GLACIERS OF THE ST. ELIAS REGION.
NATURAL DIVISIONS OF GLACIERS.
The glaciers of the St. Elias region form two groups. The ice-streams
from the mountain are of the type found in Switzerland, and hence
termed _Alpine glaciers_. The great plateau of ice along the ocean
formed by the union and expansion of Alpine glaciers from the
mountains belongs to a class not previously described, but which in
this paper have been called _Piedmont glaciers_. The representative of
the latter type between Yakutat bay and Icy bay is the Malaspina
glacier. Both types are to be distinguished from _Continental
glaciers_.
ALPINE GLACIERS.
The glaciers in the mountains are all of one type, but present great
diversity in their secondary features, and might be separated into
three or four subordinate divisions. The great trunk glaciers have
many tributaries, and drain the snows from the mountains through broad
channels, which are of low grade throughout all the lower portions of
their courses. Besides the trunk glaciers and the secondary glaciers
which flow into them, there are many smaller glaciers which do not
join the main streams, but terminate in the gorges or on the exposed
mountain sides in which they originate. These have nearly all the
features of the larger streams, but are not of sufficient volume to
become rivers of ice.
A minor division of Alpine glaciers for which it is convenient to have
a special name includes those that end in the sea and, breaking off,
form icebergs. These may be designated as "tide-water glaciers."
Typical examples of this class are furnished by the Dalton and Hubbard
glaciers, but other ice-streams having the same characteristics occur
in Glacier bay, in Taku inlet, and at the heads of several of the deep
fjords along the coast of southeastern Alaska.
{177} A noticeable feature of the Alpine glaciers of Alaska is that
they expand on passing beyond the valleys through which they flow and
form delta-like accumulations of ice on the plains below. This
expansion takes place irrespective of the direction in which the
glaciers flow, and, so far as may be judged from the many examples
examined, is independent of the débris that covers them. It should be
remembered, however, that none of the Alaskan glaciers thus far
studied show marked inequalities in the distribution of the moraines
upon their surfaces. Should one side of a glacier, on leaving a cañon,
be heavily loaded with marginal moraines, while the opposite border
was unprotected, it is to be presumed that a deflection of the ice
would take place similar to the change in direction recorded by the
moraines about Mono lake, California.[34] The normal tendency of ice,
when not confined, to expand in all directions and form a plateau is
illustrated on a grand scale by the Malaspina glacier.
[Footnote 34: Eighth Ann. Rept. U. S. Geol. Surv., 1889, part I, pp.
360-366.]
The most important ice-streams about Mount St. Elias and Mount Cook
are indicated on the map forming plate 8. The Tindall, Guyot, and
Libbey glaciers and the lower part of the Agassiz glacier there
represented are taken from a map published by H. W. Topham.[35] All of
the other glaciers indicated on the map were hastily surveyed during
the present expedition and are described to some extent in the
accompanying narrative. By far the most important of these is the one
named the Seward Glacier.
[Footnote 35: Alpine Journal, London, vol. XIV, 1887, pl. op. p. 359.]
* * * * *
The Seward Glacier is of the Alpine type, and is the largest tributary
of the Malaspina glacier. Its length is approximately 40 miles, and
its width in the narrowest part, opposite Camp fourteen, is about 3
miles. The main amphitheatre from which its drainage is derived is
north of Mount Owen and between Mount Irving and Mount Logan. The
general surface of the broad level floor of this névé field has an
elevation of approximately 5,000 feet. The snow from the northern and
western sides of Mount Irving, from the northern slope of Mount Owen,
and from numerous valleys and cañons in the vast semicircle of
towering peaks joining these two mountains, unite to form the great
glacier. There is another amphitheatre between Mount Owen and the
Pinnacle pass cliffs supplied principally by snows {178} from the
northwestern slope of Mount Cook, which sends a vast flood of ice and
snow into the main drainage channel. Other tributary glaciers descend
the steep slopes of Mount Augusta and Mount Malaspina, and a lesser
tributary flows eastward from Dome pass. All of these ice-drainage
lines converge toward the narrow outlet of Camp 14 (plate 8) and
discharge southward down a moderately steep descent several miles in
length. Below Camp 14 there are other névé fields bordering the
glacier, which contribute no insignificant amount of ice and snow to
its mass. Between the extremity of the Hitchcock range and the Samovar
hills the path of the glacier is again contracted and greatly broken
as it descends to the plateau below.
