Skies on Saturday night, 23.03, will again be star-studded and the snowpack will cool off accordingly. On steep, sunny slopes, a melt-freeze crust capable of bearing loads will form up to high altitudes in the early morning hours of Sunday. Beneath this crust the snowpack is wet or moist down to the ground at least up to altitudes of 2500 m where the slopes are steep. As a result of the intensive solar radiation typical of this juncture of the season and daytime warming, the melt-freeze crust will soften, more quickly on east-facing than on west-facing slopes. The snowpack thereby forfeits its firmness and can more easily be triggered.
Reviewing the last few days, it is apparent that the frequency of avalanches observed has increased day by day. Initially, avalanche activity was low; today, 23.03, we observed numerous releases, including four avalanches reported to headquarters in Tirol in which persons were involved. The victims sustained no injuries. (Mutmalspitze, Gurgler Massif; Arnplattenspitze and Handschuhspitze, Mieminger Massif; Malgrube, northern Stubai Alps). Currently the primary avalanche type is wet loose-snow avalanches. These can trigger naturally, in case the snowpack is sufficiently wet, or be triggered by external impulses, whether skiers, falling rocks or cornices.
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| Loose-snow avalanche above the Seegrube in the Northern Massif. A breaking cornice gave the decisive impulse for this wet loose-snow avalanche. No one was injured. (photo: 23.03.2019) |
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| Naturally triggered loose-snow avalanche in Paznauntal (photo: 23.03.2019) |
Glide-snow avalanches are triggering only in isolated cases. Nevertheless, their nature is such that they remain utterly unpredictable.
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| An unusual sight: glide-snow avalanche over smooth rocks (Gletscherschliff); NE; 2400 m in the Zillertal Alps. (photo: 21.03.2019) |
Slab avalanches are currently unusual, not the rule. Nonetheless, particularly on very steep, sunny slopes at high altitudes (above 2500 m), there are marked layers consisting of faceted snow crystals beneath melt-freeze crusts. If enough water seeps into such layers, which are generally encrusted or riddled with meltwater channels, the layer is correspondingly weakened. An avalanche triggering can therefore not be ruled out as of midday.
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| The arrow indicates a potential weak layer for slab avalanches in case the layer becomes thoroughly wet. (c) Lukas Ruetz, Stefan Herbke; profile from 21.03.2019 |
The generally small-sized snowdrift accumulations which were generated recently have no great significance. Only beneath the hardened wind crusts near the uppermost surface can we currently pinpoint weakened, faceted layers. They are of limited spread and generally not cohesive or area-wide. Such “nests” ordinarily become a problem only in extremely steep terrain when a patch breaks away and forces a skier to fall.
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| Beneath powder snow, a hardened wind crust; beneath that lurks a thin layer of faceted snow crystals. During a stability test, one part of the snow block remained in place. This fits into the overall picture of a predominantly favorable snowpack structure on shady slopes. North, 2790 m; 30 degrees (photo: 21.03.2019) |
The snowpack surface consists of...
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| ...powder snow (photo: 21.03.2019) |
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| ....of a melt-freeze crust generally capable of bearing loads, sometimes breakable, on sunny slopes in early morning (photo: 22.03.2019) |
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| ...later on, the snowpack becomes wet. With good planning, the reward is superb corn snow on steep, sunny slopes. (photo: 22.03.2019) |
Other interesting information:
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| The snow is melting away... |
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| The air-temperature and moisture sensors which were buried in snow until 20.03 are again in operation. |
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| In the snowpack surface temperature (gray line in middle graph) the shrinking time windows are particularly evident. |
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Caution on glaciers. Everything from well-covered crevices to glacial surfaces which are bare area-wide can currently be found in Tirol. Wilder Freiger, central Stubai Alps (photo: 23.03.2019)
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