I have a post-apocalyptic setting where the vast majority of humanity died off a few generations ago and the remnants were rounded up and placed on the island of Oahu, which has been made into a wildlife preserve. Packages of supplies and weapons are dropped off occasionally, to provide for basic needs, as well as entertainment and self-regulated population control.

Given that several generations have passed since the mass die-off, the modern infrastructure of Oahu has likely deteriorated substantially. What would the cities on Oahu be like after a hundred years or so without maintenance, likely also subject to substantial scavenging?

Regarding amount of maintenance from the remnant population, my current concept is that the population is quite small (maybe a few hundred people), so there's only so much time/labor to go around for repairs, even if everyone were inclined to cooperate.

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    $\begingroup$ Who is dropping off supplies, and where are they coming from? $\endgroup$ – user1975 Feb 21 '17 at 18:46
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    $\begingroup$ @Snowman, the inhabitants aren't really sure, but they probably had something to do with the apocalypse. They're never seen directly and don't interfere aside from providing supplies, excepting an occasional orbital bombardment to destroy any attempt at building a way to leave the island. $\endgroup$ – Dan Bryant Feb 21 '17 at 18:55
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    $\begingroup$ Check out the book The World Without Us by Alan Weisman from your nearest library. If they don't have it, make them get it. $\endgroup$ – a CVn Feb 21 '17 at 20:45
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    $\begingroup$ Pripyat has been unmaintained for 30 years. A few thousand people refused to leave the broader exclusion zone. You could extrapolate from that. $\endgroup$ – RedGrittyBrick Feb 21 '17 at 22:02
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    $\begingroup$ Possible duplicate of What happens to an empty, modern city? $\endgroup$ – cobaltduck Feb 22 '17 at 13:27

A quick google search tells me that the size of the island is 597 sq miles. That makes it a large island. Now let us concentrate on your question.

The first thing that would happen after the apocalypse is that the service stations would cease working. That is to say, the electric power station(s) and phone system would stop working within a few weeks of the disaster.

Scavenging for foodstuffs and other supplies would mean that the malls and stores would be the first to suffer. Humans have an inexplicable urge to stock up on supplies even when there is no need for them.

Considering that the small population of few hundred people cannot maintain the sewerage and drainage system of whole cities, the drainage pipes and sewers would get clogged within a decade and become dysfunctional. This means that during and after the rainy season, the streets would have knee-deep water in them for weeks.

The standing water will also gradually weaken the base of buildings through moisture. Moss and lichen would start growing on the walls within a few years and creepers would take root wherever any hint of soil is present within wall creeks and roofs.

Grasses will start growing on the edges of roads and pavements within a few years, followed by small shrubs.

The grasses and shrubs, combined with annual heavy rains and lack of repair, will gradually begin to damage the roads. The tarmac will begin to tear off, exposing the filling below. As the tarmac tears off, more grasses and shrubs will take hold, accelerating the process.

Unattended wooden houses would be the first to break apart and be ruined. Considering the warm, moist climate, I think most houses will start getting soggy within a few years and be ruined within a decade.

Concrete buildings and skyscrapers, with their very sturdy metallic skeletons and weather proof paints, will resist the longest. Initially, the paint layer would peel off (in a decade) and then the cement and building blocks would start falling here and there. After about seven decades or so, mostly the metallic structure would be left standing, with parts of concrete and building blocks attached here and there. Note that this would happen to the outside walls of the skyscrapers. The roofs would begin caving in after about five or six decades (a guess, based on the composition of materials used in roof construction and climatic conditions of the island). So after a decade, you would find the exterior of most multi-storey buildings softened up with metal core showing here and there. The inner parts would be mostly intact, but with fungi and mushrooms growing in all moist places.

While the electric and phone services would have long since stopped, the poles and cables would still be present at places, even after 100 years. They will be extremely rusty and weak, but it will take somewhat more than a century to completely rust away the rust-resistant poles and cables.

If zoo cages are opened after the apocalypse, you would find many types of animals thriving on the island. This would include herbivores like deer, rabbits and small bison/buffalo herds and carnivores like leopards, wolves and alligators.

