I’ve been thinking about secondary world geography a bit lately for a couple projects. There are tons of worldbuilding and writing books out there that discuss the issues of geography, many with specific reference to geology. At least a couple I have on hand include detailed chapters on geology.
On myriad blogs and other sources, geography and geology are also oft repeated subjects. One of the big examples that gets cited for “bad” worldbuilding in this sense is Tolkien’s Middle Earth, particularly Mordor. The argument goes that: “Mountains don’t form in a U-shape because plate tectonics don’t work that way, therefore Mordor is an example of bad worldbuilding, since Tolkien didn’t pay attention to geology.”
Here’s my response:
If the worldbuild is a variant Earth, then yes, Earth’s geology needs to be followed. Or a damn good explanation for working around our knowledge of geology needs to be in place.
A secondary world? Not so much.
Consider this: our knowledge of geology is based on, basically, one planet. Yes, we’ve conducted relatively minor studies of Mars and have photos and such of a few moons and planets in our solar system. This is still a very limited sample, given the sheer size of the galaxy, much less that of the universe. There really isn’t, at our current level of study, a way to be certain that geology works the same everywhere, until we get out there and see other star systems. We do know that the universe has infinite variation–we’ve discovered extra-solar planets that are theoretically made entirely of diamond, massive Earth-like worlds, planets (gas giants) with their own bio-zones, and both planets and moons with frozen seas of methane.
And that just assumes the secondary world is located in our own universe.
In short, secondary world geology doesn’t need to behave like Earth geology. For instance, look at Discworld, a successful and well built world that follows, not Earth geology, but the author’s “I want to add this feature and it needs to be X distance from Place A for the story.” (Heck, it’s a friggin’ flat world on the backs of four elephants on the back of a flippin’ turtle swimming through space.) A lot of early fantasy and science fiction took the same approach. Somewhere along the way we may have lost some of that sense of wonder and invention, perhaps.
Back to Mordor.
Even assuming an Earth geology (admittedly, Middle Earth is supposed to be a “pre-historic” Earth), Mordor exists in a fantasy world. This means magic. In Middle Earth’s case, potentially very powerful magic.
So. Sauron and Morgoth/Melkor were extremely powerful beings. Tolkien describes the Istari (Wizards) as angels. Sauron and Morgoth are said to be vastly more powerful than Saruman and Gandalf, even moreso than the entire collective of Istari (all five) plus two elf royals (Elrond, Galadriel) with a combined three Rings of Power (all three elf rings, Gandalf, for those who forgot, carries the third). That combined might only served to drive Sauron away when he was in a very weakened state. They, Sauron and Morgoth, each have potentially god-like power at their respective peaks. Therefore, who says that Sauron (before creating or losing the One Ring) or Morgoth couldn’t reshape the land to suit their needs, thereby creating a U-shaped mountain range?