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 Ski Resources | Ski Safety | Avalanche Knowledge
 

 

  Avalanche Knowledge
Avalanches are a real danger for all those who visit snowy mountainous areas. Avalanches claim hundreds of lives worldwide every year and leave thousands wounded. Almost all the people who are caught in avalanches are caught by a slide that was triggered by themselves or a member of their company. Many of these accidents could have been avoided if those involved had a higher degree of avalanche knowledge.

Learn about the distinct kinds of Avalanches, how to prevent causing one avalanche, how to identify the risks and how to perform search and rescue in such situations. Avalanches kill skiers and boarders every year. There are many risk factors and many possible causes but there’s a lot you can do to reduce your own risk.

- What Causes Avalanches?
- Types of Avalanches
- Avalanche Dangers
- Avalanche Checklist
- Avalanche Rescue
- Avalanche Rescue and Safety Equipment

 

 What Causes Avalanches?

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Avalanches happen when the force on the snow layers exceeds the weight of a mass of snow. Avalanches are obviously dangerous and unpredictable. One must know what causes an avalanche in order to prepare oneself when faced with this situation. An avalanche can be due to one or more factors.

Weather
|Weather might be the biggest element that can cause an avalanche. It plays a big role in the development of snow on the ground. One must consider the weather days before the scheduled trip so as to know if it is safe to continue or not. Moreover, rapid change in weather can have bad effects on snow for snowpacks do not adapt easily to rapid changes. Weather determines the evolution of snowpack. The most important factors are heating by solar radiation, radiational cooling, temperature gradients in snow, and snowfall amounts and type. Most avalanches happen during or soon after a storm.

Snowpack
Structure of the snowpack determines avalanche danger. The snowpack is not what you think it may seem on the surface. It may appear as a thin cover, but if you look at the cross-section of it, you may see several layers of snow that had developed through time. Snow builds up over the season, and during winter, a thicker layer is added to the previous one. Also, bonds between layers may be strong or weak. Avalanches occur if the bond is weak. Even if you have a strong bond in the upper layers of the snowpack, an avalanche may happen if the layers beneath it are weak. Avalanches require a buried weak layer (or instability) and an overlying slab. Additionally snow cover varies in space and so does stability of snow.

Terrain
Snow intensifies up on slopes. If the slope is too steep, one can expect an avalanche to occur. Avalanches develop on slopes between 25° to 55° and it starts on slopes between the 35° to 45° range. This is quite steep since the ideal angle for slopes so as not to develop an avalanche is 38°. This is the angle of repose – the steepest angle a granular substance can maintain without collapsing under the pull of gravity. And since snow is a granular substance, its target angle is 38°.
On low angled slopes, snow can start moving only if it is heavily loaded. But on steep slopes, the snow does not form slabs. Instead, it slides down continuously. Though slopes should be steep in order to start an avalanche, that does not necessarily mean than slopes with low angle are completely safe. Of course, it still depends on many conditions such as temperature and weather. Even a shallow snowpack on a safe slope can still trigger an avalanche. If it is spring time, when snowpack carry free water around the snow grain, avalanche will behave more like water and it will slide down even on low terrain.
One can measure the slope angle with an inclinometer, or "eyeball" it by dangling a Ski Pole by the strap and estimating the angle. One must also keep in mind that a slope may vary in steepness and may require different techniques to be able to trek it safely.
 
We must remember that an avalanche is not solely caused by one element. There would be times that all three causes are present. Knowing these factors can help a person be more observant of his surroundings and think twice before having fun on the snow.


 

 Type of Avalanches

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Exist different types of avalanches, although some could look like. Some avalanches are very dangerous and can cost a person’s life while others only have mild effects on people. There are many types of avalanche; each varies according to cause of occurrence.

Loose snow avalanches
Loose snow avalanches usually happen when weak surface snow is on a slope that is steeper than its critical angle of repose. Typically the cohesionless snow is either dry unsintered fresh snow or wet snow formed from melting. These are called dry loose-snow and wet loose-snow avalanches respectively.
When the snow is perturbed, the loose snow undergoes a localized rotational slip and then moves downslope in an inverted V-shape pattern. The initial slip involves very small masses of snow that range in size from one grain of snow to a the size of a large snowball. Typically they contain less than 1 cubic meter of snow. As the avalanche moves downslope, it can set other cohesiveless snow in motion. The avalanche finally comes to rest once the snow reaches its kinetic angle of repose.
This is a gentle and usually safe type of avalanche. It does not gather enough snow on the way to be able to kill or bury a person. Since the speed of a loose snow avalanche is relatively slow and the initial mass of snow is small, they typically do not cause much destruction. Nonetheless hazards are still involved.

