Glaciers and Glaciation
in
Glacier National Park
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
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 manythousands which occur in mountain ranges scattered throughout theworld. Glaciers occur in all latitudes and on every continent exceptAustralia. They are present along the Equator on high volcanic peaks ofAfrica and in the rugged Andes of South America. Even in New Guinea,which many think of as a steaming, tropical jungle island, a few smallglaciers occur on the highest mountains.
Almost everyone who has made a trip to a high mountain range hasheard the term, “snowline,” and many persons have used the word withoutknowing its real meaning. The snowline is the level above which moresnow 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 summitsof most Glacier National Park mountains down their slopes totimberline, and some snowbanks extend even lower. At that time thesnowline appears to be down near timberline. But as the summer progressesand higher temperatures melt the lower-lying snowbanks this apparentsnowline retreats higher and higher up the slopes, until late Augustor early September, when it reaches a point above which it will notretreat. This lower limit of snow is the permanent or regional snowline.It is usually referred to simply as the snowline. In Glacier National Parkthe regional snowline actually lies above the summits of most peaks, ata height of more than 10,000 feet. The only parts of the United Statessouth of Canada which project above the snowline are the highest summitsin the Cascade Range in California, Oregon, and Washington, andin the Olympic Mountains in the latter state. There are many mountainsin Alaska that lie above the snowline. This is especially true in thecoastal ranges where the snowline is around 4,500 feet above sea level.
The Olympic area is unique, for here the regional snowline descendsto about 6,000 feet lower than anywhere within the boundaries of theContinental United States south of Alaska. Extraordinarily heavy annualsnowfall and the high percentage of cloudy weather, which retards themelting of snow, combine to depress the snowline to such a low level.