About Earthquakes; Facts and Theories.

Te Aroha News, Volume IV, Issue 161, 17 July 1886, Page 5

Abo ut Earthquakes ; Facts and Theories.

<■ Our readers have been made familiar with the recent events in the world -famed Rotorua district ; they have been minutely 'informed as to the nature and extent of 'the convulsion of Nature there, so terrifying in its outburst, so fatal in its results ; and they have been enabled to come to the conclusion, from the statements made by men of scientific attainments, 'that in reality very little indeed is known as to the cause of such phenomena. There are certain geological facts and certain laws of force upon which men base their opinions. These opinions, however, differ widely, and remain mere conjectures. For ourselves, we hold with Dr. Hector that the explosive force which has buried Wairoa and the native settlements of Ariki and Morea, and has heaped up millions of cubic feet of mud ac material for possible avalanches, was caused by the sudden inletting of a body of water upon the subterranean heat, and the consequent generation of an enormous force of highpressure steam. The Subterranean Heat In the Rotorua District has been abundantly evident. In the details which have from time to time been published relative to the hot springs there, the temperaturo is in some cases given as reaching the boiling point, 2l2deg Fah., ■whilst a heat of from 10 to 20deg lees is not ! at all uncommon. And there is the pessi- i fcility— the strung probability, even— that the indications of volcanic activity in the North Island are simply one of the links in •an immense chain of volcanic energy girdling the Pacific Ocean, and appearing here and there within its area of seventy-two million square miles We may trace this, chain with considerable distinctness, commencing in the southward with those Antarctic outposts, Mounts Erebus and Terror ; through New Zealand ; thence curving round the eastern coast of Australia ; still northward through islands innumerable ; through tho Japan islands ; thence eastward via. the Aleutians ; thence, following America's western coa^t-line southward to the Shetlands. The existence of this well-definod v chain (with the known upheavals and B.ib*?idences within its area) gives rise and lends support to what we may "term The Sandwich Island Theory, mentioned by our Wellington correeponden in one of bis messages ; a volcano in the Sandwich Islands died down ; then a new volcano cone rose out of the ocean between the Sandwich Islands and New Zealand ; then White Island, off our coast, became unusually active, and lastly Tara«6ra broke into eruption. The volcano which died down was Kilauea, in the south of the island of Hawaii ; its crater has or had — an inner circumference of seven mite*, w ith a large lake of boiling lava therein. Yet this vast opening was but a subsidiary part of the volcano of Mauna Loa, " the largc?t and most remarkable in the world/ By some means this safety valve was chut down. Can we for one moment suppose that the pressure of the ocean on its bed, two, three, or more tons to the square inch, had no influence in forcing other ventp, knowing as we do that the Pacific basin alters its level?, rising here, subsiding there. In point of fact, there may be a variety of agencies at work. The ocean pressure is one of those, and allied thereto is the Effect of the Tides. Proctor and others have speculated upoc what may have been, and w hat may be, the results of an increased weight of tidal water upon a shelving roast. If we roughly compare a section through an island to an aich, we may have upon certain points of that •arch at stared times such an increased pressure a-* may exerciee a marked compressing effect, and may produce luptures in a volcanic earth-crust. Every foot of tidal rise, Professor Milne, the eei=mological authority of Japan, telis us, is *' equivalent to a load being placed on the area over which the tide takes place, of sixty two pounds to the square foot ; and the load is not evenly distributed, but stop 3 abruptly at a coast line." Professor Darwin, again, assumes that these tidal loads may have much influence upon land areas which are in a more or less critical condition. New Zealand, it is specially interesting for us to note, is curiously formed. "The investigations of the ' Challenger ' Expedition have shown that, unlike other Oceanic islands, New Zealand is surrounded by a submarine plateau or ehelf, w hich extends in varying distance from the coast. On the southwest the edge of this plateau almost coincides with the coast-line, which here presents a maseive buttress of granitoid rocks to the prevailing erosive action of the ocean from that quarter. To the eastward, the extent of the plateau is unknown, except that it probably reaches as far as the Chatham Island, The depth ot water On the plateau is about three hundred to six hundred fathoms, the surrounding water of the ocean having a depth of from two thousand to two thousand six hundred fathoms." This fact, as quoted, Dr. Hector haB given in one of his admirable handbooks prepared for the Colonial Exhibition. The Pressure of the Air is another factor that has to be borne in mind. This pressure, as the barometer every day reminds us, is a variable ona. Ordinarily it may bo fourteen pounds to the squaie inch. Let the barometer rise an inch, and we thereby know that upon •every foot of ground there has been placed an increased pressure of not less than seventy pounds. Such an added pressure over the Continent of Australia, Mr Darwin has calculated, would sink it two or three inches, even though the earth were rigid as steel, which most certainly it is not. We do not for one moment venture to assert that increased atmospheric pressure had to do with the Tarawera outburst, for the simple reason that scientific men differ quite as much on this point as on any other. But this much we may call attention to, that the season has been one of high barometers ; that on June 9 the barometer was high, and was rising. It is one of the items which systematic investigators of the observed phenomena will of course consider. The Electrical Display seen above Tarawera, on the night of the •eruption, may— as Professor Bickerton has suggested— have been caused by the rushing steam. The production of torrents of electricity by the agency ot a steam boiler and especially arranged jets will be a vivid memory with people who have visited the now defunct Polytechnic in London. We have not touched— as some of our readers will doubtless have noticed— upon some of the seismic influences insisted upon and demonstrated with more or lefts clearness by various authorities, nor can we, in view of the exigencies of newspaper space and time attempt to do so. But a very interesting feature indeed would be miesed if the fact that Earthquake Predictions have been ventured upon were not Btated. 'One of the prophets is Delauney, who bases his calculations upon the periodic theory

