THE CONTINENTAL GLACIERS OF POLAR REGIONS
[Illustration:
FIG. 299.—Map of Greenland showing the area of inland-ice and the
routes of different explorers.]
=The inland ice of Greenland.=—In Greenland and in Antarctica the land
is almost or quite buried under a cover of snow and ice—the so-called
“inland ice”—which always assumes the surface of a very flat dome or
shield. In Greenland there is found a marginal ribbon of land generally
from five to twenty-five miles in width (Fig. 299), but in Antarctica
all the land, with the exception of a few mountain peaks, is inwrapped
in a mantle of ice which is also extended upon the sea in a broad shelf
of snow and ice. Neither of these vast glaciers has been explored
except in its marginal portion, yet such is the symmetry of the
profiles along the routes traversed, and such the flatness and monotony
of the snow surface within the margins, that there is little reason to
doubt that the profile made along Nansen’s route in southern Greenland
would, save only for magnitude, fairly represent a section across the
middle of the continent (Fig. 300).
=The mountain rampart and its portals.=—As soon as we examine the
coastal belt we observe that the “Great Ice” of Greenland is held
in by a wall of mountains and so prevented from spreading out to its
natural surface in the marginal portions. Through portals of the
inclosing mountain ranges—the _outlets_—it sends out _tongues_ of ice
which in many respects resemble certain types of mountain glaciers.
[Illustration:
FIG. 300.—Profile in natural proportions across the southern end of
the continental glacier of Greenland, constructed upon an arc of the
earth’s surface and based upon Nansen’s profile corrected by Hess. The
marginal portions of the profile are represented below upon a magnified
scale in order to bring out the characters of the marginal slopes.]
Such measurements as have been made upon the inland ice of Greenland
at points back from, but yet comparatively near to, the outlets, show
that it has here a surface rate of motion amounting to less than an
inch per day, and it is highly probable that at moderate distances from
the margin this amount diminishes to zero. Upon the outlets, on the
contrary, surface rates as high as 59 feet per day have been measured,
and even 100 feet per day has been reported. We are thus justified in
saying that glacier flow within the outlets is from 700 to 1000 times
as great as it is upon the near-by inland ice, and that the glacier
is in a measure drained through the portals of the inclosing ranges.
Back from these outlet streams of ice, or tongues, the surface of the
inland ice is depressed to form a dimple or “basin of exudation” as is
the surface of a reservoir above the raceway when the water is being
rapidly drawn away (Fig. 301).
┌────────────────────────────────────────────────────────────────────┐
│ PLATE 13. │
│ │
│ [Illustration: _A._ Precipitous front of the Bryant glacier outlet │
│ of the Greenland inland-ice (after Chamberlin).] │
│ │
│ [Illustration: _B._ Lateral stream beside the Benedict glacier │
│ outlet, Greenland (after R. E. Peary).] │
└────────────────────────────────────────────────────────────────────┘
[Illustration:
FIG. 301.—Map of a glacier tongue, with dimple showing above and due
to indraught of the ice. Umanakfjord, Greenland (after von Drygalski).]
Fissures in the ice, the so-called crevasses, are the recognized
marks of ice movement, and these are always concentrated at the steep
slopes of the ice surface in the neighborhood of its margins. Upon the
Greenland ice, crevasses are restricted in their distribution to a zone
which extends from seven to twenty-five miles within the ice border.
=The marginal rock islands.=—From its margin the ice surface rises
so steeply as to be climbed only with difficulty, but this gradient
steadily diminishes until at a distance of between seventy-five and
a hundred miles its slope is less than two degrees. Where crossed by
Nansen near latitude 64° N. the broad central area of ice was so nearly
level as to appear to be a plain.
As we pass across the irregular ice margin in the direction of the
interior, larger and larger proportions of the land’s surface are
submerged, until only projecting peaks rise above the ice as islands
which are described as _nunataks_ (Fig. 302).
Though not a universal observation, it has been often noted that the
absorption of the sun’s rays by rock masses projecting through the snow
results in a radiation of the heat and a lowering by melting of the
surrounding snow and ice. For this reason nunataks are often surrounded
by a deep trench due to a melting of the snow. Such a depression in
the ice surface about the margin of a nunatak, from its resemblance to
a trench about an ancient castle, has been designated a _moat_ (Fig.
303). For the same reason, the outlet tongues of ice which descend in
deep fjords between walls of rock are melted away from the walls and a
lateral stream of water is sometimes found to flow between ice and rock
(pl. 13 B).
[Illustration:
FIG. 302.—Edge of the Greenland inland ice, showing the nunataks
diminishing in size toward the interior. The lines upon the ice are
medial moraines starting from nunataks (after Libbey).]
=Rock fragments which travel with the ice.=—Rock surfaces which are
exposed to the atmosphere are in high latitudes broken down through
the freezing of water within their crevices. The fragments resulting
from this rending process fall upon the glacier surface and are carried
forward as passengers in the direction of the ice margin. They are
either visible as long and narrow ridges or trains following the
directions of the steepest slope (Fig. 302), or they become buried
under fresh falls of snow and only again become visible where summer
melting has lowered the glacier surface in the vicinity of its margin.
