Odd parts having run away, melting as volcano (4)
I believe the answer is:
etna
'volcano' is the definition.
(Mount Etna)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for etna that I've seen before include "Active European volcano" , "a mount hotly tipped when it runs" , "Sicilian landmark" , "Neat class of volcano in Sicily" , "feature spewing lava" .)