Is the air in this cave barometrically driven?

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Is the air in this cave barometrically driven?

Postby WVCaver2011 » Apr 4, 2010 8:28 pm

I have been surveying a cave that is located in Pendleton County, West Virginia and most of my survey trips to the cave were during low pressure events however, just this past week I revisited the cave and there was a high pressure system setting right overtop of WV. The cave's air reversed from it's usual outward flow to an inward frow of approximately the same magnitude. I entered the cave at around 7pm and left the cave at around midnight on friday it was low 80's when we went in and mid to upper 50's when we left...The temperature had no effect on the airflow because it stayed the same while we were in the cave (it continuously preceded to blow inward). This is why i'm asking this question.

During the low pressure events the air will blow out of the cave with enough force to allow a piece of survey tape to flap parallel to the floor (depending on how low the pressure actually is at that time).

Is it possible that the cave is, or could be barometrically driven?
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Re: Is the air in this cave barometrically driven?

Postby Phil Winkler » Apr 5, 2010 8:31 am

Allen,

I can't imagine any cave not being affected by barometric pressure. When one considers the entire volume of a cave and that it may only have one entrance, then a change in air pressure is always going to make it "breathe". Rapid changes would have more effect then gradual ones, too.
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Re: Is the air in this cave barometrically driven?

Postby WVCaver2011 » Apr 5, 2010 9:56 am

Phil Winkler wrote:Allen,

I can't imagine any cave not being affected by barometric pressure. When one considers the entire volume of a cave and that it may only have one entrance, then a change in air pressure is always going to make it "breathe". Rapid changes would have more effect then gradual ones, too.


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?
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Re: Is the air in this cave barometrically driven?

Postby Phil Winkler » Apr 5, 2010 10:30 am

I doubt even a physicist could develop a formula for estimating the volume of a cave based on the amount of air flow coming from the entrance. Bill Varnedoe once made the statement about Skidmore Cave in Alabama that volume alone doesn't tell you much because the cave passage could be 6 inches high and 500 ft wide for 1 mile. Skidmore expels a lot of water that comes from a sinking stream on the other side of the mountain a mile away.

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.

So, your cave could be 5 miles of too tight crawlway. You'll have to explore to find out, I'm sure.
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Re: Is the air in this cave barometrically driven?

Postby Evan G » Apr 5, 2010 10:40 am

WVCaver2011 wrote: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?


I think A. Palmer came up with the mathematical formula to try an figure out the amount of air displacement. There several calculus formulas that deal with gas displacement, but the problem you run into with caves are micro voids cause by micro fractures in the rock strata which can give erroneous data. Well it not erroneous, it is just a void which you can't fit through, so it would not be applicable data but it could give a very generalized estimate of the amount of cave.

WVCaver2011 wrote: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?


Simple answer, no. I have never heard of any way to do so. But I do know that in gas displacement if you add a second exit for that gas, you double the amount of gas being displaced.


The major problem that you run into in a cave is a cave is a void, so your measuring something that is not there an empty space. So you have to take what has filled the void where the rock once rested, which is air. Air can get into some very small places that is where the problem arises. Have fun!
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Re: Is the air in this cave barometrically driven?

Postby driggs » Apr 5, 2010 1:07 pm

WVCaver2011 wrote:I have been surveying a cave that is located in Pendleton County, West Virginia and most of my survey trips to the cave were during low pressure events however, just this past week I revisited the cave and there was a high pressure system setting right overtop of WV. The cave's air reversed from it's usual outward flow to an inward frow of approximately the same magnitude. I entered the cave at around 7pm and left the cave at around midnight on friday it was low 80's when we went in and mid to upper 50's when we left...The temperature had no effect on the airflow because it stayed the same while we were in the cave (it continuously preceded to blow inward). This is why i'm asking this question.


Allen, I'm going to phrase this answer in the form of "thinking points" that you can use to refine your ideas on what processes are at work. I encourage you to check out books from the Grotto library if you would like to research this further; Art Palmer's Cave Geology has a well-written section on cave air movement that you can refer to, and it even covers barometric air movement (which generally only affects very, very large caves).

