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a barren area covered with morainal and alluvial deposits and bearing every
indication of having but recently been abandoned by the glaciers. 1 These
conditions are especially noticeable at the extremity of the Davidson
glacier. Between the present terminus of the ice and the encircling forest
there is a barren tract half a mile broad, which has been left by a retreat
of the ice so recently that vegetation has not been able to take root upon
it. A decided retreat of the ice has here recently occurred, and to all
appearances is still in progress, but no observations of its rate have been
made.

Conditions similar to those seen at Davidson glacier were observed in
connection with several other ice streams in the same region. In Taku
inlet, the Norris glacier comes down to sea level, but is separated from the
water by broad mud flats. There is no indication that this glacier has
recently advanced, and an accumulation of debris over its surface and
about its extremity indicates that it is melting away. The Taku glacier,
near at hand, is of the tide-water type ; and evidence of recent changes in
the position of its terminus is wanting.

Glacier Bay. The evidence of recent changes in Muir glacier has
been presented by Professor Wright, 2 who has shown that it has quite
recently been both more extensive and of less size than at present. Addi-
tional evidence of these changes has been supplied by Reid, 3 who con-
cludes that Muir glacier and other ice streams now discharging into Glacier
bay, were formerly much more extensive than at present, and at the time
of Vancouver's expedition, in 1794, probably occupied the whole of the

1 Bull. Geol. Soc. Am., vol. 1, 1890, p. 152.

2 " The Ice Age in North America," by G. Frederick Wright, New York, 1889, pp. 51-57.

3 " Studies of the Muir Glacier," by H. F. Reid, in National Geographic Magazine, vol.
4, 1891, pp. 34-42.



CLIMATIC CHANGES. 151

bay to a point some distance below Willoughby island. The retreat
during one hundred years is thought to be in the neighborhood of fourteen
miles. This conclusion, however, rests on certain passages in the narrative
of Vancouver's voyage, 1 which may possibly refer to floating ice, and not
to actual glaciers, and therefore do not have the quantitative value indi-
cated above. But under any plausible rendering of Vancouver's account
it does not seem possible to escape the conclusion that the ice in Glacier
bay was far more abundant at the time of his visit than in recent years.

Observations made by Wright and Reid in 1886 and 1890, respectively,
show that Muir glacier has retreated during this interval more than 1000
yards. This observed rate of recession would, if continuous for one hun-
dred years, produce a retreat of approximately fifteen miles, and affords
ground for believing that the great retreat supposed to have occurred since
Vancouver's visit is approximately correct.

John Muir has kindly contributed the following note concerning the
retreat of the glaciers of southeastern Alaska, which confirms the evidence
already presented :

" All the glaciers that have come under my observation in southeastern
Alaska have retreated and shallowed since first I became acquainted with
them in 1879 and 1880. Those in which the declivity of the channels is
least have of course receded the most. During the ten years between
1880 and 1890, Muir glacier has receded about one mile, at its mouth in
Muir inlet."

St. Elias Keg-ion. Much space could be occupied in recording obser-
vations which indicate a general recession of the glaciers about Yakutat
and Disenchantment bays and along the adjacent ocean shore, but a brief
summary of this evidence is all that seems necessary at this time.

The lower portions of a large number of glaciers in this region are
completely covered by continuous sheets of debris which has been concen-
trated at the surface through the melting of the ice. This debris is not
being carried forward and deposited in terminal moraines, but is distributed
over the surface of the ice in a thin sheet, and marks the stagnant condi-
tion of the glaciers on which it rests. In several instances, especially on
the outer border of the Malaspina glacier, the moraines resting on the ice
are clothed with vegetation, which over many square miles forms a dense
forest, composed principally of spruce trees, some of which are three feet

1 "Voyage of Discovery around the World," by Vancouver, vol. 5, pp. 420-423. Quoted
by Wright in " Ice Age of North America," pp. 55-57.