These longitudinal trains of rock fragments upon the glacier surface
always have their starting point at the lower margin of one of the
nunataks, and are known as _medial moraines_ (Fig. 301, p. 273, and
Fig. 302). Inside the zone of nunataks the glacier surface is, however,
clear of rock débris except where dust has been blown on by the wind,
and this extends for a few miles only. The material of the medial
moraines is a collection of angular blocks whose surfaces are the
result of frost rending, for in their travel above the ice they are
subjected to no abrading processes.
[Illustration: FIG. 303.—Moat surrounding a nunatak in Victoria Land
(after Scott).]
A contrasted type of surface moraines upon the Greenland glacier,
instead of being parallel to the direction of ice movement, is directed
transversely or parallel to the margins. The materials of these
moraines are more rounded fragments of rock which have come up from
the bottom layers, and we shall again refer to the origin of such
moraines after the subglacial conditions have been considered.
=The grinding mill beneath the ice.=—If, now, we examine the front of
a glacier tongue which goes out from the inland ice, we find that while
the upper portion is white and mainly free from rock débris (plate
13 A), the lower zone is of a dark color and crowded with layers of
pebbles and bowlders which have been planed, polished, and scratched in
a quite remarkable manner. The ice front is itself subject to forward
and retrograde migrations of short period, but it is easily seen that
in the main its larger movement has been a retrograde one. The ground
from which it has lately withdrawn is generally a hard rock floor
unweathered, but smooth, polished, and scratched in the same manner
as the bowlders which are imbedded within the ice. It is perfectly
apparent that the latter have been derived from some portion of the
rock basement upon which the glacier still rests, and that floor and
bowlders have alike been ground smooth by mutual contact under pressure.
This erosion beneath the ice is accomplished by two processes; namely,
_plucking_ and _abrasion_. Wherever the rock over which the glacier
moves has stood up in projecting masses and is riven by fissure planes
of any kind, the ice has found it easy to remove it in larger or
smaller fragments by a quarrying process described as plucking. The
rock may be said to be torn away in blocks which are largely bounded by
the preëxisting fissure planes. Over relatively even surfaces plucking
has little importance, but where there are noteworthy inequalities
of surface upon the glacier bed, those sides which are away from the
oncoming ice (_lee_ side) are degraded by plucking in such a manner as
sometimes to leave steep and ragged fracture surfaces. The tools of
the ice thus acquired in the process of plucking are quickly frozen
into the lowest ice layers, and being now dragged along the floor
they abrade in the same manner as does a rasp or file. These tools of
the ice are themselves worn away in the process and are thus given
their characteristic shapes. Just as the lapidary grinds the surface
of a jewel into facets by imbedding the gem in a matrix, first in one
and then in another position, each time wearing down the projecting
irregularities through contact with the abrading surface; so in like
manner the rock fragment is held fast at the bottom of the glacier
until “soled” or “shod”, first upon one side and then upon another.
Accidental contact with some obstruction upon the floor may suffice
to turn the fragment and so expose a new surface to wear upon the
abrading floor. Minor obstructions coming in contact with one side of
the fragment only, may turn it in its own plane without overturning.
Evidence of such interruptions can be later read in the different
directions of striæ upon the same facet (plate 17 A).
[Illustration:
FIG. 304.—A glacier pavement of Permo-Carboniferous age in South
Africa. The striæ running in the direction of the observer are
prominent and a noteworthy gouging of the surface is to be noted to
the right in the middle distance (after Davis).]
The floor beneath the glacier is reduced by the abrading process to a
more or less smooth and generally flattened or rounded surface—the
so-called _glacier pavement_ (Fig. 304). To accomplish this all former
mantle rock due to weathering processes must first be cleared away, and
the firm unaltered rock beneath is wherever susceptible of it given a
smooth polish although locally scored and scratched by the grinding
bowlders. The earlier projections of the surface of the floor, if not
entirely planed away, are at least transformed into rounded shoulders
of rock, which from their resemblance to closely crowded backs in a
flock of sheep have been called “sheep backs” or “_roches moutonnées_.”
Thus the effect of the combined action of the processes of plucking and
abrasion is to reduce the accent of the relief and to mold the contours
of the rock in smoothly flowing curves, generally of large radius.
=The lifting of the grinding tools and their incorporation within the
ice.=—Wherever the ice is locally held in check by the projecting
nunataks, relief is found between such obstructions, and there the flow
of the ice has a correspondingly increased velocity (Fig. 305 _b_).
If the obstructions are not of large dimensions, the ice which flows
around the outer edges is soon joined to that which passes between the
obstructions and so normal conditions of flow are restored below the
nunataks. The locally rapid flow of the ice is, therefore, restricted
to a relatively short distance, the passageway between the nunataks,
and the conditions are thus to be likened to the fall of water at a
raceway due to the sudden descent of its surface from the level of
the reservoir to the level of the stream in the outlet. As is well
known, there is under these conditions a prodigious scour upon the
bottom which tends to dig a pit just above and below the dam—a _scape
colk_—and carry the materials up to the surface below the pit. Such
a tendency was well illustrated by the behavior of the water at the
opening of the Neu Haufen dam below the city of Vienna (Fig. 305 _a_).
In the case of ice, material from the bottom may by the upward current
be brought up to the surface of the glacier at the lower edge of the
colk and thus produce a type of local surface moraine of horseshoe
form with its direction generally transverse to the direction of ice
movement (Fig. 305 _b_).
