Cave-diving and water pressure question

[Mark Michaud SELAUSAR]

My simple take on this is............the surface is sea level, any thing below it even diagonally somehow keeps the pressure based on " below sea level" from there even without a straight column of water (to the surface) above you.

 

[Thalassamania]

Atmospheric pressure is about 15 psi. If I go outside and look straight up I can see all the way up to the "surface" of the atmosphere (about 60 miles for most practical purposes) . If I then go in my house and look up, I see the ceiling about 2 feet above my head - but the pressure does not change because the air pressure at my "depth" under the "surface" pushes equally in all directions - up, down, sideways, etc.

Water does the same thing in a cave, so 60' of depth is 60' ft of depth even if the pressure has to be transmitted sideways through a half mile of cave passage.

Very well done, very well.

 

[Scott M]

I have never done any cave diving so forgive the dump question. If you walk into a cave at 60' below sea level donn your gear and enter the water, at 10' below the surface will your depth gauge read 70'? Or 10' and you need to do the math? I would assume the depth gauge would read the 70' since it is reading the pressures the same way my GPS can read sea level even though I am 500 miles from the sea.

Regards

 

[captain]

I have never done any cave diving so forgive the dump question. If you walk into a cave at 60' below sea level donn your gear and enter the water, at 10' below the surface will your depth gauge read 70'? Or 10' and you need to do the math? I would assume the depth gauge would read the 70' since it is reading the pressures the same way my GPS can read sea level even though I am 500 miles from the sea.

Regards

Your depth gauge would read 10 feet. There is no direct connection from the cave to the sea, if there was the cave would be full of water and you wouldn't be able to walk down to 60 feet. The water in the cave is completely disconnected from the sea so sea level has no effect on the depth or pressure of the water in the cave.

 

[Blackwood]

LOL - sorry for the flashback there

s'alright. I re-read that whole thread. Good times.

 

[Charlie99]

If you want another interesting mental challenge, think about a diver in a siphon.

Not a cave style siphon, but a true one ---- a tube 40' or 50' high, sealed at the top, the other end open and below the water level of a lake, with the water level in the siphon approx 33' feet above the surface of the lake. Kind of like an oversized, water-filled version of a barometer.

A diver entering the siphon from below the lake surface and swimming to the surface of the water at the top of the siphon would be in a heap of trouble.

He'd develop the bends, but before that happens he'd pass out and/or die from insufficient of oxygen, even if he was breathing from a tank of 100% O2.

Charlie Allen

 

[InkDiver]

If you want another interesting mental challenge, think about a diver in a siphon.

Not a cave style siphon, but a true one ---- a tube 40' or 50' high, sealed at the top, the other end open and below the water level of a lake, with the water level in the siphon approx 33' feet above the surface of the lake. Kind of like an oversized, water-filled version of a barometer.

A diver entering the siphon from below the lake surface and swimming to the surface of the water at the top of the siphon would be in a heap of trouble.

He'd develop the bends, but before that happens he'd pass out and/or die from insufficient of oxygen, even if he was breathing from a tank of 100% O2.

Charlie Allen

Well then, I would say a diver shouldn't do that.

 

[Blackwood]

I have never done any cave diving so forgive the dump question. If you walk into a cave at 60' below sea level donn your gear and enter the water, at 10' below the surface will your depth gauge read 70'? Or 10' and you need to do the math? I would assume the depth gauge would read the 70' since it is reading the pressures the same way my GPS can read sea level even though I am 500 miles from the sea.

Regards

Your depth gauge is calibrated to sea level atmospheric conditions. When it's out of the water, it is feeling the pressure of the atmosphere, but considering that 14.7-ish PSI to be zero. When you get to 10 feet in your cave, it will feel that 14.7PSI, plus the pressure exerted by the 10 foot water column, plus the negligible 60 extra feet of air between you and sea level. Since it already considers the 14.7 PSI (and negligible addition) to be zero, the display will be based on the water alone.

edit: added gauge

 

[perdidochas]

I have never done any cave diving so forgive the dump question. If you walk into a cave at 60' below sea level donn your gear and enter the water, at 10' below the surface will your depth gauge read 70'? Or 10' and you need to do the math? I would assume the depth gauge would read the 70' since it is reading the pressures the same way my GPS can read sea level even though I am 500 miles from the sea.

Regards

IMHO, it would read 10'. If you can walk into a cave, and there is standing water, then you know the top of the water column, which is at 60'.

 

[perdidochas]

If you want another interesting mental challenge, think about a diver in a siphon.

Not a cave style siphon, but a true one ---- a tube 40' or 50' high, sealed at the top, the other end open and below the water level of a lake, with the water level in the siphon approx 33' feet above the surface of the lake. Kind of like an oversized, water-filled version of a barometer.

A diver entering the siphon from below the lake surface and swimming to the surface of the water at the top of the siphon would be in a heap of trouble.

He'd develop the bends, but before that happens he'd pass out and/or die from insufficient of oxygen, even if he was breathing from a tank of 100% O2.

Charlie Allen

Please explain why he'd die of lack of oxygen. I don't follow.