Lava Tubes and Volcanic Caves: Fire Made Hollow
A lava tube forms when the outer surface of a flowing basaltic lava stream cools and solidifies while molten rock continues to flow beneath. When the eruption subsides and the lava drains, the hardened shell remains as an empty tunnel. The result can be tens of kilometres long, perfectly smooth-walled, and geologically young — some active lava tubes on Hawaii's Big Island formed within living memory. Lava tube caves share a distinctive appearance: dark basaltic walls, sometimes lined with lava stalactites (lavacicles) formed from drips of cooling melt, and lava benches marking former high-tide levels of the lava flow. They are structurally simpler than karst caves — no speleothems, no underground rivers, and often a near-linear plan — but their scale can be extraordinary.
Thurston Lava Tube, Hawaii Volcanoes National Park
Thurston Lava Tube (Nahuku) in Hawaii Volcanoes National Park on the Big Island of Hawaii is the most visited lava tube cave in the United States. It formed during an eruption of Kilauea approximately 500 years ago and extends roughly 600 metres, with a lit section of about 175 metres open to self-guided visitors. The tube is wide enough to walk upright throughout; the ceiling reaches 5 metres in some sections. The surrounding rainforest — tree ferns, ohia lehua trees, and native birds — makes the walk to the entrance as significant as the cave itself. Hawaii Volcanoes National Park is a UNESCO World Heritage Site.
Manjanggul, Jeju Island, South Korea
Manjanggul is part of the Geomunoreum Lava Tube System on Jeju Island and at approximately 13.4 kilometres of surveyed passage is one of the longest lava tubes in the world. The visited section — about 1 kilometre — passes through chambers up to 30 metres wide and 30 metres high. Its most celebrated feature is a 7.6-metre lava column near the far end of the accessible section, formed when lava spatter built upward from the floor while lava stalactites grew downward from the ceiling. The Geomunoreum system is inscribed on the UNESCO World Heritage List as part of the Jeju Volcanic Island and Lava Tubes designation (2007).
Cueva del Viento, Tenerife, Spain
Cueva del Viento — Cave of the Wind — on the northern slopes of Tenerife is the longest volcanic cave in Europe and the fourth longest lava tube system in the world, at approximately 18.5 kilometres of mapped passage. The cave is multi-level, with at least three superimposed lava tube systems formed during different eruptive phases of the Teide volcanic massif. Because it formed in tropical volcanic conditions and has a stable microclimate, it harbours a remarkable endemic invertebrate fauna including blind beetles and a range of troglobitic species found nowhere else on earth. Scientific access permits are required; a small guided visitor section is available.
Ape Cave, Mount St Helens, Washington
Ape Cave on the flanks of Mount St Helens in Washington State is the longest lava tube in the continental United States at approximately 4 kilometres. It was formed around 1,900 years ago during an eruption of the Mount St Helens volcanic complex. The cave is managed by the US Forest Service and offers two self-guided routes: a lower route of about 1.5 kilometres that is straightforward walking, and an upper route of approximately 2.4 kilometres that includes a lava fall requiring a rock-scramble (a ladder is provided). The cave maintains a temperature of around 4°C year-round; a jacket is required regardless of surface conditions. Lantern rental is available at the visitor station.
Lofthellir, Iceland
Lofthellir is a lava tube in northeast Iceland, near Lake Myvatn, notable for an extraordinary interior chamber where accumulations of ice have built up over centuries to form ice stalagmites, columns, and a frozen underground lake. Unlike the glacier ice caves of Vatnajokull, the Lofthellir formations are static ice in a rock cave — the cold-air-trap mechanism of a true ice cave operating within a lava tube. Access requires a guided 4WD transfer across open lava fields followed by a 30-minute walk. The cave can be visited year-round but the ice is at its most extensive and stable in winter.
Lava Beds National Monument, California
Lava Beds National Monument in northern California contains the densest concentration of lava tube caves in the continental United States: more than 800 catalogued caves within approximately 175 square kilometres of the Medicine Lake Highlands volcanic complex. Individual tubes range from crawl-size passages to large walking tubes. Fourteen caves are open for self-guided exploration with maps available from the visitor centre; a further series requires guided or permitted access. The Monument also contains a significant concentration of Native American rock art and was the site of the Modoc War of 1872-1873.
Undara Volcanic National Park, Queensland
The Undara lava tube system in north Queensland was formed approximately 190,000 years ago during an eruption of the Undara shield volcano and represents one of the longest individual lava flows on earth — the original flow extended up to 160 kilometres. The longest single lava tube sections are among the largest in the world. The accessible cave sections, managed by Undara Experience, are visited on guided tours that pass through large, archway-like openings in collapsed tube sections. The collapsed sections have developed into pockets of monsoon vine thicket — a dense, closed-canopy rainforest microhabitat in the surrounding dry savanna — which is ecologically as significant as the caves themselves.
Raufarhólshellir, Iceland
Raufarhólshellir, about 30 kilometres east of Reykjavik, is the most tourist-accessible lava tube in Iceland and one of the most significant in Europe. The main tube extends approximately 1.36 kilometres with a ceiling height reaching 10 metres in the larger sections. A commercial operation runs daily guided tours year-round, with lighting installed in the main accessible section. The cave formed during the Krísuvík volcanic system eruptions approximately 5,200 years ago. In winter, ice formations develop in the colder entrance sections.
The ecology of lava tubes
Lava tubes in humid climates often support endemic cave-adapted invertebrate fauna — blind beetles, spiders, millipedes, and isopods that have evolved in isolation from surface populations. The Canary Islands and Hawaii in particular have high rates of cave invertebrate endemism: Cueva del Viento in Tenerife alone harbours dozens of invertebrate species found nowhere else on earth. The consistent cool temperatures and high humidity of lava tubes also make them important bat roosts; several Hawaiian lava tube systems are critical habitat for the Hawaiian hoary bat (Lasiurus cinereus semotus), the state's only endemic land mammal.
Visiting lava tubes safely
Visiting a lava tube requires good headlamps — three sources as always — sturdy footwear with ankle support, and awareness that floors can be uneven. Lava surfaces often have sharp projections (called hornitos or squeeze-ups where lava broke through the tube floor), unstable lava crust sections, and lava stalactites at head height. In active volcanic areas like Hawaii's Kilauea, new lava tubes may be forming; checking current eruption and access status with the National Park Service before visiting any Kilauea-area cave is mandatory. Lava tube temperatures are typically 10-20°C depending on climate zone; a light jacket is usually sufficient. The International Society for Speleology (UIS) maintains a volcanic cave commission that coordinates global survey and research; the VULKANO (Volcanic Caves) working group publishes an international inventory of lava tube systems that is the primary reference for the scientific literature. For visitors planning dedicated lava tube trips, Hawaii Volcanoes National Park, Jeju UNESCO Global Geopark, and the Lanzarote tube system each provide well-managed, well-interpreted access points that demonstrate the full range of lava tube morphology without requiring any specialist equipment.
Find lava tube caves and tour operators on the cave map.