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This question is specifically about the mechanics of an alien creature swimming in highly viscous magma, the unlikeliness of life surviving at magma temperatures etc isn't relevant. Just imagine it's extremely thick mud if it helps. :)

My research so far:

Swimming in syrup is as easy as water:

Unless I'm mistaken, this means viscosity doesn't necessarily make you swim slower if you are big enough. (Also being a snake with gorilla arms helps, apparently.)

Magma Viscosity and mantle movement:

Upper mantle magma is estimated between $10^{19}$ and $10^{24}$ Pascal seconds (Pa·s).
Basalt lava between $10^2$ and $10^4$ Pa·s.
Water's viscosity is $8.90×10^{−4}$ Pa·s.

I don't know nearly enough physics to make heads or tails of this. I could not find more in-depth information about what I'm looking for.

Perhaps if there's a relationship between size and ability to swim in viscous fluids, the size it'd have to be could be calculated from the viscosity? Perhaps it'd have to be millions of times bigger.

Would the equivalent of jet propulsion be more or less efficient in a extremely viscous medium? I'd guess less, but I have no way of knowing. I don't know enough about the mechanics of swimming in general, or what style of locomotion would be more efficient in a high viscosity medium.

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  • $\begingroup$ How hard science do you want this? Just logical creatures or do you want to contemplate how different chemicals reacts with that kind of heat? $\endgroup$ – Mormacil Jun 24 '17 at 13:00
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    $\begingroup$ So, like a square cube law for the ratio of control surface vs. viscosity (times available horse power - or something). Excellent question. $\endgroup$ – Mazura Jun 24 '17 at 20:02
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    $\begingroup$ Anybody here a mathematically inclined geo-bio-physicist fluent in fluid dynamics? $\endgroup$ – Mazura Jun 24 '17 at 20:22
  • $\begingroup$ Will your creature use the heat to power itself/its propulsion? $\endgroup$ – Nahshon paz Jun 25 '17 at 10:33
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    $\begingroup$ It will hopefully be fireproof...? $\endgroup$ – Baard Kopperud Jun 25 '17 at 12:40
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Caecillians are limbless amphibians.

enter image description here source

Their muscles are adapted to pushing their way through the ground, with the skeleton and deep muscles acting as a piston inside the skin and outer muscles. This allows the animal to anchor its hind end in position, and force the head forwards, and then pull the rest of the body up to reach it in waves. In water or very loose mud, caecilians instead swim in an eel-like fashion.

This system would work for magma also: worm style in thick magma, eel style in thin magma. A nice side note is that caecilians are in the same class as salamanders, which in legend lived in lava.

Here is an invented addition which I stole from the earthworm system: worms secrete slippery mucus which lubricates the soil and helps them push their heads through. Mucus and magma don't mix, but what if your magma creature could route heat from the body up to the head? The hot head would decrease the viscosity of the magma there and so decrease resistance as it pushed through. Heat pulled from the magma behind would firm up that region and so offer a better substrate to push off of. I think the benefits of the hot head / heat sink system would be greater for a larger creature than a smaller.

I could also imagine a very sharp head - again to better push through the magma. Worms accomplish this by tapering their heads nearly to a point. I don't think the caecilians can do this. When I was very little I read a story about a witch whose power came from a jewel that she had taken from the head of a giant worm she had killed. I have never been able to find that story but you can find lots about animals with magic jewels in their heads.

Which, like the toad, ugly and venomous, Wears yet a precious jewel in his head; Shakespeare, As You Like It Act 2, scene 1, 12–17.

Your legless magma salamander could carry a jewel on its head: the jewel conducts heat and is the part that heats up, combining the benefits of heat and sharpness for pushing through the lava.

Yes: giant legless salamander (striped, I hope) with glowing faceted jewel protruding from its head.

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    $\begingroup$ Those are the Shrieking Eels! $\endgroup$ – Mazura Jun 24 '17 at 19:46
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    $\begingroup$ I've always understood the As You Like It quotation as referring poetically to the toad's eyes (which are considered beautiful; cf. Romeo and Juliet III.5, where Juliet refers to a folk belief that the lark and the toad must have traded eyes, because why else would toads have beautiful eyes and larks not?). So, not a literal "precious jewel". No magic required. :-) $\endgroup$ – ruakh Jun 25 '17 at 4:54
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    $\begingroup$ @ruakh The idea of a vaguely salamander-like creature with a jewel in its head has definitely existed in a more literal form; in Dungeons & Dragons it inspired the slaad, a creature not unlike a humanoid toad, which has a gemstone embedded in its head. If you can remove the gemstone, whoever holds it gains the power to command the slaad that it came from. $\endgroup$ – anaximander Jun 25 '17 at 11:50
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    $\begingroup$ That is excellent, ruakh; + for the Juliet reference. But I think people believed there were actually magic toadstones in there. You can find engravings of people digging them out. $\endgroup$ – Willk Jun 25 '17 at 14:12
  • $\begingroup$ @Will: OMG, you're right! I had no idea. It seems like such a bizarre belief, but then, I guess it's no stranger than the (correct) belief that pearls come from oysters . . . $\endgroup$ – ruakh Jun 25 '17 at 19:41
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Heavy: so it can sink into the magma. Like, heavier than rock dense.

