Desire: In my world, I would like to have a (potentially unreasonably) large mountain range that is so large both in height and width that it is both entirely impassable, and disappears into the clouds with unseen peaks, even when viewed from miles off.

Confession: My knowledge of the science on this is shaky at best. I found another answer on this site that asked for hard science, and yielded that on earth the tallest possible is around 10 km, but I would like to make it much larger, preferably without handwaving.

Goal for Answer: I have no problems with coming up with fantastical ideas for how it became that tall (Massive flooding event that crashed tectonic plates together, remains of an unimaginably large asteroid, etc.), but I am weak in an actual scientific basis. I don't need "hard science" per se, but would like an at least semi-plausable way to explain how it's possible without simply being logistically inane. I'm concerned this size might warp the rotation of the planet, or cause other issues I'm not thinking of, as I'm simply a lowly politics major ;)

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    $\begingroup$ Basically, a mountain cannot be taller than what the rocks at its base can support. This is why a mountain on Earth cannot be taller than 10 km or so -- the weight of the mountain would crush the rocks at the base and those would flow sideways like water. P.S. About those unseen peaks which disappear into the clouds: this assumes that there are clouds into which the peaks can disappear. In many places of the world there are many days in the year without clouds, when we can see the moon and the stars, which are of course very much higher up than any mountain peak... $\endgroup$
    – AlexP
    May 17 at 16:59
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    $\begingroup$ Possibly relevant questions on earthscience.SE: How high can a mountain possibly get? What were the tallest mountain ranges in Earth's geological past? $\endgroup$ May 17 at 17:40
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    $\begingroup$ If you want higher mountains, lower your gravity... $\endgroup$
    – stix
    May 17 at 21:33
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    $\begingroup$ @LoganP98: Are you saying the air is flowing toward this mountain range from both sides? Where does the air go? $\endgroup$ May 18 at 5:09
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    $\begingroup$ Found a nice explanation on how the earths crust floats on top of the mantle. It might help understanding the physics at play: rwu.pressbooks.pub/webboceanography/chapter/… $\endgroup$ May 22 at 12:49

6 Answers 6


The largest mountain in the solar system is Olympus Mons on Mars. There are comparisons to famous mountains on Earth on that wiki page.

It seems that it resulted from the usual processes of volcano formation. But, Mars has relatively low gravity, compared to Earth. And it has little to no tectonic plate movement.

Also, the atmosphere on Mars is quite thin relative to Earth, with very little water. The freeze-thaw cycle is not going to produce the same kind of erosion as on Earth, since there is little water ice. Water ice expands cracks and peels rocks off cliffs, eroding them.

The process of waterfalls is absent. This removes a massive source of erosion on Earth. The canyon that a waterfall forms is much like a knife through a cake, slicing off a huge chunk.

The lower gravity encourages higher mountains to be built. And, once the mountain was formed, there are reduced processes to reduce it in height.

It is thus a balance between a planet being large enough to have mountain building processes. And small enough such that the gravity lets the mountain be very tall. And inactive enough such that mountains are not removed before they can get that high.

  • $\begingroup$ If an unimaginably large asteroid had crashed into the planet millennia ago, leaving its remains as the mountain range, could it stay there long term or would natural forces such as erosion bring it back down to the ~10km level? $\endgroup$
    – LoganP98
    May 18 at 15:57
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    $\begingroup$ guinnessworldrecords.com/world-records/… Largest known impact basin in the solar system. On the moon the only process to remove such craters is later impacts. $\endgroup$
    – Boba Fit
    May 18 at 16:15
  • $\begingroup$ @LoganP98 As far as I know, the current theory for the existence of the Moon is that a proto-planetary body crashed into the Earth, tearing off huge chunks and basically erasing the surface of the planet. The problem with large asteroid impacts, even moderately large ones, is that on geological timescales rock acts very much like a liquid. $\endgroup$
    – Onyz
    May 22 at 16:24

So two ranges to look at for how they formed are the Himalayas and the Andes Mountains (and other mountain ranges found in the American Cordillera, which is a chain of ranges found in the western portion of both American Continents). In the case of the Himalayas, the range was fromed by two continental plates smashing into each other (The Asian Plate and the Indian Sub-continental plate). Continental Crust is thicker than Ocean Crust and thus, when Ocean and Continental Crust meets, the Ocean Crust is forced under the the Continental. However, when Continental Crusts pushes agains teach other, both plates buckle and slowly push upwards, which is what happens with the Himalayas.) which is why they are so high in some places. Moutains also do have places where it's easier to travel from one side of the range to the other, but this also makes it very easy to form chokeholds at these locations. They are infrequent, There are very few ways to pass through the Rockies in the U.S. and settlers heading were often settling west of the Rockies in areas based on which pass they took. If they arrived to late in the season, they would settle at the eastern part of the pass.


