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I was inspired by Dune, where the characters can't really go outside during the day (at least for long) because it's so hot, so they stay inside these massive buildings.

On a planet which is very hot (at the edge of human habitability, around 108 degrees F, maybe even slightly higher on most of the surface), could humans survive by taking shelter from the direct sunlight in the caldera of an exctinct volcano?

I'm thinking of a large volcano like Olympus Mons (its. caldera is 3km deep on overage). Would the temperature be reduced enough for people to survive?

Other issues would be access to water, but perhaps there could be a lake within the caldera or simply enough rainfall to prevent drought.

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    $\begingroup$ Why exactly is the temperature supposed to be lower inside the caldera of the humongous volcano? $\endgroup$
    – AlexP
    Mar 16, 2023 at 19:35
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    $\begingroup$ What AlexP said, plus the fact that in Dune the massive buildings are air-conditioned. Sietches take advantage of the fact that the average temperature of Dune is not particularly high, and the chill of the desert at night is enough to mean that having enough mass around you will keep things chill. $\endgroup$
    – jdunlop
    Mar 16, 2023 at 19:51
  • $\begingroup$ (To be clear, the average highs are high, but the overall average is not.) $\endgroup$
    – jdunlop
    Mar 16, 2023 at 19:54
  • $\begingroup$ @jdunlop that makes sense. Thanks for the feedback. I'm assuming that Arrakis has those bigger swings because it is a desert planet, as we see in many Earth deserts. Could this hypothetical planet of mine have high enough humidity, rainfall, surface water, etc., to even out day-to-night temperature changes (or maybe it's a planet with no day-night cycle, like a tidally locked planet)? Meaning that the average temperature itself would be high. $\endgroup$
    – DMacc1917
    Mar 16, 2023 at 20:29
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    $\begingroup$ Till it turns out Not to be extinct :-) $\endgroup$
    – FlaStorm32
    Mar 16, 2023 at 21:37

3 Answers 3

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Perfectly Reasonable

On Earth, temperature decreases with height.

enter image description here

In Kenya the average temperature goes from 35ish (top left) to 15ish (blue parts) over the span of less than 3000 metres. See contour map.

enter image description here

It is believable that a dead volcano -- also known as a mountain -- could be 20C colder than the surroundings. Even without a caldera.

Your 108 degrees F is just 42C. The Kenya map hits 42C in places. The 20C difference brings you down to a comfortable 22C.

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  • $\begingroup$ Thanks! Helpful answer, appreciate the visual reference. Makes sense that the elevation is really the controlling factor for temperature. I thought the caldera would make some sense if the rest of the world had severe wind and weather, as it would offer some shelter as well (and just be a cool setting, basically a civilization surrounded by cliff walls over a mile high) $\endgroup$
    – DMacc1917
    Mar 17, 2023 at 13:34
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    $\begingroup$ @DMacc1917 The shade might help but if the surface is only 40F it is not needed. I'd say bump up the planet surface to 60C if you want to keep the caldera. It'd need to be pretty darn big too, to support a civilisation. $\endgroup$
    – Daron
    Mar 17, 2023 at 13:36
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Probably not

Temperatures tend to rise as you descend. The Grand Canyon is a good example of this - see this link and scroll down to look at the difference in temperature between the exposed top and more sheltered and shaded bottom of the canyon, especially in summer. The increased shade does not translate to a lower temperature. More importantly, even if the inhabitants are able to escape being exposed to direct sunlight by terrain shadowing - which they could achieve themselves with a tarpaulin or equivalent - it is the air temperature that will cook them.

As for a 3 km deep crater - note how in the linked site the advice is that "In general, temperature increases 5.5°F with each 1,000 feet loss in elevation." If the same rule of thumb holds true on your world, then it will be roughly 55°F / 31°C hotter at the bottom of the caldera than at the top.

Living deep in a cave system is different - the exchange of air with the outside is typically low enough that the temperature will remain fairly constant at close to the average of the day/night values. (Not exactly - there are other factors - but close enough.) It is fairly plausible for inhabitants to be living reasonably deep in a cave system during the day and only emerging at night, but not living deep in a crater during the day.

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  • $\begingroup$ Thanks, that's very helpful! I'll have to rethink things a little, but I think a cave-dwelling society would still work with my general idea. I had originally thought the caldera would be a good idea because it would give them some open area with some light to do agriculture, so I'll have to rethink how the society would sustain itself while very rarely leaving the cave system (the original idea would be a society without electricity so no artificial light). $\endgroup$
    – DMacc1917
    Mar 16, 2023 at 21:41
  • $\begingroup$ Follow-up question, though. Would the temperature still be higher in the caldera if the floor of the caldera was still higher than the general surface elevation? For instance, Olympus mons is 21km tall with a 3km deep caldera, meaning the caldera floor is still 18km above the base of the mountain. These don't need to be the exact elevations, but could the elevation be high enough to cool temperatures relative to surface elevation? $\endgroup$
    – DMacc1917
    Mar 16, 2023 at 21:47
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    $\begingroup$ @DMacc1917 Once you get that high, you start running into Oxygen issues. Mount Everest is only 9KM high, and at 18km high, your humans are trapped inside the caldera. Not using it to survive. $\endgroup$
    – Shadowzee
    Mar 16, 2023 at 23:44
  • $\begingroup$ @Shadowzee right, but like I said, I'm not fixed to those exact elevations, just using them as an example. Say the floor of the caldera was somewhere around 3-5km above surface level. El Alto in Bolivia is about 4km above sea level and it's annual mean temperature is about 8 Celsius whereas the Earth's is about 14 $\endgroup$
    – DMacc1917
    Mar 16, 2023 at 23:59
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    $\begingroup$ Short answer, yes, living at a given altitude will be a similar experience temperature-wise whether inside or outside a caldera,. (Depending on the exact dimensions, it may be a bit warmer inside the caldera because the walls will act as a heat sink and prevent as much cooling during the night - I'm not certain.) However, as @Shadowzee has said, you need to look at the effects of living at altitude overall - which will depend on the exact properties of your planet. $\endgroup$ Mar 17, 2023 at 0:05
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Easy.

"a planet which is very hot" - it's a planet. Some parts of it cooler then the others.

Let's say the planet axial tilt is 0 and they are at 60 degrees latitude. They will never see the sun.

In higher latitudes they may not even need any calderas, just a mountain range would do. And, as starlight hits surface at an angle, the area gets less energy in general.

They could even freeze at the poles. Or it can be comfortably warm there. It depends on your world - axial tilt, atmosphere pressure and composition, clouds, geology, sea currents, billion other things. It is not something people can catch you lying about. Not 99.9% of them anyway. Sci Fi shows don't care about science because viewers don't.

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