Whitepeak Observatory, Tacoma, WA

Walking the Moon on the Earth: Lava Tube, Ape Cave, WA

We took the first field trip to examine luna-like volcanic features to visit the longest lava tube in the continental US. It's over two miles of cavern located on the southern flank of Mt. St. Helens in WA and known locally as Ape Cave.

How relevant to the lunar landscape are terrestrial lava tubes? Do similiar lava tubes exist on the Moon? Emminent lunar scientist Paul Spudis seems to be fairly certain they do; he labeled the picture of Hadley Rille in his book, "Once & Future Moon" as a "lava channel-tube" and further states in the text, "Although all scientists agree that sinuous rilles are lava channels and tubes, the exact mode of formation remains somewhat contentious." (italics mine) Thus investigating a lava tube would seem to be perfectly relevant to a study of lunar volcanic formations--and fascinating as an aid to visualizing possible uses for such tubes on the Moon as locations for habitation--plus something to increase one's wonder when observing such features in the telescope as well!

Ape cave is definately a pretty spectaular volcanic formation in it's own right.

I learned that lava tubes/channels naturally follow drainage patterns--a streambed in this case but any sloping gully/valley provides a suitable location for their formation. They are created by a flow characteristic of less viscous basaltic lavas (exactly the type most common on the Moon) to harden on the outer surfaces first, leaving the center flowing freely; kind of like how water runs through a partially frozen stream, eventually flowing under a 'roof' of ice. And like such a stream of water, once the flow is ceases, the channel and roof it created remains:

What really suprised me was the almost perfect shape of some of the sections of this tube---they almost looked machine bored!

Obviously the utility of such structures on the Moon as bases of operation would be phenomenal--especially when one realizes that lunar tubes can be massively larger---possibly up to a kilometer in diameter!

Walking down this tube must be much like it would be to walk down a lunar rille, or, with an uncollapsed, intact roof, a lunar lava tube. Both are formed by essentially the same processes and by similiar lava--fluidic basalt--and both leave the history of their active lifespan written in stone, as it were--the variences of flow volume and speed, even the ripples caused by segments of roof falling into the then still flowing lava are found frozen in time. I find myself looking at lunar rilles in a whole different light after this little excursion! I'd certainly encourage any 'lunatic' able to explore one of these lava tubes to do so if given the opportunity.

Next, a trip to central Oregon to visit another lava tube, some cinder cones (dark haloed lunar craters), a shield volcano (lunar domes) and some lobate flow fields, as seen upon the lunar maria--plus a ten foot wide by 40ft deep stress fracture 2 miles long---analogous to a lunar arculate rille.

Newberry Oregon Geologic Fieldtrip