300 mile column of water, what pressure at the bottom.

Gawdzilla Sama

Gawdzilla Sama

Valued Senior Member
John Varley, in Rolling Thunder posits a spot where the ocean on Europa is 300 miles deep. I'm wondering what the pressure would be at the bottom of that trench and how it would compare with the benthic pressures here on Earth. Help a fella out?
 
Gawdzilla Sama said:
John Varley, in Rolling Thunder posits a spot where the ocean on Europa is 300 miles deep. I'm wondering what the pressure would be at the bottom of that trench and how it would compare with the benthic pressures here on Earth. Help a fella out?
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Well lets see. Gravity is 13% of Earth's. Assuming the same average density of water (which is very roughly true) and assuming no gravity gradient it would be around 100,000 PSI. However, the entire moon is only 900 miles in radius, so you'd see a gravity gradient as you got closer to the core. This would tend to reduce pressures at the bottom of the ocean.
 
Gawdzilla Sama said:
Wiki article says: The hadal zone can reach far below 6,000 m (20,000 ft) deep; the deepest known extends to 10,911 m (35,797 ft).[20] At such depths, the pressure in the hadal zone exceeds 1,100 standard atmospheres (110 MPa; 16,000 psi). Lack of light and extreme pressure makes this part of the ocean difficult to explore. https://en.wikipedia.org/wiki/Hadal_zone

Both numbers given so far indicate a far higher pressure on Europa?
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300 miles deep is ridiculous. Here on Earth the average depth of the ocean just over 2 miles.
 
Seattle said:
300 miles deep is ridiculous. Here on Earth the average depth of the ocean just over 2 miles.
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And Europa adheres to that standard because...

"The deepest part of the ocean is called the Challenger Deep and is located beneath the western Pacific Ocean in the southern end of the Mariana Trench, which runs several hundred kilometers southwest of the U.S. territorial island of Guam. Challenger Deep is approximately 36,200 feet deep."
 
Gawdzilla Sama said:
And Europa adheres to that standard because...

"The deepest part of the ocean is called the Challenger Deep and is located beneath the western Pacific Ocean in the southern end of the Mariana Trench, which runs several hundred kilometers southwest of the U.S. territorial island of Guam. Challenger Deep is approximately 36,200 feet deep."
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How does Europa have anything to do with the Challenger Deep. One is 36,000 feet deep and the other (your figures) 300 miles deep.
 
Gawdzilla Sama said:
John Varley, in Rolling Thunder posits a spot where the ocean on Europa is 300 miles deep. I'm wondering what the pressure would be at the bottom of that trench and how it would compare with the benthic pressures here on Earth. Help a fella out?
Click to expand...

If I understand this correctly?
The formulas we would use to calculate the pressure of a column of water on earth won't work for europa because the gravity is different.

Can you compare europa's gravity to that of earth?

even air pressure matters
eg: average human has 3200 sq in of surface area
sea level air pressure if about 14,7 lb/sq in
so average human is experiencing 4100 lbs of atmospheric pressure at sea level
wow
and we do not even notice this.

OK
do you have to add atmospheric pressure on top of water pressure?

..............................................................
(I ain't completely confused yet---------------but I am working on it)
 
I was under the impression that the numbers would be plugged into a formula.

And there's no reason to disregard air pressure other than there isn't any air on Europa.
 
sculptor said:
If I understand this correctly?
The formulas we would use to calculate the pressure of a column of water on earth won't work for europa because the gravity is different.

Can you compare europa's gravity to that of earth?

even air pressure matters
eg: average human has 3200 sq in of surface area
sea level air pressure if about 14,7 lb/sq in
so average human is experiencing 4100 lbs of atmospheric pressure at sea level
wow
and we do not even notice this.

OK
do you have to add atmospheric pressure on top of water pressure?

..............................................................
(I ain't completely confused yet---------------but I am working on it)
Click to expand...
You do add the atmospheric pressure to the water pressure but going as deep as is being talked about here, the atmospheric pressure (whatever it is) is negligible.

For instance, on Earth the column of air from "space" to the ground is 14.69 psi. Water is much more dense than air so to get another 14.69 psi of pressure you only have to go down about 33 feet. By the time you are at 99 ft you will experience 4 atmospheres of pressure or about 59 psi. So for each additional 33 feet of depth (in water) you add another 14.69 psi.
 
And the figures for terrestrial water pressure already have that figured in, so we can "off the shelf" numbers, which I quoted. AND as I noted, there is no air pressure on Europa, so that figure in the equation would be zero or deleted, which ever way the formula required.
 
sculptor said:
If I understand this correctly?
The formulas we would use to calculate the pressure of a column of water on earth won't work for europa because the gravity is different.

Can you compare europa's gravity to that of earth?

even air pressure matters
eg: average human has 3200 sq in of surface area
sea level air pressure if about 14,7 lb/sq in
so average human is experiencing 4100 lbs of atmospheric pressure at sea level
wow
and we do not even notice this.

OK
do you have to add atmospheric pressure on top of water pressure?

..............................................................
(I ain't completely confused yet---------------but I am working on it)
Click to expand...
Of course we don't notice it. Pressure acts equally on every particle of our bodies, from all sides, so the net mechanical effect on us is zero. What it does affect is the physics and chemistry of us and our environment, through such things as concentrations of dissolved gas in the body and so forth.
 
exchemist said:
Of course we don't notice it. Pressure acts equally on every particle of our bodies, from all sides, so the net mechanical effect on us is zero. What it does affect is the physics and chemistry of us and our environment, through such things as concentrations of dissolved gas in the body and so forth.
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Divers notice in but not in the ways one might think (as you've correctly pointed out). Breath compressed air and hold your breath and ascent from as little as 30 feet and you will notice it (and die).
 
Seattle said:
Divers notice in but not in the ways one might think (as you've correctly pointed out). Breath compressed air and hold your breath and ascent from as little as 30 feet and you will notice it (and die).
Click to expand...
Sure. I was referring to "experiencing 4100lb" at sea level.

Pressures markedly different from that alter the amounts of gases that can dissolve in body fluids - hence nitrogen narcosis for example. Rapid changes in pressure can cause things like the bends - or indeed damage due to simple physical expansion.
 
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