I'm pretty sure the locate city[/b] bomb is do-able by 7th.
Let's see, locate city is a 1st-level spell, and we need Snowcasting, Frozen Spell, Energy Sub. (electricity), Born of the Three Thunders, and Explosive Spell. Energy Sub. is a +1 and Explosive is a +2 IIRC, so we should be good.
So, that's a Human Wizard 5/Incantatrix 2 to snag the right bonus feats.
If we allow flaws, we can add on Fell Drain and Arcane Thesis (Locate City) in order to hit everything within the 90-mile blast radius with a negative level. Note that this causes everything with 1 HD (or less!) to die and rise as a wight, creating a metric crapton of undead as all the minor critters and dumb commoners wither and die. Not to mention the retarded damage Explosive spell deals to anyone who flubs the save.
So, yeah, it's not really blasting as far as in-combat goes, but it sure leaves a nice crater.
