Unusual draught in new dig

[JBarty]

Hi all,

Last week, a new and (at surface-level) very promising dig was found in the same region as our other find in Ystradfellte. The initial presentation was a slumping floor within another feature. The area inside the slump was noticeably cold, and featured two limestone walls intersecting at roughly 90°, alongside that peculiar scent you often get outside of caves. Returning the next day, we did some initial probing and draught testing, finding a limestone boulder-choke at floor level. I found this quite odd as absolutely everything in this area seems to be packed full of glacial till many meters deep.

Upon testing, the draught pulled smoke inwards, through the only visible gap in the choke for about 10 seconds. The pressure would slowly be lost, and the smoke would puff out in a lazy cloud. Following this, all smoke was blown out in a channel for over 60 seconds. We didn't record the cycle, but it was observed over multiple tests. The weather was calm, without gusts, and the barometric pressure was slightly elevated.

I've spent the last few days wracking my brains for a reasonable explanation, but I don't think the typical chimney-stack effect, or surface-wind could explain the long outbreaths. My current theory is that there may be a connection to a kind of sump which opens and closes intermittently, pushing along great amounts of air. Another suggestion was "The Helmholtz effect", which mostly goes over my head.

Unfortunately, we all live in London, and I am currently hobbling around with a knee injury, so we're planning to return at the end of June to do a more thorough investigation. I would be very interested to know what people think!


Thanks,
Joe

 

[Leclused]

IMO : warm smoke is sucked in, cools down a bit and is pushed out.

Was there a difference in height? Warm air going in at higher level then air which was coming out

 

[JBarty]

That was one of the suggestions of the digging team, but I'm not sure it explains things. If this were driven by the warm smoke, I imagine the effect would be more localised/short-lived, and not such a long outbreath, as the warm smoke has such little heat in comparison to the constantly funneling cold draught. After this in-breathing period, all smoke presented to the dig-face would be funnelled out, instead of sucked in again.

It felt much more like a cycle. Sometimes the draught test would only cause it to funnel out of the dig-face. And for your question, all the draughting occured from the same space in the dig-face.

 

[The Old Ruminator]

Noticed a reversing draught below The Plug Hole in Shatter Cave. Seemed a cycle every few minutes. This deep within the cave so the draught origin unknown. You can use a draught meter for more accurate readings. Maybe big caves have little draughts and small caves big draughts. The old " Hosepipe Effect " noted in the past to underground steam flow times.

 

[Goydenman]

it is clear from our years of digging and recent exploration of Lofthouse pot in Nidderdale that drafts are produced by factors more complex than the simple models suggest - would love to know more too

 

[tim.rose2]

I have one of these on Portland which I describe as 'the cave breathing'. Discovered when I got a face full of one of the other diggers vape several times as it went back and forth. My explanation is that the passage beyond the 'end' connects to another cave/opening to the cliff essentially giving it a second entrance further along the cliff (location of this is currently unknown). As the gust travels along the cliff it pressurises the first entrance resulting in the draught travelling one way along the passage and then reverses as the gust reaches and pressurises the second entrance. Perhaps you have something linked by two blocked entrances? My conclusion is purely speculation - we have other multi-entrance caves in the same cliff line on the island which do not present this behaviour so it's clearly not as simple as just needing two entrances, gusts, and a distance between them. The draughts in all the islands caves however are directly related to the wind conditions outside as the draughts can be very strong on windy days and faint on the few occasions it's still outside.

 

[Robert Scott]

Allegedly Albert Einstein is reputed to have said "Before I die, I hope that Max Planck can explain Quantum Mechanics to me and after I die, I hope that God can explain Fluid Dynamics to me". Draughts are in the realm of Fluid Dynamics - good luck with your question.

 

[Pitlamp]

IMO : warm smoke is sucked in, cools down a bit and is pushed out.

Was there a difference in height? Warm air going in at higher level then air which was coming out

Try using cold smoke, to eliminate the possibility that the oscillating draught is related to the temperature of the smoke itself, such as this example:

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[Leclused]

it is clear from our years of digging and recent exploration of Lofthouse pot in Nidderdale that drafts are produced by factors more complex than the simple models suggest - would love to know more too

How good is your French? You should try reading ‘Vents des Tenèbres"

http://cds38.org/wp/wp-content/uploads/2013/04/climatologie_monde_souterrain-tome1.pdf

http://cds38.org/wp/wp-content/uploads/2013/04/climatologie_monde_souterrain-tome2.pdf

 

[Pitlamp]

it is clear from our years of digging and recent exploration of Lofthouse pot in Nidderdale that drafts are produced by factors more complex than the simple models suggest - would love to know more too

Agreed; there's more to it than the well known convectional and barometric draughts.