[Illustration:
FIG. 305.—_a_, Map showing pit excavated by the current below the
opening in a dam. _b_, Nunataks and surface moraines on the Greenland
ice. Dalager’s Nunataks (after Suess).]
Any obstruction upon the pavement of the glacier apparently exerts a
larger or smaller tendency to elevate the bowlders and pebbles and
incorporate them within the ice. Rock débris thus incorporated is
described as _englacial_ drift. In the case of Greenland glaciers this
material seems at the ice front to be largely restricted to the lower
100 feet (plate 13 A).
Near the front of the inland ice the increased slope of the upper
surface greatly increases the flow of the upper ice layers in
comparison with those nearer the bottom, so that the upper layers
override the lower as they would an obstruction. The englacial drift
is either for this reason or because of rock obstructions brought to
the surface, where it yields parallel ridges corresponding in direction
to the glacier margin. Such transverse surface moraines are thus in
many respects analogous to those which appear about the lower margins
of scape colks. In contrast to the longitudinal or medial surface
moraines the materials of the transverse moraines are more faceted and
rounded—they have been abraded upon the glacier pavement.
=Melting upon the glacier margins in Greenland.=—During the short but
warm summer season, the margins of the Greenland ice are subject to
considerable losses through surface melting. When the uppermost ice
layer has attained a temperature of 32° Fahrenheit, melting begins
and moves rapidly inward from the glacier margin. In late spring the
surface of the outer marginal zone is saturated with water, and this
zone of slush advances inward with the season, but apparently never
transgresses the inner border of what we have generally referred to as
the marginal zone of the ice characterized by relatively steep slopes,
crevasses, and nunataks. Upon the ice within this zone are found
streams large enough to be designated as rivers and these are connected
with pools, lakes, and morasses. The dirt and rock fragments imbedded
in the ice are melted out in the lowering of the surface, so that late
in the season the ice presents a most dirty aspect. At the front of the
great mountain glaciers of Alaska, a more vigorous operation of the
same process has yielded a surface soil in which grow such rank forests
as entirely to mask the presence of the ice beneath.
In addition to the visible streams upon the surface of the Greenland
ice, there are others which flow beneath and can be heard by putting
the ear to the surface. All surface streams eventually encounter the
marginal crevasses and plunge down in foaming cascades, producing the
well known “glacier wells” or “glacier mills.” The progress of the
water is now throughout in tunnels within the ice until it again makes
its appearance at the glacier margin.
[Illustration:
FIG. 306.—Marginal moraine now forming at the edge of Greenland inland
ice, showing a smooth rock pavement outside it. A small lake with a
partial covering of lake ice occupies a hollow of this pavement (after
von Drygalski).]
=The marginal moraines.=—Study of both the Greenland and Antarctic
glaciers has shown that if we disregard the smaller and short-period
migrations of the ice front, the general later movement has been a
retrograde one—we live in a receding hemicycle of glaciation. The
earlier Greenland glacier has now receded so as to expose large areas
of the former glacier pavement. In places this pavement is largely
bare, indicating a relatively rapid retirement of the ice front, but
at all points at which the ice margin was halted there is now found a
ridge of unassorted rock materials which were dropped by the ice as it
melted (Fig. 306). Such ridges, composed of the unassorted materials
described as _till_, come to have a festooned arrangement largely
concentric to the ice margin, and are the _marginal_ or _terminal
moraines_ (see Fig. 336, p. 312). Marginal moraines, if of large
dimensions, usually have a hummocky surface, and are apt to be composed
of rock fragments of a wide range of size from rock flour (clay) to
large bowlders (plate 17 A), which may represent many types since they
have been plucked by the glacier or gathered in at its surface from
many widely separated localities.
[Illustration:
FIG. 307.—Small lake impounded between the ice front and a moraine
which it has recently built. Greenland (after von Drygalski).]
As the glacier front retires from the moraine which it has built up,
the water which emerges from beneath the ice is impounded behind the
new dam so as to form a lake of crescentic outline (Fig. 307). Such
lakes are particularly short-lived, for the reason that the water finds
an outlet over the lowest point in the crest of the moraine and easily
cuts a gorge through the loose materials, thus draining the lake (Fig.
308). Thereafter, the escaping water flows in a braided stream across
the late lake bottom and thence at the bottom of the gorge through the
moraine.
[Illustration:
FIG. 308.—View of a drained lake bottom between the moraine-covered
ice front in the foreground and an abandoned marginal moraine in the
middle distance. The water flows from the ice front in a braided stream
and passes out through the moraine in a narrow gorge. Variegated
glacier, Alaska (after Lawrence Martin).]
=The outwash plain or apron.=—The water which descends from the
glacier surface in the glacier wells or mills, eventually arrives at
the bottom, where it follows a sinuous course within a tunnel melted
out in the ice. Much of this water may issue at the ice front beneath
the coarse rock materials which are found there, and so be discovered
with the ear rather than by the eye. The water within the tunnels not
flowing with a free surface but being confined as though it were in
a pipe, may, however, reach the glacier margin under a hydrostatic
pressure sufficient to carry it up rising grades. Inasmuch as it is
heavily charged with rock débris and is suddenly checked upon arriving
at the front it deposits its burden about the ice margin so as to build
up plains of assorted sands and gravels, and over this surface it flows
in ever shifting serpentine channels of braided type (Fig. 308). Such
plains of glacier outwash are described as _outwash plains_ or _outwash
aprons_.
