Boletín de aludes

Banner Summit

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 7 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Human triggered avalanches are possible, particularly in wind loaded terrain. Avalanches may be triggered remotely—from gentle terrain above, below, or to the sides of steep slopes. Cliffs, trees, and creek bottoms can increase the consequence of being caught in a slide. Be alert to the consequences of triggering an avalanche in the terrain you are in.

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    A layer of surface hoar buried 1-2’ deep can be found across our forecast area. This layer formed in the first few days of December, was buried on December 7th, and has produced extensive avalanche activity in the days since. The most recently reported human-triggered avalanche involving this layer occurred on Saturday in the Salmon River Headwaters, when a rider remotely triggered a small slope from below (photo). Yes, you read that right. It's been over three weeks since this surface hoar was buried and triggering avalanches that fail on it are still possible. 

    Dealing with persistent weak layers is challenging and frustrating. Even as the snowpack gives us fewer and fewer obvious signs of instability, the possibility of triggering a slide remains. Persistent slabs can fail in surprising ways, break wider than expected, and span multiple terrain features. And, as the slide on Saturday illustrated, they may be triggered remotely—from above, below, and to the sides of steeper slopes.

  • Wind Slabs

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

    On Friday and Saturday, moderate to strong N-NW winds built wind slabs out of the fresh snow left over from the storm on Christmas Eve. This weekend, multiple groups of skiers on Durance Ridge reported that stiff, freshly formed drifts were producing long, shooting cracks in low angle terrain. On Saturday, my partner and I found similar conditions along an upper elevation ridgeline in the Boulders and observed several small, natural wind slab avalanches that had recently failed (photo). 

    You’re most likely to find a sensitive wind slab in exposed, upper elevation terrain, near terrain features that slow the wind down and force it to drop the snow that it is carrying. Such features include ridgelines and mid-slope gullies.

Avalanche Discussion

We have two overlapping problems in our snowpack to be worried about. A widespread layer of surface hoar buried in 1-2 feet deep exists across our forecast areas. More recently, winds increased over the weekend, transporting snow and building fresh wind slabs. These slabs are a hazard in their own right, but they are also adding stress to the weak layers of snow buried underneath. 

Where these patterns overlap is where you are most likely to get yourself into trouble today. Yesterday, a local guide traveling near Galena Pass reported finding that exact combination. From a distance, he observed a recent avalanche that failed on buried surface hoar in a heavily wind loaded location. The weight of the recent snowfall wasn’t quite enough to push this slope over the edge, but a bit of additional loading from the wind appeared to have done the trick. 

As the days pass without a recent load, the likelihood of triggering slides is decreasing. This type of problem is a tough one for us humans to wrap our brains around. A good tactic is to think about how you deal with other unlikely problems in your life. Imagine you are driving in the dark, in a snowstorm, with elk all over the highway. Are you wearing your seatbelt? Now try this: it's still dark outside, but you are driving on a dry road that you are familiar with. Do you still have your seatbelt on? Or have you decided that since the likelihood of getting in an accident is lower you don’t need it anymore?

Most of us deal with the uncertainty of the world by building a wide margin of error into these sorts of situations. We wear our seatbelts even when road conditions are perfect. Traveling in the backcountry when you are dealing with a persistent slab problem requires a similar approach. Be aware of the consequences of being caught in a slide and make your route-finding and terrain selection decisions accordingly.

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