Galena Summit & Eastern Mtns

Lawinenprobleme

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  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Likely

  Größe

  1–2

  What is it? You are likely to trigger sensitive 2-3 feet thick slabs with last night's moderate winds and additional new snow. Expect to find these soft and hard slabs to be most sensitive in exposed middle and upper elevations. On Saturday, a rider in the Pole Creek drainage triggered a large wind slab that broke above them on the slope they were riding (observation here). Importantly, this slide occurred before the added load from recent snow and wind.

  Where is it? You'll likely find slabs in upper-elevation terrain, near ridgelines, and mid-slope terrain features like ribs and gullies. The picture to the right/above depicts the terrain where you can find this problem. Slabs may extend down into middle-elevation terrain in areas where the wind has been blowing harder. Most of the recent triggered and natural avalanche activity occurred in the Galena Summit area and north into the White Clouds, where more snow has fallen over the last week.

  How can you recognize it? Cracks shooting out from your skis or sled clearly indicate instability. Watch for drifts, dunes, and ripples on the snow surface. Wind slabs can have a smooth, chalky appearance and feel and sound hollow, like a drum. Wind-deposited snow will be stiffer and keep your skis or snowmobile on or closer to the surface. Some of these slabs might be masked by recent snow and be more hidden.     

  How can you manage it? You can significantly reduce your risk today by steering clear of wind-loaded terrain. Today's slabs might not behave like your "typical" wind slab. Various weak layers exist in the snowpack's upper 1-2 feet (watch the video at right/above). Because of this weak snow, today's slabs may break wider and deeper than expected from a "simple" wind slab.

  ADDITIONAL DISCUSSION: The layers of weak snow in the snowpack's upper 1.5-2.5 feet are being pushed toward their breaking points. Up to this point, we've needed the additional weight and stiffness from wind loading to make avalanches on these layers. Wind slabs and loose avalanches (sluffs) can step down into these deeper layers, releasing a larger avalanche than expected (see the photo above/right for an example). You are more likely to trigger these avalanches on slopes greater than 35 degrees in sheltered slopes.  

  

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  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Unlikely

  Größe

  1.5–2.5

  What is it? Triggering a large persistent slab avalanche on weak, sugary facets buried deeper in the snowpack would take some bad luck. The video to the right/above describes this problem. 

  Where is it? You are most likely to find this scenario in wind-swept alpine terrain, especially in the Pioneer, Boulder, and White Cloud Mountains. Here the snowpack has variable depths, and this problem can be found where areas are less than 2 feet deep and/or rocks poking through the snow surface.

  How can you recognize it? You may or might not see or hear obvious signs of instability (snowpack collapsing or cracking) before a very large avalanche releases. Snowpack stability tests are of little use in situations like this. 

  How can you manage it? The best way to manage this problem is to avoid terrain steeper than about 35 degrees and avoid the above-mentioned terrain.