Barbecued Heroes: Radiant Heat is Bad

Mount Ngauruhoe aka Mount Doom n the lord of t...
Mount Ngauruhoe aka Mount Doom n the lord of the rings movies, this is a very regularly shaped active volcano in tongariro national park. the famous “tongariro crossing” hike goes past it but not to the top. the climb isn’t hard, but it’s a long way up a pretty steep slope of loose ashes and rubble; not the most enjoyable terrain to hike on. (Photo credit: Wikipedia)

Remember the scene inside Mount Doom where Frodo and Gollum wrestle for the ring? In the movie, they are in a mostly enclosed space, on a bridge high over the lava. They were sweating but the bridge is high and the cave is large. Shouldn’t really be too hot, should it? Alas, Sam, Frodo and Gollum would have been cooked the moment they stepped into that cave, unless there was some magical protection that was unmentioned in book or movie.

As a thought experiment, imagine a magma chamber underground. Everything in that pool of molten rock will be pretty much at the same temperature (about 700 to 1200 degrees C, per Wikipedia.) This is because it’s a very hot body enclosed in a very good insulator (lots of rock). In fact, it will start altering and melting the adjacent rock, an effect you can see at the edges of granitic intrusions (plutons) that have weathered to the surface. Now, imagine a small gas cavity at the top of the magma. How hot is that pocket of gas? Why, just as hot as the magma because it will be heated by the magma and can’t dissipate much heat into the insulating rock.

Let’s expand that pocket of gas to the size of, say, the Mount Doom cave. How hot is the air above the magma? It is still the same temperature as the magma: there’s no where for the heat to go (technically, there is heat flow through the rock but it is very low.) Now, let’s cut a tiny window into this cave. In the real world, what you get is a volcanic eruption as the pressure on the magma is released and it boils away exactly as what happens in a shaken soda-can when suddenly opened. But let’s ignore that and pretend there is no pressure differential and, thus, no eruption. How hot is it in the cave? Well, it’s still the temperature of the magma, throughout the entire cave, including all rock surfaces and the air. A small hole will provide minimal heat loss. The cave isn’t going to cool.

Obi-Wan Kenobi and Darth Vader duel on Mustafar.
Obi-Wan Kenobi and Darth Vader duel on Mustafar. (Photo credit: Wikipedia)

Okay, let’s try a bigger hole, about the size of the opening to the Mount Doom chamber in the movie. Now is it cooler? Not really. Perhaps near the doorway it will be not quite so balmy but that opening still is fairly insignificant. The magma will have no trouble heating the walls, air, bridge, etc., to about its temperature. This means, enter the cave and, poof, you are suddenly exposed to 1200C (judging by the fluidity of the lava in the movie, let’s go with the higher temperature). That’s pretty much an instant burst into flames. But wait, what if cool air was being drawn into the cave? That is possible. Maybe old lava tubes provide conduits into the cave. A chimney effect might draw quite a lot of air through the cave and out the door. I’m just going to wave my hands here but at the very least the air flow would likely be immense, making it probably impossible to walk into the cave or a real danger of getting sucked into the lava tube. But regardless, it still wouldn’t solve the problem you would have in this cave because aside from convective heating of the air, the magma is radiantly heating everything in line of sight of it.

Anyone who has cooked knows a heating element can burn without making contact (think toasters, broilers, etc.): infra-red (light) can burn. Huge pools of molten rock create a lot of radiant heat.

So, Sam, Frodo and Gollum need something magical to protect them in this cave. Certainly something that could have been present, though, again, there was no mention of it.

English: A geologist collecting a lava sample ...
English: A geologist collecting a lava sample for chemical analyses from an active lava flow on Kilauea, using a rock hammer and a bucket of water. Notice the gloves 🙂 (Photo credit: Wikipedia)

We are used to this sort of movie physics from many action-adventure shows. How many times does the hero outrun a fireball in a tunnel, for instance? Aside from the fact that few explosions would move slow enough to be outrun, if there was a flaming ball of gas in the tunnel, all that radiant heat from the fireball would be bouncing down the tunnel at you like a big death ray. You would be badly burned long before the actual flames touched you. If you have spent any time around a fireplace or firepit, this, too, is no surprise. It’s something we all know. For me, it was really driven home when I watched a show about a fire in a large fuel tank. The tank caught fire, the fire department poured water onto it. This contained it until the water that pooled atop the oil got hot enough to boil at which point the water turned to steam which ejected the oil in a fine mist which promptly exploded like a huge fuel-air bomb. It was all rather sudden (no time to out run the fireball) and interestingly, people standing over 800 feet away were not touched by flames, were not affected much by blast (because it mostly went up) but they did suffer 3rd degree burns on exposed flesh from radiant heat. Ouch.

