Israel C. (Israel Cook) Russell.

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

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ing the ice cliffs where these children of the glaciers are born, we find that
when pinnacles already whitened by exposure to the air fall into the sea,
they float away as white bergs. If we watch them drifting over the still
water and appearing in the distance like a fleet of gleaming sails, we note
that occasionally a white berg suddenly turns over with great commotion
and joins the fleet having blue for their banner. The reason for the
change in color is that previous to turning over the porous exterior of
the submerged portion of the berg was dissolved away so as to expose the
compact ice of the interior. The sudden reversion of position is due to
unequal melting, which changes the center of gravity of the mass. A
cone of ice in which the height is about equal to the diameter of the base,
will float with its apex down. When a berg approaches a conical form,
the position of greatest stability is one in which the side having the
larger mass is uppermost. Bergs do not become top-heavy and turn over,
as is sometimes stated, but become bottom-buoyant and tend to adjust
themselves to the medium in which they float.

Blue bergs are also formed by the breaking away of portions of the
submerged ice foot of tide -water glaciers. These are frequently of large
size, and rise from below the surface of the water well in advance of the
visible end of the glacier. Their emergence is sudden. They bound to
the surface, and rising well above it carry tons of water with them. After
rocking to and fro for several minutes as if to be sure of their freedom after
centuries of imprisonment, they quiet down and float slowly away as shim-
mering islands of the most exquisite blue. The precise manner in which
the bottom ice of a tide-water glacier breaks off is not definitely known.
Reid has made observations in this connection at Muir glacier, and has
been led to think that the upper portion of the submerged ice foot extends



(Photograph by H. F. Reid.)

(Photograph by H. F. Reid.)



beyond and overhangs the lower portion, for the reason that the flow of a
glacier is greater at the top than at the bottom, and also because the melt-
ing of the submerged ice, at least near the surface of the sea, is in excess
of the melting of the portion above water. These considerations have led
to the assumption that a longitudinal section of the extremity of a glacier
terminating in deep water would present the features indicated in the
following diagram :


The broken lines extending down from the surface and curving outward
are thought to represent the direction taken by fractures, which permit
portions of the extremity to break off and leave an overhanging mass near
the summit of the cliff. The submerged portion would then break away,
and owing to its irregular form, might be thrown outward as it rose, so
as to come to the surface some distance from the visible base of the
ice cliff.

The principal objection to this explanation, so far as can be judged
from the observations available, is that the bergs rising from below reach
the surface too far out from the ice cliffs. In some instances observed by
the present writer, they came to the surface not less than a thousand feet
from the visible ice foot. Besides, the observed rapid melting of the
submerged ice pertains to the portion within a few feet of the surface.
Near Muir glacier the surface temperature of the water of Muir inlet, as
observed by Prof. Wright, was 40 F. This would insure rapid melting,
but what the temperature is below the surface no one knows.

Another explanation of the formation of bergs from the submerged
portion of a glacier, is that the falling of avalanches from the visible por-
tion of the ice cliff is greater than the melting of the submerged portion.
A terrace-like projection of the deeply submerged ice foot is then pro-
duced, and portions of the protruding base break away from time to time,
owing to their buoyancy, and rise to the surface. The conditions here
postulated are illustrated in the diagram on the following page.


Reid objects to the hypothesis just stated, and suggests that the height
to which the suddenly emerging bergs rise above the surface of the water
is not so great as should be expected if they came from a depth of several
hundred feet. Until observations or computations have shown that this
objection is valid, however, it can have but little weight. Which of these
two explanations is correct, or what portion of each may be accepted with
confidence, must be determined by future observations. It would not be
difficult, or especially dangerous, to make soundings and temperature ob-
servations in the central part of Muir inlet close to the visible base of the
ice wall, and thus ascertain the slope of the submerged portion of the
glacier, and also to what depth the warm surface temperature extends.

