Copyright
Israel C. (Israel Cook) Russell.

Glaciers of North America; a reading lesson for students of geography and geology online

. (page 5 of 24)
Online LibraryIsrael C. (Israel Cook) RussellGlaciers of North America; a reading lesson for students of geography and geology → online text (page 5 of 24)
Font size
QR-code for this ebook


effect of this change, and probably also of accompanying variations
in climatic conditions, is seen in the glaciers, which become smaller and
more widely separated and are confined to higher and higher regions
when traced westward to the Alaska peninsula and the Aleutian islands.

As one follows the great Cordilleran glacial belt northward from its
first appearance in the High Sierra, the lower limit of perennial snow, or the
"snow line," at first about 12,000 feet above the sea, descends lower and
lower, until finally in the vicinity of Mount St. Elias it has an elevation
of only 2000 or 2500 feet. Farther west, along the curve made by the
mountains about the northern shore of the Pacific, the snow line again
rises, and on the Aleutian islands has an elevation of perhaps 8000 or
10,000 feet. The glacial ice everywhere extends below the limit of peren-
nial, neVe snow, but is most thoroughly exposed in late summer or early
autumn, when the true position of the snow line is sharply defined. In
the High Sierra, the extension of glacial ice below the neves is but slight,
and during seasons of unusual snowfall, or when the summers are excep-
tionally cool, may not be recognizable. Proceeding northward, the ice
extension is more and more pronounced, until the region of maximum
glaciation is reached. Thence westward the length of the tongues of ice
below the snow fields decreases.

In the High Sierra, as already stated, the glaciers do not descend
below about 12,000 feet ; farther north they reach lower and lower limits,
until in the vicinity of Stikine river, in about latitude 57, they gain the
sea level. Thence northward and westward to beyond Mount St. Elias, a
distance along the coast of .between 700 and 800 miles, there are
hundreds and probably thousands of glaciers that descend practically to
sea level, arid scores that enter the sea and, breaking off, form bergs.
Beyond the Mount St. Elias region their lower limit gradually rises.

At the southern end of the crescent-shaped belt of glaciers under
consideration, the ice bodies are small and detached, and are separated
from each other by intervening ridges and mountain peaks. Proceeding
northward, they increase in area and in frequency, and unite one with
another in the neve region. The snow belt broadens and finally becomes
a confluent sheet 80 or 100 miles broad in southern Alaska, and narrows



DISTRIBUTION OF THE GLACIERS OF NORTH AMERICA. 35

again westward and is there broken into individual neves of limited
extent similar to those of the High Sierra. The most thoroughly snow
and ice-covered portion is in the region between Lynn, canal and Cook's
inlet, Alaska, where not less than 15,000 square miles of mountainous
country is almost completely buried beneath a single vast neve field from
which ice streams of the alpine type flow both north and south through
rugged defiles in the flanks of the mountains. The southward flowing
glaciers are larger, more numerous, and much longer than those that find
their way northward, and, in gaining the low lands adjacent to the ocean,
expand and unite one with another, so as to form broad plateaus of ice,
known as piedmont glaciers.

Could the observer obtain a bird's-eye view of the western portion of
North America, he would find that the Cordilleran glaciers form an irreg-
ular curve, broadest and reaching sea level in the Mount St. Elias region,
and narrowing and becoming more and more elevated at both its southern
and western extremities. The attenuated arms of this shining crescent are
broken, for the reason that only the more elevated mountains near its
extremities reach the horizon at which perennial snow exists. As in the
crescent of light reflected from the surface of the moon, the mountains in
the Cordilleran ice crescent where the belt is broadest are white to their
bases, while only the peaks of the most lofty elevations at the extremities
of the broken circle are brilliant. The length of this crescent of snow
and ice is about 3000 miles. Its form is less regular, however, than the
comparison made above might lead one to suppose, as its southern
prolongation is broader and more broken than its central and western
portions.

The study of the glaciers of the Cordilleras has only fairly begun, but
it is hoped that what has already been accomplished will convince the
reader that the subject is not only worthy of consideration, but of fascina-
ting interest, and that the work of exploration should be continued.

