THREE HOURS' DURATION.

New Zealand Herald, Volume LX, Issue 18317, 6 February 1923, Page 7

THREE HOURS' DURATION.

RECORD AT WELLINGTON. [BX TELEGRAPH.—PRESS ASSOCIATION.] WELLINGTON, Monday. The Government seismologist, Dr. Adams, secured a remarkable record on the new seismograph of the big earthquake reported by cable as having occurred in the Pacific. The first waves arrived about 5 p.m. on Friday, and the record extends for three hours. The maximum amplitude of the earth movement was about two-thirds of a millimeter. The record indicates that the origin was approximately 3500 miles away.

TEE DREADED TIDAL WAVE.

THEORIES OF THEIR CAUSE.

The uncr.nny behaviour of the sea which invariably accompanies an earthquake is enough* to strike terror into the heart of the bravest—even the hardened sailor familiar with the ocean in all her moods, ■ wrote Captain A.. A. Bcstic, of the mercantile marine, in an article on the recent tidal wave that swept the northern coast of Chile. The first intimation of the arrival of the terrible " tidal " wave is the receding of the sea from the shore. This recession varies; sometimes it may be only 30ft. or 40ft.; at other times it has been known to be more than a mile. The time which the dreaded sea wave takes to arrive after the recession also varies. It may take half an hour or more, or it may overwhelm the unfortunate inhabitants in the coast towns in the course of a few minutes. " ...... Various theories have been given in explanation. One is that there is an earth wave on the ocean bod which, travelling inland, carries a forced sea wave with it. As it reaches higher ground the sea wave slips off, thus causing the withdrawal. Then, reinforced by the enormous submarine disturbance and the water it has ■ accumulated by sliding back, it hurls itself forward with great destructiveness. There is another theory that the earthquake causes huge submarine landslides, and that the vast displacement sets the ocean in a state of oscillation. As a fact, there are usually marked changes in the depth of water afterwards. A hot unlikely ' explanation is that the water finds its way down fissures to the underlying heated rocks, and, turning into steam, causes the wave,, which is more dreaded on shore thai! the earthquake itself. From various records one discovers that the majority of these waves do not usually exceed about 80ft. or 90ft. in height, but the 70ft. wave which swept Lisbon after the earthquake in 1755 was sufnicently destructive to drown 50,000 people. This height, however, is by no means the limit, , for in 1737 a wave which broke near Cape Lopatka was estimated to have reached a height of 210 ft. One sea-captain has left on record an experience which few men can boast. In the year 1846, when he was off the island of Raratonga, in the* Pacific, an appalling storm arose, and a tremendous wave swept the island, carrying all before it. Catching his ship upon its course, it carried her far inland. Nobody ever measured this wave, but the captain afterwards stated that he could feel the palm trees grating against the, keel of his vessel.