@Redshirt Army, did you really mean to overwrite your vote with [] pikapika?
[X] THEORY: The specifics are hazy, but this is a known contingency plan that Borek is entirely aware of, but hoped hadn't been enacted. The result breaks all Dawi notions of acceptability, but Karak Dum survives in some capacity and continues to inflict attrition on every local and visiting Chaos force that want to take a swing at them, so it is considered a lesser evil by the pragmatic Karak Dum.
[X] THEORY: That's not Morghur. Morghur constantly changes his surroundings, Morghur does not make reality more stable near himself, Morghur does not display affection, Morghur does not not attack people, Morghur would never stay here unless he was bound, and if he was bound he'd be struggling constantly to get out. The shuddering of reality can be faked by Runesmiths if they wanted.
[X] THEORY: The Dwarves of Karag Dum did something to burn away the taint of Chaos, much as your Belt of the Unshackled Mountain does, but on a far grander scale. Perhaps it had an effect on the Beastmen here, Cor-Dum included.
[X] THEORY: Karag Dum is using a fake Morghur to make the real beastmen fight for them.
[X] THEORY: The dwarves of Karag Dum are alive and uncorrupted by Chaos, but have resorted to truly drastic measures to survive, probably undertaken by their controversial "Rune Masters", which involves having these beastmen or beastmen-appearing creatures defending the karak for the dwarves. We can assume that this is all in favour of the dwarves by Morghur's easy acceptance and non-destruction of Borek as well as Borek's mutual acceptance of the beastman. The idea of Rune Masters being critically involved is the certainty that some form of magic was used to create this whole situation, including the odd weather, and the Rune Masters' lack of corruption is supported by the lesser level of ambient dark magic in the area, even directly around Morghur himself.
[X] THEORY: Karag Dum converted their Rune of Valaya into a Rune of Valaya's Vengeance, and used it to burn away all of the surrounding Dhar, causing a cataclysmic explosion and presumably wiping out whatever threat they were facing. But having lost their Rune of Valaya, they no longer had a defence against the Winds of Chaos, and they knew it. They could not simply die, for they had a critical duty to protect their hold, for reasons that are secrets of my Guild and Karak Eight Peaks, and so they decided that if they could not survive to defend it as Dwarves they would no longer be Dwarves. They found a way for dwarves to become beastmen, and know that they must defend their Karak as though it were their herdstone. Pity them.
[X] ACTION: I'm going to have to check this out.
[X] ACTION: Project a message in the air: What the fuck Borek (but more politely worded.)
[X] ACTION: Gain more information.
[X] ACTION: Politely ask Morghur to be granted entrance into Karak Dum.
[X] ACTION: Investigate further.
[X] ACTION: Investigate by following the waystone ley line. It will be your guide through any possible illusion or trickery.
[X] ACTION: Dig up some of those bones to confirm how they died.
[X] ACTION: Enlist Journeyman Cyrston's help in identifying flora.
[X] ACTION: Very careful scouting. Both by the knights, dwarves and Mathilde. Starting with inanimate matter and other disposable stuff(like the cows) to determine where the edges-borders of the effect are and just what the hell the effect is without entering it, while the convoy digs in and readies itself to attack, from behind or from the Karag. If that doesn't lead to some clarity, more aggressive scouting may be needed. Either way, Karag Dum is still a part of the Karak Ankor, and there are ways that link them could be used by demons to hurt the whole realm, especially now that Vlag is back and the links reestablished. So while a part of me might prefer as the wise option to turn back, we cannot leave such a threat without establishing its exact nature, if only so I can bring back news of what to do to about it to King Belegar and the High King.
Edit: Added some theories and actions proposed later in the thread, because my vote wasn't long enough already.