Bollettino valanghe

Southeast Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Wed
Alta quota
1 · Debole
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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In sintesi

Persistent slabs are smaller and less common in the snow-starved Southeast Mountains. However, stay alert for exceptions because there was a notable amount of avalanche activity over the weekend in the adjacent Northwest Mountains.  Small amounts of snow and wind drifting have formed thin slabs on a few wind-loaded terrain features. In wind-sheltered areas, there are no slab avalanche concerns, but if you are riding steep terrain with soft snow surfaces, you may need to manage small, dry loose avalanches. Snow coverage is thin in most steep terrain; any avalanche, regardless of size, will rough you up over rocks and stumps.  

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1–1.5

    Over the past week, several northwest-to-southwest wind events have formed new slabs around a foot thick. These wind-drifted slabs are most commonly found at higher elevations below leeward ridgelines and rollovers on east and northeast-facing terrain. They can also be found around the northern half of the compass in a few concave terrain features that collect drifting snow, such as gullies. These slabs are often hard and difficult to manage, breaking unpredictably and with inconsistent feedback underfoot.  Because many of them formed over weak, faceted snow, instabilities are slow to heal.  Assess recent wind-loading patterns and avoid previously wind-loaded terrain features, especially in high-consequence terrain.   

     

     

    An example of a thin, hard slab that produced shooting cracks on a leeward slope above West Brush Creek on 12/13.  

  • Loose Dry

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    In terrain that has been protected from the sun and wind, the snowpack is growing increasingly weak and cohesionless. These conditions are leading to human-triggered sluffs becoming larger or more common.  These point-release instabilities are relatively small and easy to recognize, but they can spell trouble if they push you into trees, rocks, or gullies, especially in long, steep terrain features where they gain more volume.  Use sluff management techniques or move to less consequential, lower slope angles to manage the problem. 

    Small skier-triggered sluffs on the north side of Mt Emmons. 12/16.

Avalanche Discussion

Looking at the slab avalanche patterns since our first in a series of wind events started a week ago, you'll see where slabs have been most active:  east and northeast-facing slopes above 11,000' in the Northwest Mountains.  This makes sense because those aspects held rotten weak layers on their bed surfaces, and have now received the brunt of wind loading.  The NW Mountains have been significantly favored by snowfall, so more snow was available to drift into slabs.    Where are the surprises lurking?   There are isolated slopes in the Southeast Mountains with large fetches that have collected enough drifted snow to form problematic slabs.  A forecaster was targeting these concerns a few days ago in West Brush Creek without finding a significant problem, but there's a lot of alpine terrain east of town that is difficult for us to access early season, so we have less data. The other surprises are lurking on north and west aspects.  These slopes also share the same horrendous weak layers, but they've been less active because winds have done more eroding than loading.  If you find a drifted slab on those aspects, treat it as guilty.  You'll find those more isolated drifts in midslope concavities or gullies that act as catcher's mitts for drifting snow, such as these gullies on Irwin's West Wall.  

The dry loose avalanche problem will be with us for an extended period, or at least until we bury this snow with a new slab avalanche problem, whenever we start seeing some good accumulating snow again. This dry loose avalanche problem is fairly common on northerly-facing terrain that has slope angles above 37 degrees. In the Southeast Mountains, many of these steep slopes don't have enough snow to ski or ride without traveling on the ground. Still, you can trigger one of these sluffs with what snow is available, such as this avalanche in the climax chutes. The Climax Chutes are a classic terrain feature, where even a small avalanche will eventually grow in size as it accumulates mass running through this continuously steep terrain. In the NW Mountains, there is more commonly enough snow to ski and ride in this terrain, so backcountry travelers could encounter this avalanche problem more often. 

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