Canadian Alpine Journal/Volume 1/Number 2/Motion of the Yoho Glacier

by Arthur O. Wheeler

Layout 2

MOTION OF THE YOHO GLACIER.

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By A. O. Wheeler.

At the close of the Paradise Valley camp, on July 15th, 1907, the President with two assistants and a packer made a flying trip up the Yoho Valley, via Emerald Lake, to visit the Yoho Glacier and inspect the row of metal plates set out the year previous. It was intended to ascertain by trigonometric methods the extent of the movement of the ice-tongue down its bed.

The party camped for the night a short distance south of Lake Duchesney, and, early the next morning, July 16th, pushed on to a camp ground within a mile of the ice-tongue.

The glacier was at once visited, and, cutting steps in the ice forefoot, the party reached the comparatively level portion of the tongue where the plates had been set. The row of metal plates placed across the surface of the ice to mark the movement of the forefoot had been fixed in position on the 15th July, 1906, and their respective positions were now being checked, just one day later than the exact year. The method adopted in placing these plates will be found in the report given on pages 149-158, Vol. I., No. 1, of this Journal.

Of the six plates first set out, all were found, though No. 3 had fallen into a shallow crevasse. It was lifted from this and placed on the surface above at a point 10.5 feet farther to the south. As it is likely it received additional impetus from the fall one way or the other, its movement in relation to the original line of plates cannot be absolutely depended upon.

In 1906, three sets of observations were inaugurated: (1) to obtain rate of surface flow; (2) to ascertain retreat or advance; (3) to observe the annual change in the ice formation at the snout.

To Obtain Rate of Surface Flow.

Both ends of the base established in 1906 were now occupied with the transit, and readings taken upon the plates in the positions in which they had been found. Work was completed at the south end, but, while that at the north was still in progress, rain came on, stopping the work and driving the party back to camp.

Next morning, July 17th, work was resumed and the readings completed at the north end of the base. The plates were then set in line afresh and their positions fixed by angular readings from the south end. On the accompanying map the original line of plates is shown and the points at which they were found twelve months later. The table below shows the respective movements as measured from a plot of the several readings taken at the ends of the base.

Table Showing the Motion of Plates Set on the Yoho Glacier, between 15th July, 1906, and 17th July, 1907.

Plate	No. 1	No. 2	No. 3	No. 4	No. 5	No. 6
Yearly Motion	29 ft.	74 ft.	89 ft.	124 ft.	134 ft.	124 ft.
Daily Motion	0.95 in.	2.43 in.	2.93 in.	4.08 in.	4.41 in.	4.08 in.

A glance at the map shows that the greatest movement has taken place in the locality of Plates IV., V. and VI. The reason is that the main body of ice is swung to the right against the cliffs seen in illustration No. 1.

ILLUSTRATION NO 1 PANORAMA OF YOHO GLACIER FROM NORTH END OF BASE

A. O. Wheeler, Photo. 1907.

ILLUSTRATION NO 1 PANORAMA OF YOHO GLACIER FROM NORTH END OF BASE

This panorama shows the striation of these cliffs by the ice in past years, when the glacier filled up the trough as high as the upper line of dense forest. The grooving and fluting of the rock over which the ice grinds is well shown by the uncovered portion where the fragments fallen from the séracs above are lying. On the extreme right may be seen the nunatak, which spilts the icefall into two parts (Refer to map opp. page 152, Vol. I., No. I, Can, Alpine Journal). The appearance of the lateral moraine that has been left standing around this nunatak and its position with regard to the timber growing thereon, suggest strongly an advance of the glacier subsequent to the growth of the timber on the nunatak.

For Advance or Retreat.

To obtain some idea of the movement of the ice forefoot with reference to its position in the valley, measurements were made from Rocks Nos. 1 and 2, marked in July, 1906; and, also, from the "Sherzer" rock marked in August, 1904. The measurements were to the nearest ice and the results are not very satisfactory, owing to a considerable change in the structure of the forefoot during the twelve months elapsed since July, 1906.

Table Showing Measurements to Nearest Ice.

