PULSE OF RUAPEHU

Evening Star, Issue 25676, 27 December 1945, Page 6

PULSE OF RUAPEHU

ELECTRIC EARS GEOPHYSICAL REPORT Details of the work of the geophysical' observatory, which was established at Mount Ruapehu during the year, are given in a special report which... Mr N. Modriniak. geophysicist on the staff of the Geologcal Survey, lias compiled at the -request of the Prime Minister’s Department. Similar. observatories were, established, in the past, he says, at Mount Vesuvius, -Mount Pelee in Hawaii, and oil the volcanic centres of Japan, and the accumulated observations of volcanic phenomena have led to a better understanding of the .mechanism of vulcanism. “ One should not overlook the fact that, vuleanism or seismicity forms the natural environment of almost every New Zealander,” says Mr Modriniak. “The sooner it is known to him what this really entails, the better will he adjust himself to his true environment.” . Almost a year had passed since Ruapehu had “ hoisted the steam flag ” on its summit. That development was followed by intense steam and ash clouds, by rumbling noises, lightning, and earth tremors. Such activity could not but cause widespread interest, even far beyond the shores of New Zealand. Undoubtedly, the present state of the mpuntain was of great scientific interest. Mr Modriniak emphasised the importance, under such circumstances, of the practical applications o'f scientific observation at critical moments in threatening regions. Fear of the unknown, and the unconscious belief and associations of vuleanism with unpredictable disasters, were likely to upset the normal trend of life if left to thenown resources.

Persistent ash .denosits on pastures and market garcfens had an economic aspect, , apart ' from the destructive action of ash on machinery and household goods. To assist in the elucidation of problems created by volcanic action was the purpose of establishing a geophysical observatory at Ruapehu. The determination of the cause would ultimately lead to predictions oif its effect. There had already been instances where predictions had been made with reasonable accuracy and to the benefit, of many. SERIES OF MICROPHONES. The diagnostic method of the present investigation was similar to the application of a stethoscope to the chest of a patient—heart beats and lung conditions were revealed by its application, and the dynamic expression of an active volcano was detected by sensitive geophones The latter reproduced, with a great range of frequency, the volcanic pulse. The geophones had been placed, at intervals of approximately two miles, from the Chateau Tongariro to the mountain, and one was buried in the crater wall. They were connected to amplifiers which, in turn, fed into a loud-speaker system, thus making it possible to follow crater explosions and the issuing of steam and ash clouds audibly. More often than not. Mr Modriniak pointed out, the mountain was cbscured. and were it not for the microphones installed there, it would he beyond observation. Jf the tremors were of local crater origin, only the microphone situated nearest the source was affected, whereas shocks of more deeprseated origin reached mierophones situated nearer their source first. “ If a hot lava column were to move from great depths towards the surface." lie reported. “ its movements associated with earthquakes or tremors would be recorded on continuous recording seismometers. The depths and locations of these focal noints of seismity can be calculated from the time of arrival of earthquake waves at vari-

out observation stations. The.path of the moving magma is continuously under observation,.and a timely warning would •be issued should it reach a dangerous position. DETECTING LAVA FLOW. “ In the event of a slowly penetrating lava flow, or renielting of rock columns of y gases within the channel, magnetic instruments are set up to detect its presence. .When this rock reaches a temperature of oOOdeg. centigrade it loses its magnetism, and, cnosequently, changes the distribution of tlio magnetic fields in its neighbourhood.' Search coils arc laid out to detect this magnetic flux change.” . Pressures which arc associated with volcanic activities tend to tilt the mountain walls, and are detected by tiltometers. All observations are tabulated, and correlated with ‘meterological data, and possible tidal effects of the moon While the methods lie had mentioned were all within the compass of the present observatory, Mr Modriniak pointed out that additional substantial assistance was- needed to supplement the present investigation. Oscillation of magma, he ! said, could probably be detected by .measuring the vertical component of the earth’s gravitational field bv the use of a gravimeter, and additional seismometers would pprmit a more ready determination of the epicentres of seismic activity, Chemical analysis of steam and ash might also determine the nature of the laval conditions. RATE OF ASH DEPOSITION. A measured ash fall in the. locality of Ruapehu, he remarked, had totalled 17 tons per acre within 14 hours, and., approximately half a million tons of ash had been denosited over an . area of 50 square miles during the same period. The basis of comparison between active and dormant vuleanism was observations which were recorded during both periods. It was during a period oif quiescence that a volcano was more accessible to instrumental observations. Any departure from that normal state could be readily detected. For that reason lie strongly recommended the inclusion within the range of the present programme the establishment of bench marks and base recordings. Though Ngaurulioe was at .present dormant, that mountain offered a wide field and reward for such enterprise.