My son is learning about geology while reading LoTR. He wants to know if the fires of Mt Doom where the One Ring was forged were lava, magma, or something else. Are the fires described anywhere in the main books or any of the other books?

  • 7
    They're mainly Morgoth.
    – Adamant
    Commented Feb 23, 2023 at 1:17
  • youtube.com/watch?v=8MYAFfeNO00 Commented Feb 23, 2023 at 2:07
  • related: scifi.stackexchange.com/questions/96722/…
    – alexg
    Commented Feb 23, 2023 at 10:21
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    @AJM Location. Magma is molten rock deep underground, and as such is under high pressure. Lava is molten rock at the surface. Basically, if you can see it, you're looking at lava. Commented Feb 24, 2023 at 17:38
  • 1
    On the two occasions that I've walked (trampes, hiked, ...) past its base the surface was scoria. That may be useful, but probably not :-). Commented Feb 25, 2023 at 11:34

2 Answers 2


Yes, Mount Doom, or Orodruin is described in the books - it is an active volcano, and thus the molten rock under it is magma whilst underground, and lava when it erupts and flows down the mountainside. From Return of the King:

Sam was looking at Orodruin, the Mountain of Fire. Ever and anon the furnaces far below its ashen cone would grow hot and with a great surging and throbbing pour forth rivers of molten rock from chasms in its sides. Some would flow blazing towards Barad-dûr down great channels; some would wind their way into the stony plain, until they cooled and lay like twisted dragon-shapes vomited from the tormented earth.

On the side of the mountain is a door leading to a tunnel that bores into the cone of the volcano:

Then Sam saw that he was in a long cave or tunnel that bored into the Mountain’s smoking cone. But only a short way ahead its floor and the walls on either side were cloven by a great fissure, out of which the red glare came, now leaping up, now dying down into darkness; and all the while far below there was a rumour and a trouble as of great engines throbbing and labouring.

After the ring falls into the Crack of Doom the volcano erupts:

All about it the earth gaped, and from deep rifts and pits smoke and fumes leaped up. Behind them the Mountain was convulsed. Great rents opened in its side. Slow rivers of fire came down the long slopes towards them. Soon they would be engulfed. A rain of hot ash was falling.

  • 1
    According to this answer scifi.stackexchange.com/questions/96722/… Tolkien never calls it a volcano.
    – StrongBad
    Commented Feb 23, 2023 at 15:19
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    That doesn't mean it wasn't a volcano, just that Tolkien didn't use that particular Latinate word for it.
    – chepner
    Commented Feb 23, 2023 at 18:23
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    It actually makes sense that the people of Middle Earth would not use the word "volcano", since, as far as we are aware, Mt. Doom is the only one in the world, or at least the only one they know about. Thus you don't need a word to refer to a category of things that contains only one element; you can just call it by its name: "Mt. Doom" or "Orodruin" if you choose. In our world, "volcano" or "Vulcano" originally referred to just one small island in the Mediterranean, named after the Roman god Vulcan, until more of them were discovered. Commented Feb 23, 2023 at 18:35
  • 13
    Additionally, a philologist like Tolkien is incredibly unlikely to use the word "volcano" in reference to a fantasy setting without Vulcan.
    – fectin
    Commented Feb 24, 2023 at 0:35
  • 4
    @fectin Now if only someone had told Gene Roddenberry to maybe not name alien species after figures from Earth mythology... Commented Feb 24, 2023 at 14:36

Lava is just magma that is no longer inside the earth. I think the molten rock inside a volcano caldera is lava, so the answer won’t be magma.

“The fires of Mount Doom” is a phrase that doesn’t appear in the book, but it could only reasonably refer to the lava inside the volcanic caldera and possibly any associated heat and flames.

Frodo curses Gollum and says:

“Begone, and trouble me no more! If you touch me ever again, you shall be cast yourself into the Fire of Doom.”

The curse is fulfilled when Gollum falls in the lava in the Mount Doom caldera.

Inside the cavern of Mount Doom, the lava in the caldera is described as follows:

The fires below awoke in anger, the red light blazed, and all the cavern was filled with a great glare and heat.

Elsewhere, the lava that flows from the volcano is called “the fires that had poured forth”.

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