Bollettino valanghe

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

To significantly reduce the odds of triggering a large avalanche, avoid steep slopes where the wind has drifted snow, formed slabs, or stiffened the snow surface. Several natural and human-triggered avalanches occurred in wind-affected terrain in this or neighboring zones in the past four days. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    What is it?  1-3 foot thick slabs overlie persistent weak layers (sugary facets, surface hoar, and/or crusts) on some slopes, predominantly at middle and upper elevations. Wind-loaded slopes are the most dangerous. 

    Where is it?  A snowmobiler triggered an avalanche on a wind-loaded slope near 8000' in the Soldier Mtns on Monday, burying a groomed trail with 6-8 feet of debris.Several natural and human-triggered avalanches occurred in this and neighboring zones in the past 4 days. The recent activity occurred on several aspects (click here for a location graphic). Wind-exposed bowls and slopes near ridgelines, prominent gullies, and chutes are most likely to produce avalanches.  

    How can you recognize it?  Assume this problem exists until proven otherwise. You may or may not experience snowpack collapsing and/or cracking while traveling. These red flags are obvious signs of instability. Wind-loaded areas feel stiffer under your skis or sled and keep you from easily sinking into the snowpack.         

    How can you manage it?  Unfortunately, avoiding slopes steep enough to slide is the only surefire way to manage this problem. Persistent slab avalanches are tricky. These avalanches may break wider than expected or higher on the slope above you. 

    ADDITIONAL DISCUSSION: Faceted snow exists near the base of the snowpack. Triggering slides on deeply buried weak layers is unlikely, but the consequences could be severe. You're most likely to trigger a very large slide on this layer in steep, rocky, wind-affected alpine terrain where snowpack depths are variable. Here, skiers and riders can inadvertently find spots with a thinner snowpack where triggering an avalanche is possible. Digging down to this layer with the track of your sled is another "great" way to impact this deeply buried weak layer.

    (1/1/2023) Debris from a very large avalanche that was remotely triggered above Hyndman Creek in the Pioneer Mountains. This slide failed in a heavily wind loaded area and very likely involved a persistent weak layer. It covered the summer trail with a pile of debris that was 100-150' wide and 4' deep.

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1–2

    You may encounter 1-2 foot thick wind slabs in exposed terrain: below prominent ridgelines, on the sides of gullies, and in chutes and couloirs. The wind slabs have had time to stabilize, but large features on very steep slopes deserve respect. 

    Given the increased chances of triggering a large persistent slab avalanche on wind-loaded slopes, the prudent move is to avoid obviously wind-loaded avalanche terrain.  Small wind slab avalanches could "step-down" to buried persistent weak layers (Problem 1), causing a larger destructive avalanche.  

    (1/1/2023) Crown of a large, 1-2' thick wind slab that was intentionally triggered on Galena Peak on a N/NW aspect at 9,500'.

Avalanche Discussion

Updated Wednesday, Jan 4th

Since Saturday, at least 11 avalanches occurred (view Avalanche Database here). What were the common threads?

  • All of the slides were in freshly wind-loaded or wind-affected paths, and many involved persistent weak layers buried 1-3 feet deep
  • All but one were near or above 9000' in elevation (see graphic below)
  • Eight released in the Galena Summit & Eastern Mtns zone, two in the Sawtooth & Western Smoky Mtns zone, and one in the Soldier Mtns
  • Five slides released naturally Monday (4 slides in the Boulder Mtns and 1 in the Sawtooth Mtns), and a snowmobiler triggered an avalanche in the Soldier Mtns
  • Four slides were triggered remotely (from gentler terrain above or to the sides of steep slopes) over the New Year's weekend

While the danger has dropped to MODERATE, I'm still avoiding most avalanche terrain. Why?

  1. Persistent slabs: I'm not smart or experienced enough to know with certainty which avalanche paths are safe to ride or ski and which could cause trouble. Our collective tools and knowledge don't allow us to pinpoint the hazard persistent weak layers present on individual starting zones or avalanche paths. 
  2. Risk tolerance: I'm a chicken (risk averse) when dealing with persistent weak layers. Until a persistent slab-driven avalanche danger is LOW, I will generally avoid avalanche terrain where that problem exists. 

Many people are comfortable accepting more risk than me, and that's fine. While I'm not interested in riding or skiing consequential avalanche paths with a 1/20 to 1/100 chance of triggering a persistent slab avalanche, many folks will take those odds and have a blast in steep terrain. I do encourage the more risk-tolerant snow enthusiasts to picture the consequences of a large avalanche before committing to skiing or riding steep slopes, especially in alpine and wind-affected, upper elevation terrain. If you're going to play in those areas, avoid places with terrain traps (cliffs, trees, creeks, lakes, or gullies) below you. If the proverbial roll of the dice comes up snake eyes and you are caught in a slide, avalanche paths with "clean", gradual runout zones provide a far better chance of simply having a bad day versus the unthinkable alternative. 

  

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