Understanding avalanche problems! Or the danger of the danger levels

The European warning services (eaws) have agreed on the following avalanche problems and now also use standardized symbols: Fresh snow, drifting snow, wet snow, old snow, sliding snow

In addition, there is an icon for "favorable situation" (explanation of avalanche problems). In North America, other problems are sometimes named, such as cornice breakage, loose snow (wet and dry), as well as "deep slab" and "persistent slab". The latter are summarized in Europe as "old snow".

Drew Hardesty has worked intensively on avalanche problems and, together with his colleague Wendy Wagner, has developed the "Avalanche Toolbox". In the toolbox you can see schematically which "tool" is appropriate for which problem. (See also) Three factors are considered for each problem: Predictability of "behavior", probability of remote triggers, usefulness of snow observations and tests. In this way, regardless of the hazard level, the difference between old snow problems and, for example, a new snow situation is worked out.

In the following commentary, Hardesty explains more about avalanche problems and the difficulty of summarizing complex snowpack situations in a hazard level. The text originally appeared on the Utah Avalanche Center blog and has been translated and lightly edited by PG in consultation with the author:

The Danger in the Danger Levels

"Democracy is the worst of all forms of government, except for all others." Who said that again? Mark Twain? No, Winston Churchill. But it sounds like he stole it from someone (Twain?). It's a bit like democracy with our avalanche danger levels.

Recently, at a lecture, I asked the participants to determine the danger level in two different situations. Beforehand, I gave them a little crash course: When we write our situation report, we evaluate each potential avalanche problem based on a number of factors:

The likelihood of triggering

Bruce Jamieson did a study a few years ago where he asked experts (avalanche watchers and the like) about the likelihood of triggering at different danger levels. (See illustration). The probability of triggering increases approximately 10-fold with an increase in the danger level.

In the past, the factor "probability of triggering" was considered the most important point in determining the danger level. Terms such as "unlikely", "possible", "probable" played a major role. As a rule, the level was indicated as significant when self-triggering came within the realm of possibility. This system did not work well. Imagine someone offered you 10 million dollars to play Russian roulette. Would it influence your decision if you knew how many rounds were in the magazine? What if I told you it had a rubber bullet in it? A bullet? A cannonball? A nuclear missile? Would you change your mind?

I asked my lecture participants to estimate the probability of triggering per danger level. The result was something like:
Low - 1-5%
Moderate - 25-35%
Significant - 60-65%
Large - 75-85%
Very large - 90-100%

I found the jump from moderate (35%) to significant (60%) particularly interesting. What is the key difference between these two levels? After all, most people are at levels 2 and 3. Where did the missing 25% go?

Everything depends on the character of the potential avalanche, which is reflected by the 'problems'. For me, the aspect of "manageability" mentioned above is crucial. Sometimes moderately is issued instead of significantly because the spatial distribution of the critical spots is no longer as problematic as in the days or weeks before, or the probability of triggering is somewhat lower. However, the existing old snow problem does not suddenly disappear. Maintaining the higher danger level just to protect the public means that the danger levels are no longer taken seriously in the long term.

When climbing, there are well-secured routes that are rated 5.9, for example (note: Sierra/USA scale). Sometimes a 5.9 is marked with an additional X, i.e. 5.9X. The difficulty is the same, but the X means that accidents can lead to "serious injury or death", for example because the route is poorly secured or the rock is very unstable. When you see the X, you stop and think about it. Mistakes here have worse consequences than in a normal 5.9.

If such an X were also introduced for the danger levels, situations could be better described for which significant or large is not appropriate due to the distribution of danger points and the sensitivity of the snowpack, but the consequences of triggering are very high. X is a function of the avalanche problem, the size and the possible consequences, as well as the "manageability", i.e. assessability or predictability.

In the end, it is not up to the warning services to decide how the danger scale can be improved, but to the public. What can be done to convey to casual readers the difference between "low probability, high consequences" and "high probability, low consequences" in a number or a single word?

How would you have judged the situations in Hardesty's example? Do you pay attention to the avalanche problems in the situation report, or is the danger level more important to you? How do you deal with the current problem of old snow this winter? Is the danger level scale and its definition sufficient to adequately describe all avalanche problems?

In this country, there have been repeated discussions in the past as to whether level three should be split up or whether it would make sense to rename it from considerable to major and major to extreme. What do you think of Hardesty's climbing comparison? Would a moderateX or considerableX be a way to summarize complex old snow problems in one keyword?