# Could I use molten lava as a permanent design feature--like a moat?
**URL:** https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972
**Category:** Factual Questions
**Created:** [March 19, 2009, 1:36am UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972 "2009-03-19T01:36:32Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@Ranchoth](https://boards.straightdope.com/u/Ranchoth)
#### Post date: [March 19, 2009, 1:36am UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/1 "2009-03-19T01:36:32Z")
Inspired by…countless movies, TV shows, comics, novels, etc., as well as the response to [this](http://boards.straightdope.com/sdmb/showpost.php?p=10929093&postcount=27), I’m finally going to ask this one.
That is, like I said in the title, is there any way, with roughly current technology (or at least physically possible technology) to use molten lava as a design feature in my Fortress of Doom? Like for a moat, or a decorative lavafall, or something?
I know I can’t just have little koi fountains of lava sitting around the lobby, for worker safety issues if nothing else, but can I do the bigger stuff without hopelessly gumming up the works within days, or quickly killing all of my minions?
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### Author:  [@XT](https://boards.straightdope.com/u/XT)
#### Post date: [March 19, 2009, 1:48am UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/2 "2009-03-19T01:48:49Z")
No…you couldn’t keep it hot enough to stay molten. Aside from the killing of your minions and roasting your fortress of Doom, I think this is an insurmountable problem with current technology.
-XT
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### Author:  [@dracoi](https://boards.straightdope.com/u/dracoi)
#### Post date: [March 19, 2009, 1:59am UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/3 "2009-03-19T01:59:55Z")
I suspect it would be possible to keep the lava hot enough if you put enough effort into it. Induction heating can produce very high temperatures and there’s always the possibility of laser or other radiant heating. (Which begs the question “Why not use that tech to just kill any intruders instead of wasting energy keeping lava molten?” but evil overlords are not known for asking these kinds of things.)
A moat might be manageable as long as the lava can remain stationary. Trying to get a lava fall would be pretty difficult; I’m not sure what you’d use for the pump mechanism to keep the lava moving. The pump would have to handle high temperature, high viscosity and high density.
You might also consider pseudo-lava - some material that would look like lava and be sufficiently hot, but which would be designed for optimum heating and handling characteristics. A giant pit of back-lit red wax, for example.
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### Author:  [@beowulff](https://boards.straightdope.com/u/beowulff)
#### Post date: [March 19, 2009, 2:12am UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/4 "2009-03-19T02:12:40Z")
Build your fortress on the Big Island of Hawaii.
There is a pretty steady source of lava available for you to run into your moat. No high technology required.
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### Author:  [@Rhythmdvl](https://boards.straightdope.com/u/Rhythmdvl)
#### Post date: [March 19, 2009, 2:15am UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/5 "2009-03-19T02:15:52Z")
I assume there is a basic material (e.g., ceramic) that can withstand the heat of the lava. If so, then couldn’t a lava fall be powered by an [Archimedes’ screw](http://en.wikipedia.org/wiki/Archimedes%27_screw)? It could be powered remotely – say by embedding iron cores within the material (so it doesn’t come in direct contact with the lava) and using magnets to control movement.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [March 19, 2009, 2:18am UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/6 "2009-03-19T02:18:09Z")
> [@](#):
>
> Induction heating can produce very high temperatures
But only if the thing being heated is conductive, which I don’t imagine lava is. On the other hand, I can’t see that there’s really much practical difference between molten lava and molten, say, iron, and one certainly can produce flows of molten iron on an industrial scale.
Of course, you could also just build your lair into a pre-existing active volcano, if you want to go the easy route.
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### Author:  [@Shamozzle](https://boards.straightdope.com/u/Shamozzle)
#### Post date: [March 19, 2009, 2:21am UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/7 "2009-03-19T02:21:18Z")
Man, that would be one hell of an electrical bill, keeping all that lava molten. You might as well spring for a nuclear power plant as well.
Maybe some sciencey-types could calculate the radiation rate in watts, based on your average sized and shaped moat full of standard-issue Lava of Evil.
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### Author:  [@Rhythmdvl](https://boards.straightdope.com/u/Rhythmdvl)
#### Post date: [March 19, 2009, 2:21am UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/8 "2009-03-19T02:21:57Z")
> [@Chronos](#):
>
> Of course, you could also just build your lair into a pre-existing active volcano, if you want to go the easy route.
Neither the Evil Overlord nor the Doper way.
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### Author:  [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)
#### Post date: [March 19, 2009, 2:24am UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/9 "2009-03-19T02:24:50Z")
I think people
a.) Don’t appreciate how incredibly hot lava is
Read this: [http://tvtropes.org/pmwiki/pmwiki.php/Main/ConvectionSchmonvection?from=Main.ConvectionShmonvection](http://tvtropes.org/pmwiki/pmwiki.php/Main/ConvectionSchmonvection?from=Main.ConvectionShmonvection)
b.) Don’t appreciate the amount of energy required to heat or cool lava. There is a simply HUGE amount of thermal mass there. Read John McPhee’s book \*\*The Control of Nature \*\*, and the section on trying to tame lava flows, to get an idea of how immensely difficult it is to try to control where the lava will flow. Pumping enormous amounts of water simply isn’t sufficient to cool it fast enough to be useful.
