Cataclysm
Part of speech: noun
Definition: A sudden, violent event. A sudden and violent change in the earth's crust. A great flood.
Disaster
Part of speech: noun
Definition: An unexpected natural or man-made catastrophe of substantial extent causing significant physical damage or destruction, loss of life or sometimes permanent change to the natural environment.An unforeseen event causing great loss, upset or unpleasantness of whatever kind.
Example sentence: Sometimes it takes a natural disaster to reveal a social disaster.