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.