Rising as it does under hydrostatic pressure the water issuing at the
glacier front may find its way upward in some of the crevasses and so
emerge at a level considerably above the glacial floor. It may thus
come about that the outwash plain is built up about the nose of the
glacier so as partially to bury it from sight. When now the ice front
begins a rapid retirement, a depression or _fosse_ (Fig. 309 and Fig.
339, p. 314) is left behind the outwash plain and in front of the
moraine which is built up at the next halting place.
[Illustration: FIG. 309.—Diagrams to show the manner of formation
and the structure of an outwash plain, and the position of the fosse
between this and the moraine.]
=The continental glacier of Antarctica.=—In Victoria Land, upon the
continent of Antarctica, so far as exploration has yet gone, the
continental glacier is held back by a rampart of mountains, as has been
shown to be true of the inland ice of Greenland. The same flat dome or
shield has likewise been found to characterize its upper surface (Fig.
310).
The most noteworthy differences between the inland ice masses of
Greenland and Antarctica are to be ascribed to the greater severity of
the Antarctic climate and to the more ample nourishment of the southern
glacier measured by the land area which it has submerged. There is here
no marginal land ribbon as in Greenland, but the glacier covers all
the land and is, moreover, extended upon the sea as a broad floating
terrace—the shelf ice (Fig. 311). This barrier at its margin puts a
bar to all further navigation, rising as it does in some cases 280 feet
above the sea and descending to even greater depths below (plate 15 B).
[Illustration:
FIG. 310.—Map showing the inland ice of Victoria Land bordered by the
shelf ice of the Great Ross Barrier. The arrows show the direction of
the prevailing winds (based on maps by Scott and Shackleton).]
In that portion of Antarctica which was explored by the German
expedition, the inland ice is not as in Victoria Land restrained
within walls of rock, but is spread out upon the continent so as
to assume its natural ice slopes, which are therefore much flatter
than those examined in Greenland and Victoria Land. Here in Kaiser
Wilhelm Land the ice rises at its sea margin in a cliff which is
from 130 to 165 feet in height, then upon a fairly steeply curving
slope to an elevation of perhaps a thousand feet. Here the grades
have become relatively level, and on ever flatter slopes the surface
appears to continue into the distant interior (plate 14). Near the
ice margin numerous fissures betray a motion within the mass which
exact measurements indicate to be but one foot per day, and at a
distance of a mile and a quarter from the margin even this slight
value has diminished by fully one eighth. It can hardly be doubted
that at moderate distances only within the ice margin, the glacier is
practically without motion.
┌────────────────────────────────────────────────────────────────┐
│ PLATE 14. │
│ │
│ [Illustration: View of the margin of the Antarctic continental │
│ glacier in Kaiser Wilhelm Land (after E. v. Drygalski).] │
└────────────────────────────────────────────────────────────────┘
Rain or general melting conditions being unknown in Antarctica, a
striking contrast is offered to the marginal zone of the Greenland
continent. This is to a large extent explained by the existence upon
the northern land mass of a coastland ribbon which becomes quickly
heated in the sun’s rays, and both by warming the air and by radiating
heat to the ice it causes melting and produces local air temperatures
which in summer may even be described as hot. About Independence Bay in
latitude 82° N. and near the northernmost extremity of Greenland, Peary
descended from the inland ice into a little valley within which musk
oxen were lazily grazing and where bees buzzed from blossom to blossom
over a gorgeous carpet of flowers.
[Illustration: FIG. 311.—Sections across the inland ice of Victoria
Land, Antarctica, with the shelf ice in front (after Shackleton).]
=Nourishment of continental glaciers.=—Explorations upon and about the
glaciers of Greenland and Antarctica have shown that the circulation
of air above these vast ice shields conforms to a quite simple and
symmetrical model subject to spasmodic pulsations of a very pronounced
type. Each great ice mass with its atmospheric cover constitutes a sort
of refrigerating air engine and plays an important part in the wind
system of the globe. (See Fig. 291, p. 263). Both the domed surface and
the low temperature of the glacier are essential to the continuation of
this pulsating movement within the atmosphere (Fig. 312). The air layer
in contact with the ice is during a period of calm cooled, contracted,
and rendered heavier, so that it begins to slide downward and outward
upon the domed surface in all directions. The extreme flatness of
the greater portion of the glacier surface—a fraction only of one
degree—makes the engine extremely slow in starting, but like all
bodies which slide upon inclined planes, the velocity of its movement
is rapidly accelerated, until a blizzard is developed whose vigor is
unsurpassed by any elsewhere experienced.
[Illustration: FIG. 312.—Diagram to show the nature of the fixed
glacial anticyclone above continental glaciers and the process by which
their surface is shaped.]
The effect of such centrifugal air currents above the glacier is to
suck down the air of the upper currents in order to supply the void
which soon tends to develop over the central portion of the glacier
dome. This downward vortex, fed as it is by inward-blowing, high-level
currents, and drained by outwardly directed surface currents, is what
is known as an _anticyclone_, here fixed in position by the central
embossment of the dome.
