Pacific Northwest Hiking & Backpacking Group Message Board › Avalanche Awareness
Why avalanche awareness?
Mountains attract climbers, skiers and tourists who scramble up and down the slopes, hoping to conquer peaks, each in their own way. Yet, to do this they must enter the timeless haunt of avalanches.
Each year, avalanches claim more than 150 lives worldwide, a number that has been increasing over the past few decades. Thousands more are caught in avalanches, partly buried or injured. Everyone from snowmobilers to skiers to highway motorists are caught in the "White Death." Most are fortunate enough to survive.
Avalanche factors: what conditions cause an avalanche?
Several factors may affect the likelihood of an avalanche, including weather, temperature, slope steepness, slope orientation (whether the slope is facing north or south), wind direction, terrain, vegetation, and general snowpack conditions. Different combinations of these factors can create low, moderate or extreme avalanche conditions.
Keep in mind that some of these conditions, such as temperature and snowpack, can change on a daily or even hourly basis. This necessitates constant vigilance of your immediate surroundings while doing any wintertime backcountry travel. The route you chose may be safe when you begin, but may become dangerous if conditions change dramatically throughout the day.
While this may seem like a lot of work, once you understand factors that can cause avalanches, most of these signals require simple observation to evaluate your surroundings as they change. Simply ask yourself, when are conditions sufficient to cause a mass of snow to slide down a slope?
The following factors often occur in combination to produce an avalanche, but if a slope is unstable in any way, it may take only the weight of one skier to set off an avalanche. The more foresight you have about conditions and situations to avoid the safer your outing will be.
Avalanches are most likely to run either during or immediately after a storm where there has been significant snowfall. The 24 hours following a heavy snowstorm are the most critical. Consequently, it becomes important to be aware of current weather conditions as well as the conditions from the previous couple of days. Temperature, wind, and snowfall amount during storms can create fatal avalanche conditions during your outing. If there has been heavy snowfall the day or night before your trip, it may be wise to postpone the trip in order to avoid the increased avalanche danger.
Recent snowfall puts extra stress on the existing snowpack, especially if it does not adequately bond to the pre-existing surface layer. The extra weight of new snow alone can cause a slab to break off and fall down the slope, particularly in storm-induced avalanches. Snowfall amounts of one foot or more (frequent in mountainous areas) create the most hazardous situations, producing avalanches that are often large enough to block highways and cause major destruction. Amounts of six to twelve inches pose some threat, particularly to skiers and recreationists. Amounts less than six inches seldom produce avalanches.
Because snow is a good insulator, small temperature changes do not have as much effect on snowpack as larger or longer changes do. For instance, shadows from the sun crossing the snow surface throughout the day will not significantly change snowpack stability. Changes that last several hours or days, such as a warm front moving through, can gradually increase temperatures that cause melting within the snowpack. This can seriously weaken some of the upper layers of snow, creating increased avalanche potential, particularly in combination with other factors.
Wind usually blows up one side of a slope or mountain (the windward side), and down the other (the leeward side). Blowing up the windward slope, wind will "scour" snow off the surface, carry it over the summit, and deposit it on the leeward side. What this does is pack snow unevenly on the leeward side, making it more prone to avalanche. A cornice or icy overhang at the top of a mountain or ridge is a telltale sign of wind scouring. It is safer to travel on the back, or windward side of such a slope, where the snow layer is thinner and wind-packed.
Perhaps the most significant factor (but not the only one) is how the snowpack has developed over the season. We only see the surface and maybe the top few layers of snow, but it can be layers of snow several feet deep that may ultimately determine whether the slope will fail.
Snowpack conditions are extremely important because many layers of snow build up over the winter season. Each layer is built up under different weather conditions and will bond differently to the subsequent layers. Snowflakes, or snow crystals, within the snowpack eventually become more rounded due to melting/re-freezing and settlement. This metamorphism allows them to compress and (generally) form stronger bonds.