Some sort of "heat sink" so it can surface, vent excess heat, and then dive into the lava again. This could be something like wings, which are folded flat against the body when under the magma (streamlining and reduced thermal area) and then it unfolds them when it surfaces.

It's probably cold blooded, and the magma warms the blood, which is then circulated through its body. The less effective the heat transfer: the longer the creature can stay under-magma.

Probably maintain a layer of dead skin or scales or something over its outside to act as a heat-shield - kind of similar to how a layer paint protects a surface from rusting. It may not actually be "dead" so much as something like mucus - a specialised bodily excretion.

Incredibly strong: it has to push its way through molten rock.

Probably have some specialized chemistry in its blood to prevent boiling.

I have no idea what this creature eats or drinks. I can't imagine it finding much water anywhere nearby. Maybe you could base it on one of the sulphur breathing lifeforms that you get in volcanic vents.

I imagine that swimming in magma is much like swimming in any other fluid - it's thick, but the laws of streamlining and propulsion still apply. A jet turbine would need to be a lot bigger to allow the magma to flow through it, and it would be far less effective in a fluid than a gas (coefficient of expansion thing). So I'm going for flapping things. Even if it's a man-made magama-submersible, it would probably have flapping things rather than propellers or jets.

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  • $\begingroup$ A heat sink wouldn't be necessary $\endgroup$ – theonlygusti Jun 24 '17 at 20:35
  • $\begingroup$ There's no such thing as a sulphur-based lifeform :/ $\endgroup$ – theonlygusti Jun 24 '17 at 20:36
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    $\begingroup$ @theonlygusti I don't think that's what they mean from sulfur based, DIRECT QUOTE FROM LINKED TEXT------ "In a sense, these organisms "breathe" sulfate rather than oxygen in a form of anaerobic respiration." $\endgroup$ – Cameron Leary Jun 25 '17 at 0:47
  • $\begingroup$ I think heat sinking of some sort (or venting heat) would be necessary. The hottest I could find is the Pompeii Worm which can survive 80 degree heat. Hence, the animal keeps it's core temperature low by venting excess heat periodically $\endgroup$ – sdfgeoff Jun 25 '17 at 8:16
  • $\begingroup$ I have changed it from sulpher based into sulphur breathing. $\endgroup$ – sdfgeoff Jun 25 '17 at 8:16
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In order to properly "swim" anything (including your creature) has to sink into the fluid. Considering that the density of lava is high, your creature will probably sink to a certain level, not completely.

In this case it can adopt the strategy of the "Jesus Lizard", for which the higher viscosity of magma would help.enter image description here

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    $\begingroup$ The question specifies magma not lava, meaning that there is no surface for the creature to walk on. Lava is magma once it has erupted at the surface and has undergone certain processes such as out gassing dissolved gases such as sulphur dioxide. $\endgroup$ – Sarriesfan Jun 24 '17 at 16:28
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    $\begingroup$ I love the pedanticism $\endgroup$ – theonlygusti Jun 25 '17 at 13:09
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    $\begingroup$ @theonlygusti, 'pedantry', I think you'll find. $\endgroup$ – Wossname Jun 25 '17 at 13:25
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    $\begingroup$ @theonlygusti, you're totally correct. I was simply pushing the joke to the limit and apparently failing to achieve the desired mirth. $\endgroup$ – Wossname Jun 25 '17 at 13:31
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    $\begingroup$ An argument of pedantry vs. pedanticism is hilarious. :P $\endgroup$ – Fred the John Jun 25 '17 at 16:48
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The key parameter that describes the scaling of viscous forces on a body interacting with a fluid is the Reynolds number $\mathrm{Re} = uL\nu^{-1}$, where $u$ and $L$ are the body's relative speed and characteristic length, and $\nu$ is the kinematic viscosity of the fluid. If you scale up a body's size or speed or immerse it in a fluid of different viscosity, as long as the Reynolds number of the two situations is the same the behavior of the fluids will be similar.

Assuming the density of the upper mantle is on the order of $10^3\ \mathrm{kg}/\mathrm{m}^3$, its kinematic viscosity is $\nu=\mu/\rho=10^{16}\!\sim\!10^{21}\ \mathrm{m}^2/\mathrm{s}$, while that of water is only $10^{-6}\ \mathrm{m}^2/\mathrm{s}$. So a creature that wants to swim in magma the way people swim in water would have to be at least $10^{22}$ times larger, $10^{22}$ times faster, or some combination of the two. Assuming speed is proportional to size, that suggests a creature on the order of $10^{11}$ meters in size... roughly the distance from the Earth to the Sun.

