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

WILLIS GLACIER.

On the northwest side of Mount Rainier and at the head of the deep, narrow valley through which the north branch of Mowich River flows, there is a glacier, known as the Willis Glacier, which is perhaps the most interesting of any here considered. It has many of the features of the primary glaciers already described, but is of small size, and one may see all its characteristic features in a single day's excursion.

From the summit of Eagle Cliff—where may be seen the most magnificent of the views about Mount Rainier, and in fact one of the most sublime pictures of noble scenery to be had anywhere in America—the whole of Willis Glacier, from the snow fields that give brilliancy to Liberty Cap down to the dirt-stained and crevassed extremity of the ice stream, is embraced in a single view. Below the end of the glacier the river, rising in two branches from its divided extremity, rages over its bowlder-filled channels and between craggy mountains which rise in precipices on either hand. To an observer on Eagle Cliff the distant roar of the troubled waters in the wild valley at his feet is mingled with the softer music of creeks and rills that plunge down the bordering cliffs to join the torrent below.

From Eagle Cliff the manner in which Willis Glacier is divided at its extremity into two moraine-covered tongues of ice is a noticeable feature. The bold, rocky eminence that causes the division rises steeply in the center of the valley to a height of fully 1,000 feet, and is clothed on its downstream side with forest trees. For the sake of a name, I propose to call this bold, isolated eminence Division Rock. When Eagle Cliff was first reached by Willis in 1881 the glacier since named in his honor was larger than now, and extended to near the summit of Division Rock. On gaining the brink of the cliff immediately to the north of the summit of the rock, which is conspicuous from many points of view lower down the valley, the ice broke off so as to form a precipice at the summit of the rock cliff. As will be shown below, this observation enables us to make a rough measure of the amount that the end of the glacier has receded during the past fifteen years. On reaching Division Rock the glacier divides into two tapering tongues, more fully described below, and as seen from Eagle Cliff is marked by three rather faint medial moraines, separated by lanes of clear ice. The central moraine ends at the division produced by the rock, and the ones on each side follow the central portion of the tongue of ice in the valley at its sides.

Pl. LXXVII. MARGINAL CREVASSES, NISQUALLY GLACIER.

In visiting Willis Glacier I approached it from the east by way of the Guardian Rocks, and came to the brink of the canyon through which it flows midway between its terminus and the steeper portions of its névé. The crest of the cliffs of jointed andesite bordering the glacier on the northeast rise more than 1,000 feet above its surface and furnish exceedingly favorable localities for observing the glacier at their base. From such a station the entire glacier, from the clear white snow fields culminating at Liberty Cap down the steep side of the central dome, where the névé is much broken, to the blue ice below, and on to the moraine-covered terminus, is in full view. The entire distance from Liberty Cap, where the snow accumulates, to the extremity of the glaciers, where it melts away, is approximately 5 miles. The distance from the head of the slightly defined amphitheater in which the glacier heads to its terminus is about 3 miles. The breadth of the glacier where its borders are best defined, about a mile above its terminus, is approximately 3,000 feet. These measures, or rather estimates, show that the glacier is small, but the many interesting features it exhibits make it one of the most instructive of the glaciers in the system to which it belongs.

The north wall of the canyon through which the glacier flows is exposed to the sun, and the snow is melted from it early in the summer, while the south wall nearly to the end of the glacier remains heavily snow-covered throughout the year. From these snow fields broad, irregular névés descend to feed the glacier. Owing to this difference in exposure and to the manner in which the opposite sides of the canyon are affected by névé erosion and weathering, the southward facing wall is steep and rugged, with some vegetation in favored places, while the northward-facing slopes are gentle.

