Boletín de aludes

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Peligro de aludes

Mon
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
3 · Notable
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Desactualizado: este boletín caducó 2 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

You can trigger avalanches large enough to bury you on many steep slopes. Avalanches will be larger, more destructive, and easier to trigger as you gain elevation and climb into terrain affected by the wind. Some of these slides will fail on buried weak layers, producing very large, unsurvivable avalanches. These can be triggered from long distances away. Loose snow avalanches will release naturally during periods of direct sun.

 

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    2–3

    Weak layers in the snowpack were pushed to their breaking point by this week's storm (photo at right/above). On Thursday afternoon, I remotely triggered a large avalanche in this zone that failed on the prominent weak layer near the ground, leaving sharp rocks barely covered with depth hoar in its wake (video here). An additional 10-20 inches of snow fell since this avalanche. The slide broke 250 feet wide, ran over 1,000 feet, and is on the small side of what this snowpack can produce. Avalanches that fail on these layers can break thousands of feet wide and send the entire season's snowpack downslope. These slides can wipe out swaths of mature timber and will be unsurvivable. 

    Avalanches that fail on persistent weak layers behave in ways that surprise even experienced users. These slides will break wide, wrapping around entire bowls and cirques. You can trigger these avalanches from long distances away from steeper slopes, including from flat terrain below large avalanche paths. Any of the storm snow avalanches described below can trigger these much larger slides. 

    This photo shows several large to very large avalanches that failed above the Baker Creek drainage, likely overnight Friday into Saturday. The crowns span hundreds of feet of terrain, and are an estimated 3-5 feet deep in places. Getting caught in an avalanche like this and being dragged through the trees below would likely be unsurvivable. This slope faces E-SE at 9,700'.

    Photo: Ben VandenBos

  • Storm Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1.5–2

    Up to 2 feet of settled snow have fallen in this zone since Wednesday (1.5-2 inches of SWE). You will encounter a wide range of problems related to this new snow today:

    SLABS: Large slabs failing within the new snow are likely, and can occur even in sheltered terrain. Skiers on Galena Pass remotely triggered a slide that broke at the base of the new snow in apparently sheltered terrain yesterday. The size and sensitivity of these slabs will increase significantly as you climb into wind-affected terrain. If the snow you are moving through is anything but fluffy powder, you are traveling through wind-affected snow. Triggered slides will run fast and far on the stiff surfaces underneath, entraining significant amounts of snow and producing large debris piles. 

    LOOSE SNOW: Loose snow avalanches will be easy to trigger on all steep slopes. You can expect to see these slides happening naturally on slopes receiving direct sun. They'll start small but may become large as they pick up speed and material and rocket downslope. Loose snow slides can flank out into slabs, producing larger avalanches. 

    CORNICES: It has been a very windy week and there has been no shortage of snow available for the wind to blow around. Unstable cornices have grown quite large, and are struggling to hang on to their ridgeline homes. Be cautious when you are traveling on ridgelines, cornices will be easy to trigger and can behave in unpredictable ways. Large natural and human-triggered cornice failures will be effective triggers for large avalanches as they tumble downslope.

    Avalanches involving the recent snow will be large enough to bury you. Natural and triggered slides involving the new snow can be very effective triggers for the weak layers described below. Any avalanche that breaks down into these layers will be very large and destructive. 

Avalanche Discussion

Yesterday, skiers on Galena Pass remotely triggered a slab avalanche that failed at the base of the new snow. Though not huge, it is an obvious indication that you'll encounter some instabilities involving the large amount of new snow. I was looking for avalanches in this zone from the highway yesterday. Visibility was poor, but I was able to observe some large to very large avalanches that failed here during the storm (see photo above in Persistent Slab problem section). 

This zone sits in an unfortunate "Goldilocks zone". Weak layers from earlier in the season are well-developed and have produced countless massive avalanches here. Loading has been enough to produce avalanche cycles, but not enough to bury these layers deeply enough to put them to bed. On Thursday, I remotely triggered a large avalanche in this zone that failed on weak snow near the ground, clearly indicating that triggering one of these slides should be at the forefront of your mind as you travel through this zone. 

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