page_title: Igneous rock
hierarchical_section_title: Igneous rock
caption_attribution_description: English: Glowing `a`a lava flow front advancing over pahoehoe lava on the coastal plain of Kilauea Volcano, Hawaii. 'A'a (pronounced "ah-ah") is a Hawaiian term for lava flows that have a rough rubbly surface composed of broken lava blocks called clinkers. The incredibly spiny surface of a solidified 'a'a flow makes walking very difficult and slow. The clinkery surface actually covers a massive dense core, which is the most active part of the flow. As pasty lava in the core travels downslope, the clinkers are carried along at the surface. At the leading edge of an 'a'a flow, however, these cooled fragments tumble down the steep front and are buried by the advancing flow. This produces a layer of lava fragments both at the bottom and top of an 'a'a flow.
context_page_description: Igneous rock is one of the three main rock types, the others being sedimentary and metamorphic rock.
  Igneous rocks are rocks formed from molten magma. The material is made liquid by the heat inside the Earth's mantle.
  When magma comes out onto the surface of the Earth, it is called lava. Lava cools down to form rocks such as tuff and basalt. Intrusive rocks are made when the magma slowly cools to form rocks under the surface. Granite is one of these.
context_section_description: Igneous rock is one of the three main rock types, the others being sedimentary and metamorphic rock.
  Igneous rocks are rocks formed from molten magma. The material is made liquid by the heat inside the Earth's mantle.
  When magma comes out onto the surface of the Earth, it is called lava. Lava cools down to form rocks such as tuff and basalt. Intrusive rocks are made when the magma slowly cools to form rocks under the surface. Granite is one of these.
caption: Magma is called lava when it reaches the surface.
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