# What would happen if a world is full of mountains? How would it affect the geography, environment, and gravity of the planet?

I was thinking of making a world that is filled to the brim with mountains. I'm not saying that the world is just mountains, but the area or terrain is so difficult that it's hard for land vehicles to explore. I don't what else to say since this idea is new to me and I'm having a hard time molding it.

• Your question is too open-ended to be answered. Are there even oceans on this world?
– Mary
May 9, 2022 at 0:37
• Yes there's oceans. I was actually thinking of making the world like a super earth but that's just an idea for now May 9, 2022 at 0:46
• I forgot to add there bodies of water in the world sorry for not providing much information. Again still thinking May 9, 2022 at 1:06
• If your mountains are similar heights as those on Earth (i.e. the peaks are at most a few thousand metres above sea level) then it doesn't matter for your planet's gravity that there are mountains at all. A few thousand metres is less than 0.5% of Earth's radius, so even if your planet is all mountains everywhere, it is still closer to a spheroid than any round object you are likely to see in real life, including billiard balls. If your planet is larger than Earth then it matters even less. May 9, 2022 at 9:45
• I would think the more interesting aspect is what this does culturally. See: Africa or Greece, where geographical barriers helped create cultural isolation and made it nearly impossible for a conquering force to ever sweep through [the Germans managed it in Greece but in the end it was so costly that it represented the end of German paratroopers as a concept]. May 9, 2022 at 14:16

Countries with land areas mainly consisting of mountains like Nepal, Greece, and some other European countries have relatively small and stable and even declining populations. So I get that if the vast majority of the Earth's land surface was made of mountains the global population would be much smaller due to limits in agriculture. It is much harder to make crops grow in an irregular terrain than it is on the plains. Transportation would be also harder because it is harder to build roads and rails in mountains.

• It would be worth adding something about terraces and the Inca Empire, since these are so closely linked to mountains. Who can think of mountain civilizations and not think of Machu Picchu? May 9, 2022 at 3:19
• Maybe you would have more diversity of species since there would be less mobility of animals. For people, maybe more diversity of languages for the same reason with villages in some areas being more isolated. Probably trade and travel depending on the time of year when mountain passes are open when the weather is good. May 9, 2022 at 5:44
• What are these "litits" of which you speak? They sound itchy. May 9, 2022 at 6:14
• Countries that are mainly mountains also includes Japan. More than 16667 mountains, starting at 4.5 meters and ending at 3776 meters, these make up more than 80% of the country.. That minuscle 4 meter mountain was manmade and started as a 20 meter dump from a river excavation btw. May 9, 2022 at 8:54
• @Trish: Counting any elevation higher than four meters a mountain is a bit silly, though. Wikipedia has a convenient "List of countries by average elevation", and while the list shows only averages and no dispersion, I think it's rather obvious that there were hardly any countries in the world not at least half-way covered with mountains if the 4-meter metric was applied. May 9, 2022 at 9:09

I'd start by thinking about how those mountains would form. As far as I know, plate tectonics (in the long term) and volcanic activity (in the not-quite-that-long term) are mainly responsible for mountains to build up.

To get more mountains than we have on earth, I'd say your planets crust would need to be rather thin (compared to earth), so that tectonic pressure would more readily fold the plates instead of pushing one plate on top of the other. A thinner crust would also increase volcanic activity, further increasing the chance of mountains building up. Add enough water and you've got continents of mountainous islands and island chains (where tectonic plates are pushed together) paired with oceans full of underwater volcanoes (where tectonic plates move away from each other). I'd assume that you'll get a whole lot of tsunamis on that planet.

(I'm the wrong person to answer anything about hard science on this topic, though.)

• You get mountains anywhere two plates move towards each other (see the Cascade, Sierra Nevada, and Andes ranges, where the thin Pacific plate is sliding underneath the thick North American and South American plates). Thickness of plate has little to no effect on the process.
– Mark
May 10, 2022 at 1:11
• @Mark So you're saying that smaller tectonic plates would reduce flat land and increase mountain forming? May 10, 2022 at 8:52
• It would certainly increase mountain formation. I don't know what it would do to the amount of flat land -- smaller plates might tend to erase old mountains through tectonics rather than leave them around to erode.
– Mark
May 18, 2022 at 23:29

Lots of thoughts in no particular order

If you're thinking of a super Earth, your mountains will be relatively small. A bigger planet will have more gravity that will cause taller peaks to be unstable and collapse (landslides). Smaller planets have relatively larger mountains. For example, Olympus Mons on Mars is 15 miles tall and the Mountain ring on Iapetus is as tall as 10 or 12 miles. By comparison, Mauna Loa on Earth is only 6 miles tall. If you look at the list of tallest mountains in the solar system, the bigger ones tend to be on the smallest planets. Of course erosion also plays a part. Other bodies with bigger mountains tend to not have an atmosphere to cause erosion.

