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.