So how much in the way of explosives do we have on hand right now?
After the scouts give us a look we could use miracle to cast
Teleport Object and beam over around a thousand pounds of mixed explosives, alchemical napalm, and exotic shrapnel.
Fabricate only takes about ten minutes right? If we want to make it more effective we could easily pile it all up, shape it into something more likely to spread the damage to the sides rather than straight up or down, then teleport in afterwards and clean up whatever's left.
I'm not sure on the range, but if we need to get closer we could just distribute the components among the party and assemble it in closer to the target.