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### Author:  [@Duckster](https://boards.straightdope.com/u/Duckster)
#### Post date: [March 19, 2009, 3:29am UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/10 "2009-03-19T03:29:45Z")
The [Oldoinyo Lengai volcano in Africa is unique in the world](http://ngm.nationalgeographic.com/ngm/0301/feature2/) in that it produces a form of flowing carbonate magma [where its temperature won’t even burn the grasses and trees it flows over](http://columbian.com/article/20090315/NEWS02/703159959/-1/ARCHIVES).
So consider carbonatite volcanism.
😃
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### Author:  [@Rhythmdvl](https://boards.straightdope.com/u/Rhythmdvl)
#### Post date: [March 19, 2009, 4:22am UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/11 "2009-03-19T04:22:42Z")
> [@Duckster](#):
>
> The [Oldoinyo Lengai volcano in Africa is unique in the world](http://ngm.nationalgeographic.com/ngm/0301/feature2/) in that it produces a form of flowing carbonate magma [where its temperature won’t even burn the grasses and trees it flows over](http://columbian.com/article/20090315/NEWS02/703159959/-1/ARCHIVES).
> So consider carbonatite volcanism.
>
> 😃
Whoa… include a couple frozen Han Solos and you’ll have quite the intimidating front gate.
Wait — carbona_tite_ or carbo_nate_? Dang. Which one drips down from the cave ceiling, and which one…
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### Author:  [@Sage\_Rat](https://boards.straightdope.com/u/Sage_Rat)
#### Post date: [March 19, 2009, 4:57am UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/12 "2009-03-19T04:57:32Z")
From what I can tell, **pretty much** any material will glow red if you get it to around 1000F. So it’s just a matter of choosing a material that is liquid at that temperature. Sand (i.e. glass) might be the cheaper option.
But so the question is how much energy you need to maintain a pool of liquid at 1000F, and how much that costs. The cost of materials might also be a significant factor.
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### Author:  [@Incubus](https://boards.straightdope.com/u/Incubus)
#### Post date: [March 19, 2009, 7:23am UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/13 "2009-03-19T07:23:28Z")
Well, if you were willing to be flexible about molten substances, a moat of molten lead might be more practical. Sure it doesn’t glow like lava does, but the melting point is much lower, making it more manageable to contain/pump around but still hot enough to be unpleasant to unwary intruders.
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### Author:  [@Sage\_Rat](https://boards.straightdope.com/u/Sage_Rat)
#### Post date: [March 19, 2009, 8:14am UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/14 "2009-03-19T08:14:36Z")
> [@Incubus](#):
>
> Well, if you were willing to be flexible about molten substances, a moat of molten lead might be more practical. Sure it doesn’t glow like lava does, but the melting point is much lower, making it more manageable to contain/pump around but still hot enough to be unpleasant to unwary intruders.
Mercury would look roughly the same and be liquid without being heated at all.
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### Author:  [@ColdPhoenix](https://boards.straightdope.com/u/ColdPhoenix)
#### Post date: [March 19, 2009, 11:20am UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/15 "2009-03-19T11:20:11Z")
> [@Sage\_Rat](#):
>
> Mercury would look roughly the same and be liquid without being heated at all.
But it won’t kill intruders quickly enough though.
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### Author:  [@Sage\_Rat](https://boards.straightdope.com/u/Sage_Rat)
#### Post date: [March 19, 2009, 11:33am UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/16 "2009-03-19T11:33:22Z")
> [@ColdPhoenix](#):
>
> But it won’t kill intruders quickly enough though.
Yes, but my point is that you only need to heat it to the level of lethality. Lead you have to heat to the melting point, which is probably higher.
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### Author:  [@Princhester](https://boards.straightdope.com/u/Princhester)
#### Post date: [March 19, 2009, 12:30pm UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/17 "2009-03-19T12:30:51Z")
Wait, surely we need the dull glow of something red hot? A moat comprised merely of a liquid that is hot enough to kill someone (like hot lead or mercury) is dull, dull dull. Heck hot water could do that. Any evil bad guy who’d settle for a moat of hot water would have their licence revoked.
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### Author:  [@Grumman](https://boards.straightdope.com/u/Grumman)
#### Post date: [March 19, 2009, 12:49pm UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/18 "2009-03-19T12:49:58Z")
> [@Princhester](#):
>
> Wait, surely we need the dull glow of something red hot? A moat comprised merely of a liquid that is hot enough to kill someone (like hot lead or mercury) is dull, dull dull. Heck hot water could do that. Any evil bad guy who’d settle for a moat of hot water would have their licence revoked.
The problem with a moat of magma or molten lead is that everyone _knows_ it’s a moat of magma or molten lead. So while it may look awesome, it denies you the entertainment that comes from people who don’t know that your moat is boiling _finding out_ that your moat is boiling.
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### Author:  [@Wheelz](https://boards.straightdope.com/u/Wheelz)
#### Post date: [March 19, 2009, 12:53pm UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/19 "2009-03-19T12:53:02Z")
> [@Princhester](#):
>
> Any evil bad guy who’d settle for a moat of hot water would have their licence revoked.
…unless lobsters are their enemy…
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [March 19, 2009, 5:18pm UTC](https://boards.straightdope.com/t/could-i-use-molten-lava-as-a-permanent-design-feature-like-a-moat/489972/20 "2009-03-19T17:18:18Z")
> [@](#):
>
> Sand (i.e. glass) might be the cheaper option.
I understand that molten glass is actually highly corrosive, so he’d have to do a lot of maintenance on his moat if he used that.
I still think molten iron is his best bet. It’s hot, it’s relatively cheap, it can be heated inductively, and there’s already known, proven technology for working with it.
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