Every snow-fall caused a snow-slide to rush down Bobtail Gulch. This
run-off of snow was as regular as the run-off of storm-water. The snow
which accumulated at the head of this gulch was a danger to the trail
below, and if the snow showed the slightest hesitation to "run" when
the storm had ended, a miner from a neighboring mine started it by
rolling a few stones into it or by exploding a stick of dynamite near
by.
During my stay at a miners' boarding-house in the San Juan Mountains a
heavy snow-fall came to a close. "Has the Greagory run yet?" inquired
the foreman of one of the miners. "No." "Better start it, then." Ten
minutes later fifty thousand tons of snow went plunging down Greagory
Gulch.
"This cabin will never be caught by a snow-slide!" said the
prospector with whom I was having supper. "A slide hit my cabin in the
Sawtooth Mountains. No more sleeping for me in the possible
right-of-way of a slide! I sized up the territory before building this
cabin and I've put it out of the range of slides."
All this was encouraging, as I was to spend the night in the cabin and
had arrived after the surrounding mountains were hidden in darkness. A
record-breaking snow of eight days and nights had just ended a few
hours before. During the afternoon, as I came down from Alpine Pass on
snowshoes, the visible peaks and slopes loomed white and were
threateningly overladen with snow. Avalanches would run riot during
the next few hours, and the sliding might begin at any minute. Gorges
and old slide-ways would hold most of these in the beaten
slide-tracks, but there was the possibility of an overladen mountain
sending off a shooting star of a slide which might raise havoc by
smashing open a new orbit.
The large spruces around the cabin showed that if ever a slide had
swept this site it was longer ago than a century. As no steep slope
came down upon the few acres of flat surrounding the cabin, we
appeared to be in a slide-proof situation. However, to the north was a
high snow-piled peak that did not look assuring, even though between
it and the cabin was a gorge and near by a rocky ridge. Somewhat
acquainted with the ways of slides, I lay awake in the cabin, waiting
to hear the muffled thunder-storm of sound which would proclaim that
slides were "running."
Snow-slides may be said to have habits. Like water, they are governed
by gravity. Both in gulches and on mountain-sides, they start most
readily on steep and comparatively smooth slopes. If a snow-drift is
upon a thirty-degree incline, it may almost be pushed into sliding
with a feather. A slope more steeply inclined than thirty degrees does
not offer a snow-drift any visible means of support. Unless this slope
be broken or rough, a snow-drift may slide off at any moment.
In the course of a winter, as many as half a dozen slides may start
from the same place and each shoot down through the same gorge or
over the same slope as its predecessor. Only so much snow can cling to
a slope; therefore the number of slides during each winter is
determined by the quantity of snow and the character of the slope. As
soon as snow is piled beyond the holding-limit, away starts the slide.
A slide may have slipped from this spot only a few days before, and
here another may slip away a few days later; or a year may elapse
before another runs. Thus local topography and local weather
conditions determine local slide habits,--when a slide will start and
the course over which it will run.
The prospector was snoring before the first far-off thunder was heard.
Things were moving. Seashore storm sounds could be heard in the
background of heavy rumbling. This thunder swelled louder until there
was a heavy rumble everywhere. Then came an earthquake jar, closely
followed by a violently explosive crash. A slide was upon us! A few
seconds later tons of snow fell about us, crushing the trees and
wrecking the cabin. Though we escaped without a scratch, a heavy
spruce pole, a harpoon flung by the slide, struck the cabin at an
angle, piercing the roof and one of the walls.
The prospector was not frightened, but he was mad! Outwitted by a
snow-slide! That we were alive was no consolation to him. "Where on
earth did the thing come from?" he kept repeating until daylight. Next
morning we saw that to the depth of several feet about the cabin and
on top of it were snow-masses, mixed with rock-fragments, broken
tree-trunks, and huge wood-splinters,--the fragment remains of a
snow-slide.
