ELECTRIC EARS

Evening Post, Volume CXL, Issue 149, 21 December 1945, Page 8

ELECTRIC EARS

PULSE OF RUAPEHU

GEOPHYSICIST'S 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 Geological Survey, has compiled at the request of the Prime Minister's Department. Similar observatories were established m the past, he says, at Mount Vesuvius, Mount Pelee in Hawaii, and on 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 vulcanism or seismicity form 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 mountain was of great scientific, interest. Mr. Modriniak emphasised the importance, under such circumstances, of the practical applications of scientific observation at critical moments in threatening regions. Fear of the. unknown, and the unconscious belief and associations of vulcanism with unpredictable disasters, were likely to upset the normal trend of life if left to their own resources. t

Persistent ash deposits on pastures and market gardens had an economic aspect, apart from the destructive action of ash' on machinery and household goods. To assist in the elucidation of problems by volcanic action was . the purpose of * establishing a geophysical observatory at Ruapehu. The determination of the cause would ultimately lead to predictions of 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 presentinvestigation 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 sensitiye geophones. ■ The latter reproduced, with a great range of frequency, the volcanic pulse. The geophones had been placed, at intervals qf 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 obscured, and were it not for the microphones installed there, it would be beyond observation. If the tremors were of local crater origin, only the microphone situated nearest the source was affected, whereas shocks of more deep-seated origin reached microphones situated nearer their source first.

"If a hot lava column were to move from great depths towards the surface," he reported "its movements associated with earthquakes or tremors would be recorded on continuous recording seismometers. The depths and locations of these focal points of seismity.can be calculated from; the time of arrival of earthquake waves at various observation stations. The path of the moving magma is continuously under observation, and s timely warning would be issued should it reach a dangerous position. DETECTING LAVA FJLQV^. "In the event of a slowly penetrating lava flow, or remelting of"rock columns of gases within the channel, magnetic instruments are set up to detect its presence. When this rock reaches a temperature of 500 degrees centrigrade it loses its magnetism,- and. consequently, the distribution of the magnetic fields in its neighbourhood. Search coils are laid out to detect this magnetic flux change."

Pressures which are associated with volcanic activities tend to tilt the mountain walls, and are detected by tiltometers. All observations are tabulated, and correlated with meteofological data, and possible tidal effects of the moon.

While the methods he 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 by the use of a gravimeter, and additional seisometers would permit 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 localityof Ruapehu, he remarked, had totalled 17 tons per acre within .14 hours, and approximately half a million tons of ash had been deposited over an area of 50 square miles during the same period. • . The, basis of comparison between active and dormant vulcanism was ob- ! servations which were recorded during both periods. It was during a period of quiescence that a volcano was more accessible to instrumental observations. Any departure from that normal state could be readily detected. For that reason he strongly recommended the inclusion within the range of the present programme the establishment of bench marks and base recordings. Though Ngauruhoe was at present dormant, that mountain offered a wide field and reward for such enterprise.