Rifts developed initially (5)
I believe the answer is:
first
'initially' is the definition.
(I've seen this in another clue)
'rifts developed' is the wordplay.
'developed' indicates an anagram.
'rifts' with letters rearranged gives 'FIRST'.
(Other definitions for first that I've seen before include "In winning position" , "Before all else" , "Original" , "Top degree class" , "Coming before all others" .)