The air which descends in the central column is warmed by compression,
or adiabatically, just as air is warmed which is forced into a rubber
tire by the use of a pump. The moisture congealed in the cirrus clouds
floating in the uppermost layer of the convective zone, is carried
down in this vortex and first melted and in turn evaporated, due to
the adiabatic effect. This fusion and evaporation of the ice by its
transformation of latent, to sensible, heat, in a measure counteracts,
and so retards, the adiabatic elevation of temperature within the
column. Eventually the warm air now charged with water vapor reaches
the ice surface, is at once chilled, and its burden of moisture
precipitated in the form of fine snow needles, the so-called “frost
snow”, which in accompaniment to the sudden elevation of temperature is
precipitated at the termination of a blizzard.
The warming of the air has, however, had the effect of damping as it
were, the engine stroke, and, as the process is continued, to start a
reverse or upward current within the chimney of the anticyclone. The
blizzard is thus suddenly ended in a precipitation of the snow, which
by changing the latent heat of condensation to sensible heat tends to
increase this counter current.
[Illustration: FIG. 313.—Snow deltas about the margins of the Fan
glacier outlet of Greenland (after Chamberlin).]
=The glacier broom.=—During the calm which succeeds to the blizzard,
heat is once more abstracted from the surface air layer, and a new
outwardly directed engine stroke is begun. The tempest which later
develops acts as a gigantic centrifugal broom which sweeps out to
the margins of the glacier all portions of the latest snowfall which
have not become firmly attached to the ice surface. The sweepings
piled up about the margin of continental glaciers have been described
as fringing glaciers, or the glacial fringe. The northern coast of
Greenland and Grant Land are bordered by a fringe of this nature (plate
14 A, and Fig. 315, p. 288). It is by the operation of the glacier
broom that the inland ice is given its characteristic shield-like shape
(Fig. 312). The granular nature of the snow carried by the wind is well
brought out by the little snow deltas about the margins of Greenland
ice tongues (Fig. 313). Obviously because of the presence of the
vigorous anticyclone, no snows such as nourish mountain glaciers can be
precipitated upon continental glaciers except within a narrow marginal
zone, and, as shown by Nansen rock dust from the coastland ribbon and
from the nunataks of Greenland, is carried by a few miles inside the
western margin, and not at all within the eastern.
[Illustration: FIG. 314.—Sea ice of the Arctic region in lat. 80° 5´
N. and long. 2° 52´ E. (after Duc d’Orleans).]
=Field and pack ice.=—Within polar regions the surface of the sea
freezes during the long winter season, the product being known as
_sea-ice_ or _field-ice_ (Fig. 314). This ice cover may reach a
thickness by direct freezing of eight or more feet, and by breaking up
and being crowded above and below neighboring fragments may increase to
a considerably greater thickness. Ice thus crowded together and more or
less crushed is described as _pack ice_ or _the pack_.
The pack does not remain stationary but is continually drifting with
the wind and tide, first in one direction and then in another, but
with a general drift in the direction of the prevailing winds. Because
of the vast dimensions of the pack, the winds over widely separated
parts may be contrary in direction, and hence when currents blow
toward each other or when the ice is forced against a land area, it
is locally crushed under mighty pressures and forced up into lines of
_hummocks_—the so-called _pressure ridges_. At other times, when the
winds of widely separated areas blow away from each other, the pack is
parted, with the formation of lanes or _leads_ of open water.
If seen in bird’s-eye view the lines of hummocks would according to
Nansen be arranged like the meshes of a net having roughly squared
angles and reaching to heights of 15 to 25, rarely 30, feet above the
general surface of the pack. The ice within each mesh of the network
is a _floe_, which at the times of pressure is ground against its
neighbors and variously shifted in position. At the margin of the pack
these floes become separated and float toward lower latitudes until
they are melted.
=The drift of the pack.=—The discovery of the drift in the Arctic
pack is a romantic chapter in the history of polar exploration, and
has furnished an example of faith in scientific reasoning and judgment
which may well be compared with that of Columbus. The great figure in
this later discovery is the Norwegian explorer Fridtjof Nansen, and to
the final achievement the ill-fated _Jeannette_ expedition contributed
an important part.
The _Jeannette_ carrying the American exploring expedition was in 1879
caught in the pack to the northward of Wrangel Island (Fig. 315), and
two years later was crushed by the ice and sunk to the northward of
the New Siberian Islands. In 1884 various articles, including a list
of stores in the handwriting of the commander of the _Jeannette_, were
picked up at Julianehaab near the southern extremity of Greenland
but upon the western side of Cape Farewell. Nansen, having carefully
verified the facts, concluded that the recovered articles could have
found their way to Julianehaab only by drifting in the pack across the
polar sea, and that at the longest only five years had been consumed
in the transit. After being separated from the pack the articles must
have floated in the current which makes southward along the east coast
of Greenland and after doubling Cape Farewell flows northward upon the
west coast. It was clear that if they had come through Smith Sound they
would inevitably have been found upon the other shore of Baffin Bay. In
confirmation of this view there was found at Godthaab, a short distance
to the northward of Julianehaab (Fig. 315), an ornamented Alaskan
“throwing stick” which probably came by the same route. Moreover,
large quantities of driftwood reach the shores of Greenland which have
clearly come from the Siberian coast, since the Siberian larch has
furnished the larger quantity.
