In the region where the new crevasses open the surface drainage comes abruptly to an end. Here gaping chutes of deepest azure entrap the torrents and the waters rush with musical thunder to the interior of the glacier and finally down to its bed.
At its lower border the Paradise Glacier splits into several lobes. The westernmost sends forth the Paradise River, which, turning southwestward, plunges over the Sluiskin Fall (named for the Klickitat Indian who guided Van Trump and Hazard Stevens to the mountain in 1870, when they made the first successful ascent) and runs the length of Paradise Valley. The middle lobe has become known as Stevens Glacier (named for Hazard Stevens) and ends in Stevens Creek, a stream which almost immediately drops over a precipice of some 600 feet—the Fairy Falls—and winds southeastward through rugged Stevens Canyon. The easternmost lobes, known collectively as Williwakas Glacier, send forth two little cascades, which, uniting, form Williwakas Creek. This stream is a tributary of the Cowlitz River, as is Stevens Creek.
Immediately adjoining the Paradise Glacier on the northeast, and not separated from it by any definite barrier, lies the Cowlitz Glacier, one of the stateliest ice streams of Mount Rainier. It flows in a southeasterly direction, and burrows its nose deeply into the forest-covered hills at the mountain's foot. Its upper course consists of two parallel-flowing ice streams, intrenched in profound troughs, which they have enlarged laterally until now only a narrow, ragged crest of rock remains between them, resembling a partition a thousand feet in height. At the upper end of this crest stands Gibraltar Rock.
At the point of confluence of the two branches there begins a long medial moraine that stretches like a black tape the whole length of the lower course. To judge by its position midway on the glacier's back, the two tributaries must be very nearly equal in strength, yet, when traced to their sources, they are found to originate in widely different ways. The north branch, named Ingraham Glacier (after Maj. E. S. Ingraham, one of Rainier's foremost pioneers), comes from the névés on the summit; while the south branch heads in a pocket immediately under Gibraltar. No snow comes to it from the summit; hence we can not escape the conclusion that it receives through direct precipitation and through wind drifting about as much snow as its sister branch receives from the summit regions. Like the glacier troughs below, the pocket appears to have widened laterally under the influence of the ice, and is now separated from the Nisqually ice fields to the west by only a narrow rock partition, the Cowlitz Cleaver, as it is locally called. Up this narrow crest the route to Gibraltar Rock ascends. The name "cleaver," it may be said in passing, is most apt for the designation of a narrow rock crest of this sort, and well deserves to be more generally used in the place of awkward foreign terms, such as arrete and grat.
Both branches of the Cowlitz Glacier cascade steeply immediately above their confluence, but the lower glacier has a gentle gradient and a fairly uneventful course. Like the lower Nisqually, it is bordered by long morainal ridges, and toward its end acquires broad marginal dirt bands. For nearly a mile these continue, leaving a gradually narrowing lane of clear ice between them. Then they coalesce and the whole ice body becomes strewn with rock débris.
The Cowlitz Glacier, including its north branch, the Ingraham Glacier, measures slightly over 6 miles in length. Throughout that distance the ice stream lies sunk in a steep-walled canyon of its own carving. Imposing cliffs of columnar basalt, ribbed as if draped in corduroy, overlook its lower course. Slender waterfalls glide down their precipitous fronts, like silver threads, guided by the basalt flutings.
From the end of the glacier issues the Muddy Fork of the Cowlitz River, which, joining the Ohanapecosh, forms the Cowlitz River proper, one of the largest streams of the Cascade Range. For nearly a hundred miles the Cowlitz River follows a southwesterly course, finally emptying in the Columbia River a short distance below Portland, Oregon.
The name Muddy Fork is a most apt one, for the stream leaves the glacier heavily charged with débris and mud, and while it gradually clears itself as it proceeds over its gravelly bed, it is still turbid when it reaches the Ohanapecosh. That stream is relatively clear, for it heads in a glacier of small extent and little eroding power, and consequently begins its career with but a moderate load; furthermore it receives on its long circuitous course a number of tributaries from the Cascade Range, all of them containing clear water.
The name Muddy, however, might with equal appropriateness be given to every one of the streams flowing from the ice fields of Mount Rainier. So easily disintegrated are the volcanic materials of which that peak is composed, that the glaciers are enabled to erode with great rapidity, even in their present shrunken state. They consequently deliver to the streams vast quantities of débris, much of it in the form of cobbles and bowlders, but much of it also in the form of "rock flour."
A considerable proportion of a glacier's erosional work is performed by abrasion or grinding, its bed being scoured and grooved by the rock blocks and smaller débris held by the passing ice. As a result glacier streams ordinarily carry much finely comminuted rock, or rock flour, and this, because of its fineness, remains long in suspension and imparts to the water a distinctive color. In regions of light-colored rocks the glacier streams have a characteristic milky hue, which, as it fades out, passes over into a delicate turquoise tint. But the lavas of Mount Rainier produce for the most part dark-hued flour, and as a consequence the rivers coming from that peak are dyed a somber chocolate brown.
