lava cave

   , lava tube

   1. A cave that formed in a partly cooled, broadly basaltic or phonolitic lava, not by erosion but by molten material flowing away. In most cases, an initial active lava conduit is formed when a flowing surface lava stream has a roof grow over it by accretion of chilled solidified material. Insulated inside its conduit the lava can continue to flow and develop an airspace above it, which is preserved as an explorable cave when completely cooled. Most lava caves are just very long tubes, though branching and multiple levels may occur as dictated by flow patterns and reinvasions of older tubes. On Kilauea Volcano, Hawaii, the Kazumura Cave is 47km long and descends 888m, but its tubes, mostly 5m in diameter, lie less than 20m beneath the sloping surface of the lava [9].

   2. A cave in a lava flow, generally formed by gas blistering the surface or by lava flowing out from beneath a solidified crust, forming a tube or tunnel [10]. 3. An empty tubular supply channel from which liquid lava has drained [16].

   See also lava karst; pseudokarst.