Page:Popular Science Monthly Volume 2.djvu/532

514 waved like standing corn in a gale of wind, and an area 70 miles long by 30 miles wide was submerged, and became a swampy lake.

On the 13th of August, 1868, a fearful earthquake took place in Peru, which laid waste much of the country lying between the Andes and the Pacific. The shocks were felt through a distance of 1,400 miles north and south, and three important cities were destroyed. At Arequipa, in Peru, 40 miles from the sea, a slight undulatory shock was felt, followed by others so violent that in five minutes not a house was standing in that city of 44,000 inhabitants. A subterranean rumbling, like the rush of an avalanche, was heard above the crash, and a cloud of dust rose in the still air over the city. On the sea-coast were situated Iquique and Arica—both were destroyed by the shocks, and overwhelmed by a tremendous wave. The ocean thus took up the vibrations of the land, and waves of tremendous volume were put in motion, which rolled, not only upon the coast, but away from it with a velocity in the deep ocean of not less than 400 miles an hour. The great wave—for one was of much greater volume than the others—has been estimated at upward of 200 miles breadth, with a length along its curved crest of 8,000 miles. This rolled into the harbor of Yokohama, in Japan, 10,500 miles distant, and was felt at Port Fairy, in South Victoria, distant nearly one-half of the earth's circumference.

In 1797, a province of Ecuador, about 100 miles south of Quito, was visited by what is described by Humboldt as "one of the most fearful phenomena recorded in the physical history of our planet." The shocks were vertical, and occurred as "mine-like explosions." The town of Riobamba was over the central area, and many of its inhabitants were thrown 100 feet into the air.

The shocks, in this instance, were not announced by any subterranean thunder, but, just 18 minutes after, a terrific roar was heard beneath Quito. It thus appears that shocks are not always preceded by sounds, nor do the sounds increase with the violence of the shock.

Sometimes, says Humboldt, there is a "ringing noise, as if vitrified masses were struck; again, a continuous rumbling and hollow roar; at others, a rattling and clanking as of chains or near thunder." With the lightning's flash we know that the danger is over, and await the coming thunder without alarm; but thunder, rolling deep in the earth, announces possible if not certain calamity.

Throughout the region of the Andes a connection between volcanic and earthquake action has been recognized by the people. It was supposed by Strabo that volcanoes are safety-valves, and scientific observation suggests that they may relieve the pressure and tension which would otherwise lay the earth in ruins.

For two years previous to 1538 earthquakes had been violent and frequent at Pozzuoli on the Bay of Baise, and elsewhere in the vicinity of Naples. On the 27th and 28th of September they did not cease day