Science: Hole in the Ocean

Not since the Jumblies set to sea in a sieve had a less likely vessel ridden the ocean waves. Her name was the Cuss I, after Continental, Union, Shell and Superior oil companies. Squat and grey, she was 260 ft. long, lay low in the water and was crowded with stacks of pipe from stem to stern. Like a misplaced obelisk, a 95-ft. oil derrick sprouted amidships over an open well. But as the Ctiss I was towed out of San Diego harbor last week, the importance of her mission belied the oddity of her looks: when she gets to a selected point near Guadalupe, off Mexico, she will try to drill a hole in the bottom of the ocean where the water is 2.3 miles deep.

Target Mohole. This effort is part of Project Mohole, which will cost more than $20 million. It is backed by the National Science Foundation, and its goal is to drill clear through the earth’s crust to the “Moho,”* the boundary between the comparatively light rocks of the crust and the much denser mantle, which extends downward for i ,800 miles and whose properties are largely unknown. Geophysicists are sure that even one hole drilled to the Moho will tell invaluable volumes about the history, structure, content and behavior of the earth.

The easiest place to start drilling would be on land, but unfortunately the crust under the continents and the oceanic islands is too thick (up to 20 miles) to be penetrated. Under many deep parts of the ocean the crust is only three miles thick—and for this reason the leaders of Project Mohole decided that the drilling should be done from a special ship floating in three miles of water. The ship cannot be held over the drill hole by anchor cables extending sideways. Such cables hang in curves and would yield too much to changes of pull from winds and currents. Much more promising is the active system of keeping the ship accurately over the hole by means of propellers pushing it back whenever it starts to drift away from the center of a pattern of tightly moored surface and submarine buoys.

Belly & Head. The essentials of this system, plus a specially designed drill rig, got their first big test last fortnight when Cuss I, owned by Global Marine Exploration Co. and originally designed to drill oil wells in much shallower water, stationed herself off La Jolla, where the ocean is 3,140 ft. deep. Four outboard propellers driven by 200-h.p. engines churned the water fore and aft, but, according to plan, the ship did not move. Buoys moored 1,000 ft. away carried transponders to repeat sonar waves sent to them underwater. Pilot Ernie Cantu watched a sonarscope showing the ship’s position in relation to the fixed buoys. When Cuss I tended to get out of position, Cantu worked a wheel and a joy stick that changed the speed and direction of the four propellers and so kept the ship accurately over the drill hole. The trick is not easy. “It’s like rubbing your belly with one hand in one direction,” said Cantu, “and your head with the other hand in the other direction at the same time.” But he learned to master the two motions and made the clumsy ship behave while the long, thin drill point bit into the bottom.

Off La Jolla the Cuss I drilled five holes, the deepest 1,035 ft. Cores of sand, mud and soft stone with a few fossils were brought up. In spite of the loss of two diamond-studded drill points, the tests were considered highly successful.

Never had any drilling been done in such deep water. The new tests that will start soon off Guadalupe will show what modifications of ship and drilling apparatus will be needed to drill through miles of rock down to the Moho itself.

*The Mohorovicic discontinuity, discovered in 1909 by Yugoslav Seismologist A. Mohorovicic.