[Illustration: FIG. 315.—Map of the north polar regions, showing the
area of drift ice and the tracks of the _Jeannette_ and the _Fram_
(compiled from various maps).]
Pinning his faith to these indubitable facts, Nansen built the _Fram_
in such a manner as to resist and elude the enormous pressures of
the ice pack, stocked her with provisions sufficient for five years,
and by allowing the vessel to be frozen into the pack north of the
New Siberian Islands, he consigned himself and his companions to the
mercy of the elements. The world knows the result as one of the most
remarkable achievements in the long history of polar exploration. The
track of the _Fram_, charted in Fig. 315, considered in connection with
that of the _Jeannette_, shows that the Arctic pack drifts from Bering
Sea westward until near the northeastern coast of Greenland.
Special casks were for experimental purposes fastened in the ice to
the north of Behring Strait by Melville and Bryant, and two of these
were afterwards recovered, the one near the North Cape in northern
Norway, and the other in northeastern Iceland (see map, Fig. 315).
Peary’s trips northward in 1906 and 1909 from the vicinity of Smith
Sound have indicated that between the Pole and the shores of Greenland
and Grant Land the drift is throughout to the eastward, corresponding
to the westerly wind. Upon this border the great area of Arctic drift
ice is in contact with great continental glaciers bordered by a glacier
fringe. Admiral Peary has shown that instead of consisting of frozen
sea ice, the pack is here made up of great floes from 20 to 100 feet in
thickness and that these have been derived from the glacier fringe.
Whenever the blizzards blow off the inland ice from the south, leads
are opened at the margin of the fringe and may carry strips from the
latter northward across the lead. With favorable conditions these
leads may be closed by thick sea ice so that with the occurrence of
counter winds from the north they do not entirely return to their
original position. A continuance of this process may have resulted in
the heavy floe ice to the northward of Greenland, which, acting as
an obstruction, may have forced the thinner drift ice to keep on the
European side of the Arctic pack.
[Illustration: FIG. 316.—The shelf ice of Coats Land with the
surrounding pack ice showing in the foreground (after Bruce).]
About the Antarctic continent there is a broad girdle of pack ice
which, while more indolent in its movements than the Arctic pack, has
been shown by the expeditions of the _Belgica_ and the _Pourquoi-Pas_
to possess the same kind of shifting movements. In the southern spring
this pack floats northward and is to a large extent broken up and
melted on reaching lower latitudes.
[Illustration: FIG. 317.—Tidewater cliff at the front of a glacier
tongue from which icebergs are born.]
=The Antarctic shelf ice.=—It has been already pointed out that the
inland ice of Antarctica is in part at least surrounded by a thick
snow and ice terrace floating upon the sea and rising to heights of
more than 150 feet above it (plate 15 B and Fig. 316). The visible
portions of this shelf-ice are of stratified compact snow, and the
areas which have thus far been studied are found in bays from which
dislodgment is less easily effected. The origin of the shelf ice is
believed to be a sea-ice which because not easily detached at the time
of the spring “break-up” is thickened in succeeding seasons chiefly by
the deposition of precipitated and drifted snow upon its surface, so
that it is bowed down under the weight and sunk to greater and greater
depths in the water. To some extent, also, it is fed upon its inner
margin by overflow of glacier ice from the inland ice masses.
=Icebergs and snowbergs and the manner of their birth.=—Greenland
reveals in the character of its valleys the marks of a large subsidence
of the continent—the serpentine inlets or fjords by which its coast is
so deeply indented. Into the heads of these fjords the tongues from the
inland ice descend generally to the sea level and below. The glacier
ice is thus directly attacked by the waves as well as melted in the
water, so that it terminates in the fjords in great cliffs of ice (Fig.
317). It is also believed to extend beneath the water surface as a long
toe resting upon the bottom (Fig. 319).
┌───────────────────────────────────────────────────────────────────┐
│ PLATE 15. │
│ │
│ [Illustration: _A._ An Antarctic ice foot with boat party landing │
│ (after R. F. Scott).] │
│ │
│ [Illustration: _B._ A near view of the front of the Great Ross │
│ Barrier, Antarctica (after R. F. Scott).] │
└───────────────────────────────────────────────────────────────────┘
[Illustration: FIG. 318.—A Greenlandic iceberg after a long journey in
warm latitudes.]
The exposed cliff is notched and undercut by the waves in the same
manner as a rock cliff, and the upper portions override the lower so
that at frequent intervals small masses of ice from this front separate
on crevasses, and toppling over, fall into the water with picturesque
splashes. Such small bergs, whose birth may be often seen at the cliff
front of both the Greenland and Alaskan glaciers, have little in common
with those great floating islands of ice that are drifted by the winds
until, wasted to a fraction only of their former proportions, they
reach the lanes of transatlantic travel and become a serious menace to
navigation (Fig. 318).
[Illustration: FIG. 319.—Diagram showing one way in which northern
icebergs may be born from the glacier tongue (after Russell).]
