In snowy zones the avalanche is commonly called a snow-slide, or simply a slide. A slide, with its comet tail of powdered snow, makes an intense impression on all who see one. It appears out of order with the scheme of things; but, as a matter of fact, it is one of gravity's working ways, a demonstration of the laws of sliding bodies. A smooth, steep slope which receives a heavy fall of snow will promptly produce or throw off a sliding mass of snow. Raise, lower, or roughen this slope, increase or decrease the annual snow-fall, or change the direction of the wind,—and thus the position of snow-drifts,—and there will follow corresponding slide-action. Wind and calm, gravity, friction, adhesion, cohesion, geology, temperature and precipitation, all have a part and place in snow-piling and in slide-starting.
The Century slides are the damaging ones. These occur not only at unexpected times but in unexpected places. The Century slide is the deadly one. It usually comes down a course not before traversed by a slide, and sometimes crashes through a forest or a village. It may be produced by a record-breaking snow or by snow-drifts formed in new places by winds from an unusual quarter; but commonly the mass is of material slowly accumulated. This may contain the remnant snows and the wreckage spoils of a hundred years or more. Ten thousand snows have added to its slowly growing pile; tons of rock-dust have been swept into it by the winds; gravel has been deposited in it by water; and gravity has conducted to it the crumbling rocks from above. At last—largely ice—it breaks away. In rushing down, it gathers material from its predestined way.
In the spring of 1901, one of these slides broke loose and came down the slope of Gray's Peak. For years the snow had accumulated on a ridge above timber-line. The mass shot down a steep slope, struck the woods, and swept to the bottom about four thousand feet below, mowing down every tree in a pathway about three hundred feet wide. About one hundred thousand trees were piled in wild, broken wreckage in the gorge below.
Although a snow-slide is almost irresistible, it is not difficult, in many localities, to prevent slides by anchoring the small snow-drift which would slip and start the slide. In the West, a number of slides have been suppressed by setting a few posts in the upper reaches of slopes and gulches. These posts pinned fast the snow that would slip. The remainder held its own. The Swiss, too, have eliminated many Alpine slides by planting hardy shrubbery in the slippery snowy areas. This anchorage gives the snow a hold until it can compact and freeze fast. Shrubbery thus is preventing the white avalanche!
A slide once took me with it. I was near the bottom of one snowy arm of a V gulch, waiting to watch Gravity, the world-leveler, take his next fragment of filling to the lowlands. Separating these arms was a low, tongue-like rock-ledge. A gigantic snow-cornice and a great snow-field filled, with full-heaped and rounded measure, the uppermost parts of the other arm.
Deep rumblings through the earth, echoings from crags and cañons through the communicative air, suddenly heralded the triumphant starting of an enormous slide. About three hundred feet up the heights, a broken end-on embankment of rocks and snow, it came coasting, dusting into view, plunging towards me. As a rock-ledge separated the two ravines above the junction, I felt secure, and I did not realize until too late that I was to coast down on the slide. Head-on, it rumbled heavily toward me with its mixed and crumbling front, making a most impressive riot of moving matter. Again and again the snowy monster smashed its shoulder into the impregnable farther wall. At last, one hundred feet high and twice as wide, came its impinging, crumbling front. At times the bottom caught and rolled under, leaving the overhanging front to cave and tumble forward with snowy splashes.
This crumbling front was not all snow; occasionally an iceberg or a cargo of stones fell forward. With snow flying from it as from a gale-swept, snow-piled summit, this monster of half a million tons roared and thundered by in a sound-burst and reverberation of incomparable depth and resonance, to plunge into a deeper, steeper rock-walled gorge. It probably was moving thirty-five or forty miles an hour and was gaining in velocity every second.
The noise of its passing suppressed the sounds of the slide that started in the gulch above me. Before I could realize it, this slide swept down, and the snow on which I was standing burst up with me into the air, struck and leaped the low ledge, rammed the rear end of the passing slide, and landed me, snowshoes down, on top of it.
The top was unstable and dangerous; it lurched, burst up, curled under, yawned, and gave off hissing jets of snow powder; these and the plunging movements kept me desperately active, even with my broad snowshoes, to avoid being swallowed up, or overturned and smothered, or crushed in the chaotic, fissuring mass.
As its speed increased, I now and then caught a glimpse, through flying, pelting snow-particles, of shooting rocks which burst explosively through the top. At timber-line the gorge walls abruptly ended and the channel curved swiftly to the left in a broad, shallow ravine. The momentum of this monster carried it out of the ravine and straight ahead over a rough, forested ridge.