Erwin's Emaculate Eruption

You brings your arms up while holding the match and the bag and a 20ft radius mound rises from the ground in the range. This radius is considered difficult terrain for the duration. You can then cause the mound to erupt as an action on any of your turns after it is formed. Anyone within an additional 20ft of the radius must make a dexterity saving throw or take 4d10 fire damage on a failed save, half on a successful one. After the eruption, the mound remains as difficult terrain until it is dispelled. When dispelled, the mound shatters into fragments of rock. Anyone in the radius must make a dexterity saving throw or take 5d8 bludgeoning damage on a failed save and half as much on a succesful one.