Northern icebergs of large dimensions are born either by the lifting of
a separated portion of the extended glacier toe lying upon the bottom
of the fjord, or else they separate bodily from the cliff itself,
apparently where it reaches water sufficiently deep to float it. In
either case the buoyancy of the sea water plays a large rôle in its
separation.
If derived from the submerged glacier toe (Fig. 319), a loud noise is
heard before any change is visible, and an instant later the great
mass of ice rises out of the water some distance away from the cliff,
lifting as it does so a great volume of water which pours off on all
sides in thundering cascades and exposes at last a berg of the deepest
sapphire blue. The commotion produced in the fjord is prodigious, and a
vessel in close proximity is placed in jeopardy.
Even larger bergs are sometimes seen to separate from the ice cliff, in
this case an instant before or simultaneously, with a loud report, but
such bergs float away with comparatively little commotion in the water.
[Illustration: FIG. 320.—A northern iceberg surrounded by sea ice.]
The icebergs of the south polar region are usually built upon a far
grander scale than those of the Arctic regions, and are, further, both
distinctly tabular in form and bounded by rectangular outlines (Fig.
321). Whereas the large bergs of Greenlandic origin are of ice and blue
in color, the tabular bergs of Antarctica might better be described
as _snowbergs_, since they are of a blinding whiteness and their
visible portions are either compacted snow or alternating thick layers
of compact snow and thin ribbons of blue ice, the latter thicker and
more abundant toward the base. All such bergs have been derived from
the shelf ice and not from the inland ice itself. Blue icebergs which
have been derived from the inland ice have been described from the
one Antarctic land that has been explored in which that ice descends
directly to the sea.
[Illustration: FIG. 321.—Tabular Antarctic iceberg separating from the
shelf ice (after Shackleton).]
In both the northern and southern hemispheres those bergs which have
floated into lower latitudes have suffered profound transformations.
Their exposed surfaces have been melted in the sun, washed by the
rain, and battered by the waves, so that they lose their relatively
simple forms but acquire rounded surfaces in place of the early angular
ones (Fig. 318, p. 291). Sir John Murray, who had such extended
opportunities of studying the southern icebergs from the deck of the
_Challenger_, has thus described their beauties:
“Waves dash, against the vertical faces of the floating ice island as
against a rocky shore, so that at the sea level they are first cut
into ledges and gullies, and then into caves and caverns of the most
heavenly blue, from out of which there comes the resounding roar of
the ocean, and into which the snow-white and other petrels may be seen
to wing their way through guards of soldier-like penguins stationed
at the entrances. As these ice islands are slowly drifted by wind and
current to the north, they tilt, turn and sometimes capsize, and then
submerged prongs and spits are thrown high into the air, producing
irregular pinnacled bergs higher, possibly, than the original
table-shaped mass.”
READING REFERENCES FOR CHAPTERS XX AND XXI
General:—
I. C. RUSSELL. Glaciers of North America. Ginn, Boston, 1897, pp. 210,
pls. 22.
CHAMBERLIN and SALISBURY. Geology, vol. 1, pp. 232-308.
H. HESS. Die Gletscher, Braunschweig, 1904, pp. 426 (illustrated).
WILLIAM H. HOBBS. Characteristics of Existing Glaciers. Macmillan,
1911, pp. 301, pls. 34.
Special districts of mountain glaciers:—
JAMES D. FORBES. Travels Through the Alps of Savoy and other Parts
of the Pennine Chain with Observations on the Phenomena of Glaciers.
Edinburgh, 1845, pp. 456, pls. 9, maps 2.
A. PENCK, E. BRÜCKNER, et L. DU PASQUIER. Le système glaciare des
alpes, etc., Bull. Soc. Sc. Nat. Neuchâtel, vol. 22, 1894, pp. 86.
E. RICHTER. Die Gletscher der Ostalpen. Stuttgart, 1888, pp. 306, 7
maps.
JAMES D. FORBES. Norway and Its Glaciers, etc. Edinburgh, 1853, pp.
349, pls. 10, map.
I. C. RUSSELL. Existing Glaciers of the United States, 5th Ann. Rept.
U. S. Geol. Surv., 1885, pp. 307-355, pls. 32-55; Glaciers of Mt.
Ranier, 18th Ann. Rept. U. S. Geol. Surv., 1898, pp. 349-423, pls.
65-82.
W. H. SHERZER. Glaciers of the Canadian Rockies and Selkirks, Smith.
Cont. to Knowl. No. 1692, Washington, 1907, pp. 135, pls. 42.
H. F. REID. Studies of Muir Glacier, Alaska, Nat. Geogr. Mag., vol. 4,
1892, pp. 19-84, pls. 1-16.
I. C. RUSSELL. Malaspina Glacier, Jour. Geol., vol. 1, 1893, pp.
219-245.
G. K. GILBERT. Harriman Alaska Expedition, vol. 3, Glaciers, 1904, pp.
231, pls. 37.
W. M. CONWAY. Climbing and Exploration in the Karakoram Himalayas,
Maps and Scientific Reports, 1894, map sheets I-II.
FANNY BULLOCK WORKMAN and WILLIAM HUNTER WORKMAN. The Hispar Glacier,
Geogr. Jour., vol. 35, 1910, pp. 105-132, 7 pls. and map.
