About 100 people die every year in Europe during avalanches. At the same time, many Alpine regions cannot imagine their existence without ski tourism. Not surprisingly, at the initiative of European countries such as Austria and Germany, the European Avalanche Warning Services (EAWS) was founded. The purpose of this service is to prevent cases when people are killed in an avalanche or infrastructure is damaged.

The Avalanche Warning Service develops reference materials on avalanche safety, and also conducts ongoing work on monitoring, forecasting and preventing avalanches in Europe. If you are planning a trip to a European ski resort, this is the resource that will provide you with up-to-date information on the risks and snow conditions in your location. Publications are not provided in several European languages, but, unfortunately, not in Russian. In this article you will find a translation of the bulletin on the five causes of avalanches.

The five typical avalanche problems identified by the European Avalanche Warning Service (EAWS) aim to describe typical avalanche situations and support avalanche professionals and outdoor enthusiasts in their assessment of avalanche risk. The description of each avalanche problem includes:

• General characteristics of the avalanche area
• Possible types of avalanche
• Description of a typical distribution site
• Description of the position of the weak layer* in the snow cover
• Description of the avalanche mechanism
• Description of the typical duration and periods of avalanches
• Tips for travelers in the area

* Weak layer - a layer of snow that can break/slide off the spot, thereby giving rise to an avalanche.

Typical avalanche problems approved by the EAWS General Assembly, Munich 2017

fresh snow
What is this?	Characteristics	An avalanche problem is related to current or recent snowfall. The amount of additional load of new snow on the existing snow cover is a decisive factor in the new snow problem. How critical the load is depends on various factors such as temperature or the characteristics of the old snowpack.
	Possible type of avalanche	• Avalanches from snow-covered slabs • Dry loose snow avalanches • Avalanches caused by natural phenomena and people.
Where is it observed?	Spatial distribution	Usually present widely and frequently in all aspects
	The position of weak layers in the snow cover	Usually at the transition to the old snow surface, but sometimes in new layers of snow, and sometimes deeper in the old snow cover.
Why is it happening?	Characteristics of the discharge of snow-tile avalanches:	Dry loose snow avalanches: • Additional loading due to snowfall on existing or newly created light snow layers.	Dry snow avalanches: • Lack of adhesion between new snow particles.
When does it happen?	Duration	Usually during snowfall and for a few days after.
How to mitigate the risks of avalanches?	Finding a Problem on a Slope	The problem with fresh snow is fairly easy to recognize. Keep an eye on the weather and forecast, as well as information on recent avalanche activity. Be aware of small weather changes (such as changes in air humidity) that affect new snow conditions.
	Travel Tips	Dry loose snow avalanches: wait for the snow cover to stabilize.	Dry snow avalanches: the danger is the risk of falling/falling through the snow. The risk of being covered by such an avalanche is much less. Take this into account on steep slopes.

 

 

Snow moving due to the wind
What is this?	Characteristics	The avalanche problem is related to the snow brought by the wind. Snow can be carried by the wind with or without simultaneous snowfall.
	Possible type of avalanche	• Avalanches from snow-covered slabs • Avalanches caused by natural and anthropogenic factors
Where is it observed?	Spatial distribution	Very variable, but usually downwind in ravines, hollows, near distinct changes in dip, behind ridgelines, or other sheltered locations. More common above the tree line.
	The position of weak layers in the snow cover	Usually at the transition to the old snow surface or in the wind layer due to fluctuations in wind speed and fluctuations during the storm cycle, but sometimes deeper in the old snowpack.
Why is it happening?	Characteristics of the discharge of snow-tile avalanches:	Wind-blown snow puts additional stress on the weak layer and forms a slab that is particularly prone to supporting crack propagation.
When does it happen?	Duration	Wind-blown snow can develop very quickly. The problem usually persists during the snowdrift, up to a maximum of several days, depending on the development of the snowpack.
How to mitigate the risks of avalanches?	Finding a Problem on a Slope	Sometimes, the risk of an avalanche can be recognized visually. Pay attention to the wind direction indicators and look for fresh snow formations. Typical clues: snow formations, recent avalanche activity, earthquakes. and sometimes cracks in the snow.
	Travel Tips	Avoid fresh looking snow formations on steep slopes, especially where the snow cover changes from thin to thick or hard to soft.

