Abandoned sky cities

So the old culture of efectively the precursors, created sky forts and towns, and perhaps some actual cities, either island like or in one page mass eg. Lauputa, but they are now gone, replaced by a new tech race, and the sky cities have been left alone by the new race as they don't have the tech to revive/reach them, some still functional ones are used by avian races from time to time.

But my question is, what happens when one of these loses its functionality and plummets down to the land below? Assuming they are at cloud level, I imagine that they would impact the environment a little :P

edited 10th Aug '14 2:04:42 AM by Zoraxbrooks

"Can you imagine what I would do if I could do all I can?" -Sun Tzu-

How big are the largest floating landmasses?

Depends on where they are when they plummet. If they're over a city, that would be quite catastrophic. Even if it misses, precautions will have to be taken to prevent that from happening over a city.

Either way, the destroyed buildings are going to create a massive ruin and lots of environmental destruction depending on their size.

edited 10th Aug '14 11:20:19 AM by ironcommando

...eheh

If a city fell at full speed from cloud level, you can be certain that none of the buildings would survive in less than one thousand pieces. It would be more like trillions of shards of busted rock and wood. Imagine places where tornadoes go through, and multiply everything about that by 100. Some things would survive, tools, maybe toys, jewelry, and other small, sturdy objects, but art and technology is unlikely to handle impact. If they float on islands, then you basically can ignore that there is a city there, because it's going to be mostly massive chunks of rock and dirt, surrounded by gravel and dust with some other sky junk. It might even vaporize on impact, I'm not sure because I don't know exactly how fast they would be on collision. For all I know, it could functionally be a city sized meteor, but I'm doubtful.

Air resistance would tear the plummeting islands/cities to pieces before impact, meaning that it's possible, but highly unlikely, for multiple parts of the same city to land far away, and likely for two parts of the city to collide before impact. This would mean that the city itself would be unrecognizable. A large amount of the goodies would be buried under rubble, and it would take ages for the smoke and dust to clear out enough to investigate anyway. As rude as it is to point out, your city would be as salvageable as the World Trade Center, if it just so happened to be the planes instead.

Here's where the fun starts. Say the city is divided up into four sections, and each section is held up by whatever lets these kinds of cities fly. If the thingy in one section fails, but not the other three, I would guess that the whole section, plus some parts of the others, would fall. This would probably create a great pull on the sides of the other quadrants, because suddenly what was once self supported is a giant quarter of a city that the other three have to lift for a few seconds before dropping. This causes the whole place to teeter to one side, and spilling out anything that's not bolted to the floor, including vehicles, currency, hundreds of huge chunks of rock, cooking utensils, plants, dust, and some buildings. If the city is drifting, it would leave trails of this stuff behind it for maybe an hour Obviously, things like paper and cloth may drift farther.

It's quit the different story if they gently drift down, probably involving fewer craters, and more stable ruins, but when you're landing a city, even a "gentle" landing can break it up into huge sections, and make quite the mess. I'd use earthquake damage as an example for this. If you want your characters investigating real ruins, this is the way to do it, so *partial* failure of the floaty stuff would be prime destruction.

edited 10th Aug '14 10:55:40 AM by earzo700

It really depends on how the skylands lose their ability to float. There's going to be some significant damage to the skyland and the earthland either way - the question is collateral damage.

If the skyland slooooowly loses its buoyancy like a balloon, the damage will be limited to the very local area. A large mass moving slowly will still have inertia on its side, but will be settling down on something that is bigger and slower than it is. The skyland will be a complete write-off, but you might be able to land one near a city this way (and Votoms fan that I am, I can kinda see an industry revolving around this). Matter of fact, you might be able to land one in a city, and still have a functioning city outside of the impact zone.

If the skyland very suddenly stops floating... hm. That's Colony Drop territory. It'd either severely damage or completely erase the city it lands on, depending on their sizes - the difference being an area that's available for redevelopment, and a crater.

tGuys, there are calculators for this sort of thing. Using the link, I set the sky city at 5 kilometers wide, the density of porous rock, with an impact velocity of 2 km/sec (which is probably way too high), and an impact angle of 90 degrees, impacting sedimentary week.