As always with a well established trope, this can be ignored. Only we engineers seem to groan at such things (probably fire fighters, too, but I don’t know any). But, again, you might enrich your setting or story by doing something about it. It might help the verisimilitude if your smith has to figure out how to tolerate the heat of lava as part of forging the ring of doom. Because we all know, if we stop to think about it, you can get badly burned by really hot things without actually touching or falling into them.

So let’s talk Mustafar of Star Wars fame. Here, there do appear to be shields protecting the installation from the radiant heat (good). In fact, when disabled, it appears the radiant heat can quickly melt thick metal, as when the collector bends and drops into the lava stream. Strangely, the dueling Jedi don’t seem to suffer the same effect. There must be some Jedi trick to reflect heat (not entirely implausible in that universe, I think the old KOTOR games may have had a similar affect at one point). But even so, we have radiant heat that can quickly melt metal at 100 meters or so and can cause Anakin  to burst into flame while lying on the shore but don’t affect Obi-wan or Anakin while riding those little ore carts. Must be more Jedi magic that stops working once you get your legs and an arm lopped off.

But that’s the least of the implausibilities with Mustafar. Where does the breathable air come from on a lava planet? How would endemic, complex creatures evolve there? And why are they mining lava? That’s undifferentiated material and economically of little value: the important stuff is mixed in with too much unimportant stuff. On Earth, while you might quarry igneous rock as a building material, you don’t mine it until other processes have concentrated the valuable minerals and elements. Lava is almost by definition maximally undifferentiated, i.e., of the least possible mineral value. The only exception would be if you could tap a magma chamber that was mostly solidified. The remaining melt will have lots of odd elements in it that don’t play well with others and are generally of value. But in that case, you are taking advantage of differentiation in a solidifying magma body, not free running lava.

You could also ask why does Star Wars make so much use of single biome planets (Ice Planet Hoth, Lava Planet Mustafar, Forest Moon Endor, etc.)? For biomes, it doesn’t really make a lot of sense from all we know about Earth and suspect about other planets. But, while it would not have a breathable atmosphere, you could have a lava planet. We already know about planets orbiting so close to their sun they are probably molten. But in an upcoming post, I’d like to explore young planets because they will have a lot more radioactive elements and consequently be a lot hotter, which could make for interesting science fiction settings.


15 thoughts on “Barbecued Heroes: Radiant Heat is Bad

  1. Both of your examples are in movies (although LOTR famously started with a book) and I think movies really love lava because it is 1) obviously and enormously dangerous and 2) visually striking, yet not a difficult effect to create. I think this is the same reason movies (not just Star Wars) favor single-climate planets. When you say “ice planet,” that means you only have to create one set of visuals and the interesting houses, creatures, etc. which live there.

    Obviously, visuals matter in movies more than books. Hearing takes a distant second to vision in the movie experience. In a theatrical setting, it’s all too easy to overlook the other senses. In an air conditioned theater, there’s really no way to make the audience feel such heat. Or, lava also emits toxic gasses which will kill you as dead as the radiant heat, but how are you supposed to SHOW toxic gasses?

    That said, the climactic scene of LOTR was one of the stumbling points for me. Gollum has no expression of agony on falling into the lava? Gyah..!

    1. You’re definitely right that single biome settings are mostly a short cut for the author/screen writer but I think they extend to more than just visual media. Dante’s Peak showed the toxic gasses by how they killed some of the wildlife (the same way they are noticed in reality). It was also one of the first movies where the lava actually looked right (like ‘Twister’ the go-ahead for production was given after the CGI group demonstrated they could make a decent version of the the lava/tornado)

      Despite it’s faults I liked the cave scene. While an enclosed lava cave is particularly preposterous, the only real way to handle lava like that without magic is to send a tiny channel of it out to a smithy somewhere which would not be very dramatic. It was certainly dramatic 🙂

  2. “why are they mining lava?” Too funny.

    Interesting post. Planets with only one climate came up somewhere else recently, can’t remember where. But it really is kind of silly. In “Left Hand of Darkness,” Ursula LeGuin showed what you can do by paying attention to climate!

