Dead Zone
The Dead Zone was a portion of Ulgrotha with no mana. This rift also slowly drained mana from all the plane. It was created when Ravi rang the Apocalypse Chime and completed the Great Destruction begun by the Ancients and Tolgath. Any living thing that stepped foot in the Dead Zone had its life force pulled away, killing it.
Before it was the Dead Zone, it held the Ulgrothan Citadel and the Basalt Spire.