<P> The phrase "crack of doom" is the modern English for the Old English term for Ragnarök, the great catastrophe of Norse mythology . The term became used for the Christian Day of Judgement, as by William Shakespeare in Macbeth (Act 4, scene 1, line 117). This appealed to Tolkien, who was a Professor of Old English . Another possible source of the name is a long story by Algernon Blackwood . </P> <P> Reviewer Bart Higgins noted the similarity between Tolkien's Mount Doom and the volcanic caverns under Venus depicted in Perelandra by Tolkien's friend C.S. Lewis . "In both cases, the book reaches a cataclysmic scene of a struggle in an underground cavern, ending with an evil being falling into volcanic fire and being consumed . Since it is well known that Tolkien and Lewis frequently shared with each other their respective works in progress, it is reasonable to assume that the resemblance is no coincidence". </P> <P> In Peter Jackson's film adaptation of The Lord of the Rings, Orodruin was represented by two active volcanoes in New Zealand: Mount Ngauruhoe and Mount Ruapehu . In long shots, the mountain is either a large model or a CGI effect, or a combination . The production was not permitted to film the summit of Ngauruhoe because the Māori hold it to be sacred, but some scenes on the slopes of Mount Doom were filmed on the slopes of Ruapehu . </P> <P> The International Astronomical Union names all mountains on Saturn's moon Titan after mountains in Tolkien's work . In 2012, they named a Titanian mountain "Doom Mons" after Mount Doom . </P>

What mountain was used as mount doom in lord of the rings