Definitions for "Lava tube"
Keywords:  solidify, tunnel, molten, drains, crust
A tunnel below the surface of a solidified lava flow, formed when the exterior portions of the flow solidify and the molten internal material is drained away.
Lava tubes form when the surface flowing lava congeals forming a crust. The lava underneath the solidified crust continues to flow, now insulated from the cooling air. When the lava eruption ceases, and if the tube drains, a large tubular cave may be left behind.
A tunnel beneath the solidified surface of a lava flow through which lava continues to flow. Also, the hollow space left when the lava within a tube drains away.