As best I can tell, in this dramatic scene from The Fellowship of the Ring, Gandalf falls for 71 seconds, mostly in free-fall while fighting a Balrog. True, the Balrog hits the walls of the abyss a couple of times, which slows their descent. But leaving that out of the account, according to the Free Fall Calculator, a fall of 71 seconds would correspond to a descent of about 24.7 kilometers and a terminal velocity of almost 700 meters per second, at which point the two fall into a deep pool of water.

It seems like the director exaggerated things a bit, as the Earth's continental crust is only 30 to 50 km thick, and heat and pressure both increase with depth to the point where open caverns and pools of water are impossible. So we can dismiss the film version as good cinema but bad science. Did Tolkien give any indication of how deep the abyss extended?

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    If the terminal velocity is 700 meters per second, the calculator certainly disregards air resistance, which in this case gets as strong as the weight itself, and is very significant.
    – lvella
    Aug 12, 2019 at 9:08
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    @lvella What apart from air resistance would oppose the gravitational forces? ie if it is disregarding air resistance how is there a terminal velocity at all?
    – Chris
    Aug 12, 2019 at 10:12
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    @Chris: The calculator doesn't provide a terminal velocity, it provides a final velocity, i.e., the speed at the end of the distance/time specified. This may have been a misconception on the OP's part. [/physics professor] Aug 12, 2019 at 19:11
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    @EricDuminil: As noted by Ivella, the linked calculator doesn't take air resistance into account. In such a case, the velocity increases without limit as time goes on, and there is no "terminal velocity" (or, if you prefer, the terminal velocity is infinite.) Aug 14, 2019 at 11:38
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    @MichaelSeifert, He says as much in the novel--that he died, but then was sent back to finish his task. If you read Tolkein's other writings, then it becomes more obvious that Gandalf is not a human being. He is something more like an angel--sent to Earth "clothed" in human form to inspire and encourage Earth's inhabitants to rise up and resist the forces of evil. Aug 14, 2019 at 17:24

3 Answers 3


Tolkien is not at all specific:

'Long time I fell,' he [Gandalf] said at last, slowly, as if thinking back with difficulty. 'Long I fell, and he [the Balrog] fell with me. His fire was about me. I was burned. Then we plunged into the deep water and all was dark. Cold it was as the tide of death: almost it froze my heart.'

'Deep is the abyss that is spanned by Durin's Bridge, and none has measured it,' said Gimli.

'Yet it has a bottom, beyond light and knowledge,' said Gandalf. 'Thither I came at last, to the uttermost foundations of stone. He was with me still. His fire was quenched, but now he was a thing of slime, stronger than a strangling snake.

'We fought far under the living earth, where time is not counted. Ever he clutched me, and ever I hewed him, till at last he fled into dark tunnels. They were not made by Durin's folk, Gimli son of Glóin. Far, far below the deepest delving of the Dwarves, the world is gnawed by nameless things. Even Sauron knows them not. They are older than he. Now I have walked there, but I will bring no report to darken the light of day. In that despair my enemy was my only hope, and I pursued him, clutching at his heel. Thus he brought me back at last to the secret ways of Khazad-dûm: too well he knew them all. Ever up now we went, until we came to the Endless Stair.'

So we know only that Gandalf fell for a "long time" to the "the uttermost foundations of stone", a place "beyond light and knowledge" which was "far, far below the deepest delving of the Dwarves".

However, the terminal velocity of a human body is about 55 meter/sec, not 700, so even if Jackson's cinematic chosen-for-dramatic-value guess is correct, we're "only" talking a couple of kilometers.

(And if you want to get hyper-picky, two other points: First, the fall was measured from a starting point inside the Misty Mountains. They may have started a kilometer above sea level, for all we know, and thus not be very deep into the crust. Second, if they did start near sea level, after they fell the first kilometer, the density of air would exceed that at sea level and terminal velocity would actually decrease somewhat.)

