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

MORAINES

Photographs may bring out some detailed moraine and erosion patterns not noticed by an observer on the ground because film can emphasize color values and relief otherwise not very apparent. The pictures for different years can readily be examined and compared with respect to subtle features, which may easily be forgotten if observed only during occasional field inspections. An example of such a feature is the light-colored band in the large medial moraine near the east side of the glacier in figure 4. Another example is shown in the 1940 photograph taken from station 12 (fig. 26), which illustrates several small lateral moraines that had been deposited along the east side of the glacier at an altitude of 6,400 feet (1,950 in), suggesting a discontinuous rate of recession of the glacier.

CREVASSING AND GENERAL CHARACTER OF THE GLACIER SURFACE

In addition to the data presented in the preceding sections, some further examples of what photographs can show about glaciers are given below on the following subjects (all of which have not been studied herein in detail):

1. Crevassing patterns, from which the nature of the subsurface structure, the direction of ice movement, and changes in rates of movement can be interpreted.

2. Information of changes in surface slope, or the shape of its longitudinal profile, in areas not covered by surveys and contour maps.

3. Some details about advance, recession, debris load, contour, movement, thickness, and surface erosion.

Terminus to profile 1

Photographic series 1—NE (figs. 16-19) and 5 (figs. 20-25) illustrate the gradual deterioration and shrinkage of the entire glacier downstream from the nunatak and profile 1, and its subsequent reactivation. This lower area was virtually stagnant from about 1944 to 1954, but a spectacular advance of fresh ice passed the nunatak in 1954-55 and reached the terminus in 1963. By 1965 it had given form to a new, vigorous-looking terminus.

Profile 1 to about 1,000 feet (300 m) above profile 2

Captions for the photographs in series 6 (figs. 27-31), 7 (figs. 2-5), and 14—W (figs. 7-10) contain miscellaneous descriptive comments for this reach of the glacier. Certain features can be seen more clearly in one series than in the others. The following comments about the photographs in series 6 and 7, arranged in chronological order for each series, include most of the descriptive material that is contained in the captions:

Photographic series 7 (figs. 2-5)

Photographic series 6 (figs. 27-31)

1,000 feet (300 m) above profile 2 to above profile 3

For comments about this area, see captions of the photographs in series 15 (fig. 12) and 13 (figs. 32-34). Series 15 provides some coverage of upper part of glacier for the period prior to 1949, before series 13 was begun. A summary of the comments contained in the captions follows:

Series 15 (fig. 12)

Series 13 (figs. 32-34)

EROSION AND DEPOSITION

Banks and lateral moraines

Annual photographs reveal the progress of erosion along the banks of a valley glacier and along old lateral moraines. The 1947 and 1965 views in series 11 (fig. 35) illustrate 18 years of erosion of west side of the old east-bank lateral moraine. Along this part of the moraine the average lateral recession of its crest over the 18-year period has amounted to a total of 10-15 feet (3-5 m).

Figure 35.—Erosion of old (pre-1840) lateral moraine on east side of the glacier is shown by the series 11 photographs of August 25, 1947 (upper), and September 4, 1965 (lower). The total erosion during the period 1947-65, indicated by block line on the 1947 view, appears to have averaged between 10 and 15 feet (3 and 4.5 m) horizontally. (click on image for an enlargement in a new window)

In regard to erosion of the banks of a glacier, the views in series 14—W (figs. 7-10) show how some of the bedrock areas on the steep hillside above the west end of profile 2 became unrecognizable within 20 years. Note changes in the lower rock formations seen in the 1942 and 1960 views, which were photographed under similar light conditions. Thus, on photographs of a canyon wall, it may be difficult to pick out bedrock features that will be usable as long-term landmarks for measurements in photographic studies. In the present study, a few usable points were found that could be identified on pictures throughout the 24-page period of record.

Outburst floods

Repetitive photographs also portray changes in topography and vegetation in the channel and valley below a glacier that result from outburst-type floods (jokulhlaups). Three such floods emanating from Nisqually Glacier are described briefly below.

Flood of October 14, 1932. This flood tore away the reinforced concrete arch bridge which had been constructed in 1926. A precipitation total of 6.90 inches (175' mm) fell at Paradise Ranger Station October 10-13, inclusive. It is interesting to note what apparently is the deck of that bridge clearly visible in the 1947 view (fig. 37) in series 3 (figs. 36-38), just below the tree-covered island near the center of the picture.

