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I have a very large desert, approximately 15 000 km across from west to east (the north-south distance is around 4 000 km, although it's at a bit of an angle). The desert is bounded at one edge by a large mountain range running north to south which casts the rain shadow which gets the desert started. This desert is intended to be extremely inhospitable, with the bulk of it receiving no rainfall and having no sources of water available for human travellers.

About 9 000 km into the desert (from the side with the initial mountain range) is a secondary mountain range, also running north to south. The desert then continues another 4 000 km.

What I am wondering specifically is, is it technically plausible for the mountain range cutting through the desert to have accumulated snow caps? I would like for that mountain range to serve as a way through the desert (north-south), albeit a very difficult one, by virtue of having a small amount of moisture present rather than none at all.

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    $\begingroup$ Yes. The US Great Basin is similar, though on a smaller scale, with high mountains on the east & west sides, and many mountain ranges in the middle. Most if not all of them have snow caps in the winter, lasting well into summer on the higher ones. There's even a small glacier: nps.gov/grba/learn/nature/glaciers.htm $\endgroup$
    – jamesqf
    Aug 31 at 16:33
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    $\begingroup$ If the mountains are high enough, the climate there will get cold enough (because of the atmospheric pressure drop) to cause snowfalls, desert or no desert. $\endgroup$ Aug 31 at 19:29
  • $\begingroup$ Re large deserts and little moisture, note that it's known to snow on Mars. $\endgroup$
    – jamesqf
    Aug 31 at 23:58
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    $\begingroup$ NOTE: Technically, most of Antarctica is a desert. It also has snow caps. $\endgroup$ Sep 1 at 14:18
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Yes, but...

You don't describe your desert. Let's assume it's the driest form of desert there is. You also don't describe what you're looking for in terms of a "snow cap," other than your desire for it to be a source of moisture for travelers.

Can it be plausible? Yes, to a degree... You won't be able to handle much population growth.

  • A high mountain will always be cold, no matter the conditions that cause the desert. This works in your favor as what little moisture exists in your desert will have someplace to condense and be deposited.

  • But you're not working with a whole heckuva lot of water. Therefore, by "snow cap" what you should expect is that shimmery, glistening, really thin layer of icy buildup. Wind will cause it to build up in small "rivulets" where travelers can steal a bit of water for themselves and their animals.

But if you're thinking snow caps like the alps... no. You won't and cannot have those unless you have a boatload of moisture in the upper atmosphere that, for some unknown reason, never falls on your desert. That would be unbelievable.

Frankly, I think your opportunity here is pretty cool. Those icy wind-driven buildups are like dew collecting in flowers. A rare and precious commodity that would cause people to keep secret where the deeper, richer flows are (not unlike mines).

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    $\begingroup$ Although a number of replies were good I've marked this as the answer in particular because it seemed the closest tailored to an extremely dry and hot desert rather than deserts in general, and also specified what sort of snow or ice would be realistically expected to form. I do realize now that I neglected to specify that it is also meant to be very hot. $\endgroup$ Sep 1 at 6:08
  • $\begingroup$ unless you have a boatload of moisture in the upper atmosphere that, for some unknown reason, never falls on your desert - Wouldn't these same mountains be casting a rain shadow on the desert? $\endgroup$
    – Kreiri
    Sep 1 at 7:37
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    $\begingroup$ @ Kreiri: WRT never falling on the desert, are you familir with virga? It's rain (or sometimes hail or snow) that falls from clouds, but which evaporates before reaching the ground. Fairly common here in the Great Basin. en.wikipedia.org/wiki/Virga It's also not unusual for me to be in sunlight here at the base of the east side of the Sierra Nevada, while a blizzard is taking place at higher elevations. $\endgroup$
    – jamesqf
    Sep 1 at 16:54
  • $\begingroup$ @Kreiri Of course they would, but keep in mind the OP is asking about a mountain range that's inside the desert. Where there is no rain, the ability to cast a rain shadow is irrelevant. In such a desert all you're really working with is cold-weather condensation at high altitudes. NOTE: We are simplifying the issue to meet the OP's needs. Remember, this site isn't dedicated to Scientific Truth (unless the hard-science tag is used), but rather the use of science to rationalize a condition in a fictional world of the OP's own creation. $\endgroup$ Sep 2 at 0:24
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Below is from Four Peaks, Arizona

Four Peaks, Arizona

Here is the Ashgabat desert in Turkistan

enter image description here

Below Mount Kodar, Trans-Baikal area, Siberian Mountains

enter image description here

For various reasons, warm regions can have cold mountain tops. Mauna Kea in Hawaii gets snow. Mount Kilimanjaro at a latitude 3 degrees from the Equator gets snow.

  1. Higher in the atmosphere the temperature can be a lot lower. Actually as altitude rises, pressure drops, and in different altitude zones temperatures rise or fall.
  2. As prevailing winds cross the landscape, they have to rise up the mountain. This causes drop in pressure and loss of humidity (which might drop as snow). That cools the air.
  3. Also a mountain may have a different angle in relation to the sun than the flat of the desert. At Mount Kilimanjaro the sun would shine directly on level ground but be at an angle from above on the mountain. In Siberia, on level ground the sun is at an angle, but may be more or less on the sunward side and in the shadow of the mountain on the north.
  4. Finally, the desert might not be hot. In Siberia, there might be tundra or there might be arctic desert.
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    $\begingroup$ I prefer my desserts cold, actually (minor typo). $\endgroup$
    – phyrfox
    Sep 1 at 1:29
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Whatever air is flowing through that desert will capture some humidity and will release it when it cools down.

