page_title: Volcanism
section_title: Volcanic processes
hierarchical_section_title: Volcanism / Volcanic processes
caption_attribution_description: English: Hawaii Volcanoes National Park, USA, new lava flow near the Royal Gardens subdivision.
context_page_description: Volcanism is the phenomenon of eruption of molten rock onto the surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics and volcanic gases erupt through a break in the surface called a vent. It includes all phenomena resulting from and causing magma within the crust or mantle of the body, to rise through the crust and form volcanic rocks on the surface.
context_section_description: Magma from the mantle or lower crust rises through its crust towards the surface. If magma reaches the surface, its behavior depends on the viscosity of the molten constituent rock. Viscous (thick) magma produces volcanoes characterised by explosive eruptions, while non-viscous (runny) magma produce volcanoes characterised by effusive eruptions pouring large amounts of lava onto the surface.
  In some cases, rising magma can cool and solidify without reaching the surface. Instead, the cooled and solidified igneous mass crystallises within the crust to form an igneous intrusion. As magma cools the chemicals in the crystals formed are effectively removed from the main mix of the magma (by a process known as fractional crystallization), so the chemical content of the remaining magma evolves as it solidifies slowly. Fresh unevolved magma injections can remobilise more evolved magmas, allowing eruptions from more viscous magmas.
caption: Non-viscous lava during an effusive eruption of Kīlauea
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