Greenland Reg-ion. In the eastern portion of North America gla-
ciers are confined to Greenland, and to the islands adjacent to it on the
west. The vast ice sheet covering nearly all of Greenland is of the contin-
ental type, and, as is well known, is the largest existing ice body in the
northern hemisphere. Its extension northward has not been fully deter-
mined, but as nearly as can be judged it terminates in about latitude
82 . Its area is in the neighborhood of 600,000 square miles. If
transferred bodily to the eastern portion of the United States, it would



36 GLACIEKS OF NOKTH AMERICA.

extend from northern Maine to Georgia, and cover a belt of country 500
miles broad. Vast as this ice sheet is known to be, it takes what may be
said to be second or third rank when contrasted with the continental
glaciers that occupied Canada and a large portion of the United States in
Pleistocene times. The exploration of existing glaciers derives one of its
principal attractions from the fact that such studies assist in interpreting
the records left by ancient glaciers in various parts of the world. This
in turn brings one to the consideration of the still broader problems of the
cause of climatic changes w T hich favored the growth of vast Pleistocene
glaciers in regions now enjoying a temperate climate, and inhabited by
the most civilized people of the earth.

The glaciers on the islands to the west of Greenland are but imper-
fectly known, but from the somewhat meagre reports rendered by Arctic
explorers, few of whom, it is to be regretted, have been trained observers in
this direction, it appears that they are of the alpine type, although larger,
and with broader neve fields in proportion to the extent of true glacial
ice, than is found among the glaciers of Switzerland or other similar
regions. A remarkable feature of the glaciers of the far north is that
they frequently terminate in bold precipices of ice.

Having this general sketch of the distribution of glaciers in North
America in mind, the reader will be enabled to locate in the outline plan
the relations of the various ice bodies described in the following chapters.



CHAPTER III.

GLACIERS OP THE SIERRA NEVADA. 1

THE Sierra Nevada, in many respects the most attractive mountain
system in North America, attains its greatest elevation between latitude
36 and 38 30', or in a more general way, between Owen's lake and Lake
Tahoe, California.

THE HIGH SIERRA.

To the more elevated portion of the Sierra Nevada the name " High
Sierra " has been applied. Although the boundaries of the region thus
designated are indefinite, it is well worthy of especial recognition, as it is
a prominent and important topographic feature. Throughout its entire
extent it bristles with rugged peaks, narrow crests, and inaccessible cliffs,
overshadowing profound chasms, all of which combine to form one of the
most rugged and picturesque mountain ranges in North America. The
culminating point of this elevated region is near its southern limit, where
Mount Whitney rises to an elevation of 14,522 feet above the sea, and is
succeeded northward by Mount King, Mount Humphreys, and many other
elevations scarcely less magnificent. Southward from Mount Whitney the
Sierra declines rapidly, and the system is considered as terminating in that
direction at Tehichipi pass, a little north of latitude 35. Northward of
Mount Whitney, there is a vast sea of rugged peaks and narrow moun-
tain crests, separated by deep valleys, which render the region almost inac-
cessible to beings not equipped with wings. This is the High Sierra
par excellence, as will be admitted by all who attempt to scale its giddy
heights or thread its labyrinth of canons. In the neighborhood of Mono
lake a number of the more prominent peaks, of which Mount Lyell,
Mount Ritter, Mount Dana, and Tower peaks are examples, exceed 13,000
feet in elevation. The range retains its rugged character all the way to
Sonora pass, and even to Lake Tahoe, but northward of that " Gem of
the Sierra " the mountains are less elevated.

1 This account of the glaciers of the Sierra Nevada is taken almost entirely from a paper
by the present writer, on the " Existing Glaciers of the United States," 5th Annual Report
U. S. Geological Survey, 1883-84.



38 GLACIERS OF NORTH AMERICA.

Very large portions of the High Sierra are composed of light-colored
granite, but thinly clothed with vegetation, which imparts a monotonous
gray tone to the rugged scenery. The peaks and crests overlooking Mono
lake, however, have been sculptured from metamorphosed sedimentary
rocks, and are frequently richly tinted. The landscape in this portion
of the range is warm in tone, and presents pleasing and striking contrasts
in comparison with the gray of the western slopes. Rugged and angular
precipices rising to narrow crests, but softened in contour and varied in
color on their lower slopes by lichens and alpine flowers, dark billowy
forests of pine in the valleys, snow-filled amphitheatres, and hundreds of
placid lakelets and rock-rimmed tarns are there grouped in pictures that
are as delicate in detail and as pleasing in tone as they are majestic and
far-reaching.

Besides the splendor of their scenery, the mountains to the south-
ward of Mono lake present the additional attraction of living glaciers.
These, although small, are well worthy the careful attention of every
traveler.

