Go to National Library of New Zealand Te Puna Mātauranga o Aotearoa
Volume 39, 1906
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First Meeting: 8th May, 1906.
The President, Dr. P. Marshall, occupied the chair.

New Members.—Messrs. G. T. Goodman, G. Austin, G. A. Rawson, R. S. Rankin, and the Rev. Dr. Nisbet.

The President stated the steps that had been taken in regard to the Hutton Memorial Research Fund.

Some members of the Institute had subscribed to it, but he trusted others would feel sufficiently interested and sufficiently indebted to the late Captain Hutton for the work he had done to subscribe to the fund, which would be a memorial of his life's work.

The President delivered an address on “The History of Volcanic Action in New Zealand.”

It was frequently remarked, he said, by visitors to the colony that, judging by the volcanoes in the North Island and the evidences of volcanic action elsewhere, this must be a young country. It was interesting to look around and see whether, from the evidence to be everywhere found of volcanic action, this was really so. There were plenty of evidences in the North Island—the cones around Auckland, the hot springs in the neighbourhood of Rotorua, and the steaming volcanoes further south. Anybody travelling over the country could easily gain an idea of the work that volcanoes had done in forming the country. The geologist, of course, made a deeper study than did the casual observer. He looked into the rocks, and from an examination of the minerals that occurred in them he was able to say whether a rock had solidified from fusion or whether it had been deposited by water. If the former, the conclusion was that it was a volcanic rock. Thus it was in the neighbourhood of Dunedin. Certainly, the hills around showed little evidence, so far as their external formation was concerned, of volcanic activity, and a certain amount of geological knowledge was required before the district could be recognised as a volcanic district. Very often, however, volcanoes were destroyed by the action of water and air, so that not only the cone was removed but also the old reservoir through which the minerals were thrown out. Generally speaking, the material for compiling a volcanic history of a district could be found in three ways—first, in the external configuration; second, if the external configuration was destroyed, in the structure of the rocks; and finally, in old reservoirs that were probably connected with volcanoes at one time. Even after a volcano had disappeared it was possible that in other districts pebbles or rock fragments would be found that would show that a volcano had once existed in the neighbourhood. The rocks of New Zealand had been more or less carefully studied from one end to the other. In the South Island there was in the south-western district a large area showing igneous rocks, which might indicate the age of New Zealand. They contained certain structures that showed they

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were as old as any rocks on the surface of the earth. In other words, they had a position with regard to old rocks that occurred on their flanks that indicated that they were of the highest antiquity. They were formed probably when conditions on the earth's surface were entirely different from what they are now—at a time, probably, when no life at all existed on the surface of the earth, and when all was void. Rocks that were once in a molten state at an extremely remote period were found in other parts of New Zealand. Some of these rocks were of exceptional interest, being very much heavier than the ordinary surface rock. Their density indicated that at one time they were resident probably two hundred miles beneath the surface, and their presence in abundance in certain quarters pointed to the fact that New Zealand at one time in its history was subject to tremendous disturbances. If volcanoes were connected with that extreme pressure they had now disappeared Near the Bluff and elsewhere rocks were found that were once volcanic rocks, but where the volcanoes were that these rocks came from was not known. The Carboniferous beds formed an important part of the structure of New Zealand, and a study of them led one to conclude that there must have been an enormous, amount of volcanic action in this country prior to the Carboniferous age. It was of interest to conjecture where this volcanic land was. The actual Carboniferous rocks must have been on the sea-shore at that time, and the whole of New Zealand seemed to have been a sea-shore, bounding some volcanic country. Those who had investigated the question most fully were doubtful whether the land extended to the east or to the west. Obviously the easiest way to come to a conclusion was to find out where the sediments were coarsest—on the east or on the west—but as far as that was concerned there did not seem to be very much difference in them. Sir James Hector favoured one view, and Sir Julius von Haast the other So far as his own limited observations had enabled him to come to a conclusion, he thought it was likely that the land extended a greater distance to the east than to the west. This, as he had said, was in the Carboniferous days, when New Zealand was nothing more than the coast-line to some huge continental area, from which rivers were constantly bearing down great volumes of water, and carrying to the coast-line immense quantities of sediment. This sediment had compacted, and now formed much of the country of New Zealand. For a long time after that there was no evidence of volcanic action, but about the beginning of the Tertiary period, when mammalian life was beginning to assert its dominance in the animal world, some disturbance took place on the east side of the Alps. The actual volcanoes had themselves disappeared, out the nature of the rocks clearly indicated that there was volcanic activity of some intensity over the surface of the land in those days. In all probability the rocks on Coromandel Peninsula were thrown up at the same time. Then there was little evidence of any other action until the Miocene period, when there was very widespread activity throughout the greater part of New Zealand. It was about this time that the Dunedin volcanic area was formed. This area, he pointed out, presented some peculiar features in its igneous rocks. One rock was heavy and another light, and there were also important differences in colour and in the crystallized structure. Red and black rocks, and sometimes white rocks, were found side by side. Did these rocks come from the same volcano or from the same reservoir? So far there was no satisfactory explanation of any cause that would produce differently coloured and differently natured rocks from the same volcano. In this district, again, there were evidences of considerable intervals between the periods of volcanic eruption. At Anderson's Bay, for instance, on the northern side of the bay, the lower portion of the cliff was soft, while the rock lying over it was hard. They were both volcanic rocks, and were hard at the time they were emitted, but an enormous time had elapsed between the

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emitting of the two—sufficient time to allow water to percolate through the first deposit. Then another molten mass flowed over the top of it. At Oamaru the volcanic development was very peculiar, because there was every evidence there of a submarine eruption occurring at a considerable depth below the ocean's surface. This was in the Miocene period. At the end of the Miocene and at the beginning of the Pliocene period volcanic action entirely ceased in New Zealand, and had not had any effect on the South Island since. Ruapehu, Egmont, Ngauruhoe, and other mountains were the result of activity that took place probably before the middle of the Pliocene period. Touching on theoretical matters, Dr. Marshall made some interesting remarks on the connection between volcanic action and earthquakes. The eruption of Tarawera was one of the most violent eruptions that had taken place in New Zealand or in historical times. The explosions of steam were very violent, and yet the earthquakes were not felt to such a great distance. Auckland was not greatly disturbed, and at Wanganui, Napier, and Gisborne they were hardly felt. Evidently there was no connection whatever between the violent earthquakes and volcanic action. At any rate, volcanic action did not generate earthquakes of great violence. If it were the case that volcanic eruptions were associated with great earthquakes, what parts of New Zealand would be subject to most disturbance? Surely, Auckland and Napier would be; and yet it was found that it was Wellington—the neighbourhood of Cook Strait—that was most liable to earthquake disturbance. Parts of the South Island that were of volcanic origin, such as Dunedin, were particularly free from earthquakes, and those places that were situated far from volcanic action were subject to disturbance. Referring to the possible continuance of volcanic action in New Zealand, the speaker said that all he could state on this matter was of a negative nature. The geologists were still infants in regard to their knowledge of the main causes of volcanic action. They did not know the exact conditions that determined the outbreak of volcanic activity in any area. It could not be said with safety that volcanic action had died out anywhere. It was supposed that the activity of Vesuvius had ceased at the beginning of the Christian era, but recent events had shown it had continued there till the present day.

On the motion of Dr. Hocken, the President was heartily thanked for his most interesting and instructive address.

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