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SnowFlurry

SnowFlurry 1 2017/18 | The essential distinctions

New winter, new rummage

by Lukas Ruetz 11/16/2017
Winter is here, as is the snow, and the Snow Sturgeon has also returned to the keyboard from his snow profile hole in the Western Alps. With reference to last season's SnowFlurry columns, we are recalling some of the terms that regularly appear there.

First of all, for our new readers: In SnowFlurry, we don't just rummage through the snow... The priority will be on currently observable processes in snowpack development and their effects on avalanche risk, illustrated with snow profiles and their interpretation. We will often get to the bottom of the matter using models and extreme simplifications or hyperbolic language in order to focus more on the essentials. There will also be a sporadic look at other departments of Winter and Brettlrutschen. At the end of each SnowFlurry, we will find a mnemonic phrase - easy to memorize.

This year, we will use many of the terms from last season's SnowFlurry as a basis and put them into a suitable framework, the so-called "essential distinctions": The essential distinctions for survival are based on empirical values that show which terms are often not consciously perceived and cannot be distinguished or defined. Some of these words appear regularly in the management reports, others are not read there, but without having understood them, it is impossible to grasp and apply the information in the management report.

Knowledge - experience

We make an explicit distinction between knowledge and experience. Knowledge does not replace experience and experience does not replace knowledge. Not only in snow and avalanche science. The last three winters have shown us in the Eastern Alps, for example: When it comes to the old snow problem, a high level of experience is almost useless if you don't have a sound basic knowledge base.

Danger level - danger level

Three is not the same as three, two is not the same as two. The hazard level merely describes the overall situation. It is an average of the avalanche danger on all slopes of all exposures in the altitude range in question. With one and the same avalanche warning level, it is possible that slopes in the southern sector (= exposure west to south to east) are highly dangerous, e.g. in a spring situation. The same danger level also includes the situation where slopes in the northern sector (= exposure west over north to east) are easily triggered by weak layers in the old snow, but the southern sector is safe. Same danger level, but completely different areas are safe or dangerous! It always depends on the distribution and trigger readiness of the danger spots. The level only summarizes them and alone brings us as much as a touring ski without skins.

Hidden danger signs - obvious danger signs

Easily recognizable are, for example, uncovered drift snow packs, sliding snow mouths, soaking of the snow cover or the amount of new snow. Difficult to recognize are old snow problems, i.e. weak layers within the snowpack, but also snow-covered drift snow packs. They are only occasionally obliging and give off settling noises or cracks. Not every danger shows itself in the terrain! Weak layers in old snow can often only be recognized by carefully reading the situation report or bulletin. Other dangers can of course also be read there, but they are much easier for everyone to recognize in the terrain.

Avalanche times - avalanche locations

The central question in personal avalanche management is usually linked to the spatial dimension. It is: "Where can I trigger what?" If the snowpack stability changes massively on a tour day, the temporal dimension is added: "When can I trigger where and what?" We find this primarily in the spring situation, but also in snowfall, rain or persistent wind activity.

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Large scale - small scale

What is the scale of the avalanche problem? Are the danger spots only located on specific slopes in one exposure in a specific area or are they diffusely distributed across the entire country over wide altitude ranges and exposures? In the latter case, and here again a reference to the old snow problem, there is no way around defensive behavior and avoiding the affected areas.

bound snow - unbound snow

Bound snow can produce slab avalanches. Unbound snow only loose snow avalanches. Powder snow can be bound or unbound. Slab avalanches can therefore also occur on casual powder slopes that appear fluffy. These avalanches are known as "soft snow slabs".

Breaking - sliding

The snowpack can be imagined as a lump of ice with air pockets. The crystals have bonds and hold together, sometimes better, sometimes worse, but they are connected to each other. In order to trigger a snow slab, the lump of ice has to break apart somewhere. This can be caused by the load of its own weight (spontaneous avalanche) or by an external load, i.e. a person. If the lump has broken somewhere, usually in a layer where the bonds between them are not very strong due to the crystal structure (weak layers), then the part above the break slides off as a snow slab, provided the slope is steep enough. This happens from a slope inclination of roughly 30°, from here the friction is less than the forces driving down the slope. However, sliding snow avalanches do not require a break before sliding because the snowpack "only" slides on the ground, so they cannot be triggered - impossible! - and it is almost impossible to estimate if and when it will fall. So we need a fracture for a slab avalanche, but not for a sliding snow avalanche.