I don't have a link or a good source to cite, but it seems to me that most mountain forming processes would be enhanced by a thinner crust and/or increased volcanic activity. Maybe you can have a young planet that hasn't cooled enough to have a thick crust. Then put it through a period of heavy meteoric bombardment that shattered the crust. This would result in higher amounts of vulcanism so you get "extra" mountains and lots of impassable terrain from normal subduction/delamination, impact craters and volcanos. I'm not sure what that does to the atmosphere though. Is it a cool climate because of nuclear winter? Is it a hot humid climate because of vulcanism? How do the seas fair with all the extra volcanic activity? I don't think you'd get run away global warming since these aren't greenhouse gas clouds? Need someone smarter than me to answer those questions.

imtaar has a good point about the balancing of the planet. Earth has a wobble and it was made worse by all the dams built in the northern hemisphere. Crazy to think that humans managed to affect the rotation of a planet! But depending the methods you use to get your mountains, you may have to account for some crazy axial procession. Imagine what our planet would be like if the poles of the planet drifted by several feet or even miles per year. GPS would need monthly or daily updates to account for the ground not being where it was yesterday. Astronomical charts from just a few decades ago would be nearly useless. Tropical years could be days shorter than the astronomical year which would mess with planting days.

• So in a super earth, mountains are relatively smaller, would that make traversability a bit easy or harder. Also if gravity is stronger, how would aircrafts work, would it be harder than land vehicles or easy? May 9, 2022 at 23:10
• @IseedeadpeopleNOT - Traversability is going to depend on the mode of transportation, not the relative size of the mountain to the planet. 5 foot "cliffs" are impassable to a car but not a tank. 50 cliffs are impassable to all but climbers/flyers. And flying is more dependent on atmospheric density than gravity, and atmospheric density is very dependent on atmospheric composition: eg Venus has same gravity as Earth but 93 times thicker atmosphere. Ideal would be low gravity planet with a thick CO2 atmosphere. Not ideal would be heavy planet with hydrogen atmosphere.
– Tim
May 10, 2022 at 15:08

How would it affect the geography, environment, and gravity of the planet?

Geography: There would be loads of mountains. Mountains are part of geography. Source.

Environment: See above. More mountains.

Gravity: Depends only on the total size of the planet. Mountains don't make much of a difference. Source.

• What happens if it's a big planet. Like four or five times the size of earth? May 9, 2022 at 4:22
• If the Earth was 5 times bigger the gravity would be about twice as strong. May 9, 2022 at 5:26
• @IseedeadpeopleNOT The general rule is that if you replace Earth with a copy $R$ times bigger, you multiply the gravity by a factor of $\sqrt[3] R$. So five times bigger gives $\sqrt[3] 5 \cong 1.71 \cong 2$ times more gravity. May 9, 2022 at 13:02
• @Tim the mountains are so small to begin with relative to the planet, you're only going from say 0.0001% extra gravity due to mountains to 0.00003%. Note: I pulled these numbers out of my ass. May 9, 2022 at 15:47
• @IseedeadpeopleNOT additionally the higher the gravity the smaller the angle of repose will be. that is on low gravity world, mountains can be steeper then earth. On a 10g world mountains will comparatively flat. May 9, 2022 at 18:10

When the tyre of a car is balanced, certain weights are attached at certain places on the rim so that there are no vibrations when the tire is spinning at high speed.

Over millions of years, the mountains and other geography is set in such a way that earth rotates in a balanced way. If you suddenly place large mountains randomly, this could unbalance the rotation of earth.

In your world, you cannot place mountains in an artificial way. Let them be formed through natural processes.

EDIT

• Mountain roots act like pegs embedded in the ground and they work as stabilizers for the earth.
• Mountains take part in isostasy, a concept of the gravitational equilibrium that explains the balance of topographical undulations on the Earth’s surface.
• Mountains help our climate stay relatively stable in between catastrophes.

As told here:

The book "Earth" by Professor Emeritus Frank Press , is a basic reference book in many universities . The book says that mountains have underlying roots. These roots are deeply embedded in the ground, thus, mountains have a shape like a "peg".

Dr. Press explains that Mountains play an important role in stabilizing the crust of the earth. They interfere with the shaking of the earth. The modern theory of plate tectonics also states that mountains work as stabilizers for the earth.

As told here:

Isostasy, ideal theoretical balance of all large portions of Earth’s lithosphere as though they were floating on the denser underlying layer, the asthenosphere, a section of the upper mantle composed of weak, plastic rock that is about 110 km (70 miles) below the surface.

This means that an excess of mass seen as material above sea level, as in a mountain system, is due to a deficit of mass, or low-density roots, below sea level.

As told here:

Isostasy (Greek, isos: equal, stasis: standstill) in earth science is used as a concept of the gravitational equilibrium that explains the balance of topographical undulations on the Earth’s surface. The need to achieve natural balance or isostasy takes place on Earth wherever a large amount of weight is present. This weight might be due to a large mountain, ice from an ice age or even from human structures such as the weight from large man made lakes

As told here and here:.

The mountains can reduce the power of quakes but also send them to certain places, making them more powerful than expected.

As told here:

Mountain thermostats: scientists discover surprising climate stabilizer that may be key to the longevity of life on Earth.

• Mountains are small compared to the overall size of the Earth, and have no significant effect on balance.
– Mark
May 10, 2022 at 1:12
• Tyres spin fast and have a fixed axis, that's why they need to be balanced. This analogy doesn't work on an object where the center of mass (and the rotational axis) just follows the weight distribution. May 10, 2022 at 20:51
• @imtaar, it's an "opinion" that 8.8 km is much smaller than 12,600 km, or that 800,000,000,000,000 kg is much less than 5,900,000,000,000,000,000,000,000 kg? I suppose gravity is "only a theory", as well?
– Mark
May 10, 2022 at 22:04
• @imtaar, many ways, yes, but not rotational stability.
– Mark
May 16, 2022 at 21:40
• @imtaar None of the above.
– Mark
May 18, 2022 at 23:11