Werner Munter avalanche reduction method


Snow conditions

Danger level (avalanche warning)
Type of snow

Selection of reduction factors

Steepest slope
Avoidance of sectors
Constantly frequented slope
Group size & distances

The good news for winter sports enthusiasts first: nowadays, avalanches are scientifically investigated in-depth and their origin can be traced back to a combination of different factors, which are also statistically recorded and have become manageable as risks. And when we talk about risks, we implement the options for risk reduction. In his life’s work, the author, Werner Munter, has dealt with the assessment and reduction of avalanche risks in winter sports in detail and presented an easy-to-use method, in order to transfer the complex interplay of different risk factors during a ski tour into a simple Yes/no decision.

Accident prevention instead of optimisation of the salvage measures

There is always a residual risk with ski tours

But what is risk reduction in dangerous avalanche terrain all about? Here, Munter warns that a goal of “zero deaths” is unachievable, as the unmanageable residual risk alone prevents this goal from being achieved. Instead, the aim is to significantly reduce avalanche accidents and the resulting number of dead and injured winter sports enthusiasts in the outdoors. Mind you, it’s not a question of minimising the absolute number, but about optimising the relationship between risk and avoidance.

Since every area of life is afflicted with a known risk and we consciously or unconsciously take risks everyday, it is the job of the reduction method to quantify the avalanche risk and make it visible in order to provide people with a decision-making basis to navigate by hand or, if necessary, to refrain from using a vehicle.

However, it is also crucial that the method aims to avoid an accident rather than to minimise the consequences of the accident. With avalanche airbags, avalanche beacons, probes and shovels, tools are available to rescue and care for accident victims in order to reduce the impact of the accident on a body. However, the physical forces of an avalanche are so great that some of the buried victims are already crushed during the burial, another large proportion suffocate before the helpers can reach them. For these reasons, the priority is clearly to generally avoid burials.

Reduction method: quick on-site decision making

If the tour is carefully planned with the help of the 3x3 filter method, local analyses are regularly carried out on tour and a constant check routine takes place during the ascent of terrain and slopes, so this provides a very good indication of the risk situation on-site. The reduction method depicted in the calculator therefore only tries to quantify the factors and bring about a simple “to go or not to go” decision using a formula.

The reduction method is divided into the risk factor that results from the avalanche report and the risk factors (RF) that represent statically significant risks:

Residual risk = risk factor ÷ (RF steepest slope × RF abandonment of sectors × RF frequented slopes × RF group size and distances)

The calculation method makes it quick and convenient to assess the conditions. Applied consistently, it reduces the accident risk to a minimum (residual risk).

Danger level and risk factor

According to the avalanche report, a low danger warning level is assigned a risk factor of 2, a moderate one is risk factor 4, a significant one is risk factor 8 and a large one theoretically risk factor 16. The risk factor for the greatest danger level is therefore theoretical, because it cannot be sufficiently minimised by the available reduction factors. Instead, it is recommended to move in areas with a moderately steep incline of under 30° when there is a high avalanche risk. Intermediate steps are also possible between the danger levels.

European avalanche danger scale
Danger level Symbol Snow cover Avalanche trigger Information for winter sport enthusiasts
Avalanche danger warning level 5 symbol Weakly solidified and largely unstable Spontaneously, many large, multiple and very large avalanches are to be expected, even in moderately steep terrain. Very adverse conditions. Avoidance recommended.
Avalanche danger warning level 4 symbol On steep slopes (> 30°) mostly weakly solidified An avalanche can already be triggered with low additional loads (one person) on numerous steep slopes. In some cases, many medium and large avalanches can be expected spontaneously. Adverse conditions. Lots of experience in avalanche assessment required. Limiting to moderately steep terrain (< 30°) / pay attention to the avalanche run-off areas.
Avalanche danger warning level 3 symbol On many steep slopes (> 30°) only moderately to weakly solidified An avalanche can already be triggered with low additional load (one person), especially on indicated steep slopes. Sometimes and spontaneously, some medium, occasionally also large avalanches are possible. Partially adverse conditions. Experience in avalanche assessment required. Avoid steep slopes of the indicated exposure and altitude as far as possible.
Avalanche danger warning level 2 symbol On some steep slopes (> 30°) only moderately, otherwise generally well solidified An avalanche can be triggered particularly with high additional loads (a group of people, snow groomer, avalanche dispersion), especially on indicated steep slopes. Large spontaneous avalanches are not expected. Mostly favourable conditions. Careful route selection, especially on steep slopes of indicated exposure and altitude.
Avalanche danger warning level 1 symbol Generally well solidified and stable An avalanche can generally only be triggered with high additional loads (groups of people, snow groomer, avalanche dispersion) at isolated points on extremely steep terrain. Spontaneously, only slides and small avalanches are possible. Generally safe conditions.

