I understand that, as we ascent, air temperature decreases by about 3 degrees C per thousand feet , due simply to the effect of reduced pressure, and that this is called the dry adiabatic lapse rate. (I think this is a somewhat theoretical construct applying only to the International Standard Atmosphere.)

Does this also apply in reverse? i.e. if we where to descend into a sink hole, would we expect the temperature to increase by 3 degrees per thousand feet due to pressure effect? There is a borehole 40,000 feet deep – the Kola Superdeep in Russia. If lapse rate applies in reverse, the temperature at the bottom of this hole would be in excess of 120 degrees C – which strikes me as unlikely.

pesce.del.giorno said:

I understand that, as we ascent, air temperature decreases by about 3 degrees C per thousand feet , due simply to the effect of reduced pressure, and that this is called the dry adiabatic lapse rate. (I think this is a somewhat theoretical construct applying only to the International Standard Atmosphere.)

Does this also apply in reverse? i.e. if we where to descend into a sink hole, would we expect the temperature to increase by 3 degrees per thousand feet due to pressure effect? There is a borehole 40,000 feet deep – the Kola Superdeep in Russia. If lapse rate applies in reverse, the temperature at the bottom of this hole would be in excess of 120 degrees C – which strikes me as unlikely.

Yes it would apply as you go down.

Why do you think it unlikely that temperatures at that level would be so high?

The Rev Dodgson said:

pesce.del.giorno said:

I understand that, as we ascent, air temperature decreases by about 3 degrees C per thousand feet , due simply to the effect of reduced pressure, and that this is called the dry adiabatic lapse rate. (I think this is a somewhat theoretical construct applying only to the International Standard Atmosphere.)

Does this also apply in reverse? i.e. if we where to descend into a sink hole, would we expect the temperature to increase by 3 degrees per thousand feet due to pressure effect? There is a borehole 40,000 feet deep – the Kola Superdeep in Russia. If lapse rate applies in reverse, the temperature at the bottom of this hole would be in excess of 120 degrees C – which strikes me as unlikely.

Yes it would apply as you go down.

Why do you think it unlikely that temperatures at that level would be so high?

Dunno really. Just seems strange.

From: https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole

The hole reached 12,262 m (40,230 ft) in 1989. In that year, the hole depth was expected to reach 13,500 m (44,300 ft) by the end of 1990 and 15,000 m (49,000 ft) by 1993. However, because of higher-than-expected temperatures at this depth and location, 180 °C (356 °F) instead of expected 100 °C (212 °F), drilling deeper was deemed unfeasible and the drilling was stopped in 1992. With the projected further increase in temperature with increasing depth, drilling to 15,000 m (49,000 ft) would have meant working at a temperature of 300 °C (570 °F), where the drill bit would no longer work.

The Answer to Everything says that the “standard” lapse rate is about 2K / 1000 ft. It varies of course, and would vary even more underground due to hot rocks. Also I would expect it to become non-linear as the pressure increased.

The Rev Dodgson said:

From: https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole

The hole reached 12,262 m (40,230 ft) in 1989. In that year, the hole depth was expected to reach 13,500 m (44,300 ft) by the end of 1990 and 15,000 m (49,000 ft) by 1993. However, because of higher-than-expected temperatures at this depth and location, 180 °C (356 °F) instead of expected 100 °C (212 °F), drilling deeper was deemed unfeasible and the drilling was stopped in 1992. With the projected further increase in temperature with increasing depth, drilling to 15,000 m (49,000 ft) would have meant working at a temperature of 300 °C (570 °F), where the drill bit would no longer work.

Mind you, that’s the temperature of the rocks.

The Rev Dodgson said:

The Answer to Everything says that the “standard” lapse rate is about 2K / 1000 ft. It varies of course, and would vary even more underground due to hot rocks. Also I would expect it to become non-linear as the pressure increased.

FWIW it’s 1.98°C per 1,000’.
The 3°/1,000’ thing is for saturated air rising, inside clouds and that sort of thing.

Spiny Norman said:

The Rev Dodgson said:

The Answer to Everything says that the “standard” lapse rate is about 2K / 1000 ft. It varies of course, and would vary even more underground due to hot rocks. Also I would expect it to become non-linear as the pressure increased.

FWIW it’s 1.98°C per 1,000’.
The 3°/1,000’ thing is for saturated air rising, inside clouds and that sort of thing.