I wonder if there's a sump involved with a siphoning effect such as Whirlpool Rising in Speedwell, the Ebbing & Flowing Well at Giggleswick in the Dales or the Font de Fontestorbes in the French Pyrennes. Cyclic rising and falling water levels would cause air to move forwards and backwards in a cave passage. (I'd normally expect siphoning action to happen over a longer timescale though.)

 

[T pot 2]

Hi all,

Last week, a new and (at surface-level) very promising dig was found in the same region as our other find in Ystradfellte. The initial presentation was a slumping floor within another feature. The area inside the slump was noticeably cold, and featured two limestone walls intersecting at roughly 90°, alongside that peculiar scent you often get outside of caves. Returning the next day, we did some initial probing and draught testing, finding a limestone boulder-choke at floor level. I found this quite odd as absolutely everything in this area seems to be packed full of glacial till many meters deep.

Upon testing, the draught pulled smoke inwards, through the only visible gap in the choke for about 10 seconds. The pressure would slowly be lost, and the smoke would puff out in a lazy cloud. Following this, all smoke was blown out in a channel for over 60 seconds. We didn't record the cycle, but it was observed over multiple tests. The weather was calm, without gusts, and the barometric pressure was slightly elevated.

I've spent the last few days wracking my brains for a reasonable explanation, but I don't think the typical chimney-stack effect, or surface-wind could explain the long outbreaths. My current theory is that there may be a connection to a kind of sump which opens and closes intermittently, pushing along great amounts of air. Another suggestion was "The Helmholtz effect", which mostly goes over my head.

Unfortunately, we all live in London, and I am currently hobbling around with a knee injury, so we're planning to return at the end of June to do a more thorough investigation. I would be very interested to know what people think!


Thanks,
Joe

Don't poke the dragon, you're in wales after all !
I'll get me coat.

 

[SamT]

Have you factored in/considered your collective body heat too. Just your very presence is introducing warm energy into a previously stable environment.

 

[mikem]

Possibly gusts of wind across entrance causing chimney effect

 

[Lankyman]

Don't poke the dragon, you're in wales after all !
I'll get me coat.

It's true!

Welsh dragon 'discovered' slumbering on Anglesey's love island

The shape of what looks like a dragon can only be seen at low tide

www.dailypost.co.uk

 

[MarkS]

Last year on an expedition in Spain it was very noticeable that one cave periodically draughted in and out, sometimes over hours, sometimes over minutes, unlike most caves in the area that have a consistent in or out draught (or no draught!).

My feeling is that when entrances are at very different altitudes combined with very contrasting underground/overground temperatures, draughts tend to be fairly predictable and consistent. As soon as one or both of those factors is removed, draughts are far less predictable and reliable - essentially the signal to noise ratio drops. I put our in/out draughting entrance down to it being very likely to be linked to another (known) entrance at the same altitude, meaning that very small changes in local surface air pressure/temperature could influence the draught and therefore make it lest consistent and predictable.

I'd apply Occam's Razor and assume it's just some product of local air pressures/currents/conditions before assuming a siphoning sump or the like. I reckon the only truly reliable conclusion to be drawn from draughts is that draught = good!

 

[ChrisB]

I looked up the formula for a Heimholz resonator - a phenomenon that occurs with a chamber at the end of narrow tube. I doubt it's the answer but it's an interesting possibility and an incentive to keep crawling. If my maths is correct, a 50m long passage with an cross sectional area of 1 square metre and a chamber the size of Gaping Gill at the far end would give a resonant period of about 30s.

 

[The Old Ruminator]

PM Sent.

 

[Leclused]

I looked up the formula for a Heimholz resonator - a phenomenon that occurs with a chamber at the end of narrow tube. I doubt it's the answer but it's an interesting possibility and an incentive to keep crawling. If my maths is correct, a 50m long passage with an cross sectional area of 1 square metre and a chamber the size of Gaping Gill at the far end would give a resonant period of about 30s.

If you want formulas I suggest you take a look at Tome 2 vent des ténèbres

And on page 110 - 111 you can see some examples that can explain what was described in the initial post. I hope for you it's figure 2.7

 

[Pitlamp]

Possibly gusts of wind across entrance causing chimney effect

Should that be "venturi" effect? Mind you the O.P. did suggest it was a still day, "without gusts".

 

[Tritim230]

If you want formulas I suggest you take a look at Tome 2 vent des ténèbres

And on page 110 - 111 you can see some examples that can explain what was described in the initial post. I hope for you it's figure 2.7

Superb, thank you, Leclused. Very useful.