I don't think Moelach's direction was specified. Just that it was moving.
Anyway, I'm not sure what it contains, but I'm leaning towards one of the Unmade. Not Nergaoul, but possibly Moelach. Nergaoul is apparently moving towards Jah Keved, where Szeth hid the sphere. Because the Thrill didn't start to diminish in Alethkar until around the beginning of the books, Nergaoul couldn't have been directly in the sphere. Whereas the sphere containing Moelach would work as a possibility, because Moelach's effects could stretch, though diminishing in power, to Alethkar. That would be why no bridgemen until Maps uttered Death Rattles - Moelach simply wasn't strong enough in Alethkar to cause more than a few. Also, the Death Rattles didn't start until the Plains were discovered. Gavilar could have found the sphere, allowing Moelach to slowly escape. The Death Rattles would have started, and then, after ten years or so (perhaps ten years exactly), Moelach could fully escape and start moving.