National Geographic : 1954 Jan
119 .Mainiclhi Press Bayonnaise Rocks, Rim of a Mighty Crater, Guard the Approach to Myojin Eighty explosions or groups of explosions built and destroyed Myojin No. 1 . Of these, man saw but 13. News of the others flashed by ocean's natural telegraph service to electromechanical ears 5,300 miles away across the Pacific. At Point Sur and Punta Arenas, on the coast of California, the United States Navy maintained two underwater listening stations, part of a system called sofar (sound fixing and ranging). Record ing stations on shore listened in on cables running down the continental slope to hydrophones deep in the sea. Designed to locate ships in distress, sofar also detected sounds of natural origin. Sound waves from Myojin raced through Pacific waters nearly a mile a second, more than four times the speed of sound in air. At that velocity it took them 97 minutes to reach California. Sofar recorded Myojin's first weak explosion early on the morning of September 16. Twelve hours later a heavy blast sent "tidal" waves racing across the sea at 150 miles an hour. The waves struck Hachijo Island, 75 miles to the north. Myojin's initial explosions cleared an exit for lava and vapors demanding release from the earth. By the time the first visitors sailed close, the volcano had built a steaming island several hun dred feet wide. After Shikine Maru left the scene, Myojin ex ploded uninterruptedly for 70 minutes, but only sofar's ink squiggles took note. A United States Air Force plane, visiting Myojin on the 22d, found only a few black rocks jutting above the sea. Ten minutes after the flyers departed, Myojin fired 10 explosions in 40 minutes. Any one of these could have felled the plane had it been flying low. Soundings reveal that Myojin is the central vent of a 7-mile-wide caldera, a dish-shaped de pression at the summit of the sea mountain. Bayonnaise Rocks are the only part of the sau cer's rim rising above the sea. The eruption that created them went unrecorded.