A word may not be out of place here about the sharp daily fluctuations of the ice-fed rivers of the Mount Rainier National Park, especially in view of the difficulties these streams present to crossing. There are fully a score of turbulent rivers radiating from the peak, and as a consequence one can not journey far through the park without being obliged to cross one of them. On all the permanent trails substantial bridges obviate the difficulty, but in the less developed portions of the park, fording is still the only method available. It is well to bear in mind that these rivers, being nourished by melting snow, differ greatly in habit from streams in countries where glaciers are absent. Generally speaking, they are highest in summer and lowest in winter; also, since their flow is intimately dependent upon the quantity of snow being melted at a given time, it follows that in summer when the sun reaches its greatest power they swell daily to a prodigious volume, reaching a maximum in the afternoon, while during the night and early morning hours they again ebb to a relatively moderate size. In the forenoon of a warm summer day one may watch them grow hourly in volume and in violence, until toward the middle of the day they become raging torrents of liquid mud in which heavy cobbles and even bowlders may be heard booming as they roll before the current. It would be nothing short of folly to attempt to ford under these conditions, whether on horseback or on foot. In the evening, however, and still better, in the early morning, one may cross with safety; the streams then have the appearance of mere mountain brooks wandering harmlessly over broad bowlder beds.
High above the Ingraham Glacier towers that sharp, residual mass of lava strata known as Little Tahoma (11,117 feet), the highest outstanding eminence on the flank of Mount Rainier. It forms a gigantic "wedge" that divides the Ingraham from the Emmons Glacier to the north. So extensive is this wedge that it carries on its back several large ice fields and interglaciers, some of which, lying far from the beaten path of the tourist, are as yet unnamed. Separating them from each other are various attenuated, pinnacled crests, all of them subordinate to a main backbone that runs eastward some 6 miles and terminates in the Cowlitz Chimneys (7,607 feet), a group of tall rock towers that dominate the landscape on the east side of Mount Rainier.
Most of the ice fields, naturally, lie on the shady north slope of the main backbone; in fact, a series of them extends as far east as the Cowlitz Chimneys. One of the lesser crests, however, that running southeastward to the upland region known as Cowlitz Park, also gives protection to an ice body of some magnitude, the Ohanapecosh Glacier. Considerably broader than it is long in the direction of its flow, this glacier lies on a high shelf a mile and a half across, whence it cascades down into the head of a walled-in canyon. Formerly, no doubt, it more than filled this canyon, but now it sends down only a shrunken lobe. The stream that issues from it, the Ohanapecosh River, is really the main prong and head of the Cowlitz River.
The largest and most elevated of the ice fields east of Little Tahoma is known for its peculiar shape as Fryingpan Glacier. It covers fully 3 square miles of ground and constitutes the most extensive and most beautiful interglacier on Mount Rainier. It originates in the hollow east side of Little Tahoma itself and descends rapidly northward, overlooking the great Emmons Glacier and finally reaching down almost to its level. It is not a long time since the two ice bodies were confluent.
The eastern portion of the Fryingpan Glacier drains northeastward and sends forth several cascading torrents which, uniting with others coming from the lesser ice fields to the east, form the Fryingpan River, a brisk stream that joins White River several miles farther north.
Below the Fryingpan Glacier there lies a region of charming flower-dotted meadows named Summerland, a most attractive spot for camping.
Cloaking almost the entire east side of Mount Rainier is the Emmons Glacier, the most extensive ice stream on the peak (named after Samuel F. Emmons, the geologist and mountaineer who was the second to conquer the peak in 1870). About 5½ miles long and 1¾ miles wide in its upper half, it covers almost 8 square miles of territory. It makes a continuous descent from the summit to the base, the rim of the old crater having almost completely broken down under its heavy névé cascades. But two small remnants of the rim still protrude through the ice and divide it into three cascades. From each of these dark rock islands trails a long medial moraine that extends in an ever-broadening band down to the foot of the glacier.
Conspicuous lateral moraines accompany the ice stream on each side. There are several parallel ridges of this sort, disposed in successive tiers above each other on the valley sides. Most impressively do they attest the extent of the Emmons Glacier's recent shrinking. The youngest moraine, fresh looking as if deposited only yesterday, lies but 50 feet above the glacier's surface and a scant 100 feet distant from its edge; the older ridges, subdued in outline, and already tinged with verdure, lie several hundred feet higher on the slope.
The Emmons Glacier, like the Nisqually and the Cowlitz, becomes densely littered with morainal débris at its lower end, maintaining, however, for a considerable distance a central lane of clear ice. The stream which it sends forth, White River, is the largest of all the ice-fed streams radiating from the peak. It flows northward and then turns in a northwesterly direction, emptying finally in Puget Sound at the city of Seattle.
On the northeast side of the mountain, descending from the same high névés as the Emmons Glacier, is the Winthrop Glacier. Not until halfway down, at an elevation of about 10,000 feet, does it detach itself as a separate ice stream. The division takes place at the apex of that great triangular interspace so aptly named "the Wedge." Upon its sharp cliff edge, Steamboat Prow, the descending névés part, it has been said, like swift-flowing waters upon the dividing bow of a ship at anchor. The simile is an excellent one; even the long foam crest, rising along the ship's side, is represented by a wave of ice.
Undoubtedly the Wedge formerly headed much higher up on the mountain's flank. Perhaps it extended upward in the form of a long, attenuated "cleaver." It is easy to see how the ice masses impinging upon it have reduced it to successively lower levels. They are still unrelentingly at work. It is on the back of the Wedge, it may be added here, that is situated that small ice body which Maj. Ingraham named the "Interglacier." That name has since been applied in a generic sense to all similar ice bodies lying on the backs of "wedges."
