Continents on the Loose

Over southern Luzon stands a plume of ashy smoke (see cut). Mt. Mayon in the Philippines has again blown its graceful top. Most other recent seismic unrest (earthquakes and volcanoes) has also hit the shores of the Pacific: Peru, the Aleutians, Japan. Hasty guessers have therefore concluded that a wave of seismic shakes is burrowing molelike, and counterclockwise, around the Pacific. Having passed the Philippines, quivers and brimstone ought to strike the East Indies next, then the New Guinea region, then New Zealand, and back to Chile and Peru.

Calmer seismologists say that in 50 years they may be able to explain how seismic tremors in various parts of the world are related to one another. At the moment, they do not know.

One thing they do know: that a belt of crustal uneasiness surrounds the entire Pacific Ocean. The Pacific's shores are nearly all high and rugged, decorated with volcanoes or with young (a mere 100,000,000 years or so), still growing mountain ranges which shake periodically like custard on a plate. Atlantic shores, much calmer, are mostly old and stable.

Geologists are fascinated by the difference between the two great oceans. One of the more daring, Alfred Wegener of Germany, proffered an alluring theory to explain it. According to Wegener, the interior of the earth is a thick, hot, plastic substance. The continents, in large part comparatively light granite, float on it like icebergs. Under the oceans, the earth's crust is largely basalt, which is heavier than granite and inclined to sink.

The continents not only float, said

Wegener--they drift. Once North and South America were part of Europe and Africa. Hundreds of millions of years ago, they drifted apart and went their separate ways. The gap formed the Atlantic.

As proof, Wegener pointed to a map. If the drifting continents were pushed together again, they would fit rather neatly. The bulge of Brazil would poke into the Gulf of Guinea. Eastern Canada would fit roughly against Scotland. Spain would snuggle into the Caribbean.

As the continents drifted apart, Wegener maintained, they also drifted toward one another on the other side of the globe, pressing into the Pacific. Their Atlantic shores remained much as they had been before they separated; but the Pacific shores crumpled the earth's crust ahead of them, like the bows of ships plowing through thin ice. Thus were formed the still growing, earthquaky mountains which ring the Pacific today. When the crumpling broke a hole through the solid crust, hot "magma" burst to the surface, building a volcano.

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