Is the air in this cave barometrically driven?

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Re: Is the air in this cave barometrically driven?

Postby Caveair » Apr 28, 2010 8:48 pm

Is there anyway to determine weither it's a large cave by the amount of airflow? Assuming the cave only has one entrance (which is possible) how can I determine weither the cave is large (5 miles or more) only using airflow?

If there was a second entrance wouldn't it be possible to determine how far away the other entrance is by measuring the windspeed and refering to isobars on a weather map of that day?[/quote]
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Hello WVCaver,

Right now I know of no way one can determine whether one has found a large cave or not - just using cave air flow. What you get are generalities...possibilities.

Example: Brooks Cave in Pennington County, S.D. has a barometric wind. It has a barometric volume of 35-million to 50-million cubic feet - yet it has an explored volume of only about 250,000 cubic feet, and a surveyed cave length of only about 3,300 feet.

Thus the cave surveyors have discovered only about 1/2 of 1 percent of the total volume of this cave! Yet the geologic footprint of rock the cave wind resides within is 1-1/2 square miles. Thus, using the maze density of 50 miles of cave/1-sq mile at Jewel Cave, S.D. - as a representative example - Brooks Cave could be as long as 75 miles in length. ( I know where the cave wind leaves the known cave - but it would requie mining out 25 feet of almost solid rock to get into the room beyond.)

Another example is Nameless Cave, also in Pennington County, S.D. It has a documented barometric cave wind. Here again this cave also has a cave volume of 35 - 50 million cubic feet. The explored/surveyed cave volume is only about 10,000 cubic feet - for the cave is only about 200 feet long when you include all known side passages.

On average thought, caves that have a barometric cave wind tend to be much longer than normal.
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Second question: on Chimney Effect

Its possible to calculate the "geologic height" of a second cave entrance - that is above or below the first entrance using the velocity of the wind. You do this by back calculating the pressure differential needed to generate the wind in the first place - then calculate the difference in height needed to generate this pressure differential. (Its a lot like a scuba diver watching his depth gauge increase in depth as he slowly drops lower in the water column.)

You must also realize - that a geologic contact - such as your sandstone formation above your cave also will work as the upper entrance of a chimney effect cave. This is what happens at Mammoth - Flint Ridge. This cave has some 23 known entrances (or so)), yet I've been told that all the entrances respond as if they were the "low entrance" of a chimney effect wind! This was explained to me. Water flowing of f the top of the sandstone caprock hits the underlying limestone. This water finds a crack and enlarges it. This water eventually finds the cave and joins it - in doing so it completes an air flow loop alowing air flowing thru the low entrances to exit at or near the base of the sandstone contact.
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I don't know of a way to calculate how far away a second barometric entrance would be from the first one - with caves having a barometric wind. Theoretically, each cave will be responding as if it were the only cave (within its "sphere" of influence).

An example would be Lechuguilla Cave. Its huge! It's barometric. Big Manhole Cave is only one mile as the crow flies away, and it too is barometric. - but its barometric volume is X15 smaller. Then you have the big cave - Carlsbad Cavern 4-12 miles away. It strongly sounds like its barometric for it has a too-tight cave passage that blows winds upwards to 35-mph. deep inside, near the back of the cave.

Enought for now.

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Re: Is the air in this cave barometrically driven?

Postby Caveair » Apr 28, 2010 9:20 pm

jharman2 wrote:
WVCaver2011 wrote:Is it possible that the cave is, or could be barometrically driven?


The sad truth about the "real world" is that questions like this often do not yield to straightforward theoretical analysis. Having been to the cave in question I can say with certainty that there are several variables at work which are not easily decoupled; barometric and chimney effects are likely both present. I am certainly not in a position to say which effect is dominant. To determine that would require a carefully crafted experiment and observations during different weather conditions over a long period of time. As an academic exercise it would be interesting, however, you won't learn as much from the airflow analysis as you will from systematically exploring and mapping the cave.


Hi jharman2,

"The sad truth about the "real world" is that questions like this often do not yield to straightforward theoretical analysis."

Isn't it a wonderful world then - that this question actully has a straight foreward theoretical analytical answer.

Now there is a way for one to do a "short term experiment" where you collect just the air temperature, the cave wind velocity and its temperature(all timed using a quartz watch). One also gathers the barometric log sheet from the nearest weather station (air port). Then you use some computer software to analyze the basic equation: dp/dt + dt/dt = dv/dt
where p = pressure, t = temperature, and v = cave wind velocity.

In principle, what the software does is slice the data into many small increments. Then the smallest sum of the minimum error of the two variables p & t is your answer. ( A simpler example would be using the software in your school calculator to calculate the best curve fit line thru your data points for the equation y = ax + b.)

The actual experiment didnt take long to run. Just a little over 24 hours. I was baby sitting a pipewell entrance at Mammoth Cave.
We determined that this entrance to Mammoth cave was 95% chimney effect, 3% barometric, 2% random noise.

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Re: Is the air in this cave barometrically driven?

Postby Caveair » Apr 28, 2010 9:37 pm

rlboyce wrote:If you can't find Smoke In A Bottle, your talcum powder idea may suffice. Careful not to inhale that stuff too much though.

