THE TAUPO EARTHQUAKES.

Dunstan Times, Issue 3129, 7 August 1922, Page 7

THE TAUPO EARTHQUAKES.

An interesting contribution to the discussion regarding the probable causes of the recent earthquakes in the Taupo district is supplied (says the Auckland Herald) in a letter received by Mr Clement Wragge from Mr A. J. Mountfort, of Mangonui, formerly a member of the New Zealand Government Survey Staff. He was district surveyor at Tanpo from 1908 until 1911, and was engaged in a resurvey of the Taupe township during a portion of that time. Mr Mountfort states that, white on his resurvey work, he discovered that the minor trig work, south' of the Taupo township, appeared to have been poorly observed. On reobserving these tngs he made a rather startling discovery m regard to the hill Maiitngahaniu, about fonr miles to l the south-east from the Taupo township. “I found.” he says, “that this bill* was only a tongue of cooled lava, covered by about a foot of pumice ash. steep on the sides, and apparently running out to Lake Tanpo. under the plain. The rock, or lava, appeared to be pumice when first seen, but on examination it proved to ho heavy and hard. On going up the side of the hill I found that it was cracked at about half-chain intervals, right to the summit, which is practically a razor-back, and that one rent went along the ridge, .splitting the mound which hud ixx*n thrown up round the trig mint, leaving the pipe, on one side of the rift', so that I had some difficulty in setting up my theodolite.” _ . “On a closer examination I discovered that the rift had been caused by the (Splitting of the solid rook un deni oath the pumice soil, and 1 finally concluded that tlie splits were caused* by the lower portion of the tongue becoming hot; but why the rock did not close again when conditions became normal puzzled me. examined the slips that had taken place on the Taupo-Tokaanu road in the former earthquakes!, and also those by the Tenure Hotel, and concluded that the hill had been riven at the same time. On talking the matter over with some of the people who had been in Taupo during "the nineties, Mr Mountfort found that all agreed that each of the earthquakes followed a heavy report from about the hill Maungahamu. Tt would he difficult to estimate how far the fissures extended underground, as there was a deep coating of pumice all over the plain. The fissures in the rock were from 6in to 12in wide, and appeared to go right down. M “It would be interesting to know, adds Mr Mountfort, “if these fissures were closed up bv the late disturbance. The trig was erected in the eighties, and the hill could not then have been riven along the summit. I laid down standards on the flat at Taupo; by measuring these lines again, and observing a few trig hearings on the minor trigs, it could he ascertained if any permanent disturbance had taken place since 1911.” Mr Mountfort continues: ‘ 1 ins opens up the question ; What causes the rock below becoming heated, causing the upper portion to split, or the cooling of the upper rock while that below remains hot? Any one of tho splits in Maunghamu, which are parallel to its length, would have caused a considerable earthquake in that class of country. One split might let in water that would cause a. faster cooling. As all my observations went to prove that the shakes are caused by tho rock splitting from differences of temperature, there should he very little danger. One statement made by those who experienced the shakes in the former earthquakes—that the shakes used to start soon after sundown —would back up my theory. An examination of the ground shaken down by the shakes in the ninetieswould indicate that it was more likely ' that these were caused by concussion than by an earth-wave.”