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And I don't mean by nuclear bombs or meteor strikes, though the latter does come into play. Let's imagine for a moment that a meteor containing alien gray goo crashes into the sea a few miles out from major coastal city, causing a mega-tsunami that not only sweeps the city away but brings the gray goo ashore to start nibbling and munching on the bodies and debris.

How long would the goo have to finish consuming what remains of the city before it's discovered by the relief organizations and aid flooding the area? I don't know how long it usually takes to start sending support to countries afflicted by natural disasters, but could a city struck by a meteor effectively be in a dead zone of media coverage long enough for my goo to slip in, devour the wreckage and slip out again before being discovered or noticed?

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  • $\begingroup$ There are a couple problems with a meteor impacting in such a place, unstopped, in the first place - see answer $\endgroup$ – Zxyrra Oct 25 '16 at 21:06
  • $\begingroup$ Cities do not have a boundary, as long the entire continent isn't instantly wiped out, people will notice. There is always people at the edge of the disaster that can and will take pictures. $\endgroup$ – Bloc97 Oct 25 '16 at 21:07
  • $\begingroup$ I don't think it's entirely common knowledge that grey goo refers to self-replicating nano machines, not any kind of organism. That is what you mean right? $\endgroup$ – Stephen Lujan Oct 25 '16 at 21:39
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We can predict meteors

The major flaw in this scenario is that if a meteor large enough to cause a disaster on this scale were to strike, not only could we predict its path and date of arrival, but we could deflect (link is for asteroids but the same concept applies) it after realizing it was a threat. If this meteor could not be deflected for whatever reason, ex. we spotted it too late, people would still have time to evacuate the city when we determined a tsunami would occur. Erase bodies from the menu for now.

It would take a while to find the goo, but "disappear" is a strong word

If a city-scale tsunami occurred, you would see lots of pollution, and lots of murky water. Furthermore, any "gray goo", if it could survive in the vacuum of space, then the impact, then the water pollution, reached the city, it would simply appear as more pollution or waste. It could take weeks to months before a significant part of the city drains, and muck is cleared, leaving time for your organism to dissolve the rubble slowly, without being noticed. However, months is not enough time to consume an entire city; instead of "disappearing of the face of the Earth" expect "sterilized and slightly smaller"

Media doesn't matter

You mention how a media deadzone would prevent people from knowing about this organism; this is not true for two reasons.

  • Disasters, especially larger ones, receive excess media coverage
  • Aid workers would find the goo anyways, probably after it started to dissolve either a worker or an aid vehicle, regardless of the presence of media.

Goo slipping out is unlikely

Assuming the goo is like an algae, or some other collection of small organisms, the idea of controlled thought moving all of the species back into the sea is very hard to support. This could be explained if the organism(s) ran out of food, but as mentioned above, they won't.

Alternatively, the goo could stay in place, carpeting everything at an exponential rate. That way, it could still cause excessive problems without having to move out intelligently.

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Probably the best recent example is Hurricane Katrina that permanently substantially reduced the population of New Orleans and even Louisiana. Most of the critical damage before the area could be stabilized and relief crews could regain control took place in a week or less.

You might not be able to keep what is gong on secret for more than a few hours, but under the right circumstances, it might be possible to have a situation where the people in the know aren't take seriously, for example, due to a series of recent hoaxes along the same lines.

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  • $\begingroup$ Unless I'm mistaken, it wasn't so much Katrina that reduced the population of the relevant area as the psychological impact of the event. Natural disasters, or man-made disasters, can be cleaned up. Buildings, infrastructure etc. can be re-built. Whether people want to move back is a completely different question and, I think, more relevant in the Katrina case. $\endgroup$ – a CVn Oct 25 '16 at 7:45
  • $\begingroup$ The Hurricane itself did plenty of damages destroying buildings infrastructure that the owners and city did not have the means to rebuild, and disrupting businesses sufficiently that people requiring regular employment had to leave. Also, the delta does loose something like two football fields of land every day, so some damaged areas would only be buying a temporary reprieve if they had rebuilt. $\endgroup$ – ohwilleke Oct 25 '16 at 12:00
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    $\begingroup$ @MichaelKjörling I think it was less psychological and more insurance based reasons that kept people from going back. Homeowner's flood insurance is covered by FEMA, but businesses only up to $500,000, so increased flood premiums (or just not wanting to deal with risk of your business literally going under again) may have convinced the jobs to move out of town. $\endgroup$ – kingledion Oct 26 '16 at 17:19
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One night in February 1287 there was a particularly bad winter storm along the south coast of England, and by the time the night was over the third-busiest port city in England (Winchelsea) was under water and two miles out to sea (and the coastline had been reshaped in other ways as well). So it's a matter of a few hours.

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Pompeii was buried under 5+ meters of volcanic ash in a matter of hours. Sometimes, truth is more incredible than fiction. :)

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  • $\begingroup$ As an italian, I immediately thougth of Pompei too. The scary part is that the city size would've been unimportant, everyone would've died anyway. $\endgroup$ – JustPassingBy Oct 25 '16 at 21:20
  • $\begingroup$ True but unrelated to the question's method $\endgroup$ – Zxyrra Oct 26 '16 at 22:20
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If the city is not isolated, consider the immediatly adjecent area that is not destroyed, but has working helicopters, camera drones, swamp boats, etc. The people just hop over a short distance and are into the “destroyed” area.

So I’d say 2 hours before pictures start appearing on social media.

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Earthquake

Earthquakes in coastal regions/islands can do this.

The city of Port Royale was completely destroyed in a few moments in 1692.

https://en.wikipedia.org/wiki/Port_Royal

From Wikipedia:

The earthquake caused the sand under Port Royal to liquefy and flow out into Kingston Harbour. The water table was generally only two feet down before the impact, and the town was built on a layer of some 65 feet of water-saturated sand. This type of area did not provide a solid foundation on which to build an entire town. Unlike the Spanish before them, the English had decided to settle and develop the small area of land, even while acknowledging that the area was nothing but “hot loose sand”.

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