Galena Summit & Eastern Mtns

Problemi valanghivi

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Likely

  Dimensione

  1–2

  What is it? A significant amount of natural avalanches occurred in the last 48 hours. Most of the larger avalanches were in areas where the wind has added additional weight to recent snow. Today, you can trigger the same sensitive 1-3 foot thick slabs in many areas with wind-affected snow.

  Where is it? These slabs will be the largest and thickest at upper elevations, but you'll also find wind slabs in exposed lower and middle elevation terrain. Be on the lookout for wind slabs near ridgelines and on the sides of mid-slope features like gullies and ribs. The foothills of the White Clouds, Boulders, and Pioneers are common places to see lower-elevation slides. Be on the lookout for wind slabs from the valley bottom to the mountain tops and expect them to be easy to trigger. 

  How can you recognize it? Cracks shooting out from your skis or sled and collapsing clearly indicate instability. Look for ripples in the snow, dunes capping ridgelines, and drifts along the sides of gulleys or chutes. 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? 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.

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Likely

  Dimensione

  1.5–2.5

  What is it? Yesterday, a group of skiers out Mushroom Ridge watched a natural large avalanche fail in the next drainage over from them. While it would surprise me to see the same activity today, it is likely to be the trigger for similar avalanches. Today, weak snow layers in the upper snowpack can produce similar 1-3' 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. 

  Where is it? The depth of these weak layers varies from slope to slope, but it's safe to assume that they exist on most slopes. The sensitivity will be amplified in wind-affected terrain (picture to right/above) in more exposed terrain. It is also possible to trigger slides in more sheltered locations as well.

  How can you recognize it? Shooting cracks and collapsing are clear signs of an unstable snowpack. Natural and human-triggered avalanches will offer guidance on what type of terrain and slopes these avalanches are likely to be triggered on, but it's safe to assume that they exist on many slopes.  It might take some digging into the snow to reveal previous wind-affected layers that the new snow has masked in more sheltered locations. 

  How can you manage it? Persistent weak layers can fail unpredictably and break significantly wider and deeper than you might expect, producing much larger avalanches. Today I recommend you choose simple, conservative terrain to play in. Pay close attention to the terrain around you and what you are connected to in slope steepness. The combination of a recent large natural avalanche, an ugly snowpack structure, and unstable snowpack test scores is plenty of evidence to keep me out of big, steep, complex avalanche terrain.

  ADDITIONAL DISCUSSION: Triggering a very large persistent slab avalanche on weak, sugary facets buried deep in the snowpack would take a dose of bad luck. However, this scenario cannot be ruled out in rocky, wind-swept areas with variable snowpack depths. This terrain is common in the upper reaches of the Pioneer, Boulder, and White Cloud Mountains.