I've been doing a little research on the hunting product, and as far as I can tell it's just chalk in a bottle. If you can find a bottle with a similar spout to properly disperse the powder, just put some of your talcum powder or other fine powder in it and you're in business! Flour may even work as long as you don't get it wet. If you're not experimentally minded, I plan on doing it myself for one of my digging projects and I'll let you know if it actually works. There's good potential to save a few bucks... especially if you need more than one bottle.

But yeah, I agree with the others... do some more explorin'! :grin:


This subject has been discussed before by friends of mine. One suggested that we use vanilla extract, soaking it in a wad of paper towels underground.
Its organic, smells good too. Should work.
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Re: Is the air in this cave barometrically driven?

Postby WVCaver2011 » May 3, 2010 9:58 am

Thanks Caveair,

I will see what I can find out after May 8th and see if this thing has any Barometric winds according to your explination.
There's nothing that makes me more excited than finding a place underground that no one has ever seen or been in!

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Re: Is the air in this cave barometrically driven?

Postby jharman2 » May 3, 2010 11:09 am

Caveair wrote:Second question: on Chimney Effect

Its possible to calculate the "geologic height" of a second cave entrance - that is above or below the first entrance using the velocity of the wind. You do this by back calculating the pressure differential needed to generate the wind in the first place - then calculate the difference in height needed to generate this pressure differential. (Its a lot like a scuba diver watching his depth gauge increase in depth as he slowly drops lower in the water column.)



Doesn't this method depend on the internal geometry of the cave and the cross sectional area of the entrances? A constriction inside the cave that reduces the cross sectional area will effectively reduce the wind velocity at the entrance assuming the entrance cross sectional area is significantly greater than the constriction. You would then calculate less "geologic height" than if the constriction was not present. This method will certainly work with a simple tube model that maintains a constant cross sectional area. Am I missing something here?

Caveair wrote:The actual experiment didnt take long to run. Just a little over 24 hours. I was baby sitting a pipewell entrance at Mammoth Cave.
We determined that this entrance to Mammoth cave was 95% chimney effect, 3% barometric, 2% random noise.


Wow! That is an amazing result. Have you published your experimental methods and results? If not, do you plan to? I would like to hear more about this.
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Re: Is the air in this cave barometrically driven?

Postby Leclused » May 11, 2010 3:40 am

Phil Winkler wrote:I The air flow out of the EDF Tunnel at the Pierre St. Martin cave system in France is so strong sometimes it takes two or more people to push the steel door shut. That cave is long, deep, multiple higher entrances, huge rooms, etc.

.


Phil,

There even exists a smal clip of it. Made by someone of our club (Sc Avalon).

http://dl.getdropbox.com/u/1068395/Movi ... 0d'Air.wmv

BR

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Re: Is the air in this cave barometrically driven?

Postby Phil Winkler » May 11, 2010 6:53 am

Wow, that brings back some memories.

Thanks for that!
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Re: Is the air in this cave barometrically driven?

Postby rlboyce » May 11, 2010 8:05 am

Now THAT'S what I call airflow!!!
Happiness can be measured in mud/in².
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Re: Is the air in this cave barometrically driven?

Postby Leclused » May 11, 2010 9:42 am

Phil Winkler wrote:Wow, that brings back some memories.

Thanks for that!


If you want to see some other clips from the PSM please check out our videozone.

http://www.scavalon.be/avalonnl/videozone.htm (Pierre Saint Martin section)

The 2010 expedition will take place in August/September and we have very good perspectives. Here are some results of the 2009 expeditions.

- Anialarra was pushed towards the PSM-Partages system, distance still to cover is approx 90m. If linked a mega system (>100KM) will be the result.
- Anialarra is almost linked with FR3 (5 to 10 m to go)
- An509, a new -300 cave will be linked to the anialarra system next summer. During the latest september 2009 expedition the team ended in >100m deep
pitch. Stopped due to lack of time and material, rocks kept on falling for another 3-5 secs.
- An60 was pushed to -297, still 150m to go to reach the Anialarra System. Desobstruction required at 297
- Pozo Venus was pushed to -100, desobstruction required to continue.

The 2009 Anialarra expedition report can be found here : http://www.scavalon.be/avalonnl/psm/anial2009.htm (in dutch and french)

I can hardly wait to go back to the PSM this summer :big grin:

BR

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Re: Is the air in this cave barometrically driven?

Postby Phil Winkler » May 11, 2010 2:47 pm

Can I assume you have traversed the Tunnel du Vent? We had a bivouac back to the right of it in 1977, I think.
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Re: Is the air in this cave barometrically driven?

Postby Leclused » May 11, 2010 4:26 pm

Phil Winkler wrote:Can I assume you have traversed the Tunnel du Vent? We had a bivouac back to the right of it in 1977, I think.


Do you mean the 'Tunnel du Vent" in the Anialarra system, not far from Pozo Estella, or the one in travers of the PSM system?

The camp in the Anialarra is now known as the "Spanish camp". Avalon has currently a camp beyond the previous end of the the cave at -640. We broke through the collapse zone a few years ago. From that point we now climb around 100m to enter a fossil part of the system. Our underground camp is based there. From there one the cave is being pushed further.

In one of the other clips some footage was shot in the tunnel du vent in the Anialarra System. Some youngsters are holding up a glove in the airstream.

Cheers

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