The Seward glacier, like all ice rivers of its class, has its névé
region above, and its ice region below. The limit between the two is
the lower margin of the summer snow, and occurs just above the
ice-fall between the southern extremity of the Hitchcock range and the
Samovar hills. All the névé region is pure white and without moraines,
except at the immediate bases of the most precipitous cliffs. At the
bases of the Corwin cliffs, which rise fully 2,000 feet above its
border, no débris can be distinguished even in midsummer. An absence
of moraines along the base of Pinnacle pass cliffs was also noticed
during our first visit, but when we returned over the same route in
September the melting of the snow had revealed many large patches of
dirt and disintegrated rock. In several places near the bases of steep
cliffs, strata of dirty ice, containing many stones, were observed in
deep crevasses. It was evident that vast quantities of débris were
sealed up in the ice along the borders of the glacier, only to appear
at the surface far down the stream where summer melting exceeds the
winter accumulation.
The surface of the glacier below the lower fall is composed of solid
ice with blue and white bands, and has broad moraines along its
borders. The course of the glacier, after entering the great plateau
of ice to which it is tributary, may be traced for many miles by the
bands of débris along its sides. These moraines belong to the
Malaspina glacier, and have already been referred to.
At the outlet of the upper amphitheatre, about 6 miles above Mount
Owen, there is an ice-fall which extends completely across the
glacier. Below the pinnacles and crevasses formed by this fall the ice
is recemented and flows on with a broad, gently {179} descending
surface, gashed, however, by thousands of crevasses, as shown in plate
20, to the end of the Pinnacle pass cliffs. It there finds a more
rapid descent, and becomes crevassed in an interesting way. The slope
is not sufficient to be termed a fall, but causes a rapid in the
ice-stream.
The change of grade in the bed of the glacier is first felt about a
mile above Camp 14. A series of crevasses there begins, which extends
four or five miles down-stream. At first the cracks are narrow, and
trend upstream in the manner usual with marginal crevasses. Soon the
cracks from the opposite sides meet in the center and form a single
crevasse, bending upstream in the middle. A little lower down, the
crevasse becomes straight, showing that the ice in the center of the
current flows more rapidly than at the sides. The more rapid movement
of the center is indicated by the form of the crevasses all the way
down the rapid. After becoming straight they bow in the center and
form semi-lunar gashes, widest in the center and curving up-stream at
each extremity. Still farther down they become more and more bent in
the center and at the same time greatly increased in breadth. Still
lower the curve becomes an angle and the crevasses are V-shaped, the
arrow-like point directed down-stream. These parallel V-shaped gashes
set in order, one in front of the other, are what gives the glacier
the appearance of "watered" ribbon when seen from a distance.
With the change in direction and curvature of the crevasses, there is
an accompanying change in color. The cracks in the upper part of the
rapid are in a white surface and run down into ice that looks dark and
blue by contrast. Lower down, as the cracks increase in width, broad
white tables are left between them. Cross-fractures are formed, and
the sides of the table begin to crumble in and fill up the gaps
between. As the surface melts the tables lose their pure whiteness and
become dust-covered and yellow; but the blocks falling into the
crevasses expose fresh surfaces, and fill the gulfs with pure white
ice. In this way the color of the sides of the crevasses changes from
deep blue to white, while the general surface loses its purity and
becomes dust-covered. Far down the rapid where the V-shaped crevasses
are most pointed, the tables have crumbled away and filled up the
gulfs between, so that the watered-ribbon pattern is distinguished by
color alone. The scars of the crevasses formed above are shown by
white bands on a dark dust-covered {180} surface. Before the lower
fall is reached nearly all traces of the thousands of fissures formed
in the rapids above have disappeared.