Not according to wikipedia, it says dry ALR is 3.05 °C/1,000 ft. Moist ALR (inside clouds and that sort of thing) is 1.68 °C/1,000 ft. That makes sense. In a moist environment the latent heat released on condensation and absorbed on evaporation reduces the ALR below that when the air is dry.

These do not apply in the stratosphere.

As for the rest, I’m completely in agreement with Rev Dodgson.

Also from wikipedia:
“Geothermal gradient is the rate of increasing temperature with respect to increasing depth in the Earth’s interior. Away from tectonic plate boundaries, it is about 25 °C per km of depth”. Translating that back to the bastard mixed units quoted for lapse rate, that’s 7.6 °C/1,000 ft.

pesce.del.giorno said:

I understand that, as we ascent, air temperature decreases by about 3 degrees C per thousand feet , due simply to the effect of reduced pressure, and that this is called the dry adiabatic lapse rate. (I think this is a somewhat theoretical construct applying only to the International Standard Atmosphere.)

Does this also apply in reverse? i.e. if we where to descend into a sink hole, would we expect the temperature to increase by 3 degrees per thousand feet due to pressure effect? There is a borehole 40,000 feet deep – the Kola Superdeep in Russia. If lapse rate applies in reverse, the temperature at the bottom of this hole would be in excess of 120 degrees C – which strikes me as unlikely.

I need to add a bit more here. Any depth of atmosphere is said to be “stable”, “neutral” or “unstable”. A “neutral” atmosphere is one with the appropriate ALR (wet or dry, depending on humidity). A stable atmosphere is one whether the temperature decreases less rapidly than height. An unstable atmosphere is one in which the temperature decreases more rapidly with height. So, for instance, the stratosphere is always “stable”, because the temperature doesn’t decrease with altitude. In the stratosphere that’s because the upper layers are heated directly by the absorption of sunlight by atmospheric oxygen.

Now, applying that to subsurface conditions, the rock temperature subsurface normally increases more rapidly with depth than a neutral atmosphere. This makes the atmosphere in a deep mine or borehole unstable – strongly convecting – as it tries to bring the excess heat to the surface. This serves to naturally ventilate mines even without special ventilation equipment. On the other hand, it the rock temperature at depth happened less than the conditions imposed by a neutral atmosphere then the atmosphere within the mine or borehole would be stable and no natural ventilation would occur.

A further issue is the humidity in mines. Many mines become much more humid at depth, and that can lead to hot rainfall within the mine as humid air cools to dew point as it is naturally convected upwards. In this case the wet ALR applies, and working conditions within the mine become “interesting”.

This only applies to Earth I’d assume, could you expect temperature increase if you dig down on other planets and moons that don’t have an active core.

mollwollfumble said:

Spiny Norman said:

The Rev Dodgson said:

The Answer to Everything says that the “standard” lapse rate is about 2K / 1000 ft. It varies of course, and would vary even more underground due to hot rocks. Also I would expect it to become non-linear as the pressure increased.

FWIW it’s 1.98°C per 1,000’.
The 3°/1,000’ thing is for saturated air rising, inside clouds and that sort of thing.

Not according to wikipedia, it says dry ALR is 3.05 °C/1,000 ft. Moist ALR (inside clouds and that sort of thing) is 1.68 °C/1,000 ft.

That’s the adiabatic lapse rate, not the rate of temperature change with a change of altitude in the atmosphere.
The standard lapse rate for the atmosphere is 1.98°/1,000’.

FWIW …
https://en.wikipedia.org/wiki/International_Standard_Atmosphere#ICAO_Standard_Atmosphere

And …
https://en.wikipedia.org/wiki/Lapse_rate#Environmental_lapse_rate

Cymek said:

This only applies to Earth I’d assume, could you expect temperature increase if you dig down on other planets and moons that don’t have an active core.

Yes. This has been confirmed by ALSEP experiments on the Moon.

But I have to add that for most solar system objects the rate at which the temperature increases with depth is unknown. The rate of heating with depth is well understood for Jupiter and Saturn, and only slightly less well understood for Uranus and Neptune. But it remains very tentative for Mars and Venus, for Enceladus, Pluto, Ganymede, Europa, Titan and Callisto, for example. I looked for all this information only a couple of months ago, and found very little.