    1. Thanks for the comments! Yeah the single biomes are odd. They aren’t even really necessary: just because the characters are only going to see one biome on the planet (after all, unless they move around a lot, they are only going to see a tiny part of the planet, i.e., a single biome), doesn’t mean you have declare the entire planet from pole to pole, ocean to mountain, to be a single biome type. I think it is just a convenient short hand for those whose worldbuilding tends more to what looks good and less to what makes scientific sense. That’s not meant as as much of a knock as that may sound: clearly a focus on what looks cool works quite well in the Star Wars universe where appearances have come first and rationales are generally an after thought. Audiences love it.

  3. I think you’ve hit on why: audiences love it. The settings have that ‘wow’ factor that draws readers in.

    Of course, we all know we can’t get near lava and that traveling into a volcano would mean instant death. We *know* that. But fiction is there to take us into those sorts of places we can’t go (or only crazy volcanist go). Whether authors do that accurately (can’t think of any examples!) or inaccurately (pretty much all fiction), doesn’t really matter (to me). We want to go to those exotic places – no matter what. Have our characters fight in those settings? Even better!

    I agree that some plausibility in a story would be nice. But, come on, we are talking fantasy here! If a writer’s skill at getting the reader to suspend disbelief is great, then I think they can get away with implausible physics. At least, I know I fall for it most times. 🙂

    1. I’m not sure everyone really understands you can’t get that close to lava 🙂 But I agree that the main reason it is there is that it looks really cool. I enjoy watching Episode III enough. It could have been a better movie but what kept it from being better had a lot more to do with the acting, dialogue and story than the fight on the lava world. In the end, it was established that Darth Vader was injured in a ‘volcano’ shorty after the first movie so they had to end it there. My sons and I sometimes watch a truncated version of episodes 1-3 where we skip the painful Anakin-Padme scenes.

  4. Oh, consequently, this is exactly why my husband refuses to read speculative fiction. Any spec fiction. In his mind, it is all completely unbelievable precisely because of the things you pointed out here. 😦

    1. You probably can’t tell from this blog post but I used to spend a lot more time mocking the science and engineering failing of spec fiction (especially the shows) but in time I finally realized I really enjoyed them despite their bending the ‘rules’. While I still may call them out, it doesn’t keep me from enjoying them. I love the big space battle at the start of Star Wars Episode III even though it is entirely implausible in many ways (ships far too close together, what made the damaged ship fall out of orbit, what purpose could buzz-droids possible serve rather than a simple explosive warhead, etc.) It looked cool 🙂

      1. Yeah. There are times where I can’t get into the story enough to just ignore all that. But most of the time, I do ignore it. I wonder if there are just two kinds of people in the world: those who want to believe and those who don’t. 😮

  5. Excellent post!

    I do have to disagree that there would automatically be an eruption once you cut a hole in the side of Mt. Doom, or for that matter, that there is necessarily much pressure (although it’s likely, given the eruption right after the ring is destroyed, assuming that’s not triggered only by magic).
    Not all stagnant or semi-stagnant lava is under pressure; think of lava lakes, for instance, or residual magma in a magma chamber. None of that, of course, has any influence on the certainly deadly heat in the chamber.

    As for single-environment planets, in my book ice, desert, and waterworlds (and probably a few others as well) aren’t implausible at all, and neither are volcano worlds; there’s Europa (Triton, too) and Mars in our solar system, waterworlds have been proposed for at least one exoplanet (I forgot the name, sorry) as well as sub-glacial Europa, and Io is the volcanoworld by definition (Venus is a good bet for that, too, apparenty).
    Whether any of these kinds of worlds are depicted believably is another matter altogether, and I fully agree they’re often not, and are, as you already mentioned, used mostly for pretty scenery and not much else. (It would be fun to explore a single-environment world in detail with all the consequences that arise from the unusual configuration — Dune did a pretty good job there, as far as I recall.)

    Yet I know from personal experience that no writer can get everything right, and that’s alright. Still, the need for cool or convenience should never overrule the need for realism, even if that realism may not be entirely plausible. What many fail to see there, I believe, is that exotic can be done realistically, and still be awesome, if awesome in a different way.

