Fig. 1.—Zermatt Glacier (Agassiz).
A glacier is a mass of ice so situated and of such size as to have motion in itself. The conditions determining the character and rate of this motion will come up for statement and discussion later. It is sufficient here to say that ice has a capacity of movement similar to that possessed by such plastic substances as cold molasses, wax, tar, or cooling lava.
The limit of a glacier’s motion is determined by the forces which fix the point at which its final melting takes place. This will therefore depend upon both the warmth of the weather and upon the amount of ice. If the ice is abundant, it will move farther into the region of warm temperature than it will if it is limited in supply.
Upon ascending a glacier far enough, one reaches a comparatively motionless part corresponding to the lake out of which a river often flows. Technically this is called the névé.
Glacial ice is formed from snow where the annual fall is in excess of the melting power of the sun at that point. Through the influence of pressure, such as a boy applies to a snow-ball (but which in the névé-field arises from the weight of the accumulating mass), the lower strata of the névé are gradually transformed into ice. This process, is also assisted by the moisture which percolates through the snowy mass, and which is furnished both by the melting of the surface snow and by occasional rains.
The division between the névé and the glacier proper is not always easily determined. The beginnings of the glacial movement—that is, of the movement of the ice-stream flowing out of the névé-field—are somewhat like the beginnings of the movement of the water from a great lake into its outlet. The névé is the reservoir from which the glacier gets both its supply of ice and the impulse which gives it its first movement. There can not be a glacier without a névé-field, as there can not be a river without a drainage basin. But there may be a névé-field without a glacier—that is, a basin may be partially filled with snow which never melts completely away, while the equilibrium of forces is such that the ice barely reaches to the outlet from which the tongue-like projection (to which the name glacier would be applied) fails to emerge only because of the lack of material.
