Alarm bells of nature: naturally triggered slab avalanches, settling noises, fracture cracks, remote triggerings!
From all corners of Tirol, a great many reports of an unusually trigger-sensitive snowpack came in today, 14 January. Settling noises, fracture cracks and (remote) triggerings of slab avalanches unrolled regularly in flat-to-moderately steep terrain. Artificial triggerings with explosives succeeded over large-spread areas. Peter Raich, one of our observers in Ötztal, even reported that two large slab avalanches were triggered on the Gaislachkogel by just the tiny impulse of the the explosive placement on the snowpack, i.e. without detonation.
Countless danger zones
The current situation is unusual also because the distrubution of avalanche prone locations is quite high throughout the land. For that reason, a great many naturally triggered (medium to large-sized) avalanches have triggered. That means triggering slab avalanches by winter sports enthusiasts is highly likely in steep terrain. In addition, remote triggerings from flat terrain are an ongoing threat.
A selection of current photos:
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| Naturally triggered slab in a forest clearance on Geigenkamm, Ötztal (photo: 14.01.2021) |
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| Just one of countless hillside snowslides, Kitzbühel Alps (photo: 14.01.2021) |
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| Typical of a hair-trigger weak layer: avalanches release even where the snow is shallow. In such a case, snow-blockage constructions placed on the slope have no effect. Lärchfilzkogel (photo: 14.01.2021) |
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| Fracture cracks opening. Ausserfern (photo: 13.01.2021) |
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| View into the snowpack: at bottom, rough-grained old snow; at top, the mass of fresh snow. Bichlbach (photo: 13.01.2021) |
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| No, not glide-snow, but a slab avalanche on the roof, due to weak layer plus bonded fresh snow. Gerlos (photo: 14.01.2021) |
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| Fracture cracks due to additional loading of one skier. Rosshütte (photo: 14.01.2021) |
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| Slab avalanche on a hillside buries a secondary road in Sölden. The avalanche was triggered by backcountry skiers. (photo: 14.01.2021) |
Additional similar avalanches burying roads were reported in Arzl im Pitztal, Reith im Alpbachtal and between Gries am Brenner and the national border.
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| Slab avalanche with powder cloud, Venediger Massif (photo: 13.01.2021) |
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| A hidden risk in heavy snowfall areas: tree breakage. Ausserfern (photo: 14.01.2021) |
Weather of the last few days
Two cold fronts with a warm front wedged between them since 12 January are the cause of recent snowfall and precipitation in Tirol. This time it struck the northern regions (long awaited). The forecasts had to be ongoingly ratcheted up because of the warm front. Ultimately there was 100 cm of fresh snow registered regionally, in some places nearly 200 cm. Currently (14 January, 10:50 pm) it is uncertain how the warm front will further affect weather conditions. The precipitation could become even heavier than anticipated, which would have adverse effects on the magnitude of naturally triggered avalanches. That would increase risks to exposed transportation routes, particularly where snowfall has been heaviest. The especially dangerous factor was, and still is, the storm-strength W-NW-N wind which is generating such wide-ranging snowdrift accumulations.
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| 48-hr snow depths: hotspots in the north. |
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| Most snowfall was registered at the Alplhütte in the Mieming Massif. |
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| Seegrube weather station data. Lots of fresh snow, storm winds. Also the temperature rise on 13-14.01 is interesting. Nocturnal warming led to rainfall at lower altitude. Temperature fluctuations during snowfall can reinforce a weak layer inside the fresh snow (possibly delayed by dp.3 - cold on warm). |
Naturally triggered avalanches still possible
As precipitation eases (tomorrow morning 15.01 at latest) the frequency of naturally triggered slab avalanches will drop markedly. Naturally triggered slab avalanches will then be possible primarily where continuing snow transport leads to persistent additional loading of the snowpack. Also solar radiation could initiate naturally triggered slab avalanches. In our experience, artificial triggerings over the next few days promise a high degree of success.
Highly accident-prone days lie ahead of us. Play your part: keep out of harm’s way!
Better weather is forecast for the coming days, according to ZAMG Weather Service. In the past, precisely that situation (fine weather, highly trigger-sensitive snowpack, lots of fresh snow and wind) invariably has led to a host of avalanche accidents.
Thus far, all the avalanches have been without damage or injury. We sincerely hope it stays that way. For this reason we appeal to the common sense of winter sports enthusiasts: please stay on secured ski slopes for the next few days! Venture into outlying terrain only if you possess extremely good avalanche-assessing knowledge. And then, act defensively. There are uncountable dangers lurking in outlying terrain currently. Our assigning Danger Level 4 (“high”) was not undertaken haphazardly. Follow the Avalanche Bulletin at www.lawinen.report. Conditions and avalanche forecasts are updated every morning, as weather developments change.