Of greatest interest on the Winthrop Glacier are the ice cascades and domes. Evidently the glacier's bed is a very uneven one, giving rise to falls and pools, such as one observes in a turbulent trout stream. The cascades explain themselves readily enough, but the domes require a word of interpretation. They are underlain by rounded bosses of especially resistant rock. Over these the ice is lifted, much as is the water of a swift mountain torrent over submerged bowlders. Immediately above each obstruction the ice appears compact and free from crevasses, but as it reaches the top and begins to pour over it breaks, and a network of intersecting cracks divides it into erect, angular blocks and fantastic obelisks. Below each dome there is, as a rule, a deep hollow partly inclosed by trailing ice ridges, analogous to the whirling eddy that occurs normally below a bowlder in a brook. Thus does a glacier simulate a stream of water even in its minor details.
The domes of the Winthrop Glacier measure 50 to 60 feet in height. A sample of the kind of obstruction that produces them appears, as if specially provided to satisfy human curiosity, near the terminus of the glacier. There one may see, close to the west wall of the troughlike bed, a projecting rock mass, rounded and smoothly polished, over which the glacier rode but a short time ago.
Another feature of interest sometimes met with on the Winthrop Glacier, and for that matter also on the other ice streams of Mount Rainier, are the "glacier tables." These consist of slabs of rock mounted each on a pedestal of snow and producing the effect of huge toadstools. The slabs are always of large size, while the pedestals vary from a few inches to several feet in height.
The origin of the rocks may be traced to cliffs of incoherent volcanic materials that disintegrate under the frequent alternations of frost and thaw and send down periodic rock avalanches, the larger fragments of which bound out far upon the glacier's surface.
The snow immediately under these large fragments is effectually protected from the sun and does not melt, while the surrounding snow, being unprotected, is constantly wasting away, often at the rate of several inches per day. Thus in time each rock is left poised on a column of its own conserving. There is, however, a limit to the height which such a column can attain, for as soon as it begins to exceed a certain height the protecting shadow of the capping stone no longer reaches down to the base of the pedestal and the slanting rays of the sun soon undermine it. More commonly, however, the south side of the column becomes softened both by heat transmitted from the sun-warmed south edge of the stone, as well as by heat reflected from the surrounding glacier surface, and as a consequence the table begins to tilt. On very hot days, in fact, the inclination of the table keeps pace with the progress of the sun, much after the manner of a sun-loving flower, the slant being to the southeast in the forenoon and to the southwest in the afternoon. As the snow pillar increases in height it becomes more and more exposed and the tilting is accentuated, until at last the rock slides down.
In its new position the slab at once begins to generate a new pedestal, from which in due time it again slides down, and so the process may be repeated several times in the course of a single summer, the rock shifting its location by successive slips an appreciable distance across the glacier in a southerly direction.
As has been stated, the slabs on glacier tables are always of large size. This is not a fortuitous circumstance; rocks under a certain size, and especially fragments of little thickness, cannot produce pedestals; in fact, far from conserving the snow under them, they accelerate its melting and sink below the surface. This is especially true of dark-colored rocks. Objects of dark color, as is well known to physicists, have a faculty for absorbing heat, whereas light-colored objects, especially white ones, reflect it best. Dark-colored fragments of rock lying on a glacier, accordingly, warm rapidly at their upper surface and, if thin, forthwith transmit their heat to the snow under them, causing it to melt much faster than the surrounding clean snow, which, because of its very whiteness, reflects a large percentage of the heat it receives from the sun. As a consequence each small rock fragment and even each separate dust particle on a glacier melts out a tiny well of its own, as a rule not vertically downward but at a slight inclination in the direction of the noonday sun. And thus, in some localities, one may behold the apparently incongruous spectacle of large and heavy rocks supported on snow pillars alongside of little fragments that have sunk into the ice.
There is also a limit to the depth which the little wells may attain; as they deepen, the rock fragment at the bottom receives the sun heat each day for a progressively shorter period, until at last it receives so little that its rate of sinking becomes less than that of the melting glacier surface. Nevertheless it will be clear that the presence of scattered rock débris on a glacier must greatly augment the rate of melting, as it fairly honeycombs the ice and increases the number of melting surfaces. Wherever the débris is dense, on the other hand, and accumulates on the glacier in a heavy layer, its effect becomes a protective one and surface melting is retarded instead of accelerated. The dirt-covered lower ends of the glaciers of Mount Rainier are thus to be regarded as in a measure preserved by the débris that cloaks them; their life is greatly prolonged by the unsightly garment.
In many ways the most interesting of all the ice streams on Mount Rainier is the Carbon Glacier, the great ice river on the north side, which flows between those two charming natural gardens, Moraine Park and Spray Park. The third glacier in point of length, it heads, curiously, not on the summit, but in a profound, walled-in amphitheater, inset low into the mountain's flank. This amphitheater is what is technically known as a glacial cirque, a horseshoe-shaped basin elaborated by the ice from a deep gash that existed originally in the volcano's side. It has the distinction of being the largest of all the ice-sculptured cirques on Mount Rainier, and one of the grandest in the world. It measures more than a mile and a half in diameter, while its head wall towers a sheer 3,600 feet. So well proportioned is the great hollow, however, and so simple are its outlines that the eye finds difficulty in correctly estimating the dimensions. Not until an avalanche breaks from the 300-foot névé cliff above and hurls itself over the precipice with crashing thunder, does one begin to realize the depth of the colossal recess. The falling snow mass is several seconds in descending, and though weighing hundreds of tons, seemingly floats down with the leisureliness of a feather.