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    $\begingroup$ I don't think the urge is that inexplicable ... $\endgroup$ – Azor Ahai Feb 22 '17 at 7:25
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    $\begingroup$ Hah. In reality they aren't. But in the fictional world, they could be :p @martin $\endgroup$ – Youstay Igo Feb 22 '17 at 14:23
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    $\begingroup$ Reinforced concrete does not last very well if not in a maintained building, and can fail spectacularly due to the high tension steel; I think you are over-estimating the survival of modern skyscrapers once they're no longer maintained with heating and air conditioning. Brick built buildings which last much longer and if there are any stone buildings they will last even better. $\endgroup$ – Jack Aidley Feb 22 '17 at 14:36
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    $\begingroup$ Now that I think about it, I am obliged to agree with you. Indeed, metallic parts in the skyscrapers would expand and contract in summer and winter, gradually weakening the structure down. However, considering that Hawaii does not get intense summer or winter, the wear and tear due to temperature fluctuation would be very little. @JackAidley $\endgroup$ – Youstay Igo Feb 22 '17 at 15:57
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    $\begingroup$ But you aren't completely wrong either. Rainwater + sunlight + lack of maintenance would tear down the weather resistant paint within a decade, after which the environmental moisture and moss would weaken the building blocks pretty quickly. My initial estimates about the resilience of skyscrapers might be wrong by a decade or two @JackAidley $\endgroup$ – Youstay Igo Feb 22 '17 at 17:18

There have been television programs on that which provide a better answer than we could, in most regards, e.g. Life After People. The exception is the scavenging angle.

  • The survivors would be interested in maintaining buildings. Perhaps they scavenge materials from some to repair others. A house can last quite a long time if the roof is patched from time to time.
  • Oahu means not much worry about heating, and people can live without air conditioning. So they'd stay in the cities even without power.
  • $\begingroup$ I agree that survivors would be interested in maintaining the buildings... but he asked about what happens if there is neglect to that so I took it literally. I would imagine if this actually happened, the people remaining would do what they can to maintain the basics but for arguments sake, I took the extreme approach on a neglected city. $\endgroup$ – ggiaquin16 Feb 21 '17 at 16:43
  • $\begingroup$ @ggiaquin, in that case take the first sentence of my answer. $\endgroup$ – o.m. Feb 21 '17 at 18:18
  • $\begingroup$ oh don't get me wrong, I am not critiquing you at all XD I am just saying I liked what you said but I approached from a different view. $\endgroup$ – ggiaquin16 Feb 21 '17 at 18:19
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    $\begingroup$ I can't imagine they'd actually stay in the city if there are no services.There's no way a random cross-section of people is going to be able to maintain a modern electrical grid. Without electricity, you're not going to have pumps for water and sewer services, or refrigeration for food. Basically, you're going to be reduced to an 1850s level of technology. I think everyone would move out into the country where water and land will be available. $\endgroup$ – TMN Feb 21 '17 at 19:24
  • $\begingroup$ Without sewers and garbage services you neighbors will produce an anwful amount of waste making living in the place disgusting and unhealth. You really don't want to crowd in that situation $\endgroup$ – jean Feb 23 '17 at 13:13

Gunkanjima is a city-island that has been abandoned for 43 years. It is exposed to severe weather, which "accelerates" degradation time, so this island is very similar to the island you describe in your question.

It was built with very modern techniques for the time, in particular Japan's first large reinforced concrete building was built there in 1916. That means Gunkanjima is not so different from today's cities.

It also has everything a city would have: apartments, schools, water and electricity system, public baths, industry, etc.

I visited the island, and here are some findings:

  • Some buildings are in ruins, but others are well-preserved.
  • As far as there are no holes in the roof, it seems like building do not deteriorate much even after a long time. You get mold, and wall papers fall off, but no plants start growing inside, even in the humid climate. In particular, the 1916 building still seems almost livable after 100 years.
  • External elements like entrance stairs are devastated, probably due to being in the rain often. Steel cores are rust and concrete is broken.
  • Electricity machinery (like transformers) are totally rusted. Almost all electricity poles are bent. Expect balls of electricity cables here and there.
  • Vegetation is found at ground levels, but not that much on concrete areas. Think of how vegetation often does not grow on wide rocks depending on wind and sun exposure. Multi-storey buildings are certainly not "overgrown" by vegetation.
  • Obviously, there are no public services.

You can have a look by yourself using Google Street View, they even have the inside of some buildings.

The bigger buildings with solid roofs will probably offer the best living conditions for your survivors, and will most probably remain semi-livable (but without public services) for more than a century.

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The interesting thing about doing this on Oahu is that preindustrial people lived there for centuries. Today, the methods those people used to build their structures and farm the land have been preserved out of cultural pride as well as tourist attractions. I think it would be a lot easier for postapocalyptic Hawaiians to revert back to stone age ways than it would be for, say, the Swiss.

