Post 00950
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The large storm avalanches are most abundant on the Summit peaks of the range. They descend the broad, steep slopes, as well as narrow gorges and couloirs, with grand roaring and booming, and glide in graceful curves out on the glaciers they so bountifully feed.
Down in the main cañons of the middle region broad masses are launched over the brows of cliffs three or four thousand feet high, which, worn to dust by friction in falling so far through the air, oftentimes hang for a minute or two in front of the tremendous precipices like gauzy half-transparent veils, gloriously beautiful when the sun is shining through them. Most of the cañon avalanches, however, flow in regular channels, like the cascades of tributary streams. When the snow first gives way on the upper slopes of their basins a dull muffled rush and rumble is heard, which, increasing with heavy deliberation, seems to draw rapidly nearer with appalling intensity of tone. Presently the wild floods comes in sight, bounding out over bosses and sheer places, leaping from bench to bench, spreading and narrowing and throwing off clouds of whirling diamond dust like a majestic foamy cataract. Compared with cascades and falls, avalanches are short-lived, and the sharp clashing sounds so common in dashing water are usually wanting; but in their deep thunder tones and pearly purple-tinged whiteness, and in dress, gait, gestures, and general behavior, they are much alike.
Besides these common storm avalanches there are two other kinds, the annual and the century, which still further enrich the scenery, though their influence on fountains is comparatively small. Annual avalanches are composed of heavy compacted snow which has been subjected to frequent alternations of frost and thaw. They are developed on cañon and mountain sides, the greater number of them, at elevations of from nine to ten thousand feet, where the slopes are so inclined that the dry snows of winter accumulate and hold fast until the spring thaws sap their foundations and make them slippery. Then away in grand style go the ponderous icy masses, adorned with crystalline spray without any cloudy snow dust; some of the largest descending more than a mile with even, sustained energy and directness like thunderbolts. The grand century avalanches, that mow wide swaths through the upper forests, occur on shady mountain sides about ten to twelve thousand feet high, where, under ordinary conditions, the snow accumulated from winter to winter lies at rest for many years, allowing trees fifty to a hundred feet high to grow undisturbed on the slopes below them. On their way through the forests they usually make a clean sweep, stripping off the soil as well as the trees, clearing paths two or three hundred yards wide from the timber line to the glacier meadows, and piling the uprooted trees, head downward, in windrows along the sides like lateral moraines. Sears and broken branches on the standing trees bordering the gaps record the side depth of the overwhelming flood; and when we come to count the annual wood rings of the uprooted trees, we learn that some of these colossal avalanches occur only once in about a century, or even at still wider intervals.