152 GLACIERS OF NORTH AMERICA.

in diameter. Within the forest-covered border and forming a belt concen-
tric with it there is a barren tract covered with stones and boulders. The
forests growing on the glacier and also thousands of lakelets, both in the
outer border of the barren moraine and in the adjacent forest-covered
moraine, indicate conclusively that the ice sheet is stagnant and conse-
quently wasting away. On the coast bordering the Malaspina glacier on
the south, there were formerly two projections called Point Rio and Cape
Sitkagi, which were noted by the explorers one hundred years ago. In
traversing this coast in 1891 I found that no capes exist at the localities
referred to. At the site of Cape Sitkagi there is evidence that the sea
has recently invaded the glacial boundary. On the sides of many of the
alpine glaciers in the adjacent mountains there are steep slopes bare of
vegetation although well below the upper limit of tree growth on adjacent
areas, which indicate that the ice streams have recently shrunken within
their beds. My conclusion after two visits to the glaciers in the St. Elias
region is that without exception they are rapidly retreating.

Near Point Manby there is a locality where the Malaspina glacier has
recently advanced about 1500 feet into a dense spruce forest, cutting off
the trees and sweeping them into confused heaps. After advancing the
ice retreated, leaving a typical morainal surface covered with lakelets.
This is the only instance of a recent advance that has come under
my notice in Alaska.

The head of Yakutat bay was visited by Malaspina in 1791, and again
by Captain Puget in 1794. Each of these explorers found the inlet
blocked by a wall of ice from shore to shore. No other observations in
this connection were made until my visit in the summer of 1890. 1 From
what may now be observed it is evident that the Turner and Hubbard
glaciers, which come down to the water at the head of the inlet and break
off in bergs, must have extended some five or six miles beyond their
present position at the time of Malaspina's and Puget's visits, and were
then united so as to completely block the entrance to Disenchantment bay,
which is a continuation of Yakutat bay. These observations show conclu-
sively that the glaciers mentioned have retreated five or six miles within
the past one hundred years. The small recession that has here taken
place, in comparison with the changes reported in Glacier bay, during the
same time, is probably due to the fact that the neve from which Muir

1 Map indicating the position of the ice in 1791 is shown on Plate 7, and its extent in
1890 on Plate 8, of my" Report on an Expedition to Mount St. Elias," in National Geographic
Magazine, vol. 3.



CLIMATIC CHANGES. 153

glacier flows is much lower than the snow fields drained by the Hubbard
and Turner glaciers, and presumably more sensitive to climatic changes.

Korth Side of the St. Ellas Mountains. Dr. C. Willard Hayes, of
the United States Geological Survey, in crossing from Selkirk house on
the Yukon river to Copper river in 1891, passed for a portion of the way
along the northern border of the great system of mountains which culmi-
nates in Mount Logan and Mount St. Elias, and discovered several large
glaciers of the alpine type flowing northward from the neve field north of
Mount St. Elias, and also other glaciers draining neve fields about Mount
Wrangell and flowing southward. Respecting the evidence of recent
changes in these glaciers, Dr. Hayes has kindly supplied the following notes:

" Two large glaciers and many small ones were seen flowing from the
St. Elias mountains northward into the White River basin. Another flows
from the southeast into the pass and drains into both the White and Copper
River basins. About the head of the Nizzenah are four large and many
small glaciers. Flowing into Copper river from the coast range are four
or five glaciers, one of them Miles glacier being larger than any seen
further in the interior. Observations were thus made on twelve glaciers,
and, with one exception to be described later, all show a more or less
rapid recession. The evidence of this recession in most cases is the accu-
mulated moraine covering the terminal edge of the glacier ; or where
there is not sufficient englacial drift to accumulate and form a protective
mantle, the stagnant ice melting to a feather edge. The White River lobe
of Russell glacier is of the moraine-covered type, while the Nizzenah
lobe has the feather edge. On the Klutlan and Russell glaciers the outer
portion of the moraine-covered ice supports a dense vegetation, which
becomes gradually more scanty and disappears about half a mile from the
edge of the ice. The recession of the smaller glaciers along the Nizzenah
appears to have been more rapid than the advance of the vegetation, so
that between it and the ice there is a belt of bare moraine.

" Miles glacier terminates in an ice cliff fronting upon Copper river,
and the river has as yet cut only part way through the dam formed by the
northern lateral moraine. This moraine must, until very recently, have
been backed up by the glacier itself, though the front of the latter has
now retreated two miles to the eastward.

