Atomic Dents

The AEC's underground nuclear tests may not produce a fiery mushroom cloud but there is one above-ground effect that anyone can see. ] Shortly after each recent blast, a strange dent has appeared in the ground at the Yucca Flats, Nev., test center. Some of the depressions are only a few feet deep, but two of them are 50 ft. deep and several hundred feet across. The holes are not craters; nothing is blown out. There is no radioactivitiy, and the level of the ground around the depressions is not raised. But millions of cubic feet of dirt have apparently disappeared.

Last week the AEC explained that recent bomb tests have been conducted in deep vertical shafts. The walls of the test chambers are of sedimentary strata full of small pores. The irresistible pressure of a bomb's expanding fireball compresses this material, forming a spherical cavity holds its shape for 15-25 minutes; then the cooling gases lose their pressure. With a horrid noise the roof falls and all the way to the surface. With a horrid noise the roof falls, and all the way to the surface the layers of shook-up material tumble down after it. As the LASL News, house organ of the Los Alamos Scientific Laboratory, describes it in somewhat unscientific terms: "It sort of takes a guy by surprise. You hear a kind of crunching sound and you look out of the window. Half an hour ago when the bomb went off, it was plain old flat, sandy Yucca Flats. All of a sudden it's a hole big enough to float a small fleet if you had any water."

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