1060 CAN. J. EARTH SCI. VOL. 12. 1975

The great similarity in size, shape and orienta- tion of the facets on the centrum of the first lumbar vertebra of NMC 2381 to those for the tubercles of the rib on the last thoracic vertebra suggest to me that instead of being genetically programmed for fusion to the centrum, the transverse processes were somehow programmed for rib facets. Is this the result of an unusual preliminary genetic step in the process occasion- ally noted in horses of "dorsalization of the first lumbar vertebrae" (Stecher 1961, p. 193)?

SISSON, S. and GROSSMAN, J. D. 1964. Anatomy of the domestic animals. W. B. Saunders, Philadelphia, 972 p.

STECHER, R. M. 1961. Numerical variation in the vertebrae of the Prjewalsky horse, Mammalia 25(2), pp. 192- 194.

1962. Lateral facets and lateral joints in the lumbar spine of the horse-a descriptive and statistical study. Am. J. Vet. Res. 23(96), pp. 939-947.

TROXELL, E. L. 1915. The vertebrate fossils of Rock Creek, Texas. Am. J. Sci. 39(234), pp. 613-638.

Advancing Rock Glaciers in the Lake Louise Area, Banff National Park, Alberta

GERALD D . OSBORN Department of Geology, University of Calgary, Calgary, Alberta T2N IN4

Received October 22,1974 Revision accepted for publication March 3,1975

Study of aerial and ground photographs shows that three rock glaciers in the vicinity of Lake Louise in Banff National Park, Alberta have been advancing during the last 70 years. They are now overriding a lateral moraine of the Victoria glacier. Lichenometry and ratellength calcula- tions indicate that the rock glaciers originated within the last several centuries. Rates of advance between 1947 and 1974 average 0.3 to 0.6 mly.

L'etude de photographies aeriennes et de photographies prises au sol demontre que trois glaciers de pierres de la region du Lac Louise, dans le Parc National de Banff, en Alberta, ont avance durant les dernikres 70 annees. Ces glaciers chevauchent actuellement une moraine laterale du Glacier de Victoria. La lichenomktrie et la mesure du rapport taux d'avanctellongueur indiquent que ces glaciers de pierres ont ete form& au cours des derniers sibcles. Leur taux de progression entre 1947 et 1974 est en moyenne de 0.3 80.6 mlan. [Traduit par le journal]

From observations of old aerial and ground photographs, it is concluded that three rock glaciers in the vicinity of Lake Louise in Banff National Park have been advancing during the last 70 years. During this period, almost all glaciers in the Canadian Rockies have receded.

The three rock glaciers are situated on the flank of Mt. Aberdeen and are oriented perpen- dicular to the valley of Victoria Glacier (Fig. 1). The middle and southwestern rock glaciers have encroached upon and buried parts of the lateral moraine of Victoria Glacier (Fig. 2), while the front of the northeastern rock glacier is

characteristics of active rock glaciers outlined by Wahrhaftig and Cox (1959): fronts are bare of vegetation, meet tops at sharp angles, and slope at the angle of repose; fines are exposed in the fronts. Low hills, pits, and transverse ridges and furrows are found on the tops of the rock glaciers.

Thalli diameters of the lichen Rhizocarpon geographicurn indicate that the three rock glaciers date from the most recent period of Neoglacial activity. The largest thallil found on the rock glaciers are 48, 46, and 56 mm in diameter for the northeastern, middle, and

2 m from the lateral crest. southwestern rock glaciers, respectively. The All three rock glaciers are elongate and largest thallus on the moraine marking the

tongue-shaped, about 150 m wide and 300 to maximum recent extent of Victoria Glacier is 600 m long. They are composed of angular 45 mm in diameter. The comparable sizes indi- blocks of limestone, quartzite, and shale up to 3 m in size. No ice is visible. All exhibit the 'Minimum diameters of elliptical thalli are used.

