Volcano's Wrath

You call upon the wrath of the earth, unleashing a gout of magma from beneath the ground. A small volcano erupts in an unoccupied space you can see within range, spewing fire and brimstone all around it. The volcano occupies a 5-ft.-by-5-ft. space. When you cast the spell all creatures within 15 ft. of the volcano must succeed on a Dexterity saving throw or take 6d6 fire damage and 6d6 bludgeoning damage. Creatures within 5 ft. of the volcano have disadvantage on their saving throws against it. On subsequent turns you can use a bonus action to cause the volcano to erupt again from the same location.