Galena Summit & Eastern Mtns

Lawinenprobleme

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Possible

  Größe

  2–3

  What is it?  1-3 foot thick slabs overlie persistent weak layers (sugary facets, surface hoar, and/or crusts) on many slopes. Recently wind-loaded slopes are the most dangerous. The photo to the right/below is a great example of a medium-sized avalanche that you might be able to trigger in very steep terrain that is somewhat sheltered from the wind, especially in the western part of this zone.

  Where is it?  Most slopes harbor at least one of several weak layers in the upper part of the snowpack, but you're most likely to trigger avalanches on slopes where the wind has formed drifts or slabs or stiffened the snow at the surface (example photo). Wind-exposed bowls and slopes near ridgelines, prominent gullies, and chutes are most likely to produce large avalanches. Triggering avalanches is far less likely in terrain sheltered from the wind.

  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. In the western part of this zone, you may be able to trigger avalanches remotely—from gentler terrain below, above, and to the sides of steep slopes.  

  ADDITIONAL DISCUSSION: While triggering slides on faceted snow deep in the snowpack is unlikely, it can't be ruled out in steep, rocky, wind-affected alpine terrain. Slopes like these have variable snow depths, and thinner snowpack areas allow our weight to more easily impact deeply buried weak layers.

  

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Likely

  Größe

  1–2

  What is it?  The recent 12-20" of snowfall and moderate to strong winds formed 1-3 foot thick wind slabs in exposed terrain.Despite several days of poor visibility, SAC staff and other observers spotted several recent natural wind slab avalanches and triggered a few. Last night's snowfall and shifting wind direction may hide significant wind slabs beneath softer snow. 

  Where is it?  Wind slabs are largest and most widespread at upper elevations. You may find them near ridgelines, on the sides of gullies, and near prominent terrain features. The shifting wind directions may have formed thick or thin slabs on a variety of aspects. 

  How can you recognize it?  Cracks shooting out from your skis or sled are an obvious sign of instability. Watch for drifts, dunes, and ripples on the snow surface (example photo). 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 closer to the surface.       

  How can you manage it?  Avoid steep slopes with thick or hard wind slabs. Any triggered wind slab could "step-down" to buried persistent weak layers (Problem 1), causing a larger destructive avalanche.  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.