Was the Lonely Mountain in The Hobbit a volcano?

If not, how did the dwarves get enough heat to run the huge forges?

I am asking about the books, not the movies.

  • 5
    Not an answer because I don't have sources available, but I don't recall any indication in the books of dwarves using volcanic heat to run forges.
    – Deolater
    Commented Jun 12, 2019 at 20:43

4 Answers 4


Speaking as a geologist: The Lonely Mountain is probably an extinct volcano. J. R. R. Tolkien depicted the mountain several times in sketches and watercolors, and in most of them the volcano is steep-sided and conical with a flattish peak. Two of his drawings appear to show a crater at the top:

None of the depictions show any kind of stratigraphic bedding, though it might be hard to see at this scale.

This form is consistent with a stratovolcano having somewhat eroded sides and a crater. Compare Fuji, Vesuvius, Etna, Mt St Helens, and so on. Tolkien would certainly have been familiar with some of these volcanoes in illustrations. However, in Thorin's map, the Lonely Mountain has a sharp peak with no crater, so the evidence is inconsistent. It may be that Tolkien's ideas shifted over time.

Tolkien was unaware of plate tectonic theory when he wrote The Lord of the Rings, for the excellent reason that it did not exist yet, but he evidently made good use of his knowledge of European geography. The tall mountain chains within Middle-earth (Misty Mountains, White Mountains, etc.) are similar to the Alps and Pyrenees that he knew. The mountains that wrap around Mordor are more unusual, but a parallel exists in the Carpathians. A stratovolcano in the middle of a continent is an anomaly, and he probably was aware of that. Usually they occur on the margins of continents, but there are a few exceptional cases such as Kilimanjaro where they occur far inland.

As to the Lonely Mountain's composition, Tolkien mentions that it was rich in ores and gemstones. Fresh volcanic rock itself usually yields neither, but hydrothermal (hot groundwater) circulation in fractures or porous rock (e.g., tuff resulting from ash) can result in deposition of gold, silver, and copper as well as lead and sometimes nickel. Diamonds are a possibility in one kind of volcanic rock, but not in stratovolcanoes, so diamonds would not be expected.

If the Lonely Mountain is not a volcano, then the question of how it obtained its nearly symmetrical form, with a flattish or cratered peak, becomes a problem.

  • 7
    Regarding the inconsistency in the drawings, it's not completely without precedent for a stratovolcano that previously had a sharp-ish peak with a small crater to rather suddenly develop a much more flat peak with an enormous crater. Though, of course, it was not previously completely lacking a crater.
    – reirab
    Commented Jun 11, 2019 at 21:26
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    In the context of The Hobbit, one shouldn't try to apply logic to what The Lonely Mountain was; it simply was. In the wider context of the history of Middle-Earth as developed after The Hobbit was published (and as it was incorporated into his broader works), it's not much of a stretch to posit that it simply isn't a natural occurrence, and was raised by either Melkor or one of the Valar for some reason or another.
    – chepner
    Commented Jun 11, 2019 at 21:32
  • 36
    I disagree with the "It is as it is" approach. Tolkien was no geologist, granted, but he was a well educated man who went to some lengths to get his details right. For example, more than fifty pages of The Lord of the Rings contains descriptions of Aragorn tracking other people. Tolkien did not know much about tracking, so he consulted others to find out, with the result that Aragorn's actions, such as circling around to rediscover a lost trail, make perfect sense in the novel and it enriches my reading experience to be aware of that. Similarly for his geography. Commented Jun 11, 2019 at 23:46
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    @HarryJohnston A long dormant volcano may still have a geologically active magma chamber. Think the Yellowstone caldera for example. It's not erupted in a very long time, but there are a lot of bubbling geothermal pools and geysers (which is probably a factor in why it's not erupting, as there's a pressure relief valve, so to speak).
    – jwenting
    Commented Jun 12, 2019 at 9:23
  • 23
    (Personally, I've always thought that the Lonely Mountain is a sort of metaphorical volcano, with the dragon being a mythical representation of geological forces. This rings especially true given the backstory that Smaug had slept for a long time and then suddenly obliterated a town and the surrounding countryside.)
    – N. Virgo
    Commented Jun 12, 2019 at 12:25

