Note on Glacier-recession in the Landsborough and Twain Valleys, South Westland
[Read before the Science Congress of the Royal Society of N. Z., May, 1935; received by the Editor, June 18, 1935; issued separately, June, 1936.]
IN the summer of 1934—5 the writer spent a fortnight in the Upper Landsborough and Twain Valleys1, and obtained photographs which by comparison with those taken by Mr A. P. Harper in 18942 show the extent of recession which has occurred in the glaciers of the district during the intervening period of 40 years.
The Landsborough River has its source in the McKerrow Glacier on the western slopes of the Main Divide, Southern Alps, some four miles south of Mt. Sefton. It flows for forty miles between the divide and the Hooker Range till it meets the Haast River. The Twain River, a tributary of the Karangarua, is fed by the Douglas Glacier on the south-west slopes of Mt. Sefton and follows a course parallel to the Copland, from which it is separated by the Sierra and Karangarua Ranges. The sketch-map (Plate 12) was prepared for publication in the New Zealand Alpine Journal, and is here reproduced by permission of the editor of that journal.
The Spence Glacier lies below Fyfe Pass in the Upper Landsborough Valley. In 1894 the glacier was Y-shaped, two branches meeting to form a common trunk; but in 1934 not only had the trunk disappeared, but the right branch had retreated more than a hundred yards3 from the original point of junction. When Mr Harper revisited the district in 1929 he reported this recession and estimated the total retreat at 400 yards.
Mr Harper's observations in 1894 and 1929 and the writer's observations in 1935 show that this glacier has retreated approximately a quarter of a mile, leaving a flat gravel bed below the terminal face. Unfortunately, it has not been possible to determine if any retreat took place between 1929 and 1935. The general level of the McKerrow ice has dropped considerably, for while at the time of Harper's original exploration Douglas Pass was only 20 or 30 ft. above the surface of the glacier, this distance has now increased to over 100 ft.
[Footnote] (1) Messrs A. J. Scott, G. C. N. Johnson and the writer visited the district on a mountaineering trip (see A. J. Scott in N.Z. Alpine Journal, No. 22, 1935).
[Footnote] (2) The Twain Valley was first explored by Mr. Harper, who also travelled down the Landsborough Valley (Pioneer Work in the New Zealand Alps, A. P. Harper, London, 1896). In 1907, J. M. Bell, then director of the N.Z. Geological Survey, followed Harper's route (The Wildst of Maoriland. J. M. Bell. London, 1914; Geoy. Jour., vol. 32, 1908).
[Footnote] (3) All estimates of distance cited in this note are approximate only.
This glacier is situated on the eastern face of Mt. Fettes, Hooker Range. In 1894 its terminal face, forty feet thick, was washed by the Landsborough River. The writer's photographs show the terminal to be some 100 yards distant from the Landsborough, while the surface-level of the ice near the present terminal was more than 100 ft. below the 1894 level. A considerable area of moraine has thus been made available for plant colonization. Nothofagus Menziesii forest was developing on the lower moraines which are adjacent to the forest, while at higher levels subalpine shrubbery was found.
This remarkable reconstructed glacier has been described by Harper and J. M. Bell, so that no further comment on its general structure is here necessary. Attention must, however, be drawn to the fact that since 1894 a lake, washing the terminal face of the glacier, has been formed by glacier-recession. The length of the lake is estimated at about half a mile. It appears that the regression commenced before 1907, for Bell observed “… a small pond held in by a recent terminal moraine.”1 The lower end of the lake is already silting up, but owing to the turbidity of the water it was impossible to estimate its depth near-the terminal face.
Horace Walker Glacier.
The Horace Walker Glacier lies on the southern slopes of the Sierra Range. Its névé saddles with that of the Douglas and its trunk describes a semicircle so that its terminal faces up the Twain Valley. The photographs (Pl. 13) taken in 1894 and 1935 show clearly the extent of recession which has occurred.
It is not intended to discuss here the theoretical significance of the recession of these glaciers, but it may be noted that in every case, and especially the Fettes and McKerrow Glaciers, there is a sharp distinction between the moraines which have been exposed since 1894 and those previously formed. Further, Mr Harper has recorded that in 1894 there was no indication of recent recession in the Douglas Glacier.
The writer wishes to acknowledge the valuable assistance of Mr A. P. Harper, at whose suggestion the photographs on which this note is based were taken. For many years Mr Harper has collected information on the subject of glacier-retreat2 and has actively encouraged mountaineering parties to record observations on this subject.
[Footnote] (1) Geog. Jour., vol. 32, p. 128, 1908.
[Footnote] (2) e.g., New Zealand Alpine Journal, vol. iii, p. 343, 1928; vol. v. p. 323, 1934; and vol. vi, p. 173. 1935.