These avalanches were once believed to be the authors of the cirque. They were thought to have worn back the head wall little by little, even as a waterfall causes the cliff under it to recede. But the real manner in which glacial cirques evolve is better understood to-day. It is now known that cirques are produced primarily by the eroding action of the ice masses embedded in them. Slowly creeping forward, these ice masses, shod as they are with débris derived from the encircling cliffs, scour and scoop out their hollow sites, and enlarge and deepen them by degrees. Seconding this work is the rock-splitting action of water freezing in the interstices of the rock walls. This process is particularly effective in the great cleft at the glacier's head, between ice and cliff. This abyss is periodically filled with fresh snows, which freeze to the rock; then, as the glacier moves away, it tears or plucks out the frost-split fragments from the wall. Thus the latter is continually being undercut. The overhanging portions fall down, as decomposition lessens their cohesion, and so the entire cliff recedes.
A glacier, accordingly, may be said, literally, to gnaw headward into the mountain. But, as it does so, it also attacks the cliffs that flank it, and as a consequence, the depression in which it lies tends to widen and to become semicircular in plan. In its greatest perfection a glacial cirque is horseshoe-shaped in outline. The Carbon Glacier's amphitheater, it will be noticed, consists really of two twin cirques, separated by an angular buttress. But this projection, which is the remnant of a formerly long spur dividing the original cavity, is fast being eliminated by the undermining process, so that in time the head wall will describe a smooth, uninterrupted horseshoe curve.
In its headward growth the Carbon Glacier, as one may readily observe on the map, has encroached considerably upon the summit platform of the mountain, the massive northwest portion of the crater rim of which Liberty Cap is the highest point. In so doing it has made great inroads upon the névé fields that send down the avalanches, and has reduced this source of supply. On the other hand, by deploying laterally, the glacier has succeeded in capturing part of the névés formerly tributary to the ice fields to the west, and has made good some of the losses due to its headward cutting. But, after all, these are events of relatively slight importance in the glacier's career; for like the lower ice fields of the Nisqually, and like most glaciers on the lower slopes of the mountain, the Carbon Glacier is not wholly dependent upon the summit névés for its supply of ice. The avalanches, imposing though they are, contribute but a minor portion of its total bulk. Most of its mass is derived directly from the low hanging snow clouds, or is blown into the cirque by eddying winds. How abundantly capable these agents are to create large ice bodies at low altitudes is convincingly demonstrated by the extensive névé fields immediately west of the Carbon Glacier, for which the name Russell Glacier has recently been proposed. It is to be noted, however, that these ice fields lie spread out on shelves fairly exposed to sun and wind. How much better adapted for the accumulation of snow is the Carbon Glacier's amphitheater! Not only does it constitute an admirably designed catchment basin for wind-blown snow, but an effective conserver of the névés collecting in it. Opening to the north only, its encircling cliffs thoroughly shield the contained ice mass from the sun. By its very form, moreover, it tends to prolong the glacier's life, for the latter lies compactly in the hollow with a relatively small surface exposed to melting. The cirque, therefore, is at once the product of the glacier and its generator and conserver.
Of the lower course of the Carbon Glacier little need here be said, as it does not differ materially from the lower courses of the glaciers already described. It may be mentioned, however, that toward its terminus the glacier makes a steep descent and develops a series of parallel medial moraines and that it reaches down to an elevation of 3,365 feet, almost 600 feet lower than any other ice stream on Mount Rainier. A beautiful cave usually forms at the point of exit of the Carbon River.
West of the profound canyon of the Carbon River, there rises a craggy range which the Indians have named the Mother Mountains. From its narrow backbone one looks down on either side into broadly open, semicircular valley heads. Some drain northward to the Carbon River, some southward to the Mowich River. Encircling them run attenuated rock partitions, surmounted by low, angular peaks; while cutting across their stairwise descending floors are precipitous steps of rock, a hundred feet in height. On the treads lie scattered shallow lakelets, strung together by little silvery brooks trickling in capricious courses.
Most impressive is the basin that lies immediately under the west end of the range. Smoothly rounded like a bowl, it holds in its center an almost circular lake of vivid emerald hue—that mysterious body of water known as Crater Lake. Let it be said at once that this appellation is an unfortunate misnomer. The basin is not of volcanic origin. It lies in lava and other volcanic rocks, to be sure, but these are merely spreading layers of the cone of Mount Rainier. Ice is the agent responsible for the carving of the hollow. It was once the cradle of a glacier, and that ice mass, gnawing headward and deploying even as the Carbon Glacier does to-day, enlarged its site into a horseshoe basin, a typical glacial cirque. The lake in the center is a strictly normal feature; many glacial cirques possess such bowls, scooped out by the eroding ice masses from the weaker portions of the rock floor; only it is seldom that such features acquire the symmetry of form exhibited by Crater Lake. The lakelets observed in the neighboring valley heads—all of which are abandoned cirques—are of similar origin.
As for the skeleton character of the dividing crests, it will be readily seen to be the outcome of the headward gnawing of opposing cirques. In some places, even, the deploying process has attenuated the ridges sufficiently to break them through. West of Crater Lake is an instance of a crest that has thus been breached.