Most avalanches occur on slopes between 30 and 45 degrees, but can occur on any slope angles given the right conditions. Very wet snow will be well lubricated with water, meaning it might avalanche on a slope of only 10 to 25 degrees. Very dry or granular snow will most likely avalanche on a slope close to the 22 degree angle of repose. Compacted, well-bonded layers create a snowpack that can cling to steeper slopes until a weak layer is created.
Although avalanches will run on slopes facing any direction, most avalanches run on slopes facing north, east, and northeast (also the slope directions that most ski areas are located on). Because the sun is at such a low angle, particularly during the winter, a colder and deeper snowpack develops. Slopes that are under shadow throughout most of the day are suspect because the snowpack remains cooler, without much of the melting and bonding that can make the snow layers stronger.
Paying attention to where you are in the grand scheme of things can offer clues about avalanche likelihood. Bowls and gullies are suspect at any time, regardless of other conditions. Snow can accumulate deeply and quickly in these areas, increasing the possibility of an avalanche. Even if you can see that an avalanche has already run, be wary. Avalanches can fall in a "piecemeal" fashion, where one avalanche will run and leave the rest of the slope weakened, and the slightest provocation can cause subsequent avalanches on that same slope. Smaller depressions or shallow gullies in the mountainside can also be hazardous. During an avalanche, these "terrain traps" serve as accumulation points for snow and debris in which a victim could be buried.
On a snow-covered slope, heavily forested areas are much safer than open spaces, but don't assume that any vegetation at all will be protective. Lone trees, bushes, or large rocks on a mountainside can sometimes weaken the stability of the snowpack. A fracture line (the break-off point for an avalanche) may run from a lone tree to a rock to another tree. Also, during avalanches, trees and rocks catch debris and cause excessive snow pile-up, as well as provide lethal obstacles for anyone caught in an avalanche.
How to determine if the snowpack is safe
There are several ways to gauge snowpack stability. Keep any eye out for any cracks shooting across the surface, or small slabs shearing off. These are signs of weakened snowpack. Also, listen for "hollow" or "whumping" noises as you walk or ski. This indicates that there is a weaker layer underneath, leaving the surface layer more prone to collapse. Careful, continuous observations throughout your trip can reveal natural clues, but other more reliable measurements, such as snow pits and shear tests, will help you predict more accurately how stable or unstable the snowpack is.
Digging a snowpit reveals more about the snowpack structure than is visible from the surface. Making a snowpit requires a little more practice and experience, but it is quickly accomplished with a portable shovel. The most effective snowpits should be dug near potential avalanche starting zones, but without putting you or other members of your party at risk. With a shovel, dig a hole four to five feet deep and about three feet wide. Smoothen the uphill wall until it is vertical and you can see the different layers of snow. By pressing your hand against each layer to feel its hardness, you can determine whether there are weak layers.
Once you have dug the pit, a shear test is fairly easy. From the vertical, uphill wall, separate a column of snow without pulling it free from the wall. Insert a shovel at the back (uphill side) of the column and gently pull on the handle. If weak layers pull loose quite easily, the snowpack is very unstable. If it takes a few tugs on the handle before any layers pull loose, the snowpack is slightly unstable. If you really have to pry hard on the handle to loosen any layers, the slope is relatively stable, although caution should still be used at all times.
When conducting these tests throughout the day, pay attention to the slope angle. Layers that seem strong on a 30-degree slope may be much weaker on a steeper slope. Also, remember that the shear test relies on the pull of a shovel, not the weight of a person. You can test this by standing or jumping on the uphill edge of the snowpit (the "banzai jump" test), but only if you already know the snowpack is stable after conducting a shear test and if this presents no risk of injury or of triggering an avalanche.
Snowpit and shear tests should be conducted frequently during your outing, especially if you are crossing several different slopes or types of terrain. Some experts perform them dozens of times a day. While this may seem a bit time-consuming at first, experience will speed the process. More importantly, it is a fairly simple and accurate measure you can make which may save your life.
