In article ,
"Alan Erskine" wrote:

What of the lower gravity (mentioned in "Peter's Commentary" here
www.lunar-reclamation.org/lavatube_pix.htm)? Would the lower gravity cause
the gases that form in the lavatubes in the first place be able to escape
more readily than is the case on Earth (lower gravity and also no atmosphere
'outside')?

Would that cause structural problems (reducing the strength of the tubes)?

Gases are not the major cause of weakening lava basalts that are fluid
enough to form lavatubes. A much more important factor is water. Highly
siliceous material, like basalt, has microcracks. The polarized molecule
of liquid water gets into the tips of these cracks, and levers their
extension, weakening the material. This means that the extremely dry
conditions on the Moon have possibly resulted in *stronger* basalts
than we see here on Earth.

This correlates strongly with the difference between the calculated
largest size for lunar lavatubes, based soley on gravity differences
(about 385 meters in diameter, by Horz, 1988, in ' Lunar Bases and Space
Actvities of the 21st Century') and the search of lunar photo
observations by Coombs and Hawke, which indicated at least one tube of
1050 meters diameter, and several kilometers in length, with many larger
than 385 meters diameter.

Regards,

Tom Billings