Volcanic Ward

You draw a glyph over your chest with the obsidian shard, making a volatile and pulsating protective barrier over you. You gain 10 temporary hit points and resistance to fire and cold damage for the duration or until the spell ends. 

The next time you are hit with a melee attack, all creatures within 15 feet of you, including you, must make a Dexterity saving throw as the rune explodes with the fury of a volcano. You have advantage on this saving throw. All creatures take 5d6 fire damage on a failed save, or half as much damage on a successful one. After the ward explodes, the spell ends early.

At Higher Levels: When you cast this spell using a spell slot of 4th level or higher, the temporary hit points increase by 5, and the damage increases by 1d6 for each slot level above 3rd.