On looking down on the rapids from any commanding point, the definite
arrangement of the crevasses along the center of the ice-stream at
once attracts attention, and their order suggests a rapid central
current in the stream.
Below Camp 14, for at least two or three miles, as well as at many
places above that point, the Seward glacier flows between banks of
snow. Along its border there are marginal crevasses trending
up-stream, and in the adjacent banks there are similar breaks trending
down-stream. Where the two systems meet there is a line of irregular
crevasses, exceedingly difficult to cross, which mark the actual
border of the flowing ice. A similar arrangement of marginal crevasses
and of shore crevasses has been referred to in connection with the
Marvine glacier, and was observed in many other instances.
While occupying Camp 14 we could hear the murmur of waters far down in
the glacier below our tent, but there were no surface streams visible.
Crashing and rumbling noises made by the slowly moving ice frequently
attracted our attention, and sometimes at night we would be awakened
by a dull thud, accompanied by a trembling of the rocks beneath us, as
if a slight earthquake had occurred. Occasionally a pinnacle of ice
would fall and be engulfed in the crevasses at its base. These
evidences of change indicated that movements in the Seward glacier
were constantly in progress. A short base-line was measured and sights
taken to well-marked points in the Seward glacier for the purpose of
measuring its motion. The angles between the base-line and lines of
sight to the chosen points were read on several successive days, but
when these observations were compared they gave discrepant results.
The measurements which seemed most reliable indicate that the central
part of the ice-stream has a movement of about twenty feet a day. This
is to be taken only as an approximation, which needs to be verified
before much weight can be attached to it.
CHARACTERISTICS OF ALPINE GLACIERS ABOVE THE SNOW-LINE.
The surface of the névé is white, except near its lower limit in late
summer, where it frequently becomes covered with dust {181} blown from
neighboring cliffs. It is almost entirely free from moraines, but at
the bases of steep slopes small areas of débris sometimes appear at
the surface when the yearly melting has reached its maximum. The
absence of moraines is accompanied by an absence of glacial tables,
sand-cones and other details of glacial surfaces due to differential
melting. Streams seldom appear at the surface, for the reason that
usually the water produced by surface melting is quickly absorbed by
the porous strata beneath; yet the crevasses are frequently filled
with water, and sometimes shallow lakes of deep blue occur at the
bottoms of the amphitheatres and form a marked contrast to the even
white of the general surface. Crevasses are present or absent
according to the slope of the surface on which the névé rests. In the
crevasses the edges of horizontal layers of granular ice are
exhibited, showing that the névé down to a depth of at least one or
two hundred feet is horizontally stratified. In the St. Elias region
the strata are most frequently from ten to fifteen feet thick, but in
a few instances layers without partings over fifty feet thick were
seen. The surface is always of white, granular ice, but in the
crevasses the layers near the bottom appear more compact and bluer in
color than those near the surface.
Some of the most striking features of the névé are due to the
crevasses that break their surfaces. The orderly arrangement of
marginal crevasses and of the interior crevasses at the rapids in the
Seward glacier have already been referred to; but there are still
other crevasses, especially in the broad, gently sloping portions of
the snow-fields where the motion is slight, which, although less
regular in their arrangement, are fully as interesting. The crevasses
on such slopes generally run at right angles to the direction in which
the snow is moving. On looking down on such a surface, the breaks look
like long clear-cut gashes which have stretched open in the center,
but taper to a sharp point at each end. The ability of the névé ice to
stretch to a limited extent is thus clearly shown. The initiation of
the crevasses seems to be due to the movement of the névé ice over a
surface in which there are inequalities of such magnitude that the ice
cannot stretch sufficiently to allow it to accommodate itself to them,
so that strains are produced which result in fractures at right angles
to the line of general movement. Crevasses found where the grade is
gentle vary from a fraction of an inch to 10 or 15 feet in width, and
are sometimes two or three {182} thousand feet long. Broader gulfs are
seldom formed unless the slope has an inclination of 15° or 20°.
