Sinuous Rilles and Lava Tubes
Section M.
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Lava Tube Formation and Characteristics

I am afraid I have to disagree with those who feel the existence of lava tubes is uncertain and can't be counted on. It is as close to certain as can be that rilles like Hadley (Apollo 15) represent collapsed lava tubes. We have found some rilles that have "bridge-like interruptions," which can only be uncollapsed lava tube sections. Look at Hyginus rille in a good photographic atlas of the moon and you can pick these sections out one after the other. To me, this is absolute demonstration, and every lunar geologist I know agrees.

Where there are some, there are more. Lava tubes seem to be a natural aspect of the way the mare basins filled with sheets of lava. They (and the rilles degenerated from them) run gently downhill from the high points of the lava sheets, radiating outwards from the points of eruption or upwelling.

These things, to judge from the size of the sinuous rilles, are of enormous size and volume. Unlike terrestrial lava tubes, which are a few tens of meters wide at best and a few kilometers long at most, rilles are typically hundreds of meters in cross section and can run for hundreds of kilometers.

Thus, sealing one up -- even a shorter uncollapsed section -- can be a tall order. Sputtering a coating of metal on the inside surfaces may be one possibility, but it will take a lot of metal. The elements to make epoxy-like or other synthetic coatings are not present on the moon except as traces. Foamed metal is a possible development, but whether it can withstand the forces of pressurization is debatable.

The main benefits a lava tube offers is shelter from cosmic rays, solar flares, ultraviolet, and micrometeorite bombardment. Those still intact have withstood the onslaught of over 3.5 billion years of various kinds of assault. The way to proceed may be to place inflatable structures inside, even large ones, with individual flimsier buildings inside. Who knows what the future will bring? Near term, however, they can only be counted on to provide the shelter I have just described. This will be especially valuable for volume- and surface-intensive needs of industry, warehousing, and agriculture.

As the maria have all filled with more than one episode of magma outwelling (i.e., the maria are comprised of layers of lava sheets), each layer may have associated lava tubes. Those in deeper layers may contain more intact tubes than the surface sheet exposed to eons of bombardment. But they will also be harder to find and access.

Of the lava tubes in Oregon, many have natural entrances only partially filled and obstructed with removable talus collapse debris. I would expect to find the same opportunities to enter at the uncollapsed bridges of the Hyginus rille.

Additional References in the Artemis Data Book

Sinuous Rilles and Lava Tubes

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