Half a day's travel in every direction from the skull, in sheltered valleys and on high plateaus, stand "
the penitents" - closely spaced pillars of soft, dusty stone ranging from two to sixteen feet in height. People avoid them because of their vaguely humanoid shape (and because they make poor construction materials). Small birds, covered in like-colored dust for camouflage, nest among them. No other beasts dare approach.
Halfway up a plateau no one has ever climbed
sits a monk, meditating, concerned that the tremors are imperceptibly escalating. The monk will relocate to a ridge only two hours hike from the skull for more direct observation.
The Monk: I had some initial ideas about who this monk should be, but after my talk last time of killing the sun and the moon, it's hard not to go with a monk (hah, that mouseover text) of the sun.
The Birds: I like these birds as the iridescent embers of a failed wish spell, ineffectively pursuing their task in perpetuity, but I also want them to be pieces of the "penitents'" souls so as to imply that a legendary Phoenix is a piece of the Skull's soul.
I'm of two minds about the terrain immediately around the skull. On the one hand, if it's flat and frozen, then the eruption could
shatter it and make new hills and a lake where there were none before; on the other hand, having rivers and ridges
already there would give the players some choice of where to weather the event. Plus ships would get stranded upriver, bridges would be knocked out downriver, and the river could run backwards for a ways.
[The eruption is a great image, but it's more of an interruption than an adventure. Haven't worked out the larger scenario to drop it into yet.]
Eruption