Must you suffocate? It depends on the creature and how it burrows. If it must suffocate, then keep in mind that it will only be able to burrow for a number of rounds equal to its constitution (plus ever how many rounds you give it for a localized air pocket) because it will be holding its breath--if you use the swimming/drowning rules.
That seems to make sense. Not worried about it, was just wondering if anyone had any rules to quote one way or the other. Only had it come up once in a (basically) once shot game with a mineral warrior templated pc, and DM had to kind of make up soemthing on the spot on how to handle burrowing for several rounds (i didnt know enough to suggest the swimming/drowning rules, which would seem to make the best sense.).