CHAPTER II.GLACIERS AND ICEBERGS.
Beforeproceeding with our narrative we will dwell a little upon the great phenomena of nature to which the previous chapter called attention.
We have seen that the great sea of ice which covers Greenland, and makes it the Land of Desolation that it is, is formed from snow-flakes. That formation takes place only in certain conditions of temperature, which of course vary with the degrees of latitude.
The formation of glaciers has been for a long time a fruitful source of speculation among men of science. Into these we will not enter at any length, for my purpose is rather to give the results of personal observation and incidents of adventure, than to recite either the facts or reflections of others. Yet a few words of discussion may not be here out of place.
Every reader is aware that in the upper regions of the atmosphere the moisture which is precipitated on the mountain-top assumes the form of snow, while down at the mountain’s base it is rain. In descending a mountain nothing is more common than to pass from one condition to the other—first a storm of dry snow, then moist snow, then water. In Greenland the snow falls dry. The mountains are lofty, and it never rains upon them at all. A fresh layer of snow is laid on every year. Should this continue uninterruptedly, of course the mountains would rise to an indefinite extent. Enormous quantities break loose and roll down the mountain-sides in avalanches; butthis is but a small amount in comparison with the deposit. The glaciers are the means of drainage of these great snow-fields. These snow-fields are turned to ice by a very simple process, and the ice flows to the sea.
The surface snow on the mountain is white, dry, and light. Deeper down, it is hard; still deeper, it is clear transparent ice. The clear ice which forms such grand and beautiful arches of blue and green in the glaciers as seen along the Greenland coast, was once powdery snow upon the loftiest mountains, probably in the very interior of the continent. The transformation is an interesting process, and the movement of the ice itself from the mountain to the sea is one of the strange mysteries of nature. With respect to the former, Professor Tyndall has stated the case so clearly that I can not refrain from quoting the following passage from his excellent work entitled “The Glaciers of the Alps:”
“Could our vision penetrate into the body of the glacier, we should find that the change from white to blue essentially consists in the gradual expulsion of the air which was originally entangled in the meshes of the fallen snow. Whiteness always results from the intimate and irregular mixture of air and a transparent solid; a crushed diamond would resemble snow. If we pound the more transparent rock-salt into powder, we have a substance as white as the whitest culinary salt; and the colorless glass vessel which holds the salt would also, if pounded, give a powder as white as the salt itself. It is a law of light that, in passing from one substance to another possessing a different power of refraction, a portion of it is always reflected. Hence, when light falls upon a transparent solid mixed with air, at each passage of light from the air to the solid and from the solid to the air, a portion of it is reflected; and in the case of a powder, this reflection occursso frequently that the passage of the light is practically cut off. Thus, from the mixture of two perfectly transparent substances we obtain an opaque one; from the intimate mixture of air and water we obtain foam. Clouds owe their opacity to the same principle; and the condensed steam of a locomotive casts a shadow upon the fields adjacent to the line, because the sunlight is wasted in echoes at the innumerable limiting surfaces of water and air.“The snow which falls upon high mountain-eminences has often a temperature far below the freezing-point of water. Such snow isdry, and if it always continued so the formation of a glacier from it would be impossible. The first action of the summer’s sun is to raise the temperature of the superficial snow to 32°, and afterwards to melt it. The water thus formed percolates through the colder mass underneath, and this I take to be the first active agency in expelling the air entangled in the snow. But as the liquid trickles over the surfaces of granules colder than itself, it is partially deposited in a solid form on the surfaces, thus augmenting the size of the granules, and cementing them together. When the mass thus formed is examined, the air within it is found asround bubbles. Now it is manifest that the air caught in the irregular interstices of the snow can have no tendency to assume this form so long as the snow remains solid; but the process to which I have referred—the saturation of the lower portions of the snow by the water produced by the melting of the superficial portions—enables the air to form itself into globules, and to give the ice of thenévéits peculiar character. Thus we see that, though the sun can not get directly at the deeper portions of the snow, by liquefying the upper layer he charges it with heat, and makes it a messenger to the cold subjacent mass.“The frost of the succeeding winter may, I think, or may not, according to circumstances, penetrate through this layer, and solidify the water which it still retains in its interstices. If the winter set in with clear frosty weather, the penetration will probably take place; but if heavy snow occur at the commencement of winter, thus throwing a protective covering over thenévé, freezing to any great depth may be prevented. Mr. Huxley’s idea seems to be quite within the range of possibility, that water-cells may be transmitted from the origin of the glacier to its end, retaining their contents always liquid.”
