Avalanches: Dangers and advice

What is an avalanche, why do they happen, safety tips and what to do in the event of an avalanche


Powder avalanche in the Himalayan Mountains, in Nepal.
Powder avalanche in Nepal - Photo by Guillem Casanova for @Off Trail Academy

Snow is a major attraction for those who love the mountain and winter sports, but the danger of avalanches demands taking precautions. Whether one is doing backcountry skiing, cross country skiing, snowshoeing or any other activity, it is important to be well-informed and that you follow the experts’ advice to avoid risks, as well as know how to act in the event of an avalanche.

To learn more about avalanches, we spoke with Jon Apodaka Saratxo, a Geologist specialized in geological dangers and snow science, is currently an associate researcher in Andorra RI (Andorra Research and Innovation) and at the UdA (University of Andorra).

What are avalanches?

According to EAWS (European Avalanche Warning Services), an avalanche is a mass of snow that moves rapidly in volumes often exceeding 100 m³ and with a minimum length of 50 meters. Avalanches can also carry away other materials, such as rocks or vegetation.

The dimensions, characteristics and speed at which it moves are all variable and are used to determine its degree of danger.

What types of avalanches are there?

There are various classifications of avalanches for determining what type it is. The most common is classifying the avalanches based on the degree of firmness of the snow, which are divided into three types:

  • Slab avalanche
  • Powder avalanche
  • Wet snow avalanche

EAWS further defines:

A slab avalanche “the abrupt release of a slab of snow on a mountain slope”. The slab glides over the weak layer of the snowpack.

Snow fracture after a slab avalanche.
Snow fracture after a slab avalanche - Photo by Jon Apodaka (arRISKeus)

A powder avalanche “is made up of fine-grained, dry powder in which most of the flowing snow is suspended in the air by turbulence”. These avalanches can reach speeds anywhere from 100 to 300 km/h.

A wet snow avalanche “is made up of wet snow masses”. Even though the speed is slower than that of dry snow and they tend to have shorter run out distances, “the impact on the obstacles tends to be greater due to its higher density”.

Furthermore, Jon Apodaka tells us about two other types of avalanches that we should know:

  • Ice avalanche or avalanche due to the falling of a serac (slab of ice): ice breaking in steep areas on glaciers. Some ice avalanches lead to powder avalanches.
  • Full depth slab avalanche: this type of avalanche glides over the ground and sweeps away soil and other debris. These often occur in springtime.
Traces of a full depth slab avalanche triggered in the Swiss Alps.
Full depth slab avalanche in the Swiss Alps - Photo by @jaspionsky

Why do avalanches happen?

Avalanches occur when the snowpack located on a slope (generally between 28 and 45 degrees) detaches.

Jon tells us the different origins for avalanches:

  • Natural: This happens spontaneously, without any external interference or force.
  • Accidental: This is due to an additional load on the snowpack, such as that caused by a skier, a person snowboarding, an animal or machinery passing nearby.
  • Artificial: Induced, for example, with explosives to ease the danger of avalanches.

It is estimated that over 90% of avalanche related accidents are caused by the same people involved in that accident.

So that winter mountain lovers can assess the risk, it is key to knowing what the prime situations are that can lead to avalanches. Jon Apodaka talks with us about five typical avalanche problems as defined by the European Avalanche Warning Services:

  • New snow
  • Wind-drifted snow
  • Persistent weak layer 
  • Wet snow
  • Gliding snow
The typical avalanche problem icons as defined by the European Avalanche Warning Services.
The EAWS typical avalanche problem icons.

As defined by the EAWS:

The problems with new snow are due to recently fallen snow, owing just as much to it acting as an additional load to the existing snowpack or because of a lack of cohesion among the particles. In general, these problems can occur during the snowfall or in the following days.

Avalanches caused by wind-drifted snow are created by the accumulation of snow transported by wind onto other weak layers of snow. These avalanches can be triggered during a windstorm or even a few days afterwards.

Avalanches owing to persistent weak layers occur when there is an additional load on an old snowpack with weak layers. This danger can last for weeks, months or even the whole winter season.

Problems associated with wet snow appear because of the weakening of the snowpack due to rain or melting brought on by a rise in temperatures. One must be cautious during these meteorological events as well as in the following days.

Gliding snow avalanches are a risk provoked by a thick, homogeneous snowpack or even one with few layers which can slide over slippery terrain, like grassy or smooth rocky ones. This problem can last for days, months or the whole season.