It is a significant fact that the empty cirques about the Mother Mountains lie at elevations ranging between 4,500 and 6,000 feet; that is, on an average 5,000 feet lower than the cirques on Mount Rainier which now produce glaciers. Evidently the snow line in glacial times lay at a much lower level than it does to-day, and the ice mantle of Mount Rainier expanded not merely by the forward lengthening of its ice tongues but by the birth of numerous new glaciers about the mountain's foot. The large size of the empty cirques and canyons, moreover, leads one to infer that many of these new glaciers far exceeded in volume the ice streams descending the volcano's sides. The latter, it is true, increased considerably in thickness during glacial times, but not in proportion to the growth of the low-level glaciers. Nor is this surprising in view of the heavy snow falls occurring on the mountain's lower slopes. There is good reason to believe, moreover, that the cool glacial climate resulted in a general lowering of the zone of heaviest snowfall. It probably was depressed to levels between 4,000 and 6,000 feet. Not only the cirque glaciers about the Mother Mountains, but all the neighboring ice streams of the glacial epoch originated within this zone, as is indicated by the altitudes of the cirques throughout the adjoining portions of the Cascade Range. By their confluence these ice bodies produced a great system of glaciers that filled all the valleys of this mountain belt and even protruded beyond its western front.
To these extensive valley glaciers the ice flows of Mount Rainier stood in the relation of mere tributaries. They descended from regions of rather scant snowfall, for the peak in those days of frigid climate rose some 10,000 feet above the zone of heaviest snowfall, into atmospheric strata of relative dryness. It may well be, indeed, that it carried then but little more snow upon its summit than it does to-day.
The North Mowich Glacier is the northernmost of the series of ice bodies on the west flank of Mount Rainier. Like the Carbon Glacier, it heads in a cirque at the base of the Liberty Cap massif, fed by direct snow precipitation, by wind drifting, and by avalanches. The cirque is small and shallow, not as capacious even as either of the twin recesses in the Carbon Glacier's amphitheater. As a consequence the ice stream issuing from it is of only moderate volume; nevertheless it attains a length of 3¾ miles. This is due in part to the heavy snows that reënforce it throughout its middle course and in part to overflows from the ice fields bordering it on the south. These ice fields, almost extensive enough to be considered a distinct glacier, are separated from the North Mowich Glacier only by a row of pinnacles, the remnants evidently of a narrow rock partition or "cleaver," now demolished by the ice. The lowest and most prominent of the rock spires bears the appropriate name of "The Needle" (7,587 feet).
The débris-covered lower end of the glacier splits into two short lobes on a rounded boss in the middle of the channel. This boss, but a short time ago, was overridden by the glacier and then undoubtedly gave rise to an ice dome of the kind so numerous farther up on the North Mowich Glacier and also characteristic of the Winthrop Glacier.
Separated from the ice fields of the North Mowich Glacier by a great triangular ice field (named Edmunds Glacier) lies the South Mowich Glacier, also a cirque-born ice stream, heading against the base of the Liberty Cap massif. It is the shortest of the western glaciers, measuring only a scant 3 miles. Aside from the snows accumulating in its ill-shaped cirque it receives strong reënforcements from its neighbor to the south—the Puyallup Glacier.
Toward its lower end it splits into two unequal lobes, the southernmost of which is by far the longer. Sharp cut rock wedges beyond its front show that when the glacier extended farther down it split again and again.
The north lobe is of interest because the stream that cascades from the Edmunds Glacier runs for a considerable distance under it. In the near future the lobe is likely to recede sufficiently to enable the torrent to pass unhindered by its front.
What especially distinguishes the Puyallup Glacier from its neighbors to the north is the great elevation of its cirque. The Carbon, North Mowich, and South Mowich Glaciers all head at levels of about 10,000 feet. The amphitheater of the Puyallup Glacier, on the contrary, opens a full 2,000 feet higher up. Encircled by a great vertical wall that cuts into the Liberty Cap platform from the south, it has evidently developed through glacial sapping from a hollow of volcanic origin. From this great reservoir the Puyallup Glacier descends by a rather narrow chute. Then it expands again to a width of three-fourths of a mile and sends a portion of its volume to the South Mowich Glacier. In spite of this loss it continues to expand, reaching a maximum width of a mile and a total length of 4 miles. No doubt this is accounted for by the heavy snowfalls that replenish it throughout its course.
Its lower end consists of a tortuous ice lobe that describes a beautiful curve, flanked on the north by a vertical lava cliff. A lesser lobe splits off to the south on a wedge of rock.
Immediately south of the elevated amphitheater of the Puyallup Glacier the crater rim of the volcano is breached for a distance of half a mile. Through this gap tumbles a voluminous cascade from the névé fields about the summit, and this cascade, reënforced by a flow from the Puyallup cirque, forms the great Tahoma Glacier, the most impressive ice stream on the southwest side. Separated from its northern neighbor by a rock cleaver of remarkable length and straightness, it flows in a direct course for a distance of 5 miles. Its surface, more than a mile broad in places, is diversified by countless ice falls and cataracts.
