ICE AND ICEBERGS
A knowledge of the nomenclature of polar phenomena is an essential
preliminary to the study of the history of Arctic adventure. We must
know the meanings of words which constantly recur and which form, as
it were, the dialect of our subject. We begin then with the names for
different forms and appearances of polar ice.
It used to be thought that ice could only be formed in creeks and
inlets of the coast. It is now known that young ice forms on the
surface of the open sea, and thickens into dense masses, where it is
not disturbed by waves. _Young ice_ then is the thin film first formed
on the surface of the sea, when the temperature is sufficiently low in
the autumn. When it becomes rather thicker it is called _bay ice_. In
a ruffled sea the pieces of _bay ice_ strike each other on every side,
becoming rounded and having the edges turned up. This is _pancake ice_.
In a year, under favouring circumstances, the ice attains a thickness
of six feet, in two years of nine feet. Sometimes masses of ice
under-run each other, and the result is a thickness of 20 to 50 and
even 100 feet.
A _field_ is an expanse of ice of such extent that its termination is
not bounded by the horizon. A _floe_ is the same as a _field_ except
that its whole extent can be seen. _Floe bergs_, occurring on the
northern shores of the polar ocean, are large masses of sea ice, broken
off from ancient floes of great thickness, and forced upon the shore.
_Ground ice_ is formed on rivers or shallow inlets while the sea, as a
whole, remains unfrozen. _Land ice_ or the _land floe_ is ice attached
to the land.
_Field ice_ varies in thickness from 15 to 20 feet. On its surface
there is a deposit of several feet of snow which melts in the height
of summer, forming numerous fresh-water pools on the ice. Generally
an ice-field is traversed by long ridges of _hummocks_, often 40
to 50 feet high, brought about by the collision of two fields, the
irresistible pressure causing them to rise up.
The term _floe_ is applied to pieces which are from half a mile to a
mile in diameter. Pieces smaller than a floe are called _drift ice_.
When drift ice is so extensive that its limits cannot be seen, it is
called a _pack_, when the pieces do not touch an _open pack_, when they
are pressed together a _close pack_. A _patch_ is a collection of drift
ice, the limits of which are visible. A _stream_ is a drifting line
of drift ice. A _tongue_ is a projecting point of ice, under water.
A _calf_ is a mass of loose ice lying under a floe near its margin,
and, when disengaged from that position, rising with violence to the
surface. _Brash ice_ consists of fragments and nodules, the wreck of
other kinds of ice, and _sludge_ is the term applied to smaller pieces,
generally saturated by the sea.
A bright white line on the horizon, seen over an ice-field, and
denoting more ice, is known as the _ice-blink_. Over land or large
masses of ice it generally has a yellowish tinge. On the other hand a
blue streak on the horizon, denoting open water, is called a _water
sky_. A _lane_ or _lead_ is a narrow track of open water between floes
or pack ice. _Rotten ice_ is old ice partially melted, and in part
honeycombed.
When a ship is forcibly pressed by ice floes on both sides she is said
to be _nipped_, and she is _beset_ when closely surrounded by ice. To
_bore_ is to enter the ice under press of sail or steam and to force a
way through by separating the masses. _Sallying_ is causing a ship to
roll by making the men run in a body from side to side, to relieve her
from adhesion of young ice.
An _ice foot_ along a coast line is caused by the accumulation of the
autumn snow-fall, as it drifts to the beach, being met by sea-water
with a temperature just below the freezing point of fresh water. It is
at once converted into ice, forming a solid wall from the bottom of the
sea, constantly maintained. The upper surface of an ice foot is level
with high water mark. The terrace above this wall, from its edge to the
base of the _talus_, has a width dependent on the land slope. Thus an
ice foot will not be found either where there are perpendicular cliffs
or low coast lines, but only along sloping high lands under special
conditions.
The most striking features in the polar landscape are the icebergs,
and they are wholly derived from the land, the large icebergs from
Greenland, from Spitsbergen much smaller ones. To understand their
origin and movements we must turn to the great continental mass
of Greenland. It consists of a vast ice-cap fringed by a strip of
mountainous coast, which is penetrated by deep fjords and flanked by
numerous off-lying rocks and islands. The area of Greenland is believed
to be 512,000 square miles, of which 320,000 form the inland ice, and
192,000 represent the fringing margin of mountains not permanently
ice-covered. The widest part is 900 miles across; at Disco in 70° N.
it is 480 miles and thence the two coasts converge until they meet in
a point at Cape Farewell in 59° 49′ N. The length of Greenland is 1400
miles. The Greenland ice-cap is by far the largest in the northern
hemisphere--a continuous covering of snow, _névé_[1], or ice resting on
land, known as the “Inland Ice.” From it descend glaciers or rivers of
solid ice, coming from their sources in the ice-cap.
