A werebear changes form while buried neck deep in sand.

[Qintopon]

What happens?

[Allanimal]

its new form is buried neck deep in sand.

[TuggyNE]

I'd expect it depends on the relative sizes of the forms, but roughly what you'd suppose from common sense: the new form is still mostly (or as the case may be entirely, or only about half) buried in sand.

Why, what else could happen?

[Qintopon]

I figured compression would kick in and there would be some pain. But that could have been just the sadistic me.

[Ryulin18]

Depends on the density of the sand. If we're talking "sahara desert" sand, it would displace around him. "wet beach sand" would compress.

The solution is the vertical growth of the were-bear. It would grow a few feet and breach the sand that's thin between his shoulders and head.

[Togo]

Technically speaking, most forms of changing shape don't allow you to change if there is no room for the new form. I don't remember if that applies to lycanthropy, but I believe not.

In which case, yeah, the werebear would expand upwards towards the thinest barrier.

The interesting one is the reverse case. If you bury the werebear as a bear, and he turns into a human, then he should be able to wriggle out of the now-loose sand.

[supermonkeyjoe]

I normally rule for expanding creatures they have to make a strength check to bust free of anything confining/constricting them otherwise the expansion fails

edit: same rules as in the enlarge person (http://www.d20srd.org/srd/spells/enlargePerson.htm) spell