Avalanches of various kinds pose perhaps the biggest threat you will face as an ice climber. On the approach to a climb, a new snow or slab avalanche may be a possibility. Slopes above may release and funnel onto you while you are on an ice face or in a gully or couloir. Under thaw conditions, an entire winter's snowpack may slide on a gentle slope of water-lubricated granite slabs. Knowledge of the basic phenomena associated with avalanches can help you avoid exposure in the first place and lessen your chances of being caught in an avalanche if you must travel or climb in dangerous conditions. The information presented here is enough to give you a basic understanding of the factors involved in avalanche prediction and avoidance, but it is not enough to make you an expert.

Always err of the side of caution. Even the most acknowledged authorities take this approach when in the field. There are simply too many variables to gamble your life on. However, with time and sensitive awareness, you will eventually develop a feel for conditions that will serve you well.

Snow avalanches are of two main types; ioosf smok) avalanches, which start at a point and gather mass in fan-shape as they fail; and cofi«iuc slab avalanches, which start sliding over a large area all at once, creating a well-defined fracture line. Either type of avalanche requires a trigger, which may be the weight of a climber, a falling rock or cornice, the collapse of a weak layer in the snowpack, a sudden change in barometric pressure or temperature, wind, the tug of gravity, new snowfall, a combination of the above, or something else!

Of the two types, slab avalanches are frequently the most damaging and deadly, and are often triggered by the victim's weight on a stressed slab that is weakly bonded to the ground or other layers within the snowpack. An avalanche of either type need travel only a short distance to gain deadly force and mass. People have been buried at the bottom of a thirty-foot slope.

Cm mvst be exercised in negotiating corniced ridges. The potential fracture Hue Is often tower than it might qpear, requiring a traverse wel below the ridge crest. ¡Photo: Jeff Lowe)

Cm mvst be exercised in negotiating corniced ridges. The potential fracture Hue Is often tower than it might qpear, requiring a traverse wel below the ridge crest. ¡Photo: Jeff Lowe)

Steepness is one of the factors that influences whether the introduction of a trigger will release the slope. Slopes of 30° to 45° have a low enough angle to allow snow to accumulate significant depths with poor bonds. Avalanches most often occur on these slopes, but in unstable conditions they may occur at angles greater or less than this.

Slope configuration is another determinant. Slab avalanches usually occur on convex slopes, breaking at the crest, but they may also break on a concave slope if other factors overcome the natural compression.

Snow on north-facing slopes (south-facing slopes in the Southern Hemisphere) receives little or no sun and often is slower to stabilize than snow on other aspects. South-facing slopes exposed directly to the sun are especially dangerous in the spring and summer. Slopes of other aspects to the sun are variously affected. Slight changes in aspect can have dramatic effects on slope stability.

Snow tends to be removed from windward slopes and deposited as slabs on leeward slopes, which are often unstable. If surface features such as rocks, trees, or brush are present and sticking up through the snowpack in significant quantity, they help to anchor the snow. Once these features are buried, avalanche hazard increases.

If the rate of new snowfall during a storm is more than one inch per hour, avalanches are quite likely to occur. If wind is present, the danger increases rapidly. New snow is not necessarily deposited evenly on every slope, so be alert for variations in depth. When six inches or more of new snow builds up on a slope without sloughing, avalanche conditions are dangerous. In the absence of new snowfall, wind alone is a major contributor to instability. Sustained winds will transport loose snow into gullies and slopes on the leeward sides, forming slabs.

Snow crystals are not all the same. Star-shaped, angular crystals interlock better than needles or pellets, creating a more cohesive snowpack. After falling, however, snow crystals begin to change as wind rolls them along the surface, as well as under the force of gravity, the pressure of new snow on top, or the effect of atmospheric conditions.

Storms that start with low temperatures and dry snow, followed by rising temperatures, are likely to cause avalanches. The dry snow early on forms a poor bond to the old snow or ice surface. However, if a storm starts warm and gets colder, the new snow bonds well to old snow or freezes to ice, and is thus more stable. Continued cold temperatures hinder slope stabilization, while warm weather aids settling and stability.

In prolonged cold, clear winter weather, Temperature Gradient (TG) snow, commonly called ¿epth hoar, forms from the ground up whenever the snowpack is thin (two to four feet), The ground is warmer than the upper snowpack, and moisture is leached from the bottom up through sublimation, creating large, weak, angular grains. Under the weight of new snow or in the presence of another trigger, a layer of depth hoar can collapse, causing an avalanche. In the Rocky Mountains this condition is all too prevalent.

