A TRIP TO MT. SHASTA.
Report of a lecture delivered in the National Museum of Washington, D. C., by Prof. J. S. Diller, of the U. S. Geological Survey.
The Great Basin Country is bounded to the westward by the Cascade Range in Oregon and the Sierra Nevada Mountains in eastern California. The axes of these two mountain ranges make an angle of over 140° with each other, and at their point of intersection in northern California rises Mt. Shasta, one of the most conspicuous and imposing topographical features of the Pacific coast, above which it rises 14,440 feet. Early in the days of western exploration its summit was declared to be inaccessible, but whether this assertion was made to inspire greater respect for the abode of the Indian gods, or to excuse a disinclination to physical exertion, must ever remain a matter of conjecture. Certain it is that the ascent, frequently made within the last few years by ladies is not a remarkable feat of mountaineering. Under the direction of Captain Dutton of the Geological Survey, a detailed exploration of the mountain has been accomplished.
The belt of territory bordering upon the Pacific embraces two parallel mountain chains, the Sierra Nevada and Cascade Range on the east, and the illy-defined Coast Range on the west. Between these lies the valley region of the Willamette and Sacramento rivers, whose headwaters are among that complex group of mountains through which the Klamath River, in a deep cañon, finds its way to the sea.
Of all the volcanic regions of the world, the one to which Mt. Shasta belongs is the largest. It extends from Lassen’s Peak, in California, north through Oregon to Mt. Rainier in Washington Territory, and eastward far into Idaho, covering an area larger than that of France and Great Britain combined. Within this wide expanse are extensive plains, whose broad surfaces indicate that the basaltic lava beneath at the time of its eruption possessed such a high degree of fluidity that it spread out far and wide like the waters of a lake. Upon the western border the more viscous lavas built up the Cascade Range, whose mammoth arch is surmounted by numerous mighty volcanoes, among which Mt. Shasta is one of the most prominent.
Seen from all sides Mt. Shasta presents a remarkably regular outline, and its beautiful conoidal form has excited the admiration of many observers. Its slopes are exceptional for the high angle and graceful curves of their inclination. The upper 3,000 feet of the mountain, where cliffs are most abundant, dips away toward all points of the compass at an average angle of 37°. Further down the mountain the slope gradually decreases in inclination to 20°, then to 15°, 10°, and finally the long, gentle slope about the base of the mountain deviates but 5° from a horizontal plane. In all directions from the summit of Mt. Shasta its flanks increase in length as they decrease in angle of inclination, presenting a curved mountain side concave upwards, and has the greatest curvature near the top. Mr. Gilbert, in his excellent monograph of the Henry Mountains, shows that such a curve is the natural result of erosion. In the case of some volcanic mountains, however, an important coöperative cause may be found in the fact that at each successive eruption the lava decreased in quantity and became more viscous. The grandest approach to Mt. Shasta is from the north, in the broad valley of the same name, where it is presented to full view, and the deepest impression of its colossal dimensions is experienced. It stands at the head of Shasta valley, above which it rises 11,000 feet, with a volume of over 224 cubic miles, and presents, in strange contrast with the sterility of the valley, the luxuriant vegetation of the forest belt. The timbered slopes lie between the altitudes 4,000 and 7,000 feet above the sea, and belong to the most magnificent forest regions of the world. Above the forest belt the mountain rises more than a mile into the heights of eternal snow, and its brilliant white slopes present an imposing contrast to the deep green of the pines beneath. Viewed from the southeast, Mt. Shasta appears to be surmounted by a single peak, but seen from the north, the upper portion is found to be double. The smaller of the two cones, broad topped and crater shaped, has been designated Shastina, to distinguish it from the other acute cone, which rises 2,000 feet higher and forms the summit of Shasta proper.