“Could our vision penetrate into the body of the glacier, we should find that the change from white to blue essentially consists in the gradual expulsion of the air which was originally entangled in the meshes of the fallen snow. Whiteness always results from the intimate and irregular mixture of air and a transparent solid; a crushed diamond would resemble snow. If we pound the more transparent rock-salt into powder, we have a substance as white as the whitest culinary salt; and the colorless glass vessel which holds the salt would also, if pounded, give a powder as white as the salt itself. It is a law of light that, in passing from one substance to another possessing a different power of refraction, a portion of it is always reflected. Hence, when light falls upon a transparent solid mixed with air, at each passage of light from the air to the solid and from the solid to the air, a portion of it is reflected; and in the case of a powder, this reflection occursso frequently that the passage of the light is practically cut off. Thus, from the mixture of two perfectly transparent substances we obtain an opaque one; from the intimate mixture of air and water we obtain foam. Clouds owe their opacity to the same principle; and the condensed steam of a locomotive casts a shadow upon the fields adjacent to the line, because the sunlight is wasted in echoes at the innumerable limiting surfaces of water and air.
“The snow which falls upon high mountain-eminences has often a temperature far below the freezing-point of water. Such snow isdry, and if it always continued so the formation of a glacier from it would be impossible. The first action of the summer’s sun is to raise the temperature of the superficial snow to 32°, and afterwards to melt it. The water thus formed percolates through the colder mass underneath, and this I take to be the first active agency in expelling the air entangled in the snow. But as the liquid trickles over the surfaces of granules colder than itself, it is partially deposited in a solid form on the surfaces, thus augmenting the size of the granules, and cementing them together. When the mass thus formed is examined, the air within it is found asround bubbles. Now it is manifest that the air caught in the irregular interstices of the snow can have no tendency to assume this form so long as the snow remains solid; but the process to which I have referred—the saturation of the lower portions of the snow by the water produced by the melting of the superficial portions—enables the air to form itself into globules, and to give the ice of thenévéits peculiar character. Thus we see that, though the sun can not get directly at the deeper portions of the snow, by liquefying the upper layer he charges it with heat, and makes it a messenger to the cold subjacent mass.
“The frost of the succeeding winter may, I think, or may not, according to circumstances, penetrate through this layer, and solidify the water which it still retains in its interstices. If the winter set in with clear frosty weather, the penetration will probably take place; but if heavy snow occur at the commencement of winter, thus throwing a protective covering over thenévé, freezing to any great depth may be prevented. Mr. Huxley’s idea seems to be quite within the range of possibility, that water-cells may be transmitted from the origin of the glacier to its end, retaining their contents always liquid.”
We have thus briefly explained the process by which the mountain-snow changes its character, and, without actually melting and again freezing, the clearest ice may be formed from it, and go on accumulating, layer by layer, to an almost inconceivable extent.
I allude now to mountains generally, for Greenland is not the only ice-factory of the world. That country has by no means a monopoly of the business, for nearly all parts of the earth have their great reservoirs of ice formed in the same manner from snow as the ice of Greenland, only with this difference, that the climate and the temperature necessary to the formation of glaciers from snow is higher above the sea-level in most other places than in Greenland. This climate and temperature are found above what is called the “snow-line”—that is to say, a line above which the snow does not disappear in the summer, and is therefore perpetual. At the equator this snow-line is of course higher than either to the north or south of that point. Towards both poles it descends steadily. For instance, on the two great equatorial mountains of Chimborazo and Popocatapetl, it is about 15,000 feet; above which all is ice and snow, and below which vegetation, beginning with an arctic type, passes through allthe stages of climate, until at its base we find the rich vegetation of the tropics. Frequently glaciers from that upper region descend into the lower regions of vegetation to a considerable distance, but they are gradually melted away at the end, and can not, therefore, go beyond a certain line, terminating in, or rather changing from streams of ice to rivers of water.
By the time we have gone so far north as Greenland we have discovered a great depression in this snow-line. In latitude 61° north, I have observed it to be 2400 feet. I have found it to be 1700 feet at latitude 69°; at latitude 78°, it was 500; and at between 80° and 82° the snow-line appeared to touch the sea, having no belt whatever for vegetation.
