Volcanic Hazards

Volcanic eruptions are among the most spectacular and destructive natural hazards on Earth. Approximately 1,500 potentially active volcanoes exist worldwide, with around 50–70 erupting in any given year. Over 800 million people live within 100 km of an active volcano (Brown et al., 2015). This lesson examines volcanic processes, hazard types and detailed case studies at A-Level standard.

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Distribution of Volcanoes

The global distribution of volcanoes is closely linked to tectonic plate boundaries:

Location	Percentage of Active Volcanoes	Examples
Convergent boundaries (subduction zones)	~80%	Pacific Ring of Fire — Andes, Cascades, Japan, Philippines, Indonesia
Divergent boundaries	~15%	Mid-Atlantic Ridge (Iceland), East African Rift (Nyiragongo, Erta Ale)
Hot spots (intraplate)	~5%	Hawaii, Yellowstone, Réunion, Galápagos

Key Definition: The Pacific Ring of Fire is a horseshoe-shaped zone of intense seismic and volcanic activity stretching approximately 40,000 km around the margins of the Pacific Ocean. It contains about 75% of the world's active volcanoes and generates approximately 90% of earthquakes.

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Types of Volcano

Volcanoes are classified by their shape, composition and eruption style:

Shield Volcanoes