James L. Dyson

“ It is at this site that plucking is most dominant because water enters by day and freezes in the rock crevices at night. This quarrying headward and downward finally results in the formation of a steep-sided basin called a cirque or glacial amphitheatre. Because the cirque is the first place that ice forms and the place from which it disappears last, it is subjected to glacial erosion longer than any other part of the valley. Thus its floor is frequently plucked and scraped out to a comparatively great depth so that a body of water known as a cirque lake forms after the glacier disappears. ”

“ As a matter of fact, there are persons who visit Glacier National Park without seeing a single glacier, while others, although they actually see glaciers, leave the park without realizing they have seen them. This is because the highways afford only distant views of the glaciers, which from a distance appear much like mere accumulations of snow. A notable example is Grinnell as seen from the highway along the shore of Sherburne Lake and from the vicinity of the Many Glacier Entrance Station. ”

“ As the ice moves it continually breaks rock fragments loose. Some of these are ground into powder as they move against each other and against the bedrock under the glacier. Most types of rock, especially the limestones and shales on which the Park glaciers rest, when ground fine enough yield a gray powder. All melt-water streams issuing from glaciers are cloudy or milky from their load of this finely ground “rock flour.”
Water from Grinnell Glacier is so laden with rock flour that the small lake along the edge of the ice into which the water pours is nearly white. ”

“ Despite this magnificence the visitor must soon turn his attention to the tremendous accumulation upon which he stands, for it is no less interesting than the mountains and lakes. Among the many 25 boulders which lie along the path are two prominent limestone blocks each 10 to 15 feet in diameter. The underside of one was grooved and polished as the ice pushed it across the rock surface underlying the glacier. The other, partially embedded in the moraine, has a polished upper surface because the glacier flowed over it for a time. ”

“ 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. ”

“ The thicker a stream of ice, the more erosion it is capable of performing; consequently, the main valley becomes greatly deepened, whereas the smaller glacier in the tributary valley does not cut down so rapidly, leaving its valley hanging high above the floor of the major valley. ”

“ As the surface of the glacier, except that insulated by the debris, is lowered by melting, the mounds form and grow gradually higher until the debris slides from them, after which they are 7 speedily reduced to the level of the rest of the surface. They are seldom higher than 3 or 4 feet.
A glacier table is a mound of ice capped, and therefore protected from melting, by a large boulder. ”

“ Siyeh is the only other regularly visited Park glacier. It lies about half a mile beyond the end of the Cracker Lake trail, and can be reached from that point by an easy walk through grassy meadows and a short climb over a moraine. Siyeh, however, is less spectacular than either Grinnell or Sperry, being much smaller and lacking crevasses, so common on the other two. Few people make the spectacular trail trip over Siyeh Pass but those who do may visit Sexton Glacier by making a short detour of less than half a mile where the trail crosses the bench on which the glacier lies. ”

“ 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. ”

“ As the former long valley glaciers enlarged their cirques by cutting farther in toward the center of the range, the latter finally was reduced to a very narrow steep-sided ridge, the arete. The imposing height of the Garden Wall can readily be determined by using the layer of diorite as a scale. The conspicuous black band formed by the edge of this layer has an average width of 75 feet. So, from the porch of the Many Glacier Hotel a Park visitor can readily see that the Garden Wall, even though five miles distant, is about 4,200 feet high. ”

“ Several of the glaciers, however, are accessible by trail and are annually visited by many hundreds of people, either on foot or by horse. Most accessible of all Park glaciers is Grinnell. It can be reached by a six-mile trip over an excellent trail from Many Glacier Hotel or Swiftcurrent Camp. Sperry, likewise, can be reached by trail, although the distance is several miles greater than in the case of Grinnell. The trip, 6 however, can be broken and possibly made more interesting by an overnight stop at Sperry Chalet, which is located about three miles from the glacier. ”

“ Its history is similar to that of the debris cone. After a time the boulder slides off its perch, and then the mound of ice melts away.
Snow which fills crevasses and wells during the winter often melts out from below, leaving thin snowbridges in the early part of the summer. These constitute real hazards to travel on a glacier because the thinner ones are incapable of supporting a person’s weight. This is one very good reason why the inexperienced should never venture onto the surface of a glacier without a guide. ”

“ Its edge was bordered by a ridge-like moraine nearly a hundred feet high. Today, the trail from Logan Pass to Hidden Lake skirts the outside edge of the moraine. Should the hiker leave the trail and climb the few yards to the top of this moraine he could see it stretched out before him as a giant necklace encircling the base of Clements Mountain, but between mountain and moraine, where a few years ago the glacier lay, he will see only bare rock or drifted snow. ”

“ It is probable that the Park glaciers are not remnants of the large glaciers present during the Ice Age which terminated approximately 10,000 years ago, because it is known that several thousand years after that time the climate of the Glacier National Park region was somewhat drier and warmer than now. ”

“ Where there are no ice masses streams are clear, and where glaciers occur the water possesses many shades varying from clear blue through turquoise to gray, and in rare cases even pink.
MORAINE NEAR GRINNELL GLACIER IS 120 FEET HIGH. THE GLACIER EXTENDED NEARLY TO TOP OF MORAINE 50 YEARS AGO. (DYSON PHOTO)
Although the former large glaciers of the Ice Age transported huge amounts of rock debris down the valleys of the Park, the moraines which they deposited are, as a rule, not conspicuous features of the landscape. ”

“ The values for area and recession shown above indicate that changes in the area of the glacier have not been as pronounced since the mid-1940’s as they were prior to that time. Profile measurements starting in 1950 indicate a general trend of continued shrinkage although annual changes have been both positive and negative. ”

“ The forward movement in the central portion of the Sperry Glacier, based on observations since 1949, has averaged about 15 feet per year. The rate of movement is presumed to be greater in the upper reaches of the glacier. ”

“ Thus the climatic conditions which caused glaciers to shrink for fifty or more years seem to have been replaced by conditions more favorable to the glaciers. Time alone will tell whether the new conditions are temporary or mark the beginning of a long cycle of wetter and cooler climate. ”

“ Resistant layers in the lower portion of the Altyn formation, the upper part of the Appekunny, and the upper part of the Grinnell [2] normally create risers.
TYPICAL GLACIAL VALLEY WITH CHAIN OF ROCK-BASIN LAKES. GLENN AND CROSSLEY LAKES IN DISTANCE; UNNAMED LAKE IN FOREGROUND RESTS IN A HANGING VALLEY AND ITS OUTLET DROPS SEVERAL HUNDRED FEET TO THE MAIN VALLEY (HILEMAN PHOTO)
The tributaries of glacial valleys are also peculiar in that they usually enter the main valley high above its floor and for this reason are known as hanging valleys. ”

“ Examples of the hanging tributary type of fall which is due directly to the activity of the glaciers are Florence, Bird Woman, Virginia, Grinnell, Lincoln, and many others.
TRICK FALLS IN THE TWO MEDICINE RIVER
No less conspicuous than the mountains themselves are the lakes. ”

“ NOTE MELT-WATER LAKES TERMINATING AGAINST MORAINES AT EXTREME LEFT (DYSON PHOTO)
15 Park Features Resulting From Glaciation
A glacier is an extremely powerful agent of erosion, capable of profoundly altering the landscape over which it passes. ”