lagoon); volcanic pumice used in cosmetics; obsidian (volcanic glass) used historically as surgical blades.

Climate Regulation (Long-term)

Volcanic CO₂ over millions of years contributed to early Earth's warm climate that enabled life. Volcanic activity replenishes nutrients to oceans — hydrothermal vents support unique ecosystems.

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