If Ganymede had a global liquid ocean which then froze, during the freezing the ice will first expand, and then contract, as the temperature drops. Certainly some astonishing cracking will result. If there is an occasional large impact, then there will be melting and re-freezing, perhaps moon-wide. There is plenty of room in conventional physics for modest expansion and contraction on Ganymede, given these conditions. It's that, at least at present, we can't have a geologist walking around on the surface going "Oh, I see what happened!"