It is mid-summer and 30 cm of fresh snow is lying on the ground – such conditions arise from time to time. Fresh snow increases the avalanche danger, even if only briefly in most cases.
In the winter, avalanches represent the principal danger in the mountains, but in summertime, when the risk of falling, rockfalls, icefalls and sudden weather changes are the main hazards, avalanches endanger mountaineers less frequently. In the summer, an elevated avalanche danger exists only during and on the days immediately after snowfalls. Avalanche accidents remain nonetheless common. In the last 40 years, 45 people have lost their lives in avalanches in July, August and September. In view of the terrain, the danger of being swept along and of falling while climbing in the mountains is greater than the danger of being buried. For this reason, even small avalanches can have fatal consequences.
Fresh snow in the summer is not at all unusual. On the Weissfluhjoch (2540 m), more than 10 cm of snow falls in 24 hours twice on average in the period from July until September. At a 1000 m higher altitude, in the high Alpine regions, snow falls more often and the quantities of fresh snow can be substantial. When the snowfall level drops to 2000 m, wintry temperatures of -10°C prevail at 3500 m.
Two primary dangers
After snowfall, two primary dangers exist:
- The fresh snow or a recent snow drift accumulation can be released as a dry snow slab. Such occurrences are assisted by a cohesive old snowpack or slick ice.
- Strong solar radiation and the associated sharp rise in temperature can give rise to wet snow avalanches, including on very steep grassy slopes and slabs of rock.
After a fairly warm day of fine weather and a clear night, the avalanche situation generally eases quickly. If temperatures remain low, however, the danger is reversed more slowly.
Critical weak layers in the snowpack capable of serving as sliding surfaces for slab avalanches (old snowpack problem) occur more seldom in the summer. This facilitates an assessment of the avalanche danger, because attention focuses on the fresh snow in particular.
Evaluate avalanche situation - also without an avalanche bulletin
In the summer, the avalanche bulletin does not appear at regular intervals. The avalanche situation must be evaluated when outdoor activities are being planned. The following aspects are important:
- Critical quantity of fresh snow
- Snow drift accumulation (especially in combination with fresh snow)
- Fresh snow becoming moist all the way through and danger of wet snow avalanches (including natural avalanches)
To assess the avalanche danger in summer
The avalanche danger is assessed in much the same way in summer and winter. In the summer, however, the typical patterns are largely restricted to fresh and wet snow, which facilitates the assessment. Endangered areas and locations that are to be assessed especially critically are, in particular, steep slopes of ice or firn.
You will find information on avalanche accidents in summer here.