Of the three cascades that feed the Nisqually Glacier only the central one, it is to be observed, forms a continuous connection between the summit névés and the lower ice fields. The two others, viz. the one next to Gibraltar and the westernmost of the three, terminate in vertical cliffs, over great precipices of rock. From them snow masses detach at intervals and produce thundering avalanches that bound far out over the inclined ice fields below. Especially frequent are the falls from the cliff near Gibraltar. They occur hourly at certain times, but as a rule at periods of one or more days.
From the westernmost cascade avalanches are small and rare. Indeed, as one watches them take place at long intervals throughout a summer one can not but begin to doubt whether they are in themselves really sufficient to feed and maintain so extensive an ice field as lies stretched out under them. Surely much more snow must annually melt away from the broad surface of that field, exposed as it lies to the midday sun, than the insignificant avalanches can replace. Were they its only source of supply, the ice field, one feels confident, would soon cease to exist.
The fact is that the ice field in question is not dependent for its support on the avalanches from above. It may receive some contributions to its volume through them, but in reality it is an independent ice body, nourished chiefly by direct snow precipitation from the clouds. And this is true, in large measure, of all the ice fields lying under the ice cascades. The Nisqually Glacier, accordingly, is not to be regarded as composed merely of the cascading névés, reunited and cemented together, but as taking a fresh start at these lower levels. Improbable though this may seem at first, it is nevertheless a fact that is readily explained.
The winter snows on Mount Rainier are heaviest in the vicinity of its base; indeed, the snowfall at those low levels is several times greater than that on the summit. This in itself may seem anomalous. So accustomed is one to think that the snowfall on high mountains increases with the altitude that it seems strange to find a case in which the opposite is true. Yet Mount Rainier stands by no means alone in this regard. The Sierra Nevada and the Andes, the Himalayas and the Alps, all show closely analogous conditions.
In each of these lofty mountain regions the precipitation is known to be heaviest at moderate altitudes, while higher up it decreases markedly. The reason is that the storm clouds—the clouds that carry most of the rain and snow—hang in a zone of only moderate elevation, while higher up the atmosphere contains but little moisture and seldom forms clouds of any great density.
In the Rainier region the height of the storm clouds is in large measure regulated by the relief of the Cascade Range; for it is really this cooling mountain barrier that compels the moisture-laden winds from the Pacific Ocean to condense and to discharge. It follows that the storm clouds are seldom much elevated above the sky line of the Cascade Mountains; they cling, so to speak, to its crest and ridges, while the cone of Mount Rainier towers high above them into serener skies. Many a day may one look down from the summit, or even from a halfway point, such as Camp Muir (10,062 feet), upon the upper surface of the clouds. Like a layer of fleecy cotton they appear, smothering the lower mountains and enveloping the volcano's base.
Clouds, it is true, are frequently seen gathering about the mountain's crown, usually in the form of a circular cap or hood, precursor of a general storm, but such clouds yield but very little snow.
No accurate measurements have been made of the snowfall at the mountain's foot, but in the Nisqually Valley, at Longmire Springs, the winter snows are known often to exceed 20 feet in depth. The summer heat at this low level (2,762 feet) is, of course, abundantly able to remove all of it, at least by the end of May. But higher up every thousand feet of elevation suffices to prolong appreciably the life of the snowy cover. In Paradise Park, for instance, at altitudes between 5,000 and 6,000 feet, huge snowdrifts encumber the flowering meadows until far into July. Above an altitude of 6,000 feet permanent drifts and snow fields survive in certain favored spots, while at the 7,000-foot level the snow line, properly speaking, is reached. Above this line considerable snow remains regularly from one winter to the next, and extensive ice fields and glaciers exist even without protection from the sun.
It is between the 8,000 and 10,000 foot levels, however, that one meets with the conditions most favorable for the development of glaciers. Below this zone the summer heat largely offsets the heavy precipitation, while above it the snowfall itself is relatively scant. Within the belt the annual addition of snow to the ice fields is greater than anywhere else on Mount Rainier. The result is manifest in the arrangement and distribution of the glaciers on the cone. By far the greater number originate in the vicinity of the 10,000-foot level, while those ice streams which cascade from the summit, such as the Nisqually, are in a sense reborn some 4,000 feet lower down.
A striking example of an ice body nourished wholly by the snows falling on the lower slope of Mount Rainier is the Paradise Glacier. In no wise connected with the summit névés, it makes its start at an elevation of less than 9,000 feet. Situated on the spreading slope between the diverging canyons of the Nisqually on the west and of the Cowlitz on the northeast, it constitutes a typical "interglacier," as intermediate ice bodies of this kind are termed.