Existing glaciers on Mount Dana and Mount Lyell were visited by
Mr. G. K. Gilbert and myself during the summer of 1883. I also exam-
ined one at the head of Parker creek, a tributary of Mono lake. Others
on Mounts Conness, McClure, and Ritter were explored by Mr. W. D.
Johnson, my associate for several years in western explorations, while
making a topographical survey of the region draining to Mono lake.
Besides the glaciers actually traversed, a number of others were seen
from commanding points, and their general nature almost as thoroughly
determined as if their surfaces had actually been trodden. Our combined
observations show that nine glaciers exist within the southern rim of the
Mono lake drainage basin. A somewhat larger number are sheltered by
the mountains, of which the dominant peaks are McClure, Lyell, and
Ritter. It is in ice caves beneath these glaciers that the Tuolumne,
Merced, and San Joaquin rivers have their birth.

The glaciers of the High Sierra are located between latitudes 36 30'
and 38, and at their lower extremities have an approximate elevation of
11,500 feet above the sea. The lowest seen is on the northern side of
Mount Ritter, and terminates in a lakelet that is about 2000 feet below
the mountain top, or about 11,000 feet above the sea. The glaciers
observed are all small, the most extensive that on the northern slope
of Mount Lyell being less than a mile in length, with a somewhat
greater breadth. Nearly all occur in amphitheatres on the northern side



GLACIERS OF XORTH AMERICA.



PLATE 2.




FIG. A. MOUNT DANA GLACIER, CALIFORNIA.

On the northern side of the summit-peak of Mt. Dana.




FIG. B. MOUNT LYELL GLACIER, CALIFORNIA.

The highest peak is the summit of Mt. Lyell.



GLACIERS OF THE SIERRA NEVADA. 39

of lofty peaks, where they are sheltered from the noonday sun by high
cliffs and mountain ridges; and all flow northward, with the exception of
a few cradled in deep cirques on the eastern side of the Minarets and
Mount Hitter. So far as known, these are the most southern glaciers in
the United States. Snow fields are reported by Mr. Johnson, however,
as existing in the mountains to the south of Mount Ritter, at the head of
some of the many branches of Owen's river. If these should prove to be
veritable glaciers, they will extend the southern limits of the existing
glaciers of this country a few miles farther southward.



MOUNT DANA GLACIER.

On the western shore of Mono lake the mountains rise abruptly from
the water's edge to an elevation of 5000 to 6600 feet, and have been
sculptured by storms and frosts into independent peaks of remarkable
grandeur. As seen from Mono lake, the most conspicuous point along
the serrate mountain crest outlined against the western sky is Mount Dana,
which rises 6600 feet above the lake, and has an elevation of 12,992 feet
above the sea. Although of grand proportions, this peak is but one among
many prominent points crowning the divide between the drainage of Mono
lake and the Pacific. From the southward, Mount Dana presents a
somewhat rounded contour and is easy of ascent, but on the north its
culminating cliffs form a nearly perpendicular precipice more than a
thousand feet high. This northern face descends into a deep, narrow
gorge leading northward, known as Glacier canon. During the glacial
epoch the whole extent of this canon was occupied by ice, and formed a
tributary to a still larger glacier flowing into Mono valley.

At the head of Glacier canon, and surrounded on nearly all sides by
towering precipices, lies the small ice body represented on Fig. A, Plate
2, to which the name Mount Dana glacier has been given. The picture
shows nearly the entire extent of the glacier, and is from a photograph
taken on an abandoned terminal moraine now retaining a lake of opalescent
water, into which the drainage from the ice discharges. In the illustra-
tion the terminal moraine now forming about the border of the ice can be
seen, as well as the crevasses, dirt bands, etc., that mark its surface. The
glacier is about 2000 feet long in the direction of flow, but appears much
foreshortened in the illustration. " Ice tongues " are seen extending up-
ward from the neve. At the base of the largest of these peculiar ice
tributaries a portion of a wide crevasse, or bergschrund, may be recognized.



40 GLACIERS OF NORTH AMERICA.

This miniature glacier exhibits many of the essential features of greater
ice streams, such as neve and glacier proper, crevasses, dirt bands,
moraines, glacier tables, etc., as will be described in connection with simi-
lar features on neighboring ice bodies a few pages in advance.

MOUNT LYELL GLACIER.

