An avalanche is hardly an uncommon phenomenon, literally thousands occur every winter and spring in mountainous terrain, where the terrifying rumble of these flash floods of snow are common sounds to woodsmen and cross-country skiers.
Most occur naturally and spontaneously, triggered through a series of natural events, and seldom pose a threat to human life or limb. But even so, in the past 35 years some 400 people have perished in avalanches, avalanches they themselves either triggered or could have avoided had they been able to read the signs.
How avalanches form
Understanding how an avalanche works can help one to minimize the risks of being caught in the midst of one, but first, we must know a little about snow.
An avalanche put simply, is snow, a river of snow, to be more precise, that for some reason has overcome its delicate bonds between gravity and earth. Snow cover is not a homogenous mass. If one were to dig a trench about four to five feet into the snow, then smooth the vertical wall of that trench with a mitten or whisk broom, he would discover a series of lines representing layers.
Like the rings of a tree, these layers tell the history of that season’s snowfall and the quality of the snow that remains. A layer with a ridge, for example, is the sign of a harder, more compact layer, while an indented or valleyed layer shows softer weaker snow. Each of these layers is bonded to the other above and beneath it. It is when one bond gives way completely and begins to slide off, that an avalanche occurs.
A good way to test the quality of these layers is to try the “touch test.” With a glove still on, gouge into each layer of snow, making sure to note the properties of each.
If your fist can penetrate it, the layer is very soft. If four fingers go fairly easily in, it is considered soft. If only one finger can penetrate the snow layer, it is moderately hard. If it takes a pencil to penetrate it, it is hard; and if only a knife will go in. the snow is very hard.
So what does all this mean?
Knowing the quality of the snow can help one determine how well the layers are bonded together. Some conditions to watch out for are hard layers atop weak layers atop very hard layers (sliders). The hard layer above is denser and therefore heavier than the soft layer below. And because the soft layer is sitting on a very hard layer, it has a surface upon which it can easily slide.
Although knowing these things can help one to determine the relative safety of the surrounding snow, it should always be remembered that the condition of the snowfield at that moment in time can be very different a few hours or a day later.
Many have been caught in avalanches while treading in the footprints of another who had passed that way a short time before. Any avalanche safety test is only good for the here and now.
If still in doubt, the next test that one can perform is the “slider test.” With an ice saw cut uphill into the trench face about six inches, then make another cut parallel (two feet will do) to the trench face. Placing an ice axe, ski (bindings facing uphill) or ski pole into the cut, pull downhill and see how well the layers hold together. If one easily slides loose from another, you’ll know there could be problems.
Slope and weight factors
There are three main factors that are responsible for layers breaking loose, by far the most critical being slope. A severely steep slope (60 to 90 degrees) poses little danger in the form of avalanches. Snow falling on it is continually sluffing off, and therefore it seldom has the chance to build up enough to become dangerous.
Slope angles between 25 and 60 degrees, however, are subject to frequent avalanches, with the greatest danger being on slopes with an angle of 30 to 45 degrees. Anything less than 25 degrees is fairly safe, although avalanches have occurred at this range. It is only when the stress of gravity exceeds the strength of the bond of the layers that an avalanche occurs.
Besides the slope angle, slope shape is also important. Where the slope bulges outwards, the snow layer is stretched thin and therefore made weaker. Conversely, where the slope curves inward (concave), the snow is compressed and made stronger.
The second most important factor in “gravity stress” is weight. Wet snow is much heavier than dry snow, weighing upwards of 55 pounds per cubic foot, making rain a very dangerous factor in avalanche-prone terrain. Rain can also deteriorate the bonds between layers, although wet snow, upon re-freezing, is very strong indeed.
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Overall, weather (air temperature) is the prime determinant of snow strength.
If the snowpack is fairly warm (25 degrees Fahrenheit or more), it solidifies rapidly into a strong and dense mass. One of the worst weather conditions, in regards to the formation of weak snow, is “fluffy” flakes falling in extremely cold air, followed by a layer of warmer, heavier (wetter) snow. The cold, dry, fluffy snow will not bond well enough to hold the heavier wet snow on top.
