Some sweet nature, but it is liable to erupt (4)
I believe the answer is:
etna
'it is liable to erupt' is the definition.
(Mount Etna is a volcano)
'some sweet nature but' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'ETNA' is hidden within 'sweet nature but'.
(Other definitions for etna that I've seen before include "A feature of Sicily" , "it may produce steam and ash" , "It could erupt" , "source of fumes?" , "Active European volcano" .)