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VOLUME 5, ISSUE 1.
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A “flagged” tree indicates
that an Avalanche has
occurred here in the past.
Notice that the uphill
branches have been
removed due to past
avalanche activity.

“In 1986, one of the longest avalanche “runners” with an extremely small slope angle
of 18 degrees devastated
this area. “A” is where it
started and “B” is where the
run out zone stopped.

Even after 13 years the destruction of this avalanche
is still evident. Notice the
pattern of the dead tree
trunks.

An avalanche slid here in the past. The bottom layers of the snow pack did not slide, while the top layers did.


Imagine yourself on a winter, back country trip. It could easily be on skis, snowshoes or that brand new snowmobile. While enjoying the scenery of the snow-covered hills and mountains, something hits the side of your body, causing you to lose your balance. While rolling head over heels, it becomes dark and difficult to breath. Suddenly, all movement comes to an abrupt stop. It is dark and cold, and you attempt to scream for help, but no one hears your pleas. As you breathe your last breath, you wonder, “What happened?” Finally, the breathing stops, and hypothermia begins to kill you.
In this scenario, you were caught in an avalanche. A common misconception is that, “I would never be in an area where avalanches occur.” When watching an avalanche released on television, they are filmed moving down high mountain slopes. What most people do not see is that those avalanches have been triggered by some type of explosive for film crew to capture. Pretty impressive, right? The majority of all avalanches do not occur on that type of terrain.
Avalanches do not occur by accident but rather by a particular reason. As people desire to venture further into the back country, the danger increases. We allow ourselves to feel a false sense of security by our clothing, equipment and machines. Mother Nature will be unforgiving for mistakes made, and believe this—she is relentless.
During my trips into the back country, I have seen on numerous occasions snowmobiles and their tracks on snow-covered terrain that is just waiting to slide and bury anything in its path. A video tape can not capture the full impact of watching one occur in real life.
In the U.S. between 1950 and 1993, 420 people are known to have died in 310 separate snow avalanches. These are only the documented avalanche slides. Avalanches occur almost daily during the winter season unrecorded.
So what is an avalanche? An avalanche is a large mass of snow, ice, rock and/or debris detached from a slope and sliding or falling suddenly downward. It can move (without including vertical drop) as little as 100 yards or as far as a couple of thousand yards. Avalanche speeds can range from 20 to 150 mph, depending on the moisture in the snow pack, with snow depth ranging from 5 to 35 feet. The destruction left in its path is unbelievable.
Without getting into snow metamorphism, understand that as snow lies on the ground, it attempts to bond with other snow crystals. The bonding that occurs forms what is called the snow pack. Sometimes due to various reasons, some snow crystals do not bond well with older snow, forming a weak layer in the snow pack. As more snow falls the weight on top of the snow pack becomes enormous. All the snow is waiting for is something to trigger it.
A trigger can be man-made or natural. The best way to explain a trigger is to visualize an old rubber band. Snow is like a rubber band. It likes to stretch back and forth. If the old rubber band is pulled too fast and quickly, it will snap. As with snow, if it is not allowed to slowly move and bend, it too will break at the weak layer. By overloading it at the precise moment it is trying to move and bend, it breaks. This overloading is known as the trigger. Most avalanches catching people are triggered by people.
Once the avalanche has started, it has several parts: starting zone, track and run out zone. All of these areas are extremely dangerous. Imagine that you trigger an avalanche in the starting zone. The snow would immediately carry you into the track. In this area you will find yourself being bounced off of rocks and trees, almost like a pinball. Finally, the snow will bury you into the run out zone. The energy and friction of moving snow will cause it to become ice-like, so forget about being able to dig yourself out, if you are even alive.
Understanding what an avalanche is and what it can do is the first step. The best method of safe travel into the back country is avalanche recognition and avoidance. Nearly all avalanche accidents can be avoided. The signs are there if you read them.
Slope angle is one of the most important signs. Contrary to common belief, steep slopes are not prone to avalanche conditions. This is due to the constant sloughing of snow downslope. The majority of avalanches occur in the 30–45 degree range which is not very steep. In fact, it is generally a great slope for snowmobiles to conduct their “high-marking.” A clinometer on a good compass can serve as a useful tool to measure slope angles. There are other commercial products and math formulas that can be used to determine slope angle. Overall, I would use extreme caution when traveling on any slope in the 15–60 degree range.
Vegetation is another sign to tell the history of an area for such things as tracks and run out areas. Trees missing in an open area should send up a warning sign. This means that something has happened here in the past. Certain slops are historical “runners.” Even though your movement may be in a tree line, continually look at the uphill branches. Trees that are missing their uphill branches are called flat trees. A small avalanche has occurred here in the past which was strong enough to remove the branches, yet too weak to uproot the trees.
Small islands of trees are another sign. These islands are usually higher than the track. Sometimes this small island may offer protection. Look for patches of pioneer growth in a climax forest. Patches of new trees, such as aspen growing among older trees such as pine, is something else to pay attention to.
Although these are the two signs from nature I highlighted, there are many more. Slope orientation, slope configuration and elevation should also be considered. Probably one of the most important facts is information about an area from people who know the area well.
Finally, the last sign from nature is the instability and stability of the snow pack which you are traveling on. There is no one thing to consider, but rather several. To truly understand the snow pack, a rutschblock should be dug to test the bonding strength of all layers. A rutschblock is too detailed for this article but is something all back country travelers should know how to make.
When traveling in avalanche prone areas, every one should carry snow shovels, probe poles and transceivers. Should someone be caught in an avalanche, time is essential. These pieces of equipment could mean the difference between life and death for the one buried.
Should you have to travel across an avalanche-prone slope, take the following precautions; button up your jacket and place the hood over your mouth. This prevents snow from being inhaled and delays hypothermia. Cross one at a time while someone is always watching. The spotter may have noticed them somewhere in the path. Consider using the same track to minimize disturbance to the snow and exposure time to the hazard. Finally, trail an avalanche cord of approximately 100 feet. This can be parachute cord with brightly colored tape attached at various points for easier identification.
If caught in an avalanche, attempt a backstroke swimming motion to stay on top of the slide, and hopefully reducing the burial depth at the end of the ride. Attempt to remain upright with your head uphill. If those methods are not working, cover your face with your hands to create an air pocket before the slide solidifies. Remain calm and quiet to conserve energy. Only call out if you hear a rescue party, or you will use up valuable oxygen.
Statistically, after 30 minutes of burial the chance of living is 50% and 20% after one hour. Speed is essential for recovering a live victim. Hypothermia and suffocation are the main causes of death. A search should not be called off for at least 24 hours. Initially, search the last known spot and down the slope while looking for clues such as clothing and equipment. Look on the outside of bends or the uphill side of trees and boulders.
If you have no luck during a hasty search, spare what you can in manpower to send for help. An organized search has to be conducted which will include probe lines, and hopefully with the use of search dogs. Generally, by the time they arrive it is usually a body recovery operation.
Winter back country travel is a wonderful experience, but one with many dangers. Avalanche study is a science—a science with little understanding for the “tender-foot.” Although this article only touched the basics on many facets of avalanches, it cannot replace the amount of study, knowledge and experience to travel safely into a place of solace.


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