FeMO3 Dive Cruise 2008
Report Day 06 -- Saturday 27 September 2008 -- Implosion of Elevator Floatation
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FeMO3 Dive Cruise 2008 |
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Making things buoyant in the very deep-sea is difficult because of the water pressure. And most of the sea is very deep. Scuba divers regularly go no deeper than about 100 feet or 30 meters. All light is absorbed by about 300 feet or 100 meters of water, even in the clearest seas. Yet the average depth of the ocean is far deeper, 4,000 meters or about 13,000 feet. The ocean is so deep that if it were possible to scrape every single acre of dry land into the ocean – the seven continents, Mount Everest and the all the high Himalayas, all the islands – the ocean would still be hundreds of meters deep. Even humanity’s deepest diving submarine, the Japanese Shinkai 6500 can only reach about half way to the bottom of the ocean. And if we are going to recover things from the deep-sea floor, we need to have floats that can go to the bottom and return.
The problem is that most things that can survive this kind of pressure are too heavy to float in water. A depth of 5,000 meters represents 500 atmospheres of pressure, or about 7,500 pounds per square inch; the weight of two cars pressing on a postage stamp. A sphere has the largest volume for the weight of material and it is an inherently strong structure so spheres are used as floats. The surprise is that the spheres are hollow and made of glass. But glass makes sense; it’s about the ¼ the density of steel, very hard and easy to form. A commonly used glass sphere is 15 inches across and has walls about an inch thick. It is protected from bangs and chipping by thick yellow covers called “hard hats”.
The elevator started its decent with 8 of these “hard hat” spheres bolted to the top. At some point, as the pressure increased, one of the spheres imploded, and the concussion caused the others to implode as well. It was loud enough that it was heard in a stateroom in the bottom of the ship. The blast shredded the hard hats and tore a Niskin bottle off the elevator’s vertical post. It appears to have broken the acrylic panels on an instrument for measuring chemicals at the surface of the sediment. Bent legs on the elevator suggest it fell through the water column before crash landing on an ancient lava flow.
The total pressure on a 15 inch sphere at 5,000 meters is something like 5 million pounds! It’s no wonder the spheres occasionally fail.
It will not be easy to recover the elevator. The current plan is to hook it to Medea and drag it to the surface with Jason following behind. At the surface the crew will have to somehow winch Medea aboard with the elevator swinging below her, then lift the elevator aboard without tangling Jason’s tether.
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