Wet snow avalanches occur most often during the first prolonged spring thaw, but in the high mountains, wet snow avalanche hazard may exist throughout the summer, although it generally subsides later in the season.

The art of avalanche avoidance requires a combination of observation in the field and an understanding of the factors that predispose a slope to avalanche. As you travel through the mountains, watch for old avalanche paths, in particular those that show signs of having slid earlier in the winter or season, as these slopes will be most likely to slide again. Fresh avalanches indicate conditions are hazardous, at least on slopes of the same aspect, elevation, and snowpack history. If the snow settles with a "whoomp" around you, and especially if the snow cracks and the fractures travel for some distance, do not cross the slope. Avalanche danger is high! In warm weather, snowballs or "cartwheels" that roll down the slope also indicate danger.

If a slope is suspect, or if you simply have no idea of the stability of a slope, a snow pit dug through the snowpack to the ground will provide much valuable information. To be meaningful, the snow pit must be dug on the actual slope under question or on a slope of similar aspect and other characteristics. After digging the pit, lightly brush the strata to expose the cross section of the snowpack clearly. Ice crusts, weak bonds between snow layers, and particularly depth hoar will show up. Take a handful of snow from each of the layers and try to from a snowball. If it holds together well, then that layer is probably stable. If the entire snowpack exhibits this cohesive tendency, then in the absence of poor bonds between layers or an underlaying surface of ice or depth hoar, it is probably quite stable.

The safest routes follow ridge crests on the windward side below the potential fracture line of a cornice. On dangerous open slopes or wide couloirs, climb up or down the edges in a straight line; switchbacks in the middle of the slope are likely to cause an unstable slope to slide. Traverse dangerous slopes or couloirs at the top, above the release zone, if possible. If you can't cross above the release zone, it is worth making an even longer detour below the slope to cross on a flat well away from the bottom of the slope, if possible.

If you must cross a suspect slope, only one person should cross at a time, the others waiting their turn in a safe location, keeping a careful eye out for the exposed individual. Roped belays are only useful on small slopes. The force of a major avalanche makes it impossible to hold a victim. Do not assume that a slope is stable simply because one person crossed it safely,- each person must be watched carefully while crossing. Pick your line to take advantage of rock outcrops, ridges, or other havens.

While traveling in dangerous areas, unhook the waistbelt of your pack, remove your ice-axe or ski-pole straps, unhook the safety straps to your ski bindings, and ensure that you can quickly drop your pack if necessary, Beware of gear slings and runners over pack straps that make it impossible to rid yourself of this very effective "snow anchor." Wear your gloves and hat, and secure all openings in your clothing to avoid frostbite and hypothermia if you are caught and trapped in an avalanche.

If you are caught in an avalanche, get rid of all equipment and your pack, and try to stay near the surface of the tumbling snow by "swimming." Direct your efforts to making your way to the side of the avalanche. As the snow slows down, keep your hands in front of your face, trying to create an air pocket when the snow stops. You will survive longer when you are buried if you do not panic, giving your partners) time to find you.

The members of the party who are not involved in the avalanche should mentally mark the spot where the victim was first caught, and also the place last seen. A fan-shaped area bisected by an imaginary line drawn between the first and last places seen is the most likely area for the victim to be found. Articles of clothing or equipment may indicate the location of the victim and should be quickly checked by probing with a special probe, ski pole, or ice axe in the immediate vicinity If this fails to locate the victim, probe and scuff the snow in the fan-shaped area, especially in the places you somehow feel might be most likely to yield results. If the hasty search does not locate him or her, do a grid search, probing the area first at three-foot intervals, and finally every foot, Co for help only if ail this fails. You are the victim's most likely savior. Chances of survival diminish rapidly after the first half hour, but people have been known to survive for twenty-four hours.

After successfully locating and freeing the victim, treat for suffocation, shock, any traumatic injuries, and, finally, for hypothermia and frostbite, if appropriate. Do not remain any longer than necessary in an area exposed to further avalanche danger.

First Aid

Even the most careful and experienced climbers will, at some point, need to provide emergency medical assistance to themselves or to someone else. The alpinist who does not take the time to become proficient in advanced first aid is neglecting to accept a moral duty. A thorough understanding of basic bodily processes and anatomy also serves the climber well when it is time to choose clothing and food to take into the mountains. Most clubs and organizations offer first aid courses and medical seminars specially tailored to the needs of climbers. You should attend these.

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