Explode, causing pure chaos at starting time (5)
I believe the answer is:
erupt
'explode' is the definition.
(erupting is a kind of exploding)
'pure chaos at starting time' is the wordplay.
'chaos' is an anagram indicator.
'at' says to put letters next to each other.
'starting' suggests taking the first letters.
The initial letter of 'time' is 't'.
'pure' anagrammed gives 'erup'.
'erup'+'t'='ERUPT'
'causing' is the link.
(Other definitions for erupt that I've seen before include "go up" , "Burst forth, like 25" , "be active" , "Emit lava" , "Spurt lava" .)