Available reduction factors

The following reduction factors are provided as precautionary measures to minimise the risk of accident:

  1. Steepest slope (selection is obligatory for the significant danger level)
    • RF = 2: less than 40°
    • RF = 3: around 35°
    • RF = 4: less than 35°
  2. Avoidance of sectors (not applicable for wet snow)
    • RF = 2: Avoidance of the north sector (NW - N - NE)
    • RF = 3: Avoidance of the northern half (WNW- N - ENE)
    • RF = 4: Avoidance of all critical slopes and altitudes mentioned in the avalanche report
  3. Frequented slopes (not applicable for wet snow)
    • RF = 2: constantly frequented slopes
  4. Group size and relief distances (min. 10 metres in ascent)
    • RF = 2: large group (over 4 people) with relief distances
    • RF = 2: small group (2 to 4 people) without relief distances
    • RF = 3: small group (2 to 4 people) with relief distances

Go/stop decision

If the ratio of the risk factor to the product of the selected reduction factors is less than or equal to one, the slope can be travelled with a low residual risk. In the event of a result greater than one, the decision is negative - there is either a way to avoid the slope on a less dangerous route or the tour must be aborted.

However, the main pitfalls of the reduction method are incorrect assumptions by the user - if the situation on-site or, for example, the steepness of a slope is wrongly assessed, the calculator also delivers a distorted result. Thus, the calculator cannot replace long-term experience and a sharp power of observation.

Avalanche risk as a complex risk

The avalanche risk is an aggregated risk that is composed of individual factors to form a cluster risk. For his model, Munter includes the weather and snow conditions as the first factor, the terrain as the second and the person as the third factor. On closer inspection, these three factors can be assessed on aggregates of different sizes, accordingly complex and only with good, experiences and unclouded estimation ability. In the following I will now explain how the risk reduction method from Werner Munter can work in practice.

3x3 filter method

With his 3x3 method, Munter relies on the three risk factors (criteria): conditions, terrain and person. However, he is not satisfied with a simple assessment of these three criteria alone, but adds three additional filters that help to keep an eye on different perspectives and to include different dimensions of risk. The three filters relate to the focus on regional events, local characteristics that can be viewed locally and zonal events that focus on individual slopes and situations. Munter then combines these three criteria with the three filters and gets a holistic image of the risk situation. The following representation provides and overview of the resulting errors of Munter’s risk matrix.

Conditions x regional

There is no doubt that looking at the weather provides important information for assessing the avalanche risk. The regional view refers to the analysis of the avalanche situation report, the weather report, the information provided by local experts and trusted persons on-site, as well as information from other local sources. The avalanche situation report provides information about the entire situation on-site and at different altitudes. The information contained therein about snow depth, the development of the snow profile as well as special dangerous situations provide a good overview of a region and can therefore be used as basic knowledge, for which ski tours and alternatives can be considered. The weather forecast can also be considered in order to gain more information about the stability of the condition as well as further development. Snow experts on-site can provide information about possible specialities of the local landscape thanks to decades of experience in assessing the situation in a valley/region.

Conditions x local

The local filter denotes all information from the immediate vicinity on a tour, i.e. everything that’s in sight. This includes, local snow conditions as well as the terrain, wind transport, critical amounts of new snow and alarm signals. The local filter can be used to check the information from the avalanche situation report and to calculate the developments and tendencies. The local weather also has a significant influence on future developments. Here, observation criteria are view and clouds, wind, precipitation and temperature.

Our altitude calculator shows how temperature, air pressure and UV radiation normally change depending on altitude. On the tour, it can also help to follow the weather forecast< with the help of a barometric altimeter.

Conditions x zonal

The zonal filter now draws the radius even closer and focuses the view on individual slopes. It is essential to constantly check the amount of new snow with regard to snow accumulation. What is the view like from the slope, are there warming rays from the sun? Which snow surfaces are joined, how big would a possibly outward jutting snow slab be?

Terrain x regional

The standard for viewing the terrain when planning tours or possible alternatives is a topographical map on a scale of 1:25,000 (to the scale converter). In many areas there is also a wide range of guidebook literature to help you find out about worthwhile touring options and imminent dangers. In some cases, or even when there is no topographic map material available, aerial photographs provide important terrain information. Of course, our own terrain knowledge is also included in the analysis.

Terrain x local

Here, the focus is on comparing the planning information with the local situation: do my ideas correspond to the situation on-site? A binocular is useful for checking relief, dimensions, exposure, steepness and, if necessary, the existence of ski tracks. Especially in the case of tracks that have already been laid, it must be checked whether these have been laid taking into account the terrain information or whether they may have been laid over dangerous passages and require adapting.

Terrain x zonal

With a view of the nearest environment, the following is checked: what is above/below me? Where is the steepest slope, what is the exposure of a slope, am I close to a ridge, what are the altitudes and what is the shape or relief of the slope?

Person x regional

A relative novelty in Munter’s risk reduction method is the inclusion of the human factor. He queries the dynamics and requirements of the group, since this provides information about the motivation and willingness to take risks. In regional terms, the planning analyses which persons will participate in the tour and how they are physically and mentally fit. What equipment does the group have and how much experience do individuals have? Are all the group members up to the difficulty of the ski tour? Who is responsible?

Person x local

The local view is specifically about the constant routine retrieval of data on tour: who is in my group, how do performance and mood develop? What about the equipment, was the avalanche beacon checked? Who is still on the go, is there a need to make arrangements? Are the group still on schedule (to the walking time calculator) or do alternatives have to be used if necessary?

Person x zonal

This is specifically about the state of mind in the group and the behaviour of other groups on the mountain. How are the participants’ fatigue, discipline and ski technique? Has the wind chill been underestimated and does is present a risk of hypothermia? Is a slope really constantly used by other groups and, if so, less risky? How can the leadership tactics be adapted, do distances have to be maintained, corridors bridged or tracks traced? Is it necessary to set up waiting facilities or avoid certain slopes?

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