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SnowFlurry 3 2022/23 | The Arlberg effect

The more tracks, the lower the avalanche danger?

by Stefanie Höpperger • 02/25/2023
In this rummage, we take a closer look at the so-called Arlberg effect and its impact on avalanche danger. As this effect does not only occur on the Arlberg, we refer to it more generally as the "effect of off-piste descents".

What is variation riding anyway?

Off-piste skiing or freeriding refers to skiing and snowboarding through untouched snow away from the marked and controlled ski pistes in mountain regions. The basic prerequisites for freeriding are the safe mastery of deep snow skiing and knowledge of avalanche awareness. At least that is how it is described on Wikipedia.

If we take a closer look at this paragraph, the phrase untouched snow stands out. When skiing around the ski resorts, however, you rarely find untouched snow unless you are dusting off the first turns after a snowfall. The terms "busy", "heavily tracked" and "ploughed down" are more appropriate. If the slopes or the snow were always untouched, there would be no effect on the avalanche risk. I would therefore describe off-piste skiing and snowboarding as skiing and snowboarding away from the secured pistes using the lifts with little or no additional ascent in the vicinity of the ski areas.

What is it all about?

We have dealt with the topic before: Here you can read where the term comes from and what you would really have to do to really achieve a safety gain. Basically, the "effect of variation descents" is about the fact that the slopes are constantly ploughed up by heavy frequency, whereby snow crystals are destroyed by the mechanical impact. However, this is limited to the area of the track and also depends on the depth of penetration.

The use of the lifts enables quick and easy transport up the mountain, which means that variations are often skied several times a day and by far more people than on ski tours in open terrain. However, many trips on individual days are not enough to have a positive effect on the avalanche risk. The slopes must be heavily tracked, trampled and blasted on a regular basis (preferably daily) from the beginning of the first snowfall in autumn until the end of winter.

In autumn and early winter, however, descents are often not yet possible as the snow cover is not thick enough. For the development of an early winter old snow problem however, little snow is perfect.

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The process

When we make turns in the snow on skis or snowboards, pressure and friction act on the snow crystals and the snow cover. The branches of the snow crystals break, making them smaller and closer together, which strengthens the bond.

This process is also known as sintering. Sintering is a natural process that always takes place as soon as the snow crystals have reached the ground and is also the start of the decomposing transformation. If we form a snowball with our hands, sintering also takes place on the scale of the snow crystals.

If there is a possible weak layer on the snow surface and it is crushed, the crystal composition and also the surface structure change in the area of the tracks. The weak layer is destroyed in this small area and a fracture may no longer spread over such a large area.

The snow surface also becomes variable and, in contrast to unstirred slopes, where a weak layer is still evenly and extensively present, one can speak of a better starting position for the subsequent snowfall.


Let's assume that there are extensive surface rime crystals on the snow surface: a perfect weak layer as soon as it is snowed in or overlaid. If the variations in this area are then heavily travelled on, the surface frost is somewhat destroyed exactly where our tracks are visible. But only exactly there, not further to the left or right and only the crystals on the snow surface. In addition, new surface frost can form very quickly!

Weak layers that are deeper in the snow cover can at most be disturbed, but not destroyed. With snowshoes or on foot, the penetration depth is somewhat greater, but more selective. Such tracks are also much rarer and hardly ever found in classic ski terrain.

To illustrate this a little more clearly, I'll describe the whole thing using the example of a fashionable ski tour such as the Lampsenspitze in the Sellrain Valley. Let's assume the same scenario with the surface tyre, on a sunny weekend when the tour is heavily frequented. If everyone also stays directly in the main corridor of the route, this area can be described as heavily tracked. We can assume that the surface tyre has been partially destroyed and the snow surface is variable.

The main corridor then represents a lower risk for subsequent snowfall, not only due to its hilly terrain. The prerequisite is that there is no underlying weak layer or other problems.

If it snows the following days, however, neither the surface frost nor the tracks of the previous days can be seen. Semi-safe conditions are therefore right next to dangerous ones. You therefore need to know in which areas and to what extent the tour was tracked before the snowfall. You also need to know if and where there was surface rime on the previous snow surface. If you are familiar with the area, know the terrain and are aware of the other facts, the tour is quite safe.

Provided that you consistently stay in the main corridor and resist the temptation of the other powder slopes. For many, easier said than done! Of course, this also applies to off-piste descents.

When does the  "effect of variation descents" have a positive impact on the avalanche risk and when not?

  • Weak layers such as surface frost, angular crystals and facets that develop on the snow surface can be somewhat destroyed in the heavily travelled corridors before they can be overlaid by bound snow layers and become a problem.

  • The snowpack settles a little faster due to the pressure.

  • In spring, it takes a little longer to break through in heavily tracked areas, as the crystals in the area of the tracks are much more compressed and meltwater has a harder time draining into the snowpack. A film of water can form on the surface of the tracks, which freezes due to the night-time radiation. The ascent track of ski tourers is much more slippery in the morning than the structured snow right next to it.

For all other problems, the same handling and avalanche danger applies as in the rest of the unsecured terrain!

