Geological Survey 18th Annual Report (Part II) Glaciers of Mount Rainier Rocks of Mount Rainier

As stated on a previous page, the ice bodies on Mount Rainier may be classified, in reference to their position on the mountain, as primary and secondary glaciers. The secondary glaciers have also been termed interglaciers, the type being Interglacier, situated on the broad V-shaped remnant of the middle mountain slope between Winthrop and Emmons glaciers.

The primary ice streams in the order of their occurrence, beginning on the north side of the mountain and going about it toward the east, south, etc., are, as indicated on the accompanying map, the Carbon, Winthrop, Emmons, Ingraham, Cowlitz, Nisqually, Kautz, Wilson, Tahoma, Puyallup, Edmunds, and Willis glaciers.

The secondary streams, or interglaciers, as it is convenient to term them, in the order just stated, are Interglacier, Frying-pan, Little Tahoma, Williwakas, Paradise, Van Trump, and others not named. All the glaciers of this type are not represented on the accompanying map (Pl. LXVI), partly for the reason that they merge with indefinite snow fields, and some of them have not been recognized by those to whom we are indebted for the map. It is only in late summer or early autumn that the existence of glacial ice beneath the general snowy covering of the higher portions of the mountain can be distinguished. The interglaciers, as a rule, do not form well-defined ice streams, but are rather broad névés, from which a protrusion of glacial ice can be seen when the summer melting is far advanced. In some instances, as about the Guardian rocks, the glaciers of this type scarcely merit the name here applied to them, as they are little more than névés. These small ice bodies grade into snow accumulations which endure perhaps for several years, but are occasionally completely melted. A former extension of the interglaciers, and the previous existence of true glaciers where only deep snow accumulations now occur, is shown by the polish and grooves on the rocks below the positions they occupy. In common with the primary glaciers, those of the secondary type were formerly much more extensive than at present, but their condition during the Glacial period has not been fully determined.

CARBON GLACIER.

The amphitheater in which Carbon Glacier has its source, as already stated, is the largest excavation that has been made in the sides of Mount Rainier. The wall of rock rising above the head of the glacier is about 4,000 feet high. On this vast precipice little snow accumulates, but on its summit there is a vertical cliff of stratified névé snow about 200 feet high. This wall of snow, conspicuous on account of its contrast in color with the dark rocks below, exposes a section of the névé which rests on the slope leading from the crest of the precipice to Liberty Cap. The slow downward creep of the névé causes portions of it to break off from time to time and descend in avalanches to the bottom of the amphitheater.

In the amphitheater is a névé, it is true, but not of the ordinary type. A deep accumulation of snow is formed there each winter by the avalanches and by snow blown from neighboring heights, in addition to that which falls directly, but the surface of the deposit thus formed is uneven, and, as may be seen in the numerous crevasses, lacks the well-marked stratification which is such a characteristic feature of normal névés.

Pl. LXXII. TATOOSH RANGE, FROM PARADISE PARK; LOOKING SOUTH.

The avalanches from the cliffs encircling the head of Carbon Glacier bring down considerable rock débris, and in summer rock-falls are common, owing to the action of the wind, the loosening of blocks by changes of temperature, etc. The snow in the amphitheater thus becomes heavily charged with débris, which is carried down by the outward flow of the névé, and becomes concentrated on its surface as melting progresses. On account of the strong winds that prevail much dust is also scattered over the snow flooring the amphitheater, which serves to darken its surface.

With the recession of the walls at the head of the amphitheater there has been an increase in its breadth. Some of the snow drainage previously contributed to Willis Glacier on the west, and to a former inter glacier on the east, has been diverted and now feeds Carbon Glacier. As previously stated, the recession of the cliffs at the head of the amphitheater has decreased the area of snow accumulation leading to it, and thus has led to a diminution in the size of the glacier originating in it. The loss due to the recession of the cliffs, and the consequent decrease in the extent of the elevated region of snow accumulation, has apparently been much greater than the gain due to a broadening of the amphitheater and the consequent robbing of adjacent glaciers of their snow supply. Carbon Glacier, by enlarging its amphitheater, is slowly destroying the conditions on which its existence depends. On the central portion of the great wall at the head of the amphitheater there is a buttress-like ridge, which indicates the position of a former dividing wall. At an early stage in the sculpturing of the mountain there were evidently two amphitheaters which contributed their snow to Carbon Glacier. With the enlargement of these recesses in the mountain side the ridge that divided them has nearly disappeared.

The sides of the amphitheater are rocky crests, as may be seen especially on the east, where a dark ridge of rock, marked by pinnacles and crags, separates the snow drainage of Carbon Glacier from that of Winthrop Glacier. This line of crags and pinnacles is the crest of the wall of bare rock sinking westward to Carbon Glacier, but its eastern slope is much less precipitous and is heavily covered with névé snow. A small enlargement of the amphitheater will cause a break in the divide on the summit of the cliffs, and some of the snow now flowing to Winthrop Glacier will be diverted to feed its more energetic neighbor on the west.