In traveling from Mount Dana to Mount Lyell, one finds it most
convenient to pass down Dana creek, which flows southward from
Mount Dana, to its confluence with Tuolumne river, and then ascend
the deep, broad canon of the latter stream. Tuolumne river has its
birth at the extremity of the Mount Lyell glacier. It emerges from a
cavern in the ice as an insignificant, dirt-laden brook. The snowy
summit of Mount Lyell, as seen from the head of Tuolumne canon, is
shown in Plate 3. The majestic mountain, when viewed from this
portion of the valley, is far more beautiful than any illustration in
black and white can suggest. In the soft, gray light of morning, it
has all the solemn grandeur of the Bernese Oberland. At sunset,
when flushed with the rosy light of the afterglow, this shrine of the
High Sierra rivals the splendor of Mount Rosa. To the right of Mount
Lyell rises Mount McClure, which is scarcely less imposing than its
companion ; the former attains the height of 13,420 feet above the sea,
and the latter is but 150 feet less in elevation.

The Tuolumne canon, when followed still nearer its beginning, is found
to lose its gentle grade and become rugged and precipitous. Its bed is
crossed at intervals by irregular cliffs, that must have caused magnifi-
cent ice cascades in the great glacier that once flowed over them. The
top of each steep ascent is usually separated from the base of the next
higher one by a comparatively level tract, sometimes holding a grassy
meadow or small, rock-enclosed tarn. This succession of cliffs and
terraces forms a grand stairway, leading to the opening of the amphi-
theatre on the north side of Mount Lyell, where a magnificent pano-
rama of the entire glacier may be obtained. The view given on Fig.
B, Plate 2, is from near the outlet of the amphitheatre, and exhibits
nearly the whole extent of the neve of the Mount Lyell glacier and
of the small area of compact ice which projects from beneath it. In
the panorama the terminal moraine of dirt and stones, now forming
at the foot of the glacier, may be recognized, and also the rounded
and worn rock masses that rise as islands in the central portion of the



GLACIERS OF THE SIERRA NEVADA. 41

glacier. Crevasses, contorted dirt bands, and moraines on the ice,
although noticeable features when traversing its surface, are but indif-
ferently shown in the illustration.



PARKER CREEK GLACIER.

This glacier is situated at the head of a deep, high-grade canon, down
which Parker creek descends on its way to Mono lake. It is even smaller
than the ice bodies on Mount Dana and Mount Lyell, but is yet a true
glacier with a well-defined neve region, from beneath which descends
a mass of ice that is crossed by dirt bands and crevasses, and has many
minor features that duplicate the details of more extensive ice streams.
About the lower margin of the ice there are comparatively large moraines
forming concentric ridges, and indicating the rapid disintegration of the
surrounding cliffs, since the material of which they are composed was
derived entirely from that source. The mass of debris surrounding
this glacier appears to exceed the volume of the ice of which it is
formed. These moraines are more characteristic examples of the
tumultuous debris piles formed by ice streams than any other deposits
of the same nature now forming in the High Sierra. Like the majority
of the glaciers of this region, the one at the head of Parker creek is shel-
tered by overshadowing walls, and flows northward. During the glacial
epoch, the entire extent of the deep valley through which it flows was
occupied by a glacier that descended upon Mono plain, and built huge
morainal embankments more than a mile in length. These fine examples
of the peculiar parallel embankments built by overloaded glaciers on
emerging from mountain gorges are second in interest, however, to
similar deposits at the mouth of the neighboring gorge, known as
Bloody canon, 1 and illustrated on Plate 4.



CHARACTERISTICS OF THE GLACIERS OF THE HIGH SIERRA.

That the ice bodies observed in the High Sierra, although small, are yet
veritable glaciers, I trust will appear from the following somewhat detailed
statement of observations :

1 The instructive records left by Pleistocene glaciers in the neighborhood of Mono lake
are described and illustrated in " Quaternary History of Mono Valley," in the 8th Annual
Report of the U. S. Geological Survey, 1886-87, pp. 261-394.



42 GLACIERS OF NORTH AMERICA.

Nave's. The distinction between neve and true glacial ice is plainly
manifest on nearly all of the glaciers of the High Sierra. This is apparent
not only when viewing them from a distance, but also while traversing
their surfaces. In the case of the Parker Creek glacier, especially, the
change from the granular snow of the neve to the compact ice of the glacier
proper, can be discerned within the space of a very few feet. The neves,
although usually dust-covered, are invariably white as compared with the
rest of the glacier, and are composed of granular ice-snow. Their surfaces
are almost entirely free from stones and dirt, and are rendered very rough
and uneven by crests and spires of compact snow or neve ice, from two to
five feet high, that result from the unequal melting of the surface. These
" ice blades " have been described by Professor Le Conte, who refers their
origin to the unequal melting of wind-rippled snow.

