A glacier may also make periodic advances or retreats on a larger scale in obedience to climatic changes extending over many years. Thus all the glaciers on Mount Rainier, as well as many in other parts of the world, are at present, and have been for some time, steadily retreating as the result of milder climate or of a lessening in snow supply. Only so recently as 1885 the Nisqually Glacier reached down to the place now occupied by the bridge, and it is safe to say that at that time no engineer would have had the daring to plan the road as it is now laid. In the last 25 years, however, the Nisqually Glacier has retreated fully 1,000 feet.
Evidences of similar wholesale recession are to be observed at the ends of the other glaciers of Mount Rainier, but the measure of their retreat is not recorded with the precision that was possible in the case of the Nisqually Glacier. Eyewitnesses still live at Longmire Springs who can testify to the former extension of the Nisqually Glacier down to the site of the wagon bridge.
As one continues the ascent by the wagon road a partial view of the glacier's lower course is obtained, and there is gained some idea of its stream-like character. More satisfying are the views from Paradise Park. Here several miles of the ice stream (its total length is nearly 5 miles) lie stretched out at one's feet, while looking up toward the mountain one beholds the tributary ice fields and ice streams, pouring, as it were, from above, from right and left, rent by innumerable crevasses and resembling foaming cascades suddenly crystallized in place. The turmoil of these upper branches may be too confusing to be studied with profit, but the more placid lower course presents a favorable field for observation, and a readily accessible one at that.
A veritable frozen river it seems, flowing between smooth, parallel banks, half a mile apart. Its surface, in contrast to the glistening ice cascades above, has the prevailingly somber tint of old ice, relieved here and there by bright patches of last winter's snow. These lie for the most part in gaping fissures or crevasses that run athwart the glacier at short intervals and divide its body into narrow slices. In the upper course, where the glacier overrides obstacles in its bed, the crevasses are particularly numerous and irregularly spaced, sometimes occurring in two sets intersecting at right angles, and producing square-cut prisms. Farther down the ice stream's current is more sluggish and the crevasses heal up by degrees, providing a united surface, over which one may travel freely.
Gradually, also, the glacier covers itself with débris. Angular rock fragments, large and small, and quantities of dust, derived from the rock walls bordering the ice stream higher up, litter its surface and hide the color of the ice. At first only a narrow ridge of such material—a moraine, as it is called—accompanies the ice river on each side, resembling a sharp-crested embankment built by human hands to restrain its floods; but toward the lower end of the glacier, as the ice wastes away, the débris contained in it is released in masses, and forms brown marginal bands, fringing the moraines. In fact, from here on down it becomes difficult to tell where the ice of the glacier ends at the sides and where the moraines begin.
The lower part of the glacier also possesses a peculiar feature in the form of a débris ridge about midway on its back—a medial moraine. Most of the way it stretches like a slender, dark ribbon, gradually narrowing upstream. One may trace it with the eye up to its point of origin, the junction of the two main branches of the glacier, at the foot of a sharp rock spur on the mountain's flank.
In the last mile of the Nisqually's course, this medial moraine develops from a mere dirt band to a conspicuous embankment, projecting 40 feet above the ice. Not the entire body of the ridge, however, is made up of rock débris. The feature owes its elevation chiefly to the protective influence of the débris layer on its surface, which is thick enough to shield the ice beneath from the hot rays of the sun, and greatly retards melting, while the adjoining unprotected ice surfaces are rapidly reduced.
A short distance above the glacier's terminus the medial moraine and the ever-broadening marginal bands come together. No more clear ice remains exposed, irregular mounds and ridges of débris cover the entire surface of the glacier, and the moraine-smothered mass assumes the peculiar inchoate appearance that is so striking upon first view.
In utter contrast with the glacier's dying lower end are the bright snow fields on the summit in which it commences its career. Hard by the rock rim of the east summit crater the snows begin, enwrapping in an even, immaculate layer the smooth sides of the cinder cone. Only a few feet deep at first, they thicken downward by degrees, until, a thousand feet below the crater, they possess sufficient depth and weight to acquire movement. Occasional angular crevasses here interrupt the slope and force the summit-bound traveler to make wearying detours.
Looking down into a gash of this sort one beholds nothing but clean snow, piled in many layers. Only a faint blue tinges the crevasse walls, darkening but slowly with the depth, in contrast to the intense indigo hue characteristic of the partings in the lower course of the glacier. There the material is a dense ice, more or less crystalline in texture; here it is scarcely more than snow, but slightly compacted and loosely granular—what is generally designated by the Swiss term "névé."