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, névé1, 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 Greenland2. 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.
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.