This weekend, I believe, is the first trip you've taken into that cave when the outside temperature was greater than the in-cave temperature (~54-degrees). Think of the cave as a giant sealed gas bottle with only one valve. Think about how temperature affects the density of a gas. Now, given two situations - outside warmer than inside, outside colder than inside - what happens in each situation at the "valve" as the "gas bottle" tries to equalize its pressure? Consider a third situation, where the daily temperature swings from 80-degrees at noon down to 40-degrees at midnight, what would you observe if you sat in the entrance all day long?

Once you have considered these situations with a single-entrance cave, you can move on to the more complicated chimney-effect situation; imagine now that your cave has two entrances with significant elevation between them. How do the above scenarios affect airflow at each entrance, given that the temperature outside (and assumed density) is the same at both outside entrances? (hint: think about how dense or cold air "falls" to the bottom of a room)
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Re: Is the air in this cave barometrically driven?

Postby jharman2 » Apr 5, 2010 1:48 pm

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.
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Re: Is the air in this cave barometrically driven?

Postby WVCaver2011 » Apr 6, 2010 8:05 am

driggs wrote:
WVCaver2011 wrote:I have been surveying a cave that is located in Pendleton County, West Virginia and most of my survey trips to the cave were during low pressure events however, just this past week I revisited the cave and there was a high pressure system setting right overtop of WV. The cave's air reversed from it's usual outward flow to an inward frow of approximately the same magnitude. I entered the cave at around 7pm and left the cave at around midnight on friday it was low 80's when we went in and mid to upper 50's when we left...The temperature had no effect on the airflow because it stayed the same while we were in the cave (it continuously preceded to blow inward). This is why i'm asking this question.


Allen, I'm going to phrase this answer in the form of "thinking points" that you can use to refine your ideas on what processes are at work. I encourage you to check out books from the Grotto library if you would like to research this further; Art Palmer's Cave Geology has a well-written section on cave air movement that you can refer to, and it even covers barometric air movement (which generally only affects very, very large caves).

This weekend, I believe, is the first trip you've taken into that cave when the outside temperature was greater than the in-cave temperature (~54-degrees). Think of the cave as a giant sealed gas bottle with only one valve. Think about how temperature affects the density of a gas. Now, given two situations - outside warmer than inside, outside colder than inside - what happens in each situation at the "valve" as the "gas bottle" tries to equalize its pressure? Consider a third situation, where the daily temperature swings from 80-degrees at noon down to 40-degrees at midnight, what would you observe if you sat in the entrance all day long?

Once you have considered these situations with a single-entrance cave, you can move on to the more complicated chimney-effect situation; imagine now that your cave has two entrances with significant elevation between them. How do the above scenarios affect airflow at each entrance, given that the temperature outside (and assumed density) is the same at both outside entrances? (hint: think about how dense or cold air "falls" to the bottom of a room)


Thanks for the information Dave,

I'm going to see if I can check that book out to learn more about airflow within the cave as well as other significant geological processes that allow certain areas more susceptible to cave forming, etc. This would be neat to learn more thoughly. I would assume I know some of the basics but I would definately like to fill in the blanks that I don't know and have a more though understanding of these processes
Last edited by WVCaver2011 on Apr 6, 2010 8:20 am, edited 1 time in total.
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Re: Is the air in this cave barometrically driven?

Postby WVCaver2011 » Apr 6, 2010 8:15 am

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.


I have learned quite a lot already about the cave in general just by surveying it. This past week I unfornutately didn't have much time to survey because of work and other events but I was still able to get around 450 feet surveyed which was surveyed from the entrance to the intersection, that we take to get to the first tall canyon, before the first room, after the tight windy canyon. The cave dropped 66.7 feet within this distance and is still dropping. I don't think that's so bad for a days work. At least I got the crawling out of the way.