This means that over the centuries the inner mountain range will get some deposition of snow/ice, due to this mechanism: desert air will cool down while climbing on the mountain range and deposit its humidity.

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  • $\begingroup$ Right, there will always be some humidity in the air coming from outside the desert, even in rain shadow. $\endgroup$
    – Juraj
    Aug 31 at 14:39
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    $\begingroup$ Gimme some geography! I want to see some of the mountains you describe. $\endgroup$
    – Willk
    Aug 31 at 15:02
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Another example: The Peruvian and Chilean coast are exceedingly dry. Archeologists still talk about discoveries made due to the 1923 rain. The land is bleak with no green thing at all away from the rivers that flow from the Andes to the east.

This desert is dry due to the Humbolt Current. It's a cold water current flowing north along the coast. Air at saturated humidity mixes with warmer air over land, and quickly drops below saturation. That air has to cool before it can drop any water.

On the Altoplano (The highlands that include Lake Titicaca) at 12,000 feet there is enough rain to support sparse grass. As you get closer to the mountains it gets increasingly wet.

The issue is that you need to have some water in the air before the climb. You can do this by having a drier but not impossibly dry area in the first rainshadow. Afterall: The rain shadow of the cascades in Washington state still gets 9-12 inches of rain a year. This area of low rainfall allows some water back in the atmosphere. Now make your mid desert mountains even taller than the coastal range. They will wring whatever remaining moisture there is, and then the really nasty desert starts.

You can also do things like:

  • Erratic rainfall due to jet streams tht bring in storms from north or south.

  • The area is a former seabed, and there is a lot of ocean salt mixed into the soil, so that the only potable surface water is in 'tanks' on bare rock. (A tank in this sense is a hollow in a rock surface that collects rain water for a few days to weeks. Common in the Canyon lands of SE Utah and N. Arizona)

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Yes

There's two things that are important here. First is that a desert doesn't need to be hot. A desert is a definition for a mostly barren land. Because of this the heat can easily skyrocket, which is why the hot deserts are so famous. That being said, heat is not a requirement. Your incredible large desert can be a frozen wasteland for thousands of kilometers. Technically the North and South pole are deserts. They receive little precipitation, yet consist mostly out of water.

Things generally get colder with lesser pressure. Thanks to gravity and less air pushing down on itself at altitude, you'll get less air pressure the higher you go. At altitude, like in the mountains, the lesser air pressure results in colder air. Make the mountains high enough and you'll get temperatures suitable for ice and snow.

Over the years of this colder climate the water that does reach the mountain can accumulate in snow and ice for example. Eventually it'll get there.

That means a random mountain range in the middle of the hottest desert in the world can have permanent snow covered peaks. It does need to fulfil some shape and size requirements, but can lead to basically anything you want.

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    $\begingroup$ Your explanation of why mountain tops are colder is just plain wrong. Air gets colder as you go up, regardless of whether you're climbing a mountain, or flying in an airplane over a flat plain. See e.g. en.wikipedia.org/wiki/Lapse_rate In fact, you may be warmer on the surface during the day, due to solar heating of the ground. $\endgroup$
    – jamesqf
    Aug 31 at 16:27
  • $\begingroup$ @jamesqf yeah I did make a mistake. Fixed it. Altitude is however a secondary reason for the colder temperature. The true culprit is air pressure, which happens to be lower at altitude. $\endgroup$
    – Trioxidane
    Aug 31 at 18:02
  • $\begingroup$ It wasn't really wrong. Angle of the sun is why it is colder at the poles. So for the south side of a mountain in Siberia the angle with the sun would be a factor. As altitude increases and pressure decreases there are bands in the atmosphere where temperature decreases with altitude and other where it increases with altitude. The edited answer is correct though as you don't need to consider the different bands of atmosphere. $\endgroup$ Aug 31 at 18:24
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    $\begingroup$ As altitude rises, temperature decreases in the Troposphere, increases in the Stratosphere, decreases in the Mesosphere, and increases in the Thermosphere. However, Mount Everest is not above the Troposphere so we don't have to consider temperature rising with altitude. It does show that dropping pressure does not always decrease temperature. $\endgroup$ Aug 31 at 18:31
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    $\begingroup$ @JeopardyTempest: As I said, "how people imagine the state" is colored by thinking of Las Vegas, which is not typical of the rest of the state (in a great many ways, not just climate). For the rest, you're mostly just plain wrong - check any good meteorology site. And BTW, Nevada does have lots of pretty flat places: americansouthwest.net/nevada/black-rock-desert/index.html $\endgroup$
    – jamesqf
    Sep 2 at 3:53
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The mountains almost certainly will have at least a partial snow cap on them and there will be some runoff from them that gives a narrow "moisture corridor" along there flanks. The Coriolis Force is going to push storms around the rain shadow that forms the first part of the desert onto one face of the central mountain range from the north and the other when weather comes up from the south. The moisture in those storms, and in air flows that are simply a bit wet, is going to precipitate out in the mountains in the form of orographic precipitation. Now a lot of that moisture will fall as snow and sublime back into the high altitude air over time but you are probably going to get glaciation and there will be some absorption into the underlying ground and some melting and runoff. This is going to form rivers and possibly a spring line at lower altitude. The desert sands are probably going to suck down the moisture that runs off the mountains into the lowlands pretty fast but there may be a navigable corridor through the lower edge of the mountains for much of the year.

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