The grandest crevasses are in the higher portions of the névé, and
occur especially on the borders of the great amphitheatres. In such
situations the crevasses are usually fewer in number but are of
greater size than in equal areas lower down. A length of three or four
thousand feet and a breadth of fifty feet or more is not uncommon. The
finest and most characteristic glacial scenery is found among these
great cañon-like breaks. Standing on the border of one of the gulfs,
as near the brink as one cares to venture, their full depth cannot
usually be seen. In some instances they are partially filled with
water of the deepest blue, in which the ice-walls are reflected with
such wonderful distinctness that it is impossible to tell where the
ice ends and its counterfeit begins. The walls of the crevasses are
most frequently sheer cliffs of stratified ice, with occasional
ornamentations, formed of ice-crystals or a pendent icicle. After a
storm they are frequently decorated in the most beautiful manner with
fretwork and cornice of snow. The bridges spanning the crevasses are
usually diagonal slivers of ice left where the clefts overlap; but at
times, especially in the case of the larger crevasses, there are true
arches resembling the Natural Bridge of Virginia, but on a larger
scale, spanning the blue cañons and adding greatly to their strange,
fairy-like beauty. The most striking feature of these cracks is their
wonderful color. All tints, from the pure white of their crystal lips
down to the deepest blue of their innermost recesses, are revealed in
each gash and rent in the hardened snow.
Above the snow-line all of the mountain tops that are not precipitous
are heavily loaded with snow. Where the snow breaks off at the verge
of a precipice and descends in avalanches a depth of more than a
hundred feet is frequently revealed, but in the valleys and
amphitheatres the snow has far greater thickness. Pinnacles and crests
of rock, rising through the icy covering, indicate that the thickness
of the névé must be many hundreds of feet.
There are no evidences of former glaciation on the mountain crests
which project above the névé fields. There are no polished and
striated rock surfaces or glaciated domes to indicate that the
mountains were ever covered by a general capping of ice, as has been
postulated for similar mountains elsewhere. When the {183} glaciers
had their greatest expansion the higher mountains were in about their
present condition. The increase in the volume of the glaciers was felt
almost entirely in their lower courses.
CHARACTERISTICS OF ALPINE GLACIERS BELOW THE SNOW-LINE.
The first feature that attracts attention on descending from the névé
region to the more icy portion of the glaciers is the rapid melting
everywhere taking place. Every day during the summer the murmur and
roar of rills, brooks and rivers are to be heard in all of the
ice-fields. The surface streams are usually short, on account of the
crevasses which intercept them. They plunge into the gulfs, which are
many times widened out by the flowing waters so as to form wells, or
_moulins_, and join the general drainage beneath. The streams then
flow either through caverns in the glaciers or in tunnels at the
bottoms. While traversing the glacier one may frequently hear the
subdued roar of rivers coursing along in the dark chambers beneath
when no other indication of their existence appears at the surface.
When these subglacial streams emerge, usually near the margin of the
ice, they issue from archways forming the ends of tunnels, and perhaps
flow for a mile or two in the sunlight before plunging into another
tunnel to continue their way as before.
The best example of a glacial river seen during our exploration was
near the western border of the Lucia glacier. It is shown in the
illustration forming plate 12, which is reproduced mechanically from a
photograph. This Styx of the ice-world has been described on an
earlier page. The lakes formed at the southern end of nearly every
mountain spur projecting into the Malaspina glacier discharge through
tunnels in the ice, which are similar in every way to those formed by
the stream already mentioned.
In the beds of the glacial streams there are deposits of sand and
gravel, and when the streams expand into lakes these deposits are
spread over their bottoms in more or less regular sheets. When streams
from the mountains empty into the lakes, deltas are formed. While
these deltas have the same characteristics as those built in more
stable water bodies, many changes in detail occur, owing to the
fluctuation of the water level.
{184} One of the tunnels leading to a dry lake-bed at the end of the
Hitchcock range was explored for several rods and found to be a high,
arching cavern following a tortuous course, and large enough to allow
one to drive a coach and four through it without danger of collision.
