Geological Survey Professional Paper 631 Analysis of a 24-Year Photographic Record of Nisqually Glacier, Mount Rainier National Park, Washington

NETWORK OF STATIONS

Several of the photographic stations were established at sites from which miscellaneous earlier photographs had been taken—for example, the 1890 view that was published in the 18th Annual Report of the U.S. Geological Survey. Additional stations were selected to improve the overall coverage and to collect some views illustrating geomorphological changes in the hills and valley. The objective was to provide fairly complete coverage of the glacier and valley below, with at least two angles of view available for every area insofar as feasible.

Along the east side of the glacier two "tiers" of stations were used—one as high as feasible and the other not far above the glacier surface. The higher stations provide most of the information needed for study of the glacier, but the lower ones are especially useful in any analysis of longitudinal surface slope or in any photographic determinations of rates of surface movement (the latter subject was not studied in this report).

The selection of photographic stations, except near the highway bridge, was restricted to the more accessible east side of the glacier. An attempt was made to avoid hazardous areas, such as those too precipitous or subject to rolling rock, and sites where tree growth or rise of the glacier surface might later obstruct the view.

A brief description of each photographic station, including its period of record, is given in table 1; the locations are shown on plate 1. The approximate direction of every panoramic view photographed from each station is indicated on plate 1. Each view series is given a serial number corresponding to the number of the station, with direction of the view added when necessary for differentiation between series. Footnotes explain the changes that have been made in the location of each station.

PHOTOGRAPHIC SERIES NOT PUBLISHED

Several of the photographic series shown on the map and in the description list are not discussed in this report but are included to indicate their availability in the files of the U.S. Geological Survey, Tacoma, Wash., should they later become of interest. These are series Nos. 1—SW, 2—NE, 4, 5—W, 8—W, 8—N, 9, 10, 12, 14—N, 16, 17—S, 17—NW, 18—S, and 18—NW. Some have been discontinued.

TABLE 1.—Descriptions of the photographic series, 1890-1965

TIME OF YEAR AND WEATHER CONDITIONS

To obtain information on annual accretion, wastage, and movement of ice in Nisqually Glacier, the photographs have been taken as late in the ablation season as thought safe before a heavy, fresh snowfall might occur. Early in the program the photographs were taken in late August, but more recently they have been taken during the first 2 weeks of September. Although the minimum mass of glacier ice and snow normally occurs in late September, photographs are taken earlier to avoid risk of a snowfall which would conceal features such as the firn line.

The climate at Nisqually Glacier is characterized by rapid changes in weather which are difficult to predict owing to the paucity of weather data beyond the coast line. Such changes may seriously interrupt completion of the photography, and they sometimes necessitate a second trip to Mount Rainier. Weather variations make it much more difficult to schedule aerial photography or to spend a number of days in cumbersome (though more precise) phototheodolite procedure; this emphasizes the economy of using a hand camera in one quick trip that can take full advantage of a brief break in the weather.

CAMERA EQUIPMENT

Cameras used for taking the 1942-65 pictures mentioned in this report were: 1942-57—Kodak Model 3—A, film size 3-1/4 by 5-1/2 inches, focal length 170 mm, equipped with cable shutter release; 1958-65—Kodak Tourist, film size 2-1/4 by 3-1/4 inches, focal length 105 mm. Exposures normally were for 1/200th second at f—11 or f—16, and were all made with the camera handheld.

In general, Kodak Super XX film (speed ASA 100) was used from 1942 to 1955 and Kodak Verichrome Pan (ASA 80) thereafter. The relatively low graininess of these films and their latitude to accommodate the contrasting lighting encountered in glacier scenes have been satisfactory.

In this program, the experimental use of lens filters, particularly the K—2 (yellow) one, have shown no advantage over the unfiltered lens.

LIGHT CONDITIONS

An effort was made to take the annual view at each station at the same hour of the day, as well as at the same time of year, so that similar light conditions would minimize illusory effects and possible misinterpretations. This was not always feasible, but analyses made during preparation of this report emphasize the importance of following such a procedure.

SCALE CORRECTIONS ON PRINTS

The selected enlargements or prints in each photographic series utilized in the quantitative analyses in this report were reduced to the same scale by developing and applying scale-ratio coefficients. These were obtained by scaling the linear distances between identical fixed points (features in bedrock) common to all the prints, and determining the ratio between the value for each print with respect to the comparable value on a selected base print. The resulting coefficients were applied to any analytical data measured on those prints to reduce all measurements to the scale of the base print.