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.
Valentine Cave, a lava tube in Lava Beds National Monument, California shows the classic tube shape; the grooves on the wall mark former flow levels.
Thurston Lava Tube in Hawaii Volcanoes National Park, Hawaii. The step mark, more visible on the right wall, indicates the depth at which the lava flowed for a period of time.
Rare characteristics of lava tubes are lava pillars. This is the Manjanggul lava pillar located in the Manjanggul lava tubes, on the island of Jeju-do, Korea.
Lavacicles on the ceiling of Mushpot Cave in Lava Beds National Monument
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or underwater, usually at temperatures from 800 to 1,200 °C. The volcanic rock resulting from subsequent cooling is also often called lava.
Fresh lava from Fagradalsfjall volcano eruption in Iceland, 2023
Toes of a pāhoehoe advance across a road in Kalapana on the east rift zone of Kīlauea Volcano in Hawaii, United States
Columnar jointing in Giant's Causeway in Northern Ireland
Lava enters the Pacific at the Big Island of Hawaii.