Ashardalon's Igneous Rock

A burst of magma erupts from you in a 30-foot cone. Each creature in that area must make a Dexterity saving throw. On a failed save, a creature takes 3d8 fire damage and is hindered by magma that instantly hardens into lava rock for 1 minute, or until it or another creature within reach of it uses an action to break away the rock. A creature hindered by lava rock has its speed reduced to 0. On a successful save, a creature takes half as much damage and isn’t hindered. 

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, increase the fire damage by 1d8 for each slot level above 2nd.