Bread crust separated from interior I'm an amateur baker, been making bread weekly for about 9 months now, working out of Ken Forkish's "Flour Water Salt Yeast" cookbook mostly. I had something happen to my bread this week that I would like to understand.

I was making a recipe in the book called "Overnight White Bread" which takes a very small amount of yeast and then rises for 12-14 hours. As a variant suggested in the book, after shaping the loaf in the morning I placed the proofing basket in the refrigerator and then, after work, set it on the counter while pre-heating my oven (I bake in an enameled cast iron Dutch oven). This let it work with my work schedule.

The bread came out pretty good, with an excellent taste. It has great big holes, which this recipe does usually, but I notice that the bread itself sort of separated -- there were extremely big holes near the top of the loaf, but it was relatively dense near the bottom. Basically, it looked as if the bread collapsed some on the interior, but after the crust had already risen and solidified enough to hold itself up. As a side-effect, with just a few gluten filaments beneath it, the top of the loaf couldn't conduct heat away and so blackened more than I would like..

It's not a huge deal, but I'd rather have a more evenly-distributed loaf if possible. Why does this happen, and can I do anything to prevent it?
That sounds like you allowed the bread to dry while it was rising.  And also that you allowed it to rise too long.  The latter will produce large air pockets, and the former will make them form just under the crust.  Cover your rising bread with a damp towel, don't let it get more than twice as large as it started, and you should be fine.