So during my daily procrastinating at work, it sprung to mind that the spell "Call Lightning" and the mechanics changes that were made for our rise to the surface back in EFU:A now render this spell obsolete.
Seeing as it must be raining for you to call lightning, and it never rains in the UD perhaps it might be possible to alter it back to its original form and emote it as falling stalagmites or some equivalent?
It works in the UD. As falling rocks in nature zones... though it should probably work in all zones, as rocks are everywhere. It also hurts friendlies.
Rockslide
1d8/level bludgeoning damage.
Works very well.