Science: Year of Fire

Mauna Loa was ticking like a time bomb. Dr. Thomas A. Jaggar, a rugged old master of volcanology at the University of Hawaii, would not venture a guess on the day or month Mauna Loa would erupt, but according to his charts and records, 1946 is a climactic year in the volcano’s eleven-year cycle. That cycle has been rolling along as steady as moonrise since 1832—and probably well before that. When the eruption comes, says Dr. Jaggar, there is a good chance that a stream of smoking lava will writhe slowly down the north side of the mountain and fill the shallow harbor of Hilo, 23 miles away. If that should happen, the island of Hawaii, southernmost and largest of the Hawaiian group, would lose its last good port.

In periods of quiescence Mauna Loa is a rough-surfaced, gentle-sloped mountain, 13,680 ft. high, with a hole in its head. But in eruption it is a thing out of Dante’s Inferno, frothing with burning gas, squirting great cherry-red fountains from a shimmering pool of lava. Sometimes the lava overflows, oozes down the mountain; sometimes it blows a vent through the wall of the cone below the crest; and again it may rise in the crater well, put on incomparable pyrotechnics, then retire under a hardening shell.

A lava flow cannot be dammed, but in some cases it can be diverted by artificially created channels. Mauna Loa’s last serious outbreak in 1935—and a minor one in 1942—was shunted away from Hilo by bombs from Army planes.

Most volcanologists think that volcanic and earthquake activity occurs along profound rifts in the earth’s subsurface, cracks running down as much as 100 miles or more. At those depths the temperature is high, the pressure strong and steady, and earth material a homogeneous magma of plastic rock. This pressure and material are the source and force of a volcano.

After an eruption has released the pressure, the top layer of the molten rock cools and hardens, sealing the volcano temporarily. The cap can contain the pressure for a time—depending on the peculiarities of the individual volcano—when it cracks open again with a rush of burning gas. Molten magma boils up, whipped to a froth by the gases. After the pressure has been relieved, the eruption subsides, the cap forms again and the cycle of eruption is complete.

Hawaii is not the only Pacific island due to celebrate its year of fire. Some others:

Tomboro on Sumbawa, second island east of Bali, is at the end of its 131-year cycle. In 1815 Tomboro produced one of the greatest explosions of all history. Dr. Jaggar thinks that it was greater than Krakatoa’s, in 1883.

Niuafoou, in the Tongan Islands north of New Zealand, is ready to go again. Its last eruptions were in 1929 and the early ’30s.

Sakurajima in southern Japan erupted early in March for the first time since 1914. It was right on schedule.