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Lawinenprobleme

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  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Likely

  Größe

  1.5–2

  Triggering a large wind slab avalanche is likely. Most wind slabs are building on top of persistent weak layers in the snowpack (read Problem #2 below). Because of this, the wind slabs you encounter today may behave more like persistent slabs than "simple" wind slabs. Fresh slabs will be reactive to your weight and may produce avalanches that break wider and deeper than you might expect. Triggering these avalanches remotely (from a distance above, below, or to the sides of steeper slopes) is a real possibility.

  On Tuesday, I spotted a large avalanche on Copper Mountain (photo at right/above). It broke about 2 feet deep on a layer of weak, faceted snow in wind-affected terrain. The slide appeared to have been remotely triggered by a skier on a low-angle ridge above a steeper slope (photo of triggering track and crown). Yesterday on Copper, I received unstable snowpack test scores in every test I performed. Recent large avalanches, unstable snowpack test scores and an ugly snowpack structure  were plenty of evidence to keep me out of big, steep, complex avalanche terrain. 

  The wind slabs you encounter today will be largest and thickest at upper elevations, but you may also find wind affected snow in middle elevation terrain. Evidence of wind-loading may be subtle, or may have been masked by additional snow that fell after slabs formed. Be on the lookout for wind slabs near ridgelines and on the sides of mid-slope features like gullies and ribs. If the snow you are moving through becomes deeper or denser you are likely traveling on a wind slab. Cracks shooting out from your skis or sled and collapsing of the snowpack are both clear indications you've found an unstable slab. Wind slabs that fail can be effective triggers for the deeper weak layers described below.

  

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  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Possible

  Größe

  1.5–2.5

  Layers of weak snow in the upper snowpack can produce 2-3' thick slab avalanches. Expect to find weak, sugary facets on shaded slopes and crust+facet sandwiches on slopes that face the sun. You're most likely to trigger a slide involving these layers in areas where the wind has built a slab on top. However, enough snow has fallen here that avalanches failing in terrain sheltered from the wind are a very real possibility (see photo at right/above).

  Variable weather in early February produced a set of variable weak layers. The nature of these layers changes from slope to slope, it's safe to assume that they exist on most all slopes. Persistent weak layers produce avalanches that fail in unpredictable ways. They can break significantly wider and deeper than you might expect, producing much larger avalanches. Avalanches failing on persistent weak layers can be triggered from gentle terrain above, below, or to the sides of steep slopes, a process known as remote triggering.

  You can reduce your risk by avoiding slopes steeper than about 35 degrees—especially large avalanche paths and those with ugly consequences if you are caught in a slide.