The black, dirt-covered bergs occasionally seen in the vicinity of tide-
water glaciers are fragments of the bottom layer of ice, or perhaps more
frequently portions of the sides of crevasses in which stones and dirt, had


lodged. These bergs, bearing a freight of foreign material, derive their
principal interest from the fact that they carry their loads to localities
more or less remote from their place of origin, and may drop them where
fine water-borne sediments are accumulating.

An Ancient Forest Buried beneath the Ice. When the excursion
steamer to Glacier bay reaches within about a mile of Muir glacier, the
anchor is dropped and passengers are given an opportunity to go ashore.

On landing on either side of the inlet, the first fact that attracts the
attention of the geologist is the presence of a heavy deposit of cross-
stratified sand and gravel below the extremity of the glacier. This gravel
deposit passes beneath the glacier and is plainly of more ancient date
than the advance of the ice o*ver it. In this deposit there are many
trunks and branches of trees ; and on the west side of the inlet there are
a score or more trunks of spruce trees, still standing as they grew, which
have been exposed by the removal of the strata in which they were
formerly buried. A photograph of this ancient forest is presented in Fig.
B, Plate 14. The history of this deposit of sand and gravel and of the


forest entombed in it is in brief as follows : The glacier was formerly not
so extensive as now, having undergone a retreat after a preceding period
of marked extension, and a dense forest grew at least on the sides, if not
in the center, of the valley left exposed below its terminus. Coincident
with the retreat of the glacier and the growth of the forest there must
have been an elevation of the land which excluded the water from a por-
tion of the inlet now submerged. While the forest was still standing,
the streams from the glacier, then terminating in the valley to the north,
brought down large quantities of gravel and sand and built up an alluvial
cone about the extremity of the ice. As this alluvial cone, which proba-
bly ended in the sea and in fact was in part a delta, increased in size, it
invaded the adjacent forest and buried the still upright trees. A subse-
quent advance of the glacier caused the ice to override the gravel with its
entombed forest. When the glacier once more retreated the deposits were
uncovered and cut away by streams flowing from the ice, so as to expose
the trees buried within their mass. This last step in the history of the
inlet is still unfinished. The terminus of the glacier is still receding, and
as the streams flowing from it are still excavating channels through the
gravel, it is to be expected that additional portions of the buried forest
will be uncovered. In the moraines far up on the surface of the glacier
and on the islands of rock that project above its surface, there are bleached
and water-soaked branches and trunks of trees, which show that the now
desolate mountains bordering the ice were formerly more or less forest-

The process by which forests about the extremities of glaciers became
buried in alluvial cones may be observed at Norris glacier and about the
expanded extremity of Davidson glacier, but is illustrated in a far more
striking manner along the borders of Malaspina glacier, to be described on
a subsequent page. 1

Characteristics of the Glacier's Surface. At the locality on the
east side of Muir inlet, where excursionists usually land, the subglacial
gravels described above are well exposed. The border of the glacier and
the character of the ice at the extremity where it overhangs the sea may

1 The literature bearing on the gravel deposits and buried forests at Muir glacier may be
found as follows : G. Frederick Wright, " Ice Age in North America," pp. 58-63, also in
American Geologist, vol. 8, pp. 330, 331. H. P. Gushing, American Geologist, vol. 8, pp. 207.
I. C. Russell, American Geologist, vol. 9, pp. 190-197. H. Fielding Reid, National Geo-
graphic Magazine, vol. 4, pp. 38, 40, pi. 12. I. C. Russell, "The Influence of De'bris on the
Flow of Glaciers, " Jour. Geol., vol. 3, 1895, pp. 823-832.



also be examined, and the broad surface of the ice that fills the valley
easily reached. After walking over the surface of the ice between long
lines of moraines, where it is as level and smooth as a well-kept pavement,
one may climb a rocky promontory on the side of Mt. Wright, and obtain a
wide-reaching view of the remarkable scene that lies spread out before
him. There is not a tree or shrub in sight, but the crevices between the
rocks are bright with alpine flowers. The many streams of snow-covered
ice that unite to form the main trunk glacier may be distinctly traced
for a score or more of miles to their sources in the deep valleys and am-
phitheatres in the surrounding mountains. With the aid of the map


published by Prof. Reid, reproduced on a reduced scale on Plate 12, one
can obtain a most graphic idea of the entire system of ice drainage termi-
nating in Muir inlet. The area of the actual ice surface in view is about
350 square miles. The total area from which the ice drainage is derived
is not far from 800 square miles.