This slide had started from a high peak-top a mile to the north of the
cabin. For three quarters of a mile it had coasted down a slope at the
bottom of which a gorge curved away toward the west; but so vast was
the quantity of snow that this slide filled and blocked the gorge with
less than half of its mass. Over the snowy bridge thus formed, the
momentum carried the remainder straight across the gulch. Landing, it
swept up a steep slope for three hundred feet and rammed the rocky
ridge back of the cabin. The greater part came to a stop and lay
scattered about the ridge. Not one tenth of the original bulk went
over and up to wreck the cabin! The prospector stood on this ridge,
surveying the scene and thinking, when I last looked back.
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.
[Illustration: LIZARD HEAD PEAK IN THE SAN JUAN MOUNTAINS]
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.
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.
Trees before it were crushed down, and those alongside were thrown
into a wild state of excitement by the violence of swiftly created and
entangling gale-currents. From the maelstrom on the top I looked down
upon the panic through the snow-dust-filled air and saw trees flinging
their arms wildly about, bowing and posturing to the snow.
Occasionally a treetop was snapped off, and these broken tops swirled
wildly about, hurried forward or backward, or were floated upward on
rotating, slower currents. The sides of the slide crumbled and
expanded; so it became lower, flatter, and wider, as it slid forward
on a moderate up grade. A half-mile after leaving the gorge, the slide
collided at right angles with a high moraine. The stop telescoped the
slide, and the shock exploded the rear third and flung it far to right
and left, scattering it over a wide area. Half a minute later I clawed
out of the snow-pile, almost suffocated, but unhurt.
Toward the close of my last winter as government "Snow Observer" I
made a snowshoe trip along the upper slopes of the Continental Divide
and scaled a number of peaks in the Rocky Mountains of central
Colorado. During this trip I saw a large and impressive snow-slide at
a thrillingly close range. It broke loose and "ran"--more correctly,
plunged--by me down a frightful slope. Everything before it was
overwhelmed and swept down. At the bottom of the slope it leaped in
fierce confusion from the top of a precipice down into a cañon.
For years this snowy mass had accumulated upon the heights. It was one
of the "eternal snows" that showed in summer to people far below and
far away. A century of winters had contributed snows to its pile. A
white hill it was in the upper slope of a gulch, where it clung,
pierced and anchored by granite pinnacles. Its icy base, like poured
molten lead, had covered and filled all the inequalities of the
foundation upon which it rested. Time and its tools, together with its
own height and weight, at last combined to release it to the clutch
and eternal pull of gravity. The expanding, shearing, breaking force
of forming ice, the constant cutting of emery-edged running water, and
the undermining thaw of spring sent thundering downward with ten
thousand varying echoes a half-million tons of snow, ice, and stones.
Head-on the vast mass came exploding toward me. Wildly it threw off
masses of snowy spray and agitated, confused whirlwinds of snow-dust.
I was watching from the top of a precipice. Below, the wide, deep
cañon was filled with fleecy clouds,--a bay from a sea of clouds
beyond. The slide shot straight for the cloud-filled abyss and took
with it several hundred broken trees from an alpine grove that it
wrecked just above the precipice.
This swift-moving monster disturbed the air, and excited, stampeding,
and cyclonic winds flung me headlong, as it tore by with rush and
roar. I arose in time to see the entire wreckage deflected a few
degrees upward as it shot far out over the cloud-made bay of the
ocean. A rioting acre of rock-fragments, broken trees, shattered
icebergs, and masses of dusting snow hesitated momentarily in the air,
then, separating, they fell whirling, hurtling, and scattering, with
varying velocities,--rocks, splintered trees, and snow,--in silent
flight to plunge into the white bay beneath. No sound was given forth
as they fell into, and disappeared beneath, the agitated sea of
clouds. How strange this noiseless fall was! A few seconds later, as
the wreckage reached the bottom, there came from beneath the silent
surface the muffled sounds of crash and conflict.