" While the fact of recession is manifest, the rate is more difficult to
determine. In one case, however, it is possible to connect the amount of
recession with an important episode in the history of the region, namely,



154 GLACIERS OF NORTH AMERICA.

the eruption of a widespread deposit of volcanic ash which extends from
near the head of the Pelly westward to Scolai pass. With regard to the
age of this deposit Dr. Dawson says : l ' While the eruption must have
happened at least several hundred years ago, it can scarcely be supposed
to have taken place more than a thousand years before the present time.'

" For a distance of about three miles in front of the Klutlan glacier
there is a deposit of moraine material perhaps 200 feet thick, composed of
volcanic ash and angular rock fragments. This evidently fixes the position
of the glacial front at the time of the volcanic eruption, and the amount
of recession since that event. It is interesting to note that on the present
glacier surface the volcanic ash is found only a short distance from the end,
showing that since the eruption, while the front of the glacier has receded
about three miles, nearly the whole mass of the glacier has been renewed
by fresh addition from its source.

" The single exceptional case already referred to is the Frederika gla-
cier, which seems to be advancing its front instead of retreating. It has
its source in the high mountains forming the eastern members of the
Wrangell group, and flows south in a lateral valley, joining the valley of
the Nizzenah at right angles. The front of the glacier is parallel with the
river and about three-fourths of a mile from it, the intervening space being
a gravel plain. The glacier terminates in nearly a vertical ice cliff about
250 feet high. It is slightly convex, and stretches entirely across the
valley, about a mile in length. The surface of the glacier is free from
moraines, but is extremely rough and broken, unlike the ordinary surface
of stagnant ice at the end of a retreating glacier. At the foot of the cliff
is a small accumulation of gravel and fragments of ice, probably pushed
along by the advancing mass. 2

"An explanation of this anomalous case is suggested. Ten miles to
the westward of the Frederika another much larger glacier flows into the
valley of the Nizzenah. This is formed by the union of three separate
streams, and of these the eastern appears to be retreating much more
rapidly than either of the others. But this eastern branch probably has
its source in the same basin as the Frederika glacier, and it seems not
impossible that by some means the drainage has been diverted from the
western to the eastern outlet, thus causing the rapid retreat in the former
glacier and advance in the latter."

1 Report on Yukon District, p. 45, B.

2 This is the only authentic instance of an advancing glacier known on the west coast of
North America. I. C. R.



CLIMATIC CHANGES. 155

Greenland. Regarding recent changes in the ice sheet of Greenland
there is but scanty evidence, and such observations as have been made on
the advance and retreat of the margin of the ice are conflicting. Holts
found in 1880, between latitude 61 and 65 30', on the west coast, accord-
ing to Lindahl, 1 that " the border of the ice appeared to have retreated
quite recently in many places ; in others, it had decidedly advanced."
Nansen 2 remarks in this connection that we cannot even conjecture what
the present conditions are, and thinks that the observations show that
there is no strong tendency either toward advance or retreat. Warren
Upham, 3 who has recently reviewed the literature relating to the Green-
land ice sheet, informs me that in his judgment the ice is now slightly
increasing in thickness and generally in extent. This conclusion rests
largely on the general absence of debris on the borders of the ice sheet.
His studies have also led him to the conclusion that Greenland, in common
with other portions of the northeast border of this continent, is now having
an appreciable increase in cold.

The observations of those who have traversed the inland ice agree in
showing that nearly its entire surface is in the condition of a ne*ve, and
suggest that growth and not retreat must be in progress. The absence of
debris on the borders of the ice sheet referred to by Upham, is important
in this connection, and seems to indicate that no great waste of ice occurs
before it is discharged into the sea. So far as one may judge from the
observations of others, it seems as if the evidence available points to an
increase of the ice sheet, as supposed by Upham ; but the accuracy of this
conclusion is questionable, and Dufor^in a paper cited in the beginning
of this chapter, is inclined to the opposite opinion. He states that in 1880,
he made a communication on the retreat of the glaciers of Europe and
Asia before a scientific congress at Reims, and that, during the discussion
which followed, one of the persons present who had been in Greenland
several times mentioned that he " had noticed that the glaciers of that land
had also retreated considerably." It is known that the glaciers of Green-
land were much more extensive during a former epoch than at present,
and left records at an elevation of 3000 feet above the present ice surface. 4

1 American Naturalist, vol. 22, 1888, p. 593.

2 " First Crossing of Greenland," vol. 2, p. 491.