The results? The crater is a little over 600 meters deep, 13 kilometers wide, a wind velocity of 4 meters per second (about 500 kilometers per hour) and a richter magnitude of 8. Nasty if you happen to be within a few kilometers of it, but not catastrophic on a global scale. (I like this calculator because it superimposes the crater on a map of the Earth).

edited 10th Aug '14 6:23:12 PM by demarquis

"We learn from history that we do not learn from history."

"Probably way too high" is a bit of an understatement. Something going 2km/s in an atmosphere has far worse problems to deal with than the impact at the end of its journey...

I mean, we're talking about Mach 7 or thereabouts here. Objects that aren't specifically built for that tend not to come out of it in one piece :P.

edited 10th Aug '14 6:37:13 PM by MattStriker

Reality is for those who lack imagination.

I think the calculator is assuming a spherical object rather than a plate or something like what you'd build a city on, so for our purposes the mass is going to be completely off. At the very least, I don't think the crater's going to be quite that deep for a skyland, with a somewhat less catastrophic quake.

My math-fu is bad, so I tried the calculator at 1400 meters diameter with everything else the same as . This returns a 450 meter deep crater and a Richter 7. It looks like you could probably take out Staten Island with the mass in a flat 5000 meter diameter skyland, and shake up New York City for a couple of days, but with advance preparations and building codes, I think the city would go back to normal soon.

Wait, so is 2 km/s acceleration or top speed?

edited 10th Aug '14 6:45:16 PM by DeusDenuo

km/s isn't even in units of acceleration, I'm not sure how you would read that into it.

Join my forum game!

You are right about the calculator, they all assume that, but at least it gets us in the right ballpark. Not much is going to survive in the immediate vicinity of the fall, with very little but a huge pile of debris left over.

"We learn from history that we do not learn from history."

The location where the floating city stops floating may also change the impact. If it's floating very near a tall mountain range, the part of the city that impacts higher up the mountain may not be so badly ruined (as compared to getting completely pulverized if it hits at ground level).

Cloud level ranges from 1000-6000 metres, and mountains can rise up to that level or even higher.

edited 11th Aug '14 8:59:10 AM by ironcommando

...eheh

Then there's a water landing...

"We learn from history that we do not learn from history."

Depending on the depth of the water the destruction of the city would vary. In any case there would be a big wave from all the water displaced.

...eheh

Start out by finding what is roughly "cloud level". This link will be handy. Weather faqs.org.uk There is a handy chart.

The calculator you used is not of any use for this kind of question because it is for meteorite impacts. The k/s measurement is for current velocity not rate of acceleration. It also assumes starting outside the planets atmosphere and then passing through it and as already noted it assumes a spherical object.

You would need to determine a rough height for the start of the city, its overall size, shape, mass, and how it begins its fall from the sky.

How big is the mass, how regular or irregular is the shape, does it lose its ability to float uniformly or does it lose it in sectors or from the one edge to the other. Also how quick does it lose the ability to float?

If it starts to fall straight down how aerodynamic the underside is could determine how it impacts the surface. If it is from a significant height shear forces will likely cause it to partially break up. If the whole mass starts even a slow tumble parts of the city will be ripped off as it falls.

Whatever happens though something "city sized" even "small cities" is going to be quite destructive. The city on the island will very likely be utterly destroyed as would anything it lands on.

edited 11th Aug '14 7:21:42 PM by TuefelHundenIV

Who watches the watchmen?

By time one might notice the large thing In the sky falling, might one be able to evacuate in time, or would noticing take too long and the effect be too big to escape even if you thought you were safe. Barring magic and any other similar handwaves.

I'm thinking of these as metal, at least as a framework, there can be more traditional structures as I flesh things out more, set up kind of like strike vector maps, verry irregular shapes kind of a mishmash building on all axis', variable with different wealth/influence levels like in most places.

There are an undecided amount of these, they could fall anywhere

Since I was already thinking of one having landed in water, how much effect could the ensuing waves cause, and how might the new addition to the ocean floors topography effect the currents (and in turn how could that effect the nearby landmass)?

If it landed on/in a lake I imagine that would displace and/or evaporate some water causing further environmental questioning...

edited 12th Aug '14 1:37:34 AM by Zoraxbrooks

"Can you imagine what I would do if I could do all I can?" -Sun Tzu-

Chances are if you can see it fall you're already too close to run.

Reality is for those who lack imagination.