If you wouldn't mind, could you inform me of the experiment so we could possibly set something up?
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Re: Is the air in this cave barometrically driven?

Postby driggs » Apr 6, 2010 10:06 am

WVCaver2011 wrote:The cave dropped 66.7 feet within this distance and is still dropping.


What is the total surveyed vertical extent thus far? If your cave is dropping down the flank of the anticline, it could easily have very significant elevation difference between two (or more) entrances, giving you a gale-force wind at constrictions inside the cave due to the above-mentioned chimney effect. Unfortunately there is no way to tell if the other entrances are accessible to humans other than simply pushing it.

Think about the scenario with an upper and lower entrance (pretend that you found another "mystery" hole on the hillside moving air), and you should be able to come up with a surefire way to determine if a chimney effect is responsible for the air movement at both entrances and between them.
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Re: Is the air in this cave barometrically driven?

Postby WVCaver2011 » Apr 6, 2010 11:02 am

driggs wrote:
WVCaver2011 wrote:The cave dropped 66.7 feet within this distance and is still dropping.


What is the total surveyed vertical extent thus far? If your cave is dropping down the flank of the anticline, it could easily have very significant elevation difference between two (or more) entrances, giving you a gale-force wind at constrictions inside the cave due to the above-mentioned chimney effect. Unfortunately there is no way to tell if the other entrances are accessible to humans other than simply pushing it.

Think about the scenario with an upper and lower entrance (pretend that you found another "mystery" hole on the hillside moving air), and you should be able to come up with a surefire way to determine if a chimney effect is responsible for the air movement at both entrances and between them.


The total surveyed depth is 88.4 feet but the majority of the passage that has been surveyed is running perpendicular to the left limb of the anticline. There are other places in the cave that have not been surveyed yet and are going to add to the depth of the cave. In a logical guess I would say that it drops somewhere around 50 more feet in the unsurveyed portion of the cave that i've seen.

Unless the cave continues to the West for another 3/4 mile or more it will not have another entrance in this direction because everything, between the furthest western coordinate surveyed and the closest Helderberg limestone outcropping, is capped with oriskany sandstone. The Helderberg doesnt appear until around 3/4 of a mile westward. However, another entrance seems more likely North and East of the entrance because the Helderberg is outcropped all over this area at the surface. Not saying an entrance isn't possible in Oriskany Sandstone, it's just not likely.

If there is another entrance to the North or East it would probably be lower as well due to the plunge of the anticline. The average plunge of the anticline (taken from the average slope of the crawl way which is lined up directly with the axis of the anticline) is about 7.5 degrees on average. Within the plunge alone the cave dropped around 45 feet within 350 feet of cave however straight line distance would be significantly shorter.
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Re: Is the air in this cave barometrically driven?

Postby WVCaver2011 » Apr 6, 2010 11:45 am

After reviewing the Compass line plot and measuring some distances, I found out that the cave goes to a depth 57 feet within a straight line distance of 259.7 feet. I would assume that there are some left limb slopes being factored into that depth as well due to the fact that it has a 52.2 degree azimuth.

The anticline is undocumented but if it has the same trend as its neighboring anticlines, then 52.2 degrees is a fairly close azimuth to follow the plunge.

I've noticed in some areas in the crawlway there are areas where the bedding dips toward the west, and there are other areas where the bedding barely dips at all, like it's at or very near the axis.

Ponder these measurments and ideas and let me know what you think.
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Re: Is the air in this cave barometrically driven?

Postby Anonymous_Coward » Apr 6, 2010 2:47 pm

Allen,

I think everyone that has replied has given you good information, but they are perhaps being a little too pessimistic. There are lots of interesting things you can learn about a cave based on its airflow. I was involved with a multi-year study of the cave airflow of the southern Black Hills, including Wind and Jewel Caves. The things we learned about Jewel Cave were in some cases quite astonishing. It is true that cave volume and cave length are hard to correlate, but you can still compare surveyed volume to measured volume and make some predictions about potential.

