page_title: Lava
section_title: Volcanoes
hierarchical_section_title: Lava / Lava landforms / Volcanoes
caption_attribution_description: English: Matthew G. Landry, 2006. https://www.flickr.com/photo_zoom.gne?id=297589488&amp;context=set-72157594376579278&amp;size=o
context_page_description: Lava is molten rock that has been expelled from the interior of some planets and some of their moons. Magma is generated by the internal heat of the planet or moon and it is erupted as lava at volcanoes or through fractures in the crust, usually at temperatures from 700 to 1,200 °C. The solid rock resulting from subsequent cooling is also often described as lava.
  A lava flow is a moving outpouring of lava created during a non-explosive effusive eruption. When it has stopped moving, lava solidifies to form igneous rock. The term lava flow is commonly shortened to lava. Although lava can be up to 100,000 times more viscous than water, lava can flow great distances before cooling and solidifying because of its thixotropic and shear thinning properties.
  Explosive eruptions produce a mixture of volcanic ash and other fragments called tephra, rather than lava flows. The word lava comes from Italian, and is probably derived from the Latin word labes which means a fall or slide. The first use in connection with extruded magma was apparently in a short account written by Francesco Serao on the eruption of Vesuvius in 1737.
context_section_description: Volcanoes are the primary landforms built by repeated eruptions of lava and ash over time. They range in shape from shield volcanoes with broad, shallow slopes formed from predominantly effusive eruptions of relatively fluid basaltic lava flows, to steeply-sided stratovolcanoes (also known as composite volcanoes) made of alternating layers of ash and more viscous lava flows typical of intermediate and felsic lavas.
  A caldera, which is a large subsidence crater, can form in a stratovolcano, if the magma chamber is partially or wholly emptied by large explosive eruptions; the summit cone no longer supports itself and thus collapses in on itself afterwards. Such features may include volcanic crater lakes and lava domes after the event. However, calderas can also form by non-explosive means such as gradual magma subsidence. This is typical of many shield volcanoes.
caption: Arenal Volcano, Costa Rica, is a stratovolcano.
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