Ideally, avoiding avalanches in the first place is much easier than trying to survive one. Avalanche safety begins even before you begin your travel. In addition to keeping an eye out for weather and terrain conditions, there are steps you can take ahead of time to help you or other members of your party if you are caught in an avalanche.
Portable shovels made of plastic and aluminum are lightweight and compact enough that they can be carried in a pack. Digging with a shovel, as opposed to using hands or ski poles, can dramatically decrease the time it takes to dig out a victim. Digging by hand takes an average of 45 minutes to dig out one square meter of snow. Using a shovel to dig out the same amount of snow takes less than ten minutes.
Collapsible probes or ski-pole probes are also easy to carry along. Collapsible probes usually consist of two-foot lengths of tubular steel that join together to make a probe ten to twelve feet long. Ski-pole probes are made so that grips and baskets can be removed. The two poles can then be joined together to form a probe. Probing is essential to finding a buried victim if there are no visible clues on the surface.
Avalanche beacons (transceivers) are the most commonly used rescue device, and are standard equipment for ski-area patrollers and heli-ski operators. When properly used, they provide the fastest way of locating a victim. When a victim is buried, the transceiver will emit a frequency that other transceivers can home in on. However, it is critical to have the transceiver set to "transmit" during your outing. When trying to locate a buried victim, rescuers will then switch their transceivers to "receive" to locate the signal. Unfortunately, avalanche deaths have occurred due to the fact that the victims had their transceiver switched to "receive" rather than "transmit." Consequently, rescuers could not locate them in time.
Remember that more than one transceiver unit is required. A transceiver will not help locate a victim who is not also wearing one. Likewise, a victim with a transmitting beacon may not be found unless someone else has a transceiver to pick up that signal.
Using beacons requires practice. Homing in on a buried signal involves moving in increasingly smaller circles around the area of the signal. When purchasing a unit, learn how to use it properly, and practice using it frequently. Make sure those in your party carrying transceivers understand how to use them.
Time is of the essence. Carrying this equipment may mean the difference between life and death for someone buried in an avalanche. Statistics show that most survivors are dug out within 15 to 30 minutes. For victims buried longer than 30 minutes, survival chances decrease drastically. In fact, U.S. statistics show that victims buried longer than 45 minutes rarely survive. Depth of burial is also a factor in surviving, but even if a victim is near the surface, the length of time it takes to locate them and dig them out can still be the critical factor.
Avalanche quick checks
Following is a list of quick checks you can make throughout the day:
What have the weather conditions been over the past few days? Recent heavy snows?
Can you observe any wind loading on the slopes?
Do you have a good sense of the snowpack? Have you performed any snowpit or shear tests?
Have you noticed many fracture lines, heard "whumping" or cracking sounds, or hollow noises in the snowpack?
Are you keeping an eye on the orientation and steepness of the slopes as you cross them?
Are you lingering in gullies, bowls, or valleys?
Noticed any recent avalanche activity on other slopes similar to the one you are on?
If a slope looks suspect, are there alternative routes?
Extra precautions to take
If there is no alternative to crossing a suspect slope, do so one person at a time to minimize risk.
When descending or ascending a slope, try to stay as far to the sides of a potential avalanche chute as possible to decrease your chances of being caught if an avalanche runs.
Be aware of the condition of those in your party. If someone is tired, hungry, or cold they may not be using their best judgement.
Remain constantly aware of changing weather or temperature conditions, particularly if your outing will last more than a few hours.
Consider avalanche rescue equipment, such as beacons, ski-pole probes, and collapsible shovels, as a necessary part of your backcountry gear.
If you can not afford a avalanche beacon for $3-400, but at least an avalanche cord, used successfully in the Alps of Europe for 100 years: Home Depot, $2.97 for 75 ft of 2mm orange cord. You tie it around your waist and drag the line behind you.
If you get into an avalanche, hopefully a part of the light cord sticks out and searchers can dig after you.
Valentin Caspaar, www.epeaks.com