Figure 36.—Nisqually valley below the glacier, as seen from station 3 in 1934 prior to October flood (date estimated; see footnote 4, page 44). Photograph furnished by Conservation Division, U.S. Geological Survey. Note substantial stand of trees and brush on west part of flood plain, and river on east side of flood plain. (click on image for an enlargement in a new window)

Figure 37.—Nisqually valley below the glacier, as seen from station 3 on August 25, 1947. West of the island of trees, most of the vegetation present in 1934 view is gone, due to glacier outburst flood of October 1934. The river now flows west of this island of trees. The deck of the concrete highway bridge used prior to the October 13, 1932, flood is visible on flood plain just below island of trees (arrow). (click on image for an enlargement in a new window)

Figure 38.—Nisqually valley below the glacier, as seen from station 3 on August 31, 1965. Aggradation on the flood plain, caused by the outburst flood of October 25, 1955, is evidenced by altered topography and dead trees. A new bridge was constructed high above the flood-affected channels. (click on image for an enlargement in a new window)

Flood of October 24-25, 1934. A series of outburst surges from the glacier, according to the monthly report of the Superintendent, Mount Rainier National Park, dated November 5, 1934, "completely plugged the bridge and piled rock and debris 15 feet deep on top of the arch. Approach roads on both sides of the bridge were washed out." Precipitation of 8.92 inches (227 mm) occurred at Paradise Ranger Station October 20-25, inclusive. This bridge, less than 2 years old and situated at the same site as the bridge it replaced after the 1932 flood, was reconditioned and used until its wash out in 1955.

Flood of October 25, 1955. The flood occurred about noon and destroyed bridges and other property downstream. It was preceded by heavy rainfall (a total of 5.51 inches (140 mm) was measured on the 24th and 25th at Paradise Ranger Station) and was observed by a Park Ranger to flow in several large surges. The frontal wave of the first surge was estimated to be 20 feet (6 m) high, and the water carried many large rocks and chunks of ice that were visible at the surface. The first surge tore from its abutments the heavily reinforced 80-foot (24-in) span, concrete highway bridge.

Natural changes below glacier from floods and other causes

The 1934,⁴ 1947, and 1965 pictures in series 3 (figs. 36-38) illustrate the removal of vegetation, channel widening, and subsequent killing of trees that occurred for a few thousand feet (500-1,000 m) below the bridge as a result of glacier floods of the early 1930's and 1955.

The flood channel in the vicinity of the highway bridge was widened by the 1955 flood, and some vegetation was removed, as illustrated by the 1949 and 1956 views in series 2-5 (figs. 39A, C). Margins of the flood plain and vegetation as they existed a month before the flood are indicated by white lines in figure 39C (1956). Note also the automobile-size boulders that were cast up onto the parking area just to left of and above the bridge, and the much larger boulder deposited upstream. Many large trees downstream from the bridge were washed away.

The annual photographs in series 2—S (only a few of which are shown in this report) show some interesting variations in the configuration of the low-flow channel between the glacier terminus and the highway bridge. They reveal how within one season the channel would change from meandering to straight, or vice versa, then retain one form for several consecutive years. An example is evident from a comparison of the photographs shown as figures 39A and 39B, for 1949 and 1950. Note also the new terraces visible in 1950 along the flood plain. Each subsequent annual view showed that the channel remained straight from 1950 until after 1953 (which was the last view taken until 1956).

A tributary alluvial fan, first visible in 1960, was deposited on right-bank flood plain above the bridge; by 1965 (fig. 39D) it had become a little larger.

The 1932-36 photographs taken by the National Park Service looking upstream from the bridge, which are not published here, indicate that the flood of October 1934 was very substantial and erosive above the bridge as well as in the vicinity of the island 1,000 feet (300 m) downstream.

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⁴This "1934" undated photograph closely matches the appearance of the glacier terminus in a National Park Service photograph dated September 5, 1934. The match is fair, but less perfect, with their 1933 photograph; it is clearly poor with their October 1, 1932 photograph. Thus it seems likely that this "1934" picture, upon which the large amount of downstream flood plain vegetation is visible, was taken after the 1932 glacier outburst flood and before the October 1934 flood, when denudation of that vegetation probably took place.

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