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The primary mechanism for mountain formation (of which I'm aware) is uplift of the crust, with rivers eroding their way through softer sediments as the crust rises to form peaks and canyons. That sounds to me like, without rivers/glaciers, you could never have impressive mountain ranges like the Alps or Andes, only broad areas of high/low crust or wide escarpments. So, to be clear:

Is there any way for mountain ranges with peaks and valleys to form on a planet without an erosive surface fluid like water?

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    $\begingroup$ Minor, "have-you-seen-this?" frame challenge: without water, it's not clear that plate tectonics could even function like it does on earth. Consider: earthscience.stackexchange.com/questions/762/… $\endgroup$
    – Qami
    Commented Mar 4 at 6:01
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    $\begingroup$ No plate tectonics no Alps or Himalaya, Mars has tallest mountain ever yet no mountain ranges! $\endgroup$
    – user6760
    Commented Mar 4 at 6:17
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    $\begingroup$ Err... there's this planet called Venus. $\endgroup$
    – Mon
    Commented Mar 4 at 9:57
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    $\begingroup$ @Mon as far as i know Venus' mountains are volcanic, not tectonic in origin $\endgroup$
    – Seggan
    Commented Mar 4 at 16:38
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    $\begingroup$ @Qami Thanks for the link, that's a super interesting question that I hadn't considered. The planet that I'm designing is very young though, <100M years, so the crust hasn't even fully solidified yet and there is no plate tectonics; there are basically just thin crust "islands" amid planet-wide oceans of lava and a tenuous atmosphere with very little water. So I've been trying to understand what sort of landforms could exist on those islands of crust. $\endgroup$
    – Rabadash8820
    Commented Mar 4 at 18:02

3 Answers 3

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Erosion is responsible for flattening the mountains, bringing the rocks back to sea level, not for rising them. The most weathered down mountains look like gentle slopes, while the youngest ones are all ragged and spiky: compare Scotland with the Alps or the Himalaya.

Imagine a car hood before and after an impact with a wall: before the impact it is flat, after the impact it is corrugated. There is no water involved in the process, just the impact which deforms the flat surface into a corrugated one.

enter image description here

This is what happens, on time scales of millions of years, for mountains formation: tectonic plates collide and get deformed, forming mountains. The most weathered down mountains look like gentle slopes, while the youngest ones are all ragged and spiky: compare Scotland with the Alps or the Himalaya.

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  • $\begingroup$ Thanks, very interesting analogy! Now that you mention it, I have heard of fold mountains on Earth, but always figured that they have also been carved by rivers. However, the first image on that Wiki page is of the Zagros mountains in western Iran, which is a very dry region. So I think fold mountains in deserts on Earth may just be the reference that I was looking for! Might be worth expanding your answer with some of these real-world examples, but I still accept it. 👌 $\endgroup$
    – Rabadash8820
    Commented Mar 4 at 17:56
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    $\begingroup$ @Rabadash8820 canyons are carved by rivers, everything else is a tectonically-created mountain (except if you count sand dunes as mountains). Rivers then can add profile by "selectively" carving. Btw. with sand + wind you can get similar abrasive forces as water (with some handwaving), so even "polished down" mountains aren't impossible without water $\endgroup$
    – Hobbamok
    Commented Mar 5 at 15:32
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There is also temperature weathering, which alone withers stones down to sand. Constant expansion and cooling breaks it down.

Also, there can be gravitational "kneading" as in the planet cycles another graviational massive body, that applies changing gravitation to the crust.

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    $\begingroup$ Interesting, thanks. For myself and future googlers, here's the Wiki on thermal stress; I hadn't considered that. Do you know of any landforms (on Earth or elsewhere) that were primarily formed by temperature weathering? I'm also curious how long it would've taken those landforms to form... And yeah, I have heard of the tidal flexing that causes volcanism on Jupiter's moon, Io. Maybe I can find some data about landforms there. $\endgroup$
    – Rabadash8820
    Commented Mar 4 at 17:49
  • $\begingroup$ Mountains in the attacama.. en.wikipedia.org/wiki/Atacama_Desert .. but mostly wind driven erosion there $\endgroup$
    – Pica
    Commented Mar 4 at 20:30
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TL;DR: With enough bombardment by space-rocks, all sorts of landforms are possible. Moreover, asteroid bombardment is clearly possible for all objects in space, which avoids any issues that might arise from lack of water preventing plate tectonics and interfering with nonvolcanic orogeny.

Here's a slice of the moon's surface, a little to the north-east of the moon's highest mountain, Mons Huygens. This range is also known as the Montes Appeninus. It has a pleasingly mountainous and broken look, at least from here.

Montes Appeninus synthetic view showing terrain shading and 500m contour lines.

(Lunar Quickmap, using public domain NASA LRO/LROC data

Mons Hadley, in the upper-middle portion of the map, has a peak about 4.5km above the plain to its north and west. As luck would have it, Apollo 15 even took a nice photograph:

Jim Irwin with a lunar rover with Mons Hadley in the background

(image courtesy of NASA and David Scott, via wikimedia)

So there you go: mountain, of a sort. It may have started as a crater rim, but Mare Imbrium formed something like 4 billion years ago and subsequent smaller impacts and falls of regolith produce something a lot more mountain rangey than the scarps you're thinking of. The fine layer of dusty regolith rounds everything off quite a lot, but I suspect that even a thin atmosphere with a bit of a breeze would shift the finest stuff and leave a more rugged landscape, if that's what you were after.

Valleys are a little more challenging, as they really require some fluid moving under the influence of gravity. Even then, the Moon has some good examples and near to Mons Hadley you can find Rima Hadley, a sinuous rille thought to have formed from a lava flow or collapsed lava tube:

Rima Hadley

(image credit NASA via wikimedia)

It is a few tens of kilometres long, and hundreds of metres deep in places. This sort of thing is probably the most valley-like formation you're likely to get without surface ice or water.

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  • $\begingroup$ Wow, fantastic answer, I love the lunar examples. I'm torn whether I want to accept this one or keep @L.Dutch 's 😬 $\endgroup$
    – Rabadash8820
    Commented Mar 8 at 10:35

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