page_title: Volcano
section_title: Classification
hierarchical_section_title: Volcano / Classification
caption_attribution_description: English: The reason for the name "Castle of the Maidens" (after Geoffrey of Monmouth) is obscure.
context_page_description: A volcano is a mountain that has lava coming out from a magma chamber under the ground, or did have in the past. Volcanoes are formed by the movement of tectonic plates.
  The Earth's crust is broken into 17 major, rigid tectonic plates. These float on a hotter, softer layer in its mantle. Volcanoes are often found where tectonic plates are moving apart or coming together.
  Volcanoes can also form where there is stretching and thinning of the crust's plates, e.g., in the East African Rift. Volcanoes are usually not found where two tectonic plates slide past one another.
  Volcanism away from plate boundaries is caused by mantle plumes. These so-called "hotspots", for example Hawaii, are thought to arise from upwelling magma from the core–mantle boundary, 3,000 km deep in the Earth.
  Most volcanoes have a volcanic crater at the top. When a volcano is active, materials come out of it. The materials include lava, steam, gaseous sulfur compounds, ash and broken rock pieces.
  When there is enough pressure, the volcano erupts. Some volcanic eruptions blow off the top of the volcano. Sometimes, the magma comes out quickly and sometimes it comes slowly.
context_section_description: A traditional way to classify or identify volcanoes is by its pattern of eruptions. Those volcanoes which may erupt again at any time are called active. Those that are now quiet called dormant (inactive). Those volcanoes which have not erupted in historical times are called extinct.
caption: Edinburgh Castle on the site of an extinct volcano, c. 1581
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