Alpine glacier

“ Oftener it descends or moves forward through the irregular openings which the accidents of motion have developed. If it reaches a level where the temperature is below its freezing-point, it congeals. Otherwise it remains in cavities or descends to the bottom. The water produced by melting within the glacier probably follows a similar course. So far as these waters descend to the bottom, they join those produced by basal melting and issue from the glacier with them. In alpine glaciers the waters beneath the ice often unite in a common stream in the axis of the valley, and hollow out a tunnel. ”

“ It has lateral and medial moraines, ice pinnacles, crevasses, and many other details peculiar to glaciers. From its extremity, which is dark with dirt and stones, there flows a stream of turbid water. It is, in fact, a miniature similitude of the ice-streams on the neighboring mountain, some of which are forty or fifty miles in length and many times wider in their narrowest part than the little glacier before us is long. The more thoroughly we become acquainted with the mountains of southern Alaska the more interesting and more numerous do the Alpine glaciers of the third order become. ”

“ In case the melting at the lower extremity, however, just equals the forward movement, the end of the glacier comes to a halt and its load is dumped in a ridge, forming a terminal moraine, providing we have a glacier of the alpine type, which alone can be considered to have an end. In the case of the three other types of glaciers such moraines, testifying to the stages of halt of the front, but not of the ice itself, are known as frontal moraines. ”

“ I. C. Russell, taking both the Alpine and continental types into consideration, would define a glacier as an ice body, originating from the consolidation of snow in regions where the secular accumulation exceeds the loss by melting and evaporation, or above the snow-line, and flowing to regions where loss exceeds supply, or below the snow-line. Mr. S. F. Emmons described a glacier as a river of ice, possessed, like the aqueous river, of movement and plasticity. The nevé field is the reservoir from which it derives not only its supply of ice, but the impulse which gives it its first movement. ”

“ Aside from the wind-blown dust which may be more or less evenly distributed throughout the body of the ice, the bulk of the material transported by the local ice-caps and continental ice-sheets lies in the basal layers. In the case of alpine and piedmont glaciers, however, from overtowering cliffs the active atmospheric agents may detach rock fragments which find their way to the surface of the glacier. ”

“ The glaciers of the Polar lands, coming down as they do to the edge of the ocean, are responsible for the icebergs of those seas. Compared with Polar glaciers the Alpine ones are puny, no larger, as a rule, than a large iceberg—which represents just a fragment broken off an Arctic or Antarctic glacier. But the Alpine examples of glaciers, small though they be, are grandly impressive in their natural surroundings. ”

“ If the glacier is lowered greatly by melting, these circles of large angular fragments, which are called "perched blocks," are left in a singular situation near the top of a steep hill or pinnacle, the lower parts of which may be destitute of boulders.
ALPINE ERRATIC BLOCKS ON THE JURA. Now some or all the marks above enumerated,—the moraines, erratics, polished surfaces, domes, striae, and perched rocks—are observed in the Alps at great heights above the present glaciers and far below their actual extremities; also in the great valley of Switzerland, 50 miles broad ”

“ All the Greenland glaciers become confluent in the interior, so that it is not a typical mer de glace, but a sheet of ice, which overspreads the highest mountains. It is only near the edge that the several streams manifest their independent existence. Thence the usual phenomena of Alpine glaciers manifest themselves. The sub-glacial streams pouring into the sea produce certain peculiarities. Immense supplies of heat penetrate the ice from the sun's rays, which melt very much ice and discharge muddy torrents of great size. ”

“ The retreat of the first Alpine glaciers, caused partly by a lowering of that chain, may have been synchronous with the period of great submergence and floating ice in England. The second advance of the glaciers may have coincided in date with the re-elevation of the Alps, as well as of the Scotch and Welsh mountains; and lastly, the final retreat of the Swiss and Italian glaciers may have taken place when Man and the extinct mammalia were colonising the north-west of Europe and beginning to inhabit areas which had formed the bed of the glacial sea during the era of chief submergence. ”

“ Moreover, the glaciers themselves have quite a different look from alpine glaciers. They appear to be far more viscous, as in fact they are, so that if they end on a piece of flat ground and do not reach the sea, the end spreads out into a great round mass, as a stream of honey might if it emerged from some narrow gap on to a flat area. ”

“ Alpine glaciers are of the medium type, lying as they do half-way between the Arctic and tropical extremes. They have not the rapid flow of the Arctic nor the dry rigidity of the tropical sort. Their walls are not silent as in the Central Andes, nor thundered over by continual avalanches like those of the upper Baltoro. ”

“ As long as the ice streams follow the torrent-channels, they act in something like the fashions of the flowing waters—to gouge out the rocks and deepen the valleys; but as the glacial period advances and the ice sheet spreads beyond the mountains enveloping the plains as well, when the glacier attains the thickness of thousands of feet, it disregards the valleys in its movements and sweeps on in majestic march across the surface of the country. As long as the continental glaciers remain the tendency is to destroy the river valleys. ”

“ Well, many glaciers, after quitting the snow-beds by which they are fed, suddenly find themselves at the top of a precipice. Under these circumstances, as they are unable to stand still, there is but one thing for them to do, viz., go over; and as ice, though plastic, is by no means so to the extent that treacle—to which glacier ice has so often been likened—is, it is obvious that a slice will break off the advancing [Pg 88] tongue of the glacier, and come thundering down the rocks, to form material for another glacier below, or, if the quantity is insufficient, to melt gradually away. ”

“ The glaciers of the Alps, and probably those of other regions, descend to a vertical depth of nearly 4000 feet below the line of perpetual snow, and into a climate much warmer than that of our own island, before they finally melt away, and leap forth as rivers of running water. The heap of materials of all sorts and sizes which they deposit at their melting extremity is called the moraine, a term which is also applied to the lines of blocks that are being carried along on the surface of the glacier, the floating sticks and straws of the solid river. ”

