LIZARD HEAD PEAK IN THE SAN JUAN MOUNTAINS
Heavy slides sometimes rush so swiftly down steep slopes that their momentum carries their entire mass destructively several hundred feet up the slope of the mountain opposite.
Desiring fuller knowledge of the birth and behavior of avalanches, or snow-slides, I invaded the slide zone on snowshoes at the close of a winter which had the "deepest snow-fall on record." Several days were spent watching the snow-slide action in the San Juan Mountains. It was a wild, adventurous, dramatic experience, which closed with an avalanche that took me from the heights on a thrilling, spectacular coast down a steep mountain-side.
A thick, snowy, marble stratum overlay the slopes and summits. Appearing on the scene at the time when, on the steeps, spring was melting the icy cement that held winter's wind-piled snows, I saw many a snowy hill and embankment released. Some of these, as slides, made meteoric plunges from summit crags to gentler places far below.
A snow-storm prevailed during my first night in the slide region, and this made a deposit of five or six inches of new snow on top of the old. On the steeper places this promptly slipped off in dry, small slides, but most of it was still in place when I started to climb higher.
While I was tacking up a comparatively smooth slope, one of my snowshoes slipped, and, in scraping across the old, crusted snow, started a sheaf of the fluffy new snow to slipping. Hesitatingly at first, the new snow skinned off. Suddenly the fresh snow to right and left concluded to go along, and the full width of the slope below my level was moving and creaking; slowly the whole slid into swifter movement and the mass deepened with the advance. Now and then parts of the sliding snow slid forward over the slower-moving, crumpling, friction-resisted front and bottom.
With advance it grew steadily deeper from constantly acquired material and from the influence of converging water-channels which it followed. A quarter of a mile from its birthplace it was about fifty feet deep and twice as wide, with a length of three hundred feet. Composed of new snow and coasting as swiftly as a gale, it trailed a white streamer of snow-dust behind. A steeper or a rougher channel added to the volume of snow-dust or increased the agitation of the pace-keeping pennant. The morning was clear, and, by watching the wigwagging snow flag, I followed easily the fortunes of the slide to the bottom of the slope. After a swift mile of shooting and plunging, the slide, greatly compressed, sprawled and spread out over a level glacier meadow, where its last remnant lingered for the warmth of July.
Dismissing this slide, I watched along the range to the north and south, and from time to time saw the white scudding plumes of other slides, which, hidden in the cañons, were merrily coasting down from the steep-sloping crest.
These slides, unless they had run down an animal, did no damage. They were composed of freshly fallen snow and in their flight had moved in old channels that had been followed and perhaps formed by hundreds of slides in years gone by. Slides of this kind—those which accompany or follow each storm and which promptly make away with new-fallen snow by carrying it down through stream-channels—may be called Storm, or Flood, slides. These usually are formed in smooth gulches or on steep slopes.
The other kinds of slides may be called the Annual and the Century. In places of rough surface or moderate slope there must be a large accumulation of snow before a slide will start. Weeks or even months may pass before storm and wind assemble sufficient snow for a slide. Places of this kind commonly furnish but one slide a year, and this one in the springtime. At last the snow-drifts reach their maximum; warmth assists starting by melting snow-cornices that have held on through the winter; these drop, and by dropping often start things going. Crags wedged off by winter ice are also released in spring; and these, in going recklessly down, often knock hesitating snow-drifts into action. A fitting name for those slides that regularly run at the close of winter would be Spring, or Annual. These are composed of the winter's local accumulation of snow and slide rock, and carry a much heavier percentage of rock-débris than the Storm slide carries. They transport from the starting-place much of the annual crumbling and the weatherings of air and water, along with the tribute pried off by winter's ice levers; with this material from the heights also goes the year's channel accumulation of débris. The Annual slide does man but little damage and, like the Flood slide, it follows the gulches and the water-courses.