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Rivers of lava are a staple of fantasy. But in the real world, lava flows are usually very short-lived phenomenons caused by volcanic eruptions.

Is there some plausible way on an otherwise earth-like world to have a naturally occuring river of lava which is several meters wide, several kilometers long and functions as a permanent geographical feature? With "permanent" I mean permanent enough that someone would draw it on a map which is still useful a couple decades later.

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    $\begingroup$ The thing with lava is that is it molten rock. A river of lava is a massive conveyor belt carrying large amounts of rock. Where does all that huge amount of rock go? $\endgroup$ – AlexP Dec 4 '19 at 23:30
  • $\begingroup$ Good question. This is a real challenge! $\endgroup$ – Willk Dec 5 '19 at 0:36
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    $\begingroup$ @AlexP same place you put all your trash. In the ocean! $\endgroup$ – Morris The Cat Dec 5 '19 at 1:01
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    $\begingroup$ @AlexP Kilauea erupted continuously from 1983 till 2016 and it didn't affect the maps THAT much. There's a lot of room to dump stuff down the side of the big island of Hawaii without making much of a dent. $\endgroup$ – Morris The Cat Dec 5 '19 at 1:20
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    $\begingroup$ take Kilauea - active continuously for at least the recent 30...40 years with constant lava streams to the coast. though part of the lava streams run covered by a thin layer of solidified stuff - you can't step on there because its literally few inches that cover 1000 degree hot stuff $\endgroup$ – eagle275 Dec 5 '19 at 9:35
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It's not completely impossible, but it requires some unusual conditions.

First: The 'source' of your lava river is always going to be an active volcano, by definition, but volcanos don't always involve tall mountains. There are also Shield Volcanos which form relatively low, broad rises in the terrain where the lava pushes to the surface. It's important to note here that lava doesn't always come from the top of a volcanic mountain either. The heat and pressure come out through the path of least resistance and while the top of a volcanic mountain may be where the lava came out LAST time, subsequent eruptions are as likely as not to come out through cracks and newly opened fissures in the sides of the mountain.

Second: You only get lava when an enormous amount of heat is rising up from the earth's mantle. Generally speaking this occurs in one of two cases: Either you have a 'hot spot' allowing that heat (and magma) to rise up through the middle of a continental plate like the one that's been continuously forming the Hawaiian Islands for the last few million years, OR you have a place where the continental plates are being pushed apart. Now, the biggest example of this is the huge volcanic rift that runs right down the middle of the Atlantic Ocean that's pushing Europe and Africa in one direction and the Americas in the other, but another good example is the Great Rift Valley in Africa that is currently in the process of breaking Somalia off from the rest of Africa and forming two new continental plates.

Both of those examples have historically had occasions of very long-lasting continuous lava flows primarily because instead of going through cycles of cooling and heating where pressure builds up over centuries or millennia to a catastrophic eruption, these volcanoes have a continuous supply of lava constantly rising to surface.

So, all of that basically means the following. To have a river of lava that persists for decades what you need is an area of continuous low-grade volcanic activity that's near the sea, to allow somewhere for all that lava to go instead of building up a big mountain right there. Kilauea isn't venting lava like this right now, but it has done in the past, for decades at a time. You could also get a similar sort of condition from the African rift valley if Saudi Arabia weren't in the way holding the two plates together at the north end.

The main thing is that it's not going to work if you want your river of lava to be out in the middle of a desert somewhere or something. It has to flow into the ocean, and it can't take very long to get there, or the lava will cool and it'll just start forming a big blobby mountain instead.

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  • $\begingroup$ You also have flood basalts, which can involve eruption of a lot of lava over a long period, without much in the way of mountain building. IDK whether the eruptions would qualify as continuous, though. (You might ask on the Earth Science site.) In the US, a geologically recent example is southern Idaho, and particularly Craters of the Moon National Monument nps.gov/crmo/learn/nature/geologicactivity.htm which has (now solidified) lava rivers. $\endgroup$ – jamesqf Dec 5 '19 at 5:06
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    $\begingroup$ But wouldn't the lava cool as soon as it dumped in the ocean, harden, and just build up a dam there? $\endgroup$ – colmde Dec 5 '19 at 11:02
  • $\begingroup$ @colmde, no really. Water colling on lava cool only the crust. We have volcano under the see and it's no problem for them. $\endgroup$ – xdtTransform Dec 5 '19 at 14:40
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    $\begingroup$ Volcanoes can have long periods of continuous venting, but those lava flows do not follow the same path over time like a river does. Instead cooling surface and edges create dams that push the flows into new directions. Unlike rivers which erode their surroundings, lava flows tend to build their surroundings up. $\endgroup$ – Paul Sinclair Dec 5 '19 at 17:28
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    $\begingroup$ @user253751: IDK about lava flowing into the sea, but on land it is common to have lava flows with a cooled, solid outer crust, and liquid lava flowing inside. These are called lava tubes en.wikipedia.org/wiki/Lava_tube and are quite common in e.g. parts of the western US. $\endgroup$ – jamesqf Dec 5 '19 at 19:09
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River No, Lake Yes

you just can't have a steady state lava river, the shape of a river means the lava is cooling which means the river is getting smaller so even if you feed in more lava it follows a different path.

Lava Lakes however are a real thing and steady state lava lakes can exist for centuries because the lava can circulate and get reheated as it cools. Although you will want a lake with some gas to keep the lava moving the most. Basically the lava will swell, spit, and sink constantly, this will also give you a nice roiling effect.

