Nature · Earth Science
Windows into the molten heart of the Earth
A volcano is an opening in Earth’s crust through which molten rock, ash and gases escape from below. Concentrated along plate boundaries and hotspots, volcanoes build islands and mountains, enrich soils, and remind us that our planet’s interior is still fiercely alive.
Volcanoes form where magma — buoyant molten rock — rises through the crust and erupts at the surface. The magma’s chemistry decides everything: runny basaltic lava builds gentle shields, while thick, gas-rich magma erupts explosively to raise steep composite cones.
Magma rises from a deep chamber through the central conduit, erupting from the summit crater and side vents to build alternating layers of lava and ash.
Broad, gentle giants of runny lava
Thin, runny lava spreads far before it cools, stacking into a broad low dome shaped like a warrior’s shield. Hawaii’s Mauna Loa is the classic example — vast but rarely violent.
Steep, layered and often explosive
The archetypal “volcano” shape. Viscous magma traps gas and erupts explosively, layering lava and ash into a towering cone. These are the most dangerous volcanoes near populated regions.
Small, steep cones of blasted fragments
Gassy lava is blown into fragments that fall around the vent, piling into a neat steep cone. Parícutin in Mexico famously grew from a cornfield to 424 m in just nine years.
Vast craters where a volcano collapsed
When a massive eruption drains the magma chamber, the ground above collapses into a giant caldera. These structures, like Yellowstone, are capable of Earth’s largest eruptions.
Bulges of lava too thick to flow
Some magma is so thick it barely moves, piling up over the vent as a rounded dome. These domes can collapse without warning, unleashing deadly fast-moving pyroclastic flows.