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A large igneous province is a very large area that has been covered in igneous stone due to some catastrophically large volcanic even or something similar.

In my story, a large, futuristic, city has been built in the middle of an igneous sheet due to it being a rich mine of thorium and other valuable minerals. I image the igneous plains still being fairly young (only a million years or so), and thus more or less smooth instead of mountainous.

With a population this large on a not-very-arable landmass, what would their diet be like? The technology level for this society is interstellar, but there's no teleportation or any mode of instantaneous travel to go to a more fertile continent or planet. If they wanted to have at least a somewhat self-sustaining city, what could they do to get food and what kind of food would be the most efficient for them?

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    $\begingroup$ just fyi, volcanic rock actually makes for some very fertile soil. a few million years is plenty of time to convert exposed volcanic rock into soil. if you want it to be infertile you need to make it arid as well (even then the soil will be amazing in a greenhouse) $\endgroup$ – John Sep 23 '17 at 20:55
  • $\begingroup$ Think of Hawaii. $\endgroup$ – pojo-guy Sep 23 '17 at 22:23
  • $\begingroup$ @John Only if there are enough of certain elements in the volcanic material in the first place, 70,000 years has not been enough to form a fertile soil on the Oruanui Tephra, and because it has no Cobalt it can only be farmed by addition of imported trace elements. $\endgroup$ – Ash Oct 4 '17 at 11:52
  • $\begingroup$ @Ash but the sediment is already being define as mineral rich, Taupo sediment are not rich in anything but silica. $\endgroup$ – John Oct 4 '17 at 13:57
  • $\begingroup$ @John And Iron, Manganese and Aluminium from Biotite, as well as Sodium, Potassium, Lithium, Calcium all the Felspathic elements, there's Magnesium there too. It makes good soil for a number of plants just not exotic crops or animals. There's also the fact that "minerals" are NOT trace elements, they're not even bulk elements; they are crystalline compounds that the planets native lifeforms may or may not have the biological equipment to break down. Without particular elements the primary regolith may be uninhabitable to lifeforms that can access the elements that are there. $\endgroup$ – Ash Oct 4 '17 at 14:13
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Assuming that the planet was approximately earth like and the only problem was the solid rock surface, I imagine a society capable of interstellar travel would be able to subsist there if necessary, but with some provisos. The only real questions being how long do they need to stay, how much supply do they bring with them and how often can they get resupplied from external sources when they are there?

If they have to live off of the land for an extended period without resupply it would be very difficult, but perhaps not impossible. Assuming large quantities of power are available such as nuclear or similar the air could be “mined” to extract water and carbon dioxide. These could be chemically processed to produce all manner of organic materials given sufficient time, energy and equipment. Similarly atmospheric Nitrogen could be processed into nitrate fertilizer. The igneous rock itself or some of the spoil from mining (in non-radioactive areas) could be ground into a grit to act as a medium suitable for hydroponic agriculture.

Potassium could probably be extracted from the rock and converted to a useable form but phosphorous would likely be in very short supply and would have to be brought in as initial supplies would eventually be depleted even with strict recycling.

The exact details would depend on the circumstances as outlined by my questions in the first paragraph. Perhaps they can fly some (dried?) food in but the majority of the food would have to be grown hydroponically. In later years soils would develop and the range of the food available would increase.

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Layer gardening.

If the settlement is in the middle of a flat sheet of rock, or even has a very thin, potentially nutrient poor soil layer on top, it would be difficult to grow crops conventionally. But layer gardening is actually the answer to such a problem in our world, as it requires no digging (granted it's usually less sheet-of-rock and more layer of asphalt or concrete here, but the principles remain).

So, to make it work... the principle is to layer organic waste on top of the rock, wet it down and let it rot for a bit, and then plant seeds in the soil that creates. The organic matter will compost, helped by the plants growing, and so by the end of the year one should have turned the layer of organic waste into a layer of composted soil. This can be layered on top of in successive years for a deeper garden. Depending on weather, geography, and crops being grown, it may make sense to build raised beds which take more soil per area but hold the soil deeper for plants with longer roots, or to spread it out for more surface area for plants with shallower roots - or even a mix.

A city produces a fair amount of organic waste - food scraps and sewage, but also things like paper or cardboard, scraps of cloth or rope (well, not plastics, biodegradable), building materials like wood, and even inert materials like stone or concrete, pulverized into a sand-like stuff, can add extra depth and/or minerals. It helps to layer different kinds of waste, green leaf clippings vs paper or twigs vs manure, to ensure a good mix of nutrients.

