James L. Dyson

Glaciers of Glacier National Park

Shrinkage of Park Glaciers

Former Extent of Park Glaciation

Park Features Resulting From Glaciation

FOOTNOTES

GLACIER NATURAL HISTORY ASSOCIATION, Inc. Glacier National Park West Glacier, Montana

Transcriber's Notes

Price 35 Cents

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

GLACIERS AND GLACIATION IN GLACIER NATIONAL PARK

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 and on every continent except Australia. They are present along the Equator on high volcanic peaks of Africa and in the rugged Andes of South America. Even in New Guinea, which many think of as a steaming, tropical jungle island, a few small glaciers occur on the highest mountains.

Almost everyone who has made a trip to a high mountain range has heard the term, “snowline,” and many persons have used the word without knowing its real meaning. The snowline is the level above which more snow falls in winter than can be melted or evaporated during the summer. On mountains which rise above the snowline glaciers usually occur. The snowline is an elusive feature and can be seen only in late summer. For example, during the latter part of June snow extends from the summits of most Glacier National Park mountains down their slopes to timberline, and some snowbanks extend even lower. At that time the snowline appears to be down near timberline. But as the summer progresses and higher temperatures melt the lower-lying snowbanks this apparent snowline retreats higher and higher up the slopes, until late August or early September, when it reaches a point above which it will not retreat. This lower limit of snow is the permanent or regional snowline. It is usually referred to simply as the snowline. In Glacier National Park the regional snowline actually lies above the summits of most peaks, at a height of more than 10,000 feet. The only parts of the United States south of Canada which project above the snowline are the highest summits in the Cascade Range in California, Oregon, and Washington, and in the Olympic Mountains in the latter state. There are many mountains in Alaska that lie above the snowline. This is especially true in the coastal ranges where the snowline is around 4,500 feet above sea level.

The Olympic area is unique, for here the regional snowline descends to about 6,000 feet lower than anywhere within the boundaries of the Continental United States south of Alaska. Extraordinarily heavy annual snowfall and the high percentage of cloudy weather, which retards the melting of snow, combine to depress the snowline to such a low level.