In this lecture an outline was first given of the principal topographical features and geological formations of the country, with particular reference to the greater mountain ranges and groups, and to what is so far known of their structure and tectonics. New Zealand is a very mountainous country, in all three of its main islands, and geologically it is very young: this is markedly shown throughout in its scenery. Only a million years ago a large part of the North Island was under the sea, as well as certain areas of the South Island; and 60 million years ago (Lower Eocene times) most of the present land-area of New Zealand was submerged.Reference Wellman ¹ There is evidence that the geological history of New Zealand has been one of almost continuous, and intense, tectonic activity, which is in contrast with most of the continental regions of the world. While the present volcanoes of the North Island are a Recent, or Pleistocene, feature, there appears, from the succession of earlier strata in many parts of the country, to have been repeated volcanic action in the past. But no volcanic rocks have been found throughout the full extent of 250 miles (400 km.) of the Southern Alps, which form the eccentric backbone of the South Island; nor significantly, and unlike so many other great ranges of the earth, are there within the Alpine zone intrusive masses of igneous rocks.

The Southern Alps, with such high peaks as Mounts Cook (12,349 ft., 3,765 m.), Tasman (11,475 ft., 3,500 m.), Sefton (10,359 ft., 3,160 m.), Aspiring (9,957 ft., 3,040 m.) and others, are essentially an uplifted block of Mesozoic sedimentary rocks with a narrow belt of schists along its north-west side, adjacent to the great Alpine Fault. The latter is a major structural and tectonic feature, whose transverse, as well as overthrust, movements have been continuing until the present day, and directly influencing the elevation of the Alps. The volcanic massif of the North Island is in great contrast, with its highest summits, and presently or recently active centres, of Mounts Ruapehu (9,175 ft., 2,795 m.), Ngauruhoe (7,515 ft., 2,290 m.) and Tongariro (6.517 ft., 1,986 m.). These border to the north-east a great area of hill-country, which was covered by earlier pumice-showers, ejected from vents now submerged in Lake Taupo, with its important hydro-thermal district nearby. The region lies at the intersection of the two main crustal fold-systems of the North Island, and is therefore of great structural significance. The satellite centre of Mount Egmont (8,260 ft., 2,518 m.), lying some 80 miles (1:30 km.) distant on the coast to the west, is a beautiful symmetrical volcanic cone of similar Quaternary age.

With regard to the existing glaciers, in the North Island it is only on Mount Ruapehu that there are found restricted névé masses;Reference Odell ² ; and these have been greatly diminished in volume in recent years.Reference Krenek ³ There is erosive evidence that during the PIeistocene epoch glaciers descended to at least 6,000 ft. (1,830 in.). This, however, does not seem to have been the minimum altitude. The regional snow-line now stands at about 8,200 ft. (2,450 m.), whereas in Pleistocene times it appears to have been depressed to about 4,400 ft. (1,340 m.).Reference Willett ⁴ These figures are about 1,000 ft. (305 m.) higher in each case than those for the Mount Cook district in the South Island, corresponding with a difference in latitude of 3° 16’. It is well known that in the vicinity of Mt. Cook are located New Zealand’s most extensive glaciers, the longest being the Tasman Glacier of about 18 miles (29 km.). Some account of these glaciers was given, and a reference made to the early observations and measurements of Brodrick and Baker in the 1880’s and 1890’s, as to the changes in surface, front and margins of the Tasman, Hover. and Mueller Glaciers in particular; of Douglas and Harper, Speight and Bell in the case of the Franz Josef and Fox Glaciers. Sundry observations by Harrington and by the

lecturer between 1950 and 1955 confirmed the progressive changes mainly of retreat and surface-wasting that have taken place over the years. The lower six miles of the Tasman Glacier are now covered by a vast undulating blanket of ablation moraine, a veritable “Felsenmeer”. An item of some interest, photographed from the air in 1953 (Fig. 2, p. 743), were curious circular features in this “Felsenmeer” below the junction with the Murchison. Glacier valley. Later examination on the ground was inconclusive in respect of their having originally been circular crevasses, of the type recorded in the Coast Range, B.C.,Reference Morrison ⁵ or alternatively due to some kind of localized sub-glacial collapse, or “block-caving”, as reported from the Alaska Range.Reference Paige ⁶ After many years of neglect it was gratifying to record that the N.Z. Geological Survey, under the aegis of the I.G.Y. programme, has lately instituted a series of glaciological measurements on the Tasman Glacier, with a view to the determination of its regimen, etc. Its motion has been recently shown by McKellar and his party to average 1.12 ft. (0.341 m.) per day over the late winter period in 1957, and 1.45 ft. (0.442 m.) per day over the summer period, opposite the Malte Brun hut.Reference McKellar ⁷ A seismic cross-section was also to have been carried out during the current Southern summer (1958–59), which should definitely correct the exaggerated depth of ice of 1,200 ft. (366 m.) and more opposite the Ball hut, claimed to have been determined under Admiral Byrd’s auspices when he was en route to the Antarctic many years ago. In Westland the Franz Josef Glacier has received perhaps more attention than any other, in view of its accessibility (it descends to an altitude of about 700 ft., 213 m.), its grandeur and the remarkable changes in the position of its front over the years. Falling from névé to snout at a gradient of about 1,064 ft. per mile (200 m. per kilometre),Reference Harper ⁸ it displays, when in periodic advance, marked overthrusting at its terminal front. Its maximum daily movement in the middle reach was determined in 1893 to be about 12 ft. (3.66 m.). This, however, is rather more than twice the average rate also found by Harper and Douglas. In comparison, a recent estimate of average flow was made by the present lecturer in 1955, by observing the distance travelled down the glacier by a wrecked aircraft between March 1950 and January 1955. This was computed as 5 to 6 ft. (1.52 to 1.83 m.) per day.Reference Odell ⁹ So there would appear to have been little or no change in the general rate of flow in recent decades. Changes in the glacier front have been recorded by SuggateReference Suggate ¹⁰ and others, and the systematic taking of photographs from a fixed station has been organized from 1951 onwards. In the case of the Fox Glacier, southern Westland, which has consistently been in retreat in recent years, the lecturer reported that he was able to make scattered observations, including some on an interesting series of dust-layers, of Australian desert, or alternatively South American volcanic, origin.

Photograph by H. Pringle

Fig. 1. Franz Josef Glacier, c. 1867. A. P. HarperReference Harper ⁸ stales that in 1867 the ice reached the tap of Sentinel Rock on extreme right.

R.N.Z.A.F.. 31 March 1953

Fig. 2. Unexplained circular surface markings in lower reach of Tasman Glacier. Vertical photograph at 10,600 ft. (3.230 m.)

Photograph by W. A. Sara

Fig. 3. Franz Josef Glacier, May 1959. Shows extensive outwash plain and former trim lines.

Fig. 4. Fox Glacier, 1954 or 1955. Douglas Peak, 10,107 ft. (3,080 m.), ad head of glacier

Fig. 5. Shrinking snout of Fox Glacier, 1955

Many lantern-slides and maps were shown to illustrate the above features, as well as the varying aspects of the country from Milford Sound, north-eastwards through the Southern Alps, to the volcanoes of the North Island, with sundry comments, for the mountaineers present, on climbing achievements, particularly in the Mount Cook district. Mr. H. E. L. Porter kindly lent some slides from his large collection of this district, for the purposes of the lecture.

Some of the photographs shown are reproduced on p. 743–44.