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I stumbled across Vincent's answer regarding forests and deserts. He claims an elevation difference of 3,000 meters (9,800 feet) could put a forest and a desert in close proximity. That got me thinking. What if they were literally as close as possible, separated by a sheer 3,000 meter cliff face?

To be clear, I'm not asking whether forest and deserts would form around such a cliff. What interests me is the cliff itself. Is it possible for a natural, completely vertical wall to be that tall? If so, how could it form?

Requirements:

  • As close to vertical as possible. Looking at pictures of Nanga Parbat, the tallest so-called cliff in the world, it just looks like a steep mountain. I want a sheer vertical wall. The closer the angles at the top and bottom are to 90 degrees, the better.
  • Enough room on top to have a forest. I don't want a puny mountain top, or some weird spike. Bigger is always better.

Extra Credit:

  • How long could it last before it erodes?
  • How would it influence the weather patterns on either side?
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  • $\begingroup$ According to Wikipedia the world's tallest vertical drop is at en.wikipedia.org/wiki/Mount_Thor and has 1250m vertical distance (with a some overhang too) $\endgroup$ – Neil Slater Aug 5 '15 at 9:28
  • $\begingroup$ Better suit for Earth Science😤 $\endgroup$ – user6760 Aug 5 '15 at 12:12
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    $\begingroup$ The forest must be on top? The other way around is easy. At very high altitudes, the conditions are too harsh for any plants to grow, therefore mountains tops are like desert. $\endgroup$ – Vincent Aug 5 '15 at 15:32
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    $\begingroup$ @Vincent For this question I only care about the cliff itself. I will probably ask another one about the biomes. $\endgroup$ – evankh Aug 5 '15 at 16:22
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    $\begingroup$ Valles Marineris canyon on Mars is 7 km deep at points, so, yes, it is possible. It even exists if you'd care for a short jaunt. en.wikipedia.org/wiki/Valles_Marineris Not much in the way of forest though. $\endgroup$ – IchabodE Aug 5 '15 at 22:53
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Let's do an existence test to see if a stone cliff of the size started by the OP is possible. Using figures from the ASTM link for Summit granite, let's see how tall we can make a one meter square tower of granite. (A tower is a good approximation of cliff strength at the base because it eliminates any support that may be provided by surrounding stone.)

ASTM Stone strength testing data (limited set) indicates that Summit granite has a compression strength of 24,660 psi (170MPa).

35.314 cubic feet = 1 cubic meter

81.646 kg * 35.314 = 2883.246844 kg for one cubic meter of summit granite.

Pa=N*h/m^2

170MPa= (28275 * h) / 1 m^2

170,000,000/28275 = 6012.4 meters.

Granite has strength sufficient by a factor of two to support the weight of a 3000 meter plateau as the OP wishes under normal Earth gravity. Other forces/processes have contributed to why we don't see these kinds of cliff heights on Earth. Other stone types may not support these heights and this answer ignores problems of internal stress fractures that weaken a stone body (The Texas Flake is an example of internal strain found on El Cap in Yosemite.)

Formation of a cliff that tall can happen through glaciation or tectonic activity or both.

Yes, it is possible.

(In other news, a new challenge has been discovered for insane big wall climbers the world over. El Cap was becoming old hat. They thank you for the new challenge.)

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    $\begingroup$ And I see from the Wikipedia article that 170MPa is a rather low average estimate of strength. It's usually 200+MPa. en.m.wikipedia.org/wiki/Granite $\endgroup$ – Green Aug 7 '15 at 13:03
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Yes, it could be that tall. There are many examples of very tall geological features made from granite that reach near the heights requested in the OP.

For example, El Capitan is 2307.03 meters of granite. Adding another 700 meters through glacial carving or tectonic uplift should work. Heck, do both! Tectonic uplift could be done in such a way that a large plateau forms above the cliff.

Place the forest on the plateau. The cliff face is the leeward side of a mountain range so it gets very little rain.

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  • $\begingroup$ Actually the vertical cliff face is only about 900 m (3000 ft) from the valley floor. The 2300 m figure is the elevation above sea level, but the floor of Yosemite Valley is about 1200 m above sea level: en.wikipedia.org/wiki/Yosemite_Valley $\endgroup$ – jamesqf Aug 7 '15 at 4:57
  • $\begingroup$ @jamesqf thanks for the clarification on heights. I added a second answer that shows the max height a granite cliff can be. $\endgroup$ – Green Aug 7 '15 at 5:45
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There exist in a groups of mesas found in the Guiana Highlands of South America called tepuis (tepuy in spanish). Besides being one of the oldest rock formations in the world, they are exaclty what you're asking for. A mountain, high enough to have its own ecosystem, flat on top for your forrest, and with a sheer drop on the sides

https://en.wikipedia.org/wiki/Tepui

One of the most notorious is Mount Roraima. At 2.800 meters above the sea, it has a a 31 square kilometers summit area bounded on all sides by cliffs rising over 400 meters. Something interesting is that most of the tepui tend to have some form of water, and rains nearly everyday. This constant rains leads to exotic flora, including algae, that evolved to survive with so much water, While the Guiana Highlands, called "gran sabana" by the latin people, its really a ridiculously big Savannah with well, savannahish flora.

Another fun detail is that the tepuis come individually, you don't get a "tepui range", but instead several, isolated mesas. This can help to make your setting extra exotic.

For your setting you could have a desert instead of a savannah, with some tepuis. These tepuis will have lakes and waterfall, with its own misty rain forest ecosystem, and at the base of the tepui you can have an oasis (due the waterfall). I doesn't exist in our world, but there is certainly a great real base for it.

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The Grand Teton Mountains were formed from a vertical uplift at a fault line. From Wikipedia:

The Teton fault is a normal fault. Therefore movement on the fault is primarily in a vertical direction. Movement on the Teton fault occurs on a plane that averages a strike of N10°E and dips 45° to 75° to the east. The 44 mile length of the fault is broken into three segments. These segments may move separately or with other segments. The southern segment extends from the town of Wilson, Wyoming north to Taggart Lake. The middle segment extends from Taggart Lake to the south end of Jackson Lake. The northern segment extends to the north end of Jackson Lake.

The Teton fault is somewhat unique in the amount of movement that has occurred over a relatively short amount of time. The amount of movement on the fault over its lifetime has been estimated to range from about 20,000 to 30,000 feet (6–9 km). Some evidence suggests total displacement on the fault may be as high as 36,000 feet (11 km). The average rate of movement on the fault for the late Quaternary is about 1.3 millimeters per year.

To get your cliff you'd have to make the uplift faster, perhaps as erosion will certainly start eating into your cliff face rapidly.

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  • $\begingroup$ But many vertical cliffs are actually cut by glacial erosion, the classic case being Yosemite. $\endgroup$ – jamesqf Aug 5 '15 at 22:30
  • $\begingroup$ I don't think you can get a really high glacier about this proposed huge vertical cliff to start scouring. $\endgroup$ – Oldcat Aug 5 '15 at 22:45
  • $\begingroup$ But since most of the examples given, which are in that height range, were cut by glaciers, it must be possible. And indeed, the higher your mountain range is to start with, the more likely it is to have glaciers. $\endgroup$ – jamesqf Aug 6 '15 at 17:52
  • $\begingroup$ I'm talking a 30000 foot cliff here. $\endgroup$ – Oldcat Aug 6 '15 at 21:11
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    $\begingroup$ Why? That's 3X what the OP wants. And is probably more than the strength of granite (or any rock) could support under Earth gravity. $\endgroup$ – jamesqf Aug 6 '15 at 21:19

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