Can. J. Earth Sci., 12,1060-1062 (1975)

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NOTES

A MT

ABERDEEN

ALBERTA a FIG. 1. Index map showing locations of rock glaciers and moraines.

cate that the rock glaciers are products of the same Neoglacial cold period that caused the Victoria Glacier advance.

Absolute dates of these deposits can be esti- mated by using for comparison lichens on a Victoria recessional moraine deposited in about 1897. The basis for this date is a photograph taken in 1897 (Collie 1899), which shows the toe and margins of the glacier to be in the same position as the present recessional moraine. The largest Rhizocarpon geographicurn found on this deposit is 27 mm in diameter. If the species has a linear growth curve, extrapolation places the

I ages of the lichens on the rock glaciers and the outer Victoria moraine between 125 and 160 years. Many Rhizocarpon geographicurn growth curves published for North American localities indicate that growth slows down from one- fourth to one-sixth the initial rate after a century or two (Webber and Andrews 1973). If this is the case in the Canadian Rockies, the lichens and deposits in question could be several centuries old.

Rates of movement of the rock glaciers were determined by comparing present positions with positions recorded on old photographs. Dis- tances obtained from aerial photographs were corrected for relief displacement. The earliest Government of Canada aerial photos of the area (flight line A1 1085), taken in 1947, are the

I main basis for rate calculations. An oblique

photograph of Victoria Glacier taken in 1902 (Sherzer 1907a, b) is not too clear, but positions of the middle and southwestern rock glaciers can be approximately determined. The earliest known photograph of the area, that of Collie (1899), does not show the rock glaciers clearly enough to be of use.

Rates of advance average 0.7 to 0.8 m/y for the period 1902-1974 and 0.3 to 0.6 m/y fo,r the period 1947-1 974 (Table 1).

Two points of interest are raised by the data. First, the rock glaciers have been advancing while normal glaciers have been retreating. The difference is probably due to the insulative rubble cover of the rock glaciers. Ablation of ice within the rock glaciers is hindered by the cover, making them relatively unresponsive to climatic warming. However, the rates of advance are decreasing for at least two of the rock glaciers. Some of the decrease could be a result of the obstructing effect of the lateral moraine, but all

TABLE 1 . Rates of advance

Average Rate of Advance ROC^ (mlu)

glacier 1902-1974 1947-1974

Northeastern ? 0 . 3 Middle 0 . 8 0 4 Southwestern 0 . 7 or 0 .8 0 6

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1062 CAN. J. EARTH SCI. VOL. 12, 197.5

FIG. 2. Air photo showing the three rock glaciers overrunning a lateral moraine of Victoria Glacier. The glacier has retreated to the left edge of the photo. North is at top; for scale see Fig. 1. Original photo supplied by the National Air Photo Library, Department of Energy, Mines and Resources, Ottawa. Canada.

three rock glaciers had already advanced well and the middle rock glacier no older than 375 up the flank of the moraine by 1902, so at least years (300 ml0.8 m/y). some of the decrease in the last 27 vears is mob- ably climatically induced. COLLIE, J. N. 1899. Climbing in the Canadian Rocky

Mountains. Alp. J. 19, pp. 441466. a comparison of rates of advance SHERZER, W. H. 1907a. The nature and activity of Cana-

rock glacier lengths confirms the young ages of dian elaciers. Can. AID. J. I. DD. 249-263. the rock glaciers. Assuming that the average - 1!%7b. Glaciers of the daLdian Rockies and Sel- - - - rates of motion over their entire history of acti- kirks. Srnithsonian Contrib. to Knowledge, 34.

vity are at least as great as the average rates be- WAHRHAFTIG, C. and Cox, A. 1959. Rock glaciers in the Alaska Range. Bull. Geol. Soc. Am. 70, pp. 383436.

tween 1902-1974, the southwestern rock glacier WEFIBER. P. J. and ANDREWS. J. T. 1973. Lichenometrv: a - - -

can be no older than 750 years (600 ml0.8 m/y) commentary. ~ r c . ~ l p . ~ e s . 5, pp. 295-302.

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