It's a simple matter to crack stone. The mages more familiar with ice magic force ice in to every crack they can find in the stone ceiling of the cave and a few feet back. Dorian helps with the fire runes that get laid over the ice.

"If everyone could get back, please, this is going to be quite loud and dangerous," Dorian makes shooing motions to the guards and Templars, the only mage brave enough to order them around. Luckily he has enough respect to manage it. Dorian turns back to the mages with a smile. "Let's show them all it's done, shall we?"

The mages take up position and Dorian and the fire mages cast their runes, melting the ice in the rocks to create water. The ice mages follow up almost instantly to freeze the water again. It expands rapidly among the stones and cracks it immediately. The avalanche falls seconds later, completely covering the entrance to the cave.