Art. XXXVII.—Recent Changes in the Position of the Terminal Face of the Franz Josef Glacier.
[Read before the Philosophical Institute of Canterbury, 4th November, 1914.]
These notes as to the position of the terminal face, of the Franz Josef Glacier are based on observations supplied to me by Mr. Alec Graham, one of the guides of our alpine region, who resides in the immediate vicinity of the glacier, and to him my sincere thanks are due.
In the year 1909 the officers of the Geological Survey, under the direction of Dr. Bell, made a complete map of the Franz Josef Glacier, and placed pegs in position so that the changes of the face could be regularly and accurately determined. The pegs are numbered in order from the western side of the glacier, and the relative movements of the ice at each since they were put in position are given in the following list, the original situation of each peg being given first for the sake of reference:—
No. 1.—On the steep rock-face on the western side of the front, at approximately 7 ft. above the ice and 3 ft. from it. This peg was placed near the edge of the ice, but was afterwards covered, and now lies buried under the moraine left by the glacier. Since it was put in, the river has cut a huge gap, between the western wall and the ice, for about 24 chains, with a width varying from 2 to 3 chains. The nearest ice across the river is about 180 ft. distant.
No. 2.—On Harper Rock, 29 ft. from the ice-face and about 7 ft. above the river-bank. This peg is now 215 ft. from the face, so that the ice has receded 186 ft.
No. 3.—On Harper Rock, in a ridge about 10 ft. above the lowest part of the ice, but overhung by the cliffs and ice above. In 1912 this was 5O ft. from the ice, and now it is 120 ft.
No. 4.—In the ice angle of Park Rock, surrounded by ice excepting to the northward, but distant 69 ft. on the east and 75 ft. south. In 1912 it was 80 ft. from the ice, and is now 189 ft.
No. 5.—Thirteen feet above the ice, and 7 ft. from it at the inner edge of Strauchon Rock. In 1912 it was 270 ft. from the ice, and now is 350 ft. distant.
No. 6.—On Barron Rock, on a sharp ridge 17 ft. from the ice, and about 10 ft. above it. In 1912 it was 260 ft. from the ice, and is now 320 ft. away.
No. 7.—At 9 ft. above the ice, and at 7 ft. from it in the eastern rock border of the glacier. This peg stands on the top of a rock-face about 200 ft. above the face of the glacier (aneroid measurement). The ice has receded up the valley from this peg about 8O ft., whereas in 1912 it was only 45 ft. back from it.
These records show clearly that the glacier has retreated since 1909 an average of about 170 ft. across the face, and that there is a considerable shrinkage in the volume of the ice. The result is the more marked since the observation made by the Survey were at a time when the face showed signs of an extraordinary advance. There are distinct signs that another wave of movement will take place in a few years' time, for two miles up the glacier, at Cape Defiance, it has risen 20 ft. during the past year. In order to determine this movement more exactly, a mark has been placed by Mr. Graham about 50 ft. above the ice; this will enable future observers to obtain reliable data for the movements.
Marks are also being placed on the ice in order to determine the rate of movement. Bell arrived at an average maximum movement near the face of only 2 ft. per day. This was the result of observations extending over a continuous period of 134 days. Recent observations made by Graham on a boulder carried by the ice showed a rate of about 3 ft. per day.
Although no accurate observations have been made on the Fox Glacier, which lies in a parallel valley about twenty miles to the south of the Franz Josef, the conditions appear to be very much the same. There has been a recent marked retreat of the terminal face, and farther up the glacier there are signs of a pulse coming down similar to that in the Franz Josef Valley.
More accurate observations should be taken in order to determine the period of these waves of high and low ice, and to see if they accord with periods of change in the present climatic conditions of the country.