Its floor was formed of gravel and bowlders, and its arching roof was
clear ice. Here and there the courses of crevasses could be traced by
the stones and finer débris that had fallen in from above, giving the
appearance of veins in a mine. The deposit on the floor of the tunnel
rested upon ice, and would certainly be greatly disturbed and broken
up before reaching a final resting place in case the glacier should
melt. In the lake basins, also, the sand and gravel forming their
bottoms frequently rested upon substrata of ice, and are greatly
disturbed when the ice melts.
At the ends of the glaciers the subglacial and intraglacial drainage
issues from tunnels and forms muddy streams. These usually flow out
from the foot of a precipice of ice, down which rills are continually
trickling. The streams flowing away from the glaciers are usually
rapid, owing to the high grade of their built-up channels, and sweep
away large quantities of débris which is deposited along their
courses. The streams widen and bifurcate as they flow seaward, and
spread vast quantities of bowlders, sand, and gravel over the country
to the right and left, not infrequently invading the forests and
burying the still upright trees. The deposits formed by the streams
are of the nature of alluvial fans, over which the waters meander in a
thousand channels. Where this action has taken place long enough the
alluvial fans end in deltas; but should there be a current in the sea,
the débris is carried away and formed into beaches and bars along
adjacent shores. Should these glaciers disappear, it is evident that
these great bowlder washes would form peculiar topographic features,
unsupported at the apexes, and it might be perplexing to determine
from whence came the waters that deposited them. I am not aware that
similar washes have been recognized along the southern border of the
Laurentide glaciers, but they should certainly be expected to occur
there.
Another very striking difference in the appearance of the glaciers
above and below the snow-line is due to the prevalence of débris on
the lower portion. The melting that takes place {185} below the
snow-line removes the ice and leaves the rocks. In this manner the
stones previously concealed in the névé are concentrated at the
surface, and finally form sheets of débris many miles in extent. So
far as my observations go, there is nothing to indicate that stones
are brought to the surface by any other means than the one here
suggested. Upward currents in the ice that would bring stones to the
surface have been postulated by certain writers, but nothing
sustaining such an hypothesis has been found in Alaska.
The moraines on the lower extremities of the Alpine glaciers may
frequently be separated into individual ridges, which in many
instances would furnish instructive studies; but in no case has the
history of these accumulations been worked out in detail.
With the appearance of moraines at the surface come a great variety of
phenomena due to unequal melting. Ridges of ice sheathed with débris,
glacial tables, sand cones, etc., everywhere attract the attention;
but these features are very similar on all glaciers where the summer's
waste exceeds the winter's increase, and have been many times
described.
The general distribution of the moraines of the lower portion of the
Alpine glaciers of the St. Elias region merits attention. The moraines
themselves exhibit features not yet observed in other regions. From
Disenchantment bay westward to the Seward glacier the lower portions
of the ice-streams are covered and concealed by sheets of débris.
About their margins the débris fields support luxuriant vegetation,
and not infrequently are so densely clothed with flowers that a tint
is given to their rugged surfaces. On the extreme outer margins of the
moraines there are sometimes thickets and forests so dense as to be
almost impenetrable. The best example of forest-covered moraines
resting on living glaciers, however, is found along the borders of the
Malaspina ice-field.
PIEDMONT GLACIERS.
This type is represented in the region explored by the Malaspina
glacier. This is a plateau of ice having an area of between 500 and
600 square miles, and a surface elevation in the central part of
between 1,500 and 1,600 feet. It is fed by the Agassiz, Seward,
Marvine, and Hayden glaciers, and is of such volume that {186} it has
apparently displaced the sea and holds it back by a wall of débris
deposited about its margin. All of its central portion is of clear
white ice, and around all its margins, excepting where the Agassiz and
Seward glaciers come in, it is bounded by a fringe of débris and by
moraines resting on the ice. Along the seaward border the belt of
fringing moraines is about five miles broad. The inner margin of the
moraine belt is composed of rocks and dirt, without vegetation, and
separated more or less completely into belts by strips of clear ice.