The cycle of glaciation:—
WILLIAM H. HOBBS. The Cycle of Mountain Glaciation, Geogr. Jour., vol.
36, 1910, pp. 146-163, 268-284.
Upper and lower cloud zones of the atmosphere:—
R. ASSMANN, A. BERSON, and H. GROSS. Wissenschaftliche Luftfahrten
ausgeführt vom deutschen Verein zur Förderung der Luftschiffahrt in
Berlin, 1899-1900, 3 vols.
E. GOLD and W. A. HARWOOD. The Present State of our Knowledge of
the Upper Atmosphere as Obtained by the Use of Kites, Balloons, and
Pilot-balloons, Rept. Brit. Assoc. Adv. Sci., 1909, pp. 1-55.
W. H. MOORE. Descriptive Meteorology, Appleton, New York, 1910, pp.
95-136.
WILLIAM H. HOBBS. The Pleistocene Glaciation of North America Viewed
in the Light of our Knowledge of Existing Continental Glaciers, Bull.
Am. Geogr. Soc., vol. 42, 1911, pp. 647-650.
The continental glacier of Greenland:—
F. NANSEN. The First Crossing of Greenland, 2 vols, Longmans, London,
1890 (the scientific results are contained in an appendix to volume 2,
pp. 443-497).
R. E. PEARY. A Reconnaissance of the Greenland Inland Ice, Jour. Am.
Geogr. Soc., vol. 19, 1887, pp. 261-289; Journeys in North Greenland,
Geogr. Jour., vol. 11, 1898, pp. 213-240.
T. C. CHAMBERLIN. Glacier Studies in Greenland, Jour. Geol., vol.
2, 1894, pp. 649-668, 768-788, vol. 3, pp. 61-69, 198-218, 469-480,
565-582, 668-681, 833-843, vol. 4, pp. 582-592, 769-810, vol. 5, pp.
229-245; Recent glacial studies in Greenland (Presidential address),
Bull. Geol. Soc. Am., vol. 6, 1895, pp. 199-220, pls. 3-10.
R. S. TARR. The Margin of the Cornell Glacier, Am. Geol., vol. 20,
1897, pp. 139-156, pls. 6-12.
R. D. SALISBURY. The Greenland Expedition of 1895, Jour. Geol., vol.
3, 1895, pp. 875-902.
E. V. DRYGALSKI. Grönland Expedition der Gesellschaft für Erdkunde zu
Berlin 1891-1893, Berlin, 1897, 2 vols., pp. 551 and 571, pls. 53,
maps 10.
WILLIAM H. HOBBS. Characteristics of the Inland Ice of the Arctic
Regions, Proc. Am. Phil. Soc., vol. 49, 1910, pp. 57-129, pls. 26-30.
The Antarctic continental glacier:—
R. F. SCOTT. The Voyage of the _Discovery_. London, 2 vols., 1905.
E. H. SHACKLETON. The Heart of the Antarctic. London, 2 vols., 1910.
E. VON DRYGALSKI. Zum Kontinent des eisigen Südens, Deutsche
Südpolar-Expedition, Fahrten und Forschungen des “Gauss”, 1901-1903,
Berlin, 1904, pp. 668, pls. 21.
OTTO NORDENSKIÖLD and J. S. ANDERSSON. Antarctica or Two Years Amongst
the Ice of the South Pole. London, 1905, pp. 608, illustrated.
E. PHILIPPI. Ueber die fünf Landeis-Expeditionen, etc., Zeit. f.
Gletscherk., vol. 2, 1907, pp. 1-21.
Nourishment of continental glaciers:—
WILLIAM H. HOBBS. Characteristics of the Inland Ice of the Arctic
Regions, Proc. Am. Phil. Soc., vol. 49, 1910, pp. 96-110; The Ice
Masses on and about the Antarctic Continent, Zeit. f. Gletscherk.,
vol. 5, 1910, pp. 107-120; Characteristics of Existing Glaciers. New
York, 1911, pp. 143-161, 261-289. Pleistocene Glaciation of North
America Viewed in the Light of our Knowledge of Existing Continental
Glaciers, Bull. Am. Geogr. Soc., vol. 43, 1911, pp. 641-659.
Field and pack ice:—
EMMA DE LONG. The Voyage of the _Jeannette_, the ship and ice journals
of George W. de Long, etc. Berlin, 1884, 2 vols., chart in back of
vol. 1.
ROBERT E. PEARY. The Discovery of the North Pole (for further
references on both sea and pack ice and Antarctic shelf ice, consult
Hobbs’s Characteristics of Existing Glaciers, pp. 210-213, 242-244).
Icebergs:—
WYVILLE THOMSON. Challenger Report, Narrative, vol. 1, 1865, Pt. i,
pp. 431-432, pls. B-D.
I. C. RUSSELL. An Expedition to Mt. St. Elias, Nat. Geogr. Mag., vol.
3, 1891, pp. 101-102, fig. 1.
H. F. REID. Studies of Muir Glacier, Alaska, _ibid._, vol. 4, 1892,
pp. 47-48.
E. VON DRYGALSKI. Grönland-Expedition, etc., vol. 1, pp. 367-404.
M. C. ENGELL. Ueber die Entstehung der Eisberge, Zeit. f. Gletscherk.,
vol. 5, 1910, pp. 112-132.