A mere row of isolated pinnacles indicates its eastern border, and across the gaps in this row its névés coalesce with those of the South Tahoma Glacier. Farther down the two ice streams abruptly part company and flow in wide detours around a cliff-girt, castellated rock mass—Glacier Island it has been named. The Tahoma Glacier, about a mile above its terminus, spits upon a low, verdant wedge and sends a lobe southward which skirts the walls of this island rock, and at its base meets again the South Tahoma Glacier. From here on the two ice streams merge and form a single densely débris-laden mass, so chaotic in appearance that one would scarcely take it for a glacier. Numerous rivulets course over its dark surface only to disappear in mysterious holes and clefts. Profound, circular kettles filled with muddy water often develop on it during the summer months, and after a brief existence empty themselves again by subglacial passages or by a newly formed crevasse. So abundant is the rock débris released by melting that the wind at times whips it up into veritable dust storms.
Beautifully regular moraines accompany the ice mass on both sides, giving clear evidence of its recent shrinking.
The partner of the Tahoma Glacier, known as the South Tahoma Glacier, heads in a profound cirque sculptured in the flanks of the great buttress that culminates in Peak Success (14,150 feet). It is interesting chiefly as an example of a cirque-born glacier, nourished almost exclusively by direct snowfalls from the clouds and by eddying winds. In spite of its position, exposed to the midday sun, it attains a length of nearly 4 miles, a fact which impressively attests the ampleness of its ice supply.
In glacial times the glacier had a much greater volume and rose high enough to override the south half of Glacier Island, as is clearly shown by the glacial grooves and the scattered ice-worn bowlders on that eminence. As the glacier shrank it continued for some time to send a lobe through the gulch in the middle of the island. Even now a portion of this lobe remains, but it no longer connects with the Tahoma Glacier.
An excellent nearby view of the lower cascades of the South Tahoma Glacier may be had from the ice-scarred rock platform west of Pyramid Rock. From that point, as well as from the other heights of [Indian] Henrys Hunting Ground, one may enjoy a panorama of ice and rock such as is seen in only few places on this continent.
East of the South Tahoma Glacier, heading against a great cleaver that descends from Peak Success, lies a triangular ice field, or interglacier, named Pyramid Glacier. It covers a fairly smooth, gently sloping platform underlain by a heavy lava bed, and breaking off at its lower edge in precipitous, columnar cliffs. Into this platform a profound but narrow box canyon has been incised by an ice stream descending from the summit névés east of Peak Success. This is the Kautz Glacier, an ice stream peculiar for its exceeding slenderness. On the map it presents almost a worm-like appearance, heightened perhaps by its strongly sinuous course. In spite of its meager width, which averages about 1,000 feet, the ice stream attains a length of almost 4 miles and descends to an altitude of 4,800 feet. This no doubt is to be attributed in large measure to the protecting influence of the box canyon.
It receives one tributary of importance, the Success Glacier, which heads in a cirque against the flanks of Peak Success. This ice stream supplies probably one-third of the total bulk of the Kautz Glacier, as one may infer from the position of the medial moraine that develops at the point of confluence. In the lower course of the glacier this medial moraine grows in width and height until it assumes the proportions of a massive ridge, occupying about one-third of the breadth of the ice stream's surface.
A singularly fascinating spectacle is that which the moraine-covered lower end of the glacier presents from the heights of Van Trump Park. A full 1,000 feet down one looks upon the ice stream as it curves around a sharp bend in its canyon.
A short distance below the glacier's terminus, the canyon contracts abruptly to a gorge only 300 feet in width. So resistant is the columnar basalt in this locality that the ice has been unable to hew out a wider passage. Not its entire volume, however, was squeezed through the narrow portal; there is abundant evidence showing that in glacial times when the ice stream was more voluminous it overrode the rock buttresses on the west side of the gorge.
The name of P. B. Van Trump, the hardy pioneer climber of Mount Rainier, has been attached to the interglacier situated between the Kautz and the Nisqually Glaciers. This ice body lies on the uneven surface of an extensive wedge that tapers upward to a sharp point—one of the remnants of the old crater rim. A number of small ice fields are distributed on this wedge, each ensconced in a hollow inclosed more or less completely by low ridges. By gradually deploying each of these ice bodies has enlarged its site, and thus the dividing ridges have been converted into slender rock walls or cleavers. In many places they have even been completely consumed and the ice fields coalesce. The Van Trump Glacier is the most extensive of these composite ice fields. The rapid melting which it has suffered in the last decades, however, has gone far toward dismembering it; already several small ice strips are threatening to become separated from the main body.
In glacial times the Van Trump Glacier sent forth at least six lobes, most of which converged farther down in the narrow valleys traversing the attractive alpine region now known as Van Trump Park. This upland park owes its scenic charm largely to its manifold glacial features and is diversified by cirques, canyons, lakelets, moraines, and waterfalls.
In the foregoing descriptions the endeavor has been to make clear how widely the glaciers of Mount Rainier differ in character, in situation, and in size. They are not to be conceived as mere ice tongues radiating down the slopes of the volcano from an ice cap on its crown. There is no ice cap, properly speaking, and there has perhaps never been one at any time in the mountain's history, not even during the glacial epochs.
Several of the main ice streams head in the névés gathering about the summit craters, but a larger number originate in profound amphitheaters carved in the mountain's flanks, at levels fully 4,000 feet below the summit. In the general distribution of the glaciers the low temperatures prevailing at high altitudes have, of course, been a controlling factor; nevertheless in many instances their influence has been outbalanced by topographic features favoring local snow accumulation and by the heavy snowfalls occurring on the lower slopes.
XV. THE ROCKS OF MOUNT RAINIER
By GEORGE OTIS SMITH
Director George Otis Smith of the United States Geological Survey was born at Hodgdon, Maine, on February 22, 1871. He graduated from Colby College in 1893 and obtained his Doctor of Philosophy degree from Johns Hopkins University in 1896. He had begun his geological work in 1893 and from 1896 to 1907 he was assistant geologist and geologist of the United States Geological Survey. Since 1907 he has been director of that important branch of the Government work.
He had been studying the rocks of Mount Rainier before he joined Professor Russell in the explorations of 1896. The record of those studies was published at the same time as Professor Russell's report in the Eighteenth Annual Report of the United States Geological Survey for 1896-1897. With his permission the record is here reproduced in full. So far as is known to the present editor it is the most complete study yet published on the rocks of Mount Rainier.
The earliest geological observations on the structure of Mount Rainier were made in 1870 by S. F. Emmons, of the Geological Exploration of the Fortieth Parallel. The rock specimens collected at this time were studied later by Messrs. Hague and Iddings, of the United States Geological Survey. [27] This petrographical study showed that "Mount Rainier is formed almost wholly of hypersthene andesite, with different conditions of groundmass and accompanied by hornblende and olivine in places." The only other petrographical study of these volcanics is that of Mr. K. Oebbeke, of Munich, [28] upon a small collection made on Mount Rainier by Professor Zittel in 1883.
On the reconnaissance trips on the northern and eastern slopes of Mount Rainier, during the seasons of 1895 and 1896, the writer had opportunity to make some general observations on the rocks of this mountain, and the petrographical material then collected has since been studied. The observations and collections were of necessity limited, both by the reconnaissance character of the examination and by the mantle of snow and ice which covers so large a part of this volcanic cone.
Two classes of rock are to be discussed as occurring on Mount Rainier: the lavas and pyroclastics which compose the volcanic cone and the granitic rocks forming the platform upon which the volcano was built up.
Volcanic Rocks
GEOLOGIC RELATIONS
On Crater Peak a dark line of rock appears above the snow, and here the outer slope of the crater rim is found to be covered with blocks of lava. A black, loose-textured andesite is most abundant, and from its occurrence on the edge of this well-defined crater may be regarded as representing the later eruptions of Rainier. Lower down on the slopes of the mountain opportunities for the study of the structure of the volcanic cone are found in the bold rock masses that mark the apexes of the interglacial areas. Examples of these are Little Tahoma, Gibraltar, Cathedral Rock, the Wedge, and the Guardian Rocks. These remnants of the old surface of the cone, together with the cliffs that bound the lower courses of the glaciers, exhibit the structural relations very well.
Even when viewed from a distance these cliffs and peaks are seen to be composed of bedded material. Projecting ledges interrupt the talus slopes and express differences of hardness in the several beds, while variations in color also indicate separate lava flows and agglomeratic deposits. Gibraltar is thus seen to be composed of interbedded lavas and pyroclastics, and on the Wedge a similar alternation is several times repeated, a pink agglomerate being exceptionally striking in appearance.
These lava flows and beds of volcanic ejectamenta thus exposed dip away from the summit at a low angle. The steepest dip observed was in the amphitheater at the head of Carbon Glacier, where in the dividing spur the dip to the northeast is about 30°. Some exceptions in the inclination of the beds were noted on the southeastern slope, where in a few cases the layers are horizontal, or even dip toward the central axis of the cone. In general, however, the volcanics composing Mount Rainier may be said to dip away from the summit at an angle somewhat lower than that of the slopes of the present cone. In the outlying ridges to the north, the Mother Range, Crescent Mountain, and the Sluiskin Mountains, the structure seems to be that of interbedded volcanics approximately horizontal. The extent of the volcanics from the center of eruption has not been determined. Similar lava extends to the south, beyond the Tattoosh Range, and volcanics of similar composition occur to the north, in the Tacoma quadrangle. The latter lavas and tuffs may have originated from smaller and less important cones, now destroyed by erosion.
A radial dike was observed at only one locality, near the base of Little Tahoma. In several cases the lava masses, as seen in cross section, are lens-shaped, and where associated with fragmental beds have unconformable relations. This shows that some of the lava flows took the form of streams, relatively narrow, rather than of broad sheets. Such a feature is in accord with the distribution of rock types. Thus along Ptarmigan Ridge for considerable vertical and horizontal range the rock shows only slight variation. The distribution of rock types will be more fully discussed in a later paragraph.
Of how large a part of the lava flows the crater still remaining was the point of origin is a question to be answered only after more detailed observation has been made. The best section for the study of the succession of flows and ejectamenta is the amphitheater at the head of the Carbon Glacier. The 4,000 feet of rock in this bold wall would afford an excellent opportunity for this were it not that frequent avalanches preclude the possibility of geologic study except at long range.
MEGASCOPIC CHARACTERS
The volcanic rocks of Rainier are of varying color and texture. Dense black rocks with abundant phenocrysts of glassy feldspars, rough and coarse lavas of different tints of pink, red, and purple, and compact light-gray rocks are some of the types represented upon the slopes of this volcanic cone. In color, the majority of the rocks may be grouped together as light gray to dark gray. The black and red lavas are less common. In texture, the Rainier lavas are, for the most part, compact. Slaggy and scoriaceous phases are common, but probably represent only a small part of the different flows. Near the Guardian Rocks large masses of ropy lava are found which suggest ejected bombs. Agglomeratic and tuffaceous rocks are of quite common occurrence, although less important than the lavas. Vesicular lavas occur at several localities, and fragments of a light-olive pumice, many as large as a foot in diameter, wholly cover some of the long, gentle slopes southeast of Little Tahoma and in Moraine Park.
Contraction parting or jointing is often observed, being especially characteristic of the basaltic types. The platy parting is the more common, but the columnar or prismatic parting is well exhibited at several localities. The black basaltic lava east of Cowlitz Glacier shows the latter structure in a striking manner. The blocks resemble pigs of iron in size and shape, and where exposed in a vertical cliff these seem to be piled in various positions.
The rocks on the higher slopes of Mount Rainier are in general very fresh in appearance. An exception may be noted in the case of the rocks at the base of Little Tahoma, where some alteration is evident. The bright coloring of the surfaces of the lava blocks and the general appearance of the face of the cliff may indicate fumarole action at this point. There is also some decomposition along the inner edge of the crater rim, near the steam vents. On the lower slopes, some distance below the snow line, the freshness of the rock is not a noticeable feature, and it is seen that here weathering is of the nature of chemical decomposition as well as of mechanical disintegration.
MICROSCOPIC CHARACTERS
Microscopically these lavas show more uniformity than is apparent megascopically. Rocks which in color and texture appear quite diverse are found to be mineralogical equivalents. The majority of these rocks are andesites, the hypersthene-andesites predominating, as was shown by Hague and Iddings; but over large areas the andesites are decidedly basaltic, and, indeed, many of the lavas are basalts. The megascopic differences are mostly referable to groundmass characters, the color of the rock being dependent upon the color and proportion of glassy base present. Therefore the degree of crystallization of groundmass constituents is of more importance in determining the megascopic appearance than is the mineralogical composition, and the basaltic lavas are for the most part light gray in color, while the more acid hypersthene-andesites are often black or red.
In petrographic character the lavas range from hypersthene-andesite to basalt. This variation is dependent upon the ferromagnesian silicates, and four rock types are represented—hypersthene-andesite, pyroxene-andesite, augite-andesite, and basalt—any of which may carry small amounts of hornblende. A rigid separation of these rock types, however, is impossible, since insensible gradations connect the most acid with the most basic. In the same flow hypersthene-andesite may occur in one portion, while in close proximity the lava is an augite-andesite.
These lavas have groundmass textures that vary from almost holo-crystalline to glassy. The felted or hyalopilitic texture is the most common, and plagioclase is the principal groundmass constituent. The feldspars are lath-shaped, often with castellated terminations. In the more basic phases anhedrons of augite and of olivine appear, and magnetite grains are usually present. Flowage is often beautifully expressed by the arrangement of the slender laths of feldspar.
Among the phenocrysts feldspar is the most prominent. It has the usual twinning characteristic of plagioclase and belongs to the andesine-labradorite series, extinction angles proving basic andesine and acid labradorite to be the most common. Zonal structure is characteristic, being noticeable even without the use of polarized light. Zonal arrangement of glass inclusions testifies to the vicissitudes of crystallization, and often the core of a feldspar phenocryst is seen to have suffered corrosion by the magma and subsequently to have been repaired with a zone of feldspar more acid in composition.
Of the darker phenocrysts, the pyroxenes are more abundant than the olivine or hornblende. Hypersthene and augite occur alone or together, and are readily distinguished by their different crystallographic habits as well as by their optical properties. The hypersthene is usually more perfectly idiomorphic and occurs in long prisms, with the pinacoidal planes best developed, while the augite is in stout prisms, usually twinned. Both are light colored, and the pleochroism of the hypersthene is sometimes quite faint. According to the relative importance of these two pyroxenes, the lavas belong to different types, hypersthene-andesite, pyroxene-andesite, or augite-andesite.
Olivine occurs in certain of the Rainier lavas, in stout prisms somewhat rounded and often with reddened borders. The usual association with apatite and magnetite crystals is noted. The olivine varies much in relative abundance, so as to be considered now an accessory and now an essential constituent, and in the latter case the rock is a basalt.
Hornblende is not abundant in any of the rocks studied, although typical hornblende-andesite has been described among the specimens collected by Professor Zittel. Where it occurs it is in brown crystals, which have usually suffered magmatic alteration. In one case, where this alteration is less marked, the idiomorphic hornblende is found to inclose a crystal of labradorite, and thus must have been one of the latest phenocrysts to crystallize. It also surrounds olivine in this same rock, [29] which is a hypersthene-andesite, the hornblende and olivine being only accessory.
The different textures of these lavas are doubtless expressive primarily of diversity in the physical conditions of consolidation, but also in part of variations in chemical composition. The variations in mineralogical composition are likewise referable to these two factors, but here the latter is the more important. The hypersthene-augite olivine variation, already referred to, doubtless well expresses the chemical composition of the magma, and deserves to be taken as the chief criterion in the classification of the lavas. As was noted by Hague and Iddings, the hypersthene and olivine play a like rôle, the former occurring when the silica percentage is somewhat higher than in basalt. It is exceptional to find the two in the same specimen, the one being absent whenever the other is present. The following analysis [30] of the typical hypersthene-andesite from Crater Peak shows the lava to be a comparatively acid andesite:
Analysis of Hypersthene-andesite from Crater Peak, Mount Rainier