Lunar rilles

I have long accepted the standard idea that lunar rilles are mostly
collapsed lava tubes but after looking at a lot of rille pics I am now
not so sure. However, I cannot accept the odd idea of them being
electrical discharge features on a large scale. I wonder if they
could be related to collapse along faults? Why has this not been
considered more? With the extreme "Space weathering" of the lunar
surface, you'd expect the small stuff near the surface to fall into
any cracks below.

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