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    more confoundingly, you are looking for the terminal velocity of a balrog. A burning demon with wings falling in a chasm. It is likely going to be lower.
    – Stian
    Aug 12, 2019 at 12:59
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    Also, the terminal velocity of the Balrog would be lower since he has a larger cross section.
    – Kai
    Aug 12, 2019 at 17:02
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    Furthermore, the Balrog appears to span a very significant portion of the air column (perhaps even the majority), which further confounds things
    – Cireo
    Aug 12, 2019 at 22:33
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    In open air larger bodies generally have higher terminal velocity: air resistance ~ cross section ~ R², but weight ~ volume ~ R³, so 0 acceleration requires more resistance per square meter of cross section, which you achieve at higher velocity. But wings change things — that's what they're for, to get large air resistance with little weight, as does Cireo's point, so I have no idea. Aug 13, 2019 at 9:45
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    In the movie, they keep fighting during the fall, so it seems their velocities stay closely matched. Plus "he fell with me. His fire was about me." That's hardly realistic — unless a wizard can control his fall speed somewhat, which I wouldn't discount given the scene when Saruman flings Gandalf around. But I won't complain if here both Tolkien and the movie just applied the "rule of cool" artistic license :-) Look, it is cool to match swords in mid-fall. Aug 13, 2019 at 9:52

Karen Wynn Fonstad's highly regarded The Atlas of Middle-earth includes a diagram showing a vertical cross section of Moria.

enter image description here

In the diagram, the horizontal distance of 20 miles from the guardroom to the bridge appears that to be about 2.5 times the vertical drop from the "First Deep" to the bottom of the abyss. Accounting for the 7:1 exaggeration of height in the diagram, that makes the drop about (20 / 2.5 / 7 =) 1.14 miles.

While The Atlas of Middle-earth provides several references to the text of The Lord of the Rings, I can't find any that back up the height of the vertical drop to the abyss that is shown in the diagram. It does, however, provide a reference to back up the 40 miles from West-door to East-gate (20 miles from the guardroom to both the West-door and East-gate).

‘I cannot say,’ answered Gandalf. ‘It depends on many chances. But going straight, without mishap or losing our way, we shall take three or four marches, I expect. It cannot be less than forty miles from West-door to East-gate in a direct line, and the road may wind much.’

The Lord of the Rings Book Two, Chapter 4: A Journey in the Dark
Page 310 (Houghton Mifflin Harcourt; Single Volume 50th Anniversary Edition)

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    A pity that I can't mark two answers as correct. I think that Mark Olsen and Blackwood have both given helpful answers: one giving the best answer from canon, which is what I asked for, and the other from additional material that Tolkien would likely have approved. Aug 12, 2019 at 3:34
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    @InvisibleTrihedron you can always add a Bounty to one answer. :)
    – John C
    Aug 12, 2019 at 18:49
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    The reference though is a guess by Gandalf and not necessarily true. Tolkien was amazing with making sure his maps were in place but I wonder if it was ever given an actual size. What is certain is Christopher has pointed out a number of things that the Atlas gets wrong. Including with maps and I think possibly distance as well. I don't recall him saying anything about that with the drop in Moria though but then I don't recall him talking about the distance at all in the first place.
    – Pryftan
    Aug 13, 2019 at 20:14
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    I think this map contradicts Tolkien's actual text. According to Gandalf - as quoted in another answer - the abyss they fall to is "Far, far below the deepest delving of the Dwarves", whereas the depiction here is almost the same level.
    – FLHerne
    Aug 1, 2020 at 23:42

Largely attempting to see how well the answers of Mark Olsen and Blackwood correlate, I consulted the keisan online calculator for free falls including wind resistance. Keeping other parameters at the default, entering a distance of 3650 meters gives a fall time of close to 71 seconds. That distance is the same as 2.27 miles (so almost exactly twice the estimate given in @Blackwood's answer).

screenshot of fall time calculation from an online calculator with inputs set as 72kg mass, 3650m free fall distance, air resistance of 0.24 kg/m and acceleration due to gravity of 9.80665

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    well he was wearing robes and fighting a giant balrog with wings.
    – Kai
    Aug 12, 2019 at 17:05
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    @Kai : and he was full of adrenaline, and probably had superhuman reflexes, so it was slow motion, the movie registering his perception, so the fall didn't take that long, Gandalf perceived it as long. :)
    – vsz
    Aug 12, 2019 at 18:54
  • @Kai: Possibly balanced by the fact that in the first part of the fall he points himself straight downwards so as to overtake the balrog that fell earlier? Aug 12, 2019 at 20:55
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    @Kai Not this nonsense about wings again. I won't get into the debate because it's futile but I will say that it doesn't even matter what viewpoint you take. There is no proof of it so claiming it is silly. You can believe it but there is no proof one way or another. Thus if you claim it is or isn't you're introducing something that cannot be verified and if it can't be verified it cannot be part of figuring this out (not that it's even specified, the height).
    – Pryftan
    Aug 13, 2019 at 19:58

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