The gradient tool gives information about how steep a slope is to your assessment of a given slope or area. We highlight areas of terrain in three different bands: 30° to 35° 35° to 40° Over 40° These zones do not provide any indication about whether a given area is dangerous or safe. The zones can be useful in making an assessment of terrain where avalanches typically start. This should not be confused with where they can be triggered or where they can reach. It is possible to remote trigger avalanches and often reach terrain that is less steep than 30 degrees – always be aware of terrain above you and terrain traps such as gullies and depressions.
We chose to segment information into these bands because they correlate with the Elementary Reduction Method developed by Werner Munter from avalanche statistics in Switzerland. It is an easy way for a skier or boarder to make decisions about travel in the backcountry without having to be an expert. You can read more about the reduction method here
In the Elementary Reduction Method a skier or boarder simply avoids travelling on certain slopes depending on the avalanche forecast:
moderate danger level (2): avoid slopes steeper than 40°
considerable danger level (3): avoid slopes steeper than 35°
high danger level (4): avoid slopes steeper than 30°
extreme danger level (5): avoid all off-piste.
Avalanche Decision Safety Grid Using this method does NOT eliminate risk but the large majority of historical avalanche fatalities would have been avoided using this method. The principal avalanche problem this method addresses is slab avalanches which is the main problem that off-piste skiers and snowboarders have to deal with in the Alps. It is possible for wet snow avalanches to occur on gradients lower than this but these are principally a problem in late winter and spring only, often easier to predict and typically play a smaller role in skier/boarder avalanche fatalities.
FATMAP is designed to help the informed skier or boarder to make decisions by providing detailed information about the terrain. It does not provide all the information you need to decide whether a slope is safe or not – indeed you can never know with absolute certainty. Any ‘processed’ information which attempts to provide a go/no-go or safe/not-safe judgement on a slope is hugely prone to error and removes the ability to make your own decisions. We believe only you should make these critical judgements. Avalanche education is outside the scope of this post but we strongly advise taking an avalanche awareness course and informing yourself about avalanche risk. After extensive discussion with mountain guides and mountain rescue associations, we chose to design this feature to provide raw information about the terrain.
The avalanche bulletin for each area provides the most detailed up to date information for a given area and you should have read and be familiar with this before heading out. Even the bulletin is not 100% accurate all of the time and conditions can vary greatly within a small area so it is important to be able to make your own assessment. Other key factors (not an exhaustive list) that can be important to consider in your assessment of a slope are snow pack, time of day, travel techniques, weather and human factors. FATMAP does not help you with these.
It may also be worth noting that we enjoy a relatively straight forward snowpack in the Western Alps compared with some other areas in the world. We do not currently cover areas such as the US and Canada where the snow pack can be considerably different and some people argue necessitates a different approach.
When skiing off-piste, EVERYONE in your group should have basic safety equipment such as an avalanche transceiver, shovel and probe – and know how to use them!