Price 35 Cents PUBLISHED BY THE GLACIER NATURAL HISTORY ASSOCIATION IN COOPERATION WITH THE NATIONAL PARK SERVICE Cover Surveying Sperry Glacier—Arthur Johnson of U. S. G. S. N. P. S. Photo by J. W. Corson REVISED 1966 REPRINT 1971 THOMAS PRINTING 5M71 By James L. Dyson [1] Head, Department of Geology and Geography Lafayette College The glaciers of Glacier National Park are only a few of many thousands which occur in mountain ranges scattered throughout the world. Glaciers occur in all latitudes

Within the boundaries of Glacier National Park there are 50 to 60 glaciers, of which only two have surface areas of nearly one-half square mile, and not more than seven others exceed one-fourth square mile in area. All these bodies of ice lie at the heads of valleys with high steep headwalls on the east and north sides of high ridges at elevations between 6,000 and 9,000 feet, in all cases well below the snowline. Consequently, these glaciers owe their origin and existence almost entirely to win

Prior to the beginning of the present century all glaciers in the Park, and most of those in the rest of the world, began to shrink in response to a slight change in climate, probably involving both a temperature rise and a decrease in annual snowfall. From about 1900 to 1945 shrinkage of Park glaciers was very rapid. In other words these glaciers were not in equilibrium with the climate, for less ice was added to them each winter than disappeared by melting and evaporation during the remainder

During the Pleistocene Period or Ice Age when most of Canada and a large portion of the United States were covered several times by an extensive ice sheet or continental glacier, all the valleys of Glacier National Park were filled with valley glaciers. These originated in the higher parts of the Lewis and Livingstone Ranges. On the east side of the Lewis Range they moved out onto the plains. From the Livingstone Range and the west side of the Lewis Range they moved into the wide Flathead Valley

A glacier is an extremely powerful agent of erosion, capable of profoundly altering the landscape over which it passes. Glaciers erode mainly by two processes, plucking and abrasion . The first is more active near the head of the glacier, but may take place anywhere throughout its course; abrasion or scouring is effective underneath most sections of the glacier, particularly where the ice moves in a well-defined channel. MT. OBERLIN CIRQUE AND BIRD WOMAN FALLS (HILEMAN PHOTO) In plucking, the gl

Organized for the purpose of cooperating with the National Park Service by assisting the Interpretive Division of Glacier National Park in the development of a broad public understanding of the geology, plant and animal life, history, Indians, and related subjects bearing on the park region. It aids in the development of the Glacier National Park library, museums, and wayside exhibits; offers books on natural history for sale to the public; assists in the acquisition of non-federally owned lands