Looking down on the glacier from an elevated station, for the first
time, one is filled with awe and wonder at the vastness of the panorama so
clearly and distinctly visible. The rough broken ice with shining pinna-
cles overlooking blue crevasses, in the central portion of the stream, just
before it makes its final plunge into the sea, reveals the line of greatest
movement. It was in this all but impossible portion of the glacier that
Prof. Reid after great exertion placed his signals in 1891, and measured





(Photograph by H. F. Reid.)


(Photograph by H. F. Reid.)


the strength of the glacial current. The actual center of the glacier was
not reached, however, as the ice was there so shattered as to be impassable.

The number of narrow dirt-covered ridges running parallel with the
border of the glacier, and extending from the summits of the cliffs over-
hanging the sea, up the surface until they disappear beneath the neve
snow of the higher regions, or reach rocky islands in the glacier from
which they originate, mark the border of the individual ice streams com-
posing the main and highly compound central trunk in which all of the
tributaries unite. We note, also, that the long, narrow moraine belts
stand in relief above the general surface like railroad embankments. In
reality these huge piles of stones and earth, as they appear, are but a thin
sheathing, covering ridges of ice which they have preserved from melting
while the general surface wasted away.

Fully a score of secondary glaciers are in sight from the elevated
station on which the reader is supposed to stand, but there are still other
tributaries to the eastward that are concealed from view by Mt. Wright
and neighboring elevations.

With the accompanying map in hand, one may readily identify the
various features of the vast landscape. One evident fact is that the ice
fills the valleys to a depth of many hundred feet, leaving the steep moun-
tain sides above the established grade almost free of snow.

The medial moraines coming from the northeast in broad graceful
curves, as indicated on the map, do not seem to be formed by the union of
two marginal moraines, as is the rule in such instances, but appear to
begin suddenly in the region bordering Main and Berg lakes. This
apparent anomaly is due to the fact that the secondary glaciers in that
region are wasting away and have already melted at their sources and left
barren boulder-strewn areas, now filled in part with water held in check
by ice still filling the main valley. These secondary glaciers have not
only been beheaded, but a reverse flow initiated in the portion remaining.
By observing the contour lines drawn on the map where they cross the
ice in Main valley, it will be seen that the surface of the glacier has a
slope both east and west from a divide.

The most remarkable feature in the behavior of the medial moraines
shown on the map is the union of several trains of stones and dirt on
White glacier and on Southeast tributary, where they come together and
finally form a single ridge. This peculiar phenomenon has not been fully
explained, but is probably due to a decrease in volume of the several
streams by reason of their melting.


Dying glacier, on the west side of Muir inlet, presents decisive evi-
dence of recent retreat. Its surface is almost completely concealed
beneath dirt and stones, and the valley below its present terminus has
recently been abandoned by the ice and is barren and desolate. Similar
evidence of the general waste and recession that is affecting many of the
glaciers of Alaska is also manifest in Dirt glacier. In this case the ice is
so completely concealed by a superficial sheet of debris that one not familiar
with the various phases of glacial waste would scarcely recognize it as a
glacier at all. It appears more like a plowed field washed by winter
storms than like an ice body.

Recent Recession. In addition to the qualitative evidence of general
glacial retreat indicated above, we have direct quantitative measures of
the recession of the ice cliffs in which Muir glacier ends. As observed
by Wright and Reid, Muir glacier has in recent years been both of greater
and of less extent than at present. The fact of a former shrinking is shown
by an abundance of evidence. The bases of the enclosing mountains and
the summits of the rocky islands in the glacier are smoothed and striated,
and have boulders of various kinds of rocks scattered over their slopes.
These results of ice action reach, in vertical height, about 2000 feet on the
sides of the mountain near where Muir glacier now terminates, and extend
far south along the shore of Glacier bay. The absence of trees, and the
general desolation of the borders of Glacier bay and of all the valleys open-
ing from it, are in marked contrast to the densely wooded shores of
neighboring inlets, and are due to the recent occupation of the region by
glacial ice.

