Pyroclasm

9th-level evocation

Classes: sorcerer, warlock, wizard

Casting Time:1 action

Range:500 feet

Components:V, S, M (a shard of obsidian)

Duration:Concentration, up to 1 minute

You point toward an area of ground or similar surface within range. A geyser of lava erupts from the spot you choose, creating a 5-foot wide, 40-foot high cylinder of lava centered on a point you can see. When it erupts, any creature either in the area or that starts its turn there must make a Dexterity saving throw. A creature takes 10d8 fire damage on a failed save, or half as much damage on a successful one.

At the start of your turn, the lava spreads in a pool centered at the base of the geyser. The first time it spreads, it creates a 10-foot radius of lava, and the radius increases by 10 feet each subsequent round to a maximum radius of 50 feet. Creatures who start their turn in the pool take 5d8 fire damage.

Lava clings to a creature when it leaves the area, and it hardens into stone. The creature is reduced to half speed and has disadvantage on Dexterity saving throws until a creature uses an action to break the hardened lava off. If you maintain your concentration for the full minute, the lava geyser and pool permanently harden into nonmagical stone.

A creature in the hardened stone is restrained. The stone has an AC 17, 25 hit points, is resistant to all damage except thunder, and is immune to poison and psychic damage. A restrained creature can break free as an action with a successful DC 27 Strength (Athletics) check.