cataclysm

noun
cat·​a·​clysm | \ ˈka-tə-ˌkli-zəm How to pronounce cataclysm (audio) \

Definition of cataclysm

1 : flood, deluge
3 : a momentous and violent event marked by overwhelming upheaval and demolition broadly : an event that brings great changes an international economic cataclysm