How long before a skyscraper decays?

November 16, 2006 9:56 PM

How long would it take for the Empire State Building to vanish without a trace?

So I was wondering about this. Specifically, I was wondering, "What if the inhabitants of the Upper Jurassic had built skyscrapers? Would they still be around?" If it only takes 10,000 years to wipe a skyscraper, how can we be sure there weren't any 100,000,000 years ago?

More specifically, how long would something like the ESB stick around if for some reason maintenance ceased today? How long would it be a visible skyline landmark? How long before a skilled archaeologist could detect no trace that it had ever existed?

The prior thread, If you had to warn people 10,000 years in the future to stay away from a site, how would you do it? did not propose building a skyscraper, but I'm not sure that means it wouldn't work.

posted by ikkyu2 to grab bag (25 comments total)

A skyscraper, or that skyscraper? Building techniques and materials have changed quite a bit since the '30s.
posted by jjg at 10:06 PM on November 16, 2006

Either/or, jjg. With this question I'm not sure how picky I can afford to be; I haven't been able to dig much up about it.
posted by ikkyu2 at 10:15 PM on November 16, 2006

I would think that you'd have several natural disasters in that time span that dramatically overshadow all other degenerative forces combined, so you need to find out how many earthquakes(for example) it would take to reduce it to rubble, and then figure out how long it would take for them ot happen.
posted by Mr. Gunn at 10:15 PM on November 16, 2006

How close to sea level and the coast is your average skyscraper? Sea levels seem to fluctuate as much as 100 m every 10,000 - 100,000 yrs.

Were humans to disappear tomorrow, I suspect any tower in Manhattan would likewise disappear within that time period from simple erosion processes.

Along with earthquakes, ice ages (and their glaciers cutting through rock), you have many powerful geological forces acting on objects built to last maybe a few hundred years at most without those stresses.

Since most of civilization and therefore most of its archeological artifacts aggregate around coastal areas, it seems it would be pretty hard for your future archeologists to find what you're after.
posted by Blazecock Pileon at 10:23 PM on November 16, 2006

Was this inspired by the New York Times article about earthen chevrons suggesting massive life-destroying tidal waves as recent as 4,800 years ago? (article here)?

I've been wondering about this, too.

There are surviving signs of ancient architecture that date back 5,000 years, and the materials involved in building these buildings seem a lot more fragile than steel. 10,000 years seems really short by those criteria.

Steel does corrode, though.
posted by croutonsupafreak at 10:34 PM on November 16, 2006

I figure the steel inside the building will last the longest. Steel corrodes at variable rates depending on many different conditions. Throughout its lifetime, it can expect to be exposed to air, water, and earth. The main things acting on the steel will be 0₂, H₂O and salt. Since much of the steel will likely also be galvanized, the beams will be protected as long as the environment exists for a stable oxide to form with the zinc. This degrades in reduced oxygen areas with excess water and acidity, so then you have to start wondering about the ground the building is built on. What's the pH of the soil? What are the leeching qualities of the soil (and as a result, its ability to hold on to salts)?

I'd figure you're looking at losing at least 10 microns/year, so that's about 100,000 years plus. Knock an order of magnitude off to take into account major earthquakes or meteors or whatnot. So, 10,000 years where it stands.
posted by Civil_Disobedient at 10:34 PM on November 16, 2006

(Oh, that's assuming an average 1-meter girder assembly.)
posted by Civil_Disobedient at 10:44 PM on November 16, 2006

This page has some projections as to when various evidence of humanities existence would disappear if we were to suddenly vanish. This article in the New Scientist has similar estimates.

The consensus seems to be that buildings will collapse within a few hundred years, but take thousands to tens of thousands before they are completely erased. In 100,000 years there would be no visible evidence we had been here.
posted by justkevin at 10:44 PM on November 16, 2006

There isn't a whole lot of longevity data on unmaintained large scale steel framed structures, since we've only been doing them (or their predecessor iron structures) for a little more than 200 years. For one thing, large scale steel framed structures are pretty expensive, and they can only be economically justified in the first place if they are built to last, and deserve maintenance. Second thing is, when large scale things are abandoned, if they can become hazardous, their abandonment usually creates a demolition opportunity that society recognizes as a means to mitigating the hazard. So unless something like a super avian flu wiped out humanity in a vicious few weeks, this is always going to be a thought experiment.

