You create a small nuclear blast.

Tier 10th
Types Evocation (Massive, Radiation, Ritual x3, Siege, Splashx2, Unavoidable)
Cast 2 hours, last 10 minutes of which is visible for miles as it creates a massive visual effect
Target 1 mile radius perceived within 100 mile range
Resistance Fortitude for half damage
Effects Everything in the area takes 20d10 bludgeoning and 20d10 fire damage, is knocked prone and pushed away from the center of the radius by 5d10 feet, and is afflicted with deadly radiation poisoning. Creatures in the splash radius take half this damage and get only severe poisoning. A successful Fortitude save halves this damage and reduces the radiation poisoning to severe (or moderate if in the splash radius) and reduces the distance pushed by 5 feet plus an additional 5 feet per 5 points the DC was exceeded.

Tier 12 3 mile radius, 300 mile range, 24d10 bludgeoning, 24d10 fire, 5d12 feet
Tier 14 10 mile radius, 1000 mile range, 28d10 bludgeoning, 28d10 fire, 5d12+10 feet