Evoke

A shimmering, amethyst sphere extends outward from you in a 5-mile radius as you float 10 feet off the ground. Each creature in the sphere (including you) must make a DC 23 Wisdom saving throw or take 20d20 force damage, or 12d20 on a successful save. Objects, terrain, and structures in the sphere that aren't being worn or carried are destroyed. You must belong to the School of Evocation to cast this spell, and you can only ever cast this spell twice.