Fissures (5)
'fissures' is the definition.
(I know this)
This is all the clue.
(Other definitions for rifts that I've seen before include "Clefts in earth, or disagreements" , "Breaks, severances" , "Splits" , "Deep divides" , "Schisms" .)
'fissures' is the definition.
('crevice' can be a synonym of 'fissure')
This is the entire clue.
(Another definition for crevices that I've seen is " Long narrow cracks or fissures".)