Drift snow:

Can form at any time of day or night and can be easily disturbed by individual winter sports enthusiasts. Weak layers often form loose layers, for example due to fluctuations in wind or temperature during snowfall. Advantage: With good visibility, drifting snow can usually be easily recognised in the terrain.

Old snow problems (GM1, GM5, GM4, ..):

An old snow problem must also be critically assessed in the off-piste area and on fashionable ski tours!

Downhill tracks in the snow do not speak for the safety of a slope! Even the thirtieth skier can trigger an already tracked slope with an old snow problem, because nobody knows the exact hotspots where a break can be initiated.

Weak layers from autumn and early winter as well as all others that develop deeper in the existing snow cover are neither influenced nor destroyed by winter sports enthusiasts, especially when skiing is not yet possible.

The GM4 - cold to warm, warm to cold - is a particularly tricky problem, as weak layers often only develop days after the snowfall. The boundary area in which a temperature difference arises can be located at different depths in the snow cover and is usually very extensive.

The thin, angular layers that develop above or below crusts are not destroyed by snow sports enthusiasts. If the weak layer is strong enough and a suitable board is placed over it, fractures can spread over larger areas and trigger avalanches even in flat, seemingly safe terrain.

Nigg effect and grey scale deposits:

Are difficult to recognise and very poisonous. Can only be defused as long as they are on the surface of the snow.

New snow:

If the critical amounts of fresh snow are reached, there is also a risk of avalanches in the variation area. The snow load can disrupt deeper-lying weak layers and avalanches can reach a large scale. Loose snow avalanches from steep terrain are also to be expected.

Gliding snow:

It has a completely different avalanche process and travelling has no effect on this type of avalanche.

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This winter, the effect is only limited

This winter, many descents and ski tours could only be made in mid-January because there was simply not enough snow and the little snow cover consisted mainly of loose layers. Some slopes and tours are still not or hardly skied. In some areas, the structure of the snow cover was and is completely untouched by mechanical influences from humans. Where this is the case, the weak layers that formed in early winter through to January are just as present in the off-piste area as in other open terrain and vary in intensity depending on the area, altitude and exposure. The "effect of the off-piste runs" does not apply to the existing old snow problem!

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Stubborn old snow problem 2022/23

The problem of old snow has been with us for weeks. How do you deal with it and does the effect of the ski runs help?

First of all, I would like to mention that it is difficult to generalise with regard to avalanche problems, as they vary greatly from area to area and each problem has to be dealt with differently. A weak layer in old snow (old snow problem) can consist of many hazard patterns. They are different in the way they develop, but they have one thing in common: they are hardly recognisable in the terrain. Only subsidence noises, crack formation and avalanches indicate this. Although existing weak layers can be determined by means of snow profiling, no reliable slope assessment can be made. However, the LWD can usually localise old snow problems very well and indicates this in the avalanche report or blog entries.

It takes a lot of prior knowledge, technical expertise, process thinking, weather and area observations, tours and knowledge of the terrain, etc. to be able to assess the avalanche risk. If you do not know the snowpack structure and the development of the individual layers on the chosen tour, it is difficult even for a trained eye to assess the probability of a slope being triggered in the terrain.

As all of these points can only rarely be fulfilled, the only way to safely ski tour or ski downhill in the event of a pronounced old snow problem is to consistently avoid the areas mentioned or only visit them in terrain with a steepness of less than 30° (measured at the steepest part of a slope). Otherwise you are playing Russian roulette. Also make sure that you are not in the catchment area of steep slopes that you can trigger on the flat! Good tour planning is the key to safe downhill fun!

There are usually only a few days each winter when the combination of weak layer and board is a perfect match and you should avoid certain areas and tours. After all, we all want to return home from the mountain alive and well so that we can continue to practise our sport in the future. Unfortunately, these days are among the most avalanche-prone. On the weekend of 3-5 February 2023, a combination of many factors led to a very avalanche-rich period:

  • A much delayed start to winter so far only a few tours have been possible

  • Finally fresh snow!

  • A weekend with beautiful weather.

  • A lot also the still widespread misconception that a little snow is safer than a lot of snow.

  • The human factor:

It has to be a specific or steep tour, otherwise it's not worth anything. The urge to do something blatant to get more likes on social media, lack of knowledge, great willingness to take risks, ....

  • Deceptive security:

Nothing happens on fashion tours anyway, you've done the tour many times and nothing has ever happened, existing tracks, powder snow, "it's not so dangerous in the off-piste area", ....

  • The combination of fresh snow, accompanied by gale-force winds, formed very disruptive drift snow packs, which led to a perfect constellation of a weak layer and a board lying on top.

The weekend showed us very impressively that the old snow problem is very pronounced and widespread in large parts of Tyrol and that there was no "effect of the off-piste runs". Numerous avalanches were reported, unfortunately also with some fatalities that could have been avoided. Listen to the explicit warning from the avalanche report, avoid the areas indicated and don't be misled by the deceptive safety of the terrain if there are already tracks on the slope!

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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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