National Geographic : 1961 Nov
Sun sets over the Pacific as the crew continues its night-and-day probe Some have gone down almost five miles, Mohole director Bascom confirms. One in west Texas hit 25,340 feet in 1958. But on land the underlying crust averages 21 miles thick -four times as deep as anyone has drilled. "Reaching the mantle from land," he adds, "can't be done. The weight of 100,000 feet of pipe, plus the heat at the bottom of the hole, is too much for modern methods and metals. "From an island, the Moho isn't so far perhaps only 50,000 feet. But nearly all the way would be through hard volcanic basalt, the toughest sort of drilling. "Under the oceans the crust in places may be only two and a half to three miles thick. Counting the water, the Moho lies some six miles down. Drilling through three miles of rock is somewhat of a problem. But lowering a drill string, our total length of pipe, com pletely unsupported in great depths of water, 692 is a very large problem indeed." Now, in the late afternoon sun, we watched as the feat was tried. Above us the derrick stood etched against a pale blue sky. CUSS I reverberated to the thunder of heavy engines and the banshee scream of a winch brake against 100,000 pounds of pipe. On the drilling platform, five men moved in disciplined harmony and rhythm, as grace ful as acrobats juggling a 60-foot steel pole. One false move could crush them. Another length of drill pipe rode a convey er forward from racks on the stern. Yanked upright within the tower, it dangled from a pulley block taller than a man (opposite). Gently lowered, it met the previous length of pipe, and a spin locked their threaded ends. Together they dropped away through a hole in the center of the platform. Far below, the business end of the drill string-a diamond toothed, doughnut-shaped bit (right) dropped into drilling position on the sea floor.