Composting the safer materials, food scraps and paper, garden waste, cloth, etc can be grown on pretty quick - maybe a few weeks. Other materials, like sewage, may be a health hazard when fresh - though composting for some time (a year or so for human waste, I heard) should leave it relatively safe to use as soil or fertilizer.

So, the city may have to live off of stored or imported food for a few years at the beginning (depending on how much organic waste they have on hand), but each year they could dump the waste out to compost, someplace far enough to keep the smell and health risks at bay and close enough to work once it's composted, and go back a year later to garden the new soil.

The advantages are the new compost should be pretty rich, and the organic waste is not only constantly produced, but something they would have to deal with anyway. Each year they would expand their fields or deepen the soil till they have enough arable land for the city to be self-sufficient. And even if it took years to reach that point, well, each year they will have more arable soil and thus will need less imported, finding alternate sources of food and ways to get rid of the waste had to be planned anyway, so it doesn't cost them much effort and the long term gains will be sizable.

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  • $\begingroup$ In the west of Ireland they do this using seaweed. irishtimes.com/life-and-style/homes-and-property/2.770/… $\endgroup$ – Willk Mar 17 '19 at 13:27
  • $\begingroup$ @Willk - that is so cool, it's nice to see it done on a larger scale than the small project-plots I saw when researching. Though with freshly harvested seaweed, I wonder if there's ever a problem with salt concentration...hmm... (plotting and planning) $\endgroup$ – Megha Mar 17 '19 at 22:38
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Greenhouses. There's no need for a lot of soil, only a bit to hold plant roots (and some species don't even need that). Nutrients are provided by watering. You need some fairly decent recycling of waste streams, but not nearly what you need for a spaceship.

Obviously a vegetarian diet keeps the need for food down, but you can have meat as a luxury. Pigs and chicken can live off some vegetable waste. Coconuts and the like would be missing. Trees won't fit!

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The precedent here is large groups of people from advanced Western civilizations who live on not-very arable land to mine petrochemicals: for example in West Texas, or the Canadian oil shales, or Alaska.

They import food.

A society which is technologically sophisticated enough to want petrochemicals, or thorium, does not need mine workers to farm their own food locally. The miners will be supplied by the far-reaching economic interests who benefit from their labor at the site. Persons working these jobs will want foods similar to those from the cultures they are originally from: English want bread, Chinese want rice, etc. These things will be trucked, shipped or flown in to the site.

This is true for any advanced society with inhabited places unsuitable for agriculture - for example Phoenix.

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High-Tech Farming

Any society that can travel between stars should know how to produce food in closed environments with limited resources. Its ability to sustain itself depends on energy and technology rather than land, surface water, and climate.

Your city can use greenhouses, aeroponics, hydroponics, and labs for growing plant-based food. They are more energy intensive than open-air farming, but the yields are higher, water and soil requirements are lower, and farmers have much more control over the process.

Meat can be grown in lab vats (literally). Other sources of fat and protein may include algae, insects, fish. None of them requires much space or water.

In other words, the city can easily have an abundance of food. And its diet will meet the highest nutritional standards. I think there can be a small problem of the variety of raw ingredients (it is harder to grow fruits in greenhouses). However, if you look at what we eat in developed countries you would notice the same problem. As agriculture becomes more industrialised, monocropping becomes more persistent.

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If they're in a position to build a city in the province in the first place then they had to supply the workforce that did it, without any local supplies. So the city must by definition have access to bulk food imports at a sustainable price, most forms of high-tech farming that might be used to green a natural wasteland will likely be cost prohibitive. They'll share the same diet as the rest of the world with the exception of highly perishable foods and with an emphasis on processed goods rather than raw ingredients.

Now this import dependency can be a recipe for unrest, or even outright disaster, depending on the balance of payments. If the mining outpost has to spend too much on food imports compared to what they're taking out of the ground then the situation is unsustainable and as the saying goes "no society is more than three meals from revolution". If on the other hand the mines make money hand over fist then this is not an issue.

You've said "futuristic city" this could mean that the outpost consists of a single, reasonably small, Arcology in which case the city in fact grows all it's own food in what amount to giant greenhouses that are fully integrated into the fabric and structure of the city and form a vital part of it's sewers and the air-conditioning system as well. In this case they eat whatever they like since Arcologies can control the climate within their integrated farmland to grow anything they want any time of the year.

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