The outstretching ridges forming the side walls of the amphitheater extend northward and merge at their lower or northern extremities into broad, interglacier spaces at an elevation of about 9,000 feet. The amphitheater is about 8,000 feet across from east to west, and in the neighborhood of 5,000 feet in length from the base of the great cliffs at its head to the break through which the glacier outflows.

At the outlet of the amphitheater the snow, still having the characteristics of a névé, is much crevassed, especially where it passes over bosses of rock on the floor beneath. Dome-like elevations are thus caused in the glacier, which are broken by radiating fissures into castle-like blocks with precipitous walls. Domes of this nature are a characteristic feature of many of the glaciers on Mount Rainier, and the fact that they are due to the ice passing over prominent rock masses is clearly shown near the extremities of several of the primary glaciers where the rocks have been exposed by the melting and recession of the ice. The nature of these domes will be noted more in detail in connection with the descriptions which follow of Winthrop and Willis glaciers.

Just below the outlet of its amphitheater Carbon Glacier passes down a somewhat steep descent, and is much broken. Opposite Andesite Cliff the surface gradient becomes much more gentle, and for about a mile and a half downstream the glacier descends a very gentle grade. To one walking up the glacier the rise in this portion is scarcely noticeable. At the lower end of the nearly level reach just referred to the ice again descends a steep slope—which, however, scarcely merits the name of an ice fall—leading to the terminus. This last steep descent is about 1,000 feet in a mile.

In brief the glacier descends a moderately steep slope on leaving the amphitheater, flows for a mile and a half with a very gentle grade, and then goes over the edge of a precipice and descends a steep slope to its end. The alternate breaks and level reaches of the glacier, resembling a great stairway, are not a novel feature, as is well known, but a characteristic of many alpine glaciers. The level reaches separating breaks in a glacier indicate similar topographic features of the rock surface beneath. In studying existing glaciers it is instructive to examine valleys formerly glaciated. The best reported illustrations of the alternate step and terrace features in high-grade glaciated valleys occur in the Sierra Nevada, and have been described by me in a previous article.¹ In ascending Tuolumne Valley, near its source on Mount Lyell, for example, one encounters a series of steep escarpments separated one from another by almost level reaches, in some of which there are shallow rock-basin lakes. When the great valley referred to was occupied by a glacier each of the steep descents caused an ice fall. These conditions are reproduced on a small scale by Carbon Glacier.

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¹I. C. Russell, Quaternary history of Mono Valley, California: Eighth Ann. Rept. U. S. Geol. Survey, 1889, pp. 348, 354-355.

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As is explained in part in the report just referred to, and as has been still more clearly stated by Willard D. Johnson, a glacier cuts back its beds from one ice fall to another in much the same way that a cascade in a stream recedes. The formation of scarps and shelves, as the level reaches may be termed, is due to a process similar to that by which amphitheaters are enlarged.

Opposite Andesite Cliff Carbon Glacier is about half a mile broad, but it soon increases to nearly a mile in width, and maintains this increase all the way to the brink of the steep descent a mile and a half below. Indeed, but little diminution in breadth occurs until the final descent toward the terminus begins. It then contracts in width some what abruptly to about 1,000 feet, and ends in a precipitous slope.

Pl. LXXIII. THE SOURCE OF EMMONS GLACIER SHOWING THE SUMMIT AND EASTERN SLOPE OF MOUNT RAINIER.

Opposite Andesite Cliff the hard blue ice of the glacier is exposed. In this region there is a reach of the glacier about half a mile long, intervening between the lower edge of the névé and the heavily moraine-covered ice farther downstream, which is comparatively free from dirt and stones. The extent and character of this surface vary from day to day during the summer, the névé receding and the dirt-stained and stone-covered area at the same time increasing upstream, owing to the concentration of débris at the surface as melting progresses.

Downstream from the belt of clear ice just referred to the glacier is progressively more and more deeply covered with stones and dirt. In this region many of the minor features characteristic of moraine-covered ice, such as glacier tables, sand cones, surface streams, moulins, etc., may be recognized. About 1,000 feet downstream from Andesite Cliff four somewhat prominent medial moraines make their appearance, and may be traced to the brink of the steep descent a mile below. Two of these moraines are near the west side of the glacier, the nearest being about 700 feet from its western border, and separated from its companion by a lane of less completely débris-covered ice about 150 feet broad. The other pair of medial moraines occupy a similar position adjacent to the east side of the glacier. These medial moraines are not conspicuous features, but are marked by irregular débris pyramids, rising from 10 to 30 feet above the adjacent surface.

The débris along the west side of the glacier, derived largely from Andesite Cliff; is gray, corresponding with the color of the cliffs from which it comes; but on all other portions of the surface the prevailing color of the moraines is dark brown. Practically all of the morainal material is angular. Rounded or smooth and striated stones are seldom seen.

