A lava tube is a natural tunnel formed by flowing lava beneath the surface of a solidified lava flow. Lava tubes are significant in understanding volcanic processes, the movement of lava flows, and the formation of volcanic landforms. They can also serve as habitats for unique ecosystems.
Source Peterson, D. W., & Swanson, D. A. (1974). “Observations of Lava Tubes, Kilauea Volcano, Hawaii.” Bulletin Volcanologique, 38(1), 144-156.