A Shift refers to the event when all the Fragments of Vespirian move. Though we use the analogy of floating islands to describe the Fragments, the idea of drifting slowly in a current doesn't accurately describe how they move. It's more like trying to push a heavy writing desk. You push and push and then, suddenly the desk scoots forward under your surprised hands and comes to a quick rest some distance away. The Shifting fragments are much more like that. They push past each other, propelled by some unknown force, and then suddenly lock back into place again. The natives claim there is some sort of pattern to the way the Fragments shift. Something to do with their Archfey deities. However, even with all our observations, we've yet to find a way to reliably navigate too far off the Exalos Fragment.
The timing of each Shift seems somewhat random. Some Fae seem gifted with the ability to sense when one is coming, but outside of that, there seems to be little we can do to predict the timing. It ranges from weeks to months. The amount each Fragment moves also appears to be random and almost unrelated to the length of it's current state. My current theory is that the force that moves the Fragments builds and builds until it's great enough to break the bonds between Fragments. It would certainly explain the bright flash of white light reported by those near the border of a Fragment during a Shift.
This is still an area of ongoing research as we learn how best to navigate and explore this new world.
R.J. Soulsby