Below the beginning of the steep descent leading to the terminus of the glacier no ice can be seen in a general view. The entire surface is buried beneath a sheet of brown, angular débris. The larger stones range in size from a few inches to several feet, and mingled with them are large quantities of fine, earth-]ike material. This portion of the glacier is rugged, on account of numerous crevasses and unequal melting, due to variations in the thickness of the débris. Something of the manner in which surface morainal material is concentrated in depressions and then raised in relief by the melting of the adjacent surface so as to form débris pyramids may there be seen. This process, however, goes on most actively when a glacier has but little motion or is stagnant, and about Mount Rainier may be best studied near the terminus of Winthrop Glacier. At the end of Carbon Glacier the ice descends precipitously 300 or 400 feet, and presents a dirt-stained face too steep for one to climb without cutting steps. At the foot of this steep descent Carbon River emerges from a cavern in the ice, as a brown, roaring torrent, heavily encumbered with bowlders. The river is overloaded with coarse débris, and is filling, or aggrading, its valley all the way to the narrow canyon 3 miles above Carbonado. The condition of the valley bottom below that locality is not known to me.

Where the river leaves the icy cavern from which it emerges many of the stones in its bed are angular; these have come directly from the steep ice slope above. Other stones, many of them 2 feet or more in diameter and composed of hard rock, are well rounded; these have been brought out of the subglacial tunnel, and show that much erosion is performed by the stream before it comes to the light. Less than half a mile below the terminus of the glacier nearly all the stones that form its banks are well rounded.

The end of Carbon Glacier was seen by Willis in 1881 At the time of our visit the glacier had retreated about 100 yards, as nearly as could be estimated, above the position it occupied fifteen years previous, and the precipice at its terminus had become much less steep.

Accompanying the recession of the terminus during recent years, there has been a general lowering of the surface of the glacier all the way up to the névé, but no measure of the amount that the ice had shrunk could be made. The lowering of the surface is of the nature of a general shrinking, which is greatest near the crest of the lower ice fall, and progressively decreases upstream. One conspicuous result of this surface melting is a marked increase in the amount of superglacial débris, as noted by Willis.¹

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¹Seventeenth Ann. Rept, U. S. Geol. Survey, Part I, 1896, p. 53.

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A recent lowering of the surface of the glacier is recorded by abandoned lateral moraines. These are conspicuous along each side of the glacier, from the brink of the lower icefall up to Andesite Cliff on the west bank and to the entrance to the amphitheater on the east side. These moraines, composed largely of sandy clay heavily charged with stones and angular rock masses, rise from the ice in precipitous escarpments from 100 to 140 feet high, and are too steep in many places to be climbed. The angle of slope toward the glacier is from 40° to 50°. These slopes are broken faces, from which stones frequently fall, and are entirely bare of vegetation. The slope referred to rises to a sharp crest from which the slope away from the ice is more gentle, averaging between 30° and 40°. On these outer slopes spruce trees, some of them 20 to 30 feet high, are growing.

On leaving the glacier on either side and climbing the fresh slopes of morainal material bordering it, one finds other similar, parallel ridges, each of which is clothed with forest trees. These older moraines are in several instances higher than the most modern one, and show in general a progressive lowering of the surface of the ice as the width decreased.

The narrow valleys between the abandoned moraines are without forest trees, but are carpeted with moss, grasses, and a profusion of brilliant flowers. The snow lingers until late in summer in these shaded dells, and the black, humus soil, after the snowdrifts disappear, is water-soaked and in many places swampy. Thus in several ways the ridges favor the growth of forest trees, while the marshy dells between furnish conditions suitable for the growth of more lowly plants.

The abandoned lateral moraines below Andesite Cliff are in an embayment on the side of the valley. Their formation illustrates the manner in which a glacier builds moraines where the valley widens, and thus tends to make its channel even sided. The most recent moraine—the one overlooking the ice—starts from Andesite Cliff, but not at its most exposed portion. The next lateral moraine to be formed if the glacier continues to shrink will, it is to be expected, start from the extreme end of the cliffs where they now project into the glacier.

The older lateral moraines, of which there are sometimes three, and again four, abreast, terminate at their upper or proximal ends abruptly, without uniting with the cliffs from which they derived much of the material composing them. The reason for their abrupt ending is that a lateral stream following the side of the glacier cut a channel across them at their junction with the side of the valley. This process is plainly illustrated on the west border of Winthrop Glacier near its terminus.

The moraines on the east side of Carbon Glacier are in general like those just mentioned, and again all but the last formed are without connection at their proximal ends with the more elevated region above.

All of the moraines just described pertain to the present topography and were formed when the glacier had its present characteristics, except that below Andesite Cliff, when the earliest pair was formed, it was about a mile broader and its surface about 250 feet higher than now. Whether the valley was ever more deeply filled with ice than is recorded by these old moraines remains to be determined.