Giant lava tubes under the Lunar surface could be large enough to house entire cities, and they could be used to shelter humans.

These tunnels are believed to be formed through lava flows from volcanic eruptions, Purdue University reported.

"There has been some discussion of whether lava tubes might exist on the moon. Some evidence, like the sinuous rilles observed on the surface, suggest that if lunar lava tubes exist they might be really big," said Jay Melosh, a Purdue University distinguished professor of earth, atmospheric and planetary sciences who is involved in the research.

Sinuous rilles are giant channels visible on the moon's surface that are believed to have been formed from lava flows. In this recent study, a team of researchers looked into whether or not these lava tubes would be structurally stable on the moon.

"We 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," said David Blair, a graduate student in Purdue's Department of Earth, Atmospheric, and Planetary sciences. "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. In theory, huge lava tubes - big enough to easily house a city - could be structurally sound on the moon."

The researchers applied known information about lunar rock and the moon's environment as well as civil engineering techniques to make their findings. They found the stability of these lava tubes depended on width, roof thickness and the stress state of the cold lava. The results suggested these types of tunnels could be stable if they matched the determined criteria. 

The findings were presented at the Lunar and Planetary Science Conference.