Lava tubes are natural volcanic conduits that can stretch for dozens of kilometers underground.

Nature · Published 3 October 2026 Swipe more like this →

In short: Beneath the surface of volcanic landscapes lie vast, hollow tunnels formed by rivers of molten rock. These geological structures, created when lava crusts over and drains away, act as insulated transport systems for magma. Today, they are being studied as potential shelters for future human exploration of space.

Lava tubes are natural, roofed conduits that develop when low-viscosity lava, such as basaltic pahoehoe, flows from a volcanic vent. As the surface of a lava stream cools and hardens, it creates a protective crust that insulates the molten material beneath. This allows the lava to remain fluid and travel significantly further from the source than it would in an open channel. Once the eruption ceases or the lava is diverted, the remaining molten rock drains away, leaving behind an empty, cave-like tunnel.

There are three primary mechanisms for their formation: roofing over an existing channel, the extension of pahoehoe lobes, or the inflation of a lava flow due to internal pressure. These systems can be remarkably complex, often branching into braided mazes. Internal features are common in drained tubes, including wall linings, flow ledges, and various types of lavacicles—lava stalactites that form as the material cools. Because these formations are susceptible to erosion, they are typically found in relatively young volcanic fields, generally less than 20 million years old.

The scale of these systems is immense. The Kazumura Cave in Hawaii is the world's most extensive, reaching a linear extent of 65.5 kilometers. Beyond Earth, evidence of lava tubes has been identified on the Moon and Mars, where they appear as chains of pit craters or voids connected to volcanic features like Olympus Mons. Scientists view these extraterrestrial tubes as high-priority targets for research, as they could provide natural shielding against radiation for potential human habitats or serve as unique environments for extraterrestrial life.

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