Zooming in on the already mentioned near-surface weak layers, we were able to bring the picture into sharper focus. These layers were responsible for several avalanches involving persons in the regions where recent snowfall has been heaviest (
see last blog). The avalanches were without consequences for the backcountry skiers.
Slab avalanches and settling noises were registered in the following reports: west, between 2400 and 2900 m; northern aspect between 2400 and 3000 m. This mostly involved the weak layer surrounding faceted crystals, i.e. danger pattern 4 (cold on warm) immediately bordering the crust (above it and below it). Covered surface hoar also played a role, particularly near the upper limit of the fog and in high alpine terrain adjacent to ridgelines (Nigg Effect).
These regional weak layers in very steep terrain are of great significance to backcountry skiers and freeriders. Based on the weather forecasts, we assume that these near-surface weak layers will swiftly bond during the next few days. The process will take longest in extremely steep, shady terrain.
Also requiring attentiveness: As the snowpack becomes wetter and wetter, loose-snow avalanches can be expected with increasing frequency, if not with the same intensity as yesterday, 15 April; they can also be triggered by the impulse of human weight.
In the next few days, classic springtime conditions will prevail to an ever greater degree, including fluctuating threats of the daytime danger cycle. The name of the game is: start early, descend early.
Finally, a few snapshots from 15 April:
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| Avalanches on Stubai Glacier: right slab triggered by skiers; left slab triggered naturally; north 2700 m. (photo: 15.04.2019) |
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| Avalanche triggered on Rosskarscharte, northern Stubai Alps, north, 3000 m. (photo: 15.04.2019) |
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| Avalanche triggered on Oberstkogel, northern Stubai Alps, north, 2700 m. (photo: 15.04.2019) |
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| Below the Zischgenscharte in northern Stubai Alps at about 3000 m, covered surface hoar (Nigg Effect) was the weak layer. (photo: Lukas Ruetz) |
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| Fabulous powder in southern Ötztal Alps (photo: 15.04.2019) |
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| Glide-snow avalanches in Fimbatal, Silvretta (photo: 14.04.2019) |
