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In the story I'm writing, there is a city located entirely underground in a complex network of artificial and nature tunnels and chambers under and inside of a mineral-rich mountain range. An important part about their society is that they are very xenophobic and try to interact with the surface as little as possible. I need to know if they would actually be self-sufficient and if they're not, what can be done to make them self-sufficient.

Currently, the city lives off a subterranean river, which starts near the top of the mountain and pours into a sinkhole and exits another hole in a sheer cliff. The river provides drinking water and small amounts of hydroelectric power. The sinkhole also provides the main ventilation shaft. Using hydroelectric power they are able to run dim lights, simple electric stoves, and large fans to ensure proper airflow.

Grain and similar foods are grown in large chambers equipped with a system of mirrors that reflect sunlight onto crops. The people supplement their diet with mushrooms that grow on the banks of the river, large moles that they farm, rats, and sometimes insects that live in the caves. Any organic waste is used for compost.

The houses are simply carved out of the walls. The metal needed to maintain the machines and farms is gathered from the rich veins of various ores surrounding the city. The mineshafts can later be turned into additional living space once the ore runs out. Using furnaces fueled with animal fat and bellows, metals (mostly iron, aluminium and copper) are smelted or recycled to be used for the various fixtures in the city.

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  • $\begingroup$ Each individual thing could be justified, but each one is expensive in the amount of resources and effort that would need to be put into it to make it work. I think there would be simply too high a cost to do this. One economic disruption and the whole house of cards falls. It's one of the reasons people living in bunkers for centuries is unlikely to work without massive starting stockpiles of resources. $\endgroup$
    – DWKraus
    Commented Jul 19, 2021 at 6:18
  • $\begingroup$ Problems of the setting - too little energy, too much connection to surface (mirrors will take more space than a regular crop fields for the number of people - or they will die, as mushrooms they do grow by decomposing organic matter and it will deplete, so as other mentiont life are also consuments) , not enough energy for recycling - in essence they will fail on the goal or won't be so isolated and protected. $\endgroup$
    – MolbOrg
    Commented Jul 19, 2021 at 6:22
  • $\begingroup$ How bigs the sinkhole? If it's really big you might be ok - a 50 meter diameter hole gives 2.6Mw of power, going off some NASA research of growing wheat in low-light environments; (adsabs.harvard.edu/full/1985lbsa.conf..635S), that's enough to grow enough wheat to just feed 402 people. $\endgroup$
    – Ash
    Commented Jul 19, 2021 at 7:10
  • $\begingroup$ A "Subterranean river" can be inconstant. It may rise (drowning the village) or fall unexpectedly due to unexpected events downstream. The above-ground portion may freeze in winter, or dry up in summer, or be dammed by neighbors. If that river emerges from the ground again, downstream neighbors may not be amused by the sewage, trash, and occasional corpses in their water supply. $\endgroup$
    – user535733
    Commented Jul 19, 2021 at 11:23
  • $\begingroup$ This question is exactly what Dwarf Fortress game is about. This city is destined to fail, and how exactly it will fail is where all the fun is. $\endgroup$
    – void_ptr
    Commented Jul 20, 2021 at 3:41

2 Answers 2

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Something sounds off.

For example, despite on paper fat having an energy density of 37 MJ/kg, as compared with the 24 MJ/kg supplied by coal, having enough fat to cover the iron demand of a city requires a huge amount of livestock to be grown and fed. Moreover aluminum is not smelted in fire powered furnaces, but it's smelted in electricity using furnaces.

Also, to grow crops by casting mirror reflected sunlight on them, you would need a capturing area about as large as the crop cultivated area. If you are cultivating 10000 square meters of crop, you would need to capture the light falling on a 10000 square meter surface, which is a square 100 x 100 meters. This is all but an hidden project.

If you want to make things realistic, you should resort to using electricity powered solar lamps and having a large energy production unit, either a nuclear plant or something using geothermal heat.

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You can have a Isolationist City, but the resources needed depends in the demands of the population and how many people live in it and the tech available.

Remember that the larger the city, the more people dedicated to support services you need, example Healthcare/entertainment/law enforcers/emergency services/Maintenance/Administration/Education/Defense. This type of work consumes resources constantly and from different types.

Solution: I would recommend to create a group of citizens that is in charge of deals with trade caravans, exploration and gathering. As a society you can label them as xenophobic, but like in any place there is always a group of misfits.

Food:

Fish pools.- You need farms of Cavefish, with a stable current of water this isn't hard to achieve and they are reliable product of protein.

Mushroom Farms.- Just like ants, you collect organic material and set the perfect place for them to grow.

Algae Farm.- The same pools used for the fish can be use to maintain a healthy Algae farm.

Salt.- Can be obtained from the walls of some part of the cave without too much issue.

Insect Boxes.- They are a great source of protein and requiere little control and time to reach maturity.

Energy:

Geothermal.- Could work better as a source of energy for the setting.

Trade Items: Precious stones, gold and silver are something that your society could have in abundance and trade with it, while cloth/wood/feathers would be a symbool of status and wealth.

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