nearly filled with water, in which the water has been frozen solid.[1] These veins in icebergs are frequently one to three feet thick, and can be seen at several miles' distance. If veins of blue ice are not formed in the Alpine glaciers in the same manner, it is only because there are outlets from the crevasses by which the water escapes. It is rare to see a crevasse even partly filled with water in the Alps.[2]
Secondly, by the closing together of crevasses. The unequal motion of the parts of a glacier causes crevasses continually to open and to close up; and the walls of these crevasses, whether 12,000 feet or more above the level of the sea, or whether only 5000, all become weathered and more or less coated with pure ice. Even narrow crevasses in the high regions, well bridged with snow, are not exempt. The warm air of midsummer penetrates the chasms, and, assisted by the percolation of snow water, glazes the walls from top to bottom. The superficial coatings of ice which are thus formed upon the sides of crevasses vary greatly in thickness according to circumstances—in a single crevasse they may range from a thickness of less than an inch to more than a foot.[3] The crevasses close up; the surfaces of their icy walls are brought into contact; they regele, and the coalesced films will then appear as veins of pure ice in the generally whitish mass of the glacier. When one considers the myriads of crevasses which there are in any glacier, and the incessant opening and closing up that goes forward, it is easy to see that a large proportion of the veins of pure ice which constitute the veined structure of glaciers must be considered as the scars of healed crevasses.
- ↑ These veins in icebergs are frequently seen intersecting each other. Dr. Rink has shown this in an illustration in his Grönland Geographisk og Statistisk, vol. i. 1852.
- ↑ Charpentier long ago advanced the opinion that the motion of glaciers was promoted by freezing of water in crevasses. His notion is commonly regarded as exploded, but there may be something in it after all.
- ↑ The same thing is to be noticed in regard to the blue veins of the veined structure. The veins frequently thin out and are lost, or swell into lenticular masses. This is best seen when the veins are regarded in vertical sections of the glacier.
