Magma Tide

8th-level evocation
Casting time: 1 action
Range: Self
Target: --
Components: V, S, M (a fire opal worth 1000gp)
Duration: Concentration, up to 5 minutes
Classes: Sorcerer, Warlock, Druid
Subclasses: --

In an area around you, magma begins to rise up and boil out of the ground, seeping outwards 5 feet in all directions from you, burning all in its path.

When a creature enters the affected area for the first time on a turn or starts its turn there, the creature must succeed on a Dexterity saving throw or takes 4d6 fire damage on a failed save, or half as much damage on a successful one.
If a creature fails the saving throw by 5 or more the creatures is is burning (2d6).

At the start of the caster's subsequent turns the magma Tied flows further, increasing outwards another 5 feet in all directions.