" … a graduate student in Purdue's Department of Earth, Atmospheric and Planetary Sciences, led the study that examined whether empty lava tubes more than 1 kilometer wide could remain structurally stable on the moon.
The Purdue team found that if lunar lava tubes existed with a strong arched shape like those on Earth, they would be stable at sizes up to 5,000 meters, or several miles wide, on the moon.
"This wouldn't be possible on Earth, but gravity is much lower on the moon and lunar rock doesn't have to withstand the same weathering and erosion,” Blair reported. "In theory, huge lava tubes — big enough to easily house a city — could be structurally sound on the moon." Space.com
Cosmic radiation is heavy on the surface of the moon. Without a lot of shielding it will fry your innards. This Purdue University study tells us that large, long, voids exist below the surface of Luna. These were evidently created by lava flows long ago. The study also claims that in the low gravity field of the moon, these tubes would be sufficiently stable to house a large lunar base for mining of rare earths and other activities.
This brings to mind the lunar colony in Heinlein's "The Moon is a Harsh Mistress." In that novel, the lunar folk were miners whose mineral production was delivered to earth by being fired from rail guns at an impact area in the Pacific ocean from which they were retrieved by ships
For me the possibility of such a colony and base raises the issue of why the US and Russia are intent on building a lunar orbit space station. Why could not anything that would be done in lunar orbit not be done at a lunar cave base? pl