What is the difference between an apocalypse and a cataclysm? I've been told that an apocalypse is an act of God, but we seem to use it as a generic term for any grand disaster. What is the difference in original and current usage?
Apocalypse means "revelation" in Greek, from Greek καλύπτω (kalupto) "hide" and ἀπό- (apo-) "un-". It was so used in the New Testament: the last book is called Ἀποκάλυψις Ἰωάννου in Greek, Revelation of John, in which the Last Judgement is revealed to John, the time when the Christian God will end human existence as we know it. From this, apocalypse gained its secondary modern sense of armageddon, the end of the world by the forces of nature or God. In this way it is now most often used. It now means a disaster so great that it will probably destroy most of mankind, and possibly the entire universe.
Cataclysm comes from Greek κατακλυσμός (kataklusmos), "deluge", from κλύζω (kluzo), "wash away, flood", and κατά- (kata-), "down". It refers to the flooding of all Earth, usually by endless rains and rising rivers, as it is told in the story of Noah's Ark in the book of Genesis in the Old Testament. Note that this myth also exists in many other Oriental cultures. In many cultures, possibly including Judaism, this is a recurring event, by which time is cyclically ordered in periods of growth and subsequent destruction. It now means a great, uncontrollable disaster, but not necessarily so great as to destroy civilization. It should have significant destructive impact within a certain environment. There is some overlap with apocalypse.
Armageddon (Ἁρμαγεδών in Greek) is the hill in Israel where the final battle between the Christian Messiah and Satan is to take place at the end of time, the Last Judgement. The word appears only once in the Bible, so says Wikipedia, in the book of Revelation. Similar stories about a battle on a mountain at the end of time already existed in Jewish lore before Christ, and were also adopted by Islamic prophecies. Armageddon is used as a near-synonym of apocalypse in modern English; I don't see any difference except that it has a slight connotation of violence and struggle, whereas apocalypse is slightly more abstract, "cleaner". In most contexts there is no difference.
Apocalypse is a Greek word for revelation and is associated especially with the end-of-days story in the Book of Revelations. While it can be used for any disaster (and has been in modern times) the implication is that an apocalyptic event is a world-ending event.
A cataclysm on the other hand has fewer religious associations and can stand in for any major disaster, although a cataclysm can also be a world ending or changing disaster.
However the words can be used as synonyms in certain cases.
The OED defines apocalypse as:
- (With capital initial.) The ‘revelation’ of the future granted to St. John in the isle of Patmos. The book of the New Testament in which this is recorded.
- By extension: Any revelation or disclosure.
- Christian Church. The events described in the revelation of St John; the Second Coming of Christ and ultimate destruction of the world.
- More generally: a disaster resulting in drastic, irreversible damage to human society or the environment, esp. on a global scale; a cataclysm. Also in weakened use.
As you can see, the primary associations are Biblical, although when used synonymously with cataclysm the implication is that a cataclysm affected humans and human society.
To give an example, the meteor strike that wiped out the dinosaurs 65 million years ago was a definitely a cataclysmic event; however it was not an apocalyptic, as it did not affect humans or destroy the world.
Going back to the Greek roots, an apocalypse refers to the lifting of a veil, a revelation. In the Bible specifically, it refers to the final battle on earth before God's kingdom is revealed. Which is important, because if you've been good, you get in. If not, you get a good look at what you'll be missing while you wail or gnash teeth or as you will in the eternal hellfire.
A cataclysm, by contrast, refers to a physical disaster. The Greek root refers particularly to a flood. A cataclysm doesn't imply divine intervention.