Point Measured From	1904	1906	1907
Rock No. 1, left side		27.5 feet	35.8 feet
Rock No. 2, left side		33.6 feet“	43.8 feet“
Sherzer Rock, right side	79.4 feet	79.6 feet“	123.0 feet“

The above measurements would point to a slight retreat. The greatest shrinkage appears to have taken place on the right side, indicating the withdrawal of the ice to a distance of 43 feet further from the Sherzer Rock, although for the two years previous it appears to have been stationery at that point.

Annual Changes in Formation of Ice Forefoot.

A marked change had taken place. Comparison of photographs from view-point, 79.3 feet south of Rock No. 1 (illustrations Nos. 2 and 3) taken respectively on the 15th of July, 1906, and the 17th July, 1907, shows the change; and, very distinctly, the shrinkage of the forefoot.

It will be noticed that the two great cracks on the right of the 1906 picture are lacking in that of 1907; the further uncovering of the ground-floor may be seen in the centre of the 1907 picture; and the shattered and crevassed condition on the left where solid ice shows in the 1906 picture.

Comparison of the 1907 photographs, illustrations Nos. 4 and 5, with those taken in 1906 (opposite page 158, Vol. I., No. I, Canadian Alpine Journal) from Rock No. 2 and from the view-point 6½ feet nearer the ice that the Vaux marks of 1902 disclose the change to a greater degree. In the first picture the disappearance of the two great cracks, the uncovering of the floor, and the shattering of the ice on the left-hand side is still more marked. It will also be noticed that in 1906 the stream was higher than at the same time in 1907.

In the second picture the pointed nose of ice seen lifted above the ground moraine in the 1906 picture is lying broken off and nearly melted away.

Survey of Ice-Tongue.

Having completed the above observations, several camera stations were occupied at suitable points to enable, by means of the application of photogrammetry, a map of the tongue of the ice forefoot to be made. The map herewith, which is from the views taken at the

Map of Ice Forefoot of the Yoho Glacier

A. O. Wheeler, Photo

ILLUSTRATION No. 2.—FROM VIEW-POINT 79.3 FEET SOUTH OF ROCK No. 1—1906

A. O. Wheeler, Photo

ILLUSTRATION No. 3.—FROM VIEW-POINT 79.3 FEET SOUTH OF ROCK No. 1—1907

A. O. Wheeler, Photo

ILLUSTRATION No. 4
From Rock No. 2. Compare with plate opposite Page 158, Vol. 1, No. 1, Canadian Alpine Journal

A. O. Wheeler, Photo

ILLUSTRATION No. 5
From View-Point 6½ feet nearer ice than the Vaux marks of 1902. Compare with Plate 2, opposite Page 158.
Vol. 1, No, 1, Canadian Alpine Journal.

several stations, shows the positions of these stations and of the rocks from which measurements were made to the ice; also, of the other view-points and the various features of the glacier in its bed. I now wish to acknowledge the assistance given me by Mr. M. P. Bridgland, who has plotted and computed the altitudes of all the points used in outlining the glacier and in drawing the contours here shown.

It may incidentally be mentioned that it is only by the means of the science of photogrammetry that in a single day—not taking into consideration the other work done when locating plates and making measurements, etc.—sufficient data could be obtained by two persons to map the tongue so completely and accurately, without making actual measurements, a process that would entail a considerable expenditure of time and labor. The process, combined with the views taken, enables, in this case, a large amount of additional information to be gathered, such as: thickness of the ice, previous thickness of the ice, slope of ground-floor, etc. It shows how valuable the method is for a survey of this nature.

From it we may gather that the approximate thickness of the ice on the right side is 170 ft., and on the left side 130 ft.; that the height of the cliffs from the ice to the lower edge of the upper growth of timber in illustration No. 1 varies from 300 to 400 ft., a depth of ice that once filled the valley; and that the slope of the portion of the bed beneath the ice tongue is approximately 35 per cent.

The general conclusion that may be drawn from the above is that the glacier receded during the year, July 1906 to July 1907, an average distance of about 20 feet and that the shrinkage of the ice in thickness on the right side has been very considerable. These evident facts appear somewhat peculiar in view of the unusually large amount of snow that fell in that locality during the winter of 1906-07.