Based on what I understand of your cave, it could have barometric or chimney effect winds. It is really hard to say. However, your explanation of the pressure and temperature at the time of your visit sounds a bit barometric to me. I apologize if you already said it, but is your entrance near the top or bottom of the limestone? If the outside temperature is warmer, you would expect the air to rise through the cave in a chimney effect. If colder, it would sink through.

In a barometric situation, the cave would breathe in high pressure and breathe out when the pressure is low. This gets tricky when you don't know how many entrances there are. The trick is to have instrumentation at every known entrance and blowhole, coupled with pressure and temperature data. That way, you can catch it when all entrances breathe in the same direction simultaneously. In a multi-entrance cave, this is almost a sure sign of barometric airflow.

In a one entrance cave it is easier. If you set up an anemometer or temperature logger inside the entrance of your cave, and assume that it is the only entrance, and monitor the local surface pressure and temperature, you could start to make some inferences about the nature of the airflow. These would of course have to be re-evaluated as soon as you discover another entrance!
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Re: Is the air in this cave barometrically driven?

Postby WVCaver2011 » Apr 6, 2010 5:16 pm

jaa45993 wrote:Allen,

I think everyone that has replied has given you good information, but they are perhaps being a little too pessimistic. There are lots of interesting things you can learn about a cave based on its airflow. I was involved with a multi-year study of the cave airflow of the southern Black Hills, including Wind and Jewel Caves. The things we learned about Jewel Cave were in some cases quite astonishing. It is true that cave volume and cave length are hard to correlate, but you can still compare surveyed volume to measured volume and make some predictions about potential.

Based on what I understand of your cave, it could have barometric or chimney effect winds. It is really hard to say. However, your explanation of the pressure and temperature at the time of your visit sounds a bit barometric to me. I apologize if you already said it, but is your entrance near the top or bottom of the limestone? If the outside temperature is warmer, you would expect the air to rise through the cave in a chimney effect. If colder, it would sink through.

In a barometric situation, the cave would breathe in high pressure and breathe out when the pressure is low. This gets tricky when you don't know how many entrances there are. The trick is to have instrumentation at every known entrance and blowhole, coupled with pressure and temperature data. That way, you can catch it when all entrances breathe in the same direction simultaneously. In a multi-entrance cave, this is almost a sure sign of barometric airflow.

In a one entrance cave it is easier. If you set up an anemometer or temperature logger inside the entrance of your cave, and assume that it is the only entrance, and monitor the local surface pressure and temperature, you could start to make some inferences about the nature of the airflow. These would of course have to be re-evaluated as soon as you discover another entrance!


The entrance is at the top of the Helderberg formation (due to the Chert that is found near the entrance) Oriskany sandstone is just above this. The Helderberg bends around the side of the mountain making it possible for another entrance there because there are passages within the cave that trend that way and any one of them could pop out onto the surface at anytime. There was also one point in the cave which we found a root in the back reaches of a crawling passage trending to the south (back toward the main entrance). This would be located about 150 feet west of the main entrance on the same side of the mountain as the main entrance.

The Corriganville formation (part of the Helderberg group of limestones) is known in my area for producing caves with multiple entrances. I recently found a 147 foot long cave that had 6 entrances and a second cave just about 10 feet away that was only 20 feet long with 2 entrances not to mention all the other holes I found that didn't really do anything. Fortunately or unfortunately, however you look at it, I havent found another entrance to the cave that I'm currently working on. However, it's not a 147 foot long cave either. It's much much larger than that. It's a network maze cave which would make it very possible to form other entrances in opposite passagways that trend to one side or the other of the mountain. I would assume that if there was another entrance on the opposite side of the mountain it would most definately be lower that the current entrance due to the fact that the cave follows both the plunge and axes of the anticline its formed in. I figure these would be good conditions of chimney effect winds. The reversal of air movement made me think otherwise...
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Re: Is the air in this cave barometrically driven?

Postby MUD » Apr 9, 2010 5:27 pm

Keep chasin that air Allen! :woohoo:
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