    Anyway, well done, you got me thinking. 🙂

    1. Thanks for the comment!

      On the eruption, there might be scenarios where there was no pressure on an enclosed magma body and thus no eruption. This is probably very unlikely, but so is a self-supporting void so perhaps there would be some cases where there would be no eruption. Mostly, I think it would be like a punctured ‘zit’ with the pressure provided by the weight of the overlying rock 🙂 The thing to remember is that under pressure, the magma holds lots of gas and without pressure it violent froths out like a punctured soda can, thus the explosiveness of the eruption. There are also low gas magmas, so maybe that’s what you could have your in unexploding magma cave 🙂

      On the single biome planets, to be a little more precise, I’m knocking a single biome planet where humans can run around breathing air and interacting on the surface with big creatures. Lucas in particular is a little casual with having a world all of ice or lava or what have you but still having breathable air and complex lifeforms. There seem to be plenty of ice moons and some desert worlds in our solar system but I don’t think you’ll find a Tauntaun running around on Europa or on Mars, anything more than bacteria. And on Io, lots of volcanoes but even if it had an atmosphere, it would be one poisoned by volcanic gasses. (Within Europa, you might find complex life forms and there you will likely find biomes determined by how the energy harvested by life is injected into the ocean.)

      On any planet with complex life, it seems quite likely there would be at least some diversity of biomes. ‘snowball Earth’ occurred before there was any land lifeforms other than maybe lichens so its biomes must have been in the water but even there, there would have been shallow communities, deep-sea vents, and probably a few ice-less spots here and there (maybe lots of iceless spots, no one really knows how icy it got). If a snowball Earth happened again today, there would be some glacier-free spots where life might eek out a hold although it would be interesting to see what happened to the oxygen levels: probably nothing if the seas remained clear but it would depend on the scenario.

      On the single biome in fiction, the characters aren’t going to visit the entire planet. You only need to describe in detail where they walk around or fly over. That could be a single biome (forests, deserts, etc. can be very large, large enough to contain all the scenes in one book). But there is no real need to declare the planet or moon a single biome. I think it is just a bit of laziness that Lucas introduced into the genre: “Ice World Hoth, Forest Moon Endor”.

      1. Speaking of seas- that’s the other thing that bugs me about these single biome worlds. Without large bodies of water, you aren’t likely to get the rain for forests or air for a desert world. Of course, you can’t really have an entirely desert world with large oceans: near the oceans, there would be plenty of rainfall, though it might be hard desert in the continental land masses.

        No one really knows how much ocean is needed but I wouldn’t be surprised if more than half ocean is required in order to have the stability needed for very complex lifeforms to evolve. Maybe with too little water the potential of it all evaporating or freezing is too high over billions of years: suns change in solar output and impacts & flood lavas can seriously perturb the system.

      2. As for the magma chamber, I agree, it’s unlikely, but technically not impossible from what I’ve learned so far. Gas content is definitely a factor, and also whether or not the volcano is actually pressurizing at the time, i.e. whether the magma chamber is currently filling up.

        If you cut a hole in the volcano while there’s little pressure, there should be no eruption to speak of. If you keep the hole open, it will basically function like a vent, and that door in Mt. Doom has been there for quite a while (I forgot how many centuries) by the time the hobbits arrived there. Obviously, that makes walking in there no less deadly…

        As for the single-biome worlds, you’re right of course regarding breathable atmosphere and general habitability for humans. It also makes me wonder why nobody in those settings considered terraforming?

        I didn’t want to go into that much detail on the potential for life in my comment, to be honest, but since you have, I’d like to add here that there are probably more exotic places capable of supporting life, perhaps even complex life, however that life will be much unlike what we have here on Earth.

        Yet that’s obviously not what most sf aims for, as they usually want their humans being able to run around without heavy protective gear, and so I have to agree that those worlds don’t quite qualify in this context.

        The single-biome trend is certainly born out of laziness, and out of wanting more worlds in the setting, to make it look bigger, probably.

      3. It’s all good food for thought. In the end, it isn’t that important that Endor was described as all forest but if you’re a writer, why be that sloppy? Science fiction fans do evaluate their books on science to some extent.

        On the volcano, to cast another stone at the ring-chamber trope: Volcanoes are typically far too weak to maintain a large internal chamber like that. A stratovolcano might have some cementing lava flows of good basalt but that’s inter layered with ash of no structural strength. And very hot water percolates through the entire pile, altering the rock to clays and soft stones. Volcanoes are actually very weak mountains and are better known for their lahars and rockslides than the strength necessary to maintain a chamber like in the movie.

        But I like the imagery as much as anyone and it doesn’t bother me too much. On the other hand, if working on your own opus, nothing wrong with getting some of the details better and more importantly, if you work through these details, you might create some interesting hooks to hang a plot on.

        Thanks again for the comments! I love kicking around world building items.

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