Passage Types

While many lava tube passages tend to be sinuous passage, the cross-sections of lava tube passages vary from tall and narrow, to classic tube shape, to keyhole-shaped. Passages tend to be tubular or oval-shaped when they initially form, as in the top two photos. As lava continues to flow through a passage over time, it tends to melt and erode down the floor and make the passage taller, as in the two vertically oriented photos. Passages can also be stacked, with new passages forming over older ones as underground channels roof over, as shown in the next three photos. The last photo, from a cave in the Galapagos Islands, shows an amazing development of five distinct levels which later collapsed into a single taller passage.