Torrent a worry when climbing, surrounded by rock face (9)
I believe the answer is:
waterfall
'torrent' is the definition.
(a waterfall is a torrent of water)
'a worry when climbing surrounded by rock face' is the wordplay.
'worry' becomes 'fret' (to fret about something is to worry).
'when climbing' shows that the letters should be reversed in order.
'surrounded by' means one lot of letters goes inside another.
'rock face' becomes 'wall' (a wall of rock).
'a'+'fret'='afret'
'afret' backwards is 'terfa'.
'terfa' put inside 'wall' is 'WATERFALL'.
(Other definitions for waterfall that I've seen before include "Steep descent of a river" , "One of the aqueous drops" , "Cataract" , "source of power, possibly a force in the north" , "Cascade, force" .)