Its a sealed primal so one way or another it will probably follow at least some of the rules that primals do. My guess is Rhalgr. It fits with the story leading up to it. I suspect it won't end up doing much cause I think we will end up using Omega to destroy it and as a side effect burn a hole through a mountain in Ala Mhigo.

I don't think we will see another calamity in FF14. Actually showing such an event in game without entirely rebuilding the world is quite difficult.