Searching for Treasure With a Caisson

ok so here is my problem. there is this big hole in the ground some 160 feet deep, and its filled up with water. it is on a small island that is surrounded by the ocean, and the ocean water flows into the bottom of the hole at astonishing rates making the pumping out of the water futile (for the reason is that it is believed there is treasure at the bottom. what i have proposed is to use airpressure to push the water down. think of taking a drinking glass and turning it upside down and putting it underwater in your sink. what i dont know is howmuch the ocean is gonna push back. is the air pressure directly related to the amount of water you displace? or will it be related to the depth of the water/air event because the weight of the sea that is above it. basically what i need to know is what air pressure will be required to maintain the water at a depth of 160 feet, if the drinking glass had a volume of 21237 square feet. (air would be pumped in until the water is bottom rim of the cylinder) if you need more information on the problem it called the Oak Island treasure - money pit.
- Chris B (age 18)
Halixa, Nova Scotia, Canada

What you are describing is called a ’Caisson’.  These devices are used for building bridge supports under water.  You need a water-tight, air-tight, pressurized enclosure.    The pressure as a function of depth is 1 atmosphere per 33 feet so you would need 4.8 atmospheres.  That’s a whole bunch; your ears would pop when you went in and there is danger of  ’the bends’ when you come out of it.   

By the way, I enjoyed reading  and thinking about the ’Oak Island treasure’ years ago in my youth.  It is a fantastic story. 

For more information on caissons see: 
   http://en.wikipedia.org/wiki/Caisson_%28engineering%29

LeeH

(published on 10/22/2007)