Manage to cross island devastation (4)
I believe the answer is:
ruin
'devastation' is the definition.
('ruin' can be a synonym of 'devastation')
'manage to cross island' is the wordplay.
'manage' becomes 'run' (I've seen this before).
'to cross' is an insertion indicator.
'island' becomes 'i'.
'run' going around 'i' is 'RUIN'.
(Other definitions for ruin that I've seen before include "Scotch" , "Mar, lay waste to" , "Destroy completely" , "fall" , "Wreck" .)