There is no evidence that the Lonely Mountain is a volcano. The Hobbit repeatedly identifies Smaug as the mountain's sole source of heat and smoke. For instance, there is this conversation between Bilbo and Balin, near the beginning of chapter 11:

“The dragon is still alive and in the halls under the Mountain then — or I imagine so from the smoke," said the hobbit.
“That does not prove it,” said Balin, “though I don’t doubt you are right. But he might be gone away some time, or he might be lying out on the mountain-side keeping watch, and still I expect smokes and steams would come out of the gates...."

As to how the dwarves of Erebor operated their forges, the answer is presumably the same as in real life. When they needed high heat for their smithing work, they used coal. We known that coal-burning forges are used in Middle Earth, from Gandalf's sarcastic comment to Thorin in chapter 1:

"... Just let any one say I chose the wrong man or the wrong house, and you can stop at thirteen and have all the bad luck you like, or go back to digging coal.

  • 2
    The lonely mountain could be an extinct volcano even if it is not active.
    – Lexible
    Commented Jun 11, 2019 at 15:01
  • 32
    "The Hobbit repeatedly identifies Smaug as the mountain's sole source of heat and smoke": I'd say the passage you've quoted actually implies the opposite. Balin is saying that the smoke doesn't prove the dragon is alive and inside the mountain, and that he'd expect smokes and steams even if Smaug was away. Why? Well, there must be another source, other than Smaug. Otherwise, what he is saying doesn't make much sense. Commented Jun 11, 2019 at 21:31
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    @Fabio, he means that Smaug makes so much smoke and steam that it would take months or years for it to dissipate. Commented Jun 12, 2019 at 2:58
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    ... otherwise he'd have said, "The mountain smoked long before Smaug came along" or similar. Commented Jun 12, 2019 at 3:04
  • 31
    @FabioTurati The quote here ends prematurely. The end of the sentance is "[...]still I expect smokes and steams would come out of the gates: all the halls within must be filled with his foul reek." The way the colon is placed strongly implies the smoke not only comes from Smaug, but is literally draconic B.O. so thick as to be visible. Buzz- I'd suggest adding the remainder of the sentence to your quote so this is more apparent.
    – jmbpiano
    Commented Jun 12, 2019 at 3:46

As a matter of myth-construction, a mountain that periodically issues smoke and steam (i.e. a volcano) would probably give rise to local legends of occupation of that mountain by an iron-working race and/or some kind of monster that produces smoke. So as a literary or mythopoeiac matter, the Lonely Mountain is probably a volcano.

The other isolated mountain in Tolkien's geography, Mt. Doom, is explicitly a volcano. The difference in their treatment may be a result of the fact that Mt. Doom is much more violently active.


Using clearly metaphorical language Tolkien describes the Lonely Mountain in volcanic terms.

From The Hobbit, chapter 12, "Inside Information:"

The dwarves were still passing the cup from hand to hand and talking delightedly of the recovery of their treasure, when suddenly a vast rumbling woke in the mountain underneath as if it was an old volcano that had made up its mind to start eruptions once again. The door behind them was pulled nearly to, and blocked from closing with a stone, but up the long tunnel came the dreadful echoes, from far down in the depths, of a bellowing and a trampling that made the ground beneath them tremble.

  • 3
    "as if it was an old volcano" actually seems fairly conclusive that it isn't a volcano
    – Valorum
    Commented Nov 8, 2022 at 13:24
  • 2
    clearly metaphorical language <--- Commented Nov 10, 2022 at 1:32
  • 1
    In other literature, I have observed that when something is described "as if" something it is often actually the case, but the characters involved don't know it for certain. Commented Jun 26, 2023 at 14:22

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