On going from the clear ice toward the margin of the glacier one finds
shrubs and flowers scattered here and there over the surface. Farther
seaward the vegetation becomes more dense and the flowers cover the
whole surface, giving it the appearance of a luxuriant meadow. Still
farther toward the margin dense clumps of alder, with scattered spruce
trees, become conspicuous, while on the outer margin spruce trees of
larger size form a veritable forest. That this vegetation actually
grows on the moraines above a living glacier is proved beyond all
question by holes and crevasses which reveal the ice beneath. The
curious lakes scattered abundantly over the moraine-covered areas, and
occupying hour-glass-shaped depressions in the ice, have already been
described.
From the southern end of the Samovar hills, where the Seward and
Agassiz glaciers unite, there is a compound moraine stretching
southward, which divides at its distal extremity and forms great
curves and swirl-like figures indicating currents in the glacier.
All the central part of the plateau is, as already stated, of clear
white ice, free from moraines; at a distance it has the appearance of
a broad snow surface. This is due to the fact that the ice is melted
and honey-combed during the warm summer and the surface becomes
vesicular and loses its banded structure. A rough, coral-like crust,
due to the freezing of the portions melted during the day, frequently
covers large areas and resembles a thick hoar-frost. Crevasses are
numerous, but seldom more than a few feet deep. They appear to be the
lower portions of deep crevasses in the tributary streams which have
partially closed, or else not completely removed by the melting and
evaporation of the surface.
Many of the crevasses are filled with water, but there are no surface
streams and no lakes. Melting is rapid during the warm {187} summer
days, but the water finds its way down into the glacier and joins the
general subglacial drainage. It is evident that the streams beneath
the surface must be of large size, as they furnish the only means of
escape for the waters flowing beneath the Agassiz, Seward and Marvine
glaciers, as well as for the waters formed by the melting of the great
Malaspina glacier.
The outer borders of the Malaspina glacier are practically stationary,
but there are currents in its central part. Like the expanded ends of
some of the Alpine glaciers, as the Galiano and Lucia glaciers, for
example, this glacier is of the nature of a delta of ice, analogous in
many of its features to river deltas. As a stream in meandering over
its delta builds up one portion after another, so the currents in an
expanded ice-foot may now follow one direction and deposit loads of
débris, and then slowly change so as to occupy other positions. This
action tends to destroy the individuality of morainal belts and to
form general sheets of débris. The presence of such currents as here
suggested has not been proved by measurements, but the great swirls in
the Malaspina glacier and the tongues of clear ice in the upper
portions of the débris fields on the smaller glaciers strongly suggest
their existence.
The Malaspina glacier is evidently not eroding its bed; any records
that it is making must be by deposition. Should the glacier melt away
completely, it is evident that a surface formed of glacial débris, and
very similar to that now existing in the forested plateau east of
Yakutat bay, would be revealed.
The former extent of the Malaspina glacier cannot be determined, but
it is probable that during its greatest expansion it extended seaward
until deep water was reached, and broke off in bergs in the same
manner as do the Greenland glaciers at the present day. Soundings in
the adjacent waters might possibly determine approximately the former
position of the ice-front, and it is possible that submarine moraines
might be discovered in this way. The Pimpluna reefs, reported by
Russian navigators and indicated on many maps, may possibly be a
remnant of the moraine left by the Piedmont glacier from the adjacent
coast.
The glaciers west of Icy bay were seen from the top of Pinnacle pass
cliffs, and are evidently of the same character as the Malaspina
glacier and fully as extensive. A study of these {188} Piedmont
glaciers will certainly throw much light on the interpretations of the
glacial records over northeastern North America. Their value in this
connection is enhanced by the fact that they are now retreating and
making deposits rather than removing previous geological records.
* * * * *
The expedition of last summer was a hasty reconnoissance, during which
but little detail work could be undertaken. The actual study of the
ice-fields of the St. Elias region remains for those who come later.
{189}