 

 

Stable weak layers of snow
What is this?	Characteristics	The avalanche problem is related to the presence of persistent weak layers in the old snow cover. These weak layers usually include hidden surface frost, deep frost, or faceted snow crystals.
	Possible type of avalanche	• Avalanches covered with dry snow • Avalanches, mostly man-made; natural avalanches are rare, mostly in combination with other avalanche problems.
Where is it observed?	Spatial distribution	An avalanche problem can be widespread or completely isolated. It can exist in all aspects, but is more common on shady, wind-sheltered slopes.
	The position of weak layers in the snow cover	Anywhere in the old snowpack, often deep in the snowpack. However, with a deep finding, the convergence of an avalanche becomes more and more difficult.
Why is it happening?	Characteristics of the discharge of snow-tile avalanches:	The avalanche under loading exceeds the strength of the weak layer
When does it happen?	Duration	Weak layers can persist from weeks to months; probably most of the winter season.
How to mitigate the risks of avalanches?	Finding a Problem on a Slope	Permanent weak layers are very difficult to recognize. Signs of instability such as swelling are common but not necessarily present. Stability tests can be useful for finding stable weak layers. Information about the history of the snowpack is critical, as is the recent published report of the avalanche. Propagation of cracks over long distances is common, and remote vanishing is possible.
	Travel Tips	Travel carefully and avoid large steep slopes. Study the history of weather and snow cover changes in the area. Be especially careful in areas with thin snow and when changing from light to deep snow. This problem is the main cause of deaths due to avalanches during recreation.

 

Wet snow
What is this?	Characteristics	The avalanche problem is associated with the weakening of the snow cover due to the presence of melted snow masses. Water infiltrates the snowpack due to snowmelt or rain.
	Possible type of avalanche	• Wet snow avalanches on slabs • Avalanches from wet loose snow • Mostly natural avalanches
Where is it observed?	Spatial distribution	When the sun is the main cause, the spread of the problem mainly depends on the slope and altitude. In the event of rain on snow, all slopes are affected.
	The position of weak layers in the snow cover	Anywhere in the snow
Why is it happening?	Wet snow avalanche release characteristics:	loose snow avalanches: • Weakening of pre-existing weak layers in the snowpack or formation of accumulations at layer boundaries • If it rains, there is also an additional load on weak layers	Wet snow avalanches: Loss of adhesion between snow crystals
When does it happen?	Duration	• From hours to days • Rapid buckling possible • Natural avalanches may be more likely at certain times of the day, especially in the afternoon (unless rain is the dominant factor).
How to mitigate the risks of avalanches?	Finding a Problem on a Slope	Wet snow problems are usually easy to recognize. The onset of rain, snowball, pin roll, and small wet slabs or loose wet avalanches are often precursors to natural avalanche activity on wet snow slabs. Another sign of increased hydration is the deep penetration of the foot.
		In the presence of sunny weather, after cold nights with clear skies, mornings are usually favorable due to frost. After warm nights with overcast skies, the problem often occurs in the morning. Usually, rain on fresh snow creates this problem almost immediately. It is important to correctly calculate the time and plan the trip. Consider avalanche zones.

 

Sliding snow masses
What is this?	Characteristics	All snowpack slides on the ground, usually on a level surface such as grassy slopes or smooth sections of rock. High activity of sliding snow avalanches is usually associated with thick snow cover without layers or with several layers. Sliding snow avalanches can occur both in cold, dry snow cover and in warm, wet snow cover. A sliding snow avalanche is difficult to predict, although slip cracks usually open before melting.
	Possible type of avalanche	• Sliding snow avalanches; cold dry or 0°cisothermal wet snowpack • Any avalanche is usually natural. Human and artificial trigger is unlikely.
Where is it observed?	Spatial distribution	It predominates on a flat surface and on any slopes, however, more often on the southern slopes.
	The position of weak layers in the snow cover	The interface between land and snow cover.
Why is it happening?	Wet snow avalanche release characteristics:	The mechanisms of sliding snow avalanches arise from the loss of friction at the snow-ground interface.
When does it happen?	Duration	From days to months; possibly the entire winter season. Descent can occur at any time of the day. In spring, avalanches occur mainly in the afternoon.
How to mitigate the risks of avalanches?	Finding a Problem on a Slope	In the presence of slip cracks, the problem can often be localized, but the presence of slip cracks does not indicate an imminent avalanche, as it is almost impossible to predict. Also common is an avalanche without pre-existing slip cracks.
	Travel Tips	Avoid areas close to slip cracks.

 

We sincerely hope that this background information will contribute to your awareness of such a dangerous phenomenon as avalanches. We strongly recommend that you study the potential risks of avalanches at your holiday destination this winter. Whenever possible, try to find local avalanche risk resources and never neglect safety advice.

 

Have a safe holiday!