Bulletin d’avalanche

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Danger d’avalanche

Tue
Alpin
2 · Modéré
Limite forestière
1 · Faible
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 7 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Weak layers of snow buried 1-3’ deep continue to keep the avalanche danger elevated. Triggering an avalanche on one of these layers is not likely, but the resulting slide would be large and destructive. In addition, the combination of small amounts of new snow and wind may create thin, isolated wind drifts at upper elevations.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2

    Weak layers of facets and depth hoar are buried near the base of the snowpack in this zone. As time passes without major loading events, triggering a slide on one of these layers becomes unlikely. But unlikely things do happen.

    On Saturday, I was in the White Cloud Mountains and watched as a  group of riders in low angle terrain remotely collapsed a large alpine bowl nearby (photo at right). Cracks traveled over one quarter of a mile from where they were playing, up to near the top of the peak above, and the entire snowpack shifted downhill...and then stopped. Had this thick slab of snow (see photo here) continued to slide, the resulting avalanche would have been large and destructive. 

    This is the sort of problem we are dealing with when we talk about weak snow at the base of the snowpack. You are most likely to encounter this problem exactly where the riders in the White Clouds did - in steep, rocky, heavily wind loaded terrain. Be aware that even if you aren’t directly in steep terrain yourself, the snow that you are traveling on may be connected to that sort of terrain.

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1

    On Saturday, snow professionals on Galena Summit found small but sensitive wind drifts (photo at right). On Sunday, an observer south of Baker Creek reported encountering similar thin, hard, sensitive wind slabs (see photo here).  Similar slabs may be forming today with the increase in wind speed and shift in wind direction, but without much snow to transport these slabs should remain small and isolated to upper elevation slopes.

Avalanche Discussion

When we travel through the backcountry (both professionally and recreationally), we are looking for signs of instability to help guide our decisions and snowpack analysis. As the danger decreases, these indicators are more difficult to find. We know that the likelihood of triggering avalanches on the weak layers that exist in the snowpack is decreasing, but it is hard to assess exactly how quickly that happens.

Unfortunately, on years when we have buried persistent weak layers in the snowpack, we find ourselves stuck worrying about the unlikely — not because there is a great chance of it happening, but because the outcome of the unlikely would be catastrophic. I observed exactly such a situation on Saturday in the White Cloud Mountains, read about it in the persistent slab problem discussion above. Fortunately, in this case the unlikely came without catastrophic consequences. This event serves as a great illustrator of what unlikely looks like.

Régions couvertes