• U.S.

Science: Glacial Calling Cards

3 minute read
TIME

Last fortnight and again last week earthquakes shook the northeastern U. S., from Canada to Philadelphia. The epicentres of both temblors were traced to the region of Lake Ossipee, N. H., which is about 100 miles north of Boston. As quakes go, they did not amount to much, but near the epicentres they were the most violent ever recorded with modern instruments in solid old New England. Chimneys tumbled, dishes and canned goods fell from shelves, walls cracked, furniture slid. In Milton, Mass, a woman telephoned to police to find out whether the Navy ammunition depot at Hingham had blown up. In White Plains, N. Y. a filling-station attendant yelled that the Kensico dam had burst. In South Portland, Me. a woman got dizzy, fell down, hurt her head. In Manhattan’s Harlem a man fell out of bed.

In Conway, N. H. a church bell started an eerie tolling and in North Conway a house caught fire. In Salem, Mass, a rare Japanese tile gargoyle in the Peabody Museum fell and shattered. In Albany, N. Y. a huge Christmas tree in the State Office Building toppled. In Portland, Me. a butterfly came out of its cocoon, flew around. In Chicopee Falls, Mass, a water main cracked. In Central Falls, R. I. instruments and bottles in the glass cases of an operating room rattled while surgeons were operating. In Nashua, N. H. a church’s stained-glass windows were broken. In Weymouth, Mass, an automobile rolled off a jack, imprisoned the mechanic beneath it. In Fairfield, Me. a horse fell down. In Rockport, Mass, an astute dachshund named Lieda, thinking a heavy truck was passing, jumped up on a couch to look out the window.

Only one person was killed, little serious damage done. Severe quakes of the kind that ravaged Rumania last autumn are caused by gradually built up stresses and sudden slips along faults (fractures) in subterranean rock. They typically occur in geologically “young” regions where mountain building or volcanic activity are common. The rocks of the northeastern U. S. are old, have long since settled down to geological sleep. No major stresses and slips can occur.

Quakes of last fortnight’s kind are calling cards left by the huge ice masses which covered parts of the U. S. in the last Glacial Age. That ice was half a mile to two miles thick, weighed two to eight billion tons per square mile. The great weight squeezed the land below, pressed it down. Since the ice retreated northward 15,000 to 25,000 years ago, the ground once under it has been springing back upward, like a dry sponge after a weight on top of it is taken away. This recovery is not constant, takes place as a series of intermittent jerks. Long intervals may separate the jerks, but when one occurs it makes a minor quake.

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