The piling up of these mountain-snows is like the processes of a geological epoch in the steady growth by deposit. There is this difference, however, that ice formed in this manner is not, like rock, hard and unyielding, but, like putty, is, in a measure, ductile. In fact, itflowsdownward, and the superabundant accumulations find their way thus to the ocean. It is estimated that the snows of the Alps would increase the altitude of those mountains four thousand feet in a thousand years but for this strange ductile property of ice. As we have before seen, an ice-stream is, in effect, a frozen river, flowing at a very slow, but still at a very perceptible rate. The rate of flow in the Alps, variouslyestimated by different explorers and at different places, where there were different degrees of descent, is from six to fourteen inches daily. In Greenland the rate, as determined by me, is about from five to eight inches daily. The Greenland glaciers possess another marked difference from those of the Alps. The ends of the latter, descending into a lower and warmer level, are melted off, and disappear as the end of a tallow candle would disappear if held near a hot stove. Before this takes place, the ice, descending through the valley, conforms to all its inequalities, and the actual river which ultimately takes its rise from the glacier front does not more readily mould itself to the rocky bed over which it flows—widening and contracting, deepening or shoaling as the river-bed expands and narrows, or increases and diminishes its declination. An ice-stream, or glacier, like the river, has therefore its cascades, its rapids, its broad lagoons (so to speak), and its smooth, steady, even flow. It carries rocks along with it upon its surface (rocks which have fallen upon it from the cliffs along its sides), as the river carries sticks of wood and, when the ice melts, these rocks fall in front, and, rolling down the valley, formmoraines. But with the Greenland glaciers the result is different. The end of the glacier never descends into a level that is warm enough to melt away the end of it, as in the Alps, but it reaches the sea in all the glory of its cold and crystal hardness. When this happens, its end penetrates the water, and makes a coast-line of ice. The temperature of Greenland, down even to the water-level, is too low to allow of any considerable melting, but the result is the same. A fragment breaks off from the glacier and floats away upon the ocean, and is drifted to and fro with the ocean currents. Rocks which may have fallen upon the glacier from the cliffs are inclosed within it, or are carried upon the top of it.
The fragment which has been broken off, as above described, is known as aniceberg. This iceberg is dissolved but slowly as it drifts south with the arctic current, often reaching as far as the Banks of Newfoundland before it disappears entirely. Often it endangers vessels crossing the ocean, and it deposits at the bottom of the sea its burden of rock and sand, as it melts down. The Banks of Newfoundland have received constant accessions in this way. It was in like manner that those great boulders which we find upon plains, like our Western prairies, were deposited at a period when they were the bed of the ocean, and icebergs drifted that way from the Arctics.
And thus it will be seen that the Alpine glaciers and the Greenland glaciers, although disappearing by different direct processes, come to the same final end—the mountain-snows reach their natural home in the sea at last.
Many of the Greenland glaciers are of amazing extent. There is one sixty miles wide. Its front is in the water, and it is washed by the waves like any other coast-line. The rock-cliffs on either side of it are very lofty, from five hundred to a thousand feet. The ice-cliffs are from fifty to three hundred. Below the surface of the water this wall of ice extends downward to the bottom, and in places the depth is over two thousand feet. This great glacier, the largest known, lies at the head of Smith’s Sound, and was discovered by Dr. Kane, who called it the Great Humboldt Glacier.
Another, twenty miles across, may be seen in North Greenland, in the fiord of Aukpadlartok. This I have surveyed, and shall have occasion to refer to it hereafter. There are several that are five miles over; others two and three, and indeed of every size, down to the very diminutive one that might be called an ice rivulet. Many of them have reached the sea, as already stated—some ofthem ages ago, others very recently; others have not yet flowed so far; but in all cases the flow is steady, and the accumulation within the inland reservoir goes on. The flow of a glacier may be likened to the great flood which sweeps down the valley from a broken dam. Though it comes very slowly, it comes very surely. It is irresistible. It moulds itself to the hill, it swells up over an acclivity, it pours over a cliff, and pursues its course with a strength and impulse that is grand and terrible to behold. And it is not noiseless, for its movement is attended with constant breaks, sometimes extending through its entire body. The sound occasioned thereby is truly appalling. The glacier is, therefore, often an object of real terror. The whole region is, in fact, full of startling wonders and novelties of nature. Its history is replete with violent convulsions. Once those were of fire, for the country shows evidence of volcanic heat; now they are of frost. The Land of Desolation is worthy of more consideration than it has ever yet received from the learned and curious, or even the adventurous.