"We can find lava tubes on planet Earth, but also on the subsurface of the Moon and Mars according to the high-resolution pictures of lava tubes' skylights taken by interplanetary probes. Evidence of lava tubes was often inferred by observing linear cavities and sinuous collapse chains where the galleries cracked," explains Francesco Sauro [speleologist and head of the ESA programs CAVES and PANGAEA]. "These collapse chains represent ideal gateways or windows for subsurface exploration. The morphological surface expression of lava tubes on Mars and the Moon is similar to their terrestrial counterpart. Speleologists thoroughly studied lava tubes on Earth in Hawaii, the Canary Islands, Australia and Iceland."

"We measured the size and gathered the morphology of lunar and Martian collapse chains (collapsed lava tubes), using digital terrain models (DTMs), which we obtained through satellite stereoscopic images and laser altimetry taken by interplanetary probes," reminds Riccardo Pozzobon [planetary geologist at the Department of Geosciences of the University of Padua]. "We then compared these data to topographic studies about similar collapse chains on the Earth's surface and to laser scans of the inside of lava tubes in Lanzarote and the Galapagos. These data allowed to establish a restriction to the relationship between collapse chains and subsurface cavities that are still intact."

Researchers found that Martian and lunar tubes are respectively 100 and 1,000 times wider than those on Earth, which typically have a diameter of 10 to 30 meters. Lower gravity and its effect on volcanism explain these outstanding dimensions (with total volumes exceeding 1 billion of cubic meters on the Moon).

Riccardo Pozzobon adds: "Tubes as wide as these can be longer than 40 kilometers, making the Moon an extraordinary target for subsurface exploration and potential settlement in the wide protected and stable environments of lava tubes. The latter are so big they can contain Padua's entire city center."

(Via Lava tubes on Mars and the Moon are so wide they can host planetary bases)

The many fans of science fiction Grandmaster Robert A. Heinlein should know all about this, or at least not be surprised, having read about similar structures in his 1957 novel Menace from Earth:

Most of the stuff written about Bats' Cave gives a wrong impression. It's the air storage tank for the city, just like all the colonies have - the place where the scavenger pumps, deep down, deliver the air until it's needed. We just happen to be lucky enough to have one big enough to fly in. But it never was built, or anything like that; it's just a big volcanic bubble, two miles across, and if it had broken through, way back when, it would have been a crater.

Never one to neglect the adventuresome spirit of American youth, Heinlein obligingly provided lunar colonists with Storer-Gulls Wings for recreational use of lunar lava tubes.