Fracture after a gliding snow avalanche on a grassy surface.
Fracture after a gliding snow avalanche on a grassy surface - Photo by Jon Apodaka (arRISKeus)

When the snowpack is quite stable in general, it is referred to as a favorable condition. One must bear in mind that zero danger does not exist.

What dangers come with avalanches?

In order to classify the level of avalanche danger, there is the European Avalanche Danger Scale, a five-level scale in which the danger varies depending on the stability of the snowpack and the probability of it being triggered. It also considers the size of the potential avalanche and the number of slopes where it can take place.

European Avalanche Danger Scale icon key, with the five different levels.
European Avalanche Danger Scale icons.

On the European Avalanche Danger scale, danger level 1 refers to a low level of danger whereas danger level 5 relates to a very high danger.

In addition to the European Scale, there are others such as the North American Avalanche Danger Scale, which is quite similar and it also has five levels of danger. Both use the same icons.

If we take a look at physical harm to man, according to AEMET (State Meteorological Agency in Spain), a person swept away or buried by an avalanche can mainly suffer from frostbite and hypothermia, multiple trauma and asphyxiation. In the worst case scenarios, it leads to the loss of life, more often than not, of an off-piste skier.

Jon Apodaka points out that the point to reflect upon in the survival time of a victim that has been completely buried by an avalanche is at about 18 minutes and he goes on to say that “statistically, we know that the chance of survival drops drastically after around 18 minutes.” This is why he highlights the need for having specific knowledge and training in rescue: “In this kind of situation, a life can depend on every minute gained”.

“In an avalanche rescue, a life can depend on every minute gained”

According to Jon, “in the Alps, accidental avalanches make up for over a hundred deaths, almost every season; in the USA the recent yearly average is at about 30; in Canada 10 people and combining Spain, Andorra and the French Pyrenees, the yearly average in the last 20 years is at 3.5 deaths per season”. Moreover, he also points out Chile, Argentina, India, Japan and New Zealand as some of the other countries where there are also accidental avalanches with fatal consequences.

Safety tips for avalanches

In order to safely practice winter sports in the mountains, information and training are fundamental: “One must know the decision-making mechanisms based on the observation and analysis of the conditions of the terrain and the group.” Furthermore, during the outing “it is important to methodically keep communication among all the members, have good habits when circulating and bring with you rescue equipment and know how to use it without making any exceptions when enforcing this protocol.”

Avalanche safety gear

In the event of an avalanche, the safety equipment can be determinant. Apodaka explains that is comprised of four essential elements:

  • Avalanche transceiver or avalanche beacon 
  • Shovel
  • Avalanche probe
  • Helmet

Jon Apodaka with an avalanche transceiver, a shovel and a probe in his hands.
Jon Apodaka with an avalanche transceiver, a shovel and a probe in his hands - Photo by Jon Apodaka (arRISKeus)

As regards the helmet, he tells us that “you must bear in mind that the greatest cause of death in avalanche victims in Spain, Andorra and the French Pyrenees is polytrauma, so it is very important to protect the head”.

In addition, Jon points out that “there are two options in the market that increase the chance of survival if you find yourself in this situation: the airbag backpacks and Avalung, which is a breathing device for those buried by an avalanche”.

Avalanche safety equipment: Avalanche beacon, shovel, probe, helmet, airbag backpack and Avalung.
Avalanche safety equipment: Avalanche beacon, shovel, probe, helmet, airbag backpack and Avalung.

Just like while doing any activities in the mountains, it is necessary to bring other safety items such as a first aid kit and a thermal blanket as well as enough to drink and eat.

Prevention and information

Before taking off on any winter mountain trail, Apodaka reminds us that we must get informed on meteorological and snow conditions, the features of the terrain and the group that is going to take part. As a rule of thumb, it is also unadvisable to go alone, and you must tell a third party about the planned itinerary and avoid going during the hottest hours of the day.

Jon mentions that “the snow conditions can be consulted on the Avalanche Bulletin of the region.” Moreover, he goes on to say that, when possible, we should try to get more information by talking to the locals, the ski station crew or the local guides. On the other hand, the terrain information can be obtained by looking at any available map, guide book, sketches and reviews. Having previous knowledge of the place makes things much easier for us.

As regards assessing the group, he emphasizes that “we must add on the human factor, which includes physical, psychological and social traits of all those who join in on the activity, the material they have on hand, their training and experience”.

