Though actual measurements made by the Educational Department of Mount Rainier National Park since 1918 - together with data taken from historical records - show that the Nisqually Glacier has receding since 1857 at an average annual rate of 70 feet each year (See Nature Notes for October, 1931 for complete tabulation of recession figures; we knew very little about the downward movement of this great ice sheet. Proffessor LeConte of the University of California made a seasonal study and record of the Nisqually's downward movement during the summer of 1906, but with the exception no organized study from year to year had been attempted until 1930. At that time the Geological Survey, the City of Tacoma and the National Park Service began a cooperative survey of the Nisuqally's movement to be carried on into the future and which will reveal many heretofore unknown facts and clear up many hazy ones.
The results of the work so far, while still of a rudimentary nature, and interesting as well as enlightening. The basis for the work is a plane table survey and topographic map prepared in the fall of 1931. This survey covers the lower portion of the glacier to a point 10,000 feet from the snout. No effort was made to map the upper reaches of the ice sheet. Data taken from this survey made possible the preparation of a profile and cross section map - the cross section taken at 5,500 feet - by which the ice mass of today can readily be compared with that of 1910 when Mr. F.E. Matthes and party was preparing a topographic map of the entire Park. (See the sketches) The 1910 data was taken from the work of Mr. Matthes' party. Other profiles and cross sections will be made in future years for the sake of comparison.
To measure the rate of flow at different points on the ice, a row, or, rather, line, of steel tripod markers was placed at intervals across the glacier (The steel tripods replaced marked rocks laid in 1930) and these lined in with definite established points on the canyon wall of the south side. This was done at both the 5400 and 6000 foot elevations. The results of stadia measurements during 1930 and 1931 are as follows:
Sept. 2, 1930 - Maximum movement in 48 hours of 6/10 feet.
A check of this line of tripod markers on June 29, 1932 showed that most of them were still buried. One marker, however, was found to be in position from the previous year at a point 1700 feet from the south edge of the glacier. At this point a total movement of 66.5 feet since September 2, 1931, was evident. After repeated trials during the winter three range poles were set on this section February 16, 1932. One of these markers was still in place on June 29, 1932, and showed a mocement of 29.5 feet. This point was 1400 feet from the south edge of the glacier.
At the 6000 foot elevation a line of markers was placed on November 7, 1930, and re-measured on June 12, 1931. Results showed a total maximum movement downstream of 100.7 feet in 246 days. On June 29, 1932, a new line of tripods was again checked. Only one tripod was found, howeve, - this at a point 1800 feet from the south side of the glacier - and its position gave evidence that the ice at that point in the stream had moved a total of 113 feet since the last recording of data on September 2, 1931. These figures seem to show that the ice moves down the mountain, near mid-stream, at an average daily rate of some five inches during the fall, winter, and spring. Proffessor LeConte found that during the summer the ice approached a maximum downward movement of 10 to 15 inches daily. So a retarding of the downward flow during the winter months seems likely to view of the lower daily average figure arrived at by the present experiments.
Recently a check of some measurements taken at the snout of the Nisqually was made, to ascertain whether the ice advanced or retreated during the winter months. Working from points established in the fall of 1931 and the early spring, several months ago, it was found that the ice had receded one foot during the winter - from December to March. Absolutely accurate measurement at the snout of the Nisqually is not possible due to the irregularity of the ice at that point. In view of that fact, we might state that the ice remained practically stationary during the winter (that is, the melting at the snout is just about balanced by the downward flow) and that the recession as tabulated from year to year occurs largely during the summer season.
(Note: Mr. Llewlyn Evans, representing the City of Tacoma in these glacial observations, compiled the report from which this information was taken.) - (C.F.B.)
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