At the head of the canyon there is a steep ascent to the summit of the mountain, resembling the higher and more precipitous cliffs at the head of Carbon Glacier. On these cliffs irregular patches of névé snow are to be seen. The snow from these small accumulations, as well as from the less steep slopes about Liberty Cap, descends in avalanches to the head of the canyon. There is a noticeable enlargement of the canyon near its head, but it is not extensive enough to be classed as an amphitheater. The snow falling in avalanches, and also that which accumulates at the head of the canyon during the winter seasons, forms a névé, which is rugged and much broken by ice domes and crevasses. The lower limit of the névé is about 3,000 yards above Division Rock and just above a conspicuous ice fall which crosses the entire width of the glacier. In the névé region there are eight ice domes, which give to its surface an unusual topography. In these elevations the snow rises so as to form well-defined domes, which are, by estimate, from 20 to 50 feet high and from 150 to 200 feet in diameter. As the snow rises on the upstream side of a dome it becomes crevassed. The breaks at first are narrow and curve about the domes, but are highest and broadest in the central part. As the snow advances over the dome the crevasses widen and expose sections of dirt-stained snow beneath a clear white, surface layer 4 to 6 feet deep. On passing the crest the ridges between the crevasses crumble and fill the breaks with a confused mass of shattered blocks. This breaking is a characteristic feature of the downstream sides of the domes in the Willis Glacier, although not more noticeable than in many other examples seen, and gives to the lower sides of the elevation the characteristics of ice falls. In none of the crevasses about the domes could the underlying rock be distinguished.

From the behavior of the névé in passing over the domes just described we should expect the upstream sides of the rocks beneath to be rounded and otherwise glaciated, while their downstream faces would be broken and angular. This, as is well known, corresponds with what is frequently seen in glaciated regions. Division Rock, at the present terminus of Willis Glacier, illustrates the character of the bosses which cause the domes now forming such a characteristic feature of the névé region a mile or two above. This rock is worn and rounded on its upstream side, but presents a broken and angular precipice when seen from below.

The grade of the névé portion of the glacier is gentle; in fact, to one standing by its side, in its lower portion, the surface appears almost level, except that it is higher in the middle than at the margins. Below the ice fall just below the lower limit of the névé the descent to the terminus of the glacier above Division Rock is 840 feet, or about 1 foot in 10.

Above the ice fall mentioned above the névé is not only nearly flat for some 2,000 feet, but practically without crevasses. The absence of crevasses in this region is mainly due, no doubt, to the absence of inequalities on the rocky floor beneath, but is in part explained by the fact that the previous winter's snow, forming the surface, conceals the breaks that may exist in the ice beneath.

Below the névé, at the time of my visit, July 30, there was clear ice forming a belt some 500 feet broad, which extended across the glacier and was limited below by the ice fall. In this portion crevasses begin, which at first are narrow, and grow broader and broader as the ice nears the brink of the precipice over which it falls. The first crevasses to be seen are marginal, and trend upstream at angles of about 40° with the shore, but toward their distal extremities they curve down stream. Soon the crevasses from either side meet in the center of the glacier. These long breaks at first have a gentle downstream curvature in the central portion. Nearer and nearer the brink of the fall the crevasses become wider and wider, and at the same time more pronouncedly curved, until the brink of the precipice is reached. The walls of ice there become broken and fall in blocks and fragments of many shapes and sizes into the intervening crevasses. On the brink of the fall there are numerous blades and tower-like pinnacles, from 10 to 15 feet thick and 20 to 30 feet high, which are inclined forward as they pass over the precipice and fall from time to time with a crash.

The most interesting feature of the ice fall is that the surface of the glacier, as the ice approaches the steep descent, rises sharply, as it does in passing over a dome. The backward or upstream slope of the surface of the glacier in the central part, as measured with a clinometer, while on a level with it on the adjacent shore, is between 2° and 2° 30'. The total rise is about 20 feet. This rise of the surface on nearing the brink of the precipice seems to show that a ridge of hard rock there crosses the bed of the glacier. The nature of the rock in the precipice down which the ice descends is revealed at the end of the fall, but whether there is softer rock above it or not was not observed. When the ice passed over Division Rock a rise of the glacier, like that just described, must have occurred, since the surface of the rock slopes downward toward the east, forming an inclined plane, up which the glacier traveled. The inclination of the surface of the rock was not measured, but by estimate is certainly 3° to 5°. The length of the inclined plane now exposed is about 500 feet.

