Alex Acks is a geologist who thinks J.R. Tolkien, where geology is concerned, is an excellent scholar of linguistics.
Iâ€™m good with the mountain ranges on the west coast of the map. I can pretend that Eriador is like the California of Middle-earth, and itâ€™s a nice active marginâ€”I will just ignore that my housemate, who unlike me has completed the Silmarillion slog, has disabused me of that notion. And I can buy the placement of the Misty Mountains, again as a continent-continent collision, perhaps, even if there should be a lot more shenanigans going on then, in terms of elevation. But when you throw in the near perpendicular north and south mountain ranges? Why are there corners? Mountains donâ€™t do corners.
And Mordor? Oh, I donâ€™t even want to talk about Mordor.
Tectonic plates donâ€™t tend to collide at neat right angles, let alone in some configuration as to create a nearly perfect box of mountains in the middle of a continent. Iâ€™ve heard the reasoning before that suggests Sauron has made those mountains somehow, and I suppose right angles are a metaphor for the evil march of progress, but I donâ€™t recall that being in the books I read. And ultimately, this feels a lot like defending the cake in the song MacArthur Park as a metaphorâ€”okay fine, maybe itâ€™s a metaphorâ€¦but itâ€™s a silly metaphor that makes my geologist heart cry tears of hematite.
Mount Doom, Iâ€™m more likely to give a pass to, since itâ€™s obviously a place of great magic. But geologically, it posits a mantle plume creating a hot spot under Mordorâ€”since thatâ€™s the only way youâ€™re going to get a volcano away from subduction or rifting zones, and Iâ€™ve already called shenanigans on Mordor being either of those. And the hallmark of hot spot volcanism is that you get chains of volcanoes, with the youngest being the active volcano and the older ones normally quiescent. This is caused by the tectonic plates moving over the hot spot; examples include the Juan FernÃ¡ndez Ridge, the Tasmantid Seamount Chain, and the Hawaiian Islands (more properly called the Hawaiian-Emperor seamount chain). Youâ€™ll notice most hot spots can be found in the oceans, because thereâ€™s more ocean on Earth than land, and also the crust is thinner there, so a hot spot causes volcanism much more readily. On continents, youâ€™re more likely to get dike swarms (e.g.: the Mackenzie dike swarm in Nunavet, Canada) where magma filters into cracks and weak spots between formations and remains underground until unroofed by erosionâ€”or chains of massive volcanic calderas like the ones you see ranging from Yellowstone to the Valles Caldera in the US.
Okay, so maybe Mount Doom is from a really young hot spot and thereâ€™s been no drift since it started. Thatâ€™s the best Iâ€™ve got for you. Itâ€™s better than the nonsensical border mountains.