The Wadatsumi kept a distance of about 150 yards from the crest of the undersea island as it began to circle it at a speed of three knots. They were close enough to see clearly the creases that ran down the crater wall of the old volcano. As soon as he turned on the searchlight, even Onodera, layman though he was, was able to perceive the difference between water and wind erosion. The diameter of the crater at its mouth was some 200 to 300 yards. On its inside the sides of the crater fell away in a sheer, almost perpendicular drop. There was a deep V-shaped crevice in the crater wall. It seemed to have been caused not by the eruption, but by some earlier disturbance. The fathometer showed a depth of about 300 feet at the crater. Onodera felt a chill as the thought struck him that Tadokoro might say, “Let’s go down into there for a look.” There was no evidence of volcanic activity at the time of the island’s sinking.
Just as though it had been there forever, the black bulk of the island lay in the cold gloom of the ocean depths, a pall of heavy silence shrouding it.
Onodera began his descent. Using the sonar to ensure the greatest safety, he fixed upon the slope line of the volcano, pointing the nose down at an angle of nearly thirty degrees.
“We’re going down the slope, Yuki,” he said into the micro phone. “Keep a sharp watch.”
“I’ve got you.”
Onodera turned the rheostat lever. The sound of flowing water penetrated the thick metal of the gondola casing, and the vibrations of the engine shook it as the Wadatsumi began its descent at a speed of two knots. Professor Tadokoro and the young engineer tightened their seat belts, their eyes like saucers as they looked out the observation window and at the TV screen. The dull, twanging echo of the sonar reverberated through the gondola.
Schools of fish and huge shadows which might have been sharks crossed the screen. The side of the undersea crater loomed up outside the right window until at last the unmistakable traces of sea erosion came into view.
“Go back up to the water line,” said Tadokoro.
Onodera raised the nose of the submarine until the erosion mark was opposite the window.
“Where’s your level?” asked Tadokoro.
“In the drawer there.”
Tadokoro laid the level on the ledge of the observation win dow and studied it with rapt attention. Finally he spoke abruptly: “If that’s the sea-level mark as of three days ago, the whole island has tipped four to five degrees to the east.”
“Should I continue down?” asked Onodera.
Tadokoro signaled his assent with a tap on the shoulder. The Wadatsumi resumed its descent. . . . 600 feet . . . 800 feet . . . The sun was apparently high in the sky by now, for visibility remained fairly constant. The water outside the window, how ever, quickly took on a bluish cast. At 1,000 feet Onodera slowly brought up the nose of the submarine. The slope of the crater was gradually growing less steep as its skirts trailed down into the indigo-blue depths of the ocean floor. Onodera turned off both the television and the lights inside the gondola. A ghostly blue light poured in from the round observation windows. At 1,200 feet, the Wadatsumi, now almost level, continued to follow the gradual slope which trailed far off to the vanishing point in the darkness of the ocean floor. He jettisoned a small amount of ballast.
“We’ll reach the bottom in just a bit,” Onodera announced.
He turned on the searchlight. Beyond the cloudy wall of water ahead, the sea floor came dimly into view. The guide chain trailing from the bottom of the submarine struck with a thump, transmitting the shock to the gondola. Phosphorescent fish swam up to the window. The floor of the sea, beneath the powerful glare of the searchlight, seemed to loom up like some massive gray living thing. Onodera dropped their speed to a half-knot. The guide chain stirred up mud from the bottom as the Wadatsumi finally came to a gradual stop. There were only six feet between it and the ocean floor.
The bottom of the sea, as far as Onodera was concerned, showed nothing unusual. For the two men behind him, how ever, there was something that gave rise to great excitement.
“Ripple marks ...” muttered the young engineer.
“Volcanic rock projectiles—right out in the open like that!” exclaimed Tadokoro excitedly.
“It’s obvious, isn’t it, that mud on the bottom shifted violently just a little while ago?” said the engineer. “Take a look—there!”
“Hmmmmm.” Tadokoro nodded. “The sea floor here, keeping the same slope, seems to have shifted over a broad area, doesn’t it?”
“Rather than shifted, wouldn’t you say that there might have been something like a landslide?”
“Onodera,” said Tadokoro, “what we have to do next is to see what we can see on the eastern part of the shelf.”
Professor Yukinaga and a specialist in volcanoes from the expedition went aboard for the second dive. This time Onodera went down at full power and brought the submarine rapidly to a depth of 2,000 feet. And from there, following the slope of the shelf, they dove to the ocean floor, a depth of 6,050 feet. Again the two observers came across a wealth of exciting discoveries. Once even the ever-composed Yukinaga cried out shrilly. The sea was beginning to get rough when they surfaced again.
“We’ll postpone the third dive until tomorrow,” said Tadokoro. “The Daito Maru seems to have discovered some thing unusual about ninety miles east of here, in the Ogasawara Trench. This time well go down to the bottom of the trench to have a look. No difficulty in that?”
“No, sir,” said Onodera.