Ice fall avalanches
Ice fall avalanches happen when a glacier finds a steep drop. Pieces of ice "calf" off as the glacier slowly flows downhill under the force of gravity. Ice fall avalanches are unrelated to temperature, time of day or any other factors, despite conventional wisdom to the contrary. Many believe that temperature and time of the day can affect the occurrence of this type of avalanche, but the truth is that this avalanche happens when glaciers drop steeply from the mountain. The best way to avoid these avalanches is to not travel beneath ice cliffs and through ice falls, or if necessary, roll the dice and travel through quickly.

Cornice fall avalanches
Cornice fall avalanches arise when cornices break loose from the lee side of ridges. Cornices look like frozen ocean waves stretched along mountain ridges. They form their characteristic "eaves" of cantilevered snow when prevailing winds remove snow from slopes on one side of a ridge and deposit it on the other side of the ridge. The snow that forms cornices is very dense and hard, yet can be extremely fragile. It is often difficult to determine from the ridge top where the ground ends and the overhanging cornice is not supported. This type of avalanche is easily avoided by staying back from the peak of ridges, but can be deadly as the victim tumbles downhill amid massive, hard and heavy chunks of snow which often trigger secondary slab avalanches as they pass.

Slab avalanches
The most dangerous type of avalanche is the slab avalanche. Slab avalanches arise when cohesive snow begins to slide on a weak layer. The rupture line where the moving snow breaks away from the snowpack makes this type of avalanche easy to identify. Slab release is rapid. This type of avalanche is the primary cause of the most number of casualties among travelers.


 

 
 Avalanche Danger

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If we compared a dry and wet snow avalanche, the dry one is more dangerous. It can travel as fast as 120 mph while the wet snow avalanche can go for just 5 mph or less. Dry snow avalanche can create a force as powerful as an explosive. Some persons who encounter this avalanche suffer from injuries, either they are dragged through trees and cliffs or they get hurt by their own Snowboarding Equipment.
A person is buried totally in snow after being taken by an avalanche. The Asphyxia would be the biggest danger a person has to confront with being buried in snow. Avalanche debris is compact and heavy unlike how it used to start light and fluffy. When the snow stops from moving, the kinetic energy from the moving snow creates heat from fiction that makes it hard and heavy. One cannot contain the weight of the snow. Therefore, it can squeeze the person, especially his or her lungs. One may be buried alive lacking oxygen and be frozen by snow.
Even if a person can dig the ice immediately, there is still a large probability that he or she will not be able to survive. Within 15 minutes of being buried, the person has 90% of surviving. Beyond 30 minutes, the person only has 50% chance of survival, and it decreases the longer the person stays under the snow. If the person’s company is well equipped and knowledgeable of what they are going to do, the person may have a lesser chance of dying, but otherwise, it would be hard to survive such an incident. More so, given the difficulty of digging and working one’s way out through the snow, if the person is buried for more than six feet, he would most probably die.


 
 Avalanche Checklist

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It is essential to know the factors to look at that might result in an avalanche. Since an avalanche is very unpredictable. Having an avalanche checklist will not only save you effort and time but your life too. Knowing how to prognosticate a possible avalanche can help us be more prepared for a future disaster and give us one very big step ahead. The following are the things that should be included in your checklist.

The interrelation of four critical variables terrain, weather, snowpack, and man, determines whether or not a potential avalanche hazard exists. Although these important variables are frequently changing, these changes are often detectable. Not only can critical information be observed, it can be measured, tested, evaluated, and be studied. The bottom line is that our route selection and hazard evaluation decisions are only as good as the data we seek. The primary causes of avalanche accidents are attitude and ignorance. Our attitude "filters" the data and warps it to our needs or desires. Our ignorance prevents us from seeking the answers beforehand. Often, people are not willing to compromise their wants so they still push through even if they know that it is dangerous or even life-threatening.