The “Inland Ice” of Greenland rises to a height of 8000 feet, and
the deep fjords run for 80 or 100 miles before they end at the foot
of walls of ice rising abruptly from the water. These walls are the
terminations of glaciers from the inland ice, which, constantly
throwing off icebergs, are called discharging glaciers. There are eight
principal discharging glaciers on the west coast of Greenland[2]. On
the Greenland continent the snow, converted into ice by pressure, has
in the course of ages filled all the valleys, covered the mountain
tops, and formed a smooth plateau far above them, so that the thickness
of the inland ice is measured by thousands of feet. The ice walls at
the heads of the discharging glaciers are driven onwards by the force
of gravity, the pressure of the superincumbent mass behind them being
enormous. In some cases the rate of movement is as much as 28 yards in
a day.
A discharging glacier, on reaching the sea, has a thickness of at
least a thousand feet. It continues to slide along the bottom until it
reaches a point where the depth of the water has sufficient buoyant
force to lift it. Still it continues its course. The action of the
tides gives rise to fissures in the enormous mass, and at length
the foremost part is broken off, and drifts away as an iceberg. The
icebergs are discharged from the fjords in vast numbers, and are
eventually carried by the current of Baffin’s Bay and Davis Strait into
the Atlantic.
The icebergs are alike the grandest and the most beautiful features of
the Arctic seas. Only one-seventh of their bulk appears above water,
yet they may be hundreds of yards in circumference, and their peaks
reach a height of 300 ft. A grander sight can scarcely be conceived
than new-born icebergs drifting out from the fjord of their birthplace.
When the icebergs drift well out into the open sea the weathering
and consequent reduction in size begins. They eventually lose their
equilibrium and capsize. The part that has been long under water
becomes the upper part, and it is now that the bergs assume their most
fantastic shapes. Very often a large piece breaks off from the parent
berg, and falls into the sea, churning it up into creamy waves. This is
called _calving_.
The colour of an iceberg is opaque white. Scattered through the mass,
and sometimes visible on the surface, are strata of deep blue ice,
varying in width from one to several feet. They have an exquisitely
lovely effect, contrasting with the deep white of the rest of the berg.
These blue stripes may be formed by a filling up of the fissures in the
inland ice with water. Such refrigeration of the water in the fissures
may be an important agent in setting these great mountains of ice in
motion. Sometimes there is a passage right through an iceberg. But it
is when a line of icebergs is refracted on the horizon that the polar
scenery is converted into a veritable fairy land. Some are raised
up into lofty pillars. Again a whole chain of them will assume the
appearance of a long bridge or aqueduct, and as quickly change into
a succession of beautiful palaces and temples of dazzling whiteness,
metamorphosed by the fantastic wand of Nature. When the ice breaks up
in summer, the current takes many of the icebergs into the Atlantic.
[Illustration: Effects of Pressure on Antarctic Ice]
“Like a scarlet fleece the snowfield spreads
And the icy fount runs free,
And the bergs begin to bow their heads
And plunge and sail in the sea.”
_Antarctic Ice._
The difference between the two polar areas--the Arctic an ocean
surrounded by continental lands, the Antarctic a continental land
surrounded by oceans--causes the differences in the character of the
ice with which the sea is laden.
The Antarctic continent is covered with an ice-cap, which along some
coasts is buttressed by ice cliffs terminating in the sea, and on
coasts facing east is bordered with lofty mountains through which
glaciers have forced their way. Throughout the Antarctic regions there
is evidence of much more extensive glaciation in former ages. The
glaciers are for the most part receding, although there are proofs
that some are still moving down to the sea. But there are fixed masses
of ice on the sea coast, in the form of cliffs: tongues which could
not have been deposited or fed by existing glaciers. At the period of
maximum glaciation the climate was much milder, and as the severity of
the temperature, due to less precipitation, increased, there must have
been sterile ice conditions, and consequent retirement of glaciers and
ice-fields. These receding glaciers do not supply bergs; and as the
Antarctic icebergs are by far the largest in the world, their origin
must be from some other source.
The great ice barrier of Ross fills a vast bay 400 miles across, and
at least 300 miles deep, with soundings of about 600 ft. There is no
reason why other such barriers should not exist in other parts of the
Antarctic regions as yet unknown. These barriers must be the sources
of the enormous tabular icebergs which float northward in such vast
numbers. Their height is about 200 ft., and their length from one or
two to as much as twenty miles.
Large floes are not very common, but there is a great deal of drifting
ice, broken off from fixed land ice, which forms closely packed or
sailing ice according to the winds. In December this pack ice is
usually 300 miles across from 66° to 71° S. in front of the Ross Sea,
but it lies further south in the King George IV Sea of Weddell. In
February the Ross Sea is navigable, and the pack is scattered.