1911 Encyclopædia Britannica/Snow-line
SNOW-LINE. In the higher latitudes, and in the most elevated parts of the surface of the earth, the atmosphere may be normally so cold that precipitation is chiefly in the form of snow, which lies in great part unmelted. The snow-line is the imaginary line, whether in latitude or in altitude, above which these conditions exist. In the extreme polar regions they exist at sea-level, but below lat. 78° the snow-line begins to rise, since at the lower elevations the snow melts in summer. In N. Scandinavia the line is found at about 3000 ft. above the sea, in the Alps at about 8500 ft., and on high mountains in the tropics at about 18,000 to 19,000 ft. These figures, however, can only be approximate, as many considerations render it impossible to employ the term " snow-line " as more than a convenient generalization.