You can save your life, so use the checklist below. Follow these simple steps:

  • You should get and seek out critical data.
  • You must evaluate the potential level of hazard (red, green, yellow).
  • Add a level of precaution for the "unknown".
  • Study your situation on a regular basis without letting your attitude persuade you away from the facts.
PARAMETERS: KEY INFORMATION
G
Y
R
Go
No Go
TERRAIN: Is the terrain capable of producing an avalanche?
  Slope Angle (how steep, exposed?)        
  Slope Aspect (leeward, shadowed, or extremely sunny?)      
  Slope configuration (smoothness, anchoring, and shape effect?)      
  Overall Effect          
WEATHER: Has the weather been contributing to instability?
  Precipitation (added weight, stress?)        
  Wind (significant snow transport and deposition?)      
  Temperature (rapid/prolonged warming, weakening?)      
  Overall Effect          
SNOWPACK: Could the snow fail?
  Slab Configuration (depth, distribution, and structure?)        
  Bonding Ability (nature and distribution of "tender" spots?)      
  Sensitivity to Force (shears easily, clues to instability evident?)      
  Overall Effect          
HUMAN: Could you be a trigger or a victim, and are you prepared for the consequences?
  Attitude (toward life, risk, goals, data?)        
  Technical Skill Level (high/low, so what?)      
  Physical and Mental Ability (tired, weak, strong?)      
  Appropriate Equipment (prepared for the worst?)      
  Overall Effect          
DECISION/ACTION:Do better alternatives exist?
  Go/No go: why? (What assumptions are you making?)          

LEVEL SYMBOLS: Think of data as being either Red, Green, or Yellow Lights.
G = Green light (Good)
Y = Yellow light (caution, potentially dangerous)
R = Red (stop/dangerous)

If you think that a potential danger is coming, not insist on going out. It would be more prejudicial for you to maintain your attitude instead of relying and believing on facts. Remember that prevention is better that cure, so it would be better to stay out of avalanche zone if you predicted a disaster even if it means spoiling the fun.

 
 Avalanche Resque

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If you observe an avalanche, you must be far away from the area, but also you mustn't forget to rescue the victims. Rescuing an avalanche victim is very critical. Here we have some basic guidelines when it comes to avalanche rescue.

1. Don't bring more victims to the area
First thing, is to make sure that the area is safe before of directing the rescue. Verify the regions if the avalanche appeared to have finished and established. Check carefully and observe if there are no further avalanche dangers for your team. If it is not safe to continue, do not attempt to rescue first, it would be more disastrous if the rescuers were to be rescued as well.

When the area is secure, you can direct the rescue. Put an avalanche guard who will alert everyone if another avalanche is on the way. Also, have a signal for your team (a hand signal, whistle, a shout, etc.) so you will be able to communicate to others easily. Remember to make an escape plan for your team if all else fails. The minutes are important during this kind of situation so do not spend too much time on the details. Someone must take charge so that instructions will only come from one source. It is hard to rescue people if the rescuers are arguing, so make sure that a person in authority would be present in the situation.


2. Identify critical information

  • Where was the last position?
    To locate this place could save you a lot of searching on its uphill side and on either side. The victim will be hidden or buried somewhere within a cone that flows from this point down the fall line.
     
  • Where was the person's entry point into the slide area?
    This point, combined with the last seen area and any surface clues, can help to determine a line-of-flow and a high probability search area.
     
  • Was there a witness?
    A witness can be helpful, can save time and they can give you important information like the number of people you're looking for and a little description about the victims. They can also provide credible details that the rescuers can rely on. If you have a big group, assign someone to keep track of the witness/es.
     
  • Are there any surface signs?
    The position of the equipment on the slide path can help in determining the line-of-flow of the victim and his or her possible location. Clues like this might also actually be the victim.

3.Beacon Search
The best way to start a rescue is using a beacon or transceiver. Everyone in the team must have their beacons on so as to receive signal in real time.
If the route is narrow and the rescuers are skilled, one or two persons can conduct a quick and meticulous search of the entire path while the others get their beacons and shovels out. It is a good idea to limit your searchers if you aren't sure if the victim is even wearing a beacon. If he isn't, you'll need people high on the path to begin probing quickly. If they're all at the bottom, you'll waste time waiting for them to hike back up again. Once you've picked up a signal, send more searchers and diggers to help. Probing can also speed up the rescue. Of course, the search should continue if there is more than one buried victim. Clear the victim's head first. You can begin rescue-breathing and CPR while others finish excavating. People who have been buried in an avalanche get very cold and very beaten up. Check for signs of Hypothermia and traumatic injury.

