[jacquesm]

That's at odds with what I understand of the celestial mechanics of the earth-moon system, roughly the same thing happened to Saturn and even though the rings have thickness they are relatively thin compared to their width.

What reason would there be for the moon debris to form a cloud, that would require a lot of energy added to the pieces after the initial collision to get them to go into other orbits? (I'm sure Stephenson has researched this but it makes no sense to me at first sight.)

The options really are quite limited, re-unification in a 'lump', one or more large chunks escaping earth orbit or a ring, I don't see how a cloud is possible.

All but the second would result in quite a bit of debris landing on earth as the debris from the collisions would be scattered in all directions.

[jhallenworld]

Energy was added, so I'm sure it will be a dynamic mess..

On the other hand, the moon is beyond earth's Roche limit so I don't think the final result will be rings.

Also what is the tensile strength of the center of the moon? I'm not sure it's possible to have 7 large non-spheroidal shaped pieces, but google suggests ~800 km is the lower limit for rocky bodies, so maybe it's just possible.