Avalanche glossary
Slope shape
The shapes of terrain affect avalanche formation
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Slope shape
The shapes of terrain affect avalanche formation because they have a decisive influence on the wind direction and speed and thus on the extent of the snow drifts.
Gullies, shallow basins and changes of slope inclinations promote avalanches. These terrain shapes promote the formation of drift snow deposits on the lee side and compact snow accumulation on the windward side.
Obstructive to avalanches are:
The terrain is a helpful partner in the assessment of avalanche risk. However good visibility and considerable experience are required in addition.
Slope orientation
While wind and slope shape are considered together, the slope orientation (slope exposure) influences the temperature of the snowpack and thus its composition. In leeward slopes (NW to NE direction), the snowpack settles very slowly due to the low solar radiation, whereby existing threats stay longer and new dangers develop. Due to the prolonged exposure to sunlight, south-facing slopes (SW to SE) often have a more stable snowpack structure. The terrain can therefore be divided into favorable and unfavorable slopes. Avalanche bulletin and independent observations provide valuable information for classification into favorable or unfavorable. The slope orientation can be determined with a map or a compass. The slope exposure depends upon the direction in which you look with your back to the slope (e.g. if you stand on the slope and look away from it toward the north, it is a northern slope).
Slope inclination
The steepness of a slope is one of the three conditions for the formation of a snow slab. Therefore, this factor plays a major role in the assessment and the decision making. In determining the steepness of the slope, the steepest part of a slope (approx 10 x 10 m) must be considered. About 97% of all avalanche accidents occur in slopes of over 30° inclination. Slopes over 30° are referred to as steep slopes in avalanche bulletins. In 84% of the avalanche triggerings, the steepest slope was at least 35°.
Therefore, generally speaking: The steeper the slope, the easier it triggers an avalanche. The other way round, that also means: When steep slopes are avoided, the risk of an avalanche triggering is significantly reduced.
Since the descent is truly fun for many only on slopes of more than 30°, the relation of the slope steepness to the avalanche frequency is suppressed. As a reminder for a simple risk reduction, the following upper limits can be used:
Risk level in avalanche bulletin Maximum steepness
1 -
2 below 40°
3 below 35°
4 below 30°
5 Abandonment of tours
Slope steepness can be measured and estimated:
The shapes of terrain affect avalanche formation because they have a decisive influence on the wind direction and speed and thus on the extent of the snow drifts.
Gullies, shallow basins and changes of slope inclinations promote avalanches. These terrain shapes promote the formation of drift snow deposits on the lee side and compact snow accumulation on the windward side.
Obstructive to avalanches are:
- Ripples (often blown off, rarely drift snow)
- Ridges (often blown off, rarely drift snow
The terrain is a helpful partner in the assessment of avalanche risk. However good visibility and considerable experience are required in addition.
Slope orientation
While wind and slope shape are considered together, the slope orientation (slope exposure) influences the temperature of the snowpack and thus its composition. In leeward slopes (NW to NE direction), the snowpack settles very slowly due to the low solar radiation, whereby existing threats stay longer and new dangers develop. Due to the prolonged exposure to sunlight, south-facing slopes (SW to SE) often have a more stable snowpack structure. The terrain can therefore be divided into favorable and unfavorable slopes. Avalanche bulletin and independent observations provide valuable information for classification into favorable or unfavorable. The slope orientation can be determined with a map or a compass. The slope exposure depends upon the direction in which you look with your back to the slope (e.g. if you stand on the slope and look away from it toward the north, it is a northern slope).
Slope inclination
The steepness of a slope is one of the three conditions for the formation of a snow slab. Therefore, this factor plays a major role in the assessment and the decision making. In determining the steepness of the slope, the steepest part of a slope (approx 10 x 10 m) must be considered. About 97% of all avalanche accidents occur in slopes of over 30° inclination. Slopes over 30° are referred to as steep slopes in avalanche bulletins. In 84% of the avalanche triggerings, the steepest slope was at least 35°.
Therefore, generally speaking: The steeper the slope, the easier it triggers an avalanche. The other way round, that also means: When steep slopes are avoided, the risk of an avalanche triggering is significantly reduced.
Since the descent is truly fun for many only on slopes of more than 30°, the relation of the slope steepness to the avalanche frequency is suppressed. As a reminder for a simple risk reduction, the following upper limits can be used:
Risk level in avalanche bulletin Maximum steepness
1 -
2 below 40°
3 below 35°
4 below 30°
5 Abandonment of tours
Slope steepness can be measured and estimated:
