Underground Blast

An atom bomb detonated underground would leave a radioactive crater which would be dangerous indefinitely, and the "hot" dust blown into the air might paint a broad band of silent death many miles downwind. The only safe way to simulate such an explosion is to use a "low-order" chemical explosive and scale up its effects theoretically to full atomic proportions. Last week at desolate Buckhorn Wash, Utah, Army engineers came the closest yet to simulating an atomic blast.

Into a spherical cavity 18 ft. in diameter, carved deep in solid sandstone, the engineers packed 320,000 pounds of TNT, cast in close-fitting blocks. Then the shaft was blocked with material as solid as the living rock. Instruments and test structures, dug in for miles around, waited for the rock shock. When the charge exploded, the earth rose up in a mound, as if a giant fist had poked up through mud. Jets of flame burst through the debris. Jagged boulders soared through the air; good-sized chunks of rock landed a mile away, and smaller fragments covered a good three miles. The ground shook as if rocked by an earthquake, and the smoke of the TNT blacked out nine square miles of Utah.

Shock Test. In atomic lingo, a "nominal" bomb is the one used at Hiroshima, which released as much energy as 20,000 tons of TNT. The Buckhorn Wash "bomb" (160 tons of TNT) released 1/125th as much energy. But because the explosive effect of a bomb decreases only by the cube root of its comparative size, the jolt it gave the rock around it was roughly one-fifth as powerful.

To test its shock through the rock, the engineers surrounded it by scaled-down diggings representing installations such as subway tunnels, concrete foundations of buildings and other underground structures that might be damaged by rock waves in an atomic war. Elaborate special instruments (cost: $2,000,000) measured the motion of the rock and its destructive effect. The results will be kept secret as were the results of earlier tests in clay, soil and other ground materials.

Flying Poison. But one implication of the test explosions is no secret. Atomic bombs set to explode underground are expected to play a big part in future warfare. Air bursts, as used over Japan, affect only the surface of the ground. As both sides burrow deeper, placing their vital installations deep in soil or rock, the atom bombs will go after them, sending rock waves to wreck them as no air waves can.

Another military factor will be the vast amount of debris thrown out by an atom bomb that penetrates earth or heavy buildings. It will be highly radioactive, and chunks of it flying for miles will poison large areas. The Army engineers say they are not interested in the bits of rock that were thrown three miles by their scaled-down bomb. But atomic bombardiers will certainly take note.

This file is automatically generated by a robot program, so reader's discretion is required.