NASA astronauts could one day live inside caves under the moon's surface formed long ago by lunar lava. It could provide a natural shelter in which to build a future lunar base, according to a NASA astronaut in a Reddit-based Q&A. These lava tubes are long, tunnel-like structures formed after the surface of a lava flow hardens before hollowing out. Lava tubes are long, natural caves that are left behind by past volcanic activity. Lunar lava tubes can reach up to 1,600 feet (500 metres) in width before they become unstable and liable to collapse under their own weight.

Source: Daily Mail May 20, 2019 13:30 UTC