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

PHOTOGRAPHIC STATIONS

When photographic stations are being selected, possible changes in the glacier and in nearby vegetation should be anticipated. Enough stations should be selected so that, if some should be destroyed or obscured, good views of all study areas including the terminus will still be afforded from other sites as the glacier advances or recedes.

All parts of the glacier subject to analysis should be photographed from at least two different viewpoints, if feasible. Where a particular reach is subject to study, every part of each ice margin in that reach should be visible in at least one picture.

For a study of surface slope from photographs, the station should be about the same elevation as the glacier surface and, if possible, where permanent features such as bedrock strata or outcroppings can be recognized in the background. If an ice advance should block the view from such a station, photographs taken at a higher altitude on an extension of the same cross-profile axis should be satisfactory for continuing the record of slope measurements.

Where stations are not on bedrock, the possibility of encroachment by vegetation or destruction by erosion should be considered. The site should be located in reference to two or more witness rocks in the vicinity. Stations should be marked with monuments such as bronze tablets or steel stakes, which are easily recognized.

When setting up a program of this kind it is better to establish too many rather than too few photographic stations. Some stations can always be dropped, but once any photographic records are missed they are lost forever.

OPTIMUM LIGHT CONDITIONS

Ideally, glacier photography should be scheduled so that the same lighting conditions occur every year at each station. To accomplish this, the photographs should be taken at about the same time of day and on about the same date each year. Without such uniformity in lighting, the changes illustrated in a series of pictures are difficult to analyze, and interpretations may be misleading.

At stations where photographs are taken in several directions, there may be no entirely satisfactory time of day for all of the views. Furthermore, the scheduling of photographs at a series of stations must be adjusted to fit the practicable time of travel from place to place, thus requiring some compromise with the desired light conditions.

When a particular view is found to be blocked or shaded by fog or clouds, it still is advisable to take a picture even though another photograph might be obtained later under better conditions. The first picture may be of poor quality, but perhaps it could be used for study if none other should become available.

SELECTING THE VIEW

The best direction of view at a station should be selected the first year, taking into account the probable movements of the glacier, and then repeated each year without change. The exact site over which the camera is placed should be identifiable by a permanent marker, and the camera should be positioned within a foot of the same location each year. When pointing the camera, it is helpful to refer to an earlier photograph that shows the desired view at the station.

Panoramic views should overlap 20 to 30 percent so that the photographs when trimmed will match satisfactorily. The transverse axis of the camera should be held in a level position, adjusting the view as necessary by raising or lowering the camera's front but without tilting it sideways.

EQUIPMENT

The camera should be sturdy and equipped with a lens that permits high resolution over the entire image and a minimum of optical distortion toward the corners of the picture. It is understood that, as a general guide, the best results from a good lens will be obtained when its aperture is closed two to four stops from its maximum opening. Therefore, under a condition of intense light such as is available at a glacier, a rather slow film is preferable so the middle range of lens openings can be utilized.

A film with wide exposure latitude is needed for satisfactorily reproducing all the shades of contrast that are present in most glacier scenes. Color photography is superior to black and white in recording vegetation, which in the case of many receding glaciers is a very important change to be recorded. For this purpose 35 mm film should be satisfactory. If the photographic party is equipped with two cameras, it is believed worthwhile that the views at all the photographic stations be taken both in black and white and in color.

A desirable format for the photographic image is 4 by 5 because of its ready adaptation to ordinary 8- by 10-inch (20- by 25-cm) enlargements. With any other proportion, part of the negative must be masked when an 8 by 10 print is made; selecting the part or parts of each picture to be masked out and placing the guide marks on each negative for use of the enlarger operator is a time-consuming and relatively unrewarding process.

The rapid shutter speeds normally usable in this work make hand-held camera exposures generally satisfactory from the standpoint of negative sharpness. However, consistently better results, both as to sharpness and proper positioning and levelling of the camera, can be obtained with a tripod if enough time is available.

As mentioned earlier, no advantage has been found in this program in the use of a lens filter—such as a K-2 (yellow) one. A haze filter for reducing the effect of ultraviolet rays on film at high altitudes is helpful in color photography.

RECORDING THE PHOTOGRAPHIC DATA

When the annual photographs of Nisqually Glacier are taken, data are entered 011 a looseleaf "Index to Photographs" form prepared for recording the following:

A print of each form sheet that has been filled out with the data on a season's pictures is carried in the field for possible reference in succeeding years.