It’s been found that approximately 80 percent of all avalanches happen during or shortly after storms. When snow falls at a rate in excess of one inch per hour or gains an extra foot of depth, its likelihood to slide increases dramatically. Too much weight too quickly can break otherwise strong bonds.
Heavy concentrations of snow can accumulate from “wind-loading,” resulting in unstable conditions, especially whenever the wind is in excess of 15 miles per hour. Look for certain danger signals, cornices from wind loading, the pattern of snowdrifts around boulders, and trees. These are the backcountry traveler’s clues as to what’s been happening with the weather.
Nature almost seems to want to warn those who brave the outdoors of imminent danger. Dangerous weather signals are seen in the clouds, dangerous currents are seen in the eddies of rivers, and likewise, dangerous snow has signs of its own.
“Sunballing” or cartwheeling balls of snow begin rolling down slopes, leaving their telltale tracks indicating deep instability beneath. A most unnerving sign of danger is the presence of cracks in the snow radiating out around one’s feet.
Your ears are also excellent instruments for recognizing potentially hazardous ground. “Whumphing” noises occur when one layer collapses on another, a prelude of greater collapses to come.
Besides the snow factor, what does an avalanche-prone terrain look like?
There are several signs to look out for. Avalanches often careen through established tracks, natural “ski slopes.” Trees with branches sheared off on one sideshow past avalanche damage. Past avalanche damage always shows signs of present avalanche danger.
Generally speaking, it’s safer to travel on ridges than in valleys, especially the windward portions where the snow cover is more compacted and shallower. If possible, try to circumvent lee slopes and steer clear of valley bottoms. Avalanche slides have been known to travel as far as a mile, and the “blast zone” (the hurricane-force winds that accompany a major slide) extend much further than that.
If the season is mid-winter, north-facing slopes are generally more dangerous, while in spring and in spring-like weather, south-facing slopes have a greater tendency to slide. Gullies (or chutes) are infinitely more hazardous than surrounding slopes.
Densely wooded areas provide a good degree of protection by anchoring down snow, although sparse vegetation could be just temporarily holding back more weight of snow than the slope angle can accommodate.
Traveling in a group
When traveling in a group through avalanche-prone regions there’s a number of precautions a person can take to avoid being a casualty statistic if caught in an avalanche.
Rucksacks and other loose gear should be carried in the hands to jettison if necessary, so as not to drag one down, besides creating a mess of scattered debris that will give rescuers a better idea of where to begin their search. Also, if buried, a rucksack clutched to the face can provide a larger pocket of air.
If worse comes to worst and the hiker or skier finds himself about to be engulfed in an avalanche, he can increase his odds of survival by knowing what to do ahead of time. The standard recommendation is to swim on the back, kicking, and flailing for all your worth in an effort to stay on top and try to make it to the edge of the slide.
When the slide starts to slow the victim should thrust up any appendage available, before the snow settles, to aid in his being found.
Also, before the snow settles, he should take in as much air as his lungs will hold, expanding the chest and rib cage fully to make it easier to breathe later when the heavy snow has his body pinned down. A final effort should be made to cup an arm in front of one’s head, in order to create a little more airspace.
If the snow is dry and light, breathing should be no problem as plenty of air is trapped around the snow granules. Because wet snow, on the other hand, can weigh 50 to 55 pounds per square foot, it’s possible for an avalanche victim to suffocate even with his head above ground, just from the weight of the snow on his chest.
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Facilitating rescue operations
Some important equipment for a group to carry, should one member of their party become an avalanche victim, would be an avalanche rescue transceiver, ski poles or other probing devices, a snow shovel, and a first aid kit.
If each person crossing hazardous terrain were required to wear either a transceiver or a 100-foot length of brightly colored rope, the rescue process would be greatly enhanced. Remember, a person buried in the snow has only a 50 percent chance of survival if buried in the snow for a half-hour. Time will not allow for help to come from elsewhere, you are their only chance of life.