3 The conclusions of Mr. Upham are also contained in the following papers : " On the
Cause of the Cold of the Glacial Epoch," American Geologist, vol. 6, 1890, p. 336 ; and "The
Ice Sheet of Greenland," American Geologist, vol. 8, 1891, p. 150 ; " Criteria of Englacial and
Subglacial Drift," American Geologist, vol. 8, 1891, p. 385.

4 American Journal of Science, Third Series, vol. 24, pp. 100, 101.



156 GLACIERS OF NORTH AMERICA.

It may be suggested that the observations referred to by Dufor possibly
relate to these ancient records.

Weight of the Evidence. The observations summarized in this
chapter in reference to the Cordilleran region, although unsatisfactory in
many ways, indicate, with a single exception which seems to have a special
explanation, that the ice bodies in that region are retreating. This con-
clusion not only rests on direct observations of several individuals, but is
sustained by negative evidence as well. An advance of a glacier, espe-
cially in a forested country, is apt to be strongly marked, and would attract
the attention of even a casual observer ; but in no instance, with the excep-
tion reported by Dr. Hayes, and the slight extension on the border of the
Malaspina glacier already mentioned, has a recent advance been reported.

The fact that the glaciers at the head of Yakutat bay have retreated
several miles within the past one hundred years, as well as the still greater
recession of the glaciers of Glacier bay during the same period, indicates
that the present general recession of the glaciers of the Pacific coast has
probably been in progress for more than a century. During this time there
must have been many minor oscillations which our imperfect observations
do not detect, but the conclusion that the general movement has been
backward is well sustained.

THEORETICAL CONSIDERATIONS.

The variations that glaciers are undergoing have received special atten-
tion during the past few years. A large body of evidence in this connection
is being collected, especially by members of various Alpine clubs, but as
yet these ( studies have been confined principally to the glaciers of Europe.
The importance of this inquiry led the International Congress of Geolo-
gists, at its meeting at Zurich in 1894, to appoint a committee for the
special purpose of collecting data all over the world, with the view, if pos-
sible, of discovering a relation between the variations of glaciers and
meteorological phenomena. 1 An attempt to discuss systematically the
observations thus far recorded in this connection would be out of place at
the present time, since no detailed studies have been made of American gla-
ciers ; but a few suggestions in reference to the directions in which this
investigation seems to point may be of interest to the reader.

All the explanations of the observed variations in the length of gla-
ciers thus far offered are based on the supposition that they are due to

1 H. F. Reid, " Variations of Glaciers," Journal of Geology, vol. 3, 1895, pp. 278-288.



CLIMATIC CHANGES. 157

climatic changes. In respect to the greater oscillations it seems as if no
other conclusion could be expected, but minor changes, as I shall attempt
to show, may be due to other conditions.

The statement made in the opening paragraph of the present chapter,
to the effect that the glaciers of Europe and Asia are retreating, is perhaps
misleading, as it refers to the algebraic sum of advances and retreats dur-
ing a term of years. Within the cycle referred to there have undoubtedly
been many minor fluctuations which vary not only in amount but in direc-
tion, in different glaciers. In several instances, certain members of a group
of glaciers have advanced during recent years, while others in the same
group have remained stationary or retreated, and vice versa. Opposite
movements in glaciers which so far as one can judge are exposed to the
same climatic changes have not been satisfactorily explained.

Changes in the length of a glacier may evidently result from (1) vari-
ations in the amount of snow supplied to its neve region, (2) to changes in
the rate of melting, or (3) to fluctuations in the rate of flow.

