DR. HECTOR ON THE RECENT EARTHQUAKE AND TIDAL PHENOMENA.

Otago Witness, Issue 877, 19 September 1868, Page 22

DR. HECTOR ON THE RECENT EARTHQUAKE AND TIDAL PHENOMENA.

( Wellington Independent. )

One of the most important duties of the members of a local scientific Society such as this, is to obtain accurate records of phenomena of a transiftm character like the disturbances of the, tides and the earthquakes by which the colony was visited between the 14th and 18th inst. I have, therefore, attempted to collect together, in the following preliminary communication, the observations which were made in different places so far as they have been already Ascertained ; and although they are deficientj in many respects for purposes of exact scientific inquiry, I trust that their discussion may lead to the adoption of instrumental means for recording such phenomena in future, as it is in this manner alone that sufficient accuracy can be obtained.

As ihere is no 'reason to believe tbat the tidjal disturbances are in this instance directly^ connected with the earthquakes which we experienced, I shall, therefore, allude) to the two classes of phenomena separately, although they are only different manifestations of the same paroxysmic energy, but occurring in different parts of the earth's crust, and at different .times.

Respecting the tidal disturbances, from careful cons deration of the various accounts which have been received, it appears that they were experienced along the whole of the East coast of the islands, slid also in Foveaux Strait and Cook Strait, and that the irregularity of the usual flow and ebb of the tide was due to the influence of three distinct oceanic wave 3 which reached the coast from eastward on the forenoon of Saturday, the 15th inst., at about the following periods]: Ist between 3to 4 a.m. ; 2nd between 7 to 8 a.m: 3rd between 10 to 11 a. in. These waves were in each case followed by smaller waves, and the irregularities did not altogether cease for 48 hours after their first appearance. The exact time at which the three great waves were observed, and also their distinguishing features, were modified at different points of observation by local peculiarities due to the outline of the land, the depth of the water, the exposure of the coast line to the direction in which the wave reached the shore, and lastly to the local time of tide.

The intervals between the smaller oscillations appear to have been generally remarked at from fifteen to thirty minutes, and to have gradually declined in extent and frequency until the next great wave supervened.

The earliest notice of the wave which we have recorded beyond allusions to an extremely high tide the previous.evening, was at Kaiapoi, where it was reported that at three a.m. when the tide had ebbed for two hours, a wave, four feet in height, rushed up the Waimakariri River, and swept the vessels which were lying at the wharf from their moorings. This was at a distance of four miles from the mouth of the river.

At Lyttelton and Pigeon Bay, the time reported was at least half an hour later ; and for the other places no exact time is reported for the occurrence of the first wave, while at several localities it appears to have escaped observation.

From this time until 8 o'clock, only leßser waves were remarked, but about that hour a great disturbance seems to have been observed at all the stations, being described at the Bluff aB a terrific rush of water ; at Kaiapoi, sweeping up a line of breakers which would have ueen disastrous to the town had it not passed tip the south branch ; and almost simultaneously at Nelson, as having caused a reflux of the tide, atthat time half-ebbed, bo that it rose beyond the limits of high water mark, and flowed into the harbor over the Boulder Bank.

A third great rush of water appears to have been every where distinguished from the smaller oscillations which went on continuously, the time being variously stated from 10 to 12 o'clock, there being great irregularity in the hour reported. In this harbor, where 1 caused exact observations to be taken at frequent intervals, as might be expected from the wide expanse of water and the narrow entrance, these waves could not be so clearly distinguished as on more exposed parts of the coast ; but there is a general agreement among all the observations taken at the different stations which leads to the above conclusions.

The altitude of each wave, as compared •with its amplitude or breadth, has not been ascertained irrespective of the degree to which it was moditied by the local form of the shore upon which it expended its energy; anil this element is absolutely necessary for the purpose of determining the distance at which it originated. Nevertheless, as compared with the ordinary effects of th» tidal wav», we

can form some conception of the gigantic force which must have influenced the ocean along the coast ; when we find that the ebb and flow which these waves caused in most cases, appear to have exceeded the ordinary local rise and fall of the tide at the different localities. This leads me to expect that waves of Bitch magnitude must have been observed at many points beyond this Colony, such as the coast of Australia to the westward, and the Chatham Islands to the eastward ; and that we shall receive information from these, and probably other localities, which will enable us to determine with tolerable exactness the focus from which they originated. The following information appears to have escaped the notice of the journals in the Colony ; it is an extract from " Principles of Geology," by Sir Charles Lyell, 10th edition, 1868, vol. 2, p. 409. "Even in the present year (November 1867) a submarine volcano has burst out in the South Pacific, at a point 1200 geographical miles from New Zealand, and 1800 miles from Australia, between two of the most easterly islands of the Samoa or Navigator's Group, an archipelago where there had been no tradition of an eruption within the memory of man. The outburst was preceded by numerous shocks of earthquakes. Jets of mud and dense columns of volcanic sand and stones, rising 2000 feet, and the fearful crash of masses of rock hurled upwards and coming in collision with others which were falling, attested the great volume of ejected matrer, which accumulated in the bed of the ocean, although there was no permanent protrusion of anew volcano above its leveL "

