Blow up and erupt, possibly enveloping country's capital (8)
I believe the answer is:
uppercut
'blow' is the definition.
(uppercut is a kind of blow)
'up and erupt possibly enveloping country's capital' is the wordplay.
'and' says to put letters next to each other.
'possibly' indicates anagramming the letters.
'enveloping' is an insertion indicator.
'capital' says to take the initial letters.
The first letter of 'countrys' is 'c'.
'erupt' is an anagram of 'perut'.
'perut' enclosing 'c' is 'percut'.
'up'+'percut'='UPPERCUT'
(Other definitions for uppercut that I've seen before include "Punch delivered vertically to chin" , "sock" , "Part of boxer's repertoire" , "Boxer's blow" , "Swinging blow in boxing" .)