rmssetc
Contributor
What's the altitude (or, more precisely, what's the air pressure) at the surface (anyone diving in the ocean and sending up a buoy into the eye of a hurricane)?
Water is considered an incompressible fluid, and at sea level water is about 785 times more dense than air.
At altitude, the density of water doesn't change appreciably, while the density of air does, meaning that the pressure under water comes mainly from the column of water, not the air column above the water's surface. The pressure at any given depth is virtually the same regardless of the altitude.
If one was diving in the pool (too small to be a 'lake') "Ojos del Salado" at 6,400 meters (20,997) feet on the Argentina-Chile border, the air pressure at the surface is approximately 42% that of sea level, so the flexible container filled with air at 20m in the pool would expand to approximately 4.74L in volume when it first reaches the surface. Over time, that volume would reduce to about 4.25L due to the temperature difference between the air at depth (let's say 3~5C) and at the surface (approximately -24C).
Anyone want to check my math?
