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.
Glaciers of Glacier National Park
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 wind-drifted snow.
Ice within these glaciers moves slowly. The average rate in the smallest ones may be as low as 6 to 8 feet a year, and in the largest probably 25 to 30 feet a year. There is no period of the year when a glacier is motionless, although movement is somewhat slower in winter than in summer. Despite the slowness of its motion the ice, over a period of years, transports large quantities of rock material ultimately to the glacier’s end where it is piled up in the form of a moraine.
FRONT OF SPERRY GLACIER
The largest glacier in the Park is Grinnell. In 1960 it had a surface area of 315 acres.
Sperry is the second largest glacier in the Park. Its surface in 1960 was 287 acres. Both Grinnell and Sperry have probable maximum thicknesses of 400 to 500 feet.