Pattern for Suicide

On Oshima, outside Tokyo Bay, stands the active volcano Mihara. It bubbles with sulphurous vapor and at irregular intervals shoots out molten rock. Japan has many active volcanoes, but Mihara is specially famed because of the romantic lovers who frequently kill themselves by jumping down its throat. Before World War II, 80 to 90 did this each year, and the steamship company that serves Oshima got rich on tourists who flocked to the island, they said, to watch the volcano, but really to watch the suicides.

Mihara's suicide score has fallen since the war, but the volcano may become famed as the first whose eruptions can be predicted scientifically. Five years ago. Assistant Professor Tsuneji Rikitake of Tokyo University's Earthquake Research Institute started prowling around the warm rocks on its top crater, carrying apparatus to measure earth magnetism. Whenever he approached the hot crater, the strength of the magnetic field de creased appreciably.

Rikitake reasoned that the basaltic lava forced up through Mihara's throat is strongly magnetic when it is cold. Like other materials, however, it loses its magnetism when it gets hot. Therefore, the region near the volcano's white-hot core should be less magnetic than other places a little farther away. Rikitake checked this theory by circling the mountain with his instruments. A chart of the magnetic field also showed the shape of the hot and hidden core.

Rikitake set up a permanent observation station in an old air-raid shelter dug into Mihara's western slope. In October 1951 his instruments showed that the vol cano's magnetism was slowly weakening.

According to his theory, this meant that the rock in its core was getting hotter and approaching the melting point. In December came the proof: the volcano had a small but definite eruption. In 1953 and 1954 the pattern was repeated. Whenever the volcano's magnetism diminished appreciably, a period of activity followed in two to six months. The greater the change in magnetism, the stronger the activity was apt to be.

Rikitake now considers his theory pretty well proved, and he hopes that it will be used to keep tabs on basaltic volcanoes all over the world. Among these are Japan's Mount Fuji, the volcanoes in the Hawaiian Islands and Mount Vesuvius.

But the professor is not sure that he should make regular predictions of the eruptions of Mihara, once so fashionable for romantic suicides. Any increase in popular interest might make it the rage again. "There is a social problem," he says apprehensively. "The steamship company would advertise and make money."

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