100 years later in Oahu people will be living like the old Hawaiians did, probably in the same places and with the same sort of building and agriculture. One of the nicer post-apocalyptic scenarios I have ever heard of!

The other thing about the cities - Hawaii has a big storm every few decades and after the second one Honolulu would be toast. By 100 years it would be a mixed forest of native and nonnative species like the rest of Hawaii. Low hills would mark the sites of former buildings, like the Maya sites in the Yucatan.

Escaped panda bears and gorillas would be nice additions to this land. There is plenty of bamboo for the pandas and lots of wild fruit for the gorillas.

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    $\begingroup$ +1 for noting the very recent pre-industrial history in Hawaii, and the potential impact of storms. I'm not sure that exotic species will be a net gain, however; on an island, there's a pretty big danger that nonnative species will quickly out-compete and overwhelm native species. $\endgroup$ – 1006a Feb 21 '17 at 23:02
  • $\begingroup$ There are ruins in hawaii, sugar mills for instance. thumbs.dreamstime.com/z/… $\endgroup$ – John Feb 22 '17 at 21:09
  • $\begingroup$ Sadly the honolulu has neither panda, nor gorilla. they do hoaz orangutan and tigers honoluluzoo.org/animals/zoo-mammals.html $\endgroup$ – John Feb 22 '17 at 21:12

There are different types of neglect. What we should consider is the size of remaining population, its ability to perform the maintenance and location.

Your population (few hundred people) is way too small to maintain infrastructure on the entire island of Oahu. They can, however, live nicely in one of the smaller villages.

The ability to do the maintenance is not very clear. What kind of supplies will be dropped? Scavenging can only go so far, and without fresh supply of appropriate materials, keeping even a few buildings and roads up do date would be problematic. Your people would have to improvise, like, "What can we do when we run out of bags of fresh cement?" Overall, they should be able to manufacture suitable replacements for most building materials, if they have a will to do it.

Location of your site will determine the speed of deterioration (or natural restoration, if we like to call it so). Hawaii would be a very intense place for man-built structures to last. While in some dry climates I would expect buildings to last for centuries, on Oahu natural erosion and plant growth should consume Honolulu within decades. After two centuries, some skyscrapers would still stand, some would collapse, and ruins would be overgrown with plants. I don't think this is where your people would like to live.

Additional factor that concerns me is social organization of your colony. You have mentioned that among the dropped supplies there will be weapons. Why would a small community on Oahu need any weapons? I imagine there would be perpetual infighting, which would keep the population down from what it could be and affect the amount of maintenance that could be done otherwise.

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    $\begingroup$ Yeah, regarding weapons, it's possible that whoever is providing the supplies has a warped sense of what it means to 'preserve' wildlife and might be running some sociological experiments. A lot of that is yet to be defined, as this is a possible campaign setting for an Apocalypse World tabletop roleplaying game. $\endgroup$ – Dan Bryant Feb 21 '17 at 18:50
  • $\begingroup$ Most of the islands power comes from oil or coal plants so they will run out of fuel very quickly. maintenance is not a problem if there is no fuel to run the plants. The only other power plant burns garbage which they will also run out of. $\endgroup$ – John Feb 21 '17 at 20:03
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    $\begingroup$ @John Today, Oahu has more than enough solar panels for the need of a few hundred people. $\endgroup$ – Alexander Feb 21 '17 at 20:12
  • $\begingroup$ Solar panels only last a few decades and they have no way to replace them so they will not matter much. $\endgroup$ – John Feb 21 '17 at 20:50
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    $\begingroup$ @John, photovoltaic panels will degrade after a few decades, but should not shot down to 0% efficiency, at least not most of them. Also, there are wind power turbines too. $\endgroup$ – Alexander Feb 21 '17 at 21:07

Well this all depends on HOW much lack of maintenance you are referring to. Roadways would more than likely be chewed up within 10-20 years. Concrete highways have a potential life span of 30 years before needing to be repaved. Alternative means for transportation would revert to either walking, biking, or a carriage/animal of some form. Assuming an extreme lack of maintenance, the island wouldn't be getting any gas. If they do, it is in very small quantities that will need to be rationed off and used for generators and other more critical life support features than vehicles.