If there were no transceivers or colored ropes or no hands or arms sticking above the snow, then hopefully the rescuers will have watched carefully the point where the victim disappeared. If this was impossible, begin randomly probing near areas of the greatest snow accumulation, near boulders or trees, near debris (ruck-sacks. etc.),. and near the edge of the avalanche flow.
If there is no trace at all of the victim, a “search line” should be formed of rescuers probing about 30 inches apart, advancing uphill two feet at a time.
Once the victim is found, treat immediately for suffocation (first), then hypothermia and shock. If one portion of the group gets cut off from the other portion, and no one was injured, it’s best to wait till late afternoon or evening to proceed any further. By this time, the slope should be in the shade, and the colder air temperature and time have hopefully combined to give the snow a greater holding ability.
Another major hazard associated with snow travel is snow blindness. Snow blindness is simply sunburned eyes. Snow is a highly reflective substance, and the extreme amount of ultraviolet and infrared light that’s encountered in high altitudes can cause serious problems for the unprepared. Blistering of both the retina and cornea can occur.
The easiest way to safeguard against snow blindness is by wearing a good pair of sunglasses. Expensive does not necessarily mean effective, as some very poor but very costly designer sunglasses will prove. A good pair of mountaineering glasses will generally come with specifications that list how much ultraviolet and infrared light is filtered out.
A 90 percent effective lens is about right. The glasses should also come with shades that protect the eyes from glare coming in from the sides.
Stages of snow blindness
The first stages of snow blindness are accompanied by a scratchy (sandy) feeling in the eyes, followed by more watering than normal. In slightly more advanced stages, halos or ghost images are seen around lights, the head starts to ache, and temporary blindness can occur.
Fortunately, snow blindness is seldom permanent, though some permanent damage to the retina and cornea can remain. Usually, if treated properly, most snow blindness victims will recover within 18 hours—to a maximum of two to three days.
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Treatment generally consists of shading the eyes with cool, wet compresses, and strapping on two pairs of dark glasses to protect the light-sensitive eyes from further damage. Aspirin should be taken for the pain and to prevent swelling. If there is no aspirin available, a tea brewed from the leaves, bark or twigs of willow, or the leaves of quaking aspen will suffice. Both of these plants contain salicylic acid, the buffered active ingredient of aspirin.
Chop up a one-quarter cup of hot boiling water for 15 minutes before drinking. This dosage is equal to approximately two aspirins. Once a person has suffered from snow blindness, he will be more susceptible to it in the future.
If you find yourself unplanned and unprepared in the snow, a makeshift pair of snow glasses can be made from cardboard or the softer inner bark of Pine trees. If you’re able to make a fire, it’s nice to boil the inner bark first, to make it even more pliable and easier to cut, but if you can’t, the uncooked inner bark will do.
Try to fillet off a piece wide enough to cover from just below the eyebrows to the bottom of the nose, and fashion a cord to tie it securely around the head, Make two narrow slits for the eyes to see out of, and a crescent slit for the nose. Lastly, coat the inside of the bark with a thin layer of black ashes or crushed charcoal to absorb any reflections that might come through.
Not only the eyes can be seriously burned from the glare of the snow. Many novices to snow travel are quite surprised at the planes burns will occur. Sunburns under the chin and in the nostrils and ears are quite common from the ultraviolet rays being reflected upwards.
The best sunscreen protections for most exposed parts of the body use para-aminobenzoic acid as their active ingredient, while the white reflective zinc oxide creams work best for the lips.
Snow is an amazing substance. Last month we discussed its wonderful insulating properties. It’s a ready source of water wherever a traveler may go. When firm packed it makes cross-country hiking a joy that can hardly be equaled in summer. Snow is beautiful. Don’t let it become a fatal attraction. Be knowledgeable, be alert, be attentive, and be always prepared.