National Geographic : 1904 Nov
THE GLACIERS OF ALASKA HE rapidity with which the Alaskan glaciers are changing, some retreating and others ap parently advancing, gives special value to the careful record of their present character contained in "Alaska; Gla ciers and Glaciation,"* by Dr G. K. Gilbert. Dr Gilbert states that Nuna tak Glacier between Professor Russell's visit in 1891 and his own visit in 1899 retreated fully a mile and possibly twice as much; Muir Glacier between 1880 1899 retreated I miles, and since the earthquake of 1899 has retreated about three miles. On the other hand, other glaciers, like the Columbia and La Pe rouse, are now probably at their maxi mum, having been much smaller during the past 1oo years. While it is impossible to say absolutely why certain glaciers are diminishing while others a short distance away are increasing, Dr Gilbert suggests that the cause may be a change in the meteoro logic conditions. The glaciers are dif ferent, some being fed by open never fields and others by cirques. A rise in ocean temperature probably increases the wastage of the former class, but, on the contrary, enlarges the latter class by an increased fall of snow and rain, which more than counterbalances the wastage. " Nearly all the glaciers of Alaska are comprised within a belt of moderate width which follows the southern coast from the Aleutian Islands to Portland canal. Curving about the great bight of the Pacific Ocean known as the Gulf of Alaska, this belt has a length of 1,600 miles, and its extreme width, near the middle, is about 250 miles. Within it the arrangement of glaciers is irregular, but their more important groups occupy the middle region, while near the ends they are comparatively sparse and small. " The explanation of this massing of glaciers along the southern coast is not far to seek. The general circulation of the Pacific Ocean brings to the Gulf of Alaska a current of water which has been warmed in the tropics and still re tains so much heat that its mean tem perature is considerably above the nor mal for the latitude. The ocean is therefore, at some seasons, warmer than the contiguous land, and though air currents passing from ocean to land convey heat to the land they are them selves cooled. While traversing the ocean the air becomes loaded with moist ure, the cooling over the land dimin ishes its water-carrying capacity, and part of its load falls to the ground as rain or snow. Moreover, all this coast is mountainous, so that landward flow ing air is compelled to rise, and its capacity is still further reduced by rare faction. At the greater altitudes the ratio of snow to rain is comparatively large, and the mountains thus become gathering grounds for the snows that feed glaciers. Farther inland the air currents descend somewhat, and the pre cipitation is diminished until the con ditions for glacier formation cease. Hayes states that while the never line of glaciers on the southward face of the St Elias Alps lies at about 2,000 feet above sea-level, its altitude on the north ern face is over 6,000 feet. "Along the western coast of Alaska the conditions are different. Bering Sea lies practically outside the influence of the Pacific circulation, and the temper ature of its water is approximately normal. Its power to change air cur rents with moisture is small, especially in winter, and though the winter tem perature over the adjacent land is low the snowfall is heavy. There are no great mountain ranges to concentrate * "Alaska ; Glaciers and Glaciation," byGrove Karl Gilbert. Vol. III of the Harriman Alaska Expedition Series. Edited by Dr C. Hart Merriam. With 18 maps and plates and 1o8 illus rations in text. Pp. 230. 5 byI~ inches. New York: Doubleday, Page & Co. 1904.