Active volcano (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">active volcano</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for etna that I've seen before include "Sicilian landmark" , "hole in the crust" , "Highest active volcano in Europe" , "high peak" , "Constant smoker" .)