If the ice at the locality where Muir glacier now ends were 2000 feet
thicker than at present, making its total depth about 3000 feet, as was the
case when its maximum extension occurred, it is evident that its terminus
would be far to the south. At the time of the greatest extension, all of
the glaciers now pouring into Glacier bay were united and formed a trunk
stream which flowed southward and probably united with other similar ice
sheets so as to form a piedmont glacier. This great extension was during
one of the later maxima of the glacial epoch. There is evidence, how-
ever, of an extension of the ice far beyond its present limits within the
past one hundred years.

In 1794, Vancouver sailed through Icy strait and failed to discover
what is now known as Glacier bay, but states that a wall of ice existed at
its present entrance. The evidence that Vancouver actually saw the


terminus of the Glacier bay ice sheet is not conclusive, as his description
would apply equally well to a jam of bergs closing the entrance of the
inlet. When taken in connection with similar evidence of ice extension
in Disenchantment bay, 150 miles to the west, it seems reasonable to
suppose, however, that at the time of Vancouver's visit Glacier bay was
actually occupied by a great glacier.

Observations on the position of the terminus of Muir glacier made by
Muir in 1879, show that the ice then extended about one and three-fourths
miles, and when seen by Wright in 1886, about one mile below the posi-
tion of its extremity when surveyed by Reid in 1890-. Still more recent
observations indicate that this rapid retreat, with many variations in the
trend of the ice cliffs, is still in progress. 1


But little is known of the glaciers entering Glacier bay from the west,
excepting that they are of large size and set vast quantities of ice afloat.
The thunder of avalanches in that region may be heard while ascending
the bay, but the ice floes about the fronts of the glaciers are usually so
closely packed that, so far as I have been enabled to learn, no vessel has
made a near approach to them. Muir explored, this portion of the bay in
a canoe, and states that next to Muir glacier, the largest ice stream enter-
ing it is at the northwestern extension. The glacier referred to is proba-
bly the one now known as Pacific glacier. As described by Muir, " its
broad, majestic current, fed by unnumbered tributaries, is divided at the
front by an island, and from its long, blue wall the icebergs plunge and
roar in one eternal storm, sounding day and night, winter and summer,
and from century to century."

The glaciers on the west side of Glacier bay present a most attractive
field for study and are within easy reach of lines of summer travel.
Results as valuable as those gathered by Wright and Reid might there be
had during one or two summer excursions. 2

Another tide-water glacier is reported to exist at the head of Dundas
bay, opening into Cross sound to the west of Glacier bay, but there are no
authentic observations available concerning its character and "extent.

1 A discussion of observations bearing on the rate of retreat of Muir glacier is given by
Reid in The National Geographic Magazine, Washington, D.C., vol. 4, 1892, pp. 37-42.

2 Since this was written I have learned that Reid made a study of the glaciers on the
west side of Glacier bay in 1892. An account of these observations, together with a valuable
map, showing all of the glaciers that reach the sea in that region, will soon be published in
the 16th Annual Report of the U. S. Geological Survey.


Proceeding westward from Cross sound along the sublime Fairweather
coast, the next glacier met with which discharges directly into the sea, is
at the head of Disenchantment bay, 150 miles from Muir glacier and about
50 miles eastward of Mount St. Elias.


(See map forming Plate 17.)

On the shore of the narrow, winding inlet at the head of Yakutat bay,
known as Disenchantment bay, there are three glaciers which enter the
water and give origin to bergs, and at least a score of lesser ice streams
that have recently shrunken and are now separated from the bay by
narrow and exceedingly barren boulder-strewn areas. On the higher
portions of the mountains enclosing this land-locked arm of the sea; there
are hundreds of alpine glaciers descending from shining snow fields. The
tide-water glaciers referred to are the Turner, Hubbard, and Nunatak.
The positions of their extremities are shown approximately on the sketch
map forming Plate 17.

