A change or disturbance that brings about great disruption (8)
I believe the answer is:
upheaval
I believe this clue is a double definition.
'a change' is the first definition.
(upheaval is a kind of change)
'disturbance that brings about great disruption' is the second definition.
(I've seen this before)
(Other definitions for upheaval that I've seen before include "Disturbance bringing great disruption" , "Major disturbance" , "Violent or sudden disturbance" , "At university, books are taken in to cure" , "Great disturbance and disorder" .)