Just as there are fairly well defined yepra in which sun-spots are most numerous, bo, Delauney holds, there are special years of earthquake, due to planetary influences ; Jupiter and Saturn being partictlarly referred to. Here are Delauney 's predicted earthquake years : 1886 ( !), 1891, 1898, 1900. Large meteoric showers, again, have been supposed to have an earthquake connection ; and men of Rudolph Falb'a school rely upon the combined attractive force of the sun and moon. Falb has been one of the modern prophets : "In 1873 he predicted the destructive earthquake of Belluno, which earned for himself a eulogistic poem. After this, in 1874, he predicted the eruption of Etna. He also explained why, in B.C. 4000, there should have been a great flood, and fcr a.d. 6400 he predicts a repetition of such a « occurrence." From all of which it is once more demonstrated that seismology (the study of volcanic and earthquake phenomena) is a speculative science. But all is not pure speculation. In the Rotomahana district, for example, the Bolvent nature of the spring waters, and the formation of great underground channels and chambers, is unmistakeable. Froude hus noted in his " Oceana " how rapidly the underlying flint lis brought up and deposited on the surface, a rapidity which he has aptly illustrated by the case of a still growing tree he saw there, ita trunk partly enciusted with the glistening beauty of the White Terrace formation. Some of the springs deposit pure sulphur ; some, lime in one form or another. The underground volcanic system of the North Island may be interrupted by rocks ; it may be in comparatively free communication with Kilauea of the Sandwich Islands. Speculation still, and still strangely mixed up with fact ; for in the Sandwich Islands themselves '* we see the columns of lava in neighbouring mountains standing at different heights, indicating a want of subterranean connection between these vents." Considering the frequency of earthquakes, the wonder is that we In this Island of Oceania, know so little of thorn. Yet we are credited by one authority with a monthly average of 2S perceptible "shake 3," most of these being, of course, so insignificant that people generally would fail to notice them. In Japan, two shakes per day is the modest claim ; in the Andes, earthquakes occur at every instant of time. Occasionally— only occasionally — wo have been able to notice a fahake without difficulty. In the " Page of Southern History ," published the other day, we were told of a great earthquake forty years ago in the VVaiau Valley. In ISSS, on June 23, Wellington hc\d a particuirrly sharp experience, and it is on record that many fish were then killed in consequence of the sulphurous vapours which rose in the sea near the coast. The shocks, in fact, came from the sea. It is curious that on the very same day Isorth America had a rude shakmg-up, as did a part of the Austro-Hungarian territory ; and, within a few days, Japan was destructively visited. In ISGS there were notable shocks in New Zealand and New South Wales ; and of a subsequent quiver the spire of Ghristchurch Cathedral bears witness. In that spire an earthquake-recording pendulum was subsequently hung, but we never hear anything about it Y^e have al^o experienced effects. On May 9, 1577, some harbour towns on the coast of South America were destroyed, and a erreat wave carried death into Iquique ; 5,641 miles that wave-motion travelled to Lyttelton, occupying only about I!'\ hours in doing so. In 187S, again, •« earthquake- waves " absorbed 25,000 livi s on the South American coast, crossed the Pacific, and " at the Chatham Islands rushed in with such violence that whole settlements were destroyed." But articles such as this must be deliberately cut to some definite length. We will close with A Humourous Illustration, but a perfectly true one, nevertheless, of the fact that in the study of earthquakes, as in numerous other things, the almond-eyed disciple« of Confucius have anticipated European civilisation. The extract with which we conclude is translated from tne Chinese history, " Gokanio " :—: — " In the first year of Yoka, a.d. 136, a Chinese called Choko invented a seismometer. [A drawing is given ] This instrument consists of a spherically formed copper vsseel, the diameter of which i« eight feet. It is covered at its top, and in form resembles a wine-bottle. Its outer part is ornamented by the figures of different kinds of bird? and animals, and old peculiar-looking letters. In the inner part of this instrument a column is bo suspended that it can move in eight directions. [Part of the column projects through a circular opening in the top of the sphere.] Also, in the inside of the bottle, there is an arrangement by which some record of an earthquake is made according to* the movement of the pillar. On the outside of the bottle there are eight dragon heads, each of which holds a ball in its mouth. Underneath these heads there are eight frogs so placed that they appear to watch the dragon's face, so that they are ready to receive the ball if it should be dropped. All the arrangements which caupe the pillar to knock the ball out of the dragon's mouth are well hidden in the bottle. When an earthquake occurs, and the bottle is shaken, the dragon instantly drops the ball, and the frog which receives it vibrates vigorously." The particular ball dropped would of course indicate the direction of the earthwave. Choko did not labour in vain. His instrument is of interest, Professor Milne remarks, on account of the cloeo resemblance it bears to many of the instruments of modern times. ~" Canterbury Times."