A lava tube, or pyroduct, is a natural conduit formed by flowing lava from a volcanic vent that moves beneath the hardened surface of a lava flow. If lava in the tube empties, it will leave a cave.
Africa
Democratic Republic of the Congo
Unnamed cave along the Kakomeru climbing route of Mt. Nyamulagira
Ethiopia
70 m lava tube cave has been recorded southeast of Addis Ababa and a smaller example on K'one Volcano
Kazumura Cave, Hawaii – Not only the world's most extensive lava tube, but at 65.5 kilometres (40.7mi), it has the greatest linear extent of any cave known.
↑Guest, J.E; Duncan, A.M.; Stofan, E.R; Anderson, S.W. (2012). "Effect of slope on development of pahoehoe flow fields: Evidence from Mount Etna". Journal of Volcanology and Geothermal Research. 219–220: 52–62. Bibcode:2012JVGR..219...52G. doi:10.1016/j.jvolgeores.2012.01.006.