Limiting your fantasy based on Earth geology doesn't make much sense, it's just a one planet. We have no idea how typical it is in the universe. Rocks composition, crust, mantle, gravity - all of this can be wildly different and planet still can be habitable. You want 20 km high mountains - go for it. No one can definitely say they are impossible.

Just an example, BPM 37093 is a star (https://en.wikipedia.org/wiki/BPM_37093). It's core is likely one of the largest diamonds in the local region of the universe. Estimated mass is 5×10^29 kg, Earth's mass is ~6×10^24 kg. Star systems sometimes collide. If BPM 37093 ever get close to a supernova and get destroyed, diamond shards thousands kilometers long are not impossible. If one of them ever become a part of new planet, it may have very peculiar mountain ranges made of pure diamond. It is unlikely. But not impossible.

You don't really need scientific basis for high fantasy with magic. It can be harmful. The Force in Star Wars was much better before midichlorians.

Avatar is hard-ish Sci Fi. It has flying land masses. It is ridiculous, but no one blinks an eye. Pandora is a moon of other huge, very close planet, there are multiple other large bodies visible in the sky. It is most likely a completely impossible system, no one cares.


According to your tags

Your World has Magic

This means that you need not limit yourself to what is physically possible on earth. In fact doing so would be entirely unnecessary.

Soft Magic

If your world has soft magic then the simplest solution is that the mountains are enormous and impassable, simply because that is part of their fundamental nature. The 'will' of the mountain will see anyone attempting to summit or cross it faced with impassable ciffs, freezing temperatures, howling winds, walls of snow, savage beasts and generally inhospitable everything.

Keep the magic magical. Nobody knows how tall the mountain actually is, just that you can't reach the top. How did it form? Just like on Earth, no one actually remembers. There are legends of angry gods, powerful spirits or the will of nature itself. Wise men will form hypotheses of great power welling up from beneath the earth or stars falling from the sky but no-one actually knows.

More Concrete Magical Solutions

  • The mountain could be some sort of growing rock; the gowth of which outpaces erosion.
  • the base could be covered with some sort of magical forrest whose roots dig far into the rock and stabilise the entire mountain.
  • The entire plantet (if your world actually is one) could have formed around some sort of huge rigid and angular object and the mountain is simply part of the object that protrudes from bellow the crust.
  • If your world isn't a regular planet this object could simply be embedded into the surface.
  • Anything that has a logical connection to your magic system.

In the end the specifics don't necessarily matter as long as you leave enough room for there to be a plausible explanation. The people in your world aren't omniscient so you don't have to be either (in case they are omniscient I don't think explaining the minutia of mountain ranges is what they do for fun).


The major ways to get mountains:

Meteoroid impact

Impacts generally forms rings with raised center. There are several large examples of these across earth. Events large enough to form very large mountains are not life friendly on a global scale.


Glaciers and rivers can carve valleys into terrain that has been lifted by plate tectonics.


Generally form on plate boundaries, with highest counts where ocean plate subsection is occurring.

If conditions are right you can have some really tall ones such as the Hawaiian Islands and Olympus mons. But generally this isn't your primary source of large mountain ranges.

If the event is large enough such as the Siberian traps. it forms more of a plateau then mountains. Which then requires Erosion to get mountains.

Plate collisions

Many Mountain ranges were formed as result of continental plates colliding, but not subducting. Appelachian Ural mountains, are two examples of this. Swiss alps and much of south Europe are being affect by this as Afraca and Europe move towards each other.

Plate subduction

The only way to get consistent large regions of large mountains.

  • The Andes and Rockies are above where oceanic plates are/were subducting.
  • Himalayas Mountains are above the subducting Indian sub continent.


That is The most plausible way to get largest regions high average and high peak elevations is to have a continental plate subduct under another. Second best is to have a large run of oceanic crust


Extrusion of matter from core

A blob of iron/nickel was pulled from the core all the way to surface. Nobody knows how, perhaps micro small hole flew through the planet. The blob then erupted as a volcano chain, leaving very high peaks of hard and corrosion resistant metal alloy.


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