Brittle - plastic

Everyone can still imagine what brittle plastic is. Snow is ice. The ice climbers among us know: The colder it is, the more brittle ice becomes. What does brittle mean? Brittle material breaks more easily. Slab avalanches are caused by fractures in the snow structure. Snow also becomes more brittle the colder it is. We can all tell the difference between brittle snow and less brittle snow in everyday life: When it's freezing cold, it cracks under your soles with every step. For us on the mountain, this means first and foremost that drift snow packs are more prone to release the colder they are. Nevertheless, you should always stay away from fresh snow packs. This is because it takes time for the crystals to develop the necessary connection quality so that they can no longer be disturbed by us humans. However, cold temperatures continuously increase the willingness to be disturbed, meaning that with every degree that fresh drift snow gets colder, it breaks even more easily. The cold not only makes drifting snow more brittle, i.e. easier to disturb, but above all makes it disturbable for longer, because the bond takes longer to strengthen due to the cold. With cold fingers, movement only works in slow motion. If snow is at 0°C or just below - i.e. very warm by its standards - and a snow pack is formed, it is less ready to release even when it is fresh and will decrease quickly. It reacts more plastically due to the high temperature. Plastic means that it is deformed by an external impact and remains in this form afterwards. Brittle means it breaks apart before it can deform.

"Super safe" - "Super dangerous" & the state between the two

The danger of avalanches in reality knows no boundaries or divisions. It is continuous. Our "avalanche warning" system and our "avalanche handling" are based on the danger levels due to human factors. These have proven themselves in certain respects and in certain respects they cause us major problems, especially at levels 2 and 3. Please also note the now de facto danger level "3+". It is important to make a distinction in our minds: there are situations where we can assume very safe conditions. This does not mean that it is not possible to trigger an avalanche, but the probability of this happening is very low: the necessary load is rather high and there are hardly any danger spots. Then there are situations where triggering an avalanche is very likely, it is even considered possible on most slopes. And then there are an infinite number of situations in between: And right now there are a few or perhaps only a handful of slopes where avalanches can easily be triggered and next to them exist many where triggering is considered hardly possible.

Easily manageable - difficult to manage

The distinction between situations ranging from very safe to extremely dangerous brings us to the handling of the individual situations: Situations that are easy to handle, i.e. those in which decisions can be made simply and with less complex considerations, are at the two extremes: In our system, these are the danger levels Low - 1, Major - 4 and Very Major - 5. In the "Low 1" danger level, there are only very few danger spots where it is considered possible that an avalanche could be triggered. For the most part, you can worry about other problems on the tour. You often have to be careful not to fall on hard snow. Due to the high probability of spontaneous avalanches - i.e. avalanches that start on their own and do not require an external trigger - it has become common practice not to leave the secured terrain at danger level "large 4". They are therefore also very easy to handle: through the criterion of "complete abandonment".

The situations in between are difficult to handle; these are described in our system with the danger levels "Moderate 2" and "Considerable 3". Here, the avalanche triggering probability is distributed like a more or less orderly patchwork quilt in the terrain: There are places where triggering is easy, places where triggering is more difficult and places where triggering is considered unlikely. This situation is the most difficult to handle. Completely abandoning the day in the terrain is rarely the chosen option. Partial abandonment of certain areas, areas, altitudes, exposures & slopes is now the chosen remedy. These can be read explicitly from the situation report. In some cases, they can be narrowed down relatively precisely by the avalanche warning system, e.g. to a precise altitude band for the old snow problem. In some cases, they can only be roughly defined. The areas where you have to be more careful or should stay away are more or less known. We don't have to interpret the lines in the situation report subjectively, but take them as they are written and implement them in the terrain. This means, for example: In the event of an old snow problem, at best not go to the area in question at all and if you do, show maximum defensive behavior, in the event of a drift snow problem, avoid the recognizable drift snow, or be back home early in a classic spring situation.

The Schneestöberer wishes you an eventful and accident-free winter!

Note: Becoming aware of which situations you can handle easily and when it is more difficult to practice good avalanche management is a big step forward in your personal development with regard to avalanche risk management.

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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