But skyscrapers are pretty highly engineered structures. There is not a whole lot of "extra" material in them. Once the windows went (and those would be the first things to go long term) and corrosion got a good start on the steel framing elements, you'd eventually have a natural version of the WTC, if not precipitated by fire, then by wind load. If you know where to go, you can hear the ESB creak in high winds now. (I used to have a client with a corner office on the 53rd floor, and he delighted in showing people the building sway in the wind, and pointing out funny noises.) Once the steel framing failed, you'd presumably have a big debris pile slowly collapsing into itself. Anaerobic bacteria have been observed eating steel and iron structures fairly rapidly, and I doubt Civil_Disobedient's estimates for steel frame in a rubble pile would hold up all that well. There is also a lot of bio-degradable paper, wood, and other materials in a modern skyscraper that are are going to encourage colonization by wee beasties, intent on demolition salvage projects of their own. I'm thinking that in 5,000 years after a wind storm tips over the ESB, you'd have to be a trained archeologist to recognize it's rubble field.

If you want something with multi-thousand year longevity, think big freakin' pile of rocks. 'Cause big freakin' piles of rock are the artificial structures that have best stood the test of time.
posted by paulsc at 11:03 PM on November 16, 2006

The consensus seems to be that buildings will collapse within a few hundred years, but take thousands to tens of thousands before they are completely erased. In 100,000 years there would be no visible evidence we had been here.

One can presently see plenty of evidence of people from more than 100,000 years ago. And those are a few hand tools, Why would we believe that an enormous stone edifice and it's hundred foot deep foundation be completely erased along with all the glass, silicon and plastic it contains?

Paleontologists can find bones, teeth and shells from th Upper Jurassic period, They can find petrified dino-poop, wood, egg shells and even ferns leaf and possible feather impressions 100,000,000 years later.
posted by Pollomacho at 11:31 PM on November 16, 2006 [1 favorite]

Geologically speaking, it's a fragile structure (compared to mountains, glaciers, etc). Location would be important, so a skyscraper in NYC would last longer than one in San Francisco. I imagine it would get worn away slowly, but at some point the gradual erosion would mean one particularly strong gust of wind would knock the thing down.

And it'll stay in it's knocked down state for a long old time. Any mica and feldspar in it will (chemically) erode out first, but quartz will remain in the structure forever, until it is physically removed by wind or water. Since there's a significant amount of material in this big pile of rubble, I'd say that there would still be traces of it for hundreds of thousands of years into the future, and possibly millions. Any particular element that would be unique to the building and not to the environment around it will be present in trace levels for many, many millions of years.
posted by twirlypen at 11:34 PM on November 16, 2006

If we can find proof the dinosaurs lived here 65 million years ago, then I think proof of our existence will still be around in 10,000 years. I just wanted to clarify that, since it seems like some are saying if the Empire State Building and other human buildings were to collapse, all proof of human existence would cease.

Not that I know of such things, but I'm confident that if someone were looking, they'd find the shadows of human existence at least a few million years from now. Then again, we still haven't found the DC-8's left behind after we all got pushed into that volcano 75 million years ago...
posted by incessant at 11:50 PM on November 16, 2006

Some of these issues were discussed here.
posted by Steven C. Den Beste at 12:24 AM on November 17, 2006

I've wondered at this many times. I imagine there are certain artifacts--titanium hardware, maybe?--that might last relatively intact for a long, long time.
posted by maxwelton at 12:35 AM on November 17, 2006

On a long enough time line anything we can construct on earth will be erased. (In four of five billion years the sun will engulf the earth...)

Geologically the earth is slowing down. When you think about continental drift and other massive landscape altering events what will occur in say the next 400 million years will pale in comparison to the events of the previous 400 million. There will certainly be areas of the earth that will remain unchanged for the long haul. (There are rock outcroppings in Australia which are billions of years old.)

Obviously any structure we can build will be weathered and crumbled, unrecognizable to anyone but the most savvy of future archaeologists within a few tens of thousands of years.

That said I suppose several people have given accurate estimates above for the life (standing) of the ESB.

I'm too lazy to do the google-fu now, but there are lots of examples of crumbling infrastructure in Russia where steel framed buildings are collapsing after only a few decades of disuse. The area surrounding Chernobyl would probably be a good test case for this type of thing...