Pretty much like mat said. Give the scope of the object falling the shear amount of destruction and area it would cover would be immense. You would have to be outside the affected area and then seeing it fall from a distance. It would rather terrifying sight to behold. We are talking the kinds of impacts that rip the top off of mountains.

Who watches the watchmen?

Think "small atomic bomb" except without the radiation (depending on what these sky cities use for a power source).

"We learn from history that we do not learn from history."

Ok I finally figured a roughly comparable amount of destruction for such a large body crashing down. Think of the scale of destruction caused by massive landslide when Mount Saint Helen's blew. Maybe not as much fire and ash but a lot of dust and flying debris.

Who watches the watchmen?

That's easier to picture. The ash was a bugger to deal with, and it flew quite a bit further away than anyone would really expect - it'd be more localized with a skyland, I think, just because it's not being launched into the air with force.

I wouldnt make that assumption. A falling city will generate a lot of momentum, and when it hits the ground, all that kinetic energy has to go somewhere.

"We learn from history that we do not learn from history."

I agree I imagine a lot of debris of varying sizes will be thrown some surprising distances. For example aircraft crash investigators have found various bits many miles away.

Who watches the watchmen?

That'd work better if we knew the skyland was designed such that it would break up as soon as the floaty-effect goes away, but without knowing what the angle of approach is I'm not sure if airplane accidents are appropriately comparable. That incident with the Blue Angels crashing head-first into the ground during training might be, but it's hard to see a civilian accident going that way.

That's more or less what happened to United Airlines flight 93 on 9/11. You might try researching the debri field that resulted from that one.

"We learn from history that we do not learn from history."

Exactly. The force of the crash of an airplane into the ground often flings bits of debris for miles.

Who watches the watchmen?

Done. That was 50 degrees at 560 mph (I'm a little surprised The Other Wiki has this information at all), with an object that could not have weighed more than 200,000 lbs. Throw anything into the ground at that kind of speed, and parts of it will naturally bounce.

Okay, I think I've got it. This site has a bunch of calculators, one of which is free-fall time and velocity given mass and distance, using local gravity and air resistance.

I used 25,000,000,000,000 kg (25 billion tonnes) at first, but then tried 25 million tonnes, and then 25 thousand tonnes - the numbers come out more or less the same. I suspect this is the terminal velocity for something that falls out of the sky, once you get above a certain weight, but can't really be sure about that.

Long story short, it'll take 35 seconds for a skyland to hit the ground from 6 km up, and it will do so at 1200+ kph (assuming a sudden loss of floaty-effect).

That's not much time for someone on the ground to run, and that's probably a lot of force hitting the ground at a speed that will probably kick up a bit of dust. I say 'probably' because I couldn't figure out a good mass to use.

Using 25 million tonnes and 6 km (keeping the wind resistance the same, simply because I'm not sure how kg/m works), I started playing around with it a bit, to try and find out what sort of floaty-effect would make this a survivable event, instead of the Second Impact.

At 1/10th gravity (.98 m/s2), it'll take 110 seconds to hit the ground at 390 kph.

At 1/100 gravity (.098 m/s2), it's 350 seconds and 123 kph - 5:50 and about 76 mph.

At 1/1000 gravity (.0098 m/s2), 1106 seconds and 39 kph. 18:46 and 24 mph, enough time to evacuate a town of reasonable size.

Then I went and found a mass-velocity-joule calculator, then plugged in the original numbers (25 billion tonnes at 1234 kph) for shits and giggles.

1.4687e+18 joules (1,468,700,000,000,000,000 joules, I think). Which comes out to ...351 megatons. Yikes. That's seven simultaneous Tsar Bomba tests.

Krakatoa is said to have been in the 200 megaton range. It wiped most of an island off the map (sorta), triggered a seismic event felt literally across the world, and affected the climate globally for 5 years. This is still bigger than that. This is huge. This is... hm. This would easily get into Badass of the Week.

Okay, so maybe that's a bit ...unsurvivable. You'd have enough time to know you're screwed, and that you perhaps shoulda taken that job opportunity in that other town.

However, at the other end of the scale (25 million kg, 1/1000 gravity), you're going to get 1.4670e+12 joules - 350 tons of TNT. This is 32 FOABs, if you'd prefer an image, though I'm pretty sure the design of a skyland would make this (and the other explosion comparisons) something of a false analogy.