How To Survive an Avalanche

This article outlines life-saving concepts related to avalanches but does not cover all aspects of avalanche safety. To be truly safe from an avalanche, a person needs to take an avalanche safety course. Understanding avalanches is one of the more critical topics in wilderness medicine, if not for any other reason than that injury and death rates are rising.

Most avalanches occur spontaneously during storms with increased snowfall. The second-largest cause of natural avalanches is changes in the snowpack, such as melting due to the sun. Artificial triggers of avalanches include skiers, snowmobiles, and controlled explosive work. Contrary to popular belief, avalanches are not triggered by loud sounds.

Injury and death due to avalanches have dramatically increased over the past two decades. Sadly, human factors contribute to nearly all avalanche accidents. In the vast majority of avalanche burials, the victim, or someone in the victim’s party triggered the avalanche. Snowmobilers account for the largest group of backcountry users who are killed in avalanches. The most crucial factor in avalanche survival is the amount of time someone is buried in the snow. Asphyxiation (suffocation) is the predominant mechanism of death among avalanche victims. Hypothermia is a rare cause of death among avalanche victims. Avalanches can reach speeds of up to 100 mph in less than 10 seconds, so trauma is also a cause of death and injury. As many as one-third of avalanche victims sustain significant blunt trauma.

Slope Angle

Slope angle should be one of the first things that come to mind when travelling in the backcountry. It is a primary factor in every avalanche. Avalanches happen when four elements of snow are present:

1. A slab of snow

2. A weak layer of snow

3. A trigger (like new snow)

4. A slope angle steep enough for snow to slide, generally between 25-55 degrees

Not all slopes are steep enough to slide, and some are too steep to form slabs regularly. Recognizing what slopes are safe to ride and what slopes are prone to avalanching is an integral part of making safe decisions.

The best way to answer the important question of “can this slope slide” is to know the angles of the slopes you are riding. The most common slope angles on which avalanches typically happen are between 36-38 degrees, though it is important to note that not all avalanches start on slopes with these precise angles. If a gentle slope of 25 degrees or less is connected to a larger, steeper slope it is still possible to trigger a slide from below without ever getting on the steepest part of the slope. This is known as remote triggering and is a common way that riders get drawn into an avalanche in the backcountry, especially in avalanche run-out zones. When travelling in terrain that requires the crossing of avalanche run-out zones, it is imperative to cross one at a time and always keep a watchful eye on one another.

Only about one-fourth of avalanche victims have massive trauma as the primary cause of death. Multiple injuries, such as spinal and long bone fractures, blunt abdominal trauma, and head injuries are sustained as the avalanche victim is dragged over rocks and through trees. Air pressures under an avalanche are much higher than atmospheric pressure. This is due to the heavy nature of the snow and the snow’s power. Victims find that snow is ‘forced’ into their airways. If a victim can be rescued within 18 minutes, the survival rate is higher than 91%. The survival rate drops to 34% in burials between 19 and 35 minutes.

If chest movement is not restricted to the point of compromising breathing mechanics, then survival depends on the size of the air space created near the victim’s face as the snow flows downhill to a stop. All air pockets will ultimately fail for two reasons: 1) Heat from the expired air causes ice to form around the mouth and prevents fresh air to enter the lung. 2) Re-breathing expired air will cause the victim to breathe in carbon dioxide and will eventually death from asphyxiation.

Avalanche Safety and Survival

Most injuries can be avoided by good decision-making, minimizing risk by travelling wisely with good techniques, and avoiding high-risk terrain. When it comes to risk management, people behave and think differently. This is particularly true in young people, where the risk of injury from avalanches is highest.

Here are some critical rules that you are strongly urged to follow:

• When travelling on snow terrain, never go directly above any member of your party.

• Avoid gullies and narrow valleys, as these serve as run-out zones where avalanches that start further up the mountain can funnel through, and usually burying everything at the bottom of the gully.

• Travel on ridgelines above avalanche start zones, in dense forests, or well away from damaged vegetation.

• Travel from one safe zone to another, one person at a time. If an exposed area needs to be crossed, never expose more than one person at a time. Keep the rest of the party in a safe area so they can perform a rescue if an avalanche does occur.

• Be on the lookout for “red flags,” such as collapsing, cracking snow, or sinking into wet snow.

• Start on low angle slopes, which are less than 25°, before venturing to steeper slopes. This gives you the opportunity to better assess snow stability before travelling on more risky slopes.

• Always call the Forest Service or Avalanche Forecast Center for a report of the current snow conditions.

• Always carry avalanche rescue equipment including at a minimum, an electronic avalanche rescue transceiver (beacon), and a shovel and probe. Practice using them.

Avalanche Victim Rescue

If an avalanche is witnessed, the survivors should make every effort to maintain sight of the victim as he/she is pushed down the slope. Once the survivors lose sight of the victim, a mental note should be made of the area where the victim was last seen using fixed landmarks such as rocks and trees.

Since more than one avalanche is possible in the same area, extreme caution should be used by the rescuers to avoid getting caught in a second avalanche. Transceivers (beacons), shovels, and probes constitute the basis of avalanche survival and rescue equipment. Transceivers work on the assumption that an avalanche victim can be found within the “golden eighteen minutes” after burial. After 18 minutes, the chance of survival dramatically decreases. If a member of a party is buried in an avalanche, rescuers should switch their transceivers from the “send” to the “receive” mode. This will allow rescuers to pick up the signal transmitted by the victim’s beacon.

Treatment

Low oxygen and high carbon dioxide levels are significant threats to life in avalanche victims. As with any victim, primary attention should first be given to the MARCH protocol. Because major trauma is frequently associated with avalanche burial, cervical spine precautions should be used when extricating the victim. Keep in mind the patient’s exposure to the environment. Snow can be insulated, but once the victim is extracted from the snow and exposed to wind, core body cooling can accelerate if the body is not properly insulated against the environment. Any avalanche burial victim should be evacuated immediately.

MARCH protocol

To help prioritize the treatment of injuries in the wilderness, use the MARCH acronym. It’s important to note that preventing major haemorrhages is the top priority, even coming before Airway.

M Massive haemorrhage

A Airway (with C-spine precautions)

R Respiration

C Circulation

H Hypothermia/Hyperthermia (or Hike vs. Helicopter for evacuations)

Other Methods

The best way to avoid being caught in an avalanche is to not be near the trigger points for one. However, there are several devices that might increase your chance of survival if you are caught in one. Make no mistake, though, a person’s primary goal is to never be in an avalanche.

Avalanche Airbags

Avalanche airbags help a person avoid being buried by making the user an even larger object, relative to the moving snow, which forces the person toward the surface. Avalanche airbags work on the principle of inverse granular convection. Avalanches, like mixed nuts and breakfast cereal, are considered granular materials and behave in a fluid-like way, where smaller particles settle at the bottom of the flow and larger particles rise to the top. Provided the airbag is deployed correctly, the chances of a complete burial are significantly reduced.

Avalung

A device called the Avalung has been introduced for use in avalanche terrain. During an avalanche burial, victims not killed by trauma usually suffer from breathing in carbon dioxide, as the snow around them melts from the heat of the victim's breath and then refreezes, disallowing oxygen flow to the victim and allowing toxic levels of CO2 to accumulate. The Avalung helps this situation by drawing breath over a large surface area in front and pushing the warm exhaled carbon dioxide behind. This buys additional time for rescuers to dig the victim out.

The only sure way to survive an avalanche is to avoid getting caught in one!