The Witchburns are becoming a major blockade at the entrance to Volcavern. It's clear someone or something is using them to guard the passage. You must venture into the Volcavern Passage itself, just past the Smoking Foothills, and eliminate more of them. Clear the path. Bring back 15 more Burning Embers as proof.
You've braved the heat of Volcavern! The passage is now clear, for a time. This suggests a direct link between the forest's blight and whatever lies beyond. I've heard Old Man Tiber, The Cave Dweller, has made his home within the first caverns of the Volcavern Passage, seeking refuge from the forest's turmoil. He might know more about these elemental guardians. Seek him out; he lives in the Echoing Grotto just inside the passage.
QUEST (TASKS OF TRAILBLAZER) 