Noob question about cave diving: Where does the air go?

[layday]

In videos divers will often leave air pockets on the surface of caves from their spent gas.

Is this air absorbed by the water?

Does it just stay there?

What's up with this?

Best,
layday

 

[decompression]

It goes up......


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[layday]

It goes up......


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Right, but how long does it stay there? Does it accumulate over time or does it go away? If it goes away, how?

 

[John A Lewis]

As a non-cave diver, I'll take a layman's approach to this.

Depending on the materials that comprise the cave walls, the gasses will rise and slowly filter upwards through natural fissures--some extremely small--in the rock. After all, didn't the water have to get there, in some cases in a similar manner?

Like I said--a layman's approach to the problem. Feel free to correct or expand on this.

 

[layday]

As a non-cave diver, I'll take a layman's approach to this.

Depending on the materials that comprise the cave walls, the gasses will rise and slowly filter upwards through natural fissures--some extremely small--in the rock. After all, didn't the water have to get there, in some cases in a similar manner?

Like I said--a layman's approach to the problem. Feel free to correct or expand on this.

That doesn't seem satisfying, water doesn't leak through rock walls at any appreciable rate and It seems like some of these caves could be made out of solid rock. But I honestly don't know so I'll take your word on it.

Still curious about how long it takes for the air pockets to go away though. Days? Months?

 

[decompression]

It's dependent on the mineral content of the cave, temperature and many other factors. There will be a reaction between oxygen (oxidizer) and other minerals. This varies with concentrations, time etc. As well as CO will have reactions. However, generally, the exhausted air stays in the pockets.....sometimes it's added to often, others not so much.


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[Aotus]

You'll see silvery pockets the ceilings of popular caves, near the entrance of some the air finds its way out the entrance that may cue waiting friends at the surface of the soon return of divers. Some have found that if you raise an ear into one of the pockets as the bubbles from farther in slide out and merge with these pockets, such a wild electric/industrial clashing sound occurs almost like a metal band warming up.

 

[Diver0001]

Henry's law and Dalton's law will conspire to 'absorb' some of the air/trimix (or components thereof) into the water. For the same reason that an aquarium "absorbs" oxygen from the air as the fish use it up, an air bubble will be absorbed into the water if the oxygen (or other gasses) content of the air is higher than that of the surrounding water. In the case of trimix, for example, the surrounding water will have little helium in it and it will probably absorb all of the helium from the bubble.... In an area where the O2 content in the water is lean, it will absorb O2 from the air until an equilibrium has been reached.... this is the reason why you are told not to breathe the air from a submerged bubble.

etc. etc. Google Henry's law and Dalton's law.

The extent to which this occurs, however, depends entirely on the composition of dissolved gasses in the surrounding water and the depth of the air bubble. I suspect that each cave and each area of a cave will have a unique profile in this respect.

R..

 

[karstdvr]

That doesn't seem satisfying, water doesn't leak through rock walls at any appreciable rate and It seems like some of these caves could be made out of solid rock. But I honestly don't know so I'll take your word on it.

Still curious about how long it takes for the air pockets to go away though. Days? Months?

I think it depends on the permeability of the limestone. There are some places that the limestone is very crumbly and extremely porous, while other places it almost has a granite type consistency. Places that are very popular and receive a lot of traffic will probably always have some air pockets,but I dive quite a few places where I am the only diver that system sees, and diving back to back days,I never see an air pocket.
There are some interesting studies on permeability and dissolution of limestone that may bear your answer,but the problem as mentioned earlier,frequently there are no two places alike.

 

[kensuf]

It also depends on other features of the limestone -- cracks, etc will give the air a place to travel. Sometimes the sound of the air running through these features makes a very loud noise -- almost like timpani drums.