A smaller creature would have to learn to deal with life at very low Reynolds number, as described in the classic paper by Purcell. At low Reynolds number, inertia plays no role whatsoever: you can't push the fluid backwards to propel yourself, the way fish or mammals do. You have to wiggle your body repeatedly to gradually nudge yourself forwards, like a microorganism with a flagellum. There's lots more interesting stuff in that article, for example, there's no point chasing your food, whether it's animate or inanimate:

The transport of wastes away from the animal and food to the animal is entirely controlled locally by diffusion. You can thrash around a lot, but the fellow who just sits there quietly waiting for stuff to diffuse will collect just as much. ... But what it can do is find places where the food is better or more abundant. that is, it does not move like a cow that is grazing a pasture--it moves to find greener pastures.

So unfortunately, we're not talking about majestic lava whales or magma dragons or anything like that... We're talking gigantic sedentary bacteria. Sorry.

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  • $\begingroup$ Welcome to WorldBuilding! If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$ – Secespitus Jun 26 '17 at 5:51
  • $\begingroup$ That's still a super interesting answer and the idea of "gigantic sedentary bacteria" is still a super interesting organism! $\endgroup$ – Fred the John Jun 26 '17 at 9:54
  • $\begingroup$ Read through the answers to find the one that mentions Purcell's paper. One important thing (mentioned in that paper) is that in order to move forwards at low Reynolds number your motion needs to be non-reversible - you can't just wiggle something back and forth. $\endgroup$ – KraZug Jun 26 '17 at 10:04
  • $\begingroup$ Would a low Reynolds number allow something to find leverage and pull itself along? Would branching tendrils be able to dig through, spread out, find leverage in the magma and pull the body forward? Or, simply find a solid surface to anchor to, then drag the creature forward? $\endgroup$ – Fred the John Jun 26 '17 at 10:21
  • $\begingroup$ This is proof that the universes are concentric. How humbling. $\endgroup$ – Mazura Jun 29 '17 at 5:54
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At that density swimming is more like burrowing than anything we would think of as swimming. With a viscous material minimizing drag is important, but it does not need controls surfaces or much in the way of fins really just muscle mass, the magma is not going to flow around them much when they push against it. This means they also need an extremely streamlined head more like a burrowing animal except even more pointed.

so you have two likely body plans, either a limbless creature like a burrowing snake or sea snake OR you have a compact body with short powerful limbs more like a mole. You could even combine the two with something like a Bipes.

Of course you also have to consider how they get in or out of the magma, since there will be a layer of cooled solid rock no matter how they enter or exit.

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The most energy efficient way I can imagine is as follows:

  1. Let's assume the creature can change its body total density (doesn't need much, just to be able to become lighter or heavier than surrounding magma at will)
  2. It would have either fin-like horizontal appendages it can rotate in vertical plane
  3. The actual movement would work this way: decrease your body density, rotate "fins" , and let Archimedes push you up in magma. Fins will make you move to the "surface" at desired angle. Once you reach depth with same density, reposition "fins", increase body density, and dive at angle in direction you want.

And be super patient!

edit to address question in comments

That's correct, to use this method of locomotion, creature would have to be able to somehow increase or decrease it's buyoancy, overcoming enormous external pressure. I would suggest two ways to achieve it:

1) assuming it gets it's energy from fission reaction: let's say it is able to "filter" nuclear material from magma, and regulate the criticality in some way. Luckily we have CANDU reactors to prove that you can have nuclear reaction without enriched fuel. By increasing it's internal temperature, creature would expand it's volume and regulate it's density.

2) or, it can "filter" heavier elements from surrounding magma to increase it's density and "excrete" them out to lighten up.

None of methods is fast, of course.

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    $\begingroup$ That's a cool way to do it! Incredibly slow, but that might fit well for some titanic whale-thing. $\endgroup$ – Fred the John Jun 25 '17 at 16:45
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    $\begingroup$ I think that reducing your buoyancy will require lifting a substantial weight, or worse if there’s nowhere for displaced magma to go. $\endgroup$ – JDługosz Jun 25 '17 at 23:54
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Basically your magma swimming beastie would use any form of locomotion seen in marine organisms. The main difference is the remarkably viscosity of magma compared to seawater. Consider this creature would be part of a complex biosphere with a multitude of ecologies and difference biomes for magma-dwelling lifeforms.

Effectively whatever means of locomotion are used in the marine organisms will have a magma-swimming equivalent. Fish with fins, seals with flippers, manta-rays and sting rays with their wing-like bodies, and cephalopods with jet propulsion.

Basically it's all about organisms exploiting fluid dynamics to move through a viscous medium. Magma is just more viscous than most other fluids.

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  • $\begingroup$ So instead of just swimming, we also need magma jet propulsion cephalopods? $\endgroup$ – Drag and Drop Jun 26 '17 at 11:46
  • $\begingroup$ @DragandDrop Not precisely. Seawater and magma are both fluids. If creatures swim in magma, then their forms of locomotion may be similar to locomotion in seawater. Magma jet propelled creatures might be like cephalopods, but they could be different. Magma is extremely viscous. I had hoped there might be magma-dwelling jellyfish that float along. To do this, the swimming creatures requires assuming life and an entire ecology can exist in a sea of magma. $\endgroup$ – a4android Jun 26 '17 at 12:42

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