Alternate route

[Fordim Hedgethistle]

Could the Fellowship have taken a route around the Ash Mountains or maybe gone by sea through the mouth of the Anduin up the river Poros, climbed the southern portion of Ephel Duath and came to Mount Doom by the south? Is that not possible?

I doubt very much that this was an option as such a journey would have taken far too long. When it was suggested to Gandalf that they Fellowship go west around the White mountains to avoid the Gap of Rohan Gandalf said something like "you would spend a year in such a journey" and arrive too late to stop Sauron from destroying Gondor. Time was short by the time the Fellowship set out.

To make matters worse for the above plan, the Road to the south was simply crawling with Haradarim, and the Road east with Easterlings. Even if a smaller version of the Fellowship managed to make it all the way to the southern or eastern end of Mordor, they would have had to trek all the way back to Mount Doom. In terms of the distances involved, going from the Morannon to the southern end of Mordor, then to Mount Doom would be a journey of some 700 miles (that's the same distance between Rivendell and Edoras !) versus the direct route (Morannon to Mount Doom) of 100 miles.

As has been pointed out the Morannon could not have been Gandalf's plan, nor would Cirith Ungol have been a pleasant notion for him -- still, he ventured into Moria knowing that there was something there that he might have to sacrifice himself to destroy, and he could very well have been thinking the same thing about Shelob. . .

[Orcrist]

I don't think that Gandalf had any intention of taking the Pass of Cirith Ungol. When Faramir told him of Frodo going that way, Gandalf was in disbelief. He had no idea why Frodo went that way. So obviously he had no intention of going that way. But I still don't see any other plans he had. As it was mentioned before, Sauron would have controlled Middle-earth by the time they took a longer route. So, I guess that the story wouldn't have worked if Gandalf hadn't fallen in Moria. How ironic.