A lava tube is a naturally occurring, tunnel-like passage that forms beneath the surface of a lava flow. These subterranean conduits are created when molten rock continues to flow after the surface has cooled and solidified, leaving behind a hollow cavern. Scientists study lava tubes to understand the history of volcanism across different worlds, both on Earth and in space.
The Geological Process of Tube Formation
The formation of a lava tube requires specific volcanic conditions, starting with highly fluid, low-viscosity lava, typically the type known as Pahoehoe. This smooth lava flows easily and travels long distances from its vent. As the molten rock moves, the outer layer exposed to the atmosphere cools quickly, forming a solid, insulating crust. This hardening creates a roof over the moving lava stream underneath.
The liquid lava inside the tunnel is thermally insulated by the crust, allowing it to maintain its high temperature and continue flowing efficiently for many kilometers. When the eruption ceases or the lava supply stops, the molten material drains out of the conduit. This draining process leaves behind the open, cylindrical cave known as the lava tube, a feature characteristic of effusive volcanism and shield volcanoes.
Terrestrial Distribution and Key Hotspots
Lava tubes are found globally in regions that have experienced extensive effusive volcanic activity. The Hawaiian Islands represent one of the most studied hotspots for these formations, with tubes like the Thurston Lava Tube on Kilauea showcasing the extensive networks that shape the landscape.
Iceland is another significant location, where tubes are common due to the island’s location on the Mid-Atlantic Ridge and its history of fluid basaltic eruptions. The Canary Islands, particularly La Palma and Lanzarote, contain numerous tubes, with the La Cueva de los Verdes system being a notable example that runs for several kilometers.
The global distribution also includes:
- The Lava Beds National Monument in California, which protects over 700 known caves, many of which are lava tubes formed by flows from the Medicine Lake Volcano.
- Jeju Island off the coast of South Korea, home to the Manjanggul Lava Tube, which contains a massive lava pillar formed by cascading molten rock.
- Australia’s Undara Volcanic National Park, which hosts tube systems that are among the longest and most voluminous on Earth.
Lava Tubes Beyond Earth
Lava tube formation is not exclusive to Earth and has occurred on other planetary bodies, primarily the Moon and Mars. On both worlds, scientists have identified features suggesting the presence of uncollapsed tubes, including sinuous rilles and ‘skylights.’ Skylights are circular depressions seen in orbital imagery, interpreted as sections where the tube’s roof has collapsed, providing a window into the subsurface cavity.
The lower gravity environments on the Moon and Mars allowed for much larger lava flows, consequently creating tubes that far exceed terrestrial dimensions. Martian tubes could be up to 250 meters wide, and lunar tubes might be a kilometer or more in diameter. These enormous underground spaces are important for future space exploration because they offer natural shielding from surface hazards. The tubes would protect human habitats from cosmic and solar radiation, micrometeorite impacts, and extreme surface temperature fluctuations.