Volcanic emission (4)
I believe the answer is:
lava
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">volcanic emission</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for lava that I've seen before include "Volcanic emission" , "Volcano output" , "Molten rock from volcanoes" , "Volcanic flowing rock" , "Emanating magma" .)