- an opening in Earth’s crust where magma, gases, and ash reach the surface
- formed at plate tectonics boundaries: subduction zones, divergent ridges, and hotspots
- types: shield (broad, effusive), stratovolcano (steep, explosive), cinder cone, caldera
- the Ring of Fire around the Pacific ocean contains 75% of active volcanoes
- eruptions release CO2, SO2, and aerosols, connecting to the carbon cycle and climate
- volcanic soils (andisols) are among the most fertile on Earth
- cyber valley sits on volcanic soils in Bali, enriched by centuries of eruptions
- major eruptions alter global temperature: Tambora 1815 caused the “year without a summer”
- volcanic islands create isolated ecology and drive evolution (Galapagos, Hawaii)
- geothermal energy from volcanic systems provides renewable power (Iceland, Indonesia)
- lahars, pyroclastic flows, and tephra are primary hazards