VOLCANOES

Wanganui Chronicle, Volume 74, Issue 191, 14 August 1931, Page 11

VOLCANOES

j TAUPO AND TARAWERA I NORTH ISLAND OUTBURSTS. Probably some who attended the “earthquake” lecture iu the Boiuiuiou Museum ou Monday were somewhat surprised to learn that Lake Taupo—that fine sheet of water in the centre of the North Island—has not always been New Zealand’s biggest lake, states the Wellington Evening’post. In fact, it has led a kind of double life. Once it was a gigantic volcano —the lake now being the remnants of the crater —and it erupted with such stupendous energy that ash was ejected as far afield as Taumarunui, Gisborne, and Napier. But this was long ago, in prehistoric times, and there is no evidence tl.at what is now a comparatively placid lake will revert to its former volcaniK: status. The lecture, in which this information was imparted, was one of the “earthquake scries” arranged by the Wellington philosophical Society, the lecturer being Mr. L. I. Grange, of the Geological Survey Department. His subject was .“ Volcanology, with special reference to New Zealand.” His remarks, which were followed with great interest, were illustrated with numerous lantern slides. At the outset, the lecturer explained the theories advanced to account for volcanic eruptions, remarking that the phenomena were interesting and spectacular, but difficult to interpret. He showed by means of maps the connection between earthquake and volcanic belts, although volcanic eruptions, he said, wore seldom accompanied by world-shaking ’quakes. Earthquakes occurring at the time of an eruption were usually confined to a comparatively limited area round the erupting mountain. Prior to eruptions, there were often premonitory signs, such as earthquakes, and the warming-up and increased activity of hot pools and geysers. From these signs it migtu be possible at times to predict an eruption. Gases played an important part in the eruptive material, helping to keep it liquid at a lower temperature than would otherwise be the case. Dealing with the various types of volcanoes, Mr. Grange said that a well’ known example of the constant type of volcano was Stomboli, in the Mediterranean, although what kept it in a state of perpetual eruption no one knew. Amongst periodic volcanoes was Vesuvius. This, prior to 1879, was thought to be extinct, but since then it had developed a period of from nine to ten years. In this, as in other cases, gas was a predominant eruptive element. Etna was another periodic vol-

cano, erupting every four and a half years, and Kilauea was another. The outstanding example of a paroxysmal volcano was Krakatoa, in Java, which ; startled the world with its outburst in i 1883. Katmai, in Alaska, which blew iup in 1912, was another. In prehistoric times there were what is known as fissure eruptions, when basalt welled . up out of the great, fissures in the , earth s crust. The Deccan, in India, t was an example of a plain formed by - this welling-up of basalt. Nothing of 3 this nature had taken place in recent s geological periods. s Turning his attention to volcanic ac- , tivity in New Zealand, Mr. Grunge j said that he would deal chiefly with « the vulcanic belt stretching across the r centre of the North Island from Taupo s to White Is.and, ami embracing what r is known as the thermal district, al--1 though he mentioned in passing that it - had been computed that Auckland’b • volcanoes had been about 10U0 r years ago, ami that Mount Egmont had r erupted as recently as 500 years ago. i Tongariro, he suggested, was at one 3 time 1000 feet higher than it is at j t present. Jts summit is now flat, with I several craters. Nguuruhoe, had a cone built up of scoria, and had emitted - lava, within recent limes, a distinction - shared with only one other crater ia r New’ Zealand, lh.it, of To Muri in the j neighbourhood. Ruapehu, too, had bad - its eruptions in the past. Taupo, he said, had probably erupted I several times, the biggest upheaval be" ’ ing the last ami occurring thousands j of years ago on a scale comparable to that of Krakatoa. Judging by the ) deposits of ash it flung far and wide, it must have ejected something like i four or five cubic miles of material. i There were evidences of other early ■ and prehistoric eruptions in the theri mal district, Mr. Grange pointed out> and these he dealt with briefly before giving an account of the Tarawera eruption of June, 1886. Tarawera. he said, was a rhyolite volcano, but it ejected basalt. A very fine aeroplane view of Tarawera’s rent summit was thrown on the screen. After mentioning the features of I White Island and its eruptions, Mr. Grange suggested that the work of a volcanological observatory, if established in the thermal district, as J a l been mooted, would be able to take systematic records of the temperatures of hot springs and also to record their overflow. Variations might, be premonitory signs of an eruption. The gases emanating from them should be analysed, as it was thought that as volcanic energy waned the gases tended tc disappear until only carbon dioxide was left. The tilting of the ground and the recording of local shocks would also provide data useful in forecasting the likelihood or otherwise of an eruption.