Boletín de aludes

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Peligro de aludes

Tue
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Large human-triggered avalanches failing on layers of weak snow are possible. A skier-triggered slide near Galena Summit yesterday is a good reminder that these slabs are possible in both wind-affected and sheltered terrain. Recently formed wind drifts and slabs are likely to be small but may be sensitive to your weight. The consequences of being caught in even small slides can be high in terrain with rocks, cliffs, trees, and terrain traps.

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1.5–2.5

    Several weak layers exist in the snowpack. You're most likely to trigger avalanches on weak layers that are closer to the surface, but slides on deeper weak layers remain a real possibility here. Yesterday, a skier near Titus Ridge triggered a 1-1.5 foot thick slab that appears to have failed on the layer of surface hoar described below. It failed on a N/NE-facing slope at 9,100' in reportedly sheltered terrain. The distribution, sensitivity, and depth of these layers vary across the zone and from slope to slope. Let's take a closer look:

    • Surface hoar is buried 1-1.5' deep on many shady (E-N-W) slopes. On slopes that face the sun, you'll find crusts with facets on top at this depth. In this zone, this layer is most problematic where recent wind loading has created a stiffer slab in the upper snowpack. However, yesterday's slide near Titus failed in reportedly sheltered terrain. As the slab overlying this surface hoar grows, triggering slides in sheltered terrain becomes increasingly likely. 
    • Older weak layers—crusts and/or facets, and spotty surface hoar—exist deeper in the snowpack. These are buried beneath dense, 2-4' thick slabs, making them difficult to trigger but capable of producing very dangerous avalanches. You're most likely to trigger a slide involving these deeper weak layers in rocky, wind-affected, alpine terrain. Slopes like these have variable snow depths, with thinner areas of the snowpack that allow us to impact deeper weak layers. The recent persistent slab avalanche in the Pioneer Mountains is a great illustration of this terrain (above/right, details)

    Overlapping, variable weak layers make avalanche conditions hard to predict. You can reduce (but not eliminate) your risk of triggering a large persistent slab avalanche by avoiding slopes greater than about 35 degrees where the wind has shaped the snowpack. Look for obvious wind textures like drifts and dunes that indicate that the wind has been at work. Very stiff snow surfaces that support the weight of you and your machine are a clear sign the wind has been transporting snow.

    (1/24/2023) This recent large avalanche occurred on the shoulder of Duncan Ridge in the Pioneer Mountains. It appears to be a heavily wind-loaded slope that broke on a persistent weak layer. A smaller wind slab avalanche is visible further right in the image. 10,100', WSW.

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–1.5

    This area picked up 3-6" of new snow over the weekend. Northerly winds during and after the storm constructed wind slabs out of the new snow. Yesterday, JP was able to trigger a small wind slab with a ski cut on Titus Ridge and he saw a few small wind slabs that had released naturally (photo at right/above). Today, wind slabs will be variably reactive, and the most recent slabs are likely to be the most sensitive to your weight. Slabs are most likely in upper elevation terrain, though you may find them in exposed middle elevation terrain as well, thanks to the strength of the wind.

    Be on the lookout for fresh slabs—if the snow you are moving through becomes deeper or denser you've likely found one. Cracks shooting out from your skis or sled are a clear sign that you've found an unstable slab. Triggered slides will pick up speed quickly thanks to the stiff/dense snow underneath. Small slides can also pile up debris deeply in terrain traps like road cuts or creek beds (photo here). Consider the consequences of being knocked off your feet and sent downslope in the terrain you are in.

    (1/29/2023) This recent small wind slab released naturally on Titus Ridge near Galena Summit. It failed on a E/NE-facing slope at 9,600'.

Avalanche Discussion

Early season storms brought roughly equal helpings of snow across our forecast area. This helped to build a snowpack that was somewhat homogenous across the region. However, over the past month, snowfall has favored our northern and western mountains and we've seen a significant divergence in the character of our snowpacks. In a broad sense, you can lump them into two categories: shallow and deep. The Galena Summit and Eastern Mtns Forecast Zone falls into the shallow category.

3-5 feet of snow are on the ground in this zone. Weak layers buried in November and December are closer to the surface here, and impacting these weak layers with our weight remains a possibility. This is most likely on slopes steeper than about 35 degrees where the wind has created a variably thick snowpack. The prominent layer of surface hoar that was buried in January hasn't seen as much of a load in this area and in most locations, you need the additional stiffness and weight from wind-loading for this layer to be a problem. However, yesterday's triggered avalanche near Galena Summit failed on a slope that appeared to be sheltered from the wind. 

On top of these weak layers we have a few generations of wind slabs that formed this week. More snow fell in the northern portion of this zone (from Galena Summit and north into the White Clouds) and wind slabs will be larger and more sensitive here. Recently constructed slabs are likely to be softer and more reactive to your weight. Older, harder wind slabs from last week's wind event will be less reactive, but triggering a slide involving one of these slabs remains a possibility. Triggered wind slabs can be effective triggers for deeper weak layers in the snowpack. 

The consequences of triggering avalanches can vary significantly. Triggering a small slide in terrain free of rocks, trees, and terrain traps is much less dangerous than triggering a slide in extreme, rocky, treed terrain with a terrain trap at the bottom. Spend some time thinking about the consequences of being caught in a slide as you are choosing your terrain for the day. Today's very cold temperatures add another layer of hazard to the mountain environment. The consequences of even minor injuries or mechanical issues with your machine can be greatly amplified by arctic temperatures. Pack an extra layer or two and some extra food today.

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