Great disruptive change (8)
I believe the answer is:
upheaval
'great disruptive change' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for upheaval that I've seen before include "Disorder, turmoil" , "State of violent disturbance and disorder" , "Turbulence" , "Violent or sudden change or disruption" , "Great disturbance and disorder" .)