And certain environmental enchantments, [she helpfully reminds him.] In this case, there is a pall over the lower regions of the temple which muffles sound and light.

It was difficult to sense where it came from, and we spent little time in the ritual chamber with the gate itself, but I suppose it might have been centered there and radiated upward. Given Dumat's role however, I suspect it a feature of the temple rather than a product of the rift.