Chose an area within range. You then spend an hour gathering arcane energy into a single focused element. It then launches from your location, soaring into the air and ripping itself apart. 1d4 rounds later the bomb will impact the target area, creating the following effects:

All creatures within a 30ft radius automatically take 20d8 +150 magic bludgeon damage. 

Creatures within 120ft must make a CON save or take 20d8 + 50 radiant damage, taking half damage on a success.

The 30ft radius around the bomb becomes a dead magic zone.

 All nonmagical plant life within 300ft withers and dies.

For the next 1d10 days, all creatures within the created dead magic zone take 15 radient damage each turn.