Editing Homebrew Spells (section)

=== The Floor is Lava ===
''9th-level transmutation'' 

Casting Time: 1 action

Range: 400 feet

Components: V, S

Duration: Concentration, up to 1 minute

For the duration, all ground flooring in a circular area centered around a point you can see within 400 feet of you is instantaneously transformed into lava. Any creature touching the ground must succeed on a Dexterity saving throw, taking 10d10 Fire damage on a failed save, or half as much on a success. If a creature ends their turn in the lava, they become submerged in it and must repeat the saving throw, taking 18d10 Fire damage on a failed save, or half as much on a success. 

The lava is approximately six feet deep and cannot spread or leave the area it is affecting. Structures and other objects on the ground may ignite and catch fire or be totally destroyed, unless they are immune to Fire damage.