Catastrophe –
An event causing great and usually sudden damage or suffering; a disaster.
an environmental catastrophe
Calamity –
An event causing great and usually sudden damage or suffering; a disaster.
emergency measures may be necessary in order to avert a calamity
Is the only difference between these two words is where they originated/etymology?
NOTE
calamity (n.) Look up calamity at Dictionary.com
early 15c., from Middle French calamite (14c.), from Latin calamitatem (nominative calamitas) "damage, loss, failure; disaster, misfortune, adversity," origin obscure. Early etymologists associated it with calamus "straw" (see shawm); but it is perhaps from a lost root preserved in incolumis "uninjured," from PIE *kle-mo-, from base *kel- "to strike, cut" (see hilt).
Best Answer
'Calamity' is generally used to refer to only large-scale natural/man-made disasters.
However, 'catastrophe' isn't limited to that usage.
It isn't uncommon to use catastrophe in the following way:
I don't think calamity is used in that manner.
Additionally, 'catastrophe' has another meaning. I don't think it's used very often, but the ending of a tragic play is called a 'catastrophe'.
According to Oxford Dictionaries: