Cryovolcanic Explosion

A bright streak flashes from you to a point you choose within range and then blossoms with a low roar into a steamy explosion. Each creature in a 20-foot-radius Sphere centered on that point makes a Dexterity saving throw, taking 4d8 Fire damage & 4d8 Ice damage on a failed save or half as much damage on a successful one.

Using a Higher-Level Spell Slot. The damage increases by 1d8 for each spell slot level above 3.