At the ice fall described above the glacier descends precipitously 400 feet. On the face of the fall the crevasses so conspicuous above are closed and the surface slopes sharply downstream, probably at an angle of 6° or 10°, for about 500 feet, and then becomes more gentle. The ice at the base of the fall is evidently strongly compressed. Blue bands at right angles to the flow of the glacier were observed, but a careful study of them was not made. Surface streams are common on this portion of the glacier during midday in summer, but they soon reach crevasses and disappear.

Descending the glacier, one finds that the ice near the terminus is much wasted by melting, surface débris becomes abundant, and in the central portion above Division Rock deep crevasses appear, which are parallel in a general way with the direction of flow. The crevasses indicate that the ice is split on coming in contact with the rock on which it divides.

On reaching Division Rock we found that in the middle of the V formed by the division of the glacier we could step from the ice onto the rock, although at the sides of the rock the ice had melted away so as to form deep gulfs.

Just where the ice divides, a monument of rough stones about 4 feet high was built. This monument is on the top of a small rounded rock dome somewhat detached from the main mass of Division Rock, and records the position of the terminus of the glacier at the center of the V referred to on July 30, 1896. Division Rock, as stated above, rises steeply from the monument to its summit, and is strewn with stones. On its summit there are about ten small evergreen trees, which show that the actual summit was not occupied by the glacier when it was seen by Willis in 1881.

The distance from the monument described above to the brink of the cliff at the summit of which the ice broke off, as observed by Willis, at the date just stated, is about 500 feet. The glacier has retreated this distance during the past fifteen years, but this is not an accurate measure of total recession, since at the time the position of the terminus was first recorded it formed a vertical precipice of ice on the summit of the cliff referred to. In the summer of 1881 the glacier formed an ice cascade at the lower side of Division Rock but the fallen ice did not reunite below the cliff.

The appearance of Division Rock in the summer of 1885, when the glacier still ended in a precipice at its lower margin, is shown in Pl. LXXXI.

Pl. LXXIX. ICE DOMES, NISQUALLY GLACIER.

The glacier, after being parted by Division Rock, sends a sloping and rapidly tapering débris-covered tongue of ice down the deep valleys on each side of it. The southern tongue is the larger of the two, and now ends about abreast of the highest portion of the rock.

Upstream from Division Rock the ice rises somewhat steeply, is heavily covered with débris, and so broken by crevasses that it is with difficulty one can climb it. Just above the first sharp rise, and on the right or northern bank of the glacier, there is another bold rock, similar to Division Rock, but close to the border of the canyon. This eminence was formerly covered by the glacier, but has been abandoned sufficiently long to allow forest trees to grow on its summit and north western side.

The retreat of the glacier within recent years has been accompanied by a lowering of its surface, as is plainly recorded by fresh-looking ridges of débris along its border. On the northern side of the glacier, for a mile above the fall of 400 feet, there are three well-defined abandoned lateral moraines. The youngest of these, the one nearest the glacier, rises about 50 feet above the ice, and at the fall is about on a level with the pinnacles on its crest. The second moraine is about 40 feet higher than the first, and, unlike the more recent one, is partially clothed with small trees; above this again is a thick moraine, the crest of which is lower than that of the second.

Below the 40-foot fall there is an abandoned lateral moraine, probably of the same age as the youngest moraine described above, which is 100 to 120 feet above the glacier. The vertical interval between this moraine and the present surface of the ice increases gradually down stream. This moraine shows a recent recession of the ice, and probably marks a stage in the lowering of its surface, which was determined in the reach between the 400-foot fall and the present terminus by the obstruction made by Division Rock.

There are many other instructive features to be seen on Willis Glacier which would well repay detailed study, but the time available did not enable me to make accurate notes concerning them. It is to be hoped that future travelers will report especially the position of the ice with reference to the monument built on the east end of Division Rock, and, if possible, secure photographs of the glacier from the point of view from which the photograph reproduced in Pl. LXXXI was obtained.

INTERGLACIERS.