Buildings will more likely than not be overgrown by plantation and depending on how poorly they were built, may even have parts of it collapsed at this point. While the pipes underground may be able to last 100 years (assuming they were freshly placed shortly before the catastrophe) they won't be in good enough conditions to trust them for water. This again assuming that the generators and pressure systems that governs the pipes stop working. Water will have to be drawn from rivers, lakes, oceans just like we did without plumbing or create basic irrigation canals that can use gravity to transport water.

It would be unlivable in the way we know current life. Electricity would be minimal and spotty. Cell phone service will be non existent. TV would be gone. MAYBE radio but it would be doubtful. Walkie talkies would probably be the most common form of communication (assuming batteries are a part of the care package). Essentially, you would have to revert life back to life without any modern comforts. The buildings would be livable enough but everything would virtually have to be done by hand. Cleaning of clothing, getting water, food. Candle light for night time unless provided solar powered flashlights (which there is such a thing, I have 2 myself).

Again, I am imagining an extreme example of neglect as I am not sure how much neglect you are referring to but I would imagine that things would be super run down and life would be reduced to that of the pre-industrial era. You also asked about looting which yes, stores and valuable goods would be cleaned within a year or 2.

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    $\begingroup$ How long would roads last without cars to wear them down? $\endgroup$ – o.m. Feb 21 '17 at 18:18
  • $\begingroup$ hmmm that is a pretty valid point.... I didn't think about it from that angle. I would imagine it would become over grown and covered with debris anyways because there wont be any street cleaners coming around. So nature may make it not usable before the actual decay of the road. $\endgroup$ – ggiaquin16 Feb 21 '17 at 18:20
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    $\begingroup$ only a few decades, thermal expansion are more devastating to asphalt than cars unless they have very heavy traffic. the lack of freezing temperatures will help but only so much. $\endgroup$ – John Feb 21 '17 at 20:06
  • $\begingroup$ @o.m., depends on many factors. One road I know of was abandoned in the late 1940s and would be perfectly driveable if you sent a bulldozer along to clear off the built-up dirt first. Another was closed to vehicle traffic sometime between 1954 and 1981, and retains just enough asphalt to make it clear it was originally a paved road, not a dirt one. $\endgroup$ – Mark Feb 21 '17 at 23:03
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    $\begingroup$ Pipes can actually last a very long time depending on material. there are wooden pipes under new york that are more than a hundred years old. polymer lined pipes can be expected to last for several hundred years. $\endgroup$ – John Feb 22 '17 at 21:06

You can look at photos of places like Chernobyl, Fukushima etc for a sense of how nature would take over (though not quite 100 years, and not Oahu).

Chernobyl: Chernobyl & Pripyat

Fukushima: Guy Sneaks Into The Fukushima Exclusion Zone, Posts Never-Before-Seen Pics Of Town Untouched Since 2011

Other abandoned places: 21 Photos Of Nature Winning The Battle Against Civilization

  • $\begingroup$ Welcome to Worldbuilding. I understand how frustrating it is not to be able to post a comment - that's exactly how I started out, too. But it doesn't take that long to earn the priviliege to comment; it's only 50 reputation points, which is five up-votes on answers you write or ten on questions you write. Hang around and you will see. The reason for this delay is so that you get used to how the site works gradually. This comment is not that far from an answer, if you flesh it out a bit then it would easily pass as one. $\endgroup$ – Mrkvička Feb 22 '17 at 6:46
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    $\begingroup$ Yes, why not flesh it out into a proper answer? $\endgroup$ – JDługosz Feb 22 '17 at 7:42

I'm surprised no one has mentioned the challenges/consequences of fire. Even if no electrical fires were started before power failed, and most accelerants were pillaged, they'd struggle to identify and contain fires.

Hawaii does possibly benefit from possibly reduced lightning levels and from being fairly moist. But any urban fire that got going would still be a challenge to put out with limited fire-fighting understanding and resources given the decay of structures within the city.

You did well in choosing Oahu rather than the Big Island, as there's no active volcanoes. Human sources could be very problematic, but let's assume those are carefully controlled too. But even so, it could still be precarious, as this US Forest Service paper indicates that there has been a significant increase in flora fires in Hawaii in the last century due in large part to the introduction of non-native grasses.

So while you may not be in the worst location scenario, there's still probably a fair chance of at least pockets of fire damage. The citizens may be able to detect and put out fires around a small village, but protecting the big cities like Honolulu would seem very difficult. So it's likely that some parts of any areas they don't focus on would be damaged by fires. And even within their active cities, there's a fair chance of significant damage, or perhaps even a scenario where the entire population is decimated by wildfire, unless they received good knowledge or assistance for dealing with this.


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