# What height will liquid water reach in an evacuated column? A thought-experiment

Imagine an object shaped like the following sombrero.

This particular sombrero is surprisingly large; about 10 km tall, and thrice as wide. It turns out to be made entirely of perfectly rigid and indestructible unobtanium. According to ancient lore it was dropped gently from outer space onto the surface of the Pacific Ocean. Less surprisingly, it floats. Its rims far higher than the roughest of waves can reach.

Then, one day, somebody realized that all this fantastical nonsense is nothing more than an elaborate setup for a mildly interesting physics experiment. He purchases the best pump money can buy, somehow makes his way to the summit of Mt Sombrero, and --luckily-- discovers that it features a small hole, just the right size for his pump to plug into. After a great deal of time he finishes sucking all the air out of Mt Sombrero, and plugs the orifice with a bit of unobtanium paste.

What altitude does the liquid water level inside Mt Sombrero reach?

corollary questions:

• At what atmospheric pressure is said water level?
• Is there a volume of anything non-liquid above the water level? If so, is it a vacuum or is it water vapor?
• Is water in the vicinity of this level actually boiling, considering the vapor pressure required for such at room temperature? Will it keep boiling forever?

Simplifications allowed:

• Treat sea water as pure H2O.
• Consider friction/adhesion between water and the unobtanium walls to be negligible.
• How about you start us off by showing us what you think should happen, and explain to us where you're stuck and we can help you understand. Especially with a homework type question, you must demonstrate some level of effort to understand the problem Oct 13, 2016 at 4:32
• @Mason I realize it reads like a homework question, but it isn't. I'm not a student, so I never have homework. All of the above is my own creation, trying to package an aspect of physics I'm not experienced with at all into an accessible question.
– Will
Oct 13, 2016 at 4:43
• You know what atmospheric pressure is in lbs/sq in or Kg/m^2? Oct 13, 2016 at 5:13
• @WilliamBudd: the question is a homework style question (I will now tag it as such), in accordance with site policy on that type of question. It doesn't have to literally be homework. Mason's point stands. Please show your own effort.
– Gert
Oct 13, 2016 at 6:00
• Hint: think Torricelli's mercury column experiment.
– Gert
Oct 13, 2016 at 6:02