At their lower limits the neves pass into the glaciers proper, which in
part they overlie, and acquire a ribboned or laminated structure, dirt
bands, etc., characteristic of true glaciers.

Crevasses. Marginal crevasses were observed in numerous instances,
but they occurred in quite limited numbers in any individual glacier. In
some examples, more especially in the neves, they are convex toward the
head of the glacier, while others far down in the same series are straight,
or have changed their curvature so as to be concave up stream. The cre-
vasses are largest at the upper margin of the neves, and frequently corre-
spond to the bergschrund of Swiss mountaineers. They vary from narrow
cracks up to chasms six or eight feet wide, and frequently cross almost
the entire breadth of the neve, thus rendering difficult the passage to
the rocks above. The depth of the crevasses could seldom be deter-
mined, as the irregularities of their sides limited the view, but some were
certainly not less than 100 feet deep. The crevasses were frequently
partially concealed by arches of snow, hung within with vast numbers of
icicles. The walls beneath these treacherous roofs are incrusted with large
masses of well-formed ice crystals, with glittering faces half an inch in
diameter, resembling the most beautiful transparent spar. The light in
these fairy-like grottoes is of the most exquisite blue.

Lamination, or " Ribboned Structure." This structure was seen
in all the glaciers closely examined, but appeared most conspicuously
near the lower extremity of the ice, where the layers are approximately
horizontal. Hand specimens cut from the ice exhibited sections of alter-



GLACIERS OF THE SIERRA NEVADA. 43

nating narrow bands of compact blue ice and porous white ice, as plainly
as could be desired.

Dirt Bands. These were observed on nearly all of the glaciers, and
were frequently marked, and even conspicuous, features of their surfaces.
It required no peculiar condition of light and shade to make them discern-
ible ; on the contrary, they could be plainly distinguished at a distance of
two or three miles. Viewed from a distance, they were seen to sweep
entirely across the glacier in a series of graceful curves, concave toward
the neve. Sometimes this symmetry was interrupted by irregular undu-
lations, or even by contortions, as may be seen in the illustration of the
Mount Lyell glacier. On Parker Creek glacier the dirt bands are about
six inches broad over a considerable area, and occur at quite regular inter-
vals of four to six feet, with comparatively clear ice between. In this
instance, the dirt producing the bands was not confined to the surface,
but could be seen to discolor the ice in well-defined strata, dipping into
the glacier at a low angle with the surface. On all of the glaciers
examined, the dirt bands were observed only below the lower limit of
the neve.

In the study of the glaciers of Switzerland and Norway, particular
attention has been given to the influence of ice cascades in producing
lamination and dirt bands. In the Sierra Nevada glaciers, both of these
characteristics are distinct and well marked, but ice cascades are absent.
It seems evident, therefore, that the hypothesis which is apparently satis-
factory in Europe does not agree so well with the phenomena observed in
California.

In viewing many of the Sierra Nevada glaciers at a distance of a few
miles, and approximately on the same level, it is apparent that their
surfaces frequently have a slope of from 15 to more than 30 degrees, and
are, in fact, sections of the ice bodies in which the internal structure is
exposed. When seen in this manner the appearance of the glaciers is
such as to lead one to suspect that the dirt bands are strata in the ice,
or in reality "annual rings" formed by yearly accumulations of dirt
on the neves. A similar explanation was long since advanced by
Forbes after studying the dirt bands of apparently the same character on
Swiss glaciers. Prof. H. W. Brewer has suggested a modification in
this explanation to the effect that a year of exceptional melting one
of those years in which the neve is reduced to the minimum would
have the effect of combining the dirt accumulated during several years



44



GLACIERS OF NORTH AMERICA.



into a single band, which would represent a climatic cycle rather than
a single year. This explanation agrees best with the facts noted above.

Glacier Tables. Blocks of stone perched on columns of ice, and
usually designated glacier tables, did not form a marked feature on the
ice bodies of the Sierra Nevada in 1883, except in one instance. On



Online LibraryIsrael C. (Israel Cook) RussellGlaciers of North America; a reading lesson for students of geography and geology → online text (page 5 of 24)