Tarn Icewind is a foul traitor, but a most powerful gelidran that we will need to make use of.
While the Queen Pyrilonis and King Gelaqua both condone havoc in the most fundamental way to save us from boredom, that dark will should not be turned upon our own kind.
Therefore, it was decided that Tarn would be imprisoned beyond the borders of the sanctum.
In order to keep Tarn contained, we had to invoke a magic that we oft do not toy with and would certainly not use anywhere near the sanctum.
We used the Crystalcell Keep ritual to put this traitor into safekeeping. It takes much time and energy for both the gelidran and pyrilen rift elders to perform this powerful ritual.
It also uses a lot of our precious crystal resources.