Blow up causing general mayhem (7)
I believe the answer is:
enlarge
'blow up' is the definition.
('enlarge' can be a synonym of 'blow up')
'general mayhem' is the wordplay.
'mayhem' indicates an anagram.
'general' with letters rearranged gives 'ENLARGE'.
'causing' is the link.
(Other definitions for enlarge that I've seen before include "Make bigger, say photo" , "Make greater" , "Gleaner (anag.)" , "Dilate" , "Amplify" .)