Thegeology of Middle-earth is the fictionalgeology implied bythe maps inJ. R. R. Tolkien's fiction, especiallyThe Lord of the Rings, with features such as rivers, volcanoes, and mountain ranges that may suggesttectonic activity. The arrangement of some of the mountains however implies an unusual or "practically impossible"[1]geomorphology.
Thegeologists Margaret M. Howes in 1967,[3] Robert C. Reynolds in 1974,[4] and thenWilliam Sarjeant in 1992, used the information from theillustrations,maps, and text ofJ. R. R. Tolkien's fiction, especiallyThe Lord of the Rings, to create a conjectural reconstruction ofMiddle-earth's geology.[2]
Howes attempted to correlate the events in the history of Middle-earth in the"Elder Days" with periods ofglaciation andinterglacials in Earth's geological history.[3]
Reynolds identified fourtectonic plates: the Rhovanion Plate on the north of Middle-earth; the Eriador Plate on the west of the continent; and two southern plates, the Harad Plate and the Mordor Plate. TheRiver Anduin flowed through arift valley (in 1974 called an "aulacogen"). Atectonic basin occupied the area north of the White Mountains and south of the Emyn Muil. The land of Rohan was acraton, an old and stable geological region.[4][2]
Sarjeant stated that plate tectonics had evolved substantially since 1974. He increased the number of tectonic plates to six, the two oldest being the Eriador and the Forlindon Plates. They collided to build the Ered Luin mountain range, the Forlindon Plate being mostlysubducted and destroyed in the process. The Eriador Plate collided with the Rhovanion and Harad Plates, creating the Misty Mountains and the White Mountains, all three plates joining each other next to the stable craton of Rohan. Similarly, the Eriador and Rhovanion Plates collided with the Forodwaith Plate, raising the Ered Mithrin and forming another junction of three plates. Sarjeant suggests that Mount Gundabad could possibly be a block of tough rocks exactly where the three plates meet. Finally, theMordor Plate collided with the Harad and Rhovanion Plates, tearing thecrust to form the Anduin'srift valley, which issubsiding.[2]
Sarjeant identifies Mount Doom, Dol Guldur, Orthanc, and Erebor as isolatedvolcanoes; all but Mount Doom were inactive by the end of the Third Age. He comments that many other geological inferences are possible, such as that the West Gate of Moria could have been in a largevolcanic sill, anintrusion oflava between layers of country rock. He concludes that Middle-earth's geology is much like that of the Earth.[2]
The geographers Ian Smalley and Sally Bijl propose that Arnor, and in particular the Shire, was covered by the yellow-brown wind-blown dust sedimentloess. The northern part of the region would have been glaciated; when the ice retreated, elongated mounds of drift material,drumlins, would have remained as the grassy hills of Fornost on the North Downs.[5]
The geologist Alex Acks, writing onTor.com in 2017, outlines the mismatch between Tolkien's maps and thegeomorphological processes ofplate tectonics which shape the Earth'scontinents andmountain ranges. Mountains form mainly next tosubduction zones whereoceanic crust slides undercontinental crust, or where continents collide and crumple. Stretching of continental crust, by upwelling of magma, creates brokenhorst and graben landforms. Acks comments that none of these create right-angle junctions in mountain ranges, such as are seen aroundMordor and at both ends of theMisty Mountains on Tolkien's maps. Isolated volcanoes far inland, likeMount Doom, are possible but unlikely: most such volcanoes are islands and occur in roughly straight-line groups as the crust moves across ahotspot inEarth's mantle.[6]
Acks identifies a further issue, with Tolkien's rivers. The Earth's major rivers each drain a raised area of land, forming adrainage basin; the river in the basin takes water and sediment down to the sea, or looked at the other way, branches regularly into smaller and smaller streams that lead up into the hills. A river like theAnduin, on the other hand, has very few branches: it runs more or less as a single large stream for hundreds of miles, and parallel to the Misty Mountain range, rather than directly downhill and away from it. Worse, one of its fewtributaries, the Entwash, branches out into ariver delta, a basically flat place where a river ends, usually by the sea; but the Anduin goes on flowing past this spot, downhill. Acks excuses another oddity, namely that the Anduin cuts through a gap (between the White Mountains of Gondor and the Ephel Duath of Mordor); this is unusualbut can happen, as when theColorado River cuts across the mountainousBasin and Range Province: the river was there before the mountains, and cut its way down through the rock faster than the mountains grew upwards.[7]
Acks comments that the inlandSea of Rhûn seems to be in the bottom of a drainage basin. Again, this can happen; but there must be awatershed, high ground separating it from neighbouring drainage basins, in particular that of the Anduin. But the rivers ofMirkwood run eastwards towards the Sea of Rhûn, propelled by an invisible slope from invisible Mirkwood hills.[7] Fonstad draws her map of the Dwarves' route from the Anduin to the Forest River completely flat, with only small local topographic features on the way.[9]
Hazel Gibson, for theEuropean Geosciences Union, writes that Serjeant had to take "some very large leaps" to assemble a picture of the geology and geomorphology consistent with Tolkien's text. She concurs with Acks that "Several of the mountain ranges and individual mountains on the map make absolutely no sense."[1] Real mountain chains can meet almost at a right angle, but, she writes, "you have to work really hard to find them."[1] Mordor is the most egregious instance, in Gibson's opinion: a "square plain fenced by mountains at right angles to each other – it's practically impossible."[1]
The Harvard Lampoon's 1969 bookBored of the Rings parodies Tolkien's geomorphology with a double-page map by William S. Donnell. It depicts places such as "The Square Valley Between the Mounts", "The Mulsanne Straight" (a straight-line mountain range), and "The Intermittent Mountains".[8]