“ A low temperature alone can do nothing without moisture, and this fact quickly disposes of the popular notion that glaciers invariably exist in cold countries. Thibet, for instance, and also some parts of Arctic North America are destitute of ice streams, though eternal cold may be said to reign supreme in these parts.
Imagine for a moment the higher mountains clear of snow and ice, and then watch for the formation of a glacier. Snow falls and fills up all the valleys and gullies, avalanches descend from the higher parts, and a great accumulation gathers in all hollows. ”

“ The nature, origin, and aspect of the moraines, the mode of melting of the ice beneath them, and the isolated pinnacles of ice which support large solitary 478 boulders, agree so entirely with descriptions of glaciers in other parts of the world, that it is unnecessary to dwell upon them. The large glaciers are often a good deal lower in their central parts than where they are covered by a bulky moraine; and a curious ravine-like hollow, between the moraine and the bare ice, which makes the former appear as if entirely disconnected from the glacier, is of very common occurrence. ”

“ The question always arises where do all the boulders and pebbles that cover the lower parts of the glaciers come from? In the upper parts of the glaciers or névé regions, where the snow remains perpetual and increases from year to year, the stones from the mountain sides are covered as they fall, and are at length buried deep and surrounded by ice as the snow becomes compressed and solidified. As the glacier advances down the valley and descends to lower altitudes, a level is at length reached where the snowfall of winter is exactly balanced by the melting of summer. ”

“ Polar ice sheets are permanent only so long as the lands remain on which they rest. Mountain glaciers can stay only the brief time during which the ranges continue young and high. As lofty mountains, such as the Selkirks and the Alps, are lowered by frost and glacier ice, the snowfall will decrease, the line of permanent snow will rise, and as the mountain hollows in which snow may gather are worn beneath the snow line, the glaciers must disappear. ”

“ The glacier, starting in its infant purity from some white, unsullied peak, loses, before many years have past, its spotless character. The wintry frosts, gathering [Pg 70] into iron bonds the streams which trickle down the mountain-sides, expand the water in freezing, and shatter the rocks with a force that the most solid cliffs cannot resist. Broken and weathered fragments are washed down from the slopes on every fall of rain, and dropping on to the once unspotted bosom of the glacier, swell the burden which is gradually laid upon it with advancing years. ”

“ But though only a little of the snow melts, it disappears in other ways. Some is evaporated into the atmosphere; some falls off in avalanches. Most of it slowly flows down after forming itself into glaciers. For glaciers are always moving. The force of gravity makes them slide down over their rocky beds. They flow so slowly that we cannot see them move, in fact most of them advance only a few inches a day. But if a line of stakes is driven into the ice straight across a glacier, we shall notice in a few 9 weeks that they have moved down. ”

“ They are grandly alpine; open grass-lands with great shapely unbrageous spruce trees, brilliant flowers and lakelets, silver streams meandering everywhere, the green slopes rising gently to bold bare cliffs and steep slopes of scree, crowned by snowy heights, glacier-hung and showing long connecting arêtes such as the explorer loves. ”

“ Such modifications arise chiefly from the pressure to which it is subjected in its downward progress, and to the alterations, in consequence of this displacement, in the relative position of the snow- and ice-beds, as well as to the influence exerted by the form of the valleys themselves, not only upon the external aspect of the glaciers, but upon their internal structure also. The surface of a glacier varies greatly in character in these different regions. ”

“ The glacier, clear and white, without a rock on its broken surface, looked from a little distance like a vast snow-covered meadow. We were about a mile above the lower limit of the snow-fields, where the blue ice of the glacier comes out from beneath the névé. The blue ice was deeply buried, and could only be seen in the deepest crevasses. Across the glacier rose the angular cliffs and tapering spires of the Hitchcock range. Every ravine and gulch in its rugged sides was occupied by glaciers, many of which were so broken and crevassed that they looked like frozen cataracts. ”

“ This glacier, like that of Montanvert, comes close to the vale, overhanging the green meadows and the dark woods with the dazzling whiteness of its precipices and pinnacles, which are like spires of radiant 158crystal, covered with a net-work of frosted silver. These glaciers flow perpetually into the valley, ravaging in their slow but irresistible progress the pastures and the forests which surround them, performing a work of desolation in ages, which a river of lava might accomplish in an hour, but far more irretrievably ”

“ It is agreed by all, that the snow on the summit of Mont Blanc and the neighbouring mountains perpetually augments, and that ice, in the form of glaciers, subsists without melting in the valley of Chamouni during its transient and variable summer. If the snow which produces this glacier must augment, and the heat of the valley is no obstacle to the perpetual existence of such masses of ice as have already descended into it, the consequence is obvious; the glaciers must augment and will subsist, at least until they have overflowed this vale. ”

“ With a continued lowering of the annual temperature and consequent increased snowfall, the early glaciers become more and more amply nourished. Snow and ice will, therefore, cover larger areas of the upland, and the glaciers will push their fronts farther down the valleys before they are wasted in the warm air of the lower levels. As the valleys become thus more completely invested by the glacier they are likewise filled to greater and greater depths, and they may thus submerge portions of the walls that separate adjacent valleys. ”

“ This semi-icy snow descends under pressure, and, as it increases, the glacier is formed by huge blocks and masses being pressed together on the steep slopes of the mountains. Thus the glacier descends, rounding off rocks, and scouring as it goes, moving at a certain estimated rate daily,—about twenty inches on the average,—carrying stones and débris which form the moraine, and finally when the high temperature in the valley melts the ice, it issues forth as a river into the plain, or bounds down the mountain side in a cascade. ”