*As a side note Richard Milhouse Nixon's name graces a plaque on the lunar surface which will very likely outlive most surface features of the earth. Think about that when you're trying to get to sleep at night...
posted by wfrgms at 1:00 AM on November 17, 2006

Not entirely helpful, but look up photos of the chernobyl dead zone to see the beginning (it's been twenty years) of this hypothetical process - a place where for some reason, humans simply left overnight and stopped maintaining the buildings. It's quite interesting.
Kidofspeed for example is a fictional/hoax story, but has a bunch of photos from the dead zone tour. The artists behind Stalker video game also did a reference tour, which has a lot of photos online somewhere.
another gallery
more
posted by -harlequin- at 2:59 AM on November 17, 2006

Couple of things nobody's mentioned, yet:

I would expect relatively frequent lightning strikes, so the building will catch fire not long after its lightning conductors break down.

Bone, teeth, shells and in some cases the imprints of soft tissues can survive millions of years as fossils. I see no reason why a steel girder shouldn't leave some kind of right-angled, non-natural imprint in sedimentary rock.
posted by Leon at 3:08 AM on November 17, 2006

The question is with regards to a single monumental building, but if it, along with the whole city it is in, were abandoned, there would be an imprint of some massive gridded system for long after any component of that system was obliterated.

There are all kinds of metals and concretes not native to the geology of the area. Even if everything dissolves, the mineral content of the soil and the presence of synthetic chemicals would indicate civilization.

Compare this with ancient Sumer, Harappa and Mohenjo-Daro. If the streets and buildings of ancient cities made entirely of mud on top of mud (and occasionally washed away by the sea) can survive four thousand years of abandonment, a steel and concrete city ought to be capable of lasting three times as long. What's less certain is which parts will last, and how our descendents will interpret the remains.
posted by ardgedee at 5:07 AM on November 17, 2006

If you bar large natural events like earthquakes, asteroids, giant tsunami then it would probably last in the neighborhood of several thousand years. Fire could be a danger but the biggest cause of fire is from human causes. When you take people out of the picture, then the odds are dropped significantly. Lightning would doubtful cause fire in a concrete/steel structure.

The biggest reason why many large structures of antiquities vanished is mostly because they were mined for useful materials by subsequent civilizations or due to war.
posted by JJ86 at 6:13 AM on November 17, 2006

If you take into consideration the human element it may happen faster than you think. The pyramids were ravaged of their outer skin to pave streets. I wouldn't hesitate to think that any building would be stripped of anything valuable and reusable in a very short time. Once that happens all sorts of openings exist for nature to take its course. Wind-blown seeds would get into the structure and the plant's roots would seek out tiny cracks and make them bigger. Water would get in, freeze and thaw and help the process along...but it all begins with Man's search for value in the carcass of the building.
posted by Gungho at 6:30 AM on November 17, 2006

Steel structures can last a long, long time.
posted by grateful at 6:52 AM on November 17, 2006

The pyramids were ravaged of their outer skin to pave streets.

And that is a terrible loss. As impressive as they are today, can you imagine seeing them as they were built, with smooth shimmering sides?

Basically (in concept, not actual buliding materials), compare this to this. Can you imagine? Wow.
posted by Ynoxas at 7:22 AM on November 17, 2006

Wind-blown seeds would get into the structure and the plant's roots would seek out tiny cracks and make them bigger.

I guess plants are a bit of a wild card. They might burrow and scrape, but they might also protect, like they protect soil from erosion. An ESB wrapped entirely in vines might even be strengthened.
posted by hoverboards don't work on water at 7:23 AM on November 17, 2006

One can presently see plenty of evidence of people from more than 100,000 years ago.
Right, by "visible evidence" I meant what the second article described as "obvious evidence." Things an alien visitor could see just strolling around (like the pyramids). Archaeological evidence such as our landfills would persist much longer. They don't say how long it would take for those to completely disappear, but the questioner seemed to be interested in visible landmarks.
posted by justkevin at 7:55 AM on November 17, 2006

Manhattan was scraped clean by Ice Age glaciers as recently as 20,000 years ago. The glacier was a moving slab of ice more than 1000 feet thick that plowed away everything in its path. You can see evidence of the this in Central Park where there are the roche moutonnees, bare Manhattan schist bed rock that bears the grooves of the abrasive glaciers.

The retreating glacier then piled a layer of gravel, sand and clay on top of the polished surface that ranges from 20 feet thick in Times Square to over 200 feet thick in Greenwich Village. (That's why there are no skyscrapers in the Village. The bedrock is buried too deep.)

Nobody knows when the next Ice Age will occur, but you can be sure that it will obliterate any trace of civilization in Manhattan.
posted by JackFlash at 11:06 AM on November 17, 2006 [1 favorite]