Terrible Torrent

You slam your palms on the ground, and a swirling  boiling torrent of water swirls out around you in a circle, each creature within a 30 ft radius of the caster must make a dexterity saving throw, or take 6d6 fire damage, and be knocked prone. On a successful save, the targets are not knocked prone, and take half damage.

When you cast this spell using a slot of 5th level or high, the damage increases by 1d6 for each slot level above 4th