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What I want:

My world has a large mountain valley region that is about 70 miles in diameter. I would like for there to be a historical event in which a portal to the moon was created in the valley and everyone living in the valley (and maybe some people outside too, doesn't matter) ended up dying of asphyxiation as air is sucked through the portal into the lower density atmosphere of the moon.

Parameters:

1) I would like the portal to be no bigger than a city block.

2) I would like the air depletion to be rapid enough such that few valley residents had time to escape.

3) If it helps, the elevation of the mountain valley town can be basically anything you desire, even below sea level.

Question:

Is the historical event I desire possible given the above parameters? If so, how big a portal are we talking? What time span?

[Personal note: thank you for reading! I've been lurking this site for a long time. Excited to finally get involved.]

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    $\begingroup$ The air would just be constantly filling back up in the region. Its like putting a portal in the bottom of the ocean and have it suck out water, more water will just fill the region where it left. $\endgroup$ – Amoeba Apr 30 '18 at 23:24
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    $\begingroup$ @Amoeba, the pressure needn't go to zero. Just the rush of air out of the area (sudden drop in pressure) could pull it from everyone's lungs, killing them. It's a question of whether or not lung strength can overcome the pressure drop. $\endgroup$ – JBH May 1 '18 at 0:27
  • $\begingroup$ @JBH your right, but your lungs can take a lot, and considering astronauts have handled the vacuum of space for a short spurt of time, I have a hard time believing it could kill them, considering how fast the air will refill $\endgroup$ – Amoeba May 1 '18 at 2:21
  • $\begingroup$ @Amoeba that unfortunately makes sense : / But perhaps I can stretch your analogy a little. There is indeed an ocean of air surrounding the valley, but it has to creep over the tops of the surrounding mountains. This isn't just a hole in the bottom of the ocean - more like a big bowl that has water flowing over the sides. If such a bowl had a drain in the bottom, it might create a whirlpool. $\endgroup$ – Pink Sweetener May 1 '18 at 2:53
  • $\begingroup$ @PinkSweetener well a bowl isn't the best design, think of more an upside down funnel, that way less air gets in and it takes longer, that may work, i don't know of any natural formations like that, but that is your best bet. $\endgroup$ – Amoeba May 1 '18 at 3:25
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As others have said, portal to the moon will not asphyxiate people, unless your mountains are a complete ring and reach to outer space. There will be hurricane-level wind, and some people might get sucked into the portal.

If you want to asphyxiate a town, open a portal to Venus. Its atmosphere is hot carbon dioxide, and it has higher pressure, so it will flow into the valley and fill it:

[Venus atmosphere] is composed primarily of carbon dioxide and is much denser and hotter than that of Earth. The temperature at the surface is 740 K (467 °C, 872 °F), and the pressure is 93 bar (9.3 MPa), roughly the pressure found 900 m (3,000 ft) underwater on Earth.

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

Here is a real-world example of this happening (with terrestrial source of carbon): https://en.wikipedia.org/wiki/Lake_Nyos_disaster

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  • $\begingroup$ Thanks! That's a good suggestion. I'll see if I can change things up to make that possible. Can't find it right now, but this reminds me of a news story I read awhile ago about a whole bunch of people who were killed by an earthquake that burped up some CO2 that lingered over their community too long. Works well with the valley setting. $\endgroup$ – Pink Sweetener May 1 '18 at 20:06
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Don't focus on the elevation of the valley; focus on the elevation of the surrounding mountains.

I once flew into Albuquerque, New Mexico in a small unpressurized, single-engined, propeller plane. We arrived on the night before a low pressure wave rolled over that region. Flying in, we had to push our altitude a little to get over the mountains and I remember getting a little dizzy. The next day, we had wanted to depart, but the mountains had other plans. The atmosphere had thinned so much above us that our little plane couldn't get enough grip to lift us up over the mountains. After several attempts, we returned to the airport and spend a few more days in Albuquerque.

If you have a town in a valley, which is totally surrounded by mountains. And if those mountains are even taller than those around Albuquerque (relative to the thickness of your planet's atmosphere). Then if a lunar portal opens up along that valley floor while a low pressure wave is present over the area, that might do what you are looking for.

Even then it will have to be a very large portal to evacuate the air out of the valley floor faster than the thin high-altitude air can rush in over the peaks to replace it.

You will probably just make everyone a little dizzy.

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    $\begingroup$ Would this constitute "explosive decompression" and simply pull everything not welded to the ground through the portal? $\endgroup$ – JBH May 1 '18 at 0:25
  • $\begingroup$ @JBH, I don't have strong enough physics to answer that, but I've been in hurricane winds which I think were born from just a dozen points of difference in atmospheric pressure. The differential would be much higher between Albuquerque and the moon, so give a small enough portal aperture, it is safe to say that things would get pretty intense! $\endgroup$ – Henry Taylor May 1 '18 at 1:03
  • $\begingroup$ If I understand you correctly, sucking the air out of the valley can create conditions no worse than that which would exist on the lowest mountain range surrounding the valley? $\endgroup$ – Pink Sweetener May 1 '18 at 2:45
  • $\begingroup$ @PinkSweetener, I think that is a fair assessment, but if the mountains are 15-20 thousand feet tall at their lowest opening, that would still be a very low air pressure. The pilot of the plane that I mentioned used to put passengers to sleep by climbing up to 12,000 feet above sea level. He was the only one among us who could handle that elevation. $\endgroup$ – Henry Taylor May 1 '18 at 3:50
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    $\begingroup$ I suggest that you must have misunderstood what was going on with your Albuquerque flight. Having spent a couple of decades flying a light plane in mountains, including Albuquerque, it just doesn't work that way. If nothing else, the place is not surrounded by mountains. You have the Sandia Mtns to the east, but departing southwards along the Rio Grande it's all downhill. Further, low pressure does not significantly thin the air. You might have had density altitude problems due to heat, but those generally affect only takeoff. $\endgroup$ – jamesqf May 1 '18 at 5:26

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