Behind mountains, intended, we hear, to form new organisation (13)
I believe the answer is:
rearrangement
'new organisation' is the definition.
'behind mountains intended we hear' is the wordplay.
'behind' becomes 'rear' ('rear' can be a synonym of 'behind'**).
'mountains' becomes 'range' (I've seen this before).
'intended' becomes 'meant' (meaning is a kind of intending).
'we hear' shows a homophone (sound like).
'meant' sounds like 'ment'.
'rear'+'range'+'ment'='REARRANGEMENT'
'to form' acts as a link.
(Other definitions for rearrangement that I've seen before include "New layout" , "Moving around of component parts" , "Act of changing layout of items" , "Process of moving things around" , "A shuffling" .)