Turner, Hubbard, and Nunatak Glaciers. The best general idea
of the ice streams discharging into Disenchantment bay can be obtained
from the islands that break its surface. The largest of these, named
Haenke island in honor of the botanists of Malaspina's expedition, during
which portions of the southern coast of Alaska were explored in 1792, was
visited by the writer in 1890, and a landing effected -with some difficulty
through the closely packed icebergs that beset its shores. Its borders are
high and rocky. Its surface has been worn into rounded and subdued
contour by the ice that once flowed over it, with a depth of about 2000
feet. The domes of light-colored granite are smooth and polished, and
give abundant evidence of the stubborn resistance they offer to the ice
current. The summit of the island is about 800 feet above the surround-
ing waters.

The following account of the tide-water glaciers to be seen from
Haenke island is taken from the report of my first expedition to Mount
St. Elias : !

" Reaching the topmost dome of Haenke island, a wonderful panorama
of snow-covered mountains, glaciers, and icebergs lay before us. The
island occupies the position of the stage in a vast amphitheatre ; the
1 National Geographic Magazine, Washington, D.C., vol. 3, pp. 98, 99.


spectators were hoary mountain peaks, each a monarch robed in ermine
and bidding defiance to the ceaseless war of the elements. How insignifi-
cant the wanderer who confronts such an audience, and how weak his
effort to describe such a scene !

ft From a wild cliff-enclosed valley toward the north, guarded by tower-
ing pinnacles and massive cliffs, flows a great glacier, the fountains of
which are far back in the heart of the mountains beyond the reach of
vision. Having vainly sought an Indian name for this ice stream I
christened it Dalton [Turner] glacier. 1 The glacier is greatly shattered and
pinnacled in descending its steep channel, and on reaching the sea it ex-
pands into a broad ice foot. The last steep descent is made just before
gaining the water, and is marked by crevasses and pinnacles of magnifi-
cent proportions and beautiful color. This is one of the few glaciers of the
Mount St. Elias region that has well-defined medial and lateral moraines.
At the base of the cliffs on the western side there is a broad lateral moraine,
and in the center, looking like a winding road leading up the glacier,
runs a triple-banded ribbon of debris, forming a typical medial moraine.
The morainal material carried by the glacier is at last deposited in the sea
at its foot or floated away by icebergs and scattered far and wide over the
bottom of Disenchantment and Yakutat bays.

" The glacier expands on entering the water, as is the habit of all
glaciers of clear ice when unconfined, and ends in magnificent ice cliffs
some two miles in length. The water dashing against the bases of the
cliffs dissolves them away, and the tide tends to raise and lower the
expanded ice foot. The result of these agencies and of the onward flow
of the ice itself is to cause huge masses, sometimes reaching from summit
to base of the cliffs, to topple over into the sea with a tremendous
crash. Owing to the distance of the glacier from Haenke island, we
could see the ice fall long before the roar it caused reached our ears ; the
cliffs separated and huge masses seemed to sink into the sea without a
sound ; the spray thrown up as the blue pinnacles disappeared ascended
like gleaming rockets, sometimes as high as the tops of the cliffs, and then
fell back in silent cataracts of foam. Then a noise as of a cannonade
came booming across the waters and echoing from cliff to cliff. The roar
of the glacier continues all day when the air is warm and the sun is bright,
and is most pronounced when the summer days are finest. Sometimes
roar succeeds roar like artillery fire, and the salutes were answered, gun

1 The U. S. Board of Geographic Names has for sufficient reason authorized the substi-
tution of the name of J. H. Turner for the name originally given by me.


for gun, by the great Hubbard glacier, which pours its flood of ice into

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Online LibraryIsrael C. (Israel Cook) RussellGlaciers of North America; a reading lesson for students of geography and geology → online text (page 10 of 24)