Erta Ale for instance has been active for over a hundred years. enter image description here

enter image description here

Note: keep in mind a visual marker for "lava flows here" would be a perfectly valid thing to put on a map in a valley prone to lava flows, it just is not a indication of a permanent structure, as much as "this area is prone to lava flows" plan accordingly.

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Not really. There have been tons of long lived lava flows in history, but they dramatically alter the land. Lava cools as it flows, creating layers of solid rock that build up.

This happens on volcanic islands where the lava can flow into the ocean, expanding the size of the island.

Lava flows exposed to air will cool and form a crust over them while the hotter lava continues to flow underneath. This can make really cool lava tubes, but prevents standing rivers from really being a thing for long.

Your best bet is to have really, really fast flowing lava that has somewhere to go. So a tall volcano with a well established channel (maybe a lava tube with the roof caved in) that drains into an ocean could work well enough.

Lava that cools never has time to form solid sheets / gets broken up by the turbulence and gets carried out to sea.

Your island will have grown considerably in a decade though.

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River of molten metal.

This "river" does not actually flow - rather it is static. Within its impervious rocky banks, the molten iron comprising the river extends down to the mantle, and the conductivity of the metal means that the vast internal heat of the planet can keep the metal molten. Perhaps the metal is at this surface position because of an ancient meterorite impact, or maybe the molten metal has been squeezed up to the surface.

This sidesteps the problem of continuous flow and offers a solution to produce continuous heat and permanence. Convection currents within the metal would make it stir and eddy. Parts of the surface that cool from contact with the air would sink down into the depths and be replaced by hotter metal from beneath.

The molten metal is a good resource and there are industries along the banks that gather and process the molten iron into useful tools and building materials.

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    $\begingroup$ I really like this idea, but there's a problem with it. The mantle isn't just hot, it's also under INTENSE pressure. That's what drives volcanic eruptions after all, and liquid metal would provide little resistance, As written, my understanding of the physics involved would be that your entire river of molten iron would immediately get spat into the stratosphere followed by a few megatons of lava being squeezed up through the crack by the weight of the crust above. We have some places on Earth that formed from similar events, although I doubt liquid iron was involved. $\endgroup$ – Morris The Cat Dec 5 '19 at 1:52
  • $\begingroup$ @MorrisTheCat - maybe the metal is too heavy to spit? It is a lot more massive than the rocks around and below it, and its great weight keeps it in place? $\endgroup$ – Willk Dec 5 '19 at 2:01
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    $\begingroup$ Maybe... The problem is that the metal is liquid, so by definition it would just get pushed out of the way. I don't think you can have a cooler, lower pressure liquid on top of a hotter, higher pressure liguid ESPECIALLY if the liquid metal is denser. The cooler, denser liquid metal would constantly be trying to trade places with the hotter, lighter magma underneath it. It'd be like trying to keep heavy cream floating on top of hot coffee. The cream just wants to sink to the bottom of the cup. $\endgroup$ – Morris The Cat Dec 5 '19 at 2:03
  • $\begingroup$ You can do this with normal molten rock, lava lakes are a thing. $\endgroup$ – John Dec 5 '19 at 4:18
  • $\begingroup$ @MorrisTheCat Just because it's a liquid doesn't mean it can't exert pressure. The pressure exerted by a liquid at a given depth is related to the weight of all the liquid above that point. Undersea volcanos don't spray water high into the stratosphere.... $\endgroup$ – barbecue Dec 5 '19 at 14:04
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Really Big Lopsided Eruption

Some time ago, the mountain got a lot bigger, and either had one side fall over at the beginning or evolved a channel to the side as it crumbled.

Crucially, there must be significant height to drop lava at the end of its channel, or it will pile up and you won't have a channel anymore. The new lava pumped up from inside must be insulated on most sides in the mountain, with one big exit. Real world lava flows tend to form crusts if they slow down and cool, so your channel needs to have significant steepness.

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  • $\begingroup$ Most lopsided eruptions are explosive, and last no more than a day or two. $\endgroup$ – Mark Dec 6 '19 at 2:07
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As with all things worldbuilding and writing, it's just up to you to decide how much you want to bend reality or play with the rules.

My personal route, in an otherwise earthly scenario, would be to say that the rock simply comes out of a volcano and travels until it solidifies, which could actually be a fair distance.

Some applications of this would be playing with the idea that the reason the river continues is because people harvest the cooled rock and refine it/sell it.

Or, if you really wanted to get creative, you could always say that the river somehow deposits back into the mantle, thus a technically never-ending cycle.

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  • $\begingroup$ Hi JacobClark, welcome to Worldbuilding SE. Perhaps you could explain what "which could actually be a fist distance" means? Fist distance doesn't mean much to me. Tricky things lava rivers. $\endgroup$ – a4android Dec 6 '19 at 7:09
  • $\begingroup$ Ope, you spotted a typo I didn't see :) $\endgroup$ – Jacob Clark Dec 6 '19 at 7:13
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    $\begingroup$ Typos are like that. They always pop up in our blind spots and yet everybody else can see them right away. A quick edit will solve the problem. $\endgroup$ – a4android Dec 6 '19 at 7:18
  • $\begingroup$ Done right after I saw it (new to worldbuilding SE, but quite a friend to Stack Overflow) $\endgroup$ – Jacob Clark Dec 6 '19 at 7:20

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