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SnowFlurry 2 2023/24 | Avalanches in the forest

The misconception of safety in the forest

by Vinzent Letzner 02/24/2024
"Nothing can happen in the forest." - This is probably one of the most widespread misconceptions among skiers. It is true that statistically there are fewer avalanche accidents in the forest. However, those who are lulled into a false sense of security are unconsciously taking a high risk and acting carelessly. In today's SnowFlurries we therefore take a look at how the forest influences snowpack stability and what skiers need to bear in mind.

Influence of the forest on snowpack stability 

In fact, the snow cover in the forest is often very different from that in the surrounding open terrain. This difference varies depending on the type, density, age and composition of the forest.

One of the most obvious influencing factors is snow interception. This describes the effect of the treetops, which collect some of the snow during precipitation. From there, the snow sublimates - i.e. it changes directly from a solid to a gaseous state - or it falls to the ground in the form of snow clumps or meltwater. The snow cover is often less thick as a result of snow interception and the layers are less structured. The layers are therefore more heterogeneous as they are broken up by falling snow. Depending on the type of forest, the amount of snow falling on the ground can be 10-50% less than in the neighbouring treeless terrain. Evergreen conifers, such as the Scots pine, which is widespread in the Alps, have a higher interception rate than deciduous trees that are sparse in winter. In a light-covered deciduous forest, the snow cover structure can therefore only differ slightly from the neighbouring open land.

Another factor influencing the snow cover is the density of the forest. Whether coniferous or deciduous trees, the trunks can have a supporting effect on the snow cover in both cases. However, one can only speak of a complete supporting effect when the density of trees per hectare makes skiing virtually impossible. Depending on the slope inclination, up to 1000 trunks per hectare may be necessary to prevent avalanches in the forest.  

A dense forest also acts as a barrier to the wind. Wind is snow drifts and consequently bound snow layers, also known as drifting snow, occur less frequently. In addition, less snow accumulates in gullies and hollows than in forest-free areas due to snow interception and less snow transport within the forest;

The microclimate in the forest also contributes to snowpack stability. The shade provided by the trees reduces the warming of the snow cover during the course of the day. The difference can be up to four degrees compared to the open air. At the same time, the trees warm up during the day and release the heat energy at night. The night-time temperature in the forest can therefore be up to one degree warmer. This microclimate reduces the likelihood of the formation of surface frost, one of the most treacherous weak layers.

In general, the forest therefore offers great potential for stable conditions. Its structure increases the roughness of the ground and thus creates resistance for snow sliding downhill. Nevertheless, it is important to be aware that you can be exposed to all avalanche risks here too and that you should behave accordingly, as the forest can even increase the avalanche risk under certain circumstances. 

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Factors influencing forest avalanches 

All avalanches that occur in forests are summarised as forest avalanches. An analysis by the SLF has identified two typical weather scenarios that generally increase the risk of avalanches, but in which the forest offers particularly little protection: If it snows more than 50 cm within three days, in conjunction with strong winds and consistently cold temperatures, fresh snow avalanches can occur. Due to the low radiant energy of the sun and the low temperatures, the new snow does not bond well with the old snow and the transformation effect is inhibited. Fresh snow avalanches are common forest avalanches, as they can also occur in smaller forest clearings, mostly in subalpine, north-facing forests. Secondly, more old and wet snow avalanches have been observed when there is a combination of a strong snow cover and rising temperatures and thus a soaking of the snow cover.

Irrespective of meteorological factors, a forested area can even increase the risk of avalanches at certain points. Low trees that are completely covered by the snowpack and pressed to the ground can favour the onset of avalanches if the flexible branches suddenly straighten up. In addition, the formation of deep frost is often pronounced in these places. Only when a tree breaks through the snow cover can it have a supporting effect. In addition, forest clearings can lead to wind circulation, which results in increased snow accumulation and thus creates a typical drift snow situation that favours slab avalanches.

If you get caught in an avalanche in the forest, the consequences can often be much more serious than in the open country, as the risk of injury from lying or standing trees is considerably higher if you are swept away. 

What I have to consider 

As a general rule, anyone skiing in the forest is not protected from avalanches, even if the forest has a stabilising effect on the snow cover and weakens the wind. A rational and complete assessment of the terrain is therefore required in order to accurately assess the danger here. Clearings in particular should be crossed with increased caution, as the protective effect can be greatly reduced here. If there is a significant or high avalanche risk, you should carefully consider the situation, as simply avoiding the forest does not always minimise the risk.

As in open terrain, routes should be chosen carefully, the terrain interpreted and attention paid to buzzing noises.



  1. Margreth, Stefan. "The effect of the forest on avalanches."Forum for Knowledge. Vol. 2004. 2004. 

  2. Teich, M., Marty, C., Gollut, C., Grêt-Regamey, A., & Bebi, P. " Snow and weather conditions associated with avalanche releases in forests: Rare situations with decreasing trends during the last 41 years."  Cold Regions Science and Technology, 83-84, 77-88 2012 

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This article has been automatically translated by DeepL with subsequent editing. If you notice any spelling or grammatical errors or if the translation has lost its meaning, please write an e-mail to the editors.

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