Etna effluence (4)
I believe the answer is:
lava
'etna effluence' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lava that I've seen before include "dangerous fluid" , "Immature insect form" , "Volcanic flowing substance" , "Flowing extrusive magma" , "Volcanic stuff" .)