Underground Adventures, Depth, and Temperature

vicky_molokh · 11-10-2019, 01:35 AM

Greetings, all!

Underground Adventures (page 12) suggests that temperature rises by 1°F per 82½ feet of depth, or 64ºF per mile, on average. While that seems to be based on large-scale gradient, there seems to be some doubt about it being applicable to a degree-per-hundred-feet level of precision.

Is the recommended value at all a useful rule of thumb at those scales? Because it operates at rather small scales, but doesn't really indicate an error margin, and doesn't account for some big adjustments (whose impact can be huge compared to the indicated gradient value):

Mines' temperature is contributed to by mining activity itself (man and/or machine).
Local geothermal factors and variations.
Variations in air circulation. Unlike solid rock, caves tend to have some air circulation that will equalise temperature with the surface faster.
Natural caves don't seem to go as deep as mines anyway, so generalisations from per-mile data seems like a thing that shouldn't be done lightly.

Just how much do those things throw off the numbers, and what can/should be done to improve the situation without turning dungeoneering advice into hundred-page geology textbooks?

Thanks in advance!

Daigoro · 11-10-2019, 02:00 AM

In the dwarven agricultural thread we thought about this a little.

I think that's a broad rule of thumb, for all other things being equal. But to see a real world example of how temps might vary, these two graphs give a good idea.

Page 9 of this PDF.
This webpage.
And this abstract talks about the effect of subterranean waterflow.

I'm not sure air would have such a great effect, as it doesn't have as much thermal mass as rock, although significant honeycombing would break up the conductive paths for thermal flow through rock.

11-10-2019, 01:35 AM	#1
vicky_molokh GURPS FAQ Keeper Join Date: Mar 2006 Location: Kyïv, Ukraine	Underground Adventures, Depth, and Temperature Greetings, all! Underground Adventures (page 12) suggests that temperature rises by 1°F per 82½ feet of depth, or 64ºF per mile, on average. While that seems to be based on large-scale gradient, there seems to be some doubt about it being applicable to a degree-per-hundred-feet level of precision. Is the recommended value at all a useful rule of thumb at those scales? Because it operates at rather small scales, but doesn't really indicate an error margin, and doesn't account for some big adjustments (whose impact can be huge compared to the indicated gradient value): Mines' temperature is contributed to by mining activity itself (man and/or machine). Local geothermal factors and variations. Variations in air circulation. Unlike solid rock, caves tend to have some air circulation that will equalise temperature with the surface faster. Natural caves don't seem to go as deep as mines anyway, so generalisations from per-mile data seems like a thing that shouldn't be done lightly. Just how much do those things throw off the numbers, and what can/should be done to improve the situation without turning dungeoneering advice into hundred-page geology textbooks? Thanks in advance! __________________ Vicky 'Molokh', GURPS FAQ and uFAQ Keeper

11-10-2019, 02:00 AM	#2
Daigoro Join Date: Dec 2006 Location: Meifumado	Re: Underground Adventures, Depth, and Temperature In the dwarven agricultural thread we thought about this a little. I think that's a broad rule of thumb, for all other things being equal. But to see a real world example of how temps might vary, these two graphs give a good idea. Page 9 of this PDF. This webpage. And this abstract talks about the effect of subterranean waterflow. I'm not sure air would have such a great effect, as it doesn't have as much thermal mass as rock, although significant honeycombing would break up the conductive paths for thermal flow through rock. __________________ Collaborative Settings: Cyberpunk: Duopoly Nation Space Opera: Behind the King's Eclipse And heaps of forum collabs, 30+ and counting!