It's the geologic history of Middle-Earth! :D It wants narrowed down more than that (my teacher, who helped me come up with the topic, went O_O at the idea of narrowing it any further, but honestly it is a book-length topic once I get started) - I might wind up doing just Rohan and surrounding areas, because there's plenty of material for a 15-20 page paper in just Isengard, Rohan, and the Emyn Muil including the Rauros / Argonath area. Tolkien was startlingly thorough at the hard-science background of his story for a language scholar.

But for now I'm doing a read-through on the whole book, making notes. I've finished four chapters, and I've got five typed pages of book-quotes with notes like "check if silicic magma does the 'pools of fire' thing when not erupting or if this indicates more mafic magma". :-)