Caduceus is the final boss in the instance.

Magma Blast – Must be cleansed
Tectonic Disturbance – Stay stacked
Erupted Cores – Kill one at a time

Magma Blast – Places a DoT on 3 random players, must be cleansed
Earth Rumbles – Spiked AoE ground effects that ripple out from the boss’ location
Tectonic Disturbance – Jumps around if players are not stacked, dealing significant damage

Summoned Adds:
Erupted Embers – Wisps that spawn around the perimeter of the room, cast Ember Bolt missiles, will respawn if killed
Erupted Cores – Orelings, small ones explode on death, must be killed one at a time

Planar protection and earth resistance can be useful for this fight. 

The tank takes Caduceus where he stands, and the rest of the group stacks, either with the tank or directly behind the boss.  Return to this positioning whenever moved from it, such as during his knockback.

The boss casts Magma Blast, which places a DoT on 3 random players.  This must be cleansed right away off any player other than the tank.

The emote “The earth rumbles!” signals that spiked AoE ground effects will ripple out from the boss’ location.

He also will perform Tectonic Disturbance, jumping around to players who are not stacked up nearby, dealing significant damage.

Next he will spawn Erupted Ember wisps around the perimeter, a group of oreling Erupted Cores in the center, and one larger rock elemental.  Ignore the wisps, which will cast Ember Bolt missiles, but will only respawn if killed.  Kill the Erupted Cores one at a time, because they explode on death.  When all the Erupted Cores are dead, kill the larger rock elemental and return to DPS the boss.