4. Probing
If the victim doesn't have a beacon or some signal, the rescue will be more difficult and the rescue could last long time. Rescuers must now conduct probing. This is done by poking long rods into the snow until you strike the victim. From there, you can dig him out of the snow. He might have dents and bruises from the poking but it is better than being buried in the snow. Examine and quickly probe surface clues. If you find a glove, pull it out - it may have a hand attached to it. Probe high-probability areas; the uphill side of trees in the slide path, the outside of bends in the path, low angle areas of the path, etc. Establish a line-of-flow using surface clues, then set up a probe line at the bottom of this line at the toe of the debris.

5. Course and Fine Probing
The intention of a probe line is to cover the avalanche rubble with a grid of regularly spaced holes. If you are precise in your coarse-probing, you have a 70% chance of striking a buried victim. If you are not careful and exact, the odds are much lower. To conduct a coarse-probe line, space the probers out at 75 cm intervals (hands on hips, elbow to elbow). Someone needs to stand in front to give commands and watch straightness and spacing of the line. Everyone should probe just ahead and between their toes and should probe and move only on command. Here are some tips:

  • If someone discovers a strike, he or she should yell it out, then leave the probe in place. Send a shoveler to dig for whatever was hit. Give the prober a new probe so the line can keep moving (false strikes are not uncommon).
  • Work uphill. Probelines headed downhill are hard to keep straight.
  • A regular Ski Pole with the basket removed works better than nothing.
  • At this point, you're still looking for a live person, so move quickly but precisely!
  • Some probes are really long - just worry about the top six feet, for now.
  • Mark the probed areas.
  • If you have more than 10 probers, you may want to break the group into two probelines working different areas - big lines are hard to control.

If regular probing fails, you will have to use fine probing. This is 95% accurate, but long time is wasted. It's for finding bodies, not living victims. It's quite the same as the coarse probing, but have the line step forward one third as far and probe in front of both toes as well as in between.


 
 Avalanche Resque

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We must know what equipment we should use in avalanche rescue. This is important for a rescuer, especially for a beginner, to know when and how to use each of them so as he or she will be well-equipped and prepared in times of disasters. The following are the different pieces of Avalanche Rescue and Safety Equipment:

Transceivers
If someone is buried into the snow, somebody can only find him or her if he or she has a transceiver, a device that receives and transmits signal using frequency emission. It is the most practical and realistic way of locating a buried person. However, if you are a victim of an avalanche, you must remember to set your beacon to transmit and not to receive signals since everyone else in your group are set to receive frequencies from you. A beacon is the most commonly used rescue device and it is also the standard equipment for ski area patrollers and heli-ski operators. You must always keep in mind that every member of your party must have a transceiver to be able to receive or transmit signals if ever accidents happen.

Shovels
If you find a victims for cause of a avalanche but do not have a shovel at hand to dig out a person from the snow, your efforts will be useless. There are two class of shovel: Shovel of aluminum and shovel of plastic. They are both lightweight and compact enough to be carried even on a long travel. Shovels are really helpful in rescuing avalanche victims for these can speed up the digging process. Aside from digging, a shovel can also be buried to serve as an anchor, a thing to sit on instead of sitting on snow, or a tool to unstuck a snow mobile. You can also use it as a foot gear when you lose a ski. Some folks worry that the plastic ones will break, though it is more practical to carry a plastic one than the aluminum type. Shovel is very essential - it should be in your 'things to bring' list, especially when traveling in an avalanche prone mountain.

Avalanche Probes
Avalanche probes are life savers of those victims who usually do not carry beacons with them. This investigation is like tent poles used to poke around when looking for a victim who does not have visible clues on the surface. An avalanche probe usually consists of two feet long tubular steels (known as poles) which are joined together. Probes are also useful in looking for a good place to dig a snow pit and can also be used to feel the buried snow layers as well as assess snow bridges over crevasses.

If a avalanche happen, the least you need is a person who doesn't know how to operate such things. Remember that the life of a person does not only depend on the equipment but more so, on the rescuers. Being familiar with these pieces of equipment is very helpful in conducting rescue operations.


 

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