CHAPTER VI.SPECULATIONS.
I trustthat I have made plain, even to the least scientific of my readers, the nature of the glacier which we are visiting, as well as the general principles of glacier formation and movement. Why ice, a solid, firm substance, should move in obedience to the same laws which govern the movements of fluids; why, for instance, a glacier should, like a river, move more rapidly at its centre than near its banks, is a question which the wisest philosophers have sufficiently discussed without my attempting it here. Taking the fact for granted, and knowing that the vast reservoir of ice in the interior of Greenland is the great source of supply to all the glaciers that pour to the sea through the mountain-passes, we may here, I think, not inappropriately, pause a little to watch the progress of this glacier of Sermitsialik.
Even within the period of a generation it has undergone very perceptible changes. Peter Motzfeldt has told me that fifty years ago he walked across the valley in front of it, and plucked whortle-berries upon the identical spot where I had gone into the ice-cavern to hear the waters rushing to the sea. He pointed out to me the line of the glacier front at that time, so far as he could remember it (and the memory of such men is apt to be accurate); and, accepting his memory as correct, the movement of the glacier from that time to the present has been about seven (7) inches daily, the distance being a fraction over two miles.
THE GLACIER OF SERMITSIALIK.
THE GLACIER OF SERMITSIALIK.
With this positive assurance before us we may, in imagination, witness the spectacle of this glacier’s growth. Going back to the time when it first emerged from themer de glace(to the time when the ice first began to bulge downward into the valley which it now fills completely), we see the valley clothed with verdure, sparrows chirruping among the branches of the stunted trees, herds of reindeer browsing upon its abundant pastures, and drinking from a stream of limpid water which, melting from the glacier, pours down over the same precipices, and through the same defiles which the ice now fills and covers. This must have been about two hundred and fifty years ago, since the distance from the sea to where the break occurs in the mountain-chain through which the ice-stream emerges into the valley is about ten miles. We see it then just appearing, and we watch its progress through this long time. Its front is hundreds of feet high and miles across. We observe the icy flood moving steadily and irresistibly onward, over precipices, down steep declivities, upon level plains—sometimes advancing with comparative rapidity, sometimes slowly, but steadily, year by year, coming towards the fiord. We see it swallowing up rocks and pastures; we see the deer retire farther and farther down the valley with each returning year; we see the hillocks within the valley overwhelmed with the flood of ice, the crystal stream pouring over and around them as if it were some semi-fluid substance; we hear the cracking of the ice as the strain here and there becomes too great; and we hear, too, the echoing sound of the avalanche of ice and snow, crumbling from its front, and crashing down into the plain beneath. We thus watch the ice-stream until the front of it has reached the fiord. But here it does not stop. The bed of the sea is but a continuation of the same inclined plain as the bed of thevalley, and its onward course is continued. It pushes back the water; it makes a coast-line of ice where there had been a beach; and a white wall now stretches from one side of the fiord to the other. As it flows onward, it gets into deeper and deeper water, its foot still resting on the bottom of the sea. Thus the icy wall sinks gradually down as it moves along, and in course of time it has almost gone out of sight. Then it gets beyond its depth.
VERTICAL SECTION OF GLACIER.
VERTICAL SECTION OF GLACIER.
When fresh ice floats freely in sea-water, there is one-eighth of it above the surface to seven-eighths below. If these proportions become disturbed—that is to say, if the glacier should project far enough out into the sea and deep water to present more than seven-eighths below to one-eighth above, then the buoyancy of the water will lift the end of the ice-stream until it attains its natural equilibrium. To do this, of course, a break must occur, as the ice will not bend. But for a long time the continuity of the ice is not interrupted—so great is its depth (many hundreds of feet), so great is its width (two miles). But finally it is compelled to give way; the force applied becomes too great for its powers of resistance. A crack, beginning at the bottom, is opened, with a fearful crash. The crack widens, and when it is completed to the top a fragment is detached. This fragment is buoyed up to its proper level; and while the loud noise of the disruption is echoing among the hills, and the great waves of its creating are rolling away, the monstrous mass is comingslowly to rest, ready to float off with the current to the ocean. This fragment, as we have already seen, is theiceberg. Its birth, as we shall presently notice, is attended with the most violent disturbance of the sea and air, and presents a magnificent spectacle.
The accompanying vertical section of the glacier of Sermitsialik, run up its axis from the fiord to its junction with themer de glace(a distance of ten miles), will illustrate the fact I wish to prove, and the theory I wish to illustrate. The view of the same glacier, on page 147, will still further aid the reader; and this, examined in connection with the small map on page 162, will explain what any number of words would fail to make clear. This vertical section shows an iceberg just broken off and floating away. The line of the section is from A to B, as shown on the map.