Recommendations while en route

Once we have all the equipment, training and information, and are now on the path, we must keep good communication within the group, always treading in the safest place and putting ourselves in the least possible amount of danger. Jon tells us that “we must be thinking of the consequences and reevaluating our decisions, searching for, if necessary, alternatives to the danger”.

Backcountry skier following his mate’s tracks to climb up a mountain slope.
Backcountry skier following his mate’s tracks - Photo by @jorgegdihinx

To assess the snow condition, we can do some of the many fast in situ tests that there are (such as the ski pole, hand shears, parallel track test, kick turn or slope cuts) or more elaborate (such as the extended column, compression or Rutschblock tests), but “to do so you must be trained and know how to interpret the results”.

While following the path, we need to be clear about what the warning signs are that point to a possible avalanche. According to Apodaka, the five signs that everyone must bear in mind are:

  • Recent avalanches
  • Whumpfs (a hollow sound made when a weak layer collapses below the snowpack) and cracks
  • Recent wind blown mounds (cornices, dunes, erosion…) 
  • Thickening of recent snowfall (over 30 cm, generally) 
  • Sudden cohesion due to rain or a rise in temperature

In the event that we detect a real danger of avalanche in the place we find ourselves in, or in that we have to cross, he recommends “going back to avoid exposing yourself to that danger”. He also adds: “You do not need to leave your backpack behind, which ends up protecting us since it gives us more volume to stay afloat and it contains self-rescuing items”. In his opinion, we should also avoid taking our skis off “so we don’t sink much deeper which in turn causes overloading a weak layer that will trigger an avalanche”.

The Spanish State Meteorology Agency, in addition, recommends increasing the space between the group members so that only one person is in the danger zone, mutually watching out for each of the different members, only stopping in safe zones and moving gently to avoid abrupt turns or falls.

Snow cornice, a snow formation that protrudes from the crest of a mountain.
The cornices are prone to collapse and starting avalanches - Photo by @Paolo Coccia

What to do during and after an avalanche

If an avalanche comes to us by surprise in spite of all our prevention, it is important to “try to stay calm, make movements like you’re swimming to try to stay afloat and, when the snow stops moving, try to create an air chamber around your face”.

Once the avalanche stops, and we find ourselves buried in it, we should “try to relax so as to use up the least amount of oxygen possible and exhale less air, with the confidence and trust that our mates will soon rescue us”. Apodaka adds that we are incapable of knowing where the surface is and warns that it is only possible to get out on our own if the avalanche is a size 1 (small avalanche) and with very dry snow.

“If we are buried by an avalanche, it is important to be calm so we consume little oxygen and have faith in our mates”

What is the rescue procedure?

If an avalanche has not affected us, Jon Apodaka explains the steps to carry out an organized rescue: “You must stop (in a safe place) and in just a few seconds think and plan the course of action. First, you should choose a leader that will determine the search area and the protocol to follow. In the first phase, it is also essential to call the emergency services to activate the professional rescue teams and, if the accident site doesn’t have any reception, one member must leave to find a signal since it is important to activate the relief chain”. In most countries, the emergency services can be reached at 112 (used in Europe and some parts of Asia) or by dialing 911 (used in some countries in North and South America).

He goes on to say: “The next step is to make everyone put their avalanche transceivers in search mode and turn off their mobile phones and all other electronic devices (such as GPS) to avoid interfering with the signal. Afterwards, the group searches for any indication of where the victim may be until the first signal of the buried device is detected. This stage must be done as fast as possible. Next, we must follow the indications of the transceiver and lastly, the fine search”.

Rescue team after an avalanche.
Avalanche rescue procedure - Photo by Jon Apodaka (arRISKeus)

Once we have discovered the exact location of the victim, “we start with the probe and finish it off with the shovel, the rescue stage in which we lose the most time. Shoveling ends when the airways are totally unblocked and the whole body is dug up”.

At this point, we must provide the victim with first aid, adapted to whether they are conscious or not, and whether they are breathing or not. Apodaka suggests protecting them from hypothermia, looking for signs of possible hemorrhaging and handling the victim as though they suffer from polytrauma.

At the end of the interview, Jon gives us one last piece of advice about mountain safety: “Be cautious, don’t overestimate your know-how nor give way to uncertainty. It is necessary to be humble and conservative so you can endure such harsh and defiant weather and terrain that is found in the winter mountains”.

 “Be cautious, humble and conservative, don’t overestimate your know-how nor give way to uncertainty in the wintery mountains”