An earthquake shock which appears to have been felt throughout the colony a few minutes ieforelO o'clock on Monday morning, the 17th inst. , was of a character very different from the local shonks to which we are accustomed in this place. From the appended record of telegraphic announcements, it appears to have occurred about three minutes earlier in the north- east at Napier than at Hokitika, on the West Coast of the Middle Island. Napier is situated in lat. 39deg. 29min. S., long. 176deg. 55rain. E. ; Hokitika,, in lat. 42deg. 41min. S., long l7odeg. 59min. E. This gives a horizontal distance of 402 miles ; but as we do not know whether the wave was travelling from the east or the north-east, it is impossible to infer its velocity. The following telegraphic record shows the exact time at which rremulations were felt at the different telegraphic stations in each island, and the distance of the principal stations from Napier, which appears to be the northerly limit of the influence : — Napier, 9.55 a,m. ; Waipukarau, 9.55 a.m. ; Castle Point, 9.56 a.m., 106 miles; Grey town, 9.55 a.m. ; Featherston, 9.55 a.m. ; Wellington, 9.56 a.m., 169 miles ; White's Bay, 9.55 and 9.56£ a.m. ; Blenheim, 9.55 a.m. ; Nelson, 9.57 a.m., 229 miles ; Kaiapoi, 9.57 a.m. ; Christchurch, 9.57 a-m.^ 367 miles; Lyttelton, 9.57 a.m. ; Hokitika, 9.58 a.m., 402 miles.

This shock was also preceded and followed by minor shocks, felt in Wellington at the times shown in the following table :— Friday, 14th August, at 10.45 a.m.; 3.10 p.m.; Saturday, the 15th, 3 a. m. , tidal disturbance ; Sunday, 16th, 3.15 a.m. and about 11 a.m.; Monday, 17th, 9.56 a.m., great shock; Tuesday, 18 tli. daylight; Wednesday, 19th, daylight.

Telegraph stations reported the shock as from the South ; but, for mechanical reasons, we may conclude that their sensation would suggest the opposite of the true direction.

The periodical character of these Bhocks was at once evident, and they appear to be in some degree dependent on the period of maximum and minimum pressure as indicated by the hourly fluctuations of the barometer.

With regard to this I may observe, that the fluctuations of the barometer during the oscillations of the tide, indicate a frequent variation, amounting to '004 inches, which is not beyond the usual daily variation, but from the irregularity with which this oscillation occurred affecting a rising barometer, it is evident that some influence must have been at work beyond the ordinary Becular variation due to the sun's position.

The author then explained that he had only attempted to state facts in a collected form, deferring the full discussion until further detailß are obtained from Auckland and other places, where no doubt the tidal disturbances were observed.

He then described simple forms of selfregistering tide-gauges, which might be distributed to different places, for the purpose of getting exact information in future.

Referring to the great earthquake wave which occurred in the North Pacific in 1854, and comparing it with the phenoma recently observed, he was led. to infer that the late tidal disturbances must have been due to some convulsion of unusual magnitude. Descrif ing the periods of the year when earthquakes occurred with the greatest frequency in different

parts of the "world, with the assistance of a map, he indicated the particular systems or areas of the earth's surface, disturbed by seismic energy, and that particularly to which New Zealand belongs.

The Deniliqmn journal supplies the following information on pastoral matters :—: — The flookowners are busy shearing, and already a number of drays have passed through for Melbourne. The samples of the clip which we have seen indicate a good harvest, and the quality of the wool is very much better than the l»st season's clip. There will be about ten millions of sheep shorn in the pastoral districts of New South Wales west of the great dividing range. There is an active demand for fat cattle, and there is every prospect of the supply of really good beef falling short., as there are not many firstclass herds having a large amount of prime fat beasts. After shearing, it is expected that there will be large quantities of fat sheep going to market; thty must be sold, as most of the runs aie overstocked. We hear of one station-holder who will have to travel about 40,000 sheep this season in consequence of the want "of sufficient feed for them. In Adelaide, fat cattle are hLh, and promise to be j they range from 200s to 2803 each for really good beef, which is everywhere in demand ; and unless we can draw much of our supplies thereof from the Upper and Middle Darling and Northern districts, the neighbouring stockowners have very fair, if not good, prospects before them for the coming season.