Variations in the amount of snow added to the neve of a glacier, as
shown in. part at least by Professor Forel, 1 may be considered as of the
nature of a pulsation which is propagated throughout its length. The
end of a glacier might therefore alternately advance and retreat in sym-
pathy with variations in snowfall that occurred scores of years and even
centuries before. Two glaciers subject to the same climatic conditions,
but of unequal length, or of the same length but having different mean
velocities, would advance or retreat at different periods for the reason that
the time required for the increment produced by an increase of snowfall
to reach their extremities would be different. 2

It has been suggested that variations in the rate of melting might be
a factor causing the ends of glaciers to advance or retreat. But as loss
by melting is greatest at the lower extremity of a glacier, similar effects
would be expected in neighboring instances, although alpine glaciers that

1 Bibliot. Univ. de Geneve, 1881.

2 Another explanation dependent on variations in snowfall has been suggested by Pro-
fessor Richter, who, as stated by Reid (Journal of Geology, vol. 3, p. 281), "thinks that the
accumulation of snow in the ne"ve" region, even under uniform meteorological conditions, would
in time produce a great enough pressure to overcome the resistance, due to the friction against
its bed, of the glacier's tongue, which is then pushed forward with a greater velocity, result-
ing in the advance of the glacier ; this continues until the drain on the ne"ve" region, on account
of more rapid flow, exhausts the accumulation of snow ; after this the motion almost entirely
ceases, and the glacier melts back until another advance begins. Professor Forel calls this
the 'theory of intermittent flow,' and points out that according to it variations in the size
of glaciers would be entirely independent of meteorological changes."



158 GLACIERS OF NORTH AMERICA.

descend into different valleys might perhaps be influenced differently. It
is unnecessary to discuss this suggestion, however, since observation on
meteorological changes and on the variations of glaciers in the same region
do not sustain it.

While it is customary to refer the advances and retreats observed in
glaciers to climatic changes, and although opposite movements in glaciers
exposed to the same meteorological conditions may, perhaps, as shown
above, be explained in this way ; yet I venture to suggest that there is a
principle involved in the behavior of glaciers themselves that might bring
about analogous results. I refer to the influence of debris on the flow of
ice containing it.

As is well known, a concentration of debris takes place at the end of
a glacier, especially when it is slowly retreating. This is due to the fact
that while the volume of the ice decreases, the amount of debris it con-
tains remains practically the same. The percentage of foreign material in
a given volume of ice is thus increased. The rate of flow of ice, however,
other conditions remaining the same, decreases as the percentage of
contained debris increases. 1

As the percentage of debris in the extremity of a glacier increases, the
flow of the ice will slacken, and when the concentration reaches a certain
point, stagnation will result. The debris-charged ice will then act as a dam
and check the flow of the clearer ice above. The effect of such a check in
the advances of the stream will vary with conditions, particularly as there
is a delicate adjustment at the extremity of a normal glacier between the
effects of temperature tending to melt the ice and the advance of fresh ice
from above. Fresh ice may advance upon the debris-charged portion and
become in turn concentrated, thus raising the dam ; or, in the case of a
growing glacier, may flow over the obstruction and continue to advance
until melting and concentration of debris again causes stagnation at its
extremity, when the process would be repeated. If the glacier is slowly
wasting away, the dam would check the advance of ice from above and
cause it to increase in thickness and to expand in area, thus presenting a
broader surface to the atmosphere. Now, the presence of surface debris
influences the melting of a glacier in two ways. When small in amount,
especially if dark in color, it promotes liquefaction ; but if abundant, it
protects the ice from the sun and atmosphere and retards waste. In the
case of a slowly retreating glacier that has formed a debris-charged ice

1 1. C. Kussell, "The Effect of Debris on the Flow of Glaciers," Journal of Geology,
vol. 3, 1895, pp. 823-832.



CLIMATIC CHANGES. 159

dam, the melting of the clear, or but slightly charged ice, above the obstruc-
tion will go on much more rapidly than at the extremity, where the ice is
covered with earth and stones. The ice above the obstruction might then
be melted, leaving the dam to slowly waste away and finally leave a ter-
minal moraine. The retreating glacier by again concentrating debris in its
extremity would again halt, and the process be repeated.

An explanation is thus suggested of the varying behavior of glaciers
under the same climatic conditions. Two glaciers supplied in their neVe
regions with equal quantities of snow, and alike in all respects except in


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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 17 of 24)