Top of crampon abandoned in fissure (5)
I believe the answer is:
cleft
'fissure' is the definition.
(I know that fissure can be written as cleft)
'top of crampon abandoned' is the wordplay.
'top of' indicates taking the first letters.
'abandoned' becomes 'left' (leave can mean to abandon).
The first letter of 'crampon' is 'c'.
'c'+'left'='CLEFT'
'in' is the link.
(Other definitions for cleft that I've seen before include "Split; fissure" , "Narrow gap" , "Fissure in rock" , "Chin split" , "Partially divided" .)