I can offer but scanty information concerning the interglaciers about Mount Rainier, as the time available for making the reconnaissance on which this report is based was too short to admit of more than a casual examination of a few of them. That the small glaciers originating on the remnants of the mountain side, between the deep canyons carved by the primary glaciers, however, are of importance in the process of topographic development through which Mount Rainier is passing, is evident from even the hasty observations available.

The type of the interglaciers is furnished by the example from which the generic name is derived. Interglacier, named by E. S. Ingraham, occupies a broad, deep depression on the V-shaped remnant of the eastern slope of the mountain, between Winthrop and Emmons glaciers. The apex of this V-shaped mass is The Wedge, described on a previous page. The glacier receives no snow drainage from the main central dome of Mount Rainier, but is supplied by the snow falling on the V-shaped area referred to. The glacier has deepened its basin by excavation until something of an amphitheater has been formed, the rim of which is the divide between Interglacier and Winthrop Glacier on one side and Emmons Glacier on the other. The rocky ridge separating Interglacier from Winthrop Glacier has been broken at one locality, principally by the lateral erosion of the latter ice stream, so as to form what has been named St. Elmo Pass.

Interglacier flows eastward, but melts away before reaching the valley which Emmons Glacier occupies. The stream formed by its melting is tributary to White River.

The interglacier below Little Tahoma has a broad snow field, below which there is a protrusion of true glacial ice in summer. Instead of descending the slope of the mountain so as to excavate a symmetrical amphitheater, however, this glacier divides and is tributary to Emmons Glacier on the north and to Cowlitz Glacier on the south. The névé to the east of Little Tahoma divides into two branches, in much the same manner as the main névé field about the central dome of the mountain gives origin to primary glaciers. The two small glaciers fed by this snow field have excavated depressions for themselves, leaving a sharp, wedge-like mass of rock at the place of division. On the eastern slope of this secondary V-shaped remnant of the mountain side, left in relief by the cutting away of its borders, there is a small snow field, shown on the accompanying map, which probably has true glacial ice beneath it. Under the tentative system of classification used above for the glaciers about Mount Rainier the little glacier here referred to would belong to a tertiary series. This small nameless glacier demands attention from future travelers, as it supplements in an instructive manner the evidence furnished by the larger glaciers of the topographic development of an isolated peak under the influence of glacial erosion.

As may be seen on consulting the map just referred to each of the branches of the interglacier to the east of Little Tahoma again subdivides, leaving in each instance at the place of bifurcation a wedge-like rock mass facing toward the névé from which the glaciers have their source. A similar division of glaciers into branches is illustrated on a much larger scale by several of the ice streams on the southwest side of Mount Rainier. In these instances, however, it is probable that rock domes similar to Division Rock at the extremity of Willis Glacier cause the ice streams to divide, and not the increase in the area of the mountain side with distance from its apex.

The information referred to above concerning the topography of the V-shaped area east of Little Tahoma and the existence of a small glacier in that region representing a tertiary series is based entirely on the excellent sketch map forming Pl. LXVI, which is here reproduced, with some slight changes, from a manuscript map prepared by Messrs. H. M. Sarvent and G. F. Evans, of Tacoma, Washington, from surveys made by themselves.

Between Cowlitz and Nisqually glaciers there is another secondary glacier or interglacier known as Paradise Glacier. Other small ice bodies on the sides of Mount Rainier, beginning at about timber line and occupying areas more or less completely inclosed by primary glaciers, may be easily recognized, but to attempt a detailed description of them at this time would be premature.

Pl. LXXX. END OF NISQUALLY GLACIER.

The interglaciers were formerly much more extensive than now, and much of the beauty of the park-like regions in the neighborhood of the upper limit of timber growth is due to the changes they made in the relief of the mountain side, both by rounding and smoothing the rocks over which they flowed and by heaping moraines upon them. Many of the crags and pinnacles which give diversity to the scenery on the steep mountain slopes, like the Guardian Rocks near Spray Park, Gibraltar and the numerous crests near it, and other similar crags in Henry's Hunting Ground, etc., are remnants spared by the glaciers which once enveloped nearly the entire surface of the mountain, but still in their deeper portions flowed in most instances in well-defined channels.