The influence of temperature upon precipitation, and the limits which it throws about arboreal vegetation, are here most forcibly illustrated. In Shasta valley, at an elevation of about 3,000 feet above the sea, where the average temperature is high as compared with that upon the mountain itself, the precipitation is always in the form of rain, but not sufficient in quantity, especially on account of its unequal distribution throughout the year, to support more than a scanty growth of stunted trees. In the autumn storm clouds gather about the summit, and showers become frequent, spreading over the land in copious rains. Before the spring eight ninths of all the annual rain has fallen and the country is brilliant with living green. As summer advances the refreshing showers disappear and the cloudless sky affords no protection from the burning sun; the bright green fades away and the earth gradually assumes that uninviting seared aspect which pervades all nature in the season of drought. Upon the lower slopes of the mountain, by its cooling influence upon the atmosphere, the rainfall is greatly increased, and the vegetation is luxuriant. The vegetation is almost wholly coniferous. Among nearly a score of species the sugar-pine is monarch, frequently attaining a diameter of twelve and a height of over two hundred feet. Farther up the mountain these gradually give way to the firs, whose tall, graceful forms are in perfect keeping with the majestic mountain behind them. Their black and yellow spotted trunks and branches, draped in long pendant moss, present a weird, almost dismal aspect, making a fit promenade for the mythical deities supposed by the aborigines to inhabit the mountains. To assume that in the timber belt the slopes of the mountain are everywhere covered with majestic trees, would certainly be wide of the truth, for within the forests are large treeless tracts, sometimes hundreds of acres in extent. From a distance these green, velvety acres appear to be very inviting pastures, and present the most desirable path of ascent. A closer examination, however, discovers to the observer that instead of grass these green fields are clothed in such a dense shrubbery of manzanita, ceanothus, and other bushy plants, as to be almost impassable. One attempt to cross a patch of chaparral, or “Devil’s acre,” as it is sometimes appropriately called in western vernacular, will convince the traveler that his best path lies in the forest.
As the timber gradually dwindles away from the foot of the mountain to almost nothing in Shasta valley, so also it diminishes in stature, from an altitude of 7,000 feet upwards to the snow region, where the precipitation is generally, if not always, in a solid form of snow in winter and sleet in summer.
Of the tree-like vegetation, one of the pines reaches farthest up the slopes. Its stem grows shorter and the top flattens until, at an elevation of about 9,000 feet, the branches are spread upon the ground, so that not unfrequently the pedestrian finds his best path upon the tree-tops. Beyond these, on the snowless slopes, are found only scattered blades of grass, and the welcome little hulsea, the edelweiss of our Alpine regions, with its bright flowers to alleviate the arctic desolation of the place. The red and yellow lichens cling to the rocks and the tiny prolococcus flourishes in the snow, so that one is frequently surprised, upon looking back, to see his bloody footsteps.
In the Alps, between the forests and the snow, are often found extensive pastures where the herds which furnish milk for the celebrated Swiss cheese are grazed during the milder seasons of the year. In northern California similar pastures do not occur about the snow-capped summits, probably on account of the unequal distribution of the annual rainfall.
To those who are fond of novelty, the greatest interest of the upper portion of Mt. Shasta attaches to its glaciers. They are five in number, and all are found side by side upon its northern half, forming an almost continuous covering above 10,000 feet for that portion of the mountain point. Upon the northern and western slope of the mountain is the Whitney glacier, with its prominent terminal moraines. Next to the eastward is the Bulam glacier, with the large pile of debris at the lower end. Then comes the broad Hottums glacier and the Wintum. The Konwakitong, which is the smallest of the group, lies upon the southeast side of the mountain. Whitney glacier is more like those of the Alps than any other one of the group. Its snow-field lies upon the northwestern slope of the mountains, from whence the icy mass moves down a shallow depression between Shasta and Shastina. Mr. Ricksecker, who has made a careful topographical survey of the mountain, has measured the dimensions of all its glaciers. The limits of the Whitney glacier are well defined; its width varies from 1,000 to 2,000 feet, with a length of about two and one-fifth miles, reaching from the summit of the mountain down to an altitude of 9,500 feet above the sea. It is but little more than a decade since the first glaciers were discovered within the United States, and we should not be disappointed to learn that the largest of them, about the culminating point of the Cascade Range, would appear Liliputian beside the great glacier of the Bernese Oberland, and yet the former are as truly glaciers as the latter. In the upper portion of its course, passing over prominent irregularities in its bed, the Whitney glacier becomes deeply fractured, producing the extremely jagged surface, corresponding to the surfaces of the Alpine glaciers. Lower down the crevasses develop, and these, with the great fissure which separates it from the steep slopes of Shastina, attest the motion of the icy mass. They frequently open and become yawning chasms, reaching 100 feet into the clear, green ice beneath. Near its middle, upon the eastern margin, the Whitney glacier receives large contributions of sand, gravel and bowlders, from the vertical cliffs around which it turns to move in a more northerly direction. In this way a prominent lateral moraine is developed. From the very steep slopes of Shastina, upon the western side, the glacier receives additions in the form of avalanches. Here the snow clings to its rocky bed until the strain resulting from accumulation is great enough to break it from its moorings and precipitate it upon the glacier below. The most striking feature of the Whitney glacier, and that which is of greatest interest from a geological point of view, is its terminal moraine, which appears to be fully a mile in length. Its apparent length is much greater than the real, from the fact that the glacial ice extends far down beneath the covering of detritus. It is so huge a pile of light colored debris, just above the timber line, that it is plainly visible from afar off.
In comparing the morainal material about Mt. Shasta with that of Alpine glaciers, a feature that is particularly noticeable is the smallness of the bowlders. Upon Alpine glaciers they frequently have a diameter greater than ten feet, but about the Whitney and other glaciers of Mt. Shasta they are rarely as much as three feet in diameter. This is readily explained by the fact that the glaciers of Mt. Shasta do not move in deep valleys bounded by long, deep slopes, with many high cliffs which afford an opportunity for the formation of large bowlders. Although the Whitney glacier has its boundaries more clearly defined than any of the other glaciers about Mt. Shasta by the depression in which it moves, the valley is very shallow, and one looks in vain along its slopes for traces of polished rocks like those so magnificently displayed on the way from Meiningen to Grimsel, in the valley of the Aar. Below the terminal moraine the milky water of Whitney creek wends its way down the northern slope, plunges over a fall hundreds of feet high, into a deep cañon, and near the base of the mountain is swallowed up by the thirsty air and earth. The presence of marginal crevasses, lateral and terminal moraines, and the characteristic milky stream which issues from the lower end, are proofs that the Whitney glacier still moves, but the rate of motion has not yet been determined. The row of stakes planted last July were covered with snow before the party could reach them again in the latter part of October.
Upon the northwestern slope of the mountain, besides the Whitney glacier, there is the Bulam, differing chiefly in that it is contained in a broader, less definite valley, and forming an intermediate step toward the Hottum glacier, which is one of the most important and remarkable of the group. Unlike ordinary glaciers, it has no valley in which it is confined, but lies upon the convex surface of the mountain. Its upper surface, instead of being concave anywhere, is convex throughout from side to side, and its width (123 miles) is almost as great as its length (162 miles). At several places the surface of the glacier is made very rough by the inequalities of its bed. This is especially true of its southern portion, where prominent cliffs form the only medial moraine discovered upon Mt. Shasta. Throughout the greater part of its expanse the glacier is deeply crevassed, exposing the green ice occasionally to the depth of a hundred feet. The thickness of this glacier has been greatly overestimated. In reality, instead of being 1,800 to 2,500 feet thick, it does not appear where greatest to be more than a few hundred, for at a number of places it is so thin that its bed is exposed. Its terminal moraine is a huge pile, nearly half a mile in width, measured in the direction of glacial motion.
Next south of the Hottum glacier is the Wintum, which attains a length of over two miles, and ends with an abrupt front of ice in a cañon. Upon the southeastern slope of Mt. Shasta, at the head of a large cañon, is the Konwakitong glacier. Notwithstanding its diminutive size, its crevasses and the muddy stream it initiates indicate clearly that the ice mass continues to move. The amount of moraine material upon its borders is small, and yet, of all the glaciers about Mt. Shasta, it is the only one which has left a prominent record of important changes. The country adjacent to the west side of the Konwakitong cañon has been distinctly glaciated so as to leave no doubt that the Konwakitong glacier was once very much larger than it is at the present time. The rocks on which it moved have been deeply striated, and so abraded as to produce the smooth, rounded surfaces so common in glaciated regions. At the time of its greatest extension the glacier was 5.8 miles in length and occupied an area of at least seven square miles, being over twenty times its present size. Its limit is marked at several places by a prominent terminal moraine. The thickness of the glacier where greatest was not more than 200 feet, for several hills within the glaciated area were not covered. The striated surfaces and moraines do not extend up the slopes of those hills more than 200 feet above their bases. The thinness of the glacier is completely in harmony with the limited extent of its erosion, although the rocks are distinctly planed off, so that the low knobs and edges have regularly curved outlines. It is evident that a great thickness of rock has been removed by the ice, and that the period of ice erosion has been comparatively brief. During the lapse of time, however, there have been important climatic oscillations, embracing epochs of glacial advance and recession. None of the glaciers about Mt. Shasta, excepting the Wintum, terminate in cañons, but all of them give rise to muddy streams which flow in cañons to the mountain’s base. The cañons are purely the product of aqueous erosion, and contain numerous waterfalls, whence the streams in descending leap over the ends of old lava flows 50 to 300 feet in height.
In strong contrast with the arctic condition of Mt. Shasta to-day, are the circumstances attending its upbuilding, when it was an active volcano belching forth streams of fiery lava that flowed down the slopes now occupied by ice. It is the battlefield of the elements within the earth against those above it. In its early days the forces beneath were victorious, and built up the mountains in the face of wind and weather, but gradually the volcanic energy died away and the low temperature called into play those destructive agents which are now reversing the process and gradually reducing the mountain toward a general level. A microscopical examination of the rocks of Mt. Shasta reveals the fact that it is composed chiefly, if not wholly, of three kinds of lava. Several small areas of metamorphic rocks occur within its borders, but there is no evidence to show that they form any considerable portion of the mountain.
The range in mineralogical composition of the lavas is not extensive. There are only four minerals which deserved to be ranked as essential and characteristic constituents: they are plagioclase, feldspar, pyroxene, generally in the form of hypersthene hornblende, and olivine. The kind of lava which has by far the widest distribution upon the slopes of Mt. Shasta is composed essentially of plagioclase, feldspar and hypersthene, with some angite, and belongs to the variety of volcanic rocks which, on account of composition, and the place where first discovered, has been designated hypersthene andesite. Lava of this type has been shown by Messrs. Cross and Giddings of the Geological Survey to be widely distributed beyond the Mississippi. Upon the western slope of the mountain, especially in the vicinity of the prominent volcanic cone, the form of which suggests its name sugar loaf, the lava contains prominent crystals of hornblende instead of so much hypersthene and angite, and closely resembles the celebrated hornblende andesite lava from among the extinct volcanoes of central France. The third variety of lava which enters into the structure of Mt. Shasta is familiar to every one as basalt. It occurs in relatively small quantities, and has been extruded low down upon the slopes of the mountain. From the fact that there are three kinds of lava in the structure of Mt. Shasta, it must not be concluded that they all issued from the same volcanic vent, nor that they were effused from three separate and distinct openings. In reality, contributions to the upbuilding of Mt. Shasta have been made by over twenty volcanic orifices, of which two have been principal and far more prolific than all the parasitic events combined. This enumeration does not include those large fissures in the side of the cone, which are evidently attributable to the hydrostatic pressure of the molten mass within. The small number of parasitic cones on the slopes of Mt. Shasta is somewhat remarkable, especially when we compare it with the largest volcano in Europe. Although it is much higher than Etna, its base is less expansive, and its size about half that of the mighty monarch of the Mediterranean. Upon the irregular slopes of Etna there are 200 prominent subsidiary cones, beside over 400 of smaller size. On the contrary, Mt. Shasta has but a score of such accessories, and the remarkable regularity of its acute form forcibly expresses the highly concentrated type of volcanic energy which it represents.
From none of the vents upon its slopes have all three kinds of lava escaped, but from the summits of Shasta and Shastina, which are the products of the two largest and most prolific vents, both hornblende and hypersthene andesite have been effused. All the other orifices were subordinate, and each furnished but one kind of lava; from seven of them came hypersthene andesite; eight, hornblende andesite; and the remaining five, basalt. The relative age of the cones which mark the position of the volcanic vents is indicated by the amount of degradation which each has suffered. Judged by this criterion, those of hornblende andesite are the oldest and those of basalt the youngest. The latter are for the most part made of lapilli, and are not crater-shaped as is usually the case in other portions of the Cascade Range, but are elliptical in form, with dome-shaped summits. The presence of considerable piles of ejectments about the subsidiary vents indicates that the eruptions from these orifices were often of a violent character. On the other hand there are some without a trace of lapilli, or anything else to indicate an interruption in the quiet flow of lava welling out of the depths.
Upon the eastern slope of the mountain the cañon, excavated by Mud creek, brings to light the oldest Shasta lavas now exposed, and they are seen under such circumstances that their succession can be readily understood. The oldest lava known is hornblende andesite, which is now in an advanced state of disintegration, and it seems probable that in the early stages of its development a large proportion of the lavas ejected from Mt. Shasta were of the same mineralogical constitution. These were succeeded by extensive effusions of hypersthene andesite. Later in its history, several small streams of hornblende andesite again burst forth from the northeastern side of the cone, but the final effort of the volcanic energy was spent in the ejection of hypersthene andesite. The conditions which determine the oscillation in mineralogical composition of the lavas are as yet conjectural, but when discovered, and their influence demonstrated, an important step forward will have been made in determining the relations of many volcanic rocks.
A striking feature in the structure of Mt. Shasta is the paucity of volcanic ashes, lapilli, and other ejected matter. Only one important deposit of the kind has been discovered. It clings about the summit of the mountain, and is evidently the product of its last eruption. The summit of Shastina is so regular in outline, and the shape of its crater so well preserved, that many have supposed it to be composed chiefly of scoria and ashes; but this is not the case, for its slopes are of angular fragments of compact lava.
Mt. Shasta is almost a pure lava cone, and its remarkably regular form is a matter of wonder. That it is so regular is a sequence of several favorable circumstances. Although a score of parasitic cones spring from the side of the mountain, and have contributed to its upbuilding, yet their additions have been so small compared with the vast effusions from the summit craters Shasta and Shastina, as not to greatly modify the outline of the mountain. More important circumstances are to be found in the non-explosive character of the eruptions and the successive changes in the physical properties of the erupted lava, as the development of the mountain progressed.
It is well known that among the volcanoes of the Hawaiian Islands the eruptions are quiet and effusive. The fiery streams of liquid lava course down the gentle slopes for many miles.
Although the mountain is 14,000 feet high, its lavas have such a high degree of liquidity, and retain their mobility so long after eruption, that the base of the mountain spread by them has a diameter of about seventy miles, and an average slope of 5° 1,800 feet below its summit. Mauna Loa is nearly twenty miles in diameter. On the contrary, at a corresponding position its greatest diameter is less than two miles, a very remarkable difference, which is due chiefly to the unequal fluency of the two lavas. The very oldest lavas of Mt. Shasta lie buried within its mass, and we know nothing of their physical properties, but from an examination of the oldest ones now visible, it is evident that at the time of their eruption they possessed a higher degree of fluidity, and were more voluminous than those of later date. The long, gentle slopes about the base of the mountain are formed by comparatively old lavas. Ascending the mountain, one goes up as if upon a giant staircase, with long, inclined steps rising abruptly over the ends of successive shorter and newer lava flows.
It is evident in comparing the older and newer lava flows of Mt. Shasta that there has been a more or less regular decrease in the quantity of lava extruded during successive eruptions, and this is exactly what we should expect when we consider that as the pipe is lengthened by successive effusions, the hydrostatic pressure of the columns of lava within is gradually augmented. The increased compress of the lava flows toward the summit of the mountain indicates that the lava of successive extrusions became more and more viscous until at last the eruptions became explosive, and gave rise to the ejectments now clinging upon the upper slopes of the mountain to evidence the character of the final outburst.
It is not only possible, but very probable that the increased viscosity of lava toward the closing scenes of the volcano is correllated to the diminution of temperature. Since the beginning of the historic period there have been no eruptions from Mt. Shasta, but the freshness of its lavas indicate that not many centuries ago, with other volcanoes of the Cascade Range, it was in a state of vigorous activity, and groups of hot springs and fumeroles about the summit still attest the presence of smouldering volcanic energy, which may perhaps some day break through its confining walls.
The upbuilding of Mt. Shasta is but a matter of yesterday, as compared with the lapse of ages, since the birth of some of its neighbors. The complex group of mountains to the westward, embracing the Scott, Trinity, Salmon and Siskiyou, are composed in large part, at least, of ancient crystalline rocks of both aqueous and igneous origin; through these the rivers have cut deep cañons, the Klamath, on its way to the Sacramento southward, from the very base of Mt. Shasta to its broad valley stretching from the Sierra Nevada to the Coast Range. The cañon of the Sacramento was cut down to nearly its present level, and the mountains sculptured into existing forms long before the eruptions of Mt. Shasta had ceased, for a fiery deluge escaping from the southern slope of Mt. Shasta entered the Sacramento cañon, and as a lava stream 200 feet deep followed its course for over fifty miles.
Towering more than a mile above its neighbors, perhaps the youngest of the group, Mt. Shasta is the end of a long series of volcanoes in the Cascade Range, stretching northwest to Mt. Tacoma. This range, composed chiefly of volcanic material, is cut across by the cañons of the Columbia and the Klamath rivers, in the former of which, beneath a thickness of 3,500 feet of lava, are found strata containing Tertiary fossils. At the southern base of Mt. Shasta, in the cañon of the McLoud River, similar beds of volcanic debris are found, but without fossils, nevertheless it is evident that the main mass of the Cascade Range and its volcanoes originated in recent geologic times, and from the fact that solfataras, fumeroles, and hot springs are still abundant upon their slopes, they can not be reckoned among those which are wholly extinct.
A frontiersman in Washington Territory tells of an outburst of Mt. St. Helens in the winter of 1841-2.
Upon somewhat more trustworthy authority it is said that to the southward of Mt. Shasta, about forty miles, a small cone which may be considered parasitic to Lassens Peak, has been in eruption as late as January, 1850, ejecting considerable ashes and cinders, and pouring forth a mass of lava, which gradually spread, attaining a circumference of over four miles, and presenting an abrupt embankment-like termination upon all sides eighty to ninety feet in height. Trees, blackened by the fiery stream, are still standing to furnish incontestable evidence of its recency.
The country is full of rumors of subterranean rumblings, and the people are prone to attribute them to the dying throes of volcanic energy.
One of the most striking features of the region is the strongly contrasted types of volcanic action in Mt. Shasta. Both have approximately the same area. In the valley there have been many scores of volcanic vents, among which the energy has been so widely diffused that none of them have furnished lava sufficient to form a hill more than a few hundred feet in height.
On the contrary, the mountain represents a small number of vents, and the volcanic was nearly all concentrated in one place, so that the extrusions were all piled up, one upon another, and resulted in the upbuilding of one majestic elevation.
Thus it has been from a small beginning, probably in early Tertiary times, that by successive boilings over, so to speak, additions have been made to the mountain until it attained a height beyond its present altitude. The constructive agents reached their limit, dissipated their energy, and gave way to destructive ones, which are gradually undoing the work.
Mt. Shasta must ever be one of the most popular mountains among tourists of the West. It is easily accessible from a main line of travel which passes by its base, at Berryvale, where comfortable quarters and necessary outfit for the ascent can be obtained.
The streams are filled with trout, and the forest with game, so that the region affords